Steering device

Abstract

A steering device (20) is provided with: an actuator having a motor (23) configured so as to generate torque in accordance with the steering of a steering wheel (26) of a vehicle (10), and a speed reducer (25) configured so as to decelerate the rotation of the motor (23); and a ball screw mechanism (48) configured to convert rotation applied by the speed reducer (25) into rotation of an output shaft (44) interlocked with the steering wheel (13). The speed reducer (25) and the ball screw mechanism (48) are configured so that the increase / decrease characteristics of the load torque with respect to the steering direction generated when the steering wheel (26) is steered are opposite to each other between the speed reducer (25) and the ball screw mechanism (48).

Description

Technical Field

[0001] The present disclosure relates to a steering control device. Background Art

[0002] Conventionally, in so-called flat-head vehicles such as trucks, where the driver's seat is located forward of the axle of the front wheels, axle-mounted suspensions in which the left and right wheels are connected by axles are often used. In vehicles having axle-mounted suspensions, ball screw-type steering gearboxes are often used. The steering gearbox is mounted on, for example, a vehicle body frame.

[0003] The electric power steering device of Patent Document 1 has a motor and a ball screw type steering gearbox. The steering gearbox converts the rotational motion of the steering shaft into the swinging motion of the steering arm. The direction of the steering wheel changes in conjunction with the steering arm. The torque of the motor is transmitted to the ball screw shaft of the steering gearbox via a worm reducer. Thus, the steering operation of the steering wheel is assisted.

[0004] Patent Document 1: International Publication No. 2021 / 0261188

[0005] Including Patent Document 1, the following concerns exist in existing electric power steering devices with a ball screw type steering gear box. That is, when the steering gear box is mounted on a vehicle, the ball screw shaft is maintained in a posture extending in the up-down direction of the vehicle. The ball screw nut moves along the ball screw shaft extending in the up-down direction of the vehicle. At this time, gravity corresponding to the mass acts on the ball screw nut. Therefore, when observing the ball screw mechanism alone, the load torque of the ball screw mechanism is different depending on the steering control direction of the steering wheel, that is, the moving direction of the ball screw nut. The load torque is a torque generated by the resistance generated by the balls at the meshing portion of the ball screw nut and the ball screw shaft. Summary of the invention

[0006] A steering device according to one aspect of the present disclosure includes: an actuator having a motor configured to generate torque corresponding to the steering operation of a steering wheel of a vehicle, and a reducer configured to reduce the speed of rotation of the motor; and a ball screw mechanism configured to convert the rotation applied by the reducer into the rotation of an output shaft linked to a steering wheel. The reducer and the ball screw mechanism are configured so that the increase and decrease characteristics of the load torque generated in the steering direction when the steering wheel is steered are opposite to each other between the reducer and the ball screw mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0008] Figure 2 yes Figure 1Cross-sectional view of the steering gearbox.

[0009] Figure 3A Yes Figure 2 A cross-sectional view of the reducer obtained by cutting it in a direction perpendicular to the axis of the worm wheel.

[0010] Figure 3B yes Figure 3A An enlarged cross-sectional view of the portion indicated by reference numeral 3B in FIG.

[0011] Figure 4 yes Figure 3A A schematic diagram of a reducer having a worm gear set in a first direction.

[0012] Figure 5 yes Figure 3A A schematic diagram of a reducer having a worm gear set in a second direction.

[0013] Figure 6 yes Figure 2 A cross-sectional view of a steering gearbox having a right-hand threaded ball screw shaft.

[0014] Figure 7 yes Figure 2 A cross-sectional view of a steering gearbox having a left-hand threaded ball screw shaft. DETAILED DESCRIPTION

[0015] A steering system according to one embodiment will be described. The steering system is an electric power steering system.

[0016] <Overall structure>

[0017] like Figure 1 As shown, the steering device 20 is mounted on, for example, a flat-head vehicle 10. The vehicle 10 includes an axle-suspended suspension 11. The suspension 11 supports a front axle 12. Front wheels, i.e., steering wheels 13, are connected to both ends of the front axle 12. The suspension 11 includes a leaf spring 14. As an example, the leaf spring 14 is located on the upper side of the front axle 12. The leaf spring 14 extends in the front-rear direction of the vehicle. Both ends of the leaf spring 14 are attached to a vehicle frame 16 via a support member 15 such as a hook.

[0018] The steering device 20 includes a steering shaft 21, a steering gear box 22, a motor 23, a torque sensor 24, and a speed reducer 25. The steering shaft 21 and the steering gear box 22 constitute a steering mechanism of the vehicle 10. A first end of the steering shaft 21 is connected to a steering wheel 26. A second end of the steering shaft 21 is connected to the steering gear box 22 via the torque sensor 24 and the speed reducer 25. The motor 23 is connected to the steering gear box 22 via the speed reducer 25. The steering gear box 22 is, for example, an RBS type (recirculating ball type).

[0019] The steering gear box 22 is connected to the steering wheel 13 via a link mechanism 30. The link mechanism 30 includes a steering arm 31, a steering longitudinal tie rod 32, and a steering transverse tie rod 33. The base end of the steering arm 31 is connected to the side of the steering gear box 22. The steering arm 31 can swing in the front and rear direction of the vehicle with its base end as the center. The first end of the steering longitudinal tie rod 32 is rotatably connected to the front end of the steering arm 31. The second end of the steering longitudinal tie rod 32 is rotatably connected to the knuckle arm 34 of the right steering wheel 13. Both ends of the steering transverse tie rod 33 are connected to the left and right steering wheels 13 via the steering transverse tie rod arm 35.

