Abstract
Recent passenger cars have been equipped with electric power steering for both saving energy and autonomous cruising such as lane control or vehicle distance control; however heavy-duty commercial vehicles are still steered by hydro-mechanical PS due to higher steering torque compared with that of passenger cars. This paper examines a direct flow control system of PS for a commercial vehicle by using an AC-servo motor drive hydraulic-pump without a conventional 4-way valve. It assists the sector-gear hydraulic piston-force according to the difference of handle and steering angles through a torque sensor. This system can easily replace a conventional IPS or integrated hydraulic PS, and can also vary the handle operating torque continuously by such as vehicle speed signals. Its steady state characteristics, step response are measured and their stability is analyzed. In a bench test, power consumption of the valveless AC-servo hydraulic PS is about 340W under slalom driving conditions.
