CLUTCHESA clutch is a mechanism for transmitting rotation, which can be engaged and disengaged. Clutches are useful in devices that have two rotating shafts. In these devices, one shaft 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 (engaged), or be decoupled and spin at different speeds (disengaged).
TYPES OF CLUTCHESMultiple plate friction clutch Vehicular Wet and dry Automobiles Non-power train in automobiles Motorcycles Centrifugal
MULTIPLATE FRICTION CLUTCHThis type of clutch has several driving members interleaved with several driven members. It is used in motorcycles, automatic transmissions and in some diesel locomotives with mechanical transmission. It is also used in some electronically controlled all-wheel drive systems. It is the most common type of clutch on modern types of vehicles.
VEHICULARThere 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 whether the clutch is dry or wet, and on other considerations. 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 and are unsuitable for road 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, and the friction plate is released and allowed to rotate freely.When engaging the clutch, the engine speed may need to be increased from idle, using the manual throttle, so that the engine does not stall (although in some cars, especially diesels, there is enough torque at idling speed that the car can move; this requires fine control of the clutch). 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.
Wet and dryA 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. A dry clutch, as the name implies, is not bathed in fluid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle clutch bathed in transmission oil), stacking multiple clutch disks can compensate for the lower coefficient of friction and so eliminate slippage when fully engaged.
Automobiles This plastic pilot shaft guide tool is used to align the clutch disk as the spring-loaded pressure plate is installed. The transmissions drive splines and pilot shaft have an identical shape. A number of such devices fit various makes and models of drivetrains
In a car 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 would 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.
A manual transmission contains cogs for selecting gears. These cogs have matching teeth, called dog teeth, which means that the rotation speeds of the two parts have a synchronizer, a device that uses frictional contact to bring the two parts to the same speed, and a locking mechanism called a blocker ring to prevent engagement of the teeth (full movement of the shift lever into gear) until the speeds are synchronized.
Non-powertrain in automobilesThere 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 elements 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 depending on whether its a regular or heavy-duty clutch. There are also electronically engaged clutches (such as for an air conditioning compressor) that use magnetic force to lock the drive and driven shafts together
MOTORCYCLESOn 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, allowing the rider to shift gears. Motorcycle clutches are usually made up of a stack of alternating plain steel and friction plates. One type of plate has lugs on its inner diameter that key it to the engine crankshaft, while the other type of plate has lugs on its outer diameter that key it to a basket that turns the transmission input shaft. The plates are forced together by a set of coil springs when the clutch is engaged. Racing motorcycles often use slipper clutches to eliminate the effects of engine braking.
CENTRIFUGAL CLUTCHcentrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft.
WORKING OF CENTRIFUGAL CLUTCHThe input of the clutch is connected to the engine crankshaft while the output may drive a shaft, chain, or belt. As engine RPM increases, weighted arms in the clutch swing outward and force the clutch to engage. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of a housing. On the centre shaft there are an assorted amount of extension springs, which connect to a clutch shoe. When the centre shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction face.
It can be compared to a drum brake in reverse. This type can be found on most home built karts, lawn and garden equipment, fuel powered model cars and low power chainsaws. Another type used in racing karts has friction and clutch disks stacked together like a motorcycle clutch. The weighted arms force these disks together and engage the clutchWhen the engine reaches a certain RPM, the clutch activates, working almost like a continuously variable transmission. As the load increases the rpm drops, disengaging the clutch, letting the rpm rise again and reengaging the clutch. If tuned properly, the clutch will tend to keep the engine at or near the torque peak of the engine. This results in a fair bit of waste heat, but over a broad range of speeds it is much more useful than a direct drive in many applications.
Centrifugal clutches are often used in mopeds, underbones, lawnmowers, go-karts, chainsaws, and mini bikes to:keep the internal combustion engine from stalling when the blade is stopped abruptlydisengage load during starting and idleThomas Fogarty, who also invented the balloon catheter, is most often credited with first inventing the centrifugal clutch in the 1940s, although automobiles were being manufactured with centrifugal clutches as early as 1936.
