Steering device

Abstract

A steering device (20) comprises: a motor (22B); a power transmission device (22C); and a steering gear box (22A). The power transmission device includes: a first transmission device (61); a second transmission device (62); and a transmission device housing (60). The first transmission device has a first input element (61A) and a first output element (61B). The second transmission device has a second input element (62A) and a second output element (62B). The second transmission device has a transmission element (62C) in addition to the second input element and the second output element, and the transmission element transmits the motion of the second input element to the second output element. The second input element and the second output element are gears arranged apart from each other. The transmission element is an intermediate gear that meshes with the second input element and the second output element, which are gears. At least one of the second input element, the second output element, and the transmission element is configured as a no-backlash gear.

Description

Steering apparatus

[0001] The present disclosure relates to a steering apparatus.

[0002] For example, the electric power steering apparatus disclosed in Patent Document 1 includes a motor and an RBS (recirculating ball screw) steering gear box. The steering gear box converts the rotational motion of a steering shaft into the oscillating motion of a pitman arm. The orientation of steered wheels is changed in conjunction with the pitman arm. The torque of the motor is transmitted to the ball screw shaft of the steering gear box via a speed reducer, thereby assisting the steering operation of a steering wheel.

[0003] The speed reducer is a two-stage gear speed reducer. The speed reducer includes a first gear set and a second gear set. The steering gear box, the motor, and the second gear set are arranged on the same side relative to the first gear set, which side is closer to the steering wheel with respect to the first gear set. The first gear set is a combination of a pinion provided on a motor shaft and an intermediate gear. The second gear set is a combination of a pinion coaxially connected to the intermediate gear and a helical gear connected to the ball screw shaft.

[0004] United States Patent Application Publication No. 2022 / 0135118

[0005] The electric power steering apparatus of Patent Document 1 has the following concern. That is, abnormal noise may occur due to backlash between gears constituting the speed reducer.

[0006] A steering system according to one aspect of the present disclosure comprises a motor having a motor shaft, a power transmission device configured to transmit the rotation of the motor, an input shaft to which rotation is supplied from the power transmission device, and an output shaft configured to be linked to the steering wheels of a vehicle, wherein the steering gearbox is configured to convert the rotation of the input shaft to the rotation of the output shaft. The power transmission device includes only a first transmission device, a second transmission device, and a transmission device housing that houses the first transmission device and the second transmission device. The first transmission device has a first input element and a first output element connected to each other in a power-transmitting manner. The second transmission device has a second input element and a second output element connected to each other in a power-transmitting manner. The first input element is connected coaxially to the motor shaft. The first output element is connected coaxially to the second input element. The second output element is connected coaxially to the input shaft. The motor, the steering gearbox, and the first transmission device are arranged on the same side as the second transmission device. The second transmission device has a transmission element in addition to the second input element and the second output element. The transmission element is configured to transmit the motion of the second input element to the second output element. The second input element and the second output element are gears spaced apart from each other, and the transmission element is an intermediate gear that meshes with the two gears. At least one of the second input element, the second output element, and the transmission element is configured as a no-backlash gear.

[0007] Figure 1 is a schematic diagram of an electric power steering device according to the first embodiment. Figure 2 is a cross-sectional view of the steering actuator of Figure 1, cut in the axial direction. Figure 3 is a front view showing the main parts of a comparative example of the power transmission device of Figure 2. Figure 4 is a front view showing the main parts of the power transmission device of Figure 2. Figure 5 is a perspective view of the no-backlash gear of Figure 4. Figure 6 is an exploded perspective view of the no-backlash gear of Figure 5. Figure 7 is a front view showing the main parts of the meshing between the no-backlash gear and the mating gear of Figure 4. Figure 8 is a cross-sectional view showing another form of the no-backlash gear of Figure 4. Figure 9 is a front view showing a second transmission device according to another embodiment. Figure 10 is a front view showing a second transmission device according to another embodiment. Figure 11 is a front view showing a second transmission device according to another embodiment. Figure 12 is a front view showing a second transmission device according to another embodiment. Figure 13 is a front view showing a second transmission device according to another embodiment. Figure 14 is a front view showing a second transmission device according to another embodiment.

[0008] A steering device 20 according to one embodiment will be described. As shown in Figure 1, the steering device 20 is an electric power steering device, which is mounted on a cab-over type vehicle 10, for example. The vehicle 10 is equipped with an axle suspension 11. The suspension 11 supports the front axle 12. Steering wheels 13, which are the front wheels, are connected to both ends of the front axle 12. The suspension 11 has a leaf spring 14. The leaf spring 14 is located, for example, above the front axle 12. The leaf spring 14 extends in the longitudinal direction of the vehicle. Both ends of the leaf spring 14 are attached to the vehicle frame 16 via support members 15 such as shackles.

[0009] The steering system 20 includes a steering shaft 21 and a steering actuator 22 provided on the steering shaft 21. The steering actuator 22 includes a steering gearbox 22A, a motor 22B, a power transmission device 22C, and a torque sensor 22D. The power transmission device 22C is located at the bottom of the steering gearbox 22A. The torque sensor 22D is located at the top of the steering gearbox 22A.

[0010] The first end of the steering shaft 21 is connected to the steering wheel 23. The second end of the steering shaft 21 is connected to the steering gearbox 22A via a torque sensor 22D. The motor 22B is connected to the steering gearbox 22A via a power transmission device 22C. The steering gearbox 22A is of the RBS type (Recirculating Ball Screw type).

