Steering device and method for manufacturing the steering device

Abstract

In a steering device (PS1) according to the present invention, a preload applying mechanism (6) applies turn torque in one turning direction of a ball nut (4), on the basis of a reaction force generated as a result of a plunger (61) elastically engaging with tooth tips of first sector teeth (321) of a sector gear (32). As a result, unlike conventional steering devices, it is not necessary to provide the steering device (PS1) with a pressed part which is pressed, separately from the sector gear (32), by the plunger (61). This makes it possible to prevent an increase in the size of a sector shaft (3) due to the formation of the pressed part.

Description

[Technical Field]

[0001] The present invention relates to a steering device and a method for manufacturing a steering device. [Background technology]

[0002] A known conventional steering device is, for example, that described in Patent Document 1 below.

[0003] That is, the steering device according to Patent Document 1 below has a steering shaft connected to the steering wheel and a sector shaft connected to the steered wheels that are arranged in an intersecting manner, and is configured by meshing rack teeth formed on a ball nut that screws onto the steering shaft with a sector gear provided on the sector shaft.

[0004] A preload mechanism is provided between the ball nut and the sector shaft to adjust backlash between the rack teeth and the sector gear at the neutral position of the sector shaft. The preload mechanism includes a plunger embedded in the ball nut together with a biasing member at a position facing the axial end of the sector gear and biased toward the sector gear via the biasing member, and a plunger sliding contact portion provided on the sector shaft and configured with a cam profile that allows elastic contact with the plunger within a predetermined rotational range around the neutral position of the sector shaft. In other words, the preload mechanism biases the ball nut in one rotational direction based on a reaction force from the plunger sliding contact portion generated when the plunger elastically contacts the plunger sliding contact portion within a predetermined range around the neutral position of the sector shaft. This makes it possible for the preload mechanism to reduce backlash between the rack teeth and the sector gear near the neutral position of the sector shaft. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-319285 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional steering device, it is necessary to provide a plunger sliding contact portion separate from the sector gear, which results in an increase in the axial size of the sector shaft by the size of the plunger sliding contact portion, and there is still room for improvement.

[0007] The present invention has been devised in light of the above technical problem, and has an object to provide a steering device that can prevent the sector shaft from becoming large, and a method for manufacturing the steering device. [Means for solving the problem]

[0008] In one aspect, the present invention provides a steering system comprising: rack teeth formed on the outer side of a ball nut that screws onto a steering shaft that is connected to a steering wheel; a sector gear that is provided on a sector shaft that is connected to a steered wheel and includes a central tooth that meshes most deeply with the rack teeth at a neutral position of the sector shaft that corresponds to a straight-ahead steering state, the sector gear having a plurality of sector teeth that are provided in the circumferential direction of the sector shaft and that meshes with the rack teeth; and a preload applying mechanism that adjusts the meshing between the rack teeth and the sector gear near the neutral position of the sector shaft, the preload applying mechanism being biased to an area on one end side in the tooth width direction of a specific tooth bottom of the rack tooth that faces the tooth tip of the central tooth near the neutral position of the sector shaft, The ball nut has a plunger receiving hole that opens to the bottom, a plunger that is accommodated in the plunger receiving hole so that it can move back and forth, with its tip end protruding from an opening of the plunger receiving hole that faces the sector gear, a sliding ring that is press-fitted onto the outer periphery of the plunger so that it can move integrally with the plunger and slides against the inner periphery of the plunger receiving hole as the plunger moves back and forth, and a biasing member that is interposed between the bottom of the plunger receiving hole and the sliding ring and biases the plunger via the sliding ring toward the central tooth, and the ball nut is biased to one side in the rotational direction of the ball nut based on a reaction force generated when the plunger elastically contacts the tip of the central tooth.

[0009] In this way, in the present invention, the plunger, biased by the biasing member, elastically contacts the tip of the central tooth of the sector gear, thereby applying a rotational torque that acts as a preload to the ball nut. As such, in the present invention, there is no need to provide a pressed portion that is pressed by the preload applying mechanism separately from the sector gear, as in the conventional case, and therefore it is possible to prevent the sector shaft from becoming larger due to the formation of the pressed portion.

[0010] In addition, as another aspect of the steering device, it is desirable that the connection between the sliding ring and the plunger by the press-fitting restricts relative movement between the sliding ring and the plunger in relation to the biasing force of the biasing member, while allowing relative movement between the sliding ring and the plunger in relation to the meshing force of the sector gear with the rack teeth.

[0011] If the sliding ring were formed integrally with the plunger, for example, depending on the machining accuracy (machining error) of the plunger that abuts against the central tooth of the sector gear and the plunger receiving hole that houses it, the length of the plunger facing the sector gear beyond the sliding ring may become longer than necessary. In this case, the plunger is pushed in excessively when the sector gear and the rack teeth engage, which may result in excessive compression of the biasing member, which may cause damage to the biasing member or shorten its lifespan.

[0012] In contrast, in the present invention, the sliding ring is press-fitted onto the plunger to a degree that restricts relative movement between the sliding ring and plunger due to the biasing force of the biasing member, while allowing relative movement between the sliding ring and plunger due to the meshing force between the sector gear and the rack teeth. As a result, the sliding ring and plunger move together due to the biasing force of the biasing member, but when the sector gear meshes with the rack teeth, the sector gear pushes the plunger in the opposite direction of the advancing direction, causing the plunger to move relative to the sliding ring, thereby making it possible to change the positional relationship between the plunger and the sliding ring to an appropriate relative position. As a result, the plunger can be biased with an appropriate biasing force against the sector gear, and an appropriate preload can be applied to the ball nut, regardless of processing errors in the axial dimensions of the plunger receiving hole, plunger, and sliding ring.

[0013] Furthermore, since the sliding ring and plunger are allowed to move relative to each other in response to the meshing force between the sector gear and the rack teeth, there is no risk of the biasing member being excessively compressed by the meshing between the sector gear and the rack teeth, which contributes to suppressing damage to the biasing member and improving its durability.

[0014] In yet another aspect of the steering device, it is desirable that the plunger receiving hole has a recessed portion at the bottom opposite the opening, which is capable of receiving the end portion of the plunger opposite the tip portion that abuts against the tip of the central tooth.

[0015] Depending on the length of the end of the plunger that faces the biasing member side rather than the sliding ring, when the plunger is pushed in by the central tooth, the end of the plunger may come into contact with the bottom of the plunger receiving hole, which may prevent the plunger from being pushed in (moving backward).

[0016] In contrast, in the present invention, a recess is provided at the bottom of the plunger receiving hole opposite the opening, which can receive the end portion of the plunger opposite the tip portion that abuts against the central tooth of the sector gear. Therefore, when the plunger is pushed in by the central tooth, the end portion of the plunger is received in the recess, eliminating the risk of the end portion of the plunger abutting against the bottom of the plunger receiving hole and preventing the plunger from being pushed in (rearward movement). This makes it possible to appropriately adjust the relative position of the plunger and the sliding ring regardless of the length of the end portion of the plunger that faces the biasing member side beyond the sliding ring.

[0017] In yet another aspect of the steering device, the plunger receiving hole has an opening whose inner diameter is reduced to be smaller than the outer diameter of the sliding ring, and has a stopper that abuts against the sliding ring to regulate the amount of protrusion of the plunger, and when the rotation phase of the sector shaft is in the vicinity of the neutral position, the sliding ring does not abut against the stopper, allowing the plunger to abut against the central tooth, while when the rotation phase of the sector shaft has passed the vicinity of the neutral position, the sliding ring abuts against the stopper to regulate the abutment of the plunger against the central tooth.

[0018] In this way, the present invention is configured to allow the plunger to contact the central tooth when the rotation phase of the sector shaft is near the neutral position, and to prevent the plunger from contacting the central tooth by the stopper when the rotation phase of the sector shaft passes beyond the neutral position. By limiting the plunger's protrusion amount with the stopper, it is possible to adjust the meshing between the rack teeth and the sector gear only near the steering neutral position, where a sense of rigidity is required. In other words, by preventing the plunger from contacting the central tooth at positions other than the steering neutral position, where a sense of rigidity is not particularly required, it is possible to prevent deterioration of steering feel, such as a rough feeling, caused by the plunger sliding against the central tooth.

[0019] Furthermore, in the present invention, the stopper is configured by simply narrowing the opening of the plunger receiving hole, which makes it possible to restrict the amount of plunger protrusion with a relatively simple configuration without forming a complex cam profile as in the past, thereby contributing to reducing the manufacturing costs of the steering device.

[0020] In yet another aspect of the steering device, it is desirable that the bottom of the teeth of the sector gear be a flat surface parallel to the axis of the sector shaft.

