Shock absorber and method for manufacturing shock absorber

Patent metadata

Field	Value
Publication number	US-12553143-B2
Application number	US-202118022730-A
Country	US
Kind code	B2
Filing date	May 20, 2021
Priority date	Aug 27, 2020
Publication date	Feb 17, 2026
Grant date	Feb 17, 2026

Abstract

Provided is a shock absorber in which trivalent chromium is used to achieve both high hardness and low frictional force at a high level without using hexavalent chromium which is suspected of causing damage to the human body and the environment, and a method for manufacturing the shock absorber.
A shock absorber ( 100 ) of the present invention includes: a cylinder ( 1 ) which is filled with hydraulic oil ( 3 ); a piston rod ( 2 ) which is movable in the cylinder ( 1 ); and an oil seal ( 8 ) which is fixed to the cylinder ( 1 ) and slides on the piston rod ( 2 ), in which a hard layer mainly containing chromium obtained from a trivalent chromium plating bath is provided on a surface of the piston rod ( 2 ), and the hard layer contains both a crystalline material and an amorphous material, and also contains an additive other than chromium.

First claim

The invention claimed is:

1 . A shock absorber comprising:
a cylinder which is filled with hydraulic oil; a piston rod which is movable in the cylinder; and an oil seal which is fixed to the cylinder and slides on the piston rod, wherein a hard layer mainly containing chromium obtained from a trivalent chromium plating bath is provided on a surface of the piston rod, the hard layer contains both a crystalline material and an amorphous material, and also contains an additive other than the chromium, and the hard layer has a crystallization rate of 5 to 99%, as calculated from a peak integral intensity ratio of a value measured by X-ray diffraction and the following (Equation 1):
Crystallization rate(peak integral intensity ratio %)=(crystalline/(crystalline+amorphous))×100  (Equation 1).

2 . The shock absorber according to claim 1 , wherein the additive contains at least one element of hydrogen, carbon, nitrogen, or oxygen, and a content of the additive is 0.5 mass % or greater and 4.3 mass % or less.

3 . The shock absorber according to claim 1 , wherein the hard layer has a Vickers hardness HV of 800 HV or greater and a frictional force of less than 47.3 N.

4 . The shock absorber according to claim 1 , wherein the hard layer has a surface roughness Rz of 0.6 μm or less.

5 . A method for manufacturing a shock absorber
the shock absorber including: a cylinder which is filled with hydraulic oil; a piston rod which is movable in the cylinder; and an oil seal which is fixed to the cylinder and slides on the piston rod, the method comprising a plating step of forming a plating film including a hard layer mainly containing trivalent chromium on a surface of the piston rod, wherein the plating step is performed at a cathode current density of 100 A/dm2 or greater in a plating bath containing a trivalent chromium salt, a carboxylic acid, a pH buffering agent, and a conductive salt and having a pH of ≤0.1.

6 . The shock absorber according to claim 2 , wherein the hard layer has a Vickers hardness HV of 800 HV or greater and a frictional force of less than 47.3 N.

7 . The shock absorber according to claim 2 , wherein the hard layer has a surface roughness Rz of 0.6 μm or less.

8 . The shock absorber according to claim 6 , wherein the hard layer has a surface roughness Rz of 0.6 μm or less.

Assignees

• Hitachi Astemo Ltd

Inventors

• Kawamura Toshinori
• Kanemoto Hiroshi
• Nakano Hiroshi
• Hoshino Akihito

Classifications

• F16F2230/02

  Surface features, e.g. notches or protuberances · CPC title

• F16F2228/007

  of solids, e.g. hardness · CPC title

• F16F2226/02

  Surface treatments · CPC title

• F16F2224/0208

  Alloys · CPC title

• F16F2222/12

  Fluid damping · CPC title