CONE CLUTCHA cone clutch serves the same purpose as a disk or plate clutch. However, instead of mating 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.Cone clutches are generally now only used in low peripheral speed applications although they were once common in automobiles and other combustion engine transmissions.They are usually now confined to very specialist transmissions in racing, rallying, or in extreme off-road vehicles, although they are common in power boats. This is because the clutch doesnt have to be pushed in all the way and the gears will be changed quicker. Small cone clutches are used in synchronizer mechanisms in manual transmissions.
DIAGRAM OF CONE CLUTCH 1-Cones: female cone (green), male cone(blue) 2-Shaft: male cone is sliding on splines. 3-Friction material: usually on female cone, here on male cone 4-Spring: brings the male cone back after using the clutch control 5-Clutch control: separating both cones by pressing 6-Rotating direction: both direction of the axis are possible
Other clutchesDog clutchesTorque limiter 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.Overrunning clutch or freewheelHydraulic clutchElectromagnetic clutchE-Clutch
DOG CLUTCHES 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 clutchesDog clutches are used where slip is undesirable and/or the clutch is not used to control torque. Without slippage, dog clutches are not affected by wear in the same way that friction clutches are.Dog clutches are used inside manual automotive transmissions to lock different gears to the rotating input and output shafts. A synchromesh arrangement ensures smooth engagement by matching the shaft speeds before the dog clutch is allowed to engage.
Dog clutchesA good example of a simple dog clutch can be found in a Sturmey-Archer bicycle hub gear, where a sliding cross- shaped clutch is used to lock the driver assembly to different parts of the planetary geartrain.
Torque LimiterA torque limiter is an automatic device that protects mechanical equipment, or its work, from damage by mechanical overload. A torque limiter may limit the torque by slipping (as in a friction plate slip-clutch), or uncouple the load entirely (as in a shear pin). The action of a torque limiter is especially useful to limit any damage due to crash stops and jams.Torque limiters may be packaged as a shaft coupling or as a hub for sprocket or sheave. A torque limiting device is also known as an overload clutch.
TYPES OF TORQUE LIMITORDisconnect types Shear pin Synchronous magnetic Ball detent Pawl and springTorque limiting types Friction plate Magnetic particle Magnetic hysteresis
Slipper ClutchA slipper clutch (also known as a slider clutch or back- torque limiter) is a specialized clutch developed for performance oriented motorcycles to mitigate the effects of engine braking when riders decelerate as they enter corners.Slipper clutches have been used in most high displacement four stroke racing motorcycles since the early 1980s. Slipper clutches were introduced in the 1970s by John Gregory and TC Christenson on "Hogslayer" the most successful drag racing motorcycle of the 70s. Made of bronze sintered plates from an earthmover and a Rambler 2 speed transmission, the drivetrain let TC reach 180 mph in the quarter mile.
WORKINGThey are designed to partially disengage or "slip" when the rear wheel tries to drive the engine faster than it would run under its own power. The engine braking forces in conventional clutches will normally be transmitted back along the drive chain causing the rear wheel to hop, chatter or lose traction. This is especially noted on larger displacement four-stroke engines, which have greater engine braking than their two-stroke or smaller displacement counterparts. Slipper clutches eliminate this extra loading on the rear suspension giving riders a more predictable ride and minimize the risk of over- reving the engine during downshifts. Slipper clutches can also prevent a catastrophic rear wheel lockup in case of engine seizure or transmission failure. Generally, the amount of force needed to disengage the clutch is adjustable to suit the application.
USES:Slipper clutches were also used in the Honda Interceptor 750 . Before long slipper clutches could be found in nearly every big bore four-stroke race bike, and notably (due to the cruiser-style and riding position) the 1983-1985 Honda Shadow VT750/VT700 models. Another street bike application was in the 1990-1997 Suzuki VX800. Slipper clutches are now gradually being factory installed on production motorcycles such as the Aprilia RSV Mille, Ducati 1198, Honda CBR1000RR 2008+, Yamaha YZF-R6 2006-2008, Yamaha YZF-R1 SP 2006 , Yamaha YZF-R1 2007-2009, Yamaha V-Max 2009, Kawasaki ZX-10R, Kawasaki ZX-6R, Suzuki SV1000 and GSX-R1000 2005-2007, Suzuki Hayabusa 2008, Suzuki RM125 2008, Harley Davidson V-Rod VRSC 2008, and are available as retrofit for many other models.
