HND Mechanical Engineering Research: Centrifugal and Compliant Clutch

This research project investigates centrifugal clutches, focusing on their design, torque transmission capabilities at varying speeds, and the introduction of a compliant clutch alternative. The project begins with an overview of centrifugal clutches, detailing their components and functionality, followed by a discussion of compliant clutches made from polypropylene, which offer advantages in terms of cost and reduced backlash. The research includes analytical design calculations for conventional clutches and explores the design formulation of compliant clutches using graphical methods. A literature review covers clutch functions, types, and requirements for good friction clutches. The project aims to provide a comprehensive understanding of centrifugal clutch design and performance, with a comparative analysis of conventional and compliant clutch technologies. Desklib provides students access to this solved assignment and other resources for further study.

Research Project
Centrifugal clutches
Project Proposal:
A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with
the driving shaft nested inside the driven shaft.
The input of the clutch is connected to the engine crankshaft while the output may drive a shaft,
chain, or belt. As engine revolutions per minute increase, weighted arms in the clutch swing
outward and force the clutch to engage. The most common types have friction pads or shoes
radially mounted that engage the inside of the rim of a housing. On the center shaft there are an
assorted number of extension springs, which connect to a clutch shoe. When the center shaft
spins fast enough, the springs extend causing the clutch shoes to engage the friction face. It can
be compared to a drum brake in reverse. This type can be found on most home built karts, lawn
and garden equipment, fuel-powered model cars and low power chainsaws. Another type used in
racing karts has friction and clutch disks stacked together like a motorcycle clutch. The weighted
arms force these disks together and engage the clutch.
When the engine reaches a certain speed, the clutch activates, working somewhat like a
continuously variable transmission. As the load increases, the speed drops, disengaging the
clutch, letting the speed rise again and reengaging the clutch. If tuned properly, the clutch will
tend to keep the speed at or near the torque peak of the engine. This results in a fair bit of waste
heat, but over a broad range of speeds it is much more useful than a direct drive in many
applications.
The centrifugal clutch offers many advantages in motor and engine drive applications. Utilizing
the centrifugal clutch enables the selection of normal torque motors for running loads rather than
the selection of high torque motors for starting loads. The aim of this project is to be describing
the torque carrying capacity at different speed which using in transmitting power. The entire
work based on conventional design with Frodo lining, driving shaft, spring , shoe , spider, cover
plate, driven shaft. The detail design for various speed is made in the centrifugal clutch to select
an operating range of speed under which the application are designed for torque transmission. In
this project the design calculation are worked out analytically. Along with this we have
introduced a compliant clutch.
Compliant clutch is made from polypropylene material and there is no anyone connecting parts.
it has rigid body design since revolute joints are replaced by flexible segment. The potential
energy store in flexible segment can replace springs and reduction in revolute joints reduces
problem with backlash and wear. The compliant clutch includes rigid body mechanism through
dimensional synthesis by graphical method. A mechanism is evaluated and synthesized specific
force-deflection relationship. In many applications, compliant mechanism can maintain or even
improve performance relative to conventional rigid body designs. It is cost benefitted. Also
conventional clutch is expensive rather than compliant clutch.

