VARIABLE DISPLACEMENT VANE PUMP

Abstract

An object of the present invention is to provide a variable displacement vane pump capable of further reducing a pulse pressure. A vane pump (1) includes a cam ring (33). The cam ring (33) is annularly formed, and defines a plurality of pump chambers (38) on an inner peripheral side thereof in cooperation with a rotor (31) and vanes (32). An inner peripheral surface (330) of the cam ring (33) is formed in such a manner that, assuming that a confinement region refers to a region between an end portion of an intake port (221) and an end portion of a discharge port (222), at a timing when the pump chamber (38) communicates with or is disconnected from the discharge port (222) on one side corresponding to one of confinement regions or a timing close thereto, a change in a volume change amount of the pump chamber (38) on another side corresponding to the other of the confinement regions has an extreme value in a direction for reducing a change in a discharge amount at the time of the above-described communication/disconnection.

Description

TECHNICAL FIELD

The present invention relates to a variable displacement vane pump.

BACKGROUND ART

Conventionally, there has been known a variable displacement vane pump including a cam ring. For example, in a pump discussed in PTL 1, an inner peripheral surface of a cam ring has an adjusted shape with an attempt to reduce pulsation of a pressure (a pulse pressure).

CITATION LIST

Patent Literature

PTL 1: Japanese Patent Application Public Disclosure No. 2013-32739

SUMMARY OF THE INVENTION

Technical Problem

However, the conventional vane pump has left room to further reduce the pulse pressure.

Solution to Problem

In a vane pump according to one aspect of the present invention, an inner peripheral surface of a cam ring is formed in such a manner that, at a timing when a pump chamber communicates with or is disconnected from a discharge port on one side corresponding to one of confinement regions or a timing close thereto, a change in a volume change amount of a pump chamber on another side corresponding to the other of the confinement regions has an extreme value in a direction for reducing a change in a discharge amount at the time of the above-described communication/disconnection.

Therefore, the pulse pressure can be further reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-sectional view of a vane pump according to a first embodiment.

FIG. 2 is a cross-sectional view along a direction perpendicular or orthogonal to an axis of the vane pump according to the first embodiment.

FIG. 3 illustrates a characteristic of a relationship between a change rate of a vane projection amount with respect to a rotor rotational amount and the rotor rotational amount in a confinement region in a maximum eccentricity state of a cam ring in the vane pump according to the first embodiment.

FIG. 4 illustrates a characteristic of a relationship between the change rate of the vane projection amount with respect to the rotor rotational amount and the rotor rotational amount in the confinement region in a ⅓ eccentricity state of the cam ring in the vane pump according to the first embodiment.

FIG. 5 illustrates a characteristic of a relationship between the change rate of the vane projection amount with respect to the rotor rotational amount and the rotor rotational amount in a second confinement region in the maximum eccentricity state and the ⅓ eccentricity state of the cam ring in the vane pump according to the first embodiment.

FIG. 6 illustrates a characteristic of a relationship between the change rate of the vane projection amount with respect to the rotor rotational amount and the rotor rotational amount in the second confinement region in the minimum eccentricity state and the ⅓ eccentricity state of the cam ring in each of the vane pump according to the first embodiment and a vane pump according to a comparative example.

FIG. 7(a) illustrates a characteristic of a relationship between a sum of change rates of volumes of all pump chambers in communication with a discharge port with respect to the rotor rotational amount, and the rotor rotational amount in the ⅓ eccentricity state of the cam ring in the vane pump according to the first embodiment. FIG. 7(b) illustrates a characteristic of a relationship between the change rate of the volume of each of the pump chambers in communication with the discharge port with respect to the rotor rotational amount, and the rotor rotational amount in the ⅓ eccentricity state of the cam ring in the vane pump according to the first embodiment.

FIG. 8 illustrates a characteristic of a relationship between the change rate of the vane projection amount with respect to the rotor rotational amount and the rotor rotational amount in the confinement region in the maximum eccentricity state of the cam ring in a vane pump according to a second embodiment.

FIG. 9 illustrates a characteristic of a relationship between the change rate of the vane projection amount with respect to the rotor rotational amount and the rotor rotational amount in the confinement region in the ⅓ eccentricity state of the cam ring in the vane pump according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

First Embodiment

[Configuration]

First, a configuration will be described. FIG. 1 is a cross-sectional view illustrating a vane pump (hereinafter referred to as a pump) 1 according to a first embodiment, taken along a plane passing through a shaft center (a rotational axis of a rotor 31) O, which is a center of a rotation of a driving shaft 30. FIG. 2 corresponds to a cross-section as viewed from a line II-II in FIG. 1. FIG. 1 corresponds to a cross-section as viewed from a line I-I in FIG. 2. For convenience of the description, a tree-dimensional orthogonal coordinate system is set up. An x axis and a y axis extend in a radial direction of the driving shaft 30 (with respect to the shaft center O), and a z axis extends along the shaft center O. The z axis is a direction along the rotational axis of the driving shaft 30. The x axis extends in a direction in which a cam ring 33 swings, and the y axis is perpendicular or orthogonal to the x axis and z axis. An x-axis positive direction is defined to be one side closer to the shaft center O with respect to a central axis P of the cam ring 33. A y-axis positive direction is defined to be one side closer to a control portion 4 with respect to a pump portion 3. A z-axis positive direction is defined to be one side closer to a front body 21 with respect to a rear body 20. The pump 1 is used as a hydraulic supply source of a device mounted on a vehicle. More specifically, the pump 1 is used for a power steering apparatus for reducing a required force of operating a steering wheel of the vehicle. The pump 1 is driven by a crank shaft of an internal combustion engine (an engine), and introduces and discharges hydraulic liquid as hydraulic fluid. The hydraulic liquid is, for example, oil. The pump 1 is a variable displacement pump capable of changing a discharge capacity (an amount of liquid discharged per rotation, a pump capacity). The pump 1 is a pump unit including a pump housing 2, the pump portion 3, and the control portion 4. The pump portion 3 introduces and discharges the hydraulic liquid. The control portion 4 controls the pump capacity.

The pump housing 2 includes the rear body 20, the front body 21, and a side plate 22. The rear body 20 includes therein a recessed portion 200, a low-pressure chamber, a high-pressure chamber 201, a connection port 202, a valve containing hole 203, a spring containing hole 204, a bearing mounting portion 205, a hole 206, a liquid passage 207, and the like. The recessed portion 200 has a bottomed cylindrical shape, and extends in the z-axis direction to be opened at a surface of the rear body 20 on a z-axis positive direction side. The low-pressure chamber and the high-pressure chamber 201 are recessed portions provided at a bottom portion 200a of the recessed portion 200, and are opened at the bottom portion 200a. The connection port 202 extends in the x-axis direction inside an x-axis positive direction side, a y-axis positive direction side, and the z-axis positive direction side of the rear body 20, and is opened at an outer surface of the rear body 20 on the x-axis positive direction side. A member (a liquid passage forming member) 23 in which a liquid passage 230 is formed is set in the connection port 202. The connection port 202 (the member 23) is connected to, for example, a power cylinder of the power steering apparatus via a pipe. The valve containing hole 203 extends in the x-axis direction inside the y-axis positive direction side and the z-axis positive direction side of the rear body 20, and is opened at an outer surface of the rear body 20 on an x-axis negative direction side. A plug member 24 is fixed in an opening of the valve containing hole 203. The spring containing hole 204 extends in the x-axis direction inside an x-axis positive direction side and a z-axis positive direction side of a wall portion 200b surrounding the recessed portion 200, and is opened at an inner peripheral surface of the recessed portion 200 and the outer surface of the rear body 20 on x-axis positive direction side. A plug member 25 is fixed to an opening of the spring containing hole 204 on the outer surface of the rear body 20. The bearing mounting portion 205 has a bottomed cylindrical shape, and extends in the z-axis direction to be opened at a surface of the rear body 20 on a z-axis negative direction side. A bearing 27 is mounted on the bearing mounting portion 205. The bearing 27 is, for example, a ball bearing. The hole 206 extends in the z-axis direction to extend through the rear body 20, and is opened to the bottom portion 200a of the recessed portion 200 and a bottom portion 205a of the bearing mounting portion 205. An intake liquid passage inside the rear body 20 connects the low-pressure chamber to a reservoir tank. The discharge liquid passage 207 connects the high-pressure chamber 201 to the connection port 202. A metering orifice 207a is provided in the discharge liquid passage 207. A first control liquid passage 401 connects the connection port 202 to an end of the valve containing hole 203 in the x-axis positive direction. A second control liquid passage 402 connects the high-pressure chamber 201 to an end of the valve containing hole 203 in the x-axis negative direction. A damper orifice 402a is provided in the second control liquid passage 402. A third control liquid passage 403 connects an x-axis negative direction side of the valve containing hole 203 to the recessed portion 200.

The front body 21 includes a bearing mounting portion 211. The bearing mounting portion 211 has a bottomed cylindrical shape, and extends in the z-axis direction to be opened at a surface 210 of the front body 21 on the z-axis negative direction side. A bearing 28 is mounted on the bearing mounting unit 211. The bearing 28 is, for example, a needle bearing. The front body 21 is mounted on the z-axis positive direction side of the rear body 20, and is fixed to the rear body 20 by bolts 29. The front body 21 closes the opening of the recessed portion 200.

The side plate 22 is a disk-like member (a pressure plate), and is contained in the recessed portion 200 and mounted at the bottom portion 200a. A circumferential position of the side plate 226 in the recessed portion 200 is determined by being fixed to the rear body 20 (the bottom portion 200a of the recessed portion 200) due to a pin 35 extending through a hole of the side plate 22. A hole 226 extends through in the z-axis direction a generally central position of the side plate 22. A surface 220 of the side plate 22 on the z-axis positive direction side is a flat surface, and includes an intake opening (an intake port) 221, a discharge opening (a discharge port) 222, an intake-side backpressure port 223, and a discharge-side backpressure port 224 as bottomed recessed portions (grooves). The intake port 221 is located on the y-axis positive direction side with respect to the shaft center O, and extends along a circular arc centered at the shaft center O. An end portion 221a on the x-axis positive direction side is a start end portion of the intake port 221, and an end portion 221b on the x-axis negative direction side is a terminating end portion of the intake port 221. A hole is opened at a bottom portion of the intake port 221. The hole extends through the side plate 22 in the z-axis direction. The intake port 221 is connected to the low-pressure chamber of the rear body 20 via the above-described hole. The discharge port 222 is located on the y-axis negative direction side with respect to the shaft center O, and extends along a circular arc centered at the central axis 0. An end portion 222a on the x-axis negative direction side is a start end portion of the discharge port 222, and an end portion 222b on the x-axis positive direction side is a terminating end portion of the discharge port 222. A hole is opened at a bottom portion of the discharge port 222. The hole extends through the side plate 22 in the z-axis direction. The discharge port 222 is connected to the high-pressure chamber 201 via the above-described hole. The discharge port 222 includes a notch portion 225 on a start end portion 222a side thereof. The start end portion 222a of the discharge point 222 is also a start end portion of the notch portion 225. The notch portion 225 has a flattened (flat) rectangular shape in cross-section taken along the radial direction of the rotor 31. The notch portion 255 is smaller than a main body portion of the discharge port 222 in area in cross-section taken along the radiation direction of the rotor 31. No notch portion is provided on a terminating end portion 222b side of the discharge port 222. The end portion 221b of the intake port 221 faces the start end portion 222a of the discharge port 222, and the start end portion 221a of the intake port 221 faces the terminating end portion 222b of the discharge port 222 in a direction of the rotation of the rotor 31 (the driving shaft 30) that is centered at the shaft center O (hereinafter referred to a circumferential direction).

