JP2015024801A - Rack shaft for dual pinion type electric power steering device, manufacturing method thereof, and dual pinion type electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a structure precisely regulating relationship in circumferential direction between both first and second rack teeth 13, 14 while suppressing increase in manufacturing cost.SOLUTION: Both first and second rack teeth 13, 14 are respectively formed at portions at which the phases in circumferential direction agree with each other, at two points separating in axial direction on an outer peripheral surface of a metal tubular material. Then, plastic process is applied, in axial direction, to twist the portion where the second rack teeth 14 are formed against the portion where the first rack teeth 13 are formed, so that, phases in terms of circumferential direction of both first and second rack teeth 13, 14 are different from each other.

Description

  The present invention incorporates a dual pinion type electric power steering device that uses an electric motor as an auxiliary power source to reduce the force required for the driver to operate the steering wheel, and the dual pinion type electric power steering device. The present invention relates to an improvement of a rack shaft used in a state and a manufacturing method thereof.

  A power steering device is widely used as a device to reduce the force required for the driver to operate the steering wheel when giving a steering angle to the steered wheels (usually the front wheels except for special vehicles such as forklifts) Has been. In addition, an electric power steering apparatus that uses an electric motor as an auxiliary power source in such a power steering apparatus has recently become widespread. The electric power steering device can be made smaller and lighter than the hydraulic power steering device, has advantages such as easy control of the magnitude (torque) of the auxiliary force and less power loss of the engine. FIG. 5 shows a steering device incorporating an electric power steering device called a dual pinion type among such electric power steering devices.

  In this steering apparatus, the movement of the steering wheel 1 is transmitted to the input shaft 6 constituting the steering gear 5 via the steering shaft 2, the universal joint 3a, the intermediate shaft 4, and the universal joint 3b. The input shaft 6 is rotatably supported in the housing 7. The rack shaft 8 is displaced in the axial direction along with the rotation, and a pair of tie rods connected to both axial ends of the rack shaft 8 ( A steering angle is given to the steered wheel via a not-shown). For this purpose, the rack shaft 8 supports the middle portion of the rack shaft 8 on the housing 7 so as to be capable of axial displacement. The input shaft 6 is arranged in a twisted positional relationship with respect to the rack shaft 8. And the 1st pinion tooth | gear formed in the front-end | tip part (lower end part of FIG. 5) outer periphery of this input shaft 6 is meshed | engaged with the rack tooth formed in the front surface of the said rack shaft 8. FIG. That is, in the case of the illustrated example, the input shaft 6 corresponds to the first pinion shaft described in the claims.

  Further, a part of the rack shaft 8 in the axial direction, which corresponds to the second pinion shaft described in the claims, is a portion that is axially deviated from the first pinion teeth provided on the outer peripheral surface of the input shaft 6. A pinion shaft 9 is arranged. And the 2nd pinion tooth | gear provided in the front-end | tip part (lower end part of FIG. 5) outer periphery of this pinion shaft 9 is meshed | engaged with the rack tooth | gear of the said rack shaft 8. FIG. Further, an electric motor 11 is supported on the side of a housing 10 provided with the pinion shaft 9 inside. The electric motor 11 applies an auxiliary force in the rotational direction to the pinion shaft 9 via the speed reducer 12. That is, when the driver operates the steering wheel 1 and the steering shaft 2 rotates, a torque sensor (not shown) detects the magnitude of the torque applied to the steering shaft 2 and its direction of action. A signal representing the detected value is sent to a controller (not shown). Then, the controller energizes the electric motor 11 and rotates the pinion shaft 9 in the same direction as the rotation direction of the steering shaft 2 based on the operation of the steering wheel 1 via the speed reducer 12. As a result, the rack shaft 8 is axially driven by the auxiliary force generated by the electric motor 11 based on energization in addition to the force applied from the input shaft 6 based on the force applied by the driver to the steering wheel 1. Displace. Accordingly, the force required for displacing the rack shaft 8 in the axial direction and the force required for operating the steering wheel 1 can be reduced by this auxiliary force.

  FIG. 6 shows, as an example of the method for manufacturing the rack shaft 8 as described above, a manufacturing method described in Patent Document 1 manufactured by bending a metal plate such as a steel plate in the order of steps. First, a metal plate having sufficient strength and rigidity, such as a steel plate, is punched out by press working or the like, and as shown in FIG. Get. The base plate 19 has a width direction {in the axial direction of the rack shaft 8a after completion, in the left-right direction in FIGS. 6 (A) (vertical direction of (a)) The narrow portion 20 having a small dimension is provided.

