What is a lightweight car?
Lightweight is to make the car slim. On the basis of ensuring the stable improvement of performance, the energy-saving design of each assembly component is carried out to continuously optimize the vehicle type. Experiments show that if the vehicle weight is reduced by 10%, the fuel efficiency can be improved by 6%? 8%; The vehicle weight is reduced 1%, and the fuel consumption can be reduced by 0.7%; The fuel consumption per 100 kilometers can be reduced by 0.3 for every reduction of vehicle kerb quality 100kg? 0.6 liters.
The most widely used lightweight technology at present is aluminum alloy technology. The Japanese Honda NSX sedan, 1990, sold in September, adopts an all-aluminum load-bearing body, which is 200kg lighter than the same body made of cold-rolled steel plates, attracting worldwide attention.
In recent years, Audi, Jaguar and New Range Rover all adopt all-aluminum body structure, and aluminum alloy has become an ideal lightweight material. According to the different alloy addition and manufacturing process, aluminum alloy can also be used for car body, frame, brake disc, engine cylinder block, cylinder head, piston, intake manifold, rocker arm, engine suspension bracket, air compressor connecting rod, transmission housing, clutch housing, wheels and brakes.
Audi ASF all-aluminum body structure Audi ASF all-aluminum body structure
In recent years, the processing cost of automobile body material aluminum alloy has been reduced. Formerly, aluminum alloy thick plates were stamped into thin plates and then processed. At present, hot stamping forming technology similar to steel plate stamping is widely used.
This is a very strict requirement for the process, because the increase of friction coefficient in the stamping process will not only increase the difficulty for the materials in the stamping area to enter the forming area, but also cause uneven material flow in all parts of the cross section due to the friction in the forming area, which is easy to cause sharp thinning and fracture at the stress concentration. Coordinating the relationship between BHF and punching force, plus good lubrication, is the key to reduce the material cost again in aluminum alloy hot stamping.
Of course, aluminum alloy is ideal as a lightweight material for mass production, but it also has its own shortcomings, such as complex process and high maintenance cost. For this article, we don't focus on aluminum alloy materials, but we will mainly elaborate other development directions of lightweight.
Spring of carbon fiber
Of course, today's cars use more lightweight materials and technologies. The i3 and i8 lightweight technologies adopted by the 6 Series BMW 7 Series mentioned at the beginning of the article include carbon fiber body.
BMW i3 carbon fiber cockpit
Carbon fiber body is common in super-running, and the high price has always kept civilian cars away. The arrival of BMW i3 has set a new historical price in this field. We should know that the overseas price of BMW i3 is 266,000, which breaks through the cost limit. Perhaps the spring of carbon fiber for automobiles has arrived?
The carbon fiber cockpit of BMW i3 is produced in a highly automated way in a brand-new factory jointly invested by BMW and SGL Carbon Fiber Company of Germany. The strength of this material is equivalent to that of steel, but its density is 50% or even 30% lower than that of aluminum. In fact, both McLaren and Lamborghini have successfully significantly reduced the production cost of carbon fiber composites, but this time BMW's pace has obviously accelerated.
Carbon fiber material itself is not expensive, the real value lies in processing carbon fiber into finished products suitable for vehicle driving and collision.
Generally speaking, it takes four days to coat, dry and cool the body of a super sports car, such as pagani Wind Son. Interwoven fiber cloth can form a symmetrical diamond pattern. The fiber cloth has been soaked with turpentine (a chemical process, that is, impregnated with chemicals first), but it must be cooled before gluing so that turpentine can react in the furnace. In a word, this is a long process that can hardly be automated, so it is also an expensive process.
Therefore, greatly shortening the time is a way to reduce the cost of carbon fiber. Instead of carbon fiber cloth, McLaren and Lamborghini used a short and thin short carbon fiber. They are bundled, soaked in turpentine, and then shaped. The formed carbon fiber is then put into a machine made of steel, where it is pressurized and heated (forging process), causing a chemical reaction of the structure.
This process must be completed within 6 minutes, which is just suitable for the technology of mass production line. Although the good shape of carbon fiber reinforced composite material has not reached the perfect diamond shape or the perfect firmness after chemical pretreatment, the strength of the material obtained by this method can still be comparable to that of steel, and the key point is that the weight is only half of that of steel.
