Research On Collaborative Control And Optimization Of Integrated Vehicle Thermal Management

Current vehicle products had been put forward more demanding requirements to cope with the increasingly stringent emissions regulations and the energy crisis.The new generation intelligent thermal management was not only limited to solving the engine cooling problem,but also was regarded as one of the key vehicle development technology related to a number of important performance indicators such as reliability,dynamic property,economy,emission and comfort.The modern vehicle integrated thermal management system included engine cooling,oil cooling,HVAC system,supercharging inter-cooling,low frequency thermal fatigue and thermal damage,etc.For the new-energy vehicles such as HEV and PEV,it also included motor/ generator cooling,DMCM cooling and vehicle battery thermal management.The integrated thermal management system should not only satisfy the design performances of sub-systems in the limit conditions,but also took into account the dynamic temperature stability and the vehicle comprehensive energy consumption.Finally,the collaborative solution and integrated management of the three thermal management technologies of “Thermal Design”,“Thermal Control” and “Thermal Optimization” could be realized,and the kinds of vehicle performances were also optimized.Aiming at the optimization design of vehicle thermal management,this paper innovatively proposed an IVTM(Integrated Vehicle Thermal Management)technology solution,which integrated system design,scheme evaluation,performance analysis,dynamic control and collaborative optimization,which was on the basis of multi-dimensional coupling numerical calculation and multi-objective collaborative optimization control.With the integrated thermal management cooperative control strategy for the whole vehicle driving cycle,the comprehensive improvements of several evaluation indexes such as system design performance,thermal control performance and economical performance could be achieved.In the article,according to the main technical route of IVTM scheme,the following specific researchs were carried out.Regarding ICEV engine cooling sys and air conditioning sys as the research object,an 1D integrated thermal management system mathematical model was established to describe the system's thermodynamic state and flowing state by theoretical calculation and experimental data of thermal transmission,flow characteristic and energy conversion in the system and components.The aerodynamic coupling thermal transmission problem of underhood in three typical vehicle conditions of idling,climbing and high-speed driving was studied with 3D CFD simulation.The coupling thermal transmission mechanism of the integrated vehicle system was analyzed from four angles: flowing intensity,fresh intake ratio,underhood overall temperature,and aerodynamic coupling transfer transmissio pathway.The coupling factor characterization method suitable for general conditions was proposed,and the 1D/3D coupling calculation model for vehicle integrated thermal management was constructed in combination with 1D system mathematical mode.Based on the road test of the vehicle thermal adaptation conditions,the reliability of the integrated thermal management 1D/3D coupling calculation model was verified.For the problem of "Thermal Design",taking the coolant temperature and cabin temperature as evaluation indexes to check and calculate the thermal adaptation of the integrated systems.The calculation results showed that the low-speed climbing was the thermal failure condition of the cooling system,and the idling was the thermal failure condition of the air conditioning system.Based on the coupling effect of the integrated system,the heat exchangers' intake status,the coolant flow characteristics and the refrigerant flow characteristics,the thermorheologic analysis of the thermal management system was carried out,and the main causes of the thermal failure were identified.And then 5 design schemes of underhood structure were put forward,the optimization effects of thermal management system was quantitatively evaluated by comparing the thermorheologic characteristics of the integrated system with different structures.The evaluation results presented the diversion sealing scheme can reduce the matching fan speed by 20.36% and the matching compressor displacement by 8.59%.So,it improved the both design performances of cooling sys and air conditioning sys,which was conducive to the collaborative optimization of vehicle thermal management with multiple systems,multiple conditions and multiple performance indexes.For the problem of "Thermal Control",the integrated system control schemes based on Rule-based,PID and MPC were proposed,the thermal control performances of each control scheme with temperature stability as the index were compared and analyzed.Analysis results of fan single variable control schemes showed that there was an over-cooling problem of the electric fan and mechanical pump thermal management sys in low temperature conditions.The excessive coolant flux and low radiator intake temperature were the fundamental causes of over cooling.The decoupling of electric pump and engine speed should be adopted to solve the problem.The analysis of the multi-variable collaborative control schemes with pump and fan showed that the temperature fluctuation problem existed in the double PID control system.There was a gain sign uncertainty problem of the control scheme with the pump speed as the variable,which was the fundamental cause of the system control instability.The problem should be solved by applying the compound control system with the thermal balance information as the feedforward,such as MAP+PID and MPC,so as to improve the stability of the multivariable cooperative control system.In the analysis of the air conditioning control sys,there was a periodic canbin temperature fluctuation problem in the discrete control scheme of compressor displacement.Although reducing the constraint range of the rules could improve the system stability,it was also difficult to coordinate the contradictions among NVH,reliability and economy,which caused by frequently compressor displacement switching.While,the continuous compressor control scheme can accurately control the refrigerant flux according to the temperature feedback,which not only kept the compressor smoothly running and reducing the temperature fluctuation,but also avoided the excessive refrigeration.It was conducive to the comprehensive performance improvement of the refrigeration cycle in the dynamic vehicle condition.For the problem of "Thermal Optimization",taking the power consumption of the actuators as the index and the NEDC driving cycle as the analysis condition,the economy of the integrated system from the two perspectives of controller design optimization and underhood coupling thermal transmission optimization was analyzed.Based on the MPC coordinated control of engine cooling,the constraint of minimum system energy consumption was introduced to construct a multi-objective optimal control scheme that took into account both temperature stability and economic performance.In the analysis results,MPC optimization scheme could keep system in the energy consumption economic zone by reasonably coordinating the power ratio between pump and fan,saving 39.82% energy than MPC collaborative control scheme and 20.71% energy than MAP+PID collaborative control scheme.With the improvement of the underhood structure to weaken the harmful thermal transmission interaction,the energy consumption optimization results showed the system economy of the MPC optimization scheme can be further improved by 11.58%.Through the comparison of air conditioning control schemes,the PID continuous control could save 36.37% energy than high-bandwidth NODE control and 32.56% energy compared than low-bandwidth NODE control scheme due to precise regulation of refrigerant flux to avoid excessive refrigeration.If combined with the optimization and improvement of underhood,the average condenser intake temperature can be reduced by 1.38?,and the system economy can be further improved by 12.85%.Based on the above research of system design,control and optimization,an integrated thermal management cooperative control strategy for the whole vehicle drving conditions based on MPC was proposed in the article.In ICEV integrated thermal management,the control strategy of idling start and heating stop were added to achieve the coordinated thermal management of the whole driving conditions,which took into accounts the control stability,dynamic speed and vehicle comprehensive energy consumption.The IVTM technology solution was applied to solve the problem of integrated thermal management control strategy for HEV,and the local energy consumption optimization scheme and global energy consumption optimization scheme were put forward.The differences of temperature stability and economy between the two strategies were mainly reflected in the low proportion region of interval engine power.By reasonably coordinating the thermal transmission capacity and energy consumption between the air-side and liquid-side of the motor cooling system,the global optimization scheme had the better stability and economy,and it was more suitable for complex HEV integrated thermal management.Finally,the process positions and design principles of thermal management module in vehicle development system engineering were described,the specific application and important engineering significance of IVTM for vehicle development technology were discussed in the paper.