JP7799515B2 - Rack bushing and rack and pinion steering device - Google Patents

Description

The present invention relates to a rack bush and a rack and pinion steering device.

Rack-and-pinion steering devices are widely used in automotive steering systems because they can be made small and lightweight, yet have high rigidity and provide a good steering feel. Figures 18 and 19 show a rack-and-pinion steering device 100, an example of a conventional structure, described in Japanese Patent Laid-Open Publication No. 2007-112276 (Patent Document 1).

The steering device 100 applies a steering angle to the left and right steered wheels by converting the rotational movement of the steering wheel into linear movement in the width direction of the vehicle.

The steering device 100 comprises a housing 101, a pinion shaft 102 to which the rotational motion of the steering wheel is transmitted, a rack shaft 103 that converts the rotational motion of the pinion shaft 102 into linear motion, a rack guide 104, and a pair of rack bushings 105.

The housing 101 includes a rack accommodating portion 101a that accommodates the axially middle portion of the rack shaft 103, a pinion accommodating portion 101b that accommodates the tip half of the pinion shaft 102, and a guide accommodating portion 101c that accommodates the rack guide 104. The housing 101 is fixed to the vehicle body with the longitudinal direction (axial direction) of the rack accommodating portion 101a facing the width direction of the vehicle.

The pinion shaft 102 has pinion teeth 102a on the tip half of its outer circumferential surface. The pinion shaft 102 is rotatably supported inside the pinion accommodating portion 101b via a pair of bearings 106a, 106b. The pinion shaft 102 is connected to the steering wheel via a steering shaft and an intermediate shaft (not shown), and rotates in response to steering operation of the steering wheel.

The rack shaft 103 has rack teeth 103a on a portion of its outer circumferential surface in the axial direction that mesh with the pinion teeth 102a of the pinion shaft 102. The rack shaft 103 is disposed inside the rack housing 101a so that it can move back and forth in the axial direction. Both axial ends of the rack shaft 103 protrude from both axial ends of the rack housing 101a and are connected to tie rods 107.

The rack guide 104 presses the rack shaft 103 toward the pinion shaft 102 and is arranged inside the guide accommodating portion 101c. The rack guide 104 is a rolling-type rack guide and includes a roller 104a, a holder 104b, a pin 104c, and an elastic member 104d.

The roller 104a is rotatably supported by the holder 104b via the pin 104c, and is in rolling contact with the outer circumferential surface of the rack shaft 103. The outer circumferential surface of the roller 104a has a generatrice-like concave arc that roughly matches the contour shape of the outer circumferential surface of the rack shaft 103. The holder 104b is disposed inside the guide accommodating portion 101c so that it can move toward and away from the rack shaft 103. The elastic member 104d is disposed between the holder 104b and the cap 108 that covers the opening of the guide accommodating portion 101c, and presses the holder 104b toward the rack shaft 103.

Each of the pair of rack bushes 105 has a cylindrical shape and is fitted into the rack accommodating section 101a near the openings on both axial sides. The rack bushes 105 have a circular support hole 105a through which the rack shaft 103 is inserted in the axial direction. The rack bushes 105 slidably support the outer surface of the rack shaft 103 using the inner surface of the support hole 105a.

The conventional steering device 100 is configured to press the rack shaft 103 toward the pinion shaft 102 using the rack guide 104, which reduces backlash at the meshing portion between the rack teeth 103a and the pinion teeth 102a and prevents abnormal noise from occurring at that meshing portion.

Furthermore, because the steering device 100 of the conventional structure uses a rolling-type rack guide 104 equipped with rollers 104a, the resistance generated between the rack shaft 103 and the rack guide 104 can be reduced compared to when using a sliding-type rack guide such as that disclosed in Japanese Patent Application Laid-Open No. 2008-44487 (Patent Document 2). This improves the transmission efficiency from the pinion shaft 102 to the rack shaft 103 and improves the steering feel.

Japanese Patent Application Laid-Open No. 2007-112276 JP 2008-44487 A JP 2014-214810 A

The conventional steering device 100 described in JP 2007-112276 A uses a rolling rack guide 104 equipped with rollers 104a. For this reason, as shown in FIG. 19, the pressure angle α of the rack shaft 103 exerted by the rollers 104a is likely to be smaller than when a sliding rack guide is used. This means that the rack guide 104 tends to be less able to hold the rack shaft 103 in the width direction of the rack shaft 103 (the vertical direction in FIG. 19, the tooth width direction of the rack teeth 103a), which is perpendicular to both the axial direction of the rack shaft 103 and the pressing direction of the rack guide 104. In a steering device 100 with a conventional structure, the insufficient holding force in the width direction of the rack shaft 103 is compensated for by the rack bushing 105.

In recent years, there has been a demand for further weight reduction and increased power output in rack-and-pinion steering devices. In light of these circumstances, publications such as JP 2014-214810 A (Patent Document 3) disclose structures that can improve the strength of the rack teeth without increasing the weight of the rack shaft. Specifically, the structure discloses a structure in which the cross-sectional contour of only the portion (range) of the rack shaft, which has a roughly cylindrical shape, where the rack teeth are formed, is roughly D-shaped, consisting of three straight portions and one arc portion, thereby increasing the tooth width of the rack teeth.

In order to improve the strength of the rack teeth 103a in a steering device 100 with a conventional structure, it is possible to change the cross-sectional contour shape of the portion of the rack shaft 103 where the rack teeth 103a are formed from a partial circle consisting of one straight section and one arc section, as shown in Figure 19, to a roughly D-shape. However, simply changing the cross-sectional contour shape of the rack shaft 103 would cause interference between the rack teeth 103a and the rack bushing 105, making it impossible to insert the rack shaft 103 into the support hole 105a of the rack bushing 105. One possible solution would be to increase the inner diameter of the support hole 105a, but in that case, the rack bushing 105 would no longer be able to compensate for the holding force of the rack shaft 103 in the width direction.

The present invention was made to solve the above-mentioned problems, and aims to provide a rack bushing that can compensate for the holding force of the rack shaft in the width direction, even when a rack shaft with a substantially D-shaped cross-sectional contour at the portion where the rack teeth are formed is used, and a rack-and-pinion steering device equipped with such a rack bushing.

A rack bushing according to one aspect of the present invention is for supporting a rack shaft having rack teeth relative to a housing so as to allow axial movement of the rack shaft, and includes a support hole and an outer peripheral surface.
The support hole is a portion through which the rack shaft is inserted.
The outer circumferential surface is the portion that is fitted into the housing.
In one aspect of the rack bushing of the present invention, the support hole has an inner circumferential surface, and each of a pair of inner surfaces arranged on both sides in the tooth width direction of the rack teeth has an inner circumferential side convex portion that protrudes radially inward compared to the portions adjacent to both sides in the circumferential direction of the support hole.
The tooth width direction of the rack teeth coincides with the width direction of the rack shaft.
The outer peripheral surface has an outer peripheral recess that is recessed radially inward and is provided in a portion located radially outside the inner peripheral convex portion, and a stopper portion that protrudes radially outward from the radial bottom surface of the outer peripheral recess.

In one aspect of the rack bushing of the present invention, the support hole may further have inner recesses recessed radially outward in portions adjacent to both sides of the inner protrusion in the circumferential direction.

In a rack bush according to one aspect of the present invention, the stopper portion can be solid. Alternatively, the stopper portion can be hollow.

In a rack bushing according to one aspect of the present invention, the support hole may have a flat surface portion on the inner circumferential surface thereof that faces the rack teeth, and the contour shape of the support hole may be substantially D-shaped. Alternatively, the contour shape of the support hole may be substantially rectangular, substantially oval, or the like.
In the rack bush according to one aspect of the present invention, the cross-sectional shape of the stopper portion may be substantially rectangular, substantially triangular, partially circular, partially elliptical, or the like.

In the rack bushing according to one aspect of the present invention, the support hole may have a concave cylindrical surface portion having a single arc cross section on the inner circumferential surface thereof facing the rack teeth. In this case, the contour shape of the support hole may be substantially circular.
Furthermore, both circumferential ends of the concave cylindrical surface portion can be connected to the inner circumferential recess portion.

In the rack bushing according to one aspect of the present invention, the outer peripheral surface may have a back-side recess that is recessed radially inward in a portion located diametrically opposite the rack teeth.
In this case, slits may be provided in the radial bottom surface of the rear recess and in the inner peripheral surface of the support hole.

In the rack bushing according to one aspect of the present invention, the tip surfaces of the pair of inner peripheral convex portions can be inclined in directions that move away from each other with respect to the tooth height direction of the rack teeth as they approach the tips of the rack teeth. Note that the tooth height direction of the rack teeth refers to a direction that is perpendicular to both the tooth width direction of the rack teeth and the axial direction of the rack shaft, and coincides with the pressing direction of the rack guide.
Alternatively, the tip surfaces of the pair of inner circumferential projections may be arranged parallel to each other.

A rack-and-pinion steering device according to one aspect of the present invention includes a rack shaft, a pinion shaft, a rack guide, a housing, and a rack bushing.
The pinion shaft meshes with the rack shaft.
The rack guide is disposed so as to sandwich the rack shaft between itself and the pinion shaft, and presses the rack shaft toward the pinion shaft.
The housing has a rack accommodating portion that accommodates the rack shaft, a pinion accommodating portion that accommodates the pinion shaft, and a guide accommodating portion that accommodates the rack guide.
The rack bushing supports the rack shaft relative to the rack housing portion so as to allow the rack shaft to move in the axial direction.
In a rack-and-pinion steering device according to one aspect of the present invention, the rack shaft has a rack portion having a generally D-shaped cross-sectional contour and having rack teeth that mesh with the pinion shaft, and a shaft portion having a circular cross-sectional contour provided at a portion axially offset from the rack portion.
The rack portion has a width dimension that is equal to or larger than the outer diameter of the shaft portion.
The rack guide includes a roller that is in rolling contact with the rack shaft.
The rack bush is a rack bush according to one aspect of the present invention.