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an engine controller for a vehicle equipped with an automatic
centrifugal clutch, such as a snowmobile, ATV (all-terrain vehicle), motorcycle, etc., including
an idle speed control (abbreviated hereinbelow as ISC) device disposed in the engine intake
system for adjusting the amount of intake air by a throttle valve.
Description of the Prior Art
Concerning engine intake systems for regulating the amount of intake air based on control of the
opening degree at the throttle valve of an engine mounted on vehicles, such as snowmobiles,
having an automatic centrifugal clutch, there are those that adopt ISC devices for controlling the
idle speed by adjusting the amount of bypass air.
In a vehicle including such an ISC device, an ECM (electronic control module) is provided for
the ISC device, so as to control the amount of intake air at the time of the throttle valve being
fully closed, for each of the following modes (as to the prior art relating to the ISC device, refer
to Japanese Utility Model Application Laid-open Sho 64 No. 34441 (FIG. 1 and the full text of
the specification)).
In ISC, in startup mode, control at a start of the engine is performed by adjusting the amount of
bypass air to the controlled amount for start in accordance with the cooling water temperature
plus corrections for altitude and other factors.
In the complete explosion mode other than the startup mode, the basic control amount is
corrected in accordance with the cooling water temperature and at the same time the idle speed is
controlled by regulating the amount of bypass air.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above conventional problems, it is
therefore an object of the present invention to provide an engine controller of an engine unit with
an idle speed control (ISC) device for use in a vehicle including an automatic centrifugal clutch,
the controller capable of preventing unintentional increase in engine speed even if the ISC device
breaks down and capable of preventing excessive effect of engine brake resulting from fuel
cutoff or ignition cutoff hence preventing degradation of driver's sensation during traveling.
In order to achieve the above object, the present invention is configured as follows:
In accordance with the present invention, an engine controller for a vehicle using an automatic
centrifugal clutch device for power transmission, is characterized in that an idle speed control
means is provided for an engine intake system that adjusts the amount of intake air by
implementing control of the opening degree of a throttle valve, and the engine controller
comprises: a full-close state detecting means for detecting the full-close state of the throttle
valve;
an engine speed detecting means for detecting the engine speed; and an engine halt controlling
means for implementing engine halt control based on the halt control starting conditions that the
detected engine speed is equal to or greater than a first set rotational frequency, which is set to be

equal to or lower than the clutch engagement rotational frequency of the automatic centrifugal
clutch device, and that the full-closed state of the throttle valve is detected.
INTRODUCTION:
A CENTRIFUGAL CLUTCH:
A clutch is a machine member used to connect the driving shaft to a driven shaft, so that the
driven shaft may be started or stopped at will, without stopping the driving shaft. A clutch
provides an interruptible connection between two shafts. The centrifugal clutch is usually used
into motor pulley. It consists of number of shoe on the inside of a rim of pulley. The outer
surface of pulley is covered with friction material. These shoes which can move radially in
guides are held against the boss on the driving shaft by means of springs.The spring exert a
radialy inward force which assumed to be constant.
The weight shoes when revolving cause it to exert a radialy outward force (centrifugal force).The
magnitude of centrifugal force depeded on speed at which shoes is revolving. A little
consideration show that when centrifugal force is less than the spring force, the shoes remain
same position as when driving shaft was stationary, but when centrifugal force is equal to spring
force, spring is floating.
Figure: 1 Centrifugal clutch
When centrifugal force exceed the spring force, the shoe moves outward and comes in contact
with driven member and press against it. The force with which the shoe press against the driven
member is the difference of the centrifugal and spring force. The increase of speed causes the
shoe to press harder and enables to be transmitted.
COMPLIANT CLUTCH:
Compliant mechanisms are mechanisms that obtain some or all of their motion through the
deflection of their members. In a compliant mechanism, a single flexible link often replaces two
or more rigid links of an equivalent rigid-body mechanism. This decreases the mechanism’s part
count, wear points, and backlash. In the mechanism the centrifugal force is utilised to deflect the
members and get friction on rotating drum to synchronise motion.

