Viscous coupling: principle of operation and device

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42

Now crossovers have gained great popularity in the automotive market. They have both full and monodrive. 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? A viscous coupling is an automatic mechanism for transmitting torque through special fluids. It is worth noting that the principle of operation of the all-wheel drive viscous coupling and the fan is the same.

Thus, the torque on both elements is transmitted using the working fluid. Below we will look at what it is.

What's inside?

The inside of the clutch body uses a silicone-based fluid. It has special properties. If it is not rotated or heated, it remains in a liquid state. As soon as torque energy comes in, it expands and becomes very dense. As the temperature rises, it looks like a hardened glue. As soon as the temperature drops, the substance turns into a liquid. By the way, it is flooded for the entire service life.

Howworks?

What is the principle of operation of a product called "viscous coupling"? According to the algorithm of actions, it is similar to the hydraulic transformer of an automatic transmission. Here, too, the torque is transmitted by fluid (but only through gear oil). There are two types of viscous couplings. We'll take a look at them below.

First type: impeller

It includes a metal closed case. The principle of operation of a viscous coupling (including a cooling fan) consists in the action of two turbine wheels. They are located opposite each other. One is on the drive shaft, the second is on the driven. 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 slip occurs, the temperature inside the case rises. The liquid becomes thicker. Thus, the driving turbine wheel engages with the axle. All-wheel drive is connected. As soon as the car left off-road, the rotation speed of the impellers is restored. As the temperature drops, the density of the liquid decreases. Four-wheel drive is disabled in the car.

Second type: disk

Here, too, there is a closed case. However, unlike the first type, there is a group of flat disks on the driving and driven shaft. What is the principle of operation of this viscous coupling? The discs rotate in silicone fluid. As the temperature rises, it expands and presses these elements.

The clutch starts to transmit torque to the second axle. This only happens when the car has stalled and there are different wheel speeds (while some are standing, the latter are slipping). 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 has a long service life.

Where is it used?

First, let's note the element that is used in the engine cooling system. The principle of operation of the viscous fan coupling is based on the operation of the crankshaft. The clutch itself is attached to the rod and has a belt drive. The higher the crankshaft speed, the more the liquid in the clutch heated up. Thus, the connection became stiffer, and the fan element began to rotate, cooling the engine and radiator.

With a drop in speed and a decrease in fluid temperature, the clutch stops working. It should be noted that the viscous fan coupling is no longer used. Modern engines use electronic impellers with a coolant temperature sensor. They are no longer connected to the crankshaft and operate separately from it.

Four-wheel drive and viscous coupling

The principle of its operation is the same as that of the fan. However, the part is not placed in the engine compartment, but under the bottom of the car. And, unlike the first type, the all-wheel drive viscous coupling does not lose its popularity.

Now it is installed onmany 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 that the mechanical blocking, which is on the "Niva" and "UAZ". But due to urbanization, manufacturers have abandoned the real lock, which rigidly connects both axles and increases the vehicle's cross-country ability. The driver himself can choose when he needs all-wheel drive. If you need to overcome the off-road "SUV", it will quickly get stuck and after slipping, the rear axle will work for it. But it will not help him get out of the strong mud.

Benefits

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

• Easy design. Inside, only a few impellers or discs are used. And all this is powered without electronics, by physical expansion of the fluid.
• Cheap. Due to the simple design of the viscous coupling, it practically does not affect the cost of the car (if it concerns the “all-wheel drive” option).
• Reliability. The coupling has a durable housing that can withstand pressure up to 20 kilograms per square centimeter. Installed for life and does not require periodic replacement of the working fluid.
• Can work in all road conditions. It does not slip on mud or when driving on snow. Outside temperature is irrelevant for heating fluid.

Flaws

It is worth noting the lack of maintainability. The viscous coupling is permanently installed.

And if it is out of order (for example, due to mechanical deformations), then it changes entirely. Also, motorists complain about the inability to connect all-wheel drive on their own. The clutch engages the second axle only when the car is already "buried". This prevents the machine from easily climbing mud or snow obstacles. The next disadvantage is low ground clearance. The node requires a large case. 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.

You can't skid on full drive for a long time. Otherwise, there is a risk of damaging the viscous coupling. Therefore, this type of "dishonest" drive is not welcomed by off-road lovers. Under prolonged loads, the knot 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.