Steer-by-wire unit

Abstract

To improve vehicle mountability.SOLUTION: A first unit 151A for turning a wheel 7 of a vehicle is provided with a first turning motor 31, a first pinion shaft 33 to which a driving force from the first turning motor 31 is inputted, and a first rack shaft 41 which has a first rack gear 41a engaged with the first pinion shaft 33 and a tip end 41b connected to the wheel 7 of the vehicle and which turns the wheel 7, wherein the first rack shaft 41 has a terminal end 41c not connected to the wheel 7 of the vehicle on the side opposite to the tip end 41b.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a vehicle steering device with a steer-by-wire configuration. In this device, left and right tie rods connected to both ends of a rack shaft via ball joints are connected to knuckle arms of steered wheels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-030368 (see, for example, FIGS. 4-7) Summary of the Invention [Problem to be solved by the invention]

[0004] In a steer-by-wire configuration in which both ends of the rack shaft are connected to both the left and right wheels, there is a risk of interference with vehicle components near the center of the rack shaft (near the center of the vehicle in the left-right direction) or insufficient clearance, making it difficult to install in a vehicle.

[0005] The present invention has been made in view of the above problems, and has an object to improve the mountability in a vehicle. [Means for solving the problem]

[0006] The present invention is a steer-by-wire unit that steers the wheels of a vehicle, and is characterized in that it comprises a motor, a pinion shaft to which driving force from the motor is input, and a rack shaft that has a rack gear that meshes with the pinion shaft and a tip end that is connected to the wheel of the vehicle and that steers the wheel, and the rack shaft has an end end on the opposite side to the tip end that is not connected to the wheel of the vehicle.

[0007] According to this invention, the adoption of a steer-by-wire system alleviates layout restrictions, and by locating the terminal end near the center of the vehicle in the left-right direction, space can be created near the center. This makes it possible to reduce interference with vehicle components near the center and ensure sufficient clearance, thereby improving vehicle mountability.

[0008] The present invention is also characterized in that the rack shaft is connected to one of the left and right wheels of the vehicle.

[0009] According to this invention, since the structure connects the rack shaft to one of the left and right wheels, it is possible to prevent deterioration of vehicle mountability due to complex connection mechanisms such as link mechanisms that connect the left and right wheels via the rack shaft.

[0010] The present invention is also characterized in that it further comprises a cover that covers an end portion of the rack shaft.

[0011] According to this invention, the cover can be fixed or not fixed with clips at the end or at the tip of the end, so that the cover can be supported by fixing it with clips, or the clips can be eliminated to simplify the system.

[0012] The present invention is also characterized in that the cover has a deformation portion that deforms in accordance with the movement of the rack shaft.

[0013] According to this invention, the volume inside the cover can be adjusted by the deformation portion that deforms in accordance with the moving rack shaft, so that the cover can be prevented from collapsing or expanding, thereby preventing interference with other parts inside and outside the cover.

[0014] The present invention is also characterized in that it further includes a cover that covers the end portion of the rack shaft, and the cover has a deformation portion that deforms to follow the moving rack shaft, and a strength portion that is less likely to deform than the deformation portion.

[0015] According to this invention, the deformation portion can be kept to a necessary minimum while the strength of the cover can be increased by the reinforcing portion, so that it is possible to achieve both the ability of the cover to follow the moving rack shaft and the strength of the cover.

[0016] The present invention is also characterized in that it further comprises a housing that accommodates the rack shaft, a fixing member that is fixed to the terminal end of the rack shaft, and a stopper that abuts against the end of the housing to restrict movement of the rack shaft.

[0017] According to this invention, it is possible to prevent the terminal end of the rack shaft from moving too far toward the housing and causing interference. [Effects of the Invention]

[0018] According to these inventions, the vehicle mountability can be improved. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic configuration diagram of a steer-by-wire system according to an embodiment of the present invention; [Figure 2] 1 is a cross-sectional view of a main part of a steer-by-wire unit according to an embodiment of the present invention. FIG. [Figure 3] FIG. 10 is a cross-sectional view of a main part of a first modified example. [Figure 4] FIG. 10 is a cross-sectional view of a main part of a second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] Steer-by-wire system 100 according to an embodiment of the present invention will be described with reference to Figure 1. Steer-by-wire system 100 is capable of steer-by-wire control for steering wheels 7 in accordance with the state of operation of steering wheel 1 by a driver, and includes steering wheel 1 which is steered by the driver, steering shaft 2 which rotates in accordance with the steering operation by the driver, first rack shaft 41 and second rack shaft 42 which steer wheels 7, first steering motor 31 which imparts a steering force to first rack shaft 41 and second steering motor 36 which imparts a steering force to second rack shaft 42, and reaction motor 51 which imparts a steering reaction force to steering shaft 2.