[0011] The steering gearbox 22A is connected to the steering wheels 13 via a linkage mechanism 30. The linkage mechanism 30 includes a pitman arm 31, a drag link 32, and a tie rod 33. The base end of the pitman arm 31 is connected to the side of the steering gearbox 22A. The pitman arm 31 is pivotable in the longitudinal direction of the vehicle about its base end. The first end of the drag link 32 is rotatably connected to the tip of the pitman arm 31. The second end of the drag link 32 is rotatably connected to the knuckle arm 34 of the right steering wheel 13. Both ends of the tie rod 33 are connected to the left and right steering wheels 13 via tie rod arms 35.

[0012] The rotation of the steering wheel 23 is transmitted to the steering gearbox 22A via the steering shaft 21 and torque sensor 22C. The steering gearbox 22A converts the rotational motion of the steering shaft 21 into the oscillating motion of the pitman arm 31. The oscillating motion of the pitman arm 31 drives the drag link 32 in the longitudinal direction of the vehicle. The knuckle arm 34 oscillates in conjunction with the drag link 32, causing the steering wheels 13 to turn. In other words, the steering gearbox 22A converts the rotation of the steering wheel 23 into the steering motion of the steering wheels 13.

[0013] Motor 22B generates torque in response to the steering torque detected by torque sensor 22D. The torque from motor 22B is transmitted to the steering shaft 21 via power transmission device 22C and steering gearbox 22A. Power transmission device 22C converts the torque from motor 22B into assist torque. The assist torque is torque in the same direction as the steering direction of the steering wheel 23. By applying assist torque to the steering shaft 21, the steering of the steering wheel 23 is assisted.

[0014] <Configuration of Steering Gearbox 22A> Next, the configuration of the steering gearbox 22A will be described in detail. As shown in Figure 2, the steering gearbox 22A has a housing 41, a ball screw shaft 42, a ball screw nut 43, a plurality of balls 44, a sector shaft 45, and a sector gear 46. The housing 41 houses the ball screw shaft 42, the ball screw nut 43, the plurality of balls 44, the sector shaft 45, and the sector gear 46 inside.

[0015] The ball screw shaft 42 is maintained in an orientation that extends vertically within the vehicle 10 when the steering gearbox 22A is mounted to the vehicle 10. The ball screw shaft 42 has a first thread groove 42A, which is a helical groove provided on the outer circumferential surface of the ball screw shaft 42. The ball screw shaft 42 is rotatably supported relative to the housing 41 via a first bearing 47 and a second bearing 48.

[0016] The first bearing 47 rotatably supports the first end of the ball screw shaft 42 relative to the housing 41. The first end is the end of the ball screw shaft 42 that faces upward towards the vehicle 10 when the steering gearbox 22 is mounted on the vehicle 10. The second bearing 48 rotatably supports the second end of the ball screw shaft 42 relative to the housing 41. The second end is the end of the ball screw shaft 42 that faces downward towards the vehicle 10 when the steering gearbox 22 is mounted on the vehicle 10.

[0017] The first bearing 47 is, for example, a radial ball bearing, which is a type of rolling bearing. Examples of radial ball bearings include a single-row deep groove ball bearing and a single-row four-point contact ball bearing. The first bearing 47 has an inner ring 47A, an outer ring 47B, a plurality of balls 47C, and a cage (not shown). The inner ring 47A is provided on the outer circumferential surface of the ball screw shaft 42. The inner ring 47A may be formed integrally with the ball screw shaft 42, for example. The outer ring 47B faces the inner ring 47A in the radial direction. The plurality of balls 47C are interposed between the inner ring 47A and the outer ring 47B.

[0018] The second bearing 48 is, for example, a roller bearing, which is a type of rolling bearing. Examples of roller bearings include needle bearings. However, the second bearing 48 is not limited to a roller bearing and may be any type of rolling bearing.

[0019] The ball screw nut 43 is a cylindrical body having a circular cross-sectional shape and has a second screw groove 43A. The second screw groove 43A is a helical groove provided on the inner circumferential surface of the ball screw nut 43. The second screw groove 43A is opposite the first screw groove 42A in the radial direction of the ball screw nut 43. The ball screw nut 43 is screwed onto the ball screw shaft 42 via a plurality of balls 44. The helical space surrounded by the first screw groove 42A and the second screw groove 43A functions as a rolling path for the balls 44 to roll. The ball screw nut 43 has a plurality of rack teeth 43B. The rack teeth 43B are provided on the outer circumferential surface of the ball screw nut 43. The plurality of rack teeth 43B are arranged in the axial direction of the ball screw nut 43.

[0020] The ball screw shaft 42, the ball screw nut 43, and the multiple balls 44 constitute a ball screw mechanism. The sector shaft 45 extends in a direction perpendicular to the axial direction of the ball screw nut 43 (perpendicular to the plane of the paper in Figure 2). The sector shaft 45 is rotatably supported by the housing 41 via a bearing (not shown). The sector shaft 45 has an outer end that penetrates the housing 41 and is exposed to the outside. The base end of the pitman arm 31 is fixed to the outer end of the sector shaft 45. The sector shaft 45 is the output shaft of the steering gearbox 22 and is linked to the steering wheel 13.

