Electric power steering apparatus and method for manufacturing the same

Abstract

To provide an electric power steering device that is able to minimize a variation width of resistance force to linear motion of a rack shaft in an axial direction.SOLUTION: The respective center axes of a steering-side pinion shaft 10 and an assist-side pinion shaft 13 swing and rotate in accordance with rotation. A phase difference between a rotation angle of the steering-side pinion shaft 10 based on a rotation position at which a frictional force acting between an outer peripheral surface of a rack shaft 11 and a pressing part of a steering-side rack guide is maximum in one rotation of the steering-side pinion shaft 10 and a rotation angle of the assist-side pinion shaft 13 based on a rotation position at which a frictional force acting between the outer peripheral surface of the rack shaft 11 and a pressing part of an assist-side rack guide 37 is maximum in one rotation of the assist-side pinion shaft 13 falls within a predetermined angle range.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a dual pinion type electric power steering device and a method for manufacturing the same.

Background Art

[0002] An automobile steering device transmits the rotation of a steering wheel rotated by a driver to a steering side pinion shaft of a steering gear unit via a steering shaft, an intermediate shaft, etc., and further converts the rotational motion of the steering side pinion shaft into a linear motion of a rack shaft of the steering gear unit that meshes with the steering side pinion shaft, and is configured to apply a steering angle to the left and right steering wheels based on this.

[0003] In the field of steering devices, electric power steering devices configured to apply an assist driving force to a steering force transmission path are widespread in order to reduce the force required for rotating the steering wheel. There are various types of electric power steering devices in which the method of applying the assist driving force to the steering force transmission path is different.

[0004] Among these, in a dual pinion type electric power steering device, as described in, for example, Japanese Patent Application Laid-Open No. 2002-154442 (Patent Document 1), as a pinion shaft that meshes with a rack shaft, in addition to a steering side pinion shaft, an assist side pinion shaft is provided. That is, the rack shaft has a steering side rack on a part of the circumferential direction of the outer peripheral surface of one end portion in the axial direction and an assist side rack on a part of the circumferential direction of the outer peripheral surface of the other end portion in the axial direction, and both end portions in the axial direction are connected to the steering wheels. The steering side pinion shaft has a steering side pinion that meshes with the steering side rack on the outer peripheral surface, and is rotationally driven by the rotation operation of the steering wheel. The assist side pinion shaft has an assist side pinion that meshes with the assist side rack on the outer peripheral surface, and is rotationally driven by an electric motor. During the driving of an automobile, by applying an assist driving force from the electric motor to the rack shaft via the assist side pinion shaft, the force required for the rotation operation of the steering wheel is reduced.

[0005] Furthermore, a dual pinion type electric power steering apparatus usually includes a steering side rack guide and an assist side rack guide. The steering side rack guide is disposed at a position sandwiching the rack shaft between the steering side pinion shaft, and elastically presses the outer peripheral surface of the rack shaft toward the steering side pinion shaft. Thereby, by reducing the backlash at the meshing portion between the steering side pinion and the steering side rack, generation of abnormal noise at these meshing portions is suppressed. The assist side rack guide is disposed in the same manner as the steering side rack guide and acts in the same manner.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The steering side pinion shaft and the assist side pinion shaft are usually heat-treated such as quenching and tempering in order to increase their strength. The steering side pinion shaft and the assist side pinion shaft may be slightly bent about the central axis due to the heat treatment. In this case, when the steering side pinion shaft and the assist side pinion shaft rotate as the steering wheel is rotated, the central axes of the steering side pinion shaft and the assist side pinion shaft swing. Along with this, the distance from the central axis of the rack shaft to the central axis of the steering side pinion shaft or the central axis of the assist side pinion shaft varies periodically.

[0008] When the distance from the central axis of the rack shaft to the central axis of the steering side pinion shaft or the assist side pinion shaft varies periodically as the steering side pinion shaft or the assist side pinion shaft rotates, accordingly, the amount by which the steering side pinion shaft or the assist side pinion shaft presses the steering side rack guide or the assist side rack guide via the rack shaft varies periodically. As a result, the amount of elastic deformation of the elastic member for elastically pressing the steering side rack guide or the assist side rack guide against the outer peripheral surface of the rack shaft toward the steering side pinion shaft, that is, the pressing force, varies periodically. And accordingly, the frictional force F1 acting on the contact portion between the outer peripheral surface of the rack shaft and the pressing portion of the steering side rack guide, or the frictional force F2 acting on the contact portion between the outer peripheral surface of the rack shaft and the pressing portion of the assist side rack guide varies periodically (see FIGS. 9(a) and 9(b)). These frictional forces F1 and F2 serve as a resistance force against the linear motion of the rack shaft in the axial direction.

[0009] For this reason, when the phases of the peak positions of the two frictional forces F1 and F2 that each vary periodically coincide with each other in a state where the electric power steering device is assembled, the variation width of the resultant force (F1 + F2) of the two frictional forces F1 and F2 against the linear motion of the rack shaft in the axial direction becomes large (see FIG. 9(c)). The increase in the variation width of the resultant force (F1 + F2) may be disadvantageous in executing various controls related to the electric power steering device, such as the drive control of the electric motor that generates the assist driving force.

[0010] An object of the present invention is to provide an electric power steering device capable of suppressing a large variation width of the resistance force against the linear motion of the rack shaft in the axial direction, and a manufacturing method thereof.

Means for Solving the Problems

[0011] An electric power steering device according to an aspect of the present invention includes a rack shaft, a steering side pinion shaft, an assist side pinion shaft, a steering side rack guide, an assist side rack guide, and a housing.

[0012] The rack shaft has a steering-side rack on a circumferential part of the outer peripheral surface of one axial-side portion and an assist-side rack on a circumferential part of the outer peripheral surface of the other axial-side portion, and both axial-side end portions are connected to the steering wheels.

[0013] The steering-side pinion shaft has a steering-side pinion that meshes with the steering-side rack on its outer peripheral surface, and is rotationally driven by a rotational operation of the steering wheel.

[0014] The assist-side pinion shaft has an assist-side pinion that meshes with the assist-side rack on its outer peripheral surface, and is rotationally driven by an electric motor.

[0015] The steering-side rack guide is disposed at a position sandwiching the rack shaft between it and the steering-side pinion shaft, and has a pressing portion that elastically presses the outer peripheral surface of the rack shaft toward the steering-side pinion shaft.

[0016] The assist-side rack guide is disposed at a position sandwiching the rack shaft between it and the assist-side pinion shaft, and has a pressing portion that elastically presses the outer peripheral surface of the rack shaft toward the assist-side pinion shaft.

[0017] The housing has the rack shaft, the steering-side pinion shaft, the assist-side pinion shaft, the steering-side rack guide, and the assist-side rack guide assembled therein.

[0018] The center axes of the steering-side pinion shaft and the assist-side pinion shaft each wobble as they rotate. The cause of such wobbling of the center axis is mainly considered to be the bending of the center axis due to heat treatment, but it may also be other manufacturing errors or assembly errors.

[0019] Based on the rotational position at which the frictional force acting between the outer peripheral surface of the rack shaft and the pressing portion of the steering-side rack guide becomes maximum during one rotation of the steering-side pinion shaft, the rotational angle of the steering-side pinion shaft, and based on the rotational position at which the frictional force acting between the outer peripheral surface of the rack shaft and the pressing portion of the assist-side rack guide becomes maximum during one rotation of the assist-side pinion shaft, the phase difference between the rotational angles of the assist-side pinion shaft is within a predetermined angle range. In other words, by providing a phase difference between the frictional force acting between the outer peripheral surface of the rack shaft and the pressing portion of the steering-side rack guide and the frictional force acting between the outer peripheral surface of the rack shaft and the pressing portion of the assist-side rack guide, it is possible to prevent the peak of the frictional force on the steering side and the peak of the frictional force on the assist side from coinciding. That is, in the operating state, when the steering wheel is rotated, accordingly, the rotational angle of the steering-side pinion shaft and the rotational angle of the assist-side pinion shaft change, but regardless of the amount of rotation operation of the steering wheel, the phase difference between the rotational angle of the steering-side pinion shaft and the rotational angle of the assist-side pinion shaft always remains within a predetermined angle range.