It is only a matter of time before carbon fiber will transition from sports car to civilian car. The silent war has begun. In 20 1 1 year, BMW and Volkswagen competed to increase their stake in carbon fiber supplier Sigri (SGL). On February 2, 65438, BMW Germany announced its cooperation with Boeing Airlines of the United States. * * * With the development of carbon fiber material technology, it is used in new cars and airplanes. This cooperation means that BMW and competitor Volkswagen once again compete for partners in the field of carbon fiber technology, and Volkswagen has also cooperated with boeing da in carbon fiber through its Lamborghini brand.
By the way, the modification ability of various so-called carbon fibers on the market is absolutely first-class, but the prices do differ a lot. Therefore, you must compare more when buying, and the difference between the two is also very obvious.
Limitation of magnesium alloys
Although carbon fiber can be used to make many parts of cars, it is impossible to use carbon fiber completely. Therefore, you will also find that many lightweight technologies used in automobiles are diversified, and various lightweight materials are coming into battle, and magnesium alloy is one of them.
The density of magnesium is about 2/3 of that of aluminum, and it is the lightest metal in practical application. Magnesium alloy has strong vibration absorption ability, good cutting performance and good metal mold casting performance, which is very suitable for manufacturing automobile parts. Magnesium alloys are mostly used in automobiles in the form of die casting, and the production efficiency of magnesium alloy die casting is 30%~50% higher than that of aluminum. The newly developed blowhole-free die castings can produce blowhole-free and heat-treatable magnesium alloy die castings.
The earliest example of magnesium castings for automobiles is the rim. Examples of magnesium alloys used in automobiles include clutch housings, clutch pedals, brake pedal fixing brackets, instrument panel frames, seats, steering column components, steering wheel cores, gearbox housings, engine brackets, cylinder heads and cylinder head covers.
Folding magnesium alloy roof frame structure of Mercedes SL/SLK sports car
Die casting of magnesium alloy for the folding roof frame structure of Mercedes-Benz SL/SLK sports car won the first prize of the 20 1 1 Annual Automobile Magnesium Application Innovation Award of the European Magnesium Association. At the 20th annual meeting of European Magnesium Association on 20 12, experts from Mercedes-Benz Automobile Company introduced the application of magnesium alloy in Mercedes-Benz cars, especially the folding roof frame of Mercedes-Benz SLK sports car was composed of four magnesium alloy die-casting parts, namely the roof frame (3825g), the rear window frame (2075g) and the left and right C pillars (980g). These magnesium alloy die castings are produced in the magnesium alloy die casting plant of Mercedes-Benz Eslingen-Meitingen Company.
General Motors plans to expand the application of light components in automobiles. General Motors has developed a method for processing magnesium alloy sheet parts by thermoforming, which can prevent corrosion, and is testing the developed parts. The common anti-corrosion method of magnesium alloy is to minimize the riveting between the two materials. If a whole magnesium alloy can be used, it will not be divided into two pieces. In addition, the surface of magnesium alloy should be brushed with anti-oxidation and anti-corrosion chemicals.
By this method, high strength magnesium alloy plate can be used instead of steel plate and aluminum plate. General Motors has applied for a patent for this method. In this method, magnesium material is heated to 450°C and then thermoformed. In this way, General Motors developed the plate for the trunk lid of automobile, and successfully passed the related impact test.
Although the application of magnesium alloys in automobiles began a long time ago, it has not been widely promoted at present. It is estimated that GM is the first company in the automobile industry to mass-produce magnesium alloys. In terms of manufacturing and processing, magnesium alloys used to make thin plates contain 96% magnesium, 3% aluminum and 65,438+0% zinc, which need to be stamped and formed in a very slow process of about 450 degrees Celsius.
This makes the manufacturing process requirements and manufacturing costs very high. Compared with aluminum plate, the cost of magnesium alloy body plate is 3 to 4 times higher. In addition, due to the particularity of magnesium alloy plate, there may be some differences between magnesium alloy plate and traditional steel plate in repair process.
Therefore, normal temperature manufacturing is the research direction of magnesium alloy, which can better control the cost of magnesium alloy parts. The situation of magnesium in automobile manufacturing today is just like that of aluminum 25 years ago; The wider application of magnesium alloys in the future will eventually dilute the cost.
