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Design and operation principle of the center differential

Differential – this is the device that controls the distribution of torque from the input shaft to the output, and the speed of each individual element can be different. The mechanism is widely used in the automotive industry.

The differentials vary according to place of installation, the purpose and design features:

The center differential, and what axis differentials may be we discuss in more detail later.

The purpose of the center differential

The center differential is designed for distribution of the torque between the driving axles of the vehicle and gives them the opportunity to rotate with different angular velocities. This need is caused by simple conditions of traffic on uneven surfaces, when weight design presses on the axis, which is in the lowest position. So, when driving uphill significant part of the moment is fed to the rear wheels. And, Vice versa, in the case of the descent.

Device center differential is, as a rule, in the transfer box car. The center differential can be symmetrical and asymmetrical. First distributes torque between axles equally, and the second – in a relationship.

In addition, there is a center differential without locking mechanism, which allows axis to rotate at different speeds, as well as differential самоблокируемый or manual locking mechanism that forced distributes torque between actuating rod depending on road conditions. The forced locking center differential implies complete or partial shutdown of the differential, which provides rigid connection of the front and rear axes between themselves.

Most often, for the full realization of all-wheel drive capabilities of the car is used самоблокируемый differential that can have three kinds of designs and different principles of work respectively.

 The center differential

Design and principle of operation of conventional prefilled auto-disable the center differential

So, there are three types of conventional prefilled auto-disable the center differential:

Scheme of the inter-axle differential with вискомуфтой is a planetary symmetric scheme for bevel gears. This design requires a control viscous coupling, which consists of the following elements:

Coupling in its design has tightly closed cavity filled with air-silicone oil. Cavity kinetically connected with two stacks of discs, which are connected with both left.

Principle of operation:

In the rectilinear motion on a flat surface and constant velocity of the center differential transmits the torque of the engine at the front and back of the axis in the ratio 50 on 50. In case if one of the packages disks to rotate faster than the other, in a sealed cavity coupling pressure increases, and she starts mechanical brake (i.e. block) this package, thereby equalizing the angular speed of rotation.

The following examples can easily explain why you need a center differential with viscous coupling:

Widespread construction with вискомуфтой received due to simple design and low prices. To shortcomings include the lack of the manual lock, possibility of overheating of the long term, part-automatic blocking the conversion of a significant part of the kinetic energy into thermal energy.


Design of the working drive of the system consists of the following units:

It is worth noting that Torsen center differential has the most advanced design.

Principle of operation:

Center lockable differential Torsen consists of slaves and leading worm gears, otherwise called half-shaft and саттелитами. In such a system lock happens due to peculiarities of functioning of the gears of this type. In normal condition, they have a particular gear ratio. If the wheels have good traction and moving smoothly, work differential is exactly the same as symmetric. But as soon as there is a sharp increase in the moment, satellite ticket tries to start moving in the opposite direction. Полуосевая worm gear is overloaded, and lock the output shafts. The excess torque of the engine goes to another axis. The maximum degree of redistribution moment for differential Torsen – 75 to 25.

The most famous variation of this system is the Torsen Audi Quattro. This is one of the most popular mechanisms in the design of modern all-wheel drive vehicles. Its indisputable advantages are a wide range of umklapp torque, instantaneous speed of response and absence of negative impact on the brake system. But the disadvantages are the complexity of the design with all the attendant consequences.


The lock on the basis of the slip clutch seriously exceeds described above designs because there is possibility of automatic and manual locking differential. Structurally it is very similar with вискомуфтой and differs only in the main functional elements.

Principle of operation:

The principle of work of the center differential of this kind is quite simple. At monotonous smooth movement of the angular velocity are distributed equally between the axes. If one of the shafts to rotate at high speed, friction discs converge and slows down its due to friction forces.

However, due to the structural complexity and specifics of service friction differentials are not used by manufacturers of a production car, despite its obvious advantages. In addition, significant minus of such a system – fast wear of the work items and means small resource of its work.

Locking system Haldex

But we should say that on the basis of a design center differential with friction clutch in 1998 the Swedish plant Haldex was released own alternative system. It was based on the work of the electro-hydraulic element bundles. The old version of the system was rather a failure than a success, but spawned a few modifications, the latter of which became quite popular.


Haldex 4 generations, released in 2007, became a real breakthrough. The main working planes of the system are the friction discs. Through them the torque from the engine is transferred to the axis. One of the innovations was the complete failure of the manufacturer to be used as a working drive of a hydraulic pump. He was replaced by powerful all-electric pump.

But the most interesting change was the transformation of the system in a fully electronic. Thus, the inclusion of couplings and lock axes is no longer depends on the speed of rotation of a single wheel. Control is through an electronic control unit, which receives all necessary information from the sensors of motion. In addition, one of the main signals enable the coupling work is to press the gas pedal. Acceleration is almost always accompanied by certain stalling, therefore, the lock can be very useful.

Haldex 4 many called the most modern system for vehicles with an all-wheel drive. Especially often Haldex establish the modern SUVs with a center differential Asian production. Its main advantages are simplicity of design, reliability and work throughout the drive time. But the main drawback – impossibility of the transfer of more than 50% of power to the rear axle rotation.