Design of power steering systems for heavy-duty long-haul vehicles

Conventionally, all auxiliaries present in a heavy-duty vehicle (e.g., power-steering pump, air-conditioning compressor) are engine-driven systems, which put high constraints on their performance. Outputs (e.g., speed, temperature) and energy consumption are dictated by engine speed, while most auxiliary demands are not proportional to the engine speed. Dealing with worst-case scenarios leads to highly oversized components that further, dramatically reduce the overall efficiency. How to choose, in a simultaneous design step, a topology, component sizes and a control algorithm for auxiliaries is still unknown. This becomes, especially, important when an integrated general optimal design is desired for the vehicle rather than an optimal system or sub-system design. To overcome the drawbacks of a sequential design approach, this paper shows the precise combination of technology, topology, size and control for the power steering system used in a heavy-duty vehicle. Modeling of six possible topologies and optimal sizing of components, as the gear ratio between combustion engine and power steering pump, are shown. Next, a sensitivity analysis is done for control parameters and a view is presented on a suitable topology for a power steering system used in a heavy-duty long-haul vehicle.