Rack shaft and steering gear unit

Abstract

Provided is a rack shaft 2 capable of suppressing backlash between pinion teeth 18 and rack teeth 20 in a high gain region H, and capable of suppressing an excessive frictional force generated between the rack shaft 2 and a rack guide 4, without an increase in manufacturing costs. The rack shaft 2 includes: a rack central axis O2; a rack portion 21 having a low gain region L and the high gain region H in which a plurality of the rack teeth 20 are arranged at mutually different pitches; and a back surface portion 22 having a contacting portion 30 that extends parallel to the rack central axis O2. When the rack teeth 20 of the rack shaft 2 are meshed with the pinion teeth 18, a distance D from the rack central axis O2 to a pinion central axis O3 of the pinion shaft 3 is greater in at least a partial range of the high gain region H than in the low gain region L, and is greater in a first low gain region L1 at the axial center of the rack portion 21 than in a second low gain region L2 at the axial end of the rack portion 21.

Description

Rack shaft and steering gear unit

[0001] The present disclosure relates to a rack shaft and a steering gear unit including the rack shaft.

[0002] A steering device is incorporated in a vehicle such as an automobile, and transmits the movement of a steering wheel operated by a driver to a steering gear unit via a steering shaft, thereby applying a steering angle to the left and right steered wheels.

[0003] The steering gear unit includes a pinion shaft, a rack shaft, and a rack guide.

[0004] The pinion shaft is supported inside a housing fixed to the vehicle body so as to be rotatable only. The pinion shaft has pinion teeth on its outer circumferential surface and rotates in response to rotation of the steering wheel.

[0005] The rack shaft is supported inside the housing so that it can only move back and forth, with its central axis facing the width direction of the vehicle body. The rack shaft has a plurality of rack teeth that mesh with the pinion teeth on a portion of its outer circumferential surface. Both axial ends of the rack shaft are connected to tie rods via spherical joints.

[0006] The rack guide is disposed in the housing at a position where the rack shaft is sandwiched between the rack guide and the pinion shaft, and elastically presses the rack shaft toward the pinion shaft.

[0007] The rotational movement of the pinion shaft accompanying the rotation of the steering wheel is converted into linear movement of the rack shaft, which pushes and pulls the tie rod, imparting a steering angle to the left and right steered wheels according to the amount of rotation of the steering wheel.

[0008] Furthermore, because the rack shaft is pressed toward the pinion shaft by the rack guide, backlash at the meshing portion between the rack teeth and the pinion teeth is reduced, thereby reducing abnormal noise generated at the meshing portion.

[0009] In order to improve the straight-line stability and maneuverability of a vehicle, rack shafts with a VGR (variable gear ratio) structure, in which the pitch of the rack teeth varies depending on the axial position of the rack teeth on the rack shaft, have begun to be adopted in recent years.

[0010] The rack shaft having the VGR structure has a low-gain region where the rack teeth that mesh with the pinion teeth are arranged at a small pitch, and a high-gain region where the rack teeth are arranged at a large pitch. The number of rack teeth in the high-gain region is smaller than in the low-gain region. As a result, in the high-gain region, the separation force is likely to be large, making it more likely that backlash will occur between the pinion teeth and the rack teeth. As a result, abnormal noise such as rattles is likely to occur at the meshing portion between the pinion teeth and the rack teeth.

[0011] Japanese Patent Application Laid-Open Publication No. 2016-182936 discloses a rack shaft structure in which the distance (thickness dimension) between the rack teeth and the back surface portion pressed by the rack guide increases from the axial center of the rack shaft toward both ends in the axial direction.

[0012] In this rack shaft, the magnitude of the force with which the rack guide presses the rack shaft increases toward both ends of the rack shaft in the axial direction, which reduces backlash between the pinion teeth and the rack teeth in the high gain regions located on both axial sides of the rack shaft, thereby suppressing abnormal noise generated at the meshing portion.

[0013] JP 2016-182936 A

[0014] However, in the rack shaft described in JP 2016-182936 A, the thickness dimension of the rack shaft is changed by providing a thick portion on the back portion of the outer peripheral surface of the rack shaft. Therefore, it is necessary to process not only the rack teeth but also the back portion of the rack shaft with high precision, taking into consideration dimensional accuracy, which causes the manufacturing cost of the rack shaft to increase.

[0015] Furthermore, in a rack shaft, meshing adjustment between the rack teeth and the pinion teeth is generally performed using rack teeth located in the axial center of the rack section, but some twisting is unavoidable in the rack shaft due to manufacturing reasons. As a result, the meshing accuracy between the rack teeth located at the axial end of the rack section and the pinion teeth tends to be lower than the meshing accuracy between the rack teeth located in the axial center of the rack section and the pinion teeth. Therefore, when the rack teeth located at the axial end of the rack section mesh with the pinion teeth, the friction force generated between the rack shaft and the rack guide may become excessive.

[0016] An object of the present disclosure is to provide a rack shaft with a VGR structure that can suppress backlash between the pinion teeth and the rack teeth in the high gain range and prevent excessive frictional force from occurring between the pinion teeth and the rack guide, without increasing manufacturing costs.

[0017] A rack shaft according to one aspect of the present disclosure includes a rack central shaft, a rack portion, and a rear portion.

[0018] The rack portion is provided with a plurality of rack teeth that are arranged in the axial direction on a portion of the circumferential direction of the outer circumferential surface of the rack shaft and that mesh with pinion teeth of the pinion shaft in use.

[0019] The back surface portion is provided on the outer circumferential surface of the rack shaft on the radially opposite side to the rack portion, and is pressed by a rack guide during use.

[0020] The rack portion has a low gain region and a high gain region in which the rack teeth are arranged at different pitches.

[0021] The low gain regions are provided at the axial center and both axial end portions of the rack portion.

[0022] The high gain region is provided in a portion of the rack portion between the axial center portion and each of the axial end portions.

[0023] The pitch of the rack teeth provided in the high gain region is greater than the pitch of the rack teeth provided in the low gain region.

[0024] The rear surface portion has a contact portion that comes into direct or indirect contact with the rack guide and extends parallel to the central axis of the rack.

[0025] When the rack teeth are meshed with the pinion teeth, the distance from the rack central axis to the pinion central axis of the pinion shaft is greater in at least a portion of each of the high gain regions than in the low gain region, and in the low gain region, the distance is greater in a first low gain region at the axial center than in each of the second low gain regions at the axial end portions.

[0026] In the rack shaft according to one aspect of the present disclosure, the axial dimension of the first low gain region can be smaller than the axial dimension of each of the second low gain regions.

[0027] In the rack shaft according to one aspect of the present disclosure, the distance can be greater over the entire range of the high gain region than in the low gain region, i.e., the first low gain region and the second low gain region.

[0028] In the rack shaft according to one aspect of the present disclosure, the distance can be made different within each of the high gain regions.

[0029] In a rack shaft according to one aspect of the present disclosure, the distance can be made larger in at least a portion of the range of each of the high gain regions than in the first low gain region, and the distance can be made the same as in either the first low gain region or the second low gain region in the remaining range of each of the high gain regions.