[0022] The steer-by-wire device 100 is mounted on a vehicle such as an EV truck, and includes a first pinion shaft 33 to which driving force from a first steering motor 31 is input, and a second pinion shaft 38 to which driving force from a second steering motor 36 is input.

[0023] The driving force of first steering motor 31 has its rotational speed reduced by first reduction mechanism 32 and is then transmitted to first pinion shaft 33. First reduction mechanism 32 includes first worm shaft 32a connected to output shaft 31a of first steering motor 31, and first worm wheel 32b meshing with first worm shaft 32a and connected to first pinion shaft 33. First pinion shaft 33 has first pinion gear 33a that meshes with first rack gear 41a formed on first rack shaft 41, and meshes with first rack shaft 41.

[0024] The driving force of second steering motor 36 has its rotational speed reduced by second reduction mechanism 37 and is then transmitted to second pinion shaft 38. Second reduction mechanism 37 includes second worm shaft 37a connected to output shaft 36a of second steering motor 36, and second worm wheel 37b meshing with second worm shaft 37a and connected to second pinion shaft 38. Second pinion shaft 38 has second pinion gear 38a that meshes with second rack gear 42a formed on second rack shaft 42, and meshes with second rack shaft 42.

[0025] When first steering motor 31 and second steering motor 36 are driven in response to the steering operation of the driver, a steering force for steering wheels 7 is applied to first rack shaft 41 and second rack shaft 42 through first pinion shaft 33 and second pinion shaft 38. At this time, the rotation of each pinion shaft 33, 38 is converted into linear motion by each pinion gear 33a, 38a and each rack gear 41a, 42a, and the linear motion of each rack shaft 41, 42 turns wheels 7 via tie rod 91 for transmitting the steering operation to wheels 7 and knuckle arm 6 that rotatably holds wheels 7.

[0026] A steering reaction force is applied by a reaction motor 51 in response to a steering operation by the driver. The driving force of the reaction 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 connected to an output shaft 51a of the reaction motor 51, and a worm wheel 52b that meshes with the worm shaft 52a and is connected to the steering shaft 2. When the reaction motor 51 is driven, a steering reaction force is applied to the steering shaft 2, thereby imitating the weight of the steering wheel.

[0027] Steer-by-wire system 100 further comprises first turning controller 30 that controls the drive of first turning motor 31, second turning controller 35 that controls the drive of second turning motor 36, and reaction force controller 50 that controls the drive of reaction force motor 51. First turning controller 30, second turning controller 35 and reaction force controller 50 are connected so that they can communicate with each other, and controllers 30, 35 and 50 receive as input a detection signal from steering angle sensor 21 that detects the steering angle, which is the rotation angle of steering wheel 1, as well as vehicle state information such as vehicle speed. Steering angle sensor 21 is provided on steering shaft 2 and, although not shown, includes a center gear that rotates integrally with steering shaft 2 and two outer gears that mesh with the center gear, and calculates the rotation angle of the center gear, i.e., the rotation angle of steering shaft 2, based on changes in magnetic flux that accompany the rotation of the two outer gears.

[0028] In steer-by-wire control, steering controllers 30, 35 control steering motors 31, 36 in accordance with the operating state of steering wheel 1 to steer wheels 7. Steering controllers 30, 35 set a target steering angle based on the detection result of steering angle sensor 21 and the vehicle speed, and control steering motors 31, 36 so that the steering angle of wheels 7 matches the target steering angle. Also in steer-by-wire control, reaction force controller 50 controls reaction force motor 51 in accordance with the steering state of wheels 7 to apply a steering reaction force to steering wheel 1. Reaction force controller 50 sets a target steering reaction force equivalent to the reaction force received from the road surface in response to a steering operation, and controls reaction force motor 51 so that the steering reaction force applied to steering shaft 2 matches the target steering reaction force.