[0020] In the electric power steering apparatus according to one aspect of the present invention, the predetermined angle range is in the range of 90° or more and 270° or less. The predetermined angle range is preferably in the range of 120° or more and 240° or less, and more preferably in the range of 135° or more and 225° or less.

[0021] In the electric power steering apparatus according to one aspect of the present invention, on at least one of the steering-side pinion shaft and the assist-side pinion shaft and / or a member that rotates integrally with the shaft, a shaft-side mark capable of confirming the rotational angle of the shaft is provided. Note that the member that rotates integrally with the shaft can adopt various members regardless of its type, for example, a worm wheel, an inner ring constituting a rolling bearing, a retaining ring, a nut, a spacer, and the like.

[0022] In the electric power steering apparatus according to one aspect of the present invention, in the shaft with the shaft-side mark and / or the member that rotates integrally with the shaft, the shaft-side mark is provided at a circumferential position where the radius of the wobbling accompanying rotation is maximum or minimum.

[0023] In the electric power steering apparatus according to one aspect of the present invention, a housing-side mark whose positional relationship with the shaft-side mark changes as the shaft with the shaft-side mark and / or the member that rotates integrally with the shaft rotates is provided on the housing.

[0024] A method for manufacturing an electric power steering apparatus according to one aspect of the present invention is directed to manufacturing the electric power steering apparatus according to one aspect of the present invention. For each of the steering-side pinion shaft and the assist-side pinion shaft, a circumferential position where the radius of the wobbling accompanying rotation is maximum or minimum is detected, and the shaft-side mark is attached to the shaft and / or the member that rotates integrally with the shaft at the detected circumferential position. While confirming the rotation angle of the steering-side pinion shaft by the shaft-side mark attached to the steering-side pinion shaft and / or the member that rotates integrally with the shaft, the steering-side pinion shaft is assembled to the housing, and the steering-side pinion is meshed with the steering-side rack. And while confirming the rotation angle of the assist-side pinion shaft by the shaft-side mark attached to the assist-side pinion shaft and / or the member that rotates integrally with the shaft, the assist-side pinion shaft is assembled to the housing, and the assist-side pinion is meshed with the assist-side rack.

[0025] A method for manufacturing an electric power steering apparatus according to one aspect of the present invention is directed to manufacturing the electric power steering apparatus according to one aspect of the present invention. For the steering-side pinion shaft, a circumferential position where the radius of the wobbling accompanying rotation is maximum or minimum is detected, and the shaft-side mark is attached to the shaft and / or the member that rotates integrally with the shaft at the detected circumferential position. With the assist side pinion shaft assembled to the housing and the assist side pinion meshed with the assist side rack, while rotationally driving the assist side pinion shaft at a constant speed by the electric motor, torque for the rotational drive is measured to detect a rotational position at which the torque becomes minimum or maximum during one rotation of the assist side pinion shaft, and the rotation of the assist side pinion shaft is stopped at the rotational position. A step of assembling the steering side pinion shaft to the housing and meshing the steering side pinion with the steering side rack while checking the rotation angle of the steering side pinion shaft by the shaft side mark attached to the steering side pinion shaft and / or the member that rotates integrally with the shaft.

Advantages of the Invention

[0026] According to one aspect of the present invention, it is possible to provide an electric power steering device capable of suppressing a fluctuation range of resistance against linear movement of a rack shaft in an axial direction, and a manufacturing method thereof.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Embodiment for Carrying out the Invention

[0028] [First Example] The first example of the embodiment of the present invention will be described with reference to Figures 1 to 13.

[0029] In the following description, the front-rear direction means the front-rear direction of the vehicle, the up-down direction means the up-down direction of the vehicle, and the left-right direction means the width direction of the vehicle. The left-right direction coincides with the axial direction of the rack shaft 11 and the rack housing 14 described later. One side with respect to the axial direction of the rack shaft 11 and the rack housing 14 is the left side in Figures 1, 3, 4, and 7, and the other side with respect to the axial direction of the rack shaft 11 and the rack housing 14 is the right side in Figures 1, 3, 4, and 7.

[0030] The electric power steering apparatus 1 of this example is of a dual pinion type. That is, the electric power steering apparatus 1 of this example includes one rack shaft 11, a steering side pinion shaft 10, and an assist side pinion shaft 13, and is an electric power steering apparatus of a type in which steering force is input from the steering side pinion shaft 10 to the rack shaft 11 and assist driving force is input from the assist side pinion shaft 13 to the rack shaft 11. The electric power steering apparatus 1 of this example includes a steering side rack guide 24 for reducing the backlash at the meshing portion between the rack shaft 11 and the steering side pinion shaft 10, an assist side rack guide 37 for reducing the backlash at the meshing portion between the rack shaft 11 and the assist side pinion shaft 13, and a housing 7 to which the rack shaft 11, the steering side pinion shaft 10, the assist side pinion shaft 13, the steering side rack guide 24, and the assist side rack guide 37 are assembled.

[0031] As shown in Fig. 1, the electric power steering apparatus 1 of this example 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, a housing 7 (not shown in Fig. 1, see Fig. 2), a steering mechanism unit 8, and an assist mechanism unit 9.

[0032] 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 to rotate is attached to the rear end of the steering shaft 3. The front end of the steering shaft 3 is connected to a steering-side pinion shaft 10 that constitutes the steering mechanism unit 8 via the universal joint 5a, the intermediate shaft 6, and another universal joint 5b. For this reason, the rotational movement of the steering wheel 2 is transmitted to the steering-side pinion shaft 10. The rotational movement of the steering-side pinion shaft 10 is converted into a linear movement in the axial direction of a rack shaft 11 that constitutes the steering mechanism unit 8. Thereby, a steering angle corresponding to the amount of rotational operation of the steering wheel 2 is imparted to the left and right steering wheels 12. The electric power steering apparatus 1 reduces the steering force required for the driver to rotate the steering wheel 2 by applying an assist driving force to the rack shaft 11 via an assist-side pinion shaft 13 that constitutes the assist mechanism unit 9.

[0033] In this example, the housing 7 is a casting integrally formed by die-casting a light alloy such as an aluminum alloy and is fixed to the vehicle body. When implementing the present invention, the housing can also be configured by coupling and fixing a plurality of components to each other. In this example, as shown in Fig. 2, the housing 7 includes a rack housing portion 14, a steering-side pinion housing portion 15, an assist-side pinion housing portion 16, a steering-side guide housing portion 17, an assist-side guide housing portion 18, a gear housing portion 19, and a plurality of attachment portions 20a and 20b.

[0034] The rack housing portion 14 is a portion that houses an intermediate portion in the axial direction of the rack shaft 11 that constitutes the steering mechanism unit 8, has a cylindrical shape, and extends in the left-right direction.

[0035] The steering side pinion housing portion 15 is a portion that houses the front half portion of the steering side pinion shaft 10, and is disposed at a circumferential part of one axial side portion of the rack housing portion 14. More specifically, the steering side pinion housing portion 15 is disposed at the front side portion of one axial side portion of the rack housing portion 14, and has a bottomed cylindrical shape with only the upper end portion being open. The steering side pinion housing portion 15 is disposed in a twisted positional relationship with respect to the rack housing portion 14. That is, the central axis of the steering side pinion housing portion 15 and the central axis of the rack housing portion 14 are in a twisted positional relationship. When viewed from the front-rear direction which is a direction orthogonal to both the central axis of the rack housing portion 14 and the central axis of the steering side pinion housing portion 15, the central axis of the steering side pinion housing portion 15 is not disposed in a direction orthogonal to the central axis of the rack housing portion 14, but is inclined with respect to the orthogonal direction. The internal space of the steering side pinion housing portion 15 communicates with the internal space of the rack housing portion 14.