[0020] The rotation of the steering wheel 26 is transmitted to the steering gear box 22 via the steering shaft 21. The steering gear box 22 converts the rotation of the steering shaft 21 into the swinging motion of the steering arm 31. The steering trailing rod 32 is driven in the front-rear direction of the vehicle by the swinging motion of the steering arm 31. The steering wheel 13 is steered by the knuckle arm 34 swinging in conjunction with the steering trailing rod 32.

[0021] The motor 23 generates a torque in the same direction as the steering direction of the steering wheel 26 according to the steering torque detected by the torque sensor 24. The torque of the motor 23 is transmitted to the steering gear box 22 via the speed reducer 25. That is, the speed reducer 25 is configured to apply torque to the steering gear box 22. By applying the torque in the same direction as the steering direction to the steering gear box 22, the steering of the steering wheel 26 is assisted. The motor 23 and the speed reducer 25 constitute an actuator.

[0022] <Structure of Steering Gear Box 22>

[0023] like Figure 2 As shown, the steering gear box 22 has a first housing 40. A ball screw shaft 41, a ball screw nut 42, a plurality of balls 43, a sector gear shaft 44, and a sector gear 45 are provided inside the first housing 40.

[0024] When the steering gear box 22 is mounted on the vehicle 10, the ball screw shaft 41 is maintained in a posture extending in the up-down direction relative to the vehicle 10. The ball screw shaft 41 is supported via the first bearing 46 and the second bearing 47 so as to be rotatable relative to the first housing 40. The first end of the ball screw shaft 41 is connected to the steering shaft 21 via the speed reducer 25 and the torque sensor 24 in a state of penetrating the first housing 40. The first end is the end of the ball screw shaft 41 on the side facing the upper side of the vehicle 10 when the steering gear box 22 is mounted on the vehicle 10. The second end of the ball screw shaft 41 on the opposite side to the first end is the end of the ball screw shaft 41 on the side facing the lower side of the vehicle 10 when the steering gear box 22 is mounted on the vehicle 10. The second end is opposite to the end wall of the first housing 40.

[0025] The ball screw shaft 41 has a first thread groove 41A. The first thread groove 41A is a spiral groove provided on the outer peripheral surface of the ball screw shaft 41. The threaded portion is formed by providing the first thread groove 41A. The ball screw shaft 41 is a right-hand thread type or a left-hand thread type. The threaded portion of the ball screw shaft 41 of the right-hand thread type is a right-hand thread, and the winding direction of the first thread groove 41A is clockwise when viewed from the first end side. The threaded portion of the ball screw shaft 41 of the left-hand thread type is a left-hand thread, and the winding direction of the first thread groove 41A is counterclockwise when viewed from the first end side.

[0026] The ball screw nut 42 is cylindrical and has a second thread groove 42A. The second thread groove 42A is a spiral groove provided on the inner circumferential surface of the ball screw nut 42. The second thread groove 42A is radially opposite to the first thread groove 41A. The ball screw nut 42 is screwed with the ball screw shaft 41 via a plurality of balls 43. The spiral space surrounded by the first thread groove 41A and the second thread groove 42A functions as a rolling path for the balls 43 to roll. The ball screw shaft 41, the ball screw nut 42 and the balls 43 constitute a ball screw mechanism 48.

[0027] The ball screw nut 42 has a plurality of rack teeth 42B. The rack teeth 42B are provided on the outer peripheral surface of the ball screw nut 42. The rack teeth 42B are arranged in the axial direction of the ball screw nut 42.

[0028] The sector gear shaft 44 is arranged in a direction perpendicular to the axis of the ball screw nut 42 (relative to Figure 2 The sector gear shaft 44 is supported by a bearing (not shown) so as to be rotatable relative to the first housing 40. The sector gear shaft 44 has an outer end portion that penetrates the first housing 40 and is exposed to the outside. The base end of the steering arm 31 is fixed to the outer end portion of the sector gear shaft 44. The sector gear shaft 44 is an output shaft of the steering gear box 22 and is linked to the steering wheel 13.

[0029] The sector gear 45 is provided so as to be rotatable integrally with the sector gear shaft 44 . The sector gear 45 is a sector-shaped gear and has a plurality of teeth 45A. The teeth 45A of the sector gear 45 mesh with the rack teeth 42B of the ball screw nut 42 .

[0030] The rotation of the steering wheel 26 is transmitted to the ball screw shaft 41 via the steering shaft 21 and the speed reducer 25. With the rotation of the ball screw shaft 41, the ball screw nut 42 moves axially relative to the ball screw shaft 41. As a result, the sector gear 45 swings around the sector gear shaft 44. With the swing of the sector gear 45, the sector gear shaft 44 rotates, so that the steering arm 31 swings around the sector gear shaft 44.

[0031] When the ball screw shaft 41 is a right-hand thread type, if the ball screw shaft 41 rotates clockwise when viewed from the first end side, the ball screw nut 42 moves upward. In addition, when the ball screw shaft 41 is a right-hand thread type, if the ball screw shaft 41 rotates counterclockwise when viewed from the first end side, the ball screw nut 42 moves downward.

[0032] When the ball screw shaft 41 is a left-handed thread type, if the ball screw shaft 41 rotates counterclockwise when viewed from the first end side, the ball screw nut 42 moves upward. In addition, when the ball screw shaft 41 is a left-handed thread type, if the ball screw shaft 41 rotates clockwise when viewed from the first end side, the ball screw nut 42 moves downward.

