JP2022111600A - Rack shaft for dual pinion type electric power steering device and manufacturing method thereof, and dual pinion type electric power steering device - Google Patents

Abstract

To provide a structure that can reduce the weight while necessary strength of a portion of a rack tooth engageable with a second pinion shaft that is driven by an electric motor.SOLUTION: A tooth width of a second rack tooth 15 engageable with a second pinion tooth 14 of a second pinion shaft 13 that is rotatably driven by an electric motor 22 is designed to be larger than a tooth width of a first rack tooth 12 engageable with a first pinion tooth 11 of a first pinion shaft 10 that is rotatably driven by a steering wheel.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rack shaft incorporated in a dual-pinion electric power steering system.

An electric power steering system utilizes an electric motor as an auxiliary power source. Such an electric power steering device can be made smaller and lighter than a hydraulic power steering device that uses hydraulic pressure as an auxiliary power source, and can easily control the magnitude of the auxiliary power, and the power loss of the engine is small. and other advantages. Electric power steering devices are roughly classified into three types, ie, a column assist type, a pinion assist type, and a rack assist type, depending on the installation position of the electric motor.

FIG. 11 shows a conventional structure of a dual pinion type electric power steering device 100 classified as a rack assist type, described in WO 2017/010345 pamphlet (Patent Document 1).

A dual pinion electric power steering device 100 includes a steering gear unit 101 and an assist mechanism 102 .

The steering gear unit 101 has a rack shaft 103 and a first pinion shaft 104 arranged with their axial direction (longitudinal direction) directed in the width direction of the vehicle. The steering gear unit 101 converts rotational motion of a steering wheel (not shown) into linear motion of the rack shaft 103 .

The rack shaft 103 has a first rack tooth meshing with a first pinion tooth 105 provided on the outer peripheral surface of the first pinion shaft 104 at a part of the axial direction one side portion (right side portion in FIG. 11) in the circumferential direction. 106, and meshes with a second pinion tooth 108 provided on the outer peripheral surface of a second pinion shaft 107 constituting the assist mechanism 102 on the outer peripheral surface of the other axial side portion (the left portion in FIG. 11). It has a second rack tooth 109 . The first pinion shaft 104 is connected to the steering wheel 110 via a steering shaft 111, universal joints 112a and 112b, an intermediate shaft 113, and the like, and rotates as the steering wheel 110 is steered. The rotation of the first pinion shaft 104 is converted into linear motion of the rack shaft 103 by the meshing portion between the first pinion teeth 105 and the first rack teeth 106, and is connected to both ends of the rack shaft 103 in the axial direction. The tie rod 114 is pushed and pulled.

The assist mechanism 102 applies a steering assist force to the rack shaft 103 to reduce the steering force required for the driver to operate the steering wheel. The assist mechanism 102 includes a second pinion shaft 107 , an electric motor 115 , a worm speed reducer 116 and a torque sensor 117 .

The electric motor 115 is driven and controlled based on the rotational direction and torque of the first pinion shaft 104 detected by the torque sensor 117 . The worm speed reducer 116 has a worm 118 connected to the output shaft of the electric motor 115 so as to transmit torque, and a worm wheel 119 fixed to the second pinion shaft 107 and meshing with the worm 118 . Therefore, the drive torque generated by the electric motor 115 is transmitted to the rack shaft 103 via the worm speed reducer 116 and the second pinion shaft 107 as a steering assist force.

International Publication No. 2017/010345 pamphlet

The structure described in International Publication No. 2017/010345 has room for improvement in terms of weight reduction.

