Transfer case- this is an integral attribute of every car that is equipped with all-wheel drive. This device performs the function of distributing torque along the axes and increasing it when driving off-road. In today's article, you will learn detailed information about how the transfer case is arranged and what types it is divided into.
Purpose
As we noted above, this box distributes the force, that is, the torque on the vehicle axle. However, the transfer case also performs a number of other important functions. Among them, it is worth noting disabling and enabling the master front axle.
Design features
Usually, this mechanism has a 2-speed gearbox. Depending on it, the gear ratios of the car change. Thus, the number of gears in the transmission can double. The first row of the gear ratio is obtained when the highest (direct) gear is turned off. The second row can be activated in the same way, only in the reverse order - when downshifting. Thanks to this, the transfer case allows the car to move in any road conditions. Every four-wheel drive vehicle has a special mechanism that prevents downshifting while the front axle is engaged. This reduces the load on the rear axle and prevents it from being overloaded with high torque.
The transfer case of UAZ ‘a and all other four-wheel drive vehicles has the same device. It consists of:
- drive shaft.
- Center differential.
- Rear axle drive shaft.
- Chain (gear) transmission.
- differential lock mechanism.
- downshift.
- Front axle drive shaft.
In addition, there are two main types of transfer transmissions:
- Boxes for switchable 4-wheel drive.
- Transmissions for permanent drive for the same number of wheels.
The transfer box of the first type can be switched to the "4WD" (all-wheel drive) mode manually or automatically. When this mode is not enabled, such a car will operate on the principle of a mono-drive system, according to a 4x2 system. Four-wheel drive can be activated in two ways - directly by the driver and through a special module. The transfer box of the second type always works only in the mode all-wheel drive, that is, 4 wheels are involved all the time. Such a "razdatka" transmits a constant torque to the front and rear axles. The wheel formula of such a car is always 4x4 - all of the 4 wheels are leading.
Transmission operating modes
The operating modes of the dispenser are determined by its design. Basically, such a transmission can perform the following functions:
- Inclusion rear axle.
- Both bridges.
- Both axles when locking the center differential or downshifting when locking.
- The mode of inclusion of 2 axles with automatic differential lock.
As a rule, switching modes is carried out using a lever located on the front panel in the car.
Transfer case installed on all vehicles with all-wheel drive, as well as on vehicles equipped with any additional equipment. Purpose of the transfer box all-wheel drive vehicle following:
- distribution of torque between the drive axles;
- increase in torque when driving off-road.
Vehicles with additional equipment mean all kinds of special equipment, such as truck cranes, car lifts, fire fighting equipment And so on. IN this case transfer box provides pluggable drive oil pumps, water pumps and other equipment.
What is a giveaway. The purpose of the transfer case
The transfer case is installed on almost all vehicles with all-wheel drive (for example, Niva, UAZ) or on vehicles with any additional equipment that requires a separate drive, and according to the principle of operation, it is primarily intended for dividing the torque along the axes of the vehicle, hence the name - transfer case. For the first time razdatka was used at the beginning of the last century on cars, which were designed for off-road racing. But most consumers did not immediately understand the full benefits of the "gearbox" (such a name was given to the transfer case after its invention) and were rather skeptical of this innovation. But after applying the dispenser in all-wheel drive trucks the interest of producers and end users in it has increased. Although the main function of this node is the distribution of torque, most of its modifications have additional function in the form of an increase in the gear ratio. This function allows you to increase traction characteristics vehicle, thereby increasing the cross-country ability vehicle which is very useful when driving off-road.
The main functions of the transfer case can be distinguished:
1. Torque distribution over the drive axles, to ensure the vehicle's off-road patency, reducing the circulation power as much as possible.
2. Increasing the torque on the drive axles to reduce the rolling resistance of the wheels when operating the vehicle off-road.
3. Ensuring the steady movement of the vehicle on low speed at work power unit at maximum power.
Transfer box device. Design.
Usually, the transfer case is mounted on the side members of the car using brackets with cushions (buffers) whose function is to dampen vibration loads, but on different cars the layout of the dispenser may have different variants installations.
The dispenser, depending on the model, may have miscellaneous device, but since the principle of operation of the transfer case, regardless of the model, is almost the same, then its device has common basic elements:
- drive shaft
- a mechanism for locking the center differential
- chain or gear transmission for transmitting torque to drive shaft front axle
— center differential
- rear axle drive shaft
- downshift
- front axle drive shaft.
All these elements are constantly lubricated with transmission oil, which is located in the transfer case housing, thereby providing lubrication of all internal elements.
