Computer model of rotary-vane engine shaft synchronization under physical electric-drive constraints

Abstract

A coupled computational model of shaft synchronization for a rotary-vane internal combustion engine is developed that accounts for the electrical constraints of the control machines. Existing models of such engines treat the electric machines as ideal torque sources capable of producing any required torque instantly and without limits, so they cannot show whether real hardware is able to maintain synchronization. The proposed model combines the mechanical dynamics of two shafts, the variable gas torque of the working chambers, the loss of working-fluid mass past the vane seals, and a physically constrained electric drive based on a permanent magnet synchronous motor under field-oriented control. The actuating machines are treated as drives whose torque is formed through winding current dynamics and is bounded by the current and voltage available from the hardware and by the back electromotive force, which grows with rotational speed. Above the electrical level, a synchronization algorithm updates the commanded mean torque after every working stroke from the change in the kinetic energy of the shafts. The model is implemented as a browser-based simulator. Numerical experiments show that the admissible engine scale is governed primarily by the torque reserve of the drive, that is, the ratio of the maximum torque the drive can deliver to the mean gas torque of the cycle. Synchronization is lost as this reserve approaches unity. The same criterion describes the boundary for two working media: with the same drive, the admissible chamber volume for compressed air exceeds that for combustion by more than an order of magnitude, and this difference is fully explained by the ratio of the mean gas torque per unit chamber volume. The compressed-air regime is proposed as the basis for the first laboratory test bench, because it allows a considerably larger engine geometry with the same hardware.