MECHANICAL ENGINEEERING PROGRAM SCHOOL …portal.unimap.edu.my/portal/page/portal30/Lecture Notes...DESIGN SEM1-2015/2016 3 a) Dynamic representation of a clutch or brake. b) Mathematical

DR. HAFTIRMAN

School of Mechatronic

UniMAP

ENT345 MECHANICALCOMPONENTS

DESIGN SEM1-2015/2016

1

LECTURE NOTES

ENT345

CLUTCH AND BRAKES

Lecture 13

11/12/2015

Dr. HAFTIRMAN

MECHANICAL ENGINEEERING PROGRAM

SCHOOL OF MECHATRONIC ENGINEERING

UniMAP

COPYRIGHT©RESERVED 2015

Clutch and Brakes

CO3:

ABILITY TO EVALUATE

MECHANICAL COMPONENTS FOR

SELECTED MECHANICAL SYSTEMS

DR. HAFTIRMAN

School of Mechatronic UniMAP



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INTRODUCTION

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a) Dynamic representation of a clutch or brake.

b) Mathematical representation of a flywheel

Two inertias, I1 and I2

traveling at the respective

angular velocities ω1 and ω1,

one of which may be zero

in the case of brakes, are

to be brought to the same

speed by engaging the clutch

or brake.

Slippage occurs because the

two elements are running at

different speeds and energy

is dissipated during actuation,

resulting in a temperature rise.

Model of Clutch

Shigley’s Mechanical Engineering Design

Fig. 16–1

INTRODUCTION

In analyzing the performance of these devices we

shall be interested in:

1. The actuating force

2. The torque transmitted

3. The energy loss

4. The temperature rise

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INTRODUCTION

The torque transmitted is related to the actuating force, the

coefficient of friction, and the geometry of the clutch or

brake.

The various types of devices may classified:

1. Rim types with internal expanding shoes.

2. Rim types with external contracting shoes.

3. Band types

4. Disk or axial types

5. Cone types

6. Miscellaneous types

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Friction Analysis of a Doorstop

Shigley’s Mechanical Engineering Design Fig. 16–2



Fig. 16–2





Example 16–1


Example 16–1


Example 16–1


Example 16–1


Example 16–1


Example 16–1


Example 16–1


Example 16–1


Example 16–1


CLUTCH

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BRAKE

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PAD OF BRAKE

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BRAKE

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BRAKE

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CLUCTH

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CLUCTH

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Internal expanding rim clutches

and brakes

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Internal friction shoe geometry and

the geometry associated with an

arbitrary on the shoe

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Defining the angle θa at which

the maximum pressure pa occurs

when

a) shoe exists in zone θ1≤θ2≤π/2

b) shoe exists in zone θ1≤π/2≤θ2

sinsin a

app

p maximum when θ = 90°, or the

toe angle θ2 <90°, the p will be

a maximum at the toe.

When θ = 0°, the pressure is zero.

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Forces on the shoe

Figure shows the hinge-

pin reactions are Rx and Ry.

The actuating force F has

components Fx and Fy, and

operates at distance c from

the hinge pin. At any angle

θ from the hinge pin there

acts a differential normal

force dN whose magnitude is

pbrddN where b is the face width

(perpendicular to the paper)

of the friction material,

substituting the value of the

pressure from above equation.

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The normal force is

a

a dbrpdN

sin

sin

dN= the normal force has horizontal

and vertical components dN cos θ and

dN sin θ.

f dN = the frictional force has

horizontal and vertical components

whose magnitudes are f dN sin θ

and f dN cos θ.

By apllying the conditions of static

equilibrium, we may find the actuating

force F, the torque T, and the pin

reactions Rx and Ry.

For F=> the summations of the moments

about the hinge pin is zero.

The frictional forces have a moment

arm about the pin of r –a cos θ.

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2

1

)cos(sinsin

)cos(

darbrfp

arfdNMa

af

2

1

2sinsin

)sin(

dbrap

adNMa

aN

c

MMF

fN

The moment of these frictional forces (Mf ) is

The moment of the normal forces (MN) is

The actuating force F must balance these moments.

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a

a

a

a

brfpT

dbrfp

frdNT

sin

)cos(cos

sinsin

21

2

2

1

2

The torque T applied to the drum by brake shoe

is the sum of the frictional forces f dN times

the radius of the drum.

A condition for zero actuating force exist

if MN=Mf.

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xx FfdNdNR sincos

2

1

2

1

)sincossinsin

2

x

a

ax Fdfd

brpR

The hinge-pin reactions are found by taking a summation

of the horizontal and vertical forces.