[0029] First steering motor 31, first reduction gear mechanism 32, first pinion shaft 33, and first rack shaft 41 constitute first unit 151A as a steer-by-wire unit that steers wheels 7. Similarly, second steering motor 36, second reduction gear mechanism 37, second pinion shaft 38, and second rack shaft 42 constitute second unit 152 as a steer-by-wire unit that steers wheels 7. First unit 151A and second unit 152 together constitute a steer-by-wire unit that can steer each wheel 7 independently (that is, that can steer a single wheel).

[0030] It is necessary to avoid interference with vehicle components and ensure clearance between first unit 151A and second unit 152. For this reason, units 151A and 152 are configured as will be further explained below.

[0031] 1 and 2, the first unit 151A further includes a first rack housing 61 that houses the first rack shaft 41, and the second unit 152 further includes a second rack housing 62 that houses the second rack shaft 42 (see FIG. 1). Note that the configuration of the first unit 151A shown in FIG. 2 is similarly applied to the second unit 152. For this reason, the following description will mainly focus on the first unit 151A as an example.

[0032] 2, the first rack housing 61 is formed in a cylindrical shape. The first rack housing 61 has a first accommodating hole 61a that accommodates the first rack shaft 41, a second accommodating hole 61b that is formed in a direction intersecting the first accommodating hole 61a and that accommodates the first pinion gear 33a, and a third accommodating hole 61c that is formed on the opposite side of the axis O1 of the first rack shaft 41 from the meshing portion between the first pinion gear 33a and the first rack gear 41a and that accommodates the pressing mechanism 81 that presses the first rack shaft 41 toward the first pinion gear 33a.

[0033] The pressing mechanism 81 is used to adjust the backlash between the first rack gear 41a and the first pinion gear 33a. Adjusting the backlash reduces the rattle noise that occurs when the first rack shaft 41 reciprocates in response to the rotation of the first pinion gear 33a.

[0034] A bushing 82 that continues from the outer side in the left-right direction of the vehicle (left side in FIG. 2) to the first accommodating hole 61 a is provided on one end side (left side in FIG. 2) of the first rack housing 61, and a bushing 83 that continues from the inner side in the left-right direction of the vehicle (right side in FIG. 2) to the first accommodating hole 61 a is provided on the other end side (right side in FIG. 2) of the first rack housing 61. The bushings 82, 83 slidably support the first rack shaft 41.

[0035] 1 and 2, the first rack shaft 41 has a tip end 41b connected to the wheel 7 (i.e., the tip end 41b as the end portion connected to the wheel 7) and steers the wheel 7. Similarly, the second rack shaft 42 has a tip end 42b connected to the wheel 7 and steers the wheel 7 (see FIG. 1). The tip ends 41b, 42b face the wheel 7 side that the rack shafts 41, 42 (corresponding rack shaft) steer in the left-right direction of the vehicle, and are connected to the wheel 7 via a tie rod 91.

[0036] 1 and 2, one end of a tie rod 91 is connected to the tip portion 41b via a ball joint 92. The other end 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.

[0037] A tip end 41b of the first rack shaft 41 is connected to a wheel 71, which serves as one of the left and right wheels of the vehicle. Similarly, a tip end 42b of the second rack shaft 42 is connected to a wheel 72, which serves as one of the wheels (see FIG. 1). The wheels 71, 72 may be either front or rear wheels of the vehicle. The first rack shaft 41 further has a terminal end 41c, which is not connected to the wheel 7, on the opposite side from the tip end 41b (i.e., the terminal end 41c as an end not connected to the wheel 7). Similarly, the second rack shaft 42 has a terminal end 42c, which is not connected to the wheel 7, on the opposite side from the tip end 42b (see FIG. 1). A tie rod 91, which serves as a connecting member to the wheel 7, is connected to the tip ends 41b, 42b but is not connected to the terminal ends 41c, 42c. The units 151A, 152 further include extension shafts 45, which are provided at the terminal ends 41c, 42c and extend the rack shafts 41, 42.