The intake-side backpressure port 223 is basically located on the y-axis positive direction side with respect to the shaft center O, and extends along a circular arc centered at the shaft center O on one side closer to the shaft center O (a radially inner side) with respect to the intake port 221. A hole is opened at a bottom portion of the port 223. The hole extends through the side plate 22 in the z-axis direction. The port 223 is connected to the high-pressure chamber 201 via the above-described hole. The discharge-side backpressure port 224 is basically located on the y-axis negative direction side with respect to the shaft center O, and extends along a circular arc centered at the shaft center O on a radially inner side with respect to the discharge port 222. A hole is opened at a bottom portion of the port 224. The hole extends through the side plate 22 in the z-axis direction. The port 224 is connected to the high-pressure chamber 201 via the above-described hole. An end portion of the intake-side backpressure port 223 faces a start end portion of the discharge-side backpressure port 224, and a start end portion of the port 223 faces an end portion of the port 224 in the circumferential direction. Similar ports and the like are also formed on the surface 210 of the front body 21 on the z-axis negative direction side in correspondence with the ports 222 and 221 and the ports 223 and 224 of the side plate 22.

The pump portion 3 includes the driving shaft 30, the rotor 31, a plurality of vanes 32, the cam ring 33, and an adaptor ring 34. The driving shaft 30 is supported on the pump housing 2, and is rotationally driven by the crank shaft. The driving shaft 30 is mounted in the hole 206 of the rear body 20, and extends through inside the hole 226 of the side plate 22. An end of the driving shaft 30 on the z-axis positive direction side is rotatably supported on the front body 21 by the bearing 28. A z-axis negative direction side of the driving shaft 30 is rotatably supported on the rear body 20 by the bearing 27. The rotor 31, the plurality of vanes 32, the cam ring 33, and the adaptor ring 34 are contained in the recessed portion 200 on the z-axis positive direction side of the side plate 22. These components such as the rotor 31 function as pump elements, and the recessed portion 200 functions as a pump element containing portion.

The rotor 31 has a generally cylindrical shape, and extends in the z-axis direction while being coupled to the driving shaft 30 by serration coupling, thereby being rotationally driven by the driving shaft 30. The rotor 31 rotates in a counterclockwise direction in FIG. 2 about the shaft center O. The rotor 31 includes a plurality of slots 311 in the circumferential direction. The slots 311 are bottomed grooves (slits), and extend in the radial direction of the rotor 31 inside the rotor 31 to be opened at an outer peripheral surface 310 of the rotor 31. The slots 311 extend throughout an entire range of the rotor 31 in the z-axis direction. The number of slots 311 is an odd number (eleven). The plurality of slots 311 is disposed at generally even intervals in the circumferential direction. A proximal end 312 of each of the slots 311 on a radially inner side of the rotor 31 (one side toward the shaft center O) has a cylindrical shape extending in the z-axis direction that is larger in diameter than a circumferential width of a main body of the slot 311. The proximal end 312 is connected to the backpressure ports 223 and 224. Each of the vanes 32 is a plat-like member contained in each of the slots 311 one by one, and is movable by projecting and retracting (movable in a manner projectable and retractable) from and into the rotor 31. The number of vanes 32 is an odd number (eleven). Between the proximal end 312 of the slot 311 and the vane 32 contained in this slot 311, a backpressure chamber (a pressure-receiving portion) 36 of this vane 32 is formed.

The cam ring 33 is annularly formed and disposed so as to surround the rotor 31, and is provided movably in the recessed portion 200. The cam ring 33, the rotor 31 (the slots 311), and the vanes 32 have dimensions in the z-axis direction that are generally equal to one another. An inner peripheral surface 330 of the cam ring 33 has a generally cylindrical shape extending in the z-axis direction. An outer circumferential surface 331 of the cam ring 33 has a cylindrical shape generally coaxially with the inner peripheral surface 330. A central axis of the inner peripheral surface 330 (the outer peripheral surface 331) will be hereinafter referred to as a central axis P of the cam ring 33. A recessed portion 332 is provided on an outer periphery of the cam ring 33 on the y-axis negative direction side. The recessed portion 332 has a half cylinder shape extending in the z-axis direction. The adaptor ring 34 is annularly formed and is fitted to the recessed portion 200. The adaptor ring 34 is disposed so as to surround the cam ring 33. The adaptor ring 34 includes a large-diameter hole 344 and a small-diameter hole 345 extending through an inner periphery and an outer periphery thereof, respectively. The hole 344 is located on the x-axis positive direction side and surrounds the opening of the spring containing hole 204 in the recessed portion 200 of the rear body 20. The hole 345 is located on the y-axis positive direction side and is connected to the third control liquid passage 403 opened at the recessed portion 200 of the rear body 20. A first support surface 341, a second support surface 342, and a third support surface 343 are formed on an inner peripheral surface 340 of the adaptor ring 34. The first support surface 341 is positioned on the y-axis positive direction side and is a flat surface extending in the z-axis direction. A seal groove 346 extending in the z-axis direction is formed on the first support surface 341 at a position slightly offset from the shaft center O toward the x-axis negative direction side. A seal member 37 is provided in the seal groove 346. The second support surface 342 is a recessed curved surface protruding in a direction away from the shaft center O that is positioned slightly offset from the shaft center O toward the x-axis negative direction side and located on the y-axis negative direction side while extending in the z-axis direction. A half-cylindrical recessed portion 347 extending in the z-axis direction is provided on the second support surface 342 at a position slightly offset from the shaft center O toward the x-axis negative direction side. The third support surface 343 is a flat surface located on the x-axis negative direction side and extending in the z-axis direction.

The cam ring 33 is swingably provided on the inner peripheral side of the adaptor ring 34. The pin 35 is provided between the recessed portion 347 of the adaptor ring 34 and the recessed portion 332 of the cam ring 33. The pin 35 extends in the z-axis direction, and is fixed to the pump housing 2 (the rear body 20 and the front body 21). The cam ring 33 is swingable about the pin 35 or a vicinity thereof. A y-axis positive direction side of the outer peripheral surface 331 of the cam ring 33 is in contact with the seal member 37. A y-axis negative direction side of the outer peripheral surface 331 is in contact with the second support surface 342. The cam ring 33 is swingable in an xy plane with a support point therefor set to a line tangential to the second support surface 342. During a swinging movement, the cam ring 33 moves so as to slightly roll on the second support surface 342. At this time, the pin 35 prevents or reduces a positional shift of the cam ring 33 in the direction of the rotation (a relative rotation) relative to the adaptor ring 34. A swinging movement of the cam ring 33 toward the x-axis positive direction side is regulated by, for example, abutment of the outer peripheral surface 331 with the inner peripheral surface 340 of the adaptor ring 34. A swinging movement of the cam ring 33 toward the x-axis negative direction side is regulated by abutment of the outer peripheral surface 331 with the third support surface 343. An eccentricity amount δ will be defined to be a displacement amount of the central axis P from the shaft center O. The eccentricity amount δ is minimized at a position where the outer peripheral surface 331 is in abutment with the inner peripheral surface 340 on the x-axis positive direction side (a minimum eccentricity position). The eccentricity amount δ is maximized at a position illustrated in FIG. 2 where the outer peripheral surface 331 is in abutment with the third support surface 343 (a maximum eccentricity position). A coil spring 44 as an elastic member is provided on the outer peripheral side of the cam ring 33 on the x-axis positive direction side. The spring 44 is provided in the spring containing hole 204 of the rear body 20, and one end side thereof is supported by the plug member 25. An opposite end side of the spring 44 is in contact with the outer peripheral surface 331 of the cam ring 33. The spring 44 is provided in a compressed state, and constantly biases the cam ring 33 relative to the rear body 20 toward the x-axis negative direction side (in a direction for increasing δ).

First and second chambers 41 and 42 are formed on the outer peripheral side of the cam ring 33 by the cam ring 33 and the adaptor ring 34. A space between the inner peripheral surface 340 and the outer peripheral surface 331 has an opening on the z-axis negative direction side that is sealingly closed by the side plate 22, and an opening on the z-axis positive direction side that is sealingly closed by the front body 21. The above-described space is liquid-tightly divided into the two chambers 41 and 42 by a contact portion between the second support surface 342 and the outer peripheral surface 331, and a contact portion between the seal member 37 and the outer peripheral surface 331. The first chamber 41 is formed on the x-axis positive direction side, and the second chamber 42 is formed on the x-axis negative direction side. The hole 345 is opened to the second chamber 42. The second chamber 42 is connected to the third control liquid passage 403 via this hole 345. The second chamber 42 functions as a fluid pressure chamber (a control pressure chamber). The first chamber 41 is opened to an atmospheric pressure via, for example, a drain liquid passage.

A distance between the surface 220 of the side plate 22 on the z-axis positive direction side and the surface 210 of the front body 21 on the z-axis negative direction side is slightly larger than the dimensions of the rotor 31, the vanes 32, and the cam ring 33 in the z-axis direction. An annular space is formed among the outer peripheral surface 310 of the rotor 31, the inner peripheral surface 330 of the cam ring 33, the surface 220 of the side plate 22, and the surface 210 of the front body 21. This annular space is divided into a plurality of pump chambers (vane chambers) 38 by the plurality of vanes 32. In other words, the cam ring 33 forms the plurality of pump chambers 38 on the inner peripheral side thereof in cooperation with the rotor 31 and the vanes 32. The number of pump chambers 38 is an odd number (eleven). Hereinafter, a circumferential distance between the circumferentially adjacent vanes 32 (an angle around the shaft center O) will be referred to as one pitch (1P). Then, the circumferential distance between the vanes 32 is, for example, a circumferential distance (an angle) between a circumferential center of some vane 32 and a circumferential center of the vane 32 circumferentially adjacent to the above-described vane 32. Alternatively, this distance is a circumferential distance (an angle) between a surface of some vane 32 on one circumferential side (for example, one side located in a direction of a reverse rotation of the rotor 31) and a surface of the vane 32 circumferentially adjacent to the above-described vane 32 on the above-described one circumferential side. A circumferential dimension of one pump chamber 38 is little shorter than one pitch (a size acquired by subtracting the circumferential dimension of the vane 32 from one pitch). The start end portion 221a of the intake port 221 is located approximately half pitch (½P) away from a straight line passing through the shaft center O and extending in parallel with the x axis, toward the y-axis positive direction side (one side located in the direction of the rotation of the rotor 31). The end portion 221b of the intake port 221 is located approximately half pitch away from the above-described straight line toward the y-axis positive direction side (an opposite side located in the direction of the reverse rotation of the rotor 31). The start end portion 222a of the discharge port 222 (the notch portion 25) is located approximately half pitch away from the above-described straight line toward the y-axis negative direction side (the one side located in the direction of the rotation of the rotor 31). The end portion 222b of the discharge port 222 is located approximately half pitch away from the above-described straight line toward the y-axis negative direction side (the opposite side located in the direction of the reverse rotation of the rotor 31). A circumferential distance between the portions 222b and 221a and a circumferential distance between the portions 221b and 222a are each approximately one pitch.

