On the Dynamics of Pressure Relief Valves with External Pilot for ICE Lubrication

The paper analyzes the influence on the stability of the remote pilot in pressure relief valves used for engine lubrication. Such valves are mainly used to discharge the excess flow generated by a fixed displacement pump, moreover they can also be used as pilot stage to control the displacement in the new generation of vane pumps. In the paper the transfer function that relates the pressure in the main gallery with the valve spool position is determined. It was found that, when the valve is provided with an external pilot, the interaction between the hydraulic inductance of the pilot pipe and the spool decreases by many times the mechanical frequency of the valve, leading to a reduction of the stability. The experimental procedure used to measure the frequency response of the valve is also described. The test rig was provided with a servovalve used to generate a sinusoidal excitation pressure with variable frequency. The valve frequency response was evaluated by means of two pressure transducers at the two ends of the pilot channel. Finally the influence on the stability of some geometric parameters is analyzed by means of a simulation model in the AMESim environment.