JP5091041B2 - Power steering device, pinion shaft, and method of manufacturing pinion shaft - Google Patents

Description

  The present invention relates to a pinion shaft that transmits a steering force of a driver to a rack bar, and a power steering device using the pinion shaft.

  Conventionally, in the power steering device disclosed in Patent Document 1, crowning is performed in the tooth trace direction of the pinion gear to allow the tooth crossing angle change on the meshing surface of the rack gear and the pinion gear (the tooth surface is projected outward along the tooth trace). Processing to shape).

The pinion gear is processed by cutting using a hob, and a crowned pinion gear is formed by appropriately moving the bob during cutting. The pinion gear is also formed by forging. Since the metal material forming the pinion gear is hardened during forging, the tooth surface strength is higher in forging than in the case of forming by cutting.
JP 2005-53327 A

  However, when the pinion gear is formed by forging, the forging die has a cup shape, so the material is pushed in from the opening of the die, so that the die diameter is changed from the deepest part to the opening to remove the die after forming. It is necessary to enlarge it. For this reason, crowning could not be applied to the tooth surface by forging.

  The present invention has been made paying attention to the above problems, and an object thereof is to provide a pinion shaft and a power steering device capable of forming a tooth surface having the same function as a crowned tooth surface even by forging. There is to do.

In order to achieve the above object, in the present invention, the pinion shaft is configured such that the tooth thickness in a right-angle cross section of the tooth gradually decreases from the root to the tooth tip, and includes the tooth tip, and the pinion shaft at any height from the tooth root. tooth thickness tapering or gradually increases along the tooth trace direction, and have contact to the engagement position, the tooth thickness in the axial direction substantially central portion of said pinion shaft, wherein the axial root portion and the axial end portion of the pinion shaft It was decided that it was thicker than the tooth thickness.

  Therefore, it is possible to provide a pinion shaft and a power steering device that can form crowned tooth surfaces by forging.

  Hereinafter, the best mode for realizing the pinion shaft and the power steering apparatus of the present invention will be described based on the embodiments shown in the drawings.

[System configuration of power steering system]
Example 1 will be described. FIG. 1 is a system configuration diagram of an electric power steering apparatus to which the present power steering apparatus is applied. As long as a rack and pinion is used, the power steering device may be used, or a manual steering device may be used instead of the power steering device.

  The electric power steering apparatus includes a steering wheel SW, a torque sensor TS, a steering shaft SS, a rack bar 1, a power assist unit 3, a steered wheel 7, and a control unit 10.

  The steering wheel SW is connected to the pinion shaft 100 via the steering shaft SS. The power assist unit 3 is spaced apart from the upper side of the vehicle in the axial direction of the rack bar 1 and applies assist torque to the rack bar 1 via the pinion shaft 100 by driving the motor.

  The power assist unit 3 is a power assist device that drives the motor M by the control unit 10 and applies assist torque to the rack bar 1. The power assist unit 3 is provided with a torque sensor TS connected to the steering wheel SW.

  The control unit 10 applies assist torque to the rack bar 1 connected to the steered wheels 7 by driving the motor M of the power assist unit 3 based on the steering torque detected by the torque sensor TS.

[Front view]
FIG. 2 is a front view of the power steering apparatus. For the sake of explanation, only the rack tube 2 is shown in a sectional view in FIG. 2, and the axial direction of the rack bar 1 and the direction opposite to the housing 30 is defined as the positive x-axis direction.

  The rack bar 1 is accommodated in a rack tube 2 and both ends thereof are connected to steered wheels (not shown). A housing 30 is provided on the rear surface of the rack tube 2, and a pinion shaft 100 connected to a steering wheel (not shown) is provided in the housing 30. The rack bar 1 meshes with the pinion shaft 100 to transmit the steering force of the driver, and the steering is performed.

[Details inside the housing]
FIG. 3 is a partial axial sectional view of the pinion shaft 100 in the housing 30. The direction opposite to the pinion shaft 100 with respect to the rack bar 1 is defined as the y-axis positive direction.

  Inside the housing 30, a pinion shaft 100, a rack retainer 12, and a retainer support portion 13 are provided. A rack bar 1 is provided between the rack retainer 12 and the pinion shaft 100 and meshes with the pinion shaft 100.

  The rack retainer 12 has a shape in which one end of a column is cut into a cylindrical shape, and is formed in a U shape when viewed from the cylinder side. The rack retainer 12 is supported by a retainer support portion 13 via a spring 14, and abuts against the rack bar 1 at an arcuate sliding contact surface 12a to urge the rack bar 1 in the negative y-axis direction.

