Design and principle of operation of the fan’s viscous clutch

“The black box – the viscocoupler, the principle of operation

Wondering whether I have a fan viscocoupler working properly or working at all? Started to surf the net and came across an article this man – Yuri Polyakov, truck driver, St. Petersburg … One of the most obscure units of my car for a long time remained a viscous fan drive cooling system, popularly referred to as “thermo, viscocoupler”. The purpose of the viscocoupler is to smoothly change the performance of the fan, depending on the ambient temperature and engine heat. But how exactly it works, and even more – how it is designed, I must admit, for a long time I had no idea. There seems to be no difference – in both cases it rotates rather tightly. I asked all my friends, who knows anything about these things, about the mechanism of the fluid coupling and its principle of action, went to service centers. The most probable version is the following: there is a disk inside the clutch that under some conditions gets engaged in the meshing with the inside cavity of the clutch and forces it to rotate without slipping. Something like a friction clutch, but controlled by a temperature sensor. Anyway, after some discussion and consultation with the drivers, I decided to lock it. One of the guys on the radio said, that there should be some bolt on its body, with the help of which this could be done. I took it off. Looked around. No bolts. On the front cover is a coil spring, reminiscent of the bimetallic coil in a window thermometer. Apparently it has something to do with the activation mechanism of the viscocoupler. Having not found any hints on forced locking, I decided – as it is still not working, so there is nothing to feel sorry for: I will drill a couple of through holes, put bolts there and fix it. That’s what I did. I drilled the body in two places. The supposed disk was clearly seen in the created holes. Having inserted and tightened the bolts, installed the casing with the fan in its place. After starting the engine. The blocked fan with characteristic rumble began to pump air through the radiator. Well, there, I think, at least this way. Better than “fry” the engine… But my blocking didn’t work for a long time. After about 600 km of run, the bolts rumbled out, ruthlessly chopped off by the disk hanging in the clutch. With tremendous force, pieces of aluminum ricocheted off obstacles, broke fan blades, plastic diffuser, and damaged the radiator. Not only that, a sticky, oil-like fluid leaked out of the viscocoupler, fouling the entire engine. It turns out that it is the very working element, which transmits the rotation force from the engine to the fan. I didn’t expect this situation! After a while I reached home parking I started the repair. As the saying goes, a bad head never rests… Igor, a neighbor, told me that he had encountered such problems. (Where have you been before?!). On his “Mercedes” there is a special hole in the viscocoupler for filling the working fluid. At one time he filled the clutch for a few days without a syringe – “by gravity”. The funny thing is that the fluid is very thick. So, having put the viscocoupler near the car and constructed a miniature funnel, Igor announced that everyone who would pass by should add a few drops to the funnel.

