Types of Clutches by Application

Vehicular (General)

There are different designs of vehicle clutch but most are based on one or more friction discs pressed tightly together or against a flywheel using springs. The friction material varies in composition depending on many considerations such as whether the clutch is "dry" or "wet". Friction discs once contained asbestos but this has been largely eliminated. Clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient. However, these have a "grabby" action generally considered unsuitable for passenger cars. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate, depending on type. However, raising the engine speed too high while engaging the clutch will cause excessive clutch plate wear. Engaging the clutch abruptly when the engine is turning at high speed causes a harsh, jerky start. This kind of start is necessary and desirable in drag racing and other competitions, where speed is more important than comfort.

Automobile Powertrain

This plastic pilot shaft guide tool is used to align the clutch disk as the spring-loaded pressure plate is installed. The transmission's drive splines and pilot shaft have a complimentary shape. A number of such devices fit various makes and models of drivetrains

In a modern car with a manual transmission the clutch is operated by the left-most pedal using a hydraulic or cable connection from the pedal to the clutch mechanism. On older cars the clutch might be operated by a mechanical linkage. Even though the clutch may physically be located very close to the pedal, such remote means of actuation are necessary to eliminate the effect of vibrations and slight engine movement, engine mountings being flexible by design. With a rigid mechanical linkage, smooth engagement would be near-impossible because engine movement inevitably occurs as the drive is "taken up." No pressure on the pedal means that the clutch plates are engaged (driving), while pressing the pedal disengages the clutch plates, allowing the driver to shift gears or coast.

 Motorcycles

Motorcycles typically employ a wet clutch with the clutch riding in the same oil as the transmission. These clutches are usually made up of a stack of alternating plain steel and friction plates. Some of the plates have lugs on their inner diameters locking them to the engine crankshaft, while the other plates have lugs on their outer diameters that lock them to a basket which turns the transmission input shaft. The plates are forced together by a set of coil springs or a diaphragm spring plate when the clutch is engaged.

On most motorcycles the clutch is operated by the clutch lever located on the left handlebar. No pressure on the lever means that the clutch plates are engaged (driving), while pulling the lever back towards the rider will disengage the clutch plates through cable or hydraulic actuation, allowing the rider to shift gears or coast.

Racing motorcycles often use slipper clutches to eliminate the effects of engine braking which, being applied only to the rear wheel, can lead to instability.

 Automobile Non-powertrain

There are other clutches found in a car. For example, a belt-driven engine cooling fan may have a clutch that is heat-activated. The driving and driven members are separated by a silicone-based fluid and a valve controlled by a bimetallic spring. When the temperature is low, the spring winds and closes the valve, which allows the fan to spin at about 20% to 30% of the shaft speed. As the temperature of the spring rises, it unwinds and opens the valve, allowing fluid past the valve which allows the fan to spin at about 60% to 90% of shaft speed.
Other clutches such as for an air conditioning compressor electronically engaged clutches using magnetic force to couple the driving member to the driven member.

 Other General Clutches and Example Applications

• Dog clutches: Utilization in automobile manual transmissions mentioned above. Positive engagement, non-slip. Typically used where slipping is not acceptable. Partial engagement under any significant load tends to be destructive.

• Hydraulic clutch: The driving and driven members are not in physical contact; coupling is hydrodynamic.

• Electromagnetic clutch: Typically a clutch that is engaged by an electromagnet that is an integral part of the clutch assembly.

However, magnetic particle clutches have magnetically influenced particles contained in a chamber between driving and driven members which upon application of direct current causes the particles to clump together and adhere to the operating surfaces. Engagement and slippage are notably smooth.

• Overrunning clutch or freewheel: If some external force makes the driven member rotate faster than the driver, the clutch effectively disengages.

Examples include:

This was essential for the operation of Borg-Warner Overdrive transmissions in cars;

Typical bicycles have these so that the rider can stop pedaling and coast;

Another application includes an oscillating member where this clutch can then convert the oscillations into intermittent linear or rotational motion of the complimentary member;

Still others use ratchets with the pawl mounted on a moving member;

The winding knob of a camera employs a (silent) wrap-spring type as a clutch in winding and as a brake in preventing it from being turned backwards.

