Abstract: The valve controlled hydraulic system is usually used to drive the boom hydraulic cylinder of wheel loader to complete the frequent lifting and falling action, which produces a lot of throttling and overflow losses. Moreover, the gravity potential accumulated by the boom in the lifting process is dissipated into the environment through the throttling effect of the orifice in the falling process, resulting in the system heating and energy waste. In order to eliminate the overflow and throttling loss of the system, the closed loop pump controlled hydraulic system is adopted to drive the boom single-rod hydraulic cylinder. And, to balance the flow asymmetry caused by the area difference of the single-rod hydraulic cylinder and recycle the gravity potential energy of the boom, the asymmetry pump with three ports is used for driving the hydraulic system. In the asymmetry pump, the first oil port is connected with the rod chamber of the hydraulic cylinder, the second port is connected with the rodless chamber of the hydraulic cylinder, and the third oil port is connected with the accumulator, which is used to recover the gravity potential energy of the boom during the falling stage. In the research, according to the working principle of the proposed system, a co-simulation model is established to verify the feasibility of the proposed system. Then the test platform of the proposed system is constructed, and the work and energy consumption characteristics of the system are studied. The experimental results show that, in the working process, the flow matching between supply and demand flow of single-rod hydraulic cylinder can be achieved by the proposed system. And, compared with the original valve controlled system, the energy consumption can be reduced by 47.19%.

Key words: flow self-balancing pump, closed loop pump controlled, energy recovery, wheel loader lifting device