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[YesAuto Technology] While many people are still rethinking the safety of cars, the major auto brands are actually trying to “weight loss” their vehicles. In fact, cars are like people. It’s easy to grow a few kilograms of meat, but it’s difficult to reduce it! A fat man who loses weight can stay away from the “three highs”, and he has a healthier body and more flexible movements; if a car can become lighter, its handling performance can become better, and it can run faster without changing the engine. , And more importantly, it can reduce energy consumption and exhaust emissions, making it more environmentally friendly. So there is the sentence of the title: Ning less ten horsepower, not more than one kilogram! With so many benefits, of course, everyone has to find ways to reduce weight for their products. Today we will mainly talk about several classic coups that use materials to “weight loss” for cars.

Carbon fiber-the rich and willful choice

When it comes to lightweight materials, I believe everyone will first think of the three words “carbon fiber”. In fact, the carbon fiber materials we often talk about should be called carbon fiber reinforced polymer or plastic to be exact. The English is CFRP, which is Carbon Fiber Reinforced Polymer, or Carbon Fiber Reinforced Plastic. CFRP is favored by the industry for its light weight and high strength, and it is regarded as one of the development directions of future automobiles. The weight of the carbon fiber material part of the same volume is only 20% to 30% of the traditional steel part, but its strength is more than 10 times that of steel. However, CFRP materials also have shortcomings. The biggest problem is that it is expensive! Therefore, it is difficult for us to see it on a family car that is close to the people—except for the stickers and trims that some friends bought in the Auto Parts City.

Because the value of CFRP is not particularly close to the people, in the past, only those super sports cars worth hundreds of thousands of dollars (the domestic price of millions of yuan) could absorb their high costs, and some super sports cars not only used CFRP extensively to make body parts, And also use these expensive materials to make a whole cockpit structure, also known as carbon fiber monocoque. If someone tells you that his sports car uses a carbon fiber monocoque structure, there are two possibilities: 1. He is bragging*; 2. He is a trench; 3. There is another possibility, we will talk about it later.

It should be said that the carbon fiber monocoque can be regarded as at the top of the pyramid of the current body materials, so all the brands you can see using this structure are basically “tall”, but there are also some companies that have aspirations trying to make This kind of expensive materials and structure “feels to the ground”, but it has not yet been realized.

Although Honda did not realize their good wishes, BMW actually reduced the cost of CFRP materials and applied it to the i8 and i3 of its two new energy models. Especially i3, its body structure can be regarded as a carbon fiber single cockpit, the minimum price is less than 420,000 yuan, you can enjoy the “luxury” carbon fiber material, is there a sense of earning What?

In addition, BMW has also applied carbon fiber materials to traditional models. The new generation of BMW 7 Series adopts a body structure made of carbon-aluminum hybrid materials, which is lighter than the old models, and at the same time, the rigidity rises instead of decreasing. The weight of the vehicle has a positive effect on the power and handling performance of the vehicle. I believe this is one of the reasons why BMW is confident in launching the 730Li with a 4-cylinder 2.0T engine.

Generally speaking, CFRP materials are still relatively expensive today, so they are still only patented by a small number of people. However, the body material of the BMW 7 Series also leads to a material that we will talk about next. It is relatively more close to the people and can be seen everywhere in our daily lives. However, once it appears on a car, its value will also increase exponentially. ——This is aluminum alloy.

Aluminum alloy-rational consumption and light luxury route

Compared with the previous CFRP material, the application of aluminum alloy in automobiles looks closer to us. Aluminum alloy is not as light as CFRP, and its strength is somewhat worse. However, compared with traditional automotive steel, the advantage is still very obvious: the density of aluminum alloy is about 2.7 g/cm3, while steel is about 7.8 g/cm3. ; In terms of strength, the specific strength of aluminum alloy is about 85, while that of alloy steel is only 40. More importantly, aluminum alloy is not as “noble” as CFRP material, and it is relatively easier to accept.

In addition to the all-aluminum body structure, aluminum alloy can also be used in some “cellulite” parts according to local conditions, which can effectively reduce the weight of the body, while also taking into account the production cost, making the vehicle price more “friendly”. The more common parts are the engine compartment cover and the trunk cover/door, as well as some other body covering parts. Pickup trucks like the Ford F-150 that use non-load-bearing bodies, and even the entire body uses aluminum alloy materials. Of course, these parts are not the main load-bearing structure.

When it comes to aluminum alloy bodywork, the most worrying thing is the maintenance cost in daily use. In the early years, because aluminum alloy sheet metal tools and equipment were not popular, even 4S shops were reluctant to purchase equipment and open workstations for one or two high-end models with low sales. In addition, although the principle of sheet metal repair of aluminum alloy plates is similar to that of traditional steel, there are more requirements in terms of techniques and skills, and relevant training for workers is also required. Therefore, there was almost only one way to repair the aluminum alloy body at that time-change! If you ran into an Audi A8 around 2000, I believe it would have been very sour when I saw the repair quotation of a 4S shop.

