Driving force transmission device

Abstract

To provide a driving force transmission device capable of accurately performing an origin return operation of an electric motor that operates a pressing mechanism for pressing a clutch for a short time.SOLUTION: A control unit 40 that controls an electric motor 4 executes an origin return operation by controlling the electric motor 4 at start after an operation power source is supplied to the control unit 40. The origin return operation includes: a primary operation for causing the electric motor 4 to generate rotating torque in a first rotating direction to cause a cam ball 33 to abut on one movement end in the circumferential direction of a first cam groove 310 and a second cam groove 320; a secondary operation for reducing the rotating torque in the first rotating direction generated by the electric motor 4 compared to the rotating torque during the primary operation; and a tertiary operation for increasing the rotating torque in the first rotating direction generated by the electric motor 4 compared to the rotating torque during the secondary operation to cause the cam ball 33 to abut on one movement end in the circumferential direction of the first cam groove 310 and the second cam groove 320.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a driving force transmission device having a pressing mechanism operated by an electric motor. [Background technology]

[0002] Conventionally, for example, a driving force transmission device that can transmit the driving force of a vehicle intermittently includes a ball cam mechanism operated by an electric motor and a clutch that is pressed by the cam thrust generated by the ball cam mechanism (see, for example, Patent Document 1).

[0003] The device described in Patent Document 1 is configured to axially press a friction multi-plate clutch equipped with multiple clutch plates with a pressing force generated by a ball cam mechanism. The ball cam mechanism includes a pair of cam plates, each with a cam groove formed therein, and balls housed in the cam grooves. The pressing force is generated when the pair of cam plates rotate relative to each other due to the rotational torque of an electric motor having an incremental encoder. When the vehicle's ignition switch is turned on from an off state, an electronic control unit that controls the electric motor reverses the electric motor so that the cam plates rotate relative to each other until the balls hit one of the moving ends of the cam grooves, and then drives the electric motor toward a position (the "new zero point Mpos0") that is backed by an angle calculated based on the temperature of the oil that lubricates the friction multi-plate clutch. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-223869 (see

[0055] -

[0062] and Figures 10-11) Summary of the Invention [Problem to be solved by the invention]

[0005] For example, as described in Patent Document 1, when an electric motor with an incremental encoder that activates a ball cam mechanism starts its home return operation by rotating a pair of cam plates relative to one another to cause a ball to strike one of its travel ends, the relative velocity between the cam plate and the ball when it strikes the one of its travel ends varies depending on the position of the ball in the cam groove before the home return operation. That is, when the ball is close to one of its travel ends before the home return operation, the ball strikes the one of its travel ends with a low velocity relative to the cam plate. When the ball is far from the one of its travel ends, the ball strikes the one of its travel ends with a high velocity relative to the cam plate and with momentum. This can cause variations in the home position of the electric motor recognized by the electronic control unit.

[0006] Furthermore, if the relative rotational speed of the pair of cam plates is reduced during the origin return operation, it is possible to prevent the ball from hitting one of the moving ends while it is gaining momentum. However, if the relative rotational speed of the pair of cam plates is reduced, it will take a long time for the ball to hit one of the moving ends if the ball's position before the origin return operation is far from that end.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a driving force transmission device that can quickly and accurately return an electric motor that operates a pressing mechanism that presses a clutch to its origin. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a driving force transmission device for a vehicle, comprising: a clutch whose on / off state of driving force is changed by being pressed in the axial direction; a pressing mechanism that presses the clutch in the axial direction; an electric motor that operates the pressing mechanism; and a control unit that controls the electric motor, wherein the driving force of a driving source of the vehicle is transmitted by the clutch, the pressing mechanism having a disk-like first cam plate formed with a plurality of first cam grooves whose axial depth changes depending on circumferential position; a disk-like second cam plate formed with a plurality of second cam grooves whose axial depth changes depending on circumferential position; and a plurality of cam balls arranged between the first cam plate and the second cam plate, wherein the first cam plate and the second cam plate rotate relatively due to the rotational torque of the electric motor, causing the plurality of cam balls to roll in the plurality of first cam grooves and the plurality of second cam grooves, thereby changing the axial distance between the first cam plate and the second cam plate, the second cam groove is formed in an arc shape centered on the rotation axis of relative rotation between the first cam plate and the second cam plate, the control unit controls the electric motor to perform a return-to-origin operation when started after an operating power is supplied to the control unit, and controls the electric motor thereafter with the rotation position of the electric motor at the completion of the return-to-origin operation set as an original position, the return-to-origin operation including: a primary operation in which the electric motor generates a rotational torque in a first rotation direction, causing the multiple cam balls to abut against one of the moving ends in the circumferential direction of the multiple first cam grooves and the multiple second cam grooves; a secondary operation in which the rotational torque in the first rotation direction generated by the electric motor is reduced to be lower than the rotational torque during the primary operation; and a tertiary operation in which the rotational torque in the first rotation direction generated by the electric motor is increased to be higher than the rotational torque during the secondary operation, causing the multiple cam balls to abut against one of the moving ends in the circumferential direction of the multiple first cam grooves and the multiple second cam grooves. [Effects of the Invention]

