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1. Clutches and Brakes

2. Introduction
• Mechanically Same Device
• Frictional, magnetic, hydraulic or mechanical connection
• Used in Production machinery
• Clutches – Allow high inertia load to start
• Emergency disconnecting devices/production machines
– Clutch Brake Combination
• Fail Safe, stops the load in case of power failure –heavy
trucks, train
• Clutch engagement for short time/Brake for large time
• Brakes absorb more energy as compared to clutch

3. Types of Brakes and Clutches
• Means of Actuation
– Mechanical
– Pneumatic
– Hydraulic
– Electrical
• Means of Energy Transfer
• Character of Engagement

5. Positive Contact Clutches
• Toothed or Serrated Clutch
• Not useful for Brakes
• Engaged at low relative velocities
(60rpm for jaw and 300 rpm for
toothed)
• Can transmit large torque with no slip
• Sometimes engaged with friction
type clutch

6. Friction Clutches and Brakes
• Two or more surfaces with a normal
force
• Cylindrical/Conical
• Flat and perpendicular to axis of
rotation
• One is metal surface other some
friction material
• Cylindrical with normal force in radial
direction or conical
• One is cast or surface lining
• For heavy torque multiple plates
• Dry/Wet (heat transfer), Oil bath
• Most of automobiles, oil dipped (Also
protect from dirt, and good heat
transfer)
• m 0.05 oil to 0.6 dry

7. Overrunning Clutches
• One-way clutches
• Relative velocity of two
elements
• Reverse Motion – Locks up
• Lifts
• Indexing Mechanism
• Sprag Mechanism
• Roller Clutch
• Rear Hub o bicycle

8. Centrifugal Clutches
• Engage on increase of
shaft speed
• Friction Elements
thrown racially outward
against the inside of
drum cylinder
• Couple IC Engine to
Drive Train
• Go-Carts, Chain Saws,
overload protection

9. Magnetic Clutches
• Friction Clutches
Electromagnetically
operated
• Rapid Response time,
ease control, smooth
start/stop

10. Magnetic-particle clutches and Brakes
• No direct frictional contact b/w clutch disk
and housing
• Gap filled with fine ferrous powder
• Coil energized- powder particles form chains
along magnetic field flux lines
• Torque depends upon current

11. Magnetic Hysteresis Clutches and
Brakes
• No mechanical contact/no Friction
• Rotor – drag cup dragged along (braked) by
magnetic field set up by field coil.
• Winding machines
• Torque is controllable
• Long life
•

13. Fluid Couplings
• Transmit torque through a fluid
typically oil
• Impeller/set of blades turned by
input shaft imparts angular
momentum to the oil surrounds it
• Turbine/runner with similar
blades attached to output shaft
• Some slip
• Smooth
• Heat transfer
• Never totally decouple
• Use in -- marine and industrial
machine drives

14. Clutch/Brake Selection and Specs
• Catalogues
• Procedures for selection and specs
• Suggest service factors
• Standard factors
• Particular applications

15. Service Factors
• Apply adequate service
factors
• Different safety factors
and service factors
• Based upon extensive
testing field service
experience
• Slip, overheat
• Inertia, overloading
motor
• MOI
Service Condition Service Factor
Light load pickup, no
shock during operation
1.0 X Rated Torque
Medium load pickup,
medium shock during
operation
0.5 X Rated Torque
Heavy load pickup,
medium shock during
operation
0.3 X Rated Torque
Sudden load pickup,
heavy shock during
operation
0.2 X Rated Torque
Ratchet Clutch Service Factors

16. Clutch Location and Materials
• Clutch Location
– High speed
– High torque
• Clutch and Brake Materials
– Disks or Drums
• Gray CI, Steel
– Friction Surfaces – Good COF, Compressive strength, high Temperature
• Asbestos Fiber brake/clutch lining – Carcinogen
• Lining – molded, woven, sintered, solid
• Molded – polymeric resins, powdered, fibrous material
• Brass or zinc chips – improve heat wear resistance reduce scoring of drums
and disks
• Woven- long asbestos firers
• Sintered – high temp resistance, compressive strength
• Wood, cast iron lining