The rack shaft 103 described in International Publication No. 2017/010345 pamphlet has a constant outer diameter along the axial direction, and the tooth width of the first rack tooth 106 and the tooth width of the second rack tooth 109 are the same. It's becoming

Here, of the rack shaft 103, the first rack tooth 106 that meshes with the first pinion tooth 105 of the first pinion shaft 104 receives the operation force of the steering wheel by the driver. is entered via On the other hand, the auxiliary power of the electric motor 115 is applied to the second rack teeth 109 of the rack shaft 103 that mesh with the second pinion teeth 108 of the second pinion shaft 107 . is entered via

Therefore, in the rack shaft 103 described in International Publication No. 2017/010345 pamphlet, the rack shaft 103 is adjusted according to the strength required for the second rack teeth 109 to which the relatively large auxiliary power of the electric motor 115 is input. It is necessary to set the outer diameter. Therefore, the strength of the first rack tooth 106 to which the operating force of the steering wheel 110 is input is excessive, and the weight is correspondingly increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and aims to reduce the weight while ensuring the necessary strength of the portion of the rack teeth that meshes with the second pinion shaft driven by the electric motor. It is an object of the present invention to provide a rack shaft for a dual pinion type electric power steering device that can

A rack shaft for a dual pinion type electric power steering device of the present invention includes first rack teeth and second rack teeth.
The first rack tooth meshes with a first pinion shaft that is formed on one side in the axial direction and that rotates as the steering wheel is steered.
The second rack tooth meshes with a second pinion shaft that is formed on the other side in the axial direction and that is rotationally driven by an electric motor.
In particular, in the rack shaft for a dual pinion type electric power steering device of the present invention, the tooth width of the second rack tooth is larger than the tooth width of the first rack tooth.

In one aspect of the rack shaft for a dual pinion type electric power steering device of the present invention, the dimension of the portion where the second rack teeth are formed in the tooth width direction of the second rack teeth is defined by larger than the diameter of the circumscribed circle of the portion.

In one aspect of the rack shaft for a dual pinion type electric power steering device of the present invention, the twist direction of the first rack tooth and the twist direction of the second rack tooth can be opposite to each other.

A dual pinion electric power steering apparatus of the present invention includes an electric motor, a first pinion shaft, a second pinion shaft, and a rack shaft.
The first pinion shaft has first pinion teeth and rotates as the steering wheel is steered.
The second pinion shaft has second pinion teeth and is rotationally driven by the electric motor.
The rack shaft has first rack teeth that mesh with the first pinion teeth and second rack teeth that mesh with the second pinion teeth.
In particular, in the dual pinion electric power steering device of the present invention, the rack shaft is constituted by the rack shaft for the dual pinion electric power steering device of the present invention.

A method for manufacturing a rack shaft for a dual pinion type electric power steering device according to the present invention is a method for manufacturing a rack shaft for a dual pinion type electric power steering device according to the present invention, comprising:
Of the material having a circular cross-sectional shape and an outer diameter that does not change in the axial direction, the other axial side portion including the portion where the second rack teeth are to be formed is press-worked to form a flat surface portion. a step of obtaining an intermediate material by
forming the second rack teeth on the flat surface portion of the intermediate material;
forming the first rack teeth on one axial side portion of the intermediate material;
Prepare.

According to the rack shaft for a dual pinion type electric power steering device of the present invention, it is possible to reduce the weight while ensuring the necessary strength of the portion of the rack teeth that meshes with the second pinion shaft driven by the electric motor. can be done.

FIG. 1 is a schematic diagram showing an example of a steering system including a dual pinion electric power steering system according to an example of the embodiment. FIG. 2 is a front view showing the rack shaft, the first pinion shaft, the second pinion shaft, and the worm. FIG. 3 is a perspective view showing the rack shaft taken out. 4(A) is a front view showing the rack shaft taken out, FIG. 4(B) is a sectional view taken along the line AA in FIG. 4(A), and FIG. ) is a cross-sectional view along the line BB. 5(A) is a plan view showing the rack shaft taken out, FIG. 5(B) is a sectional view taken along line CC of FIG. 5(A), and FIG. ), FIG. 5D is a EE cross-sectional view of FIG. 5A, and FIG. 5E is a FF cross-sectional view of FIG. be. 6(A) to 6(C) are front views showing the steps of the method for manufacturing the rack shaft. 7(a) to 7(c) are diagrams showing the manufacturing method of the rack shaft in order of steps, where (A) is a plan view and (B) is a side view from the left side of (A). It is a diagram. 8(A) is a cross-sectional view taken along line GG of FIG. 6(B), and FIG. 8(B) is a cross-sectional view taken along line HH of FIG. 6(B). FIGS. 9(A) to 9(C) are diagrams showing another three examples of the shape of the AA cross section of FIG. 4(A), omitting the second rack teeth. FIG. 10 is a diagram similar to FIG. 2, showing a modification of one example of the embodiment. FIG. 11 is a partially cutaway front view showing a dual pinion type electric power steering of conventional structure.

