JP2022080111A - Worm reduction gear with motor and electric assist device - Google Patents

Abstract

To provide a worm reduction gear with a motor, capable of attenuating a minute displacement of a worm in an axial direction.SOLUTION: A damper mechanism 21 for attenuating the axial displacement of a worm 19 is constituted by inserting a piston part 84 fitted on a guide member 53 fixed on a housing 16 into a bottomed cylinder hole 37 opened in a front end face of the worm 19 and filling a cylinder hole 37 with viscous fluid 105.SELECTED DRAWING: Figure 5

Description

The present invention relates to a worm reducer with a motor and an electric assist device including a worm reducer with a motor.

In a steering device for an automobile, when the driver operates the steering wheel, the rotation of the steering wheel is transmitted to the input shaft of the steering gear unit by the steering shaft and the intermediate shaft. When the rack shaft of the steering gear unit is displaced in the width direction of the vehicle due to the rotation of the input shaft, the pair of tie rods is pushed and pulled to give the steering wheel a steering angle.

Japanese Patent Application Laid-Open No. 2005-42213 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2004-306988 (Patent Document 2) use an electric motor as an auxiliary power source to reduce the force required for the driver to operate the steering wheel. The electric power steering device is disclosed.

In the electric power steering device, the output torque of the electric motor is increased by the speed reducer, and then the rotating shaft such as the steering shaft or the input shaft of the steering gear unit, which rotates with the rotation of the steering wheel, or the rack of the steering gear unit. It is applied to a linear motion shaft such as a shaft or a screw shaft. As such a reducer, a worm reducer is widely used because a large reduction ratio can be obtained.

However, when a worm reducer is used to increase the output torque of the electric motor, the meshing part between the worm wheel and the worm and the bearing for rotatably supporting the worm when driving on rough roads, etc. There is a problem that a rattle sound (tapping sound) is likely to occur inside the wheel. In such rattle noise, the exciting force input to the tie rod via the wheel is transmitted to the worm wheel as torque fluctuation when driving on a rough road, and the fluctuation of the meshing reaction force generated by the torque fluctuation causes the worm to be axial. It is generated by vibrating the wheel.

In view of such circumstances, Japanese Patent Application Laid-Open No. 2014-199111 (Patent Document 3) discloses a structure of a worm reducer with a motor capable of attenuating the axial displacement of the worm and suppressing the generation of rattle noise. There is.

Japanese Unexamined Patent Publication No. 2005-42913 Japanese Unexamined Patent Publication No. 2004-306988 Japanese Unexamined Patent Publication No. 2014-199111

However, the worm reducer with a motor of the conventional structure described in Japanese Patent Application Laid-Open No. 2014-199111 has room for improvement in terms of attenuating minute displacement of the worm in the axial direction.

That is, in the conventional structure described in Japanese Patent Application Laid-Open No. 2014-199111, among the locking member locked to the outer peripheral surface of the worm and the ball bearing for rotatably supporting the worm, the inner ring fitted to the worm. A liquid pressure shock absorber is placed between and. Therefore, the magnitude of the axial displacement of the worm that can be attenuated by the liquid pressure shock absorber is limited to that larger than the axial backlash (play) existing between the outer ring and the inner ring constituting the ball bearing. Therefore, in the worm reducer with a motor having a conventional structure, it is not possible to attenuate the minute displacement of the worm in the axial direction, which is smaller than the backlash in the axial direction, and it is difficult to sufficiently suppress the generation of rattle noise.

The present invention has been made to solve the above problems, and provides a worm reducer with a motor capable of attenuating a minute displacement of the worm in the axial direction, and an electric assist device provided with the worm reducer with a motor. The purpose is.

Each of the worm reducers with a motor of the present invention includes a housing, a worm wheel, a worm, an electric motor, and a damper mechanism.
The housing has a wheel accommodating portion and a worm accommodating portion that is arranged in a twisted position with respect to the wheel accommodating portion and has an axial middle portion open to the wheel accommodating portion.
The worm wheel has wheel teeth on the outer peripheral surface and is rotatably supported inside the wheel accommodating portion.
The worm has worm teeth that mesh with the wheel teeth on the outer peripheral surface, and is rotatably supported inside the worm accommodating portion and is capable of axially relative displacement with respect to the worm accommodating portion.
The electric motor has a motor output shaft connected to a base end portion of the worm so as to be able to swing the worm.
The damper mechanism is for attenuating the axial displacement of the worm, and is formed in the cylinder hole through a gap that allows the worm to swing between the cylinder hole and the inner surface of the cylinder hole. It has an inserted piston portion and a viscous fluid filled in the cylinder hole.

In the first aspect of the worm reducer with a motor of the present invention, the cylinder hole is formed between the worm and the housing or a member arranged around the tip of the worm and fixed to the housing. The piston portion can be provided on one of the worm and the other of the housing and the members arranged around the tip of the worm and fixed to the housing.
In this case, the cylinder hole is provided in the tip portion of the worm so as to open to the tip surface of the worm, and the piston portion is provided around the housing or the tip portion of the worm. It can be provided for a member fixed to the housing.
Further, the member arranged around the tip portion of the worm may be an urging member that urges the tip portion of the worm toward the side of the worm wheel, or may be another member. You can also.

In the second aspect of the worm reducer with a motor of the present invention, the cylinder hole is provided in one of the worm and the motor output shaft, and the piston portion is provided in the worm and the motor output shaft. You can prepare for the other.
In this case, the cylinder hole may be provided in the base end portion of the worm so as to open to the base end surface of the worm, and the piston portion may be provided in the tip end portion of the motor output shaft.

In the worm reducer with a motor of the present invention, grease having a kinematic viscosity of base oil of 200 mm ² / s or more at 40 ° C. can be used as the viscous fluid.

The electric assist device of the present invention applies torque to a torque sensor for detecting torque input to the steering shaft and a rotary shaft that rotates with the rotation of the steering wheel or a linear motion shaft that constitutes a steering gear unit. It is equipped with a worm reducer with a motor.
In particular, in the electric assist device of the present invention, the worm reducer with a motor is the worm reducer with a motor of the present invention.

According to the present invention, it is possible to realize a worm reducer with a motor capable of attenuating a minute displacement of the worm in the axial direction and an electric assist device provided with the worm reducer with a motor.

FIG. 1 is a partially cut side view showing a column assist type electric power steering device incorporating the electric assist device according to the first example of the embodiment. FIG. 2 is a cross-sectional equivalent view taken along the line AA of FIG. FIG. 3 is an exploded perspective view of a worm reducer with a motor constituting the electric assist device according to the first example of the embodiment. FIG. 4 is a cross-sectional view taken along the line BB of FIG. FIG. 5 is an enlarged view of part C of FIG. FIG. 6A is a perspective view showing the urging member holding the first bearing taken out, and FIG. 6B is a perspective view seen from the opposite side to FIG. 6A. 7 (A) is a side view showing the urging member holding the first bearing taken out, and FIG. 7 (B) is a front view seen from the left side of FIG. 7 (A). C) is a rear view seen from the right side of FIG. 7 (A), FIG. 7 (D) is a plan view seen from the upper side of FIG. 7 (C), and FIG. 7 (E) is a plan view of FIG. It is a bottom view seen from the lower side of (C). FIG. 8 is a sectional view taken along line DD of FIG. 7 (C). FIG. 9 is a sectional view taken along line EE of FIG. 7 (C). FIG. 10 is a sectional view taken along line FF of FIG. 7A. 11 is a sectional view taken along line GG of FIG. 7A. FIG. 12 is a perspective view showing a state in which the first elastic member, the second elastic member, and the third elastic member are held with respect to the guide member. FIG. 13 is an exploded perspective view of the urging member. 14 (A) is a perspective view showing the guide member taken out, and FIG. 14 (B) is a perspective view seen from the opposite side of FIG. 14 (A). 15 (A) is a side view showing the guide member taken out, FIG. 15 (B) is a front view seen from the left side of FIG. 15 (A), and FIG. 15 (C) is FIG. 15 (C). A) is a rear view seen from the right side, FIG. 15 (D) is a plan view seen from the upper side of FIG. 15 (C), and FIG. 15 (E) is a plan view seen from the lower side of FIG. 15 (C). It is a bottom view as seen. FIG. 16 is a cross-sectional view taken along the line HH of FIG. 15 (C). 17 (A) is a perspective view showing the first elastic member taken out, FIG. 17 (B) is a plan view showing the first elastic member taken out, and FIG. 17 (C) is FIG. 17 (C). B) is a front view seen from the lower side, FIG. 17 (D) is a rear view seen from the upper side of FIG. 17 (B), and FIG. 17 (E) is from the left side of FIG. 17 (B). It is a side view as seen, and FIG. 17 (F) is a side view seen from the right side of FIG. 17 (B). 18 (A) is a perspective view showing the second elastic member taken out, FIG. 18 (B) is a front view showing the second elastic member taken out, and FIG. 18 (C) is FIG. 18 (C). It is a side view seen from the right side of FIG. 18B), and FIG. 18D is a bottom view seen from the lower side of FIG. 18B. 19 (A) is a perspective view showing the third elastic member taken out, FIG. 19 (B) is a front view showing the third elastic member taken out, and FIG. 19 (C) is FIG. 19 (C). B) is a side view seen from the left side, FIG. 19 (D) is a side view seen from the right side of FIG. 19 (B), and FIG. 19 (E) is a side view seen from the lower side of FIG. 19 (B). It is a bottom view as seen, and FIG. 19 (F) is a rear view seen from the right side of FIG. 19 (D). FIG. 20 is a diagram corresponding to FIG. 4, showing a second example of the embodiment. 21 is an enlarged view of part I of FIG. 20. FIG. 22 is a diagram corresponding to FIG. 4, showing a third example of the embodiment.

