Center differential lock: what it is, how it works

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:41

Off-road cars are equipped with a differential. This element is needed to provide the drive wheels with different angular speeds. When turning, the wheels are located on the outer and inner radius. The center differential on the SUV has a lock. Not everyone knows what it is - a locking center differential. Let's see what it is, why and how to use it.

Center differential

There is definitely one differential in every car. This mechanism is designed to divide the torque that is supplied to it from the input shaft between two axle shafts. All-wheel drive cars are equipped with two differentials - for each wheelset. There is also an interaxle. The need for it is due to the fact that SUVs are operated in very difficult conditions. Different axles experience different pressure, and you need to distribute the torque between them.

Lock

Any differential has, in addition to advantages, a very serious drawback. This disadvantage is a consequence of the advantage - if one of the wheels begins to slip, then the differential gives more torque to this particular wheel. This greatly reduces the performance characteristics. If for civilian cars this is the norm, then for SUVs this is completely unacceptable. For this reason, almost all center differentials are equipped with locking systems. But there are exceptions. For example, there is no center differential lock on the Niva, but you can buy and install one of the solutions offered by the market yourself.

When the lock is on, the same torque is given to each axle. Therefore, the wheels will not slip. This is necessary so that the car can easily pass slippery places.

Types of locks

We learned what it is - a locking center differential. Now it is worth getting acquainted with the types of these systems. Now you can select manual and automatic blocking. In the first and second cases, you can partially or completely disable the differential. On models of cars with increased cross-country ability, there are automatic locks. Their three varieties are a system with a viscous coupling, a Trosen lock and a friction clutch. What are the features and differences between these systems? Let's consider each in more detail.

Viscous locks

This is the most common block. It is based on a symmetrical planetary scheme. Workbased on interacting bevel gears. An important element of this design is a special sealed cavity. It contains an air-silicone mixture. The mechanism is connected to the axle shafts by disk packs.

If a car with four-wheel drive moves at some constant speed on a fairly flat surface, then a differential with such a lock transmits torque to the front and rear axles in a ratio of 50:50. If one of the packages rotates faster, then due to the increased pressure in the sealed container, the viscous coupling will begin to slow down the package. Due to this, the angular velocities will be aligned. The differential will lock up.

Among the main advantages of this system are its simplicity and low cost. It is due to these factors that the mechanism has become so widespread in modern SUVs. On the downside, automatic blocking is not fully implemented and there is a risk of system overheating if the blocking is operated long enough.

Trosen system

Here's another locking center differential. What it is? It consists of a housing, two side gears with satellites and output shafts. It is believed that blocking of this type is the most effective and perfect. Often this system can be seen on new SUVs of European and American production.

The basis is worm wheels in the amount of two pairs. Each pair has a driving and driven wheel - semi-axial and satellite. The principle of operation is based on the features of worm gears. If each wheel has the same traction, then the lock will not be engaged and the differential will work normally.

The center differential lock is activated if one wheel starts to rotate faster than the others. The satellite connected to the wheel will try to spin in the opposite direction. As a result, the worm gear is overloaded and thus the output shafts are blocked. The released torque is transferred to the other axle and the torque values are thus aligned.

What are the advantages of this system? The main advantage of such a lock is the maximum response speed and a very wide range of torque distribution from one axle to another. Among other advantages, it can be noted that these locks do not lead to an overload of the brake systems. One minus is the complexity of this design. By the way, a similar lock can be seen on the GAZ-66.

Slip Clutch Lockouts

The main distinguishing feature is that it is supposed to enable the lock automatically or manually. The design and operation of the center differential lock is similar to a viscous coupling system. But friction discs work here.

When the car moves smoothly, the angular speeds on the axles are evenly distributed. If there is acceleration on one of the semi-axes, then the disks will begin to approach, the friction force will increase between them - the semi-axle will slow down.

These systems are practically not used on serial models of cars. The reason is the complexity of the design and low resource. Discs wear out very quickly, and the design itself requires special care and meticulous maintenance.

Electronic interlocks and imitations of interlocks

Most modern cars have so-called electronic center differential locks. What it is, we will consider further. The electronic lock in most cases is only an imitation.

The ECU receives information from the wheel sensors that one of the wheels is spinning faster and starts to brake the wheel with intermittent commands. Thus, the moment is redistributed to the other side. Usually, you can find out that this system is turned on by looking at the dashboard - the center differential lock is flashing.

Disadvantages and features

When working in this mode for a long time, there is a risk of overheating and failure of the brake systems. The car has automatic protection if the temperature rises above the permissible level, but this is not available everywhere and does not always work.

If the load is heavy, then there may not be enough torque to move the car forward. It seems that the lamp is blinking, the brake system is cracking, but the car is not going anywhere. It is impossible to raise the speed - the electronics do not give.

Pajero interaxal differential lock, and it is electronic there, loses its effectiveness in water. Wet pads cannotbrake wet disc.

But even imitation is not empty fun. Naturally, it is not suitable for serious off-road, but not all owners go there. Electronic lock is enough for the most common cases. For example, they may be needed in winter. But you can’t rely heavily on the system - electronics can fail at the most inopportune moment. Therefore, Pajero additionally has a real, iron lock.