Directional Stability Enhancement of a Dual Path Front Hydrostatic Drive by Wire Off-Road Vehicle

Abstract

This paper discusses the inherent instability in a dual path front hydrostatic drive wheel, rear caster wheel off-road vehicle. A physical system model is created to simulate behavior to both normal operation and outside environmental inputs. The model starts with a simplified diesel engine and includes the hydraulic pumps, motors, and associated components. The hydraulic motor output is coupled to the ground using the drive wheel geometry. Disturbances are applied to each drive wheel. The force on each wheel is determined independently and combined to create a net vehicle acceleration, rotation, or both. A model based controller is designed to accurately steer the vehicle during both slow working speeds and high transport speeds. The control algorithm uses steering input, speed input, and yaw rate to control pump displacement for each wheel. The controller adjusts ground drive pump displacements when a disturbance is applied to either wheel to maintain longitudinal stability. The controller will be implemented on a vehicle using electro-hydraulic pump control. Steering and speed inputs have been modified for input to the controller rather than manually changing pump displacement. Additionally, joystick control has been implemented as an alternative drive mode. The joystick determines speed and steering input with a single hand while opening up the operator station for better visibility and manufacturing.