August 19, 2017 | Author: Vinu Kumar | Category: Clutch, Friction, Force, Transmission (Mechanics), Engines
Share Embed Donate

Short Description




ABSTRACT Clutches are useful in devices that have two rotating shafts. In these devices, one shaft is typically attached to a motor or other power unit (the driving member), and 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 can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged). Friction clutches

Page 1

Content A.NOMENCLATURE………………………………………………………………………..6 B.LIST OF FIGURES……………………………………………………………………….7 1. CHAPTER 1 INTRODUCTION 1.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...8 2.CHAPTER 2 HISTORY 2.1 HISTORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 9 3. CHAPTER 3 CLUTCH CONSTRUCTION 3.1 CLUTCH CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2 CLUTCH OR DRIVEN PLATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.3 PLATE TO HUB CONNECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.4 FRICTION FACING OR PADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4. CHAPTER 4 DESIGN OF CLUTCH 4.1 CLUTCH DETAILS DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 4.2 FRICTIONAL CONTACT AXIAL OR DISC CLUTCHES . . . . . . . . . . . . . . . . . . . . . . . . 21 4.3 METHOD OF ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Page 2 Friction clutches

4.4 UNIFORM PRESSURE AND WEAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.5 ELEMENTARY ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.6 UNIFORM WEAR CONDITION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 5. CHAPTER 5 OPERATION OF CLUTCH 5.1 OPERATION OF CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6.CHAPTER 6 TYPES OF CLUTCH 6.1 SINGLE PLATE CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 6.2 MULTI PLATE CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.3 CONE CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.4 CENTRIFUGAL CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 7.CHAPTER 7 MAJOR TYPES OF CLUTCHES BY APPLICATION 7.1 VEHICULAR [GENERAL] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 7.2 MOTORCYCLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 7.3 AUTOMOBILES NONPOWERTRAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34


Page 3 Friction clutches

8.1 SUMMARY……………………………………………………………………………………35 X. APPENDIX A BASIC CONCEPTS IN FRICTION………………………………………………………… 36 Y. ACKNOWLEDGEMENT

NOMENCLATURE 1.kPa – kilopascal 2.ºC – degree centigrade 3. - coeffiecient of friction 4. - area of object 5. - newton 6. - normal force 7. – frictional force 8. pi = 3.142 9. – torque 10. Rw - constant wear rate 11. P – constant pressure 12. V – sliding velocity 13. - angular velocity 14. Pmax - maximum pressure 15. Fa – axial force Page 4 Friction clutches

16. Rm –

mean radius




CHAPTER 1 1.1 INTRODUCTION A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without

Page 5 Friction clutches

stopping the driving shaft. A clutch thus provides an interruptible connection between two rotating shafts Clutches allow a high inertia load to be stated with a small power. A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gear box. Here the clutch enables to crank and start the engine disengaging the transmission Disengage the transmission and change the gear to alter the torque on the wheels. Clutches are also used extensively in production machinery of all types. It is a mechanical device, by convention understood to be rotating, which provides driving force to another mechanism when required, typically by connecting the driven mechanism to the driving mechanism. Clutches and brakes are similar; if the driven member of a clutch is fixed to the mechanism frame, it serves as a brake. Clutches are useful in devices that have two rotating shafts. In these devices, one shaft is typically attached to a motor or other power unit (the driving member), and 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 can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged).

Clutch in automobile


Page 6 Friction clutches

Transmission belt clutch from the Benz

In the course of over 100 years of automotive history, nearly all components have undergone enormous technological developments. Reliability,production costs and service-friendlinessas well as, more recently, environmental safety, have been and continue to be the criteria demanding new and better solutions from automotive engineers. The basic designs are usually known early on, but only the availability of new materials and processing procedures makes their realisation feasible.It was not until the end of the first decade of this century that the internal combustion engine surpassed the competing steam and electricity-based automotive drive concepts on a large scale. In 1902, a petrol-engined vehicle for the first time broke the overall speed record; up to then, electric and steampowered vehicles had set the standards, and proponents of the three drive concepts continued to compete for the absolute speed record throughout the first decade.Steam and electric drives have a decisive advantage over “motorised vehicles with liquid fuels”, as they used to be called. Thanks to the Almost ideal torque band, they required neither clutches nor transmissions, and thus wereeasier to operate, had fewer malfunctions and were easier to service. As an internal combustion engine only delivers its output at engine speed, there must be a division between engine and transmission. The speed-dependent drive principle of the petrol engine necessitates a mechanical aid for starting, as sufficient output (torque) is only available aftercertain engine speeds have been attained. Besides the function of a starting clutch, however, that of a Page 7 Friction clutches

