Introduction
During 120 years of automobile history many technical solutions appeared: some of them disappeared in a few years, others were accepted and universally adopted by Car Makers.
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 Fig. 1 - Space Frame of the Fiat VSS (Veicolo Sperimentale a Sottosistemi), designed in 1978 by Renzo Piano
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This is a brief summary of the evolution of the automotive body and frame, following the Industry trends and introducing some interesting solutions adopted on prototypes or production cars: even if with no market success, they all provided remarkable ideas and must be taken into consideration in the design of innovative structures.
1. From origins to the 1920's The birth of the automobile was made possible by the development of the internal combustion engines. Then, engineers had to face new practical problems, such as the steering and the braking systems for the vehicles. In this phase, the construction of a supporting frame for the body and the mechanical components was considered of secondary relevance: there was no need for severe requirements in terms of weight and stiffness, due to the limited powers of the engines. While the engineers had no previous experience with brakes, transmissions and steering systems, for the body and the chassis they could use the know-how developed for the horse coaches. At the end of the 19th Century, the first automobiles had coaches structures adapted for the internal combustion propulsion. Even the body terminology (phaeton, tonneau, landaulet, wagonette) was taken from the coaches world.
Coupé
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Phaeton |
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The structures were made of a wooden frame with wooden body panels mounted on it. The limited powers and maximum speeds enabled these structures to easily stand the static and dynamic stresses. About in 1900 with the introduction of steel and aluminum sheets and the development of drop-hammering and power-hammering manufacturing processes there was a revolution in the concept of the body structure: the wooden panels, straight or bent into very simple curves by means of steam pre-treatment, were replaced by metal sheet panels. This enabled the designers to create shapes with more freedom. The body panels were mainly made in steel, but for the more luxurious cars they were built with aluminum sheets. These body panels were mounted on conventional wooden frames, reinforced at the more stressed nodes with steel components. This type of structure (metal sheet body on a wooden frame) was the most common for about ten years, until 1910.
In 1915 H.J.Hayes introduced a new solution: a body with structural functionality, with benefits in terms of lower costs and reduction of noise and vibration.
This structure was adopted on the Ruler Frameless, a limited series car built in 3000 units.
In this car the body panels had a tubular shape and provided the necessary stiffness, while the engine and the suspensions were mounted on a horizontal floor-pan.
In the same years Edward G. Budd proposed a car made entirely of steel: the original idea had steel sheet shells welded together. Anyway, the stamping technology of that time was not very advanced and didn't enable to form sheets with complex curves, so many reinforcing members and a high number of welds were necessary.
Anyway Budd's idea was the base for the future development of the steel unibody. This solution was used on the Dodge Brothers (1914), the first high-volume (thousands of units) all-steel car.
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Dodge Brothers (1914) |
Lancia Lambda |
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Lancia Lambda (1922) - I. 3/4 Front View - II. Top and side view of the chassis and the main mechanical components (from a technical drawing of the time). |
In 1922 the Lancia Lambda was a revolution in the evolution of chassis design. It was Created by Vincenza Lancia, who found his inspiration in the monocoque structure of boats.
With the Lambda for the first time the structural issues of both the body and the frame found a common solution.
Lambda's structure was entirely made in steel. The floor-pan included the trasmission tunnel and the load-bearing body, was made by a "skeleton" covered by steel sheet panels that gave their contribute to the overall stiffness (see Figure). In the meantime, Auburn presented the "X-Frame" structure, with benefits in terms of torsional stiffness and vibration reduction.
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 Lancia Lambda (1922) Brochure |
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