CLUTCHES.pptx
- 2. What is a Clutch? • A Clutch is a mechanical device that engages and disengages the power transmission , especially from driving shaft to driven shaft. • In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). In these devices, one shaft is typically attached to an engine or other power unit (the driving member) while the other shaft (the driven member) provides output power for work. • Normally this is designed to handle 125% ~ 150% of the maximum engine torque to handle the experienced load.
- 3. Why Do We Need A Clutch? • Clutch is a vital part of the car´s working machinery as the engine generates power all the time, and has parts which are constantly rotating, but the wheels are not constantly spinning. • To allow the car to both change speed and to come to a complete stop without turning off the engine, the connection between the wheels and the engine needs to be temporarily broken.The clutch cuts off power from the engine.
- 4. Functions of the clutch • To connect and disconnect the shafts • To start or stop a machine (or a rotating element) without starting and stopping the prime mover. • To maintain constant speed, torque and power. • To reduce shocks transmitted between machine shafts. • For automatic disconnect, quick start and stop, gradual starts, and non-reversing and over running functions.
- 5. Principles of operation of a Clucth • When two friction surfaces are brought in connect with each other and pressed, they are united due to the friction between them. • The friction between the two surfaces depends upon the area of the surfaces, pressure applied upon them and coefficient of friction of the surface materials. • The two surfaces can be separated and brought into contact when required. One surface is considered as driving member and the other as driven member. • The driving member is kept rotating. When the driven member is brought in contact to the driving member, It is also starts rotating.
- 6. Classification of Clutches • 1. Friction Clutches a.Single plate clutch b.Multi plate Clutch c.Cone clutch • 2.Centrifugal Clutch • Semi Centrifugal Clutch • 3.Positive Clutch-Dog Clutch • 4.Hydraulic Clutch • 5.Electro Magnetic Clutch • 6.Vaccum Clutch • 7.Over Running Clutch •
- 7. Friction Clutch • The friction clutches work on the fact that friction is caused when two rotating discs come into contact with each other. • A friction clutch transmits power by virtue of friction developed between contacting surface. The friction surface is typically flat and perpendicular to the axis of rotation. • . Two or more surface is pressed together by using compression spring. The friction force is used to bring the driven shaft to the proper speed gradually without excessive slipping.
- 8. Single Plate Clutch • A single plate is commonly used in cars and light vehicles. It has only one clutch plate which is mounted on the splines of the clutch shaft. • A flywheel is mounted on the crankshaft of the engine. A pressure plate is connected to the flywheel through the bolts and clutch springs. It is free to slide on the clutch shaft with the movement of clutch pedal. • When clutch is in engaged position, the clutch plate remains gripped between flywheel and pressure plate. Friction linings are provided on both the sides of clutch plate.
- 9. On one side clutch plate is in touch with flywheel and on other side with pressure plate. Due to friction on both sides, the clutch plate revolves with engine flywheel. Transmission Therefore, clutch transmits engine power to clutch shaft. Clutch shaft is connected to transmission (or gear box) of automobile. Thus, clutch transmits power from engine to transmission system which inturn rotates wheels of engine. When the clutch plate is to be disengaged, the clutch pedal is pressed. Because of this pressure plate moves back and clutch plate is disengaged from flywheel. Thus, clutch shaft stops rotating even if engine flywheel is rotating. In this position, power does not reach the wheels and vehicle also stops running. Single plate clutch is shown fig.
- 11. Multi Plate Clutch The multiplate clutch is an extension of single plate type where the number of frictional and metal plates is increased. Increase in number of friction surfaces obviously increases capacity of the clutch to transmit torque. Alternatively, the overall diameter of the clutch is reduced for the same torque transmission as a single plate clutch This type of clutch is therefore used in some heavy transport vehicles and racing cars where high torque is to be transmitted. This finds application in case of scooters and motorcycles, where the space available is limited
- 12. • When your foot is off the pedal, the springs push the pressure plate against the clutch disc, which in turn presses against the flywheel. This locks the engine to the transmission input shaft, causing them to spin at the same speed. • The amount of force the clutch can hold depends on the friction between the clutch plate and the flywheel, and how much force the spring puts on the pressure plate
- 14. Cone Clutch A cone clutch serves the same purpose as a disk or plate clutch. However, instead of maintaining two spinning disks, the cone clutch uses two conical surfaces to transmit torque by friction. The cone clutch transfers a higher torque than plate or disk clutches of the same size due to the wedging action and increased surface area. The engine shaft consists of a female cone, the male cone can slide on the clutch shaft. When the clutch is engaged the friction surfaces of the male cone are in contact with that of the female cone due to the force of spring. When the clutch pedal is pressed, the male cone slides against the spring force and the clutch is disengaged.
