Lubrication characteristics on sliding surfaces between piston and cylinder in a piston pump and motor - (Effects of running-in, profile of piston top and stiffness)

Running-in tests have been carried out for a piston pump and motor and the lubrication characteristics have been investigated. The friction characteristics on the sliding surfaces have been studied with pin and V-block type of Falex friction tester before the running-in tests, to select suitable conditions of the running-in test. The running-in condition has been decided with considering parameters such as friction force, separation voltage, roughness, roundness and cylindricity. The results are summarized as follows: (1) the rate of running-in of the cylinder with low hardness and low stiffness is lower than that of the piston with high hardness and high stiffness, (2) the optimum taper angle at the piston top for friction force is found, (3) the friction force decreases with decreasing stiffness of the piston.