Steer-by-wire unit

Abstract

A first unit (151A) for turning wheels (7) of a vehicle includes: a first turning motor (31); a first pinion shaft (33) configured to allow a driving force from the first turning motor (31) to be input; and a first rack shaft (41) having a first rack gear (41a) meshing with the first pinion shaft (33) and a tip portion (41b) connected to the wheel (7) of the vehicle, and configured to turn the wheel (7). In the first unit (151A), the first rack shaft (41) has a terminal portion (41c) that is not connected to the wheel (7) of the vehicle on a side opposite to the tip portion (41b).

Description

STEER-BY-WIRE UNIT

[0001] The present invention relates to a steer-by-wire unit.

[0002] JP2010-030368A (see, for example, FIGS. 4 to 7) discloses a steering device for a vehicle having a steer-by-wire configuration. In the device, left and right tie rods coupled to both ends of a rack shaft via ball joints are coupled to knuckle arms of turning wheels.

[0003] In the steer-by-wire configuration having a structure in which both ends of the rack shaft are connected to both the left and right wheels, there is a concern that interference with vehicle components may occur near a center of the rack shaft (near center of vehicle in left-right direction) or a clearance may be insufficient, and the vehicle mountability is poor.

[0004] The present invention has been made in view of such a problem, and an object thereof is to improve the vehicle mountability.

[0005] According to one aspect of the present invention, a steer-by-wire unit for turning wheels of a vehicle, the steer-by-wire unit includes: a motor; a pinion shaft configured to allow a driving force from the motor to be input; and a rack shaft having a rack gear meshing with the pinion shaft and a tip portion connected to the wheel of the vehicle, the rack shaft being configured to turn the wheel. The rack shaft has a terminal portion that is not connected to the wheel of the vehicle on a side opposite to the tip portion.

[0006] FIG. 1 is a schematic configuration diagram of a steer-by-wire device according to an embodiment of the present invention.FIG. 2 is a cross-sectional view of a main portion of a steer-by-wire unit according to the embodiment of the present invention.FIG. 3 is a cross-sectional view of a main portion of a first modification.FIG. 4 is a cross-sectional view of a main portion of a second modification.

[0007] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0008] A steer-by-wire device 100 according to an embodiment of the present invention will be described with reference to FIG. 1. The steer-by-wire device 100 can perform a steer-by-wire control of turning wheels 7 according to an operation state of a steering wheel 1 by a driver, and includes the steering wheel 1 by which a steering operation is performed by the driver, a steering shaft 2 that rotates in accordance with the steering operation by the driver, a first rack shaft 41 and a second rack shaft 42 that turn the wheels 7, a first turning motor 31 that applies a turning force to the first rack shaft 41, a second turning motor 36 that applies a turning force to the second rack shaft 42, and a reaction force motor 51 that applies a steering reaction force to the steering shaft 2.

[0009] The steer-by-wire device 100 is mounted on a vehicle such as an EV truck, and includes a first pinion shaft 33 configured to allow a driving force from the first turning motor 31 to be input and a second pinion shaft 38 configured to allow a driving force from the second turning motor 36 to be input.

[0010] The driving force of the first turning motor 31 is transmitted to the first pinion shaft 33 after a rotation speed is reduced by a first reduction mechanism 32. The first reduction mechanism 32 includes a first worm shaft 32a coupled to an output shaft 31a of the first turning motor 31, and a first worm wheel 32b that meshes with the first worm shaft 32a and is coupled to the first pinion shaft 33. The first pinion shaft 33 has a first pinion gear 33a that meshes with a first rack gear 41a formed on the first rack shaft 41, and meshes with the first rack shaft 41.

[0011] The driving force of the second turning motor 36 is transmitted to the second pinion shaft 38 after the rotation speed is reduced by a second reduction mechanism 37. The second reduction mechanism 37 includes a second worm shaft 37a coupled to an output shaft 36a of the second turning motor 36, and a second worm wheel 37b that meshes with the second worm shaft 37a and is coupled to the second pinion shaft 38. The second pinion shaft 38 has a second pinion gear 38a that meshes with a second rack gear 42a formed on the second rack shaft 42, and meshes with the second rack shaft 42.

