Steering device

Abstract

A steering device (20) is provided with: a steering gear box (22A) having a ball screw shaft (62); a first power assist section (22B) connected to a first end of the ball screw shaft; and a second power assist unit (22C) connected to a second end of the ball screw shaft. The first power assist unit is provided with: a first motor (41) having a first motor shaft (41A); and a first speed reducer (42) that decelerates the rotation of the first motor. The second power assist unit is provided with: a second motor (51) having a second motor shaft (51A); and a second speed reducer (52) that decelerates the rotation of the second motor. The first speed reducer is provided with a worm gear (42A) and a worm (42B). The second speed reducer is provided with: a first parallel shaft cylindrical gear pair (71) having a first gear (71A) and a second gear (71B); and a second parallel shaft cylindrical gear pair (72) having a third gear (72A) and a fourth gear (72B).

Description

Technical Field

[0001] This disclosure relates to steering control devices. Background Technology

[0002] For example, the electric power steering system in Patent Document 1 includes a motor and an RBS (recirculating ball) type steering gearbox. The steering gearbox converts the rotational motion of the steering shaft into the oscillating motion of the steering arm. This changes the orientation of the steering wheels in conjunction with the steering arm. The torque of the motor is transmitted as an auxiliary force to the ball screw shaft of the steering gearbox via a reduction gear. This assists in steering wheel operation.

[0003] The speed reducer is a two-stage gear reducer. It has a first gear set and a second gear set. The first gear set is a combination of a pinion and an intermediate gear located on the motor's output shaft. The second gear set is a combination of a pinion located on the intermediate gear and a helical gear connected to the ball screw shaft. The intermediate gear and its pinion are connected coaxially and rotatably supported within the same housing.

[0004] Patent Document 1: U.S. Patent Application Publication No. 2022 / 0135118 Summary of the Invention

[0005] Depending on the size of the vehicle on which the steering system is mounted, the assistance force may sometimes be insufficient. In such cases, it is necessary to ensure the assistance force while preventing the steering system from becoming too large.

[0006] One aspect of this disclosure relates to a steering control device comprising: a steering gearbox configured to have a ball screw shaft, converting rotation of the ball screw shaft into steering action of the vehicle's steering wheels; a first power assist unit connected to a first end of the ball screw shaft; and a second power assist unit connected to a second end of the ball screw shaft. The first end is the end of the ball screw shaft facing upwards towards the vehicle when the steering gearbox is mounted on the vehicle. The second end is the end of the ball screw shaft facing downwards towards the vehicle when the steering gearbox is mounted on the vehicle. The first power assist unit comprises: a first motor having a first motor shaft; and a first reducer configured to reduce the rotation of the first motor. The second power assist unit comprises: a second motor having a second motor shaft; and a second reducer configured to reduce the rotation of the second motor. The first reducer comprises: a worm gear connected to the first end of the ball screw shaft; and a worm connected to the first motor shaft and meshing with the worm gear. The aforementioned second reducer includes: a first parallel-shaft cylindrical gear pair having a first gear and a second gear meshing with each other; and a second parallel-shaft cylindrical gear pair having a third gear and a fourth gear meshing with each other. The first gear is configured to rotate about a first axis and be connected to the second motor shaft. The second and third gears are configured to rotate about a second axis and be connected to the same shaft. The fourth gear is configured to rotate about a third axis and be connected to the second end of the ball screw shaft. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of a steering control device according to one embodiment.

[0008] Figure 2 It was cut in the axial direction. Figure 1 A cross-sectional view of the steering actuator.

[0009] Figure 3 yes Figure 2 A schematic diagram of the steering actuator. Detailed Implementation

[0010] A steering control device according to one embodiment will be described.

[0011] <Overall Composition>

[0012] like Figure 1As shown, the steering control device 20 is an electric power steering device, for example, mounted on a cab-over vehicle 10. The vehicle 10 has an axle-mounted suspension 11. The suspension 11 supports the front axle 12. Steering wheels 13, serving as front wheels, are connected to both ends of the front axle 12. The suspension 11 has leaf springs 14. The leaf springs 14 are located, for example, on the upper side of the front axle 12. The leaf springs 14 extend in the longitudinal direction of the vehicle. Both ends of the leaf springs 14 are mounted to the vehicle frame 16 via support members 15 such as hooks and loops.