  The tooth surface 111 of the pinion shaft 100 is formed by an involute curve, and even if the teeth 11 of the rack bar 1 are trapezoidal, smooth engagement is realized. The pinion shaft 100 is formed of a shaft portion 100a where the tooth portion 110 is not provided and an effective tooth portion 100b where the tooth portion 110 is provided, and a concave curved surface is provided between the shaft portion 100a and the effective tooth portion 100b. A rounded-up portion 100c is formed.

  When forming the tooth part 110 by forging, when the tooth part 110 is formed by press-fitting the axial tip 102 of the pinion shaft 100 into a cup-shaped mold, the part that is completely press-fitted into the mold is Although the highly accurate tooth part 110 is obtained, the precision of the tooth part 110 becomes insufficient at the corner part of the mold (between the part where the tooth part 110 is formed and the part where the tooth part 110 is not formed).

  Therefore, a raised portion 100c which is a concave curved surface is provided at a portion corresponding to the corner of the mold, and the mesh between the rack bar 1 and the pinion shaft 100 is ensured by distinguishing from the tooth portion 110.

[Pinion shaft]
4 is a schematic view of the tooth portion 110 of the pinion shaft 100, and FIG. 5 is an enlarged perspective view of the tooth portion 110. As shown in FIG. For explanation, FIG. 5 shows a diagram in which the tooth portion 110, which is a helical tooth, is converted into a straight line. In FIG. 5, the direction from the axial base 101 of the pinion shaft 100 toward the axial tip 102 is the ξ-axis positive direction, and the teeth of the comparative example in which the tooth thickness of the tooth tip 113 is constant are indicated by broken lines.

  FIG. 6 is a cross-sectional view in the perpendicular direction of the axial base portion 101, the axial tip portion 102, and the substantially axial central portion 103 of the tooth portion 110. The tooth thickness at the meshing position of the axial base portion 101 and the axial tip portion 102 is A, and the tooth thickness at the meshing position of the substantially axial central portion 103 is C. Furthermore, the tip circle diameter formed by the tip 113 is constant at any position in the tooth trace direction.

  Since the tooth part 110 is a helical tooth, the tooth trace is rotating with respect to the axial direction, and has a tooth surface 111 having a convex crowning process on the outside. The tooth thickness in the cross section perpendicular to the tooth trace direction gradually decreases from the tooth root 112 toward the tooth tip 113, and the tooth thickness at the tooth tip 113 is thinner than the tooth thickness of the tooth root 112.

  Further, the meshing center line with the rack bar 1 is indicated by a bold line. The meshing center line is inclined toward the tooth root 112 side toward the substantially central portion 103 in the axial direction of the pinion shaft 100, and is curved with the tooth root 112 side as a convex.

  Therefore, the distance from the tooth tip 113 to the meshing center line is b at the axial root portion 101 but B at the axial tip portion 102 (B> b). Further, the tooth thickness at the meshing center line gradually increases toward the substantially axial central portion 103, reaches the maximum value C at the axially approximately central portion 103, and becomes the minimum value A at both axial end portions 101 and 102 (C > A).

  For this reason, the tooth surface 111 has a function equivalent to a crowned tooth in which the substantially central portion 103 in the axial direction protrudes outward at the meshing position, and an error in the tooth crossing angle on the meshing surface of the rack bar 1 and the pinion shaft 100. To achieve good tooth contact.

  Further, in the case of a tooth having a normal crowning shape, the tooth thickness of the substantially central portion 103 in the axial direction is larger than the tooth thickness of the axial base portion 101. In this embodiment, the tooth thickness of the tooth portion 110 gradually decreases from the axial root portion 101 toward the axial tip portion 102 along the tooth trace direction. Therefore, it is possible to insert a die from the tip of the unprocessed pinion shaft 100 and form the tooth portion 110 by forging using this die.

  In the present embodiment, the tooth thickness of the tooth portion 110 gradually decreases from the axial root portion 101 along the tooth trace direction toward the axial tip portion 102, but the tooth portion 110 and the shaft portion 110a are separated. The tooth portion 110 is attached to the shaft portion 100a in the opposite direction to the present embodiment, and the tooth thickness of the tooth portion 110 gradually increases from the axial root portion 101 toward the axial tip portion 102 along the tooth trace direction. You may form so that it may do.

[Effect of Example 1]
(1) (6) The pinion shaft 100 is
The tooth thickness in the right-angle cross section of the tooth portion 110 gradually decreases from the tooth root 112 toward the tooth tip 113,
The tooth thickness of the tooth tip 113 gradually decreases toward the axial tip 102,
The tooth thickness C at the axially central portion 103 that is the meshing position is thicker than the tooth thickness A at the axial root portion 101 and the axial tip portion 102 of the pinion shaft 100.

