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 by the plunger (61) separately from the sector gear (32). 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

Steering device

[0001] The present invention relates to a steering device.

[0002] 2. Description of the Related Art A conventional steering device is known, for example, from Patent Document 1 below.

[0003] That is, the steering device according to Patent Document 1 listed 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.

[0005] Japanese Patent Application Publication No. 5-319285

[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 view of the above technical problem, and has an object to provide a steering device that can prevent the sector shaft from becoming large.

[0008] In one aspect, the present invention provides a steering system comprising: rack teeth formed on the outer side of a ball nut that is screwed onto a steering shaft that is linked to a steering wheel; a sector gear that is provided on a sector shaft that is linked to a steered wheel and includes central teeth that mesh most deeply with the rack teeth at a neutral position of the sector shaft that corresponds to a straight-ahead steering state, and meshes with the rack teeth by means of a plurality of sector teeth provided in the circumferential direction of the sector shaft; and a preload applying mechanism that adjusts the meshing of the rack teeth with the sector gear near the neutral position of the sector shaft, wherein the preload applying mechanism adjusts the meshing of the rack teeth with the sector gear near the neutral position of the sector shaft, in a cross section perpendicular to the rotational axis of the steering shaft from the steering shaft side toward the rack tooth side. the plunger receiving hole is formed in an inclined shape so as to gradually approach a meshing direction line perpendicular to the axis of the rack tooth, and opens to one end 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; a plunger that is accommodated in the plunger receiving hole so as to be able to advance and retreat, and whose tip side is able to protrude from an opening of the plunger receiving hole that faces the sector gear; and a biasing member that is interposed between the bottom of the plunger receiving hole and the plunger and biases the plunger toward the central tooth, and based on a reaction force generated when the plunger, biased by the biasing member, elastically comes into contact with the tooth tip of the central tooth, biases the ball nut to one side in the rotational direction of the ball nut.

[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. Therefore, unlike the conventional steering device described above, the present invention does not require a pressed portion that is used for pressing by the preload applying mechanism, separate from the sector gear. This makes it possible to prevent the sector shaft from becoming larger due to the formation of the pressed portion.

[0010] Furthermore, in the present invention, the plunger receiving hole is formed in an inclined shape so that, in a cross section perpendicular to the rotation axis of the steering shaft, it gradually approaches the meshing direction line perpendicular to the rotation axis of the steering shaft and the rotation axis of the sector shaft from the steering shaft side toward the rack tooth side. This makes it possible to ensure a relatively large distance between the rotation center of the ball nut and the plunger receiving hole, compared to when the plunger receiving hole is formed perpendicular to the specific tooth bottom, and reduces the biasing force of the biasing member. This allows for a smaller biasing member, a smaller preload applying mechanism, and ultimately a smaller steering device.

[0011] In another aspect of the steering device, it is desirable that the plunger receiving hole is provided so as to pass through the ball nut in a cross section perpendicular to the rotation axis of the steering shaft, and has a first opening that opens to the rack tooth side and a second opening that opens to the ball nut side, and that the bottom of the plunger receiving hole is formed by a plug that is screwed into the second opening of the plunger receiving hole.

[0012] In this way, in the present invention, the plunger receiving hole is formed so as to pass through the ball nut, which improves the workability of the plunger receiving hole compared to when the plunger receiving hole is formed as a blind hole, thereby contributing to improved productivity of the steering device.

[0013] Furthermore, in the present invention, the bottom of the plunger receiving hole is configured with a plug that is screwed into the second opening of the plunger receiving hole, making it possible to adjust the biasing force of the biasing member using the plug, thereby applying a more appropriate biasing force to the ball nut.

[0014] In yet another aspect of the steering device, the plunger has a large diameter portion that slides inside the plunger receiving hole, and a small diameter portion that is formed in a stepped shape with respect to the large diameter portion and is capable of protruding from the first opening, the plunger receiving hole having a diameter reduced from the first opening to an inner diameter that is smaller than the outer diameter of the large diameter portion, and has a stopper that abuts against the large diameter portion to regulate the amount of protrusion of the small diameter portion, and when the rotation phase of the sector shaft is in the vicinity of the neutral position, the large diameter portion 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 large diameter portion abuts against the stopper to regulate the abutment of the plunger against the central tooth.

[0015] In other words, in the present invention, when the rotation phase of the sector shaft is near the neutral position, the plunger is allowed to come into contact with the central tooth, and when the rotation phase of the sector shaft goes beyond the neutral position, the stopper restricts the plunger from coming into contact with the central tooth.

