Center differential lock: what is it?

Lockable differentials

The problem of proper distribution of torque between the drive wheels has attracted the attention of designers throughout the history of automotive engineering.

Today, in matters of increasing the traction and dynamic properties of a car, non-traditional power distribution mechanisms actively compete with classic planetary differentials.

We have studied some of the features of modern drive axles.

Judging by the information published in the open press, the interest of designers in the problem of power distribution between the drive wheels is constantly increasing. This is explained by the continuous improvement of the design of cars and increased requirements for their basic consumer qualities.

In particular, to controllability, stability, traction, dynamic and braking characteristics, especially when driving on roads with a low and unevenly distributed coefficient of adhesion.

If previously such requirements were imposed only on sports and off-road vehicles, now they apply to production models of various categories, including long-haul tractors and special vehicles.

Today, symmetrical bevel differentials dominate as torque distribution components in truck transmissions. The classic design consists of a housing, four freely rotating satellites and two semi-axial gears.

In a symmetrical cross-axle differential, the number of teeth of the left and right side gears are equal. In essence, this is nothing more than a planetary mechanism that has the property of uniform distribution of torque at any angular speed of the drive wheels.

Equality of traction between the left and right wheels is favorable when driving a vehicle on paved roads with relatively low resistance. In particular, this is reflected in good stability and controllability of the vehicle.

However, if one of the drive wheels, for example the right one, is on a slippery section of the road at the beginning of movement, then the torque on it is reduced to a value limited by the coefficient of adhesion of the wheel to the road. The same torque will be on the left wheel, although it is on a surface with a high coefficient of adhesion.

If the total moment is not enough for movement, then the car will not move and one of the wheels will be stationary and the other will be slipping. In this case, the planetary mechanism plays the role of a gearbox, increasing the angular speed of the rotating wheel.

By the way, a similar phenomenon is observed in the distribution of traction force between the drive axles of multi-wheel drive vehicles with 6x4, 6x6 wheel arrangements, but this is a different, more advanced topic. So, how do you get the differential to redistribute torque in favor of the stationary wheels?

The easiest way is forced blocking . In order to completely block a classic differential, it is enough to either limit the possibility of axial rotation of the satellites , or rigidly connect the differential cup to one of the axle shafts.

The first method is compact and therefore typical for light-duty vehicles, while the second is used in the drive axles of trucks - where there is no shortage of free space.

The locking function is controlled using a pneumatic, electric or electro-hydraulic drive . For example, in the Ural-63674 car, the cross-axle differential locking mechanism is pneumatically driven.

It consists of a working cylinder, a lever, a fork and a splined clutch sliding on the splines of the axle shaft. When air is supplied to the actuator, the clutch is connected by splines to the differential housing and thus creates an obstacle to the free rotation of the axle shaft. The planetary mechanism becomes blocked.

Typically, such a lock is used when driving off-road and in snow, and before driving onto a standard road surface it is turned off in order to avoid increased power circulation in the transmission and deterioration of vehicle controllability.

Unlike pneumatics, the electric locking drive acts directly on the satellites. For example, in the Eaton ELocker differential, which is standardly installed in American Hummer axles, the compact electromagnetic coil is located directly in the differential housing.

When control voltage is applied, the electromagnetic field moves the locking device, which rigidly connects the semi-axial gears, and the drive wheels begin to rotate at the same speed.

The special design of the blocker allows the mechanism to be activated not only in a static position, but also when the vehicle is moving.

As a rule, such a device is complemented by an electronic control unit - the computer protects the mechanism from incorrect activation, because the difference in rotation speed between the left and right wheels at the moment of activation should not exceed 50 rpm.

Electrohydraulic devices are more complex in design. The most famous of them is the EGerodisk differential. Here the locking mechanism consists of an oil pump, a hydraulic cylinder and a set of friction plates installed between the classic differential cup and the axle gear.

