The Hindu Business Line : Chassis

The types and technologies used in developing vehicular chassis over the last few decades have changed based on the demands of consumers, the urge to cut costs, and produce in mass scale.

FORD'S CHENNAI plant...the chassis that will roll out as a car. — S. Muralidhar

One of the most important components that go into making up a car but is least visible is the chassis. Most of us can instantly recognise many cars, but may not realise that it is chassis that defines the character of the car and gives it special abilities.

The chassis plays a role in every aspect of the automobile. From safety to fuel efficiency to stability, the chassis is crucial to each of these departments. The chassis gives the automobile its rigidity to absorb the road's undulations and its strength helps protect the car's occupants in a collision.

Chassis lends character

The car's frame and body give strength and stability to the vehicle under different conditions.

This is only the primary function of a chassis, apart from giving the car its design exclusivity. The types and technologies used in developing vehicular chassis over the last few decades have changed based on the demands of consumers (such as increased speed, off-roading capability and legislation for improved safety) the urge to cut costs, and produce in mass scale.

Mass production and its related techniques have been a big influence on the type of frames being used for today's cars. With the exception of a few super luxury performance cars and genuine sports utility vehicles, the chassis of most cars of today are steel monocoque type.

However, there are other types, too, that were popular earlier — such as the ladder chassis and tubular space frame or roll cage chassis. Among the few that have ladder chassis type construction is the Ford Endeavour, and those with tubular space frame chassis include the Lamborghini Diablo.

Monocoque

The steel monocoque chassis is the most preferred option amongst most car manufacturers simply because it is cheap and fits well with assembly-line type, automated production.

Monocoque, as the name indicates, is a one-piece frame which, unlike the previous generation of chassis, also incorporates a few of the body panels and parts that give the car its overall form and shape.

In the older types of chassis, such as in the ladder and tubular chassis, a skeletal structure, made up of arms and tubes, formed the primary structure.

The individual arms acted as stress members to which the various parts of the car were then bolted on. However, in a monocoque chassis, some of the body panels, such as the roof, door columns and floor pan, are already welded together to form a single unit that is almost immediately indicative of the car's final shape.

However, despite its name, the monocoque chassis is not built out of a single mould, but is actually created by putting together many pieces in an assembly-line welding process.

The various parts of a monocoque chassis, including the roof, the A, C and D pillars, the floor pan and the cross members, are all made individually at first by putting sheet metal through a precision stamping process on a series of presses.

The stamped components are then spot welded together (either manually or with the help of robots) in an assembly line to form the monocoque chassis.

Further, onto the assembly line in most modern cars, components such as the doors, bonnet and boot lid, and body side panels, are added to the monocoque chassis.

As such, with high volume assembly-line production, this chassis is the best choice as regards ease of manufacture.

The monocoque chassis is also clearly the best option for maximising the interior space of the car. However, on a simplistic weight-to-strength ratio, this chassis is less efficient compared to the modern ladder chassis and the more elaborate tubular chassis, which explains why the latter are more popular amongst sports utility and super car manufacturers respectively.

Apart from the engine, the chassis is the biggest contributor to the car's overall weight. The modern monocoque chassis has too much of sheet metal, which makes it heavier and, at the same time, relatively weaker compared to the other two types of chassis.

Despite its weaknesses, the monocoque chassis will continue to be popular due to its other advantages.

As a result, the automobile industry has been working on various base materials to reduce the weight of the chassis, as heavier vehicles will tend to be slower and less fuel-efficient.

New age materials

Steel has simply been the only material of choice for the chassis, thanks to its rigidity and practical pricing vis-à-vis the other options.

But a parallel development to reduce the weight of the steel chassis continues, other metals have also been tried out.

Amongst the materials that have proved to be best alternative to steel is aluminium. There has been a heightened emphasis on boosting fuel economy to reduce operating costs and lessen oil consumption.

Together with this, the increasing focus on other issues such as re-cyclability and employing environment-friendly technologies have narrowed down the choice available to carmakers.

The aluminium industry reiterates the metal's positives and says that it can absorb nearly twice as much crash energy as steel.

In the event of a collision, compared to steel, aluminium can be designed to crumple predictably and thus allow the vehicle's panels to absorb more of the crash forces, passing on much lesser of the crash's energy into the car's passenger area.

It is also claimed that vehicles made lighter with aluminium can accelerate quicker and will require shorter stopping distances than vehicles made with heavier materials, including steel, if we assume all other factors to be equal.

Owing to a greater degree of acceptance and its exclusivity, aluminium use in high-end, luxury and performance cars has been on the rise during the past few years.

Super premium car brands such as Rolls-Royce, Jaguar, Audi and Ferrari have successfully demonstrated that aluminium can replace steel for chassis and even body panel use. Cars such as the Rolls-Royce Phantom and the Audi A8 have also showed that aluminium can help enhance the performance of these cars.

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