Types of clutches : Based on type of contact

• Positive contact clutches

• Friction clutches

Positive contact clutchesTransmit power from the driving shaft to the driven shaft by means of

jaws or teeth

+ Transmit large torque with no slip+ Develop very little heat, because they do not depend

upon friction. + Generally lighter.+ Less costly than a friction clutches of similar torque

capacity.

- Can not be engaged at high speeds, max 60 rpm for jaw clutches, and 300 rpm for toothed clutches

- Shock accompanies engagement at any speed- Require some relative motion in order to engage when

both driving and driven shafts are at rest

Friction clutchesTransmit power from the driving shaft to the driven shaft by means of

plates, disks or cones

+ Because they can slip relative to each other, there is very little shock during engagement.

+ Can be used for high speed engagement applications.

- Do slip- Do wear out (requiring replacement of friction

material)- Heat is developed (might require external cooling)

Types of clutches : Based on purpose

• Power transmission clutches

• Power interrupting clutches

• Clutches and brakes are essentially the same device.

• Each provides a frictional, magnetic, hydraulic or mechanical connection between two elements.

• Clutches: if both connected elements can rotate; primary function is to transmit power on an intermittent basis.

• Brakes: if one element rotates and the other is fixed; absorbs the kinetic energy of moving bodies and controls their motions.

Requirements of the clutch :

Torque transmission -Gradual engagement –Heat dissipation –Dynamic balancing –Vibration damping –Inertia –

Torque capacity of the clutch depends on :

Coefficient of friction The diameter of the driven plateSpring thrust applied by the pressure plate

Limitations of capacity :

max available µ is 0.35 , higher than these clutch becomes unstable increasing dia increases its inertia & it will continue to spin after disengagementthere is a limit to clamping pr. To which friction lining material subjected if it is tomaintain friction properties over a long period of time.

Torque Transmitted by the clutch :

Torque transmitted T = n * F * R

F – frictional force = µ * Pµ - coefficient of friction : P – Axial load : n – number of platesR – effective mean radius of frictional surface

- Torque transmitted depends on the radius of the friction material.- A limit on the spring force is set by the magnitude of the effort a

driver may be expected to exert on a clutch pedal .- µ is constant for a given material .- n can be increased to transmit more torque.

Clutch

Types of Clutches :

Single plate clutchMultiple plate clutchCone clutch Diaphragm clutchSemi-centrifugal clutchCentrifugal clutch

Method of clutch actuation :

Mechanical Hydraulic Vacuum Electro magnetic

MaterialsVarious materials have been used for the disc friction facings, including asbestos in the past.

Modern clutches typically use acompound organic resin with copper wire facing or a ceramic material. A typical coefficient of friction used on a friction disc surface is 0.35 for organic

and 0.25 for ceramic. Ceramic materials are typically used in heavy applications such as trucks carrying large loads or racing, though the harder ceramic materials increase flywheel and pressure

plate wear.Push/Pull

Friction disk clutches generally are classified as push type or pull type depending on the location of the pressure plate fulcrum points. In a pull type clutch, the action of pressing the pedal pulls the

release bearing, pulling on the diaphragm spring and disengaging the vehicle drive. The opposite is true with a push type, the release bearing is pushed into the clutch disengaging the vehicle drive. In

this instance, the release bearing can be known as a thrust bearing (as per the image above).Pads

Clutch pads are attached to the frictional pads, part of the clutch. They are most commonly made of rubber but have been known to be made of asbestos. Clutch pads usually last about 100,000 miles

(160,000 km) depending on how vigorously the car is driven.Dampers

In addition to the damped disc centres which reduce driveline vibration, pre-dampers may be used to reduce gear rattle at idle by changing the natural frequency of the disc. These weaker springs

are compressed solely by the radial vibrations from an idling engine. They are fully compressed and no longer in use once drive is taken up by the main damper springs.

LoadMercedes truck examples: A clamp load of 33 kN is normal for a single plate 430. The 400 Twin

application offers a clamp load of a mere 23 kN. Bursts speeds are typically around 5,000 rpm with the weakest point being the facing rivet.

