is, in many respects, self-sustaining: it supplies the power that drives a number of ancillary - subordinate - components without which it could not work.
It requires a controlled
supply, a timed electric
to ignite the air-and-fuel mixture, a means of dispersing heat, and lubrication to reduce
. These ancillary functions are carried out mainly by mechanically driven components. The
is their main power source, through
or pulley-driven chains or belts.
Starting the engine
A powerful electric
connected directly to the
is used to rotate the crankshaft at a speed high enough to initiate the four-stroke
and start the engine.
Starting the car, particularly from cold, therefore makes the heaviest demand on the
, since the
has first to overcome the
of the engine. There is also a high demand from electrical equipment such as flashers and lights, so the battery needs constant replenishing in order to maintain its
of about 12
Charging the battery
Charging is accomplished by a
- a dynamo in earlier cars, or an
in later ones - driven by the crankshaft. The generator output is controlled by a charging
which ensures that the battery receives the correct amount of
necessary to keep it fully charged.
Producing the spark
To produce the timed electric spark needed to ignite the fuel mixture, the low voltage from the battery is boosted to a very high voltage, about 30,000, by the
- a form of transformer.
The low-tension (LT) voltage passes through a
and then to the contact-breaker points in the
Each time the low-tension-current circuit is interrupted by the opening of the contact-breaker points in the distributor, the electrical surge as the current suddenly collapses induces high-tension (HT) voltage in a
in the coil.
The distributor then feeds the high-tension voltage to each of the
in turn at the correct time. Each sparkplug has two
at its tip, with a gap between them. The high-tension voltage jumps this gap and produces the spark that ignites the air and fuel mixture.
Driving the pumps
that feeds the
is either a mechanical one operated by an off-centre disc - a sort of circular cam - on the engine
, or an electric pump remotely mounted, sometimes close to the petrol tank.
In water-cooled cars, the
that circulates water through the cooling passages of the engine is belt-driven from a pulley on the crankshaft.
that pressurises oil for engine lubrication works directly from the crankshaft or camshaft.
How the engine is lubricated
Friction between moving metal parts in the engine is minimised by a thin film of oil.
Stored in a
, called the
, at the bottom of the engine, the oil is sucked into the pump, which sends it under
through various feed pipes and channels to the moving parts of the engine and then back to the sump.
The oil is circulated under pressure at a rate of several gallons per minute. The pressure is controlled in the pump by a relief
; when the pressure is excessive, it leaks some of the oil back to the sump.
Oil forced out of the crankshaft
is thrown against the
walls. This is known as 'splash lubrication'.
Before reaching the engine, the oil passes through a
attached to the pump, which removes
and potentially abrasive particles such as debris resulting from engine wear.
If the pressure drops - usually through mechanical failure - or if there is an oil deficiency, the moving parts of the engine wear rapidly and eventually
How the oil is pumped
There are two basic types of oil pump - a rotor type and a gear type.
has two multi-lobed rotors - an inner one and an outer one, revolving on different axes. The gear type has two adjacent meshing gears. The pump may be mounted internally or externally.
Oil sucked from the sump is pressurised as it passes through the decreasing gap between the rotor lobes or meshing gears.
The commonest filter
used to trap the sludge and debris that collects in the sump is made from resin-impregnated, pleated paper.
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If your car's instrument panel includes an
, it will tell you how well the charging system is working - the difference between the
going into the
and the power being used from it.
Almost all car
work on the four-stroke
, so called because it
and exhaust -
to produce one firing of the
/air mixture. This means that the
rotates twice to complete each cycle.