[0021] As described above, in the present invention, the tip of the central tooth with which the plunger comes into contact has a straight shape that is parallel to the axis of the sector shaft. That is, unlike conventional systems, the rack teeth and sector gear do not have tapered gear shapes, and no mechanism for adjusting the meshing of the rack teeth and sector gear other than the preload mechanism is provided. Instead, the meshing of the rack teeth and sector gear is adjusted using only the preload mechanism. This simplifies the structure of the steering device, contributing to improved productivity and reduced manufacturing costs of the steering device.

[0022] In yet another aspect of the steering device, it is desirable that the bottom of the teeth of the sector gear has a tapered surface in which the tooth depth of the sector gear gradually increases toward one axial end of the sector shaft, and that the sector shaft be movable toward one axial end of the sector shaft by an adjusting screw that is threaded from the other axial end of the sector shaft through an internally threaded hole formed in an end wall of a housing that accommodates the sector shaft.

[0023] In this way, in the present invention, the rack teeth and sector gear have a tapered gear shape, and the meshing between the rack teeth and sector gear can be adjusted by moving the sector shaft toward one end in the axial direction with the adjust screw. This ensures appropriate meshing between the rack teeth and sector gear not only near the neutral position of the sector shaft, but throughout the entire rotation range of the sector shaft.

[0024] In yet another aspect of the steering device, the sector shaft is connected to a pitman arm, and one axial end side thereof is formed with a relatively large diameter across the sector gear, and the other axial end side thereof is formed with a relatively small diameter than the one axial end side, and the plunger receiving hole is desirably open to an end of the specific tooth bottom in the tooth width direction that corresponds to the other axial end side of the sector shaft.

[0025] In this way, in the present invention, the plunger receiving hole that constitutes the preload applying mechanism is located on the side where the sector shaft has a relatively small diameter, allowing the preload applying mechanism to be located relatively far from the center of rotation of the ball nut, which makes it possible to apply a greater rotational torque to the ball nut and more effectively adjust the meshing between the rack teeth and the sector gear.

[0026] In one aspect of the manufacturing method of the steering device, the manufacturing method includes a biasing member assembling step of accommodating the biasing member in the plunger receiving hole, a sliding ring assembling step of assembling the sliding ring to the plunger, a plunger assembling step of assembling the plunger with the sliding ring assembled to the plunger receiving hole, and a plunger adjusting step of, after the plunger assembling step, meshing the sector gear with the rack teeth to adjust the relative position of the plunger and the sliding ring, wherein the plunger adjusting step rotates the sector gear in one direction relative to the rack teeth to which the preload applying mechanism is assembled, and meshes the sector gear in a state where the sector gear is in a non-neutral position. It is desirable that the method for manufacturing a spring-loaded spring includes a first step in which the sector gear is rotated in a direction in which the distance between the central tooth and the specific tooth bottom decreases toward the neutral position after the first step, so that the central tooth presses the plunger in a direction opposite to the biasing direction of the biasing member against the biasing force of the biasing member, thereby compressing the biasing member until it is maximally contracted via the sliding ring that moves integrally with the plunger; and a third step in which, after the second step, the central tooth further presses the plunger in a direction opposite to the biasing direction of the biasing member, so that the plunger moves relatively to the sliding ring in the direction opposite to the biasing direction of the biasing member.

[0027] In this way, in the plunger adjustment process, the central tooth further presses the plunger when the biasing member is fully contracted, thereby moving the plunger relative to the sliding ring and changing the relative positions of the plunger and the sliding ring to an appropriate position. This makes it possible to bias the plunger with an appropriate biasing force against the sector gear and apply an appropriate preload to the ball nut, regardless of processing errors in the axial dimensions of the plunger receiving hole, plunger, and sliding ring.

[0028] Furthermore, in the plunger adjustment process, when the central tooth further presses the plunger with the biasing member in its maximum compressed state, the plunger is allowed to move relative to the sliding ring, eliminating the risk of the biasing member being overcompressed even if the plunger protrusion exceeds the specified dimension due to, for example, machining errors in the axial dimensions of the plunger receiving hole, plunger, and sliding ring, etc. This prevents damage to the biasing member and contributes to improving the durability of the biasing member.

[0029] In another aspect of the manufacturing method for the steering device, it is desirable that the plunger receiving hole has a recess at the bottom opposite to the opening, capable of receiving an end portion of the plunger opposite to the tip portion of the plunger that abuts against the tip of the central tooth, and that in the third step, when the plunger moves relative to the sliding ring in a direction opposite to the biasing direction of the biasing member, the end portion of the plunger is received in the recess.

[0030] In the third step, depending on the length of the end portion of the plunger that faces the biasing member side rather than the sliding ring, when the plunger is pushed in by the central tooth, the end portion of the plunger may come into contact with the bottom of the plunger receiving hole, which may prevent the plunger from being pushed in (moving backward).

[0031] In contrast, in the present invention, a recess is provided in the bottom of the plunger receiving hole opposite the opening, capable of receiving the end of the plunger opposite the tip end that abuts against the central tooth of the sector gear. Therefore, when the plunger is pushed in by the central tooth in the third step of the plunger adjustment process, the end of the plunger is received in the recess, eliminating the risk of the end of the plunger abutting against the bottom of the plunger receiving hole and preventing the plunger from being pushed in (rearward movement). This makes it possible to appropriately adjust the relative position between the plunger and the sliding ring, regardless of the length of the plunger's end that faces the biasing member relative to the sliding ring. [Effects of the Invention]

[0032] According to the present invention, the preload mechanism applies rotational torque to the ball nut by elastically contacting the tip of the central tooth of the sector gear. This eliminates the need to provide a pressed portion that is pressed by the preload mechanism separately from the sector gear, and prevents the sector shaft from becoming larger due to the formation of such a pressed portion. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a vertical cross-sectional view of a steering device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 2 is an enlarged view of a main part of FIG. [Figure 4] 10A and 10B are diagrams showing the transition of the plunger protrusion amount depending on the steering state, where (a) shows the neutral state with a steering angle of 0 degrees, (b) shows the steering state with a steering angle of 12 degrees, and (c) shows the steering state with a steering angle of 25 degrees. [Figure 5] 10A and 10B are diagrams showing the plunger adjustment process of the manufacturing method of the steering device according to the present invention, where (a) shows the first process, (b) shows the second process, (c) shows the third process, and (d) shows the maximum advanced state of the plunger after the plunger adjustment. [Figure 6] 2 is a cross-sectional view of a steering device according to a second embodiment of the present invention, corresponding to the cross-sectional view of the steering device taken along line AA in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, embodiments of a steering device and a method for manufacturing a steering device according to the present invention will be described with reference to the drawings. Note that the following embodiments show an example in which the steering device and the method for manufacturing a steering device are applied to a so-called integral type power steering device used in large automobiles such as trucks.

[0035] [First embodiment] (Configuration of steering device) FIG. 1 shows a first embodiment of a steering device according to the present invention, and is a longitudinal cross-sectional view of the steering device PS1 taken along the center of rotation of the steering shaft 2. FIG. 2 shows a transverse cross-sectional view of the steering device PS1 taken along line AA in FIG. 1. In the following description, the side of the steering shaft 2 in the direction of the rotation axis X in FIG. 1 that is connected to a steering wheel (not shown) will be referred to as the "one end side," and the side that is connected to the ball nut 4 will be referred to as the "other end side." In addition, the side of the sector shaft 3 in the direction of the rotation axis Y in FIG. 2 that is connected to a steered wheel (not shown) will be referred to as the "one end side," and the side that is connected to the ball nut 4 will be referred to as the "other end side."

[0036] 1 and 2, the steering device PS1 is a well-known ball nut type steering device, and has a steering shaft 2 connected to a steering wheel (not shown) and a sector shaft 3 connected to steered wheels (not shown). The steering shaft 2 and sector shaft 3 are housed inside a housing 1. A ball nut 4 is interposed between the steering shaft 2 and sector shaft 3, and rotation of the steering shaft 2 is converted into rotation of the sector shaft 3 via the ball nut 4.

[0037] The housing 1 has a first housing 11, a second housing 12, and a third housing 13. The first housing 11 functions as a housing main body that accommodates the steering shaft 2, the sector shaft 3, and the ball nut 4. That is, the first housing 11 has a generally cylindrical steering shaft accommodating portion 111 that extends in the direction of the rotation axis X and accommodates the steering shaft 2 and the ball nut 4, and a generally cylindrical sector shaft accommodating portion 112 that extends in the direction of the rotation axis Y that is perpendicular to the rotation axis X and accommodates the sector shaft 3.

[0038] 1, the steering shaft accommodating portion 111 has a cylindrical shape with a bottom, one end side in the direction of the rotation axis X being open to the outside through a first opening 111a, and the other end side being closed by an end wall 111b. The first opening 111a is closed by the second housing 12 that fits into the first opening 111a.

