Lecture on the most popular automobile styling des

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Automobile modeling design knowledge lecture

just as human body is supported by skeleton, automobile must also have a skeleton, which is the frame. The function of the frame is to bear the load, including the weight of auto parts and the impact, distortion, inertia force, etc. when driving. The existing frame types include girder type, load-bearing type, steel pipe type and special material integrated type

girder frame

is often called "array frame" in Hong Kong and Taiwan Automotive publications, and it is the earliest frame type (it has been used since the first car in the world). The principle of the girder frame is very simple: weld or rivet the thick steel beams together to form a steel frame, and then install the engine, suspension, body and other components on this steel frame. This steel frame is the "frame" with the real name

the advantage of girder frame is that the steel beam provides strong bearing capacity and torsional stiffness, and the structure is simple, easy to develop, and the requirements of production technology are low. The fatal disadvantage is that the steel girder is heavy, and the weight of the frame accounts for a considerable part of the total weight of the whole vehicle; In addition, the thick girder runs through the whole vehicle, affecting the layout and space utilization of the whole vehicle. The thickness of the girder raises the floor of the sitting and cargo compartments installed on it, making the center of gravity of the whole vehicle high

based on these factors, it can be seen that the girder frame is suitable for trucks, medium and large buses that require large load capacity, as well as vehicles that require high frame stiffness, such as off-road vehicles. The traditional off-road vehicle shows the poor handling of high center of gravity when driving on good roads, which is caused by the girder frame. (Figure A: large bus figure B: girder frame of Toyota Prado off-road vehicle) you can call it up at any time to check the

load-carrying frame

also known as integral or single body frame. Aiming at the problems of heavy mass, large volume and high center of gravity of the girder frame, the idea of the load-bearing frame is to make a solid body of metal, and then install the engine, suspension and other mechanical parts directly on the body. This car body bears all the loads and acts as a frame, so it should be accurately called "load-bearing car body without frame structure" (the car body with girder frame is called "non load-bearing car body")

the load-bearing frame is made of steel (the more advanced is aluminum) through stamping and welding, which has high requirements for design and production process, which is also a major difficulty in China's current body design and development. The formed frame is a skeleton with cockpit, engine compartment and floor, and the smooth car body we can see is a cover embedded in the skeleton

the load-bearing car frame is the mainstream of cars at present, because this structure combines the frame and body into one, with light weight, large available space, low center of gravity, and the stamping manufacturing method is very suitable for modern mass production. However, in addition to the high difficulty of development and manufacturing, the lack of stiffness (especially torsional stiffness) is also a major defect of the load-bearing body

this problem is not obvious in daily cars, but for high-performance sports cars with high horsepower and torque, high frame stiffness is required, and the stiffness of ordinary load-bearing body is insufficient. Therefore, for high-performance vehicles in recent years, in addition to the continuous improvement of horsepower, car manufacturers are also constantly committed to this stage should have a large polishing rate to improve the stiffness of the body. At present, the main methods are to optimize the geometry of the frame and adopt local thickening or repair welding to strengthen the torsional capacity

the innovation ability and basic ability construction have been improved. Because the load-bearing frame connects all parts of the whole vehicle, including suspension, body and passengers, it has a good handling response (the official scientific name is "operational responsiveness"), and transmits less vibration and noise, which is incomparable to the girder frame. Therefore, not only cars, but also some off-road vehicles designed for a good road environment also tend to abandon the girder frame and use a load-bearing body, which is the so-called "urbanized off-road vehicle". In addition, aiming at the disadvantage of the platform height of the girder frame

in recent years, there have also been large buses with load-carrying bodies (called "girder free body" or "array free body"). Due to the elimination of the girder, tourist buses can free up a huge luggage space under the car, and buses used in urban areas can lower the platform to the same height as the sidewalk so that they can get on and off (with a special low mounted axle). Low platform is an important development direction of passenger cars (Figure E)

steel tube frame

as mentioned earlier, the design, development and production process of load-bearing frame are complex, which is only suitable for mass production. But what about cars produced in small quantities? Although the shared platform strategy can be adopted, the so-called "shared platform" can only share chassis components such as suspension and transmission system. Since the load-bearing frame must match the shape of the body, it cannot share the frame for different body shapes. So the steel tube frame (also known as "frame bar type") came into being