[0012] When the first turning motor 31 and the second turning motor 36 are driven in accordance with the steering operation by the driver, a turning force for turning the wheels 7 is applied to the first rack shaft 41 and the second rack shaft 42 through the first pinion shaft 33 and the second pinion shaft 38. In this case, rotation of each of the pinion shafts 33 and 38 is converted into a linear motion by each of the pinion gears 33a and 38a and each of the rack gears 41a and 42a, and the wheel 7 is turned by the linear motion of each of the rack shafts 41 and 42 via a tie rod 91 for transmitting the steering operation to the wheel 7 and a knuckle arm 6 that rotatably holds the wheel 7.

[0013] A steering reaction force is applied by the reaction force motor 51 in response to the steering operation by the driver. A driving force of the reaction force motor 51 is input to the steering shaft 2 after the rotation speed is reduced by a third reduction mechanism 52. The third reduction mechanism 52 includes a worm shaft 52a coupled to an output shaft 51a of the reaction force motor 51, and a worm wheel 52b that meshes with the worm shaft 52a and is coupled to the steering shaft 2. When the reaction force motor 51 is driven, the steering reaction force is applied to the steering shaft 2, whereby a pseudo weight of a handle is applied.

[0014] The steer-by-wire device 100 further includes a first turning controller 30 that controls driving of the first turning motor 31, a second turning controller 35 that controls driving of the second turning motor 36, and a reaction force controller 50 that controls driving of the reaction force motor 51. The first turning controller 30, the second turning controller 35, and the reaction force controller 50 are communicably connected to each other, and state information of the vehicle such as a vehicle speed is input to the controllers 30, 35, and 50 in addition to a detection signal of a steering angle sensor 21 that detects a steering angle that is a rotation angle of the steering wheel 1. The steering angle sensor 21 is provided on the steering shaft 2, includes, although not illustrated, a center gear that rotates integrally with the steering shaft 2 and two outer gears that mesh with the center gear, and calculates a rotation angle of the center gear, that is, a rotation angle of the steering shaft 2 based on a change in magnetic flux accompanying rotation of the two outer gears.

[0015] In the steer-by-wire control, the turning controllers 30 and 35 control the turning motors 31 and 36 according to the operation state of the steering wheel 1 to turn the wheels 7. The turning controllers 30 and 35 set a target turning angle based on a detection result of the steering angle sensor 21 and the vehicle speed, and control the turning motors 31 and 36 such that a turning angle of the wheels 7 matches the target turning angle. In addition, in the steer-by-wire control, the reaction force controller 50 controls the reaction force motor 51 according to a turning state of the wheels 7 to apply a steering reaction force to the steering shaft 2. The reaction force controller 50 sets a target steering reaction force corresponding to a reaction force received from a road surface by the steering operation, and controls the reaction force motor 51 such that the steering reaction force applied to the steering shaft 2 matches the target steering reaction force.

[0016] The first turning motor 31, the first reduction mechanism 32, the first pinion shaft 33, and the first rack shaft 41 constitute a first unit 151A serving as a steer-by-wire unit that turns the wheels 7. Similarly, the second turning motor 36, the second reduction mechanism 37, the second pinion shaft 38, and the second rack shaft 42 constitute a second unit 152 serving as a steer-by-wire unit that turns the wheels 7. Both the first unit 151A and the second unit 152 constitute a steer-by-wire unit capable of independently turning each wheel 7 (that is, capable of turning a single wheel).

[0017] The first unit 151A and the second unit 152 are required to avoid interference with vehicle components and ensure a clearance. Therefore, the unit 151A and the unit 152 are further implemented as described below.

[0018] As illustrated in FIGS. 1 and 2, the first unit 151A further includes a first rack housing 61 accommodating the first rack shaft 41, and the second unit 152 further includes a second rack housing 62 accommodating the second rack shaft 42 (see FIG. 1). A configuration of the first unit 151A illustrated in FIG. 2 is similarly applied to the second unit 152. Therefore, hereinafter, the first unit 151A will be mainly described as an example.

[0019] As illustrated in FIG. 2, the first rack housing 61 is formed in a tubular shape. The first rack housing 61 has a first accommodation hole 61a in which the first rack shaft 41 is accommodated, a second accommodation hole 61b that is formed in a direction intersecting the first accommodation hole 61a and in which the first pinion gear 33a is accommodated, and a third accommodation hole 61c that is formed on a side opposite to a meshing portion between the first pinion gear 33a and the first rack gear 41a across an axis O1 of the first rack shaft 41 and in which a pressing mechanism 81 that presses the first rack shaft 41 toward the first pinion gear 33a is accommodated.