[0016] In this way, by restricting the amount of plunger protrusion with the stopper, it is possible to adjust the meshing between the rack teeth and the sector gear only near the neutral position of the sector shaft where a sense of rigidity is required. In other words, by restricting the contact between the plunger and the central tooth except near the neutral position of the sector shaft where a sense of rigidity is not particularly required, it is possible to suppress deterioration of steering feel, such as a rough feeling caused by the plunger sliding against the central tooth.

[0017] Furthermore, in the present invention, the stopper is configured by simply narrowing the first opening of the plunger receiving hole. Therefore, unlike the conventional steering device described above, there is no need to form a complex cam profile, and the amount of plunger protrusion can be restricted with a relatively simple configuration. This contributes to reducing the manufacturing costs of the steering device.

[0018] 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.

[0019] As described above, in the present invention, the bottoms of the sector teeth have a straight shape that is parallel to the axis of the sector shaft. In other words, unlike the conventional steering device described above, the bottoms of the sector teeth are not tapered, and no mechanism for adjusting the meshing between the rack teeth and the sector gear is provided in addition to the preload mechanism. Instead, the meshing between the rack teeth and the sector gear is adjusted only by the preload mechanism. This simplifies the structure of the steering device, contributing to improved productivity and reduced 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 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.

[0021] As described above, the present invention has a tapered gear shape in which the bottoms of the sector teeth are tapered, and it is possible to adjust the meshing between the rack teeth and the sector gear 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 the sector gear not only near the neutral position of the sector shaft but throughout the entire rotation range of the sector shaft.

[0022] As yet another aspect of the steering device, it is desirable that the sector shaft, which is connected to a pitman arm, has a relatively large diameter at one axial end thereof across the sector gear, and a relatively smaller diameter at the other axial end thereof across the sector gear, and that the plunger receiving hole is provided at one of the ends of the specific tooth bottom in the tooth width direction that corresponds to the other axial end of the sector shaft.

[0023] In this way, in the present invention, the plunger receiving hole that constitutes the preload mechanism is located on the side of the sector shaft where the diameter is relatively small. This allows the preload mechanism to be located farther from the center of rotation of the ball nut by the amount of the smaller diameter. This 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.

[0024] In yet another aspect of the steering device, the biasing member is preferably configured by a coil spring.

[0025] In this way, in the present invention, the biasing member is configured as a coil spring, which ensures better assembly workability and reduces manufacturing costs compared to when the biasing member is configured as, for example, multiple stacked disc springs.

[0026] 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.

[0027] 1 is a longitudinal sectional view of a steering device according to a first embodiment of the present invention; FIG. 1 is a sectional view taken along line A-A in FIG. 1; FIG. 2 is an enlarged view of a main portion of FIG. 1; FIG. 3 is a diagram showing the transition of the protrusion amount of a plunger according to the steering state, in which (a) shows a neutral state where the steering angle is 0 degrees, (b) shows a steering state where the steering angle is 12 degrees, and (c) shows a steering state where the steering angle is 25 degrees. FIG. 4 is a transverse sectional view of a steering device according to a second embodiment of the present invention, corresponding to the sectional view taken along line A-A in FIG. 1.

[0028] Hereinafter, an embodiment of a steering device according to the present invention will be described with reference to the drawings. In the following embodiment, an example is shown in which the steering device is applied as an integral type power steering device used in large vehicles such as trucks.

[0029] [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 A-A 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 of the steering shaft 2 that is connected to a 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 of the sector shaft 3 that is connected to a ball nut 4 will be referred to as the "other end side."

[0030] 1 and 2, the steering device PS1 is a well-known ball nut type steering device that 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.

[0031] 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.

[0032] 1, the steering shaft accommodating portion 111 has a cylindrical shape with a bottom, one end of which in the direction of the rotation axis X is open to the outside through a first opening 111a, and the other end of which is closed by an end wall 111b. The first opening 111a is closed by the second housing 12 that fits into the first opening 111a.

[0033] The second housing 12 has a cylindrical shape with an outer diameter that tapers in a step 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 fitted into the first opening 111a and has a diameter that tapers in a step relative to the second housing main body 121. A first seal member S1 that can elastically abut against the inner circumferential surface of the first opening 111a is attached to the outer periphery 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.

[0034] The second housing 12 has a steering shaft insertion hole 123 penetrating the center thereof, through which the steering shaft 2 is inserted from the outside into the steering shaft accommodating portion 111. 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 portion 123a at one end and a relatively small diameter portion 123b at the other end. A steering bearing 113, such as a ball bearing, is accommodated in the large diameter portion 123a of the steering shaft insertion hole 123, and the steering shaft 2 is rotatably supported by the steering bearing 113.