[0009] According to the driving force transmission device of the present invention, it is possible to perform the origin return operation of the electric motor that operates the pressing mechanism with high accuracy in a short time. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an example of the general configuration of a vehicle equipped with a driving force transmission device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view of a driving force transmission device and a differential device. [Figure 3] FIG. 3 is a partially enlarged view of FIG. 2. [Figure 4] 1(a) is a configuration diagram showing the surface of the first cam plate facing the second cam plate, and (b) is a configuration diagram showing the surface of the second cam plate facing the first cam plate. [Figure 5] 10(a) to 10(d) are explanatory diagrams showing the positions of the cam balls in the first cam groove of the first cam plate and the second cam groove of the second cam plate from the state before the origin return operation is performed until the origin return operation is completed. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment Mode] Embodiments of the present invention will be described with reference to Figures 1 to 5. The embodiments described below are shown as preferred specific examples for carrying out the present invention, and although some of them specifically exemplify various technically preferable aspects, the technical scope of the present invention is not limited to these specific embodiments.

[0012] 1 is a schematic diagram showing an example of the general configuration of a vehicle 1 equipped with a driving force transmission device 11 according to an embodiment of the present invention. In the following description, the terms "left side" and "right side" refer to the left and right sides of the vehicle 1 in the vehicle width direction.

[0013] The vehicle 1 has a driving force transmission device 11, a differential device 12, a driving source 13 that generates driving force, a transmission 14 that changes the output rotation of the driving source 13, a drive shaft 15 that transmits the driving force of the driving source 13 via the transmission 14 to the differential device 12, left and right wheels 16, 17, left and right hub units 161, 171 that are provided corresponding to the left and right wheels 16, 17, respectively, a left drive shaft 18 that is arranged between the left hub unit 161 and the differential device 12, and a right drive shaft 19 that is arranged between the right hub unit 171 and the differential device 12.

[0014] The vehicle 1 is also provided with a start switch 100, which is pressed by the driver to change the state from off to on, thereby enabling the vehicle 1 to run. When the driver presses the start switch 100 again to change the state from on to off, the power supply to various electrical components such as the control unit 40 described below is cut off, and the engine is stopped.

[0015] The drive source 13 is, for example, an internal combustion engine or an electric motor, and generates drive force for propelling the vehicle 1. The drive force transmission device 11 and the differential device 12 constitute a drive force distribution device 10 that distributes the drive force of the drive source 13 to drive shafts 18, 19. The left drive shaft 18 has an intermediate shaft 180, an outboard constant velocity joint 181 connected to the hub unit 161, and an inboard constant velocity joint 8 connected to the differential device 12. The right drive shaft 19 has an intermediate shaft 190, an outboard constant velocity joint 191 connected to the hub unit 171, and an inboard constant velocity joint 9 connected to the differential device 12. The outboard constant velocity joints 181, 191 are fixed constant velocity universal joints, such as ball constant velocity joints. The inboard constant velocity joints 8, 9 are sliding constant velocity universal joints, such as tripod constant velocity joints.

[0016] The differential device 12 has a ring gear 121 meshed with the drive shaft 15, a differential case 122 that rotates integrally with the ring gear 121, a pinion shaft 123 fixed to the differential case 122, a pair of pinion gears 124 journaled on the pinion shaft 123, and left and right side gears 125, 126 meshed with the pair of pinion gears 124. The outer joint member 81 of the constant velocity joint 8 is attached to the left side gear 125 so as to be non-rotatable relative to the left side gear 125. The outer joint member 91 of the constant velocity joint 9 is attached to the right side gear 126 so as not to be rotatable relative to the right side gear 126.

[0017] The driving force transmission device 11 has a clutch mechanism 2, and is capable of switching between a state in which the clutch mechanism 2 transmits driving force between the differential case 122 and the outer joint member 81 of the constant velocity joint 8 and a state in which the clutch mechanism 2 does not transmit driving force therebetween. When the clutch mechanism 2 is activated to transmit driving force between the differential case 122 and the outer joint member 81 of the constant velocity joint 8, the relative rotation between the differential case 122 and the left side gear 125 is restricted, and thus the relative rotation between the differential case 122 and the right side gear 126 is also restricted. On the other hand, when the clutch mechanism 2 is in an inactive state, the pair of pinion gears 124 rotate, allowing the left side gear 125 and the right side gear 126 to rotate relative to each other.

[0018] That is, in this embodiment, the driving force transmission device 11 functions as a differential limiting device that limits the relative rotation between the left side gear 125 and the right side gear 126. Note that, in this embodiment, the driving force transmission device 11 is described as being disposed on the left side of the differential device 12 in the vehicle width direction, but the driving force transmission device 11 may also be disposed on the right side of the differential device 12.

