Patent ID: 8215463

Claim:
A variable damping-force damper, comprising: a cylinder tube filled with a working fluid that is a magnetic fluid or a magneto-rheological fluid containing magnetic particles; and a piston that partitions an inside of the cylinder tube into first and second chambers, has a communication hole for circulating the work fluid between the first and second chambers and has an electromagnetic coil that applies a magnetic field to the work fluid within the communication hole; the variable damping-force damper controlling a damping force by changing viscosity of the work fluid within the communication hole by feeding power to the electromagnetic coil; wherein the variable damping-force damper has a sliding surface that slides under an influence of the magnetic particles during contraction; the sliding surface has a heat-treated nickel plating film on the surface thereof; wherein the sliding surface is an outer peripheral surface of the piston or an inner peripheral surface of the cylinder tube and the Ni plating film is provided at least on the inner peripheral surface of the cylinder tube; wherein a thickness of the Ni plating film is 15 μm or more when a length of sliding portion of the piston in an axial core direction is 50 mm; and when the length of the sliding portion is shorter than 50 mm, the thickness of the Ni plating film is set such that the shorter the length of the sliding portion, the thicker the thickness of the Ni plating film becomes beyond 15 μm.