[0020] The pressing mechanism 81 is used to adjust a backlash between the first rack gear 41a and the first pinion gear 33a. The adjustment of the backlash reduces a rattling noise when the first rack shaft 41 reciprocates according to rotation of the first pinion gear 33a.

[0021] On one end side (left side in FIG. 2) of the first rack housing 61, a bushing 82 connected to the first accommodation hole 61a from an outer side of the vehicle in a left-right direction (left side in FIG. 2) is provided, and on the other end side (right side in FIG. 2) of the first rack housing 61, a bushing 83 connected to the first accommodation hole 61a from an inner side of the vehicle in the left-right direction (right side in FIG. 2) is provided. The bushings 82 and 83 slidably support the first rack shaft 41.

[0022] As illustrated in FIGS. 1 and 2, the first rack shaft 41 has a tip portion 41b connected to the wheel 7 (that is, tip portion 41b serving as end portion connected to wheel 7), and the first rack shaft 41 is configured to turn the wheel 7. Similarly, the second rack shaft 42 has a tip portion 42b connected to the wheel 7, and the second rack shaft 42 is configured to turn the wheel 7 (see FIG. 1). Each of the tip portions 41b and 42b faces a side of wheel 7 turned by the rack shaft 41 or 42 (corresponding rack shaft) in the left-right direction of the vehicle. Each of the tip portions 41b and 42b is connected to the wheel 7 via the tie rod 91.

[0023] As illustrated in FIGS. 1 and 2, one end portion of the tie rod 91 is connected to the tip portion 41b via a ball joint 92. The other end portion of the tie rod 91 is connected to the knuckle arm 6, and the tip portion 41b is connected to the wheel 7 via the ball joint 92, the tie rod 91, and the knuckle arm 6.

[0024] The tip portion 41b of the first rack shaft 41 is connected to a wheel 71 serving as one of left and right wheels of the vehicle. Similarly, the tip portion 42b of the second rack shaft 42 is connected to a wheel 72 serving as one of the wheels (see FIG. 1). The wheels 71 and 72 may be front wheels or rear wheels of the vehicle. The first rack shaft 41 further has a terminal portion 41c (that is, terminal portion 41c serving as end portion not connected to wheel 7) that is not connected to the wheel 7 on a side opposite to the tip portion 41b. Similarly, the second rack shaft 42 has a terminal portion 42c that is not connected to the wheel 7 on a side opposite to the tip portion 42b (see FIG. 1). The tie rod 91 serving as a connection member to the wheel 7 is coupled to the tip portions 41b and 42b, but is not coupled to the terminal portions 41c and 42c. The units 151A and 152 further include extension shafts 45 that are provided at the terminal portions 41c and 42c and extend the rack shafts 41 and 42.

[0025] As illustrated in FIG. 2, a screw hole 41d (coupling portion) into which a fixing end portion 45a of the extension shaft 45 is screwed (coupled) is formed in the terminal portion 41c of the first rack shaft 41. The extension shaft 45 is coupled to the first rack shaft 41 by screwing the fixing end portion 45a into the screw hole 41d.

[0026] The first unit 151A further includes a stopper 46 that restricts movement of the first rack shaft 41 in an axial direction. On an outer periphery of the extension shaft 45, a convex portion 45b is provided at a position separated from the fixing end portion 45a in the axial direction, and a ring-shaped stopper 46 is provided adjacent to the convex portion 45b in a state where the fixing end portion 45a is inserted. The stopper 46 is fixed by screwing the fixing end portion 45a of the extension shaft 45 into the screw hole 41d of the first rack shaft 41 in a state of being sandwiched between an end surface of the terminal portion 41c of the first rack shaft 41 and the convex portion 45b of the extension shaft 45. The stopper 46 prevents generation of interference of the terminal portion 41c of the first rack shaft 41 with the bushing 83 due to excessively movement toward a first rack housing 61 side. The extension shaft 45 fixed to the terminal portion 41c of the first rack shaft 41 corresponds to a fixing member and constitutes a fixing member for fixing the stopper 46.

