Basics of Automotive Systems: Evolution of Design; Body Shapes

DESIGN EVOLUTION

Not too long ago, nearly every car and truck was built with body-over-frame construction, rear-wheel drive, and symmetrical designs. Today, nearly all cars don’t have a separate frame; instead, the frame and body are built as a single unit, called a unibody. Most pickup trucks and large SUVs still are built on a frame.

Another major influence to design was the switch from rear-wheel drive to front-wheel drive. Making this switch accomplished many things, the most notable being improved traction at the drive wheels, increased interior space, shorter hood lines, and a very compact driveline. Because of the weight and loads that pickup trucks are designed to move, most remain rear-wheel drive.

Perhaps the most obvious design change through the years has been body styles. Body styles have changed to respond to the other design considerations and to trends of the day. For example, in the '50s America had a strange preoccupation with the unknown, outer space, which led to cars that had rocket-like fins. Since then fins have disappeared and body styles have become more rounded to reduce air drag.

Body-Over-Frame Construction

In body-over-frame construction, the frame is the vehicle's foundation. The body and all major parts of the vehicle are attached to the frame. The frame must be strong enough to keep the rest of the vehicle in alignment should a collision occur.

The frame is an independent, separate component that is not rigidly attached to the vehicle's body. The body is generally bolted to the frame. Large, specially designed rubber mounts are placed between the frame and body to reduce noise and vibration from entering the passenger compartment.

Quite often two layers of rubber are used in these pads to provide a smoother ride. The frame rails are made of stamped steel, which are welded together. Some frames are made by a hydro-forming process, which uses high-pressure water, rather than heat, to shape the steel into the desired shape.

Unitized Construction

A unibody --- is a stressed hull structure in which each of the body parts supplies structural sup port and strength to the entire vehicle. Unibody vehicles tend to be tightly constructed because the major parts are all welded together. This helps protect the occupants during a collision. However, it causes dam age patterns that differ from those of body-over-frame vehicles. Rather than localized damage, the stiffer sections used in unibody design tend to transmit and distribute impact energy throughout more of the vehicle.

Nearly all unibodies are constructed from steel. A few cars, such as the Audi A8, use aluminum instead.

An aluminum car body and frame can weigh up to 40% less than an identical body made of steel. Most front-wheel-drive unibody vehicles have a cradle or partial frame that is used to support the powertrain and suspension for the front wheels.

BODY SHAPES

Various methods of classifying vehicles exist. Vehicles may be classified by engine type, body/frame construction, fuel consumption structure, type of drive, or the classifications most common to consumers, which are body shape, seat arrangement, and number of doors. Eight basic body shapes are used today:

+++ Sedan. A vehicle with front and back seats that accommodates four to six persons is classified as either a two- or four-door sedan.

Often, a two-door sedan is called a coupe. If the vehicle's B pillars don’t extend up through the side windows, the car is called a hardtop.

|||| The structure of a unibody car.

|||| A Toyota Camry is an example of a typical late-model sedan.

|||| In body-over-frame construction, the frame is the vehicle's foundation.

|||| A Honda Civic SI can be a coupe.

|||| A BMW 3 series may be a convertible.

|||| An Aston Martin is a UK sports car.

|||| A Toyota Prius is an example of a hybrid hatchback. Its rear luggage compartment is an extension of the passenger compartment.

+++Convertibles. Convertibles have vinyl roofs that can be raised or lowered. A few late-model convertibles feature a folding metal roof that tucks away in the trunk when it’s down ---. Some convertibles have both front and rear seats.

Those without rear seats are commonly referred to as sports cars ---.

+++Liftback or hatchback. The distinguishing feature of this vehicle is its rear luggage compartment, which is an extension of the passenger compartment. Access to the luggage compartment is gained through an upward opening hatch-type door ---. This design car can be a three- or a five-door model. The third or fifth door is the rear hatch.

+++Station wagon. A station wagon is characterized by its roof, which extends straight back, allowing a spacious interior luggage compartment in the rear. The rear door, which can be opened in various ways depending on the model, provides access to the luggage compartment. Station wagons typically have four doors and can have space for up to nine passengers.

+++Pickups. Pickup truck body designs have an open cargo area behind the driver's compartment.

There are many varieties available today: there are compact, medium-sized, full-sized, and heavy duty pickups. They also can be had in two-, three-, or four-door models. Some have extended cab areas with seats in back of the front seat. They are available in two-wheel drive, four-wheel drive (4X4), or all-wheel drive.

+++Vans. The van body design has a tall roof and a totally enclosed large cargo or passenger area.

Vans can seat from two to twelve passengers, depending on size and design. Basically, there are two sizes of vans: mini- and full-size. The most common are mini-vans.

+++Sport utility vehicles (SUVs). SUVs are best described as multipurpose vehicles that can carry a wide range of passengers, depending on their size and design. A good majority of SUVs have four-wheel drive, although some do not. Most small SUVs are based on automobile platform and take on many different looks and features ( |||| 1). Mid-size SUVs are larger and typically offer more features and comfort. There are many large SUVs available ( |||| 2). These vehicles can seat up to nine adults and tow up to 6 tons.

+++Crossover vehicles. These automobiles look like an SUV but are built lighter and offer fuel efficiency. They are actually a combination of a station wagon and an SUV. They have SUV features but are not quite the same size. The basic construction of a crossover vehicle leads to a less trucklike ride than a normal SUV ( |||| 3). They also are not designed to tow heavy loads or for off-the-road use.

|||| 0 This Dodge Caravan is an example of a late-model mini-van. Full-size vans are also available.

|||| 1 The Honda Element is considered a small SUV and has many unique features including anytime four-wheel drive.

|||| 2 The Lincoln Navigator is an excellent example of a large SUV, and it’s based on a truck chassis.

|||| 3 Audi crossover vehicle.

|||| 4 A four-cylinder automotive diesel engine.

|||| 5 An engine block for a V8 engine: Block foundry ID and date; Engine number XXXXXXXX; Crankcase area; Front Camshaft locator; Cylinder block; Rear; Cylinders; Coolant passageways

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