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New energy vehicle battery thermal management technology
First, technological innovation
(I) Project background
1. National strategic needs
March 1, 2017，The Ministry of Industry and Information Technology, the National Development and Reform Commission, the Ministry of Science and Technology, and the Ministry of Finance issued the Action Plan to promote the development of Automotive power Batteries.，specify，2020年，The energy density of the power battery system is greater than 260wh/kg，The cost should be less than 1 yuan /Wh，The operating environment reaches -30~55℃，The charging ratio reaches 3C。
2、Industry and its own development needs
The temperature of the lithium-ion battery itself is maintained in the range of 20 to 30 ° C, so high efficiency has become the development trend of battery thermal management systems。According to efficiency, the battery thermal management program is generally divided into natural cooling, forced air cooling, liquid cooling technology and refrigerant direct cooling technology, of which natural cooling design is the simplest, direct cooling technology design is the most complex, the highest cost, and there is no mature use case in the market。
At the same time, by the end of 2016, Jianghuai pure electric cars accumulated production and sales of 3.6万辆，Basically adopts air cooling system，The cooling efficiency is low, the temperature difference of the system is large, the working condition and service life of the power battery are limited, and the space utilization is low，Vehicle mileage is subject to certain limitations and other disadvantages;In this case，In response to the company's instructions on "re-creating competitive advantage" for new energy vehicles，Implementation of JAC "technology" policy，Increase customer satisfaction，Technical reserves of liquid cooling systems are urgently needed，Development of liquid-cooled power batteries。
(2) Project objectives and measures
1. Project objectives
Liquid cooling technology is the development trend of battery thermal management system, foreign Tesla, BMW
i3, GM Volt and other models of battery packs have adopted battery liquid cooling technology, stable and reliable operation。Domestic car companies are developing, but the batch application is less, in this case, our company intends to carry out the liquid-cooled power battery research and development project, to achieve the following goals:
(1) The liquid-cooled battery module achieves passive safety of thermal runaway under various failure modes;Thermal instability of the unit will not cause thermal runaway of the module and battery pack。
(2) The thermal management performance is significantly improved compared with the air-cooled system, and the improvement targets are set in extreme discharge conditions, high temperature fast charging, high temperature slow charging, and low temperature heating:
(3) Complete the performance matching and calibration of vehicle air conditioning and battery thermal management system。
(4) The liquid cooling system is frozen in digital mode and has the conditions for issuing a mold opening notification letter。
(5) Complete the feasibility assessment of mass production of key components and supplier selection。
2. Project measures
Aiming at the established development goals, according to the NAM process, the development process of putting forward the thermal management system design concept scheme release - design scheme release, A sample structure status and initial control scheme release - thermal management control strategy and performance verification test outline release - thermal management performance confirmation -SOP is established:
Thermal management system design concept scheme release: Based on system simulation analysis and theoretical calculation, fully benchmarking model, complete the thermal management system concept scheme design, and complete the selection of thermal management components;
Release of structural status and initial control scheme of sample A: Based on iEV7S vehicle space structure, arrange the spatial position of each thermal management component;According to the internal structure of the power battery, arrange the module and the liquid cooling pipeline。Release the initial control plan according to the working condition and performance of the power battery and the temperature requirements;
Release of thermal management control strategy and performance verification test outline: Based on the vehicle test conditions and the accumulated test experience in early development, learn the verification methods of relevant German Volkswagen models, and release the performance verification test outline and thermal management control strategy。
Thermal management performance and other confirmation: according to the test outline published in the early stage, conduct full test verification and parameter calibration until it is confirmed that the performance meets the design requirements。
SOP: Complete the performance confirmation;All technical documents such as: technical agreement, three-dimensional digital model, two-dimensional drawings, data confirmation letter, mold opening notice letter, EV test report, etc. are frozen and issued, and SOP is completed。
(3) Technological advantages and application effects of new technologies
1. Technical advantages
Compared with the previous generation of air cooling and heat management, although its technical complexity and development difficulty are improved, the effect is remarkable, and the system heat transfer efficiency is greatly improved。The improvement of heat transfer efficiency can ensure that the operating temperature range of the battery pack is shortened from 0~55℃ to 10~35℃, and the temperature difference is reduced from 17℃ to 5℃;Effective control of temperature difference and suppression of temperature rise can greatly improve the safety, life and charging performance of the battery pack。At the same time, compared with the air-cooled system, the liquid cooling system occupies a smaller volume in the battery pack, the space utilization rate of the battery unit is higher, and the battery pack energy can be increased from 29kwh to 40kwh。
Liquid cooling technology has three core advantages:
First, the liquid-cooled battery pack can ensure 100% thermal runaway safety, and the short circuit in the battery cell will not cause the battery pack fire, ensuring the safety of people and vehicles。
Second, the battery works in a more suitable temperature range, the life of the battery pack can be increased by 6%, and the high and low temperature charging time is shortened by 1h。
Third, the volume of the liquid-cooled battery is higher than the energy density, and the vehicle driving range can exceed 260Km。
