Design, simulation, and testing of an energy storage hydrostatic vehicle transmission and controller

This thesis documents the design, development, and testing of an energy storage hydrostatic vehicle transmission and controller. Primary benefits include regenerative braking and the decoupling between the engine and road load. The controller was developed and installed on a vehicle, demonstrating the potential fuel economy savings and feasibility of hydrostatic transmissions (HST) with energy storage. Controller algorithms maximize fuel economy and performance. Being true "drive by wire," the computer controls the engine throttle position while intermittently running the engine. The engine only operates to recharge the accumulator or under sustained high power driving.; The series hybrid configuration, developed in this thesis, allows many features to be implemented in software. The torque applied to each wheel can be controlled independently, both during braking and acceleration. The vehicle incorporates a pump/motor at each front wheel, with provisions to add units at the rear wheels, providing true all wheel drive, anti-lock braking, and traction control abilities.; Controller development involved several steps. Axial piston pump/motor models were developed and implemented into a simulation program. The simulation program allows fuel economy studies, component sizing, performance requirements, and configurations to be quickly evaluated, over a variety of driving cycles. In addition, the dynamics of inserting a valve block at each wheel were studied. The valve block allows pump/motors not capable of over-center operation to be used. In many cases, these units exhibit higher efficiencies. Successful switches were obtained in the lab and modeled analytically.; The research developed the necessary hardware and software for complete vehicle control. The hardware consists of the computer, data acquisition boards, sensors, circuit boards, and control panel. The software maintains safe and efficient operation under normal driving conditions. Engine operating and efficiency models were developed to allow future open loop control of the engine-pump system. A stepper motor is used to control the throttle position. Both distributed and centralized controllers are used on the vehicle, maximizing computer and vehicle performance.; The final result is a vehicle incorporating a hydrostatic transmission with energy storage, allowing normal driving operation and performance with increased gains in fuel economy.