• Wrap-spring clutches: These have a helical spring wound with square-cross-section wire. In simple form the spring is fastened at one end to the driven member; its other end is unattached. The spring fits closely around a cylindrical driving member. If the driving member rotates in the direction that would unwind the spring the spring expands minutely and slips although with some drag. Rotating the driving member the other way makes the spring wrap itself tightly around the driving surface and the clutch locks up.

Specialty Clutches/Applications

• Single-revolution clutch: When inactive it is disengaged and the driven member is stationary. When "tripped", it locks up solidly (typically in milliseconds or tens of ms) and rotates the driven member just one full turn. If the trip mechanism is operated when the clutch would otherwise disengage the clutch remains engaged. Variants include half-revolution (and other fractional-revolution) types. These were an essential part of printing telegraphs such as the Teletype page printers, as well as electric typewriters, notably the IBM Selectric. They were also found in motor-driven mechanical calculators; the Marchant had several of them. They are also used in farm machinery and industry. Typically, these were a variety of dog clutch.

Single-revolution clutches in teleprinters were of this type. Basically the spring was kept expanded (details below) and mostly out of contact with the driving sleeve, but nevertheless close to it. One end of the spring was attached to a sleeve surrounding the spring. The other end of the spring was attached to the driven member inside which the drive shaft could rotate freely. The sleeve had a projecting tooth, like a ratchet tooth. A spring-loaded pawl pressed against the sleeve and kept it from rotating. The wrap spring's torque kept the sleeve's tooth pressing against the pawl.

To engage the clutch, an electromagnet attracted the pawl away from the sleeve. The wrap spring's torque rotated the sleeve which permitted the spring to contract and wrap tightly around the driving sleeve. Load torque tightened the wrap so it did not slip once engaged. If the pawl were held away from the sleeve the clutch would continue to drive the load without slipping.

When the clutch was to disengage power was disconnected from the electromagnet and the pawl moved close to the sleeve. When the sleeve's tooth contacted the pawl the sleeve and the load's inertia unwrapped the spring to disengage the clutch.

Considering that the drive motors in some of these (such as teleprinters for news wire services) ran 24 hours a day for years the spring could not be allowed to stay in close contact with the driving cylinder; wear would be excessive. The other end of the spring was fastened to a thick disc attached to the driven member. When the clutch locked up the driven mechanism coasted and its inertia rotated the disc until a tooth on it engaged a pawl that kept it from reversing. Together with the restraint at the other end of the spring created by the trip pawl and sleeve tooth, this kept the spring expanded to minimize contact with the driving cylinder.

These clutches were lubricated with conventional oil but the wrap was so effective that the lubricant did not defeat the grip.

These clutches had long operating lives cycling for tens, maybe hundreds of millions of cycles without need of maintenance other than occasional lubrication with recommended oil.

• "Cascaded-Pawl" single-revolution clutches: These superseded wrap-spring single-revolution clutches in page printers (such as teleprinters) including the Model 28 Teletype (and its successors using the same design principles). As well, the IBM Selectric typewriter had several of them.

These were typically disc-shaped assemblies mounted on the drive shaft. Inside the hollow disc-shaped housing were two or three freely-floating pawls arranged so that when the clutch was tripped, the load torque on the first pawl to engage created force to keep the second pawl engaged, which in turn kept the third one engaged. The clutch did not slip once locked up. This sequence happened quite fast, on the order of milliseconds.

The first pawl had a projection that engaged a trip lever. If the lever engaged the pawl the clutch was disengaged. When the trip lever moved out of the way the first pawl engaged, creating the cascaded lockup just described. As the clutch rotated it would stay locked up if the trip lever were out of the way, but if the trip lever engaged the clutch would quickly unlock.

• "Kickback" clutch-brakes:

These mechanisms were found in some types of synchronous-motor-driven electric clocks. Many different types of synchronous clock motors were used, including the pre-World War II Hammond manual-start clocks. Some types of self-starting synchronous motors always started when power was applied, but in detail, their behavior was chaotic and they were equally likely to start rotating in the wrong direction.