[0027] The movement of the first rack shaft 41 is restricted as follows. The movement of the first rack shaft 41 toward the inner side of the vehicle in the left-right direction (right side in FIG. 2) is restricted by the ball joint 92 coupled to the first rack shaft 41 abutting against a first restriction surface 61d formed on the one end side (left side in FIG. 2) of the first rack housing 61. The first restriction surface 61d is formed by a bottom surface of a concave portion 61e formed along the axial direction on the one end side of the first rack housing 61, and the ball joint 92 enters the concave portion 61e and abuts against the first restriction surface 61d. The bushing 82 that supports the first rack shaft 41 on the one end side of the first rack housing 61 can be provided slightly on the inner side of the vehicle in the left-right direction with respect to the first restriction surface 61d.

[0028] The movement of the first rack shaft 41 toward the outer side of the vehicle in left-right direction (left side in FIG. 2) is restricted by the stopper 46 abutting against a second restriction surface 61f serving as an end portion of the first rack housing 61 formed on the other end side (right side in FIG. 2) of the first rack housing 61. The second restriction surface 61f is formed by an end surface on the other end side of the first rack housing 61. The bushing 83 that supports the first rack shaft 41 on the other end side of the first rack housing 61 can be provided slightly on the outer side of the vehicle in left-right direction with respect to the second restriction surface 61f.

[0029] The first unit 151A further includes a first boot 95 covering the tip portion 41b of the first rack shaft 41, and a second boot 96A serving as a cover covering the terminal portion 41c of the first rack shaft 41. The first boot 95 covers the tip portion 41b of the first rack shaft 41 and covers the ball joint 92. The second boot 96A covers the terminal portion 41c of the first rack shaft 41 and covers the stopper 46.

[0030] The boots 95 and 96A are formed of resin and deform by expanding and contracting. The first boot 95 has a bellows portion 95a serving as a deformation portion that deforms in accordance with the movement of the first rack shaft 41, a base end fixing portion 95b fixed to the first rack housing 61, and a tip fixing portion 95c fixed to the tie rod 91. The second boot 96A has a bellows portion 96aA serving as a deformation portion that deforms in accordance with the movement of the first rack shaft 41, a base end fixing portion 96b fixed to the first rack housing 61, and a tip fixing portion 96c fixed to the extension shaft 45.

[0031] The bellows portions 95a and 96aA have a bellows shape deformable (expandable and contractible) along the axis O1 of the first rack shaft 41, and deform by expanding and contracting along the axis O1 of the first rack shaft 41.

[0032] The bellows portion 95a of the first boot 95 is connected to the base end fixing portion 95b and the tip fixing portion 95c, and the bellows portion 96aA of the second boot 96A is connected to the base end fixing portion 96b and the tip fixing portion 96c. Therefore, in the first boot 95, an intermediate portion between the base end fixing portion 95b and the tip fixing portion 95c as a whole is formed by the bellows portion 95a, and in the second boot 96A, an intermediate portion between the base end fixing portion 96b and the tip fixing portion 96c as a whole is formed by the bellows portion 96aA.

[0033] The base end fixing portions 95b and 96b of the boots 95 and 96A are each fixed to an outer periphery of the end portion of the first rack housing 61 by a band 97. The base end fixing portion 95b of the first boot 95 is fixed to the first rack housing 61 by being pressed by the band 97 against an outer peripheral groove provided on an outer periphery of one end portion 61g (end portion on left side in FIG. 2) of the first rack housing 61, and the base end fixing portion 96b of the second boot 96A is fixed to the first rack housing 61 by being pressed by the band 97 against an outer peripheral groove provided on an outer periphery of the other end portion 61h (end portion on right side in FIG. 2) of the first rack housing 61.

[0034] The tip fixing portion 95c of the first boot 95 is fixed to the outer periphery of the tie rod 91 by a clip 98. The tip fixing portion 95c of the first boot 95 is fixed to the tie rod 91 by being pressed against an outer periphery of the tie rod 91 by the clip 98. The tip fixing portion 96c of the second boot 96A is fixed to an outer periphery of the extension shaft 45 by the clip 98. The tip fixing portion 96c of the second boot 96A is fixed to the extension shaft 45 by being pressed against an outer periphery of a free end portion 45c of the extension shaft 45 on a side opposite to the fixing end portion 45a by the clip 98. Outer peripheral grooves against which the tip fixing portions 95c and 96c are pressed by the clip 98 can be provided on the outer peripheries of the tie rod 91 and the extension shaft 45.