The rack-and-pinion steering device according to one aspect of the present invention may further include a spacer that is arranged farther from the pinion shaft than the rack bush in the axial direction of the rack shaft.
In this case, the spacer can be made of a material stronger than the material of the rack bush, such as a metal material.

A rack-and-pinion steering device according to one aspect of the present invention can further include an electric motor that rotates the pinion shaft, and a second pinion shaft that is different from the pinion shaft and rotates in response to steering operation of the steering wheel.
In this case, the rack shaft further has a second rack portion on which second rack teeth that mesh with the second pinion shaft are formed at portions axially offset from the rack portion and the shaft-shaped portion, and the housing further has a second pinion accommodating portion that accommodates the second pinion shaft.

The rack bushing according to one aspect of the present invention can compensate for the holding force in the width direction of the rack shaft, even when using a rack shaft with a substantially D-shaped cross-sectional contour at the portion where the rack teeth are formed.

FIG. 1 is a schematic diagram showing a rack-and-pinion steering device according to a first embodiment. FIG. 2 is an exploded perspective view showing some components extracted from a rack-and-pinion steering device according to a first example of the embodiment. FIG. 3 is a cross-sectional view showing one axial side portion of the rack shaft and members arranged around it. FIG. 4 is a cross-sectional view showing the other axial side portion of the rack shaft and the members arranged around it. FIG. 5 is a schematic cross-sectional view taken along line AA in FIG. Figure 6(A) is a plan view showing the rack shaft, Figure 6(B) is an enlarged cross-sectional view taken along line B-B of Figure 6(A), Figure 6(C) is an enlarged cross-sectional view taken along line CC of Figure 6(A), and Figure 6(D) is an enlarged cross-sectional view taken along line DD of Figure 6(A). FIG. 7 is a perspective view showing the rack shaft. FIG. 8 is a schematic cross-sectional view taken along line EE in FIG. FIG. 9 is a cross-sectional view taken along line FF in FIG. FIG. 10 is an enlarged cross-sectional view showing the upper portion of the rack bush. FIG. 11 is a perspective view showing the rack bush. FIG. 12 is a diagram showing a second example of the embodiment, and corresponds to FIG. FIG. 13A is a view corresponding to FIG. 10 showing a third example of the embodiment, and FIG. 13B is a cross-sectional view showing a state in which elastic deformation occurs in the stopper portion. FIG. 14 is a diagram showing a fourth example of the embodiment, and corresponds to FIG. FIG. 15 is a diagram corresponding to FIG. 9 and shows a fifth example of the embodiment. FIG. 16 is a diagram showing a fifth example of the embodiment, and corresponds to FIG. FIG. 17 is an enlarged view of a portion corresponding to the portion H in FIG. 4, showing a fifth example of the embodiment. FIG. 18 is a partial cross-sectional view showing a conventional rack-and-pinion steering device. FIG. 19 is a cross-sectional view taken along line GG in FIG.

[First Example of Embodiment]
A first example of the embodiment will be described with reference to FIGS. 1 to 11. In the following description, the front-rear direction refers to the front-rear direction of the vehicle, the up-down direction refers to the up-down direction of the vehicle, and the left-right direction refers to the width direction of the vehicle. The left-right direction also corresponds to the axial direction of the rack shaft 12 and the rack housing 15, which will be described later. One side with respect to the axial direction of the rack shaft 12 and the rack housing 15 refers to the left side in FIGS. 1, 3, 4, and 6A, and the other side with respect to the axial direction of the rack shaft 12 and the rack housing 15 refers to the right side in FIGS. 1, 3, 4, and 6A. The up-down direction also corresponds to the width direction of the rack shaft 12.

[Overall configuration of steering device]
The rack-and-pinion steering device 1 of this example is a dual-pinion electric power steering device, the overall configuration of which is shown in Fig. 1. In other words, this example is directed to an electric power steering device of the type that uses two pinions, a steering-side pinion shaft 11 and an assist-side pinion shaft 14, to input the steering force and the assist driving force independently to the rack shaft 12.

The steering device 1 includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a, 5b, an intermediate shaft 6, a housing 7, a steering mechanism 8, an assist mechanism 9, and a pair of rack bushes 10a, 10b.

The steering shaft 3 is rotatably supported inside a steering column 4 supported on the vehicle body. The steering wheel 2, which is steered by the driver, is attached to the rear end of the steering shaft 3. The front end of the steering shaft 3 is connected to a steering-side pinion shaft 11, which constitutes the steering mechanism 8, via a universal joint 5a, an intermediate shaft 6, and another universal joint 5b. Therefore, the rotational motion of the steering wheel 2 is transmitted to the steering-side pinion shaft 11. The rotational motion of the steering-side pinion shaft 11 is converted into axial linear motion of a rack shaft 12, which constitutes the steering mechanism 8. This imparts a steering angle to the left and right steered wheels 13. The steering device 1 also applies the assist drive force of an electric motor 41, which constitutes the assist mechanism 9, to the rack shaft 12 via the assist-side pinion shaft 14, reducing the steering force required for the driver to operate the steering wheel 2.

In this example, of the pair of rack bushes 10a, 10b, the rack bush 10b located on the other axial side corresponds to the rack bush described in the claims. Furthermore, the assist-side pinion shaft 14 corresponds to the pinion shaft described in the claims, and the steering-side pinion shaft 11 corresponds to the second pinion shaft described in the claims.

<housing>
The housing 7 is fixed to the vehicle body and is a casting integrally made by die-casting a light alloy such as an aluminum alloy. As shown in FIG. 2 , the housing 7 includes a rack housing 15, a steering-side pinion housing 16, an assist-side pinion housing 17, a steering-side guide housing 18, an assist-side guide housing 19, a gear housing 20, and a plurality of mounting portions 21 a, 21 b. In this example, the assist-side pinion housing 17 corresponds to the pinion housing recited in the claims, and the steering-side pinion housing 16 corresponds to the second pinion housing recited in the claims. Furthermore, the assist-side guide housing 19 corresponds to the guide housing recited in the claims.

The rack housing 15 is a cylindrical member that extends in the left-right direction. The rack housing 15 is open on both axial ends. The axial middle portion of the rack shaft 12 that constitutes the steering mechanism 8 is housed inside the rack housing 15. The rack housing 15 is positioned approximately horizontally.

The steering side pinion accommodating portion 16 has a cylindrical shape with a bottom, and only the upper end is open. The tip half of the steering side pinion shaft 11 is positioned inside the steering side pinion accommodating portion 16. The steering side pinion accommodating portion 16 is positioned in front of the rack accommodating portion 15 (the front side in Figure 2) and on one axial side of the rack accommodating portion 15 (the left side in Figure 2). The steering side pinion accommodating portion 16 is positioned in a twisted relationship with the rack accommodating portion 15. In other words, the central axis of the steering side pinion accommodating portion 16 and the central axis of the rack accommodating portion 15 are in a twisted relationship. Furthermore, when viewed from the front-to-rear direction, the central axis of the steering side pinion accommodating portion 16 is not positioned in a direction perpendicular to the central axis of the rack accommodating portion 15, but is inclined relative to the perpendicular direction. The internal space of the steering side pinion accommodating portion 16 is connected to the internal space of the rack accommodating portion 15.

The assist side pinion accommodating portion 17 has a cylindrical shape with a bottom, and only the upper end is open. The assist side pinion shaft 14 is disposed inside the assist side pinion accommodating portion 17. The assist side pinion accommodating portion 17 is disposed in front of the rack accommodating portion 15 (the near side in FIG. 2) and on the other axial side of the rack accommodating portion 15 (the right side in FIG. 2). The assist side pinion accommodating portion 17 is disposed in a twisted position relative to the rack accommodating portion 15. In other words, the central axis of the assist side pinion accommodating portion 17 and the central axis of the rack accommodating portion 15 are in a twisted positional relationship. Furthermore, when viewed from the front-to-rear direction, the central axis of the assist side pinion accommodating portion 17 is not disposed in a direction perpendicular to the central axis of the rack accommodating portion 15, but is inclined relative to the perpendicular direction. The internal space of the assist side pinion accommodating portion 17 is connected to the internal space of the rack accommodating portion 15. When implementing the present invention, the central axis of the assist-side pinion housing portion can also be positioned perpendicular to the central axis of the rack housing portion.

The steering side guide accommodating portion 18 has a cylindrical shape and extends in the fore-and-aft direction. The steering side rack guide 25, described below, is accommodated inside the steering side guide accommodating portion 18. The steering side guide accommodating portion 18 is located rearward of the rack accommodating portion 15 and on one axial side of the rack accommodating portion 15. Specifically, the steering side guide accommodating portion 18 is located at the same position as the steering side pinion accommodating portion 16 in the axial direction of the rack accommodating portion 15. The internal space of the steering side guide accommodating portion 18 is also connected to the internal space of the rack accommodating portion 15.

The assist side guide accommodating section 19 has a cylindrical shape and extends in the front-to-rear direction. The assist side rack guide 39, described below, is accommodated inside the assist side guide accommodating section 19. The assist side guide accommodating section 19 is located behind the rack accommodating section 15, on the other axial side of the rack accommodating section 15. Specifically, the assist side guide accommodating section 19 is located at the same position as the assist side pinion accommodating section 17 in the axial direction of the rack accommodating section 15. The internal space of the assist side guide accommodating section 19 is also connected to the internal space of the rack accommodating section 15.

