Torque Control Strategy for Six Wheeled Skid Steered Vehicle with Articulated Suspension

Abstract

This research work contributes to the development of multi wheeled skid steered vehicle deploying in wheel motor at each individual wheel. The response of these vehicles are greatly dependent on the way torque distributed to the skid steered vehicle wheel so it should be done wisely. It was observed that less evident was prevailed in the research field of articulated suspension skid steered vehicle and rollover mitigation control of the skid steered vehicle. Hence in this thesis virtual prototype model of articulated suspension skid steered model was developed in Msc Adams that is re-known for provision of realistic solutions and co-simulation technique was performed and elaborated with the designed Proportional Integral Derivative (PID) controller for controlling longitudinal velocity control in Matlab/Simulink. This co-simulation technique eliminates the error introduced in final physical prototype by using different model for controller system design and the development of mechanical system. The gains of PID are tuned with PID tuner. The results show successful performance of co-simulation and achievement of the desired longitudinal velocity. In addition to this contribution, driving control algorithm including rollover control for four axle skid steered combat vehicle was proposed. It comprised of longitudinal velocity control, yaw rate control, rollover control for rollover mitigation, and longitudinal tire force distribution and finally slip control to limit slip. The input to the model are desired velocity and yaw rate while output are torques needed to be applied to the skid steered vehicle wheels to achieve desired response along with vehicle stability. The velocity control was designed by Proportional Integral (PI) controller and yaw rate control through sliding mode control based on the modified bicycle model for skid steered vehicle by combining first two axles. Since the model needed tire cornering stiffness values that is explained and evaluated by curve fitting data in Excel. The output from velocity control is desired total traction force which is modified by the rollover control when threshold lateral acceleration is reached indicating rollover propensity. The rollover control is designed by potential field function technique suitable for high speed and terrain with variable profile. While output from yaw rate control is desired total yaw moment needed to be applied to achieve desired yaw rate. According to both outputs of yaw rate control and longitudinal velocity control longitudinal tire force is determined by longitudinal tire force distribution and individual wheel torque are calculated by slip control in order to keep slip in limit if it exceeds the limit slip value. The model of combat skid steered vii vehicle was set in TruckSim since it wasn’t available in the software and co-simulation was performed with the driving control algorithm in Matlab/Simulink with and without rollover control for the velocity at which the desired sinusoidal dwell yaw rate makes the vehicle to rollover. The results indicates that the vehicle achieved the desired response without rollover control keeping slip below limit value but the vehicle rollovers. While addition of rollover control prevents rollover propensity by keeping lateral acceleration below limit value and verifies the successful performance of the driving control algorithm developed.