Initially, there were few schemes for the mutual arrangement of major vehicle component parts. If we recall the very first self-moving carriages of Daimler and Benz, it should be mentioned that their engine was located at the back, above the rear axle. However, with the development of the automotive industry, designers and engineers started solving problems that were associated with a more rational use of body space.
The place where the engine, gearbox and main gear are located affects the so-called weight distribution of the car. The controllability of the car directly depends on it.
Car weight distribution is the distribution of its weight on the front and rear axles, which is expressed as a percentage. More simply, when a car stands on a surface, it presses on it with a certain force, which corresponds to its weight. Weight distribution along the axles depends on the design of the vehicle.
Note
Weight distribution is indicated as a percentage. The first digit represents the weight on the front axle, and the second represents the weight on the rear axle. For example: "60% at 40%" or "50% at 50%".
The location of the major vehicle component parts - the engine, gearbox and drive gear - relative to each other within the body is naturally called the layout diagram of the car.
1. The first and one of the most widespread until recently diagrams is the classical one.
The classic layout diagram means the installation of the engine in the front longitudinally (i.e. along the axis of the vehicle) above the front axle with rear-wheel drive (diagram is shown in Figure 3.5).
Figure 3.5 Classic layout diagram of a car.
In this case, the gearbox can be attached to the engine, or it can be located next to the main gear, and in some cases even have a common housing with the main gear (then they say that "a gearbox in a block with the drive gear"). In terms of the mutual arrangement of the chassis and engine elements, everything is extremely simple, but there is a drawback: a tunnel in the bottom of the car body, inside which a driveshaft passes, transmitting rotation from the engine to the wheels, "eats" the legroom of the rear seat passengers.
2. Front-wheel drive longitudinal engine (shown in Figure 3.6). This layout diagram is typical for Audi cars. Thanks to this layout of the major vehicle component parts, the designers practically got rid of the central tunnel in the underbody, at least in the rear of the passenger compartment.
Figure 3.6 Front-wheel drive longitudinal engine.
3. Front-wheel drive transverse engine (shown in Figure 3.7). The gearbox is connected to the engine and is located in the same housing with the drive gear. A positive aspect of this design solution is the compactness of the entire powertrain and the possibility of rational and full use of the entire space inside the car (there is no central tunnel and a tunnel for the gearbox).
Figure 3.7 Front-wheel drive transverse engine
4. Longitudinal arrangement of the engine behind the rear axle with a drive to the rear wheels (also called a "rear engine arrangement") (shown in Figure 3.8). This layout diagram is now a rarity and is mainly used by Porsche Company.
Figure 3.8 Longitudinal arrangement of the engine behind the rear axle with a drive to the rear wheels.
5. Longitudinal arrangement of the engine in front of the rear axle with a drive to the rear wheels (shown in fig. 3.9). The gearbox is located behind the engine.
Figure 3.9 Longitudinal arrangement of the engine in front of the rear axle with a drive to the rear wheels.
This layout diagram is sometimes called “engine in base”, implying that geometrically the engine is located within the wheelbase of the vehicle (see “Basic Technical Specifications of the Car”).
Note
By the way, there are options when, in order to obtain better weight distribution along the axes, the engine is located in the front longitudinally and is shifted far beyond the front axle, placing it within the wheelbase (such layout diagram is shown in fig. 3.10).
Figure 3.10 Longitudinal arrangement of the engine behind the rear axle with a drive to the rear wheels.
6. Longitudinal arrangement of the engine in front of the rear axle with a drive to the rear wheels (figure 3.11).
Figure 3.11 Longitudinal arrangement of the engine in front of the rear axle with a drive to the rear wheels.
It is worth mentioning that all-wheel drive is possible in almost any engine position (more about this in the "Transmission" chapter).
There are two main options of all-wheel drive
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