The system of full drive appeared in the middle of the last century, and the technology itself was constantly modified, providing maximum permeability and improved car handling. Let's talk in more detail about the varieties of the full drive and the advantages of such a transmission for the car.
If initially the full drive system was used only on SUVs, which were intended for utilitarian use, then subsequently many automakers began to equip their jeeps and cars with such transmissions that improved the controllability of the machine, providing excellent permeability. The company, which developed a four-wheel drive called Quatro, was the pioneer in this area and installed it for many of his cars.
Today, the full drive system is widely used by large automakers, which offer passenger modifications of their cars, having an intelligent four-wheel drive, which allows you to optimally redistribute torque, thereby providing improved handling and permeability. Thanks to the improvement of the technology, it was possible to significantly reduce fuel consumption of such machines, improving the overall reliability of transport.
It is not surprising that today many buyers, choosing new cars, prefer all-wheel drive models, which not only provide improved handling, but also allow themselves to feel confident in winter time when the roads are shut off and covered with bare ice. In this case, the all-wheel drive system allows to ensure the safety of the car operation, preventing its drift and unmanaged sliding on the icing road.
The design of the manual full drive connected was popular in the recent past, but today it is considered to be outdated and practically does not occur on modern cars. The principle of operation of such a manual all-wheel drive system is quite simple. In the usual mode, the machine is a monodiferous, and only after activating the driver of the full drive system, the torque is supplied to the front and rear axle in a percentage ratio of 50 to 50. In fact, this mode of operation of the car is possible only on off-road or slippery road. But on a solid coating, cars, which have a redistribution of torque 50 to 50 to the front and rear axle, will turn badly, and the control of the machine becomes unsafe.
Today, most large automakers have abandoned such a design, so manually connected four-wheel drive can only be found on machines that have a utilitarian value, and are designed specifically for their operation in off-road conditions.
Permanent actuator system
In the eighties of the last century, many automakers began to conduct active developments in the field of creating a system of permanent full drive. As a result, they managed to develop transmissions with axial self-locking differential, which used Torsen or Viscuft. Cars with such constant full-wheel drive combined their convenience, excellent handling and improved permeability. Today, such a full drive system is installed on Lada 4 cars 4, 200 and many others.
Subsequently, the system of permanent full drive has been developed, and began to be called the selective, in which it is possible to manually and automatically turn off the front axle, after which the car becomes, in fact, rear-wheel drive, which improves its handling with high-speed aerobatics. Such a system with automatic disabled with full drive allows to significantly reduce fuel consumption, which is appreciated by many car owners.
Today, many cars are partially managed by automatic, including a special unit is responsible for managing the full drive. The automatic system receives signals from wheels, steering, as well as other sensors and gives a signal to connect a full drive, or turns the car into a classic rear or front drive. Difference of such a system from selective is the ability to fully transfer the torque on one axis, while when there are two axes of the car, the torque can be optimally redistributed, which provides improved car handling.
If initially such an automatic four-wheel drive was installed personally on extremely expensive cars, today even budget crossovers can boast such a system that simultaneously improves their permeability, with excellent handling and fuel consumption saving. And the drive can be distributed over various technologies. It can be a multi-disc combination of Haldex, which is often used on concern cars and more advanced electronic systems in which rear semi-axis and hypoid transmissions are used. In the latter case, it is possible to change the torque even between the wheels on the same axis. All this significantly improves the car's passability, since if the wheels have dropped the wheels on the left, then the automation rolls the torque on the right wheel, which allows you to rescue the car from the captivity.
Four-wheel drive in electric car
Popular electromotivers today are also equipped with a full drive system. However, thanks to the design features, such a drive for each wheel will be significantly simplified, since it is not necessary to mount the Viscuft and the entire transmission, and a separate electric motor will be responsible for bringing each wheel. Automation only sends signals to such drives to an increase or reduction of power.
Features Maintenance of the full drive
There are no particular features in service maintenance of such cars. The only thing that could be delivered to a certain concern is often the resulting shruses, which on the all-wheel drive transmission accounts for an increased load. Therefore, the car owner will be required every 50,000 kilometers and more often carry out the replacement of shruses, which will ensure the selection of the vehicle operation.