[First example of the embodiment]
The first example of the embodiment will be described with reference to FIGS. 1 to 19. This example is an example in which the electric assist device of the present invention is applied to a column assist type electric power steering device. It should be noted that although there are some differences in the shape of details between the drawings, there is no difference in the contents and functions of the parts with the same reference numerals.

[Overall configuration of steering device]
As shown in FIG. 1, the electric power steering device 1 includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a and 5b, an intermediate shaft 6, and a steering gear unit. A pair of tie rods 8 and an electric assist device 9 are provided.

The steering shaft 3 is rotatably supported inside the steering column 4 supported by the vehicle body. A steering wheel 2 operated by the driver is attached to the rear end portion of the steering shaft 3. The front end portion of the steering shaft 3 is arranged inside the housing 16 constituting the worm reducer 15 with a motor, which will be described later, fixed to the front end portion of the steering column 4, and is arranged on the output shaft 11 via the torsion bar 10. It is connected.

The output shaft 11 is rotatably supported inside the housing 16 via a pair of rolling bearings 12a and 12b. The rotation of the output shaft 11 is transmitted to the input shaft 13 of the steering gear unit 7 via a pair of universal joints 5a and 5b and an intermediate shaft 6. The rotation of the input shaft 13 is converted into a linear motion of the rack shaft which is a linear motion shaft meshed with the input shaft 13, and the pair of tie rods 8 is pushed and pulled by the rack shaft. As a result, the steering wheel is provided with a steering angle according to the amount of operation of the steering wheel 2. The force required for the driver to operate the steering wheel 2 is reduced by the auxiliary power applied from the electric assist device 9.
The front-rear direction means the front-rear direction of the vehicle body to which the electric power steering device 1 is assembled.

[Electric assist device]
The electric assist device 9 is arranged in front of the steering column 4. As shown in FIG. 2, the electric assist device 9 includes a torque sensor 14, an ECU (electronic control unit) (not shown), and a worm reducer 15 with a motor.

The torque sensor 14 detects the torque input to the steering shaft 3 from the steering wheel 2. For this purpose, the torque sensor 14 is arranged around the output shaft 11 and detects the relative twisting direction and twisting amount of the output shaft 11 with respect to the steering shaft 3.

The ECU is a worm reducer with a motor 15 based on information on steering torque calculated based on the relative twist direction and twist amount of the output shaft 11, information on vehicle speed measured by a vehicle speed sensor (not shown), and the like. Determines the direction and magnitude of the steering assist force applied to the output shaft 11.

[Warm reducer with motor]
As shown in FIG. 4, the worm reducer 15 with a motor includes a housing 16, an electric motor 17, a worm wheel 18, a worm 19, an urging member 20, and a damper mechanism 21.

The worm reducer 15 with a motor rotatably supports a worm 19 that is rotationally driven by an electric motor 17 and a worm wheel 18 that is externally fitted so as not to rotate relative to the output shaft 11 inside the housing 16. The worm 19 and the worm wheel 18 are engaged with each other. As a result, the worm reducer 15 with a motor increases the output torque of the electric motor 17 and then applies the torque to the output shaft 11. The urging member 20 is arranged around the tip of the worm 19 and urges the tip of the worm 19 toward the side of the worm wheel 18 to suppress backlash of the meshing portion between the worm 19 and the worm wheel 18. do. The damper mechanism 21 is arranged between the worm 19 and the urging member 20 to attenuate the axial displacement of the worm 19.
Hereinafter, the constituent members of the worm reducer 15 with a motor will be described in detail.

"housing"
The housing 16 is a cast iron-based alloy, a die-cast molded product of a light alloy such as aluminum, an injection-molded product of synthetic resin, or the like, and has a twisted position with respect to the wheel accommodating portion 22 and the wheel accommodating portion 22. A worm accommodating portion 23 having an axial middle portion opened in the wheel accommodating portion 22 is provided.

The wheel accommodating portion 22 has a cylindrical shape and rotatably supports the worm wheel 18 inside. The wheel accommodating portion 22 is fixed to the front end portion of the steering column 4 so that its central axis and the central axis of the steering column 4 are coaxial with each other.

The worm accommodating portion 23 is formed in a cylindrical shape and rotatably supports the worm 19 inside. The worm accommodating portion 23 has openings at both ends in the axial direction. The opening on one side (right side in FIG. 4) of the worm accommodating portion 23 in the axial direction is closed by the electric motor 17. The opening on the other side (left side in FIG. 4) of the worm accommodating portion 23 in the axial direction is closed by a guide member 53, which will be described later, constituting the urging member 20.

Regarding the worm accommodating portion 23, the worm 19 rotatably supported inside the worm accommodating portion 23, and the members arranged around the worm 19, one side in the axial direction is the proximal end side of the worm 19. It refers to the right side of FIGS. 4 and 5. On the other hand, the other side in the axial direction is the tip side of the worm 19 and refers to the left side of FIGS. 4 and 5. Further, with respect to the members arranged around the worm 19, the radial direction and the circumferential direction refer to the radial direction and the circumferential direction of the worm 19 unless otherwise specified.

The worm accommodating portion 23 has a cylindrical fitting surface portion 24 on one side portion in the axial direction of the inner peripheral surface, and has one side in the axial direction at the end portion on the other side in the axial direction of the fitting surface portion 24. It has a stepped surface 25 facing. The worm accommodating portion 23 has a cylindrical guide holding portion 26 on the other side portion in the axial direction of the inner peripheral surface. Further, the worm accommodating portion 23 has an inward flange portion 27 protruding inward in the radial direction at a portion adjacent to one side in the axial direction of the guide holding portion 26. Further, the worm accommodating portion 23 is recessed radially outward in a part in the circumferential direction among the portions adjacent to the other side in the axial direction of the guide holding portion 26, and is on the other side in the axial direction of the worm accommodating portion 23. It has an engagement recess (not shown) that opens on the end face.

《Electric motor》
In the electric motor 17, the energization direction and the energization amount are controlled by the ECU. The electric motor 17 is fixed to the housing 16 so as to close the opening on one side in the axial direction of the worm accommodating portion 23. The electric motor 17 is provided for rotationally driving the worm 19, and has a motor output shaft 29 connected so as to be able to transmit torque to the base end portion of the worm 19.

《Warm wheel》
As shown in FIG. 2, the worm wheel 18 has wheel teeth 30 which are helical gears on the outer peripheral surface. The worm wheel 18 is rotatably supported inside the wheel accommodating portion 22. In this example, the worm wheel 18 is externally fitted to an axially intermediate portion of the output shaft 11 rotatably supported inside the wheel accommodating portion 22 so as to be unable to rotate relative to the output shaft 11. The worm wheel 18 of this example is formed by coupling and fixing an outer wheel member 32 made of synthetic resin having wheel teeth 30 on the outer peripheral surface around an inner wheel member 31 made of metal and having a circular plate shape.

