Modelling and Control of a Novel Clutchless Multiple-Speed Transmission for Electric Vehicles 2019-24-0063

Conventional electric vehicles adopt either single-speed transmissions or direct drive architecture in order to reduce cost, losses and mass. However, the integration of optimized multiple-speed transmissions is considered as a feasible method to enhance EVs performances, (i.e. top speed, acceleration and grade climbing), improving powertrain efficiency, saving battery energy and reducing customer costs. Perfectly in line with these objectives, this paper presents a patented fully integrated electric traction system, as scalable solution for electrifying light duty passenger and commercial vehicles (1.5-4.2 tons), with a focus on minibuses (<20 seats). The adoption of high-speed motor coupled to multiple-speed transmission offers the possibility of a relevant efficiency improvement, a 50% volume reduction with respect to a traditional transmission, superior output torque and power density.

The proposed clutchless four-speed transmission is specifically conceived and designed to have the good matching with the traction electric motor. Indeed, clutches and synchronizers are not required thanks to the small inertia of the traction motor and its fast regulation in both torque and speed mode (torque modulation process). Therefore, an advanced shifting control system/strategy has been developed to reduce the time shifting, linked to the degree of jerk and the power interruption, guaranteeing the coordination of all the gear-shifting actuators despite the randomness of the gear shifting process.

After the description of the system layout, the paper gives an insight of the plant dynamic model and its equations. The controller architecture along with its strategies are also presented. The effectiveness of the proposed solution is proven through an extensive set of simulations carried out for a vehicle running on a real driving cycle.