Steering device

Abstract

To provide a steering device which can enhance robust performance by buffering a large force in an axial direction while being small in size.SOLUTION: A steering device includes a worm wheel rotating integrally with a pinion shaft, a worm shaft engaged with the worm wheel, a motor shaft for rotating the worm shaft, and an electric motor for rotationally driving the motor shaft. The steering device is constituted so that the worm shaft and the motor shaft are connected to each other by a coupling mechanism which transmits rotation by the engagement of outer teeth and inner teeth. When a clearance in an axial direction between the worm shaft and the motor shaft is reduced, the motor shaft and an axial-direction elastic part having at least two protrusive pieces which are bent and deformed in an inclined direction to a rotation axial line of the worm shaft are arranged in the clearance in the axial direction between the worm shaft and the motor shaft.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a steering device for steering a vehicle such as an automobile. [Background technology]

[0002] In a conventional electric power steering device, when connecting the motor shaft of an electric motor and the worm shaft, a shaft coupling is formed by an external teeth member fixed to the motor shaft of the electric motor and an internal teeth member fixed to the worm shaft. Also, a buffer member is disposed in the space where the external teeth and the internal teeth mesh to absorb load fluctuations that occur at the meshing portion of the external teeth member of the motor shaft and the internal teeth member of the worm shaft.

[0003] However, in the conventional configuration, when assembling the external teeth member and the internal teeth member, a gap is formed between the external teeth member and the internal teeth member, which causes a problem that the external teeth member and the internal teeth member collide with each other during use, generating noise.

[0004] In order to address such issues, for example, Patent Publication No. 2020-23999 (Patent Document 1) discloses a steering device in which an elastic bush made of a resin material is placed in the space between the axial direction of the motor shaft and the worm shaft, and an axial elastic piece is provided on this elastic bush that protrudes toward the worm shaft.When the gap in the space between the axial direction of the motor shaft and the worm shaft decreases, the axial elastic piece is configured to bend and deform in a direction inclined relative to the rotation axis of the motor shaft, thereby adjusting the axial gap and suppressing noise. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-23999 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent steering devices, there is a trend to increase the power output of electric motors in order to improve steering performance. For this reason, a large axial force may act on the elastic bushing arranged in the gap between the motor shaft and the worm shaft in the axial direction. Here, the axial elastic piece of the elastic bushing is formed into a single annular protrusion when viewed in axial cross section. When an axial force acts on the elastic bushing, the axial elastic piece bends to buffer the axial force and improve robustness.

[0007] However, as mentioned above, when a larger axial force is applied, the axial elastic piece cannot withstand the force and the protruding axial elastic piece collapses, causing a so-called "sag" phenomenon. Therefore, in order to further increase robustness, a configuration that can buffer large axial forces is required. In addition, since the elastic bush is disposed between the motor shaft and the worm shaft, it is also required to be small in size.

[0008] An object of the present invention is to provide a steering device that can improve robustness by cushioning a large axial force while being compact in size. [Means for solving the problem]

[0009] The present invention comprises a rack bar having a rack tooth portion for steering a steered wheel, a pinion shaft having a pinion tooth portion that meshes with the rack tooth portion of the rack bar, a worm wheel that rotates integrally with the pinion shaft, a worm shaft that meshes with the worm wheel, an electric motor having a motor shaft and rotating the worm shaft, and a coupling having a first coupling member, a second coupling member, and an elastic member, wherein when one of the worm shaft and the motor shaft is a first shaft member and the other is a second shaft member, the first coupling member of the coupling is provided on the first shaft member and the second coupling member is provided on the second shaft member, the elastic member has an elastic member base and an axial elastic portion and is provided between the first coupling member and the second coupling member, and the axial elastic portion has two or more protruding shaped portions that bend and deform in an inclined direction with respect to the first axis which is the rotation axis of the first shaft member when the gap between the first shaft member and the second shaft member decreases.

[0010] The present invention also provides a steering device comprising: a pinion shaft having a pinion tooth portion that meshes with a rack tooth portion of a rack bar that steers steered wheels; a worm wheel that rotates integrally with the pinion shaft; a worm shaft that meshes with the worm wheel; a motor shaft that rotates the worm shaft; and an electric motor that drives and rotates the motor shaft, wherein the worm shaft and the motor shaft are connected by a coupling mechanism that transmits rotation by meshing of external teeth and internal teeth via an elastic bushing, and the elastic bushing comprises an axial elastic portion having at least two protruding pieces that bend and deform in a direction inclined with respect to the rotation axis of the motor shaft and the worm shaft when the axial gap between the worm shaft and the motor shaft decreases, and the axial elastic portion is disposed in the axial gap between the worm shaft and the motor shaft. Effect of the Invention

[0011] According to the present invention, it is possible to provide a steering device that can improve robustness by cushioning a large axial force while having a small size. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view of an external appearance of a steering device to which the present invention is applied. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is an exploded perspective view of the shaft coupling according to the embodiment of the present invention. [Figure 4] FIG. 2 is an axial cross-sectional view of a shaft coupling according to an embodiment of the present invention. [Diagram 5] FIG. 2 is a front view of a first elastic bush according to the embodiment of the present invention. [Figure 6] FIG. 2 is a side view of a first elastic bush according to the embodiment of the present invention. [Figure 7] FIG. 4 is a front view of a second elastic bush according to the embodiment of the present invention. [Figure 8] 4 is a cross-sectional view of a second elastic bushing according to an embodiment of the present invention, taken in a first axial direction. FIG. [Figure 9] 1 is an explanatory diagram showing the relationship between the crushing allowance (deformation amount) and the load of a second elastic bush in the conventional art (Patent Document 1). [Figure 10] 5 is an explanatory diagram showing the relationship between the crushing allowance (deformation amount) and the load of the second elastic bushing according to the embodiment of the present invention. FIG. [Figure 11] 6 is a cross-sectional view of an axial elastic portion of a second bushing according to a first modified example of an embodiment of the present invention. FIG. [Figure 12] FIG. 11 is a cross-sectional view of an axial elastic portion of a second bushing according to a second modified example of the embodiment of the present invention. [Figure 13] FIG. 11 is a cross-sectional view of an axial elastic portion of a second bushing according to a third modified example of the embodiment of the present invention. [Figure 14] FIG. 11 is a cross-sectional view of an axial elastic portion of a second bushing according to a fourth modified example of the embodiment of the present invention. [Figure 15] FIG. 13 is a cross-sectional view of an axial elastic portion of a second bushing according to a fifth modified example of the embodiment of the present invention. [Figure 16]FIG. 13 is a cross-sectional view of an axial elastic portion of a second bushing according to a sixth modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of a steering device according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiment, and various modifications and applications within the technical concept of the present invention are also included in the scope of the present invention.