The hydraulic cylinder body is attached to the differential cup, and the piston is attached to the axle shaft. When the system is activated, hydraulic force compresses the friction pack, thereby blocking the axle gear with the differential cup. Due to the resulting friction torque, the differential smoothly redistributes torque to the lagging wheel.

Depending on specific road conditions, the degree of blocking can be varied within wide limits. Thus, the high blocking coefficient characteristic of starting from a standstill can decrease as the vehicle speed increases.

The system response time to a control command is about 150 ms, thanks to which EGerodisk interacts perfectly with ABS and ASP. Today, such a system is standardly installed on Chrysler SUVs.

Among other devices that use the principle of frictional locking of a symmetrical differential, mention should be made of the MLocker and Elocker mechanisms, in which the compressive force in the disk package is created mechanically - due to the mutual rotation of the side gears relative to the body at the moment of slipping.

The device operates automatically and does not require any external control input. However, friction differentials are particularly demanding on the special composition of the transmission oil, and the small degree of blocking characteristic of these mechanisms (about 30%) significantly limits their scope of application.

In our case, it is more correct to classify such differentials as partially locked. By the way, it is this niche that today has the greatest variety of design solutions.

For example, in off-road vehicles, along with classic torque distribution mechanisms, so-called limited slip differentials have become widespread, the design of which initially includes the function of partial differential locking.

Among the partially lockable devices, first of all, we should mention the cam limited slip differential, which was used on the GAZ-66 car.

The basis of the mechanism is a pair of sprockets with profiled cams and a separator located between them with a set of crackers that act as satellites. The sprockets are connected to the axle shafts, and the cage is connected to the differential housing.

When the car moves in a turn or on an uneven road, the cracks move in the holes of the holder and provide the drive wheels of the car with a different frequency. At the same time, the mechanism allows you to transfer more torque to the lagging wheel in case of slipping.

Cam differentials are relatively simple in design and lightweight, but are tough in operation. Therefore, at present they are mainly used in military equipment, and among civilian examples we can mention the GAZ-3308 “Sadko” car.

Naturally, in parallel with the automakers’ own developments, well-known representatives of the auto components market are actively working on the topic of power distribution supplied to the drive wheels. Among them are companies such as Eaton, ZF, Borg Warner, JTEKT.

It was from this area that one of the most used forms of partial differential locking came into being - worm-and-screw mechanisms. Several varieties of such devices are known, and the first designated direction was discovered by a product called Torsen (from the English.

Torque sensing - “torque sensitive”).

The Torsen differential design was proposed in the USA in the mid-60s, but mass production began almost 20 years later, after an American company developed the technology and tooling for its production and built a special plant for this purpose in Belgium.

Since the early 80s, this differential began to be used on military multi-purpose vehicles of the Hummer family. Without going into details of the device, we note that in this case the blocking properties of the differential are determined by the differences in the forward and reverse efficiency of the worm gear and its dependence on the magnitude of the transmitted torque.

The maximum degree of blocking can reach 90%, and among other features of Torsen differentials are the compactness and instantaneous appearance of the blocking moment, which has a positive effect on the dynamics and directional stability of the car.

The disadvantage of this design is the difficulty in manufacturing the satellites and housing, as well as in assembling the unit as a whole, repair and maintenance. All this does not have the best effect on the final cost of the product.

The author of the second type of worm differential is the Englishman Rod Quaife. His name is fixed in the name of the type, and among specialists the mechanism is also known as helical. The main design feature is the location of the satellites.

Firstly, they are placed in two rows parallel to the axis of rotation of the case, and secondly, they are not mounted on axles, but are located in pockets of the case that are closed on both sides. The right row of satellites meshes with the right axle gear, the left one with the left one.

When one of the wheels begins to lag, the side gear associated with it begins to rotate slower than the housing and turn the satellite engaged with it. The functionality is based on friction: axial and radial forces arise in the screw engagement, pressing the semi-axial gears and satellites with their ends to the body and covers.