The main and unchanged "acting person" of all full drive systems is a transfer box: a special unit that gets torque from the gearbox and distributes it to the front and rear axles. But the method of distribution, as well as layout schemes, there are several.
Complete drive systems are made to three types:
Permanent four-wheel drive (Full-Time)
Pros:
- reliable "indelusive" design;
- the ability to drive with a full-wheel drive both off-road and on asphalt.
4Matic Permanent Dual Drive System (Mercedes-Benz)
Minuses:
- complexity compared to a rigidly connected drive;
- big mass;
- the complexity of the controlback setting;
- increased fuel consumption.
The first thing that comes to mind when there is a task to convey the torque into two axes, is to firmly connect them to the distribution of iron pipes. But here is not enough: when turning turns, the car's wheel pass different ways.
If you rigorously connect the axes, then some wheels will go, and some kind of slip. In the mud when the coating is soft, it is unstable. At the time of the Second World War, let's say, the legendary "jerseys" quietly went with rigidly connected axes, because they were exploited exclusively on off-road. But if the coating is solid, then these slips will generate the twist oscillations and slowly, but correctly destroy the transmission.
Therefore, in the transfer box of vehicles with constant full-wheel drive, the inter-sieve differential is located - the mechanism that distributes the power between the axes and allows them to rotate at different speeds. And if some wheel slows down, the turns of the other are increasing, but the torque falls on it.
All this is great while we are going on asphalt, and what to do, if we are stuck in the rear axle? On the front wheels, which will stand on a solid surface, will be the moment but there will be no revolutions, but the rear will rotate very quickly, but the moment on them will be small. Little will be the power on the rear wheel and exactly the same power of the differential will apply on the front. In this case, you can at least be a whole eternity - still do not shift.
For such cases, differential is supplied with lock - when it is turned on, the speed on all wheels is the same, and the moment depends only on the clutch of the wheels with the road.
Due to the presence of additional nodes (differential and lock), the entire system is obtained sufficiently heavy and complex. In addition, the permanent transmission of the moment on all the wheels increases energy loss, and therefore worsens the dynamics and increases fuel consumption.
The permanent four-wheel drive in the automotive industry is still used, although recently this system gradually displaces four-wheel drive on demand, which will be discussed further.
Hardly connected (part-time)
Pros:
- reliable mechanics;
- maximum simplicity at high passability.
Minuses:
- on the asphalt with a full drive can not ride.
From differential and locks, you can also refuse, provided that one of the axes will be temporarily disconnected. By such logic, the system has a rigidly connected full drive.
The axes are connected to each other without differential, and the moment is distributed in a strict ratio. As a result, high passability and minimum costs.
Part time today is almost extincted and used only on purely off-road cars. The modern driver is uncomfortable to use this system. Connect the axis only in a fixed state so as not to damage the mechanisms. Well, if after pokatushki in the forest, go on the highway and forget to turn off the four-wheel drive, that is, the risk to ruin the whole transmission.
Four-wheel drive with coupling
Pros:
- low cost and simplicity of the device;
- small mass;
- the ability to fine system settings.
Minuses:
- weak reliability and resistance to overload;
- instability characteristics.
The hard blocking of the differential is not bad on the off-road, but how to make the full drive system dose in the dynamics? There is always different sink degree ... The decision was found in the mid-50s.
Active Torque Split AWD system for Mazda CX-7 with a multid-sized coupling instead of the mid-sieve differential
An ordinary mechanical differential was supplemented with a viscous clutch (Viscounts). The Viscouft is a part in which rows of blades associated with input and output shafts rotate in a special fluid. The input and output shafts are freely rotated relative to each other, but the secret of the coupling is in the filler, which, when increasing the temperature, increases its viscosity.
With ordinary movement, light turns or slipping of the clutch wheels does not interfere with the mutual movement of the blades, but as soon as the difference in the speed of rotation of the front and rear wheels grows, the fluid begins to mix intensively and heat. At the same time, it becomes viscous and blocks the movement of the blades relative to each other. The greater the difference, the higher the viscosity and the degree of blocking.