[0038] 2, a threaded hole 41d (connecting portion) is formed in the terminal end 41c of the first rack shaft 41, into which the fixed end 45a of the extension shaft 45 is screwed (connected). The extension shaft 45 is connected to the first rack shaft 41 by screwing the fixed end 45a into the threaded hole 41d.

[0039] The first unit 151A further includes a stopper 46 that restricts axial movement of the first rack shaft 41. A protrusion 45b is provided on the outer periphery of the extension shaft 45 at a position axially spaced from the fixed end 45a. The ring-shaped stopper 46 is provided adjacent to the protrusion 45b with the fixed end 45a inserted therethrough. The stopper 46 is fixed between the end face of the terminal end 41c of the first rack shaft 41 and the protrusion 45b of the extension shaft 45, and the fixed end 45a of the extension shaft 45 is threaded into the threaded hole 41d of the first rack shaft 41. The stopper 46 prevents the terminal end 41c of the first rack shaft 41 from moving too far toward the first rack housing 61 and interfering with the bushing 83, which could cause interference. The extension shaft 45 fixed to the terminal end 41c of the first rack shaft 41 serves as a fixing member and serves as a fixing member for fixing the stopper 46.

[0040] Movement of the first rack shaft 41 is restricted as follows. Movement of the first rack shaft 41 toward the inside in the left-right direction of the vehicle (to the right in FIG. 2) is restricted when a ball joint 92 coupled to the first rack shaft 41 abuts against a first restriction surface 61d formed on one end side of the first rack housing 61 (left side in FIG. 2). The first restriction surface 61d is configured by the bottom surface of a recess 61e formed along the axial direction on one end side of the first rack housing 61, and the ball joint 92 enters the recess 61e and abuts against the first restriction surface 61d. A bushing 82 that supports the first rack shaft 41 at one end side of the first rack housing 61 can be provided slightly more inward in the left-right direction of the vehicle than the first restriction surface 61d.

[0041] Movement of the first rack shaft 41 outward in the left-right direction of the vehicle (left side in FIG. 2) is restricted by the stopper 46 coming into contact with a second restriction surface 61f serving as an end of the first rack housing 61, which is formed on the other end side (right side in FIG. 2) of the first rack housing 61. The second restriction surface 61f is configured by an end face on the other end side of the first rack housing 61. A bush 83 that supports the first rack shaft 41 on the other end side of the first rack housing 61 can be provided slightly outward in the left-right direction of the vehicle than the second restriction surface 61f.

[0042] The first unit 151A further includes a first boot 95 that covers the tip end 41b of the first rack shaft 41, and a second boot 96A that serves as a cover that covers the terminal end 41c of the first rack shaft 41. The first boot 95 covers the tip end 41b of the first rack shaft 41 and also covers the ball joint 92. The second boot 96A covers the terminal end 41c of the first rack shaft 41 and also covers the stopper 46.

[0043] The boots 95, 96A are made of resin and deform by expanding and contracting. The first boot 95 has a bellows portion 95a as a deforming portion that deforms in response to the moving first rack shaft 41, a base end fixed portion 95b fixed to the first rack housing 61, and a tip end fixed portion 95c fixed to the tie rod 91. The second boot 96A has a bellows portion 96aA as a deforming portion that deforms in response to the moving first rack shaft 41, a base end fixed portion 96b fixed to the first rack housing 61, and a tip end fixed portion 96c fixed to the extension shaft 45.

[0044] The bellows portions 95a and 96aA have a bellows shape that is deformable (expandable) along the axis O1 of the first rack shaft 41, and are deformed by expanding and contracting along the axis O1 of the first rack shaft 41.

[0045] The bellows portion 95a of the first boot 95 is connected to the base end fixing portion 95b and the tip end 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 end fixing portion 96c. Therefore, in the first boot 95, the entire intermediate portion between the base end fixing portion 95b and the tip end fixing portion 95c is formed by the bellows portion 95a, and in the second boot 96A, the entire intermediate portion between the base end fixing portion 96b and the tip end fixing portion 96c is formed by the bellows portion 96aA.

[0046] The base end fixing portions 95b, 96b of the boots 95, 96A are each fixed to the outer periphery of an 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 into an outer periphery groove provided on the outer periphery of one end 61g (the end on the 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 into an outer periphery groove provided on the outer periphery of the other end 61h (the end on the right side in FIG. 2) of the first rack housing 61.

