Patent Application
20120160594
(1) Field of the Invention
The present invention relates to a power steering system which obtains an assistance force of a steering operation according to an actuation of a pump.
(2) Description of Related Art
A Japanese Patent Application First Publication (tokkai) No. 2005-255001 published on Sep. 22, 2005 (which corresponds to a United Patent Application Publication No. 2005/0205338) exemplifies a previously proposed power steering system for an automotive vehicle in which a main pump which is driven by an engine and a sub pump is driven by an engine are installed and a steering assistance can be made even during an engine stop by a drive of the sub pump when the main pump is in an abnormal state.
However, only one switching valve to switch a supply of working oil from the main pump and the sub pump to a power cylinder is installed so that a simultaneous use of both of the main pump and the sub pump cannot be made.
It is an object of the present invention to provide a power steering system which is capable of achieving an optimum pump drive state according to a required flow quantity.
According to one aspect of the present invention, there is provided a power steering system comprising: a power cylinder equipped with a pair of pressure chambers to provide a steering force for at least one of steered wheels on a basis of a pressure difference between the pair of pressure cylinders; a steering mechanism configured to turn the steered wheel in accordance with a rotational steering operation of a steering wheel; a first pump equipped with a first drive shaft to suck and drain a working liquid along with a revolution of the first drive shaft to supply the working liquid to the power cylinder, the first pump being rotationally driven by means of a first driving source; a second pump equipped with a second drive shaft to suck and drain the working liquid along with the revolution of the second drive shaft to supply the working liquid to the power cylinder; a second driving source which is a driving source different from the first driving source, is constituted by an electric motor, and rotationally drives the second pump; a control valve disposed in the steering mechanism to selectably supply the working liquid supplied from the first pump or second pump to the pair of pressure chambers in accordance with a rotational steering operation of the steering wheel; a first switching valve disposed between the first pump and the control valve to switch a communication and an interruption of the working liquid between the first pump and the control valve; and a second switching valve disposed between the second pump and the control valve to switch the communication and the interruption of the working liquid between the second pump and the control valve, a communication state and an interruption state being selectably formed in the second switching valve when the first switching valve is in the communication state.
According to another aspect of the present invention, there is provided a power steering system, comprising: a power cylinder having a pair of pressure chambers and providing a steering force for at least one steered wheel on a basis of a pressure difference between the pair of pressure chambers; a steering mechanism configured to turn the steered wheel in accordance with a rotational steering operation of a steering wheel; a pump housing having a pump element housing section at an inner side thereof; a cam ring disposed movably within the pump element housing section and formed in an annular shape; a first drive shaft rotatably supported on the pump element housing section and formed in an annular shape; a rotor disposed within the cam ring, having a plurality of radially extended slits arranged along a circumferential direction of the rotor and rotationally driven through the first drive shaft; a plurality of vanes advanceably or retractably (namely, movably) disposed along the respective slits of the rotor to form a plurality of pump chambers together with the cam ring and the rotor; a suction inlet disposed in the pump housing and opened to a region of the plurality of pump chambers in which a volume thereof is increased along with the revolution of the rotor; a draining outlet disposed in the pump housing and opened to a region of the plurality of pump chambers in which a volume thereof is decreased along with the revolution of the rotor; a suction passage disposed in the pump housing to be communicated with the suction inlet; a draining passage disposed in the pump housing to be communicated with the draining outlet; a pair of fluid chambers formed between the pump element housing section and the cam ring, a first fluid pressure chamber thereof being formed at a side at which the volume thereof is decreased along with a movement of the cam ring in a direction toward which an eccentricity of the cam ring with respect to the drive shaft is increased and a second fluid pressure chamber thereof being formed in a direction in which the volume thereof is decreased along with the movement of the cam ring in a direction toward which the eccentricity of the cam ring with respect to the drive shaft is increased; a control valve disposed in the pump housing to control a pressure in the first fluid pressure chamber to control a displacement of the cam ring according to a pressure difference between the first fluid pressure chamber and the second fluid pressure chamber; a first pump constituted by an electromagnetic valve, disposed in the pump housing, controlled on a basis of a rotational steering operation of a steering wheel, and which controls a draining quantity per revolution of the rotor by controlling the displacement of the cam ring; a second pump having a second drive shaft and performing suction and draining of a working liquid along with the revolution of the second drive shaft to supply the working liquid to the power cylinder;
a second driving source which is the driving source different from the first driving source, is constituted by an electric motor, and rotationally drives the second pump; a control valve disposed in the steering mechanism to selectably supply the working liquid supplied from the first pump or the second pump to the pair of pressure chambers in accordance with the rotational steering operation of the steering wheel; and
switching valves disposed among the
first pump, the second pump, and the control valve to switch a communication of the working liquid and an interruption thereof between the first pump and the control valve and to switch the communication of the working liquid and the interruption thereof between the second pump and the control valve.
