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Clutches and Brakes

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Page 1: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Clutches and Brakes

Page 2: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Brakes and clutches

• Clutch is a device that connects and disconnects two

collinear shafts.

– Similar to couplings

– Friction and hence heat dissipation

• Purpose of a Brake is to stop the rotation of a shaft.

• Braking action is produced by friction as a stationary part

bears on a moving part.

– Heat dissipation is a problem

– Brake fade during continuous application of braking due to heat

generated

Page 3: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Brakes and clutches are essentially

the same devices. Each is

associated with rotation

• Brakes, absorb kinetic energy of the

moving bodies and covert it to heat

• Clutches Transmit power between

two shafts

Page 4: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Types of Brakes

• Band

• Rim/Drum

– Internal shoe

– External shoe

• Disk

• Cone

• Many others

Page 5: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Braking

• Forces applied

• Torque regenerated to ‘brake’

• Energy is lost :HEAT

• Temperature rise of brake materials

Page 6: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Energy Considerations

• 𝑇𝑜𝑟𝑞𝑢𝑒 = 𝑇 = 𝜃 𝐼𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 = Fr

• ∆𝐾. 𝐸.=Work

• ∆𝐾. 𝐸.= 1

2𝑚 𝑣𝑓

2 − 𝑣𝑖2 + 𝐼 𝜔𝑓

2−𝜔𝑖2

𝑊𝑜𝑟𝑘 = 𝑇𝑑𝜃

• Work=MC(ΔT)-Heat loss

Page 7: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Brake Friction Materials

• Sintered metal

– Cu +Fe+ Friction modifiers

• Cermet: sintered metal + ceramic content

• Asbestos

– (not used any more in general applications)

Page 8: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Characteristics:

• High friction f=0.3 to 0.5

• Repeatable friction

• Invariant to environment conditions

• Withstand high temps

– 1500F cermet

– 1000f sintered metal

– 600-1000 asbestos

• Some Flexibility

Page 9: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Model of Clutch/Brake

Remove relative rotation

Page 10: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Clutches: Couple two shafts

together

Page 11: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

An Internal Expanding

Centrifugal-acting Rim Clutch

Fig. 16–3

Page 12: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Clutch: How much force we need to

stop the relative rotation

Page 13: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Basic Band Brake: How much force

is needed to stop the Drum rotation

Page 14: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Alternate Band/Drum Brake

Page 15: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Cantilever Drum Shoe Brake

Page 16: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

External Cantilever Drum Brake

Page 17: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Common Internal Drum Brake

Page 18: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Internal Friction Shoe Geometry

Fig. 16–4

Page 19: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Internal Friction Shoe Geometry

Fig. 16–5

p is function of θ.

Largest pressure on the shoe is pa

Page 20: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Pressure Distribution Characteristics

• Pressure distribution is

sinusoidal

• For short shoe, as in (a),

the largest pressure on the

shoe is pa at the end of the

shoe

• For long shoe, as in (b),

the largest pressure is pa

at qa = 90º

Fig. 16–6

Page 21: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Force Analysis

Fig. 16–7

Page 22: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Force Analysis

Shigley’s Mechanical Engineering

Design

Self-locking condition

MN is the Normal Moment (opens brake),

Mf is Frictional Moment ( assists closing brake)

F is actuating force

Page 23: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Force Analysis

Shigley’s Mechanical Engineering

Design

Page 24: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Force Analysis

Page 25: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Basic Band Brake: How much force

is needed to stop the Drum rotation

Page 26: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Notation for Band-Type Clutches and Brakes

Shigley’s Mechanical Engineering

Design Fig. 16–

13

Page 27: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Force Analysis for Brake Band

Shigley’s Mechanical Engineering

Design

Page 28: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Force Analysis for Brake Band

Page 29: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Common Disk Brakes

Page 30: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Geometry of Disk Friction Member

Shigley’s Mechanical Engineering

Design Fig. 16–

16

Page 31: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Uniform Wear

Shigley’s Mechanical Engineering

Design

For uniform wear, w is constant, so PV is constant.

Setting p = P, and V = rw, the maximum pressure pa

occurs where r is minimum, r = d/2,

Page 32: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Uniform Wear

Shigley’s Mechanical Engineering

Design

Find the total normal force by letting r vary from d/2

to D/2, and integrating,

Page 33: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Uniform Pressure

Shigley’s Mechanical Engineering

Design

Page 34: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Comparison of Uniform Wear with Uniform

Pressure

Shigley’s Mechanical Engineering

Design

Page 35: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Automotive Disk Brake

Shigley’s Mechanical Engineering

Design

Page 36: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Geometry of Contact Area of Annular-Pad Brake

Fig. 16–19

Page 37: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Analysis of Annular-Pad Brake

Shigley’s Mechanical Engineering

Design

Page 38: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Uniform Wear

Shigley’s Mechanical Engineering

Design

Page 39: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Uniform Pressure

Shigley’s Mechanical Engineering

Design

Page 40: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Example 16–3

Shigley’s Mechanical Engineering

Design

Page 41: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Example 16–3

Shigley’s Mechanical Engineering

Design

Page 42: Belts, Clutches and Brakes - Mercer Universityfaculty.mercer.edu/jenkins_he/documents/ClutchesandBrakesIntro.pdfNotation for Band-Type Clutches and Brakes Shigley’s Mechanical Engineering

Example 16–3

Shigley’s Mechanical Engineering

Design