DRIVE APPARATUS

TECHNICAL FIELD

The present disclosure relates to a drive apparatus, which converts rotational movement of a drive source into linear reciprocating movement of a control shaft member and adjusts a control amount of a controlled subject according to an axial position of the control shaft member.

BACKGROUND

A previously known drive apparatus converts rotational movement of a drive source into linear reciprocating movement of a control shaft member through a drive cam and adjusts a control amount of a controlled subject according to an axial position of the control shaft member. In this drive apparatus, when a drive force of the drive source is stopped, it is required to hold a given constant position of the drive cam and a given constant position of the control shaft member against a load applied from the controlled subject to the control shaft member.

For example, a drive cam of a drive apparatus disclosed in JP2014-134194A (corresponding to US2014/0116197A1) has a pocket portion. In the pocket portion of the drive cam, a profile radius, which is a distance from a rotational center of the drive cam to a profile (i.e., an outer peripheral surface) of the drive cam, increases in both of a forward rotational direction (also referred to as a normal rotational direction) and a reverser rotational direction of the drive cam. When the drive force of the motor is stopped in a state where the pocket portion contacts the roller, the rotation of the drive cam is locked at a corresponding rotational position, at which the profile radius is minimized in the pocket portion. Thereby, each of the rotational position of the drive cam and the axial position of the control shaft member can be held at the given constant position.

The drive cam of JP2014-134194A (corresponding to US2014/0116197A1) has a progressively changing portion (also referred to as a gradually-varying portion), in which the profile radius progressively increases in response to rotation of the drive cam. A drive force of a motor control device is transmitted from a motor gear, which is connected to an output shaft of the motor, to a cam gear, which is connected to the drive cam.

When the drive cam is rotated in a direction, along which the profile radius progressively increases, in a state where the roller contacts the progressively changing portion of the drive cam, a tooth of the motor gear, which serves as a driving-side gear, always acts to push a corresponding tooth of the cam gear, which serves as a driven-side gear.

However, when a contact point of the roller, which contacts the drive cam, is moved into the pocket portion through a boundary between the progressively changing portion and the pocket portion, the profile radius, which has been progressively increased in response to the rotation of the drive cam, is progressively decreased. Therefore, a force is exerted from the roller to rotate the drive cam to move the contact point of the roller to the bottom (the profile radius minimum point) of the pocket portion. Because of this rotational force, the tooth of the cam gear, which is the driven-side gear, collides against the tooth of the motor gear, which is the driving-side gear, to disadvantageously generate a tooth hitting sound (a sound that is generated by hitting the tooth of the motor gear with the tooth of the cam gear). Particularly, in a case where the motor gear and the cam gear are formed as spur gears, respectively, the tooth hitting sound tends to be increased.

SUMMARY

The present disclosure is made in view of the above disadvantage. According to the present disclosure, there is provided a drive apparatus that adjusts a control amount of a controlled subject in response to an axial position of a control shaft member. The drive apparatus includes a drive source, a driving-side gear, a driven-side gear, a drive cam, a contact portion, a support member, and the control shaft member. The driving-side gear is joined to an output shaft of the drive source. The driven-side gear receives a drive force of the drive source directly from the driving-side gear or indirectly from the driving-side gear through at least one intermediate gear.

The drive cam is rotatable about a camshaft member, which is joined to the driven-side gear. A profile radius of the drive cam, which is a distance from a rotational center of the drive cam to an outer peripheral surface of the drive cam, is not uniform in a circumferential direction of the drive cam. The contact portion is placed on one radial side of the drive cam in a radial direction of the rotational center of the drive cam. The contact portion is urged by the controlled subject to contact the outer peripheral surface of the drive cam at a contact point. The support member supports the contact portion. The support member makes linear reciprocating movement in a direction perpendicular to an axial direction of the camshaft member in response to a change in the profile radius at the contact point upon rotational movement of the drive cam. The control shaft member is joined to the support member. The control shaft member makes linear reciprocating movement in an axial direction of the control shaft member together with the support member. The drive cam includes a progressively changing portion, and a pocket portion. In the progressively changing portion, the profile radius progressively changes in response to the rotational movement of the drive cam. The pocket portion is placed adjacent to the progressively changing portion in the circumferential direction. The profile radius increases in both of a forward rotational direction and a reverse rotational direction of the drive cam in the pocket portion. A profile radius change rate, which is an amount of change in the profile radius relative to a rotational angle of the drive cam in a pocket boundary section located between the progressively changing portion and the pocket portion, is set such that a boundary sound pressure, which is a sound pressure generated when the contact point passes through the pocket boundary section in response to the rotational movement of the drive cam, is included in a reference sound pressure range, which is a range of variation in a sound pressure generated when the contact point passes through the progressively changing portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1A is a schematic diagram showing a transmitting portion of a drive apparatus according to an embodiment of the present disclosure;

FIG. 1B is a cross-sectional view taken along line b-b in FIG. 1A;

FIG. 2 is a perspective view showing a speed reducing gear mechanism of the drive apparatus of the embodiment;

FIG. 3 is a schematic view of a valve lift control system, in which the drive apparatus of the embodiment is applied according to the present disclosure;

