FRICTION CLUTCHES A BRIEF DESCRIPTIONFirst Technical Report 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 8. CHAPTER 8 Page 3 Friction clutches angular velocity 14.8.newton 6. – torque 10. pi = 3. . V – sliding velocity 13.1 SUMMARY……………………………………………………………………………………35 X.area of object 5.maximum pressure 15.constant wear rate 11.coeffiecient of friction 4. Rw . – frictional force 8. P – constant pressure 12.normal force 7. .ºC – degree centigrade 3.142 9. APPENDIX A BASIC CONCEPTS IN FRICTION………………………………………………………… 36 Y. . Fa – axial force Page 4 Friction clutches . . .kPa – kilopascal 2. Pmax . ACKNOWLEDGEMENT NOMENCLATURE 1. 2 CLUTCH PLATE.4 CONE CLUTCH. 6.2 PROFESSOR HELE-SHAW FROM ENGLAND WAS THE FIRST TO EXPERIMENT WITH MULTI-PLATE CLUTCHES.2 MULTI PLATE CLUTCH.3 CONE CLUTCH IN DIFFERENTIALS.1 BASIC CLUTCH STRUCTURE. 3. 4.5 CENTRIFUGAL CLUTCH.3 DE DION AND BOUTON WERETHE FIRST TO RECORGANISE THAT SINGLE PLATE CLUTCHES WOULD BE THE WAY OF THE FUTURE. CHAPTER 1 1. 2. FIG. 6.1 CLUTCH CONSTRUCTION. Rm – mean radius FIG. FIG. FIG. 6. FIG. FIG.1 CLUTCH IN AUTOMOBILE LIST OF FIGURES FIG.16. so that the driven shaft may be started or stopped at will. FIG. 3. FIG. without Page 5 Friction clutches .1 INTRODUCTION A Clutch is a machine member used to connect the driving shaft to a driven shaft. 6.1 SINGLE PLATE CLUTCH. 2. FIG. 2. MULTI-PLATE DRY CLUTCH WITH RIVETED LINING. FIG.3 INITIAL DESIGN OF THE COIL SPRING CLUTCH WITH CLUTCH SPRINGS PERPENDICULAR TO THE CENTRAL AXIS. 2.1 TRANSMISSION BELT CLUTCH FROM THE BENZ FIG. 1. 6. FIG. Clutches are also used extensively in production machinery of all types. Clutch in automobile CHAPTER 2 2. one shaft is typically attached to a motor or other power unit (the driving member). In a drill.1 HISTORY Page 6 Friction clutches . The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged). one shaft is driven by a motor. by convention understood to be rotating. and the other drives a drill chuck. which provides driving force to another mechanism when required. Clutches and brakes are similar. if the driven member of a clutch is fixed to the mechanism frame. In these devices. for instance. A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gear box. or be decoupled and spin at different speeds (disengaged). and the other shaft (the driven member) provides output power for work to be done. typically by connecting the driven mechanism to the driving mechanism.stopping the driving shaft. It is a mechanical device. Clutches are useful in devices that have two rotating shafts. it serves as a brake. 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. 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 petrol-engined vehicle for the first time broke the overall speed record. Reliability. as they used to be called. however. Besides the function of a starting clutch. that of a Page 7 Friction clutches . As an internal combustion engine only delivers its output at engine speed. Thanks to the Almost ideal torque band. environmental safety. had fewer malfunctions and were easier to service. there must be a division between engine and transmission. electric and steampowered vehicles had set the standards. In 1902. have been and continue to be the criteria demanding new and better solutions from automotive engineers. The speed-dependent drive principle of the petrol engine necessitates a mechanical aid for starting.Steam and electric drives have a decisive advantage over “motorised vehicles with liquid fuels”. nearly all components have undergone enormous technological developments. more recently. but only the availability of new materials and processing procedures makes their realisation feasible. they required neither clutches nor transmissions. The basic designs are usually known early on. and thus wereeasier to operate.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.Transmission belt clutch from the Benz In the course of over 100 years of automotive history. and proponents of the three drive concepts continued to compete for the absolute speed record throughout the first decade. up to then.production costs and service-friendlinessas well as. as sufficient output (torque) is only available aftercertain engine speeds have been attained. By moving lever. At about the same time that the Daimler corporation were developing their spring bandclutch.for it allows load-free gear changing while driving. The compression of the springs required only slight force and effected a gentle engagement of the clutch. the belt transmitted the drive output of the engine’s belt pulley to the drive gears. When tensioned by a roller. By analogy with the transmission belts used there. which then coiled itself (self-reinforcing) more and more firmly around the drum. As this procedure caused the leather belts to wear out fast. many smaller vehicles in the early years of automotive design did not have a starting clutch. high susceptibility to wear and inadequaterunning characteristics especially pedal tensioned the spring band. Multi-plate clutches. a new tactic was adopted of installing an idler pulley of the sam size beside the drive belt pulley. The disadvantages of a belt drive. Because of the complexity of the related problems. 