An example of an embodiment will be described with reference to FIGS. 1 to 8B. 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. Moreover, the left-right direction coincides with the axial direction of the rack shaft, which will be described later. One side in the axial direction of the rack shaft refers to the right side in FIGS. 1, 2, 4A, and 5A, and the other side in the axial direction of the rack shaft refers to 4(A) and the left side of FIG. 5(A).

As shown in FIG. 1, the steering system of this example includes a steering wheel 1, a steering shaft 2, a steering column 3, a pair of universal joints 4a and 4b, an intermediate shaft 5, and a dual pinion type steering wheel. An electric power steering device 6 is provided.

The steering shaft 2 is rotatably supported inside a steering column 3 supported by the vehicle body. A steering wheel 1 that is steered by a driver is attached to the rear end of the steering shaft 2 . A front end portion of the steering shaft 2 is connected to a first pinion shaft 10, which constitutes a dual pinion electric power steering device 6, via a universal joint 4a, an intermediate shaft 5, and another universal joint 4b.

A dual pinion electric power steering device 6 includes a steering gear unit 7 and an assist mechanism 8 .

The steering gear unit 7 has a housing (not shown), a rack shaft 9 and a first pinion shaft 10, and converts rotational motion of the steering wheel 1 into linear motion of the rack shaft 9 in the axial direction.

The housing is fixed to the vehicle body using fixing members such as bolts and studs.

The rack shaft 9 is a rod-shaped member made of metal such as carbon steel or stainless steel, and is arranged with its axial direction (longitudinal direction) directed in the left-right direction. The rack shaft 9 has first rack teeth 12 on a part of the outer peripheral surface of the one axial side portion, which mesh with the first pinion teeth 11 provided on the outer peripheral surface of the first pinion shaft 10, and Part of the outer peripheral surface of the other axial side portion has second rack teeth 15 that mesh with second pinion teeth 14 provided on the outer peripheral surface of the second pinion shaft 13 that constitutes the assist mechanism 8 . In this example, the rack shaft 9 has first rack teeth 12 on the front side surface of one axial side portion and second rack teeth 15 on the front side surface of the other axial side portion. Further, the rack shaft 9 has a pair of screw holes 16 that are open on both axial end faces.

Particularly in this example, the tooth width of the second rack tooth 15 meshing with the second pinion tooth 14 of the second pinion shaft 13 (the width in the vertical direction in FIGS. 1, 2 and 4) is It is made larger than the tooth width of the first rack tooth 12 that meshes with the first pinion tooth 11 . For this reason, of the rack shaft 9, the dimension W in the tooth width direction of the second rack tooth 15 in the axial direction other side portion where the second rack tooth 15 is formed, that is, in the vertical direction, is It is made larger than the dimension D in the face width direction of the first rack teeth 12, that is, in the vertical direction, at the one axial side portion where the first rack teeth 12 are formed. Specifically, in this example, the vertical dimension (width dimension) W of the other axial half of the rack shaft 9 including the second axial side portion where the second rack teeth 15 are formed is It is made larger than the diameter D of the circumscribed circle of the half portion of the rack shaft 9 on the one axial side including the portion on the one axial side where the first rack teeth 12 are formed. In other words, the vertical dimension D of the rack shaft 9 on one axial side is smaller than the vertical dimension W of the rack shaft 9 on the other axial side. The diameter D of the circumscribed circle is the same as or substantially the same as the diameter of the material (material diameter), which will be described later.

In this example, the cross-sectional shape of the portion of the rack shaft 9 on one side in the axial direction where the first rack teeth 12 are formed is straight only on the front side surface where the first rack teeth 12 are formed, and the remaining portion is circular. It is arc-shaped, that is, a missing circle. Further, when the first rack teeth 12 are formed on one side of the rack shaft 9 in the axial direction, a tooth forming process such as pressing or cutting is performed. The cross-sectional shape of the portion axially adjacent to the portion is circular.