[0030] In the rack shaft according to one aspect of the present disclosure, the difference between the distance in at least a portion of each of the high gain regions and the distance in the first low gain region can be set to 10 μm or more.

[0031] In the rack shaft according to one aspect of the present disclosure, the difference between the distance in at least a portion of each of the high gain regions and the distance in each of the second low gain regions can be set to 100 μm or less.

[0032] In a rack shaft according to one aspect of the present disclosure, the rack portion may have a first transition region at a boundary between the first low gain region and the high gain region, and a second transition region at a boundary between the second low gain region and the high gain region, wherein the distance in the first transition region increases as the distance approaches from the first low gain region to the high gain region, and the distance in the second transition region increases as the distance approaches from the second low gain region to the high gain region.

[0033] A steering gear unit according to one aspect of the present disclosure includes: a pinion shaft having a pinion central axis and pinion teeth provided on an outer peripheral surface, the pinion shaft rotating around the pinion central axis as a steering wheel is rotated; a rack shaft having rack teeth on its outer peripheral surface that mesh with the pinion teeth; a rack guide that presses the rack shaft toward the pinion shaft; and a housing that houses the pinion shaft, the rack shaft, and the rack guide inside, wherein the rack shaft is the rack shaft according to one aspect of the present disclosure.

[0034] According to a rack shaft according to one aspect of the present disclosure, in a rack shaft with a VGR structure, backlash between the pinion teeth and the rack teeth in the high gain range can be suppressed without increasing manufacturing costs, and excessive friction force between the pinion teeth and the rack guide can be suppressed.

[0035] FIG. 1 is a perspective view showing an example of a steering device according to an embodiment of the present disclosure, including a rack shaft according to an embodiment of the present disclosure. FIG. 2 is a partially cutaway perspective view showing a steering gear unit removed from the steering device. FIG. 3 is a partial cross-sectional view of the steering gear unit. FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3. FIGS. 5(A) and 5(B) are cross-sectional views showing another example of a rack guide that can be used in the steering gear unit. FIGS. 6(A) and 6(B) are cross-sectional views showing another example of a rack shaft that can be used in the steering gear unit. FIG. 7 is a plan view showing one axial side portion of the rack shaft. FIG. 8 is a schematic cross-sectional view of the rack shaft. FIG. 9 is a schematic cross-sectional view of the steering gear unit, showing, from left to right, a state in which pinion teeth of a pinion shaft mesh with rack teeth in a low gain region L, a state in which they mesh with rack teeth in a transition region T, and a state in which they mesh with rack teeth in a high gain region H of the rack portion of the rack shaft. 10 shows the low gain region L, the transition region T, and the high gain region H provided in the rack portion, and the rack central axis O. ２ From pinion central axis O ３ 11A and 11B are graphs showing the relationship between the distance D and the pinion teeth in the low gain region L. Fig. 11A shows the state in which the rack teeth and pinion teeth in the high gain region H are meshed with each other.

[0036] A steering gear unit 5 and a rack shaft 2 that constitute a steering device 1 according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 11. FIG.

[0037] The rack shaft 2 and steering gear unit 5 of this example are suitably applied to, but not limited to, a steering device 1 for an automobile.

[0038] Below, we will explain the general structure of the steering device 1 and the steering gear unit 5 including the rack shaft 2, and then explain the detailed structure of the rack shaft 2. In the following explanation of the steering device 1, the front-rear direction means the front-rear direction of the vehicle, and the left-right direction means the width direction of the vehicle.

[0039] (1) General Structure of the Steering Device The steering device 1 of this example includes a steering gear unit 5, a steering wheel 6, a steering shaft 7, a steering column 8, two universal joints 9a, 9b, an intermediate shaft 10, and a pair of tie rods 11.

[0040] The steering wheel 6 is attached to the rear end of a steering shaft 7. The steering shaft 7 is rotatably supported inside a steering column 8 that is supported on the vehicle body. The front end of the steering shaft 7 is connected to the steering gear unit 5 via a rear universal joint 9a, an intermediate shaft 10, and a front universal joint 9b.

[0041] The steering device 1 can optionally and additionally be provided with an electric assist device 13 as an electric power steering device for reducing the force required for the driver to operate the steering wheel 6.

[0042] The electric assist device 13 applies auxiliary power to the steering shaft 7 or the steering gear unit 5. In this example, the electric assist device 13 applies auxiliary power to the steering shaft 7.

[0043] (2) General Structure of Steering Gear Unit The steering gear unit 5 has a pinion center axis O ３ and pinion teeth 18 provided on the outer peripheral surface thereof, and as the steering wheel 6 is rotated, the pinion central axis O ３ a rack shaft 2 having rack teeth 20 on its outer circumferential surface that mesh with the pinion teeth 18; a rack guide 4 that presses the rack shaft 2 toward the pinion shaft 3; and a housing 14 that houses the pinion shaft 3, the rack shaft 2, and the rack guide 4 inside.

[0044] When the driver turns the steering wheel 6, the rotation of the steering wheel 6 is transmitted to the pinion shaft 3. The pinion shaft 3 rotates at the same rotation angle as the steering wheel 6, and the pinion central axis O ３ The pinion shaft 3 is meshed with the rack shaft 2, and the rotational motion of the pinion shaft 3 is converted into the linear motion of the rack shaft 2.

[0045] As a result, the tie rod 11 connected to both axial ends of the rack shaft 2 via a spherical joint 12 is pushed and pulled, and a steering angle corresponding to the amount of rotation of the steering wheel 6 is applied to the left and right steered wheels.

[0046] In addition, when the steering device 1 is equipped with an electric assist device 13 that applies auxiliary power to the steering gear unit 5 , the assist device 13 applies auxiliary power to the rack shaft 2 or the pinion shaft 3 .

[0047] <<Housing>> The housing 14 is fixed to the vehicle body using fixing members such as bolts, studs, etc. The housing 14 is integrally formed by die-casting a light alloy such as an aluminum alloy, for example.

[0048] In this example, although not limited thereto, the housing 14 includes a rack accommodating portion 15 , a pinion accommodating portion 16 , and a guide accommodating portion 17 .

[0049] The rack housing portion 15 houses the rack shaft 2 therein. The rack housing portion 15 has a substantially cylindrical shape and is disposed with its longitudinal direction oriented in the width direction of the vehicle.

[0050] The pinion accommodating portion 16 accommodates the pinion shaft 3 therein. The pinion accommodating portion 16 has a bottomed cylindrical or cylindrical shape and is connected to a portion of the rack accommodating portion 15 on one axial side (the left side in FIGS. 2 and 3 ) in the circumferential direction. The central axis of the pinion accommodating portion 16 is disposed in a twisted position with respect to the central axis of the rack accommodating portion 15. When viewed from the front-to-rear direction, which is a direction perpendicular to both the central axis of the pinion accommodating portion 16 and the central axis of the rack accommodating portion 15, the central axis of the pinion accommodating portion 16 is not disposed in a direction perpendicular to the central axis of the rack accommodating portion 15, but is inclined with respect to the direction perpendicular to the central axis. The internal space of the pinion accommodating portion 16 is in communication with the internal space of the rack accommodating portion 15.

