Readdom: A Guide To Modern Passenger Car Layouts

2023 Author: Natalie MacDonald | [email protected]. Last modified: 2023-11-26 13:59

What distinguishes a passenger car from more exotic means of transportation? The answer seems to be simple. Four wheels, an engine that turns them all or only half of them, a cabin for passengers. Optionally - a roof over their heads and at least some kind of trunk. But there are tons of ways to put it all together. Scientifically speaking - to compose. Let's talk about the most common on modern cars. And those that did not take root, we will leave to automotive historians

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Why are some options for the location of the power unit, passenger compartment and trunk popular, while others are not? Because there are many requirements for the layout of the car. It is necessary that the cabin is spacious for the convenience of passengers and protects them in case of accidents. The engine, trunk and axles should be positioned so that the weight of the car is distributed as evenly as possible over the wheels of the car - it depends on how well it will accelerate, brake and turn. There are also requirements for aerodynamics, visibility, patency - for design, finally. And yes, the interior and all units must fit into the given dimensions. After all, every extra centimeter of length means not only parking difficulties, but also the additional weight of the car and, ultimately, a higher price.

It is clear that the ideal layout that meets all criteria equally well does not exist - engineers have to make compromises depending on the task assigned to them. And now, armed with this knowledge, let's take a look at the options they usually choose.

Front-wheel drive

Motor and gearbox - front transverse

The idea of making the front wheels drive was born not much later than the car itself, but it was difficult to implement. Reliable joints were needed so that the drive wheel could turn and turn. When they finally appeared, this arrangement quickly became the most popular.

After all, if you put the engine and the box across the machine, then an expensive bevel gear is no longer needed, and the drive axle is just two drive shafts with the same hinges. And they are all housed in the engine compartment. As a result, the car is spacious and with a large trunk (if needed). This is how our G8, KiRio, ToyotCamry, and millions of other hatchbacks, sedans and front-wheel drive crossovers work. Seems like a dream, not a layout!

Its disadvantage is that a large engine with a box across it simply does not fit. The maximum that could be so stuck into the engine compartment is an in-line "six" on the Volvo S80. And there is no point in a powerful engine: during acceleration, the car "squats" on the rear axle, the front wheels are unloaded and with a powerful engine simply skid, forcing engineers to solve a new problem.

Motor and gearbox - front longitudinally

Another variant of the front-wheel drive layout is with a motor mounted longitudinally in front of the front axle. The gearbox is then somewhere under the dashboard, and the bevel final drive is between the engine and the gearbox (more precisely, inside the gearbox, but closer to the engine). In Russian history there is such a design - this is the Moskvich-2141. And in the world the most famous cars are Audi - those versions that do not have all-wheel drive.

In theory, there are no restrictions on engine size, but in practice, cars with a large engine get too long front overhang. And most importantly, the front axle is overloaded. Yes, such a car accelerates better. But it turns badly and brakes worse, because the unloaded rear wheels can do little to help.

Rear wheel drive

Motor and gearbox - front longitudinally

The engine, standing longitudinally under the hood, the gearbox, which goes into the salon, the cardan and the rear axle with a conical final drive - a similar arrangement dominated in the automotive world until the 80s of the XX century. These were our Victories, Volga and Zhiguli. The same scheme is used to build three-wheel BMW, Mercedes-Benz S-class, MazdMX-5, Chevrolet Camaro and a bunch of executive sedans and sports cars. In short, a real "classic"!

A classic, which is good because under a long hood you can install an oh-oh-very large and powerful motor. And the bad thing is the eternal lack of "grip" on the driving rear wheels, which usually have less weight. In an effort to load the rear axle, engineers move the engine back … and get another drawback of "classic" cars - not the most spacious, if not even a two-seater saloon.

The trend with the transfer of the engine to the wheelbase, as expected, was brought to the point of absurdity by the Japanese. In 1990, they introduced a car with a motor located … under the driver's seat! And it was not a sports car, but a minivan - ToyotPrevi (in the home market - ToyotEstima). It was produced for ten years, also had an all-wheel drive version, but in the next generation, as expected, it “moved” to a cheaper front-wheel drive platform from Camry.

Motor - front longitudinally, box - rear

Some manufacturers use a different method of equalizing the weight distribution, moving only the gearbox back. This arrangement is called Transaxle. Moreover, not only sports cars were built on its basis in different years (for example, the Chevrolet Corvette C7 and Maserati of previous years), but also quite trivial cars - like the Volvo 300 series. True, this scheme is still considered not very practical, and therefore did not receive distribution outside the class of sports coupes.

Motor and gearbox - rear longitudinally

In fact, it is easy to load the rear drive units - just transfer it to the trunk … the motor. A very large one will not fit there, but neither you a gimbal, nor a central tunnel that covers it. The simplicity and compactness of this design at one time attracted the creators of small "folk" cars, be it VW Beetle, Fiat 500 or our "Zaporozhets".

However, driving such cars proved to be difficult. Heavy feed strove for the slightest reason to go into a skid, underloaded front wheels did not always direct the car where the driver wanted. And the cargo hold at the front doesn't turn out to be very large due to the chubby wheel arches and steering.

Therefore, now only the Porsche 911 is produced with a rear engine, the owners of which do not care much about the volume of the trunk. But with a heavily loaded rear axle, the sports car accelerates and brakes perfectly. Well, or set sideways if the driver is not experienced enough.

