Modelling the performance of a continuously variable supercharger drive system

This paper details a simulation-based investigation into a novel forced-induction boosting system with a centrifugal-type supercharger driven from the engine crankshaft via a continuously variable transmission (CVT). This system acts as a pre-boost to a traditional fixed-geometry turbocharger and has been identified as a possible solution to improving the low-speed engine torque and transient response of future downsized and existing turbo-charged engines. The concept was modelled around an existing baseline high-speed direct-injection diesel engine model featuring a variable-geometry turbocharger.

Conclusions are drawn comparing the potential of the proposed system with the baseline engine in terms of the brake specific fuel consumption, and both the steady state and the transient performance. A design-of-experiments approach is applied to investigate the effects of the supercharger compressor size, the turbocharger compressor and turbine size, the CVT ratio, and the engine compression ratio on the system performance. Optimization techniques are then applied to identify the best settings for these parameters in the proposed system. Transient simulation was undertaken in a MATLAB/Simulink Ricardo WAVE co-simulation environment to develop the required control strategies for the CVT supercharger.

The proposed system demonstrates a significant improvement in the low-speed engine torque and transient response of the boosting system during tip-in pedal events, which it is proposed will result in a significant improvement in the vehicle performance and driveability.