Functional Description - Ignition System Control Module (ISCM)

The ISCM's main function is to drive the ignition coils on the engine. It is connected between the Powertrain Control Module (PCM) and the ignition coils. The ISCM receives a hard-wired replica buffered crank position signal and the ignition command signal from the PCM. The ISCM duplicates the spark timing requested. However, the ISCM is responsible for controlling dwell time for all ignition coils. The ISCM also performs Ion current sensing and management in internal combustion engines. After firing each coil, the ISCM uses ion current sensing across the spark plug gap to analyze several aspects of each combustion event. These aspects include misfire, knock, Air Fuel Ratio cylinder balancing/correction, pre-ignition, and spark plug fouling. The ISCM is also capable of managing multi-strike per each ignition coil.

Courtesy of CHRYSLER GROUP, LLC

The diagnostics present in the ISCM memory allow it to analyze the ion current present in the secondary winding of the coils. If the ion current has certain values, the ISCM module can establish:

• Whether there was a spark at the spark plug electrode head.
• Whether there is combustion.

The ISCM module can identify whether the spark at the spark plug's electrode head was fired by the presence of the peak in the ignition phase. Obviously, if the spark was not fired, the peak in current is practically absent as the ionization in the air between the electrodes is nil. The second peak in ion current (Chemical Phase) occurs when oxidation of the chemical element present in the air-fuel mixture begins. The third peak in ion current (Thermal Phase) occurs when there is an increase in the release of heat (the moment the flame develops). Between the ion current peaks for the chemical and thermal phases, the ISCM module can understand whether the injection of fuel occurred and whether combustion is taking place.

Courtesy of CHRYSLER GROUP, LLC

The PCM sends command signals (2) to the ISCM to direct the Ignition to the respective coil. The ignition coils are indirectly commanded on (3) by the PCM, and controlled by the ISCM. It is typically a 3ms window in which the ISCM can dwell the ignition coil by turning on the control driver (1) for each individual coil/channel. The ISCM decides, based on the conditions, how much dwell time is needed. It may delay the timing (5) of when the dwell period starts by delaying when the driver for the given channel is turned on (6). At the end of the dwell window (4), upon the falling edge of the PCM command signal for each coil, the ISCM will turn off the driver for the given channel allowing the ignition coil to fire.