[0051] The guide accommodating portion 17 accommodates the rack guide 4 therein. The guide accommodating portion 17 has a cylindrical shape and is connected to a portion of the rack accommodating portion 15 that is diametrically opposite to the pinion accommodating portion 16. The central axes of the guide accommodating portions 17 are arranged in radial directions about the central axis of the rack accommodating portion 15. The internal space of the guide accommodating portion 17 is in communication with the internal space of the rack accommodating portion 15.

[0052] <Pinion shaft> The pinion shaft 3 is aligned with the pinion central axis O. ３ As long as the pinion shaft 3 has a front end and pinion teeth 18 on its outer circumferential surface, any structure can be adopted. In this example, although not limited to this, the pinion shaft 3 has pinion teeth 18 on the outer circumferential surface of its front half. The front half of the pinion shaft 3 is inserted inside the pinion accommodating portion 16 and is supported by a plurality of bearings 19 a, 19 b in the pinion accommodating portion 16 so as to be rotatable only. The base half of the pinion shaft 3 protrudes from the pinion accommodating portion 16 and is connected to the steering wheel 6 via universal joints 9 a, 9 b, the intermediate shaft 10, the steering shaft 7, etc.

[0053] The rack shaft 2 is the rack center axis O. ２The rack shaft 2 has a front portion 21 and a rear portion 22. The rack shaft 2 is formed of a long, rod-shaped member made of metal. The rack portion 21 is arranged in the axial direction on a portion of the circumferential direction of the outer circumferential surface of the rack shaft 2, and has a plurality of rack teeth 20 that mesh with pinion teeth 18 of the pinion shaft 3 during use. The position and range in which the rack portion 21 is provided are not particularly limited and are arbitrary. In this example, although not limited thereto, the rack portion 21 is provided on one axial side (the left side in FIG. 2 ) of the rack shaft 2, with a portion thereof facing the pinion shaft 3.

[0054] Of the plurality of rack teeth 20 provided on the rack portion 21 , the rack teeth 20 located opposite the pinion shaft 3 mesh with the pinion teeth 18 provided on the pinion shaft 3 .

[0055] The rear surface portion 22 is provided on the outer peripheral surface of the rack shaft 2 on the radially opposite side to the rack portion 21, and is pressed by the rack guide 4 during use. The axial position of the rear surface portion 22 on the rack shaft 2 and the axial position of the rack portion 21 on the rack shaft 2 are the same.

[0056] In this example, the rack shaft 2 is inserted into the rack housing 15 with its longitudinal direction directed in the width direction of the vehicle. ２ is disposed approximately coaxially with the central axis of the rack housing portion 15, with its axially intermediate portion housed inside the rack housing portion 15 and its both axial ends protruding from the rack housing portion 15. Both axial ends of the rack shaft 2 are connected to tie rods 11 via spherical joints 12.

[0057] In this example, a rack bushing 23 is optionally and additionally disposed between the other axial side portion of the outer peripheral surface of the rack shaft 2 and the other axial side end of the inner peripheral surface of the rack housing portion 15. The rack bushing 23 prevents the other axial side end of the rack shaft 2 from rattling radially relative to the rack housing portion 15.

[0058] 3 and 4, the rack guide 4 presses the rack shaft 2 toward the pinion shaft 3. The rack guide 4 is disposed at a position where the rack shaft 2 is sandwiched between the rack guide 4 and the pinion shaft 3. The rack guide 4 has a guide center axis O ４ the rack center axis O of the rack shaft 2 ２ The guide accommodating portion 17 is accommodated inside the guide accommodating portion 17 so as to face in a direction perpendicular to the guide accommodating portion 17.

[0059] The rack guide 4 elastically presses the rack shaft 2 toward the pinion shaft 3, thereby reducing backlash at the meshing portion between the pinion teeth 18 and the rack teeth 20. Furthermore, the meshing state between the pinion teeth 18 and the rack teeth 20 is maintained appropriately regardless of the force acting on the rack shaft 2 in a direction away from the pinion shaft 3 as power is transmitted through the meshing portion.

[0060] The rack guide 4 and the elastic member 24 constitute a pressing mechanism 25. The pressing mechanism 25 can have a sliding structure or a rolling structure. In this example, the pressing mechanism 25 has a sliding structure.

[0061] In this example, the rack guide 4 has a substantially cylindrical shape and is disposed inside the guide housing portion 17 so as to be movable toward and away from the rack shaft 2. That is, the rack guide 4 is disposed on the rack shaft central axis O. ２ It moves in a direction perpendicular to the

[0062] In this example, the rack guide 4 has a guide recess 26 for holding the rear surface 22 of the rack shaft 2 on its tip surface facing the rear surface 22. The surface of the guide recess 26 is coated with a material having excellent sliding properties.

[0063] Rack central axis O ２ The cross-sectional contour shape of the guide recess 26 with respect to an imaginary plane perpendicular to the plane is arbitrary. In this example, the guide recess 26 is composed of two flat inclined surfaces 27 and one flat bottom surface 28, and the cross-sectional contour shape of the guide recess 26 is composed only of straight portions. In the rack guide 4, the two inclined surfaces 27 of the guide recess 26 come into contact with the back surface portion 22 of the rack shaft 2.

[0064] Alternatively, the rack central axis O ２ The cross-sectional contour shape of the guide recess 26 with respect to an imaginary plane perpendicular to the plane may be formed only of curved portions (arcuate portions) as shown in Fig. 5(A). Alternatively, the cross-sectional contour shape of the guide recess 26 may be formed by a combination of curved portions and straight portions as shown in Fig. 5(B).

[0065] When the pressing mechanism 25 has a rolling structure, the pressing mechanism 25 is configured to include, for example, a roller-shaped rack guide 4 that comes into rolling contact with the back surface of the rack shaft 2, a holder that rotatably supports the rack guide 4 and is arranged so that it can move toward and away from the rack shaft 2, and an elastic member 24 that presses the holder.

[0066] <<Elastic Member>> The elastic member 24 is disposed in an elastically compressed state between the rack guide 4 and the cap 29 that closes the opening of the guide accommodating portion 17. The elastic member 24 presses the rack guide 4 toward the rack shaft 2. As a result, the rack guide 4 presses the rack shaft 2 toward the pinion shaft 3. The elastic member 24 may be formed of other elastic members such as a coil spring or a leaf spring. In this example, the elastic member 24 is formed of a coil spring.

[0067] (3) Detailed Structure of the Rack Shaft The rack shaft 2 has a VGR structure, and the pitch of the rack teeth 20 that make up the rack portion 21 varies depending on the axial position of the rack teeth 20 in the rack portion 21. Therefore, in the steering gear unit 5 that includes the rack shaft 2, the specific stroke (rack shaft movement amount / one pinion rotation) that corresponds to the axial movement amount of the rack shaft 2 per one rotation of the steering wheel 6 (pinion shaft 3) varies depending on the rotation angle of the pinion shaft 3 (hereinafter also simply referred to as the "rotation angle").