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. and when loosened. such as low efficiency. named “Weston clutches” after the first largePage 8 Friction clutches . e. 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. the transmission belt could be guided from the idler pulley on to the drive pulley. driving t HE transmission shaft – and engaging the clutch. 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. flat leather belts were now introduced into motor cars. it slipped through –i.dividing clutch is equally important.The motor car patented by Benz in 1886. disengaged. In this way. 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. however. especially in the oil bath. The plate pairs formed in this fashion. causing only partial disengagement.scale producer. the plates disengaged again. In the case of the multi-plate clutch. . During installation. As the spring pressure eased off. a basic clutch type could be adjusted to eachengine output. Professor Hele-Shaw from England was the first to experiment Page 9 Friction clutches . 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. had a decisive advantage over the cone friction clutch: much greater friction surface area with a lower space requirement and constant engagement.special. riveted friction linings were used. An identical number of discs with matching inner recesses are centred on a hub connected to the clutch shaft. originally with a bronze disc always turning against a steel one.The greatest drawback of the multi-plate clutch was certainly the drag effect. The discs can move longitudinally along the clutch shaft on the hub. in part supported by the spring-loaded strips bent out from the plane of the plate. De Dion & Bouton had introduced the single-plate clutch principle. inner and outer clutch plates are alternately combined to form a plate packet. By 1904. so that a driving and a driven disc always follow one another. By varying the number of plate pairs. all clutch plates were constantly engaged. allowing it to turn with the crankshaft or flywheel and at the same time to move longitudinally. and thus making gear changing difficult.Multi-plate clutches operated either immersed in oil/petroleum or dry. in which case. were pressed together by a pressure plate under the force of a clutch spring. This gradual increase of frictional effect enabled the multi-plate clutch to engage very gently. the clutch became progressively heavier. experiments were made with centrally arranged springs. engaged/disengaged. 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. Within a few years. 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. While De Dion & Bouton still lubricated the friction surfaces of their multi-plate clutches with graphite. As the cone rotated about the slip-ring disc at rest. 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.with multi-plate clutches. The clamping load could be varied by using different spring packages but had the crucial disadvantage that. In addition to this. The clutch housing was flanged onto the flywheel. and the spring housings especially when gear changing at high engine speeds. releasing the pressure plate and thus disengaging. as the engine speed increased. the bearings for the release levers were constantly under strain. lubrication was required at regular intervals load is produced by coil springs. in which the clamping disc. As the engine speed increased. The friction arising between the spring and the housing +then caused the clamp load characteristics to change. clutch technology greatly advanced with the advent of Ferodo-asbestos linings. quickly wore through. At first. which stressed or released. which were used from about 1920 to the present day. making shifting much easier – farewell to transmission brakes. e. Multi-plate dry clutch with riveted lining who towards the end of that decade granted licences to European manufacturers. the single-plate had superseded cone and multi-plate clutches. i. making them susceptible to wear. Page 10 Friction clutches . was able to gain acceptance. the intermediate The coil spring clutch. when they were replaced by asbestos-free linings. The initial design of the single-plate dry clutch was relatively complicated. the coil springs located outside on the pressure plate were pressed further outwards against the spring housings by centrifugal force. 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 .. 3. The difference between them is in the type of spring used. more generally known as the clutch plate. is shown partly cut away in Fig.CHAPTER 3 Two basic types of clutch are the coil-spring clutch and the diaphragm-spring clutch. It consists of a hub and a plate.6 uses coil springs as pressure springs (only two pressure spring is shown). The coil-spring clutch has a series of coil springs set in a circle. The coil spring clutch shown in left Fig 3. and a number of other advantages are also experienced Machine Design I Indian Institute of Technology Madras 3. Page 13 Friction clutches . 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. The clutch shown in right uses a diaphragm spring. with facings attached to the plate.