On the other hand, the cross-sectional shape of the other axial side portion of the rack shaft 9 where the second rack teeth 15 are formed is such that the front side where the second rack teeth 15 are formed, the upper side and the lower side are straight lines. and the remaining portion, ie the posterior side, is arc-shaped, ie D-shaped. The radius of curvature of the partial cylindrical surface forming the rear side surface of the rack shaft 9 on the other axial side is slightly larger than the diameter D of the circumscribed circle of the rack shaft 9 on the one axial side. Further, when the second rack teeth 15 are formed on the other side of the rack shaft 9 in the axial direction, specifically, when the second rack teeth 15 are formed, a tooth forming process such as pressing or cutting is performed. A flat surface portion 17 is provided on the front side surface of the portion that is adjacent to the portion on both sides in the axial direction and whose phase in the circumferential direction matches the second rack tooth 15 .

However, the cross-sectional shape of the portion where the second rack teeth are formed is not limited to the D shape, and may be any shape. For example, as shown in FIG. 9A, the cross-sectional shape of the portion where the second rack teeth are formed is such that the upper and lower surfaces are straight, the rear surface is arcuate, and the central portion is It can be shaped to have a concave groove 29 having a 1/4 concave circular arc cross-sectional shape. As shown in FIG. 9(B), the width of the groove 29a can be made smaller than that of the first modified example shown in FIG. 9(A). Alternatively, the cross-sectional shape of the portion where the second rack teeth are formed may be such that the upper and lower side surfaces are straight and the rear side surface is substantially trapezoidal, as shown in FIG. 9(C). can be done.

When carrying out the present invention, the twist direction of the first rack tooth and the twist direction of the second rack tooth may be the same or opposite to each other. In this example, the twist direction of the first rack teeth 12 and the twist direction of the second rack teeth 15 are opposite to each other. Specifically, as shown in FIG. 2, the twist direction of the first rack tooth 12 is right-hand twisted, and the twist direction of the second rack tooth 15 is left-hand twist. More specifically, the inclination angle ψ12 of the tooth trace of the first rack tooth ₁₂ with respect to the central axis O9 of the rack shaft ₉ is set to about 95 degrees, and the inclination angle ψ15 of the tooth trace of the second rack tooth ₁₅ is set to It is about 85 degrees. The inclination angle ψ12 of the tooth trace of the first rack tooth ₁₂ and the inclination angle ψ15 of the tooth trace of the second rack tooth ₁₅ can be arbitrarily determined within a range that does not cause any functional inconvenience.

The rack shaft 9 can reciprocate in the axial direction inside the housing in a state in which the axial direction is oriented in the left-right direction and both ends in the axial direction protrude from openings on the left and right sides of the housing. supported by Both ends of the rack shaft 9 in the axial direction are connected to tie rods 19 via spherical joints 18 . That is, a male screw portion provided at the base of a spherical joint 18 is screwed into each of the pair of screw holes 16 of the rack shaft 9 , and the base end of the tie rod 19 swings at the tip of the spherical joint 18 . movably supported. A method of manufacturing the rack shaft 9 will be described later.

The first pinion shaft 10 has first pinion teeth 11 that mesh with the first rack teeth 12 of the rack shaft 9 on the front half outer peripheral surface. The first pinion shaft 10 is rotatably supported inside the housing by bearings.

In this example, when viewed from the front-rear direction, which is a direction orthogonal to the central axis O9 of the rack shaft ₉ and the central axis O10 of the first pinion shaft ₁₀ , the central axis O9 of the rack shaft ₉ and the first pinion The center axis O10 of the shaft ₁₀ intersects obliquely. In other words, the central axis O9 of the rack shaft ₉ and the central axis O10 of the first pinion shaft ₁₀ are not orthogonal when viewed from the front-rear direction. The angle θ between the central axis _O9 of the rack shaft ₉ and the central axis O10 of the first pinion shaft 10 when viewed from the front-rear direction is not particularly limited, but is, for example, 60 degrees or more and less than 90 degrees. and preferably 65 degrees or more and 75 degrees or less. In the illustrated example, the angle θ is approximately 70 degrees. However, when carrying out the present invention, the central axis of the rack shaft and the central axis of the first pinion shaft are orthogonal to each other, that is, the angle formed by the central axis of the rack shaft and the central axis of the first pinion shaft is 90 degrees. You can also