Today, couplings are used both in diagrams with constant full-wheel drive together with mechanical differentials and independently. They are connected to the leading shaft with a distribution, and the slave with an additional axis. If necessary, when one of the axes of the buxic, part of the moment through the coupling goes to it. What's next?
The further evolution of the total drive systems, apparently, will be associated with electric motors. The first electric car with the engine on each wheel shown at the World Exhibition in Paris 1900 Ferdinand Porsche. Then it was, as if said, "non-viable concept car". Motors were too heavy, and the design is expensive. Now this scheme is clearly more prospects.
There is a potential and a hybrid scheme, where one axis is driven by an internal combustion engine, and the second is an electric motor. However, if we talk about the real SUVs, then no electricity and friction clutches will not replace cheap, simple and hardy mechanics.
The reasoning about the car with which drive is better to choose, rear, front or complete, refer to the discharge of disputes about which gearbox is better - mechanical, robotic and whether automatic, or on the advantages of a gasoline engine over diesel and vice versa.
But once the car enthusiasts of the year will mutate the topic of the drive, it means that they still have not yet realized that the advantages and disadvantages of each of the transmissions mentioned. In this article we will tell about the advantages and disadvantages of the front, rear and full drives, and let the reader on the basis of our arguments let them make a choice - the car with which transmissary it will be suitable.
Selection number 1. Rear drive
If only lists the brands that produce cars with rear-wheel drive, it will become clear why many motorists seriously think about buying a car with such a type of transmission. Just listen to these names - BMW, Mercedes-Benz, Jaguar, Porsche, Rolls-Royce, Bentley. Hands, as they say, they themselves stretch to stronger behind the wheel of cars of these companies.
Why such famous firms give preference to the rear drive? Of course, they have models in the cohort and with other types of drives (front and more often complete), but rear-wheel drive cars are most popular.
The answer is simple: it's all about comfort and better controllability than that of vehicles with front-wheel drive layout. Speaking about rear-wheel drive cars, it is impossible not to mention such sports cars as Nissan Skyline, Toyota Celica, Honda NSX - icons of lovers of automotive racing. That is, we make intermediate output, rear-wheel drive choose lovers of comfort or speed driving.
Now let's briefly stay on the design features of the rear drive. The design of the vehicle with rear-wheel drive can be with any engine layout: front-engine, medium-engine or rear-engine engineer. The power unit in such cars has a longitudinal or opposite location. The torque from the engine is transmitted to the rear axle, which is the leading.
In addition to various engine configurations, a feature of a car with a rear-wheel drive layout is the presence of a cardan, and accordingly, the tunnel walking along the bottom of the car and preventing the rear row passengers sitting on the sofa in the middle. However, since most of the modern cars with rear-wheel drive from the premium class, then the landing formula they have 2 + 2 - that is, behind two full chairs, separated by the tunnel, to which the table is placed.
Pluses of rear drive:
- almost complete lack of vibrations from the engine, which in rear-wheel drive cars has a longitudinal or opposite location and suspended on mitigating elements;
- great loading of the rear axle during overclocking, which allows you to unload the front wheels and provide the best grip with the road surface of the rear, drive wheels without slipping;
- a more controlled drift of the car, which occurs at a relatively low speed than the machines with other types of drive, and, therefore, easier to be fixed - it is enough to lose gas and turn the steering wheel towards driving;
- the lack of jet moments on the steering wheel when the car accelerates. This is explained by the fact that the front wheels that are conjugate with the steering mechanism are not leading;
- a wide variety of rear-wheel drive control techniques at speed - that racing lovers especially appreciate;
Reduced, compared with the front-wheel drive car, the rotation radius, which is due to the lack of limitations of the angles of rotation of the front wheels of the rear-wheel drive car with hinges of equal angular velocities; - the optimal distribution of torque between the front and rear axle: the front wheels are rotated, and the rear "push" the machine forward.