[0035] The steering bearing 113 includes an inner race 113a formed integrally with the second steering shaft 22, an outer race 113b inserted into the large diameter hole 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 123a, with its axial movement restricted.

[0036] 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.

[0037] 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.

[0038] 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 the end face of the third opening 112b, and a third housing fitting portion 132 that is stepped in diameter 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.

[0039] The third housing fitting portion 132 has a cylindrical shaft support portion 133 on its inner circumferential side, which supports 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.

[0040] 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 overlaps 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.

[0041] 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).

[0042] 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.

[0043] 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. In this embodiment, the first shaft portion 311 and the second shaft portion 312 are set to have approximately the same outer diameter.

[0044] One end of the first shaft 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 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.

[0045] 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. A second seal member 342 is provided on the other end 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 through a female threaded hole 136 (described later).

[0046] 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 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.

[0047] 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 tooth 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.

[0048] 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 (shaft hole 41) of the ball nut 4.

[0049] 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 is arranged that connects one end and the other end of nut-side ball groove 402 and serves to circulate the plurality of balls 43.

[0050] 2, the ball nut 4 is formed asymmetrically with respect to the meshing direction line Z that passes through the center of the ball nut 4. Specifically, the ball nut 4 has a padded portion 45 formed on the side of the first shaft portion 311 of the sector shaft 3 across the meshing direction line Z, where the ball nut 4 bulges outward from the first shaft portion 311. This padded portion 45 bulges outward from the second shaft portion 312 of the sector shaft 3 across the meshing direction line Z.

[0051] 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.

[0052] 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 within 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 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.

[0053] 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.

[0054] An inlet port 124a, a supply port 124b, and a discharge port 124c are circumferential grooves extending in the circumferential direction of the rotation axis X and arranged in parallel in the direction of the rotation axis X on the inner circumferential side of the second housing 12. 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 also provided inside the second housing 12. A supply passage L connecting the supply port 124b to the first hydraulic pressure chamber P1 is also 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).

[0055] On the outer periphery 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 periphery 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 the convex portion not shown, which is sandwiched circumferentially between the right steering recess 220a and the left steering recess not shown, and the supply communication passage 223 and the discharge communication passage 224 are arranged alternately in the circumferential direction.

[0056] 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 a 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 on a side facing the other end side of the first sector tooth 321 closer to the second shaft portion 312.

[0057] (Configuration of Preloading Mechanism) FIG. 3 is an enlarged view of the main part of FIG. 1, showing the preloading mechanism 6, which is a main part of FIG. 1, and its vicinity.

[0058] As shown in Figure 3, the preload applying 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 able to move 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.

[0059] Plunger receiving hole 60 has a substantially circular cross section and penetrates ball nut 4 so that one end opens to first rack tooth bottom 425 and the other end opens toward ball nut 4. In this embodiment, the opening of plunger receiving hole 60 on the first rack tooth bottom 425 side is defined as a "first opening 600a," and the opening on the ball nut 4 side is defined as a "second opening 600b."

[0060] The second opening 600b of the plunger receiving hole 60 is closed by a plug 64, which is a sealing member. That is, the plug 64, which has a well-known bolt shape, is screwed into the second opening 600b of the plunger receiving hole 60 via a female thread portion 603 formed in the end region on the second opening 600b side. In other words, the bottom of the plunger receiving hole 60 is formed by the plug 64 that closes the second opening 600b of the plunger receiving hole 60.

[0061] Furthermore, the first opening 600a of the plunger receiving hole 60 is formed with a tapered stepped diameter. That is, the plunger receiving hole 60 is composed of a large diameter hole portion 601 provided on the plug 64 side, which is the bottom side, and a small diameter hole portion 602 provided in the first opening 600a and having an inner diameter smaller than that of the large diameter hole portion 601. As a result, a stopper 63 is formed between the large diameter hole portion 601 and the small diameter hole portion 602. The stopper 63 abuts against the plunger large diameter portion 611 to limit 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.

[0062] When the rotation phase of the sector shaft 3 is near the neutral position, the stopper 63 does not come into contact with the plunger large diameter portion 611 and allows the plunger 61 to come into contact with the first sector tooth 321 (see FIG. 4A). On the other hand, when the rotation phase of the sector shaft 3 goes beyond the neutral position, the stopper 63 comes into contact with the plunger large diameter portion 611 and restricts the plunger 61 from coming into contact with the first sector tooth 321 (see FIG. 4C).

