Lubrication in the ball and socket joint of a swash plate mechanism

Abstract

The tribology of the ball and socket on the connecting rod in a swash plate engine is studied in the hydrodynamic regime. The engine operates at 1390rpm with an axial load on the rod as high as 1 x 10⁴N. The instantaneous load and kinematics from a previous study for a swash plate engine was used as the input. The ball and socket were assumed to be smooth surfaces. Starting with Reynolds' equation in spherical coordinates, the pressure was solved for and integrated over the surface area of the socket to calculate the force exerted on the rod. This force was matched to the input load force by adjusting the ball-socket clearance using a search algorithm provided by the software MATLAB. The calculation proceeded until the minimum clearance point approached the oil hole; the oil hole did not support the pressure so that hydrodynamic lubrication failed. Then, the dissipated friction power due to hydrodynamic shear was calculated over the range of crank angles where hydrodynamic lubrication applied. Results show that the dissipated power is essentially negligible. The frictional coefficient is on the order of 1 x 10⁻⁴. As the minimum clearance point approaches the oil hole, the clearance between the ball and socket comes within the asperity of the surfaces and there is a presence of boundary lubrication, which is outside the scope of the present study.