[0033] In addition, when the steering wheel 26 is steered to the right based on the steering neutral position, the ball screw shaft 41 rotates in the clockwise direction when viewed from the first end side. In addition, when the steering wheel 26 is steered to the left based on the steering neutral position, the ball screw shaft 41 rotates in the counterclockwise direction when viewed from the first end side. The steering neutral position is a position of the steering wheel 26 corresponding to the straight-ahead state of the vehicle.

[0034] <Structure of the reduction gear 25>

[0035] like Figure 2 As shown, the reducer 25 is connected to the first end of the ball screw shaft 41. The reducer 25 is configured to apply torque to the ball screw mechanism 48. The reducer 25 has a second housing 50. The second housing 50 is connected to the first housing 40 of the steering gear box 22. The interior of the first housing 40 and the interior of the second housing 50 are connected to each other. A motor 23 is installed on the outside of the second housing 50. The output shaft 23A of the motor 23 extends in a direction that is orthogonal to the axis of the ball screw shaft 41 and parallel to the axis of the sector gear shaft 44, for example. The output shaft 23A passes through the second housing 50 and is inserted into the interior of the second housing 50.

[0036] A shaft 51, a worm wheel 52 and a worm 53 are provided inside the second housing 50. The worm wheel 52 is connected to the first end of the ball screw shaft 41 in a manner that allows it to rotate as a whole. Specifically, as described below. That is, the shaft 51 is supported via the third bearing 54 and the fourth bearing 55 so as to be rotatable relative to the second housing 50. The first end of the shaft 51 is connected to the steering shaft 21 via the torque sensor 24 while penetrating the second housing 50. The second end of the shaft 51 is connected to the first end of the ball screw shaft 41 in a manner that allows it to rotate as a whole. The worm wheel 52 is mounted on the outer peripheral surface of the shaft 51. The worm wheel 52 can rotate as a whole with the shaft 51. The worm 53 is arranged to be rotatable as a whole relative to the output shaft 23A of the motor 23. The axis of the output shaft 23A and the axis of the worm 53 are consistent with each other. The worm 53 meshes with the worm wheel 52. The shaft angle between the worm 53 and the worm wheel 52 is, for example, 90°.

[0037] The torque of the motor 23 is transmitted to the ball screw shaft 41 via the speed reducer 25. By applying torque in the same direction as the steering direction of the steering wheel 26 to the ball screw shaft 41, the steering of the steering wheel 26 is assisted.

[0038] like Figure 3A As shown, the second housing 50 has a worm housing portion 61 and a worm wheel housing portion 62. The worm housing portion 61 is a cylindrical space for housing the worm 53, and extends in the axial direction of the worm 53. The worm wheel housing portion 62 is a cylindrical space for housing the worm wheel 52, and extends in a direction orthogonal to the axial direction of the worm 53. The worm wheel housing portion 62 is continuous with the worm housing portion 61.

[0039] The first end of the worm housing portion 61 is connected to a concave motor mounting portion 63 provided on the outer surface of the second housing 50. The motor 23 is fixed to the motor mounting portion 63. The output shaft 23A of the motor 23 is inserted into the first end of the worm housing portion 61. The second end of the worm housing portion 61 is open to the outside of the second housing 50. The opening is closed by an end cover 64.

[0040] The worm 53 is supported via the fifth bearing 65 and the sixth bearing 66 so as to be rotatable relative to the inner peripheral surface of the worm housing portion 61. The first end of the worm 53 is supported by the fifth bearing 65. The second end of the worm 53 is supported by the sixth bearing 66. A cylindrical fixed bushing 54A is mounted on the first end of the worm housing portion 61. The end wall of the fixed bushing 54A abuts against the outer ring of the fifth bearing 65 in the axial direction. Thus, the movement of the fifth bearing 65 and thus the worm 53 in the direction of approaching the motor 23 is restricted.

[0041] <Coupling 70>

[0042] The first end of the worm 53 is connected to the output shaft 23A of the motor 23 via the coupling 70. The coupling 70 includes a first connection body 71, a second connection body 72, and an elastic body 73. The elastic body 73 is interposed between the first connection body 71 and the second connection body 72.

[0043] The first connection body 71 is connected to the first end of the worm 53 so as to be rotatable as a whole. The first connection body 71 has a plurality of first engagement claws 71A. The first engagement claws 71A are provided on the side surface of the first connection body 71 that contacts the elastic body 73. The plurality of first engagement claws 71A are provided at equal intervals in the circumferential direction.

[0044] The second connection body 72 is connected to the output shaft 23A of the motor 23 so as to be rotatable as a whole. The second connection body 72 has a plurality of second engagement claws 72A. The second engagement claws 72A are provided on the side surface of the second connection body 72 that contacts the elastic body 73. The plurality of second engagement claws 72A are provided at equal intervals in the circumferential direction.

[0045] The elastic body 73 has a plurality of first engaging recesses 73A and a plurality of second engaging recesses 73B. The first engaging recesses 73A are provided on the side surface of the elastic body 73 on the side in contact with the first connecting body 71. The second engaging recesses 73B are provided on the side surface of the elastic body 73 on the side in contact with the second connecting body 72. The first engaging recesses 73A and the second engaging recesses 73B are alternately provided along the circumferential direction of the elastic body 73.