[0063] Furthermore, in a cross section perpendicular to the rotation axis X of the steering shaft 2 (see FIG. 2 ), the plunger receiving hole 60 is formed in an inclined shape so as to gradually approach an engagement direction line Z perpendicular to the rotation axis X and the rotation axis Y from the steering shaft 2 side toward the rack tooth 42 side. In other words, the plunger receiving hole 60 is formed in an inclined shape so that the distance D between the center Q of the plunger receiving hole 60 and the engagement direction line Z gradually decreases from the steering shaft 2 side toward the rack tooth 42 side. In this manner, the plunger receiving hole 60 is configured to penetrate the padded portion 45 of the ball nut 4 obliquely with respect to the engagement direction line Z, with the first opening 600 a opening at one end in the tooth width direction of the first rack tooth bottom 425 that faces the first sector tooth 321, which is the central tooth, near the neutral position of the sector shaft 3, and the second opening 600 b opening at the padded portion 45 that is formed to bulge outward from the nut-side ball groove 402 of the ball nut 4.

[0064] In this embodiment, the plunger receiving hole 60 has an inclination angle θx, which is the minor angle between the center Q of the plunger receiving hole 60 and the meshing direction line Z, set to 15°, as an example. Note that the inclination angle θx is determined depending on the shape of the ball nut 4 and the necessary preload to be applied to the ball nut 4, and can be freely changed within the range of "0<θ<90°" depending on the specifications of the steering device PS1, etc.

[0065] The plunger 61 is integrally formed from a resin material and has a tapered outer diameter that reduces in steps toward the tip. Specifically, the plunger 61 has a large-diameter plunger portion 611 that is received in the large-diameter hole portion 601 of the plunger receiving hole 60 and a small-diameter plunger portion 612 that is slidably disposed in the small-diameter hole portion 602 of the plunger receiving hole 60. The large-diameter plunger portion 611 faces the tip surface of the plug 64 that is screwed into the second opening 600b of the plunger receiving hole 60 and functions as a seating surface for the biasing member 62. Meanwhile, the small-diameter plunger portion 612 protrudes from the small-diameter hole portion 602 of the plunger receiving hole 60 and faces the outside, facing the first sector tooth 321. The plunger small diameter portion 612 has a tip formed into a smoothly curved surface with an arc-shaped longitudinal section, which makes point contact with the flat tooth surfaces of the first sector teeth 321 and allows smooth sliding contact with the tooth surfaces of the first sector teeth 321 when the sector shaft 3 rotates.

[0066] The biasing member 62 has one end seated on the plug 64 that forms the bottom of the plunger receiving hole 60, and the other end seated on the plunger large-diameter portion 611, and is housed between the plug 64 and the plunger large-diameter portion 611 with a predetermined preload. That is, the predetermined preload is applied to the biasing member 62 so that the biasing force of the biasing member 62 acts on the plunger 61 even when the plunger large-diameter portion 611 is in contact with the stopper 63, and the biasing force of the biasing member 62 is constantly applied to the plunger 61. The biasing force of the biasing member 62 changes depending on the amount of threading of the plug 64. In other words, by adjusting the amount of threading of the plug 64, the preload of the biasing member 62 changes, and the biasing force generated by the biasing member 62 can be appropriately adjusted.

[0067] Furthermore, the biasing force F of the biasing member 62 generates a moment M on the ball nut 4 that rotates it counterclockwise in FIG. 2 , with a component Fz parallel to the meshing direction line Z as the preload. Specifically, the moment M is determined by the biasing force F of the biasing member and the distance D between the center of rotation (rotation axis X) of the ball nut 4 and the center Q of the plunger receiving hole 60. Then, based on this moment M, the ball nut 4 is biased in the counterclockwise direction in FIG. 2 , thereby reducing the gap C between the first sector tooth 321 and the first rack tooth bottom 425 and reducing backlash between the sector gear 32 and the rack teeth 42.

[0068] In this embodiment, the biasing member 62 is formed of a well-known coil spring. The biasing member 62 made of this coil spring is inserted through the second opening 600b of the plunger receiving hole 60, which already has the plunger 61 housed therein, and is assembled by screwing a plug 64 into the second opening 600b to close it, so that the biasing member 62 is sandwiched between the plunger 61 and the plug 64. Note that the biasing member 62 is not limited to the coil spring as in this embodiment, and can be made of any material or shape that can continuously bias the plunger 61, such as a member made of multiple overlapping disc springs.