  Accordingly, it is possible to provide a pinion shaft and a power steering device that can form a tooth surface having the same function as a crowned tooth surface even by forging.

(2) (7) The tooth surface 111 of the pinion shaft 100 is an arcuate curved surface convex outwardly,
The tooth surface 111 at the meshing position is convex outward from the tooth surface 111 at the axial root portion 101 and the axial tip portion 102 of the pinion shaft 100.

  As a result, even if the tooth thickness gradually decreases toward the tip end portion 102 in the axial direction, it is possible to obtain a good tooth contact by absorbing the error of the intersecting angle of the teeth on the meshing surface as in the case of the crowning-shaped teeth. it can.

  (4) (9) The tooth surface 111 of the pinion shaft 100 is an involute curve. Thereby, even if the teeth 11 of the rack bar 1 are trapezoidal, smooth meshing can be realized.

(5) (10) The pinion shaft 100 is formed of a shaft portion 100a and an effective tooth portion 100b.
A raised portion 100c that is a concave curved surface is formed between the shaft portion 100a and the effective tooth portion 100b.

When the tooth part 110 is formed by forging, the tooth part 110 is formed by press-fitting the axial tip 102 of the pinion shaft 100 into a cup-shaped mold, but the part that is completely press-fitted into the mold is Although the highly accurate tooth part 110 is obtained, the precision of the tooth part 110 becomes insufficient at the corner part of the mold (between the part where the tooth part 110 is formed and the part where the tooth part 110 is not formed).
Therefore, by providing a rounded-up portion 100c that is a concave curved surface in a portion corresponding to the corner of the mold and distinguishing from the tooth portion 110, the tooth portion 110 of the rack bar 1 can be surely engaged with the tooth portion 110 with high accuracy. Thus, the meshing between the rack bar 1 and the pinion shaft 100 can be ensured.

  (11) The shaft member is inserted into the mold, and the tooth portion 110 of the pinion shaft 100 is formed by forging. Thereby, the effect similar to said (1) can be acquired.

  Example 2 will be described. The basic configuration is the same as that of the first embodiment. In the first embodiment, the diameter of the tip circle formed by the tip 113 is constant, but in the second embodiment, the diameter of the tip circle of the tooth portion 110 is gradually reduced toward the tip portion 102 in the axial direction.

  FIG. 7 is a partial cross-sectional view in the axial direction of the pinion shaft 100 in the housing 30 of the second embodiment. FIG. 8 is a schematic diagram of the tooth portion 110 of the pinion shaft 100 according to the second embodiment, and FIG. 9 is an enlarged perspective view of the tooth portion 110. 8 and 9, the tooth portion 110 in the first embodiment having a constant tooth tip circle diameter is indicated by a one-dot chain line, and in FIG. 9, the tooth in the comparative example in which the thickness of the tooth tip 113 is constant in the ξ-axis direction is indicated by a broken line. It shows with.

  As in Example 1, the tooth thickness at the meshing center line gradually increases toward the axially central portion 103, and is A at the axial root portion 101 and the tip portion 102, and C at the axially central portion 103 (C>). A). Thus, the pinion shaft 100 capable of forming a tooth surface having the same function as that of the crowned tooth surface by forging is formed.

  The diameter of the tooth tip circle gradually decreases from the axial root 101 toward the axial tip 102, and inclines toward the tooth 112 as it approaches the substantially central portion 103 in the axial direction. . In Example 2, the tooth height at the axial base 101 is higher by h than Example 1 and the comparative example, and the tooth height at the axial tip 102 is lower by h ′ than in Example 1 and Comparative Example.

  As in the first embodiment, the meshing center line with the rack bar 1 is indicated by a thick line, and the meshing center line is inclined toward the tooth base 112 toward the substantially central portion 103 in the axial direction of the pinion shaft 100, and the tooth The original 112 side is curved with a convex shape.

  Here, in Example 2, the tooth tip 113 is also inclined toward the tooth root 112 side toward the substantially central portion 103 in the axial direction, and the tooth tip 113 and the meshing center line are provided at equal intervals. Accordingly, the distance between the tooth tip 113 and the meshing center line takes a constant value B along the ξ axis direction, and the distance between the tooth tip 113 and the meshing center line is also the axial base portion even in the axially central portion 103. Similar to 101 and the axial front end 102, B is obtained.

  For this reason, the meshing depth between the teeth 110 and the teeth 11 of the rack bar 1 is a constant value B. In the second embodiment, the tooth height of the axial tip 102 is shorter by h ′ than in the first embodiment. However, since the meshing depth is a constant value B, the meshing position transitions to the tooth root 112 direction, and the axial center is approximately the center. The tooth thickness at the portion 103 is ensured.