The gear housing portion 20 houses the worm reducer 40 (described below) that constitutes the assist mechanism portion 9, and includes a worm housing portion 22 and a wheel housing portion 23. The gear housing portion 20 can also be constructed separately from the housing 7 and fixed to the housing 7 with bolts or the like.

The worm accommodating section 22 has a cylindrical shape with a bottom and is disposed above the rack accommodating section 15 and approximately parallel to it. The worm accommodating section 22 has an opening at one end in the axial direction of the rack shaft 12. The worm accommodating section 22 has an outward-facing flange-shaped mounting flange 24 on its outer circumferential surface at one end in the axial direction of the rack shaft 12. The worm accommodating section 22 is disposed in front of the wheel accommodating section 23 in the front-to-rear direction. The internal spaces of the worm accommodating section 22 and the wheel accommodating section 23 are interconnected. A worm 51 that constitutes the worm reducer 40 is rotatably supported inside the worm accommodating section 22. When implementing the present invention, the opening and mounting flange of the worm accommodating section can also be provided on the other side in the axial direction of the rack shaft.

The wheel accommodating portion 23 has a generally cylindrical shape and is provided above the assist side pinion accommodating portion 17. The wheel accommodating portion 23 and the assist side pinion accommodating portion 17 are arranged coaxially. The wheel accommodating portion 23 is arranged to cover the periphery of the worm wheel 52 that constitutes the worm reducer 40.

Of the multiple (four in the illustrated example) mounting portions 21a, 21b, a pair of mounting portions 21a located at both axial ends of the rack housing portion 15 are located on the front side of the rack housing portion 15. In contrast, a pair of mounting portions 21b located in the axial middle of the rack housing portion 15 are located on the rear side of the rack housing portion 15. The housing 7 is fixed to the vehicle body using fixing members such as bolts or studs that pass through each of the multiple mounting portions 21a, 21b.

<Steering mechanism>
The steering mechanism 8 has a steering-side pinion shaft 11 , a rack shaft 12 , and a steering-side rack guide 25 , and converts the rotational movement of the steering wheel 2 into linear movement in the axial direction of the rack shaft 12 .

<Steering side pinion shaft>
The steering side pinion shaft 11 has steering side pinion teeth 26 on the front half of its outer circumferential surface. As shown in FIG. 5 , the steering side pinion shaft 11 is rotatably supported inside the steering side pinion accommodating portion 16 by a pair of bearings 27a, 27b. The central axis of the steering side pinion shaft 11 is arranged coaxially with the central axis of the steering side pinion accommodating portion 16. The steering side pinion shaft 11 is connected to the steering wheel 2 via universal joints 5a, 5b and an intermediate shaft 6, and rotates in response to steering operation of the steering wheel 2. The rotation of the steering side pinion shaft 11 is converted into linear motion of the rack shaft 12, which pushes and pulls tie rods 28 connected to both axial ends of the rack shaft 12. This imparts a steering angle to the left and right steered wheels 13.

Rack axis
The rack shaft 12 is a solid rod-shaped member made of a metal such as carbon steel. The rack shaft 12 is disposed with its axial direction (longitudinal direction) oriented in the left-right direction. As shown in FIGS. 6 and 7 , the rack shaft 12 has steering-side rack teeth 29 on a portion of its outer peripheral surface at one axial side that mesh with steering-side pinion teeth 26 provided on the outer peripheral surface of the steering-side pinion shaft 11, and assist-side rack teeth 30 on a portion of its outer peripheral surface at the other axial side that mesh with assist-side pinion teeth 43 provided on the outer peripheral surface of the assist-side pinion shaft 14 that constitutes the assist mechanism 9. In this example, the rack shaft 12 has the steering-side rack teeth 29 on a front side surface of the one axial side and the assist-side rack teeth 30 on a front side surface of the other axial side. The rack shaft 12 has a pair of screw holes 31 opening on both axial end surfaces. In FIG. 6B, the shapes of the end portions on both sides of the assist-side rack tooth 30 in the tooth width direction (the vertical direction in FIG. 6) are drawn at right angles, but the end portions on both sides of the assist-side rack tooth 30 in the tooth width direction may be curved in an arc shape due to sagging.

The rack shaft 12 has a steering-side rack portion 32 on one axial side, on which steering-side rack teeth 29 are formed, and an assist-side rack portion 33 on the other axial side, on which assist-side rack teeth 30 are formed. The rack shaft 12 has a shaft-shaped portion 34 in an axially intermediate portion that is axially offset from both the steering-side rack portion 32 and the assist-side rack portion 33.

In this example, the assist side rack teeth 30 correspond to the rack teeth recited in the claims, and the assist side rack portion 33 corresponds to the rack portion recited in the claims. Furthermore, the steering side rack teeth 29 correspond to the second rack teeth recited in the claims, and the steering side rack portion 32 corresponds to the second rack portion recited in the claims. Note that the width direction of the rack shaft 12 refers to the direction that coincides with the tooth width direction of the steering side rack teeth 29 and the assist side rack teeth 30, and refers to the up-and-down direction in Figure 6 that is perpendicular to both the axial direction of the rack shaft 12 and the pressing direction of the steering side rack guide 25 (or assist side rack guide 39).

In this example, in order to improve the strength of the assist-side rack teeth 30 to which steering assist force is input from the assist mechanism 9 while suppressing an increase in the weight of the rack shaft 12, the cross-sectional contour shape of the assist-side rack section 33 is made to be a substantially D-shape consisting of three straight line portions 33a, 33b, and 33c and one arcuate portion 33d, as shown in Fig. 6(B) . Of the outer peripheral surfaces of the assist-side rack section 33, the front side on which the assist-side rack teeth 30 are formed is made up of the straight line portion 33a, the upper side is made up of the straight line portion 33b and a part of the arcuate portion 33d, the lower side is made up of the straight line portion 33c and a part of the arcuate portion 33d, and the rear side (back surface) is made up of the arcuate portion 33d. Of the three straight line portions 33a, 33b, and 33c and one arcuate portion 33d that constitute the cross-sectional contour shape of the assist-side rack portion 33, the pair of straight line portions 33b, 33c are arranged parallel to each other on both sides in the tooth width direction of the assist-side rack tooth 30. In other words, the pair of straight line portions 33b, 33c are arranged approximately parallel to each other with the assist-side rack tooth 30 sandwiched therebetween. The widthwise dimension _W33 of the assist-side rack portion 33 (the width dimension in the up-down direction in FIG. 6B) is set larger than the widthwise dimension _W32 of the steering-side rack portion 32 (the width dimension in the up-down direction in FIG. 6C) and the outer diameter D of the shaft-shaped portion 34 ( _W33 > _W32 , _W33 > D). For this reason, the tooth width _T30 of the assist-side rack teeth 30 is the same as the widthwise dimension _W33 of the assist-side rack portion 33 and is larger than the tooth width T29 of the steering-side rack teeth ₂₉ ( _T30 > _T29 ). The tooth width _T29 of the steering-side rack teeth 29 is smaller than the widthwise dimension _W32 of the steering-side rack portion 32 ( _T29 < _W32 ). Both widthwise side surfaces (upper and lower side surfaces) of the assist-side rack portion 33 are configured to include flat surface portions. When implementing the present invention, the widthwise dimension of the assist-side rack portion can also be made the same as the widthwise dimension of the steering-side rack portion and the outer diameter of the shaft-shaped portion. In this case as well, the tooth width of the assist-side rack teeth can be made larger than the tooth width of the steering-side rack teeth.

In contrast, as shown in Fig. 6(C), the steering-side rack portion 32 has a partially circular cross-sectional contour consisting of one straight portion 32a that forms the front side surface on which the steering-side rack teeth 29 are formed and one arc portion 32b that forms the portion other than the front side surface. Also, as shown in Fig. 6(D), the shaft-shaped portion 34 has a circular cross-sectional contour. The widthwise dimension (circumscribed circle diameter) _W32 of the steering-side rack portion 32 and the outer diameter D of the shaft-shaped portion 34 are equal to each other ( _W32 = D).

The rack shaft 12 is supported inside the rack housing 15 so that it can move back and forth in the axial direction, with its axial ends facing left and right and its axial ends protruding from the left and right openings of the rack housing 15. Both axial ends of the rack shaft 12 are connected to the tie rod 28 via a spherical joint 35. That is, male threads provided at the base of the spherical joint 35 are threaded into each of a pair of threaded holes 31 in the rack shaft 12, and the base end of the tie rod 28 is supported at the tip of the spherical joint 35 so that it can swing.

<Steering side rack guide>
The steering side rack guide 25 presses the rack shaft 12 toward the steering side pinion shaft 11 and is disposed inside the steering side guide accommodating portion 18. As a result, the steering side rack guide 25 is disposed so as to sandwich the rack shaft 12 between itself and the steering side pinion shaft 11. As shown in Figures 3 and 5, the steering side rack guide 25 of this example is a sliding type rack guide and includes a pad 36 and an elastic member 37.

The pad 36 has a generally cylindrical shape and is positioned inside the steering-side guide housing 18 so that it can move toward and away from the rack shaft 12. The pad 36 has a concave cylindrical pressing surface 36a, whose shape matches the rear surface of the rack shaft 12, on the surface facing the convex cylindrical rear surface of the rack shaft 12. Specifically, the pressing surface 36a matches the rear surface of the steering-side rack section 32 of the rack shaft 12. The pressing surface 36a is made of a synthetic resin or other material with excellent slip properties. In the illustrated example, the elastic member 37 is a torsion coil spring and is sandwiched in an elastically compressed state between the pad 36 and the steering-side cap 38 that covers the opening of the steering-side guide housing 18. This allows the elastic member 37 to press the pad 36 toward the rack shaft 12.

