The cooling system of KamAZ vehicles is arranged according to the classical principle. But there are also features. One of them is the presence of a fan fluid coupling. Due to the proper operation of this unit, the truck cooling system under load works as efficiently as possible.
Purpose of the fluid coupling
The most important unit for ensuring effective engine cooling is the fluid coupling. KamAZ without it would have a continuously working cooling fan. Its meaning is to turn on the fan at the right time, and then turn it off. Indeed, at the moments of warming up the engine, as well as in the cold time of operation of the car, airflow is not needed at all.
The direct purpose of the fluid coupling is to transmit the engine crankshaft torque to the cooling fan at the right time . It also significantly dampens sudden changes in the operation of the crankshaft and serves as a good damper for the fan drive.
How this unique unit of the cooling system works will be clear from its structure.
KamAZ fluid coupling device
Only if there is oil inside the working space will the fluid coupling work. KamAZ has the best designs for this. The operation of the clutch is based on two wheels: drive (9) and driven (10). The drive wheel has 33 vanes and is connected to the crankshaft of the engine through the splined part of the shaft (7). The driven wheel has 32 blades and is inextricably linked with the driven shaft (16), which, in turn, drives the cooling fan. The drive shaft (7) rotates in bearings 8 and 19, and the driven shaft, in turn, in bearings 4 and 13.
Clutch impellers do not touch each other without oil. That is, only the drive wheel rotates in the off state. The slave can spin passively, thanks to the rotation of the fan with the shutters of the cooling radiator open. A reliable collapsible housing, consisting of a cover (1) and a casing (2), has a fan hydraulic coupling. KamAZ has a well-thought-out system of protection against leaks. To prevent oil leakage, the hydraulic coupling has two gaskets (17, 20) and a gasket (18).
In order for the oil to enter the fluid coupling at the right time, there is a fluid coupling switch with a “flag” for three positions. We will analyze this simple, but at the same time integral component in more detail.
Fluid clutch switch
A metal case with a temperature sensor directly connected to the coolant - this is the fluid coupling switch. KamAZ has the following temperature conditions: when the temperature of antifreeze or antifreeze rises to 83-86 ° C (hot or cold switch), the working mass in the sensor begins to melt and expand, pushing the rod. The channel for the flow of oil into the fluid coupling is opened. When the coolant temperature drops back, the spring returns the opening rod of the switch to its place.
What do the three positions of the fluid coupling switch do? The “checkbox” of the switch makes it possible to select three main operating modes:
- auto;
- constantly open option;
- constantly closed.
It is clear that the automatic mode is the main working one and does not switch to other positions with a functioning fan fluid coupling. In the event of a malfunction in the switch (which is quite possible), it is set to the "constantly open" mode. And at the first opportunity, the switch is replaced.
The third mode of the hydraulic clutch switch is “permanently closed”, used in the case of overcoming deep fords by a car. In these cases, the operation of the fan is not just not needed, but will only be harmful.
The principle of operation of the fluid coupling of the fan
Now, after the internal structure of the fluid coupling has become clear, it’s quite simple to figure out how it all works. In the automatic mode, the fluid coupling sets in motion, and specifically, turns on the fan, when the temperature of the coolant rises to 83 ° C or 86 ° C. The fan, turning on, blows the radiator, thereby cooling the antifreeze and maintaining the optimum temperature of the engine.
When the temperature of the antifreeze decreases, the fluid coupling switch is activated, and it turns off the rotation of the fan. After that, it can only rotate passively, from the flow of incoming air due to the movement of the car (with the radiator shutters open).
It also now becomes clear how to ensure the smooth operation of the cooling fan. The easiest way is to set the “flag” of the fluid coupling switch to the “constantly open” position. The fan will constantly turn, as the oil will be in the fluid coupling all the time, and it will work continuously, as long as the engine’s crankshaft rotates.