The locking properties of the Quaife differential depend on the angle of the gear teeth. Thus, by changing the gearing geometry at the design stage, it is possible to adjust the characteristics of the product to a specific car model, taking into account its technical characteristics and operating conditions.

Finally, we cannot fail to mention the original design proposed by Russian engineer Valery Krasikov. The main difference between DAK (Krasikov automatic differential) is that the role of satellites is played by balls circulating along special profiled grooves inside the housing.

Compared to the Quaife differential, this design transmits more torque and is less sensitive to overheating. Currently, a pilot batch of DAK is already being tested at KamAZ OJSC, which means there is reason to believe that Krasikov’s development will be useful not only for jeeps.

In short, the improvement of the designs of power distribution mechanisms continues to this day. It is possible that in the future we will see the emergence of new types of devices, which will significantly expand the scope of their application.

Source: http://5koleso.ru/content/blokiruemye-differentialy

What is a center differential lock? Why and what is it needed for?

In this article we will try to tell everyone about what a center differential lock is. This action is intended primarily to increase the vehicle's cross-country ability.

Car device

Center differentials are used on vehicles with several drive axles, i.e. off-road vehicles, SUVs, etc.

The use of center differentials eliminates the circulation of power, which loads the transmission when the vehicle moves on roads with uneven surfaces.

This circulation occurs due to the fact that the wheels of different axles, especially on vehicles with a larger wheelbase, travel different paths while driving, as well as due to differences in air pressure in the tires and different normal loads on the drive wheels.

Symmetrical center differentials installed between equally loaded axles of off-road and all-terrain vehicles are usually made in the form of simple conical differentials with the possibility of forced locking from the driver's cabin. They are installed either in the transfer case, as, for example, on the VAZ-2121 Niva car, or on the intermediate bridge of a three-axle vehicle in the final drive, as, for example, on KamAZ cars (Fig. 1).

The design of the center symmetrical differential is similar to the design of cross-axle bevel differentials, the design and operation of which can be found here.

Asymmetrical center differentials, installed in transfer cases of KamAZ-4310, KrAZ-260 vehicles and distributing torques in proportion to normal loads on the axles, are most often made as planetary cylindrical ones.

The diagram of an asymmetrical planetary differential is shown in Figure 1, and the design of the center differential located in the transfer case of a three-axle KamAZ-4310 vehicle is shown in Figure 3.

The differential is a planetary gear, the leading element of which is the carrier 16, connected to the differential housing.
The crown gear 11 with its hub is mounted freely on a bronze bushing in the rear flange of the carrier 16 and is connected with splines to the rear axle drive shaft 9.
The sun gear 13 is mounted on the splines of the shaft 18 of the front axle.

For a fully loaded vehicle, its mass is distributed along the axles so that the front axle accounts for approximately one-third of the vehicle's mass, and the intermediate and rear axles account for two-thirds of the mass.

But since the intermediate and rear axles are driven by one driveshaft, for optimal distribution of traction force across all drive axles, the transfer case must transmit twice as much torque to the two rear axles as to the front axle.

Structurally, the sun 13 and crown 11 gears are designed so that r2 = 2r1, therefore Mrear = 2 Mfront, i.e. the differential distributes torque between the front axle and the rear bogie in a ratio of 1:2.

To block the differential, the middle part of the carrier flange 16 has splines on which a locking clutch 17 is installed. The locking clutch is moved using an electro-pneumatic drive controlled from the driver's cab.

***

Half shafts

Source: http://kat.ru/mdk.01.01_transmjssia/mosty_8/index.shtml

What is a differential lock, its types and characteristics

Not every driver thinks about the fact that when a car moves around turns, the wheels of each axle travel a path of different lengths. This is why the wheels rotate at different speeds.

This is necessary so that the tires do not slip on the asphalt, in order to reduce the load on the wheel drive when turning. This fact is ensured by a mechanism such as a differential.

The mechanism installed on the gearbox distributes the load so that the most unloaded wheel falls under the load.

