Rack bar and method for manufacturing rack bar

Patent metadata

Field	Value
Publication number	US-10562559-B2
Application number	US-201515500950-A
Country	US
Kind code	B2
Filing date	May 25, 2015
Priority date	Aug 25, 2014
Publication date	Feb 18, 2020
Grant date	Feb 18, 2020

Abstract

Rack bar 10 for transmitting a steering operation to steered wheels while converting a rotational movement of a pinion shaft rotatably connected to a steering wheel into an axial movement, the rack bar being formed by conducting a die forging process on a material having an approximately circular cross section. A pair of face width-enlarged portions 15 is provided at both ends that rack teeth 14 have in face width direction. With this, it becomes possible to ensure face width dimension W of rack teeth 14 larger than outer shape S of a circular cross section of rack main body 13 (material), which results in an improvement of a contact gear ratio between the pinion teeth and the rack teeth.

First claim

The invention claimed is:

1. A method of manufacturing a rack bar for transmitting a steering operation to steered wheels while converting a rotational movement of a pinion shaft rotatably connected to a steering wheel into an axial movement by the presence of rack teeth engageable with pinion teeth formed on the pinion shaft, the rack bar being formed by conducting a die forging process on a rod-like metal material having an approximately circular cross section, comprising:
a step of processing the material between a first shaping die and a second shaping die, the first shaping die being located on one side of the material with respect to an axis passing through a center of an approximately circular cross section of the material to contribute to the formation of rack teeth while the second shaping die is located on the side opposite to the first shaping die to contribute to die forging in cooperation with the first shaping die,
the first shaping die including a rack teeth-forming section that contributes to the formation of the rack teeth and enlarged face width-forming sections for forming a pair of face width-enlarged portions by making the material flow plastically at the time of die forging to project outwardly from an outer portion of the approximately circular cross section of the material, the face width-enlarged portions being provided at both ends of the rack teeth in a face width direction,
the first and second shaping dies defining a pair of burr-forming cavities or gaps therebetween, a center position of which being located biasedly from the axis toward the side of the rack teeth, the burr-forming cavities or gaps being able to form a pair of burrs when the material is flowed thereinto;
a forging step for performing die forging, where the material is deformed between the first and second shaping dies with pressure so that shapes of the rack teeth-forming section and the enlarged face width-forming sections are transferred to the material; and
a burr-removing step of removing a part of the burrs that have been formed by the material flowing into the pair of burr-forming cavities at the forging step, thereby forming a pair of burr-removed portions,
wherein the pair of face width-enlarged portions are formed such that a face width dimension of the rack teeth including the face width-enlarged portions is gradually decreased from a bottom land toward a top land of the rack teeth, and
wherein the pair of face width-enlarged portions are provided with a pair of arcuate portions at both ends in the face width direction, the arcuate portions having a radius of curvature smaller than that of the material.

2. The method of manufacturing a rack bar, as claimed in claim 1 , wherein the pair of arcuate portions are formed outwardly from the bottom land of the rack teeth in the radial direction originating from the axis.

3. The method of manufacturing a rack bar, as claimed in claim 1 , wherein the pair of arcuate portions are formed outwardly from the outer portion of the material in the radial direction originating from the axis.

4. The method of manufacturing a rack bar, as claimed in claim 1 , wherein:
the burr-removing step comprises removing the part of the burrs so as to thereby form a pair of burr-removed portions, and
parts of the pair of burr-removed portions located away from the rack teeth in a direction perpendicular to the face width direction are disposed coincident with the axis or biased from the axis toward the side of the rack teeth.

5. The method of manufacturing a rack bar, as claimed in claim 1 , wherein the rack teeth are formed at a middle region of the material in a longitudinal direction of the material.

6. A method of manufacturing a rack bar for transmitting a steering operation to steered wheels while converting a rotational movement of a pinion shaft rotatably connected to a steering wheel into an axial movement by the presence of rack teeth engageable with pinion teeth formed on the pinion shaft, the rack bar being formed by conducting a die forging process on a rod-like metal material having an approximately circular cross section, comprising:
a step of processing the material between a first shaping die and a second shaping die, the first shaping die being located on one side of the material with respect to an axis passing through a center of an approximately circular cross section of the material to contribute to the formation of rack teeth while the second shaping die is located on the side opposite to the first shaping die to contribute to die forging in cooperation with the first shaping die,
the first shaping die including a rack teeth-forming section that contributes to the formation of the rack teeth and enlarged face width-forming sections for forming a pair of face width-enlarged portions by making the material flow plastically at the time of die forging to project outwardly from an outer portion of the approximately circular cross section of the material, the face width-enlarged portions being provided at both ends of the rack teeth in a face width direction,
the first and second shaping dies defining a pair of burr-forming cavities or gaps therebetween, a center position of which being located biasedly from the axis toward the side of the rack teeth, the burr-forming cavities or gaps being able to form a pair of burrs when the material is flowed thereinto;
a forging step for performing die forging, where the material is deformed between the first and second shaping dies with pressure so that shapes of the rack teeth-forming section and the enlarged face width-forming sections are transferred to the material; and
a burr-removing step of removing a part of the burrs that have been formed by the material flowing into the pair of burr-forming cavities at the forging step,
wherein a bore is provided at a location opposite to the rack teeth with respect to the axis, the bore being formed so as to be scooped inwardly from the approximately circular cross section of the material in a radial direction originating from the axis.

Assignees

• Hitachi Automotive Systems Ltd

Inventors

• Oikawa Satoru
• Nakasuka Shuuji
• Yamanaka Shinichi

Classifications

• B62D3/126 Primary

  characterised by the rack · CPC title

• F16H55/26

  Racks · CPC title

• F16H19/04

  comprising a rack · CPC title

• B21K1/767 Primary

  Toothed racks · CPC title

• B62D3/12

  of rack-and-pinion type · CPC title