Hydraulic actuator device

A method for producing a hydraulic actuator device structured to be driven by being supplied with hydraulic pressure, the hydraulic actuator device comprising a piston-cylinder mechanism in which a liquid-tight seal member formed of resin material is set on an outer periphery of a piston and is in sliding contact with an inner peripheral surface of a cylinder, the method comprising:

• setting, as at least one control parameter of a surface roughness shape of the inner peripheral surface of the cylinder, a kurtosis of a roughness curve and a skewness of the roughness curve, each of which is a height direction characteristic average parameter;
• forming the inner peripheral surface of the cylinder to have a surface roughness shape whose measurement values of the kurtosis and the skewness are predetermined respective control values or less;
• and
• categorizing a formed cylinder according to whether (i) the kurtosis and the skewness of the inner peripheral surface of the formed cylinder are respectively determined to exceed a predetermined kurtosis value and a predetermined skewness value, or (ii) the kurtosis and the skewness of the inner peripheral surface of the formed cylinder are respectively determined not to exceed the predetermined kurtosis value and the predetermined skewness value.