Rethink cars with us.
Hello, everyone, I am the president of the electric car commune.
Last week, we sent an ideal article about the ideal "straight man communication mode", but after the article was sent out, I found that although it was about three different things, almost everyone focused on the ideal solution of broken shaft "hardware upgrade".
At the end of the article, I voted:
Most people are satisfied with the ideal "no appointment" communication method, and on the question of whether it should be called "hardware upgrade", most people voted "it should be called recall".
Just yesterday, the relevant recall information appeared, and Ideal also sent an apology letter:
Taking advantage of this recall, today is not ideal. Let's start with "broken shaft".
In fact, the word broken shaft is now the most sensitive topic for OEMs. Especially for a new force car-making enterprise like Ideality, once it is finally verified that its design mistakes lead to a large-scale axle break of its vehicles, it is undoubtedly a disaster for the company.
So what usually causes broken shafts? How can we avoid broken shaft? Today, we asked an engineer friend to have an in-depth conversation with you.
The following is written by an engineer friend:
0 1.？ What caused the broken shaft?
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There are many reasons for the broken shaft, but there are two main ones.
One is that there was a serious collision accident, which caused the chassis to be damaged and then the shaft was broken. Some companies will make a statement when there is such a broken shaft, which is the same as many manufacturers' statements after the electric car caught fire. The subtext is that my vehicle design will not take into account the man-made traffic accidents in the later period. After the accident, whether the ternary lithium battery spontaneously ignited or the shaft was broken, it had nothing to do with me.
The second reason for the broken shaft is that the quality of the product design/supplier management part is defective. From the design point of view, the axle shaft ensures the reliability of installation through the interference fit between the snap ring and the gearbox. In the meantime, the quality problems of any parts will lead to tragedy.
I once encountered the problem that the half axle snap ring was changed from imported to domestic, which immediately led to the failure of interference fit and the repeated problem of half axle falling off in the whole vehicle.
Another well-known case of broken shaft is Buick Angkewei, which is an obvious design problem.
Angkewei was born on the general Epsilon platform, but as a B-class SUV, its weight is obviously larger than that of its peers. At the initial stage of product launch, the problem of broken shaft appeared frequently.
At that time, SAIC-GM attributed it to the external collision of vehicles, and prevaricated that there was no large number of broken axles on the same platform vehicle.
At that time, Angkor used the design of "split control arm bushing" on the suspension control arm, and Pan Asia also applied for a patent for this structure.
But three years later, Pan Asia, a subsidiary of SAIC-GM, applied for another so-called "integrated control arm bushing" patent, and then completely replaced the previous "split control arm bushing" design on its model.
Integrated design has higher quality and cost. Returning to this seemingly backward design is mainly because it can completely solve the problem of broken shaft before.
This is undoubtedly that SAIC-GM admits that there are some defects in its design. In the end, the recall caused by Angkewei's broken axle involved as many as 3.3 million vehicles, and the direct loss caused to SAIC-GM exceeded 654.38 billion yuan, which was a painful lesson.
But things in the world are not black and white. Although collision is the main cause of shaft breakage, not every collision will lead to shaft breakage. Just like the serious car accidents we usually see, such as casualties after colliding with earth-moving vehicles, we will not criticize the design of the main engine factory too much.
But at this time, if some drivers and passengers can get away safely, we will definitely give a thumbs-up to the OEM's skill in safety design. So sometimes, if we reserve enough stable design and reliable parts quality, even if we encounter a certain degree of traffic accidents, we can still avoid the occurrence of broken shafts.
02.？ How to Avoid Broken Axle-Durability Test
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Is there any chance for ideal to avoid broken shaft? The answer is yes.
Whether it is Volkswagen or Toyota, they can gain a foothold in the fierce global market, not only by their system capabilities, but also by their test specifications and test procedures accumulated and constantly revised over the past 100 years.
It is the biggest reason that the main engine factory carries out durability test by simulating the life of the whole vehicle for ten or even twenty years through high-strength test between three months and half a year. The engineers in the R&D center are most worried about receiving a phone call from the test site.
At this time, on the one hand, the project is waiting to open the valve, on the other hand, it needs to evaluate whether the problems in the durability test are still suitable for opening the valve. Because the endurance tests of these traditional OEMs are very intense, and they are all in their own test sites, they often run out of problems that they can't run out every day.
For some new power companies, because they have not accumulated before, they can't talk about having their own strict endurance test specifications. At this time, someone will definitely say, why not follow the durability test specifications of a main engine factory?
First of all, we don't care whether it is ethical to follow a code. Even if it comes out, it may not be applicable to a new power company like Ideal. Because each OEM has its own design concept, just like Japanese fuel economy, German driving stability is good, while American cars are biased, but they can withstand collisions.
