Each vehicle has a differential. This is a specific unit, the task of which is to distribute the torque between the wheels in a different ratio (depending on the road situation). Additionally, the differential may have a lock. Usually it is on SUVs or trucks. The cross-axle differential lock allows you to compensate for the main disadvantages of the mechanism and ensure uniform distribution of torque. In today's article, we will consider what kind of device it is, how it works, what types it happens.
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 semiaxes can vary. This is necessary so that the car safely enters the turn (without skidding). This feature is provided thanks to the satellites that are available in the differential. Thus, when a car enters a turn, the angular speed of the outer wheel will be proportional to how much the inner axle shaft has reduced it.
Types of locks
Blocking the differential can be done by directly connecting the loaded axle shaft to the housing. You can also do this by restricting the rotation of the satellites. This system can be:
- Complete. Moreover, the magnitude of the transmitted moment to the wheel can reach 100 percent. All mechanisms are connected rigidly. Such a cross-axle differential lock is used on KamAZ and on many frame SUVs.
- Partial. The moment will be distributed forcibly due to the limited operation of the components of the differential.
Operating modes
Professionals are well aware that there are two modes of locking the cross-axle differential:
- Manual. How does he work? In this case, a cam differential is used to force the lock.
- Auto. Here the limited-slip differential automatically imposes restrictions on the work. The degree and necessity of blocking is determined by the difference in moment on the axle shafts. Wheel angular speeds are also taken into account. In addition, an axle differential lock sensor can be used.
Cam device
Consider the features of the cam differential. Here, the lock is forced, that is, manually. The clutch rigidly connects the differential housing to the loaded axle shaft. The cam mechanism drives these types of drives:
- Mechanical.
- Electric.
- Hydraulic.
- Pneumatic
The system is activated using a special button or through a lever mechanism. The latter option is mainly used on cars older than 2000.
Note that the automatic differential works by increasing friction due to changes in the load conditions on the drive axle shaft. This system is called LSD.
Types of Samoblok
There are four varieties of them:
- Disk.
- Vicksomufta.
- Worm.
- Electronic.
Below we will examine each mechanism in detail.
Disk
In this case, a disk clutch is used. It is based on the principle of automatic locking. It is carried out by changing the angular velocity of the semiaxes. So, the larger the difference, the higher the degree of redistribution of the moment.
In the LSD system, friction is carried out by means of friction disc packages. One package has a rigid engagement with the axle shafts, and the second - with a car differential cup.
When the drive wheels rotate equally, the friction bags have the same speed. When the angular velocity changes, the semi-axis disk, which begins to accelerate, will transmit part of the moment to the opposite axis. The differential is partially blocked due to the increase in the friction force of the friction packages. 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 semiaxes and satellites interact with each other through a worm gear. This scheme is used to create LSD locks. This drive is called the Thorsen. Very often, the cross-axle differential lock is set to "Niva". Thorsen is also used by many foreign manufacturers on their SUVs and crossovers. The essence of the system is quite simple. With increasing torque on one wheel, partial blocking occurs and power is transferred to the second. No additional nodes are required. The worm gear is initially self-locking due to the properties of the drive. Other gears cannot drive the worm gear.
Viscous coupling
Such a system of locking the cross-axle differential is used on the Duster. In this situation, the coupling consists of a set of perforated discs. All of them are placed in a sealed enclosure and filled with silicone fluid. The discs are connected to the drive shaft and to the cup. Silicone fluid has an interesting feature. It is known that when driving along the highway there is no friction of the discs, and the whole moment is transmitted to the front axle. But as soon as the slip occurs, the discs begin to rotate, thereby shaking the liquid. The latter in this situation changes its density. It becomes thick, due to which the disks can cling to each other. So there is a redistribution of torque along the axles and between the wheels.
Why is this system not used on modern SUVs? Everything is very simple. Viscous coupling does not tolerate prolonged slippage. Once it can pull you out of the mud or snow, but on off-road it quickly overheats. 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 software. When the rotation of one wheel increases, a signal is sent to the block, as a result of which a command is given for the support. As a result, the system bites the wheel that spins faster than the opposite.
This lock is also called imitation, since there is no actual redistribution of the moment. Electronics only brakes the wheel, preventing it from slipping. Such a system is often used on premium crossovers (Audi or Range Rover). Unlike viscous coupling, here the mechanisms do not overheat. But in terms of cross-country ability, this car will be inferior to the one that is equipped with a mechanical lock.
Conclusion
We examined the types of rear axle differential locks. There are so many systems that have a different device and principle of operation. Despite many new developments, 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, while you do not plan to leave for off-road, an electronic cross-axle differential lock will be the most optimal solution.