In order to improve the energy efficiency and dynamic of negative control swing systems of excavators, this paper proposes a technical scheme of adding two PRVs (pressure reducing valves) to main valve pilot control circuit, which can adjust main value opening arbitrarily according to the working condition. A pump-value compound control strategy was formulated to regulate the system power flow. During swing motor acceleration, main pump and the two PRVs are controlled to match system supply flow with motor demand flow, thereby reducing motor overflow and shortening system response time. During swing motor braking, the channel from motor to tank is opened to release hydraulic brake pressure by controlling PRVs before swing speed reduces to zero, which prevents the motor from reversing and oscillating. A simulation model of 37-ton excavator was established, and the control strategy was simulated. The original and optimized performance of the swing system were compared and analyzed, and results show that the application of new scheme with the compound control strategy can reduce overflow and increase braking stability of the swing system. In addition, system response and speed control performance are also improved when excavator performs a single-swing action.

In order to optimize the energy efficiency and action coordination of negative control excavators, a secondary control circuit of main valve is proposed, which sets an electric proportional pressure reducing valve between joystick-pilot valve and main valve, so that main valve opening can be adjusted twice according to the actual working conditions to meet system control requirements. This paper takes the swingdipper system as the research object, and studies the overload action and compound action of swing motor and dipper cylinder. In order to reduce the overflow caused by overload, an on-demand flow control strategy is designed to match the pump-valve flow with the demand flow of actuators. In order to solve the problem of uncoordinated compound actions caused by load difference, a flow-ratio control strategy is designed to make the flow ratio of actuators equal to the stroke ratio of joysticks. The system performance test of a 37ton excavator was carried out, and a simulation model of the swing-dipper system was built. Based on the test and model, the two control strategies were simulated, and the results indicate that, compared with the original hydraulic main valve, the proposed secondary controllable main valve and its control strategies can reduce the motor/pump overflow when the motor/cylinder is overloaded, and can adjust the actuator flow ratio when the excavator performs a compound action, thereby improving the energy saving and manipulation performance of the excavator.INDEX TERMS Negative control excavator, secondary control, main valve, on-demand flow, flow ratio.

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In order to optimize the acceleration performance of a large inertia hydraulic actuator, this paper proposes a main valve input shaping control strategy, which makes the valve flow supply match the load-control demand by adjusting the main valve flow growth rate. Taking a load-independent flow distribution system as the research object, and aiming at the problems of large pressure overshoot, excessive overflow and oscillation tendency during the actuator acceleration process, this paper divides the acceleration process into the pressure build-up condition, the inertia-acceleration condition and the stable-flow regulation condition according to the change characteristics of the actuator driving pressure, and divides the main valve control signal into five stages to design the valve flow growth rate, thereby smoothing the driving pressure fluctuations by adjusting the actuator inertial load and mitigating the pressure release process. Based on the key structure-hydraulic parameters and test data of a 6-ton excavator, a virtual excavator that can accurately simulate the swing action and boom lifting action is built, and the software-in-the-loop test of the input-shaping control algorithm is carried out. The test results indicate that the proposed control strategy can effectively suppress the pressure overshoot, oscillation, and flow overmatching, thereby improving the dynamic stability and energy efficiency of the system.