[0019] Fig. 2 is a cross-sectional view of the driving force transmission device 11 and the differential device 12. Fig. 3 is a partially enlarged view of Fig. 2. In Fig. 2, the rotation axis O of the differential case 122 is indicated by a dashed line. The left and right side gears 125, 126 and the outer joint members 81, 91 of the constant velocity joints 8, 9 are rotatable relative to the differential case 122 around the rotation axis O. Hereinafter, the direction parallel to the rotation axis O will be referred to as the axial direction.

[0020] The constant velocity joints 8, 9 each include an outer joint member 81, 91, a tripod member 82, 92 to which an intermediate shaft 180, 190 is connected so as not to rotate relative to one another, and a plurality of rollers 83, 93 assembled to the tripod member 82, 92. The outer joint member 81, 91 integrally includes a cylindrical, bottomed tubular portion 811, 911 that houses the tripod member 82, 92 and the plurality of rollers 83, 93, and a stem portion 812, 912 that is provided to protrude in the axial direction from the end of the tubular portion 811, 911 on the differential device 12 side.

[0021] The differential case 122 has a cylindrical portion 122a that supports both ends of the pinion shaft 123, a left side wall portion 122b, a right side wall portion 122c, a left side cylindrical portion 122d that extends axially from the inner diameter side end of the left side wall portion 122b, and a right side cylindrical portion 122e that extends axially from the inner diameter side end of the right side wall portion 122c. The left side gear 125 has a gear portion 125a that meshes with the pair of pinion gears 124 and a cylindrical portion 125b that is inserted inside the left side cylindrical portion 122d of the differential case 122. The stem portion 812 of the outer joint member 81 is fitted inside the cylindrical portion 125b so as not to rotate relative to the cylindrical portion 125b.

[0022] Similarly, the right side gear 126 has a gear portion 126a that meshes with the pair of pinion gears 124, and a cylindrical portion 126b that is inserted into the inside of the right tubular portion 122e of the differential case 122. The stem portion 912 of the outer joint member 91 is fitted into the inside of the cylindrical portion 126b so as to be unable to rotate relative to the cylindrical portion 126b. The stem portion 812 of the left outer joint member 81 is axially longer than the stem portion 912 of the right outer joint member 91, and the driving force transmission device 11 is disposed on the outer periphery of the stem portion 812 of the left outer joint member 81.

[0023] The driving force transmission device 11 includes, as its main components, a clutch mechanism 2, a pressing mechanism 3, an electric motor 4 as a rotary actuator, a control unit 40 that controls the electric motor 4, a speed reduction mechanism 5 that reduces the rotation speed of the electric motor 4, and a case 6. The clutch mechanism 2 has a clutch 20 that changes the on / off state of driving force when pressed axially. In this embodiment, the clutch 20 is a multi-plate clutch having a plurality of outer clutch plates 201 and a plurality of inner clutch plates 202. The pressing mechanism 3 is actuated by the electric motor 4 and presses the clutch 20 in the axial direction. When the clutch 20 is pressed axially, the plurality of outer clutch plates 201 and the plurality of inner clutch plates 202 come into frictional contact with each other, increasing frictional force, and this frictional force transmits the driving force.

[0024] The clutch mechanism 2 also has a clutch drum 21 that rotates integrally with the multiple outer clutch plates 201, a clutch hub 22 that rotates integrally with the multiple inner clutch plates 202, a pressure plate 23 arranged on one axial side of the clutch 20, a pressure-receiving plate 24 arranged on the other axial side of the clutch 20, and a retaining ring 25 that restricts axial movement of the pressure-receiving plate 24 relative to the clutch drum 21. The multiple outer clutch plates 201 and the multiple inner clutch plates 202 are arranged alternately along the axial direction between the pressure plate 23 and the pressure-receiving plate 24.

[0025] The clutch drum 21 integrally comprises an outer cylindrical portion 211 having on its inner periphery a spline engagement portion 210 with which the multiple outer clutch plates 201 engage to be axially movable, an annular wall portion 212 aligned with the clutch 20 in the axial direction, a coupling portion 213 coupled to the left cylindrical portion 122d of the differential case 122 so as not to rotate relative to it, and a connecting portion 214 connecting the wall portion 212 and the coupling portion 213. A retaining ring 25 engages with the outer cylindrical portion 211 of the clutch drum 21 so as not to be able to move axially.

[0026] The clutch hub 22 integrally comprises an inner cylindrical portion 221 having on its outer periphery a spline engagement portion 220 with which multiple inner clutch plates 202 engage for axial movement, a coupling portion 222 coupled to the stem portion 812 of the left outer joint member 81 so as not to rotate relative to the stem portion 812, and a connection portion 223 connecting the inner cylindrical portion 221 and the coupling portion 222. Bearings 71, 72, and 73 are respectively arranged between the connection portion 214 of the clutch drum 21 and the connection portion 223 of the clutch hub 22, between the coupling portion 222 of the clutch hub 22 and the left cylindrical portion 122d of the differential case 122, and between the coupling portion 222 of the clutch hub 22 and the case 6. The bearings 71, 72, and 73 are ball bearings in which multiple balls are arranged between an outer ring and an inner ring.