ManufacturingModern clutch development focuses its attention on the simplification of the overall assembly and/or

Wet vs. dryA wet clutch is immersed in a cooling lubricating fluid which also keeps the surfaces clean

and gives smoother performance and longer life. Wet clutches, however, tend to lose some energy to the liquid. Since the surfaces of a wet clutch can be slippery (as with a

motorcycle clutch bathed in engine oil), stacking multiple clutch discs can compensate for the lower coefficient of friction and so eliminate slippage under power when fully engaged.The Hele-Shaw clutch was a wet clutch that relied entirely on viscous effects, rather than

on friction.A dry clutch, as the name implies, is not bathed in fluid and should be, literally, dry.

Pressure plate

Diaphragm spring

Clutch housing

Clutch DiscThe clutch disc, also called friction lining, consists of a splined hub and a round metal plate covered with friction material (lining). The splines in the center of the clutch disc mesh with the splines on the input shaft of the manual transmission. This makes the input shaft and disc turn together. However, the disc is free to slide back and forth on the shaft. Clutch disc torsion springs, also termed damping springs, absorb some of the vibration and shock produced by clutch engagement. They are small coil springs located between the clutch disc splined hub and the friction disc assembly. When the clutch is engaged, the pressure plate jams the stationary disc against the spinning flywheel. The torsion springs compress and soften, as the disc first begins to turn with the flywheel. Clutch disc facing springs, also called the cushioning springs, are flat metal springs located under the friction lining of the disc. These springs have a slight wave or curve, allowing the lining to flex inward slightly during initial engagement. This also allows for smooth engagement. The clutch disc friction material, also called disc lining or facing, is made of heat-resistant asbestos, cotton fibers, and copper wires woven or molded together. Grooves are cut into the friction material to aid cooling and release of the clutch disc. Rivets are used to bond the friction material to both sides of the metal body of the disc.

Clutch Plate or Friction Plate

Torsional springs

Splined boss (hub)

Friction lining

Requirements of a friction lining :

Friction liningLinings are riveted or boned to the clutch plates .Rivet heads seated in counter bores in the friction material , and it is

made of copper or aluminium , with this only thickness of the lining down to the rivet heads can be used and remainder has to be scrapped .

Bonded lining can utilize large portion of the total volume of the friction material .

Friction materials are woven or moulded .- by spinning asbestos or other mineral fibers into a yarn , in some

instances on a brass wire core which is woven into a cloth and then impregnated with a bonding agent. It is subdivided into solid woven and laminated. In the former , the cloth is woven to the required thickness of the lining before impregnation ,while in the later several layers of the cloth are placed together and then impregnated .

- moulded types made by mixing the fibres and bonding agent into a dough and then moulding it under presure at elevated temp at dies

Components of the clutch

flywheel Friction plates Pressure plate cover

Release fingers

Pressure Plate

Working of the clutch

When the pressure is applied to the foot pedal, the pressure is When the pressure is applied to the foot pedal, the pressure is transmitted through the release finger, fork and release bearingtransmitted through the release finger, fork and release bearing. Then . Then the springs are compressed and its moves back the pressure disc the springs are compressed and its moves back the pressure disc thus thus releasing the clutch plate. Now the clutch is said to be releasing the clutch plate. Now the clutch is said to be disengaged.disengaged.

At this stage the pressure plate and flywheel are free to rotateAt this stage the pressure plate and flywheel are free to rotate with with the clutch plate stationary.the clutch plate stationary.

Similarly, when the clutch pedal is released, spring pressure isSimilarly, when the clutch pedal is released, spring pressure is fully fully applied on the clutch plate. The plate is held between the flywhapplied on the clutch plate. The plate is held between the flywheel eel and the pressure plate rotates as a single unit.and the pressure plate rotates as a single unit.

Typical friction disc travels about 0.06 inch(1.5 mm).Typical friction disc travels about 0.06 inch(1.5 mm).

Sometimes a clutch with greater holding power is needed. When Sometimes a clutch with greater holding power is needed. When limited space prevents making the clutch larger, the a clutch wilimited space prevents making the clutch larger, the a clutch with th two friction disc can be used.two friction disc can be used.