  Such a base plate 19 is placed on the upper surface of a die and pressed with a punch, for example, so that the intermediate portion in the width direction is bent and plastically deformed into a shape as shown in FIG. The material 21 is used. The first intermediate material 21 has a U-shaped cross-section in a part in the length direction (the portion where the narrow portion 20 is provided in the length direction), and the length direction starts from the portion where the narrow portion 20 is provided. The cross-sectional shape of the part deviating from the above is U-shaped. Accordingly, both end edges in the width direction of the first intermediate material 21 can be made parallel to each other in the length direction. Next, as shown in FIG. 6C, such a first intermediate material 21 is racked by press working on a part of the front surface in the longitudinal direction {upper surface in FIG. 6C). Teeth 22 are formed and used as the second intermediate material 23. Next, as shown in FIG. 6D, such a second intermediate material 23 is subjected to bending so that both edges in the width direction (circumferential direction) are brought into contact with each other (contact or close to each other). The third intermediate material 24 is substantially circular tubular. Further, as shown in FIG. 6E, the third intermediate material 24 is joined to the edges in the width direction by a welded portion 25 to form a fourth intermediate material 26. Then, as shown in FIG. 6 (F), the fourth intermediate material 26 is subjected to drawing processing in the axial intermediate portion and both end portions, or a pair of tie rods are formed on the inner peripheral surfaces of both axial end portions. A substantially circular rack shaft 8a is obtained by forming a screw hole for screwing and fixing a male screw portion provided at a base portion of a spherical joint (not shown) for connecting the end portions.

  By the way, in the case of the dual pinion type electric power steering apparatus shown in FIG. 5 described above, the input shaft 6 and the pinion shaft 9 need to be arranged in parallel to each other at two positions deviated in the axial direction of the rack shaft 8. . For this reason, the installation positions of the input shaft 6, the pinion shaft 9, the electric motor 11, and the like are limited, and the degree of freedom in designing the dual pinion type electric power steering device is reduced. On the other hand, for example, in Patent Document 2, the first rack teeth meshing with the first pinion shaft (input shaft 6) and the second rack teeth meshing with the second pinion shaft (pinion shaft 9) are arranged on the outer peripheral surface. The structure of the rack axis | shaft provided independently in the part from which the phase regarding the circumferential direction mutually differs in the two positions off of the axial direction is described. According to such a rack shaft described in Patent Document 2, the arrangement of other members (input shaft 6 and pinion shaft 9, electric motor 11, etc.) constituting the dual pinion type electric power steering device with respect to the rack shaft, The degree of freedom in designing the structure and the like can be improved.

  The rack shaft as described above is manufactured by the following process, for example. First, in order to form a first rack tooth in a part of the circumferential direction at a portion near one end in the axial direction of a cylindrical metal material, at least one of plastic processing and cutting processing is performed, and an intermediate The material. Next, a process for forming a second rack tooth is performed on a portion of the intermediate material closer to the other end in the axial direction and the phase in the circumferential direction deviates from the first rack tooth, and the rack shaft Get. In the case of such a rack shaft manufacturing method, it is necessary to perform processing for forming both the first and second rack teeth in separate steps, and it is inevitable that the manufacturing cost increases. That is, when the first rack teeth are formed, the other half portion in the axial direction of the material is held down by a jig, and processing is performed to form the first rack teeth at a portion near one end in the axial direction. On the other hand, when the second rack teeth are formed, the half piece of the intermediate material in the axial direction is held down by a jig, and processing for forming the second rack teeth is performed on the portion near the other end in the axial direction. . Further, when the material (intermediate material) is processed to form the first rack teeth (second rack teeth), a large rotational force is applied to the material (intermediate material). Of this material (intermediate material), when forming the first rack tooth (second rack tooth), the outer peripheral surface of the other half part in the axial direction (half axial part) that is restrained by the jig is simply Since it is a cylindrical surface, the rotation blocking force that opposes the force in the rotational direction is only the frictional force between the cylindrical surface and the surface of the jig. Therefore, when forming the first rack tooth (second rack tooth), the material (intermediate material) may rotate if the rotational force becomes larger than the rotation prevention force. . If this material (intermediate material) rotates even slightly, the first rack teeth (second rack teeth) cannot be formed with high accuracy, and the positional relationship between the first and second rack teeth in the circumferential direction is accurate. It may become impossible to regulate well.