[0047] 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 the outer periphery of the tie rod 91 by the clip 98. The tip fixing portion 96c of the second boot 96A is fixed to the 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 the outer periphery of the free end 45c of the extension shaft 45 opposite the fixed end 45a by the clip 98. The outer peripheries of the tie rod 91 and the extension shaft 45 can be provided with outer periphery grooves into which the tip fixing portions 95c, 96c are pressed by the clip 98.

[0048] Boots 95, 96A prevent water and foreign matter from entering the first rack housing 61. Furthermore, first boot 95 maintains the lubricity of ball joint 92 and prevents foreign matter from getting caught in ball joint 92.

[0049] The terminal end 41c of the first rack shaft 41 opposite to the tip end 41b is not connected to the wheel 7 (see FIG. 1). For this reason, for example, instead of the second boot 96A, it is also possible to provide a cylindrical boot with a bottom and close the tip of the boot.

[0050] In this case, however, when the first rack shaft 41 moves in the direction of retraction from the bottomed cylindrical boot (to the left in FIG. 2), the volume inside the boot increases by the amount of the first rack shaft 41 retracted from the boot, generating negative pressure, which may cause the boot to dent. If the boot dents, interference with the stopper 46 may occur, and unintended deformation may reduce the durability of the boot.

[0051] In this case, when the first rack shaft 41 moves in the direction of entry into the bottomed cylindrical boot (to the right in FIG. 2), the volume inside the boot decreases by the amount of entry of the first rack shaft 41 into the boot, increasing the internal pressure of the boot, which may result in the boot swelling. If the boot swelling occurs, it may interfere with vehicle components and may also result in unintended deformation, reducing the durability of the boot 96X.

[0052] In the first unit 151A, the first rack shaft 41 is extended using an extension shaft 45, and a tip fixing portion 96c of a second boot 96A is fixed to the outer periphery of a free end portion 45c of the extension shaft 45.

[0053] As a result, when the first rack shaft 41 moves in the retreating direction (leftward in FIG. 2), the bellows portion 96aA contracts, reducing the volume inside the second boot 96A, thereby absorbing (suppressing) the increase in volume that would occur if a cylindrical boot with a bottom were used. This makes it possible to suppress the generation of negative pressure and prevent the second boot 96A from collapsing. Furthermore, when the first rack shaft 41 moves in the approaching direction (rightward in FIG. 2), the bellows portion 96aA expands, increasing the volume inside the second boot 96A, thereby absorbing the decrease in volume that would occur if a cylindrical boot with a bottom were used. This makes it possible to suppress the increase in internal pressure and prevent the second boot 96A from expanding.

[0054] In this way, in first unit 151A, the volume inside second boot 96A can be adjusted by bellows portion 96aA, which deforms in response to the moving first rack shaft 41, and therefore interference with other components inside and outside second boot 96A due to depression or expansion of second boot 96A can be suppressed. Also, in first unit 151A, by providing extension shaft 45, the existing first rack shaft 41 can be reused, and boots 95, 96A can also be configured similarly to each other.

[0055] 1, the first unit 151A does not need to transmit power between the steering wheel 1 and the wheels 7. This, combined with the easing of layout restrictions, allows the terminal end 41c of the first rack shaft 41 to be located near the center of the vehicle in the left-right direction, thereby creating space near the center. This makes it possible to reduce interference with vehicle components near the center and ensure sufficient clearance, thereby improving vehicle mountability.

[0056] The first unit 151A has a structure in which the tip end 41b of the first rack shaft 41 is connected to one of the wheels 71, which is one of the left and right wheels. This makes it possible to prevent deterioration in vehicle mountability due to a connection mechanism such as a complex link mechanism that connects each of the wheels 7 (i.e., both the left and right wheels) via the first rack shaft 41.

[0057] The first unit 151A may be modified as follows.

[0058] (First Modification) 3 is a cross-sectional view of a main part of first unit 151B, which is a first modified example of first unit 151A. First unit 151B includes second boot 96B instead of second boot 96A (see FIG. 2). Note that a similar configuration can also be applied to second unit 152 (see FIG. 1).