[0068] The number and pitch of the rack teeth 20 of the rack shaft 2 are set so that the pinion shaft 3 (steering wheel 6) rotates ±360 degrees, ±540 degrees, ±720 degrees, or any angle between ±360 degrees and ±720 degrees from a state in which the pinion teeth 18 of the pinion shaft 3 mesh with the rack teeth 20 at the axial center (rack center) of the rack section 21 until they mesh with the rack teeth 20 at the axial end (rack end) of the rack section 21. In this example, the pinion shaft 3 (steering wheel 6) rotates ±540 degrees. In other words, the number of lock-to-lock rotations of the steering wheel 6 is set to 3.

[0069] <<Rack Section>> The rack section 21 has a low gain region L and a high gain region H in which the rack teeth 20 are arranged at different pitches. In Figures 7 and 10, the slopes of the rack teeth 20 in the low gain region L have a diagonal checkered pattern, and the slopes of the rack teeth 20 in the high gain region H have a diagonal line pattern.

[0070] (Low-gain region) The low-gain region L is provided at least in the axial center of the rack portion 21 and in each of the axial end portions on both axial sides of the rack portion 21. The low-gain region L is provided in at least three locations in the rack portion 21, but it is also possible to provide one or more additional low-gain regions L between the axial center of the rack portion 21 and each of the axial end portions on both axial sides.

[0071] The range of the low gain region L (the range of the rotation angle of the pinion shaft 3) is arbitrary. For example, in a setting in which the low gain region L is provided at three locations on the rack portion 21 and the pinion shaft 3 rotates by ±540 degrees, the low gain region L may be, but is not limited to, a range of −540 degrees to −440 degrees or a range of −540 degrees to −520 degrees, preferably a range of −540 degrees to −480 degrees or a range of −540 degrees to −520 degrees, at one of the axial ends on both sides of the axial direction, as the range of the rotation angle of the pinion shaft 3. , in the axial center portion, in a range of −20 degrees to +20 degrees or a range of −10 degrees to +10 degrees, preferably a range of −15 degrees to +15 degrees or a range of −10 degrees to +10 degrees, and in the other of the axial ends, in a range of +440 degrees to +540 degrees or a range of +520 degrees to +540 degrees, preferably a range of +480 degrees to +540 degrees or a range of +520 degrees to +540 degrees. The total range of all low gain regions L is at least 60 degrees to 240 degrees as the range of rotation angle of the pinion shaft 3. However, the total range of all low gain regions L may exceed 240 degrees.

[0072] The rotation angle of the pinion shaft 3 can be any value between ±360 degrees and ±720 degrees, and in these cases, the range of the low gain region L can be set to the same ratio as when the rotation angle of the pinion shaft is ±540 degrees. For example, when the pinion shaft 3 is set to rotate ±360 degrees, the range of the low gain region L is 2 / 3 of when the pinion shaft 3 is set to rotate ±540 degrees, although this is not limited thereto, and when the pinion shaft 3 is set to rotate ±720 degrees, the range of the low gain region L is 4 / 3 of when the pinion shaft 3 is set to rotate ±540 degrees, although this is not limited thereto.

[0073] Of the three low gain regions L provided in the rack portion 21, the low gain region L provided in the axial center of the rack portion 21 is referred to as the first low gain region L. １ The low gain regions L provided at both axial ends of the rack portion 21 are referred to as second low gain regions L. ２ It is called.

[0074] First low gain region L１ The second low gain region L is provided for the purpose of improving the straight-line stability of the vehicle. ２ are provided for the purpose of ensuring the strength of the rack teeth 20 at both axial ends of the rack portion 21, which is particularly likely to be a problem in large vehicles.

[0075] When the rack portion 21 has a plurality of types of low gain regions L, the pitch P of the rack teeth 20 between the different types of low gain regions L is Ｌ can be the same as each other, or the pitch P of the rack teeth 20 Ｌ In the rack shaft 2 of this example, the second low gain regions L ２ and the pitch P of the rack teeth 20 Ｌ are the same. In addition, the first low gain region L １ and the second low gain region L ２ The pitch P of the rack teeth 20 Ｌ That is, the three low gain regions L provided in the rack portion 21 are spaced apart by the pitch P of the rack teeth 20. Ｌ are all the same.

[0076] Alternatively, the first low gain region L １ and the second low gain region L ２ The pitch P of the rack teeth 20 Ｌ Specifically, from the viewpoint of ensuring the strength of the rack teeth 20 at both axial ends of the rack portion 21, the second low gain region L ２ Pitch P of the rack teeth 20 Ｌ２ The first low gain region L １ Pitch P of the rack teeth 20 Ｌ１ An appropriate value can be selected from the range of about 0.9 to 1.1 times the value of the above.

[0077] (High-gain region) The high-gain region H is provided at least in each of the portions between the axial center and both axial end portions of the rack portion 21. The high-gain region H is provided in at least two locations in the rack portion 21, but it is also possible to provide one or more additional high-gain regions H between the axial center and both axial end portions of the rack portion 21. For example, if one or more low-gain regions L are provided between the axial center and both axial end portions of the rack portion 21, the high-gain region H is provided in one location between each of the plurality of low-gain regions L.

[0078] The range of the high gain region H (the range of the rotation angle of the pinion shaft 3) is arbitrary. For example, in a configuration in which the low gain region L is provided at three locations on the rack portion 21 and the high gain region H is provided at two locations on the rack portion 21, and the pinion shaft 3 rotates by ±540 degrees, the range of the rotation angle of the pinion shaft 3 may be, but is not limited to, −400 degrees to −160 degrees or −300 degrees to −200 degrees, or preferably −360 degrees to −180 degrees or −300 degrees to −200 degrees, on one side in the axial direction, and +160 degrees to +400 degrees or +200 degrees to +300 degrees, or preferably +180 degrees to +360 degrees or +200 degrees to +300 degrees, on the other side in the axial direction. The total range of all high gain regions H is at least 200 to 480 degrees as the range of the rotation angle of the pinion shaft 3. However, the total range of all high gain regions H may exceed 480 degrees.

[0079] Similarly, when the rotation angle of the pinion shaft 3 is any angle between ±360 degrees and ±720 degrees, the range of the high gain region H can be set to the same ratio as when the rotation angle of the pinion shaft is ±540 degrees. For example, when the pinion shaft 3 is set to rotate ±360 degrees, the range of the high gain region H is 2 / 3 of the range when the pinion shaft 3 is set to rotate ±540 degrees, although this is not limited to this, and when the pinion shaft 3 is set to rotate ±720 degrees, the range of the high gain region H is 4 / 3 of the range when the pinion shaft 3 is set to rotate ±540 degrees, although this is not limited to this.

