machine elements ii - rini d - tm ft ugm clutches (kopling tidak tetap) rini dharmastiti jurusan...

Machine Elements II - Rini D - TM FT UGMMachine Elements II - Rini D - TM FT UGM

Clutches Clutches (Kopling tidak tetap)(Kopling tidak tetap)

Rini DharmastitiRini DharmastitiJurusan Teknik Mesin FT UGMJurusan Teknik Mesin FT UGM

Jl. Grafika no.2 YogyakartaJl. Grafika no.2 [email protected][email protected]


IntroductionIntroduction

Clutches and brakes are essentially the Clutches and brakes are essentially the same device same device

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

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

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


Classification of clutches and brakesClassification of clutches and brakes

Method of engagement: mechanical, Method of engagement: mechanical, pneumatic & hydraulic, electrical, pneumatic & hydraulic, electrical, automaticautomatic

Positive contact: square jaw, spiral jaw, Positive contact: square jaw, spiral jaw, toothedtoothed

Friction: axial, radial, coneFriction: axial, radial, cone Ocerrunning: roller, sprag, spring woundOcerrunning: roller, sprag, spring wound Magnetic: magnetic particle, hysterisis, Magnetic: magnetic particle, hysterisis,

eddy currenteddy current Fluid coupling: dry fluid, hydraulicFluid coupling: dry fluid, hydraulic


Positive contact clutchesPositive contact clutches Transmit power from the driving shaft to the Transmit power from the driving shaft to the driven shaft by means of jaws or teethdriven shaft by means of jaws or teeth

+ + transmit large torque with no sliptransmit large torque with no slip+ develop very little heat, because they do not + develop very little heat, because they do not

depend upon friction depend upon friction + generally lighter+ generally lighter+ less costly than a friction clutches of similar + less costly than a friction clutches of similar

torque capacitytorque capacity- Can not be engaged at high speeds, max 60 rpm Can not be engaged at high speeds, max 60 rpm

for jaw clutches, and 300 rpm for toothed for jaw clutches, and 300 rpm for toothed clutchesclutches

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

when both driving and driven shafts are at restwhen both driving and driven shafts are at rest


Positive contact clutchesPositive contact clutches

Although not as widely used as friction clutches, do Although not as widely used as friction clutches, do find important use in such applications as find important use in such applications as automotive transmissions, presses, household automotive transmissions, presses, household appliancesappliances

A synchromesh clutch in a manual automotive A synchromesh clutch in a manual automotive transmission: combined with a friction-type clutch, transmission: combined with a friction-type clutch, which drags the two elements to nearly the same which drags the two elements to nearly the same velocity before the jaws or teeth engages. velocity before the jaws or teeth engages. Automotive transmission typically use helical gears, Automotive transmission typically use helical gears, for quiet operation. The helical gears can not be for quiet operation. The helical gears can not be easily shifted in and out of engagement in manual easily shifted in and out of engagement in manual transmission because of their helix angle. Each gear transmission because of their helix angle. Each gear has a synchromesh clutch connecting it to its shaft. has a synchromesh clutch connecting it to its shaft.


Positive contact clutches Positive contact clutches

The force acting on the jaw depends upon The force acting on the jaw depends upon the horsepower and speed that the the horsepower and speed that the clutch is to transmit. clutch is to transmit.

T = torque (in-lb), hp = horse power to be T = torque (in-lb), hp = horse power to be transmitted, n = revolutions per minutetransmitted, n = revolutions per minute

.63000hpT

n



The average force, assumed to be The average force, assumed to be acting at the center of each jaw:acting at the center of each jaw:

F = average force (lb), k= number of F = average force (lb), k= number of jaws on one member, rjaws on one member, roo and r and rii = = outside and inside jaw radius (inch)outside and inside jaw radius (inch)

( ) / 2o i

TF

k r r



The shearing stress (lb/inchThe shearing stress (lb/inch22), acting on one jaw is:), acting on one jaw is:

t = thinkness of jaw (inch), t = thinkness of jaw (inch), = angle subtended = angle subtended by one jaw in degrees, 2by one jaw in degrees, 2(r(roo + r + rii )/2 represents )/2 represents the average circumference of the jaws.the average circumference of the jaws.

( ) .2 .