[0059] The second boot 96B covers the terminal end 41c of the first rack shaft 41 and has a bellows portion 96aB that deforms to follow the movement of the first rack shaft 41, and a strength portion 96d that is less likely to deform (expand or contract) than the bellows portion 96aB. The second boot 96B covers the terminal end 41c of the first rack shaft 41 and also covers the stopper 46.

[0060] The bellows portion 96aB has a bellows shape that is deformable (expands and contracts) 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.

[0061] The second boot 96B has the bellows portion 96aB and the reinforcing portion 96d, so that the bellows portion 96aB can be minimized while the reinforcing portion 96d increases the strength of the second boot 96B. Therefore, it is possible to achieve both the ability of the second boot 96B to follow the moving first rack shaft 41 and the strength of the second boot 96B.

[0062] The second boot 96B further has a bottom portion 96e at its tip. Similar to the second boot 96A (see FIG. 2) described above, the second boot 96B is fixed to the outer periphery of the other end 61h of the first rack housing 61 by the base end fixing portion 96b, while the tip of the second boot 96B is closed by the bottom portion 96e. Therefore, the second boot 96B does not have a tip end fixing portion 96c (see FIG. 2), and the bottom portion 96e is a free end of the second boot 96B.

[0063] The bellows portion 96aB is provided closer to the tip end of the second boot 96B (to the right in FIG. 3) than the reinforcing portion 96d. The base end fixing portion 96b is connected to the reinforcing portion 96d from the base end side of the second boot 96B (to the left in FIG. 3), and the reinforcing 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 the intermediate portion between the base end fixing portion 96b and the bottom portion 96e, and the reinforcing portion 96d is provided in the remaining portion of the intermediate portion between the base end fixing portion 96b and the bottom portion 96e.

[0064] In the first unit 151B, when the first rack shaft 41 moves in a direction to retract from the second boot 96B (left side in FIG. 3) and the volume inside the second boot 96B increases, the second boot 96B contracts, thereby absorbing (suppressing) the volume change. When the first rack shaft 41 moves in a direction to advance into the second boot 96B (right side in FIG. 3) and the volume inside the second boot 96B decreases, the second boot 96B expands, thereby absorbing (suppressing) the volume change. The extension shaft 45 may expand the second boot 96B by moving in the advance direction while abutting against the bottom portion 96e.

[0065] The second boot 96B has a structure in which a bottom portion 96e is a free end and a strength portion 96d is fixed to the first rack housing 61 via a base end fixing portion 96b, thereby being supported in a cantilevered manner by the first rack housing 61. By providing the strength portion 96d closer to the base end of the second boot 96B than the bellows portion 96aB (on the left side in FIG. 3), the second boot 96B is less likely to sag due to gravity compared to when the bellows portion 96aB is provided closer to the base end of the second boot 96B than the strength portion 96d. In other words, by fixing the strength portion 96d to the first rack housing 61 without using the bellows portion 96aB, sagging of the second boot 96B due to gravity is suppressed.

[0066] This allows the second boot 96B to maintain a self-standing posture, eliminating the need for the tip fixing portion 96c (see FIG. 2) to prevent sagging. Therefore, since the tip fixing portion 96c is no longer necessary, the first unit 151A can be made more compact in the axial direction.

[0067] The second boot 96B, which has a bellows portion 96aB and a bottom portion 96e on the tip side as a free end, may sag to some extent due to gravity. In contrast, the second boot 96B, which is made of resin, is advantageous in that it can tolerate contact with the stopper 46 to some extent by, for example, smoothing the corners of the stopper 46 or using a resin material that is resistant to wear.

[0068] Contact between the second boot 96B and the stopper 46 due to the second boot 96B sagging down may be avoided, for example, by setting the length of the strength portion 96d to a length that allows the stopper 46 to be accommodated within the strength portion 96d regardless of the position of the first rack shaft 41, or by adjusting the diameter of the stopper 46.

[0069] (Second Modification) 4 is a cross-sectional view of a main part of first unit 151C, which is a second modified example of first unit 151A. First unit 151C includes second boot 96C instead of second boot 96A (see FIG. 2). Note that a similar configuration can also be applied to second unit 152 (see FIG. 1).

[0070] The second boot 96C has a base end fixing portion 96b, a strength portion 96dC that is less likely to deform (expand or contract) than the bellows portion 96aA (see FIG. 2), and a bottom portion 96eC provided at the tip of the second boot 96C.