Reference will, hereinafter, be made to the drawings in order to facilitate a better understanding of the present invention. First, a power steering mechanism will be described and a whole system having the power steering mechanism will be described.
Piston 70 is housed movably in an axial direction of piston 70 within second housing 20. This piston 70 serves to partition a first oil chamber 21 at an input shaft side and a second oil chamber 22 at a cup shaped bottom section side maintaining a liquid tight structure. Input shaft 40 is coupled to an output shaft 60 by means of a torsion bar 50. A pin member 80 serves to couple torsion bar 50 and output shaft 60. This pin member 80 is disposed at a position opposing against part of a second valve groove 621 at which an exhaust oil passage 420 of an outer valve 620 is opened. Output shaft 60 is inserted in the axial direction of piston 70 and fitted into piston 70 through a ball screw mechanism (ball-and-nut) 60. A piston teeth section 71 which is inscribed along a peripheral direction is installed on an outer periphery of piston 70. This piston teeth section 71 serves to make piston 70 mesh with sector shaft 30. Second housing 20 is disposed in such a way that an axis of second housing 20 is orthogonal to an axis of sector to shaft 30. A part of second housing 20 in a diameter direction is provided with a sector shaft storing section 23 which stores a part of sector shaft 30. This sector shaft storing section 23 performs an introduction of working oil to communicate with a first oil chamber 21 and performs a is lubrication of the mesh between sector shaft 30 and piston teeth section 71.
First oil chamber 21 within second housing 20 is communicated with a control valve 600 through a first oil chamber communication passage 15 disposed in a first housing 10 and second oil chamber 22 is communicated with a control valve 600 through a second oil chamber communication passage 16 bridging between second housing 20 and first housing 10. That is to say, a power cylinder is constituted by first housing 10 and second housing 20. A pair of pressure chambers are formed between upper and lower portions of piston 70. Then, a steering mechanism configured to turn the steered wheels in accordance with a rotational steering operation of a steering wheel is constituted by the above-described elements.
Control valve 600 is constituted by an inner valve 610 formed on an outer periphery of input shaft 40 and an outer valve 620 formed on an inner periphery of output shaft 60.
Inner valve 610 is formed in such a way that an outer periphery of input shaft 40 is recessed in the inner peripheral direction and outer valve 620 is formed in such a way that an inner periphery of output shaft 60 is recessed in the outer peripheral direction.
Inner valve 610 includes a first valve groove 611 which recesses in an inner diameter direction thereof and outer valve 620 includes a second valve groove 621 which recesses in an outer diameter direction thereof. These first and second valve grooves 611, 621 are disposed in plural number in the peripheral direction and a seal material is disposed between each groove 611, 621. Second valve groove 621 is coupled to suction ports 301, 302 via oil passages 310, 320. Second valve groove 621 is coupled to drain ports 401, 402 via valve side return passages 410, 420 and a groove 430 installed on an inner periphery of first housing 10. Control valve 600 functions as a control valve mechanism which performs an introduction or exhaust of oil from suction ports 301,302 or drain ports 401, 402 to first and second oil chambers 21, 22. When input shaft 40 is relatively rotated toward a right side with respect to output shaft 60, the pump (not shown) is communicated with first oil chamber 21. When input shaft 40 is relatively rotated toward a left side with respect to output shaft 60, the pump (not shown) is communicated with second oil chamber 22.
First tank RST1 is coupled to main pump MP via a first return passage 501 and oil discharged from main pump MP is supplied to suction port 301 of main valve unit MVU via a first drain oil passage 502. In addition, first tank RST1 and exhaust port 401 of main valve unit MVU are coupled together via a first exhaust oil passage 503. Second tank RST2 and sub pump SP are coupled together via a second suction passage 504. Oil discharged from sub pump SP is supplied via a second drain oil passage 505 to suction port 302 of sub valve unit SVU. Second tank RST2 and exhaust port 402 of sub valve unit SVU are coupled together via a second return passage 506. An oil passage 310 is coupled between supply port 303 of main valve unit MVU and control valve 600. An introduction port 403 of main valve unit MVU and control valve 600 are coupled together via a valve side return passage 410. Similarly, a supply port 304 of sub valve unit SVU and control valve 600 are coupled by means of an oil passage 310. An introduction port 404 of sub valve unit SVU and control valve 600 are connected via valve side return passage 410. Main valve unit MVU and sub valve unit SVU include a main side interruption state detection sensor SW1 and sub side interruption state detection sensor SW2 both detecting electrically detecting an interruption state of the corresponding valve. On or off signal of these interruption state detection sensors SW1 and SW2 are transmitted to control unit CU1. When the interruption states are detected in a state where both pumps are actuated, control unit CU1 recognizes that an abnormality occurs and illuminates a failure lamp or so forth (not shown) to inform the driver of the interruption state. In addition, a liquid quantity sensor RS is disposed in second tank RST2 of reservoir tanks at a height position lower than partitioning wall R1 and transmits a signal of whether an oil surface is lower than a height of liquid quantity sensor RS (namely, whether the liquid quantity of second reservoir tank RST2 is smaller than a predetermined quantity) to control unit Cu1.
