TORQUE RIPPLE MINIMIZATION IN A VARIABLE DISPLACEMENT LINKAGE MOTOR (VDLM) THROUGH THE CUSTOMIZATION OF PISTON TRAJECTORY

Hydraulic motors generate torque ripple, periodic fluctuations in output torque, adversely affecting performance for many applications. Traditional efforts to mitigate torque ripple have mainly addressed kinematic aspects by altering structural motor parameters, leaving dynamic torque ripple, influenced by fluid compressibility, less explored. This study introduces a novel approach to minimize torque ripple across different operating conditions in a Variable Displacement Linkage Motor (VDLM) by optimizing piston trajectory. Torque ripple was controlled by creating a custom piston trajectory defined by control points of a B-spline and tuning motor valve timing. The research employed kinematic and cylinder models to simulate the motion of the cam-linkage mechanism of the VDLM and the pressure dynamics in the piston chambers. The torque output and ripple of the motor were predicted through a simulation, and the motion of the pistons was optimized to minimize ripple. The VDLM torque ripple was reduced below 5% for a targeted corner condition and remained under 12% for other operating conditions, including fractional displacements of the motor. The optimized trajectory was compared to a baseline sinusoidal path, showing a simultaneous reduction in torque ripple at different operating conditions. Furthermore, the simulation results show good agreement when compared to experimental data obtained from a VDLM prototype constructed with an optimal piston trajectory. These results highlight the effectiveness of piston trajectory optimization in improving hydraulic motor performance, offering substantial benefits for applications requiring smooth output torque.