Transcript Chapter 27

Chapter 26
Ignition Systems
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Ignition Systems
• Part of the
computerized engine
control system
• Three basic types
– Distributor-based
– Distributorless
– Direct ignition
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duplicated, or posted to a publicly accessible website, in whole or in part.
Purposes of the Ignition System
• It must generate spark with enough heat to
ignite the air/fuel mixture
• It must maintain the spark long enough to
allow for complete combustion
• It must deliver the spark so combustion can
begin at the precise time
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Basic Circuitry - Primary
•
•
•
•
•
•
Battery
Ignition switch
Ballast resistor (older systems)
Ignition coil primary winding
Triggering device
Switching device or control module
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Basic Circuitry - Secondary
• Ignition coil secondary
winding
• Distributor cap and
rotor (DI systems)
• High-voltage cables
• Spark plugs
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Primary Circuit Operation
• Ignition switch on
• Current flows into primary coil winding
• A primary switching device stops current flow
through the coil
• This causes the magnetic field to collapse
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duplicated, or posted to a publicly accessible website, in whole or in part.
Secondary Circuit Components
•
•
•
•
Ignition coil secondary winding
Distributor cap and rotor (DI systems)
Spark plug cables (some systems)
Spark plugs
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duplicated, or posted to a publicly accessible website, in whole or in part.
DI Secondary Circuit
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Secondary Circuit Operation
• Collapse of the magnetic field in the primary
induces high voltage into the coil secondary
• This voltage is used to establish a complete
circuit so current can flow
• The excess energy is used to maintain the
current flow across the spark plug gap
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duplicated, or posted to a publicly accessible website, in whole or in part.
Knowledge Check
• Which of the following is NOT part of the
primary circuit?
A. Ignition switch
B. Primary coil winding
C. Spark plug
D. Switching device
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duplicated, or posted to a publicly accessible website, in whole or in part.
EI Systems
• May have a single coil for each cylinder or
two cylinders may share a coil
• The ignition module controls firing order
and spark timing
• Additional energy is released as current
flow
• This allows higher firing current and longer
firing times, 1.5 ms compared to DI’s 1 ms
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Coil at Plug Secondary Circuit
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duplicated, or posted to a publicly accessible website, in whole or in part.
DIS Secondary Circuit
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Ignition Coils
• Coils are pulse
transformers
• Output dependant
upon the number of
windings and current
flow
• CEMF increases time to
become fully saturated
• Dwell is the period of
current flow
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© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Ignition Coils (Cont.)
• Typical coil requires 2-6
ms to be saturated
• Dwell period and
primary current are
controlled
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duplicated, or posted to a publicly accessible website, in whole or in part.
Secondary Voltage
• Typical voltage requirement to jump the
plug gap is 10,000 volts
• Most coils have at least 25,000 volts
available – called secondary reserve voltage
• Reserve necessary to compensate for high
cylinder pressures
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duplicated, or posted to a publicly accessible website, in whole or in part.
Spark Jumping the Gap
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Spark Plugs
• Provides the air gap
• Resistor reduces RFI
• Standard plug
electrodes are copper
• Platinum and iridium
electrodes extend plug
life
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duplicated, or posted to a publicly accessible website, in whole or in part.
• Platinum
tipped spark
plug
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duplicated, or posted to a publicly accessible website, in whole or in part.
Spark Plug Reach
• Reach is critical for proper gap placement
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Heat Range
• Heat must be
dissipated quickly
• Heat travels from the
electrode through
the insulator to the
cylinder head
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duplicated, or posted to a publicly accessible website, in whole or in part.
Spark Plug Gaps
• Correct gap is necessary
for proper operation
• Too wide can cause
misfiring
• Too narrow can cause
fouling and misfires
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duplicated, or posted to a publicly accessible website, in whole or in part.
Electrodes
• May be made of copper,
platinum, iridium, or
yttrium
• Various styles of
positive and ground
electrodes in use
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duplicated, or posted to a publicly accessible website, in whole or in part.
Ignition Cables
•
•
•
•
Carry high voltage to spark plugs
Carbon fiber core acts as a resistor
Reduces RFI and increases firing voltage
Reduces plug wear by reducing current
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© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Knowledge Check
• Which is not a common spark plug electrode
material?