[Structure of Valve Units]
A structure of each of main and sub valve units will hereinafter be described below.
Main valve unit MVU is formed with: a check valve attachment hole MV1 to which a check valve mechanism is attached; an exhaust port attachment hole MV2 to which exhaust port 401 is attached; an introduction oil passage MV3 coupled to introduction port 303; a supply oil passage MV4 coupled to supply port 303; a sensor attachment hole MV5 to which a main side interruption state detection sensor SW1 is attached; and a valve housing hole V1 which houses a main spool valve SPV (corresponds to a first switching valve). It should be noted that a sub spool valve SPV′ (corresponds to a second switching valve) is housed within a valve housing hole V2 (not shown) in sub valve unit SVU.
The check valve mechanism includes: a check valve member CH1 having a housing axle hole c6 housing slidably an annular valve member CHV at an inside thereof. This check valve mechanism is attached onto main valve unit MVU in a state in which a plug CH2 holding a return spring c5 is attached onto this check valve member CH1. A valve member CHV includes a cylindrical section c4 which houses a return spring c5 at an inner side and which is slidably contacted on housing axle hole c6, a flow passage constituting section c3 whose diameter is smaller is than the cylindrical section (c4) and on an outer periphery of which a plurality of penetrating holes are formed, and a tip section c1 in a tapered shape and which is contacted on a sheet to enable a closure of the oil passage. A cone-shaped sheet surface c2 which is contacted on tip section C1 is formed on an upper end portion of housing axle hole c6 and an upstream side supply passage opening section MV11 connected to valve housing hole V1 is formed on the lower end section.
In addition, an oil passage MV12 coupled to valve housing hole V1 is formed on a lower end section of exhaust port attachment hole MV2. A valve housing hole V1 includes a supply port V12 formed at a position coupled to supply oil passage MV4 whose diameter of an inner periphery of valve housing hole V1 is enlarged and an introduction port (a downstream side supply passage opening section) V11 formed at a position coupled to oil passage MV4 whose diameter of the inner periphery of valve housing hole V1 is enlarged. Spool valve SPV is formed with a small-diameter axle section SP4 and first spool SP1 and second spool SP2 having approximately the same diameter as an inner periphery of valve housing hole V1 and whose diameters are larger than axle section SP4. An orifice X1 is penetrated in a radial direction of a contact section SP3 of axle section SP4. A pressure introduction passage X2 having a larger diameter than orifice X1 radially fitted to second spool SP2. The axle center section of axle section SP4 is formed with an axle hole X3 which communicates between orifice X1 and downstream side pressure introduction passage X2 and with a spool lower end side SP5. A return spring a1 is disposed within a low pressure chamber (a first other side pressure chamber) closed by means of a spool lower end SP5 and low pressure chamber side land section SP11. It should be noted that a return spring a2 (not shown) is disposed in the same way as return spring a1 in the case of sub valve unit SVU.
Return spring a1 is contacted on a low pressure chamber side land section SP11 of first spool SP1 and biases with a predetermined set weight in a left side direction in
Next, an operation of spool valve SPV will be described below. When the hydraulic pressure is drained from main pump MP, valve member CHV of the check valve mechanism is pressed from suction port 301 in a downward direction so that oil passes from a penetrating hole of oil passage constituting section c3 through an inner side of cylindrical section c4 so as to be introduced into a high pressure chamber (a first one side pressure chamber) closed by a supply passage side land section within valve storing hole V1. At this time, when supply passage side land section 22 is pressed and is in excess of the spring set weight of return spring a1, spool valve SPV is stroked toward a right side of
When, in this state, an operation of main pump MP is stopped or a pump drain flow quantity (rate) cannot be secured, a flow quantity is reduced. Thus, an orifice effect (a pressure reduction effect) by means of orifice X1 cannot be obtained. Thus, equal pressures to upper end side spool SP22 and lower end side spool SP11 are acted so that spool valve SPV is returned to an initial position according to the set weight of return spring a1. Thus, main side interruption state detection sensor SW1 receives a power supply and outputs a signal indicating the interruption state due to the pump non-actuation state. It should be noted that the flow passage continued from oil passage MV4→downstream side pressure introduction passage X2→axle hole X3→orifice X1 is interrupted between main pump MP and oil passage MV4 by means of a check valve mechanism so as to prevent a reverse flow from control valve 600.