[0069] The plug 64 has a so-called socket bolt shape and includes a head 641 facing the outside of the plunger receiving hole 60 and a threaded portion 642 that screws into the plunger receiving hole 60. The head 641 has an outer diameter larger than the inner diameter of the plunger receiving hole 60 and abuts against the edge of the second opening 600b of the plunger receiving hole 60, thereby restricting the maximum threading of the plug 64. The end face of the head 641 is provided with a tool engagement portion 644 that can engage with a tool (not shown), such as a hex wrench. The threaded portion 642 has a male threaded portion 643 on its outer periphery that can mesh with a female threaded portion 603 provided near the second opening 600b of the plunger receiving hole 60. The male threaded portion 643 meshes with the female threaded portion 603 of the plunger receiving hole 60, allowing the plug 64 to be threaded into the plunger receiving hole 60. Furthermore, a flat spring seating surface 645 is formed on the end face of the threaded portion 642, and the spring seating surface 645 ensures that the biasing member 62 is seated stably.

[0070] (Explanation of operation of preload mechanism) Figure 4 is a diagram showing the transition of the protrusion amount of plunger 61 according to the steering state, where (a) shows the neutral state where the steering angle θ is 0 degrees, (b) shows the steering state where the steering angle θ is 12 degrees, and (c) shows the steering state where the steering angle θ is 25 degrees.

[0071] As shown in FIG. 4A , in the neutral state where the steering angle θ is 0 degrees, the plunger 61 is in a retracted state, the plunger large-diameter portion 611 is separated from the stopper 63, and the tip surface of the plunger small-diameter portion 612 is elastically abutting 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 urged toward one side in the rotational direction by a reaction force generated by the plunger 61 elastically abutting against the tooth tips of the first sector teeth 321. As a result, the gap C between the first sector teeth 321 and the first rack tooth bottom 425 at the other end side of the sector gear 32 is reduced. This deepens the meshing between the first sector teeth 321 and the second and third rack teeth 422, 423, reducing backlash between the first sector teeth 321 and the second and third rack teeth 422, 423.

[0072] 4B, when the steering angle θ is 12 degrees, the plunger 61 is in an advanced state, with the plunger large diameter portion 611 immediately about to abut against the stopper 63, and the tip of the plunger small diameter portion 612 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 biasing member 62 extends as the plunger 61 advances, and a biasing force that is relatively smaller than that 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 by the plunger 61 elastically abutting against the tooth tips of the first sector teeth 321 due to a biasing force that is smaller than that in the neutral state. As a result, at the other end 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.

[0073] 4(c), when the steering angle θ is 25 degrees, the plunger 61 is in its most advanced state, the plunger large diameter portion 611 abuts against the stopper 63, restricting the forward movement of the plunger 61, and the tip of the plunger small diameter portion 612 is spaced apart from the tip of the first sector tooth 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.

[0074] (Effects of the Present Embodiment) In conventional steering devices, a preload applying mechanism biases the ball nut to one side in the rotation direction based on a reaction force from the plunger sliding contact portion, which is provided inside the ball nut and can be biased toward the sector gear. The reaction force generated by the plunger sliding contact portion elastically abuts against the plunger sliding contact portion, which has a predetermined cam profile and is adjacent to the sector gear. This reduces backlash between the rack teeth and the sector gear near the neutral position of the sector shaft. However, in the conventional steering device, 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.

[0075] 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 screws into 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 a neutral position of the sector shaft 3 that corresponds to a straight-ahead steering state and that meshes with the rack teeth 42 via 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 and 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 and the sector gear 32 near the neutral position of the sector shaft 3 in a cross section (see FIG. 2 ) perpendicular to the rotation axis X of the steering shaft 2 from the steering shaft 2 side toward the rack tooth 42 side. The plunger receiving hole 60 is formed in an inclined shape so as to gradually approach a meshing direction line Z perpendicular to the rotation axis Y of the sector shaft 3, and opens at one end in the tooth width direction of a specific tooth bottom (first rack tooth bottom 425) of the rack tooth 42 that faces the tooth tip of the central tooth (first sector tooth 321) near the neutral position of the sector shaft 3, and a plunger receiving hole 60 is accommodated in the plunger receiving hole 60 so as to be able to advance and retreat, and an opening (first opening 600a) of the plunger receiving hole 60 facing the sector gear 32. The plunger 61 has a tip end that can protrude from the bottom of the plunger receiving hole 60, and a biasing member 62 that is interposed between the plunger 61 and the bottom (plug 64) of the plunger receiving hole 60 and biases the plunger 61 toward the central tooth (first sector tooth 321).The plunger 61, biased by the biasing member 62, elastically contacts the tip of the central tooth (first sector tooth 321), generating a reaction force that biases the ball nut 4 toward one side in the rotational direction of the ball nut 4.