The steering side rack guide 25 presses the rack shaft 12 toward the steering side pinion shaft 11, reducing backlash at the meshing portion between the steering side pinion teeth 26 and the steering side rack teeth 29. This prevents abnormal noise from being generated at the meshing portion between the steering side pinion teeth 26 and the steering side rack teeth 29.

<Assist mechanism>
The assist mechanism 9 applies a steering assist force to the rack shaft 12, thereby reducing the steering force required for the driver to operate the steering wheel 2. The assist mechanism 9 includes an assist side pinion shaft 14, an assist side rack guide 39, a worm reducer 40, an electric motor 41, and a torque sensor 42.

In this example, the assist side rack guide 39 corresponds to the rack guide described in the claims.

《Assist side pinion shaft》
The assist-side pinion shaft 14 has assist-side pinion teeth 43 on the front half of its outer circumferential surface. As shown in FIG. 8 , the assist-side pinion shaft 14 is rotatably supported inside the assist-side pinion accommodating portion 17 using a plurality of bearings 44 a, 44 b. Therefore, the assist-side pinion shaft 14 is disposed at a position separated from the steering-side pinion shaft 11 in the axial direction of the rack shaft 12. In addition, the central axis of the assist-side pinion shaft 14 is disposed coaxially with the central axis of the assist-side pinion accommodating portion 17. The assist-side pinion shaft 14 is rotationally driven by an electric motor 41 via a worm reduction gear 40.

Assist side rack guide
The assist-side rack guide 39 presses the rack shaft 12 toward the assist-side pinion shaft 14 and is disposed inside the assist-side guide accommodating portion 19. As a result, the assist-side rack guide 39 is disposed so as to sandwich the rack shaft 12 between itself and the assist-side pinion shaft 14. As shown in FIGS. 4 and 8 , the assist-side rack guide 39 is a rolling-type rack guide and has a roller 45, a holder 46, a pin 47, a rolling bearing 48, and an elastic member 49.

The roller 45 has a generally annular shape and is rotatably supported relative to the holder 46 via a pin 47 and a rolling bearing 48, whose axial direction is oriented vertically. As a result, the outer peripheral surface of the roller 45 is in rolling contact with the middle portion of the rear side of the rack shaft 12 in the width direction. The outer peripheral surface of the roller 45 has a generatrix shape, a concave arc, that roughly matches the contour shape of the rear side of the rack shaft 12. Specifically, the outer peripheral surface of the roller 45 has a generatrix shape that roughly matches the contour shape of the rear side of the assist-side rack section 33. The holder 46 is disposed inside the assist-side guide accommodating section 19 and is capable of moving toward and away from the rack shaft 12. In the illustrated example, the elastic member 49 is a disc spring and is disposed between the holder 46 and an assist-side cap 50 that covers the opening of the assist-side guide accommodating section 19. The elastic member 49 presses the holder 46 toward the rack shaft 12.

The assist side rack guide 39 presses the rack shaft 12 toward the assist side pinion shaft 14, reducing backlash at the meshing portion between the assist side pinion teeth 43 and the assist side rack teeth 30. This prevents abnormal noise from being generated at the meshing portion between the assist side pinion teeth 43 and the assist side rack teeth 30.

Worm reducer
The worm reducer 40 includes a worm 51 and a worm wheel 52 , and reduces the speed of rotation of the electric motor 41 (increases the torque) and transmits the rotation to the assist-side pinion shaft 14 .

The worm 51 has worm teeth on its outer circumferential surface, and its base end is connected to the output shaft of the electric motor 41 via a coupling (not shown) to enable torque transmission. The worm 51 is supported inside the worm housing 22, allowing slight oscillating displacement around its base end.

The worm wheel 52 has wheel teeth on its outer circumferential surface that mesh with the worm teeth, and is fixed to the base end of the assist-side pinion shaft 14 so that it cannot rotate relative to the assist-side pinion shaft 14. The worm wheel 52 is located inside the wheel accommodating section 23.

Electric motor
The electric motor 41 is used to apply a steering assist force to the rack shaft 12 via the worm reducer 40 and the assist-side pinion shaft 14, and is fixed to the mounting flange 24 provided in the worm housing portion 22. As a result, the electric motor 41 is disposed near the center in the left-right direction of the housing 7. However, when implementing the present invention, the electric motor can also be disposed at one of the left-right ends of the housing 7.

Torque sensor
The torque sensor 42 is disposed around the steering side pinion shaft 11 and detects the magnitude and direction of the torque input to the steering side pinion shaft 11. As a result, the torque sensor 42 outputs a signal corresponding to the torque input to the steering side pinion shaft 11 to the electronic control unit of the electric motor 41. As the torque sensor 42, for example, a non-contact torque sensor utilizing the magnetostrictive effect can be used.

The assist mechanism 9 controls the drive of the electric motor 41 based on the output signal of the torque sensor 42. As a result, the drive torque generated by the electric motor 41 is transmitted as a steering assist force to the rack shaft 12 via the worm reduction gear 40 and the assist side pinion shaft 14. As a result, the steering force required for the driver to operate the steering wheel 2 is reduced.

<Rack Bush>
Each of the pair of rack bushes 10a, 10b functions as a sliding bearing and supports the rack shaft 12 so that it can be displaced axially relative to the rack housing portion 15 without rattle.

Of the pair of rack bushes 10a, 10b, the rack bush 10a, located on one axial side closer to the steering-side pinion shaft 11, is fitted into the vicinity of the opening on one axial side of the rack housing portion 15, as shown in Figure 3. The rack bush 10a is made of a synthetic resin such as polyacetal resin or polyamide resin, and has a substantially cylindrical or substantially parted cylindrical shape. The rack bush 10a has a support hole 53 through which the steering-side rack portion 32 of the rack shaft 12 is inserted axially.

The support hole 53 is a circular hole with a circular outline and an inner diameter slightly larger than the circumscribed circle diameter of the steering side rack section 32. The rack bush 10a, via the inner peripheral surface of the support hole 53, slidably supports the convex cylindrical surface portion (arc portion 32b) of the outer peripheral surface of the steering side rack section 32, excluding the front side surface (straight portion 32a) on which the steering side rack teeth 29 are provided. The steering side rack guide 25 that presses against the steering side rack section 32 is a sliding rack guide, which can ensure sufficient holding force in the width direction of the rack shaft 12, so the rack bush 10a located on one axial side can be omitted.

Of the pair of rack bushes 10a, 10b, the rack bush 10b located on the other axial side closer to the assist-side pinion shaft 14 is fitted internally near the opening on the other axial side of the rack housing 15, as shown in FIG. 4. Specifically, the rack bush 10b is fitted internally into a small-diameter hole 54 provided on the other axial side of the rack housing 15. A large-diameter hole 55, whose inner diameter is larger than that of the small-diameter hole 54, is provided on the other axial side of the small-diameter hole 54. The small-diameter hole 54 and the large-diameter hole 55 are connected via a stepped surface 56 facing the other axial side. In this example, the one axial side portion of the rack housing 15 also has a small-diameter hole 54, a large-diameter hole 55, and a stepped surface 56, and the rack bush 10a is fitted internally into the small-diameter hole 54.

The rack bushing 10b is made of a synthetic resin such as polyacetal resin or polyamide resin and has a generally cylindrical shape. The rack bushing 10b has a support hole 57 through which the assist-side rack portion 33 of the rack shaft 12 is inserted axially, and an outer peripheral surface 58 that fits into the small-diameter hole 54 of the rack housing portion 15.

As shown in FIG. 9 , the support hole 57 is a D-shaped hole through which the assist-side rack portion 33 can be inserted, and has a substantially D-shaped outline. The support hole 57 has an outline that partially matches the cross-sectional outline of the assist-side rack portion 33 provided on the rack shaft 12. The inner circumferential surface of the support hole 57 has a flat front side surface 57a, upper and lower side surfaces 57b and 57c that are substantially parallel to each other, and a concave cylindrical rear side surface 57d. The front side surface 57a provided on the portion of the inner circumferential surface of the support hole 57 that faces the assist-side rack tooth 30 corresponds to the flat surface portion described in the claims, and the upper and lower side surfaces 57b and 57c located on both sides of the tooth width direction of the assist-side rack tooth 30 correspond to a pair of inner sides described in the claims. The upper and lower surfaces 57b, 57c are made up of straight and arcuate portions of the generally D-shaped outline of the support hole 57. However, as described below, the upper and lower surfaces 57b, 57c are provided with inner circumferential convex portions 59a, 59b and inner circumferential concave portions 61a, 61b, making the upper and lower surfaces 57b, 57c uneven rather than flat. In contrast, the front surface 57a is made up of straight portions of the generally D-shaped outline of the support hole 57, and the rear surface 57d is made up of arcuate portions of the generally D-shaped outline of the support hole 57.

In the following description of the rack bushing 10b, the axial direction, radial direction, and circumferential direction refer to the axial direction, radial direction, and circumferential direction with respect to the rack bushing 10b unless otherwise specified. Furthermore, the axial direction of the rack bushing 10b coincides with the axial direction of the rack shaft 12.

The support hole 57 has inner circumferential projections 59a, 59b that protrude radially inward on the upper and lower surfaces 57b, 57c that make up the inner circumferential surface. In other words, the support hole 57 has inner circumferential projections 59a, 59b on the upper and lower surfaces 57b, 57c, that face the upper and lower surfaces of the assist-side rack section 33, respectively. Therefore, the inner circumferential projection 59a is provided on the upper portion 60a of the rack bushing 10b located above the assist-side rack section 33, and the inner circumferential projection 59b is provided on the lower portion 60b of the rack bushing 10b located below the assist-side rack section 33. In the illustrated example, the inner circumferential projections 59a, 59b each extend linearly in the axial direction and are provided in the axially intermediate portions (excluding both axial ends) of the upper and lower surfaces 57b, 57c. The upper and lower surfaces 57b and 57c have recesses at their axial ends adjacent to the inner circumferential projections 59a and 59b, which are recessed radially outward from the inner circumferential projections 59a and 59b.

