A body (from French carrosse for carriage ) refers to the complete structure of a motor vehicle on a supporting chassis . In contrast, self-supporting bodies are not only the structure itself, but also the basic structure of the vehicle.
Not self-supporting body
In the classic sense, a motor vehicle is made up of the components chassis, drive and body. The chassis, also called the chassis or frame, forms a basic structure that supports the drive, the body and the payload and stabilizes it against external forces. Various forms of construction were used as a frame . The body, which is placed on the frame (generally screwed), forms an outer skin to protect the occupants or the transported goods.
Originally, cars mostly had an open structure, but that soon changed. The American engineer and specialist author HE Tarantous described the trend from the open to the closed body in 1925. He proved this with statistics from the largest American coachbuilder of the time, Fisher : In 1919 Fisher produced 83,500 open bodies, in 1924 there were 239,502. The closed bodies stood at 31,318 in 1919, they overtook the open bodies in 1923, and in 1924 Fisher produced 835,477 closed bodies.
The production of the bodies was sometimes carried out by external body shops. The chassis with drive supplied by the factory were often built according to individual customer requirements. The development in this regard took place in the 1920s. With the spread of automobiles, the external appearance of vehicles became more and more important. Companies specializing in sheet metal and woodworking manufactured car bodies individually according to dealer and customer requirements. The body became a distinguishing criterion in road traffic, a symbol for the personal style and wallet of the “ gentleman driver ”. The first American cars came onto the German market at the end of 1923 and changed the way we view automobiles forever. It was seen not only as an object of daily use, but as a piece of jewelry. The models of "Buick, Cadillac, Willys Knight, Studebaker, etc., [...] these wagons, tome, these locomotives, which project to the rear," were sometimes considered uncomfortable and unreliable, but their body shop impressed German automobile and body manufacturers . The Berlin auto journalist Hanns Steiner stated in 1924: “The old, boring, series-produced body that every chassis factory was still using in 1918 was no longer for sale. Life, color, movement came into the bodies. Forms had to change. Our cityscape was alive, joyful patches of color ran through the gray. It increased to the point of grotesque. "
At the beginning of the 1950s, the classic construction method in car construction was replaced by the self-supporting body. With trucks, however , the frame construction is still common today. Even vehicles produced in small series, especially in the motorsport sector, often do not have a self-supporting body, but mostly a tubular space frame. As a rule, aluminum or plastic (then often GRP / CFRP ) is used for the construction.
When the chassis and body of a motor vehicle are combined into one unit, one speaks of a self-supporting body, also known as a shell construction or monocoque . With this type of construction, the panels, reinforcements, mounting plates and profiles are permanently connected to one another using different joining techniques (gluing, spot welding, laser welding, soldering). This structure alone takes on the supporting function. There is no separation between components that are subject to bending / torsion or shear loads and parts that are used for sealing / planking (such as ladder or lattice frames). All parts act statically as shells and in their entirety absorb the forces introduced. Occasionally, subframes (subframes) are used on the axles.
The stiffness, which normally ensures the frame is, in this case by the compact skin sheet and hollow sheet metal sections with the largest possible cross-section and thus resistance torque reaches (z. B. sill ). Corrugations increase the rigidity and the natural frequency of oscillation in order to prevent resonance and thus a roar. The attachment points for the add-on parts such as doors, fenders , flaps and hinges are firmly integrated into the body, for example in the form of threaded plates and weld nuts . A high degree of rigidity is important in order to keep elastic deformations at the joints to the add-on parts low and to avoid creaking noises when driving. Small gaps are therefore only possible with very stiff bodies. Furthermore, the rigidity has an influence on the driving behavior, especially on bad roads or in extreme situations. In order to withstand vibration excitations from the engine and chassis, the natural frequency of the body must be adjusted accordingly. In the body construction, a distinction is made between static rigidity (Nm per angular unit) and dynamic rigidity (Hz). The latter is between 35 and 47 Hz for vehicles of the upper middle class (notchback sedans such as Ford Mondeo or Passat B6). With self-supporting convertible bodies, reinforcements are installed in the underbody and on the sills (diagonal struts, etc.). Stiffeners on the underbody result in a profile that is open at the top (U-cross section), while a sedan corresponds to a rectangular cross-section (closed profile) and can thus be both stiffer and stronger with a lower mass. Without countermeasures, station wagons are less rigid than sedans of the same type due to the lack of a rear wall (behind the rear seats), which stiffen the car body diagonally, i.e. acts as a sliding wall beam. Early examples of vehicles with a self-supporting body are the Adams-Farwell Model 8A from 1906 and the Lancia Lambda from 1922. The Citroën 11CV (1934) and the German Opel Olympia (1935) were the first production cars with a self-supporting all-steel body, the first self-supporting body made from In 1956 Berkeley Sports SA 322 had fiberglass-reinforced synthetic resin . The Lotus Elite from 1957 became widely known . The Kässbohrer Setra (hence the name) S 8 from 1951 and the HS 160 from Henschel & Sohn in 1955 were among the first buses with a self-supporting structure .
