magnetic braking system
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MAGNETIC BRAKING SYSTEM 1
ABSTRACT
The topic of magnetic braking has dramatically increased in popularity in
recent years. Since 1987, numerous articles about magnetic braking were published.
These articles describe both experiments dealing with magnetic braking, as well as the
theory behind the phenomenon. Magnetic braking works because of induced currents
and Lenz's law. If you attach a metal plate to the end of a pendulum and let it swing,
its speed will greatly decrease when it passes between the poles of a magnet.
When the plate enters the magnetic field, an electric field is induced in metal
and circulating eddy currents are generated. These currents act to oppose the change
in flux through the plate, in accordance with Lenz's Law. The currents in turn heat the
plate, thereby reducing its kinetic energy. The practical uses for magnetic braking are
numerous and commonly found in industry today. This phenomenon can be used to
damp unwanted nutations in satellites, to eliminate vibrations in spacecrafts, and to
separate nonmagnetic metals from solid waste
Mechatronics is a hybrid technological field which evolved from the
combination of mechanical, electronics & Software engineering. Automobiles need
high degree of safety to protect the occupants and their property. Bearing this in
senses we come up with a new concept of Electric pulse Magnetic Braking
(E.P.M.Braking).
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 2
When the driver applies force on the brake pedal the magnitude is sensed by
the pressure transducer which in turn sends the actuating signals to microprocessor.
This intelligent device sends pulsating D.C. current from the capacitor to the power
pack. The power pack develops sufficient torque to decelerate or stop the vehicle as
per the driver's requirement. The torque produced is directly proportional to the force
applied on the brake pedal, as the intensity of the actuating signal from the pressure
transducer is directly proportional to the pulsating D.C. current supplied to the power
pack.
Another important aspect of this braking system is that the power pack also
acts as a generator, which results in additional power generation. We have also
incorporated artificial intelligence. Logic gates for backup-circuit for safety and shift
current for shifting the power pack from generating mode to braking mode and vice-
versa to generator power.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 3
CONTENTS
1. INTRODUCTION
2. PRINCIPLE OF OPERATION
3. CONSTRUCTION
4. WORKING
5. MAGNETIC BRAKING SYSTEM IN TRAINS
6. BRAKING POWER CALCULATIONS
7. MAGNETIC BRAKING SYSTEM REQUIREMENTS
8. MOUNTING AND INSTALLATION
9. ADVANTAGES
10. DISADVANTAGES
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 4
11. APPLICATIONS
12. CONCLUSION
13. REFERENCES
INTRODUCTION
Many of the ordinary brakes, which are being used now days stop the vehicle
by means of mechanical blocking. This causes skidding and wear and tear of the
vehicle. And if the speed of the vehicle is very high, the brake cannot provide that
much high braking force and it will cause problems. These drawbacks of ordinary
brakes can be overcome by a simple and effective mechanism of braking system ‘The
magnetic braking system’. It is an abrasion-free method for braking of vehicles
including trains. It makes use of the opposing tendency of eddy current.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 5
Eddy current is the swirling current produced in a conductor, which is subjected to a
change in magnetic field. Because of the tendency of eddy currents to oppose, eddy
currents cause energy to be lost. More accurately, eddy currents transform more
useful forms of energy such as kinetic energy into heat, which is much less useful. In
many applications, the loss of useful energy is not particularly desirable. But there are
some practical applications. Such an application is the magnetic brake.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 6
Magnetic brake in trains
PRINCIPLE OF OPERATIONS
Magnetic brake works according to Faraday’s law of electromagnetic
induction. According to this law, whenever a conductor cuts magnetic lines of forces,
an emf is induced in the conductor, the magnitude of which is proportional to the
strength of magnetic field and the speed of the conductor. If the conductor is a disc,
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 7
there will be circulatory currents i.e. eddy currents in the disc. According to Lenz’s
law, the direction of the current is in such a way as to oppose the cause, i.e. movement
of the disk.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 8
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 9
Essentially the magnetic brake consists of two parts, a stationary magnetic field
system and a solid rotating part, which include a metal disc. During braking, the metal
disc is exposed to a magnetic field from an electromagnet, generating eddy currents in
the disc. The magnetic interaction between the applied field and the eddy currents
slow down the rotating disc. Thus the wheels of the vehicle also slow down since the
wheels are directly coupled to the disc of the magnetic brake, thus producing smooth
stopping motion.
