Effect of geometric shape of piston on power loss of sliding part between piston and cylinder in swash plate type piston pump and motor

Abstract

The power loss due to the friction and the leakage in the sliding part between piston and cylinder of a swash plate type piston pump and motor affects the equipment performance and the efficiency. The friction and the leakage in the sliding part depend on the motion of the piston which relates to the lubrication characteristics. In this paper, for each straight cylindrical piston, forward and reverse tapered pistons, the motion of the piston under mixed lubrication has been numerically calculated, each power loss due to the friction and the leakage has been estimated based on the result, and the effect of geometric shape of the piston on the power loss of the equipment has been investigated. The results are summarized as follows: (1) The effective taper angle exists from the viewpoint of the friction power loss and minimization of total power loss, and the reduction rate of both power losses is closely related to the modified Sommerfeld number Sm with constituent parameters such as equipment operating conditions and design conditions. (2) The total power loss reduces when adopting the reverse tapered piston with an optimum taper angle for the pump and the motor, but it increases by adopting the forward tapered piston. (3) The reduction rate of the friction power loss for the pump is high in the region where the Sm value is small in the forward tapered piston and in the region where the Sm value is large in the reverse tapered piston. (4) The power loss due to the leakage of the pump and the motor decreases when adopting the reverse tapered piston, but increases in the case of adopting the forward tapered piston.

Keywords

• oil hydraulics
• piston pump and motor
• swash plate type
• piston
• geometric shape
• frictional force
• leakage flow
• power loss
• minimization
• mixed lubrication
• sommerfeld number