The first pinion shaft 10 is connected to the steering wheel 1 via universal joints 4a and 4b and an intermediate shaft 5, and rotates as the steering wheel 1 is steered. Rotation of the first pinion shaft 10 is converted into linear motion of the rack shaft 9 , pushing and pulling tie rods 19 connected to both ends of the rack shaft 9 in the axial direction via spherical joints 18 . As a result, steering angles are imparted to the left and right steered wheels 20 .

The assist mechanism 8 applies a steering assist force to the rack shaft 9 to reduce the steering force required for the driver to operate the steering wheel 1 . The assist mechanism 8 includes a second pinion shaft 13 , a worm speed reducer 21 , an electric motor 22 and a torque sensor 23 .

The second pinion shaft 13 has second pinion teeth 14 meshing with the second rack teeth 15 of the rack shaft 9 on the front half outer peripheral surface. The second pinion shaft 13 is rotatably supported inside the housing by bearings. The second pinion shaft 13 is arranged at a position separated from the first pinion shaft 10 in the axial direction of the rack shaft 9 .

In this example, when viewed from the front-rear direction, which is a direction orthogonal to the central axis O9 of the rack shaft ₉ and the central axis O13 of the second pinion shaft ₁₃ , the central axis O9 of the rack shaft ₉ and the second pinion It obliquely intersects the central axis O13 of the shaft ₁₃ . The inclination direction of the central axis O13 of the second pinion shaft ₁₃ with respect to the central axis O9 of the rack shaft ₉ is opposite to the inclination direction of the central axis O10 of the first pinion shaft ₁₀ with respect to the central axis O9 of the rack shaft ₉ . direction. When viewed from the front-rear direction orthogonal to the central axis O9 of the rack shaft ₉ and the central axis O13 of the second pinion shaft ₁₃ , the central axis O9 of the rack shaft ₉ and the central axis O13 of the second pinion shaft 13 The angle φ formed with O ₁₃ is not particularly limited, but can be, for example, 60 degrees or more and less than 90 degrees, preferably 65 degrees or more and 75 degrees or less. However, the center axis of the rack shaft and the center axis of the second pinion shaft may be orthogonal when viewed from the front-rear direction. The second pinion shaft 13 is rotationally driven by an electric motor 22 via a worm reduction gear 21 .

The worm speed reducer 21 includes a worm 24 and a worm wheel 25 , reduces the speed (increases torque) of the rotation of the electric motor 22 , and transmits the speed to the second pinion shaft 13 .

The worm 24 has worm teeth on its outer peripheral surface, and its base end is connected to the output shaft 26 of the electric motor 22 via a joint (not shown) or the like so that torque can be transmitted. The worm 24 is supported inside a gear housing integrally formed with the housing or inside a gear housing supported and fixed to the housing so as to be able to swing slightly about its base end. be. Therefore, the worm 24 and the output shaft 26 are arranged substantially coaxially while allowing a slight swinging displacement of the worm 24 with respect to the output shaft 26 .

The worm wheel 25 has wheel teeth that mesh with the worm teeth on its outer peripheral surface, and is fixed to the base end of the second pinion shaft 13 so as not to rotate relative to it. That is, the central axis O13 of the second pinion shaft ₁₃ and the central axis of the worm wheel 25 are arranged coaxially with each other.

In this example, the central axis of the worm 24 and the central axis of the worm wheel 25 intersect obliquely when viewed from the front-rear direction orthogonal to the central axis of the worm 24 and the central axis of the worm wheel 25 . Thus, in this example, the central axis O9 of the rack shaft ₉ and the worm 24 are arranged in parallel. However, the central axis of the worm and the central axis of the worm wheel can be orthogonal. And/or the central axis of the rack shaft and the worm can be arranged non-parallel.