FIG. 4 is a cross sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a schematic diagram, showing details of the speed reducing gear mechanism shown in FIG. 2;

FIG. 6 is a schematic diagram of a drive cam according to the embodiment;

FIG. 7A and 7B are schematic diagrams showing application of a drive torque, which is exerted by a motor torque and a roller, to the drive cam;

FIGS. 8A and 8B are schematic diagrams showing a collision phenomenon between a driving-side gear and a driven-side gear;

FIGS. 9A and 9B are diagrams of time charts for describing the collision phenomenon between the driving-side gear and the driven-side gear;

FIG. 10 is an enlarged view showing a pocket boundary section of a drive cam of a second sample;

FIGS. 11A is a diagram indicating a profile radius change rate at a second pocket boundary section of a drive cam of a first sample;

FIG. 11B is a diagram indicating a profile radius change rate at a third pocket boundary section of the drive cam of the first sample;

FIG. 12A is a diagram indicating a profile radius change rate at a second pocket boundary section of the drive cam of the second sample;

FIG. 12B is a diagram indicating a profile radius change rate at a third pocket boundary section of the drive cam of the second sample;

FIG. 13A is a diagram indicating a change in a stroke of a control shaft member relative to a rotational angle of the drive cam at the time of rotating the drive cam of the first sample;

FIG. 13B is a diagram indicating a measured sound pressure relative to the rotational angle of the drive cam of the first sample;

FIG. 14A is a diagram indicating a change in a stroke of a control shaft member relative to a rotational angle of the drive cam at the time of rotating the drive cam of the second sample;

FIG. 14B is a diagram indicating a measured sound pressure relative to the rotational angle of the drive cam of the second sample;

FIG. 15 is a schematic diagram indicating a sound pressure measuring method; and

FIG. 16 is a schematic diagram showing a transmitting portion of a drive apparatus according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

A drive apparatus according to an embodiment of the present disclosure will be described with reference to the accompanying drawings.

As shown in FIGS. 3 and 4, the drive apparatus of the present disclosure is implemented as a drive apparatus 10 of a valve lift control system 100, which controls a lift amount L of an intake valve 91 of, for example, a four cylinder internal combustion engine 90 based on an axial position of a control shaft member 30.

The valve lift control system 100 includes the drive apparatus 10, an extension shaft 35, a plurality of helical splines 34, a plurality of rollers 36, and a plurality of rocker cams 38. The drive apparatus 10 includes a control shaft member 30, which is configured to linearly reciprocate. The extension shaft 35 is connected to the control shaft member 30. The number of the helical splines 34, the number of the rollers 36 and the number of the rocker cams 38 correspond to the number of cylinders of the engine 90.

For example, an inner wall of the helical spline 34 is meshed with an outer wall of the extension shaft 35 through helical gear teeth. The helical spline 34 is rotated in response to the linear reciprocating movement of the control shaft member 30 and the extension shaft 35. In this way, an opening angle ψ (see FIG. 4) between an imaginary line s1, which connects between a center of the extension shaft 35 and the roller 36, and an imaginary line s2, which connects between the center of the extension shaft 35 and a nose 381 of the rocker cam 38, is changed.

The roller 36 contacts a cam portion of an intake valve camshaft 93. When the position of the roller 36 is changed in response to the rotation of the intake valve camshaft 93, the rocker cam 38 is swung. The nose 381 of the rocker cam 38 contacts a base end of the intake valve 91. The intake valve 91 is lifted in response to the swing motion of the rocker cam 38. Therefore, the lift amount L of the intake valve 91 can be adjusted by changing the opening angle ψ (see FIG. 4) through the adjustment of the axial position of the control shaft member 30 and the extension shaft 35.

The valve lift control system 100 of the present embodiment does not adjust the lift amount of respective exhaust valves 92, which are lifted through rotation of an exhaust valve camshaft 94.

Here, each intake valve 91 is urged in a valve-opening direction thereof, which is an upward direction in FIG. 4, by an urging force Fs of a valve spring 95 that contacts a flange 911. The urging force Fs upwardly pushes the nose 381 of the rocker cam 38 and generates a rotational force Fr to the helical spline 34 in a counterclockwise direction in FIG. 4. In the present embodiment, the rotational force Fr of the helical spline 34 is converted into a load Fa, which is exerted in a direction (an upward direction in FIG. 3) of pulling the extension shaft 35 and the control shaft member 30.

As discussed above, in the present embodiment, the load Fa is applied from the helical spline 34, which serves as a driven subject, to the control shaft member 30 in a direction of moving the control shaft member 30 away from the drive cam 50.

Next, the structure of the drive apparatus 10 will be described with reference to FIGS. 1A to 2 and 5. As shown in FIG. 2, the drive apparatus 10 includes an electric motor (serving as a drive source) 20, the control shaft member 30, a support frame 41, a roller 44, the drive cam 50 (see FIG. 1), and an angle sensor 70. In the drive apparatus 10, the motor 20 generates a rotational drive force according to a command received from an electronic control unit (ECU) 76 and an electronic drive unit (EDU) 78.

The motor 20 is, for example, a DC motor and includes a rotor 22, and permanent magnets 24. A coil is wound around the rotor 22, and the permanent magnets 24 are placed on a radially outer side of the rotor 22. A motor gear 62, which serves as a driving-side gear, is installed to an end part of a shaft (an output shaft) 26 of the motor 20, which is rotated integrally with the rotor 22.