[0046] The first engagement claw 71A meshes with the first engagement recess 73A. The second engagement claw 72A meshes with the second engagement recess 73B. The first engagement claw 71A meshes with the first engagement recess 73A in the circumferential direction, and the second engagement claw 72A meshes with the second engagement recess 73B in the circumferential direction. Therefore, torque transmission between the worm 53 and the output shaft 23A can be performed.

[0047] The elastic body 73 is maintained in a slightly compressed state by the first connecting body 71 and the second connecting body 72. When an external force is applied to the worm 53 in the radial direction, the elastic body 73 is elastically deformed, thereby allowing the worm 53 to tilt relative to the output shaft 23A. The fifth bearing 65 has an internal gap. The internal gap is the amount of clearance between the outer ring, the inner ring and the ball of the fifth bearing 65. The worm 53 can tilt relative to the axis of the output shaft 23A with the part of the worm 53 supported by the fifth bearing 65 as the center. The swing center O of the worm 53 coincides with the center of the fifth bearing 65 when viewed from the axial direction of the worm wheel 52.

[0048] <Force applying mechanism 80>

[0049] like Figure 3AAs shown, the speed reducer 25 includes an urging mechanism 80 . The urging mechanism 80 is a structure for adjusting the backlash of the speed reducer 25 by elastically urging the worm 53 toward the worm wheel 52 .

[0050] like Figure 3B As shown, the urging mechanism 80 includes a bolt 81, a compression coil spring 82, and a pressing member 83. The bolt 81 includes a head 81A and a shaft 81B. The shaft 81B is fastened to the threaded hole 50A of the second housing 50. The threaded hole 50A is a cylindrical hole that passes through the peripheral wall of the second housing 50 and opens to the inner peripheral surface of the worm housing portion 61 corresponding to the sixth bearing 66. The compression coil spring 82 is sandwiched between the shaft 81B and the pressing member 83 in a state of being compressed in the axial direction. The pressing member 83 is fixed to the end of the compression coil spring 82 on the opposite side of the shaft 81B.

[0051] The compression coil spring 82 constantly urges the sixth bearing 66 and the second end of the worm 53 toward the worm wheel 52 via the pressing member 83. Figure 3A The counterclockwise moment in the worm 53 acts on the second end of the worm 53. The counterclockwise tilting of the worm 53 is restricted by the worm 53 abutting against the worm wheel 52.

[0052] By pressing the worm 53 against the worm wheel 52, the backlash amount of the meshing portion between the worm 53 and the worm wheel 52 can be reduced. In addition, it is assumed that the teeth of the worm 53 and the teeth of the worm wheel 52 wear due to aging. However, in this case, the increase of the backlash of the meshing portion between the worm 53 and the worm wheel 52 is suppressed by the amount of wear caused by the tilting teeth of the worm 53.

[0053] <Load torque of ball screw mechanism 48>

[0054] Next, the load torque of the ball screw mechanism 48 will be supplementally described.

[0055] When the steering gear box 22 is mounted on the vehicle 10, the ball screw shaft 41 is maintained in a posture extending in the up-down direction of the vehicle 10. The ball screw nut 42 moves along the ball screw shaft 41 extending in the up-down direction of the vehicle 10. At this time, gravity corresponding to the mass acts on the ball screw nut 42. Therefore, when the ball screw mechanism 48 is observed alone, the load torque of the ball screw mechanism 48 is different depending on the steering direction of the steering wheel 26, that is, the moving direction of the ball screw nut 42. The load torque is a torque generated by the resistance generated by the ball 43 at the meshing portion of the ball screw nut 42 and the ball screw shaft 41.

[0056] <Load torque for right-hand thread type>

[0057] like Figure 6As shown, the load torque of the ball screw mechanism 48 in the case of using the right-hand threaded ball screw shaft 41 is studied.

[0058] In this case, when the steering wheel 26 is turned right, the ball screw shaft 41 rotates in the clockwise direction DR2 when viewed from the first end side. Therefore, the ball screw nut 42 rises along the ball screw shaft 41. That is, the ball screw nut 42 moves in the direction opposite to the direction in which gravity acts. Therefore, the load torque of the ball screw mechanism 48 increases.

[0059] When the steering wheel 26 is turned to the left, the ball screw shaft 41 rotates in the counterclockwise direction DL2 when viewed from the first end side. Therefore, the ball screw nut 42 descends along the ball screw shaft 41. That is, the ball screw nut 42 moves in the same direction as the direction in which gravity acts. Therefore, the load torque of the ball screw mechanism 48 is reduced.

[0060] Therefore, as shown in the following equation (3), the load torque T generated when the steering wheel 26 is turned right is br The absolute value of the load torque T generated when the steering wheel 26 is turned left bl The absolute value of .

[0061] │T bl │<│T br │…(3)

[0062] <Load torque of left-hand thread type>

[0063] Then, if Figure 7 As shown in FIG. 1 , the load torque of the ball screw mechanism 48 in the case of using the left-handed ball screw shaft 41 is examined.

[0064] In this case, when the steering wheel 26 is turned to the left, the ball screw shaft 41 rotates in the counterclockwise direction DR2 when viewed from the first end side. Therefore, the ball screw nut 42 rises along the ball screw shaft 41. That is, the ball screw nut 42 moves in the direction opposite to the direction in which gravity acts. Therefore, the load torque of the ball screw mechanism 48 increases.

