27-10-2016, 03:00 PM
1461748111-ElectroMagneticClutch.pdf (Size: 2.65 MB / Downloads: 50)
ABSTACT
• A clutch is a device used to make and brake contact from the transmission. When it
engages, then power is transferred from engine to gear box and when it disengage,
power flow is stop, hence it is called free running of engine. There is an innovation
done in automobile industry, called electro magnetic clutch, which is recently used
by Renault Car Company, which uses the basic principle of electrical energy as well
as magnetic forces.
This project revels the manufacturing of electro magnetic clutch. In place of Engine,
shaft is directly attached to variance (variable motor) and clutch disc as well as
pressure plate is used, in between them friction material called “Asbestos” used to
grip between the pressure plate and clutch plate. This project shows, experimental
analysis of Electro magnetic clutch, and at last at which speed clutch engage as well
as disengage is measured and when clutch disengage, at that time speed of flywheel
is also measured.
INTRODUCTION
Definition of clutch:
The clutch is an important part in the transmission system of automobiles. It
transmits power from the engine to gear box at various speeds. No shock is caused
during this transmission of power.
Purpose:
The function of the clutch is to temporarily disconnect the engine from the gear box
unit. When the gear has to be changed from the first to the second ,it should be
done after disconnecting the engine from the gear box. If this is not done ,the gear
teeth might break. The clutch is thus helpful when starting, shifting gears and idling.
Principle of operation:
The clutch works on the principles of friction. When two friction surfaces are brought
in contact with each other and pressed they are united due to the friction between
them. If now one is resolved, the other will also revolve. The friction between the
two surfaces depends upon the area of the surfaces, pressure applied upon them
and co-efficient of friction of the surface materials. The two surfaces can be
separated and brought into contact when required. The driving member is kept
rotating. When the driven member is brought in contact with the driving member, it
also starts rotating. When the driven member is separated from the driving member
it does not revolve. This is the principle on which a clutch operates.
Requirement of a clutch:
1. Torque transmission: - The clutch should be able to transmit maximum torque of
the engine.
2. Gradual engagement:- The clutch should engage gradually to avoid sudden jerks.
3. Heat dissipation: - The clutch should be able to dissipate large amount of heat
which is generated during the clutch operation due to friction.
4. Dynamic balancing:- The clutch should be dynamically balanced. This is
particularly required in the case of high speed engine clutches.
5. Vibrating damping: - The clutch should have suitable mechanism to damp
vibrations and to eliminate noise produced during the power transmission.
6. Size:- The clutch should be as small as possible in size so that it will occupy
minimum space.
7. Free pedal play: - The clutch should have free pedal play in order to reduce
effective clamping load on the carbon thrust bearing and wear on it.
8. Easy in operation: - The clutch should be easy to operate requiring as little
exertion as possible on the part of the driver.
9. Lightness:- The driven member of the clutch should be made as light as possible
so that it will not continue to rotate for any length of time after the clutch has
been disengaged.
Types of friction material:-
The friction materials of the clutch plate are generally of three types :
1. Mill board type.
2. Moulded type.
3. Woven type.
Mill board type friction materials mainly include asbestos sheets treated with
different type of impregnates.
Moulded type friction materials are made from a matrix of asbestos fiber and
starch or any other suitable binding materials.
Woven type facing materials are made by impregnating a cloth with certain
binders or by wearing threads of brass or copper wires covered with long fiber
asbestos and cotton.
The woven type friction materials are further classified into types-laminated
type and solid woven type.
The most common friction materials are as follows :
1. Leather…….. Co-efficient of friction 0.27.
Properties of good friction lining :-
1. Good wearing properties.
2. High co- efficient of friction.
3. High resistance to heat.
4. Good binder in it.
5. Cheap and easy to manufacture.
Types of clutches:-
Different types of clutches are as follows:
1. Friction clutch :
(a) Single plate clutch.
(b) Multiplate clutch:
(1) Wet clutch.
(2) Dry clutch.
© Cone clutch.
(1) External clutch.
(2) Internal clutch.
2. Centrifugal clutch.
3. Semi-centrifugal clutch.
4. Diaphragm clutch.
(a) Tapered finger type.
(b) Crown spring type.
5. Positive clutch.
(a) Dog and Spline clutch.
6. Hydraulic clutch.
7. Electro-magnetic clutch.
8. Vacuum clutch.
9. Over running clutch or free-wheel unit.
ELECTROMAGNETIC CLUTCH:
Figer shows an electromagnetic clutch.