[0013] The steering control device 20 includes a steering actuator 22. The steering actuator 22 is mounted on the steering shaft 21. The steering actuator 22 includes a steering gearbox 22A, a first power assist unit 22B, and a second power assist unit 22C. The first power assist unit 22B is located at the upper part of the steering gearbox 22A, which is the portion of the steering gearbox 22A closest to the steering shaft 21. The second power assist unit 22C is located at the lower part of the steering gearbox 22A. A first end of the steering shaft 21 is connected to a steering wheel 23. A second end of the steering shaft 21 is connected to the steering gearbox 22A via the first power assist unit 22B.

[0014] The steering gearbox 22A is of the RBS (Recirculating Ball) type. The steering gearbox 22A is connected to the steering wheel 13 via a linkage mechanism 30. The linkage mechanism 30 has a steering arm 31, a tie rod 32, and a lateral tie rod 33. The base end of the steering arm 31 is connected to the side of the steering gearbox 22A. The steering arm 31 is capable of swinging in the longitudinal direction of the vehicle with its base end as the center. The first end of the tie rod 32 is connected to the front end of the steering arm 31 and is rotatable. The second end of the tie rod 32 is connected, for example, to the steering knuckle arm 34 of the right steering wheel 13 and is rotatable. Both ends of the lateral tie rod 33 are connected to the left and right steering wheels 13 via lateral tie rod arms 35.

[0015] The rotation of the steering wheel 23 is transmitted to the steering gearbox 22A via the steering shaft 21. The steering gearbox 22A converts the rotational motion of the steering shaft 21 into the swing motion of the steering arm 31. The swing motion of the steering arm 31 drives the tie rod 32 in the forward and backward direction of the vehicle. The steering wheel 13 is turned by the swinging motion of the steering knuckle arm 34 in conjunction with the tie rod 32.

[0016] The first power assist unit 22B includes a first motor 41, a first reducer 42, and a torque sensor 43. The first motor 41 is connected to the upper part of the steering gearbox 22A via the first reducer 42. The first motor 41 operates by applying a torque to the steering shaft 21 in the same direction as the steering direction of the steering wheel 23, based on the steering torque detected by the torque sensor 43. The torque of the first motor 41 is transmitted to the steering shaft 21 as a first assist force via the first reducer 42. This assists in the steering operation of the steering wheel 23.

[0017] The second power assist unit 22C includes a second motor 51 and a second reducer 52. The second motor 51 is connected to the lower part of the steering gearbox 22A via the second reducer 52. The second motor 51 operates by applying a torque in the same direction as the steering direction of the steering wheel 23 to the steering shaft 21 based on the steering torque detected by the torque sensor 43. The torque of the second motor 51 is transmitted as a second assist force to the steering shaft 21 via the second reducer 52 and the steering gearbox 22A. Thus, the steering operation of the steering wheel 23 is assisted.

[0018] <Composition of Steering Gearbox 22A>

[0019] Next, the structure of the steering gearbox 22A will be explained in detail.

[0020] like Figure 2 As shown, the steering gearbox 22A has a first housing 61, a ball screw shaft 62, a ball screw nut 63, a plurality of balls 64, a sector gear shaft 65, and a sector gear 66. The first housing 61 houses the ball screw shaft 62, the ball screw nut 63, the plurality of balls 64, the sector gear shaft 65, and the sector gear 66.

[0021] When the steering gearbox 22A is mounted on the vehicle 10, the ball screw shaft 62 is maintained in a position extending vertically relative to the vehicle 10. The ball screw shaft 62 is rotatably supported on the first housing 61 via a first bearing 67 and a second bearing 68. The first bearing 67 is, for example, a needle roller bearing, having an inner wheel, an outer wheel, and a plurality of balls sandwiched between the inner and outer wheels. The inner wheel may also be integrally formed with the ball screw shaft 62. The second bearing 68 is, for example, a needle roller bearing. However, the second bearing 68 may also be a needle roller bearing or a sliding bearing.

