The promulgation of the national new energy vehicle subsidy policy and the proposal of the new energy vehicle points system are enough to show the government's determination to develop new energy vehicles. At the same time, at the technical level, the China Society of Automotive Engineers also released the "Technical Roadmap for Energy Saving and New Energy Vehicles" Figure", the overall policy is to use pure electric power as a breakthrough and basic platform to promote the all-round development of hybrid vehicles and fuel cell vehicles, and ultimately form the overall competitive advantage of new energy vehicles. To advocate pure electric vehicles, we must first vigorously develop the core component power battery technology, because it is directly related to the cruising range, safety and cost of electric vehicles. The classification of power batteries has evolved from lead-acid batteries, nickel-metal hydride batteries, to lithium-ion batteries (lithium batteries). Vehicle power batteries have also gone through a long process. The main differences among the lithium batteries currently in mass production are the appearance of the product and the material of the cathode. The classification comparison described below is centered around these two aspects. 1. Classification of cathode materials Currently, lithium batteries can be divided into lithium cobalt oxide, lithium iron phosphate, lithium iron manganate and ternary lithium according to the cathode material. The following is a comparative analysis of the characteristics of these four typical lithium batteries in terms of cost, energy density, layout flexibility, lifespan and safety. See Figure 1 and Figure 2 for details. 2. Battery packaging type classification Although power batteries have many different shapes and size, but commonly used ones can be classified as shown in Figure 3. The power battery pack is integrated into the vehicle architecture. In the early stage architecture development of the pure electric vehicle project, how to reasonably arrange the integrated power battery pack is crucial. The specific work elements mainly involve ground clearance, passability, collision safety and power demand, etc. Each aspect will be introduced separately below. 1. The battery's ground clearance requires that the lower surface of the battery be protected by structural parts, and it also needs to meet the following conditions: Under the maximum jump state, the battery needs to ensure a certain gap from the ground; it must be competitive under full load. The ground clearance; the battery RESS needs to be protected in the forward direction; the battery RESS arrangement must not be lower than the lowest surface of the surrounding body structure. 2. The human-machine layout of the crew cabin limits the Z-direction size of the battery. It can be seen from the human-machine layout of an electric vehicle project that there are 9 engineering indicators that need to be considered in the Z-direction latitude, specifically the distance H5 from the crew H point to the ground, the crew The sitting height is H30, the head space is H61, the distance from the heel point to the ground is H8, the thickness of the battery pack in the Z direction, the battery pack ground clearance, the vehicle height is H100, the distance from the upper surface of the battery pack to the upper surface of the floor, and the carpet and sound insulation cotton. thickness of. Therefore, the height of the vehicle body is limited based on the styling requirements, and the Z-direction size limit surface of the battery pack can be derived based on the human-machine layout requirements. 3. The collapse space limits the Y-direction size of the battery. Since the working voltage of the battery is generally a high voltage greater than 300?V, and the electrolyte in the battery cell is highly corrosive, the battery pack must be installed in the vehicle. A reasonable safety collapse gap needs to be set, and lateral collision conditions are particularly harsh. Specific vehicle models need to use CAE iterative analysis methods to arrive at a reasonable design of the lateral collapse distance from the battery to the rocker panel. 4. Restrictions on the X-direction size of the battery by the rear suspension form. The corresponding relationship between the X-direction size limit of the battery in an electric vehicle project and different suspension forms. The X-direction from the front wheel center to the No. 1.5 beam specifically refers to the front surface of the battery. The X-direction distance from the No. 1.5 beam to the center of the front wheel can be approximated as the distance from the front surface of the battery to the center of the front wheel. The different lengths in the X-direction of different suspension types lead to differences in the X-direction size restrictions of the battery. The safe rear collision distance refers to the value from the rear surface of the battery to the nearest point of the rear axle in the X direction, which must be greater than 50 mm. 5. Limitations of the vehicle load transfer path on battery pack design The vehicle load transfer path can be roughly decomposed into: front cabin load path, front and center floor load transfer and rear floor load path. Since future battery pack layout plans are basically laid out under the floor, the design of the front and middle floor load transfer paths is closely related to the structural plan of the battery pack. According to a large number of CAE analyzes and research on competitive models, two cross beams are generally placed above the front and center floor. Their main function is to serve as a seat support structure to prevent the seat from being pulled during a collision, and also to carry the load during a pillar collision. transfer. Regarding the internal structure design of the battery pack under the floor, it is also hoped that the position deviation between the cross beam between the front and rear modules and the No. 2 and No. 3 beams can be minimized, which can improve the pressure resistance of the battery in a side collision. After topology optimization, the load transfer under the floor is mainly accomplished by arranging the longitudinal beam extension beam on the side of the battery and the No. 1.5 beam in front of the battery. As shown in Figure 8, the purple longitudinal beam in the figure passes through the triangular structure and the No. 1.5 beam. The beam is connected to the longitudinal beam of the front cabin for load transfer in a frontal collision; at the same time, the battery frame should also serve as a load transfer path to cooperate with the body load path; the beam structure inside the battery pack should be connected with the body's No. 2/3/4 beams and the central channel The beam position remains consistent. 6. The demand for power for the cruising range. For the same battery unit module, the cruising range is related to the energy density and capacity of the battery, and the capacity parameters of the battery are determined by the number and method of series and parallel connection of its internal battery cells. , which will ultimately lead to changes in the overall shape and size of the battery pack. Table 2 details the differences in battery power and battery pack size due to differences in the energy density and series-parallel connection methods of cells and modules under the same cruising range target requirements for battery packs from different suppliers. 7. The battery pack installation interface requires that the installation method of the battery pack on the vehicle directly affects its mode and strength. Generally, an installation point needs to be arranged at a certain distance around the battery pack. If the overall battery pack length is greater than 2?m, it is recommended that Adding a hanging point in the middle position improves the modal. 8. Battery pack external protection requirements As the battery RESS is an important safety component, a series of structural solutions need to be designed at the vehicle level to protect it. A generally mature solution is to add a steel protective plate to the bottom of the battery, which is screwed to the battery bottom plate. At the same time, sealant needs to be applied near the installation point to prevent foreign matter and water from infiltrating during vehicle use. The specific solution is as follows: As shown in Figure 9. Conclusion This article only focuses on the factors that need to be considered in the early stage architecture layout and integration of the power battery pack. It does not analyze too much the system voltage matching between the battery pack and the electric motor, the cooling design of the battery pack, and the selection of the target power. However, in actual projects, these design indicators are also key elements that directly affect the design of battery packs for vehicle models, and they all require in-depth research and analysis.

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