The advantages of the self-supporting body are lower weight due to the elimination of the frame, higher impact safety and better use of space. The large-scale production of self-supporting bodies was made possible by advances in sheet metal processing ( deep drawing , but especially spot welding). By the beginning of the 1950s, it prevailed in car manufacturing. Omnibuses are built in both frame and shell construction. In trucks , the self-supporting body has not been able to establish itself to this day due to a lack of modularity and insufficient rigidity for load build-up.
Compared to the frame construction, the self-supporting body also has some significant disadvantages. While different body variants can be mounted on a frame without great effort, this option is limited with self-supporting bodies. The variety of body variants has therefore decreased significantly in the 1950s compared to the pre-war period. Another problem with the self-supporting structure is its increased susceptibility to rust due to the numerous cavities, which relatively quickly leads to the inevitable scrapping of the entire vehicle if certain body parts are rusted. When the Silver Cloud was introduced in 1955 , the luxury car manufacturer Rolls Royce deliberately decided against the trend in favor of the frame construction so as not to lose the reputation of the vehicles' long durability. Another argument in favor of the frame construction was the avoidance of droning effects, which are more or less pronounced in self-supporting bodies. In the GDR , too, the frame construction was retained for the Wartburg cars and the Barkas small transporters. In addition to the variety of possible bodies, this resulted in the advantage that worn vehicles could be repaired relatively easily.
Skeleton body (for example "Space Frame")
This body type has a skeleton made of closed hollow profiles that are connected to one another directly or via nodes . Flat components such as the roof or the windshield can be rigidly connected to the skeleton and absorb shear forces . This promises a high degree of rigidity with a lower weight . Modern examples of this are the Audi A8 and Audi A2 with Audi space frames made of aluminum. Audi has been using aluminum as a body material since 1993 and uses nodes, deep-drawn parts and extruded profiles made from cast aluminum alloys. Various new manufacturing processes such as clinching and self-piercing riveting have been introduced in the automotive industry.
The first vehicle with a space frame (made of steel) was the Chrysler Airflow in 1934 . In the 1950s, the Trabant was developed in which the load-bearing structure consisting of the floor plate, wheel arches, vehicle pillars and roof pillars is planked with non-load-bearing plastic panels. The AWS Shopper , built in Berlin in the early 1970s , also had a simple space frame made of square tubes. Starting in 1978, Matra developed a vehicle for Simca with a skeleton made of hot-dip galvanized hollow steel profiles, which appeared in 1984 as Renault Espace .
In 1978, Fiat commissioned Renzo Piano and Peter Rice , among others , to design a car of the future. They developed the Fiat VSS (Vettura Sperimentale a Sottosistemi: subsystem experimental vehicle), in which a body frame made of steel was supplemented with attachments made of plastic. These could be simple molded parts such as fenders and roofs, but also entire assemblies such as doors or fronts with pre-assembled headlights, grilles and bumpers. Different brand identities could be implemented on the same basis by adding appropriate rear modules, station wagons and notchback sedans or using different front modules. This concept was not pursued any further. The Fiat Multipla was later the second generation of a vehicle with a steel space frame in series. The fact that closed steel profiles can only be formed to a limited extent can be seen in some places in the vehicle, for example at the transition from the roof rail to the rear.
In response to the increasing use of aluminum in body construction, the steel manufacturer Salzgitter AG , together with the automotive supplier Karmann GmbH, has developed a body structure tailored to series vehicles and tested it on prototypes that use innovative high-strength steels to reduce the body weight with increased rigidity, the same costs and the same crash behavior should reduce by 40 percent. Another example of a concept with tightly laser- welded and then hydroformed steel tubes was the 2003 “NewSteelBody” (NSB) from ThyssenKrupp Stahl .
