Now crossovers have gained great popularity in the automotive market. They have both full and single-drive. It is connected using a device such as a viscous coupling. The principle of operation of the unit is further in our article.
Characteristic
So what is this element? Viscous coupling is an automatic mechanism for transmitting torque through special fluids. It is worth noting that the principle of operation of the viscous coupling of all-wheel drive and fan is the same.
Thus, the torque on both elements is transmitted using the working fluid. Below we consider what it is.
What's inside?
Silicone-based fluid is used inside the coupling body. It has special properties. If it is not rotated and not heated, then it remains in a liquid state. As soon as the torque energy arrives, it expands and becomes very dense. With increasing temperature, it looks like a cured adhesive. As soon as the temperature drops, the substance turns into a liquid. By the way, it is flooded for the entire period of operation.
How does it work?
What is the principle of the product called "viscous coupling"? According to the algorithm of actions, it is similar to a hydraulic transformer of an automatic box. Here, torque is also transmitted through fluid (but only via gear oil). There are two types of viscous coupling. Below we will consider them.
First type: impeller
It includes a metal enclosed enclosure. The principle of operation of a viscous coupling (including a cooling fan) is the action of two turbine wheels. They are located opposite each other. One is on the drive shaft, the second on the follower. The body is filled with silicone-based fluid.
When these shafts rotate at the same frequency, mixing of the composition does not occur. But as soon as slippage appears, the temperature inside the case rises. The liquid becomes thicker. Thus, the drive turbine wheel is engaged with the axle. Four
-wheel drive is connected
. As soon as the car left off-road, the speed of rotation of the impellers is restored. With a drop in temperature, the density of the liquid decreases. Four-wheel drive is disabled in the car.
Second type: disk
There is also a closed enclosure. However, unlike the first type, there is a group of flat discs on the drive and driven shaft. What is the principle of this viscous coupling? Discs rotate in silicone fluid. As the temperature rises, it expands and presses these elements.
The clutch begins to transmit torque to the second axis. This happens only when the car has stalled and there is a different frequency of rotation of the wheels (while some are standing, the second are stalled). Both types do not use automatic electronic systems. The device is powered by rotational energy. Therefore, the viscous coupling of the fan and all-wheel drive is characterized by a long service life.
Where is it used?
First, we note the element that is used in the engine cooling system. The principle of operation of the viscous coupling fan is based on the operation of the crankshaft. The coupling itself is mounted on a rod and has a belt drive. The higher the revolutions of the crankshaft, the more the fluid in the coupling warmed up. Thus, the connection became stiffer, and the element with the fan began to rotate, cooling the engine and radiator.
With a drop in speed and a decrease in the temperature of the fluid, the coupling stops its operation. It is worth noting that the viscous fan coupling 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 work separately from it.
Four-wheel drive and viscous coupling
Its principle of operation is the same as that of a fan. However, the part is not placed in the engine compartment, but under the bottom of the car. And, unlike the first type, viscous clutch all-wheel drive does not lose its popularity.
Now it is installed on many crossovers and SUVs with switchable drive. Some use electromechanical counterparts. But they are much more expensive and less practical. Among the worthy competitors, it should be noted, perhaps, that the mechanical interlock that is on the Niva and UAZ. But due to urbanization, manufacturers abandoned the real lock, which rigidly connects both axles and increases the cross-country ability of the car. The driver himself can choose when he needs all-wheel drive. If you want to overcome the terrain "SUV", he will quickly get stuck and after slipping he will earn a rear axle. But to get out of heavy mud it will not help him.
Benefits
Let's look at the positive aspects of viscous coupling:
- Simplicity of design. Inside, only a few impellers or discs are used. And all this is powered without electronics, by physically expanding the fluid.
- Cheapness. Due to the simple design, the viscous coupling practically does not affect the cost of the car (if this applies to the option “four-wheel drive”).
- Reliability. The coupling has a robust housing that can withstand pressure up to 20 kilograms per square centimeter. It is installed for the entire service life and does not require periodic replacement of the working fluid.
- It can work in any road conditions. It does not slip on mud or when driving in the snow. External temperature does not matter for heating the working fluid.
disadvantages
It is worth noting the lack of maintainability. Viscous coupling is installed forever.
And if it fails (for example, due to mechanical deformation), then it changes completely. Also, motorists complain about the lack of the ability to connect all-wheel drive on their own. The clutch engages the second axis only when the car is already “buried”. This prevents the machine from easily overcoming mud or snow obstacles. The next minus is the low ground clearance. A large enclosure is required for the assembly. And if you use a small viscous coupling, it will not transmit the desired torque force. And the last drawback is the fear of overheating.
Long slip on all-wheel drive is impossible. Otherwise, there is a risk of damage to the viscous coupling. Therefore, this type of "dishonest" drive is not welcomed by off-road lovers. With prolonged loads, the node simply wedges.
Conclusion
So, we found out how the viscous clutch of all-wheel drive and 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.