[0021] The sector gear 46 is rotatably mounted integrally with the sector shaft 45. The sector gear 46 is a fan-shaped gear having multiple teeth 46A. The teeth 46A of the sector gear 46 mesh with the rack teeth 43B of the ball screw nut 43.

[0022] The rotation of the steering wheel 23 is transmitted to the ball screw shaft 42 via the steering shaft 21 and torque sensor 22D. As the ball screw shaft 42 rotates, the ball screw nut 43 moves axially relative to the ball screw shaft 42. As a result, the sector gear 46 oscillates around the sector shaft 45 in response to the axial movement of the ball screw nut 43. When the sector gear 46 oscillates, the sector shaft 45 rotates, causing the pitman arm 31 to oscillate around the sector shaft 45.

[0023] The torque sensor 22D is provided at the first end of the housing 41. The first end is the end of the housing 41 that faces upward when the steering gearbox 22A is mounted on the vehicle 10. The first end of the ball screw shaft 42 is rotatably connected to the steering shaft 21 via the torque sensor 22D. The first end of the ball screw shaft 42 is the end of the ball screw shaft 42 that faces upward when the steering gearbox 22 is mounted on the vehicle 10.

[0024] The torque sensor 22D includes a sensor housing 51, an input shaft 52, a torsion bar 53, and a detector 54. The sensor housing 51 is a cylindrical body with a circular cross-section and is attached to the first end of the housing 41. The sensor housing 51 has an insertion portion 51A. The insertion portion 51A is a cylindrical body with a circular cross-section and is inserted into the first end of the housing 41. An oil seal 55 is interposed between the inner circumferential surface of the insertion portion 51A and the outer circumferential surface of the first end of the ball screw shaft 42. The oil seal 55 is a cylindrical body with a circular cross-section and seals the space between the outer circumferential surface of the first end of the ball screw shaft 42 and the inner circumferential surface of the insertion portion 51A. The inner circumferential surface of the oil seal 55 has a lip portion. The lip portion is in slidable contact with the outer circumferential surface of the first end of the ball screw shaft 42.

[0025] The input shaft 52 is a hollow cylindrical body with a circular cross-sectional shape. The input shaft 52 is rotatably supported in the housing 41 via a third bearing 56. The first end of the input shaft 52 protrudes outward through the end wall of the housing 41 in the axial direction. The first end of the input shaft 52 is connected to the steering wheel 23 via the steering shaft 21. The second end of the input shaft 52 is inserted into the first end of the ball screw shaft 42. A radial gap is formed between the outer circumferential surface of the second end of the input shaft 52 and the inner circumferential surface of the first end of the ball screw shaft 42. The second end of the input shaft 52 and the first end of the ball screw shaft 42 are rotatable relative to each other.

[0026] The torsion bar 53 is inserted into the input shaft 52. The first end of the torsion bar 53 is fixed in a press-fitted or inserted state on the input shaft 52. The second end of the torsion bar 53 protrudes non-contact from the second end of the input shaft 52. The second end of the torsion bar 53 is fixed in a press-fitted or inserted state on the first end of the ball screw shaft 42. In other words, the input shaft 52 is connected to the ball screw shaft 42 via the torsion bar 53.

[0027] The steering torque applied to the steering wheel 23 is transmitted to the input shaft 52 via the steering shaft 21. This causes the input shaft 52 to rotate. The first end of the torsion bar 53 is rotatable integrally with the input shaft 51. The second end of the torsion bar 53 is rotatable integrally with the ball screw shaft 42. Therefore, the rotation of the input shaft 52 is transmitted to the ball screw shaft 42 via the torsion bar 53. This causes the ball screw shaft 42 to rotate in the same direction as the input shaft 51. Also, when the input shaft 52 rotates, the torsion bar 53 twists in accordance with the steering torque. The detector 54 detects the steering torque based on the amount of twist of the torsion bar 53. The detector 54 is provided, for example, so as to surround the outer circumferential surface of the input shaft 52.

[0028] The power transmission device 22C is provided at the second end of the housing 41. The second end of the housing 41 is the end of the housing 41 that faces downwards from the vehicle 10 when the steering gearbox 22A is mounted on the vehicle 10. The second end of the ball screw shaft 42 is connected to the power transmission device 22C. The second end of the ball screw shaft 42 is the end of the ball screw shaft 42 that faces downwards from the vehicle 10 when the steering gearbox 22 is mounted on the vehicle 10.

[0029] The torque of the motor 22B is transmitted to the ball screw shaft 42 via the power transmission device 22C. The power transmission device 22C converts the torque of the motor 22B into assist torque. The assist torque is torque in the same direction as the steering direction of the steering wheel 23. By applying assist torque to the ball screw shaft 42, the steering of the steering wheel 23 is assisted. The ball screw shaft 42 corresponds to the input shaft to which rotation is supplied from the power transmission device 22C.

[0030] The power transmission device 22C is a combination of multiple transmission devices that transmit rotational motion. A transmission device is, for example, a gear transmission device having multiple gears that mesh with each other. The power transmission device 22C has a transmission device housing 60 that houses the multiple transmission devices. The transmission device housing 60 is attached to the second end of the housing 41.