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. These problems are obviated when diaphragm type springs are used.1 Clutch Construction Clutch construction At high rotational speeds.2. 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. or transmission input shaft. enabling gradual transfer of the force . 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. This shaft is called the clutch shaft. the centre plate. on which the friction facings are mounted.On the release of the clamping force. This shaft is connected to the gear box or forms a part of the gear box. 3. but in more sophisticated designs the are arranged in pairs located diametrically opposite.3 Plate to hub Connection Secondly the plate and its hub are entirely separate components. First to ensure that the drive is taken up progressively. the plate springs back to its original position crimped (wavy) state. 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. These dampening springs are heavy coil springs set in a circle around the hub.Clutch plate . The hub is driven through these springs. 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. Page 14 Friction clutches . However. 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. The grooves break any vacuum that might form and cause the facings to stick to the flywheel or pressure plate. asbestos is being replaced with other materials in many clutches. 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 . grooves in both sides of the friction-disc facings.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. In many friction discs. There are . copper wires are woven or pressed into the facings to give them added strength. Typical characteristics of some widely used friction linings are given in the table TABLE PROPERTIES OF COMMON CLUTCH /BRAKE LINING Page 15 Friction clutches . The properties of the frictional lining are important factors in the design of the clutches.3. These grooves prevent the facings from sticking to the flywheel face and pressure plate when the clutch is disengaged. Some friction discs have ceramicmetallic facings. 45 0. resulting in temperature Page 16 Friction clutches . are to be brought to the same speed by engaging. and one of which may be zero.25-0.06-0.06 1030-2070 690-720 CHAPT ER 4 CLUTC H DESIGN 4.08-0. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation.03-0.08 0.09 0.10 0.MATERIALS Friction material against steel or cl DRY DYNAMIC COEFFIECIENT OF FRICTION IN OIL MAXIMUM PRESSURE kPa MAXIMUM TEMPERATURE o C Molded Woven Sintered metal Cast iron of hard steel 0.05-0.25-0.15-0.45 0.25 0.1 CLUTCH DESIGN DETAILS Two inertia’s and traveling at the respective angular velocities ωIand I1 1 and ω2.15-0.45 0. a knowledge on the following are required. 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.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. 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.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. Actuating spring keeps both the members in contact and power/motion is transmitted from one member to the other. 4. clutches or more specifically to the plate or disc clutches also known as axial clutches 4. The actuating force.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. The energy loss 4. The discussion here will be limited to mechanical type friction. 4. A friction plate is attached to one of the members. It consist of a driving disc connected to the drive shaft and a driven disc co9nnected to the driven shaft. The torque transmitted 2.5 Elementary Analysis Assuming uniform pressure and considering an elemental area dA Page 17 Friction clutches .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. 3. The temperature rise 4. 1. Hence the analysis here is based on uniform wear condition 4. A typical clutch is illustrated in the figure below.To design analyze the performance of these devices. 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.A.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 T= ∫2 π pf r2 dr =2/3 π pf (ro3 .2.r.ω Combining these equation.2.π.(ro3 .ri3) ri ro Integrating the normal force between the same limits we get the actuating force that need to be applied to transmit this torque.r = f.dr.p.r.p The frictional force dF on this area is therefore dF =f.ri2) 4.dN.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.dA = 2Π. r = f.r dr The normal force on this elemental area is dN=π 2. Fa= ∫2 π pf r dr = π pf (ro2 .2/3. Rw= pV= constant And the velocity at any point on the face of the clutch is V=r.p.dr.ri2) ri ro Equation 1 and 2 can be combined together to give equation for the torque T =f.r. assuming a constant angular velocity ω pr = constant = K Page 18 Friction clutches .Fa .ri3)/ (ro2 . r = f. 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. T = dF.π. dr .e. (ro + ri) / 2 Page 19 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 for p and integrating equation dN=2πpr dr F= ∫2 π p r dr ri ro Fa= ∫2 π (pmax . I.Fa.ri r f dr = f π pmax .ri2) ri ro Substituting the values of actuating force Fa The equation can be given as T= f.ri / r) r dr = 2π pmax .ri) ri ro Similarly the Torque Fa= ∫2 π pmax .e The axial force Fa is found by substituting for p=pmax .ri f (ro2 .ri (ro .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. the pressure plate and friction disc rotate with the flywheel.f. 