Fig 2: LITERATURE SURVEY
FUNCTION OF CLUTCHES:
 A clutch is a mechanical device used to connect or disconnect the driven shaft from the
driving shaft.
 A clutch is a device used to transmit the rotary motion of one shaft to another shaft when
desired.
TYPES OF CLUTCHES:
There are two types of clutch
1. positive clutch 2. friction clutch
Positive clutch:
Simplest type of positive clutch is jaw clutch, which transmit the torque from one shaft to
another shaft through interlocking jaws. jaw clutch consists of two segments as shown in fig. one
segment is permanently fasted to the driving shaft and the other segment is free to slide axially
on the splined driven shaft, thus permitting is to been engaged or disengaged by sliding. The
shapes of jaw may be square, gear toothed or spiral.
The weight shoes when revolving cause it to exert a radialy outward force (centrifugal force).The
magnitude of centrifugal force depeded on speed at which shoes is revolving. A little
consideration show that when centrifugal force is less than the spring force, the shoes remain
same position as when driving shaft was stationary, but when centrifugal force is equal to spring
force, spring is floating.
Merits of positive clutches:
1. Positive clutch do not slip.
2. No heat is generated during the engagement.
Application of positive clutches:
The positive clutches have very limited applications. They are used in some machine

tools, power presses, punches, etc.
Friction clutch:
Friction clutch transmits torque by virtue of frictional developed. Friction lining is provided on
the driven plate .axial force applied by compression spring will hold the two plates together.
Merits of friction clutch:
1. Friction on clutches can be engaged when driving shaft is rotating and driven shaft is
stationary or when both shafts are stationary.
2. Frequent engagement and disengagement is possible .
3. Friction clutches are capable of transmitting a partial power.
4. In case of overloads, the friction clutches slip momentarily, thus safeguarding the machine.
5. Friction clutches are easy to operate.
Application of friction clutches:
1. A friction clutch has its application in a transmission system where frequent engagement
and disengagement is required and where power is to be transmitted partially or fully.
2. The common application of friction clutches is in automobiles.
Requirement of good friction clutches:
A good friction clutch should satisfy the following requirement:
1. It should be capable of transmitting the required torque with the minimum amount of the
axial force.
2. The energy converted into the frictional heat during the engagement should be dissipated
rapidly, so that the temperature rise is kept within the permissible limit.
3. The pressure between the contacting surfaces should be reasonably low and uniform over the
entire surface.
4. The coefficient of friction between the contacting surfaces should be sufficiently high and
reasonably uniform over the entire surface.
5. The wear characteristics of the contacting surface should be such that they give the acceptable
life.
6. The engagement and disengagement mechanism should be simple and easy to operate.
7. The clutch should be as light as possible to minimize the inertia load.
8. The clutch should be easy to dissemble and should have the provision for the wear
compensation.
9. The clutch should have no open projecting part.

DESIGN FORMULATION
A DESIGN FORMULATION OF CONVENTIONAL CENTRIFUGAL CLUTCH:
TRANSMITTED TORQUE
T = P x 60 / 2N
Where, T = Transmitted Torque, N.mm
P = Intensity of Pressure, N/mm²
N = Running speed of Pulley, rpm
Fig3: Showing The Design
Centrifugal force acting on each shoe
Pc= m. w2.r
Where, Pc =Centrifugal force acting on each shoe ,N
m =Mass on each shoe, Kg
w = Angular running speed, rad/sec
r = Distance of center of the shoe from the center of the spider, mm
Force exerted on each shoe by the spring
Ps = m. (w1)2.r
= m(3/4w)2
=9/16mw2.r
Where, Ps = Force exerted on each shoe by the spring, N
w1 = Angular speed at which the engagement begins to take place, rad/sec
Net outward radial force = Pc-Ps
= mw2r- 9/16mw2r
=7/16mw2r
Frictional force acting on each shoe
F= μ (Pc- Ps)
Where, F=Frictional force, N
μ = Co-efficient of Friction between shoe and rim