[0031] <Configuration of Power Transmission System 22C> Next, the configuration of the power transmission system 22C will be described in detail. As shown in Figure 3, the power transmission system 22C has a first transmission system 61 and a second transmission system 62. The steering gearbox 22A, the motor 22B, and the first transmission system 61 are located on the same side as the second transmission system 62. The same side is the side of the second transmission system 62 that is closer to the steering wheel 23.

[0032] The first transmission device 61 has a first gear 61A and a second gear 61B that mesh with each other. The first gear 61A corresponds to the first input element, and the second gear 61B corresponds to the first output element. The first gear 61A and the second gear 61B are, for example, spur gears. However, depending on the specifications of the steering device 20, the first gear 61A and the second gear 61B may each be helical gears.

[0033] The second transmission device 62 has a third gear 62A, a fourth gear 62B, and a fifth gear 62C that mesh with each other. The third gear 62A corresponds to the second input element, the fourth gear 62B corresponds to the second output element, and the fifth gear 62C corresponds to the transmission element. The third gear 62A, the fourth gear 62B, and the fifth gear 62C are, for example, spur gears. However, depending on the specifications of the steering device 20, the third gear 62A, the fourth gear 62B, and the fifth gear 62C may be helical gears.

[0034] The first gear 61A is mounted on the motor shaft 22B1. The motor shaft 22b1 is the output shaft mounted on the motor 22B. The motor shaft 22B1 and the first gear 61A are arranged coaxially. The motor shaft 22B1 and the first gear 61A rotate together as a unit around the first axis O1 in conjunction with the drive of the motor 22B.

[0035] The second gear 61B is provided on the first shaft 63. The first shaft 63 is positioned between the motor shaft 22B1 of the motor 22B and the ball screw shaft 42 in the direction in which the steering gearbox 22A and the motor 22B are aligned (the vertical direction in Figure 3). The first shaft 63 is rotatably supported by the transmission housing 60 via bearings. The second gear 61B is positioned, for example, at the first end of the first shaft 63. The first end is the end of the first shaft 63 that is closer to the motor 22B in the axial direction. The second gear 61B meshes with the first gear 61A.

[0036] The third gear 62A is mounted on the first shaft 63. The third gear 62A is positioned closer to the second end of the first shaft 63 than the second gear 61B. The third gear 62A is coaxial with the second gear 61B. The second gear 61B and the third gear 62A rotate together as a single unit about the second axis O2.

[0037] The fourth gear 62B is located at the second end of the ball screw shaft 42. The second end is the end of the ball screw shaft 42 that faces downwards when the steering gearbox 22 is mounted on the vehicle 10. The fourth gear 62B is arranged coaxially with the ball screw shaft 42. The ball screw shaft 42 and the fourth gear 62B rotate integrally around the third axis O3.

[0038] The fifth gear 62C is mounted on the second shaft 64. The second shaft 64 is positioned between the first shaft 63 and the ball screw shaft 42 in the direction in which the steering gearbox 22A and the motor 22B are aligned (the vertical direction in Figure 3). The second shaft 64 is rotatably supported by the transmission housing 60 via bearings. The fifth gear 62C meshes with the third gear 62A and the fourth gear 62B, which are spaced apart from each other. In other words, the fifth gear 62C is an idler gear that fills the gap between the third gear 62A and the fourth gear 62B. An idler gear is also called an intermediate gear. The fifth gear 62C rotates about the fourth axis O4.

[0039] The first axis O1, the second axis O2, the third axis O3, and the fourth axis O4 are parallel to each other. Also, the outer diameter of the second gear 61B is larger than the outer diameter of the first gear 61A. The outer diameters of the third to fifth gears 62A, 62B, and 62C increase in the order of the third gear 62A, the fifth gear 62C, and the fourth gear 62B. Both the first transmission device 61 and the second transmission device 62 function as speed reducers.

[0040] The torque of the motor 22B is transmitted to the ball screw shaft 42 via the first gear 61A, the second gear 61B, the third gear 62A, the fifth gear 62C, and the fourth gear 62B. By applying torque to the ball screw shaft 42 in the same direction as the steering direction of the steering wheel 23, the steering of the steering wheel 23 is assisted.

[0041] <Abnormal Noise Due to Backlash> The steering device 20 has the following concern. That is, abnormal noise may occur due to backlash between the gears constituting the first transmission device 61 and the second transmission device 62. The abnormal noise includes rattle noise. Rattle noise is gear rattle generated when the rotational torque of a gear fluctuates or the gear rotates in reverse. In particular, the second transmission device 62 is easily affected by sudden steering of the steering wheel 23 or reverse input from the steered wheels 13. For this reason, there is a concern that abnormal noise may occur due to backlash between the third gear 62A and the fifth gear 62C constituting the second transmission device 62, and between the fifth gear 62C and the fourth gear 62B. The third gear 62A, the fourth gear 62B, and the fifth gear 62C are main gears mainly responsible for power transmission.

[0042] Therefore, in the present embodiment, a no-backlash mechanism 70 is provided in the second transmission device 62. The no-backlash mechanism 70 is a mechanism for eliminating or reducing backlash between gears constituting the second transmission device.

[0043] <Configuration of No-Backlash Mechanism 70> As shown in FIG. 4, the no-backlash mechanism 70 includes a first auxiliary gear 71A, a second auxiliary gear 71B, a third auxiliary gear 71C, and a fourth auxiliary gear 71D.