2 360o i

Tr r t



The bearing stress (lb/inchThe bearing stress (lb/inch22), can be ), can be found from: found from:

t = thinkness of jaw (inch), b = t = thinkness of jaw (inch), b = length of jawlength of jaw

.b

F

b t


Friction clutchesFriction clutches Transmit power from the driving shaft to the Transmit power from the driving shaft to the driven shaft by means of plates, disks or conesdriven shaft by means of plates, disks or cones

+because they can slip relative to each +because they can slip relative to each other, there is very little shock during other, there is very little shock during engagementengagement

+can be used for high speed +can be used for high speed engagement applicationsengagement applications

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

friction material)friction material)- Heat is developed (might require Heat is developed (might require

external cooling) external cooling)


Friction clutches : disk clutchesFriction clutches : disk clutches

For higher torque capacity, disk clutches are often For higher torque capacity, disk clutches are often made with multiple disks to increase the number of made with multiple disks to increase the number of friction surfaces, but the heat of friction generated friction surfaces, but the heat of friction generated can become the limiting factor on its capacitycan become the limiting factor on its capacity

Multiple clutches are more difficult to cool, so are Multiple clutches are more difficult to cool, so are appropriate for high load, low speed applicationsappropriate for high load, low speed applications

For high speed dynamic load, fewer friction For high speed dynamic load, fewer friction surfaces are bettersurfaces are better

Friction clutches may be operated either dry or Friction clutches may be operated either dry or wet. Oil: reduces the coefficient of friction, wet. Oil: reduces the coefficient of friction, increases the heat transferincreases the heat transfer

Friction coefficients of clutch/brake material Friction coefficients of clutch/brake material combination typically range from 0.05 in oil to 0.60 combination typically range from 0.05 in oil to 0.60 drydry


Friction clutches : disk clutchesFriction clutches : disk clutches

Automatic transmissions for automobiles Automatic transmissions for automobiles and trucks contain many wet clutches and and trucks contain many wet clutches and brakes operating in oil that is circulated brakes operating in oil that is circulated out of the transmission for cooling.out of the transmission for cooling.

Manual transmissions for off-road vehicles, Manual transmissions for off-road vehicles, such as motorcycles, use sealed, oil filled, such as motorcycles, use sealed, oil filled, multidisk wet clutches to protect the multidisk wet clutches to protect the friction surfaces from dust, water and dirt.friction surfaces from dust, water and dirt.

Manual transmission automobiles and Manual transmission automobiles and trucks, typically use single disk, dry trucks, typically use single disk, dry clutchesclutches


Clutch materialsClutch materials

Materials for the structural parts of clutches: typically made Materials for the structural parts of clutches: typically made of gray cast iron or steel.of gray cast iron or steel.

The friction surfaces are usually lined with material having a The friction surfaces are usually lined with material having a good coefficient of friction and sufficient compressive good coefficient of friction and sufficient compressive strength and temperature resistance: asbestos fiber, but no strength and temperature resistance: asbestos fiber, but no longer used in many applications because of its danger as a longer used in many applications because of its danger as a carcinogen.carcinogen.

Linings may be molded, woven, sintered or of solid materialLinings may be molded, woven, sintered or of solid material Molded linings: use polymeric resins to bind a variety of Molded linings: use polymeric resins to bind a variety of

powdered filled or fibrous materials.powdered filled or fibrous materials. Brass or zinc chips are sometimes added to improve heat Brass or zinc chips are sometimes added to improve heat

conduction and wear resistanceconduction and wear resistance Woven material: use long asbestos fibersWoven material: use long asbestos fibers Sintered metals provide high temperature resistance and Sintered metals provide high temperature resistance and

compressive strength than molded or woven materials. compressive strength than molded or woven materials. Materials: cork, wood and cast iron are sometimes uses as Materials: cork, wood and cast iron are sometimes uses as

lining as welllining as well


Clutch and brake material Clutch and brake material propertiesproperties

Material Maximum Temperature, ºF

Coefficient of friction, f

Maximum allowable pressure, psi

Metal on metal 500 - 600 0.25 200 – 250

Wood on metal 200 0.2 – 0.3 50 – 90

Leather on metal 150 – 200 0.3 – 0.4 15 – 40

Molded blocks 500 – 600 0.25 – 0.5 100 – 150

Asbestos on metal in oil 500 0.35 – 0.45 50 – 150

Sintered metal on cast iron in oil

450 0.2 400


Uniform pressure and uniform wearUniform pressure and uniform wear

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

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

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

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

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

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


Other types of clutchesOther types of clutches

Cone clutches : another types of axial clutch, Cone clutches : another types of axial clutch, being able to transmit a larger torque than disc being able to transmit a larger torque than disc clutches with the same outside diameter and clutches with the same outside diameter and actuating force, because increased frictional actuating force, because increased frictional area and the wedging action that takes place.area and the wedging action that takes place.

Cone clutches: low speed applicationsCone clutches: low speed applications Hydraulic or pneumatic clutch can minimize Hydraulic or pneumatic clutch can minimize

shock and vibrationshock and vibration Centrifugal clutches: engage automatically when Centrifugal clutches: engage automatically when

the shaft speed exceeds a certain magnitude. the shaft speed exceeds a certain magnitude. Friction elements are thrown radially outward Friction elements are thrown radially outward against the inside of a cylindrical drum to against the inside of a cylindrical drum to engage the clutch. engage the clutch.

machine elements ii - rini d - tm ft ugm clutches (kopling tidak tetap) rini dharmastiti jurusan...

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