On April 18-19, 2023, at the third 2023 Body and Interior Decoration Conference, Lu Houguo, Assistant Dean of the Body Design and Research Institute of Anhui Jianghuai Automobile Group Co., Ltd., stated that new energy vehicles have put forward new requirements for body design. In terms of body performance, it mainly includes three aspects: first, safety requirements for batteries; The second requirement for lightweight vehicle body; The third requirement for rigidity.

　　From the perspective of body structure, as competition intensifies, the development cycle of automobiles is further shortened; At the same time, the platformization of the battery pack drives the vehicle body to further develop towards a modular platform direction; With the advancement of technology and the pursuit of low-cost strategies for mid to high-end new energy vehicles, the integration of vehicle bodies has further developed. From the perspective of vehicle body materials, there is a requirement for multiple materials.

　　Based on the above requirements, Jiangqi Group has conducted design practices for new energy vehicle bodies from various aspects such as performance target design, framework image design, force transmission path design, material thickness design, section design, structural ring design, joint design, key component design, local detail design, and connection design.

　　Lu Houguo | Assistant to the Dean of the Body Design and Research Institute of Anhui Jianghuai Automobile Group Co., Ltd

　　The following is a summary of the speech content:

　　In the trend of the hot development of new energy vehicles, what should be done for new energy vehicle bodies? We have considered this and will now share Jianghuai's relevant designs for new energy vehicle bodies.

　　The Development Trend of Vehicle Bodies under the Background of New Energy

　　At present, new energy vehicles are indeed a hot topic. From last year's perspective, the sales of new energy have reached a new high. The sales volume from January to March this year reached 1.6 million units, a significant increase compared to the same period last year. The development of new energy vehicles is showing an unstoppable trend. On this basis, higher requirements have also been put forward for the key design elements of the vehicle body.

　　Firstly, there are performance requirements for the vehicle body. Undoubtedly, new energy vehicles have increasingly high safety requirements for their bodies.

　　From the perspective of batteries, with the continuous development of power battery technology, the safety issue of power batteries has become a hot topic in the industry. In addition, the entire vehicle is loaded with such a large battery, which is approximately 500-600 kilograms, which is not conducive to safety, energy consumption, handling, durability, and has higher requirements for the lightweight of the vehicle body. Everyone is talking about the integration of car body batteries, including CTP, CTC, and CTB. From this perspective, new energy vehicle bodies have put forward higher requirements for the overall stiffness of the body based on the batteries of future CTC and CTB. It is necessary to have higher body stiffness to protect the battery from significant torsional deformation and huge impact during use.

　　Secondly, there are structural requirements for the vehicle body. With the intensification of competition, the development cycle of automobiles is further shortened; At the same time, the platformization of battery packs drives the vehicle body to further develop towards a modular platform, putting forward higher requirements for the vehicle body structure. Therefore, it is necessary to carry out the research and development of the split body of the upper and lower bodies, ensuring that the body has a high degree of modularity, scalability, and standard upper and lower body and body and chassis design interfaces, in order to accelerate the speed of body research and development.

　　Another topic that has been discussed extensively is integration, as integrated die-casting and hot-formed door rings all demonstrate a high degree of integration. High integration is a typical trend in the development of new energy vehicle bodies, used to reduce costs and cycles in the design and manufacturing processes.

　　Finally, there are material requirements for the vehicle body. At present, materials are showing a trend of multi material design in new energy vehicle bodies, with more showing all aluminum bodies and steel aluminum magnesium hybrid bodies. Over time, steel aluminum magnesium hybrid bodies have gradually taken a dominant position. The reason is that a series of balancing requirements such as performance, cost, design cycle, and manufacturing difficulty have accelerated the development of steel aluminum magnesium hybrid vehicle bodies.

　　In short, the main requirements for body design are in terms of structure, materials, and performance. Based on this, we emphasize integration, platformization, modularity, and design of key components in terms of structure, mixing of multiple materials in terms of materials, and safety, stiffness, and lightweight design in terms of performance.

　　Source: Jianghuai Automobile

　　Design Practice for New Energy Vehicle Body

　　The following figure shows the key links and elements in the body design process, including performance target design, frame design, force transmission path design, material thickness design, section design, structural rings, joints, and key components. These designs will ultimately reflect the structure and performance of the entire vehicle. In this process, we have considered and practiced the three major requirements mentioned above.