[0065] When the steering wheel 26 is turned right, the ball screw shaft 41 rotates in the clockwise direction DR2 when viewed from the first end side. Therefore, the ball screw nut 42 descends along the ball screw shaft 41. That is, the ball screw nut 42 moves in the same direction as the direction in which gravity acts. Therefore, the load torque of the ball screw mechanism 48 is reduced.

[0066] Therefore, as shown in the following equation (4), the load torque T generated when the steering wheel 26 is turned left is blThe absolute value of the load torque T generated when the steering wheel 26 is turned right br The absolute value of .

[0067] │T bl │>│T br │…(4)

[0068] <Reaction force applied to the worm 53>

[0069] Next, the reaction force applied to the worm 53 will be described.

[0070] The tooth surface of the worm 53 is twisted relative to the axis of the worm 53. The tooth surface of the worm wheel 52 is twisted relative to the axis of the worm wheel 52. There is a pressure angle between the tooth surface of the worm 53 and the tooth surface of the worm wheel 52. The pressure angles of the two tooth surfaces of the teeth of the worm 53 located on opposite sides of the axial direction of the worm 53 are the same. The pressure angles of the two tooth surfaces of the teeth of the worm wheel 52 located on opposite sides of the rotation direction of the worm wheel 52 are the same. Therefore, as the worm 53 rotates, a reaction force is applied to the worm 53 from the worm wheel 52. The position where the reaction force is applied is the meshing portion of the worm 53 and the worm wheel 52.

[0071] like Figure 4 As shown, the reaction force acting from the worm wheel 52 on the worm 53 includes an axial force F1 applied to the worm 53 in the axial direction and a radial force F2 applied to the worm 53 in the radial direction. When the steering wheel 26 is steered, the reaction force including the axial force F1 and the radial force F2 acts as resistance.

[0072] The direction of radial force component F2 is the same when steering wheel 26 is turned right and when it is turned left. When the magnitude of the torque applied to steering wheel 26 is the same, the magnitude of radial force component F2 is the same when steering wheel 26 is turned right and when it is turned left.

[0073] The directions of the axial force component F1 are opposite when the steering wheel 26 is turned right and when it is turned left. When the magnitude of the torque applied to the steering wheel 26 is the same, the magnitude of the axial force component F1 is the same when the steering wheel 26 is turned right and when it is turned left.

[0074] When the steering wheel 26 is turned right, the worm wheel 52 rotates in the clockwise direction DR1 when viewed from the axial direction. Figure 4 As shown by the solid line, the direction of the axial component force F1 is from the meshing portion of the worm 53 and the worm wheel 52 toward the first end of the worm 53 ( Figure 4 The axial force component F1 generated when the steering wheel 26 is turned right is, for example, a positive value.

[0075] When the steering wheel 26 is turned to the left, the worm wheel 52 rotates in the counterclockwise direction DL1 when viewed from the axial direction. Figure 4 As shown by the dashed line, the direction of the axial force component F1 is from the meshing portion of the worm 53 and the worm wheel 52 toward the second end of the worm 53 ( Figure 4 When the steering wheel 26 is turned right, the axial force component F1 is positive, and when the steering wheel 26 is turned left, the axial force component F1 is negative.

[0076] The position where the reaction force is applied from the worm wheel 52 to the worm 53 is the meshing portion between the worm 53 and the worm wheel 52. The meshing portion is a position offset from the axis of the worm 53 toward the worm wheel 52. Therefore, when the swing center O of the worm 53 is located on the axis of the worm 53, due to the axial component force F1, a moment centered around the swing center O acts on the worm 53. The direction of the moment centered around the swing center O is opposite depending on the rotation direction of the worm wheel 52.

[0077] Therefore, the load torque of the speed reducer 25 may differ depending on the steering direction of the steering wheel 26, that is, the rotation direction of the worm wheel 52. The load torque is a torque generated by the resistance generated at the meshing portion between the worm wheel 52 and the worm 53.

[0078] <Load Torque of the Speed ​​Reducer 25 When the Worm 53 Is Oriented in the First Orientation>

[0079] First, the worm 53 is set to Figure 4 The load torque of the speed reducer 25 generated in the case of the first orientation shown is studied. The first orientation is the orientation of the worm 53 in which the second end of the worm 53 is located on the left side of the center line L1 of the worm wheel 52 when viewed from the first end side of the shaft 51 to which the steering shaft 21 is connected. The center line L1 is a straight line that passes through the center of the worm wheel 52 and is orthogonal to the center line L2 of the worm 53 when viewed from the axial direction of the worm wheel 52. That is, the second end of the worm 53 is located on the left side of the center of the worm wheel 52 in the axial direction of the worm 53. The urging mechanism 80 applies a preload F0 to the second end of the worm 53. The preload F0 is an elastic force generated by the compression coil spring 82 of the urging mechanism 80 in the direction toward the worm wheel 52.

[0080] When the worm wheel 52 rotates in the clockwise direction DR1, due to the axial component force F1, a moment M1 in the counterclockwise direction with the swing center O as the center acts on the worm 53. The moment M1 is a force that acts with the swing center O as the center to tilt the worm 53 in the direction close to the worm wheel 52. Therefore, the force that presses the tooth surfaces of the worm 53 and the worm wheel 52 against each other becomes larger, and the load torque of the speed reducer 25 increases.

[0081] When the worm wheel 52 rotates in the counterclockwise direction DL1, a clockwise moment M2 centered on the swing center O acts on the worm 53 due to the axial component force F1. The moment M2 is a force that acts to tilt the worm 53 in a direction away from the worm wheel 52 centered on the swing center O. Therefore, the force with which the tooth surfaces of the worm 53 and the worm wheel 52 are pressed against each other becomes smaller, thereby reducing the load torque of the speed reducer 25.

