An Off-Road Competition Hydraulic Vehicle

A 4-wheel drive off-road vehicle was designed and fabricated using extensive hydraulic technology for the SAE (Society of Automotive Engineers) Mini-Baja competition. The vehicle incorporates an open hydrostatic transmission using a single pump and four independent drive motors. A constant power controller that maintains full engine power to drive the vehicle or stores excess energy in two accumulators controls the pump. Each of the drive motors is independently controlled using a proportional meter-out pressure control valve. The use of pressure control allows the flow to each of the motors to be proportioned based on the dynamics of the vehicle. A CAN bus controller is used in conjunction with a steering sensor to provide differential motor speed control in maneuvering conditions that insures 4-wheel drive availability at all times. Steering of the vehicle is achieved by articulating the chassis using a rotary actuator and multi-motion actuator controlled by the driver. Incorporating these features in the vehicle results in a very small turning radius relative to traditional competition vehicles. The use of the hydrostatic transmission allowed the engine to be moved to the front of the vehicle giving a better weight distribution and making the 4-wheel drive effective throughout the range of the competition. Storing the excess energy in accumulators provided a “power boost” capability beyond the fixed engine power level that could be used to accelerate out of turns or pass on straight-aways. The CAN bus controller allowed the car to be “tuned” to track conditions without the need for extensive hardware changes or modifications.