Abstract
The effect of stiffness of sliding part end on the friction force has been experimentally examined for sliding part between a piston and a cylinder in a piston pump and motor. The stiffness of sliding part end was decreased by installing annular groove. The friction force was measured by means of Piezo-type load washers. It was reconfirmed that the decrease in the stiffness of the sliding part end was effective in the reduction of the friction force also even for reciprocating sliding part. The friction forces decreased remarkably with decreasing the stiffness not only of the piston top but also of the cylinder. The depth of the annular groove is one of the main factors which may affect the friction force.