[0022] The first end of the ball screw shaft 62 is connected to the steering shaft 21 via the first power assist unit 22B. The first end is the end of the ball screw shaft 62 facing upwards towards the vehicle 10 when the steering gearbox 22 is mounted on the vehicle 10. The second end of the ball screw shaft 62, opposite to the first end, is the end of the ball screw shaft 62 facing downwards towards the vehicle 10 when the steering gearbox 22 is mounted on the vehicle 10. The ball screw shaft 62 has a first threaded groove 62A. The first threaded groove 62A is a helical groove provided on the outer circumferential surface of the ball screw shaft 62.

[0023] The ball screw nut 63 is a cylindrical body with a second threaded groove 63A. The second threaded groove 63A is a helical groove located on the inner circumferential surface of the ball screw nut 63. The second threaded groove 63A is radially opposite to the first threaded groove 62A of the ball screw nut 63. The ball screw nut 63 is screwed onto the ball screw shaft 62 via a plurality of balls 64. The helical space surrounded by the first threaded groove 62A and the second threaded groove 63A functions as the rotation path for the balls 64 to rotate. The ball screw nut 63 has a plurality of rack teeth 63B. The rack teeth 63B are located on the outer circumferential surface of the ball screw nut 63. The rack teeth 63B are arranged axially on the ball screw nut 63.

[0024] In addition, the ball screw shaft 62, the ball screw nut 63, and a plurality of balls 64 constitute the ball screw mechanism.

[0025] The sector gear shaft 65 is in a direction orthogonal to the axis of the ball screw nut 63 (and... Figure 2 Extending in the orthogonal direction of the plane of the paper. The sector gear shaft 65 is rotatably supported on the first housing 61 via a bearing (not shown). The sector gear shaft 65 has an outer end that penetrates through the first housing 61 and protrudes to the outside. The base end of the steering arm 31 is fixed to the outer end of the sector gear shaft 65. The sector gear shaft 65 is the output shaft of the steering gearbox 22 and is linked to the steering wheel 13.

[0026] The sector gear 66 is configured to rotate integrally with the sector gear shaft 65. The sector gear 66 is a sector-shaped gear with multiple teeth 66A. The teeth 66A of the sector gear 66 mesh with the rack teeth 63B of the ball screw nut 63.

[0027] The rotation of the steering wheel 23 is transmitted to the ball screw shaft 62 via the steering shaft 21 and the first power assist unit 22B. As the ball screw shaft 62 rotates, the ball screw nut 63 moves axially relative to the ball screw shaft 62. This causes the sector gear 66 to oscillate around the sector gear shaft 65. As the sector gear 66 oscillates, the sector gear shaft 65 rotates, causing the steering arm 31 to oscillate around the sector gear shaft 65.

[0028] <First Power Auxiliary Unit 22B>

[0029] Next, the structure of the first power auxiliary unit 22B will be explained in detail.

[0030] like Figure 2As shown, the first power assist unit 22B has a second housing 44. The second housing 44 is connected to a first end of the first housing 61. The first end is the end of the first housing 61 facing upwards towards the vehicle 10 when the steering gearbox 22 is mounted on the vehicle 10. The second housing 44 houses the first reducer 42. In addition, the second housing 44 supports the first motor 41 and the torque sensor 43.

[0031] A first motor 41 is mounted on the outside of a second housing 44. The first motor 41 has a first motor shaft 41A. The axis of the first motor shaft 41A is, for example, orthogonal to the axis of the ball screw shaft 41 and parallel to the axis of the sector gear shaft 44. The first motor shaft 41A passes through the peripheral wall of the second housing 44 and is inserted into the interior of the second housing 44.

[0032] The torque sensor 43 is configured as follows.

[0033] The torque sensor 43 has an input shaft 43A, an output shaft 43B, a torsion bar 43C, and a detector 43D. The input shaft 43A and the output shaft 43B are connected to each other via the torsion bar 43C. The input shaft 43A and the output shaft 43B are hollow cylindrical bodies with a circular cross-sectional shape.

[0034] The first end of the input shaft 43A is connected to the steering wheel 23 via the steering shaft 21. The second end of the input shaft 43A is inserted into the first end of the output shaft 43B. The outer circumferential surface of the input shaft 43A remains in a non-contact state relative to the inner circumferential surface of the output shaft 43B. A sliding bearing 43E is sandwiched between the outer circumferential surface of the input shaft 43A and the inner circumferential surface of the output shaft 43B. The input shaft 43A and the output shaft 43B can rotate relative to each other via the sliding bearing 43E.

