Better four-wheel drive or plug-in. Which drive is the best? Front, rear or all wheel drive? Full drive type

What are we continuing to talk about car drives, today we have a global topic, namely, what is better and what to choose front or all-wheel drive for a SUV or a crossover? As we know there it is not entirely honest, that is, it is not permanent and often does not have a rigid differential lock, that is, you cannot manually lock it, it is connected only after the front axle starts to slip. And now an absolutely fair question arises - "is it necessary or the front axle will be enough for the eyes?" Everything is not unambiguous here, let's figure it out ...

Well, to say in general - that four-wheel drive is bad, I will not! Still, I think - quite the opposite, it's even good! There are large and heavy vehicles where he works constantly, which greatly improves cross-country ability. There are also not very large cars, middle class "C", sometimes "D", where it is also permanent or rigidly connected (which improves both cross-country ability and handling under certain conditions), but SUVs or crossovers are completely different. All-wheel drive in them, unfortunately, has now become the property of marketers and dealers, that is, they are trying to prove to you that they are "digging" four wheels, but in the end everything turns out completely wrong. In this article I will try to debunk all the myths, but for a better understanding, you need to tell about each type, and I think it is worth starting from the front.

As we have already said - about this topic, too, a lot of "copies broke", but there the principle of conversation is different, nevertheless, one driven axle either in front or behind, today the essence of the question is different.

The front-wheel drive is very simple in structure, and it has now been practically brought to perfection, that is, it can go for a very, very long time without any breakdowns.

Device :

Engine
Engine-mounted gearbox with differential, often in the same housing
From the box (differential) there are two axles c. On each side there are two CV joints (inner and outer)
These CV joints fit the front wheels through special hubs.

The torque is transmitted from the engine - transmission - to the axles - to the wheels. This is how a front wheel drive vehicle is set in motion.

It is worth noting that there are not a lot of transmission fluids here, that's all in the box itself, as a rule, the rest of the connections are dry (well, or almost dry, there is still grease under the anthers in the CV joints, but there it is really minuscule and it does not change). This tells us that it is possible not to follow this construction at all. Of course, all the same, I advise you, because if they break, then the hinge will soon fail, but believe me for the next 70 - 80,000 km, this can not be done. If the manufacturer is serious, then the anthers can walk 150-200,000 km.

The rear suspension in the front-wheel drive does not carry any semantic load, that is, it is a banal "support for the wheels", there is practically no weight, it is light here (either a beam or a "multi-link"). And last but not least, the rear part is practically maintenance-free, if only the brake pads are changed.

Four-wheel drive

Even a plug-in all-wheel drive through a viscous coupling has a much complex structure (I am already silent about the constants). There are more parts that spin (most of the time) at idle, there are already two axles, and not one, a propeller shaft also appears and the rear axle is no longer secondary.

Device :

Engine
A gearbox that can be combined with a front differential. However, the front differential can be carried out separately.
Front axle with CV joints on the front wheels
Center differential, it can also be in the same housing with the box, but it can also be separate (it all depends on the design)
Transfer case.
Rear cardan for transmission of torque to the rear axle
Viscous coupling or electromechanical coupling (hydromechanical) for automatic connection rear axle
Rear axle. It can be made in a cast body, from which two axle shafts come out to the rear wheels. But now often two axles with CV joints also go from the rear differential, by analogy with the front axle.

As you can see, the structure is much more complex! Two more differentials appear here, center and rear, there is also a transfer case, viscous couplings and so on. All this adds at least 100 kg of weight to the car, and possibly more. There are also many parts here that "spin" in the oil, and they really need to be monitored. Some manufacturers recommend changing them transmission oil... If any oil seal leaks, the whole assembly may fail. I think everyone understands this, but again everyone thinks that since I have a four-wheel drive, then I'm on some SUV or crossover, on RAV4 or the same Duster, I'll just become an off-road conqueror - "what do I need UAZ, I'm like UAZ myself" ! BUT is it really so?

Four-wheel drive through viscous coupling (electrofusion, hydromechanical coupling)

Well, here we come to the most interesting, for whom is the all-wheel drive of such crossovers, where can it be used? For many, this means that you can immediately go to the forest for mushrooms and berries, that you can fight such off-road that, as they say, "on the door"! Guys, stop, all-wheel drive on crossovers and SUVs is very conditional, I would even say "urban" it is not intended for serious off-road tests.