dividing clutch is equally important,for it allows load-free gear changing while driving. Because of the complexity of the related problems, many smaller vehicles in the early years of automotive design did not have a starting clutch; the motor car had to be pushed into motion.The operating principles of the first clutches originated in the mechanised factories of early modern industry. By analogy with the transmission belts used there, flat leather belts were now introduced into motor cars. When tensioned by a roller, the belt transmitted the drive output of the engine’s belt pulley to the drive gears, and when loosened, it slipped through –i. e. disengaged. As this procedure caused the leather belts to wear out fast, a new tactic was adopted of installing an idler pulley of the sam size beside the drive belt pulley. By moving lever, the transmission belt could be guided

from the idler pulley on to the drive pulley.The motor car patented by Benz in 1886, which Bertha Benz used to make the first long-distancejourney in the history of motor vehicles – from Mannheim to Pforzheim – already operated according to this clutch concept. The disadvantages of a belt drive, such as low efficiency, high susceptibility to wear and inadequaterunning characteristics especially pedal tensioned the spring band, which then coiled itself (self-reinforcing) more and more firmly around the drum, driving t HE transmission shaft – and engaging the clutch. The compression of the springs required only slight force and effected a gentle engagement of the clutch. At about the same time that the Daimler corporation were developing their spring bandclutch, Professor HeleShaw from England was already experimenting with a multi-plate clutch that can be regarded as the forerunnerof today’s conventional single-disc dry clutch. Multi-plate clutches, named “Weston clutches” after the first largePage 8 Friction clutches

scale producer, had a decisive advantage over the cone friction clutch: much greater friction surface area with a lower space requirement and constant engagement. In the case of the multi-plate clutch, the flywheel is connected to a drum-shaped housing that has grooves on the inside corresponding to the shape of the outer edge of the plate, allowing it to turn with the crankshaft or flywheel and at the same time to move longitudinally. An identical number of discs with matching inner recesses are centred on a hub connected to the clutch shaft. The discs can move longitudinally along the clutch shaft on the hub. During installation, inner and outer clutch plates are alternately combined to form a plate packet, so that a driving and a driven disc always follow one another. The plate pairs formed in this fashion, originally with a bronze disc always turning against a steel one, were pressed together by a pressure plate under the force of a clutch spring. In this way, all clutch plates were constantly engaged. This gradual increase of frictional effect enabled the multi-plate clutch to engage very gently. As the spring pressure eased off, the plates disengaged again, in part supported by the spring-loaded strips bent out from the plane of the plate. By varying the number of plate pairs, a basic clutch type could be adjusted to eachengine output.Multi-plate clutches operated either immersed in oil/petroleum or dry, in which case, however,special, riveted friction linings were used.The greatest drawback of the multi-plate clutch was certainly the drag effect, especially in the oil bath, causing only partial disengagement, and thus making gear changing difficult. By 1904, De Dion & Bouton had introduced the single-plate clutch principle, which because of the initially inadequate materials only came into widespread use in the US during the 1920s largely on demand from the supply industry,