Power steering system in the first embodiment includes the valve units installed between main pump MP and control valve 600 and between sub pump SP and control valve 600. That is to say, main valve unit MVU configured to switch the communication and the interruption of the working liquid between main pump MP and control valve 600 and sub valve unit SVU configured to switch the communication and the interruption of the working liquid between sub pump SP and control valve 600. Sub valve unit SVU is formed to enable the selection between the communication state of sub valve unit SVU and the interruption state thereof when main valve unit MVU is in the communication state.
That is to say, for example, when the working liquid is supplied by sub pump SP in a state in which main pump MP does not supply the working liquid, the steering assistance can continuously be performed during a failure of main pump MP.
In addition, sub pump SP supplies the working liquid in a state in which main pump MP supplies the working liquid.
In the state in which engine ENG is stopped, the drain flow quantity (rate) from main pump MP cannot be obtained. Hence, the supply of the working oil is carried out with sub pump SP driven. At this time, the reverse flow of the working oil drained from sub pump SP toward the main pump can be prevented by means of the check valve mechanism of main valve unit MVU.
[Driving Control for Sub Pump]
Next, a control processing of the sub pump will be described. Steering speed sensor SS is provided which detects steering speed (ω) of the driver through the steering wheel. Specifically, as the steering speed becomes increased, the drained oil flow quantity becomes more necessary. Hence, the power supply quantity that is caused to flow into electric motor M is controlled so that the revolution speed of electric motor M is raised.
For example, the motor revolution speed may be controlled or a torque of electric motor may be controlled in accordance with the power supply quantity. It should be noted that the control of power supply quantity may be a control of an electric current supplied to the motor or a control of a duty ratio value in a PWM (Pulse Width is Modulation) control for electric motor M. Thus, it is not necessary to generate a wasteful drain flow quantity and it can contribute on the energy saving.
In addition, the driving is stopped when the steering speed is smaller than the predetermined value.
As steering speed SS is small (slow), the required flow quantity per unit time is small. Hence, the energy saving effect can be improved with the steering assistance only by means of main pump MP performed. A region in which steering speed (ω) is smaller than predetermined value is a dead zone of electric motor M. Hence, a complexity of switching of drives and stops of electric motor M can be suppressed. In
It should be noted that, in the first embodiment, electric motor M is actuated when steering speed (ω) is equal to or larger (faster) than predetermined value Pre. However, another structure may be adopted to the actuation of electric motor M.
As described above, the following actions and advantages can be obtained in the first embodiment.
(1) The power steering system in the first embodiment comprises: the power cylinder having first hydraulic pressure chamber 21 and second hydraulic pressure chamber 22 (hereinafter, also called a pair of pressure chambers) and configured to provide the steering force for at least one steered wheel on a basis of the pressure difference between the pair of pressure chambers; the steering mechanism operably turning the steered wheel in accordance with the rotational steering operation through the steering wheel; main pump MP (a first pump) having first drive shaft D1, configured to perform the suction and draining of the working liquid along with the revolution of first drive shaft D1 to supply working liquid to the power cylinder, and rotationally driven through engine ENG (first driving source); sub pump SP (a second pump) having second drive shaft D2 and configured to perform suction and draining of working liquid to supply working liquid to the power cylinder along with the revolution of second drive shaft D2; electric motor M to rotationally drive sub pump SP; control valve 600 to selectively supply the working liquid supplied from main pump MP or sub pump SP to the pair of pressure chambers of the power cylinder in accordance with the rotational steering operation of the steering wheel; main valve unit MVU (the first switching valve) disposed between main pump MP and control valve 600 to switch the communication and the interruption of working liquid between sub pump SP and control valve 600; and sub valve unit SVU (the second switching valve) disposed between sub pump SP and control valve 600 to switch the communication and interruption of the working liquid between sub pump SP and control valve 600, the sub valve unit (SVU) being selectably formed between the communication state and the interruption state, when main valve unit MVU is in a communication state.
Thus, the steering assistance can continuously be performed by the supply of the working liquid by the sub pump in a state in which main pump MP cannot supply the working liquid when, for example, main pump MP has failed. In addition, the natural (or intrinsic) drain quantity of main pump MP can be reduced by sub pump SP supplying the working liquid in a state in which main pump MP supplies the working liquid. Hence, the drive load of main pump MP can be reduced. Then, the energy saving effect can be improved in a state in which the required flow rate is small in such a case of the straight road run.
