Classification of clutches

i) Positive Contact clutchesIn these clutches, power transmission is

achieved by means of interlocking of jawsor 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.

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.

The major functional difference between a clutch and a brake:

Caliper disc brake

how_disc_brakes_work.flv

• 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.

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.

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

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.)

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.