Above, we have listed the application of some materials in lightweight. The continuous progress of technology and manufacturing technology has made lightweight have more room for expansion, but don't forget that cars are all products of mechanical manufacturing in the final analysis, and mechanical composition is the most fundamental factor of continuous innovation, so structural change is another direction of lightweight.
Structural changes? Lightweight engine
The main trend in this direction is to integrate parts, reduce the number of parts and reduce the volume of assembly parts, of course, without affecting the safety and performance of automobiles. At present, many manufacturers are actively carrying out assembly lightweight, and the engine is a very typical example.
The lightweight of engine assembly has a long history, and it is actively promoted from luxury cars to civilian models. As the most important large-scale assembly of the whole vehicle, the lightweight of the engine is of great significance.
In order to control exhaust emissions and improve engine performance, the engine must introduce new components, such as turbocharger, EGR, aftertreatment and electronic control system, or strengthen the original components, such as fuel injection pump, which will increase the weight of the engine. It can be seen that it is not easy to realize engine lightweight, and it is by no means a single measure.
Reducing engine weight can be reduced by changing materials and optimizing structural composition. In addition, the modularization of parts and the structural optimization of key parts can also achieve the purpose of lightweight.
Taking the newly developed engine EA2 1 1 of Volkswagen using the modular MQB platform as an example, we can intuitively understand the impact of structural changes on engine emission reduction.
In the driving device and related accessories, the metal transmission chain used in EA11was changed to the nonmetal toothed belt used in EA2 1 1, and the weight of the latter was reduced. Thirdly, the shell part of the drive system is an important external accessory. EA 1 1 1 adopts an integrated aluminum alloy sprocket housing (including functional parts such as oil filter), but in EA2 1 1, it becomes a split structure. Of the three housing parts, the one with a filter in the middle is made of aluminum. Finally, the shell of EA11is stamped with sheet metal, and an oil pump driven by a sprocket is fixed on it for lubrication.
EA2 1 1 The oil pan is made of cast aluminum. In addition to the oil pump, an oil filter and an air conditioner compressor are fixed on it. Obviously, the latter is more complete than the former.
Lightweight crankshaft is more obvious. The crankshaft of EA2 1 1 engine reduces the number of fan discs from the traditional eight to four. Reduce the width of the fan plate and optimize the shape; Reduce the size of the master log by 10% on average.
After these trains were operated, the mass of EA2 1 1 series engines was reduced by about 22kg, reaching about 18%, and the fuel consumption was correspondingly reduced by 8% ~ 10%. At the level of carbon emission, the emission reduction effect of EA2 1 1 is also obvious. Taking the comparable 1.6L MPI engine as an example, the CO2 emission per kilometer can be reduced by about 10g.
Structural changes? Light transmission
Transmission is the main component of automobile powertrain, and the gear transmission mechanism of transmission is also called the main component of automobile transmission mechanism. Its quantification technology is also a systematic project, and lightweight technology design can take measures such as miniaturization, high quality, reduction, integration, modification, heterogeneity and optimization.
The biggest feature of CVT7 gearbox mass-produced by Nissan in 2009 is the adoption of auxiliary gearbox technology for the first time in the world. The innovation of changing the structure not only reduces the size of the transmission, but also improves the speed ratio.
We know that the traditional CVT gearbox mainly changes the transmission ratio by changing the diameters of the driving wheel and the driven wheel. However, Nissan's CVT7 gearbox innovatively added an auxiliary gearbox on this basis. This auxiliary gearbox is actually a group of planetary gear sets, located between the driven wheel and the output shaft, which can realize the functions of two gears and reverse gear. The first speed ratio is 1.82 1, and the second speed ratio is 1.000.
In addition, due to the integrated design of front and rear switching devices and auxiliary transmission, smaller driving pulleys and driven pulleys are adopted at the same time, realizing miniaturization and light weight. This gearbox reduces weight 10 kg on the original basis.
Therefore, great researchers can always achieve the lightweight of vehicles by changing the internal structure of vehicles in a breakthrough way. The lightweight of automobiles has penetrated into every component, and R&D personnel have hollowed out their ideas for this. Therefore, our vehicle consumables are more and more environmentally friendly, and their performance is constantly improving, but their fuel consumption is decreasing year by year.