[0035] The second end of the output shaft 43B is connected to the first end of the ball screw shaft 62 so as to be rotatable as a single unit. The first end of the ball screw shaft 62 has a connecting hole 52B. The second end of the output shaft 43B is axially inserted into the connecting hole 52B. The relative rotation of the output shaft 43B and the ball screw shaft 62 is restricted by the spline engagement between them. The spline engagement is an example of the mating engagement of the inner part with the external teeth and the outer part with the internal teeth. The output shaft 43B is rotatably supported on the second housing 44 via a third bearing 43F.

[0036] The steering torque applied to the steering wheel 23 is transmitted to the input shaft 43A via the steering shaft 21. This causes the input shaft 43A to rotate. The rotation of the input shaft 43A is transmitted to the output shaft 43B via a torsion bar 43C. This causes the output shaft 43B to rotate. The torsion bar 43C twists according to the steering torque. A detector 43D is configured, for example, to surround the outer circumferential surface of the input shaft 43A. The detector 43D detects the steering torque based on the amount of torsion in the torsion bar 43C.

[0037] The first reducer 42 is configured as follows.

[0038] The first reducer 42 has a worm gear 42A and a worm 42B. The worm gear 42A is a circular plate with a circular cross-section, mounted on the outer circumferential surface of the output shaft 43B. The worm gear 42A can rotate integrally with the output shaft 43B. The worm 42B is connected to the first motor shaft 41A. The worm 42B can rotate integrally with the first motor shaft 41A. The axes of the first motor shaft 41A and the worm 42B are aligned. The worm 42B meshes with the worm gear 42A. The axial angle between the worm 42B and the worm gear 42A is, for example, 90°.

[0039] The torque of the first motor 41 is transmitted to the ball screw shaft 41 via the first reducer 42. A torque in the same direction as the steering direction of the steering wheel 23 is applied to the ball screw shaft 41. This assists in the steering operation of the steering wheel 23.

[0040] <Second Power Auxiliary Unit 22C>

[0041] Next, the structure of the second power auxiliary unit 22C will be explained in detail.

[0042] like Figure 2 As shown, the second power assist unit 22C has a third housing 53. The third housing 53 has a base 53A and a fitting portion 53B.

[0043] Base 53A is a plate-shaped portion of the third housing 53 that extends in a direction orthogonal to the axial direction of the ball screw shaft 62. Base 53A has a first end face and a second end face. The first end face is the end face on the side of the ball screw shaft 62 that is close to the first housing 61 in the axial direction. The second end face is the end face on the side opposite to the first end face, and is the end face on the side of the ball screw shaft 62 that is away from the first housing 61 in the axial direction.

[0044] The fitting portion 53B is provided on the first end face of the base 53A. The fitting portion 53B is a cylindrical body with a circular cross-sectional shape. The outer peripheral surface of the second end of the first housing 61 fits into the inner peripheral surface of the fitting portion 53B. The first housing 61 is fixed to the third housing 53 by bolts (not shown) via a mounting portion (not shown) provided on the outer peripheral surface of the second end of the first housing 61.

[0045] A portion of the base 53A extends radially outward from the outer peripheral surface of the fitting portion 53B. A second motor 51 is mounted in the base 53A, extending radially outward from the outer peripheral surface of the fitting portion 53B. The second motor 51 is mounted to the base 53A from its first end face side. The second motor 51 has a second motor shaft 51A. The second motor shaft 51A passes axially through the base 53A.

[0046] The second power auxiliary unit 22C has a fourth housing 54. The fourth housing 54 is mounted on the base 53A. The fourth housing 54 is a box-shaped body that covers the second end face of the base 53A. The outline of the fourth housing 54 corresponds to the outline of the base 53A. The front end of the second motor shaft 51A is located inside the fourth housing 54.

[0047] The second reducer 52 is configured as follows.