《Warm》
As shown in FIG. 4, the worm 19 has a screw-shaped worm tooth 33 that meshes with the wheel tooth 30 of the worm wheel 18 at an axially intermediate portion of the outer peripheral surface. The worm 19 has a first support shaft portion 34 and a second support shaft portion 35, respectively, on both sides in the axial direction of the outer peripheral surface. The first support shaft portion 34 is provided on the tip end side portion (the other side portion in the axial direction) of the worm 19. The second support shaft portion 35 is provided on the base end side portion (one side portion in the axial direction) of the worm 19. The worm 19 has an outward flange portion 36 projecting outward in the radial direction between the worm teeth 33 and the second support shaft portion 35.

The motorized worm reducer 15 of this example further includes a first bearing 40 and a second bearing 41 in order to rotatably support the worm 19 inside the worm accommodating portion 23. Further, a torque transmission joint 42 is further provided in order to connect the base end portion of the worm 19 to the motor output shaft 29.

<< 1st bearing >>
The first bearing 40 rotatably supports the tip side portion of the worm 19. The first bearing 40 is a ball bearing such as a single row deep groove type, each of which includes an annular inner ring 43 and an outer ring 44, and a plurality of rolling elements 45.

The inner ring 43 is externally fitted and fixed to the first support shaft portion 34 of the worm 19. The outer ring 44 is arranged inside the urging member 20 fitted inside the guide holding portion 26 of the worm accommodating portion 23. The rolling element 45 is rotatably arranged between the inner ring track provided on the outer peripheral surface of the inner ring 43 and the outer ring track provided on the inner peripheral surface of the outer ring 44. The outer ring 44 of this example is supported so as to be capable of relative displacement in the axial direction and relative displacement in the perspective direction with respect to the worm wheel 18 with respect to the urging member 20. Therefore, the first bearing 40 can be displaced relative to the worm accommodating portion 23 in the axial direction. In this example, a ball bearing in which the rolling element 45 is a ball is used as the first bearing 40, but a radial roller bearing or the like can also be used.

<< 2nd bearing >>
The second bearing 41 rotatably supports the base end side portion of the worm 19. The second bearing 41 is a ball bearing such as a single row deep groove type or a four-point contact type, and each includes an annular inner ring 46 and an outer ring 47, and a plurality of ball 48s.

The inner ring 46 is externally fitted to the second support shaft portion 35 of the worm 19 by gap fitting. The outer ring 47 is internally fitted to the fitting surface portion 24 of the worm accommodating portion 23 without rattling. The ball 48 is rotatably arranged between the inner ring track provided on the outer peripheral surface of the inner ring 46 and the outer ring track provided on the inner peripheral surface of the outer ring 47.

The inner ring 46 is elastically sandwiched from both sides in the axial direction by a pair of elastic spacers 49a and 49b. Of the pair of elastic spacers 49a and 49b, the elastic spacer 49b arranged on one side in the axial direction is sandwiched between the inner ring 46 and the driven side transmission member 52 constituting the torque transmission joint 42, which will be described later. .. The elastic spacer 49a arranged on the other side in the axial direction is sandwiched between the inner ring 46 and the outward flange portion 36. Therefore, the inner ring 46 (second bearing 41) can be displaced relative to the worm 19 by the elastic deformation of the elastic spacers 49a and 49b.

The outer ring 47 is sandwiched from both sides in the axial direction between the stepped surface 25 provided on the inner peripheral surface of the worm accommodating portion 23 and the retaining ring 50 locked to the inner peripheral surface of the worm accommodating portion 23. As a result, the outer ring 47 is prevented from being displaced relative to the worm accommodating portion 23 in the axial direction.

Since the inner ring 46 constituting the second bearing 41 is fitted to the second support shaft portion 35 of the worm 19 by gap fitting, it is between the inner peripheral surface of the inner ring 46 and the outer peripheral surface of the second support shaft portion 35. Has a radial gap. Further, the base end portion of the worm 19 is connected to the motor output shaft 29 so as to be able to swing the worm 19 via the torque transmission joint 42. Further, an O-ring is sandwiched between the inner peripheral surface of the inner ring 46 and the outer peripheral surface of the second support shaft portion 35. Therefore, the worm 19 can swing with respect to the second bearing 41 with the center of the second bearing 41 as the swing center while being held in the radial direction regardless of the radial gap.

As described above, the first bearing 40 that rotatably supports the tip side portion of the worm 19 cannot be displaced relative to the worm 19 in the axial direction, but the urging member 20 fixed to the worm accommodating portion 23 (is fixed to the worm accommodating portion 20). ) Can be displaced relative to the axis. Further, the second bearing 41 that rotatably supports the base end side portion of the worm 19 cannot be displaced in the axial direction with respect to the worm accommodating portion 23, but can be displaced in the axial direction with respect to the worm 19. .. Therefore, the worm 19 is rotatably supported inside the worm accommodating portion 23 and is capable of axially relative displacement with respect to the worm accommodating portion 23.

《Torque transmission joint》
As shown in FIG. 4, the torque transmission joint 42 includes a drive-side transmission member 51 that is externally fitted and fixed to the tip end portion (left end portion of FIG. 4) of the motor output shaft 29 so as not to rotate relative to each other, and a base of the worm 19. A driven side transmission member 52, which is externally fitted and fixed to the end portion so as not to rotate relative to each other, and an elastic member 106, each of which is made of an elastic material such as an elastomer such as rubber, are provided.

When the torque transmitted between the motor output shaft 29 and the worm 19 is relatively small, the torque transmission joint 42 receives the rotational torque of the motor output shaft 29 from the drive side transmission member 51 via the elastic member 106. It is transmitted to the drive side transmission member 52. On the other hand, when the torque transmitted between the motor output shaft 29 and the worm 19 is large, the elastic member 106 is elastically crushed in the circumferential direction, so that the torque transmission joint 42 rotates the motor output shaft 29. Torque is directly transmitted from the drive-side transmission member 51 to the driven-side transmission member 52.

As the specific structure of the torque transmission joint 42, various conventionally known structures can be adopted. In any case, in this example, the motor output shaft 29 and the worm are wormed by connecting the tip end portion of the motor output shaft 29 and the base end portion of the worm 19 so that torque can be transmitted via the torque transmission joint 42. It prevents the generation of rattling noise in the torque transmission unit with 19 and enables the worm 19 to swing with respect to the motor output shaft 29. However, as long as torque transmission between the motor output shaft 29 and the worm 19 and swing of the worm 19 with respect to the motor output shaft 29 are possible, the tip of the motor output shaft 29 and the base end of the worm 19 The connection method is not particularly limited, and the connection can be made by spline engagement or the like.

《Bending member》
The urging member 20 has a main function of urging the tip of the worm 19 toward the side of the worm wheel 18 via the first bearing 40. The urging member 20 includes a guide member 53, an elastic ring 54, a first elastic member 55, a second elastic member 56, and a third elastic member 57.

The guide member 53 is supported and fixed inside the worm accommodating portion 23, and the first bearing 40 is internally fitted and held by gap fitting. Further, the guide member 53 holds each of the first elastic member 55, the second elastic member 56, and the third elastic member 57 around the first bearing 40. Each of the first elastic member 55, the second elastic member 56, and the third elastic member 57 elastically contacts the first bearing 40 and applies a pressing force in a predetermined direction to the first bearing 40. The elastic ring 54 is elastically sandwiched between the outer peripheral surface of the guide member 53 and the inner peripheral surface of the worm accommodating portion 23.

<Guide member>
The guide member 53 has a bottomed cylindrical shape, and as shown in FIG. 5, is internally fitted to the guide holding portion 26 of the worm accommodating portion 23 without rattling. That is, the guide member 53 is fixed to the housing 16. The guide member 53 includes a stepped cylindrical guide main body 59 and a lid 60 that closes an opening on the other side in the axial direction of the guide main body 59.