. Professor Hele-Shaw from England was the first to experiment

Page 9 Friction clutches

with multi-plate clutches. Multi-plate dry clutch with riveted lining

who towards the end of that decade granted licences to European manufacturers. Within a few years, the single-plate had superseded cone and multi-plate clutches. While De Dion & Bouton still lubricated the friction surfaces of their multi-plate clutches with graphite, clutch technology greatly advanced with the advent of Ferodo-asbestos linings, which were used from about 1920 to the present day, when they were replaced by asbestos-free linings. The advantages of the single-plate dry clutch were clear: the low mass of the clutch plate allowed it to come to rest more quickly when released, making shifting much easier – farewell to transmission brakes. The initial design of the single-plate dry clutch was relatively complicated. The clutch housing was flanged onto the flywheel, and the clutch cover screwed into the housing. This cover held lug levers which were pressed inwards by springs and which transmitted pressure from an intermediate disc via the friction plate and hence the power transmission from the flywheel The friction disc was connected to the connecting or transmission shaft by a driver The clutch was engaged and disengaged by a slip-ring disc that moved a cone back and forth The sides of the cone accordingly actuated the spring-pressured lug levers, which stressed or released, i. e. engaged/disengaged, the intermediate The coil spring clutch, in which the clamping disc. As the cone rotated about the slip-ring disc at rest, lubrication was required at regular intervals load is produced by coil springs, was able to gain acceptance. At first, experiments were made with centrally arranged springs, but clutch housing entered large-scale production only the version with several smaller coil or clutch springs distributed along the outer edge of the The levers compress the coil springs via a release bearing that moves freely on the clutch shaft, releasing the pressure plate and thus disengaging. The clamping load could be varied by using different spring packages but had the crucial disadvantage that, as the engine speed increased, the coil springs located outside on the pressure plate were pressed further outwards against the spring housings by centrifugal force. The friction arising between the spring and the housing +then caused the clamp load characteristics to change. As the engine speed increased, the clutch became progressively heavier. In addition to this, the bearings for the release levers were constantly under strain, making them susceptible to wear, and the spring housings especially when gear changing at high engine speeds, quickly wore through.

Page 10 Friction clutches

Initial design of the coil spring clutch with clutch springs perpendicular to the central axis.

Page 11 Friction clutches

. De Dion & Bouton were the first to recognise that singleplate clutches would be the way of the future


Page 12 Friction clutches

CHAPTER 3 3.1 Clutch Construction

Two basic types of clutch are the coil-spring clutch and the diaphragm-spring clutch. The difference between them is in the type of spring used. The coil spring clutch shown in left Fig 3.2.6 uses coil springs as pressure springs (only two pressure spring is shown). The clutch shown in right uses a diaphragm spring. The coil-spring clutch has a series of coil springs set in a circle.

Clutch construction

At high rotational speeds, problems can arise with multi coil spring clutches owing to the effects of centrifugal forces both on the spring themselves and the lever of the release mechanism. These problems are obviated when diaphragm type springs are used, and a number of other advantages are also experienced Machine Design I Indian Institute of Technology Madras

3.2 Clutch or Driven Plate

More complex arrangements are used on the driven or clutch plate to facilitate smooth function of the clutch The friction disc, more generally known as the clutch plate, is shown partly cut away in Fig. It consists of a hub and a plate, with facings attached to the plate.

Page 13 Friction clutches

Clutch plate


First to ensure that the drive is taken up progressively, the centre plate, on which the friction facings are mounted, consists of a series of cushion springs which is crimped radially so that as the clamping force is applied to the facings the crimping is progressively squeezed flat, enabling gradual transfer of the force .On the release of the clamping force, the plate springs back to its original position crimped (wavy) state.

3.3 Plate to hub Connection Secondly the plate and its hub are entirely separate components, the drive being transmitted from one to the other through coil springs interposed between them. These springs are carried within rectangular holes or slots in the hub and plate and arranged with their axes aligned appropriately for transmitting the drive. These dampening springs are heavy coil springs set in a circle around the hub. The hub is driven through these springs. They help to smooth out the torsional vibration (the power pulses from the engine) so that the power flow to the transmission is smooth. In a simple design all the springs may be identical, but in more sophisticated designs the are arranged in pairs located diametrically opposite, each pair having a different rate and different end clearances so that their role is progressive providing increasing spring rate to cater to wider torsional damping The clutch plate is assembled on a splined shaft that carries the rotary motion to the transmission. This shaft is called the clutch shaft, or transmission input shaft. This shaft is connected to the gear box or forms a part of the gear box.

Page 14 Friction clutches

3.4 Friction Facings or Pads It is the friction pads or facings which actually transmit the power from the fly wheel to hub in the clutch plate and from there to the out put shaft. There are . grooves in both sides of the friction-disc facings. These grooves prevent the facings from sticking to the flywheel face and pressure plate when the clutch is disengaged. The grooves break any vacuum that might form and cause the facings to stick to the flywheel or pressure plate. The facings on many friction discs are made of cotton and asbestos fibers woven or molded together and impregnated with resins or other binding agents. In many friction discs, copper wires are woven or pressed into the facings to give them added strength. However, asbestos is being replaced with other materials in many clutches. Some friction discs have ceramicmetallic facings. Such discs are widely used in multiple plate clutches The minimize the wear problems, all the plates will be enclosed in a covered chamber and immersed in an oil medium Such clutches are called wet clutches .