[0071] The second boot 96C does not have a bellows portion 96aA (see FIG. 2), and the reinforcing 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. The second boot 96C does not have a tip fixing portion 96c (see FIG. 2), and the tip of the second boot 96C is closed by a bottom portion 96eC. The bottom portion 96eC is provided at a position that does not interfere with a fixed piece 99 that serves as a fixed member that is threaded into the screw hole 41d and moves together with the first rack shaft 41. The stopper 46 is fixed by the fixed piece 99 in a state where it is sandwiched between the fixed piece 99 and the terminal end 41c of the first rack shaft 41.

[0072] In the first unit 151C, there is no need to fix the second boots 96A, 96B, 96C with clips 98 at the terminal end 41c or at the tip of the terminal end 41c, so the clips 98 can be eliminated to simplify the design, and the first unit 151C can be made compact in the axial direction of the first rack shaft 41.

[0073] In addition, in the first unit 151C, for example, by providing a vent filter that can suppress internal pressure fluctuations in the second boot 96C, it is possible to suppress deformation of the second boot 96C due to volume changes within the second boot 96C. On the other hand, the above-mentioned units 151A and 151B (see FIGS. 2 and 3) are advantageous over the first unit 151C in that they do not need to suppress internal pressure fluctuations in the second boots 96A and 96B with a vent filter or the like.

[0074] (Other variations) The second boots 96A and 96B may be made of rubber, as may the first boot 95.

[0075] The extension shaft 45 and the stopper 46 may be formed integrally with the first rack shaft 41. In this case, the terminal end 41c of the first rack shaft 41 is formed by the free end 45c of the extension shaft 45. Alternatively, the extension shaft 45 and the stopper 46 may be formed integrally with each other.

[0076] Instead of the bellows portions 96aA and 96aB, a deforming portion having another shape that can be deformed (expanded and contracted) along the axis O1 of the first rack shaft 41 may be used. As another shape, for example, a Miura fold or the like can be used. The same applies to the bellows portion 95a.

[0077] The strength portion 96d is not limited to a cylindrical shape, but may be, for example, a cylindrical shape formed in a wavy pattern along the circumferential direction, or a cylindrical shape provided with ribs arranged along the axis O1 of the first rack shaft 41.

[0078] The second boot 96B shown in FIG. 4 may be configured so that the bottom portion 96e is not a free end, but is fixed by a clip 98, similar to the tip fixing portion 96c of the second boot 96A shown in FIG.

[0079] The configuration, operation, and effects of the embodiment of the present invention will be described below.

[0080] First units 151A, 151B, 151C as steer-by-wire units that steer wheels 7 of the vehicle include steering motors 31, 36, pinion shafts 33, 38 to which driving force is input from steering motors 31, 36, and rack shafts 41, 42 that have rack gears 41a, 42a that mesh with pinion shafts 33, 38 and tip ends 41b, 42b that are connected to wheels 7 of the vehicle and that steer wheels 7, and rack shafts 41, 42 have terminal ends 41c, 42c on the side opposite tip ends 41b, 42b that are not connected to wheels 7 of the vehicle. Second unit 152 is configured in the same manner as first unit 151A.

[0081] According to this configuration, the adoption of the steer-by-wire system alleviates layout restrictions, and by locating end portions 41c, 42c near the center in the left-right direction of the vehicle, space can be created near the center. This makes it possible to reduce interference with vehicle components near the center and ensure sufficient clearance, thereby improving vehicle mountability.

[0082] The rack shafts 41 and 42 are connected to wheels 71 and 72, which serve as one of the left and right wheels of the vehicle.

[0083] According to this configuration, since the rack shafts 41, 42 are connected to the wheels 71, 72 as one of the left and right wheels, deterioration of vehicle mountability due to complex connection mechanisms such as link mechanisms that connect each of the wheels 7 as the left and right wheels via the rack shafts 41, 42 can be prevented.

[0084] The first units 151A, 151B, 151C include second boots 96A, 96B, 96C that cover the end portions 41c, 42c of the rack shafts 41, 42. The second unit 152 is configured in the same manner as the first unit 151A.