Efficiency improvement? Engine miniaturization
I think the miniaturization of various parts and assemblies can also be attributed to lightweight technology, but although these are more closely related to efficiency. The three-cylinder engine has developed rapidly in the past two years, and it is likely to start a prairie fire.
If a smaller engine can achieve the effect of a relatively higher displacement engine, why not?
Ford earlier released the ultra-small EcoBoost 1.0L three-cylinder direct injection supercharged engine. This small displacement engine with a projection area of only A4 paper is designed and developed by Ford Downton Technology Center in Britain and Merck Technology Center in Germany. Ford 1.0L Ecoboost three-cylinder engine has maximum power 123 horsepower and maximum torque of 20655. rice. It also won the International Engine of the Year Award in Germany. This engine will replace Ford's 1.6 liter four-cylinder naturally aspirated engine.
This three-cylinder engine is equipped with Valvetronic electronic valve technology and a twin scroll turbine. The compression ratio exceeds N20 and N55 to 1 1: 1. How to control engine knock is particularly important. The maximum output power of this engine can reach 165kW and the maximum torque can reach 240Nm, which will replace the existing 65438. BMW's newly developed 1.5T three-cylinder supercharged engine will become one of the main power systems of BMW's vehicles below Class B in the future.
Safety has nothing to do with severity.
This is a controversial issue, which also means that good technology may not bring good sales, and the guidance of public opinion will make consumers think twice. This is the secret of marketing. It adds complex ingredients between people, so new technologies always look weak.
Just as some people will think that these lightweight technologies are just a trick for capitalists to make money in our pockets, where aluminum alloy is strong, steel will hit; The steel plate is too thin and must be thick to be strong; A Japanese car was sawed from the middle, and the interlayer was a paper shell. This is safe and reliable. Look at the American school bus and Hummer, both of which were smashed. They have armor. Look at them!
Car safety is very important. For vehicles, automobile safety can be divided into active safety and passive safety. Active safety is mostly some auxiliary electronic systems. Passive safety refers to the protection of the occupants in the car after the accident. Now this concept of protection has extended to everyone inside and outside the car, even objects.
Usually, passive safety is easier to talk to each other, because accidents are always sudden and impressive. The frame plays a very important role in it, and the lightweight of the frame also adopts high-strength structural steel and aluminum alloy. Usually, the strength of the frame's ability to absorb energy, disperse energy and resist deformation after collision is the real protection for the people on board.
Therefore, due to the unqualified frame design, it is very likely that although the car has not been deformed, people have become energy-absorbing media. For this result, I'd rather make the car deform a little more.
Every time we point to a car that was hit in a fog, we say vaguely that the quality of this car is really poor, and it's all smashed. We are all making the same mistake. Life is far more valuable than cars. If you want to know what kind of car is of good quality, you should look at the global report on vehicle accident mortality.
In addition, the professional crash test is scientific and rigorous, which can detect the quality of the car to a certain extent. But after all, the actual collision is complicated, and the safety of a car can't be calibrated only by collision test, which only gives us a reference standard.
Lightweight is definitely the trend of automobile development. Fifty or sixty years ago, the average weight of cars ranged from 2,500 kg to 3,000 kg. Today, the average weight of cars is 65,438+0,500 kilograms, which is almost 50% lower. So, if you stubbornly believe that thick steel plates and the heavyweights of tanks are safe enough, then I have nothing to say, because fragile cars are no match for tanks at all.
However, lightweight is a gradual process. It is impossible for us to see these aluminum alloy, magnesium alloy and plastic families attack the city and plunder the land at once. On the one hand, the high toughness of steel is beyond the reach of other light metal materials. For example, the B-pillar of Audi A8 is lined with thermoformed steel. On the other hand, the mass production of these expensive process materials will affect the price and sales of automobiles. Major car companies are actively promoting the process of lightweight, and gradually make these still lightweight materials become ordinary consumables.
Lightweight cars can save energy, reduce pollution and reduce the incidence of traffic accidents. If all cars are lightweight, the overall kinetic energy will be reduced, so in the long run, the development of lightweight will reduce the casualty rate of traffic accidents. Lightweight must be the trend of automobile development, and people who like that heavy feeling also need to sigh.