Electronic Controls Improve Hydrostatic Vehicle Drivability

Hydrostatic drives offer many advantages in certain vehicle applications. In zero-turn-radius vehicles, advantages such as infinitely variable transmission, high torque transfer, transmission responsiveness, and non-clutching direction reversing make this system the transmission of choice. Currently, most hydrostatic transmissions use mechanical linkages to set the displacement of the hydrostatic pumps. The use of non-linear linkage connections and mechanical damping are used to give the required vehicle drive feel. The use of electrical actuators on hydrostatic pumps along with minimal use of sensors allows the design engineer to replace the conventional mechanical linkages on hydrostatic drive vehicles. In some instances the cost savings gained with the removal of the linkages offset the cost of the electronic circuitry, actuators and sensors. Greater advantages are gained by the use of electronic controls in the customization of vehicle drive feel, reduction in operator fatigue, and the ability to adjust the pump displacement based on engine operating parameters.

This paper will compare the mechanically actuated hydrostatic transmission on a dual drive zero-turn-radius vehicle to the electronic control of the same vehicle. The problems associated with the mechanical system will be discussed along with the approach in solving the problem using electronic controls. Also highlighted will be some of the additional vehicle features that can be explored with the use of electronic controls.