In this type of clutch, the flywheel consists of winding from the battery or
dynamo.
When the current passes through the winding. it produced an electromagnetic
field which attracts the pressure plate.
Thereby engaging the clutch.
When the supply is cut-off the clutch is disengaged.
The gear lever consists of a clutch release switch.
When the driver holds the gear lever to change the gear, the switch is operated
cutting off the current to the winding which causes the clutch disengaged.
At low speed when the dynamo output is low, the clutch is not firmly engaged.
Therefore, three springs are also provided on the pressure plate which helps the
clutch engaged firmly at low speed also.
This type of clutch is used in some Renult cars.
COMPLETE DELAILS OF THE ELECTROMAGNETIC CLUTCH:-
Why we used Electromagnetic Clutch?
• Function of clutch is to engage or disengage the engine from the transmission
system. Hence it is inserted between the flywheel as well as gear box. It is consists
of main important parts like clutch plate, pressure plate, friction disc, operating
lever etc. In clutch engage as well as disengage are very important, because due to
which clutch is used. But when clutch is applied at that time, some clearance is
there in the clutch pedal called clutch pedal play and due to which, proper
disengage of clutch is not achieve and clutch will slip or dragged.
• There is a need to use some system incorporated in clutch system, to prevent above
situation. Hence, if we shift gear and at that time clutch will disengage hence, it is
very simple for driver and force require to engage as well as disengage the clutch is
also neglected, hence a new type of clutch used in automobile vehicles called
“Renault Car” called electromagnetic clutch.
• In this clutch system, when gear shift lever is applied at that time, due to MMF clutch
will disengage and when release lever, clutch will engage.
Basic operation of electromagnetic clutch:-
• The clutch has four main parts: field, rotor, armature, and hub (output) (Figure-22).
When voltage is applied the stationary magnetic field generates the lines of flux that
pass into the rotor. (The rotor is normally connected to the part that is always
moving in the machine.) The flux (magnetic attraction) pulls the armature in contact
with the rotor (the armature is connected to the component that requires the
acceleration), as the armature and the output start to accelerate. Slipping between
the rotor face and the armature face continues until the input and output speed is
the same (100% lockup). The actual time for this is quite short, between 1/200th of a
second and 1 second
Engagement Time:
• There are actually two engagement times to consider in an
electromagnetic clutch. The first one is the time it takes for a coil to
develop a magnetic field, strong enough to pull in an armature. Within
this, there are two factors to consider. The first one is the amount of
ampere turns in a coil, which will determine the strength of a magnetic
field. The second one is air gap, which is the space between the armature
and the rotor. Magnetic lines of flux diminish quickly in the air. The
further away the attractive piece is from the coil, the longer it will take
for that piece to actually develop enough magnetic force to be attracted
and pull in to overcome the air gap. For very high cycle applications,
floating armatures can be used that rest lightly against the rotor. In this
case, the air gap is zero; but, more importantly the response time is very
consistent since there is no air gap to overcome. Air gap is an important
consideration especially with a fixed armature design because as the unit wears over many cycles of engagement the armature and the rotor will
create a larger air gap which will change the engagement time of the
clutch. In high cycle applications, where registration is important, even
the difference of 10-15 milliseconds can make a difference, in registration
of a machine. Even in a normal cycle application, this is important
because a new machine that has accurate timing can eventually see a
“drift” in its accuracy as the machine gets older.
• The second factor in figuring out response time of a clutch is actually
much more important than the magnet wire or the air gap. It involves
calculating the amount of inertia that the clutch needs to accelerate. This
is referred to as “time to speed”. In reality, this is what the end-user is
most concerned with. Once it is known how much inertia is present for
the clutch to start then the torque can be calculated and the appropriate
size of clutch can be chosen.
• Most CAD systems can automatically calculate component inertia, but
the key to sizing a clutch is calculating how much inertial is reflected
back to the clutch or brake. To do this, engineers use the formula: T =
(WK2 × ΔN) / (308 × t) Where T = required torque in lb-ft, WK2 = total
inertia in lb-ft2, ΔN = change in the rotational speed in rpm, and t = time
during which the acceleration or deceleration must take place.
• There are also online sites that can help confirm how much torque is
required to accelerate a given amount of inertia over a specific time.
Remember to make sure that the torque chosen, for the clutch, should be
after the clutch has been burnished.