(2) The power steering system described above further comprises: first tank RST1 (a first reservoir tank) and second tank RST2 (a second reservoir tank) which are the pair of reservoir tanks RST which reserve the working liquid; valve side return passage 410 which connects between each of main valve unit MVU and sub valve unit SVU and control valve 600 and supplies the working liquid fed back from control valve 600 to either main valve unit MVU or sub valve unit SVU; first return passage 501 which connects between main valve unit MVU and first tank RST1 and feeds back the working liquid fed back to main valve unit MVU via valve side return passage 410 to first tank RST1; and second return passage 506 which connects between sub valve unit SVU and second tank RST2 and feeds back the working liquid fed back to sub valve unit SVU via valve side return passage 410, wherein main valve unit MVU sets the flow of a first return side which is a flow of working liquid from valve side return passage 501 in the communication state when a flow of working liquid between main pump MP and control valve 600 (hereinafter called, a first supply side flow) is in the communication state and sets the flow of the first return side in the interruption state when the flow of first supply side is in the interruption state and sub valve unit SVU sets a flow of a second return side which is a flow of working liquid from valve side return passage 410 to second return passage 506 in the communication state when a flow of working liquid between sub pump SP and control valve 600 (hereinafter called, a second supply side flow) is in the communication state and sets the flow of the second return side in the interruption state when the flow of second supply side is in the interruption state. Thus, the continuous steering assistance is possible by means of the other side even during the liquid leakage along with a circuit breakage (reservoir tank, passage, and so forth) at one side.
(3) The power steering system as described in item (2), wherein the power steering system further comprises liquid quantity sensor RS installed in second tank RST2 for detecting the liquid quantity of second tank RST2, wherein electric motor M is stopped when the liquid quantity of second tank RST2 detected by liquid quantity sensor RS is equal to or smaller than a predetermined quantity so that sub valve unit SVU sets the flow at is second supply side and the flow of second return side in the interruption state.
In a case where second return passage 506 is broken and the liquid quantity of second tank RST2 is decreased, electric motor M is stopped so that the leakage of working liquid from the breakage section can be suppressed. In addition, due to the interruption of sub valve unit SVU, the working liquid which is in a reverse flow can be prevented from being leaked from the breakage section. In addition, since the steering assistance can be continued through main pump MP.
(4) The power steering system as described in item (1), main valve unit MVU includes: main spool valve SPV (a first spool valve) disposed movably in the axis direction within first valve housing hole V1; return spring a1 (a first biasing member) disposed within first valve housing hole V1 to bias main spool valve SPV toward one side in the axial direction of main spool valve; the high pressure chamber (a first one side pressure chamber) disposed within first valve housing hole V1 and arranged in one side of the axial direction of main spool valve SPV; the low pressure chamber (a first one side pressure chamber) disposed within first valve housing hole V1 and arranged in the other end in the axial direction of main spool valve SPV; first upstream side supply passage opening section MV11 disposed within first valve housing hole V1 to be opened to the high pressure chamber (the first one side pressure chamber) to be communicated with main pump MP; a first downstream side supply passage opening section disposed to be opened to first valve housing hole V1 to be communicated with control valve 600; first supply passage side land section SP22 disposed in main spool valve SPV to interrupt the first downstream is side supply passage opening section with respect to the high pressure chamber (first one side pressure chamber) when main spool valve SPV is located at a most one side of the axial direction and formed to increase an opening area of the first downstream side supply passage opening section with respect to the high pressure chamber (first one side pressure chamber) as main spool valve SPV moves toward the other side of the axial direction thereof; and a first downstream side supply pressure introduction passage disposed for the low pressure chamber (first other side pressure chamber), at all times, to be communicated with control valve 600 and main spool valve SPV is controlled in accordance with the pressure difference before and after the first downstream side supply passage opening section which varies in accordance with a variation of flow rate of working liquid caused to flow through the first downstream side supply passage opening section variably controlled by means of first supply passage side land section 22.
A throttling area (an area of the downstream side supply passage opening section) of the passage connecting between main pump MP and control valve 600 is variably controlled in accordance with the flow rate of working liquid. Thus, a pressure loss at the throttling section can be reduced as compared with a case where this throttling area is fixed. In addition, since the spool valve is actuated in accordance with the variation of flow rate, main valve unit MVU can be set in the interruption state along with the stop of main pump MP even if the pressure at the control valve side is high as in the case of the steering operation.
On the other hand, in a case of the switching valve which switches between the communication and interruption on a basis of the pressure in the first pressure chamber, a responsive characteristic of main valve unit MVU to the interruption state is worsened even if main pump MP is stopped. Therefore, during the switching to the interruption state, the reverse flow of the supply pressure supplied from sub pump SP to main valve unit MVU cannot be interrupted by means of main valve unit MVU.