[0027] The pressing mechanism 3 has a disk-shaped first cam plate 31 and a second cam plate 32 that face each other in the axial direction, a plurality of spherical cam balls 33 arranged between the first cam plate 31 and the second cam plate 32, a retainer 34 that rotatably holds the plurality of cam balls 33, a pressing member 35, a return spring 36, and a thrust bearing 37 that are arranged between the second cam plate 32 and the pressing plate 23 of the clutch mechanism 2. The first cam plate 31, the second cam plate 32, the plurality of cam balls 33, and the retainer 34 are made of, for example, steel, and constitute the cam mechanism 30.

[0028] The first cam plate 31, the second cam plate 32, the cage 34, the pressing member 35, the return spring 36, and the thrust bearing 37 are annularly shaped and arranged side by side in the axial direction, with the rotation axis O as their center. The first cam plate 31 and the second cam plate 32 rotate relatively about the rotation axis O due to the rotational torque of the electric motor 4. The cage 34 holds a plurality of cam balls 33 at equal intervals along the circumferential direction of the first cam plate 31 and the second cam plate 32.

[0029] The pressing member 35 has a plurality of shaft portions 351 inserted into a plurality of through holes 212a formed in the wall portion 212 of the clutch drum 21, and a disk portion 352 arranged between the return spring 36 and the thrust bearing 37. The multiple shaft portions 351 are provided so as to protrude in the axial direction from a plurality of positions in the circumferential direction of the disk portion 352. A tip end surface 351a of the shaft portions 351 faces the pressing plate 23. The return spring 36 is a disc spring, and is arranged between the wall portion 212 of the clutch drum 21 and the disk portion 352 of the pressing member 35, and urges the disk portion 352 of the pressing member 35 in a direction away from the wall portion 212 of the clutch drum 21. The multiple shaft portions 351 of the pressing member 35 are inserted into a plurality of cutout portions 360 formed in the return spring 36, respectively.

[0030] First cam plate 31 integrally includes an annular plate-shaped opposing portion 311 that faces second cam plate 32 in the axial direction, a gear portion 312 provided on the outer periphery of opposing portion 311, and a cylindrical protrusion 313 that protrudes in the axial direction from the inner circumferential end of opposing portion 311 toward clutch 20. Bearing 74, which is a ball bearing, is disposed between first cam plate 31 and connection portion 223 of clutch hub 22. Second cam plate 32 is disposed on the outer periphery of protrusion 313 of first cam plate 31.

[0031] Second cam plate 32 has, at one location in the circumferential direction, anti-rotation portion 321 that restricts rotation relative to case 6. In this embodiment, anti-rotation portion 321 is formed as a protrusion provided on the outer periphery of second cam plate 32, and case 6 is formed with a recessed groove 60 into which anti-rotation portion 321 engages. Second cam plate 32 is movable in the axial direction with respect to case 6 but is unable to rotate relative to it.

[0032] A plurality of first cam grooves 310 whose axial depth varies depending on the circumferential position are formed in the opposing portion 311 of the first cam plate 31. A plurality of second cam grooves 320 whose axial depth varies depending on the circumferential position are formed in the second cam plate 32. A portion of each cam ball 33 is housed in the first cam groove 310, and another portion is housed in the second cam groove 320.

[0033] The electric motor 4 includes a stator 41, a rotor 42, an output rotating shaft 43 fixed to the rotor 42, and an encoder 44 for detecting the rotation angle of the rotor 42 relative to the stator 41. Rotation of the output rotating shaft 43 rotates the first cam plate 31 and the second cam plate 32 relative to each other. The control unit 40 supplies a drive current to the stator 41 based on a rotation angle signal indicating the rotation angle of the rotor 42 detected by the encoder 44. The drive current generates a magnetic field, causing the rotor 42 to rotate together with the output rotating shaft 43. The rotation angle signal output by the encoder 44 is an A-phase and B-phase pulse signal that are 90° out of phase with each other, and the pulse width and pulse interval vary depending on the rotation speed of the rotor 42. The control unit 40 can determine the rotation direction of the rotor 42 based on the phase difference between the A-phase and B-phase pulse signals, and can detect the amount of rotation of the rotor 42 by counting the number of pulses. In other words, the encoder 44 is an incremental encoder.

[0034] When the first cam plate 31 and the second cam plate 32 rotate relative to each other and the multiple cam balls 33 roll in the multiple first cam grooves 310 and the multiple second cam grooves 320, the axial distance between the first cam plate 31 and the second cam plate 32 changes, generating a cam thrust. This cam thrust is transmitted to the clutch 20 via the thrust bearing 37, the pressing member 35, and the pressing plate 23, and the multiple outer clutch plates 201 and the multiple inner clutch plates 202 are pressed together by the cam thrust. The clutch 20 transmits a driving force corresponding to the rotational torque of the electric motor 4 between the clutch drum 21 and the clutch hub 22.