The control shaft member 30 is generally perpendicular to the shaft 26 of the motor 20. One end part of the control shaft member 30 is joined to a connecting portion 42 of the support frame 41 through a clip 43.

The support frame 41, which is configured into a rectangular form, is placed on one radial side of the rotational center (the rotational axis) P of the drive cam 50 in the radial direction and is placed on an opposite side, which is opposite from the control shaft member 30. As shown in FIG. 1B, the roller 44, which is configured into a cylindrical form, is rotatably supported by a pin 411 that is fixed to the support frame 41.

The support frame 41 serves as a support member of the present disclosure, and the roller 44 serves as a contact portion of the present disclosure. The support frame 41 and the roller 44 form a transmitting portion 40, which converts the rotational movement of the drive cam 50 into the linear reciprocating movement and transmits the converted linear reciprocating movement to the control shaft member 30.

The drive cam 50 has a profile radius (also referred to as a cam radius) R, which is a radial distance from the rotational center P to a profile of the drive cam 50 (i.e., an outer peripheral surface of the drive cam 50). The profile radius R of the drive cam 50 is riot uniform in a circumferential direction of the drive cam 50. The drive cam 50 is placed in an inside of the support frame 41 in such a manner that the drive cam 50 is rotatable together with the camshaft member 51 about the rotational center P. Furthermore, the roller 44, which is connected to the control shaft member 30 through the support frame 41, is urged by the load Fa discussed above to contact the profile of the drive cam 50 at a contact point C.

The rotational center P of the drive cam 50, the axis Q of the roller 44, and the contact point C are placed along an axis J of the control shaft member 30. The contact point C between the roller 44 and the drive cam 50 is a line that extends in a top-to-bottom direction of FIG. 1B, so that the contact point C is a contact line in a correct sense. However, in this description, for the sake of two-dimensional interpretation of the structure shown in, for example, FIG. 1A, this contact line is referred to as the contact point C.

When the drive cam 50 is rotated, the profile radius R at the contact point C changes. Thereby, the roller 44, the support frame 41 and the control shaft member 30 are linearly reciprocated in the left-to-right direction in FIG. 1A in response to the rotation of the drive cam 50.

Furthermore, three pocket portions 551, 552, 553 are formed in the outer peripheral surface of the drive cam 50. One of the pocket portions 551, 552, 553 contacts the roller 44 at the time of stopping the drive force of the motor 20. As recited in JP 2014-134194A (corresponding to US 2014/0116197A1), the pocket portion refers to a portion of the outer peripheral surface of the drive cam 50, in which the profile radius R increases in both of a forward rotational direction (also referred to as a normal rotational direction) and a reverse rotational direction of the drive cam 50 that is opposite from the forward rotational direction. When the contact point C is located at one of two circumferential end parts of the pocket portion, a rotational force is generated in the pocket portion in a direction that is from the one of the two circumferential end parts toward a circumferential center part of the pocket portion. Furthermore, when the contact point C is placed at the circumferential center part of the pocket portion where the profile radius R is minimized in the pocket portion, the rotational force becomes zero. Thereby, the drive cam 50 is held in the stable position at the circumferential center part of the pocket portion. This effect is referred to as a pocket effect.

The camshaft member 51 is placed generally parallel to the shaft 26 of the motor 20. A cam gear (serving as a driven-side gear) 68 is installed in one end part of the camshaft member 51, which is located on a side where the motor 20 is placed, and a sensor-side cam gear 74 is installed to the other end part of the camshaft member 51, which is opposite from the motor 20.

In FIG. 2, a portion of a drive force transmission path from the motor gear 62 to the cam gear 68 in a speed reducing gear mechanism is simplified. Therefore, this portion of the drive force transmission path will be described with reference to FIG. 5. As shown in FIG. 5, for example, two intermediate gears, i.e., first and second intermediate gears 63, 65 are installed between the motor gear 62 and the cam gear 68 in the drive force transmission path. The first intermediate gear 63 includes a first stage gear 630 and a second stage gear 64, which are concentric about a point G1. The second intermediate gear includes a first stage gear 650 and a second stage gear 66, which are concentric about a point G2.

The motor gear 62, which is centered at a point M, is meshed with the first stage gear 630 of the first intermediate gear 63. The second stage gear 64 of the first intermediate gear 63 is meshed with the first stage gear 650 of the second intermediate gear 65. The second stage gear 66 of the second intermediate gear 65 is meshed with the cam gear 68. In view of the meshed parts between each adjacent two gears, one of the two adjacent gears, which is located on the motor 20 side, corresponds to “a driving-side gear”, and the other one of the two adjacent gears, which is located on the drive cam 50 side, corresponds to “a driven-side gear”. Alternatively, any one of the gears, which is located on an upstream side (the motor 20 side) in the drive force transmission path, may be referred to as the driving-side gear, and another one of the gears, which is located on a downstream side (the drive cam 50 side) of the one of the gears in the drive force transmission path, may be referred to as the driven-side gear.