[0080] Pitch P of the rack teeth 20 provided in the high gain region H Ｈ is the pitch P of the rack teeth 20 provided in the low gain region L Ｌ is greater than (P Ｈ >P Ｌ ). The pitch P of the rack teeth 20 in the low gain region L Ｌ Pitch P of the rack teeth 20 in the high gain region H Ｈ The ratio of the size of (P Ｈ / P Ｌ ) is arbitrary, but the pitch P of the rack teeth 20 in the high gain region H Ｈ is the pitch P of the rack teeth 20 in the low gain region L Ｌ It is preferably about 1.1 to 1.4 times, and more preferably about 1.2 to 1.3 times.

[0081] When the rack portion 21 has a plurality of high gain regions H, the pitch P of the rack teeth 20 is Ｈ Alternatively, the pitch P of the rack teeth 20 may be set to be equal to each other for each high gain region H. Ｈ In the rack shaft 2 of this example, the pitch P of the rack teeth 20 is different in the two high gain regions H. Ｈ are the same as each other.

[0082] (Shape of rack teeth) In the rack shaft 2, the shape of the rack teeth 20 can be the same throughout the rack portion 21, or can be changed depending on the axial position of the rack teeth 20 in the rack portion 21. In addition, in the rack shaft 2, the inclination angle of the tooth trace of the rack teeth 20 can be the same throughout the rack portion 21, or can be changed depending on the axial position of the rack teeth 20 in the rack portion 21.

[0083] The rack teeth 20 are provided in at least a part of the high gain region H, and the low gain region L (L １ , L ２Specifically, the rack teeth 20 provided in at least a portion of the high gain region H and the rack teeth 20 provided in the low gain region L can be made to differ from each other in at least one element (size, angle, dimension, etc.) selected from the pressure angle, helix angle, tooth thickness, tooth depth (including tooth addendum and tooth root), crest width, tooth normal pitch, etc.

[0084] (Rack central axis O ２ From pinion central axis O ３ In the rack shaft 2, by making the shapes of the rack teeth 20 different in the low gain region L and the high gain region H, when the rack teeth 20 are meshed with the pinion teeth 18, the distance D from the rack center axis O ２ From pinion central axis O ３ The distance D to the low gain region L, specifically, the first low gain region L provided in the axial center of the rack portion 21, is at least partially within each of the high gain regions H. １ , and a second low gain region L provided at the axial end of the rack portion 21 ２ (D Ｈ >D Ｌ ).

[0085] That is, as shown in FIG. 9, in at least a part of the high gain region H, the rack central axis O ２ From pinion central axis O ３ Distance D to Ｈ is the first low gain region L １ The rack central axis O ２ From pinion central axis O ３ Distance D to Ｌ１ , and the second low gain region L ２ The rack central axis O ２ From pinion central axis O ３ Distance D to Ｌ２ The rack center axis O ２ From pinion central axis O ３ Distance D to (D Ｈ , D Ｌ１ , D Ｌ２) is the rack center axis O ２ The distance in the normal direction of the rack center axis O ２ 9 and the left-right direction in FIGS. 4 and 11. The normal direction of the arrows .theta. is the same as the direction of approach and retract movement of the rack guide 4, and corresponds to the up-down direction in FIG. 9 and the left-right direction in FIGS.

[0086] In this example, the rack central axis O ２ From pinion central axis O ３ The distance D to the first low gain region L １ and the second low gain region L ２ is greater than either of the above.

[0087] Rack central axis O ２ From pinion central axis O ３ The distance D to the high gain region H can be set to be approximately constant or can be set to be different in each high gain region H. In this example, the distance D Ｈ is substantially constant throughout the entire range of each high gain region H. In addition, in the two high gain regions H, the distance D Ｈ are the same as each other.

[0088] Alternatively, the rack central axis O ２ From pinion central axis O ３ When the distance D to the rack center axis O is made different in each of the high gain regions H, ２ From pinion central axis O ３ The distance D to the rack portion 21 can be set to be greater in a range close to the axial center of the rack portion 21 in each high gain region H than in a range far from the axial center of the rack portion 21.

[0089] In at least a part of each of the high gain regions H, the distance D is set to the low gain region L (first low gain region L １ and the second low gain region L ２ If the distance D is different between the first and second low-gain regions, the distance D is set to be larger than the distance D in the first low-gain region (where the distance D is larger), and in the remaining range of each of the high-gain regions H, the distance D is set to be larger than the distance D in the low-gain region L (where the distance D is larger than the distance D in the first low-gain region L １ and the second low gain region L ２When the distance D is different between the first low gain region L １ or the second low gain region L ２ In this case, for example, if the high gain region H is provided at two locations on the rack portion 21 and the pinion shaft 3 rotates by ±540 degrees, the distance D between the rack center axis O and the pinion shaft 3 may be set to, but is not limited to, the same as the distance D between the rack center axis O and the pinion shaft 3. ２ From pinion central axis O ３ The distance D to the rack portion 21 is set to a range close to the axial center of the rack portion 21 in the high gain region H, specifically, a range of rotation angles of −270 degrees to −160 degrees or −230 degrees to −200 degrees, preferably −250 degrees to −180 degrees or −230 degrees to −200 degrees, and a range of +160 degrees to +270 degrees or +200 degrees to +230 degrees, preferably +180 degrees to +250 degrees or +200 degrees to +230 degrees, and the first low gain region L １ According to this configuration, rattle noise that occurs when the vehicle is running can be effectively suppressed.

[0090] When the rack portion 21 has a plurality of types of low gain regions L, the rack central axis O ２ From pinion central axis O ３ The distance D to the first low gain region L can be set to be approximately constant or different between different types of low gain regions L. In this case, the distance D is set to be approximately constant between the low gain regions L of the same type. In this example, the first low gain region L １ Distance D at Ｌ１ is the first low gain region L １ The second low gain region L ２ Distance D at Ｌ２ Also, the second low gain region L ２ is approximately constant over the entire range.

[0091] In this example, the first low gain region L １ and the second low gain region L ２ The rack center axis O ２ From pinion central axis O ３ Distance D to ＬThat is, the first low gain region L １ Distance D at Ｌ１ and the second low gain region L ２ Distance D at Ｌ２ and are different from each other (D Ｌ１ ≠D Ｌ２ ). First low gain region L １ Distance D at Ｌ１ is the second low gain region L ２ Distance D at Ｌ２ For example, the first low gain region L １ Distance D with respect to Ｌ１ is the second low gain region L ２ Distance D at Ｌ２ It can be made larger by about 5 μm to 90 μm, preferably about 5 μm to 35 μm, and more preferably about 10 μm to 15 μm.

[0092] Distance D in each partial range of the high gain region H Ｈ and the low gain region L (L １ , L ２ ) distance D Ｌ (D Ｌ１ , D Ｌ２ ) and the difference (ΔL1 = D Ｈ -D Ｌ１ , △L2=D Ｈ -D Ｌ２ ) is the pitch P of the rack teeth 20 in the high gain region H Ｈ and the pitch P of the rack teeth 20 in the low gain region L Ｌ The difference between the pressure applied to the pressing mechanism 25 and the spring constant of the elastic member 24 can be taken into consideration when determining the pressure applied to the pressing mechanism 25 .

