Ignition System: Description and Operation

IGNITION SYSTEM

Overview
The ignition system is designed to ignite the compressed air/fuel mixture in an internal combustion engine by a high voltage spark from an ignition coil. The ignition system also provides engine timing information to the PCM for proper vehicle operation and misfire detection.

Integrated Electronic Ignition (EI) System

Typical COP Ignition System:

The EI system consists of a crankshaft position (CKP) sensor, coil(s) on plug (COP), and the PCM. The COP integrated EI system uses a separate coil per spark plug, and each coil is mounted directly onto the plug. The COP integrated EI system requires input from the camshaft position (CMP) sensor. Operation of the components are as follows:

1. NOTE: Electronic ignition engine timing is entirely controlled by the PCM. Electronic ignition engine timing is NOT adjustable. Do not attempt to check base timing. You will receive false readings.

The CKP sensor is used to indicate crankshaft position and speed by sensing a missing tooth on a pulse wheel mounted to the crankshaft. The CMP sensor is used by the COP integrated EI system to identify the top dead center of compression of cylinder 1 to synchronize the firing of the individual coils.

2. The PCM uses the CKP signal to calculate a spark target and the CMP signal to identify the top dead center of compression of cylinder 1 to synchronize the firing of the individual coils.
3. The COPs receive their signal from the PCM to fire at a calculated spark target. The COP system fires only one spark plug per coil and only on the compression stroke.

The PCM acts as an electronic switch to ground in the coil primary circuit. When the switch is closed, battery positive voltage (B+) applied to the coil primary circuit builds a magnetic field around the primary coil. When the switch opens, the power is interrupted and the primary field collapses inducing the high voltage in the secondary coil windings and the spark plug is fired. A kickback voltage spike occurs when the primary field collapses. The PCM uses this voltage spike to generate an ignition diagnostic monitor (IDM) signal. IDM communicates information by pulse width modulation in the PCM.

4. The PCM processes the CKP signal and broadcasts it to the communication network. The PCM also sends it to the TCM as a hardwired clean tachometer output (CTO) signal.

Hardware

Crankshaft Position (CKP) Sensor
For additional information on the CKP sensor, refer to Powertrain Control Module (PCM) Inputs Crankshaft Position (CKP) Sensor. Powertrain Control Module (PCM) Inputs

Camshaft Position (CMP) Sensor
The COP integrated EI system uses the CMP sensor information to synchronize the firing of the individual coils. For additional information on the CMP sensor, refer to Powertrain Control Module (PCM) Inputs Camshaft Position (CMP) Sensor. Powertrain Control Module (PCM) Inputs

Coil-On-Plug (COP)

Coil-On-Plug:

The COPs are part of the distributorless ignition system. They are the source of the high voltage which is used to generate the spark by the spark plug. The hybrid vehicle uses 4 COPs, one for each cylinder. The COPs are mounted directly onto the spark plugs. The function of the COP is to convert low voltage into a high voltage in excess of 40,000 volts.

The COP consists of primary and secondary windings. The primary winding is energized by the IGN START/RUN circuit. The PCM coil driver circuit is connected to the primary winding as well. The secondary winding is connected to the spark plug. The current flowing through the primary winding generates the magnetic field across both windings. The PCM activates the coil driver circuit by opening it. The instant the circuit opens the magnetic field collapses, inducing current flow in the secondary winding.

The COP has 3 different modes of operation: engine crank, engine running, and CMP failure mode effects management (FMEM).

Engine Crank/Engine Running
During engine crank the PCM fires 2 spark plugs simultaneously. Of the 2 spark plugs simultaneously fired, one is under compression and the other is on the exhaust stroke. Both plugs fire until the camshaft position is identified by a successful camshaft position sensor signal. Once the camshaft position is identified, only the cylinder under compression is fired.

CMP FMEM
During CMP FMEM the COP ignition works the same as during engine crank. This allows the engine to operate without the PCM knowing if cylinder 1 is under compression or exhaust.