Clutch
Overview
 
A clutch is a mechanical device
Machine
A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...

 which provides for the transmission of power
Power transmission
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.Power is defined formally as units of energy per unit time...

 (and therefore usually motion) from one component (the driving member) to another (the driven member). The opposite component of the clutch is the brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

.

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).

In the simplest application clutches are employed in devices which have two rotating shafts.
Encyclopedia
A clutch is a mechanical device
Machine
A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...

 which provides for the transmission of power
Power transmission
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.Power is defined formally as units of energy per unit time...

 (and therefore usually motion) from one component (the driving member) to another (the driven member). The opposite component of the clutch is the brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....

.

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).

In the simplest application clutches are employed in devices which have two rotating shafts. 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
Drill
A drill or drill motor is a tool fitted with a cutting tool attachment or driving tool attachment, usually a drill bit or driver bit, used for drilling holes in various materials or fastening various materials together with the use of fasteners. The attachment is gripped by a chuck at one end of...

 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.

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
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 resin with copper wire facing or a ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...

 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
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

 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
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

. Clutch pads usually last about 100,000 miles (160,000 km) 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 33 kN is normal for a single plate 430. The 400 Twin application offers a clamp load of a mere 23 kN. Bursts speeds are typically around 5,000 rpm 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
Formula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...

, IndyCar
IndyCar
IndyCar is the trade name of an American-based open-wheel auto racing sanctioning body. IndyCar sanctions three racing series, the premier IZOD IndyCar Series with its centerpiece Indianapolis 500, and developmental series Firestone Indy Lights and the U.S...

, World Rally
World Rally Championship
The World Rally Championship is a rallying series organised by the FIA, culminating with a champion driver and manufacturer. The driver's world championship and manufacturer's world championship are separate championships, but based on the same point system. The series currently consists of 13...

 and even most club racing, motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s, automatic transmission
Automatic transmission
An automatic transmission is one type of motor vehicle transmission that can automatically change gear ratios as the vehicle moves, freeing the driver from having to shift gears manually...

s and in some diesel locomotive
Diesel locomotive
A diesel locomotive is a type of railroad locomotive in which the prime mover is a diesel engine, a reciprocating engine operating on the Diesel cycle as invented by Dr. Rudolf Diesel...

s 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 discs can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged.

The Hele-Shaw clutch
Hele-Shaw clutch
The Hele-Shaw clutch was an early form of multi-plate wet clutch, in use around 1900. It was named after its inventor, Professor Henry Selby Hele-Shaw, who was noted for his work in viscosity and flows through small gaps between parallel plates...

 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

A centrifugal clutch
Centrifugal clutch
A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft....

 is used in some vehicles (e.g., Mopeds) and also in other applications where the speed of the engine defines the state of the clutch, for example, in a chainsaw
Chainsaw
A chainsaw is a portable mechanical saw, powered by electricity, compressed air, hydraulic power, or most commonly a two-stroke engine...

. 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. In the case of a chainsaw this allows the chain to remain stationary whilst the engine is idling; once the throttle is pressed and the engine speed rises, the centrifugal clutch engages and the cutting chain moves. See Saxomat
Saxomat
Saxomat was a type of automatic clutch available as an option on Fiat 1800, Saab 93, Borgward Isabella, Goliath/Hansa 1100, Auto Union 1000, BMW, Opel, Ford Taunus, NSU, Glas, Trabant Wartburg and Volkswagen cars. Opel sold it as Olymat; Trabant and Wartburg named the system Hycomat...

 and Variomatic
Variomatic
Variomatic is the stepless, fully automatic transmission of the Dutch car manufacturer DAF, originally developed by Hub van Doorne: this consists of a "V" shaped drive belt and two pulleys, each of two cones, whose effective diameter can be changed so that the "V" belt runs nearer the spindle or...

.

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

Also known as a 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 yield 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, as motors used in such calculators had high stall torque and were capable of causing damage to the mechanism if torque wasn't limited.
  • 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
    Dog clutch
    A dog clutch is a type of clutch that couples two rotating shafts or other rotating components not by friction but by interference. The two parts of the clutch are designed such that one will push the other, causing both to rotate at the same speed and will never slip.Dog clutches are used where...

     (see below) is the best-known.

Vehicular (general)

There are different designs of vehicle clutch but most are based on one or more friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

 discs pressed tightly together or against a flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

 using springs
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

. The friction material varies in composition depending on many considerations such as whether the clutch is "dry" or "wet". Friction discs once contained asbestos
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...

 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
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 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
Drag racing
Drag racing is a competition in which specially prepared automobiles or motorcycles compete two at a time to be the first to cross a set finish line, from a standing start, in a straight line, over a measured distance, most commonly a ¼-mile straight track....

 and other competitions, where speed is more important than comfort.

Automobile powertrain

In a modern car
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

 with a manual transmission
Manual transmission
A manual transmission, also known as a manual gearbox or standard transmission is a type of transmission used in motor vehicle applications...

 the clutch is operated by the left-most pedal
Automobile pedal
An automobile may have two to four foot pedals. The arrangement is the same for both right- and left-hand traffic. From left to right:* normally operated by the left foot:**clutch pedal, not in the case of automatic transmission...

 using a hydraulic or cable
Cable
A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...

 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."