[0014] Fig. 1 shows the configuration of a steering device according to an embodiment of the present invention, and Fig. 2 shows a cross section taken along line II-II in Fig. 1. The steering device according to this embodiment is an electric power steering device equipped with an electric motor.

[0015] The electric power steering device is a so-called dual pinion type rack-and-pinion electric power steering device. The rack-and-pinion electric power steering device is equipped with a rack bar having a rack tooth portion (not shown) for steering the steered wheels, and a pinion shaft having a pinion tooth portion that meshes with the rack tooth portion of the rack bar.

[0016] In Fig. 1, a steering wheel (not shown) is connected to an input shaft 1. The rotational force input from the input shaft 1 is transmitted to a first output shaft 2, which is a first pinion shaft connected to the input shaft 1 so as to be capable of relative rotation via a torsion bar (not shown), and the first output shaft 2 is linked to steered wheels (not shown) via a first rack-and-pinion mechanism RP1, which is a first steering mechanism provided on one side in the vehicle width direction.

[0017] In addition, various sensors such as a torque sensor TS are arranged on the outer periphery of the input shaft 1 and the first output shaft 2, and an electric motor 4 is driven by an electronic control unit 3 based on output signals from each sensor. A reduction gear RG consisting of a worm gear is connected to the electric motor 4, and a second output shaft 5 serving as a second pinion shaft changes the direction of the steered wheels (not shown) via a second rack-and-pinion mechanism RP2 serving as a second steering mechanism provided on the other side in the vehicle width direction.

[0018] With this configuration, a torsion bar (not shown) is twisted based on the steering torque input from a steering wheel (not shown) to the input shaft 1, and the rotational motion of the first output shaft 2, which rotates based on the rotational torque generated when the torsion bar returns to its original position due to this torsional deformation, is converted into linear motion of the rack shaft 6 via the first rack and pinion mechanism RP1, and the rotational motion of the second output shaft 5, which rotates based on the steering assist torque generated by the electric motor 4 based on the steering torque, is converted into linear motion of the rack shaft 6 via the second rack and pinion mechanism RP2, thereby changing the direction of the steered wheels (not shown) while receiving steering assistance from the electric motor 4.

[0019] 1 and 2, the reducer RG is composed of a worm shaft (second shaft member) 7 that is coaxially connected to the tip end of a motor shaft (first shaft member) 4a of the electric motor 4 via a shaft joint (coupling) 10 and has worm teeth 7a constituting a worm gear at its tip end, and a worm wheel 8 that is fixed to the outer periphery of the base end side of the second output shaft 5 so as to be integrally rotatable and that meshes with the worm shaft 7 via wheel teeth 8a formed on its outer periphery, thereby reducing the rotation speed of the electric motor 4 and transmitting it to the second output shaft 5. The electric motor 4 rotates the worm shaft 7 via the motor shaft 4a.

[0020] The worm shaft 7 has one end facing the motor shaft 4a supported so as to be swingable and rotatable by a first bearing B1 which is a swivel ball bearing, and the other end supported so as to be rotatable by a second bearing B2 which is a well-known ball bearing.

[0021] An adjustment mechanism 9 is provided on the outer periphery of the second bearing B2, which adjusts the backlash (or axis distance) between the two tooth portions 7a, 8a by constantly pressing (urging) the other end of the worm shaft together with the second bearing B2 in a direction that strengthens the meshing between the worm shaft 7 and the worm wheel 8.

[0022] An external teeth member (first coupling member) 11 is fixed to the tip side of the motor shaft 4a opposite the electric motor 4, and an internal teeth member (second coupling member) 12 is fixed to the tip side of the worm shaft 7.

[0023] In the axial space between the external teeth member 11 and the internal teeth member 12, there are provided a first elastic bush (first elastic member) 13 which is provided in a form of pressure contact between the external teeth member 11 and the internal teeth member 12 and transmits the rotational force of the motor shaft 4a transmitted via the external teeth member 11 to the internal teeth member 12, and a second elastic bush (second elastic member) 14 which fits into the first elastic bush 13 and transmits the rotational force of the motor shaft 4a to the internal teeth member 12. In this embodiment, the second elastic bush 14 is the subject of the present invention.

[0024] Next, the configuration of the shaft coupling 10 will be described. Fig. 3 shows a state in which the shaft coupling according to the first embodiment of the present invention is disassembled and viewed from diagonally above, and Fig. 4 shows a state in which the shaft coupling 10 according to the first embodiment of the present invention is cut in a direction perpendicular to the axial direction.

[0025] As shown in Figures 3 and 4, the shaft coupling 10 comprises an external teeth member 11 that is rotatably mounted on the tip end of the motor shaft 4a of the electric motor 4, an internal teeth member 12 that is rotatably mounted on one end of the worm shaft 7 and engages to receive the external teeth member 11, a first elastic bush 13 that is provided between the external teeth member 11 and the internal teeth member 12 and is in a form of pressure contact with the external teeth member 11 and the internal teeth member 12, and transmits the rotational force of the motor shaft 4a transmitted via the external teeth member 11 to the internal teeth member 12, and a second elastic bush 14 that engages with the first elastic bush 13 and transmits the rotational force of the motor shaft 4a to the internal teeth member 12.

