Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another. The opposite component of the clutch is the brake. Clutches are used whenever the ability to limit the transmission of power or motion needs to be controlled either in amount or over time. Clutches are useful in devices that have two rotating shafts. In these devices, one of the shafts is typically driven by a motor or pulley, and the other shaft drives another device. In a drill, for instance, one shaft is driven by a motor and the other drives a drill chuck. The clutch connects the two shafts so that they can either be locked together and spin at the same speed, or be decoupled and spin at different speeds. A clutch works because of friction between a clutch plate and a flywheel.

PARTS OF CLUTCHES

A clutch is that part of engine which engages or disengages power from the engine crankshaft to transmission. A clutch is mechanism by which you change the gears. In simple words, it turns on or off power to rear wheel. A clutch is made of clutch assembly which includes clutch plate, Clutch basket, Clutch hub, pressure plates, Clutch springs, and clutch cable.

Clutch Basket

It is bowl shaped basket which holds entire clutch assembly. It has teethes on the outside surfaces which fix on the primary drive teethes. It means that it is connected with the transmission. It is bolted onto the end of clutch shaft.

Clutch Hub

The clutch hub places between clutch basket and pressure plate. The clutch plates are mounted on it. It has teethes in the centre hole which rotate with main shaft. It means it is connected with the engine.

Clutch Plate and Drive (friction) plate

There are two types of plates in clutch plate. One is Drive (friction) plate another is Driven (Steel) plate. The friction plate is ring shaped and coated with fiber. It is a wear and tear part of clutch assembly. The friction plate surfaces interface between the clutch basket tangs (gaps) and pressure plate. It has teethes on the outside surfaces. These teethes fix on the cutouts between clutch hub tangs (gaps). It is coated with the same material as you see in brake pad (shoe).

Driven (steel) plate

It is ring shaped and made of steel and sometime of aluminum. The surfaces of steel or aluminum plate interfaces between pressure plate and clutch hub. It has teethes on inside surfaces. This teethes are fix on the cutouts of clutch hub. Mostly steel plates are used in clutch assembly due to their durability. The aluminum plates are used in Moto GP due to their lighter weight. These plates are worn out very fast compare to steel plate.

Pressure Plate

It is the moving part of the clutch assembly which works against clutch spring tension. It releases the clamping action on the clutch plates when the clutch lever is engaged.

  Clutch springs

The clutch springs shape is like short coil. These springs continuously hold the friction and steel or aluminum plates through spring tension. It also prevents slippage except when the clutch lever is engaged. Most of motorcycle has five or more springs used per clutch assembly. For higher engine output stiffer or more springs are used while softer or few springs used in order to lighter clutch level pulling effort.

Flywheel    mounts to the engine crankshaft

Clutch Cable

The clutch cable is a cable through which the rider’s input passes to the clutch internals.

TYPES  OF CLUTCHES

There are two types of clutches: Wet clutch & Dry clutch

Wet Clutch

Wet clutch are universal and found on any bike. Almost 99% of motorcycle manufactured uses this kind of clutch. In the wet clutch set up the entire clutch is inside the case of the bike. Here it is bathed in oil which acts like a kind of dampener. It stops the clutch from knocking on itself.

Advantages

• It has less wear and tear effect due to oil circulation.

• It has smoother engagement compare to dry clutch

• It is cooled by engine oil

• It tolerates slipping during initial clutch take off

• It is cheaper to manufacture

• The wet clutch operation is quiet and makes less noise compare to dry clutch operation.

Disadvantages

• Oil needs to be circulated specially for the clutch presence.

• Due to rotation of clutch in oil then engine losses some horse power to rear wheel

• Clutch garbage and hammer mixes in engine oil (an oil filter fitted to avoid such problem)

Dry Clutch

The dry clutch is almost identical to the wet clutch the only difference s there are seals on the shafts that keep oil out. In the dry clutch set up the entire clutch is outside the case of the bike. There is no oil circulated in to the clutch, which result into clutch knocking on itself.

Advantages

• It is very easy to replace as it is outside the case of bike.

• Oil does not need to circulate for clutch, which ultimately eliminate reduction in loss of Horse power due to oil circulation in clutch. It is the biggest reason why it is use in Moto GP racing.

• You can use friction modified oils in engine

• It is easier to use.

Disadvantages

• Sometimes it has tendency to grab during engagement which makes take off difficult.

• The clutch overheats due to grabbing effect and wears out very fast.

• The same thing makes clutch operation less progressive.

• It has very shorter life.

• Once hot it is very difficult to calm if there is no open clutch cover is there.

• It is very noisy sometimes makes you feel like hammering.

WORKING

The clutch allows engine power to be applied gradually when a vehicle is starting out and interrupts power to avoid gear crunching when shifting. Engaging the clutch allows power to transfer from the engine to the transmission and drive wheels. Disengaging the clutch stops the power transfer and allows the engine to continue turning without force to the drive wheels. To understand how a clutch works, we first need to understand who the players are and how the whole shebang works. So let’s look at the basic components: the flywheel, clutch disk, pressure plate, throw-out bearing and linkage.A large steel or aluminum “disc,” the flywheel is bolted to the crankshaft of the engine. The flywheel does many things – acts as balancer for the engine, dampens engine vibrations caused by the firing of each cylinder, and provides a smooth-machined “friction” surface that the clutch can contact. But its main function is to transfer engine torque from the engine to the transmission. The flywheel also has teeth along the circumference, allowing the starter motor to contact when turning the engine over.

The clutch disc is basically a steel plate, covered with a frictional material that goes between the flywheel and the pressure plate. In the center of the disc is the hub, which is designed to fit over the spines of the input shaft of the transmission. When the clutch is engaged, the disc is “squeezed” between the flywheel and pressure plate, and power from the engine is transmitted by the disc’s hub to the input shaft of the transmission.In layman’s terms, a pressure plate is a spring-loaded “clamp,” which is bolted to the flywheel. It includes a sheet metal cover, heavy release springs, a metal pressure ring that provides a friction surface for the clutch disc, a thrust ring or fingers for the release bearing, and release levers. The release levers lighten the holding force of the springs when the clutch is disengaged. The springs used in most pressure plates are of a diaphragm-type, however a few use multiple coil springs. Some high-performance pressure plates are “semi-centrifugal,” meaning they use small weights on the tips of the diaphragm springs to increase the clamping force as engine revolutions increase.The “throw-out bearing” is the heart of clutch operation. When the clutch pedal is depressed, the throw-out bearing moves toward the flywheel, pushing in the pressure plate’s release fingers and moving the pressure plate fingers or levers against pressure plate spring force. This action moves the pressure plate away from the clutch disc, thus interrupting power flow.

Mounted on an iron casting called a hub, the throw-out bearing slides on a hollow shaft at the front of the transmission housing. The clutch fork and connecting linkage convert the movement of the clutch pedal to the back and forth movement of the clutch throw-out bearing. To disengage the clutch, the release bearing is moved toward the flywheel by the clutch fork. As the bearing contacts the pressure plate’s release fingers, it begins to rotate with the pressure plate assembly. The release bearing continues to move forward and pressure on the release levers or fingers causes the force of the pressure plate’s spring to move away from the clutch disc. To engage the clutch, the clutch pedal is released and the release bearing moves away from the pressure plate. This action allows the pressure plate’s springs to force against the clutch disc, engaging the clutch to the flywheel. Once the clutch is fully engaged, the release bearing is normally stationary and does not rotate with the pressure plate.