Torque Actuated Rear Steering for Urban Electric Commercial Vehicles

Abstract

This thesis describes research in rear steering, using a torque differential generated by in-wheel motors acting on steerable axles ('torque actuated steering') to enhance the performance of rigid (non-articulated) commercial vehicles. The main objectives are to:

Increase vehicle length while maintaining manoeuvrability at low speeds, At high speed, improve roll-over stability and emergency braking and cornering performance while maintaining accurate path following.

Chapter 1 reviews the current state of greenhouse gas emissions within the freight industry and methods for decarbonisation, predominantly the use of electric vehicles and higher capacity vehicles. Rear steering using in-wheel motors is presented as an attractive option to both reduce emissions by switching to an electric powertrain, and also by enabling the vehicle to be made larger without degradation to manoeuvrability. In chapter 2, a set of case studies of urban commercial vehicles are analysed to determine the potential emissions reductions that can be achieved using higher capacity electric vehicles with rear steering. Results showed that a 4.25 tonne light goods van would benefit most from the technology. In chapter 3, a low speed path-following controller using two nested PID controllers is developed for the 4.25 tonne light goods van, and axle geometry and dynamics are parameterised. In chapter 4, realistic non-linear models of the 4.25 tonne van and a 32 tonne, 4 axle refuse truck are developed using Simscape Multi-body for the purpose of controller testing. Chapter 5 investigated torque actuated rear steering at high speeds using a Linear Quadratic Regulator (LQR) to enhance roll stability and reduce off-tracking. Results showed that the rear steering could provide significant improvements to both. In chapter 6, the use of rear steering in braking scenarios is investigated by using adaptive Model Predictive Control (MPC) to manage the longitudinal wheel slips and the rear steering. The results showed that enhanced directional stability could be achieved in both a vehicle with rear steering provided by an independent actuator, or by in-wheel motors, however the use of in-wheel motors resulted in longer stopping distances. In chapter 7, the path following controller developed in chapter 3 is implemented on commercial controller hardware and validated through Hardware-in-the-loop (HIL) tests. It is shown that the use of torque actuated rear steering would allow this vehicle to carry a 54% greater payload volume and maintain comparable manoeuvrability to the original-length vehicle without rear steering.