Ignition System Control Spark-ignited engines require accurate control of spark timing and spark energy for efficient combustion. The MI-07 ignition system provides this control. The system consists of the following components: • SECM • Distributer with ignition module * • Ignition coil(s) * • Crankshaft position sensor * • Crankshaft timing wheel * • Spark plugs * ( * ) Customer-supplied components The SECM, through use of embedded control algorithms and calibration variables, determines the proper time to start energizing the coil and fire the spark plug.
This requires accurate crank/camshaft position information, an engine speed calculation, coil energy information, and target spark timing. The SECM provides a TTL compatible signal for spark control. The coil must contain the driver circuitry necessary to energize the primary spark coil otherwise an intermediary coil driver device must be provided. The SECM controls spark energy (dwell time) and spark discharge timing. Figure 14. GM Distributor The MI-07 system is capable of operating with either a distributor based ignition system or a distributorless ignition system. The current application uses a distributor based ignition system.
The distributor will have no internal advance mechanisms giving the SECM consistent authority over ignition timing. The spark is sent to the appropriate cylinder in the conventional way via the rotor arm and spark plug wires. The SECM uses the signal from the GM (General Motors) Delco Ignition Module to determine the engine position and RPM at any time. It uses this information together with the information from the TPS sensor and TMAP to calculate the appropriate ignition timing settings.
The General Motors (GM) distributor (Figure 14) used in the Delco EST ignition system, incorporates a Variable Reluctance (VR) sensor, which transmits a reference signal to the GM ignition module (Figure 15) located on the distributor. A variable reluctance sensor is an electromagnetic device consisting of a permanent magnet surrounded by a winding of wire. The sensor is used in conjunction with a ferrous signal rotor on the distributor shaft. The signal rotor has six lobes, one for each cylinder. Rotation of the signal rotor near the tip of the sensor changes the magnetic flux, creating an analog voltage signal in the sensor coil. 1 (1) lgnition Coil. (2) lgnition Module. Figure 15.
GM Ignition Module The rising edge of the VR signal is converted to a rising 5-volt signal by the ignition module. As the VR signal passes back through zero volts, a falling edge is created producing a square wave or digital signal, similar to the signal produced by a Hall effect sensor. This falling edge signal provides a stable engine position reference at all engine speeds for the SECM. G643(E) Service Manual Chapter 4. Engine Electrical System 113