DESIGN AND TESTING OF A DUAL-PATH FRONT HYDROSTATIC DRIVE-BY-WIRE CONTROL SYSTEM FOR AN OFF-ROAD VEHICLE

This article discusses the design, implementation, and testing of a dual-path front hydrostatic drive wheel, rear caster wheel off-road vehicle. A mathematical model of the engine and major machine components was used to simulate vehicle behavior and design a drive-by-wire control system for stability and turning. The drive-by-wire system was implemented on the machine, and the model and controller were experimentally verified through testing. The physical system model contains a simplified diesel engine, hydraulic pumps and motors, gearboxes, wheels, and associated interconnecting components. The diesel engine was coupled to two hydraulic pumps via a gear box, with each hydraulic pump independently supplying flow to each hydraulic wheel motor. External disturbances were applied to the contact patch of each drive wheel. The force on each wheel was determined independently and combined to simulate vehicle acceleration, rotation, or both. A model-based controller was designed for and implemented on the machine. In the simulation, the control algorithm used steering input, speed input, and yaw rate to control pump displacement for each wheel. The controller adjusted ground drive pump displacements to maintain directional (yaw) stability when a disturbance was applied to either wheel. The controller algorithm was also implemented and verified on a test vehicle by removing the existing mechanical linkages previously used to control the hydraulic pump displacements and retrofitting electrohydraulic pump control. A joystick replaced the steering wheel and propulsion lever and was used to provide the driver inputs to the electronic controller. Testing the vehicle demonstrated positive results with stable operation up to 20 km/h (12 mph).