[0026] In this embodiment, the elastic member disposed between the external teeth member 11 and the internal teeth member 12 is composed of two elastic members, a first elastic bushing 13 and a second elastic bushing 14. The end of the second elastic bushing 14 on the worm shaft 7 side is pressed against the end face of the internal teeth member 12.

[0027] This embodiment is characterized in that an axially elastic portion 141 is provided at the end of the second elastic bushing 14 on the worm shaft 7 side. This axially elastic portion 141 will be described in detail with reference to FIG.

[0028] As shown in Fig. 3 and Fig. 4, the external teeth member 11 is composed of a substantially cylindrical external teeth member base (first coupling base) 110 that is press-fitted and fixed to the outer periphery of the tip end of the motor shaft 4a of the electric motor 4 via a through hole 11a provided in the center, and a first outer wing portion 110a to a sixth outer wing portion 110f that are provided in a circumferential direction on the outer periphery of the external teeth member base 110 and each of which has a shape that protrudes radially outward relative to the first axis P1 that is the rotation axis of the motor shaft 4a. Then, as shown in Fig. 3, the external teeth member 11 and the motor shaft 4a are combined to form a motor shaft assembly (first shaft member assembly) 20.

[0029] 3 and 4, the internal teeth member 12 is composed of a substantially cylindrical internal teeth member base (second coupling base) 120 that is press-fitted and fixed to the outer periphery of one end of the worm shaft 7 via a through hole 12a provided in the center, and a first inner wing portion 120a to a sixth inner wing portion 120f that are provided in a circumferential direction on the inner peripheral side of the internal teeth member base 120 and each of which has a shape that protrudes toward the radial inside of the second axis P2 that is the rotation axis of the worm shaft 7. Then, as shown in FIG. 3, the internal teeth member 12 and the worm shaft 7 are combined to form a worm shaft assembly (second shaft member assembly) 21.

[0030] In this embodiment, the external teeth member 11 and the motor shaft 4a are combined to form the motor shaft assembly 20, and the internal teeth member 12 and the worm shaft 7 are combined to form the worm shaft assembly 21, but the present invention is not limited to these combinations. For example, the combination of the external teeth member 11 and the worm shaft 7 may be the worm shaft assembly 20, and the combination of the internal teeth member 12 and the motor shaft 4a may be the motor shaft assembly 21.

[0031] The configuration of the first elastic bushing 13 will be described with reference to Figures 5 and 6. Figure 5 shows the first elastic bushing 13 according to the first embodiment as viewed from the internal teeth member 12 side, and Figure 6 shows the first elastic bushing 13 according to the first embodiment as viewed from the side.

[0032] The first elastic bushing 13 is made of a resin material, and as shown in Fig. 5 and Fig. 6, includes an elastic member base 130 formed in a substantially disk shape, and a first elastic portion 130a to a twelfth elastic portion 130l extending radially outward from the elastic member base 130. The resin material includes elastomer, synthetic resin, rubber (natural and synthetic), etc. The first elastic portion 130a to the twelfth elastic portion 130l extend in the axial direction of the motor shaft 4a, and a first opening 131a to a sixth opening 131f are formed between adjacent elastic portions.

[0033] The first elastic bushing 13 is disposed so as to cover the external teeth member 11 as shown in Fig. 4. The first opening 131a to the sixth opening 131f formed between the elastic portions are aligned with the first outer wing portion 110a to the sixth outer wing portion 110f of the external teeth member 11, respectively, and the first outer wing portion 110a to the sixth outer wing portion 110f of the external teeth member 11 are inserted into the first opening 131a to the sixth opening 131f.

[0034] Next, a description will be given of the configuration of the second elastic bushing 14. Fig. 7 shows the second elastic bushing 14 according to the first embodiment as viewed from the external teeth member 11 side, and Fig. 8 shows a cross section taken along the central axis of the second elastic bushing 14.

[0035] The second elastic bushing 14 is made of a resin material, and includes an elastic member base 140 formed in a substantially flat disk shape, a first rotational direction elastic portion 140a to a twelfth rotational direction elastic portion 140l extending radially outward from the elastic member base 140, and an axial direction elastic portion 141 (see FIG. 8) provided on the elastic member base 140. The elastic member base 140 is disposed in a form sandwiched between the external teeth member base 110 and the internal teeth member base 120. The resin material includes elastomer, synthetic resin, rubber (natural and synthetic), etc.

[0036] The first rotational direction elastic portion 140a to the twelfth rotational direction elastic portion 140l are formed in a U-shape by adjacent rotational direction elastic portions, for example, the first rotational direction elastic portion 140a and the second rotational direction elastic portion 140b, the third rotational direction elastic portion 140c and the fourth rotational direction elastic portion 140d, etc. The axial direction elastic portion 141 is provided on the elastic member base portion 140 in an annular shape.

[0037] The first rotational direction elastic portion 140a, the second rotational direction elastic portion 140b, the third rotational direction elastic portion 140c, and the fourth rotational direction elastic portion 140d each have a rotational direction elastic portion main body portion 140a1, 140b1, 140c1, 140d1 and a rotational direction elastic portion protrusion portion 140a2, 140b2, 140c2, 140d2.

[0038] The fifth rotational direction elastic portion 140e to the twelfth rotational direction elastic portion 140l each include rotational direction elastic portion main portions 140e1 to 140l1 and rotational direction elastic portion protrusions 140e2 to 140l2.

[0039] In a state where the second elastic bush 14 is assembled between the motor shaft assembly 20 and the worm shaft assembly 21, the rotational direction elastic portion main bodies 140a1-140d1 are provided so as to be spaced apart from each of the first outer wing portion 110a, the second outer wing portion 110b, and the third outer wing portion 110c in the circumferential direction about the first axis P1 (see FIG. 3) in an unloaded state where no torque is transmitted from the motor shaft assembly 20 to the worm shaft assembly 21, as shown in FIG. 4. Similarly, the rotational direction elastic portion main bodies 140e1-140l1 are provided so as to be spaced apart from each of the fourth outer wing portion 110d-sixth outer wing portion 110f in an unloaded state.