[0076] As described above, in this embodiment, the plunger 61, biased by the biasing member 62, elastically contacts the tips of the first sector teeth 321 of the sector gear 32, and based on the reaction force generated, a rotational torque (moment M shown in FIG. 2 ) 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, there is no need to provide a pressed portion to be pressed by the plunger 61, separate from the sector gear 32, as in the conventional steering device. This makes it possible to prevent the sector shaft 3 from becoming larger due to the formation of the pressed portion.

[0077] In addition, in this embodiment, the preload applying mechanism 6 includes a plunger receiving hole 60 formed in a specific tooth bottom (first rack tooth bottom 425), a plunger 61 that is accommodated in the plunger receiving hole 60 so as to be able to move back and forth and whose tip side is able to protrude from an opening of the plunger receiving hole 60 facing the sector gear 32, and a biasing member 62 that is interposed between the bottom (plug 64) of the plunger receiving hole 60 and the plunger 61 and biases the plunger 61 toward the central tooth (first sector tooth 321).

[0078] That is, in this embodiment, the preload applying mechanism 6 is composed only of a plunger receiving hole 60 formed in the ball nut 4, a plunger 61 housed in the plunger receiving hole 60, and a biasing member 62, and the plunger 61 presses against the tip of the first sector tooth 321 of the sector gear 32, thereby generating a rotational torque (moment M shown in FIG. 2 ) on the ball nut 4.

[0079] As described above, in this embodiment, the preload applying mechanism 6 has a relatively simple configuration consisting of the plunger 61, the biasing member 62, and the plunger receiving hole 60 that accommodates them. Therefore, in this embodiment, there is no need to process or form the pressed portion of the plunger 61, as in the conventional steering device. This makes it possible to configure the preload applying mechanism 6 relatively inexpensively, thereby reducing the manufacturing cost of the steering device PS1.

[0080] Furthermore, in this embodiment, the plunger receiving hole 60 is formed in an inclined shape so as to gradually approach the meshing direction line Z, which is perpendicular to the rotation axis X of the steering shaft 2 and the rotation axis Y of the sector shaft 3, from the steering shaft 2 side toward the rack tooth 42 side in a cross section (see FIG. 2 ) perpendicular to the rotation axis X of the steering shaft 2. Therefore, compared to a case where the plunger receiving hole 60 is formed perpendicular to the first rack tooth bottom 425 corresponding to the specific tooth bottom, it is possible to ensure a relatively large distance D between the rotation center (rotation axis X) of the ball nut 4 and the center Q of the plunger receiving hole 60, thereby reducing the biasing force of the biasing member 62. This makes it possible to reduce the size of the biasing member 62, the preload applying mechanism 6, and ultimately the steering device PS1.

[0081] In addition, in this embodiment, the plunger receiving hole 60 is provided so as to penetrate the ball nut 4 in a cross section (see FIG. 2 ) perpendicular to the rotation axis X of the steering shaft 2, and has a first opening 600 a that opens to the rack teeth 42 side and a second opening 600 b that opens to the ball nut 4 side, and the bottom of the plunger receiving hole 60 is formed by a plug 64 that is screwed into the second opening 600 b of the plunger receiving hole 60.

[0082] In this manner, in the present embodiment, plunger receiving hole 60 is formed to pass through ball nut 4. Therefore, compared to when plunger receiving hole 60 is formed in a blind hole shape, plunger receiving hole 60 can be made easier to process, which contributes to improving the productivity of steering device PS1.

[0083] Furthermore, in this embodiment, the bottom of the plunger receiving hole 60 is formed by the plug 64 that is screwed into the second opening 600b of the plunger receiving hole 60. Therefore, it is possible to generate a preload on the biasing member 62 by screwing in the plug 64. In other words, it is possible to apply a preload to the biasing member 62 by screwing in the plug 64 after assembling the biasing member 62. This eliminates the need to apply a preload to the biasing member 62 in advance, such as by contracting the biasing member 62, when assembling the biasing member 62, and the assembling workability of the biasing member 62 is simplified and improved. As a result, it is possible to improve the productivity of the steering device PS1.

[0084] Additionally, in this embodiment, the bottom of plunger receiving hole 60 is formed by plug 64 that is screwed into second opening 600b of plunger receiving hole 60, and therefore it is possible to adjust the biasing force of biasing member 62 by adjusting the amount of screwing of plug 64. This makes it possible to apply a more appropriate biasing force (preload) to ball nut 4.

