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Classification of clutches
i)
Positive Contact clutches
In these clutches, power transmission is
achieved by means of interlocking of jaws
or teeth. These are classified as:
a) Square Jaw Clutches
b) Spiral Jaw Clutches
c) Toothed Clutches.
Their main advantage is positive engagement
and once coupled, they can transmit
large torque with no slip.
• ii) Friction Clutches:
• In these clutches, power transmission is
achieved by means of friction between the
contacting surfaces. These are classified as:
•
a) Single-plate clutches
•
b) Multi-plate clutches,
•
c) Cone clutches and
•
d) Centrifugal clutches.
Applications: single plate clutches are used where large radial space is
available such as trucks, buses, cars, etc.
Single plate clutches
Multi-plate clutch
Fig: Single Plate Clutch
Brakes
• It is the mechanical device used to slow down or
completely stop the motion of a moving system by
applying an artificial frictional resistance.
BRAKE
• Brake is a mechanical device for applying a
force against the friction of the road, slowing
or stopping the motion of a machine or
vehicle, or alternatively it is a device to restrain
it from starting to move again.
• The kinetic energy lost by the moving part is
usually translated to heat by friction.
The capacity of a brake depends upon the following factors
1. The unit pressure between the braking surfaces,
2. The coefficient of friction between the braking surfaces.
3. The peripheral velocity of the brake drum,
4. The projected area of the friction surfaces, and
5. The ability of the brake to dissipate heat equivalent to the
energy being absorbed.
The major functional difference between a
clutch and a brake:
 Clutch is used to keep the driving and driven member moving together.
whereas
 Brakes are used to stop a moving member or to control its speed.
 In Clutch power is transmitted from rotating to stationary shaft.
whereas
 In Brakes rotating shaft is made standstill or its speed is decreased by a
stationary shaft.
Caliper disc brake
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• Caliper Disc Brake Assembly
Because a disc brake assembly can absorb
more heat than a drum brake assembly,
most cars use disc brakes for their front
brake systems. When the brake pedal is
pushed, brake fluid from the master
cylinder compresses the brake pads
against the rotors attached to the
vehicle's front wheels. The friction
between the stationary pads and the
revolving rotors causes the rotors and
wheel to slow and stop.
Advantage: Excellent Control.
Application:
i) Used in vehicle conveyers.
ii) Due to excellent control, specially used in motor cycles & racing cars.
The wagon brake (top) and the band brake
(bottom) are common forms of mechanical
brakes.
Block or Shoe brake
Brakes. (Fig. shows)
a) Single-block
brake.
The
block is fixed to the operating
lever; force in the direction of
the top arrow applies the
brake.
c)External Expanding shoe brake.
Shoes are lined with friction material.
d)Internal expanding shoe brake with
lining.
It is used in automobile vehicles (trucks,
buses, cars, motorcycles, scooters etc.)
b) Double-block brake. The
blocks are pivoted on their
levers; force in the direction of
the arrow releases the brake.
It is used in crane hoists.
The main advantage is that
braking action is doubled by
the use of two blocks & both
can be operated by the same
force.
Block or Shoe brake
The single-block is the simplest form of
brake.
It consists of a short block fitted to the
contours of a wheel or drum and pressed
against its surface by means of a lever on a
fulcrum, as widely used on railroad cars.
The block may have the contour lined with
friction-brake material, which gives long
wear and a high coefficient of friction.
The fulcrum may be located with respect to
the lever in a manner to aid or retard the
braking torque of the block.
The lever may be operated manually or by a
remotely controlled force.
Friction lining material: Asbestos, leather,
cork, wood
INTERNAL EXPANDING SHOE BRAKE.