[0035] The boots 95 and 96A prevent water and foreign matter from entering the first rack housing 61. In addition, the first boot 95 maintains the lubricity of the ball joint 92 and prevents foreign matter or the like from being caught in the ball joint 92.

[0036] The terminal portion 41c of the first rack shaft 41 on a side opposite to the tip portion 41b is not connected to the wheel 7 (see FIG. 1). Therefore, for example, it is conceivable to provide a bottomed cylindrical boot instead of the second boot 96A and close a boot tip thereof.

[0037] However, in this case, when the first rack shaft 41 moves in a withdrawal direction from the inside of the bottomed cylindrical boot (left direction in FIG. 2), a volume in the boot is increased by an amount of the first rack shaft 41 withdrawing from the inside of the boot, so that a negative pressure is generated, and as a result, the boot may be concaved. When the boot is concaved, interference with the stopper 46 may occur, and the durability of the boot may be reduced due to unintended deformation.

[0038] In addition, in this case, when the first rack shaft 41 moves in an entering direction toward the inside of the bottomed cylindrical boot (right direction in FIG. 2), the volume in the boot is reduced by an amount of the first rack shaft 41 entering toward the inside of the boot, so that an internal pressure of the boot is increased, and as a result, the boot may expand. When the boot expands, the boot may interfere with a vehicle component, and the durability of the boot may be reduced due to unintended deformation.

[0039] In the first unit 151A, the first rack shaft 41 is extended using the extension shaft 45, and the tip fixing portion 96c of the second boot 96A is fixed to the outer periphery of the free end portion 45c of the extension shaft 45.

[0040] Accordingly, when the first rack shaft 41 moves in the withdrawal direction (left direction in FIG. 2), the bellows portion 96aA is shortened to reduce a volume in the second boot 96A, so that an increase in volume that occurs when the bottomed cylindrical boot is used is absorbed (suppressed). Therefore, generation of a negative pressure can be suppressed, and the second boot 96A can be prevented from being concaved. In addition, when the first rack shaft 41 moves in the entering direction (right direction in FIG. 2), the bellows portion 96aA extends to increase the volume in the second boot 96A, so that a reduction in volume that occurs when the bottomed cylindrical boot is used is absorbed. Therefore, an increase in internal pressure can be suppressed, and the second boot 96A can be prevented from expanding.

[0041] As described above, in the first unit 151A, since the volume in the second boot 96A can be adjusted by the bellows portion 96aA that deforms in accordance with the movement of the first rack shaft 41, it is possible to suppress the second boot 96A from interfering with other components inside and outside the second boot 96A due to the second boot 96A being concaved or expanding. In addition, in the first unit 151A, by providing the extension shaft 45, the existing first rack shaft 41 can be used, and the boots 95 and 96A can be implemented similarly to each other.

[0042] As illustrated in FIG. 1, the first unit 151A does not need to transmit power between the steering wheel 1 and the wheel 7. Therefore, in combination with relaxation of a limitation on layout, a space can be formed near a center of the vehicle in the left-right direction by disposing the terminal portion 41c of the first rack shaft 41 near the center. As a result, interference with the vehicle component near the center is less likely to occur and a sufficient clearance can be ensured, and the vehicle mountability can be improved.

[0043] The first unit 151A has a structure in which the tip portion 41b of the first rack shaft 41 is connected to the wheel 71 serving as one of left and right wheels. Therefore, it is possible to suppress deterioration of the vehicle mountability due to a connection mechanism such as a complicated link mechanism that connects the respective wheels 7 (that is, left and right wheels) via the first rack shaft 41.

[0044] The first unit 151A may be modified as follows.

[0045] (First Modification) FIG. 3 is a cross-sectional view of a main portion of a first unit 151B which is a first modification of the first unit 151A. The first unit 151B includes a second boot 96B instead of the second boot 96A (see FIG. 2). The same configuration can be applied to the second unit 152 (see FIG. 1).

[0046] The second boot 96B covers the terminal portion 41c of the first rack shaft 41, and has a bellows portion 96aB that deforms in accordance with the movement of the first rack shaft 41 and a strength portion 96d that is less likely to deform (expand and contract) than the bellows portion 96aB. The second boot 96B covers the terminal portion 41c of the first rack shaft 41 and covers the stopper 46.

