Hu, B., Tang, H., Akehurst, S., De Freitas, A. et al., "Modelling the Performance of the Torotrak V-Charge Variable Drive Supercharger System on a 1.0L GTDI - Preliminary Simulation Results," SAE Technical Paper 2015-01-1971, 2015, doi:10.4271/2015-01-1971.
A supercharger system which boosts the engine via a direct drive from the engine crankshaft has been identified as a possible solution to improve low-end torque and transient response for a conventional turbocharged SI engine. However, the engine equipped with a fixed-ratio supercharger is not as fuel-efficient especially at high load and low speed due to the fact that a large portion of the intake mass air flow has to recirculate through a bypass valve causing inevitable mechanical and flow losses. In addition, the fixed drive ratio of the supercharger which is mainly determined by the full-load requirements might not be able to provide sufficient over-boost during a transient. The fact that a clutch may be necessary for high engine speed operation on the fixed-ratio supercharger system is another issue from the perspective of cost and NVH performance.This paper details a simulation-based investigation to look at alternative boosting systems applied to a Ford 1L EcoBoost engine, in order to achieve an enhanced target torque curve. The objective was to assess the performance of a centrifugal-type supercharger system driven via a Torotrak continuously variable transmission (CVT) against a fixed-ratio positive-displacement supercharger solution. Both concepts feature a fixed-geometry waste-gated turbocharger. The results show that, compared to the fixed-ratio positive-displacement supercharger counterpart, the BSFC was improved by approximately 1% at full load for the Torotrak V-Charge system. Under part load, both clutched and non-clutched configurations were assessed and discussed. It was demonstrated that a clutch may not be necessary for the Torotrak V-Charge system and only a minor decline of the part load BSFC performance was observed if a clutch was not adopted. In transient, the simulated results suggest that the Torotrak V-Charge system could provide better transient response when compared to the fixed-ratio positive-displacement supercharger counterpart.This paper also briefly discussed the performance of the Torotrak V-charge system with a novel compressor. It was demonstrated that the novel compressor allowed the drive ratios (including step-up ratio and epicyclic ratio) to be optimised to improve the full & part load BSFC without the need for a clutch. It was also demonstrated that the novel compressor configuration can achieve better transient response.