WHY THE TRANSFER BOX HAS THIS NAME
They began to name the transfer case due to the proximity of concepts with the checkpoint. The torque is transmitted at a low vehicle speed, since the transfer case has a demultiplier or a reduction gear. Thus, the machine is able to move in difficult conditions, in the absence of a road. Crossovers do not have such a device due to the fact that they are not designed for off-road use. The demultiplier helps the machine reduce the speed of rotation of the drive shafts. For this reason, a lot of torque is not lost. The low gear allows the car to have a few more gears. In the case of various traffic situations the driver will have more possibilities correctly determine the required gear ratio. 
FAULTS AND REPAIR OF THE TRANSFER BOX
transfer case enough expensive device, so it is necessary proper care And timely repair to increase service life. Very often, drivers complain about the inclusion of gears with the expenditure of effort. Most often this occurs when the rods and gear forks are worn out. This problem is often caused by scuffing on the gear wheels of mechanisms. Can't be ruled out bad job fixatives. If the rods and forks are worn out, they must be replaced immediately. When driving, there is an automatic disengagement of gears. This indicates that the gear teeth are worn out and require urgent replacement.
It also indicates that the fork mounts may be faulty. The high noise level during the operation of the transfer case indicates many factors: poor viscosity of lubricants; damage to gears; faulty clutch; high level bearing wear. You can only replace lubricants on your own, and for everything else you need to turn to specialists. With a small amount of oil, it must be restored to normal. There are cases when oil flows out of the transfer case. There can be only one reason - worn gaskets. To fix this problem, you need to disassemble the box and replace the gasket. The box needs care. The oil level must be checked periodically and topped up. In case of oil leakage, check all seals and tighten the fasteners.
It is better to entrust the repair of all malfunctions of the transfer case to specialists, since many malfunctions cannot be solved on their own. A serviceable transfer case works without extraneous noise. It should not overheat when shifting gears. If these conditions are met, then we can safely say that the box is in good condition. If we talk about the repair of its parts, then you immediately need to understand that this is an expensive procedure. To delay the replacement or repair of the transfer case, it is necessary to regularly inspect and check the entire mechanism. Many drivers who are faced with the repair of a transfer case know that this all requires significant financial investments. Therefore, do not neglect regular visual checks. All faults are best dealt with early on as this will help reduce future costs and ensure good work boxes.
CLASSIFICATION OF TRANSFER BOXES
The modern classification includes the following types of transfer cases:
- according to the location of the drive shafts (with coaxial and non-coaxial shafts);
- for a certain number of gears (one-stage, two and three-stage);
- by type of drive axles (with differential or blocked drive).
Transfer case operating modes.
The mode of operation of the transfer box, depending on design features can be divided into several types:
- center differential is locked and both drive axles work
- the differential is automatically locked and both drive axles are in operation
-both drive axles receive torque (like a Niva car)
-only the rear axle works
-both axles in operation in low gear, differential locked. In this mode, the car has the highest cross-country ability.
Switching the transfer case from one mode of operation to another occurs with the help of a lever (on older generations of vehicles with all-wheel drive) and with the help of buttons. The switching itself can be carried out mechanically, electrically, pneumatically and even hydraulically.
The principle of operation and the scheme of the transfer case.
Surely, many who have encountered all-wheel drive vehicles have wondered: how does the dispenser work? The principle of operation of the transfer box largely depends on its design.
The scheme and principle of operation of the simplest transfer case looks something like this: the gearbox transmits torque to the drive shaft of the transfer case (sometimes there is a retarder between the gearbox and the transfer case), which in turn transmits torque to the center differential. The center differential distributes torque between the rear axle drive shaft and the front axle drive shaft (it also has important function- it allows the axes to rotate at different angular speeds). Further, depending on the mode of operation of the transfer case, the torque is transmitted either to both axles, or only to one. Here also important element is a mechanism for locking the center differential, whose tasks include the complete or partial shutdown of the center differential. This function provides a rigid clutch and, accordingly, the same speed of rotation of the front and rear axle drive shafts.
The transfer case (RK) is installed in cars suitable for driving. In other words, it is present in vehicles with all-wheel drive, but not in those with front- or rear-wheel drive.
The purpose of the transfer case is to adjust the torque working in the undercarriage of the machine. She comes to the aid of cars in the passage of complex and landscape routes.
But let's talk about this device in more detail. First, let's figure out where to look for it.
Where can I find a transfer box?
The location of the PK may differ depending on the make and model of the vehicle.
Sometimes the creators of the car put it on, sharing it with this device.