[0036] The assist side pinion housing portion 16 is a portion that houses the assist side pinion shaft 13, and is disposed at a circumferential part of the other axial side portion of the rack housing portion 14. More specifically, in this example, the assist side pinion housing portion 16 is disposed at the front side portion of the other axial side portion of the rack housing portion 14, and has a cylindrical shape with both upper and lower end portions being open. The assist side pinion housing portion 16 is disposed in a twisted positional relationship with respect to the rack housing portion 14. That is, the central axis of the assist side pinion housing portion 16 and the central axis of the rack housing portion 14 are in a twisted positional relationship. When viewed from the front-rear direction which is a direction orthogonal to both the central axis of the rack housing portion 14 and the central axis of the assist side pinion housing portion 16, the central axis of the assist side pinion housing portion 16 is not disposed in a direction orthogonal to the central axis of the rack housing portion 14, but is inclined with respect to the orthogonal direction. The internal space of the assist side pinion housing portion 16 communicates with the internal space of the rack housing portion 14. When implementing the present invention, it is also possible to dispose the central axis of the assist side pinion housing portion in a direction orthogonal to the central axis of the rack housing portion.

[0037] The steering-side guide housing portion 17 is a portion that houses the steering-side rack guide 24, which will be described later. It is arranged in a portion of the rack housing portion 14 that is on the diametrically opposite side of the steering-side pinion housing portion 15. That is, in this example, the steering-side guide housing portion 17 is arranged in the rear portion of the rack housing portion 14 at the same axial position as the steering-side pinion housing portion 15. The steering-side guide housing portion 17 has a cylindrical shape and extends in the radial direction centered on the central axis of the rack housing portion 14. That is, in this example, the steering-side guide housing portion 17 extends in the front-rear direction. The internal space of the steering-side guide housing portion 17 also communicates with the internal space of the rack housing portion 14.

[0038] The assist-side guide housing portion 18 is a portion that houses the assist-side rack guide 37, which will be described later. It is arranged in a portion of the rack housing portion 14 that is on the diametrically opposite side of the assist-side pinion housing portion 16. That is, in this example, the assist-side guide housing portion 18 is arranged in the rear portion of the rack housing portion 14 at the same axial position as the assist-side pinion housing portion 16. The assist-side guide housing portion 18 has a cylindrical shape and extends in the radial direction centered on the central axis of the rack housing portion 14. That is, in this example, the assist-side guide housing portion 18 extends in the front-rear direction. The internal space of the assist-side guide housing portion 18 also communicates with the internal space of the rack housing portion 14.

[0039] The gear housing portion 19 is a portion that houses the worm reducer 38, which will be described later, and constitutes the assist mechanism portion 9. It includes a worm housing portion 21 and a wheel housing portion 22.

[0040] The wheel housing portion 22 is a portion that houses the worm wheel 50 that constitutes the worm reducer 38. It is arranged adjacent to the assist-side pinion housing portion 16 in the axial direction. Specifically, in this example, the wheel housing portion 22 is arranged above the assist-side pinion housing portion 16. The wheel housing portion 22 has a substantially cylindrical shape and is arranged coaxially with the assist-side pinion housing portion 16.

[0041] The worm housing 21 is a part that houses the worm 49 that constitutes the worm speed reducer 38, and is arranged in a part of the circumferential direction of the wheel housing 22. Specifically, in this example, the worm housing 21 is arranged at the front side part of the wheel housing 22. The worm housing 21 has a bottomed cylindrical shape, and in this example, has an opening at one end with respect to the axial direction of the rack housing 14. The worm housing 21 has a mounting flange 23 that protrudes radially outward at the end on the opening side, that is, at one end with respect to the axial direction of the rack housing 14. The internal space of the worm housing 21 and the internal space of the wheel housing 22 communicate with each other.

[0042] The plurality of mounting parts 20a, 20b are used to fix the housing 7 to the vehicle body. In this example, the plurality of mounting parts 20a, 20b are composed of two mounting parts 20a arranged at the front sides of both ends in the axial direction of the rack housing 14, and two mounting parts 20b arranged at the rear side of the intermediate part in the axial direction of the rack housing 14. The housing 7 is fixed to the vehicle body by using fixing members such as bolts and studs inserted through each of the mounting parts 20a, 20b.

[0043] The steering mechanism part 8 has a steering side pinion shaft 10, a rack shaft 11, and a steering side rack guide 24, and converts the rotational motion of the steering wheel 2 into a linear motion in the axial direction of the rack shaft 11.

[0044] The steering side pinion shaft 10 is a shaft member made of metal such as carbon steel. As shown in FIGS. 1 and 5, the steering side pinion shaft 10 has a steering side pinion 25 that meshes with the steering side rack 28 of the rack shaft 11 on the outer peripheral surface of the front half part.

[0045] The steering-side pinion shaft 10 is rotatably supported inside the steering-side pinion housing 15 by means of bearings 26a and 26b. More specifically, the steering-side pinion shaft 10 has portions located on both axial sides of the steering-side pinion 25 rotatably supported by the bearings 26a and 26b with respect to the steering-side pinion housing 15. The central axis of the steering-side pinion shaft 10 is arranged substantially coaxially with the central axis of the steering-side pinion housing 15. The steering-side pinion shaft 10 is connected to the steering wheel 2 via flexible joints 5a, 5b, an intermediate shaft 6, etc., and is rotationally driven by the rotational operation of the steering wheel 2. The rotational movement of the steering-side pinion shaft 10 is converted into the linear movement of the rack shaft 11, and pushes and pulls tie rods 27 connected to both axial ends of the rack shaft 11. Thereby, a steering angle is imparted to the left and right steering wheels 12.

[0046] The rack shaft 11 is a rod-shaped member made of metal such as carbon steel. The rack shaft 11 is arranged with its axial direction oriented in the left-right direction. As shown in FIGS. 6 and 7, the rack shaft 11 has a steering-side rack 28 that meshes with the steering-side pinion 25 of the steering-side pinion shaft 10 on a circumferential part of the outer peripheral surface of one axial-side portion, and an assist-side rack 29 that meshes with the assist-side pinion 41 of the assist-side pinion shaft 13 on a part of the outer peripheral surface of the other axial-side portion. In this example, the phases of the arrangements of the steering-side rack 28 and the assist-side rack 29 with respect to the circumferential direction of the rack shaft 11 are equal to each other. Specifically, in this example, the steering-side rack 28 and the assist-side rack 29 are arranged on the front side surface of the rack shaft 11. However, when implementing the present invention, the phases of the arrangements of the steering-side rack 28 and the assist-side rack 29 with respect to the circumferential direction of the rack shaft 11 can also be made different from each other. The rack shaft 11 has threaded holes 30 that open to the axial end faces at both axial ends.

[0047] The rack shaft 11 is supported inside the rack housing portion 14 so as to be reciprocally movable in the axial direction with both end portions on both sides in the axial direction protruding from the openings on both sides in the left-right direction of the rack housing portion 14. Both end portions on both sides in the axial direction of the rack shaft 11 are connected to the tie rod 27 via the spherical joints 31. That is, male screw portions 32 provided at the base portions of the spherical joints 31 are screwed into screw holes 30 provided at both end portions on both sides in the axial direction of the rack shaft 11, and the base end portions of the tie rod 27 are swingably supported at the tip end portions of the spherical joints 31. The rack shaft 11 is connected to the left and right steering wheels 12 via a link mechanism including the spherical joints 31 and the tie rod 27.

