The Measurement of Concentrated Flow Resistances in Periodically Operating Fluid Power Systems

Fluid power technologies have been applied for common rail fuel injection systems with great success over the last years. Another emerging application area can be found also in the automotive industry: The electro-hydraulic variable valve train system. Both applications share the problem of a hydraulic pressure rail under periodic excitation by the flow rates consumed either by common rail injectors or by the hydraulic valve drives. This excitation results in pressure oscillations in the desired constant pressure rails. For the modelling of these wave propagation phenomena, the availability of mathematical models for the dynamic influence of concentrated flow resistances like T-branches and sharp elbow bends is crucial. While there is abundant literature for the stationary flow case, the available experimental results for pulsatile flow or arbitrary periodic flow conditions are very limited. This paper describes a first experiment for the measurement of concentrated flow resistances in a rail system of straight bores with a circular cross section and a diameter of 10 mm. The test fluid is mineral oil and excitation frequencies are in the range of 10 to 1000 Hz.