A study on flow control valve characteristics in an oil hydraulic vane pump for power steering systems

In the power steering system of an automobile, the balanced and fixed displacement type vane pump is principally applied to the main power source. It is driven by a pulley that is attached to the shaft of the vehicle's engine, and the pulley ratio is about 1:1. The vane pump continuously discharges an outlet flow rate proportional to the rotating speed of the engine. In a vane pump without the flow control valve, an increase in the discharge flow rate means a linear increase in the actuator speed. At high speed when the driver rotates the steering wheel by even a small amount, there is a high risk of an accident due to the quick rotation of the tire joined to the actuator and links. We designed a flow control valve of the fixed displacement and pressure balanced type vane pump for power steering is designed and simulated using AMESim software. Its theoretical flow characteristics with respect to the rotating speed of the engine are compared and validated with experimental data. The results show that the design parameters, such as the flow area, the underlap length, the spool clearance, the main spring stiffness and the spring initial force, largely affect the flow control characteristics.