Why? Yes, it is simply not designed for this. Often on many crossovers, it is connected via a viscous coupling or an electrofusion coupling.

Viscous coupling , we have already talked about it (you can in detail). Transmits torque through a special fluid contained in the viscous coupling housing. When one axle starts to slip, the liquid quickly hardens, thereby closing the rear axle and connecting it. The disadvantages of such a drive are that it is practically impossible to turn it on yourself or lock the rear differential for work. ONLY AFTER TROUGHING. Therefore, the effectiveness of such all-wheel drive, low enough.

As it becomes clear, the work happens a little differently. There is no special liquid, but there are electromagnets that close or open the disks when voltage is applied to them, thereby connecting or disabling four-wheel drive. This clutch is dry, there are no oils in it, which is both good and bad. The good thing is that you do not need to monitor the leakage of the oil seals and change the fluid. Bad - this clutch overheats quickly. Four-wheel drive is engaged after front-wheel drive slips, usually after the second rotation of the front wheel. In some cars equipped with such a unit, there is a forced blocking, that is, you can physically block the rear axle. It seems to be the DECISION, the control is much better than that of the viscous coupling, HOWEVER THERE IS A LARGE SPOON OF MOUNT. Such a drive very quickly overheats and turns off, if you can slip on the viscous coupling for a long time, then the electromagnetic clutch will turn off after 3 - 5 minutes of slipping. They also fail faster due to high temperatures, as experts say - they just burn.

Hydromechanical clutch. Very similar design to the electromagnetic version. However, here the discs are closed by oil pressure. There is a pump inside that creates pressure to squeeze or unclench them. Pumps now can also be electrically driven, previously it was mechanical.

Actually, such designs are used on a large number of crossovers or SUVs, it is very, very difficult to find another here.

Full or front?

As you can see, to call such four-wheel drive - COMPLETE, as the language does not turn! Why are they imprisoned. You know, I once talked with a "seasoned" mechanic about such automatic connections, and this is what he told me - "it will be expensive to meddle in even (average dirt) on such machines, they are simply not designed for this off-road, do not think that you bought a car on cross-country ability similar to our UAZ, THESE ARE DIFFERENT CLASSES! Especially if you have automatic transmission gears, because it can also overheat quickly enough (with the mechanics, everything is a little better). These cars are designed maximum for the fight against a snow-covered courtyard in the city in winter, or with a couple of shallow puddles on the way to the dacha "

You know this as a shovel in your trunk or a passenger neighbor - what do I mean? On a front-wheel drive car, you will need to clear the front track a little (using a shovel), or ask your passenger neighbor to give you a little push. But such a plug-in four-wheel drive car can get out on its own. Good? Of course yes! BUT is it worth overpaying for this?

If you take apart the front and full options, you should think about where and how do you get around? It is also worth considering that an all-wheel drive car:

Costs more.
Complete sets with all-wheel drive are at least "mid-range" and "top-end", that is, you will not find it in the "standard".
The car weighs more
More vibrations. Because more nodes are spinning.
Service costs more
More rotating elements, which reduces the resource
More fuel consumption
The modest capabilities of this four-wheel drive car

Actually, if you are a 100% city dweller, the snow is removed in the cities, you go to the dacha where there are not very comfortable several meters of dirt - THEN TAKE SUCH FULL DRIVE, AS I BELIEVE THIS IS OVERPAYMENT, YES IT DOESN'T NEED IT!

If you are a resident of a rural area, you saw the asphalt only on TV, and the snow is filling up, so it is difficult to move around on the tractor - IT WILL NOT HELP YOU ALSO! Here you need to look at a more brutal technique, perhaps on the frame. YES, at least the same UAZ will be more practical.

All-wheel drive in crossovers and SUVs is not exactly what you are expecting - BELIEVE. This is rather a trick of marketers, and not an all-wheel drive car in the understanding of "off-road conqueror". Of course, there is a benefit from it (for example, you live near the city, in winter the roads seem to be cleaned, but not always), but it is so insignificant that giving 100 - 200,000 rubles more, as I think, is meaningless. YES, it is MORE EXPENSIVE to maintain such a car! Considering all the pros and cons, I personally would not buy! Although you may have other thoughts, write in the comments.