[0093] Specifically, the distance D in the high gain region H Ｈ and the first low gain region L １ Distance D with respect to Ｌ１ The difference (ΔL1) between the distance D and the distance D in the high gain region H is set to 10 μm or more, preferably 15 μm or more, and more preferably 18 μm or more, in order to effectively suppress backlash between the rack teeth 20 and the pinion teeth 18 in the high gain region H. Ｈ and the second low gain region L ２ Distance D atＬ２ The difference (ΔL2) between the above values ​​is set to 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less, in order to prevent the frictional force between the back surface portion 22 and the rack guide 4 in the high gain region H from becoming excessive.

[0094] In this example, the distance D in the high gain region H Ｈ and the first low gain region L １ Distance D at Ｌ１ The difference (ΔL1) between the distance D and the distance L is set to 20 μm. Ｈ and the second low gain region L ２ Distance D at Ｌ２ The difference (ΔL2) is set to 30 μm.

[0095] In this example, the first low gain region L is disposed in the axial center of the rack portion 21. １ and the axial dimension of the second low gain region L disposed at the axial end of the rack portion 21. ２ The axial dimensions of the first low gain region L １ The axial dimension of the second low gain region L ２ In other words, the first low gain region L １ is the second low gain region L ２ The reason for this is that the first low gain region L １ is used when driving the vehicle straight and does not require steering angle, so a narrow range is sufficient.

[0096] In this example, the first low gain region L １ The axial dimension of the second low gain region L is about 20 degrees (±10 degrees) to 40 degrees (±20 degrees) in terms of the rotation angle. ２ The axial dimensions of each of the second low gain regions L are approximately 20 to 100 degrees in terms of rotation angle. ２ The actual range of use of each of the above is a rotation angle range of about 10 to 40 degrees, but the second low gain region L ２ By providing a range of play in the axial dimension, it becomes possible to apply the rack teeth 20 to a plurality of vehicle models in which the use areas of the rack teeth 20 are different.

[0097] First low gain region L １ and the axial dimension of the second low gain region L ２ The axial dimensions of the respective shafts may be the same as each other.

[0098] In the rack shaft 2 of this example, when the rack teeth 20 are meshed with the pinion teeth 18, the rack central axis O ２ From pinion central axis O ３ The distance D to the high gain region H is within the low gain region L (first low gain region L １ and the second low gain region L ２ ) is larger than (D Ｈ >D Ｌ ), and the first low gain region L １ Then, the second low gain region L ２ is greater than (D Ｌ１ >D Ｌ２ ). The rear surface 22 of the rack shaft 2 is in contact with the rack guide 4 and is aligned with the rack center axis O. ２ The contact portion 30 extends parallel to the

[0099] Therefore, as shown in FIG. 11, the pinion central axis O ３ From the rack center axis O to the contact portion 30 ２ The distance α in the normal direction of the low gain region L (L １ , L ２ 11A) in which the pinion teeth 18 are engaged with the rack teeth 20 in the range of the high gain region H, and FIG. 11B) in which the pinion teeth 18 are engaged with the rack teeth 20 in the range of the high gain region H. Specifically, the distance α is Ｈ and the low gain region L (L １ , L ２ ) distance D Ｌ The difference (ΔL) between the low gain region L (L １ , L ２ ) in at least a part of the high gain region H. １ Then, the second low gain region L ２ is greater than (D Ｌ１ >DＬ２ ) In this case, the distance α is the distance D in the high gain region H. Ｈ and the first low gain region L １ Distance D at Ｌ１ The first low gain region L １ in at least a part of the high gain region H, and the distance D Ｈ and the second low gain region L ２ Distance D at Ｌ２ The second low gain region L ２ In at least a part of the high gain region H, the gain is larger than that in the high gain region H.

[0100] Therefore, the low gain region L (L １ , L ２ In a state where the pinion teeth 18 are engaged with the rack teeth 20 in at least a part of the range of the high gain region H, the rack guide 4 in contact with the contact portion 30 of the rack shaft 2 is shifted by the amount of the difference (ΔL (ΔL1, ΔL2)) from the state where the pinion teeth 18 are engaged with the rack teeth 20 in at least a part of the range of the high gain region H to the pinion central axis O. ３ , and the elastic member 24 contracts by the difference (ΔL).

[0101] Therefore, the force with which the rack guide 4 presses the rack shaft 2 is within the low gain region L (L １ , L ２ ) in the high gain region H, the torque is larger when the pinion teeth 18 are engaged with the rack teeth 20 in at least a partial range of the high gain region H than when the pinion teeth 18 are engaged with the rack teeth 20 in the low gain region L (L １ , L ２ ), the number of rack teeth 20 meshing with the pinion teeth 18 is smaller than in the conventional gear ratio ...

[0102] In particular, the rack shaft 2 of this example has a rack central axis O ２ From pinion central axis O ３The distance D to the low gain region L (first low gain region L) is １ and the second low gain region L ２ ), so that the backlash between the pinion teeth 18 and the rack teeth 20 is suppressed over the entire range of the high gain region H.

[0103] In the rack shaft 2 of this example, the rack central axis O ２ From pinion central axis O ３ The distance D to the first low gain region L １ The second low gain region L ２ Therefore, the force with which the rack guide 4 presses the rack shaft 2 is in the first low gain region L １ The rack teeth 20 and the pinion teeth 18 are in mesh with each other in the second low gain region L ２ Therefore, the second low gain region L ２ In the second low gain region L ２ This also reduces the frictional force between the tooth surfaces of the rack teeth 20 and the pinion teeth 18.

[0104] In this example, the rack shaft 2 has a second low gain region L at the axial end of the rack portion 21, rather than a high gain region. ２ , the strength of the axial end portion of the rack portion 21 can be ensured.

[0105] (Transition Region) In the rack shaft 2, the rack portion 21 is in the low gain region L (L １ , L ２ Optionally or additionally, a transition region T may be provided at the boundary between the first low gain region L and the high gain region H. In this case, the transition region T is located at the boundary between the first low gain region L and the high gain region H. In this example, the transition region T is located at the boundary between the first low gain region L and the high gain region H. １ and the boundary between the high gain region H and the second low gain region L ２ and the high gain region H, respectively.

[0106] The range of the transition region T (the range of the rotation angle of the pinion shaft 3) is determined appropriately depending on the range of the low gain region L and the range of the high gain region H. In this example, the transition region T is provided at four locations on the rack portion 21. In a configuration in which the low gain regions L are provided in three locations on the rack section 21, the high gain regions H are provided in two locations on the rack section 21, and the pinion shaft 3 rotates ±540 degrees, the transition regions T are provided in the following ranges of the rotation angle of the pinion shaft 3 on one axial side: a maximum range of −520 degrees to −300 degrees, a minimum range of −440 degrees to −400 degrees, a maximum range of −200 degrees to −10 degrees, and a minimum range of −160 degrees to −20 degrees, and on the other axial side: a maximum range of +10 degrees to +200 degrees, a minimum range of +20 degrees to +160 degrees, a maximum range of +300 degrees to +520 degrees, and a minimum range of +400 degrees to +440 degrees, although not limited thereto. The total range of all the transition regions T is 220 degrees to 630 degrees, as the rotation angle range of the pinion shaft 3. However, the total range of all transition regions T is not prevented from being less than 220 degrees (including 0).