Features and weaknesses of the fluid coupling
The fluid coupling is a fairly complex unit, and it may seem that this is not a very reliable design. But in practice, the fluid coupling itself practically does not break. Its reliability is extremely high. The weak point in the transmission system of torque from the crankshaft is the inclusion of a fluid coupling. KamAZ has a rather weak hydraulic clutch switch. It is the element that can bring the entire cooling system of the car.
In the fluid coupling itself, oil seals and bearings can theoretically wear out. But these components are selected based on typical loads, plus some margin of safety. For their failure, there must be an unplanned impact. In cases of uniform operation of the car and with regular maintenance, the fluid coupling can work without repair and replacement.
Clutch Advantages
If we consider other types of couplings in the fan drive, namely electric and viscous couplings, hydraulic couplings on the face have obvious advantages.
- There is no whole electrical circuit to control and control the operation of the unit.
- Higher design reliability, which increases uptime during engine operation.
- Turning the fan on and off for the fluid coupling is the fastest.
All the obvious advantages of the fluid coupling are noticeably worsened by not the most reliable element of the system - its switch. In practice, different methods are used to increase overall reliability. One of these is the use of a switch from Ural-4320.
How to identify a malfunction?
There are several factors to ensure the long and trouble-free operation of the fluid coupling. KamAZ is very reliable, but there are nuances. First of all, this, of course, is a fluid switch working switch. In practice, most problems arise precisely because of its incorrect operation. This turns this part into a consumable item, along with engine filters.
The next factor will be the quality of the engine oil. There is a good all-weather engine oil - there will be normal effective operation of the fluid coupling. KamAZ is not so demanding in everything, but not in this case. This must be taken into account in the winter operation of the car.
It is also worth noting the regular inspection of the engine cooling system for leaks. Any traces of coolant or oil must be repaired in a timely manner. The smallest leak without intervention can disable the entire engine.
The deterioration of the fluid coupling can be easily determined by reducing the cooling fan speed. If it does not spin at all on a hot engine, the damage is obvious. It’s good if you just wore or loosened the fan drive belt. If this is a fluid coupling oil seal, KamAZ will require more laborious work.
How to replace the fluid coupling?
It works for a long time without any intervention of the fluid coupling. KamAZ-740 can afford it. But sooner or later everything wears out. If this happened and the further efficiency of the cooling system is in doubt, it is necessary to dismantle the element.
The installation location of the fan drive and the fluid coupling greatly complicates the replacement work. First of all, you need to access the engine. In the case of a KamAZ car, this is done by raising the cab. The sequence for replacing a fluid coupling may look like this:
- drain the motor a little;
- remove the attachment belt;
- unscrew the cooling fan;
- remove the oil pan;
- remove the cooling radiator;
- remove the oil cooler;
- dismantle the oil filter;
- provide access to the front cover of the unit by lifting the engine;
- remove the front cover together with the fluid coupling.
After the fluid coupling is removed, the degree of wear and types of defects are revealed. If possible, some elements are replaced. But given the complexity of the operation to replace the coupling, it is recommended to replace the entire assembly. It is even better and easier to replace the fluid coupling assembly with the front cover of the unit.
After performing the reverse assembly procedure, it is necessary to check the tightness of the system and then only the operability of the fluid coupling. When replacing a unit, you must select the original part and not look for adventure when selecting any analogues.
Prevention and Maintenance
A sufficiently long time ensures the correct and uninterrupted operation of the fluid coupling drive. KamAZ as a whole has a good margin of reliability. And in order for this to continue as long as possible, there is no need for special maintenance. Failure prevention consists of a general regular inspection, scheduled maintenance with a quality replacement of oils and other technical fluids.
Also, during operation and maintenance of the fluid coupling, you should always pay attention to its weak points - the switch. Timely replacement of a faulty circuit breaker can greatly facilitate the operation of the unit as a whole.
Instead of a conclusion
Reliable unit in the cooling system - fluid coupling. KamAZ with timely maintenance allows it to work out the entire engine operation cycle without fail. In the case of replacing the coupling, it is recommended to completely replace the original assembly with the front cover of the cylinder block.