The horizontal reaction is

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yy FfdNdNR cossin

2

1

2

1

)cossinsinsin

2

y

a

ay Fdfd

brpR

c

MMF

fN

The vertical reaction is

The directional of the frictional forces is reversed if the

rotation is reversed. Thus, for CC rotation the actuating

force is

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2

1

2

1

)sincossinsin

2

x

a

ax Fdfd

brpR

2

1

2

1

)cossinsinsin

2

y

a

ay Fdfd

brpR

For CCW rotation the signs of the frictional terms

in the equations for the pin reactions change

become;

Equations can be simplified to ease computations,

2

1

2

1

2sin2

1cossin

dA

2

1

2

1

2sin4

1

2sin 2

dB

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x

a

ax FfBA

brpR )(

sin

y

a

ay FfAB

brpR )(

sin

x

a

ax FfBA

brpR )(

sin

y

a

ay FfAB

brpR )(

sin

For CCW rotation, the hinge-pin reactions are

For CW rotation,

An Internal Expanding Centrifugal-acting Rim Clutch


Internal Friction Shoe Geometry


Fig. 16–4

Internal Friction Shoe Geometry


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 a = 90º


Fig. 16–6

Force Analysis


Force Analysis


Self-locking condition

Force Analysis


Force Analysis


Example 16–2

Fig. 16–8

Example 16–2


Example 16–2


Example 16–2


Example 16–2


Example 16–2


Example 16–2


Example 16–2


An External Contracting Clutch-Brake


Notation of External Contracting Shoes


Force Analysis for External Contracting Shoes


Force Analysis for External Contracting Shoes


For counterclockwise rotation:

Brake with Symmetrical Pivoted Shoe


Wear and Pressure with Symmetrical Pivoted Shoe


Fig. 16–12b

Force Analysis with Symmetrical Pivoted Shoe


Force Analysis with Symmetrical Pivoted Shoe


Notation for Band-Type Clutches and Brakes


Force Analysis for Brake Band


Force Analysis for Brake Band


Frictional-Contact Axial Single-Plate Clutch


Frictional-Contact Axial Multi-Plate Clutch


Geometry of Disk Friction Member


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,

Uniform Wear


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

D/2, and integrating,

Uniform Pressure


Comparison of Uniform Wear with Uniform Pressure


Automotive Disk Brake


Fig. 16–18

Geometry of Contact Area of Annular-Pad Brake


Analysis of Annular-Pad Brake


Uniform Wear


Uniform Pressure


Example 16–3


Example 16–3


Example 16–3


Geometry of Circular Pad Caliper Brake


Analysis of Circular Pad Caliper Brake


Example 16–4


Example 16–4


Cone Clutch


Contact Area of Cone Clutch


Uniform Wear


Uniform Pressure


Energy Considerations


Energy Considerations


Temperature Rise


Newton’s Cooling Model


Effect of Braking on Temperature


Rate of Heat Transfer


Heat-Transfer Coefficient in Still Air

Shigley’s Mechanical Engineering Design Fig. 16–24a

Ventilation Factors

Shigley’s Mechanical Engineering Design Fig. 16–24b

Energy Analysis


Example 16–5


Example 16–5


Example 16–5


Area of Friction Material for Average Braking Power


Characteristics of Friction Materials


Table 16–3

Some Properties of Brake Linings

Shigley’s Mechanical Engineering Design Table 16–4

Friction Materials for Clutches


Positive-Contact Clutches

Characteristics of positive-

contact clutches

◦ No slip

◦ No heat generated

◦ Cannot be engaged at high

speeds

◦ Sometimes cannot be

engaged when both shafts are

at rest

◦ Engagement is accompanied

by shock


Square-jaw Clutch

Fig. 16–25a

Overload Release Clutch


Fig. 16–25b

Shaft Couplings


Fig. 16–26

Flywheels


Hypothetical Flywheel Case


Fig. 16–27

Kinetic Energy


Engine Torque for One Cylinder Cycle


Coefficient of Speed Fluctuation, Cs


Energy Change


Example 16–6


Example 16–6


Table 16–6

Example 16–6


Punch-Press Torque Demand


Fig. 16–29

Punch-Press Analysis


Induction Motor Characteristics




Deceleration:

Acceleration:



DR. HAFTIRMAN




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THANK YOU

Documents

MECHANICAL ENGINEEERING PROGRAM SCHOOL …portal.unimap.edu.my/portal/page/portal30/Lecture Notes...DESIGN SEM1-2015/2016 3 a) Dynamic representation of a clutch or brake. b) Mathematical