Abstract
The aim of the research is to investigate multiple-speed transmissions for electric vehicles. This research is driven by the requirement to reduce emissions within the automotive industry increasing the demand for electric vehicles. The typical torque characteristics of an electric motor allow a clutchless single-speed transmission to be used, yet it is suggested by literature that the adoption of multiple-speed transmissions can benefit the energy consumption and vehicle performance. However, the published research up to date is limited in this field and lacks credible quantifiable evidence and as such motivates this research. The author developed complex non-linear models in Matlab/Simulink of case study vehicles with single and multiple-speed transmissions to analyse vehicle performance and simulate driving cycles to calculate energy consumption. The main focus of the research was based around a single and two-speed transmission developed by Vocis Drivelines and Oerlikon Graziano. The two-speed transmission has a novel mechanical layout comprising a friction clutch and sprag clutch allowing seamless gearshifts, a gearshift controller was developed as part of the research. The two transmissions were modelled in simulation with the gearshift dynamics of the two-speed transmission being simulated and considered with multiple controllers. In addition, a hardware-in-the-loop test rig was built at the University of Surrey by the author to test the prototype single and two-speed transmissions. The vehicle models were validated using the hardware-in-the-loop test rig whilst allowing performance tests and driving cycles to be carried out. The research showed that the adoption of the two-speed transmission over the single-speed transmission gave rise to reductions in energy consumption over numerous driving cycles of up to 4% for the case study vehicles. The vehicle performance was also improved with the top speed increased by 12% and the 0-100 km/h time reduced by 2%. In addition, a novel four-speed dual-motor drivetrain was investigated through simulations and compared with optimised single-speed and two-speed variants. The novel four-speed transmission delivered up to a 9% and 5% improvement in energy consumption during standard driving cycles over the single-speed and two-speed transmissions, respectively. The four-speed transmission allowed up to a 25% improvement in top speed and a 10% improvement in 0-100 km/h time over the two-speed transmission.