Pc =Centrifugal force acting on each shoe , N
Ps = Force exerted on each shoe by the spring, N
Frictional torque acting on each shoe
= F x R
= μ(Pc- Ps) R
Where, R=Inside radius of pulley rim, m
μ= Co-efficient of Friction between shoe and rim
Pc =Centrifugal force acting on each shoe, N
Ps = Force exerted on each shoe by the spring, N
Total Frictional torque transmitted
T= μ(Pc- Ps)R x n
= n.F.R
Where, R =Inside radius of pulley rim, mm
μ = Co-efficient of Friction between shoe and rim
Pc =Centrifugal force acting on each shoe , N
ps = Force exerted on each shoe by the spring, N
T = Transmitted torque, N/mm
n = number of shoes
F =Frictional force, N
3. SIZE OF SHOE
Θ = l/r or l= θ.r (θ = 60)
Where l = Contact length of shoe , mm
b = Width of shoe, mm
R = Contact radius of shoe , mm
Θ = Angle subtended by shoe , rad
p = Intensity of pressure on shoe, N/𝑚𝑚2
Area contact of shoe
A = l b
Where A = Area of contact of shoe, 𝑚𝑚2
Force with which the shoe process against the rim
A . p = l .b .p
Where , A = Area contact of shoe , 𝑚𝑚2
p = Pressure intensity of pressure ,N/𝑚𝑚2
l = Contact length of shoe , mm
b = Width of shoes , mm
Force with which shoe pres against the rim at running speed
l .b .p = Pc – Ps
Where , A = Area contact of shoe , 𝑚𝑚2
p = Pressure intensity of pressure ,N/𝑚𝑚2
l = Contact length of shoe , mm
b = Width of shoes , mm
Pc = Centrifugal force acitng on each shoe N
Ps = Force extered on each shoe by spring N

DESIGN FORMULATION OF COMPLIANT CENTRIFUGAL CLUTCH:
A design of compliant clutch is based on empirical formulas. Here centrifugal and normal force
is derived graphically from force diagram. A force which is acting on a shoe has force
components in different direction at the point of contact. Here tangential and normal forces are
considered in the design.
The weight shoes when revolving cause it to exert a radialy outward force (centrifugal force).The
magnitude of centrifugal force depeded on speed at which shoes is revolving. A little
consideration show that when centrifugal force is less than the spring force, the shoes remain
same position as when driving shaft was stationary, but when centrifugal force is equal to spring
force, spring is floating.
FRICTION CLUTCHES:
A friction clutch has its principle applications in the transmission of power of shaft and machines
which must be started and stopped frequently. It’s application is also found in case in which a
power is to be delivered to machines partially or fully loaded. The force of friction is used to
start the driven shaft from restand gradually bring it up to the proper speed without excessive
slipping of the friction surfaces. In automobiles, friction clutch is used to connect the engine to
the driven shaft. In operating such a clutch, care should be taken so that friction surfaces engages
easily and gradually brings the driven shaft up to proper speed. The proper alignment of the
bearing must be maintained and it should be located as close to the clutch as possible.
The weight shoes when revolving cause it to exert a radialy outward force (centrifugal force).The
magnitude of centrifugal force depeded on speed at which shoes is revolving. A little
consideration show that when centrifugal force is less than the spring force, the shoes remain
same position as when driving shaft was stationary, but when centrifugal force is equal to spring
force, spring is floating.
1. The contact surfaces should develop a frictional force that may pick up and hold the load with
reasonably low pressure between the contact surfaces.
2. The heat of the friction should be rapidly dissipated and tendenvy to grab should be at a
minimum.
3. The surfaces should be packed by material stiff enough to ensure a raesonably uniform
distribution of pressure.
The friction clutches are of following types:
1. Disc or plate clutches
2. Cone clutches