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 . power can flow through the clutch.Rm T is the torque (Nm). N is the number of frictional discs in contact. 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. f is the coefficient of friction Fa is the actuating force (N). Fa. 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.CHAPTER 5 Operation Of Clutch 5.1 Operation Of Clutch When the driver releases the clutch pedal. Rm is the mean or equivalent radius (m). The flywheel is the clutch driving member. consisting of a pressed steel cover.1SINGLE PLATE CLUTCH Single plate clutch This is shown in the above diagram. A number of springs are arranged around the clutch ( Shown as S) so as to press the two friction surfaces together.The presser plate E is bushed internally so that it revolves freely on the driven shaft D. And a release bearing and Page 21 Friction clutches . The plate C is fixed to a boss which is free to slide axially along the driven shaft D to which it is splined.6. The Clutch operates by moving the withdrawl sleeve to the right. a pressure plate with a machined flat face. It B. It therefore rotates with shaft D.a friction-type disc.a pressure plate assembly. Two rings G of special friction material are riveted or bonded to A and E or alternatively to plate C. and a segmented diaphragm spring. with 2 friction facings and a central splined hub. The clutch unit consists of . 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 is integral with the withdrawl sleeve F.Most light vehicles use a single-plate clutch to transmit torque from the engine to the transmission input shaft. The clutch unit is mounted on the flywheel’s machined rear face. Hence it is possible to start of stop the driven shaft at will. so that the unit rotates with the flywheel. This compresses the Springs S are removes the pressure between the friction surfaces. . and drive is no longer transmitted. and the facings. discs and separator against the flywheel. The clamping force on the friction facings is provided by the diaphragm spring. This friction unit is between the flywheel and the pressure plate when the pressure plate assembly is bolted to the flywheel. torque can now be transmitted from the flywheel. clamping all components together. This clutch assembly has two friction discs. 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. and drive is restore 6. MULTI PLATE CLUTCHAdding plates to a clutch unit to form a multiplate clutch will increase its torque capacity. The separator plate locates on driving pins on the flywheel. to the operating fork and the release bearing. Releasing the pedal allows the diaphragm to re-apply its clamping force and engage the clutch.2. An internally-splined hub on each disc mates with the splines on the transmission input shaft. the movement is transferred through the operating mechanism.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.operating fork. When the clutch pedal is depressed the release bearing acts on the pressure plate diaphragm and moves the pressure plate away from the flywheel. The pressure plate spring then provides a frictional clamping force on each mating surface. Page 22 Friction clutches .The transmission input shaft passes through the center of the pressure plate. Its parallel splines engage with the internal splines of the central hub. When the clutch pedal is depressed. it is a dished shape. As the pressure plate cover tightens. When the pedal is released. and flattens out to exert a force on the pressure plate. With engine rotation. The release bearing moves forward and pushes the center of the diaphragm spring towards the flywheel. the spring tension forces the pressure plate. on the friction disc. and to the transmission. Unloaded. with friction material riveted to both sides of each. 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. without increasing spring strength or clutch diameter. through the friction disc. Torque is transmitted from the flywheel through the friction facings to the transmission input shaft. A cast-iron separator plate fits between each disc. to the central hub. The pressure plate disengages. it pivots on its fulcrum rings. 3. although they are common in power boats.Multi plate clutch 6. They are usually now confined to very specialist transmissions in racing. here on male cone 4. rallying. the cone clutch uses two conical surfaces to transmit torque by friction.CONE CLUTCH Cone clutch From Wikipedia. Clutch control: separating both cones by pressing 6. the free encyclopedia 1. 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. or in extreme off-road vehicles. Shaft: male cone is sliding on splines 3. Cones: female cone . This is Page 23 Friction clutches . male cone 2. Spring: brings the male cone back after using the clutch control 5. Friction material: usually on female cone. However. Rotating direction: both direction of the axis are possible A cone clutch serves the same purpose as a disk or plate clutch. instead of mating two spinning disks. Cone clutches are generally now only used in low peripheral speed applications although they were once common in automobiles and other combustion engine transmissions. because the clutch does not have to be pushed in all the way and the gears will be changed quicker. CONE CLUTCH IN DIFFERENTIALS CONE CLUTCH Page 24 Friction clutches . Small cone clutches are used in synchronizer mechanisms in manual transmissions. As the load increases the rpm drops. underbones. with the driving shaft nested inside the driven shaft. weighted arms in the clutch swing outward and force the clutch to engage.6. or belt. disengaging the clutch.4.