[0044] The first auxiliary gear 71A is provided on a first side surface of the fifth gear 62C. The second auxiliary gear 71B is provided on a second side surface of the fifth gear 62C. The second side surface is a side surface opposite to the first side surface of the fifth gear 62C. The fifth gear 62C is disposed between the first auxiliary gear 71A and the second auxiliary gear 71B. The first auxiliary gear 71A and the second auxiliary gear 71B are each relatively rotatably attached to the outer peripheral surface of the second shaft 64. Further, the first auxiliary gear 71A and the second auxiliary gear 71B are each axially slidable with respect to the outer peripheral surface of the second shaft 64.

[0045] The first auxiliary gear 71A and the second auxiliary gear 71B have the same structure. The modules of the first auxiliary gear 71A and the second auxiliary gear 71B are the same as the module of the fifth gear 62C. The number of teeth of the first auxiliary gear 71A and the second auxiliary gear 71B is the same as the number of teeth of the fifth gear 62C. The axial thickness of the first auxiliary gear 71A and the second auxiliary gear 71B is the same, and thinner than the axial thickness of the fifth gear 62C. The fifth gear 62C, the first auxiliary gear 71A, and the second auxiliary gear 71B mesh with the third gear 62A.

[0046] The third auxiliary gear 7C is provided on the first side surface of the fourth gear 62B. The fourth auxiliary gear 71D is provided on the second side surface of the fourth gear 62B. The second side surface is the side surface of the fourth gear 62B opposite to the first side surface. The fourth gear 62B is positioned between the third auxiliary gear 71C and the fourth auxiliary gear 71BD. The third auxiliary gear 71C and the fourth auxiliary gear 71D are each mounted on the outer circumferential surface of the ball screw shaft 42 so as to be rotatable relative to each other. In addition, the third auxiliary gear 71C and the fourth auxiliary gear 71D are each axially slidable relative to the outer circumferential surface of the ball screw shaft 42.

[0047] The third auxiliary gear 71C and the fourth auxiliary gear 71D have the same structure. The modules of the third auxiliary gear 71C and the fourth auxiliary gear 71D are the same as the module of the fourth gear 62B. The number of teeth of the third auxiliary gear 71C and the fourth auxiliary gear 71D is the same as the number of teeth of the fourth gear 62B. The axial thickness of the third auxiliary gear 71C and the fourth auxiliary gear 71D is the same, and thinner than the axial thickness of the fourth gear 62B. The fourth auxiliary gear 71D, the third auxiliary gear 71C, and the fourth auxiliary gear 71D mesh with the fourth gear 62B.

[0048] As shown in FIG. 5, for example, the first auxiliary gear 71A is attached to the fifth gear 62C in the following manner. That is, the second shaft 64 axially penetrates through the first auxiliary gear 71A. A disc spring 72 and a retaining ring 73 are attached to the second shaft 64 from the outer side of the first auxiliary gear 71A. The disc spring 72 is interposed between the first auxiliary gear 71A and the retaining ring 73. The disc spring 72 is compressed in the axial direction. The first auxiliary gear 71A is pressed in the axial direction against the first side surface of the fifth gear 62C by the elastic force of the disc spring 72. The retaining ring 73 prevents the disc spring 72 from coming off the second shaft 64.

[0049] As shown in FIG. 6, the first auxiliary gear 71A includes a first slot 74 and a second slot 75. The first slot 74 and the second slot 75 are located opposite to each other in the radial direction with respect to the center of the first auxiliary gear 71A. The first slot 74 and the second slot 75 are elongated slots extending in a direction intersecting the radial direction of the first auxiliary gear 71A, and are parallel to each other. The first slot 74 and the second slot 75 axially penetrate through the first auxiliary gear 71A.

[0050] The fifth gear 62C includes a third slot 76 and a fourth slot 77. The third slot 76 and the fourth slot 77 are located opposite to each other in the radial direction with respect to the center of the fifth gear 62C. The third slot 76 and the fourth slot 77 are elongated slots extending in a direction intersecting the radial direction of the fifth gear 62C, and are parallel to each other. The third slot 76 and the fourth slot 77 axially penetrate through the fifth gear 62C. The third slot 76 corresponds to the first slot 74. The fourth slot 77 corresponds to the second slot 75.

[0051] The anti-backlash mechanism 70 includes a first compression coil spring 78 and a second compression coil spring 79. The first compression coil spring 78 and the second compression coil spring 79 connect the first auxiliary gear 71A and the fifth gear 62C. Note that although FIG. 6 exemplifies a configuration with two sets of compression coil springs and slots, three or more sets of compression coil springs and slots can also be provided. Furthermore, the compression coil spring is an example, and an arc spring can also be used.

[0052] The first end of the first compression coil spring 78 is connected to the first end of the third groove 76. The second end of the first compression coil spring 78 is connected to the second end of the first groove 74. The second end is the end of the first groove 74 opposite to the first end of the third groove 76 when viewed from the axial direction of the first auxiliary gear 71A.

[0053] The first end of the second compression coil spring 79 is connected to the first end of the fourth groove 77. The second end of the second compression coil spring 79 is connected to the second end of the fourth groove 77. The second end is the end of the second groove 75 opposite to the first end of the fourth groove 77 when viewed from the axial direction of the first auxiliary gear 71A.