95% of cars produced are not equipped with a lock, which makes the vehicle more passable.

There are different types of differentials. Depending on their location, they are divided into interaxle and interwheel. However, any free differential will not allow the car to get out of a situation where one of the drive wheels ends up in a hole with clay. To solve such problems, developers came up with blocking, which, in turn, is divided into the following main groups:

100% blockable;
mechanical devices of increased friction;
self-locking mechanisms.

Each type has both its advantages and disadvantages. For example, “hard” locks quite often lead to wear of the rubber, destruction of the transmission and rapid failure of the gearbox. And all this is natural, since during operation the car constantly falls into holes and runs over bumps, and this has a rather detrimental effect on the transmission.

To compensate for the disadvantages of conventional and rigid devices, a cylindrical limited slip differential was created. It also has a second name - limited slip differential.

The operating principle of this design is quite simple.

If you apply a certain force to the satellites and clamp them, not allowing them to rotate between the semi-axial gears at a fairly high speed, then it turns out that, on the one hand, the mechanism will allow the wheels to rotate at different speeds when turning. On the other hand, it will distribute torque in such a way that the wheel that has the best grip on the road surface will have greater traction force.

It’s also worth mentioning the limited-slip disc differential. Most often, this design is used in rear-wheel drive cars that are planned to be used in competitions. This system blocks the wheels up to a certain load level. Its disadvantage is the fairly frequent need to change discs and gearbox oil.

The video shows how the differential lock works:

But for using a vehicle both in normal operating conditions and in competitions, differential locking with preload (worm type) is very successful. The advantages of such a system are much greater than the disadvantages. The advantages are:

wheel blocking up to 70%;
minimum maintenance;
no jerking on the steering wheel;
no need to fill the gearbox with special oil;
installation of the system is not accompanied by difficulties;
high maneuverability of the vehicle;
long service life of the structure;
excellent car handling;
excellent sense of balance;
higher cornering speed;
ease of getting the vehicle out of a skid.

As for the design flaws, they exist:

preload decreases over time;
for the design to work, you will have to change the adjusting washers every 20–40 thousand km;
If adjustments are not carried out, the system will operate as a free differential.

Difference in operating principles

Often all-wheel drive vehicles have three types of structures at the same time: one center differential and two axles. For high-quality work, both full and partial automatic or manual interaxle blocking can be used.

Already, many vehicles have begun to use all kinds of electronic control systems for vehicle movement.

The advantage of electronic locking is higher cornering traction and the ability to adjust the degree of locking depending on the driver's preferences.

The only drawback is that such a differential is insensitive to rapidly changing road conditions.

One type of self-locking mechanism is a locking cross-axle differential. On a flat road, on a hard surface, such a mechanism behaves like a regular free system.

And only when a wheel on an axle rotates relative to another with a higher frequency, the structure is automatically blocked.

The cross-country ability of the vehicle when blocking the inter-wheel type device increases significantly.

Forced blocking

The simplest way is to forcefully lock the mechanism. In this case, only the driver makes the decision to turn it on or off. This is done either using levers or using buttons located inside the car.

This type of blocking is simply ideal for SUVs that are used in Russian off-road conditions. The system is impeccably reliable when driving over mud and potholes and is practically unusable on smooth roads.

In the video, a test of forced differential locking:

In off-road conditions, locking the rear differential will also be effective. It is simply irreplaceable in cases where one of the wheels of the axle is hanging out. Then the torque from the engine will be transmitted precisely to the wheel that touches the ground.

To summarize, we can conclude that the best option is a self-locking differential. It is in many ways superior to a free mechanism and does not have the disadvantages of a rigid design. With such a system, the car becomes more passable.

Source: http://365cars.ru/remont/blokirovka-differentiala.html

What is a center differential and why is it needed?

Differential is a device that controls the distribution of torque between the input and output shafts. Although the speed of individual elements may vary.

