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Understand
40.
List the main types of couplings. How do they work? What are the
similarities and differences between them?
Apply
41.
The illustrations show three Cardan joints that form angles of 0
degrees, 30 degrees and 60 degrees. Which joint transmits rotary
force more effectively?
30
o
60
o
0
o
A CHANGE
OF GEARS
This
clutch
has various gears.
They change the gear ratio,
which is a measure of the
mechanical advantage.
7.
COUPLINGS AND CLUTCHES
Sometimes we need to transmit rotation from one axis of rotation to another. For
example, there may be a distance or an angle between two shafts and they may not
be totally aligned
24
. In these cases, we can use various coupling mechanisms.
❚❚
Rigid couplings
form a permanent connection between two shafts. These shafts
may have different diameters, but they must be perfectly aligned.
❚❚
Clutches
form a rigid connection which isn’t permanent. For example, a car has
a clutch that engages and disengages the engine and the wheels. This system
also permits various combinations that change the gear ratio between the engine
and the wheels. This is similar to the gear system of a bicycle.
Friction clutch
Jaw clutch
The ends of two shafts come into
contact. When one shaft turns, there is
friction. This turns the second shaft.
The ends of two shafts are connected by
interlocking teeth. A jaw clutch is more
reliable because it doesn’t slip easily.
friction
surface
Superficie
de fricción
❚❚
Flexible couplings
are also useful.
Oldham coupling
Cardan joint (Universal joint)
An Oldham coupling is used to connect
shafts that are not perfectly aligned.
The grooves permit lateral movement.
Oldham couplings can also connect
shafts that have different diameters.
A Cardan joint connects two shafts that
are at an angle to each other. Cardan
joints are used in cars. They transmit
rotary motion from the car’s engine to
its back wheels.
Coupling mechanisms include:
❚
rigid couplings, such as
flanges.
❚
flexible couplings, such as
Oldham couplings and
Universal joints.
❚
friction clutches and jaw
clutches.
Key concept
24
align
: place in a straight line
ADVANCE EDITION