Cons rear drive:
- the cost of producing a rear-wheel drive car is higher than the front-wheel drive due to a more complex design; - the presence of a massive cardan shaft and a tunnel coming from the motor to the rear axle, beautifies the useful space in the cabin and increases the curb weight of the car;
- the worst, compared to the front and all-wheel drive vehicles, the patency on loose snow, a big tendency to drift on the icing road.
Selection # 2 Front Drive
Most modern cars have obtained an advanced arrangement mainly due to the simplicity of such a design and a lower cost in production. In addition, more compact motors were installed on cars with front-wheel drive, located not along the rear-wheel drive, but across the body.
And the absence in the design of the cardan makes the front-wheel drive car on one side more compact, and on the other, it allows you to get a more voluminous useful space in the cabin and the luggage separation of the machine.
Since the windows with the front-wheel drive are most common, more economical and relatively cheap, they choose a greater number of buyers.
A little about the design features of such cars. As can be seen from the name, the main feature of this type of drive is the transmission of torque from the power plant to the front wheels. The front-wheel drive layout allows you to create six variations of engine placement - three in longitudinal and transverse planes. At the rear-wheel drive layout of such variations four.
Transversely arranged motors at front-wheel drive cars can be located before the front axle, above it and behind it. Exactly the same installation options have a longitudinally located engine. In addition, the front-wheel drive cars have the ability to differently compose the power unit.
In a sequential layout, the engine is located the main transmission, behind it - the gearbox. In parallel layout, the motor and gearbox are located on parallel axes and at the same altitude, and, finally, in the so-called "floor" layout, the engine is above the transmission.
Pluses of the front drive:
- relative cheapness of production and maintenance;
- the absence of the cardan and the rear axle crankcase allows you to make a car compact, easier and spacious both in the cabin and in the luggage compartment;
- the best front wheel grip strength with slippery expensive due to the fact that the engine and transmission are located in the neighborhood, and not separated, like rear-wheel drive cars;
- the best dynamics and efficiency of front-wheel drive cars due to lower exhaust mass;
- the best, compared to rear-wheel drive cars, permeability on loose snow due to the fact that the front wheels have an optimal adhesion with a road surface due to the mass of the engine located in the front;
- excellent course stability and an easy degree of insufficient turning, in which the velocity car is trying to return to the straight trajectory of the movement itself. This is definitely affecting the best safety of the front-wheel drive car.
Cons front drive:
- due to the location of the engine on the front axle and its rigid "coupling" with the core, vibrations from the engine are transmitted on the body, which makes comfort inside the cabin below than in a rear-wheel drive car;
- the steering wheel are transmitted to the steering wheel when overclocking, which complicates the management of them;
- there is a torque of the wheel slip with a sharp acceleration of the car. This is due to the fact that when accelerating the weight from the front axle goes to the back, the front wheels lose the grip with the road surface;
- large load on the front tires that perform a major role when accelerating, braking, car corners. Accordingly, their life is reduced.
Selection number 3 four-wheel drive
Perhaps the most desired one of all drives for Russians is complete. It is great for riding on our, far from ideal roads, and is a reliable assistant when overcoming off-road. Currently, the popularity of cars with full drive is growing.
Moreover, this refers to machines that are involved in the system connected full drives, which allows such models to have good dynamics and be economical. The most optimal option is crossovers that the base is the drive to the front wheel, and the rear axle is connected (departure to off-road).
It turns out that all-wheel drive cars will come up by the one who often drives off the road.
A few words about the design features of all-wheel drive cars. The four-wheel drive allows you to transfer torque on both axes simultaneously, which ensures optimal clutch of the wheels with the road surface. Three groups of all-wheel drive transmissions are distinguished: a permanent four-wheel drive, connected four-wheel drive and automatically connected four-wheel drive.
A permanent four-wheel drive in its design has an inter-seed differential with locks, a transfer box. The automatically connected full drive in the design does not have an inter-axis differential, the master is only one axis (most often - rear), and the second connects automatically, as soon as the intelligent full drive system detects that the wheel of the drive axis has lost the adhesion with the road.
