Normal contact analysis for spherical pump based on fractal theory

Spherical pump has a ball-in-socket contact pattern between piston and cylinder. Therefore, traditional Hertz contact theory is not applicable and fractal theory is employed to investigate the conformal contact between piston and cylinder in this paper. The asperities contact on roughness surface is regarded as Hertz contact and friction effects are considered. Besides, the contact coefficient is proposed, which is affected by the structural parameters of piston radius and radial clearance as well as the material properties. Effects of fractal parameters, structural parameters, material property and friction coefficient on normalized normal contact stiffness are investigated and analyzed. Results indicate the normal contact stiffness can be improved by enlarging piston radius, material hardness and decreasing radial clearance, friction coefficient.