The development of new energy vehicles is an important way to effectively alleviate pressure on energy and the environment and promote the sustainable development of the automotive industry. As the core component of the energy supply of new energy vehicles, the performance of power batteries directly affects the performance of new energy vehicles.
Among them, the power battery box, as the carrier of the power battery, plays a key role in the safe work and protection of the power battery. Most of the traditional electric vehicle power battery boxes are made of metal materials. With the development of manufacturing materials, in order to improve the economical efficiency of new energy vehicles and reduce the weight of power batteries, composite materials have been gradually applied to power box designs.
Taking pure electric vehicles as the research object and combining the characteristics of carbon fiber composite material design, a carbon fiber power battery case is designed to meet the light weight demand of power batteries. Increase the sensor power supply or increase the front-end amplifier to achieve.
1.Design of carbon fiber battery box
1.1 Functional requirements of the battery box on the product
As the protective parts of electric vehicle power batteries, the battery box has high requirements on structural design and weight. After the weight and size of the battery module are determined, many factors are considered when designing the battery box. First, the battery box is the carrier of the battery module. The battery module needs to be connected to the vehicle body through it. Secondly, the power battery is generally installed in the lower part of the car body. Considering the working environment of the battery module, the battery box needs to have a protective function for the module. The waterproof and dustproof of the module and the corrosion of the battery box by the road environment must be considered It is also necessary to consider withstanding vibration and shock during vehicle operation.
1.2 Advantages of carbon fiber materials
The requirements for the material of the power battery box are: high strength; light weight; excellent corrosion resistance. Carbon fiber has great advantages in these three aspects. First, the carbon fiber composite material has a high specific strength (the tensile strength of the material and Density ratio) and specific modulus (ratio of the material's elastic modulus to density), its specific strength is 5 times that of steel. The density of carbon fiber and epoxy resin composite is 1.4kg / m3. This material also has excellent Corrosion resistance and flame resistance｡
1.3 Process design of carbon fiber battery box for vehicle
There are many molding methods for carbon fiber composite products. Among them, the processing technology suitable for carbon fiber battery cabinets is molding, vacuum assisted molding (VARI), RTM, etc., molding, and RTM is suitable for large parts. VARI Technology Institute The cost of the required mold is low, and the fiber content of the molded product is relatively high, but the entire molding process takes a long time, which is suitable for the production of small batches. Process capability, comparing these 3 processes, this product chose VARI processARI
VARI is a vacuum-assisted process for introducing dry fabrics. The process principle is to cover a single-sided rigid mold with a flexible vacuum bag film and seal the fiber-reinforced material. Vacuum negative pressure is used to eliminate the gas in the cavity. The process of impregnating the resin and fibers with resin through vacuum negative pressure driving the resin and the process of the battery box is as follows: a negative mold forming mold, the surface is glossy or matt treated, and a certain number of layers of carbon fiber cloth are laid on the mold. Then, with the assistance of the diversion net, the diversion tube, and the sealing strip, the mixed resin material is sucked into the fiber cloth by a vacuum pump, and finally cured. After the mold is cured, the mold is released, and the boundary and the part that needs to be cut are cut.
1.4 Structural design of carbon fiber battery case
The position section of the power battery on the vehicle body is shown in Figure 1.
1.4.1 Overall structural design
According to the shape and arrangement of the battery module and the position of the power battery on the vehicle body, in accordance with the principle of using space as much as possible, the outer envelope of this battery box is designed to be a nearly square box structure.
The main structure layer is made of carbon fiber cloth and is supplemented with resin. Metal joints are used at the joints. The metal joints and the main structure layer are connected by structural glue. The battery module group and the box are connected by metal fasteners.
In order to increase the strength and modal of parts, on some large-area structural surfaces, stiffeners are a typical form of improving structural stability, and hat-shaped ribs are relatively high in loading efficiency and low in weight. The structure is reinforced by hat-like ribs and ribs. In view of the characteristics of continuous fiber composite materials, the carbon fiber reinforced structure is designed with equal thickness at the convex and concave ribs.
1.4.2 Laminate design
The carbon fiber woven fabric of the battery box adopts T300-3K and T300-12K. The two types of woven fabrics are mixed. There are a total of 10 layers of carbon fiber plain woven fabric with resin design. The following considerations were taken into account when laying: the balance of the ply angle, the number of requirements for the same ply direction, the symmetry of the ply, the deviation of the angle between the ply, and the maximum number of continuous plies. The battery box parts use 10 layers of plain weave cross-tiling, and the layering method is [0/45/0/45/0/0/45/0/45/0].
1.4.3 Connection Design
The battery module needs to be connected to the car body through a battery box. The battery box is connected with metal fasteners at the connection. Some of these fasteners are embedded. By controlling the depth of the embedment, the connection can withstand relatively High tensile strength; some fasteners and carbon fiber body are bonded together with structural glue.
2. Simulation results of carbon fiber power battery cabinet
The carbon fiber power battery box is simulated and analyzed from four aspects of G-Load, modal analysis, vibration and shock, so as to provide a reference for the durability research and structural optimization of the power battery system.
2.1 G-Load analysis
According to the values in Table 1, the power battery is loaded in four operating conditions. The main purpose is to investigate the structural strength of the battery system under different loads due to braking, cornering, and jumping during normal vehicle driving.
2.2 Modal analysis
Modal mode is the natural vibration characteristic of mechanical structure. Modal analysis is used to determine the vibration characteristics of the design structure or machine component, that is, the natural frequency and mode shape of the structure. For the power battery box, the modal analysis is mainly to examine the first six natural frequencies and mode shapes of the battery system structure.
Because of the random vibration standard J2380 in the Z direction vibration requirements, the frequency band below 35 ~ 40Hz belongs to the high vibration energy region, so the low-order mode in the Z direction of the battery pack should be higher than 35 ~ 40Hz as much as possible. After modal analysis of the model, the results show that the first-order mode of the battery case structure is 61 Hz, which meets the requirements for low-order modes (see Figure 2).
2.3 Mechanical shock
The method of ISO16750 was used to analyze the mechanical shock resistance of the power battery box structure. The shock pulse uses a half-sinusoidal pulse waveform with a peak acceleration of 500m / s2 and a duration of 6ms. The acceleration of the impact occurs in the 6 directions used. The analysis results show that the maximum stress of the battery tray and case is 76.5MPa, which is far less than the allowable stress of the material.
2.4 Vibration analysis
The vibration analysis of the power battery box uses the standard in SAEJ2380. According to the method specified in SAEJ2380, the ability of the power battery box structure to resist mechanical vibration is analyzed. The analysis results show that the maximum stress of the battery tray and the case is much smaller than the allowable stress of the material. The carbon fiber battery case meets the design requirements.