Numerical analysis of the influence of ball-joint clearance on the elastohydrodynamic performance of slipper interfaces in axial piston motors

The tribological behavior of the slipper–swashplate interface is a primary factor limiting the operational lifespan and power density of swashplate axial piston motors. Under high hydraulic loading, the assumption of rigid body motion becomes invalid because elastic deformations within the slipper assembly substantially modify the geometry of the lubricating film. This study examines the typically overlooked influence of non-conformal contact mechanics in the piston-ball/slipper-socket joint and its role in driving deformation of the sealing land. Hertzian contact theory was employed to characterize the pressure distribution across the ball–socket interface, and a series of finite element simulations were conducted in ANSYS to quantify the effects of varying joint clearances. The results demonstrate that increasing the clearance significantly reduces the effective contact area, thereby generating localized stress concentrations. These stress concentrations impose a more concentrated mechanical load on the slipper body, inducing significant elastic warping and geometric nonlinearity across the sealing land interface. The resulting increase in local contact pressures not only amplifies structural distortion but also may promote higher frictional losses within the ball–socket joint, as higher normal loads between relatively moving surfaces intensify boundary and mixed lubrication conditions. This effect contributes to greater energy dissipation and accelerated wear, further affecting the overall tribological performance of the assembly. To evaluate the influence of structural deformation on the interface’s load-carrying capacity, a hypothetical contact region was defined to simulate the mechanical interaction within the ball-socket joint. This was achieved by isolating the slipper and performing a parametric study in which the contact angle, measured radially from the central axis, was systematically varied. For each discrete angular increment, the specific pressure distribution required to equilibrate the piston’s axial force was numerically determined and applied as the primary boundary condition. A comparative analysis shows that a clearance of 15 μm, corresponding to a contact angle of 60°, minimizes sealing land distortion. The resulting deformation field was then incorporated into the MULTICS Multiphysics framework to evaluate its influence on the load capacity of the slipper–swashplate interface.