- 15. • “Uniform wear” principle is used in cone clutches. The only advantage of the cone clutch is that the normal force acting on the friction surfaces is greater that the axial force, as • compared to the single plate clutch in which the normal force acting on the friction surfaces is equal to the axial force. • The semi cone angle a is kept greater than a certain value to avoid self-engagement; otherwise disengagement of clutch would be difficult. This is kept around 12.50
- 17. Centrifugal Clutch • It’s working totally depends upon the centrifugal force created by the driving member (engine or motor). The centrifugal force is used to engage the clutch with driven shaft. As the engine starts rotating, it produces a centrifugal force which makes the sliding shoes to move outward. The friction lining of the shoes gets connected to the inner surface of the drum and it starts moving. Since the drum is connected to the driven shaft, so the power is transmitted from the engine shaft to the transmission shaft and finally to the load. • As the engine rotates, the inside assembly of the centrifugal clutch starts rotating but drum remains stationary and no power is transmitted. At lower speed, the centrifugal force produced is not sufficient to overcome the spring force. So the clutch remains disengaged. But as the speed increases, the centrifugal force also increases and now the centrifugal force becomes greater than the spring force.
- 18. • As the centrifugal force becomes greater than the spring force, this allows the sliding shoes to move outward against the spring and get engaged with the inner surface of the drum. • The drum starts rotating and transfers the rotating power from the engine to the driven shaft of the transmission. • When the load on the engine increases, its speed decreases and disengages the clutch.
- 20. Semi Centrifugal Clutch • Semi Centrifugal Clutches used in high powered engines and racing car engines where clutch disengagements require appreciable and tiresome drivers effort. The power transmitted with partly by clutch springs and remaining by the centrifugal action of an extra weight provided in the system. • When the engine at low speed the spring keeps the clutch engaged to transmit power, the weighted levers do not have any pressure on the pressure plate. • When engine at high speed the weights fly off and levers exert pressure on the pressure plate which keeps the clutch firmly engaged to transmit high torque.
- 21. • When the engine at low speed the spring keeps the clutch engaged to transmit power, the weighted levers do not have any pressure on the pressure plate. • When engine at high speed the weights fly off and levers exert pressure on the pressure plate which keeps the clutch firmly engaged to transmit high torque.
- 22. • Thus instead of having more stiff springs for keeping the clutch engaged firmly at high speeds, they are less stiff because of centrifugal forces of weighted levers, so that the driver may not get any strain in operating the clutch. • when the engine speed decreases, the weights fall and the weighted levers do not exert any pressure on the pressure plate and only spring pressure is exerted on the pressure plate to keep the clutch engaged.
- 24. Dog Clutch • Dog clutch is a type of clutch that is used to lock two shafts or shaft and the gearbox. The two parts of clutch one push the other and it causes both shafts to rotate with the same speed and without slipping. • This type of clutch is used to connect or lock two shafts. It has a sleeve having two sets of internal splines. The internal splines slide on a splined shaft with smaller diameter splines and the bigger diameter spline match with the external diameter
- 25. • The sleeve is made to slide on the splined shaft and its teeth match with the dog clutch teeth of the driving shaft. Thus the sleeve turns the splined shaft with a driving shaft. When the clutch is engaged this process is dun. • In order to disengage the clutch, the sleeve is moved back on the splined shaft to avoid contact with the driving shaft. The driven shaft revolves exactly with the driving shaft with same speed when the clutch is engaged. This is also known as the Positive clutch. • It is used in Sturmey Archer bicycle hub gear. • It is used in manual automobile gearbox.