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August 20, 2020

Do you know fan clutch?

Do you know fan clutch?


Everyone knows that the role of the engine cooling system fan is to maintain the engine's operating temperature between the best 85-95°C, so that diesel has the best operating environment and keeps fuel consumption low.

Many car owners don't know much about fan clutches, and there are even some misunderstandings in use.


Introduction to Fan Clutch


The fan is mainly an important consumer of engine power, and the maximum is about 10% of engine power. In order to effectively reduce fan power consumption, reduce noise and wear, prevent overcooling of the engine, reduce pollution, and save fuel, some cars mostly use fan clutches. The silicon oil fan clutch is composed of a front cover, a housing, a driving plate, a driven plate, a valve plate, a driving shaft, a bimetallic temperature sensor, a valve plate shaft, a bearing, a fan, etc.

During the driving of the car, due to changes in environmental conditions and operating conditions, the thermal condition of the engine is also changing. Therefore, the cooling intensity of the engine must be adjusted at any time. It is very important to adjust the cooling intensity at any time according to the thermal condition of the engine. Installing a silicone oil fan clutch between the fan pulley and the cooling fan is one of the ways to achieve this adjustment.


Fan clutch principle


When the engine is cold-started or working under light load, the temperature of the cooling water and the airflow passing through the radiator is not very high. At this time, the oil inlet hole will be effectively closed by the valve plate, and there is no silicone oil in the working chamber. Will be in a separated state. When the driving shaft rotates, only due to the friction between the sealing felt ring and the bearing, the fan will slip on the driving shaft along with the casing, and the speed is extremely low.

When the engine load is effectively increasing, the temperature of the coolant and the airflow passing through the radiator will also increase accordingly. At this time, the temperature sensor is heated and deformed to drive the valve plate shaft and valve plate to rotate. When the temperature of the airflow flowing through the temperature sensor exceeds 338K (65°C), the oil inlet hole is completely opened, and the silicone oil enters the working cavity from the oil reservoir. The silicone oil is very viscous, and the active board can use the viscosity of the silicone oil to drive the casing and the fan to rotate. At this time, the fan clutch is in the engaged state, and the fan speed increases rapidly.

When the engine load decreases and the temperature of the gas flowing through the temperature sensor is lower than 308K (35°C), the temperature sensor returns to its original state, the valve plate closes the oil inlet hole, and the oil in the working chamber continues to flow from the oil return hole to the oil reservoir Cavity until it is empty. The fan clutch returns to the disconnected state.


Control temperature to reduce fuel consumption

In addition to controlling the temperature, the fan clutch can also effectively reduce fuel consumption. According to estimates, an engine with a 240-280 horsepower range requires a cooling fan of up to 4-7 horsepower. If it is a heavy-duty engine with more than 400 horsepower, the required power may be Will be higher.


In the engine thermal management system, the design of the fan has gone through three stages of development: the early rigid fan; the ordinary silicone oil clutch fan; the current more advanced multi-speed fan (including electromagnetic clutch fan, electronic control clutch fan).


But no matter which type is used, the ultimate goal is the same:

First, control the coolant temperature

Second, reduce power loss and reduce fuel consumption

● The locking device can only be used for emergency and long-term use is prohibited

In actual use, the fan clutch will inevitably have some failures. The most common one is the failure of the fan clutch. The fan speed cannot be adjusted according to the temperature of the coolant, resulting in a decrease in heat dissipation capacity and causing the engine to "high temperature boiling".


For this reason, many fan clutches are designed with locking devices for emergency use in the event of failure, but this seemingly intimate emergency device will cause a lot of trouble if it is used improperly.


Because the locking device of the fan clutch can only be used for emergency, it only provides a safety for everyone and cannot be used for a long time. However, after locking the fan clutch, many car owners do not replace or repair the fan clutch, but think one-sidedly This thing is not very useful and expensive, so there is no need to replace it.


Little do you know that the result of doing so will make you lose more than you gain, because after the fan clutch is locked, the following results will be caused:

First, the fan continues to run at the maximum power, causing a waste of fuel.

Second, the accuracy of engine coolant temperature control becomes worse.

Third, the locking device of the fan clutch is limited in strength and cannot withstand the full speed of the fan for a long time.

● Cannot be replaced with flanges, otherwise heavy losses

In addition to locking, many car owners choose to remove the fan clutch and replace it with a flange. They think that the steel flange is cheap, only tens of dollars, and the strength is high and not easy to break.

In fact, it is not. The use of flanged direct-connected fans poses a very big safety hazard, especially for engines with fans installed at the front end of the crankshaft.


I have encountered this kind of case before. After a fan clutch equipped with a Xichai CA6DL1 engine was damaged, the owner used a flange instead.

But because the fan of the engine has a very large inertia when it is running, the bolts used to connect the flange cannot withstand the impact. After the fracture, the flying fan broke the radiator, causing serious failure.


Therefore, you must not use a flange instead of a fan clutch, otherwise it is very likely that you will lose more than you gain.

In short, the fan clutch is an indispensable and important part of the cooling system. Its running state is directly related to the performance of the engine. It needs to be replaced immediately after a failure. You must not use speculative methods to achieve your goal of saving money and trouble. .


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