Now a short video.

When choosing a new car, the future car owner is faced with the question of which drive to choose? Front, rear, or full? To find the answer to this question, you need to know the advantages and disadvantages of all types of drive, so that the choice is fully conscious.

Characteristic

So let's take a look at four-wheel drive vehicles. There are two types of this drive - AWD and 4WD. The AWD type implies the operation of the mechanism in automatic or constant mode, and the 4WD mode provides for manual on and off. That is, the transmission of torque is provided only to one axle, usually to the rear, and if necessary, the front axle is connected. On the other hand, the AWD all-wheel drive scheme is constantly in automatic mode, transferring torque evenly to both the front and rear axles.

Control

Driving a car has its own characteristics and difficulties. While manual four-wheel drive vehicles typically behave on the road in the same way as rear-wheel drive vehicles, the same cannot be said for permanent four-wheel drive vehicles.

For example, if in a situation where a front-wheel drive car requires an increase in engine speed, and a rear-wheel drive, on the contrary, requires a decrease in speed, then an all-wheel drive car will need either one or the other, depending on various factors, such as the quality of tire grip. , speed of movement, trajectory of turn, etc. This complicates driving, as you need to be able to predict the behavior of the car and plan your actions in advance. The situation is also aggravated by the fact that an all-wheel drive vehicle can suddenly lose stability, without visible prerequisites.

Cons of 4WD cars

The negative qualities of all-wheel drive systems, in particular systems with manual control, include increased wear of transmission parts, increased noise,. This is due design features the system itself. For example, there is a rigid connection between the axles of a car equipped with a permanently connected four-wheel drive, which consumes additional energy.

The all-wheel drive system has a number of limitations during operation - the system cannot be used when driving on a hard and dry road, which means incomplete use of engine traction. In addition, four-wheel drive vehicles are more expensive to manufacture, so their cost is higher. They are also more expensive to maintain, repair and operate.

pros

Of course, in addition to the aforementioned disadvantages, all-wheel drive vehicles have their own unconditional advantages, the main of which is increased cross-country ability. Also, four-wheel drive cars have better dynamics, they are stable on slippery roads.

However, it should be noted that all the advantages of all-wheel drive can be obtained only if the driver fully understands the "behavior" of such a car, which is called "feel" it. In other words, a lot also depends on the professionalism of the driver, regardless of what kind of drive the car is equipped with.

At first glance, the principle of operation of the transmission of an all-wheel drive car is simple: the torque from power unit distributed between the four driving wheels. Such a car is very convenient due to its pronounced advantages associated with unpretentiousness to the quality of the coating under the wheels. On a dirt road, in ice, on wet country terrain or on a highway in a heavy rain, an all-wheel drive car will show itself at its best. Plus, on it you can not be afraid to move off the asphalt surface and cross the terrain without even a hint of roads, and on the asphalt, four-wheel drive makes itself felt with a good start and acceleration, with practically no slippage.

But sometimes incidents occur, which, it would seem, are difficult to explain due to the advantages that all-wheel drive cars have. It so happens that the driver sits behind the wheel of an SUV with an impressive ground clearance, and the car got stuck in a "mess" and lay down on its belly.

Interesting to know! In 1883, the American farmer Emmet Bandelier patented a design similar to the current all-wheel drive system.

Of course, there can be many reasons for this, the most common of which is, as experienced drivers jokingly put it, "the gasket between the steering wheel and the seat." But it also happens that the transmission of the "all-terrain vehicle" is not supposed to cope with the tests. And then reasonable questions arise: "Why can't they cope?", "And which one can cope?" We will talk about this further in the provided material.

Manual all wheel drive (Part-Time)

This type of transmission can rightfully be called the "firstborn" among all-wheel drives. Its principle of operation is the rigid connection of the front axle. Thus, all wheels rotate at the same speed, and there is no center differential. The torque is distributed equally between all wheels. In this case, nothing can be done so that the axles rotate at different speeds, except to penetrate into the "womb" of the car and install a new differential.