This mechanism is successfully used in the automotive industry and is widely applicable in it. The difference between differentials is manifested in their installation location, purpose and design features.

Cars with only rear or front axle drive are equipped with one differential - a cross-axle differential.

The need for a differential is caused by the peculiarities of the behavior of the wheels in corners. They travel different distances at these moments.

Trucks with 6x6 and 8x8 drives are equipped with an additional inter-bogie differential. In models with all-wheel drive, three differentials are installed: in addition to two inter-axle differentials, there is also one inter-axle differential.

We will talk further about the operation of the center differential, its design and purpose in more detail.

Center differential design

Let's look at the design of a center differential using the most common example - a bevel differential. The bevel differential is similar in design to other types of differentials.

A bevel differential is a planetary gearbox with semi-axial satellite gears, which are placed in a housing.

The housing, or as it is also called the “differential cup,” receives the torque from the main gear and distributes it through the satellites to the axle gears. The driven gear of the main gear is rigidly attached to the housing. The satellites rotate on the internal axes of the housing.

The satellites act as a planetary gear. They provide contact between the housing and the semi-axial gears. Depending on the magnitude of the torque transmitted, the differential design has two or four satellites.

Differentials of passenger cars usually have two satellites. Semi-axial (sun) gears transmit rotation to the drive wheels through the axle shafts via a spitz connection.

The right and left axle gears have both equal and different numbers of teeth.

Gears with an equal number of teeth form a symmetrical differential, while an unequal number of teeth is characteristic of an asymmetrical differential.

A symmetrical differential distributes rotation along the axes in equal proportions, regardless of the angular speed of the drive wheels.

Due to its properties, a symmetrical differential is successfully used as a cross-axle differential.

An asymmetrical differential divides torque in a certain ratio, so it is installed between the axles of an all-wheel drive vehicle.

Operating principle of the center differential

When a car moves along a straight path on a flat road, the distance traveled by the drive wheels will be equal, since both wheels will have the same angular velocity.

During this movement, all satellites, gears and the differential housing are synchronized. The transmission of torque to this mechanism is provided by a gear.

We also note the fact that with such movement the torque on each of the driven wheels is the same, and the semi-axial gears are jammed by satellites, which are static relative to their axis.

When a car enters a turn, the path taken by the wheel on the inner edge is shorter than that of the wheel on the outer circle, therefore their rotation speed is different. To stabilize the situation, the side gear slows down, and the satellites and housing at this time rest against the side gear on the left.

Due to the fact that the satellites rotate around their axis, the speed at which the right side gear rotates also increases. This allows the drive wheels to rotate at different speeds, which prevents slipping and slipping. Note that a wheel with a higher rotation speed receives less torque.

Let's look at a differential with a classic design. Its main disadvantage will be the slipping of one wheel when it loses contact with the road surface.

The thing is that the suspended wheel rotates approximately twice as fast as the wheel that is in contact with the road at the same number of revolutions of the differential driven gear. The second wheel remains static.

The reason for this is the very small torque supplied to it, since the rotating suspended wheel receives little torque resistance. Based on this, it is clear that the torque of the opposite wheel is similarly small, which is why it is stationary.

If a wheel slips at high speeds in an environment with significant resistance, the torque supplied to it will be greater in comparison with the slipping wheel, and therefore the second wheel will be provided with more torque to rotate.

Thanks to this distribution, the car can slowly but surely get out of the trap. A slipping wheel wastes a lot of power, which is spent on heating the road surface, tires, etc. Slipping significantly reduces the maneuverability of a vehicle with a free differential.

To avoid such problems, cars are equipped with differentials with the ability to lock them, both manually and automatically.

Purpose of the center differential

As you already understand, the purpose of the center differential is to distribute torque between the drive axles in all-wheel drive vehicles , which gives them the ability to rotate at different angular speeds.

The need for such a mechanism arose as a result of the movement of cars on uneven surfaces, when the mass of the structure itself presses on the axle, which is in a much lower position. So, if you are driving downhill, most of the torque is transmitted to the rear axle. In the case of descent, the opposite happens.

