PEPM
AEL2501
Charging & Starting Systems
Lecture delivered by:
Prof. Ashok.C.Meti
MSRSAS--Bangalore
MSRSAS
M.S Ramaiah School of Advanced Studies - Bangalore
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Session Objectives
• To understand the need for battery and its
charging system on a vehicle.
• To understand the construction and working
of a starting system for an automotive
engine
• To study the need, construction and
working of various ignition systems for
modern gasoline engines
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Topics
•
•
•
•
•
•
•
•
•
•
Introduction to electrical systems
Automotive batteries
Ch i systems
Charging
t
Alternators
Charging systems
Starter motors
g
systems
y
Ignition
Conventional ignition system
Electronic ignition system
Distributor-less ignition systems
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Introduction- Electrical System
• The electrical system is the most important
support system of a vehicle.
• Electricity is provides the power needed for:
–
–
–
–
–
–
Ignition systems
Fuel systems
Starting
Lighting and signaling
Instrumentation
Safety devices and many other systems….
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Automotive Batteries
Introduction
• Battery is an important part of
automotive Electrical system.
• Supplies electric current to
operate all the electrical and
electronic systems in the
vehicle.
• Battery is an electrochemical
device.
device
• Amount of electricity it can
produce is limited.
limited
• The chemicals – sponge lead,
lead
lead oxide and sulfuric acid
react chemically to produce
flow of current.
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• Lead oxide and sponge lead are held
in plate grids to form +ve and –ve
plates.
• The grid plates are made of lead and
other elements.
• The liquid in the battery is the
electrolyte consisting of Sulfuric
acid and water.
water
• When fully charged
charged, the electrolyte
is about 40% sulfuric acid and about
60% water.
• As battery gets discharged
discharged, the
electrolyte mostly becomes water.
water
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Battery Ratings:
Reserve Capacity:
• Length of time that a fully charged
battery at 26.70C can deliver
25Amps [Typical 125 min].
• This rating represents the electrical
load that must be supplied by the
battery in the event of a charging
system failure.
failure
Cold Cranking Amperes (CCA):
Ability of the battery to crank an
engine when the battery and engines
are cold.
– One rating is the number of Amps a
12V battery can deliver for 30 sec
when it is at –180C without bat
voltage falling below 7.2 Volts.
[With reserve cap 125 min, 430
Amps.]
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• Older method of rating the
battery is Ampere
Ampere--hour
capacity.
– It is the amount of current
that a battery can deliver for
certain duration without the
temperature-corrected cell
voltage dropping below
1.75 volts per cell.
Ex:
• If a battery can be
discharged for 20 hrs at a
rate of 2.2A before its
terminal voltage reads
10.75 Volts, it would have
a rating of 44 A-hr.
However, in practice, it does not work out like this for most batteries
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Battery Testing
• Two ways:
– State-of-charge
State of charge
– Performance
• State-of-charge
• Hydrometer
• Charge indicator
• Open –circuit voltage (OCV) test. Measuring terminal voltage
[Typical 12.40V or higher]
• Performance – Load test- measures the terminal
voltage while the battery is discharging at high
rate.
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Acid values of diluted sulphuric acid
State of charge
Battery
version
Charged
Half-charged
Discharged
Electrolyte
Sp.gr. Kg/l)
Freezing
threshold oC
Normal
1.28
For tropics
1.23
- 68
- 40
Normal
1.16/1.20*
-17…-27
For tropics
1.13/1.16*
-13…-17
Normal
1.04/1.12*
- 3…-11
For tropics
1.03/1.08*
- 2…-8
# At 20oC: when the temperature rises, the specific gravity sinks by approx. 0.01kg/l for each 14oC change in
temperature.
* Lower figure: High acid utilization. Higher figure: Low acid utilization.
Battery open circuit Voltage as an indicator of state of charge
Open Circuit Voltage
State of charge
12.6 or greater
100%
12.4 to 12.6
75-100%
12.2 to 12.4
50-75%
12.0 to 12.2
25-50%
11.7 to 12.0
0-25%
11.7 or less
0%
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• Electronic battery sensor (EBS) avoids most of the breakdowns due
to run-down batteries.
• The sensor with integrated evaluation capability measures
– Voltage
– Current
– Temperature.