A distance between the outer peripheral surface 310 of the rotor 31 and the inner peripheral surface 330 of the Cam ring 33 in the radial direction of the rotor 31 increases from the x-axis positive direction side toward the x-axis negative direction side, with the cam ring 33 (the central axis P) positioned eccentrically from the rotor 31 (the shaft center O) toward the x-axis negative direction side. The vanes 32 project and retract from and into the slots 311 according to this change in the distance, thereby liquid-tightly defining the respective pump chambers 38. The pump chamber 38 on the x-axis negative direction side has a larger volume v than the pump chamber 38 on the x-axis positive direction side. Due to this difference in the volume v of the pump chamber 38, the volume v of the pump chamber 38 is increasing on the y-axis positive direction side with respect to the shaft center O as the pump chamber 38 is traveling toward the x-axis negative direction side, which is the direction of the rotation of the rotor 31 (the counterclockwise direction in FIG. 2). On the other hand, the volume v of the pump chamber 38 is reducing on the y-axis negative direction side with respect to the shaft center O as the pump chamber 38 is traveling toward the x-axis positive direction side, which is the direction of the rotation of the rotor 31. A region in which the volume v of each of the plurality of pump chambers 38 increases according to the rotation of the rotor 31 (a section on the y-axis positive direction side) is an intake region. A region in which the volume v of each of the plurality of pumps 38 reduces according to the rotation of the rotor 31 (a section on the y-axis negative direction side) is a discharge region. The intake port 221 is opened to the intake region, and the discharge port 222 is opened to the discharge region. The pump chamber 38 located in the intake region is in communication with the intake port 221 and the pump chamber 38 located in the discharge region is in communication with the discharge port 222 regardless of the eccentricity amount δ. A region between the terminating end portion 221b of the intake port 221 and the start end portion 222a of the discharge port 222 (the notch portion 225) is a first confinement region A. A region between the terminating end portion 222b of the discharge port 222 and the start end portion 221a of the intake port 221 is a second confinement region B. Both the regions A and B are each approximately one pitch (1P). The pair of surfaces 210 and 220 facing each of the regions A and B in the z-axis direction in the pump housing 2 are each formed into a flat surface. In other words, no recessed portion (groove) and no hole are provided on the surfaces 210 and 220 in each of the regions A and B. These surfaces 210 and 220 are disposed generally in parallel with each other. Each of the regions A and B confines the hydraulic liquid in the pump chambers 38 located in their own regions, thereby preventing the discharge port 222 (including the notch 225) and the intake port 221 from communicating with each other via the pump chambers 38.

When the rotor 31 rotates with the cam ring 33 (the central axis P) positioned eccentrically from the rotor 31 (the shaft center O) toward the x-axis negative direction side, the pump chambers 38 periodically repeat an increase and a reduction of the volume v while rotating around the shaft center O. The pump chamber 38 in communication with the intake port 221 in the intake region introduces therein the hydraulic liquid from the intake port 221. The pump chamber 38 in communication with the discharge port 222 in the discharge region discharges the hydraulic liquid to the discharge port 222. The pump chambers 38 are liquid-tightly maintained out of communication with both the intake port 221 and the discharge port 222 (the notch portion 225) in each of the regions A and B. A discharge pressure is applied to the backpressure chamber 36 of the vane 32 via the backpressure port 223 or 224. Therefore, a performance of the vane 32 regarding the projection, for example, when the number of rotations of the pump is small, can be improved, whereby the liquid-tightness of the pump chambers 38 can be improved.

The control portion 4 is provided in the rear body 20, and includes the liquid passages 207 and 401 to 403, the chambers 41 and 42, a control valve 43, the coil spring 44, and a relief valve 45. The control valve 43 is a spool valve, and includes a spool 43a and a coil spring 43b. The spool 43a and the spring 43b are provided in the valve containing hole 203. The spool 43a is a valve body that switches a flow passage, and includes a first land 431 and a second land 432. The first land 431 defines a pressure chamber 433 and a drain chamber 434 in the valve containing hole 203. The second control liquid passage 402 is normally or constantly opened to the pressure chamber 433. The drain liquid passage is normally or constantly opened to the drain chamber 434. The drain liquid passage is opened to the atmospheric pressure. The second land 432 defines the drain chamber 434 and a spring chamber 435 in the valve containing hole 203. The first control liquid passage 401 is normally or constantly opened to the spring chamber 435. The coil spring 43b is an elastic member, and is set in the spring chamber 435. One end side of the spring 43b is in contact with the bottom portion of the valve containing hole 203 on the x-axis positive direction side, and an opposite end side of the spring 43b is in contact with an end of the spool 43a on the x-axis positive direction side. The spring 43b is set in a compressed state, and constantly biases the spool 43a relative to the rear body 20 toward the x-axis negative direction side. The first land 431 is located slightly offset toward the x-axis negative direction side from the opening of the third control liquid passage 403 on the inner peripheral surface of the valve containing hole 203 with the spool 43a maximally displaced toward the x-axis negative direction side as illustrated in FIG. 2. The first land 431 blocks the communication between the pressure chamber 433 and the liquid passage 403 and also establishes communication between the drain chamber 434 and the liquid passage 403. The relief valve 45 is a normally-closed valve set at the spool 43a, and is opened when a pressure in the spring chamber 435 reaches or exceeds a predetermined pressure to establish communication between the spring chamber 435 and the drain chamber 434.

A pressure in the pressure chamber 433 and a pressure in the spring chamber 435 are applied to both axial ends of the spool 43a from opposite directions from each other. The pressure in the pressure chamber 433 is a discharge pressure on an upstream side of the metering orifice 207a that is supplied from the high-pressure chamber 201 (the discharge port 222) of the rear body 20 via the second control liquid passage 402. The pressure in the spring chamber 435 is a discharge pressure on a downstream side of the orifice 207a that is supplied from the high-pressure chamber 201 (the discharge port 222) of the rear body 20 via the discharge liquid passage 207 and the first control liquid passage 401. A pressure loss at the orifice 207a increases according to an increase in the number of rotations of the pump 1 (a discharge flow amount), so that the discharge pressure on the downstream side of the orifice 207a falls below the discharge pressure on the upstream side of the orifice 207a. A difference between these upstream and downstream discharge pressures (hereinafter referred to as a differential pressure) generates a force biasing the spool 43a in the x-axis positive direction. When the biasing force due to this differential pressure exceeds the above-described biasing force of the spring 43b, the spool 43a is displaced in the x-axis positive direction. The first land 431 blocks communication between the drain chamber 434 and the third control liquid passage 403, and also establishes the communication between the pressure chamber 433 and the liquid passage 403. As a result, the second chamber 42 and the pressure chamber 433 are brought into communication with each other, allowing the hydraulic liquid to be supplied from the chamber 433 to the second chamber 42. When the force with which the cam ring 33 is biased by the pressure in the second chamber 42 in the x-axis positive direction exceeds a sum of the pressure in the first chamber 41 (the atmospheric pressure) and the force with which the cam ring 33 is biased by the coil spring 44 in the x-axis negative direction, the cam ring 33 swings in the x-axis positive direction, followed by a reduction in the eccentricity amount δ. As a result, the pomp capacity reduces. On the other hand, when the biasing force due to the differential pressure falls below the above-described biasing force of the spring 43b, the spool 43a is displaced in the x-axis negative direction. The first land 431 blocks the communication between the pressure chamber 433 and the liquid passage 403, and also establishes the communication between the drain chamber 434 and the liquid passage 403. As a result, the pressure in the second chamber 42 reduces, so that the cam ring 33 swings in the x-axis negative direction, followed by an increase in the eccentricity amount δ. Due to that, the pump capacity increases. In this manner, the control valve 43 controls the inflow of the hydraulic liquid into the second chamber 42 and the outflow of the hydraulic liquid from the chamber 42 according to the number of rotations of the pump 1 (the discharge flow amount), thereby varying the pump capacity. The control portion 4 such as the control valve 43 functions as a cam ring control mechanism that controls the eccentricity amount δ. A fixed capacity region is such a region where the number of rotations of the pump is small that the eccentricity amount δ is kept maximized and the pump capacity is kept constant even when the number of rotations of the pump changes. A variable capacity region is such a region where the number of rotations of the pump is large that the eccentricity amount δ reduces and the pump capacity reduces according to an increase in the number of rotations of the pump.

The inner peripheral surface 330 of the cam ring 33 is formed in the following manner. Hereinafter, focusing on two vanes 32 forming some single pump chamber 38, the vane 32 on the one side located in the direction of the rotation of the rotor 31 will be referred to as a front vane 32, while the vane 32 on the opposite side located in the direction of the reverse rotation of the rotor 31 will be referred to as a rear vane 32. A distance from the shaft center O to the inner peripheral surface 330 of the cam ring 33 (a movement radius) will be referred to as a vane projection amount r. A rotational angle of the rotor 31 will be referred to as a rotational amount θ of the rotor 31. A distance from the outer peripheral surface 310 (the opening of the slot 311) of the rotor 31 to the inner peripheral surface 330 of the cam ring 33 may be used as the vane projection amount r. Further, a rotational speed of the rotor 31 may be used as the rotor rotational amount θ. FIGS. 3 to 6 are characteristic diagrams each illustrating a relationship between a change rate dr/dθ of the amount r with respect to θ, and θ. Assume that a sign of θ is positive in the direction of the rotation of the rotor 31 (negative in the direction of the reverse rotation of the rotor 31). When the sign of dr/dθ is positive, the amount r increases according to the rotation of the rotor 31. When the sign of dr/dθ is negative, the amount r reduces according to the rotation of the rotor 31. FIG. 3 illustrates the above-described relationship in the first confinement region A, the second confinement region B, and vicinities of these regions A and B in such a state that the cam ring 33 is located at a position where the eccentricity amount δ is maximized (hereinafter referred to a maximum eccentricity state). FIG. 4 illustrates the above-described relationship in the regions A and B and the vicinities of these regions A and B in such a state that the cam ring 33 is moved by ⅓ of the entire eccentricity amount δ from the position where the amount δ is maximized toward a position where the amount δ is minimized (in the x-axis positive direction) (hereinafter referred to as a ⅓ eccentricity state). FIG. 5 illustrates the above-described relationship in the region B and the vicinity thereof in each of the maximum eccentricity state and the ⅓ eccentricity state. FIG. 6 illustrates the above-described relationship in the region B and the vicinity thereof in such a state that the cam ring 33 is located at the position where the amount δ is minimized (hereinafter referred to as a minimum eccentricity state), and the ⅓ eccentricity state. A characteristic of a comparative example is indicated by a long dashed double-dotted line.