[0107] Similarly, when the rotation angle of the pinion shaft 3 is any angle between ±360 degrees and ±720 degrees, the range of the transition region T can be set to the same ratio as when the rotation angle of the pinion shaft is ±540 degrees. For example, when the pinion shaft 3 is set to rotate ±360 degrees, the range of the transition region T is 2 / 3 of the range when the pinion shaft 3 is set to rotate ±540 degrees, although this is not limited to this, and when the pinion shaft 3 is set to rotate ±720 degrees, the range of the transition region T is 4 / 3 of the range when the pinion shaft 3 is set to rotate ±540 degrees, although this is not limited to this.

[0108] Pitch P of the rack teeth 20 provided in the transition region T Ｔ is the low gain region L (L １ , L ２ ) the pitch P of the rack teeth 20 Ｌ and the pitch P of the rack teeth 20 provided in the high gain region H is larger than Ｈ is smaller than (P Ｌ <P Ｔ <P Ｈ).

[0109] The pitch P of the rack teeth 20 provided in each transition region T Ｔ may be the same in the axial direction of the rack shaft 2 or may vary in the axial direction of the rack shaft 2. In this example, the pitch P of the rack teeth 20 in the transition region T is Ｔ changes in the axial direction of the rack shaft 2. The manner in which the pitch of the rack teeth in the transition region changes may be arbitrary, and may be, for example, linear, curved, or stepwise (in steps).

[0110] In this example, of the four transition regions T provided in the rack portion 21, the first low gain region L １ and a first transition region T provided at the boundary between the high gain region H. １ Pitch P of the rack teeth 20 Ｔ is the first low gain region L １ It increases linearly from the second low gain region L ２ and a second transition region T provided at the boundary between the high gain region H. ２ Pitch P of the rack teeth 20 Ｔ is the range from the high gain region H to the second low gain region L ２ It decreases linearly as it approaches .

[0111] In each transition region T, the shape of the rack teeth 20 may be the same or may vary. １ , T ２ The shape of the rack teeth 20 provided in the transition region T (T １ , T ２ The rack teeth 20 provided on the rack shaft 2 are varied in the axial direction of the rack shaft 2 in at least one element (size, angle, dimension, etc.) selected from the pressure angle, helix angle, tooth thickness, tooth depth (including tooth addendum and tooth root), crest clearance, face width, and tooth normal pitch.

[0112] By changing the shape of the rack teeth 20 in the transition region T, the rack shaft 2 has a rack center axis O ２ From pinion central axis O３ Distance D to Ｔ becomes larger as it approaches the high gain region H from the low gain region L in the axial direction. １ Distance D at Ｔ is the first low gain region L in the axial direction １ , the closer to the high gain region H, the larger the gain. ２ Distance D at Ｔ is the second low gain region L in the axial direction ２ , the closer to the high gain region H, the larger the gain.

[0113] Rack central axis O in transition region T ２ From pinion central axis O ３ The manner in which the distance D changes to the target point is arbitrary, and for example, a manner in which the distance changes in a curve or in a stepwise manner (step-like manner) can be adopted. １ , T ２ ) the distance D Ｔ is the low gain region L (L １ , L ２ ) to the high gain region H, the gain increases linearly.

[0114] The rack shaft 2 of this example is in the low gain region L (L １ , L ２ ) and the high gain region H, the rack central axis O ２ From pinion central axis O ３ The distance D to the rack shaft 2 is in the low gain region L (L １ , L ２ ) and the transition region T (T １ , T ２ ) for the rack teeth 20 that mesh with the pinion teeth 18. １ , L ２ When switching between the rack teeth 20 in the high gain region 10 and the rack teeth 20 in the high gain region H, the rack guide 4 can be moved smoothly.

[0115] However, in a mode in which the rack guide 4 can move smoothly when the rack teeth 20 meshing with the pinion teeth 18 switch between the rack teeth 20 in the low gain region L and the rack teeth 20 in the high gain region H, it is possible to omit the transition region T.

[0116] The rack portion 21 may have a configuration, but is not limited to, such that it has a "second low gain region L" extending from one axial side to the other axial side. ２ (Axial end) - Second transition region T ２ - High gain region H - First transition region T １ First low gain region L １ (Center in axial direction) - 1st transition region T １ - High gain region H - Second transition region T ２ - Second low gain region L ２ (axial end portion)”, ２ (Axial end) - High gain region H - First low gain region L １ (Axial center) - High gain region H - Second low gain region L ２ (axial end portion) ３ (Axial end) - Second high gain region H ２ - Second low gain region L ２ First high gain region H １ First low gain region L １ (Axial center) - First high gain region H １ - Second low gain region L ２ - Second high gain region H ２ -Third low gain region L ３ (axial end portion)".

[0117] The rear portion 22 is in contact with the rack guide 4 and is parallel to the rack central axis O. ２ The rear surface portion 22 has a contact portion 30 extending parallel to the rear surface portion 22. The contact portion 30 is provided over substantially the entire length of the rear surface portion 22.

[0118] The contact portion 30 can be in direct contact, indirect contact, or rolling contact with the rack guide 4. In this example, the contact portion 30 is in direct contact with the rack guide 4. Specifically, the contact portion 30 is in direct sliding contact with the inclined surface 27 that constitutes the guide recess 26 of the rack guide 4.

[0119] The cross-sectional contour shape of the rear portion 22 is arbitrary. In this example, the rear portion 22 has a cross-sectional contour shape of a single arc, and is configured as a partial cylindrical surface. Furthermore, the cross-sectional contour shape of the rear portion 22 does not change over the entire axial length of the rear portion 22. Therefore, the generatrix of the rear portion 22 is aligned with the rack central axis O. ２ is placed parallel to the

[0120] Alternatively, the cross-sectional contour shape of the back surface portion 22 may be formed, for example, from two straight line portions and one arc portion as shown in FIG. 6(A), or may be formed from a single arc with a rectangular recess at the top as shown in FIG. 6(B).

[0121] The shape of the contact portion 30 is determined by a combination of the cross-sectional contour shape of the back surface portion 22 of the rack shaft 2 and the cross-sectional contour shape of the guide recess 26, which are each arbitrarily selected. In this example, the partially cylindrical back surface portion 22 of the rack shaft 2 comes into contact (line contact) with the two flat inclined surfaces 27 that form the guide recess 26 of the rack guide 4. For this reason, the contact portion 30 is in line contact with the rack central axis O. ２ It has a linear shape extending parallel to the

[0122] Alternatively, the contact portion 30 can be configured in a surface shape, specifically, a partial cylindrical surface shape, a flat surface shape, or the like, depending on the combination of the cross-sectional contour shape of the rear portion 22 and the cross-sectional contour shape of the guide recess 26. When the contact portion 30 has a partial cylindrical surface shape, the generatrix of the contact portion 30 is aligned with the rack central axis O. ２ and arranged parallel to the rack central axis O ２ When the contact portion 30 has a planar shape, the contact portion 30 extends parallel to the rack central axis O. ２ extends parallel to

[0123] The positions and number of contact portions 30 on the rear surface portion 22 are determined by a combination of an arbitrarily selected cross-sectional contour shape of the rear surface portion 22 of the rack shaft 2 and a cross-sectional contour shape of the guide recess 26. In this example, the contact portions 30 are provided at positions on the partially cylindrical rear surface portion 22 of the guide shaft 2 where the two inclined surfaces 27 come into contact. Specifically, the contact portions 30 are provided at two positions on the rear surface portion 22 that are spaced apart in the circumferential direction.

