When the vehicle is
going at high speed with a light load, the natural draft of air passing through
the radiator may be sufficient for cooling the engine, but when the vehicle
is moving under a heavy load and at a slow speed for instance driving uphill, the
natural draft is certainly insufficient to produce the desired cooling. This explains
why a fan is a necessary part of the engine cooling system.
It is mounted behind the radiator on the same shaft on
which the water pump is mounted. It is driven by a V-belt from the crankshaft
pulley. It is generally made of sheet metal, but these days moulded plastic
materials, for example, nylon and polypropylene are also being used for making
fans.
For efficient and
economical running, it required that the fan must give adequate air flow at all
the conditions of vehicle load and speed. More flow than the minimum necessary
for effecting cooling at any particular time is simply uneconomical.
Thus the
commonly used method of running the fan at one constant speed ratio with the engine
is not desirable.
For example, the fan is designed to give adequate airflow
at low vehicle speeds. Say, when going uphill when the airflow due to vehicle
speed is tiny, obviously the air drought at high vehicle speed will be
much more than the desired when the airflow due to vehicle speed itself is
quite high.
Thus the fan will be unnecessarily consuming engine power, which
has been estimated as much as 5 percent of the engine. This is clearly waste
and must be avoided.
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technology