[0039] The second housing 12 has a cylindrical shape with an outer diameter that decreases in a stepped manner toward the other end, and includes a second housing main body 121 that abuts against the end face of the first opening 111a, and a second housing fitting portion 122 that is stepped relative to the second housing main body 121 and fits into the first opening 111a. A first seal member S1 that can elastically abut against the inner circumferential surface of the first opening 111a is attached to the outer circumferential side of the second housing fitting portion 122, and the inside of the steering shaft accommodating portion 111 is kept liquid-tight by the first seal member S1 elastically abutting against the inner circumferential surface of the first opening 111a.

[0040] The second housing 12 has a steering shaft insertion hole 123 penetrating the center thereof, and the steering shaft 2 is inserted into the steering shaft accommodating portion 111 from the outside through this steering shaft insertion hole 123. The steering shaft insertion hole 123 is configured so that the inner diameter thereof decreases in steps from one end to the other end, with a relatively large diameter hole portion 123a at one end and a relatively small diameter hole portion 123b at the other end. A steering bearing 113, such as a ball bearing, is accommodated in the large diameter hole portion 123a of the steering shaft insertion hole 123, and the steering shaft 2 is rotatably supported by this steering bearing 113.

[0041] The steering bearing 113 has an inner race 113a formed integrally with the second steering shaft 22, an outer race 113b inserted into the large diameter hole portion 123a, and a plurality of ball members 113c interposed between the inner race 113a and the outer race 113b. The outer race 113b is held in place by a lock nut 114 threaded into the large diameter hole portion 123a, with its axial movement restricted.

[0042] 2, the sector shaft accommodating portion 112 is disposed substantially tangentially to the steering shaft accommodating portion 111, and shares a portion of its circumference with the steering shaft accommodating portion 111, thereby enabling communication with the steering shaft accommodating portion 111. One end of the sector shaft accommodating portion 112 in the direction of the rotation axis Y opens to the outside through a second opening 112a, and the other end opens to the outside through a third opening 112b.

[0043] That is, in the sector shaft accommodating portion 112, one end of the sector shaft 3 inserted into the sector shaft accommodating portion 112 via the third opening 112b faces the outside via the second opening 112a and is connected to the pitman arm (not shown) outside the housing 1. On the other hand, after the sector shaft 3 is inserted into the sector shaft accommodating portion 112 via the third opening 112b, the third opening 112b is closed by the third housing 13 which fits into the third opening 112b.

[0044] The third housing 13 has a cylindrical shape with an outer diameter that tapers in a step toward one end, and includes a third housing main body 131 that abuts against an end face of the third opening 112b, and a third housing fitting portion 132 that is tapered in diameter in a step relative to the third housing main body 131 and fits into the third opening 112b. A second seal member S2 that can elastically abut against the inner circumferential surface of the third opening 112b is attached to the outer periphery of the third housing fitting portion 132, and the inside of the sector shaft accommodating portion 112 is kept liquid-tight by the second seal member S2 elastically abutting against the inner circumferential surface of the third opening 112b.

[0045] The third housing fitting portion 132 has a cylindrical shaft support portion 133 with a bottom on the inner circumferential side thereof, which serves to support the rotation of the other end of the sector shaft 3. The shaft support portion 133 has a third housing tubular portion 134 that opens at one end, and a third housing end wall 135 that closes the other end of the third housing tubular portion 134.

[0046] 1, the steering shaft 2 has a first steering shaft 21, one end of which is connected to a steering wheel (not shown), and a second steering shaft 22, which is connected to the other end of the first steering shaft 21 via a torsion bar 23 so as to be rotatable relative to the first steering shaft 21 and partially overlap with the first steering shaft 21 in the radial direction. The first steering shaft 21 is connected to the torsion bar 23 via a first pin member 241 that penetrates the other end of the first steering shaft 21 in the radial direction. Similarly, the second steering shaft 22 is connected to the torsion bar 23 via a second pin member 242 that penetrates the other end of the second steering shaft 22 in the radial direction.

[0047] Although not shown in the drawings, in this embodiment, the steering shaft 2 may be mechanically connected to the steering wheel (not shown), or may be electrically connected to the steering wheel (not shown) like a well-known steer-by-wire system. Furthermore, the steering shaft 2 may be connected to the steering wheel (not shown) and a steering torque is input via the steering wheel during manual driving, or may be connected to a motor (not shown) and a steering torque is input via the motor during automatic driving. The manual driving mode also includes a mode in which a steering torque is input from the steering wheel (not shown) and a steering assist torque is input from the motor (not shown).

[0048] 2, the sector shaft 3 has a sector shaft portion 31 extending along a rotation axis Y that intersects the rotation axis X of the steering shaft 2 at a substantially right angle, and a sector gear 32 disposed at the other end of the sector shaft portion 31 so as to face the ball nut 4. The sector shaft portion 31 and the sector gear 32 are formed integrally, and as the sector gear 32 rotates, the sector shaft portion 31 rotates integrally with the sector gear 32.

[0049] 2, the sector shaft portion 31 has a first shaft portion 311 provided on one end side of the sector gear 32, and a second shaft portion 312 provided on the other end side of the sector gear 32. Here, in this embodiment, the first shaft portion 311 and the second shaft portion 312 are set to have approximately the same outer diameter.

[0050] One end of the first shaft portion 311 is connected to the pitman arm (not shown), and the other end is rotatably supported by a first bearing 331 accommodated on the inner circumferential side of the second opening 112a. A first seal member 341 is disposed on one end of the first bearing 331 to provide a liquid-tight seal between the outer circumferential surface of the first shaft portion 311 and the inner circumferential surface of the second opening 112a. This prevents the hydraulic fluid filled inside the housing 1 (sector shaft accommodating portion 112) from leaking out through the second opening 112a.

[0051] On the other hand, the second shaft portion 312 is rotatably supported by a second bearing 332 housed on the inner circumferential side of the third housing cylindrical portion 134. In addition, a second seal member 342 is provided on the other end side of the second bearing 332 to provide a liquid-tight seal between the outer circumferential surface of the second shaft portion 312 and the inner circumferential surface of the third housing cylindrical portion 134. This prevents the hydraulic fluid filled inside the housing 1 (sector shaft accommodating portion 112) from leaking out to the outside through a female threaded hole 136, which will be described later.

[0052] As shown in FIGS. 1 and 2 , the sector gear 32 is provided between the first shaft portion 311 and the second shaft portion 312 and includes a connection base portion 320 connected to the first shaft portion 311 and the second shaft portion 312, and first sector teeth 321, second sector teeth 322, and third sector teeth 323 provided on the side of the connection base portion 320 so as to face the rack teeth 42 of the ball nut 4. When the sector gear 32 is in a neutral state, the first sector teeth 321 protrude along a meshing direction line Z that is perpendicular to the rotation axis X and the rotation axis Y. The second sector teeth 322 protrude diagonally to the right of the first sector teeth 321 toward one end of the rotation axis X. The third sector teeth 323 protrude diagonally to the left of the first sector teeth 321 toward the other end of the rotation axis X.

[0053] 2, in this embodiment, the tooth bottom of the sector gear 32 is a flat surface parallel to the rotation axis Y so that the tooth depth T of the sector gear 32 is constant in the face width direction. In other words, in this embodiment, the tooth bottom of the sector gear 32 is configured to have a straight shape parallel to the rotation axis Y.

[0054] 1 and 2, the ball nut 4 is cylindrical and has a shaft hole 41 formed along the direction of the rotation axis X. That is, the ball nut 4 is provided so as to be movable back and forth along the direction of the rotation axis X via a plurality of balls 43 interposed between a shaft-side ball groove 401 provided on the outer periphery of the second steering shaft 22 housed in the steering shaft housing 111 and a nut-side ball groove 402 provided on the inner periphery of the ball nut 4 (shaft hole 41).

[0055] Furthermore, rack teeth 42 (first rack teeth 421, second rack teeth 422, third rack teeth 423, and fourth rack teeth 424, which will be described later) that mesh with sector gear 32 are formed on the outer periphery of ball nut 4 in a predetermined range facing sector gear 32. Meanwhile, on the back side of rack teeth 42 on the outer periphery of ball nut 4, i.e., on the opposite side of rack teeth 42 with rotation axis X in between, a cylindrical tube member 44 that connects one end and the other end of nut-side ball groove 402 and serves to circulate the plurality of balls 43 is arranged.

[0056] 1, the rack teeth 42 include first rack teeth 421, second rack teeth 422, third rack teeth 423, and fourth rack teeth 424 that are arranged in parallel along the direction of the rotation axis X on a side of the ball nut 4 that faces the sector gear 32. A first rack tooth bottom 425, which is a specific tooth bottom that faces the first sector tooth 321 that is the central tooth, is formed between the second rack teeth 422 and the third rack teeth 423. A second rack tooth bottom 426 that faces the second sector tooth 322 is formed between the first rack teeth 421 and the second rack teeth 422. A third rack tooth bottom 427 that faces the third sector tooth 323 is formed between the third rack teeth 423 and the fourth rack teeth 424.