  On the other hand, Patent Document 3 describes a structure of a rack shaft formed by connecting a pair of bowl-shaped members having rack teeth on their outer peripheral surfaces by spherical joints. However, in the case of the structure described in Patent Document 3, all of the processing, component management, and assembly work for forming the spherical joint become troublesome and the manufacturing cost increases. Further, in Patent Document 4, in a hollow tubular rack shaft made by bending a metal plate, the first and second phases are different from each other at two positions separated in the axial direction and having different phases in the circumferential direction. A technique is described in which both rack teeth are formed simultaneously by a single press process. However, the technique described in Patent Document 4 depends on the phase difference in the circumferential direction between the first and second rack teeth (specifically, when the phase difference is about 90 degrees), It cannot be applied.

JP 2002-1432 A JP 2013-63723 A JP 2003-21214 A Japanese Patent Application Laid-Open No. 2002-178094

  In view of the circumstances as described above, the present invention provides a rack shaft for a dual pinion type electric power steering apparatus capable of accurately regulating the positional relationship in the circumferential direction between the first and second rack teeth while suppressing the manufacturing cost, and Invented to realize the manufacturing method and the dual pinion type electric power steering apparatus.

  A rack shaft for a dual pinion type electric power steering apparatus that is an object of the present invention is made of metal and is entirely tubular or bowl-shaped, and is formed in a part in the axial direction and a part in the circumferential direction. One rack tooth, and a second rack tooth formed at a portion where the axial position deviates from the first rack tooth in the axial direction and a phase in the circumferential direction deviates from the first rack tooth. .

  In particular, in the method for manufacturing a rack shaft for a dual pinion type power steering apparatus according to the present invention, the phases in the circumferential direction are mutually different at two positions separated in the axial direction on the outer circumferential surface of the tubular or bowl-shaped material. The first and second rack teeth are respectively formed by simultaneously performing at least one of plastic working and cutting on the matching portions. After that, the portion where the second rack teeth are formed in the axial direction is subjected to plastic working that is twisted (relatively rotated) with respect to the portion where the first rack teeth are formed. The phases in the circumferential direction are made different from each other.

Preferably, when carrying out the method of manufacturing a rack shaft for a dual pinion type electric power steering apparatus according to the present invention as described above, before the plastic working is performed, the axial direction is preferably set as described above. A constricted portion having a smaller cross-sectional area than a portion adjacent in the axial direction is provided between the portion where the first rack teeth are formed and the portion where the second rack teeth are formed.
In this case, preferably, as in the invention described in claim 3, the tool is locked to the axially intermediate portion of the constricted portion during the plastic working (gripped by the tool or part of the tool). For the insertion).

Alternatively, as in the invention described in claim 4, as the metal material, a long metal plate is subjected to a bending process, and both end edges in the width direction are butted together to form a hollow tube as a whole. .
In this case, preferably, as in the invention described in claim 5, the metal material is arranged between the portion where the first rack teeth are formed in the axial direction and the portion where the second rack teeth are formed. It is assumed that a thinning portion is provided in a portion where the both edges in the width direction are abutted with each other in the circumferential direction and a portion located on the opposite side in the radial direction of the portion.

  A dual pinion type electric power steering apparatus rack shaft according to a sixth aspect of the present invention is manufactured by the above-described method for manufacturing a dual pinion type electric power steering apparatus rack shaft of the present invention.

A dual pinion type electric power steering apparatus according to a seventh aspect includes a rack shaft, a first pinion shaft, a second pinion shaft, and an electric motor.
Of these, the rack shaft is supported in the housing so as to be axially displaceable, and is provided with first and second rack teeth at two positions separated from each other in the axial direction and having different phases in the circumferential direction. Yes.
The first pinion shaft is rotatable by a steering shaft in a state where first pinion teeth provided on a part of the outer peripheral surface in the axial direction mesh with the first rack teeth.
The second pinion shaft has second pinion teeth provided on a part of the outer peripheral surface in the axial direction meshing with the second rack teeth.
The electric motor applies an auxiliary force in the rotational direction to the second pinion shaft.
In particular, in the dual pinion type electric power steering apparatus of the present invention, the rack shaft is the rack shaft for the dual pinion type electric power steering apparatus of the present invention as described above.

