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Hydraulic power steering systems traditionally are sized in a straightforward manner with easily verifiable results. The source of power in conventional systems is an engine driven pump that is effectively a source of hydraulic flow. As energy consumption of auxiliary functions becomes significant, on-demand power sources are considered. Best typified by hydraulic pumps driven by electric motors, these on-demand sources are often power limited, and established sizing practices should be re-visited.

Electrically Powered Hydraulic Steering (EPHS) has provided value in passenger car applications by reducing power consumption at engine idle, providing only the required power during high speed lane-keeping, and allowing engine-off operation of vehicles with alternative power sources. This work discusses the design modifications made to use EPHS for medium duty commercial vehicle applications. Configuration options along with communication and diagnostic interface are discussed. Bench tests show the steady-state performance of the system. Experiments are done on a medium duty truck with the EPHS as the sole source of steering power to determine the speed of steer at various vehicle speeds. Finally, the power consumption for the EPHS system is compared to a conventional engine driven pump.

This paper is concerned with power consumption analysis for conventional steering system, the importance of duty cycle before choose appropriate pump drive system, and the energy saving potential of the proposed systems. After reviewing the recent efforts in developing energy-efficient steering system, two new on-demand pump drive systems are proposed to provide varying flow according to vehicle/engine speed: one is the combination of a sized pump without flow control valve and an Electrical Power Hydraulic Steering (EPHS) unit; the other is the combination of multiple EPHS units. The energy saving advantage of the combinations will be emphasized for different duty cycles.

Today's hydraulic steering systems suffer from poor efficiency due to their use of throttling valves to build pressure inside the steering gear. In this work, we propose a novel way to build and control pressure by controlling the flow from the pump and without throttling. As a result, such a system will be more energy efficient. Moreover, the ability to control pressure inside a steering gear, and thus assistance torque, allows the steering system to become an active closed-loop system rather than a passive open-loop system. Specifically, by controlling pressure, one can closely control the hand wheel torque the operator feels. Consequently, the new pressure control concept has the potential to not only significantly improve the efficiency of steering systems, but also offers the numerous benefits of torque overlay without the use of an electric motor.

A computer controlled steering system providing an artificial feel or synthetic torque feedback to the driver has recently been launched into production in the commercial vehicle market. This work compares the artificial feel control strategy with prior electric power steering control strategies and hydraulic power steering. Suitability for integration with other vehicle control systems such as lane sensing and electronic stability enhancement is explored.