In the device of each car there is a differential. This is a specific unit, the task of which is to distribute the torque between the wheels in different ratios (depending on the road situation). Additionally, the differential may have a lock. Usually it is on SUVs or trucks. Blocking the cross-axle differential allows you to compensate for the main disadvantages of the mechanism and ensure an even distribution of torque. In today's article, we will look at what kind of device it is, how it works, what types it comes in.
Differential features
The main function of this mechanism is to distribute the moment that comes from the main gear between the drive wheels. In this case, the speed of rotation of the semi-axes can vary. This is necessary in order for the car to safely enter the turn (without skidding). This possibility is provided thanks to the satellites that are available in the differential. Thus,when the car enters a turn, the angular velocity of the outer wheel will be proportional to how much the inner axle shaft lowered it.
Varieties of locks
You can block the operation of the differential by direct connection of the loaded axle shaft with the housing. You can also do this by limiting the rotation of the satellites. This system can be:
- Full. In this case, the value of the transmitted torque to the wheel can reach 100 percent. All mechanisms are rigidly connected. Such an interwheel differential lock is used on KamAZ and on many frame SUVs.
- Partial. The moment will be distributed forcibly by limiting the operation of the components of the differential.
Operating modes
Professionals are well aware that there are two modes of cross-axle differential lock:
- Manual. How does he work? In this case, a cam differential is used for forced locking.
- Automatic. Here, the self-locking differential automatically imposes restrictions on operation. The degree and necessity of blocking are determined by the difference in torque on the axle shafts. The angular speeds of the wheels are also taken into account. Optionally, a center differential lock sensor can be used.
Cam device
Consider the features of the cam differential. Here the blocking isforcibly, that is, manually. The coupling rigidly connects the differential housing to the loaded axle shaft. The cam mechanism drives the following types of drives:
- Mechanical.
- Electrical.
- Hydraulic.
- Pneumatic.
The system is activated by a special button or by means of a lever mechanism. The latter option is used mainly on cars older than 2000.
Note that the automatic differential works by increasing friction forces by changing the load conditions on the semi-axle of the driving wheels. This system is called LSD.
Types of self-blocks
There are four varieties:
- Disk.
- Viksomut.
- Worm.
- Electronic.
We'll take a closer look at each mechanism below.
Disk
In this case, a disc clutch is used. It is based on the principle of automatic blocking. It is carried out by changing the angular velocity of the semiaxes. So, the greater the difference, the higher the degree of momentum redistribution.
In the LSD system, friction is provided by friction disc packs. One package has a rigid engagement with the axle shafts, and the second - with the auto differential cup.
When the driving wheels turn the same, the friction packs have the same speed. When the angular velocity changes, the axle disk that starts to accelerate will transfer some of the torque to the opposite axle. There is a partial blocking of the differential due to an increase in the friction force of the friction packs. Depending on the device, the mechanism may have a constant or variable compression ratio. In the first case, it is regulated by springs, in the second - by a hydraulic drive.
Worm
What are the features of this mechanism? In this case, the axle shafts and satellites interact with each other through a worm gear. Such a scheme is used to create LSD locks. This drive is called "Thorsen". Very often, a cross-axle differential lock is installed on the Niva. Also, "Torsen" is used by many foreign manufacturers on their SUVs and crossovers. The essence of the system is quite simple. With an increase in torque on one wheel, partial blocking occurs and power is transferred to the second. It does not require additional nodes. The worm mechanism is initially self-locking due to the properties of the drive. The worm gear cannot be driven by other gears.
Viscous coupling
This cross-axle differential lock system is used on the Duster. In this situation, the clutch consists of a set of perforated discs. All of them are placed in a sealed case and filled with silicone fluid. The disks are connected to the drive shaft and to the cup. Silicone fluid has an interesting feature. It is known that when driving on the highway, there is no disc friction, and the entire moment is transferred to the front axle. But as soon as slip occurs, the discs begin torotate, thus shaking the liquid. The latter under such conditions changes its density. It becomes thick, due to which the discs can catch on to each other. This is how the torque is redistributed along the axles and between the wheels.
Why is this system not used on modern SUVs? Everything is very simple. The viscous coupling does not tolerate prolonged slippage. It can get you out of mud or snow at one time, but off-road it will quickly overheat. Since it cannot be repaired, you will have to buy a new mechanism.
Electronic lock
In this case, the limited slip differential is equipped with electronics that respond to changes in wheel speed. The mechanism is controlled automatically by the software. With an increase in the rotation of one wheel, a signal is sent to the block, as a result of which a command is given to the caliper. As a result, the system bites the wheel that rotates faster than the opposite one.
This lock is also called imitation because there is no actual torque distribution. Electronics only slows down the wheel, preventing it from slipping. Such a system is often used on premium crossovers (Audi or Range Rover). Unlike a viscous coupling, the mechanisms here do not overheat. But in terms of cross-country ability, this car will be inferior to the one equipped with a mechanical lock.
Conclusion
We looked at varietiesrear axle differential locks. There are a lot of systems that have a different device and principle of operation. Despite many new developments, the mechanical forced locking of the cross-axle differential is still the most reliable and practical. But such a mechanism has a high cost and requires more free space under the bottom. If you need a car with all-wheel drive, and you do not plan to go off-road, an electronic cross-axle differential lock will be the best solution.
