Self-locking differential: how does it work?

The term "lock differential", or "self-locking differential" (self-block), heard by many motorists, but how this process looks in practice, only know a few. And if before this "option" automakers equipped mainly off-road vehicles, but now it can be found on a quite city car. In addition, often owners of cars not equipped with self-blocks, realizing what benefit they bring, install them independently.

But before you understand how the self-locking differential works, you need to understand how it functions without blocking.

What is the differential

Differential (diff) can rightly be considered one of the main elements of the design of the transmission of the car. With its help, the transmission, change, as well as distribution of the torque output by the engine between a pair of consumers occurs: by wheels located on one axis of the machine or between its bridges. Moreover, the force of the flow of the distributed energy, if necessary, can be different, and hence the speed of rotation of the wheels is different.

In the transmission of the car, the diff can be installed: in the rear axle crankcase , gearbox and transfer case, depending on the drive device (s).

Those diffs that are installed in the bridge or gearbox are called inter-wheeled, and which is located between the axles of the machine, respectively - the interaxial.

Differential assignment

As you know, the car makes various maneuvers during the movement: turns, rebuilds, overtaking, etc. In addition, the surface of the road may contain unevenness, which means that the wheels of the car, depending on the situation, at the same time can Pass a different distance. Therefore, for example, when turning, if the speed of rotation of the wheels on the axis is the same, one of them will inevitably become stalled, which will lead to accelerated wear of the tires. But this is not the worst thing. Much worse is that the vehicle significantly reduces handling.

To solve such problems, a differential was invented - a mechanism that will redistribute the energy coming from the engine, between the axles of the car in accordance with the rolling resistance value: the smaller it is, the greater the speed of rotation of the wheel, and vice versa.

Differential Mechanism

To date, there are many varieties of diffs, and their device is quite complicated. However, the principle of work is generally the same, so it will be easier to understand the simplest type - the open differential, which consists of the following elements:

1. Gears fixed on the semiaxes.
2. The driven (crown) gear, made in the form of a truncated cone.
3. The drive gear fixed to the end of the drive shaft, which, together with the crown, forms the main gear. Since the driven gear is larger in size, the latter will have to make several turns around its axis before the crown executes only one. Consequently, it is these two elements of the differential that reduce the amount of energy (speed) that will eventually reach the wheels.
4. Satellites, which form a planetary mechanism, playing a key role in providing the necessary difference in the speed of rotation of the wheels.
5. Shells.

How does the differential work?

During the rectilinear movement of the car, its semi-axles, and hence the wheels, rotate at the same speed as the drive shaft with its helical gear. But during the turn, the impact load on the wheels becomes different (one of them tries to spin faster), and due to this difference, satellites are released. Now the energy of the engine passes through them, and since the pair of satellites are two separate, independent gears, a different speed is transmitted to the semi-axes. Thus, the power generated by the engine is distributed between the wheels, but unevenly, and depending on the load acting on them: what moves along the outer radius, experiences less rolling resistance, so diff transfers more energy to it, spinning faster.

Differences in how the inter-axle and inter-wheel differential works, no: the principle of operation is similar, only in the first case the distributed torque is directed to the axles of the car, and in the second - to its wheels located on one axis.

The need for inter-axis diff is particularly noticeable during the movement of the machine over rough terrain, when its weight presses on the axis that is below another, for example, on the rise or descent.

Differential Problem

Despite the fact that the differential certainly plays a big role in the design of the car, its work sometimes creates problems for the driver. Namely: when one of the wheels is on a slippery road section (mud, ice or snow), the other one, which is located on a harder ground, begins to experience a higher load, the diff tries to fix it, redirects the engine's energy to the sliding wheel. Thus, it turns out that it receives the maximum rotation, while the other, having a tight grip on the ground, simply remains motionless.

That's it to solve these problems was invented locking (turning off) the differential.

The principle of blocking and its types

Having understood the principle of the differential, it can be concluded that if you lock it, the torque on that wheel or axle that has better grip will increase. This can be done by connecting its body to one of the two semi-axes or to stop the rotation of the satellites.

The lock can be full - when parts of the differential are connected rigidly. It is carried out, as a rule, with the help of a cam clutch and is controlled by the driver through a special drive from the car's cabin. Or it can be partial, in this case only a limited effort is transmitted to the wheels - this is how a self-locking differential works, to which human participation is not required.

How the self-locking differential works

The self-locking differential is, in fact, a compromise between the full unit and the free diff, and allows you to reduce the slippage of the wheels of the machine in the event of a difference in the coefficient of adhesion with the ground between them. Thus, significantly increases the throughput, off-road control, as well as the dynamics of the acceleration of the car, and regardless of the quality of the road.

The self-locking device eliminates the complete blocking of the wheels, which protects the axle shafts from the critical loads that can occur on differentials with forced off.