Use of second disc adds area, thereby providing greater torque Use of second disc adds area, thereby providing greater torque carrying capacity (used in medium and heavy trucks). carrying capacity (used in medium and heavy trucks).

Coil spring clutch

Working of Diaphragm spring clutch

Used with most Used with most mostmost manual transaxles and in many rear manual transaxles and in many rear wheel drive vehicles.wheel drive vehicles.A A belevillebeleville (diaphragm) spring supplies the force that holds (diaphragm) spring supplies the force that holds the friction disc against the flywheel.the friction disc against the flywheel.The spring has tapered fingers pointing inwards from a solid The spring has tapered fingers pointing inwards from a solid ring. These act as release levers to take up the spring ring. These act as release levers to take up the spring action as the clutch disengages.action as the clutch disengages.As the clutch pedal is pressed, the release bearing pushes As the clutch pedal is pressed, the release bearing pushes against the fingers, which cause the diaphragm to pivot against the fingers, which cause the diaphragm to pivot about the inner pivot ring, and outer section moves about the inner pivot ring, and outer section moves outwards, and pushes the pressure plates away from friction outwards, and pushes the pressure plates away from friction disc.disc.Spring force varies according to the size and thickness of Spring force varies according to the size and thickness of diaphragm spring. diaphragm spring.

It has a It has a hubhub and and plateplate, , cushion springscushion springs, and , and dampening springsdampening springs..The slightly waved cushion springs attach to plate and friction The slightly waved cushion springs attach to plate and friction facing facing

attach to these springs.attach to these springs.The dampening springs are heavy coil springs set in circle arounThe dampening springs are heavy coil springs set in circle around the d the

hub (central hub (central splinedsplined portion where input shaft fits).portion where input shaft fits).The facings are mostly made of cotton and asbestos The facings are mostly made of cotton and asbestos fibresfibres woven or woven or

mouldedmoulded together, and the together, and the thethe material is saturated with binding agents.material is saturated with binding agents.Copper wire is pressed sometimes into facings to give added streCopper wire is pressed sometimes into facings to give added strength.ngth.

FunctionsFunctions::when clutch engages, the cushion springs compress slightly to twhen clutch engages, the cushion springs compress slightly to take up ake up

the shock load.the shock load.Dampening springs reduce the Dampening springs reduce the torsionaltorsional vibrations caused by impulses.vibrations caused by impulses.Friction facings provide the necessary locking force in power Friction facings provide the necessary locking force in power

transmission.transmission.

Multiple plate clutch

driver driven

Pressure plates

Friction plates

21 43 65

No. of driving pairs n = 6

Plate ClutchesIn a plate clutch, the torque is transmitted by friction between one (single plate clutch) or more (multiple plate clutch) pairs of co-axial annular driving faces maintained in contact by an axial thrust.

Both sides of each plate are faced with friction material, so that a single-plate clutch has two pairs of driving faces in contact.

n = no. of pairs of driving faces.

Then, for a plate clutch, the maximum torque transmitted is

mWrnT µ=

Performance characteristic of multiplate clutch

Centrifugal clutch

Driving shaft

Driven shaft

Friction lining

The maximum torque transmitted, T = Aω2 - B

where, A and B are constants for a given clutch.

mrω2

ω

ω

Functioning of the clutch is automatic and depends upon the Functioning of the clutch is automatic and depends upon the engine speed .engine speed .As the speed increases ,the flyweights move out wards due to As the speed increases ,the flyweights move out wards due to the centrifugal forcethe centrifugal forceThis movement operates a bell crank lever and presses the This movement operates a bell crank lever and presses the floating plate.floating plate.No need for specific operation to disengage the clutch.No need for specific operation to disengage the clutch.The vehicle can also be stopped with the gear load, without The vehicle can also be stopped with the gear load, without stalling the engine.stalling the engine.The vehicle is controlled by the accelerator pressure and gear The vehicle is controlled by the accelerator pressure and gear transmission at the starting only. transmission at the starting only. This arrangement makes the driving operation very easy and This arrangement makes the driving operation very easy and convenient convenient

Semi – Centrifugal clutch

Cone Clutch

Cone-clutch

Driving shaft

Driven shaft

Friction lining

α

w

The maximum torque transmitted, T = µWrm cosecα

α = semi-apex angle of the cone

Only one pair of driving surfaces is possible, n =1

Cone Clutch

• Cone clutches are used where large torque have to be transmitted but where heavyclutch engagement spring have been impracticable .