[1] That being said. which connect to a clutch shoe. the springs extend causing the clutch shoes to engage the friction face. go-karts. disengage loads when starting and idling. letting the rpm rise again and reengaging the clutch. chain. If tuned properly. the clutch activates. This type can be found on most home built karts. but over a broad range of speeds it is much more useful than a direct drive in many applications. The input of the clutch is connected to the engine crankshaft while the output may drive a shaft. lawn and garden equipment. The weighted arms force these disks together and engage the clutch. When the center shaft spins fast enough.[2] CENTRIFUGAL CLUTCH Page 25 Friction clutches . who also invented the balloon catheter. As engine RPM increases. is credited with inventing a centrifugal clutch in the 1940s. Centrifugal clutches are often used in mopeds. and. working almost like a continuously variable transmission. It can be compared to a drum brake in reverse. CENTRIFUGAL CLUTCH A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts. fuel-powered model cars and low power chainsaws. only three months after a Canadian boy named Andrew Wilson drew up the first recognized design. Another type used in racing karts has friction and clutch disks stacked together like a motorcycle clutch. chainsaws. lawnmowers. This results in a fair bit of waste heat. automobiles were being manufactured with centrifugal clutches as early as 1936. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of a housing. the clutch will tend to keep the engine at or near the torque peak of the engine. and mini bikes to • • keep the internal combustion engine from stalling when the blade is stopped abruptly. Thomas Fogarty. When the engine reaches a certain RPM. On the center shaft there are an assorted number of extension springs. However. raising the engine speed too high while engaging the clutch will cause excessive clutch plate wear. The plates are forced together by a set of coil springs or a diaphragm spring plate when the clutch is engaged. Friction discs once contained asbestos but this has been largely eliminated. while pulling the lever back towards the rider will disengage the clutch plates through cable or hydraulic actuation.CHAPTER 7 Major Types of Clutches by Application 7. Racing motorcycles often use slipper clutches to eliminate the effects of engine braking which. On older cars the clutch might be operated by a mechanical linkage. However. Some of the plates have lugs on its inner diameter locking it to the engine crankshaft.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. smooth engagement would be near-impossible because engine movement inevitably occurs as the drive is "taken up. while the other plates have lugs on the outer diameter that lock it to a basket which turns the transmission input shaft. Even though the clutch may physically be located very close to the pedal. The friction material varies in composition depending on many considerations such as whether the clutch is "dry" or "wet". where speed is more important than comfort. can lead to instability.2 Motorcycles Motorcycles typically employ a wet clutch with the clutch riding in the same oil as the transmission. 7. allowing the driver to shift gears or coast. On most motorcycles the clutch is operated by the clutch lever located on the left handlebar. jerky start. being applied only to the rear wheel. These clutches are usually made up of a stack of alternating plain steel and friction plates. No pressure on the lever means that the clutch plates are engaged (driving). Page 26 Friction clutches . engine mountings being flexible by design. while pressing the pedal disengages the clutch plates. such remote means of actuation are necessary to eliminate the effect of vibrations and slight engine movement. The spring pressure is released when the clutch pedal is depressed thus either pushing or pulling the diaphragm of the pressure plate." No pressure on the pedal means that the clutch plates are engaged (driving). Engaging the clutch abruptly when the engine is turning at high speed causes a harsh. allowing the rider to shift gears or coast. Clutches found in heavy duty applications such as trucks and competition cars use ceramic clutches that have a greatly increased friction coefficient. these have a "grabby" action generally considered unsuitable for passenger cars. depending on type. This kind of start is necessary and desirable in drag racing and other competitions. With a rigid mechanical linkage.