Motor and gearbox - transversely at the rear

In addition to the Porsche, the engine also carries a short Smart at the back. Its motor is so compact that it fits across the rear wheels! And above it there is still a little space for luggage - but in front of the passenger compartment, the car has nothing but headlights and a radiator.

Motor and gearbox - in the middle transversely

How to divide the engine mass equally between the axles? The obvious answer is to center it. Where most cars have a salon. With such a layout, convenience and space cannot be counted on, but there are cars that do not need them. We are talking about sports cars designed for two passengers.

In reality, the engines are not placed quite in the middle, but nevertheless closer to the stern - right behind a pair of seats. Smaller ones fit across, and the engine compartment comes out more compact. Small Lotus Elise, Alpine A110, ToyotMR2 …

Motor and gearbox - in the middle longitudinally

Well, if within the base you need to fit a huge V8 or V12 - in Ferrari, McLaren and other large supercars - then the engine has to be placed along, even more crowding the passenger compartment. But such a motor often turns into an attractive design element, open to the eyes under the glass cover.

Due to the excellent weight distribution, the mid-engined cars are coolly controlled, they have no problems with either braking or acceleration. These advantages more than compensate for the lack of space for your beloved mother-in-law. However, it has long been invented how to achieve good acceleration performance on any surface without pushing the motor into the cabin. To do this, all the wheels must be made leading.

Four-wheel drive

Motor and gearbox - front longitudinally

Initially, all-wheel drive was required for off-road vehicles so that they would not get stuck in mud or snow. The "classic" front-engine layout was taken as a basis, only after the gearbox was another gearbox installed - a transfer case. Through it, the engine can simultaneously rotate both the front and rear wheels, and even on a very slippery surface, one of them will pull the car forward.

Another advantage of the hand-out layout is the relative simplicity of the design. And a huge disadvantage is that the front and rear axles can be rigidly connected only on slippery surfaces. When returning to the asphalt, the front axle has to be turned off (otherwise the car is less controlled) - and its main gear, transfer case and the shaft connecting them become a dead weight. Nevertheless, such a plug-in four-wheel drive is still used in many real jeeps and pickups, including our UAZ.

In modern powerful cars that need the help of the front wheels when accelerating on asphalt, a differential is built into the transfer case, with which all-wheel drive can be permanent. Or they install a clutch instead, which automatically connects the front axle when it is needed. This is how all-wheel drive versions of "classic" sedans or coupes work. And at the same time, crossovers created on their platform. With the modern development of electronics, only a very experienced driver can feel the difference between these schemes on the go.

If the blank for a car with all the leading ones was originally front-wheel drive, it doesn't matter either. Cars with a longitudinally standing motor are even easier to convert to 4WD. A center differential is integrated into the gearbox, a propeller shaft and a final drive at the rear, like in rear-wheel drive cars, are added - and now the Audi model with the quattro nameplate is ready. Or Subaru with its famous symmetrical all-wheel drive.

Motor and gearbox - front transverse

Even more popular today are crossovers and all-wheel drive sedans with a transverse engine and basic front-wheel drive. The moment to the rear wheels is transmitted by an additional bevel gearbox in a box, a cardan shaft and a multi-plate clutch. On the pavement, such cars are, in fact, front-wheel drive, but when the front wheels begin to slip, the clutch is locked (it used to be mechanically locked, and now - at the command of the electronics) and the rear axle comes to the rescue. However, the crossover sometimes manages to get stuck even faster. In addition, clutches tend to overheat off-road - and the car temporarily turns into a front-wheel drive one. However, for trips on a snow-covered road to the dacha, such a design suits perfectly well - because it is cheap and practical.

Motor and gearbox - rear longitudinally

On the rear-engined Porsche 911, the drive wheels are always perfectly loaded. But even the wide rollers on the rear axle are not enough to realize the full power of its engine. Therefore, the engineers made an all-wheel drive version of the sports car. Although fans of the brand still consider only a two-wheel drive car to be a real Porsche.

In the layout of the nine hundred and eleventh all-wheel drive, a cardan from the gearbox to the front axle was added to the canonical design and, accordingly, the second bevel main gear (the first is hidden in the box). As a result, the car looks like a backward-facing Audi quattro. Only in Porsche there is no center differential - the second axle is connected by a clutch. Because superpowers are not expected from the front wheels - their load is still weak, and they also have to turn the car …

Motor and gearbox - in the middle longitudinally

It is clear that four-wheel drive will not interfere with supercars. However, most of these powerful and even super-powerful machines do without it. After all, it is more difficult to hook up a four-wheel drive to a mid-engined car - the drive axles are on both sides of the engine.

Lamborghini is more willing than others to use this layout - most of the cars it produces now are all-wheel drive. With this arrangement, the drive shaft from the gearbox to the front axle is passed to the side of the motor, and sometimes through it. The Bugatti Veyron deserves a special mention, in which the gearbox is installed in front of the engine, and the shaft passing by the engine transmits the rotation to the rear wheels.

Bonus

It is impossible not to mention one more layout, when the drive is full, and there are… two motors! This scheme is used for hybrid versions of their models, for example, the Peugeot and Lexus brands. In their cars, the internal combustion engine drives the front wheels, and the electric motor drives the rear wheels. And it is clear that they are not always four-wheel drive, but only when the electronics give the command to connect the rear axle. Moreover, the electric motors in the back are usually low-power and are needed only to help the car move on a slippery surface.

And the two-engine layout with the light hand of Elon Musk was adopted by the manufacturers of electric vehicles. And, perhaps, after a dozen years, it is she who will already be called the "classic" …