In the meantime, it is not recommended to dissect in traffic with the front axle connected. Even if you move straight in a low gear for short distances, nothing terrible will happen, but if you need to turn around, then the arising difference in the length of the bridge paths becomes a hindrance. Since the distribution is 50/50% between the axles, the power surplus comes out only through the slippage of the wheels of one of the axles.

On sand, gravel or in mud, the wheels can slip if necessary, and nothing will interfere with them, since the grip on the surfaces is weak. But if the weather is dry, and you are driving on an asphalt road, then the power will have nowhere to go, as on the off-road. Thus, the transmission is exposed to increased loads, rubber wears out faster, handling deteriorates and directional stability is lost at high speeds.

If the car is used more often off-road or is generally purchased only for cross-country driving, then the all-wheel drive system with forced connection of the front axle will fully meet your expectations. The bridge connects immediately and hard, so you don't have to block anything. The design is very simple and reliable, there are no locks and differentials, there are no electric or mechanical drives, there is no unnecessary hydraulics and pneumatics.

But if you are an urban "dandy", value your time and do not want to bother about weather conditions and alternating sections of the city with its loose and slippery road surfaces, treacherous deep puddles, then the version of this all-wheel drive system is absolutely not suitable for you. If you move with the front axle always forcibly connected, then this is fraught with wear and tear with subsequent damage, it is not very convenient to constantly manipulate it, and in general you may not have time to connect it.

Cars with Part-Time: Suzuki Vitara, Toyota Land Cruiser 70, Great Wall Hover, Nissan Patrol, Ford Ranger, Nissan Navara, Suzuki Jimni, Mazda BT-50, Nissan NP300, Jeep Wrangler, UAZ.

Permanent four-wheel drive (Full-Time)

The drawbacks of plug-in all-wheel drive were the root cause of a newer invention - permanent all-wheel drive, which is devoid of all the problems that Part-Time had. This is the same uncompromising "4WD", which is devoid of any "and if" there: all the wheels are driven, there is a free differential between the axles, which releases the accumulated excess power due to the rotation of one of the gear satellites, which contributes to the movement of the car with permanent all-wheel drive. The main nuance of cars with this type of all-wheel drive is slipping. If the car starts to skid with one axle, the second is automatically turned off.

Now the car has turned into furniture or a house, as you wish, in general, into real estate. How does this happen? If one wheel starts to slip, the inter-wheel differential disables the second, and the second axle is also automatically disabled by the differential, but already by the center differential. Of course, in reality, the stop does not happen so quickly. Movement is a dynamic process, therefore, there is a power reserve, inertial force. The wheel turns off, moves by inertia for a couple of meters and turns on again.

But in this case, sooner or later, the car will stall somewhere. Therefore, in order to preserve all the off-road qualities of a "rogue", such cars, as a rule, are fitted with one or two forced center differential locks. In the front differential, it is very rare to see a factory lock. It is installed separately if desired.

But the permanent all-wheel drive system is also far from ideal driving performance on asphalt roads. Such cars drive, let's say, it would be better. In critical situations, the SUV pulls out of the corner and does not immediately respond to steering and gas puffing. Drivers of these vehicles require special skills and excellent vehicle feel.

To improve handling, they began to install interaxle limited slip differentials with a forced locking system. Different automakers used different solutions: some with a Torsen type differential, some with a viscous coupling, but the task for all is the same - to improve the car's handling, and this requires a partial differential lock.

If one of the axles starts to slip, the self-locking mechanism is triggered, and the differential does not affect the second axle, to which torque continues to flow. A number of cars were also equipped with a self-locking mechanism for the rear axle differential, which had a positive effect on the sharpness of control.

Among the cars with permanent all-wheel drive, one can distinguish Toyota Land Cruiser 100, 105, Land Cruiser prado, Land Rover Discovery, Land Rover Defender, Lada 4x4.

Automatic all-wheel drive Torque on-demand (AWD)

Time and the inquisitive minds of automotive engineers have done their job, developing the all-wheel drive system into something new with the introduction of electronically controlled systems with the redistribution and transfer of torque. As a result, there were stabilization and directional stability systems, traction control systems, as well as systems that distribute torque. All of them are implemented using the involved electronics. The more expensive the cost of the car and the more modern its filling, the more complex schemes are applied to it.