EDDY CURRENT INDUCED IN A CONDUCTOR
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 10
CONSTRUCTION
Essentially a magnetic brake consists of two members, a stationary
magnetic field system and a solid rotary member, generally of mild steel, which is
sometimes referred to as the secondary because the eddy currents are induced in it.
Two members are separated by a short air gap, they’re being no contact between the
two for the purpose of torque transmission. Consequently there is no wear as in
friction brake.
Stator consists of pole core, pole shoe, and field winding. The field
winding is wounded on the pole core. Pole core and pole shoes are made of cast steel
laminations and fixed to the state of frames by means of screw or bolts. Copper and
aluminium is used for winding material the arrangement is shown in fig. 1. This
system consists of two parts.
1. Stator
2. Rotor
Stator:-
It is supported frame members of the vehicle chassis. It has introduced
magnetic poles energized by windings. Current is supplied to the winding from the
battery.
Rotor:-
It is a rotating disc, which is fitted on the line of crankshaft with small air gap to
stator. When disc rotates a flux change occur in the section of the disc passing the
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 11
poles of stator. Due to the flux change there is a circulatory or eddy current in the
disc around the magnetic lines of force. The effect of this eddy current induces ‘N’
and ‘S’ poles at the surface of the disc. Then there will be a ‘drag’ or braking effect
in between eddy current induced poles and magnetic poles in the stator. By
changing current from the battery we can change the braking force. In this breaking
system kinetic energy of the vehicle is converted to heat and this heat is dissipated
through the rotating disc.
Total resistance of field winding
R = L/A
where, L = total length of field winding in meter.
= Resistivity of the wire in ohm meter
A = the area of cross section of field winding in m2
Total no: of terms = total length /mean length of one term
The rotor is a rotating disc on shaft, which is placed very near to the stator
with small air gap (1 mm to 2 mm). Rotating disc may be one or both side of stator.
The two units have common ring member, poles cores on which winding are
provided being fixed to ring number. If a malleable casting is employed, then the
pole core could be cast integrally with the right. After fitting the windings on the
cores, poles shoes are fitted to provide pole faces of appropriate shape and area. The
rotor disc should be provided with properly designed fins for faster heat removal.
The magnetic circuits of the two units are substantially the same, non-undue and
thrust would be imposed on the motor bearings. Slight axial displacement of rotor
could however, cause quite appreciable discrepancy, the air gap of two units. The
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 12
effect would be to increase the magnetic pull in one air gap and diminish it on other
which could give to rise to excessive and thrust on rotor bearing to overcome the
inherent defect, the air gaps of both units could be put in series by making the central
number non magnetic and providing a continues pole core for each pair axially
opposite poles. This modification could possibly reduce the length of the combined
pole course or permits a larger winding length.
The maximum diameter of the magnetic brake is decided by
1. The spacing of vehicle chassis frame
2. Vehicle floor clearance
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 13
WORKING
When the vehicle is moving, the rotor disc of magnetic brake which is coupled
to the wheels of the vehicle rotates, in close proximity to stationary magnetic poles.
When we want to brake the vehicle, a control switch is put on which is placed on the
steering column in a position for easy operation.
When the control switch is operated, current flows from a battery to the field
winding, thus energizing the magnet. Then the rotating disc will cut the magnetic
field. When the disc cuts the magnetic field, flux changes occur in the disc which is
proportional to the strength of the magnetic field. The current will flow back to the
zero field areas of the metal plate and thus create a closed current loop like a whirl or
eddy. A flow of current always means there is a magnetic field as well. Due to Lenz’s
law, the magnetic field produced by the eddy currents works against the movement
direction. Thus instead of mechanical friction, a magnetic friction is created. In
consequence, the disc will experience a “drag” or the braking effect, and thus the disc
stops rotation. The wheels of the vehicle, which is directly coupled to the disc, also
stop rotation. Faster the wheels are spinning, stronger the effect, meaning that as the
vehicle slows, the braking force is reduced producing a smooth stopping action.
The control switch can be set at different positions for controlling the
excitation current to several set values in order to regulate the magnetic flux and
consequently the magnitude of braking force. i.e. if the speed of the vehicle is lpw, a
low braking force is required to stop the vehicle. So the control switch is set at the
lowest position so that a low current will be supplied to the field winding. Then the
magnetic field produced will be of low strength, so that a required low braking force
is produced.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 14
When the control switch is operated during the standby position of the vehicle, the
magnet will be energized and magnetic field is created. But since the wheels are not
moving, magnetic lines of force are not cut by it, and the brake will not work.