  According to the rack shaft for the dual pinion type electric power steering device of the present invention configured as described above, the manufacturing method thereof, and the dual pinion type electric power steering device, the first and second rack teeth are connected to each other while suppressing the manufacturing cost. The positional relationship in the circumferential direction can be regulated with high accuracy. That is, these first and second rack teeth are placed on two portions of the outer peripheral surface of the material that are spaced apart in the axial direction at portions where the phases in the circumferential direction coincide with each other. It is formed by applying at least one process. For this reason, the first and second rack teeth can be formed at one time (for example, simultaneously in one press process or continuously without removing the jig), thereby reducing the number of processes and reducing the manufacturing cost. it can. Further, after forming the first and second rack teeth, a plastic working is performed by twisting the portion where the second rack teeth are formed with respect to the portion where the first rack teeth are formed. The phases of the two rack teeth in the circumferential direction are made different from each other. For this reason, the positional relationship in the circumferential direction between the first and second rack teeth can be accurately regulated.

The top view (A) which shows the 1st example of embodiment of this invention, aa sectional drawing (B) of (A), and bb sectional drawing (C) similarly. A plan view (A) showing the second example, a cc cross-sectional view (B) of (A), a dd cross-sectional view (C), and an ee cross-sectional view (D) of (A) . Plan view (A) showing the third example, FF sectional view (B) of (A), gg sectional view (C), and hh sectional view (D) of (A). . The figure similar to (D) of Drawing 3 showing the 4th example. The figure which cuts part and shows the dual pinion type electric power steering conventionally known. It is a figure which shows one example of the manufacturing method of a rack axis | shaft in order of a process, (A) is an end view (b) seen from the left of a top view (a) and (a), (B)-(F) are Sectional view (a), ii sectional view (b) of (a) and jj sectional view (c) of (a).

[First example of embodiment]
FIG. 1 shows a first example of an embodiment of the present invention corresponding to claims 1 to 2 and 6 to 7. The feature of this example is that the positional relationship in the circumferential direction between the first and second rack teeth 13 and 14 is accurately controlled while suppressing the manufacturing cost of the rack shaft 8b. Since the configuration and operation of other parts are the same as those of the conventional structure shown in FIG. 5, the overlapping illustrations and explanations are omitted or simplified.

  In the case of this example, the rack shaft 8b is formed in a substantially tubular shape as a whole by subjecting a metal material such as carbon steel to forging or cutting. A portion of the rack shaft 8b closer to one end in the axial direction {the left side portion in FIG. 1A) has a peripheral portion on the front end portion (lower end portion in FIG. 5) of the input shaft 6 (see FIG. 5). The first rack teeth 13 are provided to mesh with the first pinion teeth formed in the first. On the other hand, at the portion closer to the other end in the axial direction of the rack shaft 8b (the right portion in FIG. 1A), the phase in the circumferential direction is the angle θ from the first rack tooth 13 (0 degree <θ ≦ 180 degrees). In the case of the example shown in the range, the second pinion teeth provided on the outer peripheral surface of the tip end portion (lower end portion in FIG. 5) of the pinion shaft 9 (see FIG. 5) are engaged with each other at a position shifted by about 45 degrees. The second rack teeth 14 are formed. Further, flat surface portions 15a and 15b are respectively provided on portions of the outer peripheral surface of the rack shaft 8b that are slightly deviated from the portions where the first and second rack teeth 13 and 14 are formed toward the middle in the axial direction. Yes. Further, a constricted portion 16 having a smaller cross-sectional area than the portion near both ends in the axial direction is provided at the axially intermediate portion of the rack shaft 8b.