Magnetic Particle ClutchA magnetic particle clutch is a special type of electromagnetic clutch which does not use friction plates. Instead, it uses a fine powder of magnetically susceptible material (typically stainless steel) to mechanically link an otherwise free wheeling disc attached to one shaft, to a rotor attached to the other shaft
WORKING:When a magnetic field is applied to the powder, it forms chains connecting the disc and rotor. The strength of the chains depends on the strength of the magnetic field.Some advantages over friction plate clutch is:it doesnt exhibit stick-slip phenomenon or stictionthe torque may be easily and quickly controlledit is more resistant to wearmay be used for continuous slip applicationshas a very fast response time
Fluid CouplingA 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. It also has widespread application in marine and industrial machine drives, where variable speed operation and/or controlled start-up without shock loading of the power transmission system is essential.
HistoryThe fluid coupling originates from the work of Dr. Hermann Föttinger, who was the chief designer at the Vulcan Works in Stettin. His patents from 1905 covered both fluid couplings and torque converters.In 1930 Harold Sinclair, working with the Daimler company, devised a transmission system using a fluid coupling and planetary gearing for buses in an attempt to mitigate the lurching he had experienced while riding on London buses during the 1920s.In 1939 General Motors Corporation introduced Hydramatic drive, the first fully automatic automotive transmission system installed in a mass produced automobile. The Hydramatic employed a fluid coupling.The first Diesel locomotives using fluid couplings were also produced in the 1930s.
OverviewA fluid coupling consists of three components, plus the hydraulic fluid:The housing, (which must have an oil tight seal around the drive shafts) - contains the fluid and turbines. (also known as the shell)Two turbines (fan like components): One connected to the input shaft; known as the pump or impellor, primary wheel input turbine The other connected to the output shaft, known as the turbine, output turbine, secondary wheel or runner
Stall speedStall speedAn important characteristic of a fluid coupling is its stall speed. The stall speed is defined as the highest speed at which the pump can turn when the output turbine is locked and maximum input power is applied. Under stall conditions all of the engines power would be dissipated in the fluid coupling as heat, possibly leading to damage.
SLIP A fluid coupling cannot develop output torque when the input and output angular velocities are identical.Hence a fluid coupling cannot achieve 100 percent power transmission efficiency. Due to slippage that will occur in any fluid coupling under load, some power will always be lost in fluid friction and turbulence, and dissipated as heat.
Hydraulic fluidAs a fluid coupling operates kinetically, low viscosity fluids are preferred.Generally speaking, multi-grade motor oils or automatic transmission fluids are used. Increasing density of the fluid increases the amount of torque that can be transmitted at a given input speed.
Hydrodynamic brakingFluid couplings can also act as hydrodynamic brakes, dissipating rotational energy as heat through frictional forces (both viscous and fluid/container). When a fluid coupling is used for braking it is also known as a retarder.
IndustrialFluid couplings are used in many industrial application involving rotational power, especially in machine drives that involve high-inertia starts or constant cyclic loading.
Rail transportationFluid couplings are found in some Diesel locomotives as part of the power transmission system.
AutomotiveIn automotive applications, the pump typically is connected to the flywheel of the engine—in fact, the couplings enclosure may be part of the flywheel proper, and thus is turned by the engines crankshaft. The turbine is connected to the input shaft of the transmission. While the transmission is in gear, as engine speed increases torque is transferred from the engine to the input shaft by the motion of the fluid, propelling the vehicle. In this regard, the behaviour of the fluid coupling strongly resembles that of a mechanical clutch driving a manual transmission.
AviationThe most prominent use of fluid couplings in aeronautical applications was in the Wright turbo-compound reciprocating engine, in which three power recovery turbines extracted approximately 20 percent of the energy or about 500 horsepower (370 kW) from the engines exhaust gases and then, using three fluid couplings and gearing, converted low-torque high-speed turbine rotation to low-speed, high- torque output to drive the propeller.