[0048] like Figure 3 As shown, the second reducer 52 has a two-stage parallel-axis cylindrical gear pair. Specifically, the second reducer 52 has a first parallel-axis cylindrical gear pair 71 and a second parallel-axis cylindrical gear pair 72. The first parallel-axis cylindrical gear pair 71 has a first gear 71A and a second gear 71B that mesh with each other. The second parallel-axis cylindrical gear pair 72 has a third gear 72A and a fourth gear 72B that mesh with each other. The first gear 71A, the second gear 71B, the third gear 72A, and the fourth gear 72B are, for example, helical gears.

[0049] The first gear 71A is housed inside the fourth housing 54. The first gear 71A is connected to the second motor shaft 51A. The second motor shaft 51A and the first gear 71A are arranged coaxially. The second motor shaft 51A and the first gear 71A rotate together around the first axis O1, driven by the second motor 51.

[0050] The second gear 71B is housed inside the fourth housing 54. The second gear 71B meshes with the first gear 71A.

[0051] The third gear 72A is housed inside the third housing 53. The third gear 72A is connected to the second gear 71B via a shaft 73. The second gear 71B and the third gear 72A are arranged coaxially. The second gear 71B and the third gear 72A rotate together about the second axis O2.

[0052] The fourth gear 72B is housed inside the first housing 61. The fourth gear 72B is connected to the second end of the ball screw shaft 62. The ball screw shaft 62 and the fourth gear 72B are arranged coaxially. The ball screw shaft 62 and the fourth gear 72B rotate integrally about the third axis O3.

[0053] Furthermore, the first axis O1, the second axis O2, and the third axis O3 are parallel to each other. Additionally, the outer diameters of the first gear 71A, the second gear 71B, the third gear 72A, and the fourth gear 72B increase in the order of first gear 71A, third gear 72A, fourth gear 72B, and second gear 71B. That is, the outer diameter of the first gear 71A is the smallest, and the outer diameter of the second gear 72B is the largest.

[0054] The torque of the second motor 52 is transmitted to the ball screw shaft 62 via the first gear 71A, the second gear 71B, the third gear 72A, and the fourth gear 72B. By applying torque to the ball screw shaft 62 in the same direction as the steering direction of the steering wheel 23, the steering operation of the steering wheel 23 is assisted. The ball screw shaft 62 corresponds to the input shaft that receives rotation from the first reducer 42 and the second reducer 52. The sector gear shaft 65 corresponds to the output shaft or linkage component that is linked to the steering wheel 13.

[0055] <Effects of this implementation method>

[0056] According to this embodiment, the following effects are achieved.

[0057] (1) The steering control device 20 includes a steering gearbox 22A, a first power assist unit 22B, and a second power assist unit 22C. The steering gearbox 22A has a ball screw shaft 62 and converts the rotation of the ball screw shaft 62 into the steering action of the vehicle's steering wheels 13. Converting the rotation of the ball screw shaft 62 into the steering action of the vehicle's steering wheels 13 means converting the rotation of the ball screw shaft 62 into the rotation of the sector gear shaft 65. The first power assist unit 22B provides a first assist force to the ball screw shaft 62. The second power assist unit 22C provides a second assist force to the ball screw shaft 62. Therefore, compared with the case where only the first assist force or the second assist force is provided to the ball screw shaft 62, it is easy to ensure that the assist force is provided to the ball screw shaft 62.

[0058] (2) The first power assist unit 22B is connected to the first end of the ball screw shaft 62. The first end is the end of the ball screw shaft 62 facing upward toward the vehicle when the steering gearbox 22A is mounted on the vehicle. The second power assist unit 22C is connected to the second end of the ball screw shaft 62. The second end is the end of the ball screw shaft 62 facing downward toward the vehicle when the steering gearbox 22A is mounted on the vehicle. In this way, the first assist force and the second assist force can be provided in a balanced and appropriate manner from both ends of the ball screw shaft 62.

[0059] (3) The first power assist unit 22B includes a first motor 41 and a first reducer 42. The first motor 41 has a first motor shaft 41A. The first reducer 42 reduces the rotation of the first motor 41. The second power assist unit 22C includes a second motor 51 and a second reducer 52. The second motor 51 has a second motor shaft 51A. The second reducer 52 reduces the rotation of the second motor 51. In this way, the output of the first motor 41 and the second motor 51, as well as the reduction ratio of the first reducer 42 and the second reducer 52, can be set independently. Therefore, the output characteristics of the first power assist unit 22B and the second power assist unit 22C, and thus the design related to the specifications of the steering control device 20, have a high degree of freedom.

