Monocoque Automobile Design and Pillars

With the introduction of monocoque design in automobiles, supporting pillars have become increasingly important:

Monocoque (French for "single" and "eggshell") is a construction technique that supports structural load using an object's external skin. This stands in contrast with using an internal framework (or truss) that is then covered with a non-load-bearing skin. Monocoque construction was first widely used in aircraft, starting in the 1930s.

Structural skin is another term for the same concept. Unibody is a related technique that is the predominant automobile construction technology today.


Automobiles and Monocoque:

The first automotive application of the monocoque technique was 1923's Lancia Lambda. Chrysler and Citroën built the first mass-produced monocoque vehicles, both in 1934, with the innovative Chrysler Airflow and the Traction Avant, respectively. The popular Volkswagen Beetle also used a partly monocoque body (its frame required the body for support) in 1938.

In the post-war period the technique became more widely used. Nash Motors introduced this type of construction in 1941 with the new Ambassador 600, generally credited with being the first popular mass-produced unibody construction automobile made in the United States. The all-welded steel with sturdy bridge-like girders that arched front to rear made for greater strength, safety, and longer life. Nash engineers claimed that about 500 pounds of excess weight was cut out (compared to body-on-frame automobiles) and the body's lower air drag helped it to achieve excellent gas mileage for its day. Prophetically, the company's 1942 news release text attached to the X-ray drawing describes how "... all auto bodies will built ... as this some day..." The Alec Issigonis Morris Minor of 1948 featured a monocoque body. The Hudson Hornet, along with the rest of Hudson range, featured a monocoque body at the same time.

Other automakers incorporated this type of construction and the terms unit body and unibody became more common in general use. The Ford Consul was the first Ford built in England using a unibody. American Motors (AMC) continued its engineering heritage from Nash and Hudson with breakthroughs such as in 1963 of combining separate parts into single stampings. The Rambler Classic had "uniside" door surrounds from a single stamping of steel that reduced weight and assembly costs, as well as increasing structural rigidity and impoving door fitment.

Spot welded unibody construction is now the dominant technique in automobiles, though some vehicles (particularly trucks) still use the older body-on-frame technique.

Some American automobiles, such as the 1967 Chevrolet Camaro and virtually all Chrysler Corporation automobiles from 1960 until the early 1980s, used a compromise design with a partial monocoque combined with a subframe carrying the front end and powertrain. The intention was to provide some of the rigidity and strength of a unibody while easing manufacture, although the results were mixed, in large part because the powertrain subframe contained the greatest single portion of the vehicle's overall mass, and thus movement of the subframe relative to the rest of the body could cause distortion and vibration. Subframes or partial subframes are still sometimes employed in otherwise monocoque construction, typically as a way of isolating the vibration and noise of powertrain or suspension components from the rest of the vehicle.

In automobiles, it is now common to see true monocoque frames, where the structural members around the window and door frames are built by folding the skin material several times. In these situations the main concerns are spreading the load evenly, having no holes for corrosion to start, and reducing the overall workload. Compared to older techniques, in which a body is bolted to a frame, monocoque cars are less expensive and stronger.

Monocoque design is so sophisticated that windshield and rear window glass now often make an important contribution to the designed structural strength of automobiles. Unfortunately, when a vehicle with a unibody design is involved in a serious accident, it may be more difficult to repair than a vehicle with a full frame. Rust is also more of a problem, since the structural metal is part of the load bearing structure making it more vulnerable, and must be repaired by cutting-out and welding rather than by simply bolting on new parts (as would be the case for a separate chassis). Older cars with separate chassis can still pass vehicle inspection tests (such as the British MoT) with quite advanced rust in the sills (rocker panels) and pillars, whereas in more modern cars these parts are structural and would lead to a test failure. In the United States, vehicles will not pass state inspections if rust has perforated components such as rocker panels, floor pans, or pillars - regardless of the type of body construction.

For more information on Monocoque Automobile Design Please visit: http://en.wikipedia.org/wiki/Monocoque