• Clutch is kept engaged by the axial force P exerted by the spring .• The normal force Q is greater than P , since it is augmented by the wedging action of

the cones . usually Q is five times that of P .• α- cone angle , it must be less than 20degree(in wet clutches it is 7 degree)

otherwise the cones tend to stick.• with a more acute angle , even a small amount of wear of the friction faces would

introduce a large axial displacement of the cone .

ELECTRO MAGNETIC CLUTCH

Engagement: Electromechanical clutches operate via an electric actuation, but transmit torque mechanically. When voltage/current is applied to the clutch coil, the coil becomes an electromagnet and produces magnetic lines of flux. This flux is then transferred through the small air gap between the field and the rotor. The rotor portion of the clutch becomes magnetized and sets up a magnetic loop, which attracts both the armature and the friction disks. The attraction of the armature compresses or squeezes the friction disks, transferring the torque from the inner driver to the outer disks. (In order for the unit to be used as a clutch, a drive hub is required. This hub would be attached to a pulley, sprocket or coupling.) Within a relatively short time, the load is accelerated to match the speed of the rotor, thereby engaging the armature and the output portion of the clutch.

Disengagement: When current/voltage is removed from the clutch, the armature is free to turn with the shaft. Springs hold the armature away from the rotor surface when power is released, creating minimal drag.

Slippage should occur only during acceleration. When the clutch is fully engaged, there is no relative slip (if the clutch is sized properly). Torque transfer is 100% efficient.

Clutch actuating mechanism

Mechanical Linkage

Hydraulic Linkage

Hydraulic clutch release mechanism

Currently, two types of overrunning clutches predominate - the pragclutch and roller ramp clutch. These devices Rely on a wedging action to lock-up, which means sprags and races must endure extremely high radial stresses to transmit even a moderate amount of tangential force, or useful torque.

As a result, these clutches must be made from expensive, high quality bearing steel which has been hardened to withstand the forces generated by the wedging action.

In additional, conventional one-way clutches offer limited functionality and greatly reduced load capacity in applications with very-high overrun speeds, high engagement speeds, and vibration - all of which are present to some degree in most automotive environments.

All of these factors combine to make conventional one-way clutches the weakest link in automatic transmissions.

The over running clutch acts like a ratchet. You know how you can turn hard on a ratchet one way to tighten a bolt & then it spins easily the other way? Same thing with the overrunning clutch. It allows the tractor to apply power to spin the mower but the mower can't apply its momentum back to spin the transmission. When installed you can depress the clutch & the tractor will stop instantly but the mower will gradully spin to a safe stop. You can also depress the clutch to shift gears, for example, andthe mower will continue to free spin. This makes it easier to resume mowing since you don't have to spin up the mower from a complete stop again.

There are five types of clutch problems- slipping, grabbing, dragging, abnormal noises, and vibration. It is important to know the symptoms produced by these problems and the parts that might be the cause.

Slipping Slipping occurs when the driven disc fails to rotate at the same speed as the

driving members when the clutch is fully engaged. This condition results whenever the clutch pressure plate fails to hold the disc tight against the face of the flywheel. If clutch slippage is severe, the engine speed will rise rapidly on acceleration, while the vehicle gradually increases in speed. Slight but continuous slippage may go unnoticed until the clutch facings are ruined by excessive temperature caused by friction.

Normal wear of the clutch lining causes the free travel of the clutch linkage to decrease, creating the need for adjustment. Improper clutch adjustment can cause slippage by keeping the release bearing in contact with the pressure plate in the released position. Even with your foot off the pedal, the release mechanism will act on the clutch fork and release bearing.