The guide main body 59 has a large diameter cylinder portion 61 on one side in the axial direction, a small diameter cylinder portion 62 on the other side in the axial direction, an end portion on the other side in the axial direction of the large diameter cylinder portion 61, and one axial direction of the small diameter cylinder portion 62. It is provided with a side wall portion 63 that connects to the side end portion. The guide body 59 is made of synthetic resin or metal having sufficient strength and rigidity.

The large-diameter tubular portion 61 has a bearing holding portion 58 for internally fitting the first bearing 40 with respect to the worm wheel 18 on the other side portion in the axial direction of the inner peripheral surface. The inner diameter of the bearing holding portion 58 is larger than the outer diameter of the outer ring 44 of the first bearing 40, and the axial dimension of the bearing holding portion 58 is shorter than the axial dimension of the outer ring 44 of the first bearing 40. .. Therefore, the bearing holding portion 58 internally fits the other side portion of the outer ring 44 in the axial direction by gap fitting. In other words, with the outer ring 44 fitted and held inside the bearing holding portion 58, one side portion of the outer ring 44 in the axial direction is arranged inside the third elastic member holding portion 74, which will be described later.

As shown in FIGS. 11 and 15 (C), the bearing holding portion 58 has a distal partial cylindrical surface portion 64 at two locations on the side (half portion) far from the worm wheel 18 in the circumferential direction. Moreover, a first elastic member holding recess 65 recessed outward in the radial direction is provided between the distal side partial cylindrical surface portions 64. Further, the bearing holding portion 58 has a second elastic member holding recess 66 recessed outward in the radial direction in a portion (half portion) closer to the worm wheel 18 in the circumferential direction.

Each of the distal partial cylindrical surface portions 64 has a radius of curvature equal to or slightly larger than the radius of curvature of the outer peripheral surface of the outer ring 44 of the first bearing 40.

The first elastic member holding recess 65 has a flat pedestal surface portion 67 on a bottom surface facing inward in the radial direction. The guide main body 59 has a rectangular columnar distal-side protruding portion 68 that protrudes from the surface facing one side in the axial direction toward one side in the axial direction in the first elastic member holding recess 65. Then, the flat surface-shaped holding surface portion 69 provided on the radial outer surface of the distal side protruding portion 68 is opposed to the pedestal surface portion 67.

The second elastic member holding recess 66 has convex portions 70 protruding inward in the radial direction at two positions in the circumferential direction of the bottom surface facing inward in the radial direction. The guide main body 59 is a proximal side having a substantially bow-shaped (substantially arcuate) end face shape that protrudes from the surface of the second elastic member holding recess 66 facing one side in the axial direction toward one side in the axial direction. It has a protrusion 71. The proximal side protrusion 71 has a proximal side partial cylindrical surface portion 72 on the radial inner side surface and a partially cylindrical surface-shaped holding surface portion 73 on the radial outer surface.

The proximal side partial cylindrical surface portion 72 has a radius of curvature equal to or slightly larger than the radius of curvature of the outer peripheral surface of the outer ring 44 of the first bearing 40.

The holding surface portion 73 is located slightly outward in the radial direction from the tip end portion (diameterally inner end portion) of the convex portion 70.

As shown in FIGS. 14 (A) and 16 and the like, the large-diameter tubular portion 61 has a cylindrical third elastic member holding portion 74 at one end of the inner peripheral surface in the axial direction.

The large-diameter tubular portion 61 has an engaging convex portion 75 protruding outward in the radial direction at a part in the circumferential direction of the end portion on the other side in the axial direction of the outer peripheral surface. Further, the large-diameter tubular portion 61 has a locking groove 76 over the entire circumference in the axial intermediate portion of the outer peripheral surface, and toward one end in the axial direction of the outer peripheral surface toward one side in the axial direction. It has an inclined surface portion 77 inclined inward in the radial direction. In this example, the central axis of the locking groove 76 is aligned with the central axis of the large diameter tubular portion 61. However, the central axis of the locking groove 76 may be offset to a side farther from the worm wheel 18 than the central axis of the large diameter tubular portion 61.

Further, the large-diameter tubular portion 61 has a first engaging notch 78 at the end of the end on one side in the axial direction, which is closer to the worm wheel 18 in the circumferential direction, and has an axial direction. The second engaging notch 79 is provided at two positions on one side of the end, which are 90 degrees out of phase with the first engaging notch 78 in the circumferential direction.

The small-diameter tubular portion 62 has an inward flange portion 80 protruding inward in the radial direction at the end on the other side in the axial direction.

The lid 60 has a small diameter portion 81 on one side in the axial direction and a large diameter portion 82 on the other side in the axial direction. The small diameter portion 81 has a concave groove 83 over the entire circumference at the end on the other side in the axial direction of the outer peripheral surface. As the material constituting the lid 60, a material having high rigidity that can sufficiently prevent the axial displacement of the piston 84 can be preferably used.

The lid 60 is attached to the guide body 59 by inserting the small diameter portion 81 into the inside of the small diameter cylinder portion 62 of the guide main body 59 and engaging the inward flange portion 80 with the concave groove 83 to guide the lid body 60. The opening on the other side of the main body 59 in the axial direction is closed. The method of fixing the lid 60 to the guide main body 59 is not limited to the structure in which the inward flange portion 80 is engaged with the concave groove 83, and if the lid 60 can be fixed to the guide main body 59 with high rigidity, the small diameter portion Other fixing methods such as directly press-fitting the 81 into the small diameter cylinder portion 62 can also be adopted. Further, a sealing member for preventing the grease (including the viscous fluid 105 described later) sealed in the housing 16 from leaking to the outside can be separately provided between the lid 60 and the guide main body 59.

The guide member 53 is fitted inside the guide holding portion 26 in a state where the engaging convex portion 75 is engaged with the engaging concave portion of the worm accommodating portion 23 and the elastic ring 54 is locked in the locking groove 76. Has been done. This prevents the guide member 53 from rotating inside the guide holding portion 26. Further, with the guide member 53 fitted in the guide holding portion 26, the retaining ring 91 is locked to the portion of the inner peripheral surface of the worm accommodating portion 23 adjacent to the other side in the axial direction of the guide holding portion 26. There is. This prevents the guide member 53 from being displaced to the other side in the axial direction.

<Elastic ring>
The elastic ring 54 has a circular cross section and is composed of an O-ring made of an elastic material such as an elastomer such as rubber. However, the cross-sectional shape of the elastic ring 54 is not limited to a circular shape, and various shapes such as a rectangular shape and an elliptical shape can be adopted. The elastic ring 54 is elastically sandwiched between the bottom surface of the locking groove 76 provided on the outer peripheral surface of the guide member 53 and the guide holding portion 26 provided on the inner peripheral surface of the worm accommodating portion 23. As a result, the elastic ring 54 prevents the grease (including the viscous fluid 105 described later) sealed in the housing 16 from leaking to the outside.

In this example, the central axis of the locking groove 76 is aligned with the central axis of the large-diameter tubular portion 61, but the central axis of the locking groove 76 is set to the worm wheel 18 rather than the central axis of the large-diameter tubular portion 61. It can also be offset to the far side from. As a result, the guide member 53 is elastically urged toward the side closer to the worm wheel 18, and the side portion of the outer peripheral surface of the large-diameter tubular portion 61 close to the worm wheel 18 is pressed against the guide holding portion 26. You can also.

<First elastic member>
The first elastic member 55 places the first bearing 40 on the side of the worm wheel 18 (FIG. 4, FIG. 5, FIGS. 7 (A) to 7 (C), FIG. 8, FIG. 10 and the lower side of FIG. 11). Elastically urge towards. In this example, the first elastic member 55 is composed of a leaf spring formed by bending and molding an elastic metal plate. The first elastic member 55 is arranged between the outer ring 44 of the first bearing 40 and the guide member 53. As shown in FIG. 17, the first elastic member 55 includes a locking plate portion 92, a pressing plate portion 93, a connecting plate portion 94, and a bent plate portion 95.

The locking plate portion 92 is configured in a flat plate shape.

The pressing plate portion 93 is formed in a flat plate shape and is provided substantially parallel to the locking plate portion 92.

The connecting plate portion 94 is curved in a substantially U-shape when viewed from the axial direction, and one end portion (diametrically outer end portion) in the circumferential direction is used as the circumferential end portion of the locking plate portion 92. It is connected and the other end in the circumferential direction (the end on the inner side in the radial direction) is connected to the circumferential end of the pressing plate portion 93.

