Electronic Ignition System Description
Electronic Ignition System Operation
The electronic ignition system produces and controls the high
energy secondary spark. This spark ignites the compressed air/fuel
mixture at precisely the correct time, providing optimal
performance, fuel economy, and control of exhaust emissions. The
engine control module (ECM) collects information from the
crankshaft position sensor and the camshaft position sensor -
intake and camshaft position sensor - exhaust to determine the
sequence, dwell, and timing of the spark for each cylinder. The ECM
transmits a frequency signal to the ignition coil assembly on the
appropriate ignition control circuit to fire the spark plugs.
Crankshaft Position Sensor
The crankshaft position sensor circuits consist of an engine
control module (ECM) supplied 5-volt reference circuit, low
reference circuit, and an output signal circuit. The crankshaft
position sensor is an externally magnetically biased digital output
integrated circuit sensing device. The sensor provides a pulse for
each magnetic pole of the magnetic encoder wheel on the crankshaft.
Each pole on the encoder wheel is spaced at 60-pole spacing, with 2
missing poles for the reference gap. The crankshaft position sensor
produces an ON/OFF DC voltage of varying frequency, with 58 output
pulses per crankshaft revolution. The frequency of the crankshaft
position sensor output depends on the velocity of the crankshaft.
The crankshaft position sensor sends a digital signal, which
represents an image of the crankshaft encoder wheel, to the ECM as
each pole on the wheel rotates past the crankshaft position sensor.
The ECM uses each crankshaft position sensor signal pulse to
determine crankshaft speed and decodes the crankshaft encoder wheel
reference gap to identify crankshaft position. This information is
then used to determine the optimal ignition and injection points of
the engine. The ECM also uses crankshaft position sensor output
information to determine the camshaft position sensor - intake and
camshaft position sensor - exhaust relative to the crankshaft, to
control camshaft phasing, and to detect cylinder misfire.
Crankshaft Encoder Wheel
The crankshaft encoder wheel is part of the crankshaft. The
encoder wheel consists of 58 poles and a reference gap. Each pole
on the encoder wheel is spaced 6° apart with a 12° space
for the reference gap. The pulse from the reference gap is known as
the sync pulse. The sync pulse is used to synchronize the coil
firing sequence with the crankshaft position, while the other poles
provide cylinder location during a revolution.
Camshaft Position Sensor
The camshaft position sensor - intake and camshaft position
sensor - exhaust is triggered by a notched reluctor wheel built
onto the intake camshaft sprocket. The camshaft position sensor -
intake and camshaft position sensor - exhaust provides four signal
pulses to every camshaft revolution. Each notch, or feature of the
reluctor wheel is of a different size which is used to identify the
compression stroke of each cylinder and to enable sequential fuel
injection. The camshaft position sensor - intake and camshaft
position sensor - exhaust is connected to the ECM by the following
circuits:
• |
A 5-volt reference
circuit |
• |
A low reference circuit
|
Ignition Coil Assembly
The ignition coil assembly used on this engine integrates the 4
coils and the module within a single sealed component.
The ignition coil has the following circuits:
• |
An ignition voltage
circuit |
• |
4 ignition control
circuits |
The ECM controls the individual coils by transmitting timing
pulses on the electronic ignition circuit of each ignition coil to
enable a spark event.
The spark plugs are connected to each coil by a short boot. The
boot contains a spring that conducts the spark energy from the coil
to the spark plug. The spark plug electrode is coated with platinum
for long wear and higher efficiency.
Engine Control Module (ECM)
The ECM controls all ignition system functions, and constantly
adjusts the spark timing. The ECM monitors information from various
sensor inputs that include the following:
• |
The crankshaft position
sensor |
• |
The accelerator pedal position
(APP) |
• |
The manifold absolute pressure
(MAP) sensor |
• |
The intake air temperature
(IAT) sensor |
• |
The vehicle speed sensor
(VSS) |
• |
The engine knock sensor
|
• |
The engine coolant temperature
(ECT) sensor |
• |
The mass airflow (MA)
sensor |
• |
The camshaft position
sensors |
|