This is tracking the steering angle, body rolls and speed, up to how often the wheels oscillate over a certain distance. The car carries out the most complete collection of information about its behavior while driving. The ECU processes it and regulates the transfer of torque between the axles by means of an electronically controlled clutch, which has changed the differential. In modern sports cars, this invention has become quite noteworthy.

Today electronic systems can be called almost ideal in their behavior. It is only necessary for manufacturers to add several new sensors and parameters, thanks to which the system works ahead of the curve.

But here, too, there are some nuances of use: this type of all-wheel drive transmission is suitable for operation only on asphalt roads with rare interspersed with symbolic off-road, primer, for example. Basically, electronic clutches, when slipping off-road, begin to get very hot and fail. And for this you do not need to plow the tank tracks for hours, ten minutes of skidding on the ice will be enough. And if it is overheated systematically, then breakage cannot be avoided, as well as expensive repairs.

The "cooler" the system, the more susceptible it is to breakdowns. So you need to choose a car wisely, having determined for yourself on which routes you will ride it. Don't go to extremes: if it's an SUV, then only into the forest and the village, and if it's a car, then only around the city. There are plenty of cars from this segment that are versatile in their driving characteristics. But also without fanaticism. On passenger car you can, of course, go to a country road, but which one and which one is another question.

If one of the ABS sensors breaks the wiring, then the entire system will fail at once and will not receive information from the outside. Or gasoline was filled with not the best quality - and that's it, the low gear does not turn on, there is a trip to the car service ahead. Or it may happen that the electronics will put the car into service mode, completely shutting off all its vital systems.

Among these cars, it is worth highlighting Kia sportage(after 2004 onwards), Cadillac escalade, Nissan Murano, Nissan x-trail, Ford Explorer, Toyota RAV4 (after 2006), Land Rover Freelander, Mitsubishi outlander XL.

Multi-mode (Selectable 4wd)

This system is perhaps the most versatile in relation to all-wheel drive with its various manipulations: it can be activated manually or automatically, as well as forcibly deactivate the rear or front axles. The Selectable 4wd system does not increase fuel consumption. The leader in terms of fuel overspending is the part-time vehicles mentioned at the beginning.

Some cars with a selective transmission, which can be called permanent all-wheel drive, with the ability to forcibly disable the front axle, stand apart. On such vehicles, the transmission combines part-time and full-time. Among them Mitsubishi pajero, Nissan pathfinder, Jeep Grand Cherookee.

In "Padzherik", for example, you can choose one of several transmission modes: 2WD, 4WD with an automatic central differential lock, 4WD with a hard differential lock, or a lower gear. As you can see, here you can find references to all of the above all-wheel drive systems.

Some front wheel drive cars may have a driving rear axle. A small electric motor is mounted in the main gear housing, which is connected at the request of the driver - the e-4WD system. The electric motor is powered by a car generator. Such a system improves vehicle handling on the track in a rainstorm, and also helps to confidently navigate snow-covered, icy and muddy sections of the track. The latest BMW models are a striking representative of cars with this system.

Let's talk about all-wheel drive, you will learn about the advantages and disadvantages of all-wheel drive, as well as what four-wheel drive is like.

Once a similar topic has already been raised, I reasoned in it, Today I decided to supplement the series of articles on car drives with another, quite logical topic about all-wheel drive vehicles.

For some, this topic will seem strange, since most motorists consider all-wheel drive to be flawless and reliable, but practice and numerous reviews cast doubt on this statement.

To begin with, I want to make some clarity about what all-wheel drive is and how it happens. Four-wheel drive is a type of drive in which, coming from the transmission, is transmitted to all four wheels. Four-wheel drive cars can have permanent all-wheel drive (AWD) or plug-in (4WD). The differences between the first and the second type are quite understandable, in my opinion, in the first case you constantly have four driving wheels without the ability to turn off the front or rear axle. In the second case, such an opportunity exists, and the driver decides at his own discretion when and under what circumstances to connect the front or rear axle, and turn his car into an all-wheel drive and vice versa.