The bent plate portion 95 is bent outward in the radial direction from one end of the pressing plate portion 93 in the axial direction.

As shown in FIGS. 10 and 11, the first elastic member 55 is arranged inside the first elastic member holding recess 65 of the guide member 53, and is between the outer ring 44 of the first bearing 40 and the guide member 53. It is sandwiched in an elastically compressed state. Specifically, the first elastic member 55 sandwiches the locking plate portion 92 between the pedestal surface portion 67 and the holding surface portion 69, and the radial inner surface of the pressing plate portion 93 and the connecting plate portion 94. The radial inner surface of the radial inner portion is elastically pressed against the end portion of the outer peripheral surface of the outer ring 44 on the side farther from the worm wheel 18. As a result, the first bearing 40 is elastically urged toward the worm wheel 18.

<Second elastic member>
In the second elastic member 56, the outer ring 44 of the first bearing 40 is urged by the first elastic member 55 in the first direction (FIGS. 4, 5, 7 (A) to 7 (C), FIGS. 7 (C), FIG. 8. Elasticity from both sides in the second direction (horizontal directions of FIGS. 7 (B) to 7 (E) and FIG. 9) orthogonal to the central axis of the worm accommodating portion 23 (vertical direction of FIGS. 10 and 11). The first bearing 40 is restrained from being vigorously displaced in the second direction.

In this example, the second elastic member 56 is composed of a leaf spring formed by bending and molding an elastic metal plate. The second elastic member 56 is arranged between the outer ring 44 of the first bearing 40 and the guide member 53. As shown in FIG. 18 and the like, the second elastic member 56 has a partially cylindrical portion 97 having a semi-circular end face shape. The ends of the partial cylindrical portion 97 on both sides in the circumferential direction function as a pair of holding pieces 96 that elastically hold the outer ring 44 of the first bearing 40 from both sides in the second direction. The second elastic member 56 includes a first engaging piece 98 bent radially outward from the circumferential middle portion of the end portion on one side in the axial direction of the partial cylindrical portion 97, and one axial portion of the partial cylindrical portion 97. Of the side ends, a pair of second engaging pieces 99 that are bent radially outward from the ends on both sides in the circumferential direction are further provided.

As shown in FIG. 11 and the like, the second elastic member 56 is supported inside the second elastic member holding recess 66 of the guide member 53. Specifically, the second elastic member is formed by sandwiching the partial cylindrical portion 97 in the radial direction between the tip portion of the convex portion 70 provided inside the second elastic member holding recess 66 and the holding surface portion 73. 56 is supported with respect to the guide member 53. In this state, the pair of holding pieces 96 are elastically pressed against the ends on both sides of the outer peripheral surface of the outer ring 44 of the first bearing 40 in the second direction. Further, with the second elastic member 56 supported by the guide member 53, the first engaging piece 98 is engaged with the first engaging notch portion 78, and the second engaging piece 99 is radially outside. The portion is engaged with the second engaging notch portion 79. As a result, the second elastic member 56 is positioned in the circumferential direction with respect to the guide member 53.

<Third elastic member>
In the third elastic member 57, even when the meshing reaction force Fr is applied to the worm 19 from the meshing portion between the wheel tooth 30 and the worm tooth 33, the tip portion of the worm 19 is vigorously displaced in the direction of the meshing reaction force Fr. Suppress doing.

In this example, the third elastic member 57 is made of an elastomer such as rubber. As shown in FIG. 19, the third elastic member 57 has a partial arc shape (substantially 3/4 arc shape, C shape) in which a portion far from the worm wheel 18 in the circumferential direction is a discontinuous portion. A held portion 101 having an end face shape is provided.

The held portion 101 has a pair of elastically deformed portions 100 protruding inward in the radial direction at two positions on the inner peripheral surface on the side portion far from the worm wheel 18 in the circumferential direction. Each of the elastically deformed portions 100 is provided in the direction of the meshing reaction force Fr in the periphery of the outer ring 44 of the first bearing 40. In this example, of the held portion 101, the elastically deformed portion 100 provided on one side portion in the circumferential direction (the left portion in FIG. 10) is composed of one elastic protrusion 104, whereas the covered portion is covered. Of the holding portions 101, the elastically deformed portion 100 provided on the other side portion in the circumferential direction (the right portion in FIG. 10) is composed of three elastic protrusions 104 separated in the circumferential direction. Each of the elastic protrusions 104 has a substantially triangular end face shape when viewed from the axial direction. However, the structure of the elastically deformed portion may be any structure as long as it can be elastically deformed based on the meshing reaction force Fr and absorb the meshing reaction force Fr.

The held portion 101 has a convex portion 102 that protrudes radially outward from the end portion on the side close to the worm wheel 18. Further, the held portion 101 further has recesses 103 opened in the inner peripheral surface and the outer peripheral surface at two positions on one side surface in the axial direction, which are 90 degrees out of phase with the convex portion 102 in the circumferential direction.

The third elastic member 57 is supported by the guide member 53 by elastically fitting the held portion 101 into the third elastic member holding portion 74 of the guide member 53. With the third elastic member 57 supported by the guide member 53, the convex portion 102 engages with the first engaging notch portion 78, and the other side surface of the convex portion 102 in the axial direction is the second elastic member 56. Is pressed against one side surface of the first engaging piece 98 in the axial direction. Further, with the third elastic member 57 supported by the guide member 53, the other side surface in the axial direction of the radial inner portion of the second engaging piece 99 of the second elastic member 56 is pressed against the recess 103, and The elastically deformed portion 100 elastically abuts or faces the outer peripheral surface of the outer ring 44.

Further, with the guide member 53 assembled to the guide holding portion 26, the third elastic member 57 is elastically compressed in the axial direction between the guide member 53 and the inward flange portion 27. As a result, the guide member 53 is sandwiched between the third elastic member 57 and the retaining ring 91 in the axial direction and is positioned in the axial direction. Further, the elastic restoring force of the third elastic member 57 can apply a preload to the meshing portion between the wheel teeth 30 and the worm teeth 33.

As described above, in this example, the outer ring 44 constituting the first bearing 40 is internally fitted into the bearing holding portion 58 constituting the guide member 53 by gap fitting, and the worm wheel 18 side is provided by the first elastic member 55. It is elastically urged toward the surface and is sandwiched by the second elastic member 56 from both sides in the second direction. Further, a pair of elastically deformed portions 100 constituting the third elastic member 57 are arranged in the direction of the meshing reaction force Fr around the outer ring 44.

《Damper mechanism》
In this example, the outer ring 44 constituting the first bearing 40 that rotatably supports the worm 19 is internally fitted to the guide member 53 of the urging member 20 so as to be relatively displaced in the axial direction, and the worm 19 is formed. The inner ring 46 constituting the second bearing 41 that rotatably supports the worm 19 is fitted on the outside so as to be relatively displaced in the axial direction with respect to the worm 19. Therefore, the worm 19 can be displaced relative to the worm accommodating portion 23 in the axial direction. Therefore, if it is left as it is, rattle noise is likely to be generated in the meshing portion between the wheel teeth 30 and the worm teeth 33, and inside the first bearing 40 and the second bearing 41 when traveling on a rough road. Therefore, the worm reducer 15 with a motor of this example is provided with a damper mechanism 21 in order to attenuate the axial displacement of the worm 19.

The damper mechanism 21 has a function of attenuating the axial displacement of the worm 19. As shown in FIG. 5, the damper mechanism 21 of this example is provided with a bottomed cylinder hole 37 opened only on the tip surface of the worm 19 and a guide member 53 of the urging members 20 fixed to the housing 16. The piston portion 84 is provided, and the viscous fluid 105 filled in the cylinder hole 37 is provided.

The cylinder hole 37 is provided at the tip of the worm 19. The end of the cylinder hole 37 on the other side in the axial direction is open to the tip surface of the worm 19, and the end (bottom) of the cylinder hole 37 on the other side in the axial direction is fitted with the inner ring 43 of the first bearing 40. It is located on one side in the axial direction from the first support shaft portion 34. The cylinder hole 37 has a circular cross-sectional shape and has a central axis that coincides with the central axis of the worm 19. The cylinder hole 37 is provided in the main body hole 38, which is a cylindrical hole whose inner diameter r ₃₈ does not change in the axial direction, and is provided on the inner side of the main body hole 38, and the inner diameter is smaller toward one side in the axial direction. It is composed of a conical hole 39.

