Reducing Fatigue Loading Due to Pressure Shift in Discrete Fluid Power Force Systems

Discrete Fluid Power Force Systems is one of the topologies gaining focus in the pursuit of lowering energy losses in fluid power transmission systems. The cylinder based Fluid Power Force System considered in this article is constructed with a multi-chamber cylinder, a number of constant pressure lines and a valve manifold. The valve manifold is used to control the connections between the cylinder chambers and the pressure lines and hereby the resulting force form the cylinder. The valve manifold is equipped with fast on/off valves. However, shifting between pressure lines may yield pressure oscillations in the cylinder chamber, especially for systems with long connections between the cylinder and the valve manifold. Hose pressure oscillations will induce oscillations in the produced piston force. Hence, pressure oscillations may increase the fatigue loading on systems employing a discrete fluid power force system. The current paper investigates the correlation between pressure oscillations in the cylinder chambers and valve flow in the manifold. Furthermore, the correlation between the pressure shifting time and the pressure overshoot is investigated. The study therefore focus on how to shape the valve flow in the manifold to reduce the added fatigue loads. A simple transmission line model is developed for the analysis. Two inputs are given in the Laplace domain and the time domain solution of the cylinder pressure to the given inputs are derived through inverse Laplace transformation. Based on the time domain solutions the pressure overshoot for various pressure shifting times is investigated. With the two input functions defined by the pressure shifting time, T, the main results of the current paper show the correlation between the minimum shifting time and the pressure overshoot in a given cylinder chamber with a given line connection.