(5) The steering system as described in item (4), wherein sub valve unit SVU comprises: sub spool valve SPV′ installed movably in the axial direction of sub spool valve SPV′ within second valve housing hole V2; return spring a2 (second biasing member) disposed within second valve housing hole V2 to bias sub spool valve SPV′ toward one side in the axial direction of sub spool valve SPV′; one low pressure chamber (second other side pressure chamber) disposed within second valve housing hole V2 and arranged at one side of the axial direction of sub spool valve SPV′; second upstream side supply passage opening section MV11′ disposed within second valve housing hole V2 so as to be opened to low pressure chamber (second one side pressure chamber) and communicated with sub pump SP; the second downstream side supply passage opening section disposed so as to be opened to second valve housing hole V2 and to be communicated with control valve 600; second supply passage side land section SP22′ disposed in sub spool valve SPV′ to interrupt the second downstream side supply passage opening section with respect to the high pressure chamber (second one side pressure chamber) when sub spool valve SPV′ is located at the most one side of the axial direction of sub spool valve SPV′ and formed to increase the opening area of second downstream side supply passage opening section with respect to high pressure chamber (second one side pressure chamber) as sub spool valve SPV′ moves toward the other side in the axial direction of sub spool valve SPV′; the second downstream side supply pressure introduction passage disposed for the low pressure chamber (second other side pressure chamber) to be at all times communicated with control valve 600; and sub side interruption state detection sensor SW2 configured to detect electrically that sub valve unit SVU is in the interruption state when sub spool valve SPV′ (second spool valve) is located at a most one side of the axial direction, and wherein sub spool valve SPV′ is controlled in accordance with the pressure difference before and after the second downstream side supply passage opening section which varies in accordance with the variation in the flow rate of working liquid caused to flow through second downstream side supply passage opening section which varies in accordance with second supply passage side land section SP22.
A switching responsive characteristic of sub valve unit SVU to the interruption state along with the stop of sub pump SP can be increased. Hence, the information of the interruption state by means of the interruption state detection sensor can be carried out at an earlier timing.
(6) The power steering system as described in item (4), the power steering system further comprises: a first check valve mechanism disposed between main pump MP and first upstream side supply passage opening section MV11 to allow the flow of working liquid only from the main pump side toward sub valve unit SVU direction; and a second check valve mechanism disposed between sub pump SP and second upstream side supply passage opening section MV11 to allow the flow of working liquid is only from sub pump side to sub valve unit SVU side direction. These check valve mechanisms prevent the reverse flow of working liquid from a drive side pump to a stop side pump. Hence, for example, in a case where the pump is stopped due to the breakage of the piping, the drain pressure of drive side pump is reversely streamed toward the pump side and such an event that working liquid leaks from the broken position can be prevented.
(7) The power steering system as described in item (4), wherein the power steering system further comprises contact section SP3 disposed in main valve unit MVU and on which one side of the axial direction of main spool valve SPV is contacted when main spool valve SPV is located at a most one side of the axial direction and a main side interruption state detection sensor SW1 which electrically detects that main valve unit MVU is in the interruption state when main spool valve SPV is contacted on contact section SP3.
Hence, main side interruption state detection sensor SW1 can inform the driver of the interruption state. In addition, since main side interruption state detection sensor SW1 is arranged in the one side in the axial direction of main spool valve SPV, an appropriate interruption state detection can be achieved even if main valve unit MVU is the switching valve in which the throttling area of the throttle passage is variably controlled. It should be noted that the same advantage can be obtained when the same structure as this sensor is mounted as a sub side interruption state detection sensor SW2 within sub valve unit SVU.
(8) The power steering system as described in item (1), wherein the power steering system further includes orifice X1 and axle hole X3 (a first throttling passage) disposed in main spool valve SP to at all times communicate between high pressure chamber (first one side pressure chamber) and low pressure chamber (first other side pressure chamber).
Since the pressure within high pressure chamber (first one side pressure chamber) is exhausted to low pressure chamber (first other side pressure chamber) via orifice X1 and axle hole X3 (first throttling passage), an interruption failure due to a closure of pressure within the high pressure chamber can be suppressed. In addition, since the throttling passage is formed by orifice X1, the pressure difference between the high pressure chamber and the low pressure chamber can be maintained and the flow rate control of main valve unit MVU can be performed.
(9) The power steering system as described in item (1), wherein a power supply turning on quantity caused to flow into electric motor M which is the second driving source is controlled in accordance with the steering speed.
As the steering speed becomes higher, the higher flow rate becomes needed. Hence, the required flow rate can be assured by controlling the power supply turning in quantity such that a revolution speed of electric motor M is raised. It should, herein, be noted that the electric motor is such that its control method is identified if the power supply quantity of electric motor is controlled and, for example, the torque of electric motor M which generates in accordance with the power supply quantity may be controlled. In addition, the control of the power supply quantity may be based on the current value or may be based on a duty ratio value in the PWM control.
(10) The power steering system as described in item (9), wherein electric motor M which is the second driving source is stopped when the steering speed is smaller than a predetermined value.