The properties of the frictional lining are important factors in the design of the clutches. Typical characteristics of some widely used friction linings are given in the table TABLE PROPERTIES OF COMMON CLUTCH /BRAKE LINING

Page 15 Friction clutches

MATERIALS Friction material against steel or cl DRY

Molded Woven Sintered metal Cast iron of hard steel



0.25-0.45 0.25-0.45 0.15-0.45 0.15-0.25

0.06-0.09 0.08-0.10 0.05-0.08 0.03-0.06


1030-2070 690-720

CHAPT ER 4 CLUTC H DESIGN 4.1 CLUTCH DESIGN DETAILS Two inertia’s and traveling at the respective angular velocities ωIand I1 1 and ω2, and one of which may be zero, are to be brought to the same speed by engaging. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in temperature

Page 16 Friction clutches

To design analyze the performance of these devices, a knowledge on the following are required. 1. The torque transmitted 2. The actuating force. 3. The energy loss 4. The temperature rise 4.2 FRICTION CLUTCHES As in brakes a wide range of clutches are in use wherein they vary in their are in use their working principle as well the method of actuation and application of normal forces. The discussion here will be limited to mechanical type friction. clutches or more specifically to the plate or disc clutches also known as axial clutches

4.2 Frictional Contact axial or Disc Clutches An axial clutch is one in which the mating frictional members are moved in a direction parallel to the shaft. A typical clutch is illustrated in the figure below. It consist of a driving disc connected to the drive shaft and a driven disc co9nnected to the driven shaft. A friction plate is attached to one of the members. Actuating spring keeps both the members in contact and power/motion is transmitted from one member to the other. When the power of motion is to be interrupted the driven disc is moved axially creating a gap between the members as shown in the figure.

4.3 METHOD OF ANALYSIS The torque that can be transmitted by a clutch is a function of its geometry and the magnitude of the actuating force applied as well the condition of contact prevailing between the members. The applied force can keep the members together with a uniform pressure all over its contact area and the consequent analysis is based on uniform pressure condition.

4.4 Uniform Pressure and wear However as the time progresses some wear takes place between the contacting members and this may alter or vary the contact pressure appropriately and uniform pressure condition may no longer prevail. Hence the analysis here is based on uniform wear condition

4.5 Elementary Analysis

Assuming uniform pressure and considering an elemental area dA

Page 17 Friction clutches

dA = 2Π.r dr The normal force on this elemental area is dN=π 2.r.dr.p The frictional force dF on this area is therefore dF =f.π.2.r.dr.p

Now the torque that can be transmitted by this elemental are is equal to the frictional force times the moment arm about the axis that is the radius ‘r’ i.e. T = dF. r = f.dN. r = f.p.A.r = f.p.2.π.r. dr .r The total torque that could be transmitted is obtained by integrating this equation between the limits of inner radius ri to the outer radius ro ro

T= ∫2 π pf r2 dr =2/3 π pf (ro3 - ri3) ri

Integrating the normal force between the same limits we get the actuating force that need to be applied to transmit this torque. ro

Fa= ∫2 π pf r dr = π pf (ro2 - ri2) ri

Equation 1 and 2 can be combined together to give equation for the torque T =f.Fa .2/3.(ro3 - ri3)/ (ro2 - ri2)

4.6 Uniform Wear Condition According to some established theories the wear in a mechanical system is proportional to the ‘PV’ factor where P refers the contact pressure and V the sliding velocity. Based on this for the case of a plate clutch we can state The constant-wear rate Rw is assumed to be proportional to the product of pressure p and velocity V. Rw= pV= constant And the velocity at any point on the face of the clutch is V=r.ω Combining these equation, assuming a constant angular velocity ω pr = constant = K Page 18 Friction clutches

The largest pressure pmax must then occur at the smallest radius ri , K=pmax .ri Hence pressure at any point in the contact region p=pmax .ri / r In the previous equations substituting this value for the pressure term p and integrating between the limits as done earlier we get the equation for the torque transmitted and the actuating force to be applied. I.e The axial force Fa is found by substituting for p=pmax .ri / r for p and integrating equation

dN=2πpr dr ro

F= ∫2 π p r dr ri ro

Fa= ∫2 π (pmax .ri / r) r dr = 2π pmax .ri (ro - ri) ri

Similarly the Torque ro

Fa= ∫2 π pmax .ri r f dr = f π pmax .ri f (ro2 - ri2) ri

Substituting the values of actuating force Fa The equation can be given as T= f.Fa. (ro + ri) / 2