The tip surfaces of the inner circumferential convex portions 59a, 59b are substantially flat. The vertical distance between the tip surface of the inner circumferential convex portion 59a provided on the upper portion 60a of the rack bushing 10b and the tip surface of the inner circumferential convex portion 59b provided on the lower portion 60b of the rack bushing 10b is slightly smaller than the widthwise dimension _W33 of the assist-side rack portion 33 (see FIG. 6B ) before the assist-side rack portion 33 is inserted into the support hole 57. Therefore, when the assist-side rack portion 33 is inserted into the support hole 57, the tip surfaces of the inner circumferential convex portions 59a, 59b contact the upper and lower surfaces that constitute the outer peripheral surface of the assist-side rack portion 33 with a tightening margin. In other words, the inner circumferential convex portions 59a, 59b elastically hold the assist-side rack portion 33 in the widthwise direction of the rack shaft 12 in an elastically deformed state. 9 depicts the shapes of the inner circumferential convex portions 59a, 59b in a free state, so that the tip ends of the inner circumferential convex portions 59a, 59b overlap with the assist-side rack portion 33, but in reality, the inner circumferential convex portions 59a, 59b each come into contact with the outer circumferential surface of the assist-side rack portion 33 and elastically deform. In this example, the tip ends of the pair of inner circumferential convex portions 59a, 59b are arranged approximately parallel to each other.

The support hole 57 has inner recesses 61a, 61b recessed radially outward in the circumferentially adjacent portions on both sides of the inner protrusions 59a, 59b. Each of the inner protrusions 59a, 59b protrudes radially inward further than the inner recesses 61a, 61b. In the illustrated example, each of the inner recesses 61a, 61b is an axial groove extending linearly in the axial direction and is provided across the entire axial width of the inner surface of the support hole 57. Each of the inner recesses 61a, 61b has a substantially semicircular cross-sectional shape. The inner recesses 61a, 61b function to reduce the rigidity of the portion of the upper portion 60a where the inner protrusion 59a is provided and the portion of the lower portion 60b where the inner protrusion 59b is provided.

While the support hole 57 has a generally D-shaped contour, the outer peripheral surface 58 of the rack bush 10b has a generally circular cross-sectional contour. As a result, the wall thickness (plate thickness) of the rack bush 10b is non-uniform in the circumferential direction. In particular, the wall thickness of the upper portion 60a and the lower portion 60b of the rack bush 10b tends to be thicker than when the support hole is a round hole.

In this example, therefore, to reduce the thickness of the portion of the upper portion 60a that includes the inner circumferential convex portion 59a and the portion of the lower portion 60b that includes the inner circumferential convex portion 59b, outer circumferential recesses 63a, 63b that are recessed radially inward are provided on the portion of the outer surface 58 that is located radially outward of the inner circumferential convex portions 59a, 59b. In the example shown, the outer circumferential recesses 63a, 63b are provided over a wider range of the outer circumferential surface 58, including portions that are in phase (circumferential position) with the inner circumferential convex portions 59a, 59b. This reduces the thickness and rigidity of the portion of the upper portion 60a that includes the inner circumferential convex portion 59a and the portion of the lower portion 60b that includes the inner circumferential convex portion 59b.

Each of the outer peripheral recesses 63a, 63b has a substantially rectangular cross-sectional shape. The inner surfaces of the outer peripheral recesses 63a, 63b consist of a pair of circumferential side surfaces that face each other in the circumferential direction and a radial bottom surface that faces radially outward. In the illustrated example, the outer peripheral recesses 63a, 63b are provided across the entire axial width of the outer peripheral surface 58.

The circumferential width of the outer recesses 63a, 63b (the distance between a pair of circumferential side surfaces) is approximately the same as the circumferential width between the groove bottoms of the circumferentially adjacent inner recesses 61a, 61b, and is larger than the circumferential width of the inner protrusions 59a, 59b.

The radial depth of the outer recesses 63a, 63b is determined in relation to the holding rigidity of the assist-side rack portion 33 in the width direction of the rack shaft 12, which is required for the inner protrusions 59a, 59b. For example, the radial depth of the outer recesses 63a, 63b can be approximately 1/2 to 2/3 of the thickness of the upper portion 60a and the lower portion 60b before the outer recesses 63a, 63b and the inner recesses 61a, 61b are formed. This allows the thickness of the portions of the upper portion 60a and the lower portion 60b sandwiched between the outer recesses 63a, 63b and the inner recesses 61a, 61b to be approximately 1/3 to 1/6 of the thickness of the upper portion 60a and the lower portion 60b before the outer recesses 63a, 63b and the inner recesses 61a, 61b are formed.

The rack bushing 10b has stopper portions 64a, 64b that protrude radially outward from the circumferentially intermediate portion of the radial bottom surface of the outer peripheral recesses 63a, 63b on the outer peripheral surface 58. Each of the stopper portions 64a, 64b is positioned radially outward from the circumferentially intermediate portion (circumferential center portion in the illustrated example) of the inner peripheral protrusions 59a, 59b. The tip surfaces (radially outer end surfaces) of the stopper portions 64a, 64b closely face or lightly contact the inner peripheral surface of the small diameter hole portion 54 when the rack bushing 10b is fitted into the small diameter hole portion 54 and the assist side rack portion 33 is inserted inside the support hole 57.

In this example, each of the stopper portions 64a, 64b is solid and has a substantially rectangular cross-sectional shape. The tip surface of each of the stopper portions 64a, 64b is configured as a partially cylindrical surface (substantially flat surface). In the illustrated example, the stopper portions 64a, 64b are provided across the entire axial width of the outer peripheral surface 58. When the assist-side rack portion 33 is displaced in the width direction of the rack shaft 12, the stopper portions 64a, 64b abut the tip surfaces of the stopper portions 64a, 64b against the inner peripheral surface of the small-diameter hole portion 54 and elastically deform (crush in the vertical direction), thereby gently preventing the assist-side rack portion 33 from displacing in the width direction of the rack shaft 12. Note that when implementing this example, the tip surfaces of the stopper portions 64a, 64b can also be in surface contact with the inner peripheral surface of the small-diameter hole portion 54. For this reason, for example, the curvature of the tip surfaces of the stopper portions 64a and 64b may be the same as the curvature of the inner circumferential surface of the small diameter hole portion 54.

The rack bushing 10b slidably supports the upper surface (straight portion 33b and part of the arc portion 33d) and lower surface (straight portion 33c and part of the arc portion 33d) that constitute the outer surface of the assist-side rack section 33, using the upper surface 57b (straight portion and part of the arc portion) and lower surface 57c (straight portion and part of the arc portion) that constitute the inner surface of the support hole 57. In particular, in this example, the upper surface and lower surface that constitute the outer surface of the assist-side rack section 33 are slidably supported by inner protrusions 59a, 59b sandwiched between a pair of inner recesses 61a, 61b of the upper surface 57b and lower surface 57c that constitute the inner surface of the support hole 57.

A gap is formed between the rear side surface 57d (concave cylindrical surface portion) that constitutes the inner circumferential surface of the support hole 57 and the rear side surface (arc portion 33d, convex cylindrical surface portion) that constitutes the outer circumferential surface of the assist-side rack section 33. This minimizes friction between the inner circumferential surface of the support hole 57 and the outer circumferential surface of the assist-side rack section 33. It also improves the ease of inserting the rack shaft 12 into the support hole 57. A space 65 with a substantially trapezoidal cross section is formed between the front side surface 57a of the inner circumferential surface of the support hole 57 and the assist-side rack teeth 30. In the illustrated example, the front side surface 57a and the upper side surface 57b that constitute the inner circumferential surface of the support hole 57 are smoothly connected, and the front side surface 57a and the lower side surface 57c that constitute the inner circumferential surface of the support hole 57 are smoothly connected.

The rack bushing 10b has a locking protrusion 66 that protrudes radially outward on the outer peripheral surface 58 at a portion circumferentially offset from the outer peripheral recesses 63a, 63b (a portion 90 degrees out of phase in the illustrated example). The locking protrusion 66 is locked into a locking recess 67 formed in the small diameter hole 54. This prevents the rack bushing 10b from rotating relative to the rack housing 15.

<Spacer>
The steering device 1 of this example further includes a pair of spacers 68a, 68b to prevent the spherical joint 35 fixed to the axial end of the rack shaft 12 from directly colliding with the rack bushings 10a, 10b made of synthetic resin when the rack shaft 12 is displaced in the axial direction.

Each of the spacers 68a, 68b has an annular shape and is made from a material stronger than the synthetic resin that makes up the rack bushings 10a, 10b. Specifically, each of the spacers 68a, 68b is made from metal. The inner diameter of each of the spacers 68a, 68b is smaller than the outer diameter of each of the rack bushings 10a, 10b, and larger than the inner diameter (inscribed circle diameter) of each of the rack bushings 10a, 10b.