The lock from the semi-axes is automatically removed if, in case of rectilinear motion, the speed of rotation of the wheels is equalized.

The most common types of self-blocks

The disk self-block is a set of frictional (rubbing) disks installed between the diff gear case and the semi-axle gear.

To understand how the differential works with such a block, it's easy: as long as the car is traveling in a straight line, the body of the diff and the two semiaxes rotate together as soon as there is a difference in the speed of rotation (the wheel hits a slippery area), friction occurs between the disks, reducing it. That is, the wheel left on solid ground will continue to rotate, and not stop, as in the case of a free differential.

Viscous coupling, or else the viscous coupling, as well as the previous diff, contains two packs of disks, only this time perforated, installed with each other with a small gap. One part of the discs has a clutch to the body, the other - to the drive shaft.

The disks are placed in a container filled with a silicone fluid, which, if uniformly rotated, remains unchanged. As soon as there is a difference in speed between packets, the liquid begins to thicken quickly and strongly. There is resistance between the perforated surfaces. The overclocked package thus brakes and the speed of rotation is equalized.

Toothed (screw, worm) self-block. His work is based on the ability of the worm pair to wedge and thereby block the semi-axles when they experience a difference in torque.

The cam self-block. In order to understand how a differential of this type works, it is enough to imagine an open diff, in which instead of a planetary gear mechanism there are gear teeth (cams) pairs. The cams rotate (jumps) when the wheel speeds are almost the same, and are rigidly locked (jammed) as soon as any of them starts to slip.

Differences in how the interlock and interwheel lock works, no - the principle of operation is the same, the differences are only in the end points: in the first case - two bridges, in the second - two wheels mounted on one axis.

Domestic "Niva" and its differentials

In the line of domestic VAZs, "Niva" occupies a special place: unlike its "relatives" along the conveyor belt, this machine is equipped with a non-disconnected all-wheel drive.

In the transmission of the VAZ off-road car three differentials are installed: inter-wheeled - in each bridge, and interaxial - in the distribution. Despite this amount, it is not necessary to sort out the difference in how the differentials work on the Niva. Everything is exactly the same as described above. That is, during the rectilinear movement of the machine, under the condition that there are no squeaking on the wheels, the traction force between them is evenly distributed and has the same value. When one of the wheels begins to slip, then all the energy from the engine, passing through the diff, is sent to this wheel.

Blocking of differentials of "Niva"

Before talking about how the locking differential works on the "field", it should be noted one point, namely, to clarify the purpose of the front (small) transfer case handle.

Some drivers believe that with its help the front-wheel drive is turned on by the car - this is not the case: both the front and rear drives of the Niva are always used, and this handle controls the dispensing differential. That is, while it is set to the "forward" position, diff works in the nominal mode, and when "back" it is turned off.

And now directly about the blocking: when the differential is turned off, the shafts of the transfer box are closed with each other by the clutch, thereby forcibly leveling their rotation speeds, that is, the total speed of the front axle wheels is equal to the total speed of the rear. The distribution of thrust is in the direction of greater resistance. For example, if the rear wheel slides, if the lock is turned on, the pulling force will go to the front axle, the wheels of which will pull the car, but if the front wheel also zabuksuet and the front wheel, then the Niva itself will not get out.

To prevent this from happening, motorists install bridges in bridges, which will help pull the jammed car. To date, the most popular among the owners of the Niva is the Nesterov differential.

Self-bloc Nesterov

It is in the way the Nesterov differential works that the secret of its popularity is concluded.

The design of the diffus allows not only to optimally adjust the angular speed of the wheels of the car when making maneuvers, but also in the case of stalling or hanging the wheel, the device gives him a minimum amount of energy from the engine. And the reaction of the self-block to the change in the traffic situation is almost instantaneous. In addition, the Nesterov differential significantly improves the controllability of the car even on slippery bends, improves the course stability, improves the dynamics of acceleration (especially in winter), reduces fuel consumption. And the installation of the device does not require any changes in the design of the transmission and is installed in exactly the same way as the classic diff.

The differential found application not only in automotive engineering, it proved to be very useful on motoblocks, greatly facilitating the life of its owners.

Differential for motoblock

The motor block is quite heavy, and it takes a lot of effort to turn it, and with unregulated angular speed of the wheels it becomes even more difficult. Therefore, the owners of these machines, if the diffs were not originally designed, acquire and install them themselves.

How does the motoblock differential work? In fact, it only provides an easy turn of the car, stopping one of the wheels.

Another of its functions is not related to the redistribution of power - this is an increase in the base of the wheels. The design of the differential provides for its use as an extension of the axles, which makes the motor block more manoeuvrable and resistant to tipping, especially at corners.

In a word, the differential is a very useful and indispensable thing, and its blocking at times improves the passability of the car.