[0054] As shown in Figure 7, the elastic force between the first compression coil spring 78 and the second compression coil spring 79 causes a slight phase difference between the first auxiliary gear 71A and the fifth gear 62C. Gear phase refers to the relative positional difference between the teeth of two gears. The teeth of the first auxiliary gear 71A and the teeth of the fifth gear 62C are strongly gripped by the elastic force between the first and second compression coil springs 78 and 79, respectively, by the teeth of the mating gear, the third gear 62A.

[0055] In other words, in the left-right direction of Figure 7, the right tooth surface of the fifth gear 62C meshes with the left tooth surface of one tooth of the third gear 62A, the left tooth surface of the first auxiliary gear 71A meshes with the right tooth surface of one tooth of the third gear 62A, and the teeth of the third gear 62A are sandwiched between the teeth of the fifth gear 62C and the teeth of the first auxiliary gear 71A. In short, the teeth of the mating gears are sandwiched between the teeth of the main gear and the teeth of the auxiliary gear. This eliminates or reduces backlash.

[0056] The second auxiliary gear 71B is mounted on the second side of the fifth gear 62C, similar to the first auxiliary gear 71A. The second side is the side of the fifth gear 62C opposite to the first side to which the first auxiliary gear 71A is mounted. The fifth gear 62C, the first auxiliary gear 71A, and the second auxiliary gear 71B constitute the first scissors gear. A scissors gear is a type of no-backlash gear. A no-backlash gear is a gear configured to eliminate or reduce backlash between itself and the mating gear.

[0057] The third auxiliary gear 71C and the fourth auxiliary gear 71D are mounted on both sides of the fourth gear 62B, similar to the first auxiliary gear 71A and the second auxiliary gear 71B. The fourth gear 62B, the third auxiliary gear 71C, and the fourth auxiliary gear 71D constitute the second scissors gear.

[0058] <Regarding friction gears> Incidentally, as shown in Figure 8, for example, the first auxiliary gear 71A may be a friction gear. A friction gear is also a type of backlash gear.

[0059] In this case, the first auxiliary gear 71A is formed so that it functions as a disc spring. The first auxiliary gear 71A is interposed between the fifth gear 62C and a retaining ring 73 mounted on the outer surface of the second shaft 64. The first auxiliary gear 71A is compressed in the axial direction. The first auxiliary gear 71A is pressed in the axial direction against the fifth gear 62C by the elastic force of the first auxiliary gear 71A itself. The module of the first auxiliary gear 71A is the same as the module of the fifth gear 62C. The number of teeth of the first auxiliary gear 71A is, for example, one less than the number of teeth of the fifth gear 62C.

[0060] When the mating gear, the third gear 62A, rotates, the frictional force generated between the first auxiliary gear 71A and the fifth gear 62C acts as rotational resistance for the first auxiliary gear 71A. Therefore, the first auxiliary gear 71A, which has fewer teeth than the third gear 62A, rotates while sliding against the fifth gear 62C in the rotational direction. Consequently, as shown in Figure 7, the first auxiliary gear 71A and the fifth gear 62C rotate such that the teeth of the mating gear, the third gear 62A, are sandwiched between the teeth of the first auxiliary gear 71A and the teeth of the fifth gear 62C. This eliminates or reduces backlash.

[0061] The second auxiliary gear 71B, the third auxiliary gear 71C, and the fourth auxiliary gear 71D may also be friction gears having the same configuration as the first auxiliary gear 71A shown in Figure 8.

[0062] <Effects of the Embodiment> According to this embodiment, the following effects are achieved: (1) The second transmission device 62 includes a no-backlash mechanism 70. The no-backlash mechanism 70 is a mechanism for eliminating or reducing backlash between the gears constituting the second transmission device 62. Therefore, it is possible to suppress the generation of abnormal noise caused by backlash between the gears constituting the second transmission device 62.

[0063] (2) The second output element and transmission element are configured as no-backlash gears. The third gear 62A corresponds to the second input element, the fourth gear 62B corresponds to the second output element, and the fifth gear 62C corresponds to the transmission element. With this configuration, backlash between the second input element and the transmission element, and backlash between the transmission element and the second output element are eliminated or reduced. Therefore, the generation of abnormal noise caused by backlash between the second input element and the transmission element, and backlash between the transmission element and the second output element can be suppressed.

[0064] (3) The second input element, the second output element, and the transmission element are main gears primarily responsible for power transmission. The third gear 62A corresponds to the second input element, the fourth gear 62B corresponds to the second output element, and the fifth gear 62C corresponds to the transmission element. The no-backlash gear is configured to have auxiliary gears that rotate coaxially with the main gears, and to sandwich the teeth of the mating gear between the teeth of the main gear and the teeth of the auxiliary gears. The first to fourth auxiliary gears 71A to 71D correspond to auxiliary gears. The third gear 62A corresponds to the mating gear of the fifth gear 62C. The fifth gear 62C corresponds to the mating gear of the fourth gear 62B. With this configuration, backlash between the main gear and the mating gear can be eliminated or reduced by sandwiching the teeth of the mating gear between the teeth of the main gear and the teeth of the auxiliary gears.

[0065] (4) Auxiliary gears are provided on one or both sides of the main gear. The fourth gear 62B and the fifth gear 62C are main gears primarily responsible for power transmission. By providing auxiliary gears on both sides of the main gear, backlash between the main gear and the mating gear can be more reliably eliminated or reduced. For example, even when the main gear rotates in reverse, backlash between the main gear and the mating gear can be properly eliminated or reduced.