In this example, the spacers 68a and 68b are each fitted and secured to the rear end of the large-diameter hole 55 of the rack housing 15 by an interference fit. However, the method of securing the spacers 68a and 68b is not limited to interference fit. Other methods include threading a male thread formed on the outer surface of the spacer into a female thread formed on the inner surface of the large-diameter hole, or using adhesives. In either case, in this example, with the spacers 68a and 68b secured to the large-diameter hole 55, the axial side surfaces of the spacers 68a and 68b abut against the stepped surface 56 along their entire circumference. This positions the spacers 68a and 68b axially and appropriately restricts axial displacement of the rack shaft 12. Note that when implementing this invention, if collision between the spherical joint 35 and the rack bushings 10a and 10b can be avoided by control or other means, the spacers 68a and 68b can be omitted. Furthermore, if the inner diameter of the small diameter hole portion 54 on one axial side is sufficiently small and a sufficient collision area between the stepped surface 56 and the spherical joint 35 can be secured, the spacer 68a can also be omitted.

According to the steering device 1 of this example having the above-described configuration, even when a rack shaft 12 having an approximately D-shaped cross-sectional contour shape of the assist-side rack section 33 is used, the rack bushing 10b can compensate for the holding force of the rack shaft 12 in the width direction.
That is, in this example, the support hole 57 of the rack bushing 10b, through which the assist-side rack portion 33 is inserted, is a D-shaped hole having a substantially D-shaped outline. This allows the assist-side rack portion 33 to be inserted into the support hole 57 without the assist-side rack teeth 30 interfering with the rack bushing 10b. The inner circumferential surface of the support hole 57 (inner circumferential convex portions 59a, 59b) can slidably support both upper and lower side surfaces that constitute the outer circumferential surface of the assist-side rack portion 33. Therefore, the rack bushing 10b can supplement the holding force in the width direction of the rack shaft 12.

In particular, in this example, the inner circumferential protrusions 59a, 59b provided on the upper and lower surfaces 57b, 57c of the inner circumferential surface of the support hole 57, enable the assist-side rack section 33 to be elastically held in the width direction of the rack shaft 12. In other words, the pair of inner circumferential protrusions 59a, 59b apply preload to the assist-side rack section 33 in the width direction of the rack shaft 12. This ensures sufficient holding force in the width direction of the rack shaft 12.

In addition, in this example, inner recesses 61a, 61b are provided on the inner surface of the support hole 57 in portions located on both circumferential sides of the inner protrusions 59a, 59b, and outer recesses 63a, 63b are provided on the outer surface 58 of the rack bush 10b in portions located radially outward of the inner protrusions 59a, 59b. This allows the rigidity of the portion of the upper portion 60a of the rack bush 10b that is provided with the inner protrusion 59a and the portion of the lower portion 60b of the rack bush 10b that is provided with the inner protrusion 59b to be kept sufficiently low. This prevents the retaining rigidity of the assist-side rack section 33 provided by the inner protrusions 59a, 59b from becoming excessive.

On the other hand, if the radial depth of the outer recesses 63a, 63b were increased to reduce the holding rigidity of the inner protrusions 59a, 59b, it would be difficult to control (keep small) the amount of widthwise displacement of the rack shaft 12 of the assist-side rack section 33. Therefore, in this example, the outer peripheral surface 58 of the rack bushing 10b is further provided with stopper portions 64a, 64b that protrude radially outward on the radial bottom surfaces of the outer recesses 63a, 63b. The stopper portions 64a, 64b control the amount of widthwise displacement of the rack shaft 12 of the assist-side rack section 33. In other words, the tip surfaces of the stopper portions 64a, 64b abut against the inner peripheral surface of the small-diameter hole 54 of the rack housing 15, and the elastic deformation of the stopper portions 64a, 64b prevents excessive widthwise displacement of the rack shaft 12 of the assist-side rack section 33. As a result, in this example, it is possible to achieve both a reduction in the holding rigidity of the inner peripheral convex portions 59a, 59b and control of the displacement of the assist side rack portion 33 in the width direction of the rack shaft 12.

Furthermore, the cross-sectional contour of the assist-side rack portion 33 is generally D-shaped, and the widthwise dimension _W33 of the assist-side rack portion 33 is larger than the outer diameter D of the shaft-shaped portion 34. Therefore, the tooth width _T30 of the assist-side rack teeth 30 can be increased to the widthwise dimension _W33 of the assist-side rack portion 33. Therefore, compared to a method of increasing the tooth width of the rack teeth by, for example, increasing the outer diameter of the entire rack shaft without changing the cross-sectional shape of the rack shaft to a circular shape, the strength of the assist-side rack teeth 30 can be improved while suppressing an increase in the weight of the rack shaft 12. This makes it possible to transmit a large torque from the assist-side pinion teeth 43 to the assist-side rack teeth 30. As a result, a high-output electric motor 41 can be used, thereby increasing the output of the steering device 1.

The assist side rack guide 39 that constitutes the assist mechanism 9 is a rolling type rack guide equipped with rollers 45 that make rolling contact with the rack shaft 12. This reduces the resistance that occurs between the rack shaft 12 and the assist side rack guide 39 compared to when a sliding type rack guide is used, thereby improving the steering feel. It also improves the transmission efficiency from the assist side pinion shaft 14 to the rack shaft 12, which is advantageous in terms of achieving higher output.

In this example, the widthwise dimension _W32 of the steering-side rack portion 32 is smaller than the widthwise dimension _W33 of the assist-side rack portion 33. Therefore, the vertical dimension of the portion of the rack housing 15 that houses the steering-side rack portion 32 can be made smaller than the vertical dimension of the portion that houses the assist-side rack portion 33, as long as the stroke of the rack shaft 12 can be ensured. By adopting such a configuration, the housing 7 can be made smaller, making it easier to ensure installation in the engine compartment. However, when implementing the present invention, the widthwise dimension of the steering-side rack portion may be made the same as the widthwise dimension of the assist-side rack portion.

In addition, in this example, the central axis of the rack shaft 12 and the central axis of the output shaft of the electric motor 41 are arranged approximately parallel. As a result, the amount by which the electric motor 41 protrudes in the front-to-rear direction from the rack housing section 15 can be made smaller than when the central axis of the rack shaft and the central axis of the output shaft of the electric motor are arranged non-parallel. This also makes it easier to ensure ease of installation in the engine room.

[Second Example of Embodiment]
A second example of the embodiment will be described with reference to FIG.

In this example, only the shape of the stopper portion 64c of the rack bush 10b differs from the structure of the first embodiment.

The stopper portion 64c has a tapered, approximately triangular cross-sectional shape, with its circumferential width decreasing radially outward. The tip of the stopper portion 64c is in close contact with or lightly contacts the inner circumferential surface of the small-diameter hole portion 54.

In this example having the above-described configuration, the tip of the stopper portion 64c can be more easily elastically deformed than in the structure of the first example of the embodiment, and therefore, displacement in the width direction of the rack shaft 12 (see FIGS. 4 and 9, etc.) of the assist-side rack portion 33 can be more gradually prevented.
The other configurations and effects are the same as those of the first embodiment.

[Third Example of Embodiment]
A third example of the embodiment will be described with reference to FIG.

In this example, only the shape of the stopper portion 64d of the rack bush 10b differs from the structure of the first and second embodiments.

Similar to the structure of the first embodiment, the stopper portion 64d has a generally rectangular cross-sectional shape, but has an oval through-hole 69 in the center. Therefore, the stopper portion 64d is hollow rather than solid.

In this example having the above-described configuration, the stopper portion 64d can be more easily elastically deformed than in the structure of the first example of the embodiment by virtue of the inclusion of the through-hole 69. Therefore, as shown in FIG. 13B, the stopper portion 64d can be easily elastically deformed (crushed). Therefore, displacement of the rack shaft 12 (see FIGS. 4 and 9, etc.) of the assist-side rack portion 33 in the width direction can be more gradually prevented.
The other configurations and effects are the same as those of the first embodiment.

[Fourth Example of Embodiment]
A fourth example of the embodiment will be described with reference to FIG.

In this example, only the shape of the stopper portion 64e of the rack bush 10b differs from the structure of the first to third embodiments.

In other words, unlike the structure of the second embodiment, the stopper portion 64e has a trapezoidal cross-sectional shape with a circumferential width that decreases radially inward. The stopper portion 64e has a constricted portion 70 at its base end (the radially inner end) where the circumferential width is at its smallest. In addition, the tip surface of the stopper portion 64e is configured as a flat surface.

In this example having the above configuration, the constricted portion 70 is provided at the base end of the stopper portion 64e, and therefore the provision of the stopper portion 64e can prevent the rigidity of the inner peripheral convex portion 59a (59b) located radially inside the stopper portion 64e from becoming too high. Furthermore, because the tip surface of the stopper portion 64e is flat, when the tip surface of the stopper portion 64e abuts against the inner peripheral surface of the small diameter hole portion 54, the stopper portion 64e can be prevented from tilting in the circumferential direction of the rack bushing 10b.
The other configurations and effects are the same as those of the first embodiment.

[Fifth Example of Embodiment]
The fifth example of the embodiment will be described with reference to FIGS.

In this example, the outer peripheral surface shape of the assist-side rack portion 71 that constitutes the rack shaft 12 and the structure of the rack bushing 10c differ from the structures in the first to fourth examples of the embodiment.

The assist-side rack portion 71 has a generally D-shaped cross-sectional contour consisting of three linear portions 71a, 71b, and 71c and one arc portion 71d. However, the upper and lower surfaces of the outer peripheral surface of the assist-side rack portion 71, located on both sides in the tooth width direction of the assist-side rack teeth 72, are not parallel to each other. Instead, they are inclined in directions that move away from each other in the tooth height direction of the assist-side rack teeth 72 (left-right direction in FIG. 15) toward the tip of the assist-side rack teeth 72. Therefore, the linear portion 71b that forms the contour of the upper surface of the assist-side rack portion 71 and the linear portion 71c that forms the contour of the lower surface of the assist-side rack portion 71 are inclined in directions that move away from each other in the tooth height direction of the assist-side rack teeth 72 toward the tip of the assist-side rack teeth 72. In the illustrated example, the straight line portions 71b and 71c are each inclined at approximately 5 degrees with respect to an imaginary line L that is perpendicular to the straight line portion 71a that defines the outline of the front side of the outer circumferential surface of the assist-side rack portion 71.