  The rack shaft 8b of this example as described above is manufactured by the following process. First, a material made of a metal such as carbon steel and having a tubular shape is placed in a die, and portions where phases in the circumferential direction coincide with each other at two positions separated in the axial direction are simultaneously pressed by a punch. Thereby, the first rack teeth 13 and the flat surface portion 15a are located near the one end of the material in the axial direction {leftward in FIG. 1 (A)}, and the portion near the other end in the axial direction {rightward in FIG. 1 (A)}. The second rack teeth 14 and the flat surface portion 15b are formed at the same time (by one press work). In this case, the pressure angles of the first and second rack teeth 13 and 14 are not necessarily the same, and may be different from each other. Also, before or after the press work, the intermediate part in the axial direction of the material is subjected to cutting work, plastic working such as forging work, drawing work, etc., and the cross-sectional area of the part is made smaller than the part near the axial end. Thus, the constricted portion 16 is provided and used as an intermediate material. Next, the flat surface portions 15a and 15b of the intermediate material are each gripped by a tool, and in the state where the rotation of the half piece in the axial direction of the intermediate material is prevented, the other half portion in the axial direction is also used as the half piece in the axial direction. Twist (relatively rotate in the rotational direction. Preferably twist both axial halves to the opposite side in the circumferential direction) to perform plastic working, and plastically deform the constricted portion 16 in the circumferential direction. Thereby, the phase in the circumferential direction between the first and second rack teeth 13 and 14 is made different from each other to obtain the rack shaft 8b. It should be noted that the part gripped by the tool during the plastic working may be a part other than the two flat surface parts 15a and 15b. That is, the first and second rack teeth 13 and 14 may be gripped by a tool, and the constricted portion 16 may be plastically deformed in the twisting direction.

  According to the rack shaft 8b of this example as described above, the positional relationship in the circumferential direction between the first and second rack shafts 13 and 14 can be regulated with high accuracy while suppressing the manufacturing cost. That is, in the case of this example, the two first and second rack teeth 13 are obtained by simultaneously pressing with a punch portions where the phases in the circumferential direction coincide with each other at two positions separated in the axial direction of the metal material. 14 can be formed simultaneously. For this reason, the number of processing steps for forming the first and second rack teeth 13 and 14 can be reduced, and the manufacturing cost can be reduced. Further, after the first and second rack teeth 13 and 14 are formed, plastic working is performed by twisting the portion where the second rack teeth 14 are formed with respect to the portion where the first rack teeth 13 are formed. For this reason, the positional relationship in the circumferential direction between the first and second rack teeth 13 and 14 can be accurately regulated. Further, since the constricted portion 16 provided at the intermediate portion in the axial direction of the rack shaft 8b is twisted and plastically deformed, the portion can be plastically deformed with high accuracy without using a large facility.

[Second Example of Embodiment]
FIG. 2 shows a second example of an embodiment of the present invention corresponding to claims 1 to 3 and 6 to 7. In the case of this example, a mounting portion 17 having a rectangular cross-sectional shape is provided at the axially intermediate portion of the constricted portion 16a that connects both axial ends of the rack shaft 8c, and a part of the tool is placed on the mounting portion 17. A locking hole 18 which is a locking portion described in the claims is provided for insertion and locking. The rack shaft 8c of this example is made of a metal such as carbon steel and is subjected to plastic processing such as cutting or forging on a circular tubular material, thereby making the cross-sectional shape of both axial ends circular, and the cross-section of the intermediate portion in the axial direction. The attached portion 17 is provided by making the shape rectangular, and the constricted portion 16a is formed by making the cross-sectional area of the portion adjacent to both sides in the axial direction of the attached portion 17 smaller than other portions. ing. Then, the first and second rack teeth 13 and 14 are provided on the axially opposite end portions with the outer peripheral surface of the mounted portion 17 as a reference surface. Further, the attached portion 17 is cut or punched before or after the process for providing the constricted portion 16a or the first and second rack teeth 13 and 14. The locking hole 18 that penetrates the portion 17 in the radial direction is provided. A part of the tool is inserted into the locking hole 18 and locked in a state in which the rotation with respect to the rack shaft 8c is prevented. Furthermore, at least any of the axial half piece provided with the first rack teeth 13 and the other axial half portion provided with the second rack teeth 14 in a state in which the rotation of the mounted portion 17 is prevented. The rack shaft 8c is obtained by performing plastic working by twisting one of them against the intermediate portion in the axial direction.
Since the configuration and operation of the other parts are the same as those of the first example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