[0057] The ball nut 4 functions as a piston of a power cylinder that is actuated by the hydraulic pressure of hydraulic fluid filled in the steering shaft accommodating portion 111, and is slidably provided within the steering shaft accommodating portion 111. That is, the ball nut 4 defines two hydraulic chambers, a first hydraulic chamber P1 and a second hydraulic chamber P2, that face each other in the direction of the rotation axis X with the ball nut 4 sandwiched between them inside the steering shaft accommodating portion 111. The second hydraulic chamber P2 is configured to be able to communicate with the sector shaft accommodating portion 112 via a communication hole 115 provided in the first housing 11, and the hydraulic fluid from the second hydraulic chamber P2 is guided into the sector shaft accommodating portion 112, thereby enabling lubrication between the sector gear 32 and the rack teeth 42.

[0058] A well-known rotary valve RV is arranged inside the second housing 12 as a control valve that can selectively supply hydraulic fluid, supplied by a hydraulic pressure source (e.g., a pump, not shown), to the first hydraulic pressure chamber P1 or the second hydraulic pressure chamber P2 of the power cylinder in accordance with the relative rotation of the first steering shaft 21 and the second steering shaft 22. The rotary valve RV has a rotor 210 that is integrally formed with the other end of the first steering shaft 21, and a sleeve 220 that is provided on the outer circumferential side of the rotor 210 and is integrally provided with one end of the second steering shaft 22.

[0059] An inlet port 124a, a supply port 124b, and a discharge port 124c are provided on the inner circumferential side of the second housing 12. The inlet port 124a, the supply port 124b, and the discharge port 124c are circumferential grooves extending in the circumferential direction of the rotation axis X and are arranged in parallel in the direction of the rotation axis X. An inlet passage 124d connecting an inlet pipe (not shown) to the inlet port 124a and a discharge passage 124e connecting the discharge port 124c to a discharge pipe (not shown) are provided inside the second housing 12. A supply passage L connecting the supply port 124b to the first hydraulic pressure chamber P1 is provided inside the first housing 11 and the second housing 12, straddling the first housing 11 and the second housing 12. Specifically, the supply passage L is composed of a first-housing supply passage 116 provided inside the first housing 11 and a second-housing supply passage 126 provided inside the second housing 12 and connecting the supply port 124b to the first-housing supply passage 116. The inlet port 124a is connected to the hydraulic pressure source (not shown) via an inlet passage 124d and the inlet piping (not shown). The supply port 124b is connected to the first hydraulic pressure chamber P1 via a supply passage L. The discharge port 124c is connected to a reservoir tank (not shown) via a discharge passage 124e and the outlet piping (not shown).

[0060] On the outer circumferential side of the rotor 210, supply recesses 210a and discharge recesses (not shown) are provided alternately in parallel in the circumferential direction, and extend like vertical grooves along the direction of the rotation axis X. Similarly, on the inner circumferential side of the sleeve 220, right steering recesses 220a and left steering recesses (not shown) are provided alternately in parallel in the circumferential direction, and extend like vertical grooves along the direction of the rotation axis X. Furthermore, the sleeve 220 is provided with a first communication passage 221, a second communication passage 222, a supply communication passage 223, and a discharge communication passage 224 to communicate between the inner periphery and the outer periphery of the sleeve 220. The first communication passage 221 opens into the right steering recess 220a, and the second communication passage 222 opens into the left steering recess (not shown). In addition, a supply communication passage 223 or a discharge communication passage 224 opens into a convex portion not shown that is sandwiched between the right steering recess 220a and the left steering recess not shown in the circumferential direction, and the supply communication passage 223 and the discharge communication passage 224 are arranged alternately in the circumferential direction.

[0061] 1 and 2, a preload mechanism 6 is provided between the sector gear 32 and the rack teeth 42 to adjust the meshing between the sector gear 32 and the rack teeth 42 near the neutral position (the position shown in FIG. 1) of the sector shaft 3, which corresponds to the straight-ahead steering state. As shown in particular in FIG. 2, this preload mechanism 6 is provided at a position on the other end side in the tooth width direction of the first rack tooth bottom 425, which is a specific tooth bottom that meshes with the first sector tooth 321, which is the central tooth, and at a position opposite to the other end side of the first sector tooth 321 closer to the second shaft portion 312.

[0062] (Configuration of preload applying mechanism) FIG. 3 is an enlarged view of the main part of FIG. 1, showing the preload applying mechanism 6 and its vicinity, which are the main part of FIG.

[0063] As shown in Figure 3, the preload mechanism 6 includes a plunger receiving hole 60 formed in the first rack tooth bottom 425, a plunger 61 accommodated in the plunger receiving hole 60 so as to be movable back and forth, and a biasing member 62 interposed between the bottom of the plunger receiving hole 60 and the bottom of the plunger 61 and biasing the plunger 61 toward the first sector tooth 321.

[0064] The plunger receiving hole 60 has a substantially circular cross section, one end opening to the first rack tooth bottom 425, and the other end closed by the bottom wall 600. The plunger receiving hole 60 is a circular hole having a constant inner diameter in the axial direction, and is formed with a tapered stepped diameter by press-fitting an annular member 63 from the opening side. That is, the plunger receiving hole 60 has a large-diameter hole portion 601 provided on the bottom wall 600 side and having a relatively large diameter, and a small-diameter hole portion 602 provided on the opening side and formed on the inner periphery of the annular member 63 and having a relatively small diameter. Between the large-diameter hole portion 601 and the small-diameter hole portion 602, the annular member 63 forms a stepped stopper 630 that abuts against a sliding ring 64 (described later) provided on the outer periphery of the plunger 61 to regulate the amount of advancement of the plunger 61, i.e., the amount of protrusion of the plunger 61 from the small-diameter hole portion 602.

[0065] When the rotation phase of the sector shaft 3 is near the neutral position, the stopper 630 does not come into contact with the sliding ring 64 but allows the plunger 61 to come into contact with the first sector tooth 321 (see FIG. 4(a)). On the other hand, when the rotation phase of the sector shaft 3 goes beyond the neutral position, the stopper 630 comes into contact with the sliding ring 64 and restricts the plunger 61 from coming into contact with the first sector tooth 321 (see FIG. 4(c)).

[0066] The bottom wall 600 of the plunger receiving hole 60 has a recessed recess 603 at its center that can receive the end portion 612 of the plunger 61 opposite the tip portion 611 that faces the first sector tooth 321. The recess 603 is formed in a stepped recess shape with a circular cross section, and is provided opposite the end portion 612 of the plunger 61. The recess 603 has a predetermined inner diameter that is larger than the outer diameter of the end portion 612 of the plunger 61 and smaller than the inner diameter of the biasing member 62. The recess 603 has a depth that is larger than machining errors that may occur in the plunger receiving hole 60, the plunger 61, and the sliding ring 64, and receives the end portion 612 of the plunger 61 that is pushed aside by the sector gear 32 (first sector tooth 321) in a plunger adjustment process described below. In other words, the recessed portion 603 receives the end portion 612 of the plunger 61 when the plunger 61 is pushed aside by the first sector tooth 321 during the plunger adjustment process described below, thereby preventing the plunger 61 from colliding with the bottom wall 600 and ensuring a recession allowance for the plunger 61.

[0067] The recessed portion 603 functions according to the extension amount (amount of overlap with the biasing member 62) of the end portion 612 of the plunger 61 that extends toward the bottom wall 600 beyond the sliding ring 64. Therefore, if the relative positional relationship between the plunger 61 and the sliding ring 64 is such that the end portion 612 of the plunger 61 does not abut against the bottom wall 600 when the plunger 61 is pushed in by the sector gear 32 (first sector teeth 321) in a plunger adjustment process described later, the recessed portion 603 is not an essential component of the preload applying mechanism 6.

[0068] The plunger 61 is made of a resin material and is cylindrical with a constant outer diameter. An annular sliding ring 64 is press-fitted onto the outer periphery, forming a stepped diameter. That is, the plunger 61 is configured to be movable integrally with the sliding ring 64, and is slidably housed in the plunger receiving hole 60 via the sliding ring 64. The plunger 61 has an outer diameter slightly smaller than the inner diameter of the annular member 63, and a tip portion 611 that protrudes distally beyond the sliding ring 64 protrudes from the small-diameter hole portion 602 of the plunger receiving hole 60 to face the outside and confront the first sector teeth 321. The tip portion 611 of the plunger 61 has a gently curved surface, allowing it to smoothly slide against the tooth surfaces of the first sector teeth 321 when the sector shaft 3 rotates.

[0069] Here, it is desirable that the plunger 61 has an outer diameter set slightly larger than the inner diameters of the biasing member 62 and the annular member 63. In other words, by reducing the gap between the outer circumferential surface of the plunger 61 and the inner circumferential surfaces of the biasing member 62 and the annular member 63, the forward and backward movement of the plunger 61 can be guided by the inner circumferential surfaces of the biasing member 62 and the annular member 63, thereby facilitating the forward and backward movement of the plunger 61.