The default state of the clutch is engaged - that is the connection between engine and gearbox is always "on" unless the driver presses the pedal and disengages it. If the engine is running with clutch engaged and the transmission in neutral, the engine spins the input shaft of the transmission, but no power is transmitted to the wheels.

The clutch is located between the engine and the gearbox, as disengaging it is required to change gear. Although the gearbox does not stop rotating during a gear change, there is no torque transmitted through it, thus less friction between gears and their engagement dogs. The output shaft of the gearbox is permanently connected to the final drive, then the wheels, and so both always rotate together, at a fixed speed ratio. With the clutch disengaged, the gearbox input shaft is free to change its speed as the internal ratio is changed. Any resulting difference in speed between the engine and gearbox is evened out as the clutch slips slightly during re-engagement.

Clutches in typical cars are mounted directly to the face of the engine's flywheel
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

, as this already provides a convenient large diameter steel disk that can act as one driving plate of the clutch. Some racing clutches use small multi-plate disk packs that are not part of the flywheel. Both clutch and flywheel are enclosed in a conical bellhousing, which (in a rear-wheel drive car) usually forms the main mounting for the gearbox.

A few cars, notably the Alfa Romeo Alfetta
Alfa Romeo Alfetta
Alfa Romeo GTV redirects here. For 916 series GTV see Alfa Romeo GTV & SpiderThe Alfa Romeo Alfetta is an Italian rear-wheel drive executive saloon car and fastback coupé produced from 1972 until 1987 by Alfa Romeo...

 and Porsche 924
Porsche 924
The Porsche 924 is an automobile produced by Porsche AG of Germany from 1976 to 1988. A two-door, 2+2 coupé, the 924 replaced the 914 as the company's entry-level model, and was the model that finally retired the 912. In production terms, the 924 was the first Porsche model powered by a...

 series, sought a more even weight distribution between front and backThis more even weight distribution gives better handling, particularly for fast cornering. It offers much of the balance advantage of a mid-engined layout, whilst still using a front-engined rear-drive bodyshell. by placing the weight of the transmission at the rear of the car, combined with the rear axle to form a transaxle
Transaxle
In the automotive field, a transaxle is a major mechanical component that combines the functionality of the transmission, the differential, and associated components of the driven axle into one integrated assembly....

. In this arrangement the clutch is also rear-mounted, inside the transmission housing. The propeller shaft between front and rear rotates continuously as long as the engine is running, even if the clutch is disengaged or the transmission in neutral.

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 motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...

s 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 clutch
Slipper clutch
A slipper clutch is a specialized clutch developed for performance oriented motorcycles to mitigate the effects of engine braking when riders decelerate as they enter corners....

es to eliminate the effects of engine braking
Engine braking
Engine braking is where the retarding forces within an engine are used to slow a vehicle down, as opposed to using an external braking mechanism, for example friction brakes or magnetic brakes....

 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
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 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
Air conditioning
An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle...

 compressor electronically-engaged clutches using magnetic force to couple the driving member to the driven member.

Other clutches and applications

  • Belt clutch: Used on agricultural equipment and some piston-engine-driven helicopters. Engine power is transmitted via a set of vee-belts that are slack when the engine is idling, but by means of a tensioner pulley can be tightened to increase friction between the belts and the sheaves.
  • Dog clutch
    Dog clutch
    A dog clutch is a type of clutch that couples two rotating shafts or other rotating components not by friction but by interference. The two parts of the clutch are designed such that one will push the other, causing both to rotate at the same speed and will never slip.Dog clutches are used where...

    : Utilized 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
    Fluid coupling
    A fluid coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch...

    : The driving and driven members are not in physical contact; coupling is hydrodynamic.
  • Electromagnetic clutch
    Electromagnetic clutch
    Electromagnetic clutches operate electrically, but transmit torque mechanically. This is why they used to be referred to as electro-mechanical clutches. Over the years, EM became known as electromagnetic versus electro mechanical, referring more about their actuation method versus physical operation...

    : 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
    Direct current
    Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

     causes the particles to clump together and adhere to the operating surfaces. Engagement and slippage are notably smooth.
  • Overrunning clutch or freewheel
    Freewheel
    thumb|Freewheel mechanismIn mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft...

    : If some external force makes the driven member rotate faster than the driver, the clutch effectively disengages. Examples include:
    • Borg-Warner overdrive
      Overdrive (mechanics)
      Overdrive is a term used to describe a mechanism that allows an automobile to cruise at sustained speed with reduced engine RPM, leading to better fuel economy, lower noise and lower wear...

       transmissions in cars
    • Ratchet: typical bicycles have these so that the rider can stop pedaling and coast
    • An oscillating member where this clutch can then convert the oscillations into intermittent linear or rotational motion of the complimentary member; 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.
    • The rotor drive train in helicopters uses a freewheeling clutch to disengage the rotors from the engine in the event of engine failure, allowing the craft to safely descend by autorotation.
  • 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.

Single-revolution clutch

When inactive it is disengaged and the driven member is stationary. When "tripped", it locks up solidly (typically in a few to tens of milliseconds) 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 teleprinter
Teleprinter
A teleprinter is a electromechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the...

 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
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

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 teleprinter
Teleprinter
A teleprinter is a electromechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the...

s, including the Teletype Model 28 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.

External links

  • HowStuffWorks has a detailed explanation of the working of an automobile clutch.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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