A study on the implementation of in-wheel motors in a VW Lupo

This report presents the results of the study on the implementation of an In-Wheel Motor (IWM) propulsion system and the design of a rear suspension for such a system for a Volkswagen Lupo. Previous research has been conducted at the Eindhoven University of Technology on the impact of in-wheel motors on the ride comfort of electric cars. The study shows that addition of unsprung mass reduces ride comfort and can increase suspension travel and dynamic wheel loads. But additional sprung mass, due to batteries in an electric vehicle in fact improves ride comfort. The study also concluded that improvements to the suspension system can mitigate the issues caused by unsprung mass. Designing and implementing the IWM propulsion system in an already existing ICE vehicle like the VW Lupo 3L would need further study with respect to the suspension design and its kinematics. The University is currently converting a VW Lupo diesel to a battery vehicle which uses a conventional front wheel drive system, i.e. a centrally mounted motor powers the wheels via drive shafts and a single reduction gear. It is called the Lupo EL, with EL being the abbreviation for Electric Lightweight. The technical specifications of several electric cars are studied to get an idea of the common design solutions of several manufacturers, especially in the area of battery capacity and motor specifications. These specifications, including others such as the vehicle mass and range gives an idea of where the Lupo EL stands in comparison to the electric vehicles on the market today. In order to design an IWM propulsion system for a car, the application of the car has to be understood. Based on the application, a set of performance requirements for the car are formulated. The electric motor specifications are then calculated for these requirements. Since the University is already working on converting a ICE VW Lupo 3L, the specifications of the Lupo EL are used to make a first estimation of the range that the IWM propelled car can achieve. The car will be called the Lupo EL2, with the two in-wheel motors at the rear. Furthermore, the design and layout of the Lupo EL’s battery compartment and rear suspension is described in this report. The current suspension system is not a feasible solution for the Lupo EL2. Initial simulation results of a SimMechanics multibody model of the Lupo EL2 shows that the car would lift considerably while accelerating forward. Also, assembling the IWM’s in this current configuration is found to be difficult. Hence,a new battery box design and several rear suspension designs have been proposed. The proposed designs are only preliminary and further simulations will have to be conducted.