(Maximum Eccentricity State)

As illustrated in FIG. 3, the sign of the change rate dr/dθ is negative in the entire range of the first confinement region A in the maximum eccentricity state. In other words, the vane projection amount r constantly reduces as the vane 32 travels from the terminating end portion 221b of the intake port 221 (corresponding to a rotational amount θ_1S) toward the start end portion 222a of the discharge port 222 (corresponding to a rotational amount θ_1E) according to the rotation of the rotor 31. As illustrated in FIG. 5, the sign of dr/dθ is negative in the entire range of the second confinement region B in the maximum eccentricity state. In other words, the amount r constantly reduces as the vane 32 travels from the terminating end portion 222b of the discharge port 222 (corresponding to a rotational amount θ_2S) to the start end portion 221a of the intake port 221 (corresponding toward a rotational amount θ_2E) according to the rotation of the rotor 31.

(⅓ Eccentricity State)

As illustrated in FIG. 4, the sign of dr/dθ is negative in the entire range of the first confinement region A in the ⅓ eccentricity state. In other words, the amount r constantly reduces as the vane 32 travels from the terminating end portion 221b (θ_1S) of the intake port 221 toward the start end portion 222a (θ_1E) of the discharge port 222. Further, the amount r gradually reduces as the vane 32 travels from θ_1S toward θ_1E. An absolute value of dr/dθ (the negative value) gradually reduces, and then gradually increases after reaching an extremely small value dr/dθ₁* at θ₁*, as the vane 32 travels from θ_1S toward θ_1E. θ₁* is located in a range from ⅓ pitch to ⅔ pitch from θ_1S inclusive. In other words, the point θ₁* is located between a point θ_1(1/3) positioned ⅓ pitch (⅓p) away from θ_1S and a point θ_1(2/3) positioned ⅔ pitch (⅔P) away from θ_1S. The region A is one pitch (1P). Therefore, θ₁* is located in a range of a central portion when the region A is divided into three portions (θ_1(1/3) to θ_1(2/3)). More specifically, θ₁* is located slightly offset toward the θ_1S side from a point θ_1(1/2) positioned ½ pitch (½P) away from θ_1S. Assume that Δ1 (a first change gradient) represents a gradient of a change in dr/dθ since the absolute value of dr/dθ starts reducing until reaching the extremely small value dr/dθ₁* (more specifically, a change from θ_1S to θ₁*) in the region A in the ⅓ eccentricity state. Δ1 is Δ1=|dr/dθ₁*−dr/dθ_(1S)|/|θ₁*−θ_1S|. Assume that Δ2 (a second change gradient) represents a gradient of a change in dr/dθ since the absolute value of dr/dθ reaches the extremely small value dr/dθ₁* until stopping increasing (more specifically, a change from θ₁* to θ_1E). Δ2 is Δ2=|dr/dθ₁*−dr/dθ_(1E)|/|θ₁*−θ_1E|. Δ2 is greater than Δ1 (Δ1<Δ2). In other words, the absolute value Δ2 of an average change rate of dr/dθ on a second half side of the region A (when the absolute value of dr/dθ is increasing) is greater than the absolute value Δ1 of an average change rate of dr/dθ on a first half side of the region A (when the absolute value of dr/dθ is reducing). In the present embodiment, Δ2/Δ1, i.e., a ratio of Δ2 to Δ1 is approximately 1.24. As illustrated in FIGS. 5 and 6, the sign of dr/dθ is switched from negative to positive at θ_2M in the direction of the rotation of the rotor 31 in the second confinement region B in the ⅓ eccentricity state. In other words, as the vane 32 travels from the terminating end portion 222b (θ_2S) of the discharge port 222 toward the start end portion 221a (θ_2E) of the intake port 221, the amount r gradually reduces, and then gradually increases after reaching an extremely small value at θ_2M. The amount r gradually increases in the region B at least in a partial (a θ_2E side) range (θ_2M to θ_2E) continuous from the terminating end portion (θ_2E) thereof.

(Minimum Eccentricity State)

As illustrated in FIG. 6, a function of dr/dθ with respect to θ has an extreme value dr/dθ₂* at θ₂* in the second confinement region B in the minimum eccentricity state. In other words, there are a θ region where the change rate of dr/dθ with respect to θ (a second-order differential of the amount r with respect to θ, a slope of the above-described function) has a negative value, and a θ region where this change rate has a positive value. The change rate of dr/dθ has a negative value in a region Ba on a first half side of the region B, and has a positive value in a region Bb on a second half side of the region B. Whether dr/dθ increases or reduces changes at the point θ₂* separating the regions Ba and Bb according to the rotation of the rotor 31 (the function of the amount r with respect to θ has an inflection point at θ₂*).

[Function]

Next, a function will be described. The volume v of each of the pump chambers 38 changes (increases or reduces) according to the rotation of the rotor 31 with the cam ring 33 positioned eccentrically. An amount dv/dθ of the change in the volume v of some pump chamber 38 with respect to the rotational amount θ of the rotor 31 (in other words, an amount of the change in the volume per rotor rotational amount) correlates with the change rate dr/dθ of the vane projection amount r with respect to θ at each of the positions of the two vanes 32 sandwiching this pump chamber 38. A function of dv/dθ with respect to θ can be drawn in a generally same form as the function of dr/dθ with respect to θ. The change amount dv/dθ of the pump chamber 38 communicating with the discharge port 222 while overlapping either the confinement region A or B can be approximated by, for example, dr/dθ at the position of the rear vane 32 (passing through the region A) of the two vanes 32 sandwiching this pump chamber 38 on the region A side. The change amount dv/dθ can be approximated by dr/dθ at the position of the front vane 32 (passing through the region B) of the two vanes 32 sandwiching this pump chamber 38 on the region B side.

FIG. 7(b) is a characteristic diagram illustrating a relationship between dv/dθ of each of the pump chambers 38 in communication (connection) with the discharge port 222, and θ in the ⅓ eccentricity state. FIG. 7(b) omits illustration of dv/dθ before θ_1S where the pump chamber 38 starts communicating with the discharge port 222 (the rear vane 32 passes through the terminating end portion 221b of the intake port 221) on the first confinement region A side for each of the pump chambers 38. Further, FIG. 7(b) omits illustration of dv/dθ after θ_2E where the pump chamber 38 is disconnected from the discharge port 222 (the front vane 32 passes through the start end portion 221a of the intake port 221) on the second confinement region B side. FIG. 7(a) is a characteristic diagram illustrating a relationship between dV/dθ (=Σdv/dθ), which is a sum of dv/dθ of all of the pump chambers 38 in communication with the discharge port 222, and θ in the ⅓ eccentricity state. The change amount dV/dθ corresponds to a discharge flow amount Q of the entire pump 1. The change amounts dv/dθ of the individual pump chambers 38 in communication with the discharge port 222 each contribute to the amount Q. When dv/dθ of some pump chamber 38 in communication with the discharge port 222 is a negative value, this pump chamber 38 is in a compression process, and this pump chamber 38 is supplying the liquid to the discharge port 222 (operates in a discharge phase). The change amount dv/dθ of this pump chamber 38 contributes to an increase in the amount Q. On the other hand, when dv/dθ of some pump chamber 38 in communication with the discharge port 222 is a positive value, this pump chamber 38 is in an expansion process, and this pump chamber 38 is introducing the liquid from the discharge port 222 (operates in an intake phase). The change amount dv/dθ of this pump chamber 38 contributes to a reduction in the amount Q. When the volume change amount dV/dθ of all of the pump chambers 38 in communication with the discharge port 222 is a negative value, the pump 1 is discharging the hydraulic liquid by the amount Q that is large if an absolute value of this dV/dθ is large.

A high pressure in the pump chamber 38 in communication with the discharge port 222 is applied to the inner peripheral surface 330 of the cam ring 33, and generates the force for radially moving the cam ring 33. A difference in the above-described force between these confinement regions A and B acts on the cam ring 33 in a direction connecting these regions A and B, and this serves as a cause of oscillation of the cam ring 33. Now, the number of vanes 32 is the odd number. Therefore, the communication between the pump chamber 38 and the discharge port 222 on the region A side, and the communication between the pump chamber 38 and the intake port 221 on the region B side are started at different timings from each other. More specifically, while some vane 32 is passing through the region A after being separated from the terminating end portion 221b (θ_1S) of the intake port 221 (when the pump chamber 38 defined in front of this vane 32 is in communication with the discharge port 222), before this vane 32 reaches the start end portion 222a (θ_1E) of the discharge port 222 (the pump chamber 38 defined behind this vane 32 is separated from the intake port 221 and starts communicating with the discharge port 222), another vane 32 passing through the region B reaches the start end portion 221a (θ_2E) of the intake port 221 (the pump chamber 38 defined behind this vane 32 is separated from the discharge port 222 and starts communicating with the intake port 221). In other words, when the pump chamber 38 starts communicating with the intake port 221 on the region B side (the pressure applied from the pump chamber 38 to the inner peripheral surface 330 of the cam ring 33 is switched from the high pressure to the low pressure), the pump chamber 38 remains in communication with the discharge port 222 or the intake port 221 on the region A side (the pressure applied from the pump chamber 38 to the inner peripheral surface 330 is not largely switched). Further, when the pump chamber 38 starts communicating with the discharge port 222 on the region A side (the pressure in the pump chamber 38 that is applied to the inner peripheral surface 330 is switched from the low pressure to the high pressure), the pump chamber 38 remains in communication with the discharge port 222 or the intake port 221 on the region B side (the pressure applied from the pump chamber 38 to the inner peripheral surface 330 is not largely switched). Therefore, the difference in the above-described force that acts in the direction connecting these regions A and B can be eliminated or reduced compared to when the above-described timings overlap each other, such as when the pump chamber 38 starts communicating with the discharge port 222 on the region A side (the pressure in the pump chamber 38 that is applied to the inner peripheral surface 330 is switched from the low pressure to the high pressure) at an approximately same timing as the timing at which the pump chamber 38 starts communicating with the intake port 221 on the region B side (the pressure in the pump chamber 38 that is applied to the inner peripheral surface 330 is switched from the high pressure to the low pressure). Therefore, the oscillation of the cam ring 33 is prevented or reduced, which makes it easy to alleviate the change in the discharge flow amount Q, thereby reducing the pulse pressure. The number of vanes 32 is not limited to eleven, and may be, for example, nine, thirteen, or the like. In the present embodiment, the discharge port 222 includes the notch portion 225 on the start end portion 222a thereof. Therefore, when the pump chamber 38 starts communicating with the discharge port 222 on the region A side, the inflow of the hydraulic liquid from the discharge port 222 into the pump chamber 38 is restricted by the notch portion 225, which prevents or cuts down a sudden increase in the pressure in the above-described pump chamber 38. As a result, the pulse pressure can also be reduced. The shape of the notch portion 225 is not limited to the shape in the present embodiment.