[0040] In addition, in a state where the second elastic bush 14 is assembled between the motor shaft assembly 20 and the worm shaft assembly 21, the rotational direction elastic part protrusions 140a2-140d2 are provided on the rotational direction elastic part main body parts 140a1-140d1, have shapes protruding toward the first outer wing part 110a, the second outer wing part 110b, and the third outer wing part 110c, respectively, and are provided so as to contact the first outer wing part 110a, the second outer wing part 110b, and the third outer wing part 110c, respectively, in a no-load state. Similarly, the rotational direction elastic part protrusions 140e2-140d2 are provided so as to contact the fourth outer wing part 110d-sixth outer wing part 110f, respectively, in a no-load state.

[0041] The rotational direction elastic portion protrusions 140a2 to 140d2 are provided outside the rotational direction elastic portion main bodies 140a1 to 140l1 in a radial direction relative to the first axis P1.

[0042] According to this embodiment, by providing an elastic portion in the rotational direction, it is possible to suppress the effects (vibration, torque fluctuations, etc.) on the worm gear (worm wheel and worm shaft) when the electric motor is driven, which are caused by misalignment of the axial centers of the motor shaft assembly and the worm shaft assembly.

[0043] According to this embodiment, since the moment arm of the protruding rotational direction elastic portion is longer, a larger rotational torque can be transmitted in the rotational direction elastic portion, and thus the rotational torque can be transmitted over a wider range by the protruding rotational direction elastic portion having a lower rigidity.

[0044] Next, the assembled state of the external teeth member 11, the internal teeth member 12, and the elastic member 30 (the first elastic bushing 13, the second elastic bushing 14) will be described with reference to FIGS.

[0045] The outer teeth member 11 includes an outer teeth member base 110 and a first outer wing portion 110a to a sixth outer wing portion 110f. The outer teeth member base 110 is provided on the motor shaft 4a. The first outer wing portion 110a is provided on the outer teeth member base 110 and has a shape that protrudes radially outward with respect to the first axis P1, which is the rotation axis of the motor shaft 4a. The second outer wing portion 110b is provided on the outer teeth member base 110 and has a shape that protrudes radially outward with respect to the first axis P1. The third outer wing portion 110c is provided on the outer teeth member base 110 and has a shape that protrudes radially outward with respect to the first axis P1. Although not described, the fourth outer wing portion 110d, the fifth outer wing portion 110e, and the sixth outer wing portion 110f are similar.

[0046] The internal teeth member 12 includes an internal teeth member base 120 and a first inner wing portion 120a to a sixth inner wing portion 120f. The internal teeth member base 120 is provided on the worm shaft 7. The first inner wing portion 120a is provided on the internal teeth member base 120, has a shape that protrudes radially inward with respect to the second axis P2, which is the rotation axis of the worm shaft, and is provided between the first outer wing portion 110a and the second outer wing portion 110b in the circumferential direction with respect to the first axis P1. The second inner wing portion 120b is provided on the internal teeth member base 120, has a shape that protrudes radially inward with respect to the second axis P2, and is provided between the second outer wing portion 110b and the third outer wing portion 110c in the circumferential direction with respect to the second axis P2. Although explanation is omitted, the same is true for the third inner wing portion 120c, the fourth inner wing portion 120d, the fifth inner wing portion 120e, and the sixth inner wing portion 120f.

[0047] The second elastic bushing 14, which is an elastic member, is made of a resin material as described above, and includes an elastic member base 140, a first rotational direction elastic portion 140a to a twelfth rotational direction elastic portion 140l, and an annular axial direction elastic portion 141 (see FIG. 8) provided on the elastic member base 140. The elastic member base 140 is disposed so as to be sandwiched between the motor shaft assembly 20 and the worm shaft assembly 21 in the direction of the first axis P1 as shown in FIG.

[0048] The first rotational direction elastic portion 140a provided on the elastic member base portion 140 is provided between the first outer wing portion 110a and the first inner wing portion 120a in the circumferential direction about the first axis P1, and the second rotational direction elastic portion 140b is provided between the second outer wing portion 110b and the first inner wing portion 120a in the circumferential direction about the first axis P1. The third rotational direction elastic portion 140c is provided between the second outer wing portion 110b and the second inner wing portion 120b in the circumferential direction about the first axis P1, and the fourth rotational direction elastic portion 140d is provided between the third outer wing portion 110c and the second inner wing portion 120b in the circumferential direction about the first axis P1.

[0049] The fifth rotational direction elastic portion 140e provided on the elastic member base 140 is provided between the third outer wing portion 110c and the third inner wing portion 120c in the circumferential direction relative to the first axis P1, and the sixth rotational direction elastic portion 140f is provided between the fourth outer wing portion 110d and the third inner wing portion 120c in the circumferential direction relative to the first axis P1.

[0050] The seventh rotational direction elastic portion 140g provided on the elastic member base 140 is provided between the fourth outer wing portion 110d and the fourth inner wing portion 120d in the circumferential direction relative to the first axis P1, and the eighth rotational direction elastic portion 140h is provided between the fifth outer wing portion 110e and the fourth inner wing portion 120d in the circumferential direction relative to the first axis P1.

[0051] The ninth rotational direction elastic portion 140i provided on the elastic member base 140 is provided between the fifth outer wing portion 110e and the fifth inner wing portion 120e in the circumferential direction relative to the first axis P1, and the tenth rotational direction elastic portion 140j is provided between the sixth outer wing portion 110f and the fifth inner wing portion 120e in the circumferential direction relative to the first axis P1.