The full drive connected at the request is also there is also no mid-sieve differential leading is the front axle, and the rear is connected through multi-disc clutches.
Pluses of a full drive:
- excellent clutch of all wheels with a road surface, which ensures the absence of slipping when attaching on slippery surface, as well as high cargo vehicles;
- the best controllability at high speed due to optimal rapes along the axes (characteristic of all-wheel drive sports cars);
- high reliability of the design (especially in a permanent full drive);
- relative simplicity of designs in vehicles with connected full drive (cars with constant full-wheel drive construction is more complex);
Cons of full drive:
- increased noise of transmission;
- uncomfortable control in conditions of movement in the city streets;
- the high weight of the all-wheel drive transmission, which directly affects the dynamics and efficiency of such a car;
- high maintenance and repair.
So, weighing all the "for" and "against" cars with rear, front and full drive, every car enthusiast can make its reasonable and subjective choice.
Recently, crossovers are increasingly gaining their popularity, and are in constant demand among consumers.
What is the whole secret? And how to choose the right crossover with the necessary equipping? Let's try to answer these questions.
The logic of reasoning when choosing the right equipment
The crossover can be attributed to a light SUV. In one car, the car combines all the consumer quality of the car: from large clearance to the all-wheel drive system. Using the big clearance, the crossover can easily come on the highest borders, and using the all-wheel drive system, you can easily leave the most complex snowdrifts.
Each crossover has its own characteristics, some consumers choose high clearance, some drive, and someone spacious interior. How to make the right choice? Crossovers can be with a plug-in front or rear axle, or can go with a constant full-wheel drive. In order to navigate in such a system, it is necessary to consider which there are crossovers with constant full-wheel drive.
The Chinese supplier Greatwall suggested a complete drive crossover, among them the Chevrolet Niva can be noted in the price category of 459000-55700 rubles and the LADA 4 × 4 crossover with a price of 354,000 rubles. These cars, regardless of the year of production, are always widely popular with consumers, with a constantly connected full-wheel drive and the same distribution of the torque of wheels to all axis of the crossover.
All all-wheel drive crossovers need good driving skills and understanding the work of the car. All cars are practically going with an independent rear suspension type McPherson. This feature is necessary in order to fully sense the properties of the car.
Usually when the car enthusiast is going to buy a crossover, he draws attention to all-wheel drive crossovers with large clearance. In such cars there is no blocking of differential and a decrease in transmission transmissions. Such a crossover is great for a comfortable ride in winter, and for the roads in the warm season he will delight his even ride. Big clearance does not affect the price category of the car, because basically everyone pays attention to the compactness of the model and on its dynamism. Basically, these crossovers are not found on off-road, but on the usual highway, which also eliminates the choice of crossover with high clearance.
The list of the most popular crossovers with large clearance includes: Opel Moka (with clearance in 19cm), Chevrolet Tracker (with a clearance of 15.9 cm) - We learned about it in detail in detail, Nissan Juke Nismo (with 18cm's clearance), Toyota RAV4 (with clearance 19.7 cm), Infiniti JX (with 18.7 cm), Subaru Forester (with clearance 21.5 cm), Volvo XC60 (with magnitude 23cm) and Range Rover E-VOQUE (with 21.5 cm). The Range Rover E-Voque crossover is considered the best in its class by passability.
Crossovers can hardly be called real SUVs, as the road clearance of SUVs is 30 cm, but they have less opportunities than in crossovers. Depending on the configuration of the car, their ground clearance will change. Basically, if the model refers to microkers (model Chevrolet Tracker), then the lumen will be less. Microcrossums due to their compact configuration often include cars type sedan. The main reason which distinguishes crossovers from SUVs, this is a comfortable ride of the first in urban areas and light off-road.
Crossovers with plug-in drive
If the drive is connected via the coupling, in this case the aggregates are called - crossovers with a plug-in. That is, the coupling connects the second axis depending on how the wheels from the non-connected axis are scrolled. This type of drive can be rightfully attributed to the intellectual type. Usually the second axis is automatically connected depending on the type of road: road / off-road. If you use a four-wheel drive on an uncharacteristic road, you can damage the mechanisms in the car.
