Clutch n Brakes

Clutch

A clutch is a machine used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driving shaft.

-function

Used to transmit power from driven shaft to driving shaft In automobiles, help vehicle to change the gear, the requirement is needed so that while the

driven shaft is stopped, the engine should run naturally under no load condition. Achieved by using clutch mounted between engine shaft and gearbox shaft and which is

operated by a lever.

-Type

1. single plate clutch

-Clutch plate

By using the formula:

W=total axial load

R1=External radius of clutch plate

R2=internal radius of the clutch plate

P=intensity of pressure between contacting surfaces.

µ=coefficient of friction between contacting surfaces

single plate clutch

Consider a elemental ring of radius ‘r’ and thickness δr on the contacting surface.

therefore,

Area of the ring on contacting surface is,

Axial load on the ring is,

δW = Pressure × Area of the ring

Frictional resistance offered by ring is,

Frictional torque acting on the ring is,

Torque transmitted by single plate clutch is obtained by considering following two assumptions

(a)uniform pressure theory

(b)uniform wear theory

(a)uniform pressure theory:

Assuming that the intensity of pressure over the entire contacting surface area is constant,

Then, p=constant

Total torque transmitted by single plate clutch can be obtain by integrating Equation

(b) Uniform Wear Theory

In this theory, we are considering that wear which take place is uniform over the entire contacting surface i.e.

P.r=constant

P.r=C

P=C/r

Axial load acting on the ring is

δW=p 2π r δr

δr C 2π r

CδW

Integrating above equation within limit we get,

w

0

R

R

1

2

δr C 2πδW

21

21RR

RR 2π

WC

RR C 2r C 2πW 1

2

We know that frictional torque acting on ring is,

δr r Cμ 2πΤδrrr

Cμ π2Τ

δr r pμ 2πΤ

r 2

r

2r

Torque transmitted by single plate clutch can be obtain by integrating the above equation within the limit R2 to R1 we get,

2

RRCμ 2π

2

rCμ 2πΤ

δrr Cμ 2πΤ

δrr Cμ 2πΤ

22

21

R

R

2

R

R

T

0

r

R

R

T

0

r

1

2

2

2

2

2

μW π2

1Τ

RR

RRμW π

2

1Τ

RRRR2π

Wμ πΤ

21

22

21

22

21

21

This is the torque transmitted by single plate due to friction considering uniform wear theory.

Power transmitted by single plate clutch is given by,

rpmin shaft of SpeedN where,

Watt60

NΤ 2πP

Τ ωP

Multiplate Clutch

Multiplate clutch is used when large torque is to be transmitted e.g. motor cars and machine tools

Multiplate clutch is used when compact construction is required e.g. scooters and motor cycles.

2. Multiplate clutch

For uniform pressure theory,

22

21

32

31

RR

RRμ W

3

2nΤ

For uniform wear theory,

21 RRμW 2

1nΤ

In case of new clutch ,the intensity of pressure is uniform along the surface of clutch but in case of old clutch uniform theory is more correct.

For single plate clutch normally both sides of the plate are effective .there for single plate clutch has two pairs of contacting surface i.e. n=2.

In actual practice, usually the theory of uniform wear is used in analysis of clutch.

Intensity of pressure is maximum at the inner radius R2 of the friction or contact surface,

2max2max R

CP OR CRP

Intensity of pressure is minimum at the inner radius R1 of the friction or contact surface,

1max1max R

CP OR CRP

In mutilate disc clutch

no of disc on driving shaft

no of disc on driven shaft

So no. of pairs in contact,

1nnn 21

-Multiplate clutch figure

1n

2n

-Clutch plate

Application

-three basic application of clutch

Overrunning clutch

This class of applications is typified by standby and compound drives. For example, a steam turbine and a standby electricmotor may be connected to a single driven shaft through overrunning clutches. The shaft can then be driven by either the turbine or the motor or both with no further modification of the installation. The turbine drive clutch automatically engages when the turbine starts to drive, but automatically overruns when the load is transferred to the electric motor.

Example of using overrunning clutch:• Dual motor/engine drives• Conveyor belts• Creep and starter drives• Disengagement of centrifugal masses

Indexing clutch

In this type of application, reciprocating motion applied to the driving race is transformed into intermittent motion in only one direction at the driven race. For example, if a pinion is connected to the driving race, a rack meshing with the pinion can givereciprocating motion to the driving race. The clutch will then advance or “index” the work (driven race) on each forward stroke of the rack, but will not return or back-up on the return stroke of the rack.

