Design of Friction clutch

requirements
• The contact surfaces should develop a frictional force that may pick
up and hold the load with reasonably low pressure between the
contact surfaces.
• The heat of friction should be rapidly dissipated and tendency to grab
should be at a minimum.
• The surfaces should be backed by a material stiff enough to ensure a
reasonably uniform distribution of pressure.
•
•
material characteristics
• It should have a high and uniform coefficient of friction.
• It should not be affected by moisture and oil.
• It should have the ability to withstand high temperatures caused by
slippage.
• It should have high heat conductivity.
• It should have high resistance to wear and scoring.
Design Considerations
• low weight in order to minimise the inertia load
• should not require any external force to maintain
• The provision for taking up wear of the contact surfaces must be
provided.
• facilitating repairs.
• provision for carrying away the heat generated
• should be covered by guard.
Single plate clutch
• whose both sides are faced with a frictional material
• free to move axially along splines
• The pressure plate is mounted to the flywheel
• The pressure plate pushes the clutch plate towards the flywheel by a
set of strong springs
• release levers on pivots suspended from the case of the body.
pressure plate moves away from the flywheel by the inward
movement of a thrust bearing.
• The bearing is mounted upon a forked shaft and moves forward when
the clutch pedal is pressed.
T = Torque transmitted by the
clutch.
p = Intensity of axial pressure
with which the contact surfaces
are held together,
r1 and r2 = External and internal
radii of friction faces,
r = Mean radius of the friction
face, and
 = Coefficient of friction.
Normal or axial force on the ring W = Pressure x Area = p x 2 . r. dr
• the frictional force on the ring acting tangentially at radius r,
• Fr =  x W = .p x 2 r. dr
• Frictional torque acting on the ring,
• Tr = Fr x r = .p x 2 r. dr x r = 2  p. r2 dr
Wear patterns
• when the friction surface is new,
there is a uniform pressure
distribution
• This pressure will wear most rapidly
where the sliding velocity is
maximum.
• This wearing-in process continues
until the product p.V is constant
over the entire surface.
• After this, the wear will be uniform
 uniform pressure, P=F/A
W
p=

 (r1 )2 − (r2 )2 
W = Axial thrust

r1 r 3  r1
T =  2..p.r .dr = 2..p  
2
r2
 3  r
2

 (r1 )3 − (r2 )3  W  (r1 )3 − (r2 )3 

= 2..p 
 3
 = 2. 
 
 (r1 )2 − (r2 )2  
 3


uniform axial wear
• The work of friction is proportional to the product of normal pressure
(p) and the sliding velocity (V).
• Therefore,
• Normal wear  Work of friction  p.V.
• or p.V = K (a constant) or p = K/V
• pωr = K ,
p.r. = C (a constant) or p = C / r

and the normal force on the ring,

C
W = p.2. r. dr =  2r.dr = 2C.dr
r
• Total force acing on the friction surface

W =  2C dr = 2 C r r12 = 2C (r1 − r2 )

r1 r
r2

W
C=
2(r1 − r2 )
• We know that the frictional torque acting on the ring
C
Tr = 2.p.r .dr = 2   r .dr = 2.C.r.dr
2 2
r
• Total frictional torque acting on the friction surface (or on the clutch),
r1 r 2  r1
T =  2..C.r.dr = 2..C  
r2
 2  r
2

 (r1 )2 − (r2 )2 
= 2..C 
 = .C (r1 ) − (r2 )
2 2

 2 

= .. 
W
2(r1 − r2 )
 2 2
2

(r1 ) − (r2 ) =  .W(r1 + r2 ) = .W.R
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