The piston portion 84 is provided on the lid 60 constituting the guide member 53. Specifically, the piston portion 84 is provided at the radial center portion of the end face on one side in the axial direction of the small diameter portion 81 constituting the lid 60, and extends toward one side in the axial direction. The piston portion 84 has a substantially T-shaped cross-sectional shape, and includes a piston rod 85 having a cylindrical shape and a piston body 86 having a disk shape provided at the tip end portion of the piston rod 85.

The piston portion 84 is inserted into the cylinder hole 37 opened in the tip surface of the worm 19 with the lid 60 attached to the guide main body 59. In this example, the piston main body 86 is arranged in the axial intermediate portion of the main body hole 38 with the piston portion 84 inserted in the cylinder hole 37. Although the piston portion 84 is provided integrally with the lid body 60, the piston portion may be configured separately from the lid body and fixed to the lid body.

The outer diameter dimension R ₈₆ of the piston main body 86 is larger than the outer diameter dimension of the piston rod 85 and smaller than the inner diameter dimension r ₃₈ of the main body hole portion 38 of the cylinder hole 37. Therefore, a radial gap 87 is provided over the entire circumference between the outer peripheral surface of the piston main body 86 and the inner peripheral surface of the main body hole 38. In this example, the size of the radial gap 87 is large enough to allow the worm 19 to swing without interfering with the outer peripheral surface of the piston main body 86 and the inner peripheral surface of the main body hole 38. It is supposed to be. However, if the size of the radial gap 87 becomes excessive, sufficient damping force cannot be obtained. Therefore, the size of the radial gap 87 is set to the outer peripheral surface of the piston main body 86 and the inner peripheral surface of the main body hole 38. It is set small enough to prevent interference.

The worm reducer 15 with a motor of this example covers the tip of the worm 19 in order to prevent the viscous fluid 105 from flowing out or scattering from the cylinder hole 37 as the worm 19 rotates. As described above, the covering cylinder portion 88 is provided. The covering cylinder portion 88 has a cylindrical shape, and extends from the radially outer end portion of the end face on one side in the axial direction of the small diameter portion 81 constituting the lid 60 toward one side in the axial direction. The covering cylinder portion 88 has a throttle cylinder portion 89 bent inward in the radial direction at one end in the axial direction.

The covering cylinder portion 88 is arranged around the tip portion of the worm 19 with the lid 60 attached to the guide main body 59. In other words, the tip portion of the worm 19 is inserted inside the covering cylinder portion 88. In this example, by providing the covering cylinder portion 88 on the lid 60, an annular space 90 serving as a grease pool is formed in the radial portion between the base end portion of the piston rod 85 and the covering cylinder portion 88. The inner diameter of the throttle tube portion 89 is slightly larger than the outer diameter of the tip portion (first support shaft portion 34) of the worm 19. Specifically, the inner diameter of the throttle tube portion 89 is set so that the inner peripheral edge portion of the throttle tube portion 89 and the outer peripheral surface of the tip end portion of the worm 19 do not interfere with each other even when the worm 19 swings. It is larger than the outer diameter of the tip of the.

The viscous fluid 105 is filled (enclosed) in the cylinder hole 37. In this example, the viscous fluid 105 is filled in the peripheral portion of the piston body 86 (including the radial gap 87) and the portion between the end surface of the piston body 86 on one axial direction and the bottom surface of the cylinder hole 37. There is. In addition, in FIGS. 4 and 5, the viscous fluid 105 is represented by a pear-skin pattern.

As the viscous fluid 105, for example, a lubricant such as grease (high viscosity grease) having a kinematic viscosity of the base oil at 40 ° C. of 150 mm ² / s or more, preferably 200 mm ² / s or more can be used. In this example, as the viscous fluid 105, a grease composed of a base oil having a kinematic viscosity of 150 mm ² / s or more, preferably 200 mm ² / s or more, a thickener, and an additive is used. .. Further, in this example, the grease as the viscous fluid 105 is not used only for the damper mechanism 21, but also for lubrication of the rolling contact portions of the first bearing 40 and the second bearing 41, and the wheel teeth 30 and the worm teeth 33. It is also used for lubrication of the meshing part with. However, when the present invention is carried out, the viscous fluid 105 constituting the damper mechanism 21 is used as a lubricant for lubricating the rolling contact portions of the first bearing 40 and the second bearing 41, as well as the wheel teeth 30 and the worm teeth 33. It is also possible to use a different type of lubricant from the lubricant that lubricates the meshing portion with.

The magnitude of the damping force generated by the damper mechanism 21 is the viscosity of the viscous fluid 105, the size of the radial gap 87, the shape and size of the piston portion 84 (outer diameter dimension, axial dimension), and the shape of the cylinder hole 37. And the size (inner diameter dimension, axial dimension) and the like can be adjusted as appropriate.

The work procedure for filling the cylinder hole 37 with the viscous fluid 105 is not particularly limited. For example, after assembling the worm reducer 15 with a motor, the lid 60 can be removed from the guide body 59 to fill the cylinder hole 37 with the viscous fluid 105, or the worm reducer 15 with a motor can be in the process of being assembled. , The cylinder hole 37 can be filled with the viscous fluid 105.

In this example as described above, the minute displacement of the worm 19 in the axial direction can be attenuated.
That is, in this example, the damper mechanism 21 for damping the axial displacement of the worm 19 is provided in the bottomed cylinder hole 37 opened in the tip surface of the worm 19 in the guide member 53 fixed to the housing 16. The piston portion 84 is inserted, and the cylinder hole 37 is filled with the viscous fluid 105. Therefore, when the worm 19 is displaced relative to the worm accommodating portion 23 in the axial direction based on the axially exciting force acting on the worm 19 when traveling on a rough road, a pumping action, that is, a viscous fluid The resistance acting on the cylinder hole 37 from 105 can sufficiently attenuate the axial displacement of the worm 19. Specifically, according to the damper mechanism 21 of this example, it is possible to attenuate the axial displacement smaller than the axial backlash existing between the outer ring 47 and the inner ring 46 constituting the second bearing 41. As a result, the generation of rattle sound can be sufficiently suppressed.

The worm 19 provided with the cylinder hole 37 is a rotating member, whereas the guide member 53 provided with the piston portion 84 is a non-rotating member fixed to the housing 16. Therefore, torque loss occurs in the worm 19 due to the shear resistance and stirring resistance of the viscous fluid 105. However, in this example, since the piston body 86 having a large outer diameter is provided only at the tip of the piston portion 84, the shear resistance and stirring resistance of the viscous fluid 105 can be suppressed to a small value, and torque loss can be reduced. It is sufficiently suppressed.

Further, even when the worm 19 swings the size of the radial gap 87 existing between the outer peripheral surface of the piston main body 86 and the inner peripheral surface of the main body hole 38, the outer peripheral surface of the piston main body 86 and the main body It is set sufficiently small so as not to interfere with the inner peripheral surface of the hole 38. Therefore, the swing of the worm 19 and the attenuation of the axial displacement of the worm 19 can be compatible with each other.

Further, the tip portion of the worm 19 is covered with a covering cylinder portion 88 provided in the lid 60, and the tip portion of the covering cylinder portion 88 is provided with a throttle cylinder portion 89 bent inward in the radial direction. Therefore, the viscous fluid 105 leaking from the cylinder hole 37 can be held in the annular space 90. Therefore, it is possible to prevent the viscous fluid 105 from flowing out or scattering around the worm 19.

In this example, the tip portion of the worm 19 is elastically urged toward the worm wheel 18 side via the first bearing 40 by the first elastic member 55 constituting the urging member 20. Therefore, backlash between the wheel teeth 30 and the worm teeth 33 can be suppressed.

Further, the first elastic member 55 elastically urges the outer peripheral surface of the outer ring 44 not only by the radial inner surface of the pressing plate portion 93 but also by the radial inner surface of the radial inner portion of the connecting plate portion 94. is doing. Therefore, it is possible to sufficiently secure the contact area of the first elastic member 55 with respect to the outer peripheral surface of the outer ring 44, and it is possible to suppress the surface pressure of the contact portion between the outer peripheral surface of the outer ring 44 and the first elastic member 55 to be small. Therefore, the wear of the first elastic member 55 can be suppressed.