In this example, the upper and lower surfaces that make up the outer circumferential surface of the assist side rack portion 71 are each tapered, so the widthwise dimension of the assist side rack portion 71 (the vertical direction in FIG. 15) increases the closer it is to the assist side rack teeth 72 in the tooth height direction of the assist side rack teeth 72. In this example, by making the upper and lower surfaces that make up the outer circumferential surface of the assist side rack portion 71 tapered, it becomes easier to remove (pull out) the assist side rack portion 71 of the rack shaft 12 from the cavity of the press die when manufacturing the rack shaft 12 by press working.

In this example, the rack bush 10c has a support hole 73 through which the assist side rack portion 71 described above is axially inserted, and the contour shape of this hole is generally circular rather than generally D-shaped.

The inner circumferential surface of the support hole 73 has a concave cylindrical front side 73a provided in the portion facing the assist side rack teeth 72, an upper side 73b and a lower side 73c located on either side in the tooth width direction of the assist side rack teeth 72, and a concave cylindrical rear side 73d provided on the opposite side of the assist side rack teeth 72 in the diameter direction.

The front side surface 73a has a cross-sectional shape that is a single arc, and corresponds to the concave cylindrical surface portion described in the claims. The rear side surface 73d also has a cross-sectional shape that is a single arc. In this example, the center of curvature Oa of the front side surface 73a and the center of curvature Od of the rear side surface 73d are approximately coincident with each other. However, the centers of curvature Oa of the front side surface 73a and the rear side surface 73d do not have to coincide with each other. The radius of curvature Ra of the cross-sectional shape of the front side surface 73a is greater than the radius of curvature Rd of the cross-sectional shape of the rear side surface 73d. In this example, the front side surface 73a, which is part of the inner circumferential surface of the support hole 73, is made a concave cylindrical surface having a cross-sectional shape that is a single arc, thereby making the thickness t of the front portion of the rack bushing 10c thinner and more uniform in the circumferential direction than the structure of the first embodiment in which the front side surface is a flat surface.

When the assist side rack portion 71 is inserted inside the support hole 73, the circumferential ends on both sides of the front side surface 73a are located in the portions that face both side surfaces in the tooth width direction of the assist side rack teeth 72, i.e., the upper and lower sides. In this example, both circumferential ends of the front side surface 73a are connected to the inner peripheral recess 75a, which will be described later. Specifically, both circumferential ends of the front side surface 73a are smoothly connected to the bottom of the inner peripheral recess 75a, which has a semicircular cross-sectional shape.

In this example, the support hole 73 also has inner circumferential convex portions 74a, 74b that protrude radially inward on the upper and lower surfaces 73b, 73c that make up the inner circumferential surface. In other words, the support hole 73 has inner circumferential convex portions 74a, 74b on the upper and lower surfaces 73b, 73c, of the inner circumferential surface that face the upper and lower surfaces of the assist-side rack portion 71, respectively. The tip surfaces of the inner circumferential convex portions 74a, 74b are generally flat. In this example, the tip surfaces of the pair of inner circumferential convex portions 74a, 74b are inclined in directions that move away from each other toward the tip of the assist-side rack tooth 72 in the tooth height direction of the assist-side rack tooth 72, matching the inclination of the upper and lower surfaces of the assist-side rack portion 71.

The inclination angle X of the inner circumferential convex portion 74a relative to the virtual line L and the inclination angle Y of the inner circumferential convex portion 74b relative to the virtual line L can be set, for example, between 1 degree and 10 degrees. It is preferable that the inclination angle X and the inclination angle Y are the same, but they may also be different.

In this example, when the assist-side rack section 71 is inserted inside the support hole 73, the tip surfaces of the inner circumferential convex sections 74a, 74b contact the upper and lower surfaces that make up the outer peripheral surface of the assist-side rack section 71 with a tightening margin. In other words, the inner circumferential convex sections 74a, 74b elastically hold the assist-side rack section 71 in the width direction of the rack shaft 12 when in an elastically deformed state. In particular, in this example, because the tip surfaces of the inner circumferential convex sections 74a, 74b are inclined, a force F including a component force Fa in the gear meshing direction (leftward in Figure 15) can be applied from each of the inner circumferential convex sections 74a, 74b to the upper and lower surfaces of the assist-side rack section 71.

The support hole 73 has inner recesses 75a, 75b recessed radially outward in the portions adjacent to both sides of the inner protrusions 74a, 74b in the circumferential direction. Of the pair of inner recesses 75a, 75b, the inner recess 75a, which is located toward the tip of the assist side rack tooth 72 in the tooth height direction of the assist side rack tooth 72, smoothly connects to the front side surface 73a that constitutes the inner surface of the support hole 73.

The rack bushing 10c has a back-side recess 77 recessed radially inward on the outer peripheral surface 76, located on the radially opposite side of the assist-side rack teeth 72. In other words, the back-side recess 77 is located on the outer peripheral surface 76 of the rack bushing 10c, at a position circumferentially offset by 90 degrees from each of the outer peripheral recesses 63a, 63b. The back-side recess 77 has a substantially rectangular cross-sectional shape. The inner surface of the back-side recess 77 consists of a pair of circumferential side surfaces that face circumferentially opposite each other, and a radial bottom surface that faces radially outward. In this example, the back-side recess 77 is located across the entire axial width of the outer peripheral surface 76. Therefore, the back-side recess 77 opens to both axial end faces of the rack bushing 10c.

As shown in Figure 16, the rack bushing 10c of this example has slits 78a, 78b that open to the radial bottom surface of the rear recess 77 and the inner circumferential surface (rear side surface) of the support hole 73, respectively. Each of the slits 78a, 78b extends in the axial direction. The slits 78a, 78b open to both circumferential ends of the radial bottom surface of the rear recess 77 and the inner circumferential surface of the support hole 73, respectively, and also open to the end face on the other axial side of the rack bushing 10c. The axial ends of the slits 78a, 78b on one side are closed ends and are located in the axial middle of the rack bushing 10c.

As shown in Figures 16 and 17, the rack bushing 10c of this example has anti-slip protrusions 79 that protrude radially outward on the outer peripheral surface 76 at both circumferential sides of the outer peripheral recesses 63a, 63b and at the other axial end. The anti-slip protrusions 79 engage with anti-slip recesses 80 formed in the small diameter hole 54 of the rack accommodating section 15, preventing the rack bushing 10c from coming out of the small diameter hole 54 in the axial direction. A total of four anti-slip protrusions 79 are provided.

In this example having the above configuration, the front side surface 73a of the inner circumferential surface of the support hole 73 is a concave cylindrical surface with a single arc-shaped cross section. This allows the thickness t of the front portion of the rack bushing 10c to be thinner than the structure of the first example embodiment, in which the front side surface is flat. This reduces the rigidity of the front portion of the rack bushing 10c. This also reduces the force required to reduce the diameter of the rack bushing 10c in the direction of bringing the pair of inner circumferential protrusions 74a, 74b closer together (the vertical direction in Figure 15) in order to install the rack bushing 10c into the predetermined position in the small-diameter hole 54 of the rack accommodating section 15. This improves the ease of fitting the rack bushing 10c into the small-diameter hole 54 of the rack accommodating section 15 and engaging the retaining protrusions 79 with the retaining recesses 80.

In addition, a rear recess 77 is provided on the outer peripheral surface 76 of the rack bushing 10c, on the diametrically opposite side of the assist-side rack teeth 72, which also reduces the rigidity of the rear portion of the rack bushing 10c. Furthermore, in this example, slits 78a, 78b are provided on the rear portion of the rack bushing 10c, which further reduces the rigidity of the rear portion of the rack bushing 10c. Therefore, the force required to reduce the diameter of the rack bushing 10c in the direction of bringing the pair of inner peripheral protrusions 74a, 74b closer together can be further reduced.

In addition, in this example, the inner peripheral surface of the support hole 73 has both circumferential ends of the front side surface 73a, which is a concave cylindrical surface with a single arc cross-section, positioned opposite the side surface of the assist side rack tooth 72 and connected to the inner peripheral recess 75a. This allows a gap 81 to be formed between the side surface of the assist side rack tooth 72 and the front side surface 73a, preventing interference between the inner peripheral surface of the support hole 73 and both side surfaces of the assist side rack tooth 72 in the tooth width direction.

Furthermore, in this example, the tip surfaces of the pair of inner peripheral convex portions 74 a, 74 b are inclined in directions that move away from each other in the tooth height direction of the assist-side rack teeth 72 as they approach the tip of the assist-side rack teeth 72, so that a rack shaft 12 having tapered upper and lower surfaces of the assist-side rack portion 71 can be used. Also, a force F including a component force Fa in the gear meshing direction can be applied to the upper and lower surfaces of the assist-side rack portion 71 from each of the inner peripheral convex portions 74 a, 74 b, so that the meshing state between the assist-side rack teeth 72 and the assist-side pinion teeth 43 (see FIG. 8 , etc.) can be improved. Also, the generation of abnormal noise at the meshing portion between the assist-side rack teeth 72 and the assist-side pinion teeth 43 can be suppressed.
The other configurations and effects are the same as those of the first embodiment.

The above describes an embodiment of the present invention, but the present invention is not limited to this and can be modified as appropriate without departing from the technical concept of the invention. Furthermore, the structures of each example embodiment can be combined as appropriate as long as no contradictions arise.

