Viscous coupling: operating principle and device

Now the crossovers have become very popular in the automobile market. They have both a full and a single drive. It is connected with a device such as viscous coupling. The principle of the unit - later in this article.

Characteristic

So, what is this element? Viscous coupling is an automatic mechanism for transferring torque through special fluids. It is worth noting that the principle of operation viskomufty four-wheel drive and the fan is the same. Thus, the torque on both elements is transferred by means of a working fluid. Below we will consider what it is.

What is inside?

Inside the clutch housing, a silicone-based fluid is used. It has special properties. If it is not rotated or heated, it remains in a liquid state. As soon as the energy of the torque arrives, it expands and becomes very dense. As the temperature rises, it looks like frozen glue. As soon as the temperature drops, the substance becomes a liquid. By the way, it is filled for the whole period of operation.

How does it work?

What kind of product called "viskomufta" principle of operation? According to the algorithm of actions, it is similar to the hydraulic transformer of an automatic box. Here, too, the torque is transmitted by liquid (but only by transmission oil). There are two varieties of viscous. Below we will consider them.

First type: impeller

It includes a metal enclosure. The principle of viscous coupling (cooling fan including) consists in the operation of two turbine wheels. They are located opposite each other. One is on the drive shaft, the second is on the driven shaft. The body is filled with a silicone-based fluid. When these shafts rotate with the same frequency, there is no mixing of the composition. But as soon as the slip occurs, the temperature inside the hull is increasing. The liquid becomes thicker. Thus, the driving turbine wheel enters the clutch with the axle. The all-wheel drive is connected . As soon as the car left off-road, the speed of rotation of the impellers is restored. With the drop in temperature, the density of the liquid decreases. In the car, the all-wheel drive turns off.

Second type: disk

Here, too, there is a closed case. However, unlike the first type, there is a group of flat discs on the leading and driven shaft. What does this viskomufta work principle have? The discs rotate in silicone fluid. As soon as the temperature rises, it expands and presses these elements. The clutch begins to transmit torque to the second axis. This happens only in the case when the car stalled and there is a different frequency of rotation of the wheels (while some stand, the second stall). Both types do not use automatic electronic systems. The device operates on the energy of rotation. Therefore viskomufta fan and full drive features a long service life.

Where is it used?

First, note the element that is used in the engine cooling system. The principle of the viscous coupling of the fan is based on the operation of the crankshaft. The coupling itself is attached to the rod and has a belt transmission. The higher the speed of the crankshaft, the more heated liquid in the clutch. Thus, the connection became stiffer, and the element with the fan started to rotate, cooling the engine and the radiator. With a drop in speed and a drop in the temperature of the fluid, the clutch stops working. It is worth noting that the viscous coupling of the fan is no longer used. On modern engines, electronic impellers with a coolant temperature sensor are used. They are no longer connected to the crankshaft and operate separately from it.

All wheel drive and viscous coupling

The principle of its operation is the same as that of the fan. However, the part is placed not in the engine compartment, but under the bottom of the car. And, unlike the first type, viskomufta all-wheel drive does not lose its popularity. Now it is installed on many crossovers and off-road vehicles with a disconnectable drive. Some use electromechanical analogs. But they are much more expensive and less practical. Among worthy competitors, it should be noted that there is a mechanical lock, which is on the "Niva" and "UAZ". But due to urbanization, manufacturers abandoned the present lock, which rigidly connects both axles and improves the passability of the car. The driver himself can choose when he needs a four-wheel drive. If you want to overcome the off-road "parketniku", he quickly get stuck and after the slant he will earn the rear axle. But getting out of the strong mud will not help it.

Benefits

Let's look at the positive aspects of viscous coupling:

• Simplicity of design. Inside, only a few impellers or disks are used. And all this is activated without electronics, by physical expansion of the liquid.
• Cheapness. Due to the simple design viskomufta practically does not affect the cost of the car (if it concerns the option "all-wheel drive").
• Reliability. The coupling has a sturdy housing that can withstand pressures of up to 20 kilograms per square centimeter. It is installed for the whole service life and does not require a periodic replacement of the working fluid.
• Can work in any road conditions. It does not slip on dirt or when driving on snow. The external temperature does not matter for heating the working fluid.

disadvantages

It is worth noting the lack of maintainability. Viskomufta set forever. And if it is out of order (for example, due to mechanical deformations), it changes entirely. Also, motorists complain about the lack of the ability to connect the full drive itself. The coupling inserts the second axle into engagement only when the car is already "buried". This does not allow the car to easily overcome mud or snow obstacles. The next minus is a low ground clearance. A large housing is required for the unit. And if you use a small viskomuftu, it will not transfer the right torque force. And the last drawback is the fear of overheating. Long slip on the full drive can not. Otherwise, there is a risk of disabling viscous. Therefore, this type of "dishonest" drive is not welcomed by fans of off-road. With long loads, the node simply jams.

Conclusion

So, we found out how the viscous coupling of the all-wheel drive and the fan works. As you can see, the device thanks to a special fluid can transmit torque at the right time without involving additional sensors and systems. This is a very useful invention.