Research On Control Strategy Of Engine Variable Flow Cooling System

In recent years,the engine cooling system has developed rapidly,and the key components have been basically electrified.At present,the relevant research focuses on the design and optimization of the cooling system control strategy.Among them,the highly integrated thermal management model（TMM）has excellent flow regulation characteristics and coolant control accuracy.It has great control potential,but the research on the corresponding control strategy is still lacking.In addition,most of the control strategies control the cooling system based on the temperature measured by the current sensors,which has a certain lag.This paper proposes to take the TMM as the main control object,supplemented by the speed control strategy of the electronic water pump.On the basis of constructing the mathematical model of the variable flow cooling system,the coolant flow and component temperature are predicted according to the real-time operating conditions of the engine,the cooling system is adjusted with the target water temperature as a reference,and the relevant software is developed based on the model for integration with the engine control system,Achieve more efficient water temperature control based on the engine variable flow cooling system,reduce energy consumption and exhaust pollutant emission.The main contents of this paper are as follows:（1）Taking a hybrid vehicle equipped with turbocharged engine as the object,the whole vehicle test platform is built,and the application of data acquisition tool chain is briefly introduced;（2）Based on the physical structure of the engine variable flow cooling system and the laws of thermodynamics and heat transfer,the mathematical model of the cooling system is established to predict and calculate the coolant temperature,flow and heat dissipation of the key components of the engine;（3）Based on the mathematical model of the engine variable flow cooling system,the control strategy model is developed to judge the current state of the engine,and realize the accurate control of the coolant volume flow of each branch through the control of the water pump speed and TMM opening.In the high temperature stage,the tracking adjustment is carried out based on the deviation between the main water temperature and the target water temperature of the engine,so as to indirectly improve the engine performance;（4）The developed mathematical model and control strategy are simulated and verified.After the verification,the thermal management function module automatically generates code by using the tool based on model design,integrates with other functional modules of engine management system,and completes the test and verification on the whole vehicle.The verification results show that the mathematical model of engine variable flow cooling system studied in this paper,including the model water temperature of cylinder block,cylinder head and engine inlet,can better follow the actual water temperature,and the water temperature deviation is small（the water temperature error under steady-state condition is within 1.5℃,and the maximum error under intense change of engine speed is controlled within 4.8℃）,which shows the accuracy of the water temperature model to a certain extent.On the premise that other vehicle conditions are consistent,the cooling system with engine variable flow control strategy has better warming up effect during low-temperature cold start than the cooling system with traditional thermostat.Under the condition of rapid warming up,the engine temperature rise is about 7.2% in the same time,and the water temperature is less affected by the fluctuation of engine speed;Under the wltc working condition,the engine equipped with variable flow cooling system heats up faster in the low-speed section,and the shutdown working condition between the medium and low-speed sections reflects a good thermal insulation effect.Under the partial load working condition of the medium and high-speed section,the coolant is maintained at a higher temperature to ensure the lubricity of the engine oil and reduce friction.Under the full load working conditions such as high-speed and ultra-high-speed sections,it can achieve a good cooling effect and avoid overheating of the engine.