Therefore, to the question "Does the crossover need a four-wheel drive?" It can be answered in this way: "It is necessary if the transport is dealing with constant off-road, and constant complex situations on the road, bad weather conditions, snowdrifts and mud. If the crossover hold most of the time on the road highway, it is better to use a single-groove car, most often with the rear axis. The ideal option will be the purchase of a crossover car with a plug-in. "
Among the rear-wheel drive vehicles with a connected front-wheel drive, such popular crossovers can be distinguished: Suzuki Jimny sums of 746,000 rubles, UAZ Patriot and UAZ Hunter sum of 529,000 rubles and 454,000 rubles. Also crossover Hoverm2, HoverH3, HoverH5, HoverH6 from 549,000 rubles to 749,000 rubles.
A bright example of front-wheel drive crossovers with a plug-in with a clutch is: Renault Duster in the amount of 541,000 rubles, Chery Tiggo sum of 619,000 rubles and Suzuki SX4 Classic amount of 729,000 rubles.
Excluding all-wheel drive for SUVs, single-groove cars appear, mainly with front-wheel drive, which are called crossovers for use in urban areas. These crossovers have a much lower than the price than all-wheel drive relatives. The front-wheel drive crossovers will behave perfectly on the off-road, rather than the rear-wheel drive. The leading axis of such cars is always under load, since the engine is constantly weighing from above, making the best grip with a road surface. Using rotation wheels with steering wheel, you can easily maneuver in any situations on the road.
Formation of prices for crossovers
Usually, front-wheel drive crossovers are obtained from a simplified version of the all-wheel drive unit. To familiarize yourself with the prices of such a management system, it is proposed to view the front-wheel drive crossover overview:
- Suzuki SX4 NEW cost 779,000 - 1,019,000 rubles;
- Nissan Qashqai cost 789,000 - 1,096,000 rubles;
- Nissan Qashqai +2 cost 844000-1049500 rubles;
- Citoren C4 Aircross cost 849,000 - 1 124 000 rubles;
- KIA Sportage cost 889 900 - 1,049,900 rubles;
- Hyundai IX35 cost 899000 - 1 144 900 rubles;
- Mitsubishi Outlander cost 969,000 - 1,249,990 rubles;
- Peugeot 4007 cost 989 000 - 1,074,000 rubles.
Mostly, the price of cars depends on whether complete drive will be complete or not, which ground clearance is installed in a crossover, what type of suspension front and rear McPherson type (mostly semi-dependent), which brakes of the rear and front axle. As a rule, in front-wheel drive crossovers, the road lumen is at least 175 mm, the wheelbase is 2.5-2.6 m. They can easily pass the border and pit on the primer, which makes them indispensable in the choice for Russians.
The front-wheel drive crossovers have the insides of a small or medium-power gasoline engine. Crossovers go with one engine, only some models use two options immediately. Some models of front-wheel drive crossover types KIA SOUL go with a diesel engine, only the price policy goes beyond the limits of budget vehicles.
Due to the fact that the car is equipped with one drive, it consumes fuel 2-3 times less than the all-wheel drive crossover. Most crossovers go with a manual transmission, an automatic gearbox is not included in category 750000 rubles. Basically in Europe, on the contrary, choose a mechanical transmission, as it consumes less fuel.
Thus, than installed more configurations in the crossover, the more expensive it is worth it. Optional, acquiring an advanced-drive crossover, you can constantly supply it with new items and install new packages, thereby the price will not be so expensive when buying. Do you need a four-wheel drive? The question is serious, it all depends on the real necessity or the vast desire for the driver. Before buying a car, appreciate everything and against the purchase of the necessary drive.
In this detailed test drive, the new Great Wall Hover H6 is absolutely justified by the "thoroughbred" for its four-wheel drive:
The all-wheel drive car is now perceived as something of granted: all drive wheels, allegedly, provide tremendous safety on the road and confidence in their abilities. That is why, if there is money, we buy all-wheel drive crossovers for their wives. However, the full drive systems even in the first approximation there are quite a lot, and they differ fundamentally among themselves.