However, you can often find gearboxes that include transfer cases.
What are transfer boxes?
The purpose and design of the transfer case are inextricably linked. Not all vehicles have the same RC. Most often, these mechanisms differ from each other in their type and structure. There are three main criteria by which one such mechanism differs from another.
- Types of drive shafts. In step-down boxes, they can be misaligned and, conversely, coaxial.
- Locations of drive shafts.
- The number of gears available. This number determines the gradation of the box. They are one-, two- and three-stage.
What is the distribution box made of?
The distribution mechanism itself may differ. There are several ways to collect it. However, there are components that a transfer case device cannot do without.
- First, it is the drive shaft. When using one gear, he is responsible for receiving torque.
- Second, there are four drive shaft. They are placed on the axle at the back and front. They are connected in pairs.
- Thirdly, in such a mechanism there is necessarily a gear or chain transmission of torque.
- Most all-wheel drive cars there is also a downshift. However, we draw your attention to the fact that it is not present in all transfer boxes. So, this link in the chain of the mechanism is absent, for example, in crossovers, which, although they have all-wheel drive, are not designed to drive through difficult landscapes.
- Also in the boxes of some cars with all-wheel drive there is a differential that is installed between the axles, and a lock for the differential.
How does the box work and is it needed?
How does it work?
First, let's figure out how the transfer case works. The principle of operation of the transfer case is that differentials, which are of two types (symmetrical and asymmetrical), divide the torque into axles. The first type of mechanism distributes the torque equally, and the second - not equally, depending on the specified indicators. One way or another, thanks to this device, drive shafts can work with different speed, which increases the maneuverability and stability of the machine when turning and when.
The principle of operation of the dispenser:
Also, a lock can be installed under the differential. This device helps to lock the differential that distributes the torque. After such blocking, the wheels will rotate strictly at the same speed. You can control this function yourself from the inside of the car, or you can set up automatic locking. Such a function is in demand on those machines that have to drive, for example, through long fields.
The transfer box has several modes of operation. It can function:
- with two active axles and differential lock, which is carried out automatically;
- with two active axles, but in a reduction gear with the condition of permanent differential lock;
- with two working axles and with the condition of permanent differential lock;
- with two working bridges;
- provided that only the rear axle is working.
If the box doesn't work
Transfer case malfunctions are different. However, there are several most common ailments of the device:
- Difficult to shift into gear. If you have such a problem, check the rods and plugs of the device. They could wear out as a result long service life. If so, they should be replaced as soon as possible. Also, the cause may be seizures formed on the gears. If none of these reasons applies to you, it remains only to check the latches. Perhaps this problem is caused by their laxity.
- Gears are automatically disengaged while driving. Most likely the gears need to be replaced. Their teeth must have already worn out. If the gears are in order, check the integrity of the fork fasteners. They can jump.
- The box is terribly noisy. First, remember what lubricants do you use? Perhaps their viscosity is not enough and you need to pick up something thicker. The gears could be worn out. Then they need to be replaced. The same reason can be caused by problems with the operation of the clutch or wear of the bearings.
- Oil is leaking from the AC. If you have determined that the oil is flowing from it, just buy new gaskets and ask the master to install them.
Unfortunately, it is almost impossible for an amateur to repair the box on his own. The only thing that a beginner in the repair business can do with his own hands is to produce. For all other procedures, specialist assistance will be required.
Do you need a transfer case?
Like any mechanism, RK has its advantages and disadvantages.
Let's start with the cons. More precisely, from one, but significant minus of the transfer case. The fact is that most of its parts are quite expensive. Therefore, their replacement will be expensive. And those parts that are sold by reasonable prices, are difficult to repair, therefore, they may also require funds from the car owner for the work of the master.
Now the pros:
- When the “razdatka” is operating while the car is moving at low speed, the torque is transmitted to the axles. This increases the cross-country ability of the SUV.
- It is noteworthy that during the operation of the "razdatka" a large torque cannot be lost. This is achieved thanks to the demultiplier. He is an assistant to the machine in reducing the intensity of torsion of the drive shafts.
- Also, the driver of a car equipped with a transfer case has the opportunity to independently determine the gear number.
- When driving in difficult conditions RK will become a friend and assistant to the motorist, helping him " iron horse» overcome terrain obstacles effectively.
- And, of course, one of the leading benefits is that the operation of the transfer case extends the life of the transmission.
But do not forget that no transfer case detracts from the importance of the skill of the driver who decides to drive along difficult areas. After all, even when driving the most “fancy” car, the rider’s inexperience can play a cruel joke on him.