Example of using indexing clutch:• Metal stamping• Pressworking• Packing machines• Indexing tables• Assembling machines• Printing machines

Backstopping clutch

In backstopping or holdback* applications, one race is always fixed to a stationary ground member. The function of the clutch is to permit rotation of the mechanism, connected to the other race, in one direction only, and to prevent any rotation in the reverse direction at all times. Although the clutch normally overruns most of the time, it is referred to as a holdback or backstop in conveyors, gear reducers and similar equipment because its function is to prevent reverse rotation.

Example of using backstopping clutch:• Inclined conveyors• Escalators• Pumps• Gear drives• Fans

BrakesBrakes hydraulic theory

The fundamental concept behind hydraulics is the incompressible fluid. A fluid is a material that can flow into any volume. Gases and liquids are all fluids, the principle difference being the amount of compressibility they exhibit. The other unique characteristic that all fluids share is that the pressure is the same everywhere within the fluid region (neglect the effects of gravity, it doesn’t play on the size scales we are talking about). For example, let’s fill a 55 gallon drum completely with water, so that there is no air in the tank. If I push on the bottom of the tank the top of the tank will start to bulge (so will the sides, but not as much since they are thicker material). The force on the bottom of the tank got transmitted to every part of the tank. Now let’s get another 55 gallon drum and completely fill it with water as well. Connect it to the first tank with a hose, and get rid of all the air from the system. Again if I push on the bottom (or the top) of the first tank, the force will be felt every within the fluid, even the second tank that we just connected. Now we are starting to see our hydraulic system, the drums are the master and slave cylinders and the hose is, well, the hose.

This is our first hydraulic system. On the left is our master cylinder, on the right our slave cylinder. The key to remember is that the hydraulic fluid is incompressible. It will always have the same volume no matter what we do. If we move the master cylinder piston, then the volume inside the master cylinder changes, the volume of the rest of the system has to change in order to keep the total volume constant. Assuming that the hydraulic lines are perfect and never change the volume change in the master cylinder is going to have to be matched by a volume change in the slave cylinder.The volume change in the master cylinder is

Where is the distance the master cylinder piston moved, and is the cross sectional area of the master cylinder. Since the volume change in the slave cylinder is the same as the volume change in the master cylinder the distance the slave cylinder moves must be:

OK, but what about pressure? That’s easy, the pressure is the same everywhere. And we find it by dividing the force on the master cylinder piston by the master cylinder area:

Now what is the force exerted by the slave cylinder piston? We know the pressure in the slave cylinder, it is the same as in the master cylinder. The force on the slave cylinder piston is the pressure times the area of the slave cylinder:

So now we have the entire picture. If the slave cylinder is bigger (in diameter, and therefore area) than the master cylinder we get a bigger force out of the slave than we put into the master, but a smaller movement. Just like a lever.

-Working principle

The driver pushes the brake pedal; it applies mechanical force to the piston in the master cylinder. The piston applies hydraulic pressure to the fluid in the cylinder, the lines transfer the pressure – which is undiminished in all directions within the confines of the brake lines – to the wheel cylinders, and the wheel cylinders at the wheel assemblies apply the brakes.

Force is transmitted through the fluid. For cylinders the same size, the force transmitted from one is the same value as the force applied to the other. By using cylinders of different sizes, forces can be increased or reduced.

In an actual braking system, the master cylinder is smaller than the wheel cylinders, so the force at all of the wheel cylinders is increased.

When brakes are applied to a moving vehicle, they absorb the vehicle’s kinetic energy. Friction between the braking surfaces converts this energy into heat.

In drum brakes, the wheel cylinders force brake linings against the inside of the brake drum. In disc brakes, pads are forced against a brake disc. In both systems, heat spreads into other parts and the atmosphere, so brake linings and drums, pads and discs must withstand high temperatures and high pressures.

On modern vehicles this basic system has some refinements, such as a power booster. This helps the driver apply the brakes.

-brakes figure

-Application-broke pipe air : reducing to apply brake-brake cylinder air : increasing to apply brake-hydraulic brake : mostly in automotive transport

-bicycle brake : help to stop the bicycle and to slow down the vehicle