A Coupled Elastohydrodynamic Lubrication Model for Radial Piston Motors Incorporating Piston Tilt and Deformation

This study presents a coupled Elastohydrodynamic Lubrication (EHL) simulation model for a multi-lobe radial piston motor and its experimental validation under high-load and low-speed conditions. These operating regimes pose challenges such as severe wear and excessive power loss due to complex lubricating interfaces, which are difficult to characterize experimentally. To address this, the model solves a density-based Reynolds equation incorporating multi-body dynamics, throttling losses, and elastic deformations of components. Simulation results reveal that lubrication regimes and asperity contact pressures depend strongly on chamber pressure and motor speed. The roller–bushing interface operates under mixed lubrication, while the piston–cylinder interface exhibits boundary lubrication during high-load conditions due to severe asperity contact. Piston tilt and asymmetric deformation significantly affect film thickness and pressure distribution of lubricating interfaces. Incorporating a friction model based on experimental data enabled a realistic analysis of power loss, identifying the upper piston–cylinder interface and throttling loss as major contributors. The model provides a detailed framework for simulating and analyzing tribological behaviors in radial piston motors and can be used to evaluate the effects of design parameters such as clearance, geometry, and material properties.