The bodies of the first cars were made entirely of wood . This type of construction was familiar from coach construction . Wood was later only used for the framework of the superstructure. The body shell was made of nailed steel or aluminum sheet. This so-called composite construction was predominant until the 1920s and is practically only used today by the Morgan Motor Company . More rarely, the framework was planked with plywood and covered with leather or synthetic leather. Well-known examples of this are the pre-war DKW , such as the DKW F8 .
The French coachbuilder and businessman Charles Terrès Weymann had a special construction method derived from early aircraft construction with an artificial leather-covered wooden frame patented in all major countries. Wood was used as a material for roof inserts in closed superstructures (e.g. Ford Model A ) until large and powerful presses for all-steel roofs were available in the mid-1930s.
With a 90% market share, sheet steel is the most widespread material for body construction (as of 2014). Budd developed the all-steel body in the late 1920s. General Motors adapted it in 1934 in the USA ("Turret Top" design). For a very long time, however, there were no presses that were strong enough to press complete car roofs; therefore, vehicle roofs were made with impregnated materials until the 1950s.
To prevent corrosion , sheet steel is mostly galvanized today; From the mid-1980s to 2005, Audi manufactured most vehicles from sheet steel that was galvanized on both sides. Many other manufacturers (e.g. VW and Daimler-Benz ) only built parts of the body e.g. B. the floor pan made of galvanized sheet steel. In all cases, this is done at the factory, i. H. Galvanized steel with a high quality cold rolled surface used in the rolling mill .
Hot-dip galvanized sheet metal is always galvanized on both sides, the thickness of the zinc layer is 5 to 10 micrometers. Electrolytically galvanized sheet metal can have a surface that is galvanized on one or both sides with a zinc layer thickness of 2.5 to 7.5 micrometers; with galvanization on both sides, different values are possible. Asian and American manufacturers often use sheet metal with a " galvannealed " surface, which is created through the thermal treatment of a hot-dip galvanized surface. Sheet metal with an electroplated zinc-nickel layer is rarely used for body panels. In all cases, the fully assembled body is intensively cleaned, phosphated and subjected to cathodic dip painting in an immersion bath . In addition, seams, joints and cavities are sealed with adhesives or sealants and subsequently preserved with wax. The galvanizing of the sheet metal, regardless of the type, always plays the role of cathodic corrosion protection . In synergy with the painting, preservation and sealing measures, this provides the multiple duration of protection of the individual measures. Corrosion damage is usually no longer the decisive factor in the effective service life of vehicles with high-quality bodies.
The often rumored “full galvanization” of entire bodies in the automobile plant was never practiced, since it would not be possible to completely coat the complex shape of a finished body with cavities, multiple sheet doubling, adhesions and sealing seams.
For cost reasons, some manufacturers have switched to restricting the scope of the use of galvanized sheets to areas that are actually at risk. In order to save weight, many hybrid components made of aluminum and galvanized sheet steel are also used in more recent designs . In these, the load-bearing structure is usually made of galvanized sheet steel and the externally visible planking is made of aluminum sheet. For technical reasons and to avoid bimetal corrosion , such components are only mechanically interlocked with one another and are also extensively glued.
Occasionally, vehicle bodies have also been made from stainless steel . In the 1970s, Porsche built prototypes in the shape of the 911. DeLorean manufactured a sports car with a central tubular frame, the body of which consisted of a GRP supporting structure that was planked with unpainted stainless steel.
In order to meet the current requirements for stability (crash behavior), weight and appearance of the body, many new types of steel have been developed that are either very soft and easily deformable (e.g. IF steel ) or, with acceptable forming properties, are nevertheless much stronger (e.g. DP steel ).
Despite the higher density compared to the materials mentioned below, a suitable combination of steel parts can be used to produce a body that is not heavier, but cheaper to manufacture than from light metals, which are less strong and stiff than steel.
In the bodies produced in Europe, aluminum currently has an average share of 50 kg, making it the second most widely used body material (as of 2015). Since the density of aluminum is lower than that of steel, it has been used successfully as a body material. Despite the higher cost, aluminum can compete with steel in many applications because of its advantageous lower density. However, the significantly lower modulus of elasticity of the material must also be taken into account, which means that either more material (for example approx. 40% greater sheet metal thickness) or more installation space is required for the same rigidity. Car bodies made entirely of aluminum have already been mass- produced (for example Panhard Dyna , Tesla Model S , Audi A2 and A8, Jaguar XJ , Mercedes-Benz SL or Opel Speedster ). In the middle class, individual vehicle parts are also made of aluminum, for example the hoods of the Citroën DS and the Subaru Legacy of the fourth series were made of aluminum, and the Subaru also had the tailgate. The production of components made of aluminum and the joining of the individual components does not take more time than, for example, steel parts. The reduction in consumption and emissions (weight savings in the vehicle) through lightweight aluminum construction contrasts with the energy-intensive production of the raw material. An Audi A8, for example, only saved the amount of CO 2 that was released during the production of the aluminum required for its body after a mileage of 170,000 km . Pierce-Arrow used a particularly elaborate aluminum construction : Between 1904 and 1920, there were essential parts of the body such as torpedo sheet (cowl, the piece between the bonnet, fenders and windshield), side panels and doors made of cast aluminum .