2、Technical implementation effect
(1) Security
The passive safety of thermal runaway under various failure modes is ensured by optimizing the liquid cooling module, coating the collector plate insulating paint, adding fuses, strengthening the module end plate and positive insulation gasket.Develop battery safety fault diagnosis strategies to identify and resolve potential safety failure risks in a timely and effective manner to avoid battery fire。100 module thermal runaway safety tests were carried out and all passed。The liquid-cooled battery module achieves passive safety of thermal runaway under various failure modes, and the thermal instability of the unit will not cause thermal runaway of the module and battery pack。
(2) Thermal performance
The thermal management performance is significantly improved compared with the air-cooled system, and 100% of the design goals are achieved, which is reflected in the following aspects:
1) Extreme discharge conditions
Target: maximum speed 130km/h, ambient temperature 40℃, initial temperature of the battery pack 35±2℃, full discharge of the vehicle to protection, maximum temperature of the battery pack reduced from 65℃ to 45℃, temperature difference reduced from 10℃ to 5℃。
Actual: the maximum speed is 130km/h, the ambient temperature is 40℃, the starting temperature of the battery pack is 35℃, the vehicle is fully charged and discharged to SOC4%, the maximum temperature of the battery pack is reduced to 45℃, and the temperature difference is 5℃。
2) High temperature fast charging condition
Target: The ambient temperature is 35±2℃, the maximum temperature of the battery pack is 45℃, the maximum temperature of the battery at the end of charging is controlled within 35℃, the temperature difference is controlled within 5℃, and the opening time of the air conditioner is shortened from the original 4 hours to 1 hour due to the thermal management needs。
Actual: The ambient temperature is 36 ° C, the battery pack temperature is 40 to 42 ° C, the maximum temperature of the battery is 30 ° C, the temperature difference is 0 ° C, and the air conditioner starts for 1 hour。
3) High temperature slow charging condition
Target: The ambient temperature is 35±2 ° C, the maximum temperature of the battery pack is 45 ° C, the maximum temperature of the battery at the end of charging is controlled within 35 ° C, the temperature difference is controlled within 5 ° C, and the opening time of the air conditioner is shortened from the original 4 hours to 30 minutes due to thermal management requirements。
Actual: The ambient temperature is 35 ° C, the battery pack temperature is 40-42 ° C, the maximum battery temperature after charging is completed is 30 ° C, the temperature difference is 2 ° C, and the air conditioner starts for 21 minutes。
4) Low temperature heating condition
Target: The ambient temperature is -10℃, the battery pack temperature is -8±2℃, the heating rate is increased from 1℃ to 7℃ in 15min of the air cooling system, and the temperature difference is reduced from 17℃ to 5℃。
Actual: The ambient temperature is -15 ° C, the battery pack temperature is -10 ° C, the heating rate is 10 minutes, the temperature rise is 7 ° C, and the temperature difference is 5 ° C。
(3) Matching of air conditioning system
Complete the performance matching and calibration of vehicle air conditioning and battery thermal management system: speed maximum speed 130km/h，The ambient temperature is 40℃，The starting temperature of the battery pack is 35±2 ° C，Full vehicle discharge to protection，The maximum temperature of the battery pack is within 45 ° C，温差5℃，Crew cabin refrigeration meets Q/JQ8101.11, the average temperature of the outlet is less than 15℃。
(4) NVH performance
The pump is opened according to the maximum duty cycle, and the running noise value is tested < 39dB(A).。
(5) Air tightness
Completed the design and development of the internal cooling pipe assembly of the battery pack, aiming at 21 liquid cooling pipes and 46 quick-insert joints, which are at high risk of leakage。By identifying the factors that affect the welding quality and surface roughness of the liquid cooling pipe, the quick-plug selection, side tension testing and precision control are implemented, and the parts import and export testing standards are formulated.Verify that the system air tightness test standard is 2.5bar, leakage 0.5ml/min。
(6) Data freezing
Through the battery pack trial production and vehicle assembly verification, completed the expansion kettle, battery cooler, water heater, external pipeline assembly, module assembly, shell assembly, liquid cooling pipe assembly and quick tube circuit 8 parts of the data freeze, meet the conditions of issuing the mold opening notification letter。
(7) Confirm the feasibility of mass production
Completed the mass production feasibility evaluation and supplier selection of 6 major components including battery cooler, water heater, module assembly, housing assembly, liquid cooling pipe assembly and quick tube circuit。
After the concept scheme - heater replacement and inlet and outlet position adjustment - battery cooler replacement - water pump position adjustment - expansion kettle design optimization，More than 20 optimizations，Confirm the liquid cooling system structure design scheme;Verified by 2 battery packs and 4 vehicles，Complete the process verification of component assembly and assembly assembly，Confirm the feasibility of the process;It was verified by 9 special tests and more than 30 special tests，Ensure system and component performance meet design requirements;The control strategy and calibration parameter thresholds are gradually optimized during the test development，The policy and software have been published;Through 5 rounds of CFD simulation analysis，It effectively guides the normal development of structure，And confirm the test results;Through temperature distribution test and thermal management performance test，It has been confirmed that the high and low temperature cooling performance meets the design requirements。
89 deliverables were formed, and eight scientific and technical papers were written: "Design of liquid cooling System for power car battery Pack" (CN61-1394/TH)
Automotive practical technology);Lightweight Design of Electric Vehicle Battery Pack Box (CN61-1394/TH
Automotive practical technology), etc.;Thirteen patents: one kind of electric vehicle power battery liquid cooling heating device, one kind of electric vehicle power battery liquid cooling plate, one kind of liquid cooled battery pack device, one kind of liquid cooled battery module structure design, one kind of battery pack anti-collision beam design, etc., has been accepted and authorized, and other items are under review。
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