In the present embodiment, as discussed above, the drive force (the motor torque) of the motor 20 is transmitted from the motor gear 62 to the cam gear 68 through the intermediate gears 63, 65. In another embodiment, the motor gear 62 and the cam gear 68 may be directly meshed with each other, as indicated in FIG. 2.

Furthermore, the motor gear 62, the intermediate gears 63, 65 and the cam gear 68 of the present embodiment are spur gears, respectively. In another embodiment, a bevel gear may be used as the driving-side gear and the driven-side gear.

The angle sensor 70 senses a rotational angle of a sensor gear 72, which is meshed with the sensor-side cam gear 74, through a magnetic sensing device, such as a Hall element.

The ECU 76 receives a measurement signal of the angle sensor 70 and other measurement signals (e.g., a measurement signal from an accelerator opening degree sensor). The ECU 76 outputs a control signal to the EDU 78 based on the inputted sensor measurement signals.

The EDU 78 drives the motor 20 based on the control signal received from the ECU 76.

Next, details of the structure of the drive cam 50 will be described with reference to FIG. 6.

As shown in FIG. 6, the drive cam 50 has the pocket portions (the first to third pocket portions) 551, 552, 553, which are formed one after another in the circumferential direction about the camshaft member 51 and which are respectively configured into a form of a planar surface at three locations in the outer peripheral surface of the drive cam 50. A cam angle θ is defined to have a positive value on one side (a counterclockwise side) of a reference axis x (θ=θ0) in a counterclockwise direction in FIG. 6. Furthermore, a clockwise direction in FIG. 6 is defined as the forward rotational direction, and the counterclockwise direction in FIG. 6 is defined as the reverse rotational direction.

The first pocket portion 551 is set to extend over the reference axis x between a cam angle 81 and a cam angle θ1e e in the circumferential direction and includes a portion having a profile radius R1. The second pocket portion 552 is set to extend between a cam angle θ2 and a cam angle θ2e and includes a portion having a profile radius R2. The third pocket portion 553 is set to extend between a cam angle 83 and a cam angle 83e and includes a portion having a profile radius R3. The profile radius R1 of the first pocket portion 551, the profile radius R2 of the second pocket portion 552, and the profile radius R3 of the third pocket portion 553 satisfy a relationship of R3>R2>R1. In FIG. 6, the cam angle 82 is indicated as 82 by using a subscript 2.

A first progressively changing portion 531 is formed to extend from the first pocket portion 551 to the second pocket portion 552. In the first progressively changing portion 531, the profile radius R progressively increases in response to the forward rotation of the drive cam 50. A second progressively changing portion 532 is formed to extend from the second pocket portion 552 to the third pocket portion 553. In the second progressively changing portion 532, the profile radius R progressively increases in response to the forward rotation of the drive cam 50. Particularly, in the present embodiment, a rate of change in the profile radius R (hereinafter referred to as a profile radius change rate) relative to the cam angle θ is constant in each of the first progressively changing portion 531 and the second progressively changing portion 532. In other words, the profile radius R is increased at a constant gradient in each of the first progressively changing portion 531 and the second progressively changing portion 532.

Furthermore, a transition portion 57, in which the profile radius R is linearly and rapidly decreased, is formed between the third pocket portion 553 and the first pocket portion 551.

Furthermore, a boundary section between the first progressively changing portion 531 and the second pocket portion 552 will be defined as a second pocket boundary section 542, and a boundary section between the second progressively changing portion 532 and the third pocket portion 553 will be defined as a third pocket boundary section 543. When the drive cam 50 is rotated in the forward rotational direction, the contact point C between the drive cam 50 and the roller 44 is moved from the first progressively changing portion 531 to the second pocket portion 552 through the second pocket boundary section 542. Geometric characteristics of the pocket boundary sections 542, 543 will be described in detail later.

Now, the operation of the drive apparatus 10 will be described.

When the motor 20 is driven by the command outputted from the EDU 78, the drive force of the motor 20 is conducted to the camshaft member 51 and the drive cam 50 through the motor gear 62, the intermediate gears 63, 65, and the cam gear 68. When the drive cam 50 is rotated, the support frame 41, which supports the roller 44 that is in contact with the drive cam 50, is reciprocated in the direction that is perpendicular to the camshaft member 51 in response to the change in the profile radius R at the contact point C. Thereby, the control shaft member 30, which is joined to the support frame 41, is linearly reciprocated, so that the extension shaft 35 of the valve lift control system 100 is linearly reciprocated.

In response to the axial position of the control shaft member 30 and the axial position of the extension shaft 35, each helical spline 34 of the valve lift control system 100 is rotated to change the opening angle ψ (see FIG. 4), which is defined according to the position of the roller 36 and the position of the rocker cam 38. Thus, the lift amount L of the intake valve 91 is changed.

At the time of stopping the engine 90, the ECU76 selects one of the first to third pocket portions 551-553 of the drive cam 50, which corresponds to the axial position of the control shaft member 30 at the time of stopping the engine 90, and the ECU76 commands the selected one of the first to third pocket portions 551-553 to the EDU 78. The EDU 78 stops the energization of the motor 20 in such a manner that the drive cam 50 stops at a corresponding position where the commanded one of the first to third pocket portions 551-553 contacts the roller 44 in response to the command outputted from the ECU 76.

