| Hydraulic system is widely used in high-power mobile equipment and industrial equipment.It is an indispensable support technology in the development of national economy.The annual sales revenue of China’s construction machinery industry alone has exceeded 760 billion yuan,ranking first in the world.Due to the throttling loss and overflow loss in the hydraulic system,as well as the friction and leakage loss of components,the system average energy efficiency is only about 25%.The large energy loss causes high heat production and obvious oil temperature rise.High temperature can adversely affect oil characteristics,system leakage and seal lifetime,also significantly affecting the operation and energy characteristics of hydraulic systems,as well as safety and reliability.To keep the oil temperature within reasonable limits,hydraulic drive equipment usually needs to be equipped with a cooling system.However,the cooling system also cause large energy consumption,which account for more than 5% of the whole machine energy consumption.The traditional cooling method of hydraulic system usually consumes energy,transfering the heat inside the hydraulic system to the environment for dissipation.It results in the double waste of available energy and heat energy in the process.Therefore,an Organic Rankine Cycle(ORC)method was proposed to recover the waste heat of hydraulic system.Thus the comprehensive energy efficiency of the system is improved by eliminating cooling energy consumption and heat-work conversion.Based on the technology problems related to recovery and utilization of waste heat with ORC method in hydraulic system,the research work is carried out from the thermal characteristics of hydraulic drive equipment,the characteristics of waste heat recovery system,and the coupling characteristics of hydraulic drive equipment and waste heat recovery system,by means of theory,simulation and experiment.The main research contents of this paper are as follows:Research on energy system characterization method of hydraulic drive equipment.Based on the analysis of the basic principles of the energy system thermodynamic analysis method,the waste heat of hydraulic system was included in the energy system of hydraulic drive equipment as thermal exergy.On the basis of the energy balance analysis model,the exergy balance analysis model and energy level balance analysis model were supplemented to improve the energy system characterization method of hydraulic drive equipment.The hydraulic excavator,which is the typical hydraulic drive equipment,is taken as the object,and the model and analysis are carried out with the complete energy system characterization method.Aiming at rational energy use and energy level matching,the waste heat recovery scheme of hydraulic system is proposed,and the feasibility and beneficial effect of the proposed scheme are analyzed theoretically.Research on thermal characteristics of hydraulic System driven by data and mechanism.Aiming at the problems of difficulty in testing thermal characteristics of hydraulic driving equipment and low accuracy of mechanism model,a modeling method of thermal characteristics of hydraulic system with mixed drive of data and mechanism was proposed.According to the modeling theory of thermal characteristics of hydraulic system,combined with the test data and the working mechanism of components,the thermal characteristics models of a 260-ton super large hydraulic excavator and hydraulic power unit are established by using power loss method and control body method respectively.Through the testing and simulation analysis,the energy characteristics of the hydraulic components and the system,the heat generation and heat dissipation characteristics of each part of the hydraulic components,as well as the temperature change rule of each part are obtained.Configuration design and theoretical research on ORC waste heat recovery of hydraulic system.A new structure of organic Rankine cycle-heat pump(ORC-HP)combined system was proposed for the super large hydraulic excavator with high preheating energy consumption and local overheating accelerating oil deterioration.The steady-state numerical model of ORC-HP combined system was established based on the cooling power demand obtained from thermal analysis of 260-ton super large hydraulic excavator.The thermodynamic and economic characteristics of the combined system were comprehensively compared,and R152 a was selected as the best working fluid.The performance of ORC waste heat recovery system was studied,and the influence of ambient temperature and oil temperature on the operating characteristics and energy characteristics of ORC system was summarized.Research on operating characteristics of ORC waste heat recovery of hydraulic system prototype.To go into the efficient cooling and power generation capacity of ORC in the waste heat recovery and utilization of hydraulic system with low temperature and large flow rate,a waste heat recovery of hydraulic system test prototype was built.According to the structure parameters,working mechanism and testing data,combined with the thermal characteristics simulation model of the hydraulic power unit,a precise and reliable dynamic simulation model of the test prototype was established.Through the testing and simulation analysis,the steady-state and dynamic characteristics of the waste heat recovery of the hydraulic system prototype were studied.And the influences of generator load,oil flow rate and working fluid flow rate on the steady-state operation characteristics and energy characteristics of the system were studied.The dynamic characteristics of ORC system are studied under the conditions of oil flow and electric load step change,and system startup and shutdown.Under the test conditions,the maximum heat transfer of evaporator in the prototype is 4.18 k W,and the maximum output power of expander is 356 W.Research on application exploration of waste heat recovery of hydraulic system.To study the working characteristics and economic feasibility of the waste heat recovery system in the practical application of hydraulic drive equipment,a 38-ton large hydraulic excavator was taken as the research object to be studied.An accurate and reliable simulation model of thermal characteristics of large hydraulic excavator is established by integrating experimental data and working mechanism with control body method.Based on the oil return flow and cooling power requirements obtained from thermal characteristics analysis,and combined with the waste heat recovery simulation model,the structural parameters and operating parameters of the waste heat recovery system were designed for the large hydraulic excavator.Then the combined simulation model of the hydraulic excavator and waste heat recovery system was established to study the coupling characteristics.Compared with the traditional oil cooler cooling method,the waste heat recovery system can reduce the energy consumption of hydraulic excavator by more than4.4%. |
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