The durability tests of major OEMs are usually in line with their own design concepts. If a new enterprise randomly chooses a test specification of a main engine factory, it may appear? Either the specification requirements are too strict, resulting in their vehicles failing to meet the standards; Either the requirements for some working conditions in the specification are low and the problem of the whole vehicle cannot be exposed.
Even regardless of whether the vehicle durability specification is appropriate, the proving ground is another problem.
International automobile giants have their own durability test bases, and the construction of these test factories is billions.
There are only a handful of OEMs with their own test sites in China, and most OEMs will borrow the test sites of the Ministry of Communications. To what extent can the public test site reproduce the effectiveness of some international automobile giants' test specifications? This is a big question mark in itself.
Many people will ask questions and say that not every joint venture brand has its own testing ground in China. Isn't it all right after all these years?
In this regard, you may have overlooked a problem. The models of the joint venture are only made in China. In the research and development stage, numerous rounds of durability tests have been conducted overseas to verify, and only the quality of assemblies and supplier parts has been verified at home.
Therefore, for some new enterprises, durability testing is an insurmountable obstacle. Without a good durability test process, it is difficult to expose potential problems, and broken shafts can only be exposed in extremely harsh environments.
03.？ Is it reliable to use plastic parts
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Lightweight of the whole vehicle is the top priority of major OEMs at present. Fuel vehicles need to reduce fuel consumption, and new energy vehicles need to increase their cruising range. Chassis, as a mechanical structure, is naturally the key area of weight reduction. One of the criticisms of this ideal is that in order to reduce the weight, it uses a composite material of plastic parts and stamped steel plates on the lower control arm of the suspension.
For plastic parts, we should abandon the traditional impression of "very easy to break" in our minds.
In fact, modern chemical technology has long made plastic parts very strong. We can also find that the strength of Li one's lower control arm is not less than that of traditional high-strength steel through the relevant data published by Ideal before. Therefore, it is irresponsible for many people to simply use plastic parts to say that Li Yi broke the shaft.
However, compared with the simple and cold data in the statement at that time, I would rather see the announcement of the tensile curve of all materials and the difference between the composite material and aluminum or high-strength steel.
Therefore, before Idea announces the reason this time, as an engineer, I hope that Idea can announce whether the test process of the control arm is the same as that of the traditional part control arm. And these are the best ways for experts to really help themselves clean up.
Compared with traditional high-strength steel, there are still many unknown fields because of the use of new materials.
Finally, the real reason for the broken shaft is the same as my previous guess: the previous data accumulation and project experience are slightly lacking, which leads to defects in the testing and certification process of the lower control arm.
This may also be what many new enterprises need to pay attention to besides the lower arm. After all, the car is not only a means of transportation, but also related to the safety of each of us and our loved ones.
04.？ How do engineers design suspension systems?
When designing the suspension, our engineers have to carry out repeated multi-wheel simulation calculation and topology optimization.
In this design process, how much design margin the OEM is willing to leave is the accumulation of product design experience before each OEM tests itself. The load difference of 0. 1g will lead to different final part design results.
Especially in today's automobile lightweight, especially in the case of electric vehicle cruising range, whether the structural strength of suspension will be sacrificed to ensure the completion of the automobile lightweight task is also a test of the coordination of the company's internal systems.
Finally, I will turn the topic back to Li's broken shaft:
Objectively speaking, because Li ONE is an extended-range car, its weight reaches an astonishing 2.3 tons; From the design point of view, Li Yi adopted new materials to reduce the weight of the lower arm; From the experience point of view, there is still a certain gap between Li and the old OEM in terms of simulation and real vehicle verification.
-This is a little familiar with Angkor's heavier vehicle quality and brand-new bushing design.
In view of these factors, before the listing of Li ONE, our company asserted that the most difficult thing for such a heavy car is not the configuration of the three electric appliances or the networking of vehicles, but how to keep the axle running, especially when some minor collisions occur, which is a high test for the chassis design department of the main engine factory.
Ideally, in order to solve the anxiety of cruising range, the technology of program extension is adopted, but its heavy vehicle weight will adversely affect the pure electric mileage of the whole vehicle. In order to improve the pure electric mileage again, we must use our brains to reduce the weight of the whole vehicle.
However, reducing design redundancy, using innovative materials and innovative design are all taboos in chassis design.
The chassis is not designed for interior and exterior decoration, nor is it fancy. As long as it can be designed safely and without design defects, it will burn high incense. However, I have to admit that nothing is perfect in this world, and what is gained will be lost.
But building a car, I always think it is a sacred thing and needs awe.
This article comes from car home, the author of the car manufacturer, and does not represent car home's position.