Some clutch linkages are designed to allow only enough adjustment to compensate for the lining to wear close to the rivet heads. This prevents damage to the flywheel and pressure plate by the rivets wearing grooves in their smooth surfaces. Other linkages will allow for adjustment after the disc is worn out. When in doubt whether the disc is worn excessively, remove the inspection cover on the clutch housing and visually inspect the disc.

Binding linkage prevents the pressure plate from exerting its full pressure against the disc, allowing it to slip. Inspect the release mechanism for rusted, bent, misaligned, sticking, or damaged components. Wiggle the release fork to check for free play. These problems result in slippage.

A broken motor mount (engine mount) can cause clutch slippage by allowing the engine to move, binding the clutch linkage. Under load, the engine can lift up in the engine compartment, shifting the clutch linkage and pushing on the release fork. Grease and oil on the disc will also cause slippage. When this occurs, locate and stop any leakage, thoroughly clean the clutch components, and replace the clutch disc. This is the only remedy.

If clutch slippage is NOT caused by a problem with the clutch release mechanism, then the trouble is normally inside the clutch. You have to remove the transmission and clutch components for further inspection. Internal clutch problems, such as weak springs and bent or improperly adjusted release levers, will prevent the pressure plate from applying even pressure. This condition allows the disc to slip.

To test the clutch for slippage, set the emergency brake and start the engine. Place the transmission or transaxle in high gear. Then try to drive the vehicle forward by slowly releasing the clutch pedal. A clutch in good condition should lock up and immediately kill the engine. A badly slipping clutch may allow the engine to run, even with the clutch pedal fully released. Partial clutch slippage could let the engine run momentarily before stalling. NOTE Never let a clutch slip for more than a second or two. The extreme heat generated by slippage will damage the flywheel and pressure plate faces.

Grabbing A grabbing or chattering clutch will produce a very severe vibration or jerking

motion when the vehicle is accelerated from a standstill. Even when the operator slowly releases the clutch pedal, it will seem like the clutch pedal is being pumped rapidly up and down. A loud bang or chattering may be heard, as the vehicle body vibrates.

Clutch grabbing and chatter is caused by problems with components inside the clutch housing (friction disc, flywheel, or pressure plate). Other reasons for a grabbing clutch could be due to oil or grease on the disc facings, glazing, or loose disc facings. Broken parts in the clutch, such as broken disc facings, broken facing springs, or a broken pressure plate, will also cause grabbing.

There are several things outside of the clutch that will cause a clutch to grab or chatter when it is being engaged. Loose spring shackles or U-bolts, loose transmission mounts, and worn engine mounts are among the items to be checked. If the clutch linkage binds, it may release suddenly to throw the clutch into quick engagement, resulting in a heavy jerk.

However, if all these items are checked and found to be in good condition, the trouble is inside the clutch itself and will have to be removed for repair.

Dragging

A dragging clutch will make the transmission or transaxle grind when trying to engage or shift gears. This condition results when the clutch disc does not completely disengage from the flywheel or pressure plate when the clutch pedal is depressed. As a result, the clutch disc tends to continue turning with the engine and attempts to drive the transmission.

The most common cause of a dragging clutch is too much clutch pedal free travel. With excessive free travel, the pressure plate will not fully release when the clutch pedal is pushed to the floor. Always check the clutch adjustments first. If adjustment of the linkage does not correct the trouble, the problem is in the clutch, which must be removed for repair.

On the inside of the clutch housing, you will generally find a warped disc or pressure plate, oil or grease on the friction surface, rusted or damaged transmission input shaft, or improper adjustment of the pressure plate release levers causing the problem.

Abnormal NoisesFaulty clutch parts can make various noises. When an operator reports that a

clutch is making noise, find out when the noise is heard. Does the sound occur when the pedal is moved, when in neutral, when in gear, or when the pedal is held to the floor? This will assist you in determining which parts are producing these noises.

An operator reports hearing a scraping, clunking, or squeaking sound when the clutch pedal is moved up or down. This is a good sign of a worn or unlubricated clutch release mechanism. With the engine off, pump the pedal and listen for the sound. Once the source of the sound is located, you should clean, lubricate, or replace the parts as required. Sounds produced from the clutch, when the clutch is initially ENGAGED, are generally due to friction disc problems, such as a worn clutch disc facing, which causes a metal-to-metal grinding sound. A rattling or a knocking sound may be produced by weak or broken clutch disc torsion springs. These sounds indicate problems that require the removal of the transmission and clutch assembly for repair.