With permanent all-wheel drive, everything is more or less clear, but why is it possible to connect the drive? And you need it in the following cases:

When one drive does not cope with its task, for example, when a car is bogged down in mud;
In the case when the track is slippery and the driver can use four-wheel drive to increase stability;
Four-wheel drive allows better acceleration from a standstill, and improves the dynamics of the car.

Why is it necessary to turn off the four-wheel drive?

All-wheel drive is disabled most often for the following reasons:

Driving on a flat, clean track, where there is no need to use four-wheel drive and spend torque to rotate another axle;
Reducing the noise level, which increases when connecting additional. axles;
Driving in certain conditions where only rear-wheel drive or front-wheel drive is required (for example, sports).

The distribution of torque is due to the differential. In modern four-wheel drive cars, as many as three differentials can be used. Each of them allows you to distribute torque to one or another axle, depending on the needs of the driver or according to the settings laid down during the production of this car. A distinction is made between center, front and, of course, rear differentials. The central one is more stressed than others, since its task is to receive torque and distribute it between the rest of the differentials.

It should also be noted that the four-wheel drive does not always evenly distribute the torque along the axes. Quite often, the owners do not even realize that, for example, the front axle in their car receives only 40% of the torque, and the remaining 60% goes to the rear axle. Also, in the new all-wheel drive systems, the electronics are able to “cleverly” distribute the force along the axles on which there is better grip on the road surface.

All-wheel drive advantages

Now I propose to briefly list the main advantages of four-wheel drive cars.

Well, first of all, it is increased cross-country ability when it comes to SUVs and crossovers.
Stability. Today, you will not surprise anyone with an all-wheel drive sedan, hatchback or coupe. Four drive wheels improve the dynamics and stability of the car on the road. An abrupt start without slipping is common for an all-wheel drive car, while on a front- or rear-wheel drive car, a sharp start almost always ends in slipping.
On slippery roads, four-wheel drive cars are more stable, and the wheels are less prone to slipping, since all four wheels work.

Cons of all-wheel drive

As I said, despite the many advantages, all-wheel drive has its drawbacks.

The main disadvantage is, perhaps, fuel consumption. In four-wheel drive cars, it is, as a rule, always higher than in similar cars with mono-drive, take at least one that is found in both front-wheel and all-wheel drive versions.
The second drawback is expensive repair and maintenance. Due to the complex design and serious loads, the drive mechanisms often fail, complicating the situation by the fact that repairs are not cheap. Plus, it is not possible to repair the "bridge" or replace the gears at every service station, you will have to look for a service that specializes in this kind of work.
The weight. Four-wheel drive cars have a more complex device and more nodes, which make it heavier in order.
As strange as it may sound, sometimes the presence of an all-wheel drive on a slippery road turns out to be a big drawback. Of course, a car is more resistant to drifts and slippage, but if the car already suffers, then it is much more difficult to align an all-wheel drive car, especially for beginners. As you know, when driving on a rear-wheel drive car on a slippery road, if the car starts to sway, most often it is enough just to release the gas and make a few correct steering movements. On the front-wheel drive, on the contrary, it is recommended to add gas, as a result of which the car comes out of a skid. But on all-wheel drive cars, as I said, if the car goes into a skid, then only a professional can cope with this unpleasant phenomenon, and even then not always. Newbies in most cases simply do not know how to behave, release throttle, like on the rear wheel drive, or add, like on the front one?

Also, I often heard about the inadequate operation of all-wheel drive systems, when the car for no apparent reason fell into a skid and generally refused to respond to the steering wheel and pedals. While mono-drive cars crossed this section without any problems.

Summing up the above, I want to note that any type of drive has its pros and cons. Four-wheel drive is no exception, in some situations these are solid pluses, and in others - some minuses. If you love to drive and know a lot about cars, then an all-wheel drive sedan or station wagon will come in handy for you. The same can be said for off-road enthusiasts, if you often travel on bad roads or rough terrain, then four-wheel drive is what you need. If you mainly drive around the city or village, save fuel, do not plan to participate in races and do not like off-roading, then I can safely say that four-wheel drive is not yours!

