Simulation And Test Research On The Thermal Management System For PHEV

New energy vehicles include Battery Electric Vehicles(BEV),Plug-in Hybrid Electric Vehicles(PHEV),Hybrid Electric Vehicles(HEV),Fuel Cell Vehicles(FCV),and so on.Due to the practical problems faced by BEV in terms of battery mileage and charging convenience,PHEV is still one common choice for consumers.Energy management and thermal management are the core technical problems faced by PHEV.In order to solve these engineering problems,an energy management model of power system was built based on a large number of component tests,engineering experiences,classical theories,up-to-date advanced calculation methods,three-dimensional CFD flow-field model,and thermal management model based on one-dimensional safety and comfortability.These complex models were coupled to perfrom high-performance calculation for joint simulation,and strategical and structural optimization were also carried out.On the basis of meeting extreme working conditions,the energy utilization rate of the whole vehicle was optimized,and at the same time,the comfort of the passengers in the vehicle was greatly improved.The main content and conclusions were given as follows:Firstly,based on the deterministic rules,PHEV power system modeling was established.With the speed following,power following rules and battery SOC,the control strategy of engine start-stop was determined.According to the principles of safety and economy,reasonable SOC thresholds and strategies of battery charging and discharging were set up.Taking the vehicle power demand,engine power,motor power,SOC state,vehicle speed and acceleration as logical judgment parameters,the power distribution of the engine and the motor were controlled.The comparative analysis between simulation and test showed that the control logic was effective,and the maximum deviation between the simulation results,which consisted of power performance and fuel economy(power consumption and fuel consumption),and the drum test results was within a small range,which validated the control logic and simulation model,this model can be used in prediction of energy management and optimization on method research for PHEV.Secondly,the energy consumption of the whole vehicle was optimized based on fuzzy rules.Taking the ratio of engine optimal power(based on fuel consumption)to vehicle demand power and battery SOC as optimization parameters,the corresponding fuzzy control rules were designed.The principle of fuzzy control is to reduce fuel consumption by increasing battery usage time and frequency under high power conditions;under low power conditions,the engine is suppoed to work more efficiently and charge the battery to reduce battery usage time and frequency,ensuring that the battery power is maintained in a safe interval.In this context,the fuzzy control of the engine start-stop strategy was added.Simulation results of different cycles based on NEDC operating conditions showed that the proposed fuzzy control was a very effective method to improve the use economy of PHEV.Under the pure electric mode,and its dynamic performance variation was within the acceptable range;under the same level of vehicle power consumption,the vehicle fuel consumption can be reduced.Thirdly,a thermal management model of one-dimensional safety was built,as well as a thermal management model of comfort and a CFD model of engine bay with air intake from the front-end.The hardware,boundary conditions,key parameters and control logic of each system were combined together,hence a highly-integrated and coupled model of vehicle energy management and thermal management system was established.This model can perform all-weather joint simulation of vehicle economy,safety and comfort.Fourthly,based on the vehicle thermal management model for joint simulation,simulation analysis of thermal safety,thermal comfort,etc.was carried out,and the optimization direction was proposed.A comparison of various domestic and foreign test standards of thermal management safety was made.According to the test analysis,the maximum power rather than the maximum vehicle speed was proposed as the evaluation principle of thermal safety.The heat production characteristics of PHEV were analyzed,and the method of reducing the heat production by adjusting the power output distribution ratio of the motor and the engine was proposed.On this basis,a extrme work condition evaluation method for PHEV was set up,thereby the grille configuration was optimized to reduce wind resistance and energy consumption.In the integrated research of management system of thermal safety and comfort,the relationship between the vehicle speed and the intake air volume was analyzed,the reflux volume was quantitatively calculated by the heat-flux marking method,and the reflux distribution was visualized,realizing the recognition of the composition ratio of different hot gases.The serious backflow problems that usually occurred at the condenser of the air conditioning system in engineering practice was optimized through adding the seals added and optimizing air guides,which reduced the backflow rate and improved the efficiency of the air conditioning system and comfort of the passenger compartment.