Design and realization of a One-Pedal-Driving algorithm for the TU/e Lupo EL

Abstract

Since 2011 the Eindhoven University of Technology (TU/e) is using an in-house developed battery electric vehicle based on a Volkswagen Lupo 3L for educational and research projects. The TU/e Lupo Electric Lightweight (EL) is able to recuperate kinetic energy by using regenerative braking. A brake pedal based regenerative braking strategy demands applying a combination of hydraulic and regenerative brake force. A proper control of this brake blending proves to be challenging. An advantage of an electric vehicle compared to an ICE car is that substantial amounts of deceleration can be achieved without applying the friction brakes. These observations have led to the concept of One Pedal Driving (OPD) where the accelerator pedal can also be used to perform regenerative braking. A similar concept is applied in for example the BMW i3 and Tesla Model S and is rated quite positively by drivers. Since kinetic energy cannot be recuperated with 100% efficiency, for some driving conditions the best thing to do is neither propel nor brake the vehicle and just let the car roll freely, which is known as coasting. During coasting minimal energy is used which improves the overall energy efficiency. To assess regenerative braking strategies that are currently applied in electric vehicles, a selection of vehicles has been investigated. These vehicles are subjectively evaluated by driving tests on public roads where special attention is paid to the regenerative braking and coasting characteristics. Before designing a suitable OPD algorithm, a list of requirements is composed. The overall motor performance limits are investigated and based on the OPD requirements a general accelerator pedal map is designed and implemented. Based on a limited number of driving tests, subjective and objective conclusions regarding energy efficiency and drivability are drawn. The tests with various drivers indicate a slightly improved driving efficiency. Furthermore, all drivers comments positively on using OPD as being very intuitively and are able to adapt to it quickly.