[Third example of embodiment]
FIG. 3 shows a third example of an embodiment of the present invention corresponding to claims 1, 4 and 6 to 7. The rack shaft 8d of this example is bent into a long, strip-shaped metal plate having sufficient strength and rigidity, such as a steel plate, in the same manner as the rack shaft 8a manufactured by the conventional manufacturing method shown in FIG. It is made by applying, and the whole is formed in a substantially tubular shape. That is, in order to manufacture the rack shaft 8d, first, a long and rectangular (strip-shaped) base plate is obtained by punching a metal plate having sufficient strength and rigidity, such as a steel plate, by pressing. . Next, such a base plate is placed on, for example, the upper surface of a die and pressed with a punch, whereby the intermediate portion in the width direction is bent to form a first intermediate material having a U-shaped cross section. Alternatively, the first intermediate material is bent at two positions in the length direction (axial direction of the rack shaft 8d after completion) by bending a base plate provided with a narrow portion whose width direction dimension is smaller than other portions, The cross-sectional shape of the two positions in the length direction (the portion where the narrow portions are provided in the length direction) is a U-shape, and the cross-sectional shape of the portion deviating in the length direction from the portions where the narrow portions are provided. It can also be U-shaped.

  In any case, the first and second rack teeth 13a and 14a are respectively formed by press working on the front surface of the first intermediate material at two positions in the length direction, thereby forming the second intermediate material. Next, by bending the second intermediate material, both end edges in the width direction (circumferential direction) are brought into contact with each other (abutting or close to each other) to obtain a substantially intermediate third intermediate material.

  Of the outer peripheral surface of the third intermediate material obtained as described above, the portions slightly deviated from the portion where the first and second rack teeth 13a and 14a are formed slightly toward the middle in the axial direction are each gripped by a tool. , One half of the third intermediate material in the axial direction (half on the side on which the first rack teeth 13a are formed) and the other half in the axial direction (half on the side on which the second rack teeth 14a are formed) Torsion (relatively rotating in the direction of rotation. That is, twisting the other half or twisting both halves to the opposite side in the circumferential direction while preventing rotation of either half) Processing is performed to plastically deform the axially intermediate portion of the third intermediate material. Thereby, the phases in the circumferential direction between the first and second rack teeth 13a, 14a are made different from each other, and further, if necessary, after drawing the axial intermediate portion and both ends, The rack shaft 8d is obtained by joining the edges in the width direction with the welded portion 25. If sufficient rigidity and strength can be secured, the both ends in the width direction do not necessarily have to be joined by the welded portion 25. In this case, a cylindrical sleeve made of metal can be press-fitted into the end of the rack shaft 8d in the width direction. In addition, before twisting one axial half portion of the third intermediate material with respect to the other axial half portion, the axial intermediate portion of the third intermediate material is drawn to reduce the force required for the plastic processing. Reduction can also be achieved. Further, during this plastic working, a metal core material having rigidity higher than that of the metal constituting the third intermediate material (rack shaft 8d) is inserted inside the third intermediate material, Of the three intermediate materials, the portion gripped by the tool can be prevented from being deformed (crushed) in the radial direction. Furthermore, during the plastic working, by covering the outer peripheral surface of the axial half piece and the other axial half of the third intermediate material with a sleeve, the axial half piece and the axial direction of the third intermediate material It is also possible to prevent the other half from being deformed (expanded) in the radial direction and the first and second rack teeth 13a, 14a from being deformed.

In the case of the manufacturing method of the rack shaft 8d of the present example as described above, since the rack shaft 8d is formed by bending a metal plate, the rack shaft 8b according to the first example of the above-described embodiment ( As shown in FIG. 1, the manufacturing cost can be reduced and the weight can be reduced compared to the case of forging or cutting a metal material.
Since the configuration and operation of the other parts are the same as those in the first example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

[Fourth Example of Embodiment]
FIG. 4 shows a fourth example of the embodiment of the invention corresponding to claims 1, 4 to 7. In the case of the rack shaft 8e of this example, a portion including the welded portion 25 in the circumferential direction between the portions where the first and second rack teeth 13a, 14a (see FIG. 3) are formed in the axial direction, and the portion. The thinning portions 27a and 27b are provided in the portion located on the opposite side in the radial direction. For this reason, after the first and second rack teeth 13a and 14a are formed by press working, it is easy to perform plastic working by twisting the other half in the axial direction on one half of the axial direction (force required for plastic working) Can be reduced). Further, when the first and second rack teeth 13a and 14a are formed by pressing, stress concentrates on the welded portion 25 and is joined by the welded portion 25 in the width direction both ends. Can be prevented from spreading in a direction away from each other. Such metal removal parts 27a and 27b are provided with notches at both ends in the width direction of the middle part in the length direction and punch holes at the center part when punching out the metal plate as the raw material. It is provided by bending the plate.
Since the configuration and operation of the other parts are the same as in the third example of the above-described embodiment, illustration and description regarding the overlapping parts are omitted.