[0035] The reduction mechanism 5 has a gear shaft 51 attached to the output rotation shaft 43 of the electric motor 4, and a reduction gear 52 supported by a support pin 50 attached to the case 6. The reduction gear 52 has a large diameter gear portion 521 that meshes with the gear shaft 51, and a small diameter gear portion 522 that meshes with the gear portion 312 of the first cam plate 31. The control unit 40 can calculate the rotational position of the first cam plate 31 relative to the second cam plate 32 by applying the reduction ratio of the reduction mechanism 5 to the amount of rotation of the rotor 42.

[0036] The case 6 houses the clutch mechanism 2, the pressing mechanism 3, the reduction gear mechanism 5, and the differential gear 12, and is fixed to the vehicle body. Lubricating oil (not shown) is sealed inside the case 6. Seal members 75, 76 that prevent leakage of the lubricating oil are arranged between the case 6 and the stem portions 812, 912 of the outer joint members 81, 91. A bearing 77 is arranged between the case 6 and the right cylindrical portion 122e of the differential case 122. The electric motor 4 is fixed to the outside of the case 6 with bolts 78. A seal member 79 is arranged between the gear shaft 51 and the case 6.

[0037] FIG. 4(a) is a configuration diagram showing the surface of first cam plate 31 facing second cam plate 32. FIG. 4(b) is a configuration diagram showing the surface of second cam plate 32 facing first cam plate 31. Six first cam grooves 310 are formed in first cam plate 31, and the same number of second cam grooves 320 are formed in second cam plate 32. Each of first cam grooves 310 and second cam grooves 320 is formed in an arc shape centered on rotation axis O. Gear portion 312 of first cam plate 31 is provided over an angular range wider than twice the arc angle of each first cam groove 310 (approximately 60° in this embodiment). The inner diameter of second cam plate 32 is formed slightly larger than the outer diameter of protrusion 313 of first cam plate 31.

[0038] Each first cam groove 310 is recessed in the axial direction from a facing surface 311a of the facing portion 311 of the first cam plate 31 that faces the second cam plate 32. The facing surface 311a is a flat surface perpendicular to the axial direction. Two first cam grooves 310 that are adjacent in the circumferential direction of the first cam plate 31 are separated by a wall portion 311b. Furthermore, each second cam groove 320 is recessed in the axial direction from a facing surface 32a of the second cam plate 32 that faces the first cam plate 31. The facing surface 32a is a flat surface perpendicular to the axial direction. Two second cam grooves 320 that are adjacent in the circumferential direction of the second cam plate 32 are separated by a wall portion 32b.

[0039] The axial depth of first cam groove 310 gradually decreases from deepest end 310a, which is one circumferential end of first cam plate 31, to shallowest end 310b, which is the other circumferential end. Similarly, the axial depth of second cam groove 320 gradually decreases from deepest end 320a, which is one circumferential end of second cam plate 32, to shallowest end 320b, which is the other circumferential end. First cam plate 31 and second cam plate 32 are relatively rotatable within a range in which cam ball 33 rolls between deepest ends 310a, 320a and shallowest ends 310b, 320b of first cam groove 310 and second cam groove 320.

[0040] The first cam plate 31 and the second cam plate 32 are closest when the cam ball 33 is at the deepest ends 310a, 320a of the first cam groove 310 and the second cam groove 320, and are farthest apart when the cam ball 33 is at the shallowest ends 310b, 320b of the first cam groove 310 and the second cam groove 320. When the cam ball 33 is at the deepest ends 310a, 320a of the first cam groove 310 and the second cam groove 320, the clutch 20 is not pressed, and as the cam ball 33 rolls in the first cam groove 310 and the second cam groove 320 toward the shallowest ends 310b, 320b, the clutch 20 is gradually pressed and the driving force that can be transmitted by the clutch 20 increases.

[0041] The control unit 40 determines the magnitude of the driving force to be transmitted by the clutch 20 based on the vehicle state, and controls the electric motor 4 so that the driving force of that magnitude is transmitted. The vehicle state includes the vehicle speed, the rotational speeds of the left and right wheels 16, 17, the steering angle, the amount of depression of the accelerator pedal, the magnitude of the driving force generated by the drive source 13, the yaw rate, etc. The control unit 40 can acquire information about these vehicle states via an in-vehicle network such as a CAN (Controller Area Network).

[0042] Here, the encoder 44 of the electric motor 4 is of the incremental type as described above, and when the vehicle start switch 100 is turned off and the power supply to the control unit 40 is cut off, the control unit 40 is unable to grasp the rotational positions of the electric motor 4 and the first cam plate 31. For this reason, the control unit 40 controls the electric motor 4 to perform a return-to-origin operation when the control unit 40 is started after the operating power is supplied to the control unit 40, and thereafter controls the electric motor 4 with the rotational position of the electric motor 4 when the return-to-origin operation is completed as the original position.