The transfer case is a device that is designed to distribute the vehicle's torque directly between the drive axles. In addition, the transfer case itself can also increase the torque that is supplied to the drive wheels of the vehicle. Often, the transfer case has a device that is responsible for turning on and off the front drive axle. Quite often you can find designs when the drive of additional vehicle units will be provided from the transfer case itself.
In order to increase the torque that is supplied directly to the driving wheels of the car (and this procedure will be necessary under difficult driving conditions), the boxes dispensing type are performed and manufactured in two stages. In this case, the highest gear will have a gear ratio that will be equal to one, and the lowest, that is, the first gear will have the same number of about two. Two gears, if provided in the vehicle, will increase both the number of steps, as well as the range in fluctuations in the change in the transmission gear ratio of the vehicle. It is this that will increase the possibility of an advantageous selection of an optimized transmission, which will correspond to all operating conditions of the car.
Often, transfer case devices with a locking drive are used, when all axle drives are tightly and tightly connected to each other, as a result of which their rotation will always occur at the same angular speeds. Such transfer boxes usually have a device that is designed to disable the front axle drive. This kind of function has its own need when the car is moving at good conditions, on a good road, which will significantly reduce fuel consumption, reduce the load in the transmission part, as well as tire wear.
Some designs of transfer boxes have a special mechanism in their arsenal - center differential. This device distributes the torque that is supplied from the engine internal combustion directly to the transfer box. In addition, this kind of differential allows the wheels of the drive axle to rotate at different angular speeds, which will completely eliminate the possibility of their slippage, as well as reduce the load on the transmission and tire wear of the car. Differentials are used with spur and bevel gears. In order to maximize the throughput of the transmission, differentials are sometimes made with a forced locking device.
1. Classification of transfer boxes.
Due to the rapid development automotive technology, manufacturers have already predetermined several types, the main differences of which will depend on the purpose of the vehicle on which they are provided. So, design engineers distinguish three types of the main transfer case:
- behind the location of the drive shafts of the drive axles (with misaligned and coaxial shafts);
By number and quantity variable gears(1,2,3-speed);
Drive axles (with differential and blocked drive).
All cars that are equipped in factories all-wheel drive systems, V without fail will be equipped with a transfer case.
2. The purpose of the transfer case nodes.
It is important to note that many transfer cases have many peculiar design differences, however, there are shared devices that make up the distribution box. These include: drive shaft, front axle drive shaft, reduction gear, chain drive, rear axle drive shaft, center differential lock mechanism, center differential.
The inclusion of two bridges and automatic locking of the center differential;
The inclusion of two bridges in a reduction gear, which provides for a locking center differential.
Switching the operating mode in the transfer case is carried out by means of a special control lever, buttons on the instrument panel or a special rotary switch.
3. Typical breakdowns of the transfer case.
Transfer case is quite complicated technical node, and there may be many reasons why this device will fail. The main signs of a breakdown of the transfer case will be hidden in the howling sound that occurs during the direct movement of the vehicle on high speeds, vibration of the floor of the body, when the car is just starting to move or accelerate. All the noises and the kind that occur when the car is directly turned, wheel slip will also be witnesses to the fact that certain problems have arisen in the operation of the transfer case. most common problem that occurs with the transfer case is the differential lock. In addition, quite often there is another important problem that comes from spontaneous shutdown gears.
It is important to note that if the motorist is faced with this kind of problem, then you should immediately contact service center, since postponing the solution of this problem indefinitely can "bury" the transfer case of the vehicle alive. Another reason why you should immediately go to repair this unit is the unsafe movement of the car along the highway. This is directly related to the fact that the ability to spontaneously turn off the gear can lead the car into an accident, for example, during any overtaking, at any intersection.
If you look at it, then this device is not too difficult to master and understand, since it has no difficulties in its structural component and mechanical functional. However, its simplicity has nothing to do with its great importance for the successful functioning of the entire vehicle.
The transfer case is an integral part of any four-wheel drive vehicle. Despite the general purpose - changing the amount of torque and its distribution between the rear and front axles, the transfer case device is highly dependent on the type of all-wheel drive. Consider the principle of operation of the main types of handouts.
gear transfer case
The mechanical transfer case is the most archaic and at the same time the most reliable type of design.
As we can see in the VAZ-2121 all-wheel drive diagram, the transfer case is the link between the manual transmission and the drive shafts that transmit torque to the rear and front axle differentials. In the case of the Niva, the transfer case is a separate transmission unit, but on most cars its body is screwed to the gearbox, so there is no cardan to the front axle as such. An all-wheel drive system with such a transfer case is called Full-time.