[0085] In this embodiment, the plunger 61 has a large diameter portion (plunger large diameter portion 611) that slides inside the plunger receiving hole 60, and a small diameter portion (plunger small diameter portion 612) that is formed in a stepped shape with respect to the large diameter portion (plunger large diameter portion 611) and is provided so as to be able to protrude from the first opening 600a. The plunger receiving hole 60 has a diameter reduced so that the first opening 600a has an inner diameter that is smaller than the outer diameter of the large diameter portion (plunger large diameter portion 611), and the small diameter portion (plunger small diameter portion 612) abuts against the large diameter portion (plunger large diameter portion 611). The plunger 61 has a stopper 63 that restricts the amount of protrusion of the diameter portion (plunger small diameter portion 612). When the rotation phase of the sector shaft 3 is near the neutral position, the large diameter portion (plunger large diameter portion 611) does not abut against the stopper 63, 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 goes beyond the neutral position, the large diameter portion (plunger large diameter portion 611) abuts against the stopper 63, restricting the abutment of the plunger 61 against the central tooth (first sector tooth 321).

[0086] 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 63 restricts the plunger 61 from coming into contact with the first sector tooth 321.

[0087] In this way, in this embodiment, by restricting the amount of protrusion of the plunger 61 with the stopper 63, 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, except 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.

[0088] Furthermore, in this embodiment, the stopper 63 is configured simply by narrowing the opening of the plunger receiving hole 60 with the large diameter hole portion 601. Therefore, in this embodiment, the amount of protrusion of the plunger 61 can be restricted with a relatively simple configuration, without forming a complex cam profile as in, for example, the conventional steering device. This can contribute to reducing the manufacturing cost of the steering device PS1.

[0089] In addition, in this embodiment, the tooth bottom of the sector gear 32 has a straight shape that is generally 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 no mechanism (backlash adjustment mechanism) for adjusting the meshing between the rack teeth 42 and the sector gear 32 is 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.

[0090] In this embodiment, the biasing member 62 is formed of a coil spring.

[0091] The biasing member 62 can be changed as desired as long as it can exert a biasing force; however, if the biasing member 62 is made up of multiple disc springs stacked on top of each other, for example, each disc spring must be assembled in a predetermined orientation in order to exert an appropriate biasing force, which makes the assembly process complicated.

[0092] In contrast, in the present embodiment, the biasing member 62 is configured from a single coil spring. Therefore, in the present embodiment, when assembling the biasing member 62, it is sufficient to insert a single coil spring into the plunger receiving hole 60, thereby ensuring good assembly workability of the biasing member 62. Furthermore, by using a single coil spring, the manufacturing cost of the steering device PS1 can be reduced in terms of productivity of the steering device PS1 and the cost related to the biasing member 62, compared to when the biasing member 62 is configured by stacking a plurality of disc springs.

[0093] [Second Embodiment] Figure 5 shows a second embodiment of a 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. The other configuration is the same as that of the first embodiment. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted.

[0094] FIG. 5 shows a steering device PS2 according to a second embodiment of the present invention, and shows a cross-sectional view of the steering device PS2 corresponding to the cross-sectional view taken along line AA in FIG.

[0095] 5, in the steering device PS2 according to this embodiment, the sector shaft 31 is configured as a large-diameter shaft 313 having a relatively large diameter on one end side closer to the sector gear 32, and as a small-diameter shaft 314 having a relatively small diameter on the other end side closer to the sector gear 32. One end of the large-diameter shaft 313 is connected to a pitman arm (not shown), and the other end is rotatably supported by a large-diameter bearing 333 accommodated on the inner periphery of the second opening 112a. That is, since a large torque is applied to the steered wheels (not shown) via the pitman arm (not shown) connected to one end of the large-diameter shaft 313, the large-diameter shaft 313 is formed with a relatively large diameter to ensure rigidity capable of withstanding the large torque.

[0096] 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.

[0097] On the other hand, the small diameter shaft portion 314 is rotatably supported by a small diameter bearing 334 housed on the inner periphery 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.

[0098] Additionally, a small diameter seal member 344 is provided on the other end 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 hydraulic fluid filled inside the housing 1 (sector shaft accommodating portion 112) from leaking out through the female threaded hole 136 (described later).

[0099] The sector gear 32 is configured as a so-called tapered gear. That is, as shown in Fig. 5, 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 such that 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.