[0048] The steering-side rack guide 24 is disposed at a position sandwiching the rack shaft 11 between the steering-side pinion shaft 10, and in this example, it is disposed inside the steering-side guide housing portion 17. The steering-side rack guide 24 in this example is a sliding-type rack guide as shown in FIGS. 3 and 5, and includes a pad 33 and an elastic member 34.

[0049] The pad 33 has a substantially cylindrical shape and is disposed inside the steering-side guide housing portion 17 so as to be movable closer to and farther from the rack shaft 11. The pad 33 has a pressing surface 35 having a concave cylindrical surface shape that matches the rear surface of the rack shaft 11 on the surface facing the convex cylindrical surface-shaped rear surface of the rack shaft 11. The pressing surface 35, which is a pressing portion, is made of a synthetic resin or the like having excellent slidability. The elastic member 34 is a torsion coil spring in the illustrated example, and is sandwiched between the pad 33 and a steering-side cap 36 that closes the opening of the steering-side guide housing portion 17 in an elastically compressed state. Thereby, the elastic member 34 presses the pad 33 toward the rack shaft 11.

[0050] The steering-side rack guide 24 reduces the backlash at the meshing portion between the steering-side pinion 25 and the steering-side rack 28 by pressing elastically based on the elastic force of the elastic member 34 with the rear surface, which is the outer peripheral surface of the rack shaft 11, facing the steering-side pinion shaft 10. Thereby, generation of abnormal noise at the meshing portion between the steering-side pinion 25 and the steering-side rack 28 is suppressed.

[0051] The assist mechanism unit 9 reduces the steering force required for the driver to rotate the steering wheel 2 by applying an assist driving force to the rack shaft 11. The assist mechanism unit 9 includes an assist side pinion shaft 13, an assist side rack guide 37, a worm reducer 38, an electric motor 39, and a torque sensor 40.

[0052] The assist side pinion shaft 13 is a shaft member made of metal such as carbon steel. As shown in FIGS. 1 and 8, the assist side pinion shaft 13 has an assist side pinion 41 that meshes with the assist side rack 29 of the rack shaft 11 on the outer peripheral surface of the front half portion.

[0053] The assist side pinion shaft 13 is rotatably supported inside the assist side pinion housing portion 16 by using bearings 42a and 42b. More specifically, the assist side pinion shaft 13 is rotatably supported with respect to the assist side pinion housing portion 16 by the bearings 42a and 42b at portions located on both axial sides of the assist side pinion 41. The central axis of the assist side pinion shaft 13 is disposed substantially coaxially with the central axis of the assist side pinion housing portion 16. The assist side pinion shaft 13 is rotationally driven by the electric motor 39 via the worm reducer 38. In this example, the opening portion of the assist side pinion housing portion 16 on the side opposite to the wheel housing portion 22 in the axial direction is closed by a cap 51.

[0054] The assist side rack guide 37 is disposed at a position sandwiching the rack shaft 11 between the assist side pinion shaft 13, and in this example, is disposed inside the assist side guide housing portion 18. As shown in FIGS. 4 and 8, the assist side rack guide 37 is a rolling type rack guide and has a roller 43, a holder 44, a pin 45, a rolling bearing 46, and an elastic member 47.

[0055] The roller 43 has a substantially annular shape and is rotatably supported with respect to the holder 44 via a pin 45 and a rolling bearing 46 arranged with the axial direction facing the vertical direction. As a result, the outer peripheral surface of the roller 43, which is a pressing portion, is in rolling contact with the middle portion in the width direction of the rear side surface of the rack shaft 11. The outer peripheral surface of the roller 43 has a concave arc-shaped generatrix shape that substantially conforms to the contour shape of the rear side surface of the rack shaft 11. The holder 44 is arranged inside the assist-side guide housing portion 18 so as to be able to move closer to and farther from the rack shaft 11. The elastic member 47 is a disc spring in the illustrated example and is arranged between the holder 44 and an assist-side cap 48 that closes the opening of the assist-side guide housing portion 18. The elastic member 47 presses the holder 44 toward the rack shaft 11.

[0056] The assist-side rack guide 37 faces the rear side surface, which is the outer peripheral surface of the rack shaft 11, toward the assist-side pinion shaft 13 and elastically presses it based on the elastic force of the elastic member 47, thereby reducing the backlash at the meshing portion between the assist-side pinion 41 and the assist-side rack 29. Thereby, generation of abnormal noise is suppressed at the meshing portion between the assist-side pinion 41 and the assist-side rack 29.

[0057] As shown in FIG. 8, the worm reducer 38 includes a worm 49 and a worm wheel 50, decelerates the rotation of the electric motor 39, that is, increases the driving torque of the electric motor 39, and transmits it to the assist-side pinion shaft 13.

[0058] The worm 49 has worm teeth on its outer peripheral surface and is rotatably supported inside the worm housing portion 21. The base end portion of the worm 49 is connected to the motor output shaft of the electric motor 39 via a joint (not shown) or the like so as to enable torque transmission.

[0059] The worm wheel 50 has wheel teeth that mesh with the worm teeth on its outer peripheral surface and is disposed inside the wheel housing portion 22. The worm wheel 50 is non-rotatably externally fitted and fixed to the base end portion of the assist side pinion shaft 13. In this example, among the wheel housing portion 22, the opening on the side opposite to the assist side pinion housing portion 16 in the axial direction is closed by a cap 52.

[0060] The electric motor 39 is fixed to the mounting flange 23 of the worm housing portion 21.

[0061] The torque sensor 40 is disposed around the steering side pinion shaft 10 and detects the magnitude and direction of the torque input to the steering side pinion shaft 10. Thereby, the torque sensor 40 outputs a signal corresponding to the torque input to the steering side pinion shaft 10 to the electronic control unit of the electric motor 39. As the torque sensor 40, various torque sensors such as a non-contact torque sensor utilizing the magnetostrictive effect can be used.

[0062] The assist mechanism unit 9 drives and controls the electric motor 39 based on the output signal of the torque sensor 40. Thereby, the drive torque generated by the electric motor 39 is transmitted as an assist driving force to the rack shaft 11 via the worm reducer 38 and the assist side pinion shaft 13. As a result, the steering force required for the driver to rotate the steering wheel 2 is reduced.

[0063] The structure of this example includes a pair of rack bushes 53a and 53b (see FIGS. 3 and 4) that support the rack shaft 11 so that it can move axially without play with respect to the rack housing portion 14. These rack bushes 53a and 53b are made of synthetic resin such as polyacetal resin and polyamide resin, have a substantially cylindrical shape, and are fitted inside the vicinity of the openings on both axial sides of the rack housing portion 14. The rack bushes 53a and 53b support the outer peripheral surface of the rack shaft 11 so that it can slide axially. Note that the steering-side rack guide 24 that presses the rack shaft 11 is a sliding-type rack guide, and since it can sufficiently ensure the holding force in the width direction (vertical direction in FIG. 5) of the rack shaft 11, the rack bush 53a arranged on one axial side can be omitted.

[0064] The structure of this example includes annular spacers 54a and 54b that are fitted and fixed adjacent to the opening side with respect to the rack bushes 53a and 53b in positions near the openings on both axial sides of the rack housing portion 14. The spacers 54a and 54b are made of a material with higher strength than the synthetic resin that constitutes the rack bushes 53a and 53b.

[0065] In this example, the rack shaft 11 can be linearly moved axially within the range from the position where the annular abutting surface 55 facing the other axial side provided at the radially outer end of the spherical joint 31 on one axial side (see FIG. 3) abuts against the side surface on the one axial side of the spacer 54a on one axial side to the position where the annular abutting surface 55 facing the one axial side provided at the radially outer end of the spherical joint 31 on the other axial side (see FIG. 4) abuts against the side surface on the other axial side of the spacer 54b on the other axial side. In this example, by adjusting this range, the restricted range of the rotation operation amount of the steering wheel 2 is set. In this example, the restricted range is set to a range of approximately 1.5 rotations (540° in terms of rotation angle) on each of the one side and the other side from the neutral position of the steering wheel 2.