The electric motor 22 is for applying a steering assist force to the rack shaft 9 via the worm speed reducer 21 and the second pinion shaft 13, and is fixed to the gear housing. The electric motor 22 has an output shaft 26 that is connected to the worm 24 in a torque-transmissible manner.

In this example, the electric motor 22 is arranged on one side of the worm 24 with respect to the axial direction of the rack shaft 9 . That is, the base end of the worm 24 on one side in the axial direction of the rack shaft 9, and the tip of the output shaft 26 of the electric motor 22 on the other side in the axial direction of the rack shaft 9. are connected by a joint or the like so that torque can be transmitted. As a result, the electric motor 22 is arranged near the center of the dual-pinion electric power steering device 6 in the left-right direction. However, the electric motor can also be arranged on the other side of the worm with respect to the axial direction of the rack shaft.

The torque sensor 23 is arranged around the first pinion shaft 10 and detects the rotational direction and torque of the first pinion shaft 10 . As a result, the torque sensor 23 outputs a signal corresponding to the rotational direction and torque of the first pinion shaft 10 to the electronic control unit of the electric motor 22 . As the torque sensor 23, for example, a non-contact torque sensor using the magnetostrictive effect can be used.

The assist mechanism 8 drives and controls the electric motor 22 based on the output signal of the torque sensor 23 . As a result, the drive torque generated by the electric motor 22 is transmitted to the rack shaft 9 via the worm speed reducer 21 and the second pinion shaft 13 as a steering assist force. As a result, the steering force required for the driver to operate the steering wheel 1 is reduced.

A method of manufacturing the rack shaft 9 will now be described.

First, a metal bar having a circular cross-sectional shape is cut into a predetermined length to obtain a columnar preliminary material whose outer diameter does not change along the axial direction. Next, the end faces on both sides in the axial direction of the preliminary material are perforated to form screw holes 16. As shown in FIGS. obtain the material 27 of

Next, of the material 27, only the portion on the other side in the axial direction including the portion where the second rack teeth 15 are to be formed is press-worked (flat-pressed), so that the portion that will become the front side surface after completion has a flat surface portion. 17z is formed to obtain an intermediate material 28 as shown in FIGS. 6(B) and 7(b). Specifically, the material 27 is set in the cavity of the mold with the front side facing upward, and the screw hole 16 is formed radially inward of the other half of the front side in the axial direction. A flat surface portion 17z is formed by pressing the portion other than the flattened portion with a punch. The width dimension of the flat surface portion 17z, that is, the vertical dimension W of the other half of the intermediate material 28 in the axial direction is larger than the diameter of the one half of the intermediate material 28 in the axial direction, that is, the material diameter D.

Next, a part of the flat surface portion 17z of the intermediate material 28 is subjected to tooth forming processing such as pressing and/or cutting to form the second rack teeth 15 and the remaining portion is the flat surface portion 17 . Further, the first rack teeth 12 are formed by performing tooth forming such as pressing and/or cutting on one axial side portion of the intermediate material 28 . Thus, a rack shaft 9 as shown in FIGS. 6(C) and 7(c) is obtained.

As for the procedure for manufacturing the rack shaft 9 from a metal bar, as described above, the order can be changed or the procedures can be carried out at the same time as long as there is no contradiction. For example, the tooth forming process for forming the second rack teeth 15 and the tooth forming process for forming the first rack teeth 12 can be performed simultaneously or sequentially.

In the rack shaft 9 of this example, the tooth width of the second rack tooth 15 meshing with the second pinion tooth 14 of the second pinion shaft 13 is set to the first rack tooth meshing with the first pinion tooth 11 of the first pinion shaft 10 . It is made larger than the tooth width of 12. Therefore, the weight of the rack shaft 9 is unnecessarily increased while ensuring that the strength of the second rack tooth 15 to which the relatively large auxiliary power of the electric motor 22 is input is higher than the strength of the first rack tooth 12 . can be prevented.

