Research On Flow Coupling And Toruqe Coupling Based Power-train Of Hydraulic Hybrid Excavator

Hybrid technology is an effective approach for energy saving and low emission, which has become one of the most focused research topics in the field of hydraulic excavators. With the merits of high power density and low cost, hydraulic hybrid technology begins to draw worldwide attention from industry and academia. However, few abroad excavator manufacturers have released their hydraulic hybrid excavator so far, while the domestic research level is still at the initial stage. This paper is mainly focused on the theoretical and experimental research of the power system of hydraulic hybrid excavator, including hybrid structure design, parameter optimization, control strategies, energy management et.al. The achieved research progress is listed below.1. Based on flow coupling structure, a multiple working device energy regeneration system is proposed. The identification of boom descending movement and swing movement status, as well as the energy regeneration of boom potential energy and swing brake kinetic energy, are realized automatically via the designed hydraulic circuits. And the recovered energy is released to the main pump outlet through the flow coupling structure.2. For the flow coupling hydraulic hybrid structure, a flow distribution control strategy is specially designed, with the control objectives of minimizing the energy loss and suppressing the flow fluctuation during flow coupling. The control strategy could realize the matching between the total flow output and the load demand, the flow distribution between the main and the auxiliary power sources, and the smooth and steady of the flow output. Simulation and experiment results validate that the output flow oscillation is restrained, and the energy saving effect is improved by around 10%.3. A compound hydraulic hybrid excavator system, which integrates the torque coupling based engine optimization and energy regeneration, is used as the research object. Based on the Dynamic Programming method, a power system parameter optimization approach is proposed for torque coupling hydraulic hybrid excavator system. The objective function of the optimal control problem is defined as minimizing the fuel consumption. The power system parameters are optimized, and the energy saving effect of the engine optimization and working device energy regeneration are studied.4. Based on the Lagrange Multiplier method, an offline optimization approach is proposed for energy management strategy of the torque coupling based hydraulic hybrid system. And then the online energy management optimization strategy is further proposed, which is adaptive to the changes of load condition and accumulator SOC. Dynamic simulation results validate the feasibility of the online strategy, as well as an improvement of 20% on fuel economy for the compound hydraulic hybrid system.