  In each example of the above-described embodiment, the case where the present invention is implemented with a rack shaft that is made by forging or cutting a metal and tubular material is described. It can also be cylindrical. Further, a forging process or a cutting process may be applied to a prismatic or rectangular tube-shaped material having a polygonal cross-sectional shape such as a rectangular column or a rectangular cylinder.

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3a, 3b Universal joint 4 Intermediate shaft 5 Steering gear unit 6 Input shaft 7 Housing 8, 8a-8e Rack shaft 9 Pinion shaft 10 Housing 11 Electric motor 12 Reducer 13, 13a First rack tooth 14, 14a Second rack teeth 15a, 15b Flat surface portion 16, 16a Constricted portion 17 Mounted portion 18 Locking hole 19 Base plate 20 Narrow portion 21 First intermediate material 22 Rack tooth 23 Second intermediate material 24 Third intermediate material 25 Welding Part 26 Fourth intermediate material 27a, 27b Carbide part

Claims (7)

A first rack tooth made of metal and formed in a part in the axial direction and in a part in the circumferential direction, a part in which the axial position deviates from the first rack tooth in the axial direction, and a phase in the circumferential direction Is a method of manufacturing a rack shaft for a dual pinion type electric power steering apparatus, comprising a second rack tooth formed on a portion deviated from the first rack tooth,
After the first and second rack teeth are formed in portions where the phases in the circumferential direction coincide with each other at two positions spaced apart in the axial direction on the outer peripheral surface of the tubular or bowl-shaped metal material, the axial direction With respect to the portion where the second rack teeth are formed, the phase in the circumferential direction of the first and second rack teeth can be made different from each other by applying plastic working to twist the portion where the first rack teeth are formed. A method of manufacturing a rack shaft for a dual pinion type electric power steering apparatus.   Before the plastic working, the constricted portion having a smaller cross-sectional area than the portion adjacent in the axial direction between the portion where the first rack teeth are formed in the axial direction and the portion where the second rack teeth are formed The manufacturing method of the rack shaft for dual pinion type electric power steering devices according to claim 1 provided with.   The method of manufacturing a rack shaft for a dual pinion type electric power steering apparatus according to claim 2, wherein a locking portion for locking a tool at the time of the plastic working is provided in an intermediate portion in the axial direction of the constricted portion.   The metal material according to any one of claims 1 to 3, wherein the metal material is formed into a hollow tubular shape by bending a long metal plate and abutting both edges in the width direction. A method of manufacturing a rack shaft for a dual pinion type electric power steering apparatus as described.   Between the portion where the first rack teeth are formed with respect to the axial direction and the portion where the second rack teeth are formed with respect to the axial direction, the metal material is a portion where the both edges in the width direction are butted together, and the portion The manufacturing method of the rack shaft for dual pinion type electric power steering devices according to claim 4, wherein a thinning portion is provided on a portion located on the opposite side in the radial direction. A first rack tooth made of metal and formed in a part in the axial direction and in a part in the circumferential direction, a part in which the axial position deviates from the first rack tooth in the axial direction, and a phase in the circumferential direction In a rack shaft for a dual pinion type electric power steering apparatus, comprising: a second rack tooth formed on a portion off the first rack tooth;
A rack shaft for a dual pinion type electric power steering apparatus, characterized by being manufactured by the manufacturing method according to any one of claims 1 to 5. A rack shaft provided with first and second rack teeth in portions where phases in the circumferential direction are different from each other at two positions spaced apart in the axial direction, supported in the housing so as to be capable of axial displacement.
A first pinion shaft that is rotatable by a steering shaft in a state in which the first pinion teeth provided on a part of the outer peripheral surface in the axial direction mesh with the first rack teeth;
A second pinion shaft in which a second pinion tooth provided on a part of the outer peripheral surface in the axial direction meshes with the second rack tooth;
In a dual pinion type electric power steering apparatus provided with an electric motor that applies auxiliary force in the rotational direction to the second pinion shaft,
A dual pinion type electric power steering apparatus, wherein the rack axis is a rack axis for a dual pinion type electric power steering apparatus according to claim 6.

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