Viskomufta: what is it, the principle of work, the purpose

In recent years, more and more popularity is gaining crossovers, or so-called parkets. These cars differ from these SUVs not only by the lack of a carrier frame (this function is performed by the body), but also by the "dishonest" all-wheel drive with electronic locks. And it connects automatically. To connect the two axles, viscous coupling is used. What is this element, not every motorist knows. In today's article we will consider this mechanism in more detail.

Characteristic

What is viscous coupling for? What is this mechanism? The viscous coupling is a device for automatically transmitting torque through viscous properties. In other words, the connection of the second axle of the car is made by changing the density of the liquid that is filled inside this clutch.

What kind of liquid

It is in a closed case of a device called viscous coupling. What it is? Inside the coupler is a dilatant fluid, which is made of silicone. Has special properties. In a calm state, it is liquid. But as soon as the molecules are mixed, it changes its density. The dilatant liquid is poured in for the entire life of the mechanism.

The device and the principle of operation

The viscous coupler operates on the principle of a torque converter, which is the automatic transmission. In both cases, the torque is transmitted by fluid. However, the coupling is slightly different from the torque converter. It is a sealed enclosure. Inside it rotate the leading and driven impellers (two turbines). When the shafts of the wheels rotate synchronously, the composition inside is in a liquid state. Once one axis has stalled, the torque of one turbine is transferred to the other. The liquid mixes and becomes firm. Thus, the transfer of torque to the axis is resumed. As soon as the car has overcome the obstacle, the mixing stops. The torque is again transmitted to one axis.

But this is not a single scheme of the viscous coupling device. Some turbines have leading and driven friction discs instead of turbines (see photo below). They work on the same principle. Inside, too, a dilatant liquid is poured. When the shafts rotate at different speeds, it is mixed and becomes dense (thus expanding). So, the torque is leveled, and both wheels (front and rear) rotate the same. Due to the expansion of the liquid, the driven and driving discs are pressed against each other. As you can see, the mechanism is quite simple. The element serves for a long time, therefore repair viskomufty can be needed soon.

Where is it used?

There are two main directions, where viscous coupling is used. What are these spheres? Below we will look at them:

• Cooling system. The viscous coupling is used for forced cooling of the radiator. The mechanism is mounted on the rod and driven from the crankshaft using a belt drive. A multi-bladed fan is mounted on top of the part. How it works? The stronger the pulley rotates, the faster the liquid thickens in the clutch. Thus, at medium and high revs, the engine cooler is forced to cool. With a drop in speed, the heat exchanger cools naturally. The fan stops working. Now this method of cooling is practically not used. The viscous coupling was replaced by electric fans. They are driven by the engine temperature sensor. The element is not connected to the crankshaft of the engine and is more technologically advanced.
• Connecting the all-wheel drive. And if in the first case the problem could be solved by electronics, then it is not possible to transfer the torque to the second axis in this way. Therefore, the main sphere of application of a viscous coupling is crossovers.

Benefits

What are the advantages of this mechanism? Let's consider some of them:

• Simplicity of design. The device has a liquid and two turbines (or disks), tightly closed in the body.
• Strength. The housing in the coupling is able to withstand a pressure of up to 20 atmospheres. Therefore, do not be afraid that the fluid will sometimes flow from outside.
• Practicality. Can work both on a dirt road, and on asphalt (for example, if you start with slipping). Does not require the presence of electronics. The drive is connected and switched off in automatic mode.

disadvantages

Despite such significant advantages, it is worth noting the disadvantages of a viscous coupling:

• Low maintainability. In the event of a failure, the whole viscous product is replaced with a new one. The cost of such a detail is quite large. Viscous coupling repair is not performed.
• Low efficiency of all-wheel drive. Both wheels will rotate at the same speed only when the car is heavily skidded. There can be no question of a rigid interaxle lock.
• Impossibility of forced connection. For example, you need to cross the ford. To do this, it is desirable to have a permanent all-wheel drive. However, the viscous coupling will not allow you to do this. Wheels will rotate fully only after you zabuksuete.
• Lowering the ride height. The body of the mechanism is quite large, which calls into question the characteristics of the cross-over of the crossover.
• Low resistance to overheating. The element can not work for a long time in the all-wheel drive mode (the properties of the liquid change, the viscous coupling bearing wears out). Otherwise it will fail. Therefore, you should not slip off-road for a long time.

Withdrawal viskomufty UAZ

Let's consider how to extract this part together with a fan, for example, cars of the Ulyanovsk Automobile Plant. So, for convenience, you need to remove the radiator and the fan cover (blinds). Then, by means of a key on 12, the two mounting bolts of the pulley pulley are loosened. Note: the viscous coupling nut has a left-hand thread. Therefore, it must be turned clockwise, and vice versa. After that, the coupling nut is loosened by a key on the 32. Hold the crankshaft pulley from scrolling. If the nut goes with difficulty, you can use a hammer. Gently strike the key in the direction of the turn. Then the coupling is successfully removed from the pump shaft. The 4 screws fixing the fan impeller are twisted by 13 keys . We get the mechanism out and put a new one. Install the element in the reverse order. The bolt rods are screwed into place using pliers with thin jaws. Then put the coupling, twist "by hand" mounting nuts. It is not necessary to screw the bolt on the coupling itself. It self-tightens when the engine starts.

So, we found out what viskomufta is.