Coupled to the rotor by one (or possibly two) stages of reduction gearing was a wrap-spring clutch-brake. The spring did not rotate. One end was fixed; the other was free. It rode freely but closely on the rotating member, part of the clock's gear train. The clutch-brake locked up when rotated backwards, but also had some spring action. The inertia of the rotor going backwards engaged the clutch and "wound" the spring. As it "unwound", it re-started the motor in the correct direction. Some designs had no explicit spring as such; it was simply a compliant mechanism. The mechanism was lubricated; wear did not seem to be a problem.

Friction Clutches

Friction clutches are by far the most well-known type of clutches.

Materials

Various materials have been used for the disc friction facings, including asbestos in the past. Modern clutches typically use a compound organic resin with copper wire facing or a ceramic material. A typical coefficient of friction used on a friction disc surface is 0.35ų for organic and 0.25ų for ceramic. Ceramic materials are typically used in heavy applications such as trucks carrying large loads or racing, though the harder ceramic materials increase flywheel and pressure plate wear.

Push/Pull

Friction disk clutches generally are classified as "Push Type" or "Pull Type" depending on the location of the pressure plate fulcrum points. In a pull type clutch, the action of pressing the pedal pulls the release bearing, pulling on the diaphragm spring and disengaging the vehicle drive. The opposite is true with a push type, the release bearing is pushed into the clutch disengaging the vehicle drive. In this instance, the release bearing can be known as a thrust bearing (as per the image above).

Pads

Clutch pads are attached to the frictional pads, part of the clutch. They are most commonly made of rubber but have been known to be made of asbestos. They are usually around $120 dollars (£77 pounds) but different car manufactures vary. Clutch pads usually last about 100,000 miles, depending on how vigorously the car is driven.

Dampers

In addition to the damped disc centres which reduce driveline vibration, pre-dampers may be used to reduce gear rattle at idle by changing the natural frequency of the disc. These weaker springs are compressed solely by the radial vibrations from an idling engine. They are fully compressed and no longer in use once drive is taken up by the main damper springs.

Load

Mercedes truck examples: A clamp load of 33KN (33,000N) is normal for a single plate 430. The 400 Twin application offers a clamp load of a mere 23KN (23,000N). Bursts speeds are typically around 5,000rpm with the weakest point being the facing rivet.

Manufacturing

Modern clutch development focuses its attention on the simplification of the overall assembly and/or manufacturing method. For example drive straps are now commonly employed to transfer torque as well as lift the pressure plate upon disengagement of vehicle drive. With regards to the manufacture of diaphragm springs, heat treatment is crucial. Laser welding is becoming more common as a method of attaching the drive plate to the disc ring with the laser typically being between 2-3KW and a feed rate 1m/minute.

 Multiple plate clutch

This type of clutch has several driving members interleaved or "stacked" with several driven members. It is used in race cars including F1, Indy car, World rally and even most club racing, motorcycles, automatic transmissions and in some diesel locomotives with mechanical transmissions. It is also used in some electronically controlled all-wheel drive systems.Wet vs. dry
A "wet clutch" is immersed in a cooling lubricating fluid which also keeps the surfaces clean and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in engine oil), stacking multiple clutch disks can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged.
The Hele-Shaw clutch was a wet clutch that relied entirely on viscous effects, rather than on friction.
A "dry clutch", as the name implies, is not bathed in fluid and should be, literally, dry.

Centrifugal

Some vehicles such as mopeds use a centrifugal clutch. This clutch system employs centrifugal force to automatically engage the clutch when the engine rpm rises above a threshold and to automatically disengage the clutch when the engine rpm falls low enough. The system involves a clutch shoe or shoes attached to the driven shaft, rotating inside a clutch bell attached to the output shaft. The shoe(s) are held inwards by springs until centrifugal force overcomes the spring tension and the shoe(s) make contact with the bell, driving the output. See Saxomat and Variomatic.

 Cone clutch

Distinguished by conical friction surfaces. The cone's taper means that a given amount of movement of the actuator makes the surfaces approach (or recede) much more slowly than in a disc clutch. As well, a given amount of actuating force created more pressure on the mating surfaces.