[0066] In this example, each of the steering side pinion shaft 10 and the assist side pinion shaft 13 is subjected to heat treatment such as quenching and tempering in order to enhance its strength. In this example, due to the heat treatment, the steering side pinion shaft 10 and the assist side pinion shaft 13 are slightly bent with respect to their respective central axes О1, O2 as exaggeratedly shown in Fig. 11.

[0067] Therefore, as the steering wheel 2 is rotated, when the steering side pinion shaft 10 and the assist side pinion shaft 13 rotate, the central axis O1 of the steering side pinion shaft 10 and the central axis O2 of the assist side pinion shaft 13 wobble. Along with this, the distance from the central axis of the rack shaft 11 to the central axis O1 of the steering side pinion shaft 10 or the central axis O2 of the assist side pinion shaft 13 varies periodically.

[0068] When the distance from the central axis of the rack shaft 11 to the central axis O1 of the steering side pinion shaft 10 or the central axis O2 of the assist side pinion shaft 13 varies periodically as the steering side pinion shaft 10 or the assist side pinion shaft 13 rotates, accordingly, the amount by which the steering side pinion shaft 10 or the assist side pinion shaft 13 presses the steering side rack guide 24 or the assist side rack guide 37 via the rack shaft 11 varies periodically. As a result, the elastic deformation amount of the elastic member 34 or the elastic member 47 for elastically pressing the steering side rack guide 24 or the assist side rack guide 37 against the outer peripheral surface of the rack shaft 11 toward the steering side pinion shaft 10 or the assist side pinion shaft 13, that is, the pressing force, varies periodically. And accordingly, the frictional force F1 acting on the contact portion between the outer peripheral surface of the rack shaft 11 and the pressing surface 35 which is the pressing portion of the steering side rack guide 24, or the frictional force F2 acting on the contact portion between the outer peripheral surface of the rack shaft 11 and the outer peripheral surface of the roller 43 which is the pressing portion of the assist side rack guide 37 varies periodically as shown in, for example, FIG. 9(a) or FIG. 9(b). These frictional forces F1 and F2 serve as a resistance to the linear motion of the rack shaft 11 in the axial direction. In this example, since the contact between the outer peripheral surface of the rack shaft 11 and the pressing surface 35 of the steering side rack guide 24 is a sliding contact and the contact portion between the outer peripheral surface of the rack shaft 11 and the outer peripheral surface of the roller 43 of the assist side rack guide 37 is a rolling contact, the value at the peak position of the frictional force F2 is smaller than the value at the peak position of the frictional force F1.

[0069] As described above, since the two frictional forces F1 and F2 vary periodically, in the state where the electric power steering apparatus 1 is assembled, when the phases of the peak positions of the two frictional forces F1 and F2 coincide with each other as shown in, for example, FIGS. 9(a) and 9(b), as shown in FIG. 9(c), the variation range of the resultant force (F1 + F2) of the two frictional forces F1 and F2 with respect to the linear motion of the rack shaft 11 in the axial direction becomes large. The fact that the variation range of the resultant force (F1 + F2) becomes large may be disadvantageous in executing various controls related to the electric power steering apparatus 1, such as the drive control of the electric motor 39 that generates the assist driving force.

[0070] Therefore, in this example, in the usage state, specifically within the limit range of the rotation operation amount of the steering wheel 2, a configuration is adopted in which the phases of the peak positions of the two frictional forces F1 and F2 that each vary periodically do not match. For this purpose, in this example, among one rotation of the steering-side pinion shaft 10, the rotation angle of the steering-side pinion shaft 10 based on the rotation position at which the frictional force F1 is maximum, and among one rotation of the assist-side pinion shaft 13, the rotation angle of the assist-side pinion shaft 13 based on the rotation position at which the frictional force F2 is maximum, a configuration is adopted in which the phase difference between them falls within a predetermined angle range. That is, in the usage state, when the steering wheel 2 is rotationally operated, accordingly, the rotation angle of the steering-side pinion shaft 10 and the rotation angle of the assist-side pinion shaft 13 change, but regardless of the rotation operation amount of the steering wheel 2, always, a configuration is adopted in which the phase difference between the rotation angle of the steering-side pinion shaft 10 and the rotation angle of the assist-side pinion shaft 13 falls within a predetermined angle range.

[0071] The predetermined angle range is preferably in the range of 90° or more and 270° or less, more preferably in the range of 120° or more and 240° or less, and even more preferably in the range of 135° or more and 225° or less. That is, the phase difference is most preferably 180°, and the closer to 180° the better. In this example, the phase difference is set to 180°.

[0072] Here, in this example, by adjusting the mutual relationship between the specifications such as the pitch circle diameter of the steering side pinion 25 on the steering side pinion shaft 10 and the specifications such as the pitch circle diameter of the assist side pinion 41 on the assist side pinion shaft 13, a configuration is adopted in which the rotation period of the steering side pinion shaft 10 and the rotation period of the assist side pinion shaft 13 are equal to each other. That is, in this example, when the steering side pinion shaft 10 makes one rotation, the assist side pinion shaft 13 also makes one rotation. For this reason, the periods of the two frictional forces F1 and F2 that vary periodically are equal to each other. Therefore, in this example, regardless of the amount of rotation operation of the steering wheel 2, the phase difference between the rotation angle of the steering side pinion shaft 10 and the rotation angle of the assist side pinion shaft 13 is substantially maintained at 180°.

[0073] In short, in this example, by setting the phase difference between the rotation angle of the steering side pinion shaft 10 and the rotation angle of the assist side pinion shaft 13 to 180°, as shown in FIGS. 10(a) and 10(b), the phase difference Δθ between the peak positions of the two frictional forces F1 and F2 is configured to be 180°, so that, as shown in FIG. 10(c), the variation range of the resultant force (F1 + F2) of the two frictional forces F1 and F2 is minimized.

[0074] In the structure of this example, shaft side marks SM1 and SM2 capable of confirming the rotation angles of the shafts 10 and 13 are attached to the steering side pinion shaft 10 and the assist side pinion shaft 13 respectively (see FIGS. 12(a) and 13). The shaft side marks SM1 and SM2 will be further described later.

[0075] Next, a method for manufacturing the electric power steering apparatus 1 by assembling the steering side pinion shaft 10 and the assist side pinion shaft 13 to the housing 7 as described above will be specifically described.

[0076] The manufacturing method of the electric power steering apparatus 1 in this example includes step A and step B. Step A is a step of detecting, for each of the steering side pinion shaft 10 and the assist side pinion shaft 13, the circumferential direction position where the radius of the wobbling accompanying rotation becomes maximum, and attaching shaft side marks SM1 and SM2 to the detected circumferential direction position. Step B is a step of assembling the steering side pinion shaft 10 to the housing 7 while confirming the rotation angle of the steering side pinion shaft 10 by the shaft side mark SM1 attached to the steering side pinion shaft 10, meshing the steering side pinion 25 with the steering side rack 28, and assembling the assist side pinion shaft 13 to the housing 7 while confirming the rotation angle of the assist side pinion shaft 13 by the shaft side mark SM2 attached to the assist side pinion shaft 13, and meshing the assist side pinion 41 with the assist side rack 29. In addition, when implementing the present invention, the shaft side mark SM1 can be attached to a member that rotates integrally with the steering side pinion shaft 10 in addition to or instead of the steering side pinion shaft 10, and the shaft side mark SM2 can be attached to a member that rotates integrally with the assist side pinion shaft 13 in addition to or instead of the assist side pinion shaft 13. Examples of these members include a worm wheel, an inner ring constituting a rolling bearing, a retaining ring, a nut, a spacer, and the like.