Page 19 Friction clutches

CHAPTER 5 Operation Of Clutch 5.1 Operation Of Clutch When the driver releases the clutch pedal, power can flow through the clutch. Springs in the clutch force the pressure plate against the friction disc. This action clamps the friction disk tightly between the flywheel and the pressure plate. Now, the pressure plate and friction disc rotate with the flywheel. As both side surfaces of the clutch plate is used for transmitting the torque, a term ‘N’ is added to include the number of surfaces used for transmitting the torque By rearranging the terms the equations can be modified and a more general form of the equation can be written as T= N.f. Fa.Rm T is the torque (Nm). N is the number of frictional discs in contact. f is the coefficient of friction Fa is the actuating force (N). Rm is the mean or equivalent radius (m). Note that N = n1 + n2 -1 28Where n1= number of driving discs n2 = number of driven discs Values of the actuating force F and the mean radius for the two conditions of analysis

CHAPTER 6 TYPES OF CLUTCH Page 20 Friction clutches


Single plate clutch

This is shown in the above diagram. The operation is as follows: The flywheel A is bolted to to a flange on the drive shaft

axially along the

driven shaft D to which it is splined. It B. The plate C is fixed to a boss which is free to slide axially along the driven shaft D to which it is splined. It therefore rotates with shaft D. Two rings G of special friction material are riveted or bonded to A and E or alternatively to plate C.The presser plate E is bushed internally so that it revolves freely on the driven shaft D. It is integral with the withdrawl sleeve F. A number of springs are arranged around the clutch ( Shown as S) so as to press the two friction surfaces together. The Clutch operates by moving the withdrawl sleeve to the right. This compresses the Springs S are removes the pressure between the friction surfaces. Hence it is possible to start of stop the driven shaft at will.Most light vehicles use a single-plate clutch to transmit torque from the engine to the transmission input shaft. The flywheel is the clutch driving member. The clutch unit is mounted on the flywheel’s machined rear face, so that the unit rotates with the flywheel. The clutch unit consists of - a friction-type disc, with 2 friction facings and a central splined hub. - a pressure plate assembly, consisting of a pressed steel cover, a pressure plate with a machined flat face, and a segmented diaphragm spring. And a release bearing and Page 21 Friction clutches

operating fork. The friction disc is sandwiched between the machined surfaces of the flywheel and the pressure plate when the pressure plate is bolted to the outer edge of the flywheel face. The clamping force on the friction facings is provided by the diaphragm spring. Unloaded, it is a dished shape. As the pressure plate cover tightens, it pivots on its fulcrum rings, and flattens out to exert a force on the pressure plate, and the facings.The transmission input shaft passes through the center of the pressure plate. Its parallel splines engage with the internal splines of the central hub, on the friction disc. With engine rotation, torque can now be transmitted from the flywheel, through the friction disc, to the central hub, and to the transmission. When the clutch pedal is depressed, the movement is transferred through the operating mechanism, to the operating fork and the release bearing. The release bearing moves forward and pushes the center of the diaphragm spring towards the flywheel. The diaphragm pivots on its fulcrum rings causing the outer edge to move in the opposite direction and act on the pressure-plate retraction clips. The pressure plate disengages, and drive is no longer transmitted. Releasing the pedal allows the diaphragm to re-apply its clamping force and engage the clutch, and drive is restore

6.2. MULTI PLATE CLUTCHAdding plates to a clutch unit to form a multiplate clutch will increase its torque capacity, without increasing spring strength or clutch diameter. This clutch assembly has two friction discs, with friction material riveted to both sides of each. An internally-splined hub on each disc mates with the splines on the transmission input shaft. A cast-iron separator plate fits between each disc. The separator plate locates on driving pins on the flywheel. This friction unit is between the flywheel and the pressure plate when the pressure plate assembly is bolted to the flywheel. The pressure plate spring then provides a frictional clamping force on each mating surface. Torque is transmitted from the flywheel through the friction facings to the transmission input shaft. When the clutch pedal is depressed the release bearing acts on the pressure plate diaphragm and moves the pressure plate away from the flywheel.This releases the clamping force on the facings and separator plate and allows each clutch driving member to rotate freely without turning the transmission input shaft. When the pedal is released, the spring tension forces the pressure plate, discs and separator against the flywheel, clamping all components together.