[0047] The bellows portion 96aB has a bellows shape deformable (expandable and contractible) along the axis O1 of the first rack shaft 41, and deforms by expanding and contracting along the axis O1 of the first rack shaft 41. The strength portion 96d has a cylindrical shape that is less likely to deform (expand and contract) along the axis O1 of the first rack shaft 41 than the bellows portion 96aB.

[0048] Since the second boot 96B has the bellows portion 96aB and the strength portion 96d, the strength of the second boot 96B can be increased by the strength portion 96d while minimizing the bellows portion 96aB as necessary. Therefore, it is possible to achieve both the followability of the second boot 96B to the first rack shaft 41 that moves and the strength of the second boot 96B.

[0049] The second boot 96B further has a bottom portion 96e at a tip thereof. Similarly to the above-described second boot 96A (see FIG. 2), the second boot 96B is fixed to an outer periphery of the other end portion 61h of the first rack housing 61 by the base end fixing portion 96b, and the tip of the second boot 96B is closed by the bottom portion 96e. Therefore, the second boot 96B does not have the tip fixing portion 96c (see FIG. 2), and the bottom portion 96e is a free end of the second boot 96B.

[0050] The bellows portion 96aB is provided on a tip side (right side in FIG. 3) of the second boot 96B with respect to the strength portion 96d. The base end fixing portion 96b is connected to the strength portion 96d from a base end side (left side in FIG. 3) of the second boot 96B, and the strength portion 96d is connected to the bellows portion 96aB from the base end side of the second boot 96B. The bottom portion 96e is connected to the bellows portion 96aB from the tip side of the second boot 96B. Therefore, the bellows portion 96aB is provided in a part of an intermediate portion between the base end fixing portion 96b and the bottom portion 96e, and the strength portion 96d is provided in the remaining part of the intermediate portion between the base end fixing portion 96b and the bottom portion 96e.

[0051] In the first unit 151B, when the first rack shaft 41 moves in a withdrawal direction (left side in FIG. 3) from the inside of the second boot 96B and a volume in the second boot 96B is increased, the second boot 96B contracts to absorb (suppress) a volume change. In addition, when the first rack shaft 41 moves in an entering direction (right side in FIG. 3) toward the inside of the second boot 96B and the volume in the second boot 96B is reduced, the second boot 96B expands to absorb (suppress) the volume change. The extension shaft 45 may cause the second boot 96B to extend by moving in the entering direction while abutting against the bottom portion 96e.

[0052] The second boot 96B has a structure in which the strength portion 96d is fixed to the first rack housing 61 via the base end fixing portion 96b with the bottom portion 96e as a free end, and thus is supported by the first rack housing 61 in a cantilever manner. By providing the strength portion 96d on the base end side (left side in FIG. 3) of the second boot 96B with respect to the bellows portion 96aB, hanging down of the second boot 96B due to gravity is less likely to occur as compared to a case where the bellows portion 96aB is provided on the base end side of the second boot 96B with respect to the strength portion 96d. That is, by fixing the strength portion 96d to the first rack housing 61 without using the bellows portion 96aB, the hanging down of the second boot 96B due to gravity is suppressed.

[0053] Accordingly, the second boot 96B can maintain a self-standing posture, so that it is not necessary to provide the tip fixing portion 96c (see FIG. 2) in order to suppress the hanging down. Therefore, since the tip fixing portion 96c is unnecessary, the first unit 151A can be made compact in the axial direction accordingly.

[0054] The second boot 96B having the bellows portion 96aB and having the bottom portion 96e on the tip side as a free end may hang down to some extent due to gravity. On the other hand, a second boot 96B formed of resin is advantageous in that contact with the stopper 46 can be allowed to some extent by, for example, smoothing a corner portion of the stopper 46 or using a resin material resistant to wear or the like.

[0055] The contact of the second boot 96B with the stopper 46 due to the hanging down of the second boot 96B may be avoided, for example, by setting a length of the strength portion 96d to a length by which the stopper 46 is accommodated in the strength portion 96d or adjusting a diameter of the stopper 46, regardless of a position of the first rack shaft 41.