[0082] That is, the speed reducer 25 is configured so that the preload F0 applied by the urging mechanism 80 to the worm 53 in the steering direction in which the ball screw nut 42 descends acts greater than the preload F0 applied by the urging mechanism 80 to the worm 53 in the steering direction in which the ball screw nut 42 ascends.

[0083] Therefore, as shown in the following equation (1), the load torque T of the speed reducer 25 generated when the steering wheel 26 is turned right is dr The absolute value of the torque T of the reducer 25 generated when the steering wheel 26 is turned left is greater than dl The load torque is also the loss torque generated when the steering wheel 26 is steered.

[0084] │T dr │>│T dl │…(1)

[0085] In this way, when the load torque of the speed reducer 25 is different depending on the steering direction of the steering wheel 26, the force required by the driver to operate the steering wheel 26 may be different depending on the steering direction. In other words, there is a concern that the difference between the force required to steer the steering wheel 26 to the right and the force required to steer the steering wheel 26 to the left will become larger.

[0086] <Load Torque of the Speed ​​Reducer 25 When the Worm 53 Is Oriented in the Second Orientation>

[0087] Next, the worm 53 is set to Figure 4 The load torque of the reduction gear 25 in the case of the second orientation opposite to the first orientation shown will be examined.

[0088] like Figure 5 As shown, the second orientation is an orientation of the worm 53 in which the second end of the worm 53 is located to the right of the center line L1 of the worm wheel 52 when viewed from the first end side of the shaft 51 to which the steering shaft 21 is connected. That is, the second end of the worm 53 is located to the right of the center of the worm wheel 52 in the axial direction of the worm 53.

[0089] When the worm wheel 52 rotates in the clockwise direction DR1, due to the axial component force F1, a moment M1 in the counterclockwise direction with the swing center O as the center acts on the worm 53. The moment M1 is a force that acts with the swing center O as the center to tilt the worm 53 in the direction away from the worm wheel 52. Therefore, the force with which the tooth surfaces of the worm 53 and the worm wheel 52 are pressed against each other becomes smaller, and the load torque of the speed reducer 25 is reduced.

[0090] When the worm wheel 52 rotates in the counterclockwise direction DL1, a clockwise moment M2 centered on the swing center O acts on the worm 53 due to the axial component force F1. The moment M2 is a force that acts in a manner to tilt the worm 53 toward the worm wheel 52 centered on the swing center O. Therefore, the force that presses the tooth surfaces of the worm 53 and the worm wheel 52 against each other becomes larger, thereby increasing the load torque of the speed reducer 25.

[0091] That is, the speed reducer 25 is configured so that the preload F0 applied by the urging mechanism 80 to the worm 53 in the steering direction in which the ball screw nut 42 descends acts greater than the preload F0 applied by the urging mechanism 80 to the worm 53 in the steering direction in which the ball screw nut 42 ascends.

[0092] Therefore, as shown in the following equation (2), the load torque T generated when the steering wheel 26 is turned left is dl The absolute value of the load torque T generated when the steering wheel 26 is turned right dr The absolute value of .

[0093] │T dr │<│T dl │…(2)

[0094] When the worm 53 is set in the second orientation, the load torque T generated when the steering wheel 26 is turned rightward dr The absolute value of the load torque T generated when the steering wheel 26 is turned left dl The magnitude relationship of the absolute values ​​of is opposite to the magnitude relationship when the worm 53 is set in the first orientation.

[0095] In this case, the load torque of the speed reducer 25 differs depending on the steering direction of the steering wheel 26, so the force required for the driver to operate the steering wheel 26 may differ depending on the steering direction. That is, there is a concern that the difference between the force required to steer the steering wheel 26 to the right and the force required to steer the steering wheel 26 to the left may become larger.

[0096] Therefore, in this embodiment, the combination of the orientation of the worm 53 and the type of the ball screw shaft 41 is determined by focusing on the fact that the load torque of the ball screw mechanism 48 also differs depending on the steering direction of the steering wheel 26. There are two modes of the combination.

[0097] <First Group>

[0098] As shown in Table 1, the orientation of the worm 53 is set to Figure 4 In the first direction shown, use Figure 7 The ball screw shaft 41 shown is a left-hand threaded type.

[0099] [Table 1]

[0100]

[0101] In the case of the first combination shown in Table 1, when the steering wheel 26 is turned right, the load torque of the reducer 25 increases, while the load torque of the ball screw shaft 41 decreases. In addition, when the steering wheel 26 is turned left, the load torque of the reducer 25 decreases, while the load torque of the ball screw shaft 41 increases. That is, the increase and decrease characteristics of the load torque generated when the steering wheel 26 is turned are opposite to each other between the reducer 25 and the ball screw mechanism 48. Therefore, with respect to the total load torque generated by the reducer 25 and the ball screw mechanism 48, the difference between when the steering wheel 26 is turned right and when the steering wheel 26 is turned left becomes smaller.

[0102] <Second Group>

[0103] As shown in Table 2, the orientation of the worm 53 is set to Figure 5 In the case of the second orientation shown, use Figure 6 The ball screw shaft 41 shown is a right-hand threaded type.