However, a warning lamp is provided on the instrument panel to indicate whether
the brake is energized. This provides a safe guard for the driver against leaving the
unit energized.
When control switch is put in any one of the operating positions, the
corresponding conductor in the contractor box is energized and current flows from the
battery to the field winding to the contractor box. This current magnetizes the poles
in stator, which placed very near to the rotor. When rotor rotates it will cut magnetic
lines and eddy current will set up in the rotor. The magnetic field of this eddy current
produces a breaking force or torque in the opposite direction of rotation disc. This
kinetic energy of rotor is converted as heat energy and dissipated from rotating disc to
surrounding atmosphere. Current in the field can change by changing the position of
the controls switch. Thus we can change the strength of the braking force.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 15
Magnetic field lines across the magnetic material inside a copper tube
Direction of magnetic lines of force due to magnet in copper tube
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 16
Induction of Eddy current due to the motion of magnet in the copper tube
Direction of magnetic lines of force produced by induced eddy current
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 17
MAGNETIC BRAKING SYSTEM IN TRAINS
In the case of trains, the part in which the eddy current is induced is rail. The
brake shoe is enclosed in a coil, forming an electromagnet. When the magnet is
energized, eddy currents are induced in the rail by means of electromagnetic
induction, thereby producing braking action.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 18
MAGNETIC BRAKING SYSTEM IN TRAINS
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 19
TYPES OF MAGNETIC BRAKE
There are two types of magnetic brakes according to the method of excitation.
1. Electrically excited - magnetic brake
2. Permanent magnet - magnetic brake
1. ELECTRICALLY EXCITED - MAGNETIC BRAKE
Electrically excited - magnetic brakes are abruption-free method for
braking. In high-speed trains they offer a good alternative to the mechanical rail
brakes which are being used now a days. During braking, the brake comes in contact
with the rail, and the magnetic poles of brakes are energized by a winding supplied.
Magnetic poles of brakes are energized by a winding supplied with current from the
battery. Then the magnetic flux is distributed over the rail. The eddy currents are
generated in the rail, producing an electromagnetic braking force. This types of
braking need an additional safety power supply when there are breakdowns in the
electrical power supply.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 20
ELECTRICALLY EXCITED - MAGNETIC BRAKE
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 21
2. PERMANENT MAGNET- MAGNETIC BRAKE
Recently, permanent magnet - magnetic brakes have been developed for
subways, trams and local trains. These brakes need a mechanical actuator to turn the
magnets in an on and off position. The main advantage of this type of brake is safety.
i.e. it does not need electrical power supply to energize the magnet.
PERMANENT MAGNET- MAGNETIC BRAKE
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 22
BRAKING POWER CALCULATIONS
Sophisticated calculation methods for the determination of braking forces of
magnetic brakes are important for the design of the brakes.
For a simple magnetic brake employing a thin non-magnetic disc as copper the
drag or braking force on the disc.
where
H = Magnetic field strength in Webers.
A = Pole force area in cm2.
V = Velocity in cm/sec of mean radius of disc under the poles.
T = disc thickness in cm.
= specific resistance of disc material at its operating temperature in micro
ohms/cm3.
Torque = F * R Nm
Where R = mean pole radius in meter.
Power P = 2 NT/60 watts.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 23
MAGNETIC BRAKE REQUIREMENTS
An magnetic brake is an energy converter functions is to convert the kinetic
energy of a vehicle into heat and dissipate it such a rate to maintain the temperature of
unit with in reasonable limits under maximum and prolonged braking conditions. The
energy absorbed by the brake is transformed into heat by the currents induced in the
motor, and this is heat manly dissipated in surrounding air through the medium of
suitable designed fins the rotating member.
In mountains area, continues braking force is needed for a long time (say
about half an hour), at this condition, magnetic braking is more suitable to function
without over heating. The use of these retarders is by no means limited to mountain
on country. They can be advantageously employed on public service vehicles on city
routes without frequent stops. But in this braking system there with out be any
braking force in the vehicle is rest. So the magnetic brake is used as an auxiliary
heavy-duty retarder. By using auxiliary retarder very smooth retardation is assumed
and likely hood of skidding on slippery roads surfaces is minimized. Smooth braking
action cuts down tier were and since brake is used as an auxiliary heavy-duty retarder.