A. Copper
B. Yttrium
C. Nickel
D. Platinum
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Triggering and Switching Devices
• A triggering device
monitors crankshaft
position
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duplicated, or posted to a publicly accessible website, in whole or in part.
Triggering and Switching Devices
(Cont.)
• A switching device controls current flow
through the coil primary winding
• Electronic switching components are part of
an ignition control module or the PCM
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duplicated, or posted to a publicly accessible website, in whole or in part.
Engine Position Sensors
• Magnetic Pulse
Generator
– Consists of a reluctor
and pickup coil
• Metal Detection Sensor
– The electromagnet is in
the pickup coil
• Hall-effect Sensor
• Magnetoresistive
Sensor
– Looks like a magnetic
sensor but outputs a
signal like a Hall-effect
• Photoelectric Sensor
– Uses an LED and moving
slotted disc
– Produces a square wave
signal
– Is most commonly used
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duplicated, or posted to a publicly accessible website, in whole or in part.
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duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
DI System Operation
• The camshaft drives the
distributor at one-half
crankshaft speed
• The position sensor
triggers the switching
device
• The coil is triggered by
the switching device
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duplicated, or posted to a publicly accessible website, in whole or in part.
Distributor
• May contain pick up assembly, ignition
module, and coil
• Rotor sits on top of distributor shaft and spins
inside of distributor cap
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duplicated, or posted to a publicly accessible website, in whole or in part.
Electronic Ignition Systems
•
•
•
•
•
•
No moving parts
Cylinders individually controlled
Flexible mounting locations
Less radio frequency interference
No timing adjustments
More time for coil saturation
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duplicated, or posted to a publicly accessible website, in whole or in part.
Double-Ended Coil or
Waste Spark Systems
• One coil fires two plugs
• These are the
companion cylinders
• One plug fires positive
to negative
• The other fires negative
to positive
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duplicated, or posted to a publicly accessible website, in whole or in part.
Coil-Per-Cylinder Ignition
• Coil-on-plug and coil-near-plug
• Allows for more time between firings and
increased saturation time
• A single coil failure affects only one cylinder
• COP require adaptors or plug wires to connect
an ignition scope
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duplicated, or posted to a publicly accessible website, in whole or in part.
© 2015 Cengage Learning. All Rights Reserved. May not be scanned, copied,
duplicated, or posted to a publicly accessible website, in whole or in part.
Twin Spark Plug Systems
• One plug on intake side of combustion
chamber and one on exhaust side
• Results in cleaner combustion
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duplicated, or posted to a publicly accessible website, in whole or in part.
EI System Operation
• Biggest differences are in number of coils and
the use of CKT and CMP sensors
• Layout and operation of the sensors are
designed to provide fast engine starts and
synchronization of the fuel and ignition
systems
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duplicated, or posted to a publicly accessible website, in whole or in part.
Hall-Effect Sensors
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Magnetic Pulse Generators
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Knowledge Check
• Technician A says a waste-spark system uses
one coil per plug. Technician B says a wastespark system fires one plug positive to
negative and the other plug negative to
positive. Who is correct?
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duplicated, or posted to a publicly accessible website, in whole or in part.
Misfire Detection
• The CKP identifies which cylinder
• Detected by variation in crank speed
• PCM uses wheel speed data to determine if
crank speed variation is from rough road
conditions or misfire
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Basic Timing
• The PCM controls timing
and is not adjustable
• Timing is fixed during
cranking
• Once a certain engine
speed is reached, the PCM
adjusts timing
• Timing inputs include RPM,
load, throttle position, and
coolant temperature
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Timing Retard and Advance
• Timing controlled by ignition module
• Older systems used mechanical and vacuum
systems
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Timing Corrections
• Temperature
– Advanced with low coolant temperature
• Engine Knock
– Timing retarded when knock is detected
• Stabilizing Idle
– Used if desired idle speed is not correct
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Timing Corrections (Cont.)
• EGR
– Advanced when EGR is opened
• Transition Correction
– During rapid acceleration/decelerations
• Torque Control
– To smooth automatic transmission shifting
• Traction Control
– Reduces engine torque by retarding timing
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