[0077] FIG. 11 is a schematic diagram for explaining step A of this example. In step A of this example, the same operation is performed for each of the steering side pinion shaft 10 and the assist side pinion shaft 13. Therefore, in the following description of step A of this example, the operation for the steering side pinion shaft 10 will be described as a representative. Also, in the following description of step A of this example, in FIG. 11 and FIG. 12, the names and symbols related to the assist side pinion shaft 13 are also simultaneously given in parentheses.

[0078] In step A of this example, a test device 56 as shown in FIG. 11 is used. The test device 56 includes a support pin 57, a rotor 58, a master gear 59, a support 61, a coil spring 62, and a linear gauge 63. The support pin 57 has a conical tip and supports the tip of the steering-side pinion shaft 10 (assist-side pinion shaft 13) in a state where it is inserted into a support hole formed in the end face (left end face in FIG. 11) of the steering-side pinion shaft 10 (assist-side pinion shaft 13) so as to enable rotation about its linear central axis Ca. The rotor 58 is arranged coaxially with the support pin 57 and rotates the steering-side pinion shaft 10 (assist-side pinion shaft 13) about the central axis Ca while gripping the base end portion (left end portion in FIG. 11) of the steering-side pinion shaft 10 (assist-side pinion shaft 13). The master gear 59 has a master pinion 60 on its outer peripheral surface that meshes with the steering-side pinion 25 (assist-side pinion 41) of the steering-side pinion shaft 10 (assist-side pinion shaft 13). The master pinion 60 of the master gear 59 meshes with the upper end portion of the steering-side pinion 25 (assist-side pinion 41) in FIG. 11. The support 61 rotatably supports the master gear 59. The master gear 59 and the support 61 are held by a fixture (not shown) so as to enable sliding movement in a direction perpendicular to the central axis Ca (vertical direction in FIG. 11). The coil spring 62 elastically presses the support 61 toward the steering-side pinion 25 (assist-side pinion 41). The linear gauge 63 can detect the amount of movement of the support 61 in a direction perpendicular to the central axis Ca (vertical direction in FIG. 11).

[0079] The test device 56 supports both ends of the steering side pinion shaft 10 (assist side pinion shaft 13) by support pins 57 and a rotor 58, and the rotor 58 rotates the steering side pinion shaft 10 (assist side pinion shaft 13) about the central axis Ca. Since the steering side pinion shaft 10 (assist side pinion shaft 13) is bent about its central axis O1 (O2), when the steering side pinion shaft 10 (assist side pinion shaft 13) rotates about the central axis Ca, the central axis O1 (O2) of the steering side pinion shaft 10 (assist side pinion shaft 13) swings around. Along with this, the master gear 59 reciprocates in the direction perpendicular to the central axis Ca (the vertical direction in FIG. 11) together with the support 61 while rotating about its own central axis.

[0080] FIGS. 11 and 12(a) show the state when the central axis O1 (O2) of the steering side pinion shaft 10 (assist side pinion shaft 13) moves to the upper end position due to the swinging around, and accordingly, the master gear 59 and the support 61 move to the position farthest from the central axis Ca. FIG. 12(b) shows the state when the central axis O1 (O2) of the steering side pinion shaft 10 (assist side pinion shaft 13) moves to the lower end position due to the swinging around, and accordingly, the master gear 59 and the support 61 move to the position closest to the central axis Ca.

[0081] In step A of this example, the steering side pinion shaft 10 (assist side pinion shaft 13) is rotated one or more revolutions (360°), and during that time, the rotational position when the master gear 59 and the support 61 move to the position farthest from the central axis Ca as shown in FIGS. 11 and 12(a) is specified as a specific rotational position, and the rotation of the steering side pinion shaft 10 (assist side pinion shaft 13) is stopped at that position. Then, the upper end position of the steering side pinion shaft 10 (assist side pinion shaft 13) at this stop position is detected as the circumferential direction position where the radius of the swinging around accompanying the rotation is maximum with respect to the steering side pinion shaft 10 (assist side pinion shaft 13).

[0082] In step A of this example, an axial mark SM1 (SM2) is attached to the circumferential position of the steering-side pinion shaft 10 (assist-side pinion shaft 13) so that the operator can visually confirm the circumferential position detected in this way. More specifically, in this example, as shown in Fig. 12(a), the axial mark SM1 (SM2) is attached to the circumferential position on the outer peripheral surface of the axial intermediate portion of the steering-side pinion shaft 10 (assist-side pinion shaft 13). The axial mark SM1 (SM2) can be attached in any manner such as ink marking or laser engraving. When implementing the present invention, the shape, size, color, etc. of the axial mark SM1 (SM2) can be arbitrarily set as long as the circumferential position can be confirmed.

[0083] Fig. 13 is a schematic diagram for explaining step B of this example.

[0084] In this example, among one rotation of the steering-side pinion shaft 10 or the assist-side pinion shaft 13, the rotational position at which the frictional force F1 or F2 becomes maximum is the rotational position at which the axial mark SM1 or SM2 approaches the rack shaft 11 most closely. Therefore, when assembling the steering-side pinion shaft 10 or the assist-side pinion shaft 13 to the housing 7 (see Fig. 8), by checking the positional relationship between the rack shaft 11 and the axial mark SM1 or SM2, the rotational angle of the steering-side pinion shaft 10 or the assist-side pinion shaft 13 can be confirmed with reference to the rotational position at which the frictional force F1 or F2 becomes maximum among one rotation of the steering-side pinion shaft 10 or the assist-side pinion shaft 13.

[0085] Therefore, in Process B of this example, while checking the rotation angle of the steering-side pinion shaft 10 by the shaft-side mark SM1 attached to the steering-side pinion shaft 10, as shown in FIG. 13, the steering-side pinion shaft 10 is assembled to the housing 7 (see FIG. 8) at the rotational position where the shaft-side mark SM1 is closest to the rack shaft 11, and the steering-side pinion 25 is meshed with the steering-side rack 28. Also, while checking the rotation angle of the assist-side pinion shaft 13 by the shaft-side mark SM2 attached to the assist-side pinion shaft 13, as shown in FIG. 13, the assist-side pinion shaft 13 is assembled to the housing 7 at the rotational position where the shaft-side mark SM2 is farthest from the rack shaft 11, and the assist-side pinion 41 is meshed with the assist-side rack 29.

[0086] By the above Process B, in the use state, the rotation angle of the steering-side pinion shaft 10 and the rotation angle of the assist-side pinion shaft 13 are configured to be shifted by 180°, that is, to be in opposite phases. Thereby, as shown in FIGS. 10(a) and 10(b), by making the phase difference between the two frictional forces F1 and F2 be 180°, as shown in FIG. 10(c), the fluctuation range of the resultant force (F1 + F2) of the two frictional forces F1 and F2 is minimized.

[0087] As described above, according to this example, the fluctuation range of the resultant force (F1 + F2), which is the resistance to the linear movement of the rack shaft 11 in the axial direction, can be suppressed to be small. Furthermore, the structure in which the fluctuation range of the resultant force (F1 + F2) can be suppressed to be small can be easily assembled based on the execution of Process A and Process B.

[0088] When implementing the present invention, as a modification of the first example, in step A, as shown in FIG. 12(b), when the master gear 59 and the support 61 move to the position closest to the central axis Ca, the rotation of the steering side pinion shaft 10 (assist side pinion shaft 13) is stopped at the rotational position, and the upper end position of the steering side pinion shaft 10 (assist side pinion shaft 13) at this stop position is detected as the circumferential direction position where the radius of the wobbling accompanying rotation is minimized with respect to the steering side pinion shaft 10 (assist side pinion shaft 13), and an axial side mark SM1 (SM2) can be attached to the circumferential direction position. Then, in step B, as shown in FIG. 13, the steering side pinion shaft 10 is assembled to the housing 7 (see FIG. 8) at the rotational position where the axial side mark SM1 is closest to the rack shaft 11, and the steering side pinion 25 is meshed with the steering side rack 28, and the assist side pinion shaft 13 is assembled to the housing 7 at the rotational position where the axial side mark SM2 is farthest from the rack shaft 11, and the assist side pinion 41 is meshed with the assist side rack 29. Also in this case, in the usage state, the phase difference between the rotation angle of the steering side pinion shaft 10 and the rotation angle of the assist side pinion shaft 13 is configured to be 180°.

