Page 55 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

1
40 Automobile mechanical and electrical systems

Increasing pressure

50 bar Maximum pressure after
combustion in an engine
cylinder

Fuel pressure
3 bar (injection system)
Typical tyre pressure

2 bar

Fuel pressure
(carburettor system)
Pressure less than 1 bar Atmospheric pressure
atmospheric can
be called a Inlet manifold pressure
depression or a at idle speed
vacuum
0 bar

Zero pressure

Figure 1.53 Absolute pressure

discussing subjects such as the operation of an engine, or at least make sure you
do not confuse the different fi gures.

1.4.6 Centre of gravity or centre of mass

The centre of gravity (or mass) is a point in or near to an object about which it

would turn if it could rotate freely. A symmetrical object, such as a cube or ball,
has its centre of mass at its geometrical centre; a hollow object such as a beer
glass may have its centre of gravity in the space inside it.
For an object such as a car to be stable, a perpendicular line down through its
centre of gravity must run within the boundaries of its wheelbase ( Fig. 1.54 ). If the
car is tilted until this line falls outside the wheelbase, it will become unstable and
fall over.
Defi nition

Time period 1.4.7 Oscillation
For any vibration, the time for one
complete oscillation. An oscillation is one complete to-and-fro movement of a vibrating object or
system ( Fig. 1.55 ). For any vibration, the time for one complete oscillation is its
time period.
The number of oscillations in one second is the frequency. In most mechanical
systems in the car, oscillations are damped down. The dampers (shock
absorbers) fi tted to the suspension help to prevent the springs oscillating.
Key fact

Energy cannot be destroyed, only 1.4.8 Energy, work and power
converted to another form.
Energy can be thought of as the ability to do work or the amount of work stored
up, and is measured in joules. When you have no energy it’s hard to work! Energy