[0060] (4) The first reducer 42 has a worm gear 42A and a worm 42B. The worm gear 42A is connected to the first end of the ball screw shaft 62. The worm 42B is connected to the first motor shaft 41A and meshes with the worm gear 42A. The first reducer 42 is a so-called worm reducer.

[0061] The second reducer 52 has a first parallel-shaft cylindrical gear pair 71 and a second parallel-shaft cylindrical gear pair 72. The first parallel-shaft cylindrical gear pair 71 has a first gear 71A and a second gear 71B that mesh with each other. The second parallel-shaft cylindrical gear pair 72 has a third gear 72A and a fourth gear 72B that mesh with each other. The first gear 71A is connected to the second motor shaft 51A and rotates about the first axis O1. The second gear 71B is connected to the third gear 72A on the same shaft and rotates about the second axis O2. The fourth gear 72B is connected to the second end of the ball screw shaft 62 and rotates about the third axis O3. The second reducer 52 is a so-called parallel-shaft reducer.

[0062] Worm gear reducers achieve higher reduction ratios. Parallel shaft reducers can achieve a wide range of reduction ratios by combining multiple stages of gears. However, the parallel shaft reducer, i.e., the second reducer 52, tends to be larger than the worm gear reducer, i.e., the first reducer 42. Therefore, compared to using a parallel shaft reducer as the first reducer 42, it is possible to install the parallel shaft reducer in the lower part of the engine compartment, which has more space, thus providing an advantage in terms of vehicle mounting capacity.

[0063] <Other Implementation Methods>

[0064] This implementation method can also be modified as follows.

[0065] The torque sensor 43 can also be installed separately from the first power assist unit 22B.

[0066] The steering control device 20 can be applied to a steer-by-wire type steering control device that mechanically separates the steering wheel 23 from the steering wheel 13. In this case, for example, the ball screw shaft 60 is separated from the steering wheel 23 so that mechanical power transmission is not possible. Additionally, the first motor 41 and the second motor 51 function as steering motors that generate steering force. Steering force is the force used to turn the steering wheel 13.

Claims

1. A steering control device, wherein, have: The steering gearbox is configured to have a ball screw shaft, which converts the rotation of the ball screw shaft into the steering action of the vehicle's steering wheels. The first power auxiliary unit is connected to the first end of the aforementioned ball screw shaft; and The second power auxiliary unit is connected to the second end of the aforementioned ball screw shaft. The aforementioned first end is the end of the ball screw shaft facing upwards towards the vehicle when the steering gearbox is mounted on the vehicle. The second end is the end of the ball screw shaft facing downwards from the vehicle when the steering gearbox is mounted on the vehicle. The aforementioned first power auxiliary unit includes: a first motor having a first motor shaft; and a first reducer configured to reduce the rotational speed of the first motor. The aforementioned second power auxiliary unit includes: a second motor having a second motor shaft; and a second reducer configured to reduce the rotational speed of the second motor. The aforementioned first reducer has the following features: The worm gear is connected to the first end of the aforementioned ball screw shaft; and The worm gear is connected to the first motor shaft and meshes with the worm wheel. The aforementioned second reducer has: A first parallel-axis cylindrical gear pair, having a first gear and a second gear meshing with each other; and The second parallel-axis cylindrical gear pair has a third gear and a fourth gear that mesh with each other. The first gear is configured to connect to the second motor shaft and rotate about the first axis. The second gear and the third gear are configured to be connected on the same axis and rotate about the second axis. The aforementioned fourth gear is configured to connect to the aforementioned second end of the aforementioned ball screw shaft and rotate around the third axis.

2. The steering control device according to claim 1, wherein, The aforementioned ball screw shaft is connected to the steering wheel of the aforementioned vehicle to enable mechanical power transmission.

3. The steering control device according to claim 1, wherein, The aforementioned ball screw shaft is separated from the steering wheel of the aforementioned vehicle so that mechanical power transmission is impossible.

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