[0066] (5) Depending on the specifications of the steering device 20 or the constraints of the mounting layout, it may be necessary to secure a longer axial distance between the motor 22B and the ball screw shaft 42. In this regard, according to this embodiment, the steering gearbox 22A, the motor 22B, and the first transmission device 61 are arranged on the same side as the second transmission device 62. The same side is the side closer to the steering wheel 23 relative to the second transmission device 62. Therefore, it is possible to secure a longer axial distance between the motor 22 and the ball screw shaft 42 while suppressing the enlargement of the first gear 61A and the second gear 61B, as well as the enlargement of the third gear 62A, the fourth gear 62B, and the fifth gear 62C. The enlargement of the transmission device housing 60 that houses the first transmission device 61 and the second transmission device 62 is also suppressed, so interference between a part of the transmission device housing 60 and parts of the vehicle is suppressed.

[0067] For example, consider the case where the steering gearbox 22A, motor 22B, and second transmission device 62 are located on the same side as the first transmission device 61, as a comparative example. If, due to the specifications of the steering device 20 or constraints on the mounting layout, it is necessary to ensure a longer distance between the motor 22B and the ball screw shaft 42, then, for example, the size of the second gear 61B of the first transmission device 61 needs to be increased in proportion to the increase in distance between the axes. This may increase the size of the transmission device housing 60. For example, as shown by the dashed line in Figure 2, in order to accommodate the larger second gear 61B, it becomes necessary to form a protrusion 60A that projects radially outward in the portion of the transmission device housing 60 corresponding to the second gear 61B. This protrusion 60A may interfere with vehicle components.

[0068] (6) The first transmission device 61 has a first gear 61A and a second gear 61B that mesh with each other. The first gear 61A is connected to the motor shaft 22B1 of the motor 22B. The second transmission device 62 has a third gear 62A, a fourth gear 62B, and a fifth gear 62C that mesh with each other. The third gear 62A is connected coaxially to the second gear 61B via the first shaft 63. The fourth gear 62B is connected to the end of the ball screw shaft 42. The fifth gear 62 meshes with the third gear 62A and the fourth gear 62B. That is, the gap between the third gear 62A and the fourth gear 62B is filled by the fifth gear 62C. As a result, the torque of the motor 22B can be properly transmitted to the ball screw shaft 42 via the first transmission device 61 and the second transmission device 62.

[0069] (7) Since both the first transmission device 61 and the second transmission device 62 are composed solely of gears, it is easy to ensure strength. <Other Embodiments> This embodiment may be implemented with the following modifications.

[0070] As shown in Figure 9, the second transmission device 62 may be configured without the third auxiliary gear 71C and the fourth auxiliary gear 71D. The second transmission device 62 has a first auxiliary gear 71A and a second auxiliary gear 71B. As a result, backlash between the third gear 62A and the fifth gear 62C is eliminated or reduced. Therefore, the generation of abnormal noise caused by backlash between the third gear 62A and the fifth gear 62C can be suppressed.

[0071] As shown in Figure 10, the second transmission device 62 may have a configuration that omits the first auxiliary gear 71A and the second auxiliary gear 71B. The second transmission device 62 has a third auxiliary gear 71C and a fourth auxiliary gear 71D. As a result, backlash between the fifth gear 62C and the fourth gear 62B is eliminated or reduced. Therefore, the generation of abnormal noise caused by backlash between the fifth gear 62C and the fourth gear 62B can be suppressed.

[0072] As shown in Figure 11, the second transmission device 62 may have a configuration in which the first auxiliary gear 71A and the fourth auxiliary gear 71D are omitted and a fifth auxiliary gear 71E is added. The second transmission device 62 has a second auxiliary gear 71B and a third auxiliary gear 71C. The fifth auxiliary gear 71E is provided on the first side surface of the third gear 62A. The first side surface is the side of the third gear 62A that is further in the axial direction from the second gear 61B (see Figure 4). The fifth auxiliary gear 71E has the same configuration as the first auxiliary gear 71A.

[0073] The teeth of the fifth auxiliary gear 71E and the teeth of the third gear 62A sandwich the teeth of the mating gear, the fifth gear 62C. As a result, backlash between the third gear 62A and the fifth gear 62C is eliminated or reduced. Furthermore, the presence of the second auxiliary gear 71B and the third auxiliary gear 71C eliminates or reduces backlash between the fifth gear 62C and the fourth gear 62B. Therefore, the generation of abnormal noise caused by backlash between the third gear 62A and the fifth gear 62C, and between the fifth gear 62C and the fourth gear 62B, can be suppressed.

[0074] As shown in Figure 12, the second transmission device 62 may have a configuration that omits the first auxiliary gear 71A, the third auxiliary gear 71C, and the fourth auxiliary gear 71D. The second transmission device 62 has a second auxiliary gear 71B. As a result, backlash between the third gear 62A and the fifth gear 62C is eliminated or reduced. Therefore, the generation of abnormal noise caused by backlash between the third gear 62A and the fifth gear 62C can be suppressed.