The inner peripheral surface 330 of the cam ring 33 is formed in such a manner that the front vane 32 in the region B passes through the start end portion 221a (θ_2E) of the intake port 221 when the rear vane 32 passing through the region A is positioned slightly offset toward the one side located in the direction of the rotation (one side where the start end portion 222a (θ_1E) of the discharge port 222 is located) from the position ½ pitch away from the terminating end portion 221b (θ_1S) of the intake port 221 (toward the one side located in the direction of the rotation). In other words, when the front vane 32 passing through the region B is positioned slightly offset toward the opposite side located in the direction of the reverse rotation (one side where the terminating end portion 222b (θ_2S) of the discharge port 222 is located) from the position ½ pitch away from the terminating end portion 222b (θ_2S) of the discharge port 222 (toward the one side located in the direction of the rotation), the front vane 32 in the region A passes through the start end portion 222a (θ_1E) of the discharge port 222. Therefore, at the point that a range occupied by the pump chambers 38 (applying the high pressure to the inner peripheral surface 330) in communication with the discharge port 222 on the region B is relatively small, the pump chamber 38 starts communicating with the discharge port 222 on the region A side and the high pressure is applied from this pump chamber 38 to the inner peripheral surface 330. As a result, the difference in the above-descried force that acts in the direction connecting these regions A and B as a whole works in a direction pushing the cam ring 33 toward one side where the eccentricity amount δ thereof increases, which can prevent or cut down an unintentional reduction in δ (a cam drop).

Further, when the pump chamber 38 passing through either the region A or B starts communicating with the discharge port 222 or stops communicating with the discharge port 222 with the volume v thereof changing (increasing or reducing), the volume change amount dV/dθ (the negative value) of all of the pump chambers 38 in communication with the discharge port 222 may discontinuously change and the discharge flow amount Q may change every time. The changing direction (increase or decrease) of this amount Q varies according to whether the volume v of this pump chamber 38 is increasing or reducing (the sign of dv/dθ) at the time of the communication (the disconnection) with the discharge port 222. More specifically, when the pump chamber 38 passing through the region A starts communicating with the discharge port 222, if the volume v of this pump chamber 38 is in a reducing state (dv/dθ is negative), the liquid amount (corresponding to the absolute value of dV/dθ) supplied from all of the pump chambers 38 in communication with the discharge port 222 to the discharge port 222 suddenly increases due to the start of the above-described communication. Therefore, the amount Q discontinuously increases. On the other hand, if the volume v of the above-described pump chamber 38 is in an increasing state (dv/dθ is positive), the liquid amount supplied from all of the pump chambers 38 in communication with the discharge port 222 to the discharge port 222 suddenly reduces due to the start of the above-described communication. Therefore, the amount Q discontinuously reduces. Similarly, when the pump chamber 38 passing through the region B is disconnected from the discharge port 222, the liquid amount supplied from all of the pump chamber 38 in communication with the discharge port 222 to the discharge port 222 suddenly increases due to the above-described disconnection (the isolation from the discharge port 222) if the volume v of this pump chamber 38 is in the increasing state (dv/dθ is positive). Therefore, the amount Q discontinuously increases. On the other hand, the liquid amount supplied from all of the pump chamber 38 in communication with the discharge port 222 to the discharge port 222 suddenly reduces due to the above-described disconnection (the isolation from the discharge port 222) if the volume v of the above-described pump chamber 38 is in the reducing state (dv/dθ is negative). Therefore, the amount Q discontinuously reduces. As described above, the number of vanes 32 is the odd number, whereby the timing of the communication/disconnection between the discharge port 222 and the pump chamber 38 is asynchronous between the region A and the region B. The number of times that the amount Q discontinuously changes while the driving shaft 30 rotates once is twice when the above-described timing is synchronous between these regions A and B, and twice (twenty-two times) the number of pump chambers 38 (the vanes 32) (eleven).

As illustrated in FIG. 3, the sign of dr/dθ in the region A is negative in the maximum eccentricity state. This means that the vane projection amount r reduces according to the rotation of the roto 31 in the region A. In other words, the sign of dv/dθ is negative and the volume v of the pump chamber 38 in communication with the discharge port 222 reduces according to the rotation of the rotor 31 on the region A side in the maximum eccentricity state. In other words, the above-described pump chamber 38 in the region A is brought into a compressed process, i.e., the discharge phase. As a result, a further larger discharge flow amount Q can be secured. Especially, in the case where the variable displacement vane pump is used for the power steering apparatus, a large flow amount is required in the maximum eccentricity state. Securing the large flow amount Q as described above can prevent or reduce deterioration of a steering feeling caused due to insufficiency of the flow amount. The sign of dr/dθ is negative in the entire range of the region A, whereby the above-described effect can be enhanced. Further, if the vane 32 is spaced apart from the inner peripheral surface 330 of the cam ring 33 in the region A or B, the pressure pulsation (the pulse pressure) may occur due to a sudden inflow of the liquid from the pump chamber 38 on the high-pressure side to the pump chamber 38 on the low-pressure side that sandwich this vane 32. Especially in the maximum eccentricity state, the vane 32 being spaced apart (vane separation) from the inner peripheral surface 330 likely occurs due to, for example, a small number of rotations of the pump. To avoid this risk, the amount r reduces in the direction of the rotation (as the vane 32 travels from the terminating end portion 221b (θ_1S) of the intake port 221 toward the start end portion 222a (θ_1E) of the discharge port 222) in the region A in the maximum eccentricity state. Therefore, the vane separation and thus the occurrence of the pulse pressure can be prevented or reduced. Similarly, as illustrated in FIG. 5, in the maximum eccentricity state, the sign of dr/dθ in the region B is negative and the volume v of the pump chamber 38 in communication with the discharge port 222 reduces according to the rotation of the rotor 31. In other words, the above-described pump chamber 38 in the region B is brought into the discharge phase. As a result, a large flow amount Q can be secured similarly to the above-described region A. Because the sign of dr/dθ is negative in the entire range of the region B, the above-described effect can be enhanced. Further, the vane separation and thus the occurrence of the pulse pressure can be prevented or reduced in the region B.

As illustrated in FIG. 4, the sign of dr/dθ is negative in the region A in the ⅓ eccentricity state. This means that the vane projection amount r reduces according to the rotation of the rotor 31 in the region A. In other words, the sign of dv/dθ is negative and the volume v of the pump chamber 38 in communication with the discharge port 222 reduces according to the rotation of the rotor 31 on the region A side in the ⅓ eccentricity state. Therefore, the above-described pump chamber 38 in the region A is brought into the discharge phase similarly to the maximum eccentricity state. As a result, a further large flow amount Q can be secured. Since the sign of dr/dθ is negative in the entire range of the region A, the above-described effect can be enhanced. Further, the vane separation can be prevented or reduced in the region A.

As described above, dV/dθ may discontinuously change and the discharge flow amount Q may discontinuously change (vary) every time the pump chamber 38 passing through either the confinement region A or B, while the volume v thereof is changing, communicates with or is disconnected from the discharge port 222. This may lead to the pulse pressure (the pulsation). As illustrated in FIGS. 4 and 7(b), in the ⅓ eccentricity state, immediately before O_1S where the pump chamber 38 starts communicating with the discharge port 222 (the rear vane 32 passes through the terminating end portion 221b of the intake port 221) on the region A side, dv/dθ of this pump chamber 38 (dr/dθ at the rear vane 32) is a negative value (v and r are reducing). Therefore, when this pump chamber 38 communicates with the discharge port 222 at θ_1S, the absolute value of dV/dθ (the negative value) immediately increases, and this contributes in a direction for increasing the amount Q. On the other hand, immediately before θ_2E where the pump chamber 38 is disconnected from the discharge port 222 (the front vane 32 passes through the start end portion 221a of the intake port 221) on the region B side, dv/dθ of this pump chamber 38 (in communication with the discharge port 222) (dr/dθ at the front vane 32) is a positive value (v and r are increasing). Therefore, when this pump chamber 38 is disconnected from the discharge port 222 at θ_2E, the absolute value of dV/dθ (the negative value) suddenly increases, and this also contributes in the direction for increasing the amount Q. The conventional technique has failed to take into consideration such a change in the amount Q when the pump chamber 38 is disconnected from the discharge port 222 on the region B side, and has left room to reduce the pulse pressure due to that. Especially, the pulse pressure has a further significant influence in the ⅓ eccentricity state. More specifically, noise (whine noise) likely becomes a problem.

The absolute value of dr/dθ gradually reduces, and then gradually increases after reaching the extremely small value dr/dθ₁* at θ₁*, as the vane 32 travels from θ_1S toward θ_1E in the region A in the ⅓ eccentricity state. The absolute value of dv/dθ gradually reduces, and then gradually increases after reaching the extremely small value dv/dθ₁* at θ₁** (≈θ₁*), according to the rotation of the rotor 31. Therefore, when the front vane 32 of the pump chamber 38 (the vane 32 passing through the region B) reaches the start end portion 221a of the intake port 221 (the rear vane 32 reaches the terminating end portion 222b of the discharge port 222) and the communication between this pump chamber 38 and the discharge port 222 is blocked at θ_2E on the region B side, the absolute value of dr/dθ at the position of the rear vane 32 of the pump chamber 38 (the vane 32 passing through the region A) falls within a predetermined range where the extremely small value dr/dθ₁* is set as a minimum value therein and the absolute value of dv/dθ of this pump chamber 38 falls within a predetermined range where the extremely small value dv/dθ₁* is set as a minimum value therein on the region A side. The absolute value of dv/dθ (the negative value) falling within the predetermined range where the extremely value dr/dθ₁* is set as the minimum value therein in the region A means that the rate of the contraction of the pump chamber 38 contracting in the region A is low, and the rate of the reduction in dV/dθ due to the contraction of this pump chamber 38 is small, i.e., the rate of the increase in the absolute value of dV/dθ (the negative value) is small. The sudden increase in the absolute value of dV/dθ (the negative value) (at θ_2E) when the pump chamber 38 is disconnected from the discharge port 222 on the region B side is alleviated due to the low rate of the increase in the absolute value of dV/dθ (the negative value) on the region A side. In other words, when the expanding pump chamber 38 is disconnected from the discharge port 222 (θ_2E) in the region B, the rate of the contraction of the pump chamber 38 communicating with the discharge port 222 and also contracting is close to dv/dθ₁* and has a small absolute value in the region A, which prevents or cuts down a considerable change (a sudden increase) in dV/dθ. As a result, the change in the amount Q is alleviated, so that the pulse pressure in the entire pump 1 can be reduced. In this manner, the inner peripheral surface 330 of the cam ring 33 is formed in such a manner that dr/dθ or dv/dθ has the above-described characteristic in the ⅓ eccentricity state in which the pulse pressure has a significant influence, whereby a function of reducing the pulse pressure when the pump 1 is driven can be further effectively acquired. The above-described advantageous effects can be acquired by forming the inner peripheral surface 330 in such a manner that the absolute value of dr/dθ gradually reduces, and then gradually increases after reaching the extremely small value, as the vane 32 travels from θ_1S toward θ_1E in at least a part of the region A.