[0052] The 11th rotational direction elastic portion 140k provided on the elastic member base 140 is provided between the sixth outer wing portion 110f and the sixth inner wing portion 120f in the circumferential direction relative to the first axis P1, and the 12th rotational direction elastic portion 140l is provided between the first outer wing portion 110a and the sixth inner wing portion 120f in the circumferential direction relative to the first axis P1.

[0053] Next, the configuration of the axial elastic portion 141 formed in the second elastic bushing 14 shown in Fig. 3, which is a feature of this embodiment, will be described with reference to Fig. 8. Fig. 8 shows a cross section taken along the axis (first axis P1) of the second elastic bushing 14 in this embodiment.

[0054] The feature of this embodiment, as described in claim 1, is that it comprises a rack bar having a rack tooth portion for steering a steered wheel, a pinion shaft having a pinion tooth portion that meshes with the rack tooth portion of the rack bar, a worm wheel that rotates integrally with the pinion shaft, a worm shaft that meshes with the worm wheel, an electric motor having a motor shaft for rotating the worm shaft, and a coupling having a first coupling member, a second coupling member, and an elastic member, and when one of the worm shaft and the motor shaft is defined as a first shaft member and the other is defined as a second shaft member, The first coupling member of the coupling is provided on the first shaft member, and the second coupling member is provided on the second shaft member; the elastic member includes an elastic member base portion and an axial elastic portion, and is provided between the first coupling member and the second coupling member; The axial elastic portion has two or more protruding portions that are bent and deformed in a direction inclined with respect to a first axis, which is a rotation axis of the first shaft member, when the gap between the first shaft member and the second shaft member decreases. A specific description will be given below. The axial elastic part 141 is provided on the elastic member base part 140, and has a shape that protrudes from the motor shaft 4a toward the worm shaft 7 in the direction of the first axis P1. That is, the axial elastic part 141 has two annular protruding pieces that surround the first axis P1, and is composed of an annular inner protruding piece 141a that has a predetermined length in the direction of the first axis P1 and is located on the inside, and an annular outer protruding piece 141b that has a predetermined length in the direction of the first axis P1 and is located on the outside.

[0055] The height of the inner protruding piece 141a and the outer protruding piece 141b in the direction of the first axis P1 is set to the same height (H) from the surface of the elastic member base 140 on the worm shaft 7 side toward the worm shaft 7 side in the direction of the first axis P1.

[0056] The inwardly protruding piece 141a is inclined in a direction approaching the first axis P1 (so-called inward), and the outwardly protruding piece 141b is inclined in a direction away from the axis P1 (so-called outward).

[0057] Thus, as described in claims 2 to 5, at least one of the protruding shapes of the axial elastic portion faces outward in the radial direction of the first axis P1 (outer protruding piece 141b), and the other faces inward (inner protruding piece 141a).

[0058] The axial elastic portion is provided with an inner protruding piece 141a and an outer protruding piece 141b, which are annular portions surrounding the first axis P1.

[0059] Further, the annular portion, which is the inner protruding piece 141a and the outer protruding piece 141b, is provided at the tip of the axially elastic portion.

[0060] Further, the axially elastic portion has an outer diameter that gradually decreases with respect to the first axis P1 from the first shaft member toward the second shaft member.

[0061] The base portions of the inner protruding piece 141a and the outer protruding piece 141b are spaced apart from each other by a predetermined distance D in the radial direction and stand upright from the elastic member base portion 140 toward the worm shaft 7 side.

[0062] The thickness (Lm) of the elastic member base (middle portion) 145m in the first axis P1 direction within this predetermined distance D is greater than the thickness (Li) of the elastic member base (inner portion) 145i inside the inward protruding piece 141a and the thickness (Lo) of the elastic member base (outer portion) 145o outside the outer protruding piece 141b. Here, the relationship is "Li = Lo".

[0063] As described above, as described in claims 7 and 8, the elastic member base (elastic member base (inner portion) 145i on the inner side of the inward protruding piece 141a) is formed so that the thickness on the axial center side of the first shaft member (motor shaft 4a) is thinner than the thickness of other portions (elastic member base (middle portion) 145m).

[0064] In addition, in the radial direction of the first axis P1, the thickness of the elastic member base (elastic member base (middle portion) 145m) between the shaped portion (outer protruding shaped piece 141b) facing the outer diameter direction and the shaped portion (outer protruding shaped piece 141b) facing the inner diameter direction is formed to be thicker than other portions.

[0065] The cross-sectional shape of the inwardly protruding piece 141a and the outwardly protruding piece 141b is formed so that the thickness gradually decreases from the base portion to the tip portion as shown in the drawing.

[0066] The axial elastic portion 141 has an annular inwardly protruding piece 141a so as to surround the first axis P1, and a space 142a is formed in the portion surrounded by the inwardly protruding piece 141a. Similarly, the axial elastic portion 141 has an annular outwardly protruding piece 141b so as to surround the first axis P1, and a space 142b is formed in the portion surrounded by the outwardly protruding piece 141b. In addition, an annular space 142c is formed between the inwardly protruding piece 141a and the outwardly protruding piece 141a.

[0067] As described above, this embodiment is characterized in that the elastic member base 140 is provided with the axial elastic portion 141 consisting of the inwardly protruding piece 141a and the outwardly protruding piece 141a.

[0068] The inwardly protruding piece 141a and the outwardly protruding piece 141b of the axially elastic portion 141 are shaped to bend and deform in a direction inclined inward and outward relative to the first axis P1 when the gap distance between the motor shaft assembly 20 and the worm shaft assembly 21 in the direction of the first axis P1 decreases.

[0069] In other words, when the axially elastic portion 141 comes into contact with the end face of the internal teeth member 12 of the worm shaft assembly 21 and the distance between the end faces of the internal teeth member 12 and the external teeth member 11 becomes shorter, the inner protruding piece 141a bends toward the inner space portion 142a, and conversely, the outer protruding piece 141b bends toward the outer space portion 142b. In other words, the inner protruding piece 141a is given the function of bending inward when an axial force is applied, and the outer protruding piece 141b is given the function of bending outward when an axial force is applied.