Further, in the first elastic member 55, the locking plate portion 92 locked to the guide member 53 and the pressing plate portion 93 for pressing the outer peripheral surface of the outer ring 44 are curved in a substantially U shape when viewed from the axial direction. It is configured by connecting with a connection plate portion 94. Therefore, as the first elastic member, the locking plate portion supported by the guide member and the pressing plate portion that presses the outer peripheral surface of the outer ring are curved in a substantially U shape when viewed from the circumferential direction (second direction). The axial dimension can be kept short compared to the case where the structure is connected by the connecting plate portion.

Further, the first bearing 40 is sandwiched from both sides in the second direction by a pair of sandwiching pieces 96 of the second elastic member 56. Therefore, even if the rotation direction of the worm wheel 18 changes based on the driver operating the steering wheel 2, it is possible to prevent the tip portion of the worm 19 from being vigorously displaced in the second direction.

When the force applied to the tip of the worm 19 in the second direction becomes larger than the elasticity of the holding piece 96, the holding piece 96 is elastically deformed and the tip of the worm 19 is displaced in the second direction. However, also in this case, the outer peripheral surface of the outer ring 44 of the first bearing 40 abuts on the distal side partial cylindrical surface portion 64 provided on the inner peripheral surface of the guide main body 59, and the outer peripheral surface of the guide main body 59 is the housing 16. By being pressed against the guide holding portion 26 of the above, the force based on the change in the rotation direction of the worm wheel 18 can be supported by the housing 16. As described above, in this example, the force based on the change in the rotation direction of the worm wheel 18 is absorbed by the elastic deformation of the holding piece 96 in the first stage, and can be supported by the housing 16 in the second stage.

Further, a pair of elastically deformed portions 100 constituting the third elastic member 57 are arranged in the direction of the meshing reaction force Fr in the periphery of the outer ring 44 of the first bearing 40. Therefore, even when the meshing reaction force Fr is applied to the worm 19, it is possible to prevent the tip of the worm 19 from being vigorously displaced in the direction of the meshing reaction force Fr.

When torque is transmitted from the worm 19 to the worm wheel 18, the worm 19 is engaged with and a reaction force Fr is applied. This meshing reaction force Fr includes not only a component related to the first direction but also a component related to the second direction perpendicular to the first direction. Of the meshing reaction force Fr, the directions of the components in the second direction are opposite to each other depending on whether the worm 19 rotates in one direction or in the other direction. That is, the meshing reaction force Fr in the direction inclined with respect to the first direction is applied to the tip portion of the worm 19 according to the rotation direction of the worm 19. In this example, the pair of elastically deformed portions 100 constituting the third elastic member 57 can prevent the tip portion of the worm 19 from being vigorously displaced in the direction of the meshing reaction force Fr.

When the meshing reaction force Fr becomes larger than the elasticity of the elastically deformed portion 100 and the elastically deformed portion 100 is crushed outward in the radial direction, the tip portion of the worm 19 is displaced in the direction of the meshing reaction force Fr. However, also in this case, the outer peripheral surface of the outer ring 44 of the first bearing 40 comes into contact with the circumferential middle portion of the distal side partial cylindrical surface portion 64 provided on the inner peripheral surface of the guide main body 59, and the guide main body 59 By pressing the outer peripheral surface of the housing 16 against the guide holding portion 26 of the housing 16, the meshing reaction force Fr can be supported. As described above, in this example, the meshing reaction force Fr applied to the worm 19 is absorbed by the elastic deformation portion 100 by elastic deformation in the first stage, and can be supported by the housing 16 in the second stage.

Further, the distal partial cylindrical surface portion 64 is provided at two positions in the circumferential direction of the inner peripheral surface of the guide main body 59. Therefore, regardless of the rotation direction of the worm 19, the contact portion between the outer peripheral surface of the outer ring 44 and the distal partial cylindrical surface portion 64 can be positioned in the direction of the meshing reaction force Fr, and the meshing reaction force Fr can be positioned. Can be efficiently supported by the housing 16.

As a modification of this example, for example, a piston portion inserted into a cylinder hole opened in the tip surface of the worm may be provided in the housing instead of the guide member constituting the urging member. Alternatively, the cylinder hole is provided in the guide member or housing so that the opening faces the tip surface of the worm and the piston portion extends from the tip surface of the worm toward the other side in the axial direction. You can also prepare. Even when such a configuration is adopted, the minute displacement of the worm in the axial direction can be sufficiently attenuated.

[Second example of the embodiment]
A second example of the embodiment will be described with reference to FIGS. 20 to 21. In this example, the same components as those of the first example of the embodiment are designated by the same reference numerals as those of the first example of the embodiment, and detailed description thereof will be omitted.

In the worm reducer 15a with a motor of this example, the damper mechanism 21a is arranged not between the worm 19a and the urging member 20 but between the worm 19a and the electric motor 17a.

The damper mechanism 21a includes a bottomed cylinder hole 37a opened only at the base end surface of the worm 19a, a piston portion 84a provided in the motor output shaft 29a of the electric motor 17a, and a viscous fluid 105 filled in the cylinder hole 37a. To prepare for.

The cylinder hole 37a is provided at the base end portion of the worm 19a. The cylinder hole 37a has a circular cross-sectional shape and has a central axis that coincides with the central axis of the worm 19a. The cylinder hole 37a is provided on the inner side of the main body hole 38a, which is a cylindrical hole whose inner diameter does not change in the axial direction, and on the inner side of the main body hole 38a, and the inner diameter becomes smaller toward the other side in the axial direction. It is composed of a conical hole portion 39a.

The piston portion 84a is provided on the motor output shaft 29a. Specifically, the piston portion 84a is provided at the radial center portion of the tip end surface (end surface on the other side in the axial direction) of the motor output shaft 29a, and extends toward the other side in the axial direction. The piston portion 84a has a cylindrical shape and has a constant outer diameter over the entire length in the axial direction.

The piston portion 84a is inserted into the cylinder hole 37a opened in the base end surface of the worm 19a in a state where the electric motor 17a is fixed to the housing 16. Specifically, with the piston portion 84a inserted into the cylinder hole 37a, the tip surface of the piston portion 84a is arranged in the axial intermediate portion of the main body hole portion 38a. Although the piston portion 84a is provided integrally with the motor output shaft 29a, the piston portion may be configured separately from the motor output shaft and fixed to the motor output shaft.

The outer diameter of the piston portion 84a is smaller than the inner diameter of the main body hole portion 38a of the cylinder hole 37a. Therefore, a radial gap 87a is provided over the entire circumference between the outer peripheral surface of the piston portion 84a and the inner peripheral surface of the main body hole portion 38a. In this example, the size of the radial gap 87a is set sufficiently small so that the outer peripheral surface of the piston portion 84a and the inner peripheral surface of the main body hole portion 38a do not interfere with each other even when the worm 19a swings. ing.

The viscous fluid 105 is filled (enclosed) in the cylinder hole 37a. In this example, the viscous fluid 105 is filled in the peripheral portion of the piston portion 84a (including the radial gap 87a) and the portion between the end surface of the piston portion 84a on the other side in the axial direction and the bottom surface of the cylinder hole 37a. There is.

Also in the case of this example, as the viscous fluid 105, a grease composed of a base oil having a kinematic viscosity of 150 mm ² / s or more, preferably 200 mm ² / s or more, a thickener, and an additive is used. is doing.

In this example as described above, the damper mechanism 21a for damping the axial displacement of the worm 19a is provided in the bottomed cylinder hole 37a opened in the base end surface of the worm 19a, and the piston portion provided in the motor output shaft 27a. It is configured by inserting 84a and filling the cylinder hole 37a with the viscous fluid 105. Therefore, when the worm 19a is displaced relative to the worm accommodating portion 23 in the axial direction based on the axially exciting force acting on the worm 19a when traveling on a rough road, the worm 19a is affected by the pumping action. Axial displacement can be sufficiently damped.

