| It is very important to design and match reasonable cooling system for a vehicle.If the engine wants to run stably and reliably for a long time,it must be properly cooled,neither insufficient nor excessive cooling,otherwise it will have a serious adverse impact on the power,economy and reliability of the engine.Generally speaking,the engine is at the most suitable working temperature,and the temperature of the coolant in the water jacket of the cylinder block is 85??95?.Having a good engine doesn't mean developing a good vehicle power.A good engine doesn't produce a good power.The unreasonable design of the cooling system is one of the key paths for troubleshooting.In this paper,a new light truck model developed by a motor company is equipped with ISUZU exclusive diesel engine for cooling system matching development and verification method.The basic state of the prototype diesel engine is:the rated power is 110kW,the maximum torque is 385 N.m,which meets the CN5 emission level.The post-treatment technology route used is DOC+DPF+SCR.After being introduced into China,due to different regulations and market demands,the engine has been upgraded:the rated power is increased to 125kW,the maximum torque is increased to 450N.m,which meets the national CN6b emission level requirements.At the same time,the localization development of key parts such as high-pressure oil pump,high-pressure oil rail and fuel injector has been carried out.Due to performance changes and differences in key performance parts,the engine's heat loading has changed greatly.The cooling system matched with the original Japanese vehicle cannot be applied to this project.Moreover,the cooling system developed by Japan has high requirements for processing accuracy and assembly process of parts and components,so it has been developed and stored in China.In case of large quality risk and various differences in the development of comprehensive cooling system,the cooling system of this research project needs new development matching and verification.In the development of matching and verifying the cooling system of this subject,research and analysis are carried out according to the following steps:The first step is to use CATIA model to complete the layout of electronic prototype of cooling system.The cooling system is preliminarily arranged,the boundary of the whole vehicle is set,the arrangement of radiator and intercooler is basically determined on the whole vehicle according to the arrangement position of engine,and the cooling system type is determined according to the position relationship between radiator and engine,and the open water cooling system is adopted.The gap between the mechanical fan and the air shield is 24mm,protruding 15mm from the air shield,accounting for 1/3 of the fan thickness.In the second step,theoretical calculation and CFD analysis are combined to match the performance of the cooling system.According to the engine displacement and rated power,combined with the existing product series of the supplier,a radiator core and intercooler core are selected.According to the boundary of the whole vehicle,the radiator water supply chamber,water supply chamber,side plate and intercooler air chamber are developed.Make the radiator sample,carry out the basic performance test,and get the amount of heat dissipation under different flow and wind speed.Based on this,we can get the water resistance characteristics and wind resistance characteristics of the radiator;estimate the water resistance of the whole vehicle through the water resistance of the radiator,and get the relationship between the speed and flow of the water pump according to the relationship between the flow and head of the water pump;combined with the known water pump transmission ratio of 1.247 and the limit working condition Speed(rated power point speed of the engine 2800rpm,maximum torque point speed 1800rpm),the flow of the engine can be obtained under the limit condition,and then according to the flow under the limit condition,combined with the basic performance data of the radiator,the relationship between the wind speed under the limit condition and the heat dissipation can be obtained under different wind speeds.With the aid of CFD,we can get the wind speed under the limit condition,and then we can get the heat dissipation under the limit condition.According to the empirical calculation formula,the calorific value of the starting engine under the limit condition can be calculated.The calorific value of the radiator under the limit condition is about 20%higher than that of the engine,which meets the use requirements.The performance margin of about 20%is the theoretical calculation experience summary.The third step is to design the working condition reasonably.Through environmental simulation test,the system verifies the rationality of the cooling system performance matching.At the same time,through the road test,the effectiveness of environmental simulation test results is verified.The light truck platform of the project matches with different tonnage(light load 4.5t,standard load 6T,heavy load 7.5t),and the operation conditions are complex.The operation environment of the project covers the whole territory of China,including Turpan(above 40?)and Mohe(below-35?),Golmud(above 3500m altitude)and Yungui mountain area,as well as expressways in northwest dry environment and Haihai highway in the humid South China.Through the reasonable design of the test conditions,the verified cooling system can cover the whole range of use.There are 8 verification conditions designed in this project,including continuous high-speed condition of 100km/h,maximum torque point condition,maximum power point condition,ultra-high speed condition of 110km/h,and post boiling condition after the completion of the above four conditions.In the verification process,the coolant temperature in the engine cylinder and the oil temperature in the engine oil pan are focused.Through the comparison of road test results,it is consistent with environmental simulation test results,which further proves that the ring model test is reasonable and effective.In the fourth step,in order to ensure the durability and reliability of the cooling system,bench test is designed to strengthen the assessment of the key components of the cooling system.The key parts of the cooling system are radiator and intercooler.In this project,sweep frequency vibration test,blasting test,high temperature pulse test,vibration durability test and external corrosion durability test are designed.The result shows that both the radiator and intercooler have passed the bench durability test.The project organized the reliability and durability assessment of the whole vehicle,which was carried out in Dongfeng test field and Hainan test field respectively,and 45000km multi-road test was carried out in both places,and there was no test failure of the cooling system.This project is a medium and exclusive light truck jointly developed by a company and ISUZU of Japan.Through systematic analysis and research on the cooling system of the vehicle type of this project,combined with CFD tool aided design,to ensure that the cooling system of the whole vehicle works reasonably,a set of performance matching method of theoretical calculation and a complete set of environmental test verification method are explored,which will provide a reference for the development of subsequent light truck type projects for theoretical basis and practical reference.The project will be launched in the second quarter of 2020.The cooling system has been verified and assessed in multiple rounds,and the subjective driving evaluation reflects well.It is expected to obtain good market reputation and social and economic benefits for the company. |
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