4.8.6 Fan
Long ago, the fan was installed on the same axis with the water pump shaft. It was rigidly attached to the drive pulley and drove air for additional cooling of the radiator constantly while the engine was running, because it was actuated by the crankshaft. In summer, this may be good. But in winter, when the ambient temperature is already enough for cooling, additional cooling is not good. Also, when driving a car in summer, when you often have to spend time idle in traffic jams, and the engine runs at low speeds, the cooling will be insufficient due to the lack of normal air flow from the fan.
Note
The importance of a certain (rather narrow) range of engine operating temperature, regardless of the season or load during its operation is worth mentioning here. As a conclusion: overheating is bad, but overcooling is also far from good.
But progress did not stand and does not stand still, therefore, realizing that there is no benefit in a constantly “turned on” fan neither in winter nor in summer, designers decided to install a fan with an electric motor, which turns on at the command of the temperature sensor. This is convenient, because the car warms up quickly, and when a certain temperature is reached, the electric fan starts working. In modern cars, the electric fan also has two modes of operation: fast and slow. It is controlled by electronics.
But there is another way to make the fan work without electronics in specified operating modes - install a viscous coupling.
This coupling is driven by a belt from the crankshaft pulley. The fan "sits" on the axis and, if unnecessary, does not rotate. As soon as there is a need for cooling, this coupling is triggered and the fan starts rotating, as if connected through a drive belt to the crankshaft.
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