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. A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gear box. it unwinds and opens the valve. In these devices. which allows the fan to spin at about 20% to 30% of the shaft speed. It is a mechanical device. for instance. which provides driving force to another mechanism when required. without stopping the driving shaft. CHAPTER 8 8. As the temperature of the spring rises. one shaft is typically attached to a motor or other power unit (the driving member). and the other drives a drill chuck.7.1 SUMMARY A Clutch is a machine member used to connect the driving shaft to a driven shaft. by convention understood to be rotating. typically by connecting the driven mechanism to the driving mechanism.3 Automobile Non-powertrain There are other clutches found in a car. When the temperature is low. In a drill. Page 27 Friction clutches . it serves as a brake. 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. allowing fluid past the valve which allows the fan to spin at about 60% to 90% of shaft speed. Clutches are useful in devices that have two rotating shafts. Clutches and brakes are similar. and the other shaft (the driven member) provides output power for work to be done. the spring winds and closes the valve. or be decoupled and spin at different speeds (disengaged). For example. so that the driven shaft may be started or stopped at will. a belt-driven engine cooling fan may have a clutch that is heat-activated. A clutch thus provides an interruptible connection between two rotating shafts Clutches allow a high inertia load to be stated with a small power. Clutches are also used extensively in production machinery of all types. one shaft is driven by a motor. The driving and driven members are separated by a silicone-based fluid and a valve controlled by a bimetallic spring. if the driven member of a clutch is fixed to the mechanism frame. The clutch connects the two shafts so that they can either be locked together and spin at the same speed (engaged). Page 28 Friction clutches . Because of the complexity of these interactions friction cannot be calculated from first principles. wider tires on cars provide more traction than narrow tires for a given vehicle mass because of surface deformation of the tire. which may lead to performance degradation and/or damage to components. but instead must be found empirically. Friction is not a fundamental force but occurs because of the electromagnetic forces between charged particles which constitute the surfaces in contact. • Fluid friction describes the friction between layers within a viscous fluid that are moving relative to each other.APPENDIX –A BASIC CONCEPTS OF FRICTION Friction is the force resisting the relative motion of solid surfaces. 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. Another important consequence of many types of friction can be wear.[1][2] • Lubricated friction is a case of fluid friction where a fluid separates two solid surfaces. the force resisting the motion of a solid body through a fluid. It may be thought of as the opposite of "slipperiness". Friction is a component of the science of tribology. • Amontons' 2nd Law: The force of friction is independent of the apparent area of contact. Dry friction is subdivided into static friction between nonmoving surfaces. fluid layers.[3][4][5] • Skin friction is a component of drag. and kinetic friction between moving surfaces. For example. When surfaces in contact move relative to each other. Amontons' 2nd Law is an idealization assuming perfectly rigid and inelastic materials. This property can have dramatic consequences. There are several types of friction: • Dry friction resists relative lateral motion of two solid surfaces in contact.and/or material elements sliding against each other. • Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation. • Coulomb's Law of Friction: Kinetic friction is independent of the sliding velocity. The two regimes of dry friction are static friction between non-moving surfaces. the friction between the two surfaces converts kinetic energy into heat. as illustrated by the use of friction between pieces of wood to start a fire. Dry friction Dry friction resists relative lateral motion of two solid surfaces in contact. 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. the frictional force is exactly what it must be in order to prevent motion between the surfaces. is an approximate model used to calculate the force of dry friction. It is important to note that in all cases. In the Page 29 Friction clutches .and kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces. and its direction is perpendicular to the surfaces. which is an empirical property of the contacting materials. named after Charles-Augustin de Coulomb. above which motion would commence. 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. the drive wheels of an accelerating car experience a frictional force pointing forward. and the rubber would slide backwards along the pavement. the wheels would spin. it balances the net force tending to cause such motion. Coulomb friction. Newton's first law of motion holds. The direction of the static friction force can be visualized as directly opposed to the force that would otherwise cause motion. it is the direction of (potential) sliding between tire and road. rather than providing an estimate of the actual frictional force. equals zero. and the direction of the frictional force against a surface is opposite to the motion that surface would experience in the absence of friction. Main article: Normal force The normal force is defined as the net force compressing two parallel surfaces together. • is the normal force exerted between the surfaces. Note that it is not the direction of movement of the vehicle they oppose. a curling stone sliding along the ice experiences a kinetic force slowing it down. so the net force given by the vector sum. the maximum possible magnitude of this force). if they did not. • is the coefficient of friction. were it not for the static friction preventing motion. In the case of kinetic friction. 