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Ignition Transformer
Illustration 1 g00326433
Components Of The Gas Engine Ignition Group (1) High energy ignition transformer. (2) Tube. (3) Extension with a spring loaded rod. (4) Spark plug.The ignition transformer causes an increase of the primary voltage. The increased voltage is needed to send a spark (secondary electrical impulse) across the electrodes of the spark plugs. For good operation, the connections (terminals) must be clean and tight. The negative transformer terminals for each transformer are connected together and the terminals are connected to ground.Timing Control System
The Caterpillar Detonation Sensitive Timing Control (DSTC) system provides detonation protection for the engine and electronic adjustment of ignition timing with a variable timing. This ignition system consists of four basic groups (Timing Control Module, Magneto Interface Box, Variable Timing Magneto, and Sensors).
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Timing Control SystemTiming Control Module (TCM)
The TCM determines the ignition timing. The TCM communicates the ignition timing with the Magneto Interface Box (MIB). The TCM provides the system diagnostics.Engine timing, controlled by the TCM, is based upon the desired timing signal received from the ECM. The desired timing signal from the ECM varies depending on engine speed, engine load and engine detonation.The ignition timing is controlled by three signals that are sent from the TCM to the MIB. The MIB sends a signal that indicates that the plug is firing to the TCM. The TCM uses this signal to calculate actual engine timing.Magneto Interface Box (MIB)
The MIB receives three signals from the TCM. These signals define how much the timing should be retarded in order to provide the desired engine timing. The MIB then closes the connection between pins "A" and "F" or "E" and "F", going to the magneto. This occurs when the magneto is sending primary voltage of 170 to 200 VDC in order to fire the spark plugs.In order to identify the timing of the primary ignition pulses, the magneto capacitor voltage signals are also sent to the MIB. The primary ignition pulses are when the spark plugs fire. The MIB converts the odd bank capacitor voltage into a lower voltage ignition pulse signal that is sent to the TCM. When operating in Magneto Calibration Mode, the connections between "A" and "B" or "E" and "F" in the MIB are continuously made.Variable Timing Magneto
Standard magnetos discharge the ignition capacitor to the ignition coil. This occurs as soon as the rotor enters the magnetic field of a stationary pole. For the variable timing magnetos, the ignition capacitor will discharge while the rotor is within the magnetic field of the stationary pole. The ignition timing window is defined as the timing when the rotor enters the magnetic field to the timing when the rotor exits the magnetic field. For variable timing magnetos, the capacitor will discharge only when the rotor is within the timing window and an external switch, provided by the MIB, is closed. To retard the timing, the external switch is closed farther through the timing window. To operate the variable timing magneto the same way as a standard magneto, the external switches are permanently closed.Timing Control Sensors
The TCM uses two sensor signals for the ignition timing control. The TCM uses the detonation sensors for detonation protection. The Crank Angle Sensor (CAS) and the Speed Sensor (TCMPU) provide top center (TC) and rotational position needed to control timing. The detonation sensors provide an electrical signal of the engine's mechanical vibrations that are used in order to calculate the detonation levels.Crank Angle Sensor (CAS)This passive magnetic speed sensor indicates the crankshaft angle to the TCM. The crank angle sensor provides the TC signal used to control timing and calculate actual timing. The signal is generated when the TC hole (for the No. 1 piston) in the flywheel face passes the sensor.Speed Sensor (TCMPU)This passive magnetic speed sensor indicates engine speed to the TCM. The speed sensor produces a signal whenever a ring gear tooth on the flywheel passes the sensor. The signal is used to calculate engine speed, to monitor the crankshaft angle between TC pulses and to clock the MIB electronics.Detonation SensorsThe detonation sensor is a powered device that outputs a filtered electrical signal and a amplified electrical signal of the engine's mechanical vibrations. When increased levels of vibration are occurring, the ECM calculates the engine detonation. If necessary, the ECM will adjust the ignition timing in order to control detonation. This is done by sending a desired timing signal that is retarded as much as six crank degrees to the TCM. When the level of vibration has returned to normal, the ECM will adjust the desired timing signal in order to gradually allow the ignition timing to return to operation. This adjustment is based on the desired timing map that is part of the personality module. Timing Control And Magneto Interface Box
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G3600 Ignition Timing SystemThe Timing Control provides three signals to the Magneto Interface Box (MIB) in order to communicate the desired ignition timing. These signals are the Ignition Interface Clock, the Reset Pulse signal, and the Manual Override signal. The MIB returns the Ignition Pulses to the Timing Control. The Timing Control calculates the Actual Engine Timing. The Timing Control performs some ignition diagnostics from this signal.Ignition Interface Clock
The Ignition Interface Clock signal is a square wave version of the speed sensor signal. This signal provides a timing clock for the MIB.
Illustration 4 g00329509
Relationship Between Speed Sensor And Clock SignalsSent from Timing Control (pin-G) to MIB (pin-E, 10 pin Connector).The waveform is a square wave version of the speed sensor signal, with peak voltage of 2.5 V and minimum voltage of 1 V. The positive-going edge of the clock signal should align with the negative-going zero-crossing of the speed sensor signal.Reset Pulse
The Reset Pulse signal indicates to the MIB the ignition timing desired by the Timing Control. The pulse is sent once from TC to TC.
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Interface Reset Pulse Signal Relative To Crank Angle TC Signal