Principle of operation
Schematic device on the example of VAZ 2121. 
When driving on stable surfaces with high traction, permanent all-wheel drive is not necessary, so the sliding clutch (8) through the hub (7) articulates the drive shaft (12), which receives torque from the engine, with the gear top gear(6). The splines of the top gear are in engagement with the countershaft constant mesh gear. From it, the torque is transmitted to the driven gear (29) and differential (23).
The purpose of the differential is to redistribute torque between the shafts of the rear and front axles. It is extremely difficult to understand its principle of operation and the device without a visual representation, so we recommend watching the video.
In this mode of operation, the distribution of torque is determined by the level of rolling resistance of the wheels on the front and rear axles. Uniform distribution tractive effort along the axes is carried out by the mechanism of blocking the center differential (23). Acting on the transfer case control lever in the cabin, the driver moves the sliding clutch (31), thereby articulating the front axle drive shaft (32) with the teeth on the differential housing. Thus, the satellites are no longer involved in the operation of the differential, which leads to an even distribution of torque between the front and rear universal joints.
Down row
The driver, changing the position of the lever, moves the clutch (8) through the hub (7), provoking blocking of the drive shaft (12) with the lower gear (9). The difference between the drive shaft gears in gear ratio, which when downshifting provides:
- stable minimum speed;
- increase in torque transmitted to the wheels.
Part Time
The transfer case in the Part-Time all-wheel drive system does not have a center differential. By default, these cars have a leading rear axle. Front-wheel drive is connected forcibly at the request of the driver. The absence of a differential means that all-wheel drive can only be turned on on surfaces with a reduced friction coefficient. If this advice is neglected, the forces arising from the different wheel speeds when turning will very quickly disable the transfer case. Video with disassembly of the handout Part-Time.
To summarize, the processes inside the transfer case can be reduced to the movement of sliding clutches that change combinations of rotating gears. The movement of the forks of the sliding sleeves can be carried out both directly through the levers in the cabin, and by pressing the keys on dashboard. In the latter case, the movement of the clutch is carried out by a servo, which is attached to the transfer case.
The Part-Time system is equipped with: Toyota Land cruiser 70 Opel Frontera, Great Wall Hover, UAZ and many other SUVs. 
Why Part-time and Full-time are no longer relevant
Mechanical transfer gearboxes have one undeniable dignity – great resource. The device, in which the distribution of torque between the drive axles is carried out due to the engagement of gears, has no equal in terms of reliability. Therefore, this type of handout is installed on off-road vehicles designed for operation in severe off-road conditions, military equipment.
But since for SUVs and SUVs, which are used mostly in urban areas, reliability mechanical interlocks is not so important, then it becomes impractical to put up with the rather serious shortcomings of an archaic transfer case. Negative sides:
Advantages of modern all-wheel drive systems
Modern all-wheel drive systems make it possible to implement blocking of interaxle and interwheel differentials using an ECU and sensor equipment. By detecting wheel slippage with the help of sensors, the system slows down freely rotating wheels with pads. The rolling resistance force is equalized on both sides of the axle. Therefore, the torque can always be transferred to the drive axle drive with a high friction coefficient.
This is how the electronic simulated differential lock works. Briefly consider the device and the principle of operation of transfer boxes modern systems full drive.
Viscous clutch
The viscous coupling is used both to block the center differential and to connect one of the axles. Structurally, the clutch is a set of discs placed in a dilatant liquid. When there is a sharp difference angular velocities on metal and friction discs, the silicone fluid changes its viscosity, causing clutch lockup and even torque distribution.
The lack of viscous couplings in delayed operation, weak force holding the clutched friction and steel discs. Therefore, the viscous coupling overheats during active operation.
The viscous coupling can be installed in the transfer case or at the rear differential.
Torque on-demand
On this moment all-wheel drive transmission Torque on-demand is the most advanced for use on . Device features of the most common types of TOD transfer boxes:
- hydrodynamic clutch with electronic control. There is no center differential in the design of the transfer case, but there is a lowering row. The inclusion of both bridges is carried out by an incoming clutch, which presses the clutch pack. The pressing force depends on the magnitude of the current supplied to solenoid valve. The transmission of torque between the gears of the input and output shafts is carried out by a chain gear train. The device and principle of operation of a transfer case with a chain drive are perfectly shown in the video;
For a better understanding of the operation of transfer boxes of modern all-wheel drive systems, we recommend that you read the article "".