[0056] (Second Modification) FIG. 4 is a cross-sectional view of a main portion of a first unit 151C which is a second modification of the first unit 151A. The first unit 151C includes a second boot 96C instead of the second boot 96A (see FIG. 2). The same configuration can be applied to the second unit 152 (see FIG. 1).

[0057] The second boot 96C has the base end fixing portion 96b, a strength portion 96dC that is less likely to deform (expand and contract) than the bellows portion 96aA (see FIG. 2), and a bottom portion 96eC provided at a tip of the second boot 96C.

[0058] The second boot 96C does not have the bellows portion 96aA (see FIG. 2), and the strength portion 96dC is formed in a cylindrical shape that is less likely to deform (expand and contract) along the axis O1 of the first rack shaft 41 than the bellows portion 96aA. In addition, the second boot 96C does not have the tip fixing portion 96c (see FIG. 2), and the tip of the second boot 96C is closed by the bottom portion 96eC. The bottom portion 96eC is provided at a position where a fixing piece 99 serving as a fixing member that is screwed into the screw hole 41d and moves together with the first rack shaft 41 does not interfere. The stopper 46 is fixed by the fixing piece 99 in a state of being sandwiched between the fixing piece 99 and the terminal portion 41c of the first rack shaft 41.

[0059] In the first unit 151C, since the second boots 96A, 96B, and 96C need not be fixed by the clip 98 at the terminal portion 41c and beyond the terminal portion 41c, the clip 98 can be eliminated for simplification, and the first unit 151C can be made compact in the axial direction of the first rack shaft 41.

[0060] In the first unit 151C, for example, by providing a vent filter capable of suppressing an internal pressure fluctuation of the second boot 96C, deformation of the second boot 96C due to a volume change in the second boot 96C can be suppressed. On the other hand, it can be said that the above-described unit 151A and unit 151B (see FIGS. 2 and 3) are more advantageous as compared to the first unit 151C in that internal pressure fluctuations of the second boots 96A and 96B can be suppressed by a vent filter or the like.

[0061] (Other Modifications) The second boots 96A and 96B may be formed of rubber. The same applies to the first boot 95.

[0062] The extension shaft 45 and the stopper 46 may be formed integrally with the first rack shaft 41. In this case, the terminal portion 41c of the first rack shaft 41 is formed by the free end portion 45c of the extension shaft 45. In addition, the extension shaft 45 and the stopper 46 may be integrally formed with each other.

[0063] Instead of the bellows portions 96aA and 96aB, a deformation portion having another shape that is deformable (expandable and contractible) along the axis O1 of the first rack shaft 41 may be applied. As the another shape, for example, miura-ori or the like can be used. The same applies to the bellows portion 95a.

[0064] The strength portion 96d is not limited to the cylindrical shape, and may have, for example, a tubular shape formed in a wavy shape along a circumferential direction, a tubular shape provided with a rib disposed along the axis O1 of the first rack shaft 41, or the like.

[0065] The second boot 96B illustrated in FIG. 4 may be formed to be fixed by the clip 98 similarly to the tip fixing portion 96c of the second boot 96A illustrated in FIG. 2 without using the bottom portion 96e as a free end.

[0066] Hereinafter, configurations, operations, and effects of the embodiment of the present invention will be collectively described.

[0067] The first units 151A, 151B, and 151C serving as the steer-by-wire unit that turns the wheels 7 of the vehicle include: the turning motors 31 and 36; the pinion shaft 33 and 38 configured to allow the driving force from the turning motor 31 and 36 to be input; and the rack shaft 41 and 42 having the rack gears 41a and 42a meshing with the pinion shaft 33 and 38 and the tip portions 41b and 42b connected to the wheels 7 of the vehicle, and turn the wheels 7. The rack shaft 41 and 42 include the terminal portions 41c and 42c not connected to the wheels 7 of the vehicle on the side opposite to the tip portions 41b and 42b. The second unit 152 is formed similarly to the first unit 151A.

[0068] According to the configuration, by adopting a steer-by-wire system, in combination with relaxation of a limitation on layout, a space can be formed near the center of the vehicle in the left-right direction by disposing the terminal portions 41c and 42c near the center. Therefore, interference with the vehicle component near the center is less likely to occur and a sufficient clearance can be ensured, and the vehicle mountability can be improved.

[0069] The rack shafts 41 and 42 are connected to the wheels 71 and 72 serving as one of the left and right wheels of the vehicle.

