Modeling and dynamics of epitrochoid generated orbital rotary piston LSHT hydraulic motor: A bondgraph approach

In this paper the dynamics of epitrochoid generated Orbital 'rotary piston machine' (ROPIMA) type 'low speed high torque' (LSHT) hydrostatic unit are studied. The complex variation of the volume of a chamber of such a machine with shaft rotation along with dynamic characteristics of the rotary flow distributor valve, interchamber leakages, fluid compressibility, inertia of orbiting rotor, etc. demand a structured approach to arrive at its mathematical model. In conventional approaches the system morphology gets obscured as the mathematical model is arrived at. Owing to the lack of modularity the errors in deduction of equations may remain eclipsed. Bondgraphs provide a structured approach to model engineering systems. The bondgraph model of the LSHT orbital motor is presented in this work. Relevant simulation results are discussed. The mathematical model was found to be stiff and its integrations were costly and time consuming. A tractable approach to estimate its steady state behavior is suggested and validated. The authors believe that such an approach would be suitable in the initial stages of design of such machines and in the development of control systems where these machines are used as actuators.