Method for combining valves with symmetric and asymmetric cylinders for hydraulic systems
Electro-hydraulic position control systems are widely applied in several fields. The valve and cylinder configuration and the dimensioning of these systems is dependent on the requested transient response and the load profile. One of the primary factors in this regards is the selection of an asymmetric or symmetric cylinder, considering issues such as the area available for installation and the asymmetry of the external loading. According to the classical literature, the valve control orifice areas must be matched with the cylinder areas to ensure balanced pressure variation in the cylinder chambers. Moreover, considering that several real applications use non-matched components, it is evident that, depending on the system parameters and load characteristics, good performance can be obtained with this system configuration. Based on non-linear dynamic modelling and experimental results, the transient instants when cavitation or high pressure peaks can occur are determined. Subsequently, a set of equations establishing the relationship between the valve control orifice ratio and cylinder area ratio are derived. A method for determining the valve characteristics, based on parameters such as moved mass, external load force and cylinder asymmetry, is presented. The results obtained are also valid for speed control in open or closed loop system.
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