The center differential mechanism itself is usually located in the transfer case of the vehicle.

The type of center differential can be either symmetrical or asymmetrical.

The first variant of the differential distributes torque in a ratio of 50/50, while the second in different ratios, for example, 60/40.

In addition, there are center differentials that do not have a locking mechanism, which does not allow the wheels to move at different speeds. There are self-locking differentials and manual locking.

The second option allows you to forcibly distribute torque between the axles. This helps to overcome various road obstacles in the form of mud, sand or snow. Forced blocking of the center differential can be complete or partial.

This ensures a rigid connection of the axle shafts to each other. Often, to realize the full off-road potential of a vehicle, a differential with an automatic locking mechanism is used.

It has three types of designs and, accordingly, different principles of operation.

Operating modes of the center differential

The operation of the symmetrical center differential is divided into three inherent modes:

– rectilinear movement;

– movement in a turn;

– driving on a slippery road.

When driving straight, the wheels take on the equally distributed resistance of the road surface. Torque is transmitted to the differential housing from the main gear. The satellites move along with it.

The satellites, bypassing the axle gears, transmit all the torque in equal proportions to the drive wheels. In the absence of rotation of the satellites on the axles, the gears of the axle shafts move at the same angular speed.

They rotate at the same frequency as the main drive driven gear.

When entering a turn, the drive wheel running along the inner radius takes on more resistance than the wheel on the outer radius. The internal semi-axial gear slows down its movement and causes the satellites to rotate around its axis. They, in turn, accelerate the rotation of the outer axle gear.

Wheels moving at different angular speeds allow the car to turn without excessive slipping. The sum of the rotation speeds of the side gears inside and outside is equal to the speed of the driven gear multiplied by two. Torque is distributed equally between the drive wheels.

And this is not affected by the difference in angular speeds.

When a car moves on a slippery road, one wheel takes up most of the resistance while the other wheel spins or slips. The differential causes the “problem” wheel to rotate at a higher speed. The second wheel is forced to stop.

The traction force generated on a slipping wheel is very small due to low traction, so its rotation also occurs at low speed. And due to the design of the symmetrical differential, the other wheel will have the same characteristics at that time. The situation has reached a dead end - the car does not budge.

This problem can be solved by increasing the torque on the non-slip wheel. This is easily accomplished by locking the differential.

Source: https://auto.today/bok/3177-chto-takoe-mezhosevoy-differencial-razbiraemsya-vmeste.html

What is a differential: device, principle of operation and 3 types of locking

In the modern automotive industry, there are many technical solutions for implementing differentials.

Depending on the drive of the car, different types of units are used: for rear-wheel drive, front-wheel drive and differential devices for SUVs.

In addition, this transmission unit is classified according to its internal structure (conical, cylindrical, worm) and locking method.

The purpose of the differential in a car

The main task of the differential is to provide the wheels with different rotation speeds. This method of rotational movement is necessary for the correct entry of the car into turns, when wheels slip and at other times.

When a car turns, different wheels describe different trajectories. If the drive wheels move at the same speed, then it will be very difficult to turn on such a car.

The distribution of torques between the driven wheels occurs using a differential.

When one of the wheels slips, the conventional planetary mechanism will begin to work in the direction of increasing torque. The wheel begins to slip even more. A wheel placed on a hard surface will stop spinning.

To solve such problems, differential devices are provided with various types of locking mechanisms: manual or automatic. Differential locking significantly increases the cross-country ability of an all-wheel drive vehicle.

As long as at least one wheel touches the road, the car moves.

Classification of differentials

There are two main types of differential mechanisms: inter-wheel and inter-axle. Interwheel is intended for various vehicles with two-wheel drive. The interaxle divides the torque among all four.

Depending on the differential model, different design solutions of the mechanism are used. In front-wheel drive cars, this unit is usually placed in the gearbox housing.