[Effect of Example 2]
(3) (8) The diameter of the tip circle of the pinion shaft 100 is gradually reduced toward the axial tip portion 102. Thereby, in addition to the effect of Example 1, since a meshing depth is the constant value B, a meshing position can be changed to the direction of the tooth root 112, and the tooth thickness in the substantially axial center part 103 can be ensured.

[Other embodiments]
The best mode for carrying out the present invention has been described based on the embodiments. However, the specific configuration of the present invention is not limited to each embodiment, and the scope of the invention is not deviated. Design changes and the like are included in the present invention.

1 is a system configuration diagram of an electric power steering apparatus to which a pinion shaft of the present application is applied. It is a front view of a power steering device. It is a pinion shaft direction fragmentary sectional view near the rack bar in a housing. It is a schematic diagram of the teeth of a pinion shaft. It is an expansion perspective view of a tooth. It is a right-angle direction sectional view of an axial direction root part, an axial direction tip part, and an axial direction approximate center part of a tooth. 6 is a partial cross-sectional view in the axial direction of a pinion shaft in Embodiment 2. FIG. It is a schematic diagram of the teeth of the pinion shaft in Example 2. It is an expansion perspective view of the tooth in Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rack bar 7 Steering wheel 11 Rack tooth | gear 100 Pinion shaft 100a Shaft part 100b Effective tooth part 100c Round-up part 101 Axial root part 102 Axial front-end | tip part 110 Tooth part 111 Tooth surface 112 Tooth root 113 Tooth tip M Motor SS Steering shaft SW Steering wheel

Claims (11)

A steering wheel and a steering shaft that are rotated by the steering operation of the driver;
A rack bar connected to the steered wheels and having rack teeth;
A pinion shaft connected to the steering shaft;
A power steering device having a motor for applying a steering assist force to the steering shaft or the pinion shaft;
The pinion shaft is
The tooth thickness in the right cross section of the tooth gradually decreases from the root to the tip,
The tooth thickness at any height from the root including the tooth tip gradually decreases or gradually increases along the direction of the tooth trace,
And have your meshing position, the tooth thickness in the axial direction substantially central portion of the pinion shaft, the power steering apparatus characterized by thicker than the tooth thickness in the axial direction the root portion and the axial end portion of the pinion shaft. The power steering apparatus according to claim 1, wherein
The tooth surface of the pinion shaft is an outwardly convex arcuate curved surface,
Wherein the tooth flanks at the engagement position, the power steering apparatus wherein the axial root portion of the pinion shaft and than the tooth surfaces in the axial tip portion is convex outwardly. In the power steering device according to claim 1 or 2,
The diameter of a tip circle of the pinion shaft gradually decreases or gradually increases along the tooth trace direction. The power steering apparatus according to any one of claims 1 to 3,
The tooth surface of the pinion shaft is an involute curve. In the power steering device according to any one of claims 1 to 4,
The pinion shaft is formed of a shaft portion and an effective tooth portion,
A power steering device, wherein a rounded-up portion that is a concave curved surface is formed between the shaft portion and the effective tooth portion. A pinion shaft,
The tooth thickness in the right cross section of the tooth gradually decreases from the root to the tip,
The tooth thickness at any height from the root including the tooth tip gradually decreases or gradually increases along the direction of the tooth trace of the pinion shaft,
And have your meshing position, the tooth thickness in the axial direction substantially central portion of said pinion shaft, pinion shaft, wherein thicker than the tooth thickness in the axial direction the root portion and the axial end portion of the pinion shaft. The pinion shaft according to claim 6,
The tooth surface is an outwardly convex arcuate curved surface,
The meshing the tooth surface at the position, the pinion shaft, characterized in that the axial root portion of the pinion shaft and than the tooth surfaces in the axial tip portion is convex outwardly. The pinion shaft according to claim 6 or 7,
The pinion shaft is characterized in that a tip circle diameter gradually decreases toward the tip in the axial direction. The pinion shaft according to any one of claims 6 to 8,
The tooth surface is an involute curve. The pinion shaft according to any one of claims 6 to 9,
Formed from a shaft and an effective tooth,
A pinion shaft having a concave curved surface formed between the shaft portion and the effective tooth portion. A method of manufacturing a pinion shaft that meshes with a rack,
Insert the shaft member into the mold, form the teeth of the pinion shaft by forging,
The tooth thickness in the right-angle cross section of the tooth gradually decreases from the root to the tip,
The tooth thickness at any height from the root including the tooth tip gradually decreases or gradually increases along the direction of the tooth trace of the pinion shaft,
And have your meshing position, the tooth thickness in the axial direction substantially central portion of the pinion shaft, the manufacture of the pinion shaft, wherein thicker than the tooth thickness in the axial direction the root portion and the axial end portion of the pinion shaft Method.

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