[0070] Furthermore, it is desirable that the plunger 61 has an axial length that allows it to penetrate the inner circumferential side of the biasing member 62 and is set to an axial length that allows it to be located near the bottom wall 600 of the plunger receiving hole 60 when the biasing member 62 is fully contracted in the neutral position (see, for example, FIGS. 1 and 4(a)). That is, it is desirable that the plunger 61 is configured to overlap the inner circumferential side of the biasing member 62 over a relatively long region when viewed in the radial direction of the plunger 61. This makes it possible for the outer circumferential side of the end portion 612 of the plunger 61 to be supported by the inner circumferential side of the biasing member 62, which contributes to smooth forward and backward movement of the plunger 61.

[0071] The sliding ring 64 is generally annular, has an inner diameter that allows it to be press-fitted onto the outer peripheral surface of the plunger 61, and has an outer diameter that allows it to slide in contact with the plunger receiving hole 60. The sliding ring 64 is provided to face the bottom wall 600 of the plunger receiving hole 60 on one side in the biasing direction of the biasing member 62, and functions as a seating surface for the biasing member 62 that is interposed between the bottom wall 600 of the plunger receiving hole 60 and the sliding ring 64. The sliding ring 64 is also provided to face the annular member 63 on the other side in the biasing direction of the biasing member 62, and functions as an abutment surface that abuts against the annular member 63, and by abutting against the annular member 63, it helps to regulate the amount of advancement of the plunger 61.

[0072] The sliding ring 64 is press-fitted onto the plunger 61 with a degree of fit that restricts relative movement between the sliding ring 64 and the plunger 61 against the biasing force of the biasing member 62, while allowing relative movement between the sliding ring 64 and the plunger 61 against the meshing force between the sector gear 32 and the rack teeth 42. In other words, when the biasing force of the biasing member 62 is applied, the sliding ring 64 is maintained fixed to the plunger 61 and is movable forward and backward integrally with the plunger 61. On the other hand, when the meshing force between the sector gear 32 and the rack teeth 42 is applied in a plunger adjustment process described later, the sliding ring 64 is configured so that the plunger 61 is movable relative to the sliding ring 64.

[0073] The biasing member 62 has an annular or cylindrical shape with its inner periphery penetrating in the biasing direction. One end of the biasing member 62 is seated on the bottom wall 600 of the plunger receiving hole 60, and the other end of the biasing member 62 is seated on the sliding ring 64. The biasing member 62 is accommodated between the bottom wall 600 of the plunger receiving hole 60 and the sliding ring 64 with a predetermined preload. More specifically, the biasing member 62 is preloaded with the predetermined preload so that the biasing force of the biasing member 62 acts on the plunger 61 even when the sliding ring 64 is in contact with the stopper 630, thereby constantly applying a biasing force to the plunger 61. In this embodiment, the biasing member 62 is formed by stacking multiple well-known disc springs in series. Note that the biasing member 62 is not limited to the multiple disc springs stacked as in this embodiment, and the material and shape can be arbitrarily changed as long as it is hollow and can continuously bias the plunger 61, such as a coil spring.

[0074] (Explanation of the operation of the preload mechanism) FIG. 4 is a diagram showing the change in the amount of protrusion of plunger 61 depending on the steering state, where (a) shows the neutral state with a steering angle of 0 degrees, (b) shows the steering state with a steering angle of 12 degrees, and (c) shows the steering state with a steering angle of 25 degrees.

[0075] As shown in FIG. 4( a), in the neutral state where the steering angle is 0 degrees, the plunger 61 is in its most retracted position, the sliding ring 64 is separated from the stopper 630, and the tip end 611 of the plunger 61 elastically abuts against the tooth tips of the first sector teeth 321 due to the biasing force of the biasing member 62. In this state, the ball nut 4 is biased toward one side in the rotational direction by a reaction force generated when the tip end 611 of the plunger 61 abuts against the tooth tips of the first sector teeth 321. As a result, at the other end side of the sector gear 32, the gap C between the first sector tooth 321 and the first rack tooth bottom 425 becomes smaller. This deepens the meshing between the first sector tooth 321 and the second and third rack teeth 422, 423, reducing backlash between the first sector tooth 321 and the second and third rack teeth 422, 423.

[0076] As shown in Figure 4(b) , when the steering angle is 12 degrees, the plunger 61 is in an advanced state, and the sliding ring 64 is about to abut against the stopper 630, and the tip 611 of the plunger 61 is in elastic contact with the tooth tips of the first sector teeth 321 due to the biasing force of the biasing member 62. In this state, the forward movement of the plunger 61 extends the biasing member 62, and a relatively smaller biasing force than in the neutral state acts on the plunger 61. In other words, the ball nut 4 is biased to one side in the rotational direction by a reaction force generated when the tip 611 of the plunger 61 abuts against the tooth tips of the first sector teeth 321 based on a biasing force smaller than that in the neutral state. As a result, on the other end side of the sector gear 32, the gap C between the first sector tooth 321 and the first rack tooth bottom 425 decreases, and the backlash between the first sector tooth 321 and the second and third rack teeth 422, 423 decreases.

[0077] 4(c), when the steering angle is 25 degrees, the plunger 61 is in its most advanced state, the sliding ring 64 abuts against the stopper 630, restricting the forward movement of the plunger 61, and the tip end 611 of the plunger 61 is spaced apart from the tooth tips of the first sector teeth 321. In this state, no biasing force acts on the ball nut 4, so the gap C between the first sector tooth 321 and the first rack tooth bottom 425 does not change, and the backlash between the first sector tooth 321 and the second and third rack teeth 422, 423 is not adjusted.

[0078] (Method of manufacturing a steering device) Figure 5 shows the plunger adjustment process for adjusting the amount of protrusion of the plunger 61 in the manufacturing method of the steering device PS1, where (a) shows the first process, (b) shows the second process, (c) shows the third process, and (d) shows the maximum protrusion state of the plunger after the plunger adjustment.

[0079] The following describes a manufacturing method of the steering device PS1. In the manufacturing method of the steering device PS1, the following description focuses on a preload mechanism assembling step for assembling the preload applying mechanism 6, which is a characteristic component of the steering device PS1.

[0080] That is, the manufacturing method of the steering device PS1 includes, as a preload mechanism assembly process, a biasing member assembly process for assembling the biasing member 62, a sliding ring assembly process for assembling the sliding ring 64, a plunger assembly process for assembling the plunger 61, and a plunger adjustment process for adjusting the relative positions of the plunger 61 and the sliding ring 64.

[0081] In the biasing member assembling process, the biasing member 62 is accommodated inside the plunger receiving hole 60 from the opening side. In the sliding ring assembling process, the sliding ring 64 is assembled to the outer periphery of the plunger 61. The biasing member assembling process and the plunger assembling process may be carried out in any order. In the plunger assembling process, after the biasing member assembling process, the plunger assembly 610, which is formed by integrating the plunger 61 and the sliding ring 64, is accommodated inside the plunger receiving hole 60 from the opening side. In the plunger adjustment process, after the plunger assembling process, the sector gear 32 and the rack teeth 42 are meshed to adjust the relative positions of the plunger 61 and the sliding ring 64.

[0082] Here, the plunger adjusting step mainly includes a first step, a second step, and a third step, which will be described in detail below.

[0083] 5(a), in the first step, the sector gear 32 is rotated in one direction relative to the rack teeth 42 to which the preload applying mechanism 6 is attached, and the sector gear 32 is engaged in a non-neutral position. At this point, the plunger assembly 610 is in a state of being fully advanced with the sliding ring 64 abutting against the stopper 630, while the first sector tooth 321 is not abutting against the plunger 61 and is in a state immediately before abutting against the plunger 61.

[0084] In the second step, after the first step, the sector gear 32 is rotated toward the neutral position in a direction (the direction of arrow R in the figure) in which the distance C between the first sector tooth 321 and the first rack tooth bottom 425 decreases. As the sector gear 32 rotates, the first sector tooth 321 presses the plunger 61 in the direction opposite to the biasing direction of the biasing member 62 against the biasing force of the biasing member 62, and as shown in Figure 5(b), the biasing member 62 is compressed until it is at its maximum contraction via the sliding ring 64 which moves integrally with the plunger 61.

[0085] In the third step, after the second step, with the biasing member 62 in a state of being fully contracted (see FIG. 5(b)), the first sector teeth 321 further press the plunger 61 in a direction opposite to the biasing direction of the biasing member 62. As a result, as shown in FIG. 5(c), the plunger 61 moves (retracts) relative to the sliding ring 64 in a direction opposite to the biasing direction of the biasing member 62. At this time, the end portion 612 of the plunger 61 pushed aside by the first sector teeth 321 is received in the recessed portion 603, so the bottom wall 600 does not prevent the plunger 61 from moving backward. In this way, the relative movement (retraction) of the plunger 61 with respect to the sliding ring 64 automatically adjusts the relative position of the plunger 61 and the sliding ring 64 to an appropriate position so that the tip portion 611 of the plunger 61 abuts against the tooth tip of the first sector tooth 321 at the neutral position when the biasing member 62 is fully compressed.