[0075] As shown in Figure 13, the second transmission device 62 may be configured without the first auxiliary gear 71A, the second auxiliary gear 71B, and the fourth auxiliary gear 71D. The second transmission device 62 has a third auxiliary gear 71C. As a result, backlash between the fifth gear 62C and the fourth gear 62B is eliminated or reduced. Therefore, the generation of abnormal noise caused by backlash between the fifth gear 62C and the fourth gear 62B can be suppressed.

[0076] As shown in Figure 14, the second transmission device 62 may be configured by omitting the first auxiliary gear 71A, the second auxiliary gear 71B, the third auxiliary gear 71C, and the fourth auxiliary gear 71D. The second transmission device 62 has a fifth auxiliary gear 71E. The fifth auxiliary gear 71E is provided on the first side surface of the third gear 62A, as in the case shown in Figure 11. The fifth auxiliary gear 71E meshes with the fifth gear 62C. As a result, backlash between the third gear 62A and the fifth gear 62C is eliminated or reduced. Therefore, the generation of abnormal noise caused by backlash between the third gear 62A and the fifth gear 62C can be suppressed.

[0077] The first compression coil spring 78 and the second compression coil spring 79 may be replaced with arc-shaped springs. The arc-shaped springs are interposed between the auxiliary gear and the main gear. The third gear 62A, the fourth gear 62B, and the fifth gear 62C are main gears primarily responsible for power transmission. The first to fifth auxiliary gears 71A to 71E correspond to auxiliary gears. The first end of the arc-shaped spring is connected to the auxiliary gear, and the second end is connected to the main gear. Therefore, when the auxiliary gear and the main gear are twisted in a predetermined direction, an elastic force is generated by the arc-shaped spring. The auxiliary gear and the drive gear are shifted circumferentially against the elastic force of the arc-shaped spring, and the teeth of the mating gear are sandwiched between the teeth of the auxiliary gear and the teeth of the drive gear. In this way, backlash between the main gear and the mating gear can be eliminated or reduced. Torsion coil springs may be used instead of arc-shaped springs.

[0078] The auxiliary gear may be attached to the main gear as follows: the auxiliary gear is connected to the main gear, for example, by bolts. The bolt hole in either the auxiliary gear or the drive gear is an elongated hole extending in the circumferential direction. With the bolts loosened, the auxiliary gear and the drive gear are shifted circumferentially, and the teeth of the mating gear are sandwiched between the teeth of the auxiliary gear and the teeth of the drive gear. In this state, the bolts are tightened to secure them. This method also eliminates or reduces backlash between the main gear and the mating gear.

[0079] - At least one of the second input element, second output element, and transmission element constituting the second transmission device 62 may be configured as a no-backlash gear. The third gear 62A corresponds to the second input element, the fourth gear 62B corresponds to the second output element, and the fifth gear 62C corresponds to the transmission element. With this configuration, at least one of the backlash between the second input element and the transmission element, and the backlash between the transmission element and the second output element is eliminated or reduced. Therefore, the generation of abnormal noise caused by at least one of the backlash between the second input element and the transmission element, and the backlash between the transmission element and the second output element, can be suppressed.

[0080] Auxiliary gears may be provided on one or both sides of the main gear. The third gear 62A, the fourth gear 62B, and the fifth gear 62C are main gears primarily responsible for power transmission. The first to fifth auxiliary gears 71A to 71E correspond to auxiliary gears. By providing auxiliary gears on one side of the main gear, backlash between the main gear and the mating gear can be eliminated or reduced. Furthermore, by providing auxiliary gears on both sides of the main gear, backlash between the main gear and the mating gear can be eliminated or reduced more reliably.

[0081] As used herein, the expression "at least one" means "one or more" of the desired options. For example, as used herein, if there are two options, the expression "at least one" means "only one option" or "both of the two options." As another example, as used herein, the expression "at least one" means "only one option" or "any combination of two or more options" if there are three or more options.

Claims

1. A steering gearbox comprising: a motor having a motor shaft; a power transmission device configured to transmit the rotation of the motor; an input shaft to which rotation is supplied from the power transmission device; and an output shaft configured to be linked to the steering wheels of a vehicle, wherein the steering gearbox is configured to convert the rotation of the input shaft into the rotation of the output shaft, the power transmission device includes a first transmission device, a second transmission device, and a transmission device housing housing the first transmission device and the second transmission device, the first transmission device having a first input element and a first output element connected in a power-transmitting manner, the second transmission device having a second input element and a second output element connected in a power-transmitting manner, the first input element being connected coaxially to the motor shaft, the first output element being connected coaxially to the second input element, and the second output element being connected coaxially to the input shaft. A steering device comprising the motor, the steering gearbox, and the first transmission device, arranged on the same side as the second transmission device, wherein the second transmission device further includes a transmission element in addition to the second input element and the second output element, the transmission element being configured to transmit the motion of the second input element to the second output element, the second input element and the second output element being gears spaced apart from each other, the transmission element being an intermediate gear meshing with the two gears, and at least one of the second input element, the second output element, and the transmission element being configured as a no-backlash gear.

2. The steering device according to claim 1, wherein the second input element, the second output element, and the transmission element are main gears primarily responsible for power transmission, and the no-backlash gear is provided with an auxiliary gear that rotates coaxially with the main gear, and is configured to sandwich the teeth of a mating gear between the teeth of the main gear and the teeth of the auxiliary gear.

3. The steering device according to claim 2, wherein the auxiliary gear is provided on one or both sides of the main gear.

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