Intelligent mobility control of a hybrid electric off-road vehicle with individual wheel control
This work focuses on the potential benefits that can be gained from the use of Individual Wheel Control on a large off-road vehicle. The vehicle concerned is a theoretical, six-wheel drive, off-road Hybrid-Electric Vehicle based on an existing conventional six-wheel-drive Combat Support Vehicle developed by QinetiQ (formerly DERA). The proposed vehicle utilises Individual Wheel Control through the use of six, in-wheel, Hub Mounted Electric Drives. A novel intelligent mobility control system is developed to fully exploit the capability that this configuration offers. Initially, simplified vehicle models are developed to design and test the mobility control components. The control systems developed are Traction Control, Anti-lock Braking and Direct Yaw-moment Control. These controllers are developed individually, with the aim of improving vehicle stability and handling behaviour. Once tested, they are combined into a single system on a basic non-linear handling model, where the controller co-ordination scheme is demonstrated. Preliminary testing shows the full controller to reduce driver workload by offering predictable vehicle handling and improved vehicle stability. An eighteen-degree of freedom vehicle model is then developed, incorporating the vehicle suspension and load transfer characteristics, based on the conventional vehicle. Field test data taken from the existing vehicle trials is used to partially validate the on-road handling behaviour of the vehicle model. On this model, the full mobility controller is tuned to offer optimal performance for a large range of driving conditions and an extension of the controller to limit side-slip at high lateral accelerations is introduced. The controller is then tested on and off-road against a fixed torque distribution system and also the conventional vehicle equipped with various differentials. By exploiting the high torque capability and controllability of the electric drive, the potential of Individual Wheel Control is demonstrated, along with the benefits offered by the hybridelectric drivetrain with respect to mobility. Through the simulation work conducted, the major benefits of Individual Wheel Control are shown to be: improved stability and manoeuvrability; more predictable vehicle behaviour leading to reduced driver workload; accurate yaw rate tracking and increased safety at handling limits.