Page 63 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

1
48 Automobile mechanical and electrical systems

Ramp or wedge

When forced, it
will raise the block

Lever
When force is applied,
it will raise the block
Fulcrum or
pivot point

The block is
raised when force
is applied

Figure 1.67 The three basic types of machine

1.4.20 Mechanical machines
Defi nition
A simple mechanical machine is a device that allows a small force to overcome a
Machine
larger force. There are only three basic machines ( Fig. 1.67 ):
A simple mechanical machine is a
device that allows a small force to ramps – such as a wedge
●
overcome a larger force.

levers – such as a lever!
●
A machine is a device that converts wheels and axles – such as pulleys and a belt.
●
one form of energy to another.
All other machines are combinations of these three. This is a good way of
making any complicated machine easier to understand. The main features of a
machine are:
mechanical advantage, which is the ratio of load to effort (think of a car jack)
●
velocity ratio, which is the velocity input compared to the velocity output (think
●
of a car gear box)
effi ciency, which is the work output divided by the work input as a percentage.
●
In a perfect machine, with no friction, the effi ciency would be 100%. All practical
machines have effi ciencies of less than 100% – otherwise perpetual motion
would be possible!

1.4.21 Gears

Gears are toothed wheels (with lots of small levers) that transmit the turning
movement of one shaft to another. Gear wheels may be used in pairs or in threes
if both shafts need to turn in the same direction. The gear ratio, which is the ratio
of the number of teeth on the two wheels, determines:
the torque ratio – the turning force on the output shaft compared with the
●
turning force on the input shaft