Page 22 Friction clutches

Multi plate clutch

6.3.CONE CLUTCH Cone clutch

From Wikipedia, the free encyclopedia 1. Cones: female cone , male cone 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 A 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

Page 23 Friction clutches

because the clutch does not 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.



Page 24 Friction clutches

6.4. 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. The 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 center shaft there are an assorted number of extension springs, which connect to a clutch shoe. When the center 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 clutch. When 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 abruptly; and, disengage loads when starting and idling.

Thomas Fogarty, who also invented the balloon catheter, is credited with inventing a centrifugal clutch in the 1940s, only three months after a Canadian boy named Andrew Wilson drew up the first recognized design.[1] That being said, automobiles were being manufactured with centrifugal clutches as early as 1936.[2]


Page 25 Friction clutches

CHAPTER 7 Major Types of Clutches by Application

7.1 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.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.

7.2 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 its inner diameter locking it to the engine crankshaft, while the other plates have lugs on the outer diameter that lock it 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. Page 26 Friction clutches

7.3 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.

CHAPTER 8 8.1 SUMMARY A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driving shaft. A clutch thus provides an interruptible connection between two rotating shafts Clutches allow a high inertia load to be stated with a small power. A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gear box. Here the clutch enables to crank and start the engine disengaging the transmission Disengage the transmission and change the gear to alter the torque on the wheels. Clutches are also used extensively in production machinery of all types. It is a mechanical device, by convention understood to be rotating, which provides driving force to another mechanism when required, typically by connecting the driven mechanism to the driving mechanism. Clutches and brakes are similar; if the driven member of a clutch is fixed to the mechanism frame, it serves as a brake. Clutches are useful in devices that have two rotating shafts. In these devices, one shaft is typically attached to a motor or other power unit (the driving member), and 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 can either be locked together and spin at the same speed (engaged), or be decoupled and spin at different speeds (disengaged).

Page 27 Friction clutches

APPENDIX –A BASIC CONCEPTS OF FRICTION Friction is the force resisting the relative motion of solid surfaces, fluid layers,and/or material elements sliding against each other. It may be thought of as the opposite of "slipperiness". There are several types of friction: • Dry friction resists relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction between nonmoving surfaces, and kinetic friction between moving surfaces. • Fluid friction describes the friction between layers within a viscous fluid that are moving relative to each other.[1][2] • Lubricated friction is a case of fluid friction where a fluid separates two solid surfaces.[3][4][5] • Skin friction is a component of drag, the force resisting the motion of a solid body through a fluid. • Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation. When surfaces in contact move relative to each other, the friction between the two surfaces converts kinetic energy into heat. This property can have dramatic consequences, as illustrated by the use of friction between pieces of wood to start a fire. Another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology. Friction is not a fundamental force but occurs because of the electromagnetic forces between charged particles which constitute the surfaces in contact. Because of the complexity of these interactions friction cannot be calculated from first principles, but instead must be found empirically.

Basic properties Basic properties of friction have been described as laws: • Amontons' 1st Law: The force of friction is directly proportional to the applied load. • Amontons' 2nd Law: The force of friction is independent of the apparent area of contact. • Coulomb's Law of Friction: Kinetic friction is independent of the sliding velocity. Amontons' 2nd Law is an idealization assuming perfectly rigid and inelastic materials. For example, wider tires on cars provide more traction than narrow tires for a given vehicle mass because of surface deformation of the tire.

Dry friction Dry friction resists relative lateral motion of two solid surfaces in contact. The two regimes of dry friction are static friction between non-moving surfaces, Page 28 Friction clutches

and kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces. Coulomb friction, named after Charles-Augustin de Coulomb, is an approximate model used to calculate the force of dry friction. It is governed by the equation: where • is the force exerted by friction (in the case of equality, the maximum possible magnitude of this force). • is the coefficient of friction, which is an empirical property of the contacting materials, • is the normal force exerted between the surfaces. The Coulomb friction may take any value from zero up to , and the direction of the frictional force against a surface is opposite to the motion that surface would experience in the absence of friction. Thus, in the static case, the frictional force is exactly what it must be in order to prevent motion between the surfaces; it balances the net force tending to cause such motion. In this case, rather than providing an estimate of the actual frictional force, the Coulomb approximation provides a threshold value for this force, above which motion would commence. This maximum force is known as traction. The force of friction is always exerted in a direction that opposes movement (for kinetic friction) or potential movement (for static friction) between the two surfaces. For example, a curling stone sliding along the ice experiences a kinetic force slowing it down. For an example of potential movement, the drive wheels of an accelerating car experience a frictional force pointing forward; if they did not, the wheels would spin, and the rubber would slide backwards along the pavement. Note that it is not the direction of movement of the vehicle they oppose, it is the direction of (potential) sliding between tire and road. In the case of kinetic friction, the direction of the friction force may or may not match the direction of motion: a block sliding atop a table with rectilinear motion is subject to friction directed along the line of motion; an automobile making a turn is subject to friction acting perpendicular to the line of motion (in which case it is said to be 'normal' to it). The direction of the static friction force can be visualized as directly opposed to the force that would otherwise cause motion, were it not for the static friction preventing motion. In this case, the friction force exactly cancels the applied force, so the net force given by the vector sum, equals zero. It is important to note that in all cases, Newton's first law of motion holds.

The normal force Block on a ramp (top) and corresponding free body diagram of just the block (bottom). Main article: Normal force The normal force is defined as the net force compressing two parallel surfaces together; and its direction is perpendicular to the surfaces. In the Page 29 Friction clutches

simple case of a mass resting on a horizontal surface, the only component of the normal force is the force due to gravity, where . In this case, the magnitude of the friction force is the product of the mass of the object, the acceleration due to gravity, and the coefficient of friction. However, the coefficient of friction is not a function of mass or volume; it depends only on the material. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block. However, the magnitude of the friction force itself depends on the normal force, and hence the mass of the block. If an object is on a level surface and the force tending to cause it to slide is horizontal, the normal force between the object and the surface is just its weight, which is equal to its mass multiplied by the acceleration due to earth's gravity, g. If the object is on a tilted surface such as an inclined plane, the normal force is less, because less of the force of gravity is perpendicular to the face of the plane. Therefore, the normal force, and ultimately the frictional force, is determined using vector analysis, usually via a free body diagram. Depending on the situation, the calculation of the normal force may include forces other than gravity.

Coefficient of friction The 'coefficient of friction' (COF), also known as a 'frictional coefficient' or 'friction coefficient' and symbolized by the Greek letter µ, is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one – under good conditions, a tire on concrete may have a coefficient of friction of 1.7. For surfaces at rest relative to each other , where is the coefficient of static friction. This is usually larger than its kinetic counterpart. For surfaces in relative motion , where is the coefficient of kinetic friction. The Coulomb friction is equal to , and the frictional force on each surface is exerted in the direction opposite to its motion relative to the other surface. The coefficient of friction is an empirical measurement – it has to be measured experimentally, and cannot be found through calculations. Rougher surfaces tend to have higher effective values. Both static and kinetic coefficients of friction depend on the pair of surfaces in contact; for a given pair of surfaces, the coefficient of static friction is usually larger than that of kinetic friction; in some sets the two coefficients are equal, such as teflon-on-teflon. Most dry materials in combination have friction coefficient values between 0.3 and 0.6. Values outside this range are rarer, but teflon, for example, can have a coefficient as low as 0.04. A value of zero would mean no friction at all, an elusive property – even magnetic levitation vehicles have drag. Rubber in contact with other surfaces can yield friction coefficients from 1 to 2. Occasionally it is maintained that µ is always < 1, but this is not true. Page 30 Friction clutches

While in most relevant applications µ < 1, a value above 1 merely implies that the force required to slide an object along the surface is greater than the normal force of the surface on the object. For example, silicone rubber or acrylic rubber-coated surfaces have a coefficient of friction that can be substantially larger than 1.



1. Crouse W.H., ‘Automotive Mechanics’, Tata McGraw Hill Publishing Company. 2. Joseph Heitner, ‘Automotive Mechanics’, C.B.S.Publisher and Distributors. 3. Narang G.B.S., ‘Automobile Engineering’, S.Chand and Company Ltd 4. Newton, Steeds & Garrett, ‘Motor vehicle’, ‘The English language book society 5. Singh Kripal, ‘Automobile Engineering’, Vol.II., New Chand 6. A.W.Judge, ‘Automotive systems’, Volume 1 to 8. 7. Harbans Singh Reyat, ‘The Automobile’ 8. A Book of Car.


Page 31 Friction clutches

Page 32 Friction clutches

View more...


Copyright ©2017 KUPDF Inc.