The electrohydraulic power steering (EHPS) system is a new approach to the supply of power steering to vehicles requiring supplementary assist. It may be used in vehicles where a standard engine-driven pump system cannot be packaged. An additional benefit is the ability of the system to shift to manual operation as a function of road speed. Such a shift to manual operation could be based on input signals from the driver as well.The unit as presently designed is most efficiently used in a vehicle with a front end weight of less than 600 KG (1320 lbs.). However, if upsizing of the system should be required, the overall package has been designed with this option in mind.The electrohydraulic power steering system is designed in a modular format. The pump package consists of an electronic controller, motor, pump, and reservoir, attached to a main bracket. A unique hydraulic fluid is utilized to allow adequate performance over a wide temperature range.Other components of the overall system include the rack and pinion assembly and the intermediate shaft. The influence of the rack and pinion gear valve is significant, and plays a major role in determining driver feel during evasive maneuvers, transitions, and vehicle on-center modes of operation.Design features and limitations of each component which are crucial to overall system function are detailed in the appropriate section.