[0100] 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 (external) 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 and urges the sector shaft 3 toward the one end. In other words, when the adjusting screw 5 is screwed in and the sector shaft 3 moves toward the one end, 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.

[0101] 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.

[0102] 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 axial end of the sector shaft 3, and the sector shaft 3 is configured to be movable toward one axial end of the sector shaft 3 by the adjusting screw 5 that is screwed into the other axial end of the sector shaft 3 through the 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.

[0103] 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.

[0104] 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 small diameter at the other axial end side sandwiching the sector gear 32, and the plunger receiving hole 60 is provided at one 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.

[0105] As described above, in this embodiment, the plunger receiving hole 60 that constitutes 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 greater 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.

[0106] 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 parts directly related to the configuration of the present invention, such as the preload mechanism 6, for example, the inclination angle θx of the plunger receiving hole 60, the specific shapes of the plunger 61 and the biasing member 62, can be freely changed within the scope of the spirit of the present invention in accordance with the specifications of the steering device and vehicle to which the present invention is applied.

Claims

1. A steering device comprising: a rack tooth formed on the outside of a ball nut screwed onto a steering shaft linked to a steering wheel; a sector gear provided on a sector shaft linked to a steering wheel, the sector gear including a central tooth that most deeply meshes with the rack tooth at a neutral position of the sector shaft corresponding to a straight-ahead steering state, and having a plurality of sector teeth provided in a circumferential direction of the sector shaft and meshing with the rack tooth; and a preload applying mechanism that adjusts the meshing between the rack tooth and the sector gear in the vicinity of the neutral position of the sector shaft, wherein the preload applying mechanism is formed in an inclined shape that gradually approaches a meshing direction line orthogonal to the rotation axes of the steering shaft and the sector shaft from the steering shaft side toward the rack tooth side in a cross section orthogonal to the rotation axis of the steering shaft, and includes a plunger receiving hole that opens at one end in a tooth width direction of a specific tooth bottom of the rack tooth facing the tooth tip of the central tooth in the vicinity of the neutral position of the sector shaft; a plunger that is retractably accommodated in the plunger receiving hole and has a tip side that can protrude from an opening of the plunger receiving hole facing the sector gear; and a biasing member interposed between a bottom of the plunger receiving hole and the plunger and biasing the plunger 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 when the plunger biased by the biasing member elastically contacts the tooth tip of the central tooth.

2. The steering device according to claim 1, wherein the plunger receiving hole is provided so as to penetrate the ball nut in a cross section orthogonal to the rotation axis of the steering shaft, and has a first opening that opens to the rack tooth side and a second opening that opens to the ball nut side, and a bottom of the plunger receiving hole is formed by a plug screwed into the second opening of the plunger receiving hole.

3. The steering device according to claim 2, wherein the plunger has a large-diameter portion that slides inside the plunger receiving hole, and a small-diameter portion that is formed with a reduced diameter in a stepped manner with respect to the large-diameter portion and is provided so as to be able to protrude from the first opening; the plunger receiving hole has a reduced diameter so that the first opening has an inner diameter smaller than the outer diameter of the large-diameter portion, and has a stopper that regulates the protruding amount of the small-diameter portion by coming into contact with the large-diameter portion; in a state where the rotation phase of the sector shaft is near the neutral position, the large-diameter portion does not come into contact with the stopper, and contact between the plunger and the central tooth is allowed, while in a state where the rotation phase of the sector shaft exceeds near the neutral position, the large-diameter portion comes into contact with the stopper to regulate contact between the plunger and the central tooth. A steering device characterized by the above.

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

5. The steering device according to claim 1, wherein the bottom of the teeth of the sector gear has a tapered surface in which the tooth thickness of the sector gear gradually increases toward one end side in the axial direction of the sector shaft; the sector shaft is configured to be movable toward one end side in the axial direction of the sector shaft by an adjustment screw screwed in from the other end side in the axial direction of the sector shaft through a female screw hole formed in an end wall of a housing that houses the sector shaft. A steering device characterized by the above.

6. The steering device according to claim 1, wherein the sector shaft is connected to a pitman arm, has a relatively large diameter on one end side in the axial direction with the sector gear interposed therebetween, and has a relatively small diameter on the other end side in the axial direction with the sector gear interposed therebetween; the plunger receiving hole opens at an end corresponding to the other end side in the axial direction of the sector shaft among the end portions in the tooth width direction of the specific tooth bottom. A steering device characterized by the above.

7. The steering device according to any one of claims 1 to 6, wherein the biasing member is constituted by a coil spring. A steering device characterized by the above.

Images