[0104] [Table 2]

[0105]

[0106] In the case of the second combination shown in Table 2, when the steering wheel 26 is turned right, the load torque of the speed reducer 25 decreases, while the load torque of the ball screw shaft 41 increases. In addition, when the steering wheel 26 is turned left, the load torque of the speed reducer 25 increases, while the load torque of the ball screw shaft 41 decreases. That is, the increase and decrease characteristics of the load torque generated when the steering wheel 26 is turned are opposite to each other between the speed reducer 25 and the ball screw mechanism 48. Therefore, with respect to the total load torque generated by the speed reducer 25 and the ball screw mechanism 48, the difference between when the steering wheel 26 is turned right and when the steering wheel 26 is turned left becomes smaller.

[0107] <Effects of implementation>

[0108] This embodiment has the following effects.

[0109] (1) The speed reducer 25 and the ball screw mechanism 48 are configured so that the increase and decrease characteristics of the load torque generated when the steering wheel 26 is steered are opposite to each other between the speed reducer 25 and the ball screw mechanism 48. Therefore, the difference between the total load torque generated by the speed reducer 25 and the ball screw mechanism 48 when the steering wheel 26 is steered to the right and when the steering wheel 26 is steered to the left becomes smaller. Therefore, the difference between the force required for steering the steering wheel 26 to the right and the force required for steering the steering wheel 26 to the left can be reduced.

[0110] (2) The orientation of the worm 53 is set to Figure 4 In the first direction shown, use Figure 7 The left-handed ball screw shaft 41 is shown. In this way, the increase and decrease characteristics of the load torque of the speed reducer 25 and the increase and decrease characteristics of the load torque of the ball screw mechanism 48 can be opposite to each other when the steering wheel 26 is turned right and when the steering wheel 26 is turned left.

[0111] (3) The orientation of the worm 53 is set to Figure 5 In the case of the second orientation shown, use Figure 6 The right-handed threaded ball screw shaft 41 is shown. In this way, the increase and decrease characteristics of the load torque of the speed reducer 25 and the increase and decrease characteristics of the load torque of the ball screw mechanism 48 can be opposite to each other when the steering wheel 26 is turned right and when the steering wheel 26 is turned left.

[0112] (4) Depending on the specifications of the steering device 20, the first combination shown in Table 1 and the second combination shown in Table 2 can be selected as the combination of the orientation of the worm 53 and the type of the ball screw shaft 41. This increases the product variety of the steering device 20.

[0113] <Other embodiments>

[0114] This embodiment may be modified and implemented as follows.

[0115] The posture of the steering gear box 22 when mounted on the vehicle 10 may be changed as appropriate as long as gravity acts on the moving direction of the ball screw nut 42 .

[0116] The motor 23 may be controlled as follows to further reduce the left-right difference in the load torque relative to the steering direction generated when the steering wheel 26 is steered, and ideally, to 0 (zero). That is, the motor 23 is controlled in such a manner that the torque applied to the ball screw mechanism 48 in the steering direction in which the ball screw nut 42 is lowered is smaller than the torque applied to the ball screw mechanism 48 in the steering direction in which the ball screw nut 42 is raised. The motor 23 is controlled by, for example, a control device of the steering device 20.

[0117] Thus, the left-right difference of the load torque generated in the ball screw mechanism 48 when the steering wheel 26 is turned is smaller. The left-right difference is the difference between the load torque when the steering wheel 26 is turned right and the load torque when the steering wheel 26 is turned left. Therefore, compared with the case where the increase and decrease characteristics of the load torque generated when the steering wheel 26 is turned are only configured to be opposite to each other between the speed reducer 25 and the ball screw mechanism 48, the left-right difference of the total load torque generated in the speed reducer 25 and the ball screw mechanism 48 can be further reduced.

[0118] As the speed reducer 25, a structure in which the urging mechanism 80 is omitted may also be adopted. In addition, the worm 53 may not be set to be tiltable relative to the output shaft 23A of the motor 23. In this case, the left-right difference in load torque generated in the speed reducer 25 when the steering wheel 26 is turned can be basically ignored. Therefore, only the left-right difference in load torque generated in the ball screw mechanism 48 when the steering wheel 26 is turned can be focused on.

[0119] Therefore, the motor 23 may be controlled as follows so as to reduce the left-right difference in the load torque generated in the ball screw mechanism 48 relative to the steering direction when the steering wheel 26 is steered, and ideally, to 0 (zero). That is, the motor 23 is controlled in such a manner that the torque applied to the ball screw mechanism 48 in the steering direction in which the ball screw nut 42 is descending is less than the torque applied to the ball screw mechanism 48 in the steering direction in which the ball screw nut 42 is ascending. In this way, the left-right difference in the load torque generated in the ball screw mechanism 48 when the steering wheel 26 is steered can be reduced, and ideally to 0. The increase and decrease characteristics of the load torque of the ball screw mechanism 48 are generated by the control of the motor 23.

[0120] In this case, as a combination of the orientation of the worm 53 and the type of the ball screw shaft 41 (left-handed thread type and right-handed thread type), a combination different from the combination shown in the previous Tables 1 and 2 can be adopted. For example, when the orientation of the worm 53 is the first direction, a right-handed threaded ball screw shaft 41 can also be adopted. In addition, when the orientation of the worm 53 is the second direction, a left-handed threaded ball screw shaft 41 can also be adopted.