• Aided by complex software algorithms, it computes all factors which
accurately describe the condition of the car battery, computes capacity
andd state
statet t -of
off-charge
h
as well
ll as presentt andd future
f t
performance.
f
• The information is utilized for the management of alternator and
engine.
– It allows for
• lower fuel consumption
• consequently less exhaust emission
• enhanced battery service life.
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Charging System
Generation of electrical power:
•
Motor vehicles need their own efficient
and reliable source of energy that is
always available to supply power for the
the–
–
–
–
Starter
Ignition system
Fuel injection system
For the ECU to control electronic
equipment
– Lighting system
– Safety and convenience electronics and
so on…
•
•
When the engine is stopped the battery is
the source of energy
When the engine is running the
alternator or the Dynamo is the
electricity generating device supplying
power to all electrical loads.
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Alternators
• Alternators have higher electromagnetic efficiency than DC
generators and have much wider rotational speed range
range.
• Produce about 1/3 of rated power at idling.
• Designed to generate charging voltage of 14V (28V for
commercial vehicles).
• 3-phase winding is used in the stator and the excitation
winding is used in the rotor.
• A rectifier* converts the 3-phase AC in to DC.
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*Rectifier also prevents the discharge of battery due to reverse flow
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• The alternator output,
battery capacity and
the starter
requirements together
with the remaining
electrical loads need
to be matched to each
other as optimally
p
y as
possible.
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Typical Alternator with built-in regulator
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A simplified Alternator schematic
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A Star and Delta Connections
A rotor with magnetic poles
Field current: 4.5 to 6.0 Amps.
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*Claw poles
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DC Rectification: 3-phase bridge circuits
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Star connection
High voltage at low RPM
Delta connection
High current at low RPM
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• Voltage Regulation:
– Output of an
alternator can be as
high as 250V if not
controlled.
– The voltage regulator
controls the voltage
output.
– Voltage regulation is
achieved byy varying
y g
the current flowing
through the rotor.
Field Circuits
A-Circuit – regulator on the ground side of field coil.
A-Circuit – regulator on the power side of field coil.
The third type is isolated field
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• Electronic regulators:
Solid state integrated regulator
– They can be external or
internal to alternators.
– They are quick and
accurate in controlling
field current.
– Normally use ground
side field control using
PWM.
– IC based
b d regulators
l t are
extensively used in
recent times.
In modern computer controlled engines, the voltage regulation circuitry is
located in the vehicle’s powertrain control module or a in a separate ECU.
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Bosch AL9960LH Alternator
84 Amps /160 Amps
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Starting System
AEL2501
• IC engines in the vehicles need separate systems for starting.
• When starting these engines, considerable resistance resulting from– Compression
p
– Piston friction
– Bearing friction(static) must be overcome.
• These forces in turn dependent on:
– Number of cylinders
– Lubricant characteristics
– Engine temperature
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• The DC series wound electric motor
is the most commonly used type of
starter motor.
• It generates the high initial torque
required to overcome cranking
resistance and to accelerate the
engine’s internal masses.
• In majority of the cases, the starting
motor torque is transmitted to the
engine via starter pinion and ring
gear (very high gear ratio).
• Other
O h means off torque transmission
i i
are-
Gear & Pinion
– V-belts
– Toothed belts
– Chain drive.
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• The starter must meet the following
requirements:
– Continuous readiness for starting
– Sufficient starting power at different
temperatures
– Long service life for high number of starts
– Robust design to withstand meshing, cranking,
vibration,, corrosion due to dampness
p
and dirt,,
etc.
– Low weight and small size
– Longest possible maintenance
maintenance--free service life.
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• a Starter speed; decreases as
the temperature drops due to
increased internal resistance of
the battery.
• b Minimum required initial
engine speed; increases as
temperature drops due to
increased cranking resistance.
• The intersection of both curves
yields the starting limit
temperature.
*Battery internal resistance
Starting limit temperature
Engines for
Starting limit
temperatures
-18…. –250C
-15…. –200C
-12…. –150C
Passenger cars
Trucks and buses
Tractors
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• Ms Starter torque for various temperatures
(referred to the engine crankshaft).
• MM Torque required for starting a 3-liter SI
•
•
engine at different temperatures shown.