If clutch noises are noticeable when the clutch is DISENGAGED, the trouble is most likely the clutch release bearing. The bearing is probably either worn, binding, or, in some cases, loses its lubricant. Most clutch release bearings are factory lubricated; however, on some larger trucks and construction equipment, the bearing requires periodic lubrication. A worn pilot bearing may also produce noises when the clutch is disengaged. The worn pilot bearing can let the transmission input shaft and clutch disc vibrate up and down, causing an unusual noise.

Sounds heard in NEUTRAL, that disappear when the clutch pedal is pushed, are caused by problems inside the transmission. Many of these sounds are due to worn bearings. However, always refer to the troubleshooting chart in the manufacturer's manual.

Pedal Pulsation

A pulsating clutch pedal is caused by the runout (wobble or vibration) of one of the rotating members of the clutch assembly. A series of slight movements can be felt on the clutch pedal. These pulsations are noticeable when light foot pressure is applied. This is an indication of trouble that could result in serious damage if not corrected immediately. There are several conditions that can cause these pulsations. One possible cause is misalignment of the transmission and engine.

If the transmission and engine are not in line, detach the transmission and remove the clutch assembly. Check the clutch housing alignment with the engine and crankshaft. At the same time, the flywheel can be checked for runout, since a bent flywheel or crankshaft flange will produce clutch pedal pulsation. If the flywheel does not seat on the crankshaft flange, remove the flywheel. After cleaning the crankshaft flange and flywheel, replace the flywheel, making sure a positive seat is obtained between the flywheel and the flange. If the flange is bent, the crankshaft must be replaced.

Other causes of clutch pedal pulsation include bent or maladjusted pressure plate release levers, warped pressure plate, or warped clutch disc. If either the clutch disc or pressure plate is warped, they must be replaced.

Fluid Coupling

Flat-plate Friction Clutches and

Thrust BearingsThere are many instances in machines where two surfaces, usually flat or conical in shape, are in contact under the action of transmitted load.

The two applications to be considered here are

•The thrust bearing (where one member is rotating and the other stationary)and

•Friction clutch (where both members rotate, normally in the same direction, but not necessarily at the same speed)

Thrust bearing (collar type)

Bearing surface

(an annular surface)

r1 = inner radius

r2 = outer radius

T ( torque applied)

ω (angular speed)

W (axial load)

r1r2

Minimum Torque required to rotate the bearing

T = µ WrmWhere

rm = frictional mean radius

Frictional torque on the annular bearing surface

r1

r2

r

dr

dFTangential friction forces

The axial thrust W produces a pressure p at radius r on the contacting surfaces.

Relative rotation of these surfaces sets up tangential friction forces dF

Consider an elementary ring of thickness dr at radius r

From the symmetry of the element about the centre,

normal reaction on the element dN = p dA = p (2πrdr)

At the point of slip or when slipping occurs, frictional force on the element dF = µ dN

Frictional torque on the element

dT = dF r = µ dN r = 2π µp r2 dr

Frictional torque on the entire surface

T = ∫dT = ∫2

1

r

r

2drpr2πµ

Frictional mean radius (rm)

Case (I) Uniform pressure

In a newly assembled bearing, intensity of pressure acting on the flat collar may be assumed uniform over the entire bearing surface because of the exact tolerance to which the machine components are manufactured, i.e. the fit between the two surfaces is assumed to be perfect

When the pressure distribution is uniform over the bearing surface; frictional mean radius;

⎟⎟⎠

⎞⎜⎜⎝

⎛

−

−= 2

122

31

32

mrrrr

32r

Case (II) Uniform Wear

When the

Rate of wear is uniform

over the bearing surface⎟⎠⎞

⎜⎝⎛ +

=2

rrr 21m

When slipping takes place wear will occur, and over a certain period of running (in an old bearing) this wear must be uniform for the surfaces to remain in contact.

