Foreword
Today, with the rapid development of new energy and intelligence, the car has gradually become a brand new way of life from simple transportation. Since technology makes life colorful, the goals and requirements of "design" for car products cannot be kept in line, stagnant, and require constant adjustment and innovation.
The power battery system is a core part of new energy vehicles. The system structure is also an important link to ensure its functional integrity and security. From the perspective of global product analysis in recent years, structural design has developed very rapidly and matured. There are also many boutiques, and the technology is in full swing.
I have been groping and summarizing through years of system integration design. A set of methods for their own design work is gradually formed: the structure "three + 6" design pattern. And applied in multiple projects. Made a good result. Of course, as awareness increases, it is constantly being summarized and expanded.
This paper focuses on the safety design of the "three" large structure of the battery system, and through the classic case of leaf, the "three +6" idea is built up for easy understanding.
What is the "three +6" mode: it is not difficult to understand from the literal: "three" represents a large structure; "6" represents a small structure of a functional unit. It is mainly to reorganize and define many different functional structures and functional features of the battery system. Highlight its design points.
The "three + 6" mode advantage: let the design "targeted." Make the function design "completer".
The three +6" mode makes the place that needs "strong" stronger: for example, the functional safety design of the frame. Functional integrity: for example, the development of the battery system housing design, from the simple "box" simple structure, to a variety of fusion The "advanced shell" of the characteristic elements has progressed.
The characteristics of the “three + 6†model: understanding the relevance, subdividing the “big†structure, and strengthening the “small†structure.
The following is an explosion diagram of the leaf structure, and the complexity of the structural unit can be seen. At the same time, the structural elements are very strong, and the internal frame structure must not only take into account the bearing capacity of the module, but also consider the safety characteristics design and the bracket characteristic design. Therefore, it is necessary to extract large structural elements and focus on design. Another example is the small IP structure, which seems to have small structural requirements, but its design is very difficult. Not only the design of the strip, but also the multi-layer sealing structure, the sealing essence of the "redundant" design (that is, the "tooth edge" structure of the inner guard), the "compression amount" seal essence, very distinctive. More need to strengthen the design. In short, the structural relationship is inextricably linked. It is necessary to distinguish and generalize these structural characteristic factors, highlight their main features, and take into account other characteristics. Next, some structural "dot" designs are further developed and analyzed:
1) Frame structure: It is the most important "three" large structure design soul, focusing on "safety"
Many of our early new energy vehicle designs were restructured from existing bodywork. Not a positive design. The battery system is passively matched with the body structure, and the system structure is also designed with a "box" structure (also synonymous with simple design). The design was completed by bending and welding a certain thickness of the steel plate. The load-bearing function relies mainly on “thicknessâ€. In addition, the simulation is not sufficient, resulting in cracking of the battery system cabinet and fracture of the bracket. This structural function is vaguely designed, and the functions of weight bearing, reinforcement, protection, and so on are integrated. It's hard to be safe. Functional integrity is also not guaranteed.
The "three" large structure, the frame structure design is different, and the function definition is very clear. For example, the main task of the inner frame is to complete the bearing of the module, for example, it can be completed with 1.5mm and 1.8mm medium and high strength steel; the outer frame structure is similar to the inner frame design requirement, but its function is to carry the system through the bracket. The combination with the assembly of the body; the protective panel (including the lower casing protective panel, the upper cover), the lower casing protection plate, and the inner and outer frames have no bearing effect, but complete the protection and sealing of the system. At this time, because the weight is not taken up, the sheet can be made very thin, and the thickness of the leaf sheet is measured to be 0.7 mm (after varnishing). Greatly reduce the weight of the system structure. Although the upper cover plate is thin, it does not feel deformed and has good strength. This is the goal achieved through design.
In terms of lightweighting, we have done a calculation (with an envelope structure of about 1500 × 1200 × 45mm). After the frame structure design, the weight loss can reach about 20%. More importantly, the "safety" is strengthened by the structural design. . Really let the design "targeted."
(The colored part is the inner/outer frame and the white is the protective plate)
2. "Multi-layer" safety structure design for battery system protection
The first layer comes from the safety structure of the body: Of course, this layer is not a battery system structure and requires a body design. However, the battery system needs to be put forward, and the integrated design is completed with the whole vehicle.
After the collision:
The second layer comes from the shell material design: a variety of material applications to meet structural functional requirements
The choice of different materials is the perfect embodiment of “targetedâ€. It is also a system lightweight requirement. After all, the battery system is too heavy. Need to reduce the burden. Of course, from a cost perspective, it is not suitable for small batch or sample production. More suitable for mass production products.
The third layer is protected by the structural feature design: the feeding structure is the energy absorption of the “back†of the collision, and is the passive anti-collision structure; the outer frame hollow inner reinforcing beam structure is the collision “front†active anti-collision structure. It has both a strengthening effect and a light weight. This structural feature is also used in Tesla (in fact, in the body design, it is a very mature technology). However, in the design of the battery system casing, this technology has not been transplanted many times, and sometimes the pursuit of lightweight, and sacrificed the safety structure.
The fourth layer layout structure, effective security protection for plug-ins and electrical boxes
We all know that in the ASIL rating, the electrical function of the electrical box (relay) is generally defined as the C level, but from the perspective of the entire battery system, the sequence analysis of the failure step is not allowed to fail before other system parts. Therefore, from the perspective of design protection, it is important to consider. We look at the leaf design, which is basically placed in the "central" position of the system and the vehicle. Tesla and volt are also designed this way.
This is very worth learning. How are we doing it? Two words: design "willful". Place the plug-in or service switch on the side of the system or vehicle position (concession design for reasons of ease of operation or structural constraints). The vehicle is in a side collision state and the side is weak. At this time, the battery system plug-in placed on the side will greatly increase the risk and failure rate.
The above analysis mainly focuses on the framework structure and safety focus design. Mainly want to explain that only when the structural function is clear, the design can highlight the key points. Of course, we will also ask a question, in the face of today's various materials (non-metallic shell, cast aluminum shell, extruded aluminum tailor welded shell), a variety of structural forms (box, half box, tray ), can the "three + 6" mode be applied? Let me answer the answer.
summary
1, "three + 6" mode, the essence of design is refined. It is suitable for a variety of materials, a variety of shells. However, in the specific design, there will be certain limitations and serious choices. For example, in the tray type extrusion experiment, there is no shell effect after the box frame design is good, because the structure is limited. I am very touched by this (I just witnessed the extrusion experiments of two well-known brand battery systems abroad, and concluded)
2. The “three + 6†mode can help us “standardize†structural design elements. Easy to migrate to different projects, mature design can reduce design errors.
3, "three + 6" mode is more important or "safe" design. This is the core.
Note: Why do you refer to the leaf more?
First of all, the leaf is a classic in terms of security design. The reason is that the leaf released the first paragraph to the 2016 version in December 2010. Although the energy density of the battery system is constantly increasing, the cell is adjusted, and the module frame is adjusted, the essence of its structural design has not changed. In particular, from the 2010 version of the five-star collision award (European safety performance), its sales of hundreds of thousands of vehicles, rarely heard of battery safety accidents, the success of these is just the accumulation of these basic designs.
Secondly, compared to the shell structure design of tesla, BMW, etc., the leaf still does not lose to them. At the same time, I found that there are many similarities. As for who said who to learn, it is not known. Let us stand on the shoulders of giants, this is the truth.
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