The intersection point of the relevant curves
determines the speed at which the engine is
cranked at –250C, -180C, and –100C.
The torque curve is referred to as a 20%
discharged 55Ah battery.
Empirical values for minimum cranking speeds
Required cranking speeds at –200C
Cranking speed (RPM)
Reciprocating –piston SI engines
60…90
Direct-injection diesel engine without start assist
With start assist (e.g glow plug)
80…200
60…140
Pre-chamber and whirl-chamber diesel engines w/o start assist
With glow-plug start assist
100…200
60…100
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• Starting systems for passenger cars:
– Nominal output – approx 2kW
– Rated voltage 12V
– Can start gasoline engines (7 lts) and diesel
engines (3 lts)
– Usually simple starter circuits
– Usually
y do not have start protection
p
and
monitoring devices.
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Starter subassemblies:
1.
Electric starter
2.
Solenoid switch with
electrical connections
3.
Pinion engaging drive
Starter components:
1.
Armature shaft
2.
Armature winding
3
3.
Armature stack
4.
Commutator
5.
Pole shoes
6.
Excitation winding
7.
Carbon brushes
8.
Brush holder
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• Pinion
– As soon as the engine
starts and accelerates
past the cranking
speed, the pinion must
automatically dede-mesh
in order to protect the
starter.
– Normally a starter uses
an overrunning clutch
and a mechanism to
mesh and de-mesh the
pinion.
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The Ignition Systems - Introduction
• To ignite the combustible charge of air and fuel in
the cylinder, and thereby initiate the power stroke,
stroke
some form of ignition
g
system
y
is required
q
in petrol
p
engines.
• For many years there were two systems of electrical
ignition systems used for motor vehicle engines.
• These were:
– High-tension
g
magneto
g
systems
y
– Battery and coil system*
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Basic requirements of ignition system:
• An electric spark forms a convenient means of
producing a rapid temperature rise in the engine
cylinder.
• But generation of spark requires a very high voltage
from the ignition system.
– Ex: for a typical air gap of 0.50mm, the voltage required
,
volts.
is of the order of 10,000
– The voltage requirement would be few hundred volts at
normal atmospheric pressure,
pressure and it is raised as the
compression ratio of an engine is increased.
increased
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• Other factors that raise the voltage requirement– Electrode surface deterioration
– Burning of weak mixture
– Cold starting conditions
• Other requirements:
– The number of sparks necessary in a given interval of
time.
• Ex: 4 Cylinder, 4S engine say @ 4500 rpm (i.e 75rps) would
require 150 high-voltage sparks every second.
– Important requirement – spark must be timed to occur
in each cylinder at an optimum point in the engine
operating cycle.
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Components of a Coil ignition system
• The basic operation of the ignition system has
changed little over the years but innovations in the
last few years have made it more precise.
• The basic components of non-electronic batterycoil ignition system (conventional) are:
–
–
–
–
–
–
Battery and charging system
The ignition coil
Spark plugs
CB point
Rotor arm and distributor
High voltage ignition wires
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Conventional Ignition System
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6 Cylinder engine
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Ignition Coil:
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• The ignition coil contains
both the primary and
secondary winding circuits.
• The coil primary winding
contains 100 to 150 turns of
heavy copper wire.
wire The
primary circuit wire goes
into the coil through the
positive terminal and exits
through the negative
terminal.
• The coil secondary winding
circuit contains 15,000 to
30,000 turns of fine copper
wire.
• To further increase the coils
magnetic field both
windings are installed
around a soft iron core.
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• To withstand the heat of the current
flow, the coil is filled with oil for
cooling.
• The ignition coil is the heart of the
ignition system.
system As current flows
through the primary coil a strong
magnetic field is built up.
• When the current is shut off, the
collapse of this magnetic field
induces a high voltage which is
released through the large center
terminal through the distributor to
the spark plugs.
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Distributor
Basic arrangement:
• Consists of a CB point assembly,
assembly a
t ti switch
it h to
t distribute
di t ib t the
th
rotating
induced high tension secondary
current to the correct sparking
plug at right moment and a means
of automatically varying the
ignition timing from its static
setting, according to the changes
in
i engine
i load
l d andd speed.
d
• The distributor is driven at onehalf the speed of the crank
shaft.(Normally driven by cam shaft)
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Need for a capacitor:
• Due to self-induction, the voltage induced across the primary
coil always opposes the action producing it.
