Development of the Variable Displacement Vane Pump for the Automotive Power Steering System

Recently, fuel economy, ride comfort and saving resources for automobiles are strongly required. In this situation, energy savings has been required in a power steering system which lessens the driver's fatigue. In order to respond to these needs, we have to increase the efficiency of the oil pump, which is an important piece of equipment of the power steering system. It is an important issue for us to find a solution. Therefore, we have paid attention to the surplus flow at the middle and high revolutions of the fixed displacement vane pump which decreases efficiency.

We have developed a variable displacement vane pump which is able to stop the surplus flow and has flow down characteristics to apply to the automotive power steering system while keeping the size of the pump compact as with a conventional pump. The pump uses hydraulic power generated by the pumping action at the bottom of the vane slots for variable displacement mechanism. The power consumption of the variable mechanism is very small. The pump also includes a relief valve which decreases the displacement to almost zero. Thanks to the variable displacement mechanism and the relief valve, a sharp cut of the power consumption of the power steering oil pump is realized. By using a variable displacement vane pump for the automotive power steering system, it will be able to save fuel and eliminate the oil cooling system, as oil temperature does not increase when compared to a conventional pump, due to a non surplus flow.