More specifically, the point θ₁* where the absolute value of dr/dθ (dv/dθ) reaches the extremely small value dr/dθ₁* (dv/dθ₁*) is located in the range from ⅓ pitch to ⅔ pitch from the terminating end portion 221b (θ_1S) of the intake port 221, inclusive, in the region A in the ⅓ eccentricity state. Since the number of vanes 32 is the odd number, the front vane 32 passing through the region B passes through the start end portion 221a (θ_2E) of the intake port 221 when the rear vane 32 passing through the region A is located at or around the point θ_1(1/2) ½ pitch away from the terminating end portion 221b (θ_1S) of the intake port 221. Therefore, θ₁* can be arranged closer to θ_2E where dV/dθ suddenly changes on the region B side, by placing θ₁* in the above-described range (θ_1(1/3) to θ_1(2/3)). This results in that the absolute value of dr/dθ (dv/dθ) of the rear vane 32 in the region A substantially has the extremely small value dr/dθ₁* (dv/dθ₁*) when the front vane 32 passes through θ_2E in the region B, thereby succeeding in further effectively reducing the pulse pressure.

Further, as illustrated in FIG. 4, the change gradient Δ2 is greater than the change gradient Δ1 in the region A in the ⅓ eccentricity state. The change gradient Δ2 greater than Δ1 means that, according to the rotation of the rotor 31, compared to how much the rate of the contraction (the absolute value of dv/dθ) of the pump chamber 38 contracting on the region A side reduces on the first half side from θ₁*, how much the above-described contraction rate increases on the second half side from θ₁* after that is larger, i.e., the rate of the increase in the absolute value of dV/dθ (the negative value) is high on the above-described second half side. The volume v of the pump chamber 38 in communication with the discharge port 22 on the region A side further swiftly reduces on the above-described second half side and the absolute value of dV/dθ (the negative value) increases at the high rate on the above-described second half side, which allieviates the change in dV/dθ (after θ_2E) after the pump chamber 38 is disconnected from the discharge port 222 and the absolute value of dV/dθ (the negative value) suddenly increases on the region B side (an angle δ illustrated in FIG. 7(a) increases). Therefore, the pulse pressure can be further effectively reduced. It is preferable that Δ2/Δ1 is 1.1 or higher. In this case, the change in dV/dθ after the pump chamber 38 is disconnected from the discharge port 222 (after θ_2E) on the region B side can be further effectively reduced. It is preferable that Δ2/Δ1 is 1.15 or higher. By that, the above-described change in dV/dθ can be further effectively reduced. In the present embodiment, Δ2/Δ1 is approximately 1.24 (i.e., 1.15 or higher), and therefore can acquire the above-described effect.

The characteristic of dr/dθ or the like in the maximum eccentricity state may also be set in a similar manner to the ⅓ eccentricity state, besides the above-described setting. For example, the inner peripheral surface 330 of the cam ring 33 may be formed in such a manner that the absolute value of dr/dθ gradually reduces, and then gradually increases after reaching the extremely small value, as the vane 32 travels from θ_1S toward θ_1E in the region A in the maximum eccentricity state. Alternatively, the inner peripheral surface 330 of the cam ring 33 may be formed in such a manner that the amount r gradually increases in the region B at least in a partial (the θ_2E side) range continuous from the terminating end portion (θ_2E) thereof. In these cases, advantageous effects similar to those in the above-described ⅓ eccentricity state can also be acquired.

In the comparative example indicated by the long dashed double-dotted line in FIG. 6, the inner peripheral surface 330 of the cam ring 33 is formed in such a manner that the change rate of dr/dθ with respect to θ is a positive value in the entire range of the region B in the minimum eccentricity state. Therefore, the absolute value of the above-described change rate of dr/dθ generally does not change as the vane 32 travels from θ_2S toward θ_2E in the region B in the ⅓ eccentricity state. As a result, dr/dθ has a large change gradient in the range from θ_2S to θ_2E and dr/dθ has a great magnitude at θ_2E (when the communication between the pump chamber 38 and the discharge port 222 is blocked in the region B) in the ⅓ eccentricity state. On the other hand, in the present embodiment, the inner peripheral surface 330 is formed in such a manner that there is the region Ba where the above-described change rate of dr/dθ has at least a negative value (there are the θ region Ba where the above-describe change rate of dr/dθ has a negative value and the θ region Bb where the above-described change rate of dr/dθ has a positive value) in the region B in the minimum eccentricity state as indicated by a solid line in FIG. 6. Therefore, the absolute value of the above-described change rate of dr/dθ (the slope of the graph of dr/dθ with respect to θ) generally gradually reduces as the vane 32 travels from θ_2S toward θ_2E in the region B in the ⅓ eccentricity state. As a result, dr/dθ has a small change gradient in the range from θ_2S to θ_2E in the ⅓ eccentricity state. Therefore, dr/dθ_2E, which is dr/dθ at θ_2E, has a small magnitude. In other words, the magnitude dv/dθ_2E of dv/dθ at θ_2E, i.e., a width of the change in dV/dθ when the communication between the pump chamber 38 and the discharge port 222 is blocked in the region B is reduced as illustrated in FIG. 7. Therefore, the change in the amount Q is alleviated, and the pulse pressure is reduced.

The sign of dr/dθ (dv/dθ) may be positive in a partial range (the θ_1E side) of the region A. In other words, the amount r (the volume v) may gradually increase in the direction of the rotation of the rotor 31 (as the vane 32 travels from the θ_1S side toward θ_1E) in this range. This means that the pressure in the pump chamber 38 may increase excessively (for example, increase to higher than the discharge pressure) on the θ_1E side in the region A in the minimum eccentricity state when the inner peripheral surface 330 of the cam ring 33 is formed in such a manner that the amount r gradually reduces in the region A in the maximum eccentricity state. In this case, a large difference is generated in the force applied to the inner peripheral surface 330 between the region A and the region B, so that the cam ring 33 may oscillate (the pulse pressure may occur). To avoid this risk, the difference in the above-described force and thus the occurrence of the pulse pressure can be prevented or reduced by, for example, forming the inner peripheral surface 330 in such a manner that the sign of dr/dθ (dv/dθ) becomes positive in at least a partial range (the θ_1E side) of the region A in the minimum eccentricity state.

Further, the sign of dr/dθ (dv/dθ) may be negative in at least a partial range (the θ_2E side) of the region B. In other words, the amount r (the volume v) may gradually reduce in the direction of the rotation of the rotor 31 (as the vane 32 travels from the θ_2S side toward θ_2E) in this rage. In this case, the absolute value of dV/dθ (the negative value) suddenly reduces when the pump chamber 38 is disconnected from the discharge port 222 at θ_2E in the region B. This contributes in the direction for reducing the amount Q. At this time, if dv/dθ of the pump chamber 38 communicating with the discharge port 222 while passing through the region A is a negative value (if v is reducing), this contributes in the direction for increasing the amount Q as described above. Therefore, the change (the sudden reduction) in the amount Q due to the sudden change in dV/dθ at θ_2E on the region B side can be controlled or cut down by making an arrangement in such a manner that dv/dθ (dr/dθ) on the region A side changes so as to cause the absolute value of dv/dθ (the negative value) on the region A side to have a large value at the time of this sudden change. More specifically, the inner peripheral surface 330 of the cam ring 33 is formed in such a manner that the absolute value of dr/dθ (the negative value) gradually increases and then gradually reduces after reaching an extremely large value in the direction of the rotation of the rotor 31 (as the vane 32 travels from θ_1S toward θ_1E) in the region A. The absolute value of dv/dθ (the negative value) (the rate of the contraction of the pump chamber 38) gradually increases and then gradually reduces after reaching an extremely large value according to the rotation of the rotor 31. As a result, the change (the sudden reduction) in the amount Q due to the sudden change in dV/dθ on the region B side can be alleviated by the change (the facilitated increase) in the amount Q due to the increase in the absolute value of dv/dθ (amplification of the negative value toward an extremely large value side) on the region A side. In other words, the rate of the contraction (the absolute value of dv/dθ) of the pump chamber 38 contracting in the region A increases toward the extremely large value when the contracting pump chamber 38 is disconnected from the discharge port 222 in the region B (θ_2E), by which a large change in dV/dθ is prevented or cut down.

On the other hand, if dv/dθ of the pump chamber 38 communicating with the discharge port 222 while passing through the region A is a positive value (if v is increasing), this contributes in the direction for reducing the amount Q. Therefore, the change (the sudden reduction) in the amount Q due to the sudden change in dV/dθ at θ_2E on the region B side can be controlled or cut down by making an arrangement in such a manner that dv/dθ (dr/dθ) on the region A side changes so as to cause the absolute value of dv/dθ (the positive value) on the region A side to have a small value at the time of this sudden change. More specifically, the inner peripheral surface 330 of the cam ring 33 is formed in such a manner that the absolute value of dr/dθ (the positive value) gradually reduces and then gradually increases after reaching an extremely small value in the direction of the rotation of the rotor 31 in the region A. The absolute value of dv/dθ (the rate of the expansion of the pump chamber 38) gradually reduces and then gradually increases after reaching an extremely small value according to the rotation of the rotor 31. As a result, the change (the sudden reduction) in the amount Q due to the sudden change of dV/dθ on the region B side can be alleviated by the change (a suppressed reduction) in the amount Q due to the reduction in the absolute value of dv/dθ (suppression of the positive value toward an extremely small value side) on the region A side.

In each of the above-described cases, the characteristic of dr/dθ or the like may be exchanged between the region A side and the region B side. In other words, the inner peripheral surface 330 may be formed in such a manner that dv/dθ (dr/dθ) on the region B side changes in a direction for reducing the change in dv/dθ (dr/dθ) when the pump chamber 38 starts communicating with the discharge port 222 according to the rotation of the rotor 31 on the region A side (θ_1S). In this case, the change in the amount Q due to the sudden change in dV/dθ on the region A side can be reduced. An important point is that the present embodiment can be realized as long as, at the timing when the pump chamber 38 communicates with or is disconnected from the discharge port 222 on one side corresponding to one of the confinement regions or a timing close thereto, the change in dv/dθ (dr/dθ) on another side corresponding to the other of the confinement regions has an extreme value in the direction for reducing the change in dv/dθ (dr/dθ) at the time of the above-described communication/disconnection.

The range of each of the regions A and B does not have to be approximately one pitch, and may be, for example, 1.5 pitch or the like. Setting the size of the region to approximately one pitch or larger can prevent the pump chamber 38 passing through either the region A or B from communicating with both the intake port 221 and the discharge port 222. Reducing the range to as small as approximately one pitch allows the pump 1 to further efficiently intake and discharge the hydraulic liquid as a whole, thereby increasing the discharge flow amount.

