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 swing-dipper 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 37-ton 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.

In order to improve the swing braking stability and flow distribution characteristics of negative control excavator, this paper proposes a hybrid electro-hydraulic main valve, which sets a pressure reducing valve in each of the two control chambers of main valve to adjust its control pressure difference, so that the valve opening can be adjusted to optimize the excavator maneuverability. For the braking oscillation tendency of swing action, an anti-reverse control strategy is designed, which actively releases the motor brake pressure by adjusting the flow area of oil return orifice, thereby preventing the brake pressure from outputting power to the motor in the reverse direction. For the uncoordinated flow distribution of swing-boom compound action, an action priority control strategy is designed, which redistributes the dual-pump flow to swing motor and boom cylinder according to the operator’s manipulation needs. Based on the key hydraulic-structural parameters and test data, a simulation model of a 37-ton negative control excavator that can accurately simulate the swing action and boom lifting action is built, and the system operating characteristics before and after optimization are analyzed, the results show the proposed control strategies can suppress the swing rebound phenomenon and improve the controllability of actuator flow ratio.

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.