What role does the battery pack play in new energy vehicles?

　The design of the power battery system is based on the premise of meeting the power requirements of the vehicle and other designs. At the same time, we must consider the internal structure and safety of the battery system and management design. The design process is: determining the design requirements of the vehicle, determining the vehicle power and energy requirements, selecting and matching the appropriate batteries, determining the combined structure of the battery modules, determining the battery management system and designing the system design, simulation and specific test verification.

　Battery pack housing design requirements

　The battery pack case acts as a carrier for the battery module and plays a key role in the safe operation and protection of the battery module. Its design is mainly based on materials, surface corrosion protection, insulation treatment, product identification and so on.

　To meet the strength and stiffness requirements and IP67 design requirements of the electrical equipment enclosure and provide collision protection, the battery module in the box takes root in the bottom plate, and the harness direction is reasonable, beautiful and reliable.

　1. General requirements

　(1) It has the convenience of maintenance.

　(2) In the case of accidents such as collision of vehicles or self-ignition of batteries, it is advisable to consider the structure or protective measures to prevent pyrotechnics, liquids, gases, etc. from entering the compartment.

　(3) The battery box should be left with the nameplate and safety mark layout position, leaving sufficient space and fixed foundation for the installation of insurance, power line, collection line and various sensing elements.

　(4) All joints, terminals and electrical contacts with infinite basic insulation shall be protected. After the joints, terminals and electrical contacts are joined, the requirements of GB4208-2008 protection class 3 shall be met.

　2, appearance and size

　(1) The outer surface has no obvious defects such as scratches and deformation, and the surface coating layer is uniform.

　(2) The parts are securely fastened, free of defects such as rust, burrs and cracks.

　3, mechanical strength

　(1) Vibration resistance and impact strength. There should be no mechanical damage, deformation and looseness of the fastening parts after the test. The locking device should not be damaged.

　(2) Take the battery box fixed by the locking device, the locking device should be reliable and have anti-misoperation measures.

　4, safety requirements

　(1) After the test, the battery box protection level is not lower than IP55.

　(2) Personnel's electric shock protection shall comply with relevant requirements.

　Selection of battery pack housing

　The battery case is a carrier for the new energy vehicle power battery, which is generally installed in the lower part of the vehicle body, and is mainly used to protect the lithium battery from being damaged when it is subjected to external collision and extrusion.

　The conventional vehicle battery case is cast from a steel plate or an aluminum alloy. The surface is then spray coated. With the development of energy saving, environmental protection and light weight of the automobile, various lightweight materials such as glass fiber reinforced composite materials, SMC sheet materials and carbon fiber reinforced composite materials have emerged in the battery casing material.

　Steel housing. The steel battery case is the most original power battery case material, which is usually welded by cast steel. High strength, high rigidity and heavy weight. The surface needs to be treated with anti-corrosion treatment, so that it has good anti-corrosion effect under long-term high temperature conditions.

　Aluminum alloy housing. The automotive power battery pack is made of aluminum alloy material with easy processing, high temperature corrosion resistance, good heat transfer and electrical conductivity. The aluminum alloy shell (except the shell cover) can be stretched at one time. Compared with the stainless steel, the bottom welding process can be omitted, and the problem of the cold wind quality caused by the burning of the metal element does not occur during the welding. In addition, the aluminum alloy housing has the following four advantages.

　(1) Long service life. The simulated aging test of the aluminum alloy shell shows that its service life is more than 20 years, far exceeding the traditional materials such as metal.

　(2) Flame retardant, smokeless and non-toxic. The flame retardancy grade of aluminum alloy materials can reach FV0, the level of smoke generation is up to 15 grades under high temperature burning, the smoke is non-toxic, and the toxicity level is ZA1 (quasi-safe level 1).

　(3) Explosion-proof performance. The explosion-proof device is specially provided on the aluminum battery cover of the power battery. When the internal pressure of the battery core is too large, the explosion-proof device will automatically open the pressure relief to prevent the explosion.

　(4) Anti-aging properties. Among metal materials, aluminum has excellent anti-aging properties. The anti-aging performance test shows that the location of the climatic zone is different, and the maximum aging thickness of the surface is less than 50μm in 20 years. Most cabinets have a minimum thickness of 5 mm, which is less than 1% of the thickness of the cabinet, so there is no significant effect on the mechanical properties of the cabinet.

　SMC conforms to the material. That is, the sheet molding compound, the main raw material is composed of GF (special yarn), UP (unsaturated resin), low shrinkage additive, MD (filler) and various additives. It has the following 7 major features.

　(1) Good electrical performance. The SMC compliant material not only has excellent electrical insulation, but also maintains good dielectric properties at high frequencies, is immune to electromagnetic effects, and does not reflect electromagnetic waves.

　(2) Chemical resistance. SMC conforming materials have good corrosion resistance to acids, alkalis, salts, organic solvents, seawater, etc., while metal materials are not resistant to acid and seawater.

　(3) Lightweight and strong. SMC conforms to the material's specific modulus comparable to steel, but its specific strength can reach four times that of steel.

　(4) Notch sensitivity. When an overload is constructed with a small amount of fiber breakage, the load is rapidly distributed to regain the mechanical balance on the broken fiber. This is incomparable with metal components.

　(5) Low thermal conductivity and small expansion coefficient. The thermal stress generated when there is a temperature difference is much smaller than that of metal.

　(6) Excellent UV resistance and aging resistance. The maximum aging thickness of the surface is less than 50 μm in 20 years. Most cabinets have a minimum thickness of 5 mm, which is less than 1% of the thickness of the cabinet, so there is no significant effect on the mechanical properties of the cabinet.

　(7) Good anti-fatigue performance. The tensile strength of SMC composites is slightly better than that of steel. The fatigue resistance of steel and most metal materials is generally higher than this value, up to 70%-80%.

　Carbon fiber reinforced composite materials are one of the effective ways to solve the lightweight development of automobiles. At present, carbon fiber composite materials have become an ideal substitute for traditional metal battery cases. The carbon fiber density is about 1.7 g/cm3 compared to the metal material. Tensile strength 3000MPa, elastic modulus 230GPa, light weight, high strength, high temperature resistance, friction resistance, shock resistance, low thermal expansion coefficient.

　The density of steel is 7.85g/cm3, tensile strength is 300-600MPa, elastic modulus is 190GPa, specific heat capacity is 0.42J/(KG.K), thermal expansion coefficient is 10.6-1.22×10-6/°C, and its density is higher than carbon fiber. Many, tensile strength is not as good as carbon fiber. The aluminum density is 2.7g/cm3, the tensile strength is 110-136MPa, and although the weight is lighter than steel, the strength is lower and the safety performance is slightly worse.

　In addition, carbon fiber composites have an absolute advantage in impact resistance, sealing, and weight reduction.