What is better four-wheel drive, front or rear
Useful tips for motorists

What is better four-wheel drive, front or rear

The drive in the car is the transfer of torque from the engine to any wheel, which then becomes the drive. Accordingly, all vehicles begin to have such an important characteristic as the wheel formula, where the first digit means the total number of wheels, and the second - the number of driving ones.

What is better four-wheel drive, front or rear

But this concept does not reflect another important property of the automobile chassis, which axles are leading with part-time drive, rear or front? Although for all-wheel drive cars 4 × 4 or even 6 × 6 this does not matter.

What is four-wheel drive, differences from rear and front

Each type has its own advantages and disadvantages, so they still exist in relative balance. From a theoretical point of view, a front- or rear-wheel drive car is obtained from an all-wheel drive by simply eliminating the transmission parts that transmit traction to one or another wheel. In fact, technology is not so easy to achieve.

What is better four-wheel drive, front or rear

A mandatory unit of an all-wheel drive vehicle is a transfer case or transfer case, which distributes torque along the axles.

In mono-drive cars, it is not needed, but it simply cannot be excluded, the razdatka is integrated into the general scheme of the power unit, so the entire car is subject to rearrangement.

As in the opposite case, if an all-wheel drive modification is added to the line of initially, for example, front-wheel drive cars of the same model, this will entail great complications.

A lot of manufacturers do not even try to add a 4 × 4 version to their hatchbacks and sedans, limiting themselves to an increase in ground clearance and a plastic body kit for cross-modifications.

What is better four-wheel drive, front or rear

This also applies to the overall layout. Historically, it has already developed that in front-wheel drive vehicles the power unit is located across the engine compartment, the gearbox is equipped with two shafts with constant velocity joints (CV joints) going to the front wheels, which are simultaneously driven and controlled.

For rear-wheel drive, on the contrary, the motor with the box is located along the axis of the car, then the driveshaft goes to the rear axle. Four-wheel drive can be implemented with different levels of complexity in both of these cases.

The device and the principle of operation

To transmit torque, a set of components and assemblies that form the transmission is used.

It includes:

  • gearbox (gearbox), responsible for changes in the total gear ratio, that is, the ratio of the engine shaft rotation speed to the speed of the drive wheels;
  • transfer case, dividing the torque in a given ratio (not necessarily equally) between the drive axles;
  • cardan gears with CV joints or Hooke's joints (crosses) that transmit rotation at a distance at varying angles;
  • drive axle gearboxes, additionally changing the speed of rotation and the direction of torque transmission;
  • axle shafts connecting gearboxes with wheel hubs.
How does the four-wheel drive car Niva Chevrolet

As already mentioned, two main ones, characteristic of transverse and longitudinal power units, stood out from the total set of schemes.

  1. In the first case, the transfer case is attached to the side of the gearbox, while it is also called the angular gearbox. For layout reasons, the drive shaft of one of the front wheels is passed through it, here the moment is removed to the rear axle by a gear pair with hypoid gearing, for which the rotation turns 90 degrees and goes to the cardan shaft running along the car.
  2. The second case is characterized by the placement of the transfer case on the same axis as the gearbox output shaft. The cardan shaft to the rear wheels is located coaxially with the input shaft of the transfer case, and the front ones are connected through the same cardan transmission, but with a 180-degree turn and a shift down or sideways.

The razdatka can be quite simple, being responsible only for the branching of the moment, or complex, when additional functions are introduced to increase cross-country ability or controllability:

Drive axle gearboxes on 4×4 machines can also be complicated by the presence of controlled differentials or electronic clutches. Up to forced locks and separate wheel control of one axle.

Types of all-wheel drive

In different driving modes, it is very useful to redistribute the torque between the wheels to increase efficiency on the one hand, and cross-country ability on the other. Moreover, the more complex the transmission is, the more expensive it is, so different types and classes of machines use different drive schemes.

Constant

The most logical would be to use all-wheel drive always and in all road conditions. This will ensure the predictability of reactions and the constant readiness of the machine for any change in the situation. But this is quite expensive, requires additional fuel costs and is not always justified.