[0086] Thereafter, when the sector gear 32 is further rotated in one direction, the plunger 61 and the sliding ring 64 again move forward toward the first sector tooth 321 while maintaining the relative positions adjusted in the third step, as shown in Figure 5(d).

[0087] (Effects of this embodiment) In conventional steering devices, a preload mechanism biases the ball nut in one direction of rotation based on a reaction force from the plunger sliding contact portion, which has a predetermined cam profile and is adjacent to the sector gear. The plunger, which is provided inside the ball nut and can be biased toward the sector gear, elastically abuts on the plunger sliding contact portion. This generates a reaction force from the plunger sliding contact portion, reducing backlash between the rack teeth and the sector gear near the neutral position of the sector shaft. However, in these conventional steering devices, it was necessary to provide a plunger sliding contact portion separate from the sector gear. This resulted in an increase in the axial size of the sector shaft by the size of the plunger sliding contact portion, leaving room for improvement.

[0088] In contrast, the steering device PS1 according to this embodiment includes rack teeth 42 formed on the outer side of a ball nut 4 that is screwed onto a steering shaft 2 (second steering shaft 22) that is linked to a steering wheel (not shown), a sector gear 32 that is provided on a sector shaft 3 that is linked to a steered wheel (not shown), and that includes a central tooth (first sector tooth 321) that meshes most deeply with the rack teeth 42 at the neutral position of the sector shaft 3 that corresponds to a straight-ahead steering state, and that meshes with the rack teeth 42 using a plurality of sector teeth (first sector tooth 321, second sector tooth 322, and third sector tooth 323) that are provided in the circumferential direction of the sector shaft 3, and a preload applying mechanism 6 that adjusts the meshing of the rack teeth 42 with the sector gear 32 near the neutral position of the sector shaft 3, and the preload applying mechanism 6 adjusts the meshing of the rack teeth 42 with the sector gear 32 near the neutral position of the sector shaft 3. The plunger receiving hole 60 is biased toward one end of the rack tooth bottom 425 in the tooth width direction and opens to the specific tooth bottom (first rack tooth bottom 425). The plunger 61 is accommodated in the plunger receiving hole 60 so as to be able to advance and retreat, and the tip side is provided so as to be able to protrude from the opening of the plunger receiving hole 60 facing the sector gear 32. The plunger 61 is press-fitted to the outer periphery of the plunger 61 so as to be able to move integrally with the plunger 61, and the plunger 61 moves in accordance with the advance and retreat of the plunger 61. The plunger receiving hole 60 has a sliding ring 64 that slides against the inner peripheral surface thereof, and a biasing member 62 that is interposed between the bottom (bottom wall 600) of the plunger receiving hole 60 and the sliding ring 64 and biases the plunger 61 via the sliding ring 64 toward the central tooth (first sector tooth 321). The ball nut 4 is biased toward one side in the rotation direction of the ball nut 4 based on the reaction force generated when the plunger 61 elastically contacts the tip of the central tooth (first sector tooth 321).

[0089] As described above, in this embodiment, the plunger 61, biased by the biasing member 62, elastically contacts the tip of the first sector tooth 321 of the sector gear 32, and based on the reaction force generated, a rotational torque acting as a preload is applied to the ball nut 4 in one direction of rotation of the ball nut 4. Therefore, in this embodiment, unlike the conventional steering device described above, there is no need to provide a pressed portion to be pressed by the plunger 61, separate from the sector gear 32. This makes it possible to prevent the sector shaft 3 from becoming larger due to the formation of the pressed portion.

[0090] Furthermore, in this embodiment, the connection between the sliding ring 64 and the plunger 61 by press-fitting restricts the relative movement between the sliding ring 64 and the plunger 61 in relation to the biasing force of the biasing member 62, while allowing the relative movement between the sliding ring 64 and the plunger 61 in relation to the meshing force of the sector gear 32 with the rack teeth 42.

[0091] If the sliding ring 64 were formed integrally with the plunger 61, the length of the tip 611 of the plunger 61 facing the sector gear 32 (first sector teeth 321) side beyond the sliding ring 64 may be longer than necessary depending on the machining accuracy (machining error) of the plunger receiving hole 60, plunger 61, sliding ring 64, etc. In this case, the plunger 61 may be pushed in excessively when the sector gear 32 and the rack teeth 42 mesh, and as a result, the biasing member 62 may be compressed excessively, which may cause damage to the biasing member 62 or shorten its lifespan.

[0092] In contrast to this, in this embodiment, the sliding ring 64 is press-fitted into the plunger 61 by a fit that restricts relative movement between the sliding ring 64 and the plunger 61 against the biasing force of the biasing member 62, while allowing relative movement between the sliding ring 64 and the plunger 61 against the meshing force between the sector gear 32 and the rack teeth 42. As a result, the sliding ring 64 and the plunger 61 move together due to the biasing force of the biasing member 62, but when the sector gear 32 meshes with the rack teeth 42, the sector gear 32 (first sector teeth 321) pushes the plunger 61 in the opposite direction of the advancing direction, causing the plunger 61 to move relative to the sliding ring 64, and it becomes possible to change the relative position between the plunger 61 and the sliding ring 64 to an appropriate positional relationship. As a result, regardless of the processing errors in the dimensions (axial dimensions) of the plunger receiving hole 60, plunger 61, and sliding ring 64 related to the biasing direction of the biasing member 62, the plunger 61 can be biased against the sector gear 32 with an appropriate biasing force, and an appropriate preload (rotational torque) can be applied to the ball nut 4.

[0093] Furthermore, since the sliding ring 64 and the plunger 61 are allowed to move relative to each other in response to the meshing force between the sector gear 32 and the rack teeth 42, there is no risk of the biasing member 62 being excessively compressed by the meshing between the sector gear 32 and the rack teeth 42. This contributes to suppressing damage to the biasing member 62 and improving the durability of the biasing member 62.

[0094] In addition, in this embodiment, the plunger receiving hole 60 has a recess 603 at the bottom (bottom wall 600) opposite the opening, which can receive the end portion 612 opposite the tip portion 611 of the plunger 61 that abuts against the tip of the central tooth (first sector tooth 321).

[0095] Depending on the length of the end portion 612 of the plunger 61 facing the biasing member 62 side relative to the sliding ring 64, when the plunger 61 is pushed in by the central tooth (first sector tooth 321), the end portion 612 of the plunger 61 may come into contact with the bottom (bottom wall 600) of the plunger receiving hole 60, which may prevent the plunger 61 from being pushed in (moving backward).

[0096] In contrast, in this embodiment, a recess 603 capable of receiving an end portion 612 of the plunger 61 opposite to the tip portion 611 of the plunger 61 that abuts against the central tooth (first sector tooth 321) of the sector gear 32 is provided on the bottom (bottom wall 600) of the plunger receiving hole 60 on the opposite side to the opening. Therefore, when the plunger 61 is pushed in by the central tooth (first sector tooth 321), the end portion 612 of the plunger 61 is received in the recess 603, and there is no risk that the end portion 612 of the plunger 61 will abut against the bottom (bottom wall 600) of the plunger receiving hole 60 and hinder the plunger 61 from being pushed in (rearward movement). This makes it possible to appropriately adjust the relative positions of the plunger 61 and the sliding ring 64 regardless of the length of the end portion 612 of the plunger 61 that faces the biasing member 62 side relative to the sliding ring 64.

[0097] In addition, in this embodiment, the plunger receiving hole 60 has an opening which is reduced in diameter so that its inner diameter is smaller than the outer diameter of the sliding ring 64, and has a stopper 630 which abuts against the sliding ring 64 to regulate the amount of protrusion of the plunger 61. When the rotation phase of the sector shaft 3 is near the neutral position, the sliding ring 64 does not abut against the stopper 630, allowing the plunger 61 to abut against the central tooth (first sector tooth 321). On the other hand, when the rotation phase of the sector shaft 3 has passed beyond the neutral position, the sliding ring 64 abuts against the stopper 630 to regulate the abutment of the plunger 61 against the central tooth (first sector tooth 321).

[0098] That is, in this embodiment, when the rotation phase of the sector shaft 3 is near the neutral position of the steering, the plunger 61 is allowed to come into contact with the first sector tooth 321, but when the rotation phase of the sector shaft 3 goes beyond the neutral position, the stopper 630 restricts the plunger 61 from coming into contact with the first sector tooth 321.

[0099] In this way, in this embodiment, by restricting the amount of protrusion of the plunger 61 with the stopper 630, it is possible to adjust the meshing between the rack teeth 42 and the sector gear 32 only near the neutral position of the sector shaft 3 where a sense of rigidity is required. In other words, by restricting the contact between the plunger 61 and the first sector teeth 321 in positions other than near the neutral position where a sense of rigidity is not particularly required, it is possible to suppress deterioration of the steering feel, such as a rough feeling, caused by the plunger 61 sliding against the first sector teeth 321.