[0089] When implementing the present invention, in step A, for each of the steering side pinion shaft 10 and the assist side pinion shaft 13, the operation of detecting the circumferential direction position where the radius of the wobbling accompanying rotation is maximum or minimum can be performed by various methods different from the first example, such as a method using a laser distance meter or the like.

[0090] [Second Example] A second example of the embodiment of the present invention will be described with reference to FIGS. 14(a) to 14(c).

[0091] In the electric power steering apparatus 1 of this example, among the steering side pinion shaft 10 and the assist side pinion shaft 13, only the steering side pinion shaft 10 is provided with an axial side mark SM1.

[0092] The manufacturing method of the electric power steering apparatus 1 of this example includes step C, step D, and step E.

[0093] In step C of this example, for the steering side pinion shaft 10, a circumferential position where the radius of the wobble accompanying rotation becomes maximum is detected, and an axial side mark SM1 is attached to the detected circumferential position. In this example, such step C is performed in the same manner as step A of the first example (see FIGS. 11 and 12).

[0094] In step D of this example, first, as shown in FIG. 14(a), the assist side pinion shaft 13 is assembled to the housing 7 (see FIG. 8), and the assist side pinion 41 is meshed with the assist side rack 29.

[0095] Then, in this state, by rotationally driving the motor output shaft of the electric motor 39 at a constant speed, the assist side pinion shaft 13 is rotationally driven at a constant speed via the worm reducer 38, thereby moving the rack shaft 11 axially at a constant speed. At this time, the assist side pinion shaft 13 is rotated one or more times. While performing this operation, the torque for rotating the assist side pinion shaft 13 at a constant speed, that is, the torque for rotating the motor output shaft of the electric motor 39 at a constant speed is measured, and at the same time, the rotation angle of the assist side pinion shaft 13 is measured.

[0096] When performing the measurement as described above, the motor output shaft of the electric motor 39 can be rotationally driven at a constant speed, for example, by performing angular velocity feedback control with a constant target speed. Also, the torque of the motor output shaft of the electric motor 39 can be measured based on the energization amount to the electric motor 39 or by a torque sensor incorporated in the electric motor 39. Further, the rotation angle of the assist side pinion shaft 13 can be obtained by calculation from the rotation angle of the motor output shaft of the electric motor 39 and the reduction ratio of the worm reducer 38.

[0097] By measuring the torque and the rotation angle as described above, a relationship between the torque and the rotation angle, as illustrated in Fig. 14(b), can be obtained. Therefore, from the relationship in Fig. 14(b), the rotation position (rotation angle α) at which the torque is minimized during one rotation of the assist-side pinion shaft 13 can be detected. This rotation position is the circumferential direction position where the radius of the wobbling of the assist-side pinion shaft 13 is maximized and is the rotation position farthest from the rack shaft 11.

[0098] In process D of this example, the assist-side pinion shaft 13 is rotated up to the rotation position (rotation angle α), and the rotation of the assist-side pinion shaft 13 is stopped at this rotation position (see Fig. 14(c)).

[0099] In process E of this example, in this state, while checking the rotation angle of the steering-side pinion shaft 10 by the shaft-side mark SM1 attached to the steering-side pinion shaft 10, at the rotation position where the shaft-side mark SM1 is closest to the rack shaft 11, the steering-side pinion shaft 10 is assembled to the housing 7 (see Fig. 5), and the steering-side pinion 25 is meshed with the steering-side rack 28 (see Fig. 14(c)).

[0100] Through the above processes D and E, in the usage state, the phase difference between the rotation angle of the steering-side pinion shaft 10 and the rotation angle of the assist-side pinion shaft 13 is configured to be 180°. As a result, as shown in Figs. 10(a) and 10(b), by making the phase difference between the two frictional forces F1 and F2 be 180°, as shown in Fig. 10(c), the fluctuation range of the resultant force (F1 + F2) of the two frictional forces F1 and F2 is minimized. Other configurations and operational effects are the same as those in the first example.

[0101] When implementing the present invention, as a modification of the second example, in step C, it is also possible to detect the circumferential position where the radius of the swing of the steering side pinion shaft 10 is minimized, and attach an axial side mark SM1 to the detected circumferential position. Then, in step D, it is also possible to detect the rotational position where the torque becomes maximum during one rotation of the assist side pinion shaft 13, and stop the rotation of the assist side pinion shaft 13 at the detected rotational position. Then, in step E, at the rotational position where the axial side mark SM1 is closest to the rack shaft 11, the steering side pinion shaft 10 can be assembled to the housing 7 (see FIG. 5), and the steering side pinion 25 can be meshed with the steering side rack 28. Also in this case, in the use state, the phase difference between the rotation angle of the steering side pinion shaft 10 and the rotation angle of the assist side pinion shaft 13 is configured to be 180°.

[0102] [Third Example] A third example of the embodiment of the present invention will be described with reference to FIG. 15.

[0103] This example is a modification of the first example, and is an example in which a housing side mark HM2 is attached to the housing 7 in order to facilitate the assembly work of the assist side pinion shaft 13 to the housing 7.

[0104] That is, in this example, a housing side mark HM2 is attached to the housing 7, the rotational direction positional relationship of which with the axial side mark SM2 changes as the assist side pinion shaft 13 rotates. Specifically, in this example, the housing side mark HM2 is attached to the circumferential position (the lower end position in FIG. 15) farthest from the rack shaft 11 (see FIG. 8) accommodated in the rack accommodating portion 14 among the end faces on the opening side of the wheel accommodating portion 22 of the housing 7. The housing side mark HM2 can also be attached in any manner such as ink marking or laser engraving. When implementing the present invention, the shape, size, color, etc. of the housing side mark HM2 can be arbitrarily set as long as the rotational direction positional relationship with the axial side mark SM2 can be confirmed.

[0105] In this example, the axial side mark SM2 on the assist side pinion shaft 13 is attached to the circumferential position on the radially outer end of the axial base end surface of the assist side pinion shaft 13 where the radius of the wobbling due to rotation is the maximum.

[0106] In this example, as shown in FIG. 15, by assembling the assist side pinion shaft 13 to the housing 7 such that the circumferential position of the axial side mark SM2 and the circumferential position of the housing side mark HM2 coincide, in the usage state, a configuration in which the phase difference between the two frictional forces F1 and F2 becomes 180° can be easily realized. Other configurations and operational effects are the same as those in the first example.

[0107] [Fourth Example] The fourth example of the embodiment of the present invention will be described with reference to FIG. 16.

[0108] In this example, on both ends in the circumferential direction of a predetermined circumferential range φ (in the illustrated example, a circumferential range with a central angle of about 40°) centered on the circumferential position X (the lower end position in FIG. 16) which is the circumferential position farthest from the rack shaft 11 (see FIG. 8) accommodated in the rack accommodating portion 14 on the end face on the opening side of the wheel accommodating portion 22 of the housing 7, housing side marks HM2 are attached. When implementing the present invention, the central angle of the circumferential range φ can also be set to an angle different from 40°.

[0109] In this example, as shown in FIG. 16, by assembling the assist side pinion shaft 13 to the housing 7 such that the circumferential position of the axial side mark SM2 is located between the two housing side marks HM2 in the circumferential direction, in the usage state, a configuration in which the phase difference between the peak positions of the two frictional forces F1 and F2 falls within the range of 160° or more and 200° or less can be easily realized. Other configurations and operational effects are the same as those in the first example.