When implementing the present invention, the shapes, sizes, and positions of the inner circumferential convex portions, inner circumferential concave portions, outer circumferential concave portions, stopper portions, rear surface concave portions, and slits are not limited to the structures of the exemplary embodiments and can be modified as appropriate. Furthermore, the shapes and sizes of a pair of inner circumferential convex portions, a pair of outer circumferential concave portions, and a pair of stopper portions arranged on opposite radial sides of the rack bush can also be made different from each other.

In each of the above-described embodiments, a sliding rack guide is used as the steering side rack guide 25, but when implementing the present invention, a rolling rack guide can also be used as the steering side rack guide. Alternatively, sliding rack guides can be used for both the steering side rack guide and the assist side rack guide.

In each of the above-described embodiments, the rack shaft 12 is described as being solid, but the rack shaft can also be hollow throughout its entire length.

In addition, in each of the above-described embodiments, the steering side rack teeth 29 and the assist side rack teeth 30 are both formed on the front side of the rack shaft 12, but when implementing the present invention, the steering side rack teeth and the assist side rack teeth can also be formed on a portion other than the front side, such as the rear side of the rack shaft. Furthermore, the steering side rack teeth and the assist side rack teeth can also be formed at different positions in the circumferential direction.

In each of the above-described embodiments, the present invention has been described as being applied to a dual-pinion electric power steering device. However, the present invention is not limited to dual-pinion electric power steering devices, and can be applied to various types of electric power steering devices, such as column-assist, rack-assist, and pinion-assist types, which have only one pinion shaft that meshes with the rack shaft. Furthermore, the present invention is not limited to electric power steering devices, and can also be applied to hydraulic power steering devices and manual steering devices. Furthermore, the present invention can also be applied to steer-by-wire steering devices.

REFERENCE SIGNS LIST 1 steering device 2 steering wheel 3 steering shaft 4 steering column 5a, 5b universal joint 6 intermediate shaft 7 housing 8 steering mechanism 9 assist mechanism 10a, 10b, 10c rack bush 11 steering side pinion shaft 12 rack shaft 13 steering wheel 14 assist side pinion shaft 15 rack accommodating portion 16 steering side pinion accommodating portion 17 assist side pinion accommodating portion 18 steering side guide accommodating portion 19 assist side guide accommodating portion 20 gear housing portion 21a, 21b mounting portion 22 worm accommodating portion 23 wheel accommodating portion 24 mounting flange 25 steering side rack guide 26 steering side pinion teeth 27a, 27b bearing 28 tie rod 29 steering side rack teeth 30 assist side rack teeth 31 Screw hole 32 Steering side rack portion 32a Straight portion 32b Arc portion 33 Assist side rack portion 33a, 33b, 33c Straight portion 33d Arc portion 34 Shaft-shaped portion 35 Spherical joint 36 Pad 36a Pressing surface 37 Elastic member 38 Steering side cap 39 Assist side rack guide 40 Worm reducer 41 Electric motor 42 Torque sensor 43 Assist side pinion teeth 44a, 44b Bearing 45 Roller 46 Holder 47 Pin 48 Rolling bearing 49 Elastic member 50 Assist side cap 51 Worm 52 Worm wheel 53 Support hole 54 Small diameter hole portion 55 Large diameter hole portion 56 Step surface 57 Support hole 57a Front surface 57b Upper surface 57c Lower surface 57d Rear surface 58 Outer surface 59a, 59b Inner peripheral convex portion 60a Upper portion 60b Lower portion 61a, 61b Inner peripheral concave portion 63a, 63b Outer peripheral concave portion 64a to 64e Stopper portion 65 Space 66 Locking convex portion 67 Locking concave portion 68a, 68b Spacer 69 Through hole 70 Narrowed portion 71 Assist side rack portion 71a, 71b, 71c Straight portion 71d Arc portion 72 Assist side rack tooth 73 Support hole 73a Front surface 73b Upper surface 73c Lower surface 73d Rear surface 74a, 74b Inner peripheral convex portion 75a, 75b Inner peripheral concave portion 76 Outer surface 77 Rear recess 78a, 78b Slits 79 Anti-slip protrusion 80 Anti-slip recess 81 Gap 100 Steering device 101 Housing 101a Rack accommodating portion 101b Pinion accommodating portion 101c Guide accommodating portion 102 Pinion shaft 102a Pinion teeth 103 Rack shaft 103a Rack teeth 104 Rack guide 104a Roller 104b Holder 104c Pin 104d Elastic member 105 Rack bush 105a Support hole 106a, 106b Bearing 107 Tie rod 108 Cap

Claims (8)

A rack bushing for supporting a rack shaft having rack teeth relative to a housing so as to allow the rack shaft to move in an axial direction,
a support hole through which the rack shaft is inserted, and an outer peripheral surface fitted into the housing,
the support hole has, on each of a pair of inner side surfaces arranged on both sides in the tooth width direction of the rack teeth, inner peripheral convex portions that protrude radially inward compared to portions adjacent to both sides in the circumferential direction of the support hole,
the outer peripheral surface has an outer peripheral side recess that is recessed radially inward and is provided at a portion located radially outward of the inner peripheral side protrusion, and a stopper portion that protrudes radially outward from a radial bottom surface of the outer peripheral side recess,
The stopper portion is hollow.
Rack bushing. A rack bushing for supporting a rack shaft having rack teeth relative to a housing so as to allow the rack shaft to move in an axial direction,
a support hole through which the rack shaft is inserted, and an outer peripheral surface fitted into the housing,
The support hole has, on each of a pair of inner surfaces arranged on both sides in the tooth width direction of the rack teeth, inner circumferential convex portions that protrude radially inward compared to portions adjacent on both sides in the circumferential direction of the support hole, and inner circumferential concave portions that are recessed radially outward in portions adjacent on both sides of the inner circumferential convex portions in the circumferential direction,
the outer peripheral surface has an outer peripheral side recess that is recessed radially inward and is provided at a portion located radially outward of the inner peripheral side protrusion, and a stopper portion that protrudes radially outward from a radial bottom surface of the outer peripheral side recess,
the support hole has an inner circumferential surface, at a portion facing the rack teeth, a concave cylindrical surface portion having a cross-sectional shape of a single arc,
Both circumferential ends of the concave cylindrical surface portion are connected to the inner peripheral recess portion.
Rack bushing. A rack bushing for supporting a rack shaft having rack teeth relative to a housing so as to allow the rack shaft to move in an axial direction,
a support hole through which the rack shaft is inserted, and an outer peripheral surface fitted into the housing,
the support hole has, on each of a pair of inner side surfaces arranged on both sides in the tooth width direction of the rack teeth, inner peripheral convex portions that protrude radially inward compared to portions adjacent to both sides in the circumferential direction of the support hole,
the outer peripheral surface has an outer peripheral side recess that is recessed radially inward and is provided in a portion located radially outward of the inner peripheral side protrusion, a stopper portion that protrudes radially outward from a radial bottom surface of the outer peripheral side recess , and a back surface side recess that is recessed radially inward and is provided in a portion located on the opposite side of the rack teeth in the diameter direction .
Rack bushing. 4. The rack bushing according to claim 3 , wherein a slit is formed in each of a radial bottom surface of the rear recess and an inner peripheral surface of the support hole. A rack bushing for supporting a rack shaft having rack teeth relative to a housing so as to allow the rack shaft to move in an axial direction,
a support hole through which the rack shaft is inserted, and an outer peripheral surface fitted into the housing,
the support hole has, on each of a pair of inner side surfaces arranged on both sides in the tooth width direction of the rack teeth, inner peripheral convex portions that protrude radially inward compared to portions adjacent to both sides in the circumferential direction of the support hole,
the outer peripheral surface has an outer peripheral side recess that is recessed radially inward and is provided at a portion located radially outward of the inner peripheral side protrusion, and a stopper portion that protrudes radially outward from a radial bottom surface of the outer peripheral side recess,
tip surfaces of the pair of inner peripheral convex portions are inclined in directions that move away from each other toward the tip ends of the rack teeth in the tooth height direction of the rack teeth,
Rack bushing. A rack shaft,
a pinion shaft that meshes with the rack shaft;
a rack guide disposed between the rack shaft and the pinion shaft and configured to press the rack shaft toward the pinion shaft;
a housing having a rack accommodating portion that accommodates the rack shaft, a pinion accommodating portion that accommodates the pinion shaft, and a guide accommodating portion that accommodates the rack guide;
a rack bushing that supports the rack shaft relative to the rack housing portion so as to allow movement of the rack shaft in an axial direction,
the rack shaft has a rack portion having a substantially D-shaped cross-sectional contour and having rack teeth formed thereon to mesh with the pinion shaft, and a shaft-like portion having a circular cross-sectional contour provided at a portion axially offset from the rack portion,
the rack portion has a width dimension that is equal to or larger than the outer diameter of the shaft portion,
The rack guide includes a roller that is in rolling contact with the rack shaft,
The rack bush is a rack bush according to any one of claims 1 to 5 .
Rack and pinion steering system. a spacer disposed farther from the pinion shaft than the rack bush in the axial direction of the rack shaft,
The spacer is made of a material stronger than the material of the rack bush.
7. A rack and pinion steering device according to claim 6 . an electric motor that rotates the pinion shaft;
a second pinion shaft different from the pinion shaft that rotates in response to a steering operation of a steering wheel,
the rack shaft further includes a second rack portion, the second rack portion having second rack teeth formed thereon and meshing with the second pinion shaft, at portions axially offset from the rack portion and the shaft-like portion,
The housing further includes a second pinion accommodating portion that accommodates the second pinion shaft.
A rack and pinion steering device according to any one of claims 6 to 7 .