[0070] According to this embodiment, since the second elastic bush 14 is made of a resin material, the region with low rigidity can be made wider than when it is made of a metal material. Also, since the axial elastic portion 141 is provided with the inwardly protruding piece 141a and the outwardly protruding piece 141b, it has a shape that exerts an appropriate elastic force by bending deformation, and it is possible to obtain a sufficient elastic force while reducing the rigidity compared to when it is compressed. Furthermore, compared to when there is a single protruding piece as in Patent Document 1, the occurrence of the "sag" phenomenon can be suppressed.

[0071] Fig. 9 shows the relationship between the crushing allowance (deformation amount) of one protruding piece in the axial elastic portion and the axial force acting on the protruding piece in Patent Document 1. As can be seen from Fig. 9, when a load of a predetermined value or more is applied, the protruding piece experiences a "sag" phenomenon, and it can be understood that robustness cannot be obtained.

[0072] On the other hand, Fig. 10 shows the relationship between the crushing allowance (deformation amount) of the two protruding pieces in the axial elastic part of this embodiment and the axial force acting on the protruding pieces. As can be seen from Fig. 10, even if a load exceeding the predetermined value in Patent Document 1 acts on the protruding pieces, the "sag" phenomenon does not occur, and it can be understood that sufficient robustness is obtained.

[0073] Furthermore, the axial elastic portion 141 in this embodiment is provided on the elastic member base 140 and is formed in a shape that protrudes in the direction from the motor shaft 4a toward the worm shaft 7 in the direction of the first axis P1. Therefore, despite its simple and compact shape, it is able to exert sufficient elastic force due to bending deformation.

[0074] Therefore, the second elastic bushing 14 of the present embodiment has a small shape, yet is capable of buffering a large axial force and improving robustness.

[0075] Furthermore, in the axial elastic portion 141 of this embodiment, the root portions of the inward protruding piece 141a and the outward protruding piece 141b are separated by a predetermined distance D, and the thickness (Lm) of the elastic member base (middle portion) 145m between the predetermined distance D is formed to be thicker than the thickness (Li) of the elastic member base (inner portion) 145i on the inside of the inward protruding piece 141a and the thickness (Lo) of the elastic member base (outer portion) 145o on the outside of the outward protruding piece 141b.

[0076] For this reason, when the inward protruding piece 141a bends inward and the outward protruding piece 141b bends outward, a tensile force is generated in the elastic member base (middle part) 145m over the specified distance D, but since the elastic member base (middle part) 145m is formed thick over the specified distance D, it can withstand this tensile force. Furthermore, this tensile force acts to suppress the bending of the inward protruding piece 141a and the outward protruding piece 141b, making it difficult for the above-mentioned "sagging" phenomenon to occur.

[0077] The elastic member base 140 of the second elastic bush 14 includes an elastic member base (inner portion) 145i, an elastic member base (outer portion) 145o, and an elastic member base (middle portion) 145m. Here, the elastic member base (inner portion) 145i is provided inside the inwardly protruding piece 141a in the radial direction with respect to the first axis P1, and has a flat plate shape perpendicular to the first axis P1, consisting of a motor shaft side flat surface (first surface) and a worm shaft side flat surface (second surface). Thus, as in claim 6, the elastic member base has a plate shape perpendicular to the first axis.

[0078] According to this, the inside of the inwardly protruding piece 141a is closed by the elastic member base portion (inner portion) 145i, so that the rigidity of the inwardly protruding piece 141a can be improved.

[0079] The elastic member base (middle portion) 145m and the elastic member base (outer portion) 145o have a plate shape perpendicular to the first axis P1, similar to the elastic member base (inner portion) 145i. Therefore, the elastic member base (middle portion) 145m has a motor shaft side flat surface (first surface) and a worm shaft side flat surface (second surface) in the direction of the first axis P1, and the elastic member base (outer portion) 145o has a motor shaft side flat surface (first surface) and a worm shaft side flat surface (second surface) in the direction of the first axis P1.

[0080] The elastic member base (inner portion) 145i is recessed from the elastic member base (middle portion) 145m toward the motor shaft, and the plate thickness of the elastic member base (inner portion) 145i is formed to be thinner than the plate thickness of the elastic member base (middle portion) 145m. As a result, since the elastic member base (inner portion) 145i is provided at a position deeper than the elastic member base (middle portion) 145m, when the inwardly protruding piece 141a is bent and deformed so as to fall inward, the internal stress in the inner peripheral portion can be alleviated.

[0081] Similarly, the elastic member base (outer portion) 145o is recessed from the elastic member base (middle portion) 145m toward the motor shaft, and the thickness of the elastic member base (outer portion) 145o is formed to be thinner than the thickness of the elastic member base (middle portion) 145m. As a result, since the elastic member base (outer portion) 145o is provided at a position deeper than the elastic member base (middle portion) 145m, when the outer protruding piece 141b is bent and deformed so as to fall outward, the internal stress in the outer circumferential portion can be alleviated.

[0082] The axial elastic portion 141 is provided with an inner protruding piece 141a and an outer protruding piece 141b, the tip of which is formed in an arc shape and which comes into contact with the worm shaft assembly 21. The inner protruding piece 141a and the outer protruding piece 141b have an arc shape at the tip thereof which comes into contact with the worm shaft assembly 21 in a cross section passing through the first axis P1.

[0083] According to this, the point where the tip of the inner protruding piece 141a and the outer protruding piece 141b contacts the motor shaft assembly moves as the inner protruding piece 141a and the outer protruding piece 141b are bent. On the other hand, since the tip of the inner protruding piece 141a and the outer protruding piece 141b has an arc shape, they smoothly slide against the worm shaft assembly.