[0043] In this embodiment, the rotational position of electric motor 4 when the multiple cam balls 33 are at the deepest ends 310a, 320a of the multiple first cam grooves 310 and second cam grooves 320 is defined as the original position. In the following description, the "first rotational direction" refers to the rotational direction of electric motor 4 when moving first cam plate 31 and second cam plate 32 closer to each other, and the "second rotational direction" refers to the rotational direction of electric motor 4 when moving first cam plate 31 and second cam plate 32 away from each other. In FIG. 4(a), the rotational direction of first cam plate 31 when electric motor 4 rotates in the first rotational direction is indicated by arrow A1, and the rotational direction of first cam plate 31 when electric motor 4 rotates in the second rotational direction is indicated by arrow A2.

[0044] The original position may be the rotational position of the electric motor 4 when the multiple cam balls 33 are at the shallowest ends 310b, 320b of the multiple first cam grooves 310 and second cam grooves 320, respectively, or the original position may be the position where the rotation of the electric motor 4 stops when the electric motor 4 is rotated with a predetermined torque so that the cam balls 33 roll from the deepest ends 310a, 320a toward the shallowest ends 310b, 320b. In these cases, the "first rotation direction" and "second rotation direction" are opposite to those in the above case.

[0045] In this embodiment, the origin return operation performed by the control unit 40 at startup includes a primary operation in which the electric motor 4 generates a rotational torque in a first rotational direction, causing the multiple cam balls 33 to abut against one of the circumferential moving ends of the multiple first cam grooves 310 and the multiple second cam grooves 320; a secondary operation in which the rotational torque in the first rotational direction generated by the electric motor 4 is reduced to be lower than the rotational torque during the primary operation; and a tertiary operation in which the rotational torque in the first rotational direction generated by the electric motor 4 is increased to be higher than the rotational torque during the secondary operation, causing the multiple cam balls 33 to abut against one of the circumferential moving ends of the multiple first cam grooves 310 and the multiple second cam grooves 320. Furthermore, the origin return operation may further include a quaternary operation in which the rotational torque in the first rotation direction generated by the electric motor 4 after the tertiary operation is reduced to be less than the rotational torque during the tertiary operation, and a quinary operation in which the rotational torque in the first rotation direction generated by the electric motor 4 is increased to be more than the rotational torque during the quaternary operation, causing the multiple cam balls 33 to abut against one of the circumferential moving ends of the multiple first cam grooves 310 and second cam grooves 320.

[0046] In this embodiment, the cam balls 33 are moved to the deepest ends 310a, 320a of the first cam grooves 310 and the second cam grooves 320 in the primary and tertiary operations of the origin return operation. If the origin return operation includes a quintic operation, the cam balls 33 are moved to the deepest ends 310a, 320a of the first cam grooves 310 and the second cam grooves 320 in the quintic operation. That is, in this embodiment, the above-mentioned movement ends are the deepest ends 310a, 320a. However, the shallowest ends 310b, 320b may also be the movement ends, or the positions at which the electric motor 4 stops rotating when the electric motor 4 is rotated with a predetermined torque so that the cam balls 33 roll toward the shallowest ends 310b, 320b may also be the movement ends.

[0047] The rotational torque generated by the electric motor 4 in the tertiary operation is smaller than the rotational torque generated by the electric motor 4 in the primary operation, and if the origin return operation includes a quinary operation, the rotational torque generated by the electric motor 4 in the quinary operation is even smaller than the rotational torque generated by the electric motor 4 in the tertiary operation.

[0048] The secondary action is performed when the rotation of the electric motor 4 stops as a result of the primary action causing the multiple cam balls 33 to abut against the deepest ends 310a, 320a of the multiple first cam grooves 310 and the multiple second cam grooves 320. The control unit 40 can detect that the rotation of the electric motor 4 has stopped based on a signal from the encoder 44. Similarly, the quaternary action is performed when the rotation of the electric motor 4 stops as a result of the tertiary action causing the multiple cam balls 33 to abut against the deepest ends 310a, 320a of the multiple first cam grooves 310 and the multiple second cam grooves 320.

[0049] The control unit 40 may set the rotational torque generated by the electric motor 4 in the secondary action to zero or to rotational torque in the second rotational direction. When generating rotational torque in the second rotational direction in the secondary action, the resulting movement distance of the cam ball 33 in the first cam groove 310 and the second cam groove 320 is, for example, a very small distance smaller than the diameter of the cam ball 33. When the origin return action includes a quaternary action, the rotational torque generated by the electric motor 4 may be set to zero or to rotational torque in the second rotational direction, as in the secondary action. When generating rotational torque in the second rotational direction in the quaternary action, the movement distance of the cam ball 33 is a very small distance smaller than the diameter of the cam ball 33, and when generating rotational torque in the second rotational direction in the secondary action, the movement distance may be set to a distance shorter than the movement distance of the cam ball 33 during the secondary action. Next, the operation and effects of the origin return action will be described in detail with reference to FIG. 5.

[0050] 5(a) to 5(d) are explanatory diagrams showing the positions of cam ball 33 for one first cam groove 310 and one second cam groove 320 of first cam plate 31 and second cam plate 32, respectively, from a state before the origin return operation is performed until the origin return operation is completed. 5(a) to 5(d) show first cam plate 31 and second cam plate 32 together with cam ball 33 in a circumferential cross section centered on rotation axis O. 5(a) to 5(d) omit illustration of cage 34.