Torque limiter

AKA slip clutch, or Safety clutch:
This device allows a rotating shaft to "slip" when higher than normal resistance is encountered on a machine. An example of a safety clutch is the one mounted on the driving shaft of a large grass mower. The clutch will "slip" or "give" if the blades hit a rock, stump, or other immobile object. Motor-driven mechanical calculators had these, between the drive motor and gear train, to limit damage when the mechanism jammed. (Motors had high stall torque.)

Carefully-designed types disengage (but continue to transmit torque) in such tools as controlled-torque screwdrivers.

Many safety clutches are NOT friction clutches, but belong to the "interference clutch" family of which the dog clutch (discussed briefly later) is the most well-knowN.

CLUTCH

A clutch is a mechanical device which provides for the transmission of power (and therefore usually motion) from one component (the driving member) to another (the driven member). 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 (e.g. electric screwdrivers limit how much torque is transmitted through use of a clutch; clutches control whether automobiles transmit engine power to the wheels).
Clutches are usually employed in devices which have two rotating shafts so we will use this as in the most basic example. In these devices one shaft is typically attached to a motor or other power unit (the driving member) while the other shaft (the driven member) provides output power for work to be done. 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 may be locked together and spin at the same speed (engaged), locked together but spinning at different speeds (slipping), or unlocked and spinning at different speeds (disengaged).
The rest of this article is dedicated to discussions surrounding types of clutches, their applications, and similarities and differences of such.
                                                

1.SINGLE PLATE CLUTCH
2.DOUBLE PLATE CLUTCH
3.MULTI PLATE CLUTCH

Types of Clutches

There are many other types of clutches in your car and in your garage.
An automatic transmission contains several clutches. These clutches engage and disengage various sets of planetary gears. Each clutch is put into motion using pressurized hydraulic fluid. When the pressure drops, springs cause the clutch to release. Evenly spaced ridges, called splines, line the inside and outside of the clutch to lock into the gears and the clutch housing. You can read more about these clutches in How Automatic Transmissions Work.

Car air conditioning compressor with magnetic clutch

An air conditioning compressor in a car has an electromagnetic clutch. This allows the compressor to shut off even while the engine is running. When current flows through a magnetic coil in the clutch, the clutch engages. As soon as the current stops, such as when you turn off your air conditioning, the clutch disengages.
Most cars that have an engine-driven cooling fan have a thermostatically controlled viscous clutch -- the temperature of the fluid actually drives the clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This type of clutch is a lot like the viscous coupling sometimes found in all-wheel drive cars. The fluid in the clutch gets thicker as it heats up, causing the fan to spin faster to catch up with the engine rotation. When the car is cold, the fluid in the clutch remains cold and the fan spins slowly, allowing the engine to quickly warm up to its proper operating temperature.
Many cars have limited slip differentials or viscous couplings, both of which use clutches to help increase traction. When your car turns, one wheel spins faster than the other, which makes the car hard to handle. The slip differential makes up for that with the help of its clutch. When one wheel spins faster than the others, the clutch engages to slow it down and match the other three. Driving over puddles of water or patches of ice can also spin your wheels. You can learn more about differentials and viscous couplings in How Differentials Work.
Gas-powered chain saws and weed eaters have centrifugal clutches, so that the chains or strings can stop spinning without you having to turn off the engine. These clutches work automatically through the use of centrifugal force. The input is connected to the engine crankshaft. The output can drive a chain, belt or shaft. As the rotations per minute increase, weighted arms swing out and force the clutch to engage. Centrifugal clutches are also often found in lawn mowers, go-karts, mopeds and mini-bikes. Even some yo-yos are manufactured with centrifugal clutches.
Clutches are valuable and necessary to a number of applications. For more information on clutches and related topics, check out the links on the following page.

Mannual clutches

MANUAL CLUTCHES

---

Clutches come in a number of designs, but they all are made to do two things.

Help the motorcycle make a smooth start from a stationary position.