Magnesium is an even lighter material than aluminum. So far, only individual parts are made from magnesium, not complete bodies.
Its use is accompanied by various problems. The hexagonal lattice structure of magnesium allows only low degrees of deformation at room temperature; Magnesium can be formed better when hot. The high tendency to corrode and flammability also prevent their use on car bodies.
Porsche has successfully brought magnesium into series production in the interior - the comparatively small number of units should certainly have had a positive influence on this decision. The use of magnesium sheets in the interior is not critical, as problems such as dirt, water or aggressive media tend to occur there rarely.
In the mid-1930s, “the glass car” was presented at the Berlin automobile exhibition , with not only the windows but also the roof, bonnet and side doors made of Plexiglas . To reduce the amount of sunlight, “sun curtains” and a sliding “sunshine canopy” were provided in the roof. The vehicle was primarily used for advertising purposes.
Both thermoset fiber-reinforced synthetic resin and thermoplastic were used in the body shop . Whole body shells, including self-supporting ones, can be made from fiber composite materials; injection-molded or blow-molded parts made from thermoplastics do not reach this size. they are used for fenders and smaller parts. The exception is the CityEl's floor pan, which is blown in one piece . The first mass-produced car with a plastic body was the Woodill Wildfire , built between 1952 and 1956 with a body by Glasspar . In February 1953 the Kaiser Darrin was presented, the body of which also supplied Glasspar, and at the end of the 1953 model year the Chevrolet Corvette appeared . 1954–1955 Glasspar built the G-2, a roadster with the body of the Woodill.
Not for reasons of virtuoso design or weight savings, but to avoid costly deep -drawn sheet imports, the P 70 went into series production in East Germany in 1955 with a cladding made of phenolic resin- cotton plastic ( duroplast ) and a wooden frame. It was used to test this technology for the later Trabant , in which the wooden frame was replaced by a steel frame and the duroplastic was retained for the planking. Advantages such as easy repairability and absolute resistance to corrosion faced challenges in production. Long curing times of the pressed plastic parts in the presses prevented efficient production.
Self-supporting plastic bodies, i.e. without a supporting frame made of steel, existed from 1956, if they could also be reinforced with steel inserts at the force introduction points (see self-supporting body). Reliant , too , has been building small three-wheeled delivery vans and passenger cars with GRP bodies since the 1950s, and later sports cars as well. Reliant also developed a concept for automobile production in emerging countries: this resulted in Otosan Anadol in Turkey and Carmel and Sabra by Autocars in Israel . Because of the plastic bodies, the manufacturers managed without expensive press lines. A newer construction with GRP paneling on a steel frame was the Renault Espace from 1984 to 2002. Today plastic is used for many body parts. But there are still no mass-produced cars with a body made entirely of plastic. In contrast, the use of plastics for external modernization or tuning is almost as old as the plastic body. The 1958 Packard is the first facelift with GRP . Small series vehicles like the Renault Rodéo or the Lotus Elise as well as conversions like the VW buggy have GRP bodies.
Plastic has the advantage of not corroding and can also be made from renewable raw materials such as vegetable oil. Small and medium-sized series of such a body can also be produced by hand.
Nowadays, solar cars and energy saving cars are often built with a plastic body to reduce weight. Instead of pure plastic, GRP or CFRP is usually used to further increase strength and stability compared to pure plastic. For the year 2025 it is forecast that around 100,000 t of CFRP will be used in automobile construction (for comparison: 100 million t of steel are to be used in the same period).
In a current project, Imperial College in London, together with Volvo and other organizations, wants to develop a new composite material made of carbon fibers and polymer resins that could also be used for body construction. The special feature is that it should be able to store energy and thus turn the body into an accumulator for future electric vehicles .
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- The gentleman driver defined himself as a rich, usually young man who did not allow himself to be driven by a chauffeur, but drove himself.