STABILITY AND ENERGY EFFICIENCY IMPROVEMENT OF HYDRAULIC EXCAVATOR ARM CONTROL SYSTEM WITH A NOVEL ASYMMETRIC PUMP

Pump controlled hydraulic circuit is an energy efficient alternative to valve controlled system, as they eliminate the throttling loss and require less cooling power. In all pump controlled systems, the internal and external leakages of the pump and actuator, especially the unequal flow rates of the single rod cylinder must be compensated. In presently existing solutions, an additional pump or some valves are used to compensate the unequal flow rates, leakages and to pressurize the system. However, these approaches increase the system complexity and complex control strategies are required to improve the overall system dynamic performances. Also, some of them suffer from undesired and uncontrolled pressure and velocity oscillations when the load force is small or its direction changes. This paper addresses the unequal flow rates compensation problem and stability problem of pump controlled single rod cylinder system, and proposes a novel solution for it. The system under consideration utilizes a new designed asymmetric pump which can match the unequal flow rates of the single rod cylinder basically. The feasibility of the new circuit is validated by both mathematics and multi-body simulation model. The results show that the undesired velocity oscillations can be removed up. Furthermore, the operating characteristics and energy efficiency of the arm cylinder with the new scheme based on the designed open-loop and closed loop strategies are studied on a real excavator. The results show that there is no obvious velocity fluctuation with the asymmetric pump and the position controlled precision is satisfied. Compared with the independent metering circuit, the energy-saving ratio reaches to 57% during a working cycle.