　　Source: Jianghuai Automobile

　　The first is performance target design. In the design of new energy vehicles, more attention should be paid to the performance goals of the upper and lower split type. Based on this, how can we meet the requirements of fast and modular design? We have set performance targets for the lower body, with a focus on the torsion of the lower body, including the torsion of the battery pack, the deformation of the CTP and CTC intermediate frames, as well as the torsion mode and local stiffness of the lower body. A series of vehicle models developed based on modular lower body can meet the design index requirements. In addition, for collision requirements, we have also designed the energy distribution ratio of the lower body, including the subframe and critical path load ratio, as well as the total collision energy.

　　Secondly, framework design. Whether it is a new energy vehicle or a traditional fuel powered vehicle, there is no difference in the overall framework of the upper body. The main difference lies in the central channel. Currently, there are two types: with and without a central channel. In the early conceptual design stage, rapid parameter model analysis can be used to determine whether with or without a central channel.

　　Based on the framework form, we have made some attempts to meet the conceptual requirements of skateboard chassis. Standard interfaces and dimensions have been defined on the side, front, and rear of the vehicle body, ensuring that the upper body can use the lower body platform for different wheelbases, front and rear overhangs, and different body width requirements. Simultaneously applying the independent performance design of the vehicle body, ensuring that the upper body of different series can meet the design performance requirements of the entire vehicle.

　　Thirdly, design the transmission path. For the design of the force transmission path on the lower body platform, we are unable to directly transmit energy to the rear of the car through the longitudinal beams at the bottom of the body due to the lack of left and right floor beams. The collision energy of the front longitudinal beam and the energy transfer from the lower part of the front wall are achieved from the central channel to the two floor crossbeams, and from the side to the threshold beam through a torque box. The design of the force transmission path needs to pay attention to some key dimensions, such as the height of the rear of the front longitudinal beam being about 100 millimeters, which can ensure that the entire force does not bend during the collision process, and at the same time, more force is directed towards the rear body in this area.

　　Fourthly, material thickness design. At present, for the design of typical materials for steel aluminum hybrid car bodies, we hope to use a large amount of high-strength steel in the front to ensure energy absorption and transmission in front and side collisions. At the same time, large-sized extruded aluminum is used at the threshold to ensure energy absorption during the collision process.

　　Fifth, section design. There is not much difference between the upper body and the traditional section, but the difference lies more in the specific material thickness and the overlap of key parts. But the three parts of the lower body are particularly important. The front part is to ensure that it can resist the front collision force during the collision process and ensure that there is no significant deformation in the member cabin. The specific working principle can be referred to in the following figure.

　　Source: Jianghuai Automobile

　　Let's briefly talk about the design of key components. A typical component is the integrated die-casting component of the rear floor, which currently mainly uses heat treatment free materials. At present, the main non heat treated materials have little difference in yield strength and tensile strength, including elongation and casting performance, but the yield strength is relatively low. From the design stress level of the vehicle body, if the stress is to reach below 100 megapascals, the difficulty of the design challenge is actually very high. As shown in the figure below, in terms of structure, a special material thickness design is applied to the longitudinal beam, using a wall thickness of 5-6mm to ensure both the requirements for torsional stiffness and the load-bearing capacity of the chassis. The other several parts are basically at the level of 2.5-3.0, mainly from a lightweight perspective.

　　Finally, there is the connection design. From the perspective of connection, the steel aluminum body includes SPR, FDS, laser welding, etc. Today's discussion is not about this type of connection, but rather about the structural overlap of key parts, the connection below the A-pillar. We hope that the A-pillar and the inner plate of the A-pillar can be fully connected at multiple levels and overlapped on multiple sides to ensure the strength of the connection at this location to ensure smooth force transmission and meet the protection of the battery during the collision process. The rear longitudinal beam also hopes for multi sided overlap to achieve higher torsional stiffness requirements, smooth connection on the side, and transmission of collision force from left to right.

　　In the era of new energy, we hope to have a deeper reflection on vehicle body design, focusing on critical design of structure, materials, and performance to ensure better quality of new energy vehicles.

　　(The above content is from Lu Houguo, Assistant Dean of the Body Design and Research Institute of Anhui Jianghuai Automobile Group Co., Ltd., who delivered a keynote speech on "Thinking and Practice of Body Design for New Energy" at the 3rd Body and Interior Decoration Conference on April 18-19, 2023.)