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This is how we refueled … At the disassembly I found exactly the same as I did, the viscous clutch- radiator fan assembly. On the outside everything seemed to work, but when cranking intensely, the viscosity when spinning is clearly not enough. On the advice of “the wisest” I bought special silicone oil with great viscosity for filling these clutches and a big disposable syringe at the drugstore. Since there were no holes for filling with working fluid on my clutch, I decided to drill it in the case myself. After carefully studying what was left of the old clutch, I chose a suitable place. Using a syringe I rather quickly filled the inside cavity and after cutting a thread in the hole I screwed in a screw which was greased with “thread locker” for tightness. HOW DOES THIS COUPLING WORK? The protracted repair strained my nervous system greatly, and I felt it necessary to find out everything connected with this “black box”. Gradually digging out the material and analyzing what I’ve read, I understood how this “engineering miracle” works. So. According to one of the versions, the engine warms up, pressure (or viscosity?) of the fluid in the working cavity increases – the viscous clutch begins to transmit torque. The fan rpm increases. In this way the fan performance is smoothly regulated. But then why in the front part of the clutch is there mounted the spiral thermal sensor? I take a tiny vessel, fill it with silicon oil and… submerge it in a kettle with boiling water. According to our version, the oil should thicken. But it didn’t! The oil became much more liquid than when it was cold, and its viscosity reminded me not of epoxy, but rather of transmission fluid. So, the option of thickening when heated is out of the question. So, the secret is in something else. After one more day of research in the literature (I should have studied it right away!), I finally figured out how it works. Now look at pictures and carefully look into a masterpiece of design idea. The shaft of the clutch is rigidly mounted on the pump pulley. On the shaft the bearing and the drive disk 6 are pressed. There are grooves on the drive disc to increase the area of the working surface. The same grooves are present on the bearing housing 5 (not all!) and the clutch cover 4. Outside the front cover of the housing is a bimetallic spiral 3, which under the influence of heat, moves the plate 2, opening and closing the outlet holes in the cover of the inner tank 1. How does it work? The engine is switched off. Oil gradually collects at the bottom of the viscous clutch. When the engine is started and the fan drive starts rotating under the centrifugal force the oil is first displaced along the outer radius of the drive disk 6 and then from there through special drilled channels into the internal reservoir of the viscous clutch 7. Back through the same channels the oil can not come out as the speed of rotation of the viscous clutch is much lower than that of the driving disk. Transfer of force through the fluid is reduced and the speed of the fan becomes much lower than the speed of the driving disk. If too much oil is poured into the fluid coupling during repair, it will not be able to fit into the internal reservoir, and by continuing to sit on the working surfaces, will continually transmit maximum speed. Engine in operation. Gradually the hot air from the radiator heats the bimetallic sensor 3, forcing it to turn the locking plate 2, and open the holes in the inner reservoir cover.

The oil squeezed by the centrifugal force from the holes formed in the reservoir cover gets on the grooves of the working surface of the drive disc, bearing housing and viscous clutch cover. “Viscous friction” between them increases and the speed difference decreases. The greater the heat, the more the stop plate rotates, the more oil goes through this continuous closed loop, and the more actively the fan rotates. So how do you check if the radiator’s viscous clutch is working? Indeed, on both hot and cold engines, if there is no rotation, the oil (if there is any) will be on the working surfaces of the viscous clutch and viscous friction between them will be maximum. The fan impeller can be turned by hand with effort. Therefore, with the motor turned off, you can’t check it properly. The easiest way to check it, which I have deduced for myself, is an ordinary newspaper rolled up in a tight tube. When the clutch is cold, with the engine running try to brake the fan impeller with a paper tube (don’t use your hands! they are still needed!). If you meet resistance, the blades will stop after a while. Now try the same on the well warmed up engine. If the clutch is working properly, you will not be able to stop it. That’s about it. I hope this article will help somebody get rid of unnecessary loss of effort, time and money…

Fuel consumption of Lada Kalina per 100 km

increased fuel consumption.

How the fan viscocoupler is designed, why it is needed, why and how it breaks

There is such an interesting mechanism in the design of the cooling system of the car, as a viscocoupler. On car forums often ask questions related to this mechanism. We have concluded that it is necessary to study this topic in detail.

What is a viscocoupling fan

  • Under such a strange name refers to a special mechanism, which has the function of selective transmission, determined by external conditions and torque. The clutch has the form of a sealed housing. Inside it there are discs arranged in two rows. One row of discs is connected to the driven shaft, respectively, the second row is connected to the driven shaft. The mechanism is designed so that the discs can alternate with each other. Their design has holes and protrusions.
  • Inside the viscous clutch there is a special fluid with a viscous structure, so the mechanism is often called viscous. Most often silicone is used to make this substance. The fluid is characterized by unique features that determine its effective use. The capabilities of this substance boil down to the following:

when the intensity of mixing increases, the viscosity index increases;

increased fuel consumption.

when heated, the coefficient of expansion increases.

Such features determine the principle of the viscous coupling, which will be studied further.