[0124] In the rack shaft 2 of this example, the generating line of the rear portion 22 is aligned with the rack central axis O. ２ Therefore, unlike the conventional structure described in JP 2016-182936 A, the rack shaft 2 does not need to have a thick portion on the back surface 22. Instead, the rack shaft 2 is in contact with the rack guide 4 and is arranged parallel to the rack central axis O. ２ The contact portion 30 extends parallel to the rack central axis O. ２ The contact portion 30 extending parallel to the rear surface 22 can be easily processed by press forging, cutting, etc. Therefore, there is no need to process the rear surface 22 including the contact portion 30 with high precision, taking into consideration dimensional accuracy.

[0125] Furthermore, similar to conventional rack shafts with a VGR structure, the rack portion 21 can be machined by press forging or the like using a punch with a shape that matches the desired rack portion 21 (with the concave and convex portions being the inverse of the finished shape). Therefore, the rack shaft 2 of this example can suppress backlash between the pinion teeth 18 and the rack teeth 20 in the high gain range H without increasing manufacturing costs.

[0126] The generatrix of the rear portion 22 is the rack central axis O ２ In the inspection process of the rack shaft 2, the rack teeth 20 are meshed with the pinion teeth of the inspection master pinion shaft, and the distance from the pinion central axis of the master pinion shaft to, for example, the top of the back surface portion 22 is measured, thereby determining the distance D in the high gain region H. Ｈ and the low gain region L (L １ , L ２ ) the distance D ＬTherefore, it is possible to easily check whether the difference (ΔL) between the measured value and the actual value is appropriate, thereby reducing the number of steps required for inspecting the rack shaft 2.

[0127] Only the contact portion 30 of the rear surface portion 22 is aligned with the rack central axis O ２ In the case where the rack shaft 2 has a shape extending parallel to the rack center axis O in the high gain region H, the rack teeth 20 are meshed with the pinion teeth of an inspection master pinion shaft, and an inspection master rack guide is brought into contact with the rear surface 22, and the distance from the pinion center axis of the master pinion shaft to, for example, the base end face of the master rack guide is measured, thereby determining the rack center axis O in the high gain region H. ２ From pinion central axis O ３ The distance D to the rack center axis O in the low gain region L ２ From pinion central axis O ３ It is easy to check whether the difference between the distance D and the distance to the target point is appropriate.

[0128] According to the rack shaft 2 of this example, in a rack shaft with a VGR structure, backlash between the pinion teeth 18 and the rack teeth 20 in the high gain region H can be suppressed without increasing manufacturing costs, and the friction force generated between the pinion teeth 18 and the rack teeth 20 and the rack guide 4 can be prevented from becoming excessive.

[0129] REFERENCE SIGNS LIST 1 steering device 2 rack shaft 3 pinion shaft 4 rack guide 5 steering gear unit 6 steering wheel 7 steering shaft 8 steering column 9a, 9b universal joint 10 intermediate shaft 11 tie rod 12 spherical joint 13 electric assist device 14 housing 15 rack accommodating portion 16 pinion accommodating portion 17 guide accommodating portion 18 pinion teeth 19a, 19b bearing 20 rack teeth 21 rack portion 22 back portion 23 rack bush 24 elastic member 25 pressing mechanism 26 guide recess 27 inclined surface 28 bottom surface 29 cap 30 contact portion

Claims

1. A rack comprising: a rack central axis; a rack portion having a plurality of rack teeth arranged in the axial direction on a portion of the circumferential direction of the outer peripheral surface and meshing with pinion teeth of a pinion shaft in use; and a back surface portion provided on the outer peripheral surface on the radially opposite side of the rack portion and pressed by a rack guide in use, wherein the rack portion has a low gain region and a high gain region in which the rack teeth are arranged at different pitches, the low gain region is provided at the axial center portion and at both axial end portions of the rack portion, and the high gain region is provided in a portion of the rack portion between the axial center portion and each of the axial end portions, the pitch of the rack teeth provided in the high gain region is larger than the pitch of the rack teeth provided in the low gain region, and the back surface portion has a contact portion that comes into direct or indirect contact with the rack guide and extends parallel to the rack central axis, a rack shaft, wherein, with the rack teeth meshing with the pinion teeth, the distance from the rack central axis to the pinion central axis of the pinion shaft is greater in at least a part of each of the high gain regions than in each of the low gain regions, and in each of the low gain regions, the distance is greater in a first low gain region at the axial center than in each of the second low gain regions at the axial end portions.

2. The rack shaft according to claim 1, wherein the axial dimension of said first low gain region is smaller than the axial dimension of each of said second low gain regions.

3. A rack shaft according to claim 1 or 2, wherein the distance is greater over the entire range of the high gain region than in the low gain region.

4. A rack shaft according to any one of claims 1 to 3, wherein the distance varies within each of the high gain regions.

5. The rack shaft according to claim 4, wherein the distance is greater in at least a portion of the range of each of the high gain regions than in the first low gain region, and is the same as in either the first low gain region or the second low gain region in the remaining range of each of the high gain regions.

6. A rack shaft according to any one of claims 1 to 5, wherein the difference between the distance in at least a portion of each of the high gain regions and the distance in the first low gain region is 10 μm or more.

7. A rack shaft according to any one of claims 1 to 6, wherein the difference between the distance in at least a portion of each of the high gain regions and the distance in each of the second low gain regions is 100 μm or less.

8. A rack shaft according to any one of claims 1 to 7, wherein the rack section has a first transition region at a boundary between the first low gain region and each of the high gain regions, and a second transition region at a boundary between the second low gain region and each of the high gain regions, and the distance in the first transition region increases as the distance approaches from the first low gain region to each of the high gain regions in the axial direction, and the distance in the second transition region increases as the distance approaches from each of the second low gain regions to each of the high gain regions in the axial direction.

9. A steering gear unit comprising: a pinion shaft having a pinion central axis and pinion teeth provided on its outer peripheral surface, the pinion shaft rotating around the pinion central axis as a steering wheel is rotated; a rack shaft having rack teeth on its outer peripheral surface that mesh with the pinion teeth; a rack guide that presses the rack shaft toward the pinion shaft; and a housing that houses the pinion shaft, the rack shaft, and the rack guide inside, wherein the rack shaft is a rack shaft as defined in any one of claims 1 to 8.

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