[0084] Moreover, the inner protruding piece 141a and the outer protruding piece 141b have a shape that gradually decreases toward the tip in a cross section passing through the first axis P1. The plate thickness of the inner protruding piece 141a and the outer protruding piece 141b is the thickest at the base and the thinnest at the tip. In this embodiment, the inner protruding piece 141a and the outer protruding piece 141b have a so-called cantilever shape when viewed in a cross section passing through the first axis. Therefore, by making the base thick and the tip thin, it is possible to alleviate stress concentration during bending deformation.

[0085] Here, the axial elastic portion 141 is configured to come into contact with the worm shaft assembly 21. Since the axial elastic portion 141 is provided in an annular shape on the elastic member base portion 140, when the axial elastic portion 141 comes into contact with the worm shaft assembly 21, air is trapped in the space portion 142a, and the trapped air may change the elastic properties of the second elastic bushing 14.

[0086] Therefore, in this embodiment, a through hole 146 penetrating in the direction of the first axis P1 is formed in the elastic member base (inner portion) 145i. One through hole 146 is provided in approximately the center of the elastic member base (inner portion) 145i. The number of through holes 146 is not limited to one, and multiple through holes may be provided. Furthermore, the location of the formation is not limited to the center, and may be selected as appropriate. In this way, as described in claim 9, the elastic member base has the through hole 146 in the first axial direction.

[0087] When the axial elastic portion 141 and the worm shaft assembly 21 come into contact with each other, the air in the space 142a can move toward the motor shaft assembly 20 through the through hole 146. This makes it possible to prevent air from being trapped inside the second elastic bushing 14, and to prevent the elastic characteristics of the second elastic bushing 14 from changing.

[0088] Next, some modified examples of this embodiment will be briefly described. The modified examples described below are basically elastic bushings having an axial elastic portion 141 with an inner protruding piece 141a and an outer protruding piece 141b, and have in common the point that the bending deformation of the inner protruding piece 141a and the outer protruding piece 141b can buffer a large axial force and increase robustness despite their small size. Note that the axial elastic portion 141 is shown in the drawings.

[0089] <<Variation 1>> In the first modification, the inward protruding piece 141a and the outward protruding shape 141b stand upright on the worm shaft 7 side while maintaining a parallel relationship from the elastic member base 140. Spaces 142a and 142b are formed on the inside of the inward protruding piece 141a and on the outside of the outward protruding shape 141b, respectively. The spaces 142a and 142b serve to weaken the strength of the inside of the inward protruding piece 141a and the outside of the outward protruding shape 141b.

[0090] Therefore, when the worm shaft assembly 21 presses the inner protruding shape piece 141a and the outer protruding shape piece 141b, the inner protruding shape piece 141a tilts inward and the outer protruding shape piece 141b tilts outward. As a result, as described above, even with a simple and small shape, it is possible to exhibit sufficient elastic force due to bending deformation.

[0091] <<Variation 2>> In the second modification, the inner protruding piece 141a and the outer protruding shape 141b are inclined obliquely inward from the elastic member base 140 and stand on the worm shaft 7 side while maintaining a parallel relationship. Spaces 142a, 142b are formed on the inside of the inner protruding piece 141a and on the outside of the outer protruding shape 141b, respectively. The height of the inner protruding piece 141a is slightly shorter than that of the outer protruding shape 141b.

[0092] Therefore, when the worm shaft assembly 21 presses the inner protruding shape piece 141a and the outer protruding shape 141b, the inner protruding shape piece 141a tilts inward, and the outer protruding shape 141b also tilts inward. As a result, as described above, even with a simple and small shape, it is possible to exhibit sufficient elastic force due to bending deformation.

[0093] <Modification 3> In the third modification, in addition to the inner protruding piece 141a and the outer protruding shape 141b, an outermost protruding shape 141c is further inclined diagonally inward from the elastic member base 140 and stands up toward the worm shaft 7 while maintaining a parallel relationship. A space 142d is formed between the outer protruding shape 141b and the outermost protruding shape 141c. The heights of the inner protruding piece 141a, the outer protruding shape 141b, and the outermost protruding shape 141c are set to be higher toward the outside.

[0094] Therefore, when the worm shaft assembly 21 presses the inner protruding piece 141a, the outer protruding shape 141b, and the outermost protruding shape 141c, the inner protruding piece 141a, the outer protruding shape 141b, and the outermost protruding shape 141c are tilted inward. As a result, as described above, even with a simple and small shape, it is possible to exhibit sufficient elastic force due to bending deformation.

[0095] <Modification 4> Modification 4 is a modification of Modification 2. In Modification 4, the length of the inward protruding piece 141a is further shortened.

[0096] In this example, the worm shaft assembly 21 also presses the inner protruding shape 141a after contacting the outer protruding shape piece 141b. In this way, the outer protruding shape piece 141b tilts inward, and then the deformation of the outer protruding shape piece 142b is suppressed by the inner protruding shape 141a. As a result, as described above, even with a simple and small shape, it is possible to exhibit sufficient elastic force due to bending deformation.

[0097] <Variation 5> Variation 5 is also a variation of Variation 2. In Variation 5, the inward protruding piece 141a is inclined outward toward the outward protruding shape 141b. Therefore, the inward protruding piece 141 functions to receive the bending of the outward protruding shape 141b, so the height of the inward protruding piece 141a is formed slightly shorter than the outward protruding shape 141b.

[0098] Therefore, the worm shaft assembly 21 presses the inward protruding shape 141a after contacting the outward protruding shape piece 141b. In this way, the outward protruding shape piece 141b tilts inward, and then the deformation of the outward protruding shape piece 142b is suppressed by the inward protruding shape 141a. As a result, as described above, even with a simple and small shape, it is possible to exhibit sufficient elastic force due to bending deformation.

[0099] <Variation 6> Variation 6 is a variation of Variation 5. In Variation 6, the inward protruding piece 141a and the outward protruding shape 141b are integrally formed. Therefore, the inward protruding piece 141a and the outward protruding shape 141b function to accommodate bending of each other.