Today, as more and more models adopt aluminum alloy body parts or body structures, although they have not yet become mainstream, aluminum sheet metal equipment is no longer a rare thing in 4S shops or slightly larger auto repair shops— —Of course, the price of these devices is much cheaper than before. Therefore, many brands say that today's aluminum alloy body is no different from traditional steel in terms of use cost or maintenance cost.

In addition to the application in the car body, aluminum alloy is also widely used in the manufacture of vehicle chassis suspension parts. The aluminum alloy lower control arm that many people talk about is the best example. Compared with the aluminum alloy body, the chassis parts made of aluminum alloy are closer to us, and the chassis of many home models have been using this material for a long time.

On the whole, the application of aluminum alloy materials on the car body is not uncommon, but it is still limited to relatively high-end luxury brand models. Of course, some more friendly models use this material on some body panels. As for the chassis, the visibility of aluminum alloy parts is relatively higher. In general, the use of lightweight aluminum alloy materials to reduce the weight of vehicles is considered a “light luxury” route. However, for those cars that do not use lightweight materials, there is really no way to “weight loss”. ?

Steel-many methods of careful planning

Although aluminum alloy materials are much closer to the people than before, the cost of construction is still much higher than that of traditional steel materials. For some models that cannot absorb these additional costs due to positioning and selling prices, they are still “random.” . But for economic cars that pay more attention to economy, because consumers who choose these models are more sensitive to fuel consumption, the advantage of lightweight is undoubtedly more important, so many companies have used their brains in traditional steel.

The prerequisite for weight reduction is to ensure strength. The strength of the body structure is not only related to the safety level of the vehicle, but also affects the handling. The expensive carbon fiber materials and aluminum alloys can be far lower than the weight of steel under the same strength, so can steel with similar properties be made through some special processes? The answer is the high-strength steel that many people have heard of.

This “partial metal die casting” technology was developed by Honda and supplier Gestamp for three years. Before pressing the structural parts, the steel plate is first heated to 930 degrees Celsius; in the next step of stamping and shaping, Honda covers some cooling pipes in the target area of the structural parts, so the tempering rate of different areas of the whole structure is different. So this makes it possible to form areas of different strength on the same steel plate. According to Honda's data, this die-casting technology can achieve tensile strength ranging from 590 to 1500Mpa in different areas of the same steel plate.

The biggest advantage of this locally variable strength die casting method is that it creates an energy-absorbing crumple zone without sacrificing the overall torsion and bending rigidity of the body, and the frame is lighter. According to Honda, the torsional stiffness of the body of the new Civic sedan is 25% higher than that of the previous generation.

In addition to high-strength steel, through accurate calculations and analysis, engineers can also reduce the use of steel by drilling holes in the steel parts or redesigning the shape or structure of the parts, thereby reducing weight. Compared with the method of replacing materials, this method of weight reduction is relatively cheaper, but it requires very scientific and accurate computing power.

In the field of economical family cars, it is the most common phenomenon to reduce the weight of vehicles through the transformation of steel. Although there is a certain gap between the weight reduction and those expensive lightweight materials, the advantage lies in the economic benefits. Consumers can also enjoy the results of lightweight without spending too much money.

Engineering plastics and polymer materials-internally and externally

The last material we want to talk about is the most closely related to our daily lives, and that is plastic. Many people think that soft and light plastic can only be used to make toy cars. Wouldn't it be a joke if you made a real car? This is back to our usual topic: It is the body structure, not the skin of the vehicle, that determines the safety of the vehicle. Of course, we won't discuss this topic with the risk of tearing today, but here to tell you that engineering plastics have been used in some body covers that are not strong.

In addition to covering parts outside the car, plastic or polymer materials are also used for interior parts, pipelines and even chassis parts, as well as the stomach of the car-the fuel tank that everyone is very familiar with. Through the application of this material, the weight of the car body can be reduced from the details.

In addition to traditional engineering plastics, there is also a polymer material worth mentioning, that is, glass fiber materials. The full name of glass fiber material is GFRP, which is Glass Fiber Reinforced Plastic. Is it similar to carbon fiber material CFRP? In fact, the two have a certain similarity in structure, and both are a mixture of fiber materials and substrates (that is, plastics). If the name GFRP seems a bit strange, then there is another name you must have heard, and that is FRP.

The application of plastics and other polymer materials to reduce weight will not bring about particularly large cost pressures. At the same time, because these materials are easy to shape, they not only contribute a lot to lightweight, but also bring many changes in function and layout. And advantages.

to sum up:

Regardless of the material used, the ultimate goal is to “weight loss” for the vehicle. From the point of view of effect, of course expensive materials will have better performance and lighter weight, but different levels of models will also be positioned according to their own different And pricing to choose the material that suits you. With the increasingly stringent emission regulations, automobile lightweight has become a compulsory course for all automobile brands. I believe that with the continuous advancement of material science, automobiles will also go further and further on the road of lightweight.