• This effect will tend to delay the build-up of current in the
primary winding when the CB points close, and prolong the
duration of current flow after they open.
• This leads to :
– An electrical discharge with arcing would occur across the CB
points.
– A rapid collapse of magnetic field would be prevented, thus highvoltage available from the secondary will be reduced.
• A capacitor which acts as a temporary storage for electrical
energy is connected in parallel with the CB points.
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Spark Plugs
The spark plug has two primary
functions:
– To ignite the air/fuel mixture
– To remove heat from the combustion
chamber
• Spark plugs transmit electrical
energy that turns fuel into working
energy. A sufficient amount of
voltage must be supplied by the
ignition system to cause it to spark
across the spark plug's gap.
gap This is
called "Electrical
Electrical Performance
Performance".
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• The temperature of the spark
plug's firing end must be kept low
enough to prevent pre-ignition,
but high enough to prevent
fouling. This is called "Thermal
Thermal
Performance" and is determined
Performance",
Performance
by the heat range selected.
• The heat range is defined as a
plug's ability to dissipate heat.
• The rate of heat transfer is
determined by:
– The insulator nose length
g
– Gas volume around the insulator
nose
– The materials/construction of the
center electrode and porcelain
insulator
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• The distance or gap between the
tips of the central and side
electrodes of a sparking plug is
important
• It
I ddetermines
i
the
h magnitude
i d off the
h
high tension current or voltage
that is required to produce a
spark.
spark
• The gap setting depends on –
–
–
–
–
Engine compression ratio
Combustion chamber characteristics
Air-fuel ratio
Ignition system design
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Electronic ignition systems
AEL2501
• The concept of introducing electronics for ignition system
was originally to improve the life of the CB points and later
to eliminate them altogether.
• Later, other factors such as the following lead to the
d l
development
t off ignition
i iti systems:
t
– Demand for better performance from the ignition system,
– As a contribution to reducing emissions
– Improving fuel consumption
• Advantages derived from Modern electronic ignition
systems :
– Increased energy
gy and duration of the spark
p
((higher
g
value of primary
p
y current,
upto 30KV sec voltage)
–
–
–
–
–
More consistent sparking (low speed, cold starting, speed independent)
Less restricted rate of sparking (No limit on the engine speed)
More stable ignition timing ( No CB point gap to alter with time)
Reduced maintenance requirement ( No mechanical parts to maintain)
Easy integration with EMS
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Typical Electronic Ignition System
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The Distributorless Ignition System (DIS)
• Newer automobiles (1980 onwards) have
evolved from a mechanical system
(di t ib t ) to
(distributor)
t a completely
l t l solid
lid state
t t
electronic system with no moving parts (Direct
Ignition type - SAAB)
SAAB).
• These systems are completely controlled by
the onon-board computer
p
((ECU)
(ECU).
)
• In place of the distributor, there are multiple
coils that each serve one or two spark
plugs.
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• A typical 6 cylinder engine has 3 coils that are mounted
together in a coil "pack".
• A spark plug wire comes out of each side of the individual
coil and goes to the appropriate spark plug.
• The coil fires both spark plugs at the same time.
time
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• One spark plug fires on
the compression stroke
igniting the fuel-air
mixture to produce
power, while the other
spark plug fires on the
exhaust stroke and does
nothing.
nothing
• This
Thi is
i a method
h d called
ll d
simultaneous ignition
(waste spark).
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• On some vehicles, there is
an individual coil for each
cylinder mounted directly
on top of the spark plug (
Coil--oon
Coil
Co
on--Plug
ug ).
• This design completely
eliminates the high tension
spark plug wires for even
better reliability.
• Most of these systems use
spark plugs that are
designed to last over
100,000 miles, which cuts
down on maintenance
costs.
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Summary
• The constructional details of battery,
alternators and complete charging system
have been discussed
discussed.
• The starter motor and the complete
arrangement of the starting system has been
explained
• Details about various components of an
ignition system,
system their arrangement in a
complete circuit including recent
developments have been discussed.
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