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 normal force Block on a ramp (top) and corresponding free body diagram of just the block (bottom). in the static case. For example. Thus. The Coulomb friction may take any value from zero up to . This maximum force is known as traction. In this case. the friction force exactly cancels the applied force. In this case. It is governed by the equation: where • is the force exerted by friction (in the case of equality. For an example of potential movement. the Coulomb approximation provides a threshold value for this force. where is the coefficient of kinetic friction. and hence the mass of the block. and ultimately the frictional force. also known as a 'frictional coefficient' or 'friction coefficient' and symbolized by the Greek letter µ. Both static and kinetic coefficients of friction depend on the pair of surfaces in contact. For surfaces in relative motion . in some sets the two coefficients are equal. for example.3 and 0. Values outside this range are rarer. Most dry materials in combination have friction coefficient values between 0. the magnitude of the friction force is the product of the mass of the object. If the object is on a tilted surface such as an inclined plane. is determined using vector analysis. Rougher surfaces tend to have higher effective values.6.7. However. g. and the frictional force on each surface is exerted in the direction opposite to its motion relative to the other surface. usually via a free body diagram. In this case.simple case of a mass resting on a horizontal surface. but teflon. it depends only on the material. The coefficient of friction is an empirical measurement – it has to be measured experimentally. the normal force. the acceleration due to gravity. where . while rubber on pavement has a high coefficient of friction. the normal force is less. for a given pair of surfaces. an elusive property – even magnetic levitation vehicles have drag. the only component of the normal force is the force due to gravity. is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. For instance. A value of zero would mean no friction at all. Rubber in contact with other surfaces can yield friction coefficients from 1 to 2. Coefficient of friction The 'coefficient of friction' (COF). the magnitude of the friction force itself depends on the normal force. The coefficient of friction depends on the materials used. but this is not true. for example. Coefficients of friction range from near zero to greater than one – under good conditions. the coefficient of friction is not a function of mass or volume. Depending on the situation. Page 30 Friction clutches . and the coefficient of friction. a tire on concrete may have a coefficient of friction of 1. and cannot be found through calculations. a large aluminum block has the same coefficient of friction as a small aluminum block. Therefore. Occasionally it is maintained that µ is always < 1. the calculation of the normal force may include forces other than gravity. the coefficient of static friction is usually larger than that of kinetic friction. the normal force between the object and the surface is just its weight. The Coulomb friction is equal to . If an object is on a level surface and the force tending to cause it to slide is horizontal. because less of the force of gravity is perpendicular to the face of the plane. such as teflon-on-teflon. where is the coefficient of static friction. However. This is usually larger than its kinetic counterpart.04. can have a coefficient as low as 0. ice on steel has a low coefficient of friction. For surfaces at rest relative to each other . which is equal to its mass multiplied by the acceleration due to earth's gravity. Judge.While in most relevant applications µ < 1. Singh Kripal.S. ‘Automobile Engineering’..COM Jain.Chand and Company Ltd 4. C. ‘The Automobile’ 8. Newton. Tata McGraw Hill Publishing Company. 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. Page 31 Friction clutches . ‘Automotive systems’. S.S.B. GOOGLE LINKS 3. 7. 2. For example. Narang G. INTERNET REFERENCES 1. 3.. ‘Automotive Mechanics’.II. A Book of Car. ‘Automotive Mechanics’. HOWSTUFFWORKS. REFERENCES BOOKS 1. Steeds & Garrett. Harbans Singh Reyat. New Chand 6. A..H. ‘Motor vehicle’. Volume 1 to 8. silicone rubber or acrylic rubber-coated surfaces have a coefficient of friction that can be substantially larger than 1. AUTOMOBILE ENGINEERING. ‘Automobile Engineering’.W.COM 2. Joseph Heitner.B. Vol. Crouse W. ‘The English language book society 5.Publisher and Distributors. Page 32 Friction clutches .