[0051] 5(a) shows an example of the position of the cam ball 33 relative to the first cam plate 31 and the second cam plate 32 before the origin return operation, i.e., when the start switch 100 is in the OFF state. When the start switch 100 is in the OFF state and no drive current is supplied to the electric motor 4, the restoring force of the return spring 36 presses the second cam plate 32 toward the first cam plate 31. The pressing force of the return spring 36 acts to roll the cam ball 33 toward the deepest ends 310a, 320a of the first cam groove 310 and the second cam groove 320. However, because the inclination angles of the first cam groove 310 and the second cam groove 320 relative to the circumferential direction of the first cam plate 31 and the second cam plate 32 are shallow, the cam ball 33 does not necessarily reach the deepest ends 310a, 320a, and may stop between the shallowest ends 310b, 320b and the deepest ends 310a, 320a. FIG. 5(a) shows, as an example, a state in which the cam ball 33 stops at a midpoint between the deepest ends 310a, 320a and the shallowest ends 310b, 320b.

[0052] When adjusting the electric motor 4 to the original position from a state in which the cam ball 33 is stopped between the shallowest ends 310b, 320b and the deepest ends 310a, 320a in this way, it is conceivable to rotate the electric motor 4 in the first rotation direction, and set the rotation position of the rotor 42 when the cam ball 33 hits the deepest ends 310a, 320a and the rotation of the output rotation shaft 43 of the electric motor 4 stops as the original position. However, in this case, the cam ball 33 stops in a state in which the first cam plate 31, the second cam plate 32, and the cam ball 33 are elastically deformed due to the influence of the momentum when the cam ball 33 hits the deepest ends 310a, 320a and the rotational torque of the electric motor 4. Therefore, a deviation occurs depending on the amount of elastic deformation of each member from the rotation position of the rotor 42 when the cam ball 33 is at the deepest ends 310a, 320a in a state in which these elastic deformations do not occur.

[0053] Furthermore, if the initial position of the cam ball 33 when the start switch 100 is in the off state is close to the deepest ends 310a, 320a, the cam ball 33 will hit the deepest ends 310a, 320a while the electric motor 4 and first cam plate 31 are in the middle of accelerating, and if the position of the cam ball 33 is far from the deepest ends 310a, 320a, the cam ball 33 will hit the deepest ends 310a, 320a when the rotational speed of the electric motor 4 has reached a certain speed. Therefore, the rotational speed of the first cam plate 31 when the cam ball 33 hits the deepest ends 310a, 320a varies depending on the initial position of the cam ball 33, and as a result, the amount of elastic deformation of each component when the cam ball 33 hits the deepest ends 310a, 320a also varies.

[0054] For this reason, the original position cannot be set with high accuracy by simply rotating the electric motor 4 in the first rotation direction and setting the rotation position of the rotor 42 when the cam ball 33 hits the deepest ends 310a, 320a as the original position. Therefore, in this embodiment, the control unit 40 executes the original point return operation including the above-mentioned primary operation, secondary operation, and tertiary operation at startup.

[0055] Figure 5(b) shows the state when the primary operation of abutting cam ball 33 against deepest ends 310a, 320a is completed. In this state, wall portions 311b, 32b of first cam plate 31 and second cam plate 32 and cam ball 33 are elastically deformed due to the force of cam ball 33 abutting against deepest ends 310a, 320a and the influence of the rotational torque of electric motor 4. Note that in Figure 5(b), the deformation amounts of first cam plate 31, second cam plate 32 and cam ball 33 are exaggerated for clarity of explanation.

[0056] FIG. 5(c) shows the state at the completion of the secondary operation in which the rotational torque in the first rotational direction generated by the electric motor 4 is reduced compared to the primary operation. Here, "reducing the rotational torque in the first rotational direction compared to the primary operation" refers to not only generating rotational torque in the first rotational direction in the electric motor 4 but also reducing the magnitude (absolute value) of the rotational torque compared to the primary operation, but also including reducing the rotational torque generated by the electric motor 4 to zero and generating rotational torque in the second rotational direction in the electric motor 4. By reducing the rotational torque in the first rotational direction generated by the electric motor 4 compared to the primary operation, the amount of elastic deformation of each component is reduced, and the cam ball 33 moves closer to the shallowest ends 310b and 320b than at the completion of the primary operation. Note that in FIG. 5(c), the return amount of the cam ball 33 is exaggerated for clarity.