[0085] According to this configuration, the second boots 96A, 96B, 96C can be fixed or not fixed with clips 98 at the terminal end 41c or at the tip of the terminal end 41c, so that the second boot 96A can be fixed with clips 98 to provide support, as in the case of second boot 96A, or the clips 98 can be eliminated to simplify the configuration, as in the case of second boots 96B, 96C.

[0086] In the first units 151A and 151B, the second boots 96A and 96B have bellows portions 96aA and 96aB as deformation portions that deform in accordance with the moving rack shafts 41 and 42. The second unit 152 is configured similarly to the first unit 151A.

[0087] According to this configuration, the volume inside the second boots 96A, 96B can be adjusted by the bellows portions 96aA, 96aB, which deform in accordance with the moving rack shafts 41, 42, so that the second boots 96A, 96B can be prevented from interfering with other parts inside and outside the second boots 96A, 96B due to the second boots 96A, 96B collapsing or expanding.

[0088] The first unit 151B includes a second boot 96B that covers the terminal end 41c of the first rack shaft 41. The second boot 96B has a bellows portion 96aB as a deformation portion that deforms in response to the movement of the first rack shaft 41, and a strength portion 96d that is less susceptible to deformation than the bellows portion 96aB. The second unit 152 can be configured in a similar manner.

[0089] According to this configuration, the bellows portion 96aB can be minimized while the strength of the second boot 96B can be increased by the strength portion 96d, thereby achieving both the ability of the second boot 96B to follow the moving first rack shaft 41 and the strength of the second boot 96B.

[0090] The first units 151A, 151B, and 151C further include a first rack housing 61 that houses the first rack shaft 41, an extension shaft 45 or a fixed piece 99 as a fixed member fixed to the terminal end 41c of the first rack shaft 41, and a stopper 46 that abuts against a second regulating surface 61f as an end of the first rack housing 61 to regulate movement of the first rack shaft 41. The second unit 152 is configured similarly to the first unit 151A.

[0091] This configuration can prevent the terminal end 41c of the first rack shaft 41 from moving too far toward the first rack housing 61, thereby preventing interference.

[0092] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0093] 7... Wheel, 71, 72... Wheel (single wheel), 31... First steering motor (motor), 33... First pinion shaft (pinion shaft), 41... First rack shaft (rack shaft), 41a... First rack gear (rack gear), 36... Second steering motor (motor), 38... Second pinion shaft (pinion shaft), 42... Second rack shaft (rack shaft), 42a... Second rack gear (rack gear), 41b, 42b... Tip portion, 41c, 42c... End portion, 45... Extension shaft (fixing member), 46... stopper, 61... first rack housing (housing), 61f... second regulating surface (end portion), 62... second rack housing (housing), 96A, 96B... second boot (cover), 96aA, 96aB... bellows portion (deformation portion), 96d... strength portion, 99... fixing piece (fixing member), 100... steer-by-wire device, 151A, 151B... first unit (steer-by-wire unit), 152... second unit (steer-by-wire unit)

Claims

1. A steer-by-wire unit for steering the wheels of a vehicle, A motor; a pinion shaft to which a driving force from the motor is input; a rack shaft having a rack gear that meshes with the pinion shaft and a tip end that is connected to a wheel of the vehicle, and that steers the wheel; The rack shaft has an end portion opposite to the tip portion that is not connected to a wheel of the vehicle. A steer-by-wire unit characterized by:

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

3. 3. The steer-by-wire unit according to claim 1 or 2, a cover for covering the end portion of the rack shaft; A steer-by-wire unit characterized by:

4. 4. The steer-by-wire unit according to claim 3, The cover has a deformation portion that deforms in accordance with the movement of the rack shaft. A steer-by-wire unit characterized by:

5. 3. The steer-by-wire unit according to claim 1 or 2, a cover for covering the end portion of the rack shaft; The cover has a deformation portion that deforms in accordance with the movement of the rack shaft, and a strength portion that is less likely to deform than the deformation portion. A steer-by-wire unit characterized by:

6. 3. The steer-by-wire unit according to claim 1 or 2, a housing that accommodates the rack shaft; a fixing member fixed to the terminal end of the rack shaft; a stopper that abuts against an end of the housing to restrict movement of the rack shaft, A steer-by-wire unit characterized by:

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