[0070] According to the configuration, since the rack shafts 41 and 42 and the wheels 71 and 72 serving as one of the left and right wheels are connected to each other, it is possible to suppress deterioration of the vehicle mountability due to a complicated connection mechanism such as a link mechanism that connects the respective wheels 7 serving as both the left and right wheels via the rack shaft 41 and 42.

[0071] The first units 151A, 151B, and 151C include the second boots 96A, 96B, and 96C covering the terminal portions 41c and 42c of the rack shafts 41 and 42. The second unit 152 is formed similarly to the first unit 151A.

[0072] According to the configuration, since the second boots 96A, 96B, and 96C can be fixed or not fixed by the clip 98 at the terminal portion 41c or beyond the terminal portion 41c, the clip 98 can be used to fix and support the second boot 96A as in the second boot 96A, or the clip 98 can be eliminated for simplification as in the second boots 96B and 96C.

[0073] In the first units 151A and 151B, the second boots 96A and 96B have the bellows portions 96aA and 96aB serving as deformation portions configured to deform in accordance with the rack shafts 41 and 42. The second unit 152 is formed similarly to the first unit 151A.

[0074] According to the configuration, since the volumes in the second boots 96A and 96B can be adjusted by the bellows portions 96aA and 96aB configured to deform in accordance with the rack shafts 41 and 42, it is possible to suppress interference with other components inside and outside the second boots 96A and 96B due to the second boots 96A and 96B being concaved or expanding.

[0075] The first unit 151B has the second boot 96B covering the terminal portion 41c of the first rack shaft 41, and the second boot 96B includes the bellows portion 96aB serving as a deformation portion configured to deform in accordance with the movement of the first rack shaft 41, and the strength portion 96d that is less likely to deform as compared to the bellows portion 96aB. The second unit 152 can be formed in the same manner.

[0076] According to the configuration, since the strength of the second boot 96B can be increased by the strength portion 96d while minimizing the bellows portion 96aB as necessary, it is possible to achieve both the followability of the second boot 96B to the first rack shaft 41 that moves and the strength of the second boot 96B.

[0077] The first units 151A, 151B, and 151C further include the first rack housing 61 accommodating the first rack shaft 41, the extension shaft 45 or the fixing piece 99 serving as a fixing member fixed to the terminal portion 41c of the first rack shaft 41, and the stopper 46 abutting against the second restriction surface 61f serving as an end portion of the first rack housing 61 to restrict the movement of the first rack shaft 41. The second unit 152 is formed similarly to the first unit 151A.

[0078] According to the configuration, it is possible to prevent generation of interference due to excessively movement of the terminal portion 41c of the first rack shaft 41 toward the first rack housing 61 side.

[0079] Embodiments of the present invention were described above, but the above embodiments are merely examples of applications of the present invention, and the technical scope of the present invention is not limited to the specific constitutions of the above embodiments.

[0080] With respect to the above description, the contents of application No. 2024-45215, with a filing date of March 21, 2024 in Japan, are incorporated herein by reference.

Claims

1. A steer-by-wire unit for turning wheels of a vehicle, the steer-by-wire unit comprising: a motor; a pinion shaft configured to allow a driving force from the motor to be input; and a rack shaft having a rack gear meshing with the pinion shaft and a tip portion connected to the wheel of the vehicle, the rack shaft being configured to turn the wheel, wherein the rack shaft has a terminal portion that is not connected to the wheel of the vehicle on a side opposite to the tip portion.

2. The steer-by-wire unit according to claim 1, wherein the rack shaft is connected to one of left and right wheels of the vehicle.

3. The steer-by-wire unit according to claim 1, further comprising: a cover covering the terminal portion of the rack shaft.

4. The steer-by-wire unit according to claim 3, wherein the cover has a deformation portion configured to deform in accordance with the movement of the rack shaft.

5. The steer-by-wire unit according to claim 1, further comprising: a cover covering the terminal portion of the rack shaft, wherein the cover has a deformation portion configured to deform in accordance with the movement of the rack shaft, and a strength portion configured to be less likely to deform compared with the deformation portion.

6. The steer-by-wire unit according to claim 1, further comprising: a housing accommodating the rack shaft; a fixing member fixed to the terminal portion of the rack shaft; and a stopper configured to abut against an end portion of the housing to restrict movement of the rack shaft.

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