When the drive force of the motor 20 is stopped in this manner, the rotational position of the drive cam 50 can be maintained at the corresponding cam angle, which corresponds to the minimum profile radius of the selected one of the first to third pocket portions 551-553, and thereby the axial position of the control shaft member 30 can be maintained at a selected one of a most retarded position, an intermediate position and a most advanced position.

Next, the objective of the present disclosure will be described with reference to FIGS. 7A to 9B.

In FIGS. 7A and 7B, the progressively changing portion of the drive cam 50 (serving as a generalized representation of the progressively changing portions of the drive cam 50 of the embodiment) is indicated by reference numeral 53, and the pocket boundary section of the drive cam 50 (serving as a generalized representation of the pocket boundary sections of the drive cam 50 of the embodiment) is indicated by reference numeral 54. Furthermore, the pocket portion of the drive cam 50 (serving as a generalized representation of the pocket portions of the drive cam 50 of the embodiment) is indicated by reference numeral 55. Here, it is assumed that the roller 44 sequentially contacts the progressively changing portion 53, the pocket boundary section 54, and the pocket portion 55 in this order. In such a circumstance, FIG. 7A indicates a time point when the roller 44 contacts the progressively changing portion 53, and FIG. 7B indicates a time point when the roller 44 contacts the pocket portion 55. In both of FIGS. 7A and 7B, the motor torque Tm is exerted to rotate the drive cam 50 in the clockwise direction in FIGS. 7A and 7B.

At this time, the drive cam 50 is driven in a profile radius decreasing direction, along which the profile radius R is progressively decreased, by the roller 44, which is urged toward the center P of the drive cam 50. In the state of FIG. 7A, the drive torque Tr of the roller 44 is exerted in the profile radius decreasing direction, along which the profile radius Rn of the progressively changing portion 53 is progressively decreased, i.e., in an opposite direction, which is opposite from a direction of the motor torque Tm (more specifically, the direction of the motor torque vector). Furthermore, in the state of FIG. 7B, the drive torque Tr of the roller 44 is exerted in the profile radius decreasing direction, along which the profile radius Rp of the pocket portion 55 is progressively decreased, i.e., in the direction of the motor torque Tm (more specifically, the direction of the motor torque vector). Therefore, in the state of FIG. 7B, the large torque, which is larger than the motor torque Tm, is applied to the drive cam 50.

FIGS. 8A and 8B indicate a relationship of forces exerted between the driving-side gear and the driven-side gear. Here, as an example, the second stage gear 66 of the second intermediate gear 65 shown in FIG. 5 is used as the driving-side gear, and the cam gear 68 sown in FIG. 5 is used as the driven-side gear.

In the state of FIG. 8A, which corresponds to FIG. 7A, a tooth 672 of the driving-side gear (the second stage gear) 66 contacts and urges a tooth 692 of the driven-side gear (the cam gear) 68, which is located on a front side of the tooth 672 of the driving-side gear (the second stage gear) 66 in the rotational direction, so that the motor torque Tm is conducted from the tooth 672 of the driving-side gear (the second stage gear) 66 to the tooth 692 of the driven-side gear (the cam gear) 68. At this time, backlash (also referred to as play) is formed between the tooth 672 of the driving-side gear (the second stage gear) 66 and a tooth 691 of the driven-side gear (the cam gear) 68, which is located on a rear side of the tooth 672 of the driving-side gear (the second stage gear) 66 in the rotational direction. The presence of the backlash enables the smooth rotation of the gears 66, 68.

In a state of FIG. 8B, which corresponds to FIG. 7B, the driven-side gear (the cam gear) 68, which is joined to the camshaft member 51 of the drive cam 50, is rotated by the drive torque Tr of the roller 44. Thus, the tooth 691 of the driven-side gear (the cam gear) 68, which is located on the back side of the tooth 672 of the driving-side gear (the second stage gear) 66, collides against the tooth 672 of the driving-side gear (the second stage gear) 66 before occurrence of contact of the tooth 672 of the driving-side gear (the second stage gear) 66 against the tooth 692 of the driven-side gear (the cam gear) 68, so that tooth hitting sound (commonly known as rattle sound) may possibly be generated. This collision may possibly occur between other adjacent two of the gears in the drive force transmission path from the motor gear 62 to the cam gear 68 shown in FIG. 5. In the case of the drive apparatus 10, which is installed on the vehicle, this tooth hitting sound may possibly deteriorate the salability of the vehicle.

FIGS. 9A and 9B indicate diagrams showing the behavior at this time. As shown in FIG. 9A, at the time point tx, at which the roller 44 passes through the pocket boundary section 54, the tooth 691 of the driven-side gear (the cam gear) 68 is accelerated by the drive torque Tr exerted by the roller 44. In contrast, the teeth 671, 672 of the driving-side gear (the second stage gear) 66 are rotated at a constant speed by the motor torque Tm.