[0100] In addition, in this embodiment, stopper 630 is configured by placing an annular member 63 in the opening of plunger receiving hole 60. Therefore, in this embodiment, the amount of protrusion of plunger 61 can be restricted with a relatively simple configuration without forming a complex cam profile as in, for example, the conventional steering device described above. This can contribute to reducing the manufacturing cost of steering device PS1.

[0101] In addition, in this embodiment, the tooth bottom of the sector gear 32 has a straight shape that is approximately parallel to the rotation axis Y of the sector shaft 3. In other words, in this embodiment, the tooth bottom of the sector gear 32 is not tapered, and a mechanism (backlash adjustment mechanism) for adjusting the meshing between the rack teeth 42 and the sector gear 32 is not provided in addition to the preload applying mechanism 6, and the meshing between the rack teeth 42 and the sector gear 32 can be adjusted only by the preload applying mechanism 6. This simplifies the structure of the steering device PS1, contributing to improved productivity of the steering device PS1 and reduced manufacturing costs.

[0102] Furthermore, the manufacturing method of the steering device PS1 according to this embodiment includes a biasing member assembling step of accommodating the biasing member 62 in the plunger receiving hole 60, a sliding ring assembling step of assembling the sliding ring 64 to the plunger 61, a plunger assembling step of assembling the plunger 61 with the sliding ring 64 assembled thereto into the plunger receiving hole 60, and a plunger adjusting step of, after the plunger assembling step, meshing the sector gear 32 with the rack teeth 42 to adjust the relative positions of the plunger 61 and the sliding ring 64. The plunger adjusting step includes a first step of rotating the sector gear 32 in one direction with respect to the rack teeth 42 to which the preload applying mechanism 6 is assembled, and meshing the sector gear 32 in a state where the sector gear 32 is in a non-neutral position; and a third step in which, after the second step, the sector gear 32 is rotated toward the neutral position in a direction in which the distance C between the central tooth (first sector tooth 321) and the specific tooth bottom (first rack tooth bottom 425) becomes smaller, so that the central tooth (first sector tooth 321) presses the plunger 61 in the direction opposite to the biasing direction of the biasing member 62 against the biasing force of the biasing member 62, thereby compressing the biasing member 62 until it is fully contracted via the sliding ring 64 that moves integrally with the plunger 61.

[0103] As described above, in the present embodiment, in the plunger adjustment process, when the biasing member 62 is at its maximum contraction, the central tooth (first sector tooth 321) further presses the plunger 61, thereby moving the plunger 61 relative to the sliding ring 64 and changing the relative positions of the plunger 61 and the sliding ring 64 to an appropriate positional relationship. As a result, regardless of the processing errors in the axial dimensions of the plunger receiving hole 60, plunger 61, sliding ring 64, etc., the plunger 61 can be biased against the sector gear 32 with an appropriate biasing force, and an appropriate preload can be applied to the ball nut 4.

[0104] Furthermore, in the plunger adjustment process, when the central tooth (first sector tooth 321) further presses the plunger 61 in a state where the urging member 62 is maximally compressed, the plunger 61 is allowed to move relative to the sliding ring 64. This eliminates the risk of the urging member 62 being excessively compressed, even if the amount of protrusion of the plunger 61 exceeds a specified dimension in relation to the bottom wall 600 of the plunger receiving hole 60 due to machining errors in the axial dimensions of the plunger receiving hole 60, plunger 61, sliding ring 64, etc. This prevents damage to the urging member 62 and contributes to improving the durability of the urging member 62.

[0105] Furthermore, according to the manufacturing method of the steering device PS1, the plunger receiving hole 60 has a recess 603 at the bottom (bottom wall 600) opposite the opening, which can receive the end portion 612 opposite to the tip portion 611 of the plunger 61 that abuts against the tip of the central tooth (first sector tooth 321), and in the third step, when the plunger 61 moves relative to the sliding ring 64 in the direction opposite to the biasing direction of the biasing member 62, the end portion 612 of the plunger 61 is received in the recess 603.

[0106] In the third step, depending on the length of the end portion 612 of the plunger 61 facing the biasing member 62 side relative to the sliding ring 64, when the plunger 61 is pushed in by the central tooth (first sector tooth 321), the end portion 612 of the plunger 61 may come into contact with the bottom (bottom wall 600) of the plunger receiving hole 60, which may prevent the plunger 61 from being pushed in (moving backward).

[0107] In contrast, in this embodiment, a recess 603 capable of receiving an end portion 612 of the plunger 61 opposite to the tip portion 611 of the plunger 61 that abuts against the central tooth (first sector tooth 321) of the sector gear 32 is provided on the bottom (bottom wall 600) opposite the opening of the plunger receiving hole 60. Therefore, when the plunger 61 is pushed in by the central tooth (first sector tooth 321) in the third step of the plunger adjustment process, the end portion 612 of the plunger 61 is received in the recess 603, and there is no risk that the end portion 612 of the plunger 61 will abut against the bottom (bottom wall 600) of the plunger receiving hole 60 and hinder the plunger 61 from being pushed in (rearward movement). This makes it possible to adjust the relative position between the plunger 61 and the sliding ring 64 to an appropriate state regardless of the length of the end portion 612 of the plunger 61 that faces the biasing member 62 side relative to the sliding ring 64.

[0108] [Second embodiment] 6 shows a second embodiment of the steering device according to the present invention. This embodiment mainly changes the configuration of the sector shaft 3 and provides a backlash adjustment mechanism capable of adjusting the backlash of the sector gear 32 relative to the rack teeth 42, separate from the preload applying mechanism 6, but the other configurations are the same as those of the first embodiment. Therefore, the same components as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0109] FIG. 6 shows a steering device PS2 according to a second embodiment of the present invention, and shows a transverse cross-sectional view of the steering device PS2 corresponding to the cross-sectional view taken along line AA in FIG.

[0110] 6, in the steering device PS2 according to this embodiment, the sector shaft portion 31 is configured as a large-diameter shaft portion 313 having a relatively large diameter on one end side from the sector gear 32, and as a small-diameter shaft portion 314 having a relatively small diameter on the other end side from the sector gear 32. One end side of the large-diameter shaft portion 313 is connected to a pitman arm (not shown), and the other end side is rotatably supported by a large-diameter bearing 333 accommodated on the inner periphery side of the second opening 112a. That is, since a large torque is applied to the steered wheel (not shown) via the pitman arm (not shown) connected to one end of the large-diameter shaft portion 313, the large-diameter shaft portion 313 is formed with a relatively large diameter to ensure rigidity capable of withstanding the large torque.

[0111] Furthermore, a large diameter seal member 343 capable of providing a liquid-tight seal between the outer peripheral surface of the large diameter shaft portion 313 and the inner peripheral surface of the second opening 112a is provided on one end side of the large diameter bearing 333. This prevents the working fluid filled inside the housing 1 (sector shaft accommodating portion 112) from leaking out through the second opening 112a.

[0112] On the other hand, the small diameter shaft portion 314 is rotatably supported by a small diameter bearing 334 accommodated on the inner periphery side of the third housing cylindrical portion 134. That is, the small diameter shaft portion 314 serves to support the rotation of the other end of the sector shaft 3, and since a large torque is not applied to the small diameter shaft portion 314 as is the case with the large diameter shaft portion 313, high rigidity capable of withstanding the large torque is not required, and therefore the small diameter shaft portion 314 is formed to have a relatively small diameter.

[0113] Additionally, a small diameter seal member 344 is provided on the other end side of the small diameter bearing 334, which is capable of providing a liquid-tight seal between the outer peripheral surface of the small diameter shaft portion 314 and the inner peripheral surface of the third housing cylindrical portion 134. This prevents the working fluid filled inside the housing 1 (sector shaft accommodating portion 112) from leaking out to the outside through the female thread hole 136, which will be described later.

[0114] The sector gear 32 is configured as a so-called tapered gear. That is, as shown in Fig. 6, the sector gear 32 has a first sector tooth bottom 325 located between the first sector tooth 321 and the second sector tooth 322 and a second sector tooth bottom 326 located between the first sector tooth 321 and the third sector tooth 323, which are configured by tapered surfaces in which the tooth depth T of the first sector tooth 321, the second sector tooth 322, and the third sector tooth 323 gradually increases toward one end of the sector shaft 3.