17. Disk Clutches
• Two disks - high friction
• Normal force – Mechanically, hydraulically, electromagnetically
• Uniform pressure – if disks flexible
• Wear pV
• pV=Const
• uniform wear more conservative

18. Uniform Pressure

19. Uniform Wear
Maximum torque for any outside radius ro will be
obtained when the inside radius is:

20. • uniform-wear assumption gives a lower torque
capacity for the clutch than does the uniform-
pressure assumption.
• The higher initial wear at the larger radii shifts
the center of pressure radially inward, giving a
smaller moment arm for the resultant friction
force.
• Clutches are usually designed based on uniform
wear. They will have a greater capacity when new
but will end up close to the predicted design
capacity after they are worn in

24. Disk Brakes
• No Lining covering
entire circumference
to avoid overheat
• Ventilation
• N is at least 2
• Automobiles
• Good Controllability
• Linearity

25. Drum Brakes
• Apply Friction material to the circumference
of a cylinder (ext/int)
• Brake Shoe + Brake Drum
• Brakes/Clutches
• Shoe/Drum
• Band Brake
• Short Shoe
• Long Shoe

26. Short-Shoe External Drum Brakes
•Self Energizing cFf adds to aFa-increase the braking torque
•Self –deenergizing -
Reverse rotation- cFf
•Self Locking mc≥b
Angle of contact < 45o
distributed force between shoe and drum
to be uniform, and it can be replaced by
the concentrated force Fn in the center of
the contact area

27. • This self-energizing -potential advantage –
reduces the force compared to a disk brake
• Drum brakes typically have two shoes, one of
which can be made self-energizing in each
direction, or both in one direction.
• SELF-LOCKING: If the shoe touches the drum,
it will grab and lock. Not a desired condition
except in so-called backstopping applications,
- overrunning clutches; hoists

28. • Problem: Determine a suitable size and
required force for an axial disk clutch.
• Given: The clutch must pass 7.5 hp at
1725 rpm with a service factor of 2.
• Assumptions: Use a uniform-wear model.
Assume a single dry disk with a molded
lining.
• service factor of 2 requires derating the
clutch by that factor, so we will design for
15 hp instead of 7.5. pmax = 225 psi and μ
= 0.35.
• The clutch specification is then a single
disk with 3.6-in outside diameter and 2-in
inside diameter, a molded lining with μ
dry ≥ 0.35, and an actuating force ≥ 1108
lb.
EX: 17.1

29. Ex 17.2
• For the drum-brake arrangement shown in,
determine the ratio c / r that will give a self-
energizing ratio Fn / Fa of 2. Also find the c / r
ratio that will cause self-locking
• Given The dimensions are a = b = 6, r = 5.
• Assumptions Coefficient of friction μ = 0.35.
• For self-locking to begin, Fa becomes zero,
making Fn / Fa = ∞ and Fa / Fn = 0. The second
of these ratios will need to be used to avoid
division by zero.
• Form the c / r ratio for self-locking with the
given brake geometry.
• Note that these ratios are specific to the
dimensions of the brake. The length a was set
equal to b in this example in order to eliminate
the effect of the lever arm ratio a / b, which
further reduces the application force Fa
required for any normal force Fn

30. Long Shoe External Drum Brakes
• Angle of contact  >45
• Real shoe brake not; rigid
• Assume; Drum velocity const, wear
friction work
pbsin sin
P=Ksin
K=p/Sin =pmaxSin /Sinmax

31. Long Shoe External Drum Brakes

32. Long Shoe External Drum Brakes

33. Controlling input Torque-FlyWheels
• Large Oscillations due to
torque variations
• Average Torques – Small
• Sizing of motor

34. Controlling input Torque-FlyWheels
• Large Oscillations due to
torque variations
• Average Torques – Small
• Sizing of motor

35. • Torque Peak Values + 341.7 lb-in, -166.4 lb-in
• Average Torque – 70.2 lb-in

36. • Torque Peak Values + 341.7 lb-in, -166.4 lb-in
• Average Torque – 70.2 lb-in

37. Flywheel Energy

38. Sizing flywheel
• K is coefficient of fluctuation

39. Sizing flywheel
• K is coefficient of fluctuation

40. Energy Considerations and Temp Rise