In FIG. 9B, a width of the tooth 691 is ignored for the descriptive purpose. At the time when the roller 44 contacts the progressively changing portion 53, the tooth 691 of the driven-side gear (the cam gear) 68 is rotated while the tooth 691 of the driven-side gear (the cam gear) 68 is pushed by the tooth 671 of the driving-side gear (the second stage gear) 66, which is located on the rear side of the tooth 691 of the driven-side gear (the cam gear) 68. However, when the tooth 691 of the driven-side gear (the cam gear) 68 is accelerated at the time point tx, the tooth 691 of the driven-side gear (the cam gear) 68 is spaced from the tooth 671 of the driving-side gear (the second stage gear) 66 located on the rear side of the tooth 691 of the driven-side gear (the cam gear) 68 in the rotational direction and then collides against the tooth 672 of the driving-side gear (the second stage gear) 66.

In order to reduce the tooth hitting sound caused by this kind of collision, it is effective to alleviate the rapid acceleration at the time point tx, as indicated by an arrow (countermeasure) in FIG. 9B. It is the objective of the present disclosure to provide an appropriate configuration of the pocket boundary section 54 of the drive cam 50, which is appropriate for reducing the tooth hitting sound.

Next, cam profiles of two types of samples (i.e., samples A and B) of the drive cam 50, which are prepared for achieving the above objective, as well as a result of a sound pressure measurement experiment will be described with reference to FIGS. 10 to 15.

In the sample (the first sample) A, the progressively changing portion 53 (531, 532), in which the profile radius R is increased at the constant gradient, is simply connected to the pocket portion 55 (552, 553), which is configured into the form of the planar surface, through an apex S (see FIG. 6).

In contrast, as shown in FIG. 10, in the sample (the second sample) B, a transition portion 54n, which corresponds to an angle ψn, is formed on one side of the apex S where the progressively changing portion 53 is placed, and a transition portion 54p, which corresponds to an angle ψp, is formed on the other side of the apex S where the pocket portion 55 is placed. On the one side of the apex S where the progressively changing portion 53 is placed, the gradient is progressively decreased from a positive constant value to 0 [mm/deg] during a period of increasing the profile radius R from a inflection point In to the apex S by As. In other words, the pressure angle is progressively decreased from the positive constant value to 0 [deg]. Furthermore, on the other side of the apex S where the pocket portion 55 is placed, the pressure angle is kept to be 0 [deg] in an angular range between the apex S and a inflection point Ip, and the profile radius R becomes constant. It is desirable that the angle ψn of the transition portion 54n eand the angle φp of the transition portion 54p are set to be as large as possible.

FIG. 11A is a diagram indicating a relationship between the cam angle θ and the profile radius R at the second pocket boundary section 542 in the sample A, and FIG. 11B is a diagram indicating a relationship between the cam angle θ and the profile radius R at the third pocket boundary section 543 in the sample A. FIG. 12A is a diagram indicating a relationship between the cam angle θ and the profile radius R at the second pocket boundary section 542 in the sample B, and FIG. 12B is a diagram indicating a relationship between the cam angle θ and the profile radius R at the third pocket boundary section 543 in the sample B.

In FIGS. 11A to 12B, the cam angle θ indicated at the axis of abscissas is set such that the position of the apex S of the pocket boundary section serves as a reference (0 degrees), and a right direction along the axis of abscissas corresponds to the forward rotational direction. Furthermore, in FIGS. 11A, 11B, 12A, and 12B, a scale of the axis of abscissas and a scale of the axis of ordinates are equally set.

The profile radius change rate corresponds to an inclination of a straight line (=ΔR/Δθ). Here, the profile radius change rate in the second pocket boundary section 542 is indicated by k2, and the profile radius change rate in the third pocket boundary section 543 is indicated by k3. Furthermore, a third character A added after k2 or k3 indicates the sample A. Also, a third character B added after k2 or k3 indicates the sample B. Furthermore, a fourth character + added after k2 or k3 indicates the forward rotational direction. Also, a fourth character − added after k2 or k3 indicates the reverse rotational direction.

As shown in FIG. 11A and 11B, in the sample A, the apex S is formed as an edge, and the pocket boundary section 54 (the pocket boundary sections 542, 543) is indicated as a dot. In the progressively changing portion 53 (the progressively changing portions 531, 532), the gradient is constant up to the apex S, and an inflection point does not exist in the middle of the progressively changing portion 53 (the progressively changing portions 531, 532). Therefore, in the forward rotational direction for moving the roller 44 from the progressively changing portion 53 to the pocket portion 55 (from the progressively changing portions 531 to the pocket portion 552 and from the progressively changing portions 532 to the pocket portion 553), the profile radius change rates k2A+, k3A+ is defined as a gradient of the progressively changing portion.

In contrast, in the reverse rotational direction for moving the roller 44 from the pocket portion 55 to the progressively changing portion 53 (from the pocket portion 552 to the progressively changing portion 531 and from the pocket portion 553 to the progressively changing portion 532), the minimum point V at the bottom of the pocket portion 55 (the pocket portions 552, 553) is an inflection point, which is closest to the apex S, and thereby the inclination of the straight line, which connects between the minimum point V and the apex S, is defined as the profile radius change rates k2A−, k3A−.