When the steering speed is small, the required flow rate per unit time is small. Thus, electric motor M is stopped. Hence, the steering assistance only through first driving source, namely, only through main pump MP is performed so that the energy saving effect can be improved. In addition, since a region in which the steering speed is smaller (slower) that the predetermined value provides a dead zone of electric motor M, a repetition complexity of switching between the drive and stop of electric motor M can be suppressed.
(11) The power steering system as described in item (9), wherein the power supply turning on quantity is caused to flow into electric motor M which is the second driving source is increased as the steering speed becomes higher.
Since electric motor M can drivingly be controlled in accordance with the increase in the required flow rate, the further energy saving can be achieved.
(12) The power steering system as described in item (9), wherein the power supply turning on quantity caused to flow into the electric motor which is the second driving source is controlled to be decreased as the vehicle speed becomes higher.
Since, as the vehicle speed (VS) becomes higher, the required flow rate is decreased, the electric motor can drivingly be controlled in accordance with the decrease in the required flow rate and the further energy saving can be achieved.
(13) The power steering system as described in item (1), wherein main valve unit MVU and sub valve unit SVU are configured to be in the communication state when working liquid is supplied from both of main pump MP and sub pump SP and main valve unit MVU or sub valve unit SVU is provided with interruption state detection sensor SW1, SW2 which electrically detects the interruption state of either main valve unit MVU or sub valve unit SVU.
The interruption state of each of main and sub valve units MVU, SVU means the stop of pump or leakage of drain pressure. In a case where the stop of pump (leakage of drain pressure) is detected and the stop of pump (leakage of the drain pressure), the abnormality of the system can be informed to the driver.
Next, a second preferred embodiment of the power steering system according to the present invention will, hereinafter, be described.
In the first embodiment, main pump MP is such that, when the drain (flow) quantity of main pump MP reaches to the preset natural (or intrinsic) drain quantity, the flow rate equal to or larger than the preset natural drain quantity is cut out. On the other hand, in the second embodiment, an electronically controlled variable displacement (capacity) pump is adopted in which the natural drain quantity is modifiable by means of electromagnetic valve SOL.
It should be noted that, although a command signal is outputted to electromagnetic valve SOL and electric motor M from separate control units as viewed from
If the flow in the pump occurs, the downstream side pressure decreased than the upstream side of metering orifice P10 is supplied to control valve 600 as the drain pressure.
The upstream side section and downstream side section of metering orifice P10 are connected to control valve P7. Control valve P7 controls the pressure supplied to first fluid pressure chamber P5 and second fluid pressure chamber P6 to maintain a pressure difference relationship set according to a predetermined spring set weight to control the eccentricity of cam ring P2. It should be noted that electromagnetic valve SOL is structured so that the biasing force can be provided which opposes against the spring set weight of control valve P7 and, thus, the drain flow quantity is modifiable by controlling the spring set weight to the desired set weight.
Since main pump MP is engine driven, main pump MP is at all times rotationally driven during the engine driving and the revolution speed of main pump MP in accordance with the required flow rate cannot be performed. Hence, it is favorable from the viewpoint of is energy saving to use maximally the drained flow quantity from main pump MP irrespective of the increase or decrease in the required flow quantity. Thus, the drain quantity of main pump MP is set to be small so that a wasteful work of main pump MP is not carried out even if the required flow quantity is small. When the required flow quantity is large, an insufficient quantity according to the drive of main pump MP is compensated for by sub pump SP so that, while the pump load of main pump MP is reduced and the required flow quantity is secured, the energy saving can be achieved. In addition, since main pump MP is the electronic control type variable displacement (capacity) vane pump in which the natural drain quantity is variably controlled in accordance with the steering state, the further reduction of the pump load of main pump MP can be achieved.
As described hereinabove, the power steering system in the second preferred embodiment described above can achieve the following action and advantages.