In the pump housing 2, the pair of surfaces (the surface 210 of the front body 21 on the z-axis negative direction side and the surface 220 of the side plate 22 on the z-axis positive direction side) facing the region A and the region B in the direction along the rotational axis of the driving shaft 30 (the z-axis direction) is formed so as to extend in parallel with each other and is each shaped into a flat surface. Therefore, the volume v of the pump chamber 38 does not change in the z-axis direction, and the volume v of the pump chamber 38 in each of the regions A and B does not change depending on the shape of the surface of the pump housing 2. In other words, the change in the shape of the inner peripheral surface 330 of the cam ring 33 in the direction of the rotation of the rotor 31 (dr/dθ, hereinafter this will be referred to as a cam profile) is generally directly reflected as the change in the volume v. Therefore, the characteristic of the volume change dv/dθ of the pump chamber 38 in each of the regions A and B can be adjusted only by an adjustment of the change in the above-described shape (the cam profile). Therefore, the adjustment for reducing the pulse pressure can be easily achieved. The cam profile in each of the eccentricity states may be adjusted not only by the adjustment of the shape of the inner peripheral surface 330 of the cam ring 33 itself but also by an adjustment of the shape of the inner peripheral surface 340 (the second support surface 342) of the adaptor ring 34 (changing the position of the central axis P in the y-axis direction relative to the shaft center O according to the eccentricity amount δ).

The discharge port 222 includes the notch portion 225 only on the start end portion 222a side thereof (the terminating end portion θ_IE side of the region A). In other words, there is no notch portion on the terminating end portion 222b side of the discharge port 222 (the start end portion θ_2S side of the region B). Actually, it is also conceivable to, for example, by providing a notch portion like the one in communication with the intake port 221 via the pump chamber 38 on the terminating end portion 222b side of the discharge port 222, reduce the pulse pressure due to the change in the volume when the communication of this pump chamber 38 with the discharge port 222 is blocked. However, in this case, the discharge port 222 and the intake port 221 are in communication with each other via the notch portion (via the pump chamber 38 in communication with the notch portion) in the region B, so that a leak amount increases. Therefore, this method may lead to deterioration of the pump efficiency. Then, it is also conceivable to employ a layout that prevents the discharge port 222 and the intake port 221 from communicating with each other via the notch portion (via the pump chamber 38 in communication with the notch portion) while providing the notch portion on the terminating end portion 222b side of the discharge port 222. However, this case results in that, with the rear vane 32 overlapping with the notch portion (with the notch portion causing a change in the volume of the pump chamber 38 sandwiched by the front vane 32 and the rear vane 32) in the region B, the projection amount r of the front vane 32 (the volume v of this pump chamber 38) is adjusted by the cam profile. Therefore, it may become difficult to appropriately reduce the above-described pulse pressure due to the change in the volume at the time of the disconnection between this pump chamber 38 and the discharge port 222, by adjusting the shape of the inner peripheral surface 330 of the cam ring 33. On the other hand, in the present embodiment, no notch portion is provided on the terminating end portion 222b side of the discharge port 222. Therefore, the present embodiment can further effectively achieve both the reduction in the pulse pressure and the prevention or reduction in the deterioration of the pump efficiency. In the region A, the notch portion 225 on the start end portion 222a side of the discharge port 222 is not in communication with the intake port 221 via the pump chamber 38. Therefore, the deterioration of the pump efficiency can be prevented or reduced. Further, this method results in that, without the front vane 32 overlapping with the notch portion 225 (with the notch portion 225 causing no change in the volume of the pump chamber 38 sandwiched between the front vane 32 and the rear vane 32), the projection amount r of the front vane 32 (the volume v of this pump chamber 38) is adjusted by the cam profile. Therefore, the above-described pulse pressure due to the change in the volume when this pump chamber 38 starts communicating with the discharge port 222 (the notch portion 225) can be easily appropriately reduced by the adjustment of the above-described camp profile.

Second Embodiment

The inner peripheral surface 330 of the cam ring 33 is formed in the following manner. In the maximum eccentricity state, as illustrated in FIG. 8, the sign of the change rate dr/dθ is negative in the entire range of the first confinement region A, and the sign of dr/dθ is negative at least on one side where the start end portion 221a (θ_2E) of the intake port 221 is located in the second confinement region B. In the ⅓ eccentricity state, as illustrated in FIG. 9, the sign of dr/dθ is negative in the region A. The absolute value of dr/dθ gradually reduces, and then gradually increases after reaching the extremely small value dr/dθ₁* at θ₁*, as the vane 32 travels from the terminating end portion 221b (θ_1S) of the intake port 221 toward the start end portion 222a (θ_1E) of the discharge port 222. The point θ₁* is located in a range from ½ pitch to ⅔ pitch from θ_1S inclusive. In other words, the point θ₁* is located between the point θ_1(1/2) positioned ½ pitch away from θ_1S, and the point θ_1(2/3) positioned ⅔ pitch away from θ_1S. The region A is one pitch. Therefore, θ₁* is located on a second half side (a θ_1(2/3) side) of the range of the central portion (θ_1(1/3) to θ_1(2/3)) when the region A is divided into the three portions. In the ⅓ eccentricity state, the second change gradient Δ2 is greater than the first change gradient Δ1 (Δ1<Δ2). In the present embodiment, Δ2/Δ1 is approximately 1.76. Other configurations are similar to the first embodiment.

Similarly to the first embodiment, when the rear vane 32 passing through the region A is located slightly offset toward the θ_1E side from the position ½ pitch away from θ_1S, the front vane 32 in the region B passes through the start end portion 221a of the intake port 221. In the present embodiment, in the ⅓ eccentricity state, θ₁* is located in the range from the position ½ pitch away from θ_1S to the position ⅔ pitch away from θ_1S in the region A. As a result, the point θ₁* where the absolute value of the contraction rate dv/dθ (the negative value) of the pump chamber 38 communicating with the discharge port 222 (while also contracting) on the region A side reduces to dv/dθ₁* can be further adapted to (arranged closer to) the point θ_2E where the (expanding) pump chamber 38 is disconnected from the discharge port 222 on the region B side. Therefore, the pulse pressure can be further effectively reduced. Further, since Δ2/Δ1 is approximately 1.76 (i.e., 1.15 or higher), the change in dV/dθ after the pump chamber 38 is disconnected from the discharge port 222 on the region B side (after θ_2E) can be further effectively controlled or reduced. Other advantageous effects of the second embodiment are similar to the first embodiment.

Other Embodiments

Having described the vane pump according to the present invention based on the embodiments thereof, the specific configuration of the present invention is not limited to the embodiments, and the present invention also includes a design modification and the like thereof made within a range that does not depart from the spirit of the present invention. For example, the vane pump to which the present invention is applied may be used as a hydraulic supply source of another apparatus (an engine of a vehicle or the like) than the power steering apparatus. The slots (or the vanes) of the vane pump do not have to extend in the radial direction of the rotor, and may be inclined at some angle from the radial direction of the rotor. The specific configuration of the cam ring control mechanism is not limited to the configuration in the first embodiment, and may be, for example, such a configuration that the pressure is also supplied to the first chamber and the first chamber functions as the fluid pressure chamber.

[Technical Ideas Recognizable from Embodiments]

Technical ideas (or technical solutions, the same applies hereinafter) recognizable from the above-described embodiments can be provided as described below.

• (1) One aspect of a variable displacement vane pump according to the present technical ideas, in one embodiment thereof, includes

a pump housing including a pump element containing portion,

a driving shaft supported on the pump housing,

a rotor provided in the pump housing and configured to be rotationally driven by the driving shaft while also including an odd number of slots in a circumferential direction,

an odd number of vanes provided in the slots in a manner projectable therefrom and retractable therein,

a cam ring movably provided in the pump element containing portion and annularly formed while forming a plurality of pump chambers on an inner peripheral side in cooperation with the rotor and the vanes,

an intake port formed in the pump housing and opened to a region where a volume of each of the plurality of pump chambers increases according to a rotation of the rotor,

a discharge port formed in the pump housing and opened to a region where the volume of each of the plurality of pump chambers reduces according to the rotation of the rotor, and

a cam ring control mechanism provided in the pump housing and configured to control an amount of eccentricity of the cam ring from the rotor.

Then, assume that a distance between the vanes adjacent to each other in a direction around a rotational axis of the driving shaft is one pitch, a vane projection amount refers to a distance from a center of a rotation of the driving shaft to an inner peripheral surface of the cam ring, and

a first confinement region is defined to be a region between a terminating end portion of the intake port and a start end portion of the discharge port.

The inner peripheral surface of the cam ring is formed in the following manner. At least in a part of the first confinement region, an absolute value of a change rate of the vane projection amount with respect to a rotational amount of the rotor gradually reduces and then gradually increases after reaching an extremely small value as the vane travels from the terminating end portion of the intake port toward the start end portion of the discharge port.

A point where the absolute value of the change rate reaches the extremely small value is located in a range from ⅓ pitch to ⅔ pitch from the end portion of the intake port, inclusive.

In the first confinement region, a change gradient of the change rate since the absolute value of the change rate reaches the extremely small value until stopping the increase is greater than a change gradient of the change rate since the absolute value of the change rate starts the reduction until reaching the extremely small value.

• (2) In a further preferable embodiment, the variable displacement vane pump according to the above-described embodiment is configured in the following manner. Assuming that a second confinement region is defined to be a region between an end portion of the discharge port and a start end portion of the intake port, in the pump housing, a pair of surfaces facing the first confinement region in a direction along the rotational axis of the driving shaft is formed so as to extend in parallel with each other and each shaped as a flat surface, and a pair of surfaces facing the second confinement region in the direction along the rotational axis of is formed so as to extend in parallel with each other and each shaped as a flat surface.
• (3) In another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that the point where the absolute value of the change rate reaches the extremely small value is located in a range from ½ to ⅔ pitch from the end portion of the intake port, inclusive, at least in a part of the first confinement region.
• (4) In still another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that, when the cam ring is moved by ⅓ of an entire eccentricity amount from a position where the eccentricity amount of the cam ring is maximized toward a position where the eccentricity amount of the cam ring is minimized, the absolute value of the change rate gradually reduces and then gradually increases after reaching the extremely small value as the vane travels from the end portion of the intake port toward the start end portion of the discharge port at least in a partial range of the first confinement region, the point where the absolute value of the change rate reaches the extremely small value is located in a range from ⅓ pitch to ⅔ pitch from the end portion of the intake port, inclusive, and the change gradient of the change rate since the absolute value of the change rate reaches the extremely small value until stopping the increase is greater than the change gradient of the change rate since the absolute value of the change rate starts the reduction until reaching the extremely small value in the first confinement region.
• (5) In still another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that the vane projection amount constantly reduces as the vane travels from the end portion of the intake port toward the start end portion of the discharge port according to the rotation of the rotor in the first confinement region when the cam ring is located at the position where the eccentricity amount of the cam ring is maximized.
• (6) In still another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that a ratio of the change gradient of the change rate since the absolute value of the change rate reaches the extremely small value until stopping the increase to the change gradient of the change rate since the absolute value of the change rate starts the reduction until reaching the extremely small value is 1.1 or higher in the first confinement region.
• (7) In still another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that a ratio of the change gradient of the change rate since the absolute value of the change rate reaches the extremely small value until stopping the increase to the change gradient of the change rate since the absolute value of the change rate starts the reduction until reaching the extremely small value is 1.15 or higher in the first confinement region.
• (8) In still another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that there is a region where a change rate of the change rate with respect to the rotational amount of the rotor has a negative value in the second confinement region, which is the region from the end portion of the discharge port to the start end portion of the intake port, when the cam ring is located at the position where the eccentricity amount of the cam ring is minimized.
• (9) In still another preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The discharge port includes a notch portion only on a start end portion side of the discharge port.
• (10) Another aspect of a variable displacement vane pump according to the present technical ideas, in one embodiment thereof, includes

a pump housing including a pump element containing portion,

a driving shaft supported on the pump housing,

a rotor provided in the pump housing and configured to be rotationally driven by the driving shaft while also including an odd number of slots in a circumferential direction, an odd number of vanes provided in the slots in a manner projectable therefrom and retractable therein,

a cam ring movably provided in the pump element containing portion and annularly formed while forming a plurality of pump chambers on an inner peripheral side in cooperation with the rotor and the vanes,

an intake port formed in the pump housing and opened to a region where a volume of each of the plurality of pump chambers increases according to a rotation of the rotor,

a discharge port formed in the pump housing and opened to a region where the volume of each of the plurality of pump chambers reduces according to the rotation of the rotor, and

a cam ring control mechanism provided in the pump housing and configured to control an amount of eccentricity of the cam ring from the rotor.

