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.

Highlights

  • 1.1 TU/e Lupo Electric Lightweight (EL)In 2009 the Dynamics and Control group of the TU Eindhoven (TU/e) started the development of battery electric vehicle, using a VW Lupo 3L as donor vehicle [1]

  • To assess regenerative braking strategies that are currently applied in electric vehicles, a selection of vehicles is investigated that are popular in the Netherlands

  • This paper describes the development and implementation of a One Pedal Driving algorithm

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Summary

Introduction

In 2009 the Dynamics and Control group of the TU Eindhoven (TU/e) started the development of battery electric vehicle, using a VW Lupo 3L as donor vehicle [1]. An important characteristic of the vehicle is the large battery capacity (27 kWh LiFePO4) in comparison to the vehicle dimensions and mass (1060 kg). This is the reason why the vehicle is named TU/e Lupo EL, with EL being the abbreviation of Electric Lightweight. This paper discusses the changes to the control software that affects the behavior of the accelerator and brake pedal, which have resulted in a major improvement of the driving experience and an improved energy efficiency

Powertrain and braking control
Motivation for OPD and coasting
Outline of the paper
Driving tests with existing electric cars
Tesla Model S
Renault Zoe
Mitsubishi Outlander PHEV
Volkswagen e-Up!
BMW i3
General requirements
Inverter settings for OPD
OPD accelerator pedal mapping
Coasting
Regenerative braking
Vehicle acceleration map
Controller enhancements
Driving tests
Energy usage
Pedal operation
12 OPD Default
Subjective evaluation
Findings
Conclusions
Full Text
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