(14) The power steering system (in the second embodiment) comprises: the power cylinder having the pair of first and second hydraulic pressure chambers 21, 22 (the pair of hydraulic pressure chambers) and configured to provide the steering force for the steered wheel on a basis of the pressure difference between the pair of pressure chambers; the steering mechanism which turns the steered wheel in accordance with the rotational steering operation of the steering wheel; pump housing PH having pump element housing section P1 at the inner side thereof; cam ring P2 movably mounted within the pump element housing section P1 and formed in the annular shape; first driving shaft D1 rotatably supported on pump housing P1 and to which the rotational driving force is transmitted from engine ENG of the vehicle which is the first driving source; rotor P3 rotationally driven by means of first driving shaft D1 and having the plurality of radially extended slits P31 disposed within cam ring P2 and arranged along the circumferential direction; vane P4 advanceably or retractably (namely, movably) disposed along slits P31 of rotor P3 to form the plurality of pump chambers together with cam ring P2 and rotor P3; suction inlet mounted within pump housing PH to be opened to the region of the plurality of pump chambers in each of which to the volume is increased along with the rotation of rotor P3 from among the plurality of pumps; the suction passage mounted within pump housing PH to be communicated with the suction inlet; the draining outlet mounted within pump housing PH to be opened to the region of the is plurality of pump chambers in each of which the volume is decreased along with the rotation of rotor P3 from among the plurality of pumps; the drain passage mounted within pump housing PH to be communicated with the suction inlet; fluid pressure chamber P5, P6 which are the pair of liquid chambers formed between pump element housing section P1 and cam ring P2, first fluid pressure chamber P5 being formed toward the side at which the volume is decreased along with the movement of cam ring P2 in the direction at which the volume is decreased in the direction in which the eccentricity of cam ring P2 with respect to drive axle D1 is increased and second fluid pressure chamber P6 being formed toward the side at which the volume is increased along with the movement of cam ring P2 in the direction at which the volume is decreased in the direction in which the eccentricity of cam ring P2 with respect to drive axle D1 is increased; main pump MP constituted by control valve P7 mounted within pump housing PH for controlling the movement quantity (displacement) of cam ring P2 according to the pressure difference between first fluid pressure P5 and second fluid pressure chamber P6 by controlling the pressure within first fluid pressure chamber P5; electromagnetic valve SOL mounted within pump housing PH controlled on a basis of the revolution operation of the steering wheel for controlling the drained quantity per revolution of the rotor by controlling the displacement of cam ring P2; sub pump SP for sucking and draining working liquid along with the revolution of second drive shaft D2 and which supplies from main pump MP or sub pump SP: electric motor M which is the driving source which is different from engine ENG and rotationally drives sub pump SP; control valve 600 having second drive shaft D2 and installed in the steering mechanism which selectively supplies working liquid to the power cylinder by sucking or draining working liquid along with the revolution of second drive shaft D2; and main valve unit MVU and sub valve unit (switching valve) SVU disposed from among main pump MP, sub pump SP, and control valve 600 for switching the communication and interruption of working liquid between main pump MP and control valve 600 and for switching the communication and the interruption of working fluid between sub pump SP and control valve 600.
Since main pump MP is engine driven, main pump MP is at all times rotationally driven during the engine driving and the revolution speed of main pump MP in accordance with the required flow rate cannot be performed. Hence, it is favorable from the viewpoint of the energy saving to use maximally the drained flow quantity from main pump MP irrespective of the increase or decrease in the required flow quantity. It should be noted that the drain quantity of main pump MP is set to be small so that a wasteful work of main pump MP is not carried out even if the required flow quantity is small and, when the required flow quantity is large, an insufficient quantity according to the drive of main pump MP is compensated for by sub pump SP so that, while the pump load of main pump MP is reduced and the required flow quantity is secured, the energy saving can be achieved. In addition, since main pump MP is the electronic control type variable displacement (capacity) vane pump in which the natural drain quantity is variably controlled in accordance with the steering state, the further reduction of the pump load of main pump MP can be achieved.
(15) The power steering system as described in item (14), the power steering system further comprises: the single chip CPU which is the integrated circuit; the electromagnetic valve control program stored in the chip CPU which drivingly controls electromagnetic valve SOL; and the motor control program stored in the chip CPU which drivingly controls electric motor M.
Since the respective control programs for electromagnetic valve SOL and electric motor M are stored in the same chip (or a microcomputer), the coordinate control of both of electromagnetic valve SOL and motor M becomes facilitated.
Next, a third preferred embodiment of the power steering system will be described below.
(16) The power steering system as described in item (14), the power steering system includes: the first chip; the electromagnetic valve control program stored in the first chip CPU to drivingly control electromagnetic valve SOL; the second chip CPU2 which is another integrated circuit than first chip CPU1; the motor control program stored in the second chip CPU2 to drivingly control electric motor M; and a frame housing both of the first chip CPU1 and second chip CPU2.
Thus, the steering assistance is possible continuously by another chip even if either one of first and second chip CPUs CPU1, CPU2 becomes abnormal.
Next, the power steering system of a fourth preferred embodiment according to the present invention will be described below. In each of the first, second, and third embodiments, an example in which, as main pump MP, a type which is at all times driven by engine ENG has been adopted. On the other hand, in the fourth embodiment, main pump MP is driven by means of main electric motor MM and sub motor SP is driven by means of sub electric motor SM. This is the difference point from each of the first, second, and third embodiments. In this way, even if a plurality of electric motors are provided, the same action and advantages as each of the first, second, and third embodiment can be obtained.
This application is based on a prior Japanese Patent Application No. 2010-288182 filed in Japan on Dec. 24, 2010. The entire contents of this Japanese Patent Application No. 2010-288182 are hereby incorporated by reference. Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the to following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-288182 | Dec 2010 | JP | national |