Ease the transition of going from one gear to another.
Clutches are basically round baskets filled with alternating fiber and steel plates held together, tightly, with springs. One set of plates, usually the steel ones, is connected to the transmission. The other set, usually the fiber plates, is connected to the engine. The clutch lever compresses the springs so the plates are not pressed tightly together. This allows the clutch to disengage. This works pretty well and most times clutch life is quite good. However, as the clutch wears, the plates get thinner. This lessens the spring pressure. In addition, if you slip the clutch a lot as you engage it you can burn the plates a bit. All this is not good for the clutch and sooner or later you are going to need new plates. Most of the Japanese bikes have a wet plate clutch. This means the clutch runs in a bath of oil.
Dry plate clutches run dry with no oil. BMWs, some Harley-Davidsons, a few Japanese bikes, and others have dry clutches.
Repair is really quite simple. Remove the clutch cover, being careful to check for any washers from the kick starter that may stick to the inside of the clutch cover. Then loosen the nuts or bolts that hold and tension the clutch springs. Now remove the the clutch plates. On some clutches you pull the plates and the inner clutch basket as a unit after removing the nut or circlip holding it on. On others, you remove an outer clutch plate/spring carrier and then pull out the plates individually. There may be large rubber rings or large flat spring like things between the plates. There might be only one or there could be one between every plate. Sometimes the steel plates have a sort of dished out edge on one side, for better oiling I guess. Each one is staggered from the one before it and the one after it. Be sure and put all the plates, o-rings, washers, etc. back in the same order you took them out. Measure the thickness of the fiber plates and compare that measurement to the one given in your shop manual. If they are too thin replace them. If you do not have the thickness measurement just look at them. Most times if they are worn out they will LOOK worn out and/or smell burnt. If they smell burnt, replace them. Even if they look and measure good. Turn them on edge, both fiber and steel plates. If they are bent replace them. Look at the inner and outer fingers. If they are damaged or worn, replace them. Look at the clutch basket. Inspect the grooves the clutch plate fingers slide into. Both inner and outer. if they are badly worn, consider replacing the clutch basket.
Take the new fiber plates and soak them in a pan of oil for an hour or two before assembly. If you are reusing the old plates you can just coat them with oil. Make sure that the outer clutch plate that carries the springs meshes right with the clutch basket. On some, they will only go in the right way, but on others the grooves will not line up right and this prevents the springs from pushing the plates together. Some clutches will have arrows that must match. Others won't have anything... you just have to make sure they mesh up right.
Most clutches have the disengagement mechanism in the center of the clutch. Some activate it from the clutch cover and some use a rod going through the mainshaft of the transmission. This rod is activated by a cam or worm on one end of the rod, pushing the rod against the spring plate, releasing the clutch. This rod passes in front of the counter shaft sprocket and can easily be bent by small twigs and branches and gook thrown off by the rear chain. If you have this type and your clutch suddenly stops working, check here first for a bent clutch rod, before you tear the clutch apart. These rods can also be in two parts with a ball bearing between them. Some have a ball bearing only on the worm end. Don't let that ball bearing fall out and get lost.
Sometimes, when a bike has been sitting a long time, like over winter, the clutch plates will stick together. You pull the clutch lever in but the plates will not disengage. About 60-70% of the time you can get them to release by running the bike up to 15-20 MPH and locking up the rear brake while you hold the clutch lever in (disengaged). If this does not break it loose, you will have to take the clutch cover off and with the lever held on, pry the plates apart with a screwdriver and reoil them a bit.
Remember, most engines have a flat metal shim on the kick starter shaft. Lots of times it will stick to the clutch cover when you pull it off. Make sure you put it back on the kick starter.
After everything is finished and the clutch cover back on, don't forget to refill the engine with oil.
Some clutches, like the BMWs, Norton Commandos and some Harleys, have a single (or two) Heavy spring that is held in by a large circlip. These require a special tool to remove.
The BSAs and Triumphs require a special puller to get the clutch basket off.
All clutches must have a bit of free play in the cables and rods so the clutch springs can exert the maximum amount of pressure on the plates. If there is an adjustment screw on the rod, loosen the lock nut and tighten the screw until there is no more free play, then loosen it about 1/8 of a turn and tighten the lock nut. The adjustment screw can be right OR left thread, so watch out. A shop manual would be of help here. The adjusting screw can also be UNDER the clutch cover on the clutch spring plate. After you have made this adjustment, adjust the clutch cable keeping at least a little free play in the cable. Remember, on some bikes, the only adjustment is the free play of the clutch cable. Depending on the bike, the cable can be adjusted on both ends and in the center somewhere, only on both ends or only on one end