The motor output shaft 27a constituting the electric motor 17a is also rotatably supported by a rolling bearing (not shown) having backlash in the axial direction, similarly to the worm 19a. However, since the motor output shaft 27a is integrally configured with a rotor having a large mass and a magnetic attraction force by a magnet acts on the rotor, the motor output shaft 27a is more axial than the worm 19a. It has a large resistance to displacement. Therefore, by using the piston portion 84a provided at the tip of the motor output shaft 27a, a sufficient damping force can be applied to the worm 19a.

Further, in this example, the motor output shaft 29a provided with the piston portion 84a and the worm 19a provided with the cylinder hole 37a are connected via the torque transmission joint 42, and the motor output shaft 29a and the worm 19a are connected to each other. Substantially no relative rotation. Therefore, even when the outer diameter of the total length of the piston portion 84a is increased, torque loss due to the shear resistance of the viscous fluid 105 or the like can be prevented. Therefore, the degree of freedom in designing the piston portion 84a can be improved.

Further, the distance from the swing center of the worm 19a to the damper mechanism 21a can be made smaller than that of the structure of the first example of the embodiment. Therefore, the size of the radial gap 87a can be made smaller than that of the structure of the first example of the embodiment. Therefore, the damping force generated by the damper mechanism 21a can be increased.
Other configurations and actions and effects are the same as those of the first embodiment.

As a modification of this example, a cylinder hole is provided at the tip of the motor output shaft so as to open at the tip surface of the motor output shaft, and the piston portion extends from the base end surface of the worm toward one side in the axial direction. You can also prepare to do so.

[Third example of the embodiment]
A third example of the embodiment will be described with reference to FIG. In this example, the same components as those of the first and second examples of the embodiment are designated by the same reference numerals as those of the first and second examples of the embodiment, and detailed description thereof will be omitted. ..

The motorized worm reducer 15b of this example is provided with two damper mechanisms for attenuating the axial displacement of the worm 19b. That is, in this example, a damper mechanism 21 having the same configuration as that of the first embodiment is provided between the worm 19b and the urging member 20, and between the worm 1b and the electric motor 17a. A damper mechanism 21a having the same configuration as that of the second embodiment is provided.

In this example as described above, since each of the damper mechanisms 21 and 21a capable of attenuating the axial displacement of the worm 19b is provided, the axial displacement of the worm 19b can be sufficiently attenuated. Further, since the two damper mechanisms 21 and 21a are provided, the respective damper mechanisms 21 and 21a are miniaturized as compared with the structures of the first and second examples of the embodiment having only one damper mechanism. You can also do it.
Other configurations and actions and effects are the same as those of the first and second embodiments of the embodiment.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto and can be appropriately modified without departing from the technical idea of the present invention.

For example, when the present invention is carried out, the shape and size of the cylinder hole (inner diameter dimension, axial dimension), the shape and size of the piston portion (outer diameter dimension, axial dimension), the viscosity of the viscous fluid, etc. Is not limited to the structure of each example of the embodiment, and can be appropriately changed.

The electric assist device of the present invention is not limited to the column assist type electric power steering device, and can be incorporated into an electric power steering device having various structures.

Further, the worm reducer with a motor of the present invention can be incorporated not only in an electric assist device but also in various mechanical devices.

1 Electric power steering device 2 Steering wheel 3 Steering shaft 4 Steering column 5a, 5b Flexible joint 6 Intermediate shaft 7 Steering gear unit 8 Tie rod 9 Electric assist device 10 Torsion bar 11 Output shaft 12a, 12b Rolling bearing 13 Input shaft 14 Torque sensor 15 , 15a, 15b Worm reducer with motor 16 Housing 17, 17a Electric motor 18 Warm wheel 19, 19a, 19b Warm 20 Bouncer 21, 21a Damper mechanism 22 Wheel accommodating part 23 Warm accommodating part 24 Fitting surface part 25 Step surface 26 Guide holding part 27 Inward flange part 29, 29a Motor output shaft 30 Wheel tooth 31 Inner wheel member 32 Outer wheel member 33 Warm tooth 34 1st support shaft part 35 2nd support shaft part 36 Outward flange part 37, 37a Cylinder hole 38, 38a Main body hole 39, 39a Conical hole 40 1st bearing 41 2nd bearing 42 Torque transmission joint 43 Inner ring 44 Outer ring 45 Rolling element 46 Inner ring 47 Outer ring 48 Ball 49a, 49b Elastic spacer 50 Stop ring 51 Drive side transmission member 52 Drive side transmission member 53 Guide member 54 Elastic ring 55 1st elastic member 56 2nd elastic member 57 3rd elastic member 58 Bearing holder 59 Guide body 60 Lid 61 Large diameter cylinder 62 Small diameter cylinder 63 Side wall 64 Distal Side part Cylindrical surface part 65 First elastic member holding recess 66 Second elastic member holding recess 67 Pedestal surface part 68 Distal side protruding part 69 Holding surface part 70 Convex part 71 Proximal side protruding part 72 Proximal side part Cylindrical surface part 73 Holding surface part 74 Third elastic member holding part 75 Engagement convex part 76 Locking groove 77 Inclined surface part 78 First engagement notch part 79 Second engagement notch part 80 Inward flange part 81 Small diameter part 82 Large diameter part 83 Concave groove 84, 84a Piston part 85 Piston rod 86 Piston body 87, 87a Radial gap 88 Covered cylinder part 89 Squeezing cylinder part 90 Circular space 91 Stop ring 92 Locking plate part 93 Pressing plate part 94 Connection plate part 95 Bent plate part 96 Holding piece 97 Partial Cylindrical part 98 1st engaging piece 99 2nd engaging piece 100 Elastic deformation part 101 Held part 102 Convex part 103 Concave part 104 Elastic protrusion 105 Viscous fluid 106 Elastic member

Claims (4)

A housing having a wheel accommodating portion and a worm accommodating portion arranged at a twisted position with respect to the wheel accommodating portion and having an axial middle portion open to the wheel accommodating portion.
A worm wheel that has wheel teeth on the outer peripheral surface and is rotatably supported inside the wheel housing.
A worm having worm teeth that mesh with the wheel teeth on the outer peripheral surface and rotatably supported inside the worm housing portion and capable of axially relative displacement with respect to the worm housing portion.
An electric motor having a motor output shaft connected to the base end of the worm so as to be able to swing the worm.
A damper mechanism for attenuating the axial displacement of the worm is provided.
The damper mechanism has a piston portion inserted into the cylinder hole and a viscosity filled in the cylinder hole through a gap that allows the worm to swing between the cylinder hole and the inner surface of the cylinder hole. Has fluid and
The cylinder hole is provided in one of the worm and one of the members arranged around the housing or the tip of the worm and fixed to the housing.
The piston portion is provided on the other of the worm and a member of the housing or a member arranged around the tip of the worm and fixed to the housing.
Warm reducer with motor. The worm reducer with a motor according to claim 1, wherein the member arranged around the tip of the worm is a urging member that urges the tip of the worm toward the side of the worm wheel. A housing having a wheel accommodating portion and a worm accommodating portion arranged at a twisted position with respect to the wheel accommodating portion and having an axial middle portion open to the wheel accommodating portion.
A worm wheel that has wheel teeth on the outer peripheral surface and is rotatably supported inside the wheel housing.
A worm having worm teeth that mesh with the wheel teeth on the outer peripheral surface and rotatably supported inside the worm housing portion and capable of axially relative displacement with respect to the worm housing portion.
An electric motor having a motor output shaft connected to the base end of the worm so as to be able to swing the worm.
A damper mechanism for attenuating the axial displacement of the worm is provided.
The damper mechanism has a piston portion inserted into the cylinder hole and a viscosity filled in the cylinder hole through a gap that allows the worm to swing between the cylinder hole and the inner surface of the cylinder hole. Has fluid and
The cylinder hole is provided in one of the worm and the motor output shaft.
The piston portion is provided on the other of the worm and the motor output shaft.
Warm reducer with motor. A torque sensor for detecting the torque input to the steering shaft, and
It is equipped with a worm reducer with a motor that applies torque to the rotating shaft that rotates with the rotation of the steering wheel or the linear motion shaft that constitutes the steering gear unit.
The electric assist device, wherein the worm reducer with a motor is the worm reducer with a motor according to any one of claims 1 to 3.

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