[0121] As a combination of the orientation of the worm 53 and the type of the ball screw shaft 41 (left-handed thread type and right-handed thread type), the combination shown in the previous Table 1 and Table 2 may not be adopted. In this case, the motor 23 may be controlled as follows to reduce the left-right difference in the load torque for the steering direction generated when the steering wheel 26 is steered, and ideally become 0 (zero). That is, the motor 23 is controlled in such a way that the torque applied to the ball screw mechanism 48 in the steering direction in which the ball screw nut 42 descends is less than the torque applied to the ball screw mechanism 48 in the steering direction in which the ball screw nut 42 rises. In this way, the left-right difference in the load torque generated in the ball screw mechanism 48 when the steering wheel 26 is steered can be reduced, and ideally become 0. The increase and decrease characteristics of the load torque of the ball screw mechanism 48 are generated by the control of the motor 23. Therefore, the left-right difference in the total load torque generated by the reducer 25 and the ball screw mechanism 48 can be reduced by the amount by which the left-right difference in the load torque generated in the ball screw mechanism 48 is reduced.

[0122] The steering device 20 may also be an electric steering type steering device. As the steering device 20, a so-called linkless structure in which the power transmission between the steering wheel 26 and the steering wheel 13 is separated may be adopted. In addition, as the steering device 20, a structure in which the power transmission between the steering wheel 26 and the steering wheel 13 can be separated by a clutch may be adopted. When the clutch is disconnected, the power transmission between the steering wheel 26 and the steering wheel 13 is disconnected. When the clutch is connected, the power transmission between the steering wheel 26 and the steering wheel 13 is connected.

Claims

1. A steering control device, characterized in that: have: The actuator includes a motor configured to generate torque corresponding to a steering operation of a steering wheel of the vehicle, and a speed reducer configured to reduce the speed of rotation of the motor; and The ball screw mechanism is configured to convert the rotation applied by the speed reducer into the rotation of the output shaft linked to the steering wheel. The speed reducer and the ball screw mechanism are configured such that increase and decrease characteristics of a load torque in a steering direction generated when the steering wheel is steered are opposite to each other.

2. The steering control device according to claim 1, characterized in that: The ball screw mechanism includes: a ball screw shaft to which rotation is imparted by the speed reducer, and the ball screw shaft extends in the vertical direction relative to the vehicle; a plurality of balls; and a ball screw nut screwed into the ball screw shaft via the balls. The reducer has: a worm having a first end portion tiltably connected to the motor and a second end portion opposite to the first end portion; a worm wheel provided to be rotatable integrally with the ball screw shaft and configured to mesh with the worm; and a force applying mechanism for applying a preload to the second end portion of the worm in a direction toward the worm wheel, The speed reduction mechanism is configured such that the preload applied by the urging mechanism to the worm is greater when the ball screw nut is in a steering direction in which the ball screw nut descends than when the ball screw nut is in a steering direction in which the ball screw nut ascends.

3. The steering control device according to claim 2, characterized in that: The increase and decrease characteristics of the load torque of the ball screw mechanism are generated by controlling the motor. The motor is controlled in such a manner that the torque applied to the ball screw mechanism in the steering direction in which the ball screw nut is descending is smaller than the torque applied to the ball screw mechanism in the steering direction in which the ball screw nut is ascending, so as to eliminate the difference in load torque in the steering direction generated when the steering wheel is steered.

4. The steering control device according to claim 1, characterized in that: The ball screw mechanism includes: a ball screw shaft to which rotation is imparted by the speed reducer, and the ball screw shaft extends in the vertical direction relative to the vehicle; a plurality of balls; and a ball screw nut screwed into the ball screw shaft via the balls. The increase and decrease characteristics of the load torque of the ball screw mechanism are generated by controlling the motor. The motor is controlled in such a manner that the torque applied to the ball screw mechanism in the steering direction in which the ball screw nut is descending is smaller than the torque applied to the ball screw mechanism in the steering direction in which the ball screw nut is ascending, so as to eliminate the difference in load torque relative to the steering direction generated when the steering wheel is steered.

5. The steering control device according to claim 4, characterized in that: The reducer has: a worm having a first end portion tiltably connected to the motor and a second end portion opposite to the first end portion; a worm wheel provided to be rotatable integrally with the ball screw shaft and configured to mesh with the worm; and The urging mechanism applies a preload to the second end portion of the worm in a direction toward the worm wheel.

6. The steering control device according to claim 1, characterized in that: The ball screw mechanism includes: a ball screw shaft to which rotation is imparted by the speed reducer, and the ball screw shaft extends in the vertical direction relative to the vehicle; a plurality of balls; and a ball screw nut screwed into the ball screw shaft via the balls. The reducer has: a worm having a first end portion tiltably connected to the motor and a second end portion opposite to the first end portion; a worm wheel connected to the end of the ball screw shaft in a manner that allows integral rotation therewith and configured to mesh with the worm; as well as a force applying mechanism for applying a preload to the second end portion of the worm in a direction toward the worm wheel, The second end of the worm is located to the left of the center of the worm wheel in the axial direction of the worm when viewed from the end side of the ball screw shaft connected to the worm wheel, and the ball screw shaft is a left-handed thread type having a spiral thread groove wound in a counterclockwise direction when viewed from the end side of the ball screw shaft connected to the worm wheel, or, The second end of the worm is located to the right of the center of the worm wheel in the axial direction of the worm when viewed from the end side of the ball screw shaft connected to the worm wheel. The ball screw shaft is a right-hand thread type and has a spiral thread groove wound in a clockwise direction when viewed from the end side of the ball screw shaft connected to the worm wheel.

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