as the name suggests, the steel tube frame is a frame welded with many steel tubes, and then the parts are installed on the frame. Its production process is simple, which is very suitable for small-scale workshops. In the s, many small-scale car factories in Britain produced all kinds of cars, all of which were made of self-developed steel tube frames, which was the heyday of steel tube frames

up to now, some sports car manufacturers with less output still use steel tube frames, such as Lamborghini and TVR, because they can save huge investment in stamping equipment. Because it is very easy to locally strengthen the steel tube car frame (only need to weld steel tubes), under the condition of equal mass, it can often obtain stronger stiffness than the load-bearing frame, which is also the reason why many sports car manufacturers are still willing to use it. (Figure f shows the steel pipe skeleton of Lamborghini Diablo, which becomes figure G after installing the covering parts)

aluminum alloy frame

the frame of Audi A8 is made of aluminum alloy, but it is a stamping structure, but the materials are different, and it still belongs to a load-bearing frame. The aluminum alloy frame mentioned here is another type. Welding, riveting or bonding aluminum alloy bars and beams together to form a frame can be understood as a variant of the steel pipe frame, but the aluminum alloy is square beam rather than tubular. The biggest advantage of aluminum alloy frame is light (under the same stiffness). However, the cost is high and it is not suitable for mass production. Moreover, the bearing capacity of aluminum alloy is limited due to its own characteristics. For the time being, only a few car factories are used in small mass-produced sports cars, such as Lotus Elise and Renault spider (Figure h)

carbon fiber frame

is also the "special material integrated frame" mentioned at the beginning. The manufacturing method is to cast carbon fiber into an integrated floor, cockpit and engine compartment structure, and then install mechanical parts and body coverings. Carbon fiber frame is extremely rigid, lighter than any other frame, and the center of gravity can also be made very low

but the manufacturing cost is its fatal injury, so at present, it is only used for racing cars without cost and a few production cars. Carbon fiber frame first appeared in Formula One cars in the 1980s, and then extended to group C cars and GT cars in the 1990s. So far, the only two mass-produced cars with carbon fiber frame are McLaren F1 in 1994 and Ferrari F50 in 95. (figure I: the integrated carbon fiber platform and cockpit of Ferrari F50 is its frame)

the stiffness of carbon fiber is not only conducive to control, but also plays a great role in improving safety. A typical example is that in 1995, the president of BMW drove a McLaren F1 (street version) with a full load of three people out of control at the speed of 280 kilometers per hour on the highway in Germany. He rushed out of the highway and rolled countless times before stopping. The three people on the car actually suffered only minor injuries. At that time, the shell of the whole car was completely destroyed, but the frame and cabin were still in good shape. If the frame was not made of carbon fiber, it would certainly be unstoppable. This is also one of the reasons why Formula One cars still use it


finally, we should add the concept of "subframe", which is a new term often appearing in car books. The subframe is not a complete frame, but a support that supports the front and rear axles and suspensions, so that the axles and suspensions are connected to the "main frame" through it, which is customarily called "subframe". The subframe is used to block vibration and noise and reduce its direct entry into the carriage, so it mostly appears on luxury cars and SUVs, and some cars are also equipped with subframes for engines

future development

girder type and load-bearing frame are the most mainstream frame forms, but they have significant shortcomings respectively, namely bulkiness and insufficient stiffness. Therefore, in recent years, there has been a frame design scheme combining the advantages of the two. The original frame of Mitsubishi Pajero IO is shown in the figure. An independent steel frame (the blue part in Figure J) is added to the bottom of the carriage of the load-bearing structure, which can be considered as a simplified girder structure. Therefore, while ensuring the stiffness, the weight and center of gravity are greatly reduced compared with the girder structure. Another example is the Honda S2000. Due to the high performance requirements and the insufficient stiffness of the convertible body, a reinforcement structure similar to a large cross beam is welded at the bottom of the load-bearing frame to enhance the stiffness. In the future, this form of "hybrid" frame will certainly emerge in an endless stream

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