[0110] When implementing the present invention, a housing side mark HM2 whose rotational positional relationship with the axial side mark SM1 changes as the steering side pinion shaft 10 rotates can also be attached to the housing 7.

[0111] [Example 5] Example 5 of the embodiment of the present invention will be described with reference to FIG. 17.

[0112] In this example, by adjusting the mutual relationship between the specifications such as the pitch circle diameter of the steering side pinion 25 (see FIG. 1) of the steering side pinion shaft 10 and the specifications such as the pitch circle diameter of the assist side pinion 41 (see FIG. 1) of the assist side pinion shaft 13, the rotation period of the steering side pinion shaft 10 and the rotation period of the assist side pinion shaft 13 are different from each other. This is an example in which the present invention is applied to a structure.

[0113] In this example, specifically, when the steering side pinion shaft 10 makes one rotation, the assist side pinion shaft 13 has a structure in which it makes about 0.9 rotations. In the structure of this example, the phase difference between the rotation angle of the steering side pinion shaft 10 and the rotation angle of the assist side pinion shaft 13 changes according to the rotation operation amount of the steering wheel 2, and accordingly, the phase difference Δθ between the two frictional forces F1 and F2 changes. However, in this example, a configuration is adopted in which the phase difference Δθ is maintained within a sufficiently large amount, for example, in the range of 160° or more and 200° or less, in the use state. Therefore, also in the case of this example, the fluctuation range of the resultant force (F1 + F2) of the two frictional forces F1 and F2 can be suppressed to be small. Other configurations and operational effects are the same as those in the first example.

[0114] The present invention can be implemented by appropriately combining the structures of the above-described embodiments within a range that does not cause contradictions.

Explanation of Reference Numerals

[0115] 1 Electric power steering device 2 Steering wheel 3 Steering shaft 4 Steering column 5a, 5b Universal joint 6 Intermediate shaft 7 Housing 8 Steering mechanism section 9 Assist mechanism section 10 Steering side pinion shaft 11 Rack shaft 12 Steering wheel 13 Assist side pinion shaft 14 Rack housing part 15 Steering side pinion housing part 16 Assist side pinion housing part 17 Steering side guide housing part 18 Assist side guide housing part 19 Gear housing part 20a, 20b Mounting part 21 Worm housing part 22 Wheel housing part 23 Mounting flange 24 Steering side rack guide 25 Steering side pinion 26a, 26b Bearings 27 Tie rod 28 Steering side rack 29 Assist side rack 30 Thread hole 31 Spherical joint 32 Male thread part 33 Pad 34 Elastic member 35 Pressing surface 36 Steering side cap 37 Assist side rack guide 38 Worm reducer 39 Electric motor 40 Torque sensor 41 Assist side pinion 42a, 42b Bearings 43 Roller 44 Holder 45 Pin 46 Rolling bearing 47 Elastic member 48 Assist side cap 49 Worm 50 Worm wheel 51 Cap 52 Cap 53a, 53b Rack bush 54a, 54b Spacer 55 Contact surface 56 Test device 57 Support pin 58 Rotor 59 Master gear 60 Master pinion 61 Support 62 Coil spring 63 Linear gauge

Claims

1. A rack shaft having a steering-side rack on a circumferential part of the outer peripheral surface of one axial-side part and an assist-side rack on a circumferential part of the outer peripheral surface of the other axial-side part, with both axial ends connected to a steering wheel; A steering-side pinion shaft having a steering-side pinion meshing with the steering-side rack on the outer peripheral surface and being rotationally driven by a rotational operation of a steering wheel; An assist-side pinion shaft having an assist-side pinion meshing with the assist-side rack on the outer peripheral surface and being rotationally driven by an electric motor; A steering-side rack guide disposed at a position sandwiching the rack shaft between it and the steering-side pinion shaft and having a pressing part that elastically presses the outer peripheral surface of the rack shaft toward the steering-side pinion shaft; An assist-side rack guide disposed at a position sandwiching the rack shaft between it and the assist-side pinion shaft and having a pressing part that elastically presses the outer peripheral surface of the rack shaft toward the assist-side pinion shaft; A housing in which the rack shaft, the steering-side pinion shaft, the assist-side pinion shaft, the steering-side rack guide, and the assist-side rack guide are assembled. Each of the steering-side pinion shaft and the assist-side pinion shaft has a center axis that wobbles as it rotates. The phase difference between the rotation angle of the steering-side pinion shaft based on the rotation position at which the frictional force acting between the outer peripheral surface of the rack shaft and the pressing part of the steering-side rack guide is maximized during one rotation of the steering-side pinion shaft, and the rotation angle of the assist-side pinion shaft based on the rotation position at which the frictional force acting between the outer peripheral surface of the rack shaft and the pressing part of the assist-side rack guide is maximized during one rotation of the assist-side pinion shaft is within a predetermined angular range. An electric power steering device.

2. The electric power steering device according to Claim 1, wherein the predetermined angular range is in the range of 90° or more and 270° or less.

3. The electric power steering device according to Claim 1, wherein the predetermined angular range is in the range of 120° or more and 240° or less.

4. The electric power steering device according to Claim 1, wherein the predetermined angular range is in the range of 135° or more and 225° or less.

5. In the steering-side pinion shaft and the assist-side pinion shaft, at least one of the shafts and / or a member that rotates integrally with the shaft is provided with a shaft-side mark capable of confirming the rotation angle of the shaft. The electric power steering apparatus according to any one of claims 1 to 4.

6. In the shaft provided with the shaft-side mark and / or the member that rotates integrally with the shaft, the shaft-side mark is provided at a circumferential position where the radius of the wobbling accompanying rotation is maximum or minimum. The electric power steering apparatus according to claim 5.

7. The housing is provided with a housing-side mark whose positional relationship with the shaft-side mark changes as the shaft provided with the shaft-side mark and / or the member that rotates integrally with the shaft rotates. The electric power steering apparatus according to claim 5 or 6.

8. A method for manufacturing an electric power steering apparatus according to any one of claims 5 to 7, For each of the steering-side pinion shaft and the assist-side pinion shaft, detecting a circumferential position where the radius of the wobbling accompanying rotation is maximum or minimum, and attaching the shaft-side mark to the detected circumferential position with respect to the shaft and / or the member that rotates integrally with the shaft; While confirming the rotation angle of the steering-side pinion shaft by the shaft-side mark attached to the steering-side pinion shaft and / or the member that rotates integrally with the shaft, assembling the steering-side pinion shaft to the housing, meshing the steering-side pinion with the steering-side rack, and while confirming the rotation angle of the assist-side pinion shaft by the shaft-side mark attached to the assist-side pinion shaft and / or the member that rotates integrally with the shaft, assembling the assist-side pinion shaft to the housing, and meshing the assist-side pinion with the assist-side rack. The method for manufacturing an electric power steering apparatus includes these steps. A method for manufacturing an electric power steering apparatus.

9. A method for manufacturing an electric power steering apparatus according to any one of claims 5 to 7, For the steering-side pinion shaft, detecting a circumferential position where the radius of the wobbling accompanying rotation is maximum or minimum, and attaching the shaft-side mark to the detected circumferential position with respect to the shaft and / or the member that rotates integrally with the shaft. With the assist side pinion shaft assembled to the housing and the assist side pinion meshed with the assist side rack, while rotationally driving the assist side pinion shaft at a constant speed by the electric motor, measuring the torque for the rotational drive, detecting the rotational position at which the torque becomes minimum or maximum during one rotation of the assist side pinion shaft, and stopping the rotation of the assist side pinion shaft at the rotational position; While confirming the rotational angle of the steering side pinion shaft by the shaft side mark attached to the steering side pinion shaft and / or the member that rotates integrally with the shaft, assembling the steering side pinion shaft to the housing and meshing the steering side pinion with the steering side rack; A method for manufacturing an electric power steering apparatus.

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