By using auxiliary retarder very smooth retardation is assumed and likely hood of
skidding on slippery roads surfaces is minimized. Smooth braking action cuts down
tier were and since the conventional brakes are relieved of heavy duty being required
only to bring vehicles to rest.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 24
MOUNTING AND INSTALLATION
A typical mounting of an eddy current brake consists of two discs in which
pole salient type, supported between the frame numbers of a vehicle chassis. Rotor is
coupled to road wheels being often mounted on a shaft that is interposed between the
gearbox and propeller shaft and stator is mounted on the frame of the vehicle.
The driver who can select one or four excitation settings according to the
breaking effect required mounts a control switch on a steering column in a position
for easy operation. In the operative positions of this switch 1, 2, 3, 4 contractors are
energized to supply current to the excitation windings of the retarder. Warning lamp is
also provided on the instrument panel to indicate when the retarder is energized. This
provides a safe guard for the driver against leaving the unit energized when the
vehicle is stationary.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 25
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 26
ADVANTAGES
Less maintenance
Wide range of braking force available within the temperature limit
Prolonged braking is possible
Long life
Less strain to the operation
Smooth retardation, which cuts down, the tire wears
Independent of wheel/rail adhesion.
No noise or smell.
Adjustable brake force.
High brake forces at high speeds.
Used also as service brake.
It uses electromagnetic force and not friction.
Non-mechanical (no moving parts, no friction.
Can be activated at will via electrical signal.
Light weight.
Magnetic brakes offer smooth retardation of vehicles without skidding. It is
totally free of wear and tear. So it has long life compared to ordinary brakes. These
need less maintenance.
In mountain areas continuous braking is needed for a long time. At this
condition, magnetic braking is more suitable to function without overheating.
By changing the excitation current to the field winding, i.e. by adjusting the
position of the control switch, we can vary the braking force to required range. The
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 27
operation of magnetic brake is very simple. i.e. the control switch is a soft switch
which can be operated without any strain.
Magnetic brakes works even under the toughest environmental conditions. For
example, in larger water slides and water coasters where the humidity would
immediately result in reduction of friction and thus impair the effectiveness of
ordinary brakes. It works even in highly corrosive environments and heavily
contaminated areas.
DISADVANTAGES
No breaking force at rest, braking force diminishes as speed diminishes with
no ability to hold the load in position at standstill.
Need of electric power
It can not be used at low speed vehicles or vehicle running at low speed.
Magnetic brakes are used with ordinary mechanical brakes.
Nowdays Magnetic brakes is using only for safety purpose.
The main disadvantage of the magnetic brake is that it needs electric power to
work. Researches are going on to overcome this disadvantage by making the brake
regenerative i.e. by converting the kinetic energy of the vehicle into electric energy
and storing it back into the battery.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 28
APPLICATIONS
For additional safety on long decants in mountain area
For high speed passenger and goods vehicle
It is used as a stopping mechanism in trains.
It is also used in the smooth breaking and functioning of roller coasters and
such fast moving machines
Magnetic brakes are best substitutes for ordinary brakes, which are being used
nowadays in road vehicles even in trains, because of their jerk-free operation. In
mountain areas where continuous braking force is needed, for a long time, the
magnetic braking is very much useful for working without overheating. Magnetic
brakes are very much useful for high-speed passengers and good vehicles. It can also
be used to slow down the trolleys of faster roller coasters.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 29
Conclusion
Magnetic brakes are the best choice when demands for reliability and safety
are the highest. They work even in the toughest environmental conditions. Even the
strike of lightning will not result in the loss of the braking force.
Magnetic braking system is not popular now a days. But we hope that the
magnetic braking system which is simpler and more effective will take the place of
the ordinary braking system and we can do expect it to be the norm one in few years
of time.
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
MAGNETIC BRAKING SYSTEM 30
REFERENCES
1. Manual 1 Gonzalez, Volume 25,Issue 4,July 2004
2. IEEE Transactions on magnetics, Volume 34, Issue 4, July 1998
3. Analysis of eddy current brake for high-speed railway by Wang.P.J.&
Chiuch.S.J.
4. Automobile electrical equipments by Young &Griffith.
5. Automatic engineering by Kripal Sing.
6. Clutches and brakes by William.C.Orthwin.
7. www.reelectromagneticbrakes.com
8. www.lineareddycurrentbrakes.com
Dept. of Mechanical Engineering P.K.C.E.T, Kandala
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