SINGLE PLATE CLUTCH:
A disc clutch consist of a cluct plate attached to a splined hub which is free to slide axially on
splines cut on the driven shaft. The clutch plate is made of steel and has a ring of friction lining
on each side. The engine shaft supports a rigidly fixed flywheel.
The weight shoes when revolving cause it to exert a radialy outward force (centrifugal force).The
magnitude of centrifugal force depeded on speed at which shoes is revolving. A little
consideration show that when centrifugal force is less than the spring force, the shoes remain
same position as when driving shaft was stationary, but when centrifugal force is equal to spring
force, spring is floating.
A spring loaded pressure plate presses the clutch plate firmly against the flywheel when the
clutch is engaged. When disengaged, the spring press against a cover attached to the flywheel.
Thus, both the flywheel and pressure plate rotate with the input shaft. The movement of the
clutch pedal is transferred to the pressure plate through a thrust bearing.
Fig shows the pressure plate pulled back by the release levers and the friction linings on the
clutch plate are no longer in contact with the pressure plate or the flywheel. The flywheel rotates
without driving the clutch plate and thus, the driven shaft.
When the foot is taken off the clutch pedal, the pressure on the thrust bearing is released. As a
result of the spring become free to move the pressure plate to bring it in contact with the clutch
plate. The clutch plate slides on splined hub and is tightly gripped bet the pressure plate and
flywheel. The friction bet the linings on the clutch plate and flywheel on one side and the
pressure plate on the other.
Requirement of good friction clutches:
A good friction clutch should satisfy the following requirement:
1. It should be capable of transmitting the required torque with the minimum amount of the
axial force.
2. The energy converted into the frictional heat during the engagement should be dissipated
rapidly, so that the temperature rise is kept within the permissible limit.
3. The pressure between the contacting surfaces should be reasonably low and uniform over the
entire surface.
4. The coefficient of friction between the contacting surfaces should be sufficiently high and
reasonably uniform over the entire surface.
5. The wear characteristics of the contacting surface should be such that they give the acceptable
life.
6. The engagement and disengagement mechanism should be simple and easy to operate.
7. The clutch should be as light as possible to minimize the inertia load.
8. The clutch should be easy to dissemble and should have the provision for the wear
compensation.
9. The clutch should have no open projecting part.

CONCLUSION:
Here we have calculated torque by Conventional analytical method for clutch used in different
applications like Lawn mower, Chain saw, String Trimmer, TVS Moped. Then we introduced
compliant clutch in place of conventional one. It is design graphically and compared their
capabilities with respect to torque transmitting capacity.
The shaft diameter and drum diameter are considered same for both the methods for comparison
of clutch used in different applications. Further the power and rotational speed of shaft are taken
as specified in standard applications.
From this comparison we conclude that compliant clutch is more efficient if we used in chain
saw and in other applications, it gives nearly same value of torque than conventional clutch. The
main advantage of compliant clutch is cost benefitted and having no movable component in its
design. The problem of backlash and wear is eliminated by using this type of clutch.
The weight shoes when revolving cause it to exert a radialy outward force (centrifugal force).The
magnitude of centrifugal force depeded on speed at which shoes is revolving. A little
consideration show that when centrifugal force is less than the spring force, the shoes remain
same position as when driving shaft was stationary, but when centrifugal force is equal to spring
force, spring is floating.
References:
[1] R.S.Khurmi, J.K.Gupta, “Machine Design Book”, fourteenth edition, S.Chand & company
ltd, New Delhi.
[2] B.L.Singhal, F.B.Sayyad, “Machine Design Book”(GTU),second edition,Tech-max
publication,Pune.
[3] Cook, B., and Parker, B., “Tensile Test Analysis of Polypropylene at different Sizes and Pull
Speeds”, Unpublished class project for
Mechanical Engineering 352, December1996
[4] P.S.G.Design Data Book, second editon, Koimbtoor.
[5] Richard G. Budynas, J. Keith Nisbett, “Mechanical engg. Design”,ninth edition, Mcgraw hill
publication, New Delhi.
[6] Achi, P. B. U, “Design and Testing of an Automatic Clutch”, Sadhana, Vol. 9, No.3, pp 23-
238.
[7] Ananthasuresh, G.K., and Kota, “Designing Compliant Mechanisms”, Mechanical
Engineering, Vol. 117, No.11, pp. 93-96.