Then, assume that a distance between the vanes adjacent to each other in a direction around a rotational axis of the driving shaft is one pitch, a vane projection amount refers to a distance from a center of a rotation of the driving shaft to an inner peripheral surface of the cam ring, and a first confinement region is defined to be a region from a terminating end portion of the intake port to a start end portion of the discharge port.

The inner peripheral surface of the cam ring is formed in such a manner that, when the cam ring is moved by ⅓ of an entire eccentricity amount from a position where the eccentricity amount of the cam ring is maximized toward a position where the eccentricity amount of the cam ring is minimized, an absolute value of a change rate of the vane projection amount with respect to a rotational amount of the rotor gradually reduces and then gradually increases after reaching an extremely small value as the vane travels from the terminating end portion of the intake port toward the start end portion of the discharge port at least in a part of the first confinement region,

a point where the absolute value of the change rate reaches the extremely small value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, and

a change gradient of the change rate since the absolute value of the change rate reaches the extremely small value until stopping the increase is greater than a change gradient of the change rate since the absolute value of the change rate starts the reduction until reaching the extremely small value in the first confinement region.

• (11) In a further preferable embodiment, the variable displacement vane pump according to the above-described embodiment is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that the vane projection amount constantly reduces as the vane travels from the terminating end portion of the intake port toward the start end portion of the discharge port according to the rotation of the rotor in the first confinement region when the cam ring is located at the position where the eccentricity amount of the cam ring is maximized.
• (12) In a further preferable embodiment, the variable displacement vane pump according to any of the above-described embodiments is configured in the following manner. The inner peripheral surface of the cam ring is formed in such a manner that there is a region where a change rate of the change rate with respect to the rotational amount of the rotor has a negative value in a second confinement region, which is a region from a terminating end portion of the discharge port to a start end portion of the intake port, when the cam ring is located at the position where the eccentricity amount of the cam ring is minimized.

Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teaching and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. It is also possible to combine together the above-described embodiments as desired.

The present application claims priority to Japanese Patent Application No. 2016-058149 filed on Mar. 23, 2016. The entire disclosure of Japanese Patent Application No. 2016-058149 filed on Mar. 23, 2016 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.

REFERENCE SIGNS LIST

• 1 vane pump
• 2 pump housing
• 200 recessed portion (pump element containing portion)
• 221 intake port
• 222 discharge port
• 30 driving shaft
• 31 rotor
• 311 slot
• 32 vane
• 33 cam ring
• 330 inner peripheral surface
• 38 pump chamber
• 4 control portion (cam ring control mechanism)
• A first confinement region
• B second confinement region

Claims

1. A variable displacement vane pump comprising: a pump housing including a pump element containing portion;a driving shaft supported on the pump housing;a rotor provided in the pump housing and configured to be rotationally driven by the driving shaft, the rotor also including an odd number of slots in a circumferential direction of the rotor;an odd number of vanes provided in the slots in a manner projectable therefrom and retractable therein;a cam ring movably provided in the pump element containing portion and annularly formed, the cam ring forming a plurality of pump chambers on an inner peripheral side of the cam ring in cooperation with the rotor and the vanes;an intake port formed in the pump housing and opened to a region where a volume of each of the plurality of pump chambers increases according to a rotation of the rotor;a discharge port formed in the pump housing and opened to a region where the volume of each of the plurality of pump chambers reduces according to the rotation of the rotor; anda cam ring control mechanism provided in the pump housing and configured to control an amount of eccentricity of the cam ring from the rotor,wherein the cam ring has an inner peripheral surface formed in such a manner that,assuming that a distance between the vanes adjacent to each other in a direction around a rotational axis of the driving shaft is one pitch,in a first confinement region that is a region from a terminating end portion of the intake port to a start end portion of the discharge port,a vane projection amount, which is a distance from a center of a rotation of the driving shaft to the inner peripheral surface of the cam ring, gradually increases from the terminating end portion of the intake port and then gradually reduces toward the start end portion of the discharge port after passing through a point where the vane projection amount reaches a maximum value,the point where the vane projection amount reaches the maximum value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, andan absolute value of a gradient of a cam profile, which is a change rate of the vane projection amount, is larger in a range from a position ½ pitch away from the terminating end portion of the intake port to the start end portion of the discharge port than in a range from the terminating end portion of the intake port to ½ pitch therefrom.

2. The variable displacement vane pump according to claim 1, wherein, assuming that the second confinement region is a region between a terminating end portion of the discharge port and a start end portion of the intake port, the pump housing has a pair of surfaces facing the first confinement region and the second confinement region in a direction along the rotational axis of the driving shaft, the pair of surfaces being formed so as to extend in parallel with each other and each shaped as a flat surface.

3. The variable displacement vane pump according to claim 1, wherein the cam ring is formed in such a manner that the point where the vane projection amount reaches the maximum value is located in a range from a position ½ away from the terminating end portion of the intake port to a position ⅔ away from the terminating end portion of the intake port.

4. The variable displacement vane pump according to claim 1, wherein the inner peripheral surface of the cam ring is formed in such a manner that, when the cam ring is moved by ⅓ of an entire eccentricity amount from a position where the eccentricity amount of the cam ring is maximized toward a position side where the eccentricity amount of the cam ring is minimized, in the first confinement region that is the region between the terminating end portion of the intake port to the start end portion of the discharge port, the vane projection amount, which is the distance from the center of the rotation of the driving shaft to the inner peripheral surface of the cam ring, gradually increases from the terminating end portion of the intake port and then gradually reduces toward the start end portion of the discharge port after passing through the point where the vane projection amount reaches the maximum value,the point where the vane projection amount reaches the maximum value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, andthe absolute value of the gradient of the cam profile, which is the change rate of the vane projection amount, is larger in the range from the position ½ pitch away from the terminating end portion of the intake port to the start end portion of the discharge port than in the range from the terminating end portion of the intake port to ½ pitch therefrom.

5. The variable displacement vane pump according to claim 4, wherein the cam ring is formed in such a manner that the vane projection amount constantly reduces according to the rotation of the rotor in the first confinement region when the cam ring is located at the position where the eccentricity amount of the cam ring is maximized.

6. The variable displacement vane pump according to claim 1, wherein the cam ring is formed in such a manner that the absolute value of the gradient of the cam profile satisfies 1.1<=(the range from the position ½ pitch away from the terminating end portion of the intake port to the position of the start end portion of the discharge port)/(the range from the position of the terminating end portion of the intake port to the position ½ pitch therefrom).

7. The variable displacement vane pump according to claim 6, wherein the cam ring is formed in such a manner that the absolute value of the gradient of the cam profile satisfies 1.15<=(the range from the position ½ pitch away from the terminating end portion of the intake port to the position of the start end portion of the discharge port)/(the range from the position of the terminating end portion of the intake port to the position ½ pitch therefrom).

8. The variable displacement vane pump according to claim 1, wherein the cam ring is formed so as to have a region where the gradient of the cam profile has a negative value in a second confinement region, which is a region from a terminating end portion of the discharge port to a start end portion of the intake port, when the cam ring is located at a position where an eccentricity amount of the cam ring is minimized.

9. The variable displacement vane pump according to claim 1, wherein the discharge port includes a notch portion only on a start end portion side of the discharge port.

10. A variable displacement vane pump comprising: a pump housing including a pump element containing portion;a driving shaft supported on the pump housing;a rotor provided in the pump housing and configured to be rotationally driven by the driving shaft, the rotor also including an odd number of slots in a circumferential direction of the rotor;an odd number of vanes provided in the slots in a manner projectable therefrom and retractable therein;a cam ring movably provided in the pump element containing portion and annularly formed, the cam ring forming a plurality of pump chambers on an inner peripheral side of the cam ring in cooperation with the rotor and the vanes;an intake port formed in the pump housing and opened to a region where a volume of each of the plurality of pump chambers increases according to a rotation of the rotor;a discharge port formed in the pump housing and opened to a region where the volume of each of the plurality of pump chambers reduces according to the rotation of the rotor; anda cam ring control mechanism provided in the pump housing and configured to control an amount of eccentricity of the cam ring from the rotor,wherein the cam ring has an inner peripheral surface formed in such a manner that, assuming that a distance between the vanes adjacent to each other in a direction around a rotational axis of the driving shaft is one pitch, when the cam ring is moved by ⅓ of an entire eccentricity amount from a position where the eccentricity amount of the cam ring is maximized toward a position side where the eccentricity amount of the cam ring is minimized, in a first confinement region that is a region from a terminating end portion of the intake port to a start end portion of the discharge port,a vane projection amount, which is a distance from a center of a rotation of the driving shaft to the inner peripheral surface of the cam ring, gradually increases from the terminating end portion of the intake port and then gradually reduces toward the start end portion of the discharge port after passing through a point where the vane projection amount reaches a maximum value,the point where the vane projection amount reaches the maximum value is located in a range from ⅓ pitch to ⅔ pitch from the terminating end portion of the intake port, inclusive, andan absolute value of a gradient of a cam profile, which is a change rate of the vane projection amount, is larger in a range from a position ½ pitch away from the terminating end portion of the intake port to the start end portion of the discharge port than in a range from the terminating end portion of the intake port to ½ pitch therefrom.

11. The variable displacement vane pump according to claim 10, wherein the cam ring is formed in such a manner that the vane projection amount constantly reduces according to the rotation of the rotor in the first confinement region when the cam ring is located at the position where the eccentricity amount of the cam ring is maximized.

12. The variable displacement vane pump according to claim 10, wherein the cam ring is formed so as to have a region where the gradient of the cam profile has a negative value in a second confinement region, which is a region from a terminating end portion of the discharge port to a start end portion of the intake port, when the cam ring is located at a position where an eccentricity amount of the cam ring is minimized.