The classic scheme of permanent all-wheel drive (PPP) in all its simplicity is used on the ageless Soviet car Niva. A longitudinal engine, then a box, a gear transfer case is connected to it through a short cardan shaft, from where two shafts go to the front and rear axles.

What is better four-wheel drive, front or rear

To ensure the possibility of rotation of the front and rear wheels at different speeds, which is important on dry pavement in corners, there is an interaxle free differential in the transfer case, which can be blocked in order to have at least two drive wheels off-road when the other two slip.

There is also a demultiplier, which approximately doubles the thrust with the same decrease in speed, which greatly helps a relatively weak engine.

There is always torque on the drive wheels until one of them stalls. This is the main advantage of this type of transmission. No need to think about its mobilization manually or create complex automation.

Naturally, the use of PPP is not limited to one Niva. It is used on many expensive premium cars. Where the price of the issue does not really matter.

At the same time, the transmission is supplied with a mass of additional electronic services, mainly to improve controllability with excess power, the scheme allows this.

Automatic

Connecting an additional drive axle with automatic equipment has many versions, two specific schemes can be distinguished, used on BMW and many other premiums, and a clutch in the rear wheel drive typical for mass crossovers.

In the first case, everything is assigned to the clutches in the razdatka with an electronic drive. Clamping or dissolving this clutch working in oil, it is possible to change the distribution of moments along the axes over a wide range.

Usually, when starting with a powerful engine, when the main drive rear wheels begin to slip, the front ones are connected to help them. There are other redistribution algorithms, they are hardwired in the memory of control units that read the readings of numerous sensors.

What is better four-wheel drive, front or rear

The second case is similar, but the main wheels are front, and the rear ones are connected for a short time through a coupling between the cardan shaft and the axle gearbox.

The clutch overheats quickly, but it is not expected to work for a long time, just sometimes you need to slightly push the car over the rear axle on a slippery road or in a difficult turn. This is how almost all crossovers in the 4 × 4 modification are built.

Forced

The simplest and cheapest type of all-wheel drive, used in utility SUVs whose permanent place of work is off the pavement. The rear axle serves as a constant driving axle, and if necessary, the driver can turn on the front axle, hard, without a differential.

Therefore, on a hard surface, the car must be rear-wheel drive, otherwise the transmission will be damaged. But such machines have a large margin of safety, are simple and inexpensive to repair.

Many imported pickups and SUVs have such modifications, sometimes expensive and complex in more advanced optional drive versions.

Pros and cons of 4WD (4×4)

Minus, in fact, one - the price of the issue. But it shows up everywhere:

Everything else is merit:

All this makes it possible to widely use all-wheel drive on powerful and expensive machines, where the addition to the price is not so significant.

How to drive a four-wheel drive car

In order to realize all the possibilities of all-wheel drive, it is necessary to study the design features of a particular car, to understand how its transmission scheme works.

  1. Do not use a plug-in all-wheel drive without a center differential on asphalt, this will result in rapid wear and tear.
  2. To practice driving on slippery roads in corners, often all-wheel drive cars, especially those with a free differential or automatic torque transfer, can behave unpredictably, changing behavior from front-wheel drive to rear-wheel drive and vice versa. And it is necessary to work with the gas pedal in a turn with a diametrically opposite tactic, a car to add traction can either go away with a skid inside the turn, or start sliding the front axle out. The same applies to the damping of the rear axle skid that has begun.
  3. The good stability of a 4×4 in winter can be lost suddenly for the driver. You need to be prepared for this, because mono-drive cars always warn of a loss of traction in advance.
  4. Excellent cross-country ability should not lead to thoughtless visits to mud “ambushes” or snow fields. The ability to get out of such conditions without a tractor depends more on the tires chosen than on the ability of the automation in the transmission.

At the same time, in a reasonable driving strategy, an all-wheel drive car will always help to avoid troubles that monodrives will get into much earlier. Just don't overuse it.

In the future, all cars will receive all-wheel drive. This is due to the progress in the technology of electric vehicles. It is very easy to implement a scheme with an electric motor for each wheel and advanced power electronics.

These cars no longer require engineering knowledge about the type of drive. The driver will only control the accelerator pedal, the car will do the rest.

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