Research On Overflow Energy Loss Recovery System Based On Hydraulic Motor-electrical Generator

Hydraulic transmission is widely used with its unique technical advantages such as high power density,fast dynamic response,stepless speed regulation,easy realization of linear motion and rotary motion,but due to a large amount of overflow loss and throttling loss in hydraulic system,the efficiency of hydraulic transmission is low.At present,throttling loss has been furtherly studied in the area of energy-saving technology,but less overflow loss.When the overflow valve is working,the high-pressure oil in the hydraulic system directly overflows into the oil tank,causing a large amount of overflow loss at the valve port.With the development of high pressure and large flowrate in hydraulic systems,the problem of overflow pressure loss is becoming more serious.Overflow loss is related to the type of hydraulic system,actual working conditions and operation methods,it is considered to be a technical bottleneck that reducing overflow loss,especially reducing the pressure drop of the overflow valve port.Pilot-operated proportional overflow valve is taken to be the research object in this thesis,and overflow loss energy recovery system based on the volume pressure difference control of the hydraulic motor generator is proposed by analyzing the principle of the pressure difference loss of the traditional proportional overflow valve.Combined with the characteristics of electric energy recovery unit,a valve pressure control strategy based on minimum volume pressure difference is proposed,in which the proportional overflow valve port pressure difference is controlled to the minimum value that can ensure the working characteristics to achieve energy saving.In view of the low efficiency of the traditional throttle speed regulation system based on fixed displacement pump,a new type of throttling system based on overflow loss energy recovery is proposed.A mathematical model of the energy recovery system is established to analyze the stability of the system during the process of energy recovery.The principle of the back pressure at the outlet of the overflow valve is analyzed in order to study the relationship between the inlet and outlet pressures of the overflow valve and the static and dynamic working characteristics of the overflow valve.Through establishing simulation model of system,the working characteristics of the proportional overflow valve and the controllability of the energy recovery system are studied.A test platform for electric energy recovery of proportional overflow valves and a new type of throttle speed regulation were built in order to study the working characteristics of the proportional overflow valve,system control characteristics and recovery efficiency.The experiment results show that the steady-state hydraulic power is reduced when existing the back pressure at the outlet of the proportional overflow valve,causing the inlet pressure of the overflow valve to decrease as the back pressure increases.When the overflow valve is operating under the minimum control pressure difference,there is 3% pressure drop between the actual pressure of the overflow valve and the target pressure,the pressure control accuracy of the overflow valve is improved.The system has good characteristics of pressure step response and slope following,and the recovery efficiency is up to 79%.The new speed control system with overflow loss energy recovery has good control characteristics and energy saving.Compared with the traditional throttle speed control system based on fixed displacement pump,the loss energy of the new throttle speed control system reduced by 65%.The electric overflow loss energy recovery system and the new throttling speed regulation system proposed in the thesis are effective and feasible.