The rate of wear is a function of the intensity of pressure p and linear velocity of sliding vS

Wear is proportional to p, vS

vS = rω

Uniform wear => pr = c (constant)

Flat-plate Friction ClutchesA clutch enables two co-axial shafts to be engaged or disengaged while at rest or in relative motion

T

TW (axial thrust)W

Friction plate

Friction liningPressure plates

springs

Single-plate Friction Clutch (Disengaged position)

Driving shaft

Driven shaft

Clutch Cable Adjustment Like the mechanical linkage, a clutch cable adjustment may be required to maintain the correct pedal height and free travel. Typically the clutch cable will have an adjusting nut. When the nut is turned, the length of the cable housing increases or decreases. To increase clutch pedal free travel, turn the clutch cable housing nut to shorten the housing, and, to decrease clutch pedal free travel, turn the nut to lengthen the housing.

Uniform pressure and uniform wear

The pressure between the clutch surfaces can approach a uniform distribution over the surface if the disks are flexible enough.

The wear will be greater at larger diameters because wear is proportional to pressure times velocity (pV) and the velocity increases linearly with radius.

As the disks wear preferentially toward the outside, the loss of material will change the pressure distribution to a non-uniform one and the clutch will approach a uniform wear condition of pV=constant.

A flexible clutch may be close to a uniform pressure condition when new, but will tend toward a uniform wear condition with use.

A rigid clutch will more rapidly approach the uniform wear condition when use.

The uniform wear assumptions gives a more conservative clutch rating, because clutch capacities are lower than the uniform pressure assumption

Problems

1.A multi-plate clutch is to transmit 12kW at 1500rev/min. The inner and outer radii for the plates are to be 50mm and 100mm respectively. The maximum axial spring force is restricted to 1kN. Calculate the necessary number of pairs of surfaces if µ=0.35 assuming constant wear. What will be the necessary axial force?

(Answer, 3; 970N)

2.A plate clutch consists of a flat driven plate gripped between a driving plate and presser plate so that there are two active driving surfaces, each having an inner diameter 200mm and an outer diameter 350mm. µ=0.40. The working pressure is limited to 170kN/m2. Assuming the pressure is uniformly distributed calculate the power which can be transmitted at 1000rev/min. If the clutch becomes worn so that the intensity of pressure is inversely proportional to the radius, the total axial force on the presser plate remaining unaltered, calculate the power which can now be transmitted at 1000rev/min and the greatest intensity of pressure on the friction surfaces.

(Answer: 130kW; 127kW; 234kN/m2)

3. An electric motor drives a co-axial rotor through a single-plate clutch, which has two pairs of driving surfaces, each of 275mm external and 200mm internal diameter, the total spring load pressing the plates together is 500N. The mass of the motor armature and shaft is 800kg and its radius of gyration is 260mm; the rotor has a mass of 1350kg and its radius of gyration is 225mm.The motor is brought up to a speed of 1250rev/min; the current is then switched off and the clutch suddenly engaged. Determine the final speed of the motor and rotor, and find the time taken to reach that speed and the kinetic energy lost during the period of slipping. How long would slipping continue if a constant torque of 50Nm were maintained on the armature shaft? Take µ=0.35. (Answer: 552rev/min; 95s; 259kJ; 288.5s)

4. A power shaft running at 180rev/min drives a countershaft through a single-plate friction clutch of internal and external radii 75mm and 150mm respectively, µ being 0.3. The countershaft has a total moment of inertia of 8.4kgm2. If the time taken for the countershaft to attain full speed from rest is 6s, determine the axial spring force in the clutch, and also the energy dissipated due to clutch slip. Assume uniform wear.

(Answer: 391N; 1.49kJ)

5. The axial spring force operating a single-plate clutch is 8250N. To each side of the plate is attached a ring of friction material having an inner diameter of 200mm and an outer diameter of 350mm. Assuming that the normal pressure p varies with radius r mm according to the relation p (r + 50) = c, and that µ =0.3, calculate the maximum power the clutch can transmit at 300rev/min.

(Answer: 21.5kW)