In this example, the width dimension D in the vertical direction of the one axial side portion of the rack shaft 9 where the first rack teeth 12 are formed is the same as the width dimension D of the other axial side portion where the second rack teeth 15 are formed. It is smaller than the width dimension W in the vertical direction. For this reason, the vertical dimension of the portion of the housing that accommodates the rack shaft 9 and that is arranged around the one axial side portion of the rack shaft 9 is adjusted to ensure the stroke of the rack shaft 9. As much as possible, it can be made smaller than the portion arranged around the other portion of the rack shaft 9 in the axial direction. As a result, the size of the steering gear unit 7 can be reduced, so that the dual pinion electric power steering apparatus 6 can be easily mounted in the engine room.

In addition, in this example, by press working (flat pressing) on the other axial side portion of the cylindrical material 27 whose outer diameter does not change in the axial direction, the vertical dimension of the other axial half portion is reduced. After obtaining the intermediate material 28 whose W is larger than the diameter D of the half portion on one axial side, the one axial side portion and the other axial side portion of the intermediate material 28 are subjected to tooth forming processing to form the first The rack shaft 9 is obtained by forming the rack teeth 12 and the second rack teeth 15 respectively. Therefore, it is possible to manufacture the rack shaft 9 with high material yield while ensuring high strength of the second rack tooth 15 to which the auxiliary power of the electric motor 22 is input and preventing an unnecessary increase in weight.

Further, in the rack shaft 9 of this example, the twisting direction of the first rack teeth 12 and the twisting direction of the second rack teeth 15 are opposite to each other. Therefore, of the meshing reaction force applied to the rack shaft 9 from the meshing portion between the first pinion tooth 11 and the first rack tooth 12, the component in the direction orthogonal to the rack shaft 9 (vertical direction in FIG. 2) Of the meshing reaction forces applied to the rack shaft 9 from the meshing portion between the pinion teeth 14 and the second rack teeth 15, the directions perpendicular to the rack shaft 9 are opposite to each other, and these components can be canceled out. can. Therefore, it is possible to effectively prevent rack rolling, in which the rack shaft 9 rotates around the central axis O ₉ as torque is input from the first pinion shaft 10 and the second pinion shaft 13 to the rack shaft 9 . . As a result, fluctuations in the torque transmitted to the steering wheel 1 and the force required to displace the rack shaft 9 in the axial direction can be prevented.

In this example, the central axis O9 of the rack shaft ₉ and the worm 24 are arranged in parallel, and the central axis of the output shaft 26 of the electric motor 22 is arranged coaxially with the central axis of the worm 24. ing. Thus, in the dual-pinion electric power steering device 6 of this example, the central axis O9 of the rack shaft ₉ and the central axis of the output shaft 26 of the electric motor 22 are arranged in parallel.

Thus, by arranging the central axis O9 of the rack shaft ₉ and the central axis of the output shaft 26 of the electric motor 22 in parallel, the electric motor 22 can be moved from the portion of the housing that accommodates the rack shaft 9. Among them, the amount of protrusion in the front-rear direction of the motor housing that houses the drive unit consisting of the rotor and stator is compared with the structure in which the central axis of the rack shaft and the central axis of the output shaft of the electric motor are not parallel. can be kept small. From this point of view as well, it is possible to easily secure the mountability of the dual-pinion electric power steering device 6 of the present embodiment in the engine room.

If the central axis O9 of the rack shaft ₉ and the central axis O22 of the output shaft 26 of the electric motor ₂₂ can be arranged in parallel, the central axis O of the rack shaft 9 can be arranged as in the modification shown in FIG. ₉ and the central axis O13 of the second pinion shaft ₁₃ may be orthogonal, and the central axis of the worm 24 and the central axis of the worm wheel 25 may be orthogonal. Alternatively, the central axis of the rack shaft and the output shaft (worm) of the electric motor can be arranged non-parallel.

Although one example of the embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate without departing from the technical idea of the invention.

For example, in the above-described embodiment, both the first rack teeth 12 and the second rack teeth 15 are formed on the front side surface of the rack shaft 9, but when carrying out the present invention, the first rack teeth The teeth and second rack teeth can also be formed on other than the front side, such as the rear side of the rack shaft. Also, the formation positions in the circumferential direction of the first rack teeth and the second rack teeth may be different from each other.