When a predetermined change rate threshold value is defined as K, as indicated in FIGS. 11A and 11B, a relationship between each profile radius change rate and the threshold value K of the sample A is expressed as follows.

k2A+>K, k3A+≦X, k2A->K, k3A->K

As shown in FIGS. 12A and 12B, in the sample B, the pocket boundary section 54 (the pocket boundary sections 542, 543) includes the apex S and is expressed by a cam angle range from the inflection point In, which is closest to the apex S on the progressively changing portion 53 side (the progressively changing portion 531 side and the progressively changing portion 532) side, to the inflection point Ip, which is closest to the apex S on the pocket portion 55 side (the pocket portion 552 side and the pocket portion 553 side). With respect to the profile radius change rate, the inclination of the straight line, which connects between the inflection point In and the apex S, is defined as k2B+, k3B+ in the forward rotational direction, and the inclination of the straight line, which connects between the inflection point Ip and the apex S, is defined as k2B−, k3B− in the reverse rotational direction.

A relationship between each profile radius change rate and the threshold value K of the sample B is expressed as follows.

k2B+≦K, k3B+>K, k2B-≦K, k3B->K

FIG. 13A indicates a change in a stroke of the control shaft member 30 relative to the rotational angle of the drive cam 50 at the time of rotating the drive cam 50 of the sample A in the forward rotational direction and the reverse rotational direction in the drive apparatus 10. FIG. 14A indicates a change in a stroke of the control shaft member 30 relative to the rotational angle of the drive cam 50 at the time of rotating the drive cam 50 of the sample B in the forward rotational direction and the reverse rotational direction in the drive apparatus 10. A rotational angle θ2, at which the inclination of the stroke changes, corresponds to the second pocket boundary section 542 (see FIG. 6). Furthermore, a rotational angle θ3, at which the inclination of the stroke changes, corresponds to the third pocket boundary section 543 (see FIG. 6).

FIG. 13B indicates a result of measurement of the sound pressure generated from the drive apparatus 10 during the rotational operation shown in FIG. 13A. FIG. 14B indicates a result of measurement of the sound pressure generated from the drive apparatus 10 during the rotational operation shown in FIG. 14A.

Now, a sound pressure measuring method will be briefly described with reference to FIG. 15. The sound pressure measurement is performed at a place where another sound source or another vibration source is eliminated as much as possible. In a state where the drive apparatus 10 is installed to a jig 89, which is used in placed of the engine 90 (see FIG. 3), a distal end of a microphone 82 connected to a sound pressure measuring device 81 is set at a position that is spaced from an end of the drive apparatus 10 by about 10 mm. In this way, the sound pressure of the tooth hitting sound, which is generated by the non-driving-side gear (the driven-side gear) at the time of rotating the motor 20, is measured.

In the sample A shown in FIG. 13A, a reference sound pressure range A0 is about ±2 Pa at the time when the contact point C of the roller 44 passes through the progressively changing portion 531, 532 in response to the rotation of the drive cam 50 A boundary sound pressure is compared with this reference sound pressure range A0. Here, the term “boundary sound pressure” is defined as a sound pressure that is generated at the time when the contact point C of the roller 44 passes through the pocket boundary section 542, 543 in response to the rotation of the drive cam 50. In a case where the boundary sound pressure measured at the corresponding rotational angle 82 or 83 is within the reference sound pressure range A0, a blank circle is indicated at the top side of the corresponding rotational angle θ2 or θ3 in FIG. 13B. Also, in a case where the boundary sound pressure measured at the corresponding rotational angle θ2 or 03 exceeds the reference sound pressure range A0, a multiplication mark is indicated at the top side of the corresponding rotational angle θ2 or θ3 in FIG. 13B.

At the rotational angle θ3 in the reverse rotational direction, the boundary sound pressure is within the reference sound pressure range A0. In contrast, at the rotational angles θ2, θ3 in the forward rotational direction and the rotational angle θ2 in the reverse rotational direction, the boundary sound pressure exceeds the reference sound pressure range A0. That is, a user may possibly hear the tooth hitting sound generated at the pocket boundary section as a noisy sound (annoying sound).

In the sample B shown in FIG. 14B, the reference sound pressure range A0 is about ±2 Pa like the sample A shown in FIG. 13B, and the blank circle and the multiplication mark are indicated at the top side of FIG. 14B in a manner similar to that of FIG. 13B.

As shown in FIG. 14B, at the rotational angle θ3 in the forward rotational direction and the reverse rotational direction, the boundary sound pressure exceeds the reference sound pressure range A0. However, at the rotational angle θ2 in the forward rotational direction and the reverse rotational direction, the boundary sound pressure is within the reference sound pressure range A0. Thus, with respect to the second pocket boundary section 542, the hitting sound is reduced in comparison to the sample A.

The location of the pocket boundary section, at which the boundary sound pressure is within the reference sound pressure range A0, in FIGS. 13B and 14B, coincides with the location of the part, at which the profile radius change rate is equal to or less than the threshold value K in FIGS. 11A to 12B. According to the above result, it is understood that the profile radius change rate and the boundary sound pressure correlate with each other. Thus, when the cam profile is set such that the profile radius change rate is equal to or less than the threshold value K in all of the pocket boundary sections in the forward rotational direction and the reverse rotational direction, the tooth hitting sound in the entire rotational angle range can be reduced.