In general, everything largely depends on a particular situation, as well as the skills of the driver and his ability to control the car. I have everything, I hope I was able to reveal the topic and weigh all the pros and cons. Write in the comments what you think about this and what the pros and cons of four-wheel drive are known to you, and of course, share your experience of owning and driving four-wheel drive vehicles. I will also be grateful for reposting this article on social networks, for this there are special buttons at the bottom of the article.

Good luck to everyone on the road! Bye!

For confident off-road travel and cornering, all four wheels need to be “worked”.

Currently, there are several ways to distribute torque to the front and rear axles. Consider which four-wheel drive is better - permanent or plug-in.

This scheme is equipped with three differentials (interaxle, front interwheel and rear interwheel). The classic ratio of the distribution of torque between the axles is 50:50. In some modern cars used asymmetric differentials 40:60 or 30:70. To improve off-road performance, various central differential locking systems (viscous couplings, electronic hydromechanical couplings) are also used.

Permanent all-wheel drive according to this scheme is installed on Land Rover Defender, Land Rover Discovery, Mercedes G-class, Lada Niva, etc.

Pseudo-permanent all-wheel drive

Most often found on crossovers that are not structurally four-wheel drive vehicles. In them, the four-wheel drive is connected automatically by means of a viscous clutch. For the first time this technology was introduced by Toyota, which called this scheme V-Flex Fulltime 4WD.

There was no center differential in it, and the transfer case was an angular gearbox connected to the cardan. A V-Flex II viscous clutch was installed in front of the rear gearbox. When the front wheels slipped, it closed and connected the gearbox input shaft to the cardan. Thus, in the absence of a speed difference, the car remained rear-wheel drive.

Over time, problems were discovered associated with the impossibility of complete blocking, slow response of the viscous coupling, its low durability and reliability. Therefore, the viscous coupling was replaced by an electronic hydromechanical coupling. In the new scheme, the torque was transmitted by a package of hydraulically compressed friction discs.

The electronic control unit made it possible to connect a rear-wheel drive with a metered distribution of torque in different proportions. It is triggered both when slipping and depending on driving conditions. Until the moment the all-wheel drive is connected, the car remains mono-drive. The most common electronically controlled hydromechanical couplings are Haldex couplings today.

Pseudo-permanent all-wheel drive according to this scheme is put on BMW cars X5, Ford Kuga, Chevrolet Captiva, Honda cr-v, Hyundai Tucson, Hyundai santa Fe, Infiniti EX / QX / FX35, Nissan X-Trail, etc.

This is the simplest all-wheel drive option. The scheme provides for the possibility of connecting a rear or front drive in addition to the drive axle. There is no center differential. V transfer case there is a reduction gear for driving in especially difficult conditions. Four-wheel drive can be engaged with a special lever, pneumatic or electric drive. To reduce fuel consumption when driving on public roads, mechanical freewheel clutches (with an electric drive or manual) are provided, which disconnect the drive shafts from the wheels.

The plug-in all-wheel drive is simple in design and reliable in operation. The disadvantage is the ability to use it only in off-road conditions. This scheme is used for Jeep Wrangler, SsangYong Rexton, SsangYong Kyron, Suzuki Jimny, Great Wall Haval, UAZ, etc.

The ability to disable all-wheel drive with a center differential was the first to be implemented by Mitsubishi engineers who created the Super Select system. This decision was then repeated at Toyota, where, after several improvements, a similar MultiMode system was created. The switchable four-wheel drive allowed to save fuel on public roads and at the same time to move on the most severe off-road.

In fact, in this system, the designers have combined all options for all-wheel drive, giving drivers unlimited freedom of choice. Disconnectable four-wheel drive according to this scheme is installed on Mitsubishi Pajero, Lexus / Toyota Land Cruiser cars.

Which is the best all-wheel drive - permanent or plug-in?

For fans of high-speed driving, cars with permanent all-wheel drive with electronic control are preferable. If the machine is operated in moderation and 4WD is needed as insurance, plug-in 4WD (manual or automatic) is fine. For outdoor enthusiasts, the possibility of "hard" engaging all-wheel drive or locking the central differential with a downshift in the transfer case is suitable.

In any case, always remember that an all-wheel drive car will cost you more. Therefore, think carefully before purchasing vehicle with this option.