Fluid Temperature Control Method Of Piston Pump Test Bench For HFC Fire Resistant Fluid Performance Assessment

With the characteristics of fire resistance,environmental protection,non-toxicity and use safety,HFC fire resistant fluid is an ideal working medium for hydraulic systems in flammable or closed places.Test bench is widely used at home and abroad to investigate the adaptability of hydraulic fluid and hydraulic systems,and indirectly reflects the service performance of hydraulic fluid through the operation of the tested pump.The fluid temperature has a significant influence on the physical,chemical and mechanical properties of HFC fire resistant fluid.The fluctuation of fluid temperature will cause large errors in the test results,reducing the objectivity and consistency of performance evaluation.According to MIL-H-22072 standard of U.S.Navy,this paper has developed a test bench for HFC fire resistant fluid performance assessment and studied the automatic control method of fluid temperature.A temperature control loop is designed for the working condition of intermittent fluid return of the hydraulic system of the test bench.An electric proportional control system is used to control the fluid temperature at the inlet of plunger pump,and a fuzzy PID control strategy is proposed to improve the fluid temperature control performance.Based on these,a test bench for HFC fire resistant fluid performance assessment was built,and its temperature control performance was tested and analyzed.The main research contents and results of the control method of the fluid temperature on the test bench are as follows.(1)According to the main technical parameters and influencing factors of fluid temperature control,the composition principle of temperature control circuit of hydraulic system is drawn up;On this basis,the main hydraulic components such as the plunger pump,hydraulic motor,water cooler and electric proportional water valve are selected through calculation.The structure design of the main components of the temperature control circuit and the general arrangement of the test bench are completed,which provides an application platform for the modeling and simulation of the test bench.(2)According to the heat transfer mechanism of the hydraulic system of the test bench,the energy exchange of HFC fire resistant fluid is mainly realized by convection heat transfer.Based on reasonable assumptions,a simplified model for the composition principle of the hydraulic system of the test bench is proposed.According to the test conditions,the heat transfer of the hydraulic system is divided into two parts: the fluid filling stage and the fluid discharging stage of the pressure fluid tank.The heating and heat dissipation power of the hydraulic system are calculated respectively.The calculation results show that the fluid discharging stage of the pressure fluid tank is the key point to the temperature control.The control body method is used to analyze the fluid tank,and the fluid temperature control model of the hydraulic system is built,which provides a theoretical basis for the simulation analysis of the system fluid temperature control.(3)In order to improve the temperature control performance of the test bench,a fuzzy PID control algorithm is proposed.Simulink simulation comparison analysis is made for unitary PID control and fuzzy PID control respectively.The results show that there is no obvious distinction in control precision between the two systems under the condition of low delay time,while fuzzy PID control has higher robustness and fast response in time-varying systems with large delay.(4)A test bench for HFC fire resistant fluid performance assessment is built and preliminary debugging is carried out for 48 hours.The test results show that the fluid temperature at the suction port of the plunger pump is controlled within the range of(51.5±1)℃,which meets the index requirements of the hydraulic system of the test bench for fluid temperature.Therefore,the temperature control loop of the test bed designed in this paper has the characteristics of high control precision,good adaptability,reasonable structure,economy and environmental protection,which can provide theoretical basis and reference for the design of temperature control loops in related types of systems.