[0057] FIG. 5(d) shows the state at the completion of the tertiary operation, in which the rotational torque in the first rotation direction generated by the electric motor 4 is increased compared to the secondary operation, causing the cam ball 33 to abut against the deepest ends 310a and 320a. When performing the tertiary operation, the rotational torque generated by the electric motor 4 is reduced compared to the primary operation, and the elastic deformation of each component is reduced compared to the primary operation. This allows the cam ball 33 to stop in a state in which it abuts against the deepest ends 310a and 320a while the elastic deformation of the first cam plate 31, the second cam plate 32, and the cam ball 33 is small. By storing the rotational position of the electric motor 4 at this time as the original position, subsequent control of the electric motor 4 can be performed with high precision. Specifically, the axial position of the pressing member 35 that presses the clutch 20 can be adjusted with high precision, enabling the driving force transmitted by the clutch 20 to be controlled with high precision. Performing the quaternary and quinary operations described above during the origin return operation further ensures accurate alignment to the original position.

[0058] Furthermore, according to this embodiment, even if the electric motor 4 is rotated at a high speed in the primary operation to cause the plurality of cam balls 33 to hit the deepest ends 310a, 320a of the plurality of first cam grooves 310 and second cam grooves 320, the amount of elastic deformation of each member at that time does not affect the accuracy of the original position alignment, so it is possible to perform the original position return operation accurately in a short time. Note that it is desirable to set the rotation speed of the electric motor 4 in the primary operation as high as possible within a range in which the impact sound caused by the cam balls 33 hitting the deepest ends 310a, 320a is not perceived as an abnormal sound by the driver or passengers of the vehicle 1.

[0059] (Addendum) Although the present invention has been described above based on the embodiments, the invention according to the claims is not limited to these embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified by omitting, adding, or substituting certain components without departing from the spirit of the invention. For example, in the above embodiment, the driving force transmission device 11 transmits driving force between the differential case 122 and the outer joint member 81 of the constant velocity joint 8. However, the present invention is not limited to this. A vehicle may be configured so that the driving force transmission device of the present invention transmits driving force between the transmission 14 and the drive shaft 15. Alternatively, the vehicle may be configured so that the driving force is transmitted between the side gear 125 and the outer joint member 81 of the constant velocity joint 8, or between the side gear 126 and the outer joint member 91 of the constant velocity joint 9. [Explanation of symbols]

[0060] 11... Driving force transmission device 20... Clutch 3...Pressing mechanism 31...First cam plate 310...First cam groove 310a...Deepest end 310b...Shallowest end 32...Second cam plate 320...Second cam groove 320a...Deepest end 320b...shallowest end 33...cam ball 4... Electric motor 40... Control unit 44...Encoder O...Rotation axis

Claims

1. A driving force transmission device for a vehicle includes: a clutch that changes the on / off state of a driving force by being pressed in an axial direction; a pressing mechanism that presses the clutch in the axial direction; an electric motor that operates the pressing mechanism; and a control unit that controls the electric motor, and the driving force of a driving source of the vehicle is transmitted by the clutch, the pressing mechanism has a disk-shaped first cam plate on which a plurality of first cam grooves are formed, the depth of which in the axial direction varies depending on the circumferential position; a disk-shaped second cam plate on which a plurality of second cam grooves are formed, the depth of which in the axial direction varies depending on the circumferential position; and a plurality of cam balls arranged between the first cam plate and the second cam plate, wherein the first cam plate and the second cam plate rotate relatively due to the rotational torque of the electric motor, causing the plurality of cam balls to roll in the plurality of first cam grooves and the plurality of second cam grooves, thereby changing the axial distance between the first cam plate and the second cam plate; the plurality of first cam grooves and the plurality of second cam grooves are formed in an arc shape centered on a rotation axis of relative rotation between the first cam plate and the second cam plate, the control unit controls the electric motor to perform a return-to-origin operation at the time of startup after an operating power supply is supplied to the control unit, and thereafter controls the electric motor using the rotational position of the electric motor when the return-to-origin operation is completed as an original position; The origin return operation includes a primary operation in which the electric motor generates a rotational torque in a first rotational direction, causing the plurality of cam balls to abut against one of the moving ends in the circumferential direction of the plurality of first cam grooves and the plurality of second cam grooves; a secondary operation in which the rotational torque in the first rotational direction, generated by the electric motor, is reduced to a value lower than the rotational torque during the primary operation; and a tertiary operation in which the rotational torque in the first rotational direction, generated by the electric motor, is increased to a value higher than the rotational torque during the secondary operation, causing the plurality of cam balls to abut against one of the moving ends in the circumferential direction of the plurality of first cam grooves and the plurality of second cam grooves. Drive force transmission device.

2. the plurality of first cam grooves and the plurality of second cam grooves have axial depths that gradually decrease from a deepest end, which is an end on one side in the circumferential direction, to a shallowest end, which is the other end, abutting the plurality of cam balls against the deepest end in the primary operation and the tertiary operation; The driving force transmission device according to claim 1 .

3. a rotational torque generated by the electric motor in the tertiary operation is smaller than a rotational torque generated by the electric motor in the primary operation; 3. The driving force transmission device according to claim 1 or 2.

4. a rotational torque generated by the electric motor in the secondary operation is set to zero or a rotational torque in a second rotational direction opposite to the first rotational direction; 3. The driving force transmission device according to claim 1 or 2.

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