For rear-wheel drive vehicles, the transfer gears are placed in the rear axle housing.

All-wheel drive SUVs most often use a separate transfer case (Land Cruiser, Niva) to accommodate the differential mechanism. Some manufacturers use a design with two separate differentials (Jeep “Cherokee”, UAZ “Hunter”) located in the front and rear axles.

The simplest device based on a planetary gearbox is a free differential. Let us briefly consider the principle of its operation. Rotation from the engine is transmitted to the mechanism by the main gear. The teeth rigidly transmit movement to a large driven gear located in the differential housing.

Two bevel satellites with two degrees of freedom are attached to the driven gear: they rotate together with the driven gear, and at the same time can rotate along their axis.

When the car is driving straight, the satellite runs in a large circle and transmits the same rotational motion to both axle shafts. As soon as the car turns, the satellites perform rotational movements around their axis, and the rotation speed of the axle shafts changes.

As a result, one of the wheels moves slower, and the other, which describes a larger turning radius, moves faster.

Why is a differential lock necessary?

The free differential has one big drawback. At the moment one of the wheels slips, the satellite begins to scroll and transfers the entire momentum of movement to it. The slipping wheel spins at high speed, while the second wheel standing on solid ground is inactive. It is especially dangerous when such processes occur at high speed.

If there is an area on the road with an uneven icy surface, then a car with a free differential may go into an uncontrollable skid. To solve this problem, a differential lock is used.

A natural solution to prevent slippage is to temporarily suspend one of the components of the mechanism. There are several solutions to this problem: you can temporarily block one of the wheels, the axle shaft, the differential unit itself, or even the engine. According to the method of implementation, locking is divided into the following types: manual, self-locking, electronic.

The simplest option for blocking the differential mechanism is to manually disable it. Typically, this function is implemented using a special lever or button in the interior of an SUV.

The movement of the lever blocks the possibility of rotation of the satellites along its axis, and the planetary gear becomes a regular clutch.

This operation should only be performed when the vehicle is at a complete stop with the clutch depressed.

The lock should be used when driving at low speeds on difficult roads. With the differential disabled, the car becomes difficult to control and tends to drive in a straight line.

Therefore, manual control of the mechanism for distributing power to the wheels requires certain driving skills. SUVs with a rigid frame are equipped with manual differential locking: Land Cruiser, Hilux, Niva and others.

Self-locking differentials

To increase the vehicle's cross-country ability and simplify control in difficult conditions, several models of self-locking differentials were created. The principle of operation of these nodes is based on the occurrence of blocking of the node under certain circumstances.

Speed sensitive differentials

Let's take a closer look at the Speed sensitive differentials, which are triggered if the axle shafts begin to rotate at different angular speeds.

An example of a car where this type of differential is installed is the Toyota “Rav4” with a viscous coupling. One part of this assembly is attached to the differential cup, the other part to the axle shaft.

In normal driving mode or slight divergence in a turn, the working surfaces of the coupling move independently and do not interfere with the rotation of the axle shafts.

Rotation of one of the axes at a noticeably higher speed leads to the viscous coupling being activated and beginning to slow down the movement.

As the speed drops, the friction force decreases and the parts of the assembly again become independent. This differential is quite suitable for car owners who do not strive to conquer all off-road peaks.

In city mode and on dirt roads, cars with such differentials have proven themselves to be excellent.

But the viscous coupling has problem areas - in a difficult situation it does not support the load, begins to heat up, is delayed in turning on and may become inoperative.

On special equipment, another type of self-locking differential mechanisms is installed - cam pairs. An example of implementation is the GAZ-66.

This design of the unit makes it possible to significantly increase the vehicle’s maneuverability, but is fraught with dangerous situations when the differential spontaneously jams. The scheme of action is simple, like everything ingenious. Instead of a planetary gear, the mechanism uses gear pairs.

They turn freely at the slightest discrepancy in wheel speeds, and when the discrepancy is significant, they jam.

