Year

2016

Degree Name

Master of Philosophy

Department

School of Mechanical, Materials and Mechatronic Engineering

Abstract

Torque vectoring in electric ground vehicles (EGV) with individually actuated in-wheel motors (IAIWM) presents the opportunity to implement a wide range of control strategies for controlling vehicle yaw rate to improve vehicle stability and performance. The use of IAIWMs allows for alternative vehicle layout configurations which previously would have been unavailable to conventional internal combustion engine vehicles. The use of higher level control architectures to distribute torque amongst the two front wheel-drive, rear wheel-drive or four wheel-drive in-wheel motors of an electric ground vehicle has presented the opportunity to design characteristics of electric ground vehicles through active control of power trains. Previously in internal combustion engine vehicles, these characteristics have been indirectly tuned via common chassis parameters. The use of modern components such as in-wheel motors in electric ground vehicles also provides additional benefits such as precise torque generation, fast motor response and the capability to produce forward and reverse torque as well as regenerative braking to improve energy efficiency, and enabling the estimation or measurement of useful feedback information. This feedback information can be applied to direct yaw-moment control (DYC) strategies which can be used to improve vehicle performance. The application of these new vehicle configurations can allow for differential torque output to the left and right hand side of vehicles, generating a yaw moment, and hence directly affecting the yaw rate of the vehicle in a practice known as direct yaw-moment control. In addition to the potential electric ground vehicles possess for superior vehicle stability and performance, they are also a viable solution for the environmental concerns pertaining to transport needs and meeting lower emissions targets. In this thesis the process of converting an internal combustion engine vehicle to a fully electric vehicle with IAIWM will be presented. The first aim of this thesis is to conduct a literature review in which control strategies available for allocating torque to individually actuated in-wheel motors on an electric ground vehicle are investigated, with the objectives of improving vehicle dynamics performance through control of yaw rate response. Secondly, this thesis will present the development of a simulation framework which models vehicle behaviour and addresses the major performance indicators relevant to evaluating vehicle dynamics performance with regards to torque vectoring(TV)/DYC strategies. Next, this thesis aims to show the effects of a traction control strategy, developed for active differentials, when adapted and extended for use as a direct yaw-moment control strategy on an electric ground vehicle with individually actuated in-wheel motors. This torque vectoring control strategy’s effect on a vehicle’s dynamic performance will be validated and analysed through use of simulations, using the platform developed as part of the work involved in this thesis. The simulation platform presented in this thesis is also intended for use as tool for investigation on future projects pertaining to the experimental electric vehicle. The next objective of this thesis is to establish the measurement and estimation techniques available and how they could be implemented through suitable hardware to measure and record the relevant performance indicators of vehicle dynamics in relation to a DYC strategy. Finally, this thesis aims to prove the accuracy of the simulation platform developed using experimental data acquired from sensors implemented on the experimental vehicle. The simulation platform is validated experimentally as an accurate representation of the experimental system and its performance in terms of realistic vehicle dynamics. Experimental data is used to recreate real-life driving manoeuvres in the simulation platform, and verify its performance by comparing results.

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