Choosing a car and targeting the "full-wheel drive", you need to imagine very well, where and why the car will use. Probably, 90% of buyers are not going to move from a normal road in the forest, fields, and climbing the mountains and cross the brodes. Why do you need a car with all the leading wheels? First, she attaches confidence during rain on a slippery road; Secondly, the car is bought with an exploitation of exploitation by long winter; Finally, it's easier to move easier from the asphalt and get there Polkilometer to the cottage along the primer and Uhabam.
The simplest thing you can remember, and then close this article: the above three tasks solves the car with the drive only on one axis. It is desirable, right to be with a manual transmission. Well, the clearance would be good more.
Suppose such a solution to the problem does not satisfy you. Then the second consideration: the all-wheel drive crossover is not at all equal to the present SUV. The wheels of these cars are given in motion, let's say, in principle in different ways. And the third: Yes, the designated need for a full drive can be satisfied with the purchase of the crossover. Just on a similar car, you do not need to travel through the right off-road. And on the road - not to get involved in speed.
So, as in general terms, a four crossover drive is arranged. Almost always you are on such a car ... Monophoderous mode, only one axis works in motion. Most often - the front, because almost all are not too expensive crossovers are built on platforms of ordinary hatchbacks. The four-wheel drive manifests itself only in the slip of the leading wheels - this moment is recognized by electronics, which connects to the second axis to help. The slip in this case does not mean that you are standing in place and long grinding asphalt - it's literally about milliseconds. It is unlikely that the buyer is interested in the technique, let's just say that it is transferred to the moment between the axes - and it is dynamically distributed at every moment of time - a special coupling is engaged. This device itself may have a different design.
Now about off-road abilities: if the scheme fully corresponds to the description above, there are practically no. To overcome the minimum off-road, it has to "hang" additional functionality. For example, the coupling give the ability to partially or completely blocked. Methods may be different, but, again, the electronics are most often maintained. Also in the design, self-locking differential or viscous coupling can be used.
Why do you need blocking? Free coupling (or free differential) will not give the car to go if some of the wheels will completely lose the clutch with the road. And the blocking will turn the wheel, which is still able to pull you. It overheats the coupling in this case very quickly, so you will not work for a long time with such a system.
As in any design, there are many nuances here. The main thing is that the coupling in advanced automatically plugging full drive can work on a preventive algorithm, without waiting for the wheel slip. Here, always on the second axis will be served a small percentage of torque. In other words, you really get a permanent four-wheel drive! So work AUDI systems with Torsen differential, as well as, for example, some BMW or Mercedes-Benz.
Repeat: A similar type of full drive has almost all crossovers and all-wheel drive cars. Pros: Indeed, the car gives some confidence on a slippery road. Cons: the same confidence can lead to the fact that you will choose an incorrect speed for movement in difficult conditions. The result may be curb. Also because the nature of such a car in turn - it will be prone to this dangerous moment to demolition or drift, or will be neutral - it is quite difficult to predict. As for giving the car "SUV", controllability improves with electronics - the main auxiliary system here is ESP.
Now - about off-road full drive. Here the second axis is connected by the driver manually. On the way you are traveling on a monolarier, and if you need to move to some kind of problem area, you turn on the full one. There is no inter-axis differential, so the blocking of one of the interc differentials must be present. And, of course, a four-wheel drive with such a scheme must immediately turn off on the road - it is not provided for work at high speeds.
Finally, the classic of the genre is an honest four-wheel drive. Ideally, it is not just three differentials - the inter-axis and two intercoles, but also downward transmission, and all locks. And, of course, auxiliary electronics. With such a set of properties, the car, really, can stand on the road, and overcome off-road.
Separately, we mention extremely advanced systems: for example, Super SELECT at Mitsubishi allows you to choose from many modes of operation of a full drive that is suitable for both the track and off-road. Some Jeep models can be ordered with significantly different types of full drive. Finally, the Systems in Subaru Impreza WRX STI or Mitsubishi Lancer Evolution each deserve a separate big article.