An interesting version of the design solution for a self-locking differential is implemented in the Kia “Sportage”. Based on similar techniques to viscous couplings, this type uses plates to brake unwanted rotations. The fundamental difference or significant improvement is the use of a hydraulic system to bring the friction plates together.

When a large difference occurs in the speeds of the axle shafts, a pump is activated, which builds up oil pressure in the clutch system and forces the plates to move closer together. Thus, the rotation speed of the slipping wheel begins to decrease, and torque is redistributed.

More modern and efficient are Torque sensitive differentials, which come into operation when the rotation speed on one of the axle shafts decreases. Such a unit monitors rotation speeds and reduces them automatically.

Structurally, such differential devices are a conventional free differential with a set of spring-loaded friction speed absorbers located between the axle shafts and the differential cup. The operating principle is based on the properties of hypoid gears, which can spontaneously unlock. There are three main design implementations of this type of differential.

The first type was used on the Toyota Celica GT-4 SUV and was called T-1. Each axle shaft in this unit has its own satellites connected to each other. Thus, as soon as there is a difference in the torque of the satellites, the worm synchronizes them, and the wheels will spin at the same speed. The range of their difference is determined by the angle of inclination of the teeth of the intersatellite shaft.

This mechanism leads to the fact that the wheels either move at the same speed (when driving in a straight line), or, thanks to synchronized satellites, rotate at different speeds (when turning). There are no slippages. A transmission unit model with such characteristics became popular not only among SUVs; it was installed on the Mazda RX-7 sports car (1991).

To continue the series, the T-2 model was released, more sensitive to differences in speed. Like the similar Rod Quaife mechanism, this design features a more complex gearing between the pinions instead of a worm.

This model has gained even more popularity and is applicable for a large number of cars: BMW “Z3”, Audi “A4”, “A6”, “A8”, Honda “S2000” roadsters, Volkswagen “Passat” (B6), Mazda “MX-5” ", SUVs "Range Rover", Hummer.

The third type of differentials of the Torque sensitive model is called T-3 and is most often used as center units.

This more advanced design allows the load to be automatically distributed between the rear and front axles at a certain interval. This usually occurs in the 65 to 35 range.

If there is an obstacle in the way of the Lexus GX 470, equipped with such a differential, then its traction force will be applied to those wheels that can still grip the road surface.

Electronically controlled differentials

The mechanical method of differential locking should not be considered as the only development aimed at improving cross-country ability and increasing vehicle control.

An example is a transmission control system using electronics - Traction Control (TRAC) - a circuit for controlling traction and wheel traction.

TRAC is based on a simple principle: monitoring and correcting wheel speed using special sensors.

As soon as the wheel begins to slip, the brake is activated and the torque is transferred to the other axle shaft. At first glance, the car will behave as if its differential was locked.

In fact, this system is even more effective than mechanical locking, easier to implement and more reliable. In addition, TRAC does not interfere with the operation of any differential mechanisms, but is a successful addition to them.

That is why modern SUVs such as Hilux, Lexus, Prado are equipped with electronic Traction Control.

Active differentials

The most popular and modern solution in the field of designing a differential unit was the invention of the active differential. The idea of this mechanism is not to slow down the axle shafts and wheels, but, on the contrary, to accelerate them to greater speed. With the help of electronics and friction clutches, the wheel running in the outer circle receives many times more torque than the inner one.

Thanks to this technical solution, turning sharp turns is easy and stable. This circumstance was immediately taken into account by sports car manufacturers. But this type of differential is still far from entering widespread production.

Conclusion

Over the years of its existence, the differential has come a long way in evolutionary development and this is not surprising.

Car designers have done everything possible to make this unit reliable and ensure comfortable and unhindered movement of the car.

If you are wondering which differential to choose a car with, then this is the most improved model from the Torque sensitive category, with the addition of electronic Traction Control.

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Source: https://motorsguide.ru/system/chto-takoe-differentsial-avtomobilya