[0115] In addition, in accordance with the tapered gear configuration, an internally threaded hole 136 penetrating along the rotation axis Y is formed in the third housing end wall 135, and an adjusting screw 5 is screwed into this internally threaded hole 136 from the other end side (outside) of the third housing 13. When this adjusting screw 5 is screwed in while abutting against the other end (small diameter shaft portion 314) of the sector shaft 3, it advances toward one end side and urges the sector shaft 3 toward the one end side. In other words, when the adjusting screw 5 is screwed in and the sector shaft 3 moves toward the one end side, the gaps between the first sector tooth bottom 325 and the second sector tooth bottom 326 and the second rack teeth 422 and the third rack teeth 423 decrease, making it possible to reduce backlash of the sector gear 32 relative to the rack teeth 42.

[0116] As described above, in this embodiment, a backlash adjustment mechanism is provided which is made up of the sector gear 32 formed by the tapered gear and the adjusting screw 5 which biases the sector shaft 3, and which can adjust the backlash between the sector gear 32 and the rack teeth 42 by manually rotating (threading) the adjusting screw 5. This makes it possible to adjust the backlash between the sector gear 32 and the rack teeth 42 which increases due to wear of the sector gear 32 and the rack teeth 42 when servicing the vehicle.

[0117] As described above, in the steering device PS2 according to this embodiment, the tooth bottoms (first sector tooth bottom 325 and second sector tooth bottom 326) of the sector gear 32 have tapered surfaces in which the tooth depth T of the sector gear 32 gradually increases toward one end of the axial direction of the sector shaft 3, and the sector shaft 3 is configured to be movable toward one end of the axial direction of the sector shaft 3 by the adjusting screw 5 screwed in from the other end of the axial direction of the sector shaft 3 through a female threaded hole 136 formed in the end wall (third housing 13) of the housing 1 (first housing 11) that accommodates the sector shaft 3.

[0118] As described above, in this embodiment, the first sector tooth bottom 325 and the second sector tooth bottom 326 of the sector gear 32 have a tapered gear shape with tapered surfaces, and it is possible to adjust the meshing between the rack teeth 42 and the sector gear 32 by moving the sector shaft 3 toward one end in the axial direction with the adjusting screw 5. This ensures appropriate meshing between the rack teeth 42 and the sector gear 32 not only near the neutral position of the sector shaft 3 but throughout the entire rotation range of the sector shaft 3.

[0119] In addition, in this embodiment, the sector shaft 3 is formed with a relatively large diameter at one axial end side sandwiching the sector gear 32, which is connected to the pitman arm (not shown), and is formed with a relatively smaller diameter at the other axial end side sandwiching the sector gear 32, and the plunger receiving hole 60 is provided at the end of the specific tooth bottom (first rack tooth bottom 425) in the tooth width direction, which end corresponds to the other axial end side of the sector shaft 3.

[0120] As described above, in this embodiment, the plunger receiving hole 60 constituting the preload applying mechanism 6 is disposed on the side of the small diameter shaft portion 314 where the sector shaft 3 has a relatively small diameter. Therefore, since the sector shaft portion 31 has a smaller diameter like the small diameter shaft portion 314, the space available for disposing the preload applying mechanism 6 is expanded by the amount, and the preload applying mechanism 6 can be disposed at a position farther away from the rotation center of the ball nut 4. This makes it possible to apply a larger rotational torque to the ball nut 4, and more effectively adjust the meshing between the first sector teeth 321 and the second and third rack teeth 422, 423.

[0121] The present invention is not limited to the configurations exemplified in the above-described embodiments, and not only the detailed configuration of the steering device, such as the configuration of the steering shaft 2, the input mode to the steering shaft 2, and the shapes of the sector gear 32 and the rack teeth 42, which are not directly related to the configuration of the present invention, but also the parts directly related to the configuration of the present invention, such as the preload mechanism 6, can be freely modified according to the specifications of the steering device or vehicle to which the present invention is applied, within the scope that does not deviate from the spirit of the present invention, such as the specific shape of the plunger 61 and the biasing member 62, the presence or absence of the recessed portion 603, the dimensions of the plunger 61 and the sliding ring 64, etc.

Claims

1. rack teeth formed on the outer side of a ball nut that is screwed onto a steering shaft that is linked to the steering wheel; a sector gear provided on a sector shaft linked to the steered wheels, the sector gear including a central tooth that meshes most deeply with the rack teeth at a neutral position of the sector shaft corresponding to a straight-ahead steering state, and having a plurality of sector teeth provided in the circumferential direction of the sector shaft that mesh with the rack teeth; a preload applying mechanism that adjusts the meshing between the rack teeth and the sector gear near a neutral position of the sector shaft; Equipped with The preload applying mechanism includes: a plunger receiving hole provided near a neutral position of the sector shaft and biased toward one end of a specific tooth bottom of the rack tooth that faces the tip of the central tooth, the specific tooth bottom opening in the tooth width direction; a plunger accommodated in the plunger receiving hole so as to be able to advance and retreat, the plunger being provided so that a tip side thereof can protrude from an opening of the plunger receiving hole facing the sector gear; a sliding ring that is press-fitted onto the outer circumferential side of the plunger and is movable integrally with the plunger, and that slides against the inner circumferential surface of the plunger receiving hole as the plunger moves forward and backward; a biasing member interposed between the bottom of the plunger receiving hole and the sliding ring, for biasing the plunger via the sliding ring toward the central tooth; and The ball nut is biased toward one side in a rotation direction of the ball nut based on a reaction force generated by the plunger elastically contacting the tip of the central tooth, The coupling between the sliding ring and the plunger by the press-fitting restricts relative movement between the sliding ring and the plunger in relation to the biasing force of the biasing member, while allowing relative movement between the sliding ring and the plunger in relation to the meshing force of the sector gear with the rack teeth. A steering device characterized by:

2. 2. The steering device according to claim 1, The plunger receiving hole has a recessed portion at a bottom opposite to the opening, the recessed portion being capable of receiving an end portion of the plunger opposite to a tip portion of the plunger that abuts against the tip of the central tooth. A steering device characterized by:

3. 2. The steering device according to claim 1, the plunger receiving hole has an opening whose inner diameter is reduced to be smaller than the outer diameter of the sliding ring, and has a stopper that abuts against the sliding ring to restrict the amount of protrusion of the plunger, When the rotation phase of the sector shaft is near the neutral position, the sliding ring does not contact the stopper, and contact between the plunger and the central tooth is allowed. When the rotation phase of the sector shaft exceeds the vicinity of the neutral position, the sliding ring abuts against the stopper to restrict abutment between the plunger and the central tooth. A steering device characterized by:

4. 2. The steering device according to claim 1, The bottom of the sector gear is a flat surface parallel to the axis of the sector shaft. A steering device characterized by:

5. 2. The steering device according to claim 1, a bottom of the sector gear has a tapered surface in which the tooth depth of the sector gear gradually increases toward one end of the sector shaft in the axial direction; the sector shaft is configured to be movable toward one axial end of the sector shaft by an adjusting screw that is screwed into the other axial end of the sector shaft through a female threaded hole formed in an end wall of a housing that accommodates the sector shaft. A steering device characterized by:

6. 2. The steering device according to claim 1, the sector shaft is connected to a pitman arm, and one axial end side thereof across the sector gear is formed to have a relatively large diameter, and the other axial end side thereof across the sector gear is formed to have a relatively small diameter than the one axial end side, the plunger receiving hole is open to an end of the specific tooth bottom in the tooth width direction that corresponds to the other axial end side of the sector shaft, A steering device characterized by:

7. A method for manufacturing a steering device according to claim 1, a biasing member assembling step of accommodating the biasing member in the plunger receiving hole; a sliding ring assembling step of assembling the sliding ring to the plunger; a plunger assembling step of assembling the plunger, to which the sliding ring is assembled, into the plunger receiving hole; a plunger adjusting step of adjusting a relative position between the plunger and the sliding ring by meshing the sector gear with the rack teeth after the plunger assembling step; Including, The plunger adjusting step includes: a first step of rotating the sector gear in one direction relative to the rack teeth to which the preload applying mechanism is attached, and engaging the sector gear in a non-neutral position; a second step of rotating the sector gear in a direction in which the distance between the central tooth and the specific tooth bottom decreases toward the neutral position after the first step, so that the central tooth presses the plunger in a direction opposite to the biasing direction of the biasing member against the biasing force of the biasing member, thereby compressing the biasing member until it is at its maximum contraction via the sliding ring that moves integrally with the plunger; a third step in which, after the second step, the central tooth further presses the plunger in a direction opposite to the biasing direction of the biasing member when the biasing member is in a maximum contracted state, thereby moving the plunger relative to the sliding ring in the direction opposite to the biasing direction of the biasing member; having A method for manufacturing a steering device comprising the steps of:

8. A method for manufacturing a steering device according to claim 7, the plunger receiving hole has a recessed portion at a bottom opposite to the opening, the recessed portion being capable of receiving an end portion of the plunger opposite to a tip portion of the plunger that abuts against the tip of the central tooth, In the third step, when the plunger moves relative to the sliding ring in a direction opposite to the biasing direction of the biasing member, the end portion of the plunger is received in the recessed portion. A method for manufacturing a steering device comprising the steps of:

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