Performance Evaluation of a Newly Designed Robotized Gearbox for Electric City Buses
Automated manual transmissions (AMT) play an important role in reducing energy consumption in electric vehicles. However, a major concern that limits the usage of AMTs is their poor gear shifting quality that reduces the driving comfort. In this study, a new pneumatically driven robotized gearbox without clutch and synchronizer is introduced and a gear shifting control scheme is developed for an electric city bus. A six speed manual transmission has been robotized (automated) by using two pneumatic double acting cylinders, four three position double solenoid air control valves and a transmission control unit. The speeds of the electric motor and the output shaft of the gear mechanism are well synchronized during shifting process. Experimental study carried out on a prototype electric bus revealed that the new design improves the gear shifting quality such that the shift speed is quite fast and the shift jerk is within the acceptable. The performance of the proposed gearbox has been also compared with that of fixed ratio gearbox and the comparative test results showed that, thanks to the proposed gearbox system, the electric motor is operated efficiently within rated torque limits and the energy consumption is reduced to a large extent.