[0100] Therefore, the worm shaft assembly 21 presses the outer protruding shape piece 141b and the inner protruding shape 141a. In this way, the outer protruding shape piece 141b and the inner protruding shape 141a are tilted inward and deformation is suppressed. As a result, as described above, even with a simple and small shape, it is possible to exhibit sufficient elastic force due to bending deformation.

[0101] In the above-mentioned variants 1 to 6, the relationship between the crushing allowance (deformation amount) of the protruding shaped piece and the axial force acting on the protruding shaped piece has characteristics similar to those shown in Figure 10, and it was confirmed that the protruding shaped piece does not experience the "sagging" phenomenon and sufficient robustness is obtained.

[0102] As described above, the present invention is characterized in that an axial elastic part having at least two protruding pieces that bend and deform in an inclined direction relative to the rotation axis of the motor shaft and the worm shaft when the axial gap between the worm shaft and the motor shaft decreases is disposed in the axial gap between the worm shaft and the motor shaft.

[0103] This makes it possible to provide a steering device that is compact in size but can absorb large axial forces and has high robustness.

[0104] The present invention is not limited to the above-described embodiments, but includes various modified examples. The above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace other configurations with respect to the configuration of each embodiment. [Explanation of symbols]

[0105] 4...electric motor, 4a...motor shaft (first shaft member), 6...rack shaft, 7...worm shaft (second shaft member), 7a...worm tooth portion, 8...worm wheel, 8a...wheel tooth portion, 10...shaft coupling (coupling), 11...external tooth member (first coupling member), 12...internal tooth member (second coupling member), 13...first elastic bush (elastic member), 14...second elastic bush (elastic member), 140...elastic member base, 141...axial elastic portion, 141a...inwardly protruding shaped piece (shaped portion), 141b...outwardly protruding shaped piece (shaped portion), 145i...elastic member base (inner portion), 145m...elastic member base (middle portion), 145o...elastic member base (outer portion) 146...through hole.

Claims

1. In the steering device, a rack bar having a rack tooth portion for steering a steered wheel, a pinion shaft having a pinion tooth portion that meshes with the rack tooth portion of the rack bar, a worm wheel that rotates integrally with the pinion shaft, a worm shaft that meshes with the worm wheel, an electric motor having a motor shaft for rotating the worm shaft, and a coupling having a first coupling member, a second coupling member, and an elastic member, wherein one of the worm shaft and the motor shaft is a first shaft member and the other is a second shaft member, The first coupling member of the coupling is provided on the first shaft member, and the second coupling member is provided on the second shaft member, the elastic member includes an elastic member base portion and an axial elastic portion, and is provided between the first coupling member and the second coupling member, The axial elastic portion has two or more protruding portions that are bent and deformed in a direction inclined with respect to a first axis that is a rotation axis of the first shaft member when the gap between the first shaft member and the second shaft member decreases. A steering device characterized by:

2. 2. The steering device according to claim 1, At least one of the protruding portions of the axial elastic portion faces outward in the radial direction of the first axis, and the other faces inward. A steering device characterized by:

3. 3. The steering device according to claim 2, The axial elastic portion is provided with an annular portion surrounding the first axis. A steering device characterized by:

4. 4. The steering device according to claim 3, The annular portion is provided at a tip of the axially elastic portion. A steering device characterized by:

5. 5. The steering device according to claim 4, The axial elastic portion has an outer diameter with respect to the first axis that gradually decreases from the first shaft member toward the second shaft member. A steering device characterized by:

6. 3. The steering device according to claim 2, The elastic member has the elastic member base and is in a plate shape perpendicular to the first axis. A steering device characterized by:

7. 7. The steering device according to claim 6, A steering device, wherein the elastic member base portion has a thickness on an axial center side of the first shaft member that is thinner than other portions.

8. 7. The steering device according to claim 6, The steering device is characterized in that, in the radial direction of the first axis, a thickness of the elastic member base between the protruding shape portion facing an outer diameter direction and the protruding shape portion facing an inner diameter direction is thicker than other portions.

9. 7. The steering device according to claim 6, The elastic member base has a through hole in the direction of the first axis. A steering device characterized by:

10. A steering device comprising: a pinion shaft having pinion teeth that mesh with a rack tooth portion of a rack bar that steers steerable wheels; a worm wheel that rotates integrally with the pinion shaft; a worm shaft that meshes with the worm wheel; a motor shaft that rotates the worm shaft; and an electric motor that rotationally drives the motor shaft, the worm shaft and the motor shaft being connected by a coupling mechanism that transmits rotation by meshing of external teeth and internal teeth via an elastic bush, the elastic bushing includes an axial elastic portion having at least two protruding pieces that are bent and deformed in a direction inclined with respect to rotation axes of the motor shaft and the worm shaft when an axial gap between the worm shaft and the motor shaft decreases, The axial elastic portion is disposed in the gap in the axial direction between the worm shaft and the motor shaft. A steering device characterized by:

11. The steering device according to claim 10, The axial elastic portion includes a flat elastic member base extending in a direction perpendicular to the rotation axis, The two protruding pieces are provided on the elastic member base and extend along the direction of the rotation axis. The two protruding pieces are an annular inner protruding piece centered on the rotation axis, and an annular outer protruding piece located outside the inner protruding piece and centered on the rotation axis. A steering device characterized by:

12. The steering device according to claim 11, The annular inwardly protruding piece is inclined toward the rotation axis, and the annular outwardly protruding piece is inclined away from the rotation axis. A steering device characterized by:

13. 13. The steering device according to claim 12, The thickness of the elastic member base (middle portion) between the inner protruding piece and the outer protruding piece is set to be thicker than the thickness of the elastic member base (inner portion) on the inside of the inner protruding piece and the thickness of the elastic member base (outer portion) on the outside of the outer protruding piece. A steering device characterized by:

14. 14. The steering device according to claim 13, The cross-sectional shapes of the annular inner protruding piece and the outer protruding piece taken along the rotation axis are gradually tapered toward the tip. A steering device characterized by:

Images