Rim and tyre investigation for the in-wheel motor of an electric vehicle using simulations

Abstract

Global demands for sustainability and compelling requirements to reduce environmental impacts have greatly influenced the transportation industry to look into ways to reduce carbon emissions. In recent years, electric vehicle (EV) development has taken a new paradigm due to environmental pollution, global warming and depletion of fossil fuels. Unlike automobiles with internal combustion engines (ICEs), EVs have intrinsic advantage of zero emission during operation, when used with renewable energy source for charging batteries. To date most of the commercial EVs use permanent magnet motors (PMMs) due to specific low weight, and compact size (as it relies on use of permanent magnets for magnetic path). The key disadvantage of PMM is the need for rare earth elements, which also influence costs. To overcome the cost and availability issues associated with PMM, a new material or motor type is required to sustain EV growth. In this research alternative in-wheel (series mounting arrangement) switch reluctance motor (SRM) is designed which is fitted to a small car. The in-wheel SRM is selected due to specific advantages, i) use of non-rare earth element for magnetic path (stators and rotors), ii) low transmission losses (increased energy efficiency as it is direct drivetrain), iii) simplifies the design due to redundancy of mechanical systems (packaging of gearboxes, differentials, drive shafts and axles are not required, thus reducing the weight, cost and space requirements), and iv) increased ground clearance (due to redundancy of gear boxes and drive shafts). Small car provided substantial advantages with light vehicle weight, low power requirements, and enough mud guard clearances to implement in-wheel SRM. In a wheel, the rim has typically been designed as a cylindrical metallic component, functioning as holder between car chassis and tyres. Tyres were added onto the rim perimeter, as a link between roads and rims, providing required cushioning effect. Consequently, in-wheel SRM EV had the intrinsic advantage of direct drive. However, this design increased the overall mass, as the wheel required an appropriate rim-tyre construction. Moreover, the in-wheel design with an SRM added further weight at the rear of the vehicle, changing its dynamics and performance. In this research, different rim-tyre models were analysed in context of an in-wheel SRM for developing the customised rim design and tyre selection. The suitability of the rim- tyre based on an in-wheel drivetrain required performance simulation pertaining to loads and dynamics at tyre-road interface. The rim selection was based on finite element (FE) simulation of five different sets. The standards and regulations for producing passenger car wheels in Victoria, Australia, were studied and successfully implemented in the development phase of this study. This paper describes the rim-tyre study conducted for in-wheel SRM. Starting with the rim optimisation, an appropriate tyre based on low rolling resistance was selected. The development of the rim-tyre configuration of the in-wheel SRM featured: • Designing a rim for an in-wheel SRM design based on low unsprung mass and appropriate space that can accommodate motor, focusing on the rim size, shape and materials. • Optimising rim topology by comparing different types of rims based on low weight characteristics for thermal and deflection simulations, as well as following recommendations for Rim & Tyre Standards- Australia. • Tyre selection that meets two main objectives—low road resistance and clearance with mudguards—as well as detailed character mapping simulations to determine the appropriate tyre for the in-wheel design. • Designing motor-to-wheel attachments, whereby making the wheel an integral part does not affect maintenance.