As discussed above, in the sample A and the sample B, which are exemplified above, the boundary sound pressures at all of the pocket boundary sections are not kept within the reference sound pressure range A0. However, a person skilled in the art can implement the present disclosure based on the above disclosure, which clearly and sufficiently discloses the principle of the present disclosure. The threshold value K may be appropriately designed in view of results of experiments and/or simulations based on the specifications of the structure and the gears of the drive force transmission system, which may or may not include intermediate gear(s).

Now, advantages of the embodiment will be described.

(1) In the present embodiment, the profile radius change rate at the pocket boundary section 54 is set such that the boundary sound pressure, which is the sound pressure generated at the time when the contact point C passes through the pocket boundary section 54 in response to the rotation of the drive cam 50, is within the reference sound pressure range, which is a range of variation in the sound pressure generated at the time when the contact point C passes through the progressively changing portion 53. Thereby, when the contact point C passes through the boundary section 54 between the progressively changing portion 53 and the pocket portion 55 in response to the rotation of the drive cam 50, it is possible to limit or reduce the tooth hitting sound that is generated through the collision of the driven-side gear (e.g., the cam gear 68) against the driving-side gear (e.g., the second stage gear 66 of the second intermediate gear 65).

(2) The profile radius change rate at the pocket boundary section 54 is defined as an inclination of a straight line that connects between the apex S of the pocket boundary section 54 and the inflection point In, Ip, which is closest to the apex S and is located in the progressively changing portion 53 or the pocket portion 55. Furthermore, in the case where the progressively changing portion 53 is formed to have the profile radius, which changes at the constant gradient in response to the rotation of the drive cam 50, the profile radius change rate at the progressively changing portion 53 side is defined as the gradient of the progressively changing portion 53. Based on this definition, the profile radius change rate [mm/deg] can be objectively compared and evaluated.

(3) In the present embodiment, the drive force (the motor torque) of the motor 20 is transmitted from the motor gear 62 to the cam gear 68 through the intermediate gears 63, 65, so that the tooth hitting sound is more likely generated in comparison to the case where the motor gear 62 and the cam gear 68 are directly meshed with each other. Therefore, the advantage of limiting or reducing the tooth hitting sound can be particularly prominent in such a case.

(4) The motor gear 62, the intermediate gears 63, 65, and the cam gear 68 are formed as the spur gears. Therefore, the tooth hitting sound is more likely generated in the present embodiment in comparison to the case where the bevel gears are used in place of the spur gears. Thus, when the present embodiment is adapted, the tooth hitting sound can be effectively reduced while using the inexpensive spur gears.

Other Embodiments

(A) The specific configuration of the profile of the drive cam is not limited to the one discussed in the above embodiment. For example, the number of the pocket portions is not limited to three and may be changed to any number, which is equal to or larger than one. Furthermore, the change of the profile radius of the progressively changing part does not need to have the constant gradient.

(B) The structure, which urges the roller 44 against the drive cam 50, is described as follows in the above embodiment. That is, the load Fa is applied from the driven subject to the control shaft member 30 in the direction of pulling the control shaft member 30. Besides this, the drive apparatus of the present disclosure may be also applied to a case where the control shaft member 30 pushes the drive cam 50 directly or indirectly through another member.

For example, in another embodiment shown in FIG. 16, a load Fb is applied from a right side of FIG. 16 to a control shaft member 49 in a direction of pushing the control shaft member 49. A ball 492, which is formed separately from the control shaft member 49, is rotatably received in a recess 491, which is formed at a distal end of the control shaft member 49, in a manner that enables rotation of the ball 492 in all directions. While the ball 492 makes point contact with the pocket portion 55 of the drive cam 50 at the contact point C, the control shaft member 49 reciprocates in the left-to-right direction of FIG. 16 in response to the rotation of the drive cam 50. The control shaft member 49 of this embodiment shown in FIG. 16 is a member, in which the support member and the control shaft member of the present disclosure are formed integrally, and the ball 492 serves as the contact portion of the present disclosure.

(C) The drive source of the present disclosure is not limited to the DC motor of the above embodiment. That is, the drive source of the present disclosure may be an AC motor or another type of electric motor, or an actuator, which is operated by hydraulic pressure (oil pressure), compressed air or electromagnetic force.

(D) The mechanism, which adjusts the lift amount at the valve lift control system, is not limited to the above described structure. Furthermore, the valve lift control system is not limited to the one, which controls the lift amount of the respective intake valves. That is, the valve lift control system of the present disclosure may be one, which controls, for example, the lift amount of the respective exhaust valves.

(E) The details of the specification of the sound pressure measuring device and the measurement conditions discussed with reference to FIG. 15 are not limited to the above described ones. That is, according to the present disclosure, the reference sound pressure range and the boundary sound pressure are simultaneously measured with the measuring device and under the predetermined condition. The reference sound pressure range and the boundary sound pressure are relatively evaluated, so that the degree of the boundary sound pressure can be objectively evaluated.

(F) The drive apparatus of the present disclosure is not necessarily provided in the valve lift control system. That is, the drive apparatus of the present disclosure may be provided in any apparatus, which can control the control amount of a corresponding controlled subject in response to the axial position of the control shaft member.

As discussed above, the present disclosure is not limited the above embodiments and modifications thereof. That is, the above embodiments and modifications thereof may be modified in various ways without departing from the principle of the present disclosure.

DRIVE APPARATUS

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