In the example of FIG. 2, the width in the vertical direction of the other axial half of the rack shaft 9 including the portion where the second rack teeth 15 are formed is the vertical width of the axially one half. About width is bigger than . However, in terms of ensuring the strength of the second rack teeth, it is sufficient to make the width of the portion of the rack shaft where the second rack teeth are formed larger than the width of the remaining portion. That is, it is also possible not to form the flat surface portion on the portion of the rack shaft that is adjacent to the second rack tooth in the axial direction.

Further, the rack shaft having the tooth width of the second rack tooth larger than the tooth width of the first rack tooth is press-worked (flat pressing) only on the other axial side portion of the cylindrical material whose outer diameter does not change in the axial direction. By forming the flat surface portion by applying the above, it is not limited to the method of increasing the width dimension of the other side portion in the axial direction, but can be manufactured by any method. Specifically, for example, cutting is performed only on one axial side of a cylindrical material, or a small-diameter cylindrical member arranged on one axial side and a large-diameter cylindrical member arranged on the other axial side are used. can also be obtained by forming the first rack teeth and the second rack teeth on a stepped columnar member obtained by coupling in the axial direction by friction welding or the like.

REFERENCE SIGNS LIST 1 steering wheel 2 steering shaft 3 steering column 4a, 4b universal joint 5 intermediate shaft 6 dual pinion type electric power steering device 7 steering gear unit 8 assist mechanism 9 rack shaft 10 first pinion shaft 11 first pinion tooth 12 first rack tooth 13 second pinion shaft 14 second pinion tooth 15 second rack tooth 16 screw hole 17, 17z flat surface portion 18 spherical joint 19 tie rod 20 steering wheel 21 worm reduction gear 22 electric motor 23 torque sensor 24 worm 25 worm wheel 26 output shaft 27 Material 28 Intermediate material 29, 29a Groove 100 Dual pinion electric power steering device 101 Steering gear unit 102 Assist mechanism 103 Rack shaft 104 First pinion shaft 105 First pinion tooth 106 First rack tooth 107 Second pinion shaft 108 Second Pinion tooth 109 Second rack tooth 110 Steering wheel 111 Steering shafts 112a, 112b Universal joint 113 Intermediate shaft 114 Tie rod 115 Electric motor 116 Worm reducer 117 Torque sensor 118 Worm 119 Worm wheel

Claims (5)

a first rack tooth that is formed on one side in the axial direction and meshes with a first pinion shaft that rotates as the steering wheel is steered;
a second rack tooth meshing with a second pinion shaft formed on the other axial side portion and rotationally driven by the electric motor;
with
The face width of the second rack tooth is larger than the face width of the first rack tooth,
Rack shaft for dual pinion type electric power steering device. The dimension in the face width direction of the portion where the second rack teeth are formed is larger than the diameter of the circumscribed circle of the portion where the first rack teeth are formed.
A rack shaft for a dual pinion electric power steering device according to claim 1. The twist direction of the first rack tooth and the twist direction of the second rack tooth are opposite to each other,
A rack shaft for a dual pinion electric power steering device according to claim 1 or 2. an electric motor;
a first pinion shaft having first pinion teeth and rotating in accordance with the steering operation of the steering wheel;
a second pinion shaft having second pinion teeth and driven to rotate by the electric motor;
a rack shaft having first rack teeth meshing with the first pinion teeth and second rack teeth meshing with the second pinion teeth;
with
The rack shaft is configured by the rack shaft for a dual pinion electric power steering device according to any one of claims 1 to 3,
Dual pinion type electric power steering device. A method for manufacturing a rack shaft for a dual pinion electric power steering device according to claim 2 or claim 3 depending on claim 2,
Of the material having a circular cross-sectional shape and an outer diameter that does not change in the axial direction, the other axial side portion including the portion where the second rack teeth are to be formed is press-worked to form a flat surface portion. a step of obtaining an intermediate material by
forming the second rack teeth on the flat surface portion of the intermediate material;
forming the first rack teeth on one axial side portion of the intermediate material;
A method for manufacturing a rack shaft for a dual pinion electric power steering device, comprising:

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