Clutches and Brakes and

• is a device that connects and disconnects two collinear shafts. – Similar to – and hence heat dissipation • Purpose of a 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 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 Types of Brakes

• Band • /Drum – Internal shoe – External shoe • Disk • Cone • Many others Braking

• Forces applied • Torque regenerated to ‘brake’ • Energy is lost :HEAT • Temperature rise of brake materials Energy Considerations

• 푇표푟푞푢푒 = 푇 = 휃 퐼푒푓푓푒푐푡푖푣푒 = Fr • ∆퐾. 퐸. =Work 1 2 2 2 2 • ∆퐾. 퐸. = 2 푚 푣푓 − 푣푖 + 퐼 휔푓 −휔푖

푊표푟푘 = 푇푑휃

• Work=MC(ΔT)-Heat loss

Brake Friction Materials

• Sintered metal – Cu +Fe+ Friction modifiers • Cermet: sintered metal + content • Asbestos – (not used any more in general applications)

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 Model of Clutch/Brake Remove relative rotation Clutches: Couple two shafts together

An Internal Expanding Centrifugal-acting Rim Clutch

Fig. 16–3 Clutch: How much force we need to stop the relative rotation Basic Band Brake: How much force is needed to stop the Drum rotation Alternate Band/ Cantilever Drum Shoe Brake External Cantilever Drum Brake Common Internal Drum Brake Internal Friction Shoe Geometry

•

Fig. 16–4 Internal Friction Shoe Geometry

p is function of θ.

Largest pressure on the shoe is pa

Fig. 16–5 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 Force Analysis

Fig. 16–7 Force Analysis

F is actuating force

MN is the Normal Moment (opens brake), Mf is Frictional Moment ( assists closing brake) Self-locking condition

Shigley’s Mechanical Engineering Design Force Analysis

Shigley’s Mechanical Engineering Design Force Analysis Basic Band Brake: How much force is needed to stop the Drum rotation Notation for Band-Type Clutches and Brakes

Shigley’s Mechanical Engineering Fig.Design 16– 13 Force Analysis for Brake Band

Shigley’s Mechanical Engineering Design Force Analysis for Brake Band Common Disk Brakes Geometry of Disk Friction Member

Shigley’s Mechanical Engineering Fig.Design 16– 16 Uniform Wear

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,

Shigley’s Mechanical Engineering Design Uniform Wear

Find the total normal force by letting r vary from d/2 to D/2, and integrating,

Shigley’s Mechanical Engineering Design Uniform Pressure

Shigley’s Mechanical Engineering Design Comparison of Uniform Wear with Uniform Pressure

Shigley’s Mechanical Engineering Design Automotive Disk Brake

Shigley’s Mechanical Engineering Design Geometry of Contact Area of Annular-Pad Brake

Fig. 16–19 Analysis of Annular-Pad Brake

Shigley’s Mechanical Engineering Design Uniform Wear

Shigley’s Mechanical Engineering Design Uniform Pressure

Shigley’s Mechanical Engineering Design Example 16–3

Shigley’s Mechanical Engineering Design Example 16–3

Shigley’s Mechanical Engineering Design Example 16–3

Shigley’s Mechanical Engineering Design