  1. Where is the viscocoupler located?
  2. This mechanism occupies a place between the vehicle cooling radiator and the pump pulley. It performs a number of important functions:
  3. Controlling the rotation speed of the blades of the fan, which cools the power unit of the car.

Ensuring the efficiency of the engine by activating the fan at the right moments.

Reducing the load experienced by the power unit.

The clutch can be mounted on a flanged shaft, which in turn is mounted on the pump pulley. The shaft can also be screwed onto the pump shaft. Next, you need to figure out how the cooling fan viscocoupler works.

  1. How the cooling fan viscocoupler works
  2. Getting acquainted with the viscous fan clutch will be impossible without learning the principle of operation of this mechanism. Inexperienced motorist this process may seem complicated, although, in fact, everything is simple and clear. The principle of operation of the cooling fan viscocoupler is based on the functioning of a bimetallic sensor. It is located in front of the viscous fan. This element reacts to the temperature that is transmitted through the radiator of the cooling system.
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When the temperature is low, the sensitive sensor causes the valve to compress. This causes the oil inside the viscous clutch to remain within the reservoir. The clutch on the fan is deactivated and continues to rotate at only 20% of the motor rotation rate.

As the temperature rises to the operating level, the sensor expands and forces the valve to rotate. This causes the oil to move through the chamber to the outer edges. The fan clutch is activated and the clutch speed increases from 20% to 80%.

When the vehicle is moving at a constant speed, the rotation of the discs is uniform and not accompanied by oil mixing between the discs. When there is a difference between shaft speeds (driven and driven) the discs also start to work in different modes. This causes the viscosity of the silicone fluid to increase. In this state, it has an effect on the transmission of torque.

When a large difference between the speeds of the discs occurs, the fluid becomes nearly solid, causing the clutch to lock. The device of the fan’s viscous clutch has been studied, now you need to learn how to check the malfunction of this mechanism.

How to check the viscous clutch

The operation of the fan’s viscous clutch should be checked on a cold and hot power unit. This is evidenced in the operational manuals for the repair of the vehicle. When the engine is cold, overdrive will not change the clutch rotation frequency. In the case of a hot motor, this indicator will greatly increase.

Also, the longitudinal play is necessarily checked, if detected, you will have to perform work to eliminate it. The presence of extraneous sounds during the rotation of the coupling will indicate a malfunction of the bearings.

  • Main Causes of Failure
  • The mechanism can fail for several reasons. We have highlighted the main and most common ones:
  • The use of different sized tires, which also have different levels of wear;
  • fluid leakage from the clutch;
  • wear and tear of parts as a result of intensive operation, exposure to aggressive factors and high temperature;
  • improper alignment of the drive mechanism;
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increased fuel consumption.

loss of bimetallic sensor properties, which can occur as a result of surface oxidation and clutch jamming;

faulty bearing condition.

Signs of failure

The first and main sign, which may indicate a malfunctioning state of the viscous clutch, is excessive heating of the motor. Such a situation can occur as a result of fluid leakage or lack of timely operation of the bimetric plate. The motor temperature rises, and the fan does not work at all or operates at low speeds, consequently, no cooling of the unit is provided.

It also happens that when the engine is cold, the fan rotates at full power. Such a situation may occur due to spoiled gel, breakage of some nodes of the mechanism or the grease turning into a solid substance.

  • What a faulty viscocoupler can lead to
  • Working reserve of the viscous clutch is on average 200 thousand km. After that the mechanism requires increased attention. It is necessary to control constantly the moment of its operation, especially in summer. It is also necessary to check the operating temperature of the engine in traffic jams. If values, close to critical are marked, you will have to deal with the clutch seriously. A new part costs a lot, and it is often impossible to find the right model. Therefore, many car owners decide to install the electric system. In any case, it is impossible to ignore such a situation, since it is possible to encounter the following troubles:
  • overheating of the motor;

reduction of pump service life;

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