Friction characteristics on sliding part between piston and cylinder of swash plate type piston pump (Effect of geometric shape of piston)

Abstract

The friction characteristics on sliding part between piston and cylinder in a swash plate type piston pump in which improvement of the power density is demanded affect the equipment performance and the efficiency. In this paper, targeting a straightly cylindrical piston and tapered pistons, the effects of geometric shape of the piston on the friction characteristics have been investigated based on both the results of friction force measurement using a model machine and the numerical calculation considering mixed lubrication. Moreover, the effectiveness of adopting each of the pistons to the swash plate type piston pump has been examined from view point of friction characteristics. The results are summarized as follows: (1) Optimum taper angle of the piston which can improve the friction characteristics will exist under severe lubrication conditions. (2) The degree of friction characteristics improvement can be formulated as a function of the Sommerfeld number which is one of important parameters to determine the bearing performance. (3) Adoption of tapered pistons may improve the friction characteristics under mild lubrication conditions. (4) The tapered piston will whirl widely in the cylinder than in the case of the straightly cylindrical piston, load carrying capacity due to squeeze effect of the fluid can be expected to increase.