Ignition Transformer
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| 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
- Ignition Control
- Detonation Mixing Control (DMC) System
- Sensors
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| Illustration 2 | g00494465 |
Timing Control System | |
Timing Control Module (TCM)
The TCM determines the ignition timing. The TCM communicates the ignition timing with the Ignition Control. 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 Ignition Control. The Ignition Control sends a signal that indicates that the plug is firing to the TCM. The TCM uses this signal to calculate actual engine timing.
Caterpillar Ignition System (CIS)
The Caterpillar Ignition System has been designed for gas engine applications in conjunction with the TCM. The ignition system is intended to replace both the magneto and the magneto interface box. The existing ignition coils and the wire connection to the TCM are still utilized. The addition of a Cam Position Sensor and a trigger magnet are required as a cycle trigger. The sensor and the magnet are installed on the cam at the oil mist drive location at the front right hand side of the engine. New features include advanced spark control, spark diagnostics, self-diagnostics, diagnostics, sensor diagnostics and serial port communications. The system consists of two main parts: The engine mounted ignition control module and the remote mounted optional user interface display module. The system requires 24 VDC at 5 amp nominal for typical application.
Note: The ignition system must be configured prior to use on an engine. All components from the factory and parts departments are properly configured for your engine. Ensure that you have the correct part number for your application.
Ignition Control Module
The ignition control module is equipped with a 16 position manual timing switch in the output module and a start-up retard that is adjustable via the terminal software. The maximum allowable ambient temperature exposure of the control module is 65.5°C (150°F) .
The manual timing switch affects the timing that is reported to the TCM during the engine crank, or while in the "MAG CAL" mode. The ignition control module was designed to be transparent to the TCM, which fires at the fully advanced ignition timing while the engine is under 500 rpm. Therefore, in order to avoid a "MAG CAL" fault, the ignition must report the timing to the TCM in order to match the fully advanced timing by 1 degree. When the engine speed is above 500 rpm, then the electronic timing is activated. The manual timing switch has no effect on the engine timing.
In order to facilitate better starting, the ignition control module is configured to permit the timing to be retarded from the full advance setting while the engine is below 500 rpm. This adjustment is a retard offset from the Reported Timing. Once the engine speed is above 500 rpm, the electronic timing is activated. The start-up retard timing adjustment setting has no effect on the engine timing.
The timing reported to the TCM is calculated as follows:
Reported timing=Opening of Cam Position Window-6 degrees-manual switch setting
The actual engine timing is calculated as follows:
Actual timing=Reported timing-Retard adjustment
Note: The Retard Adjustment has no effect on the timing that is reported to the TCM and will not cause a "MAG CAL" fault.
Note: Changing the Reported Timing changes the Actual Timing by the same amount.
Cam Position Sensor And Trigger Magnet
The Cam Position Sensor senses a magnet which must be fixed at the proper angular position of the cam gear. The leading edge of the Cam Position Sensor signal represents the reset signal of the ignition in manual/start-up timing mode. In the electronic timing mode, the Cam Position signal is used to select the reset pulse from the TCM that occurs during the compression stroke (the TCM generates reset pulses during both the compression stroke and the exhaust stroke). The air gap between the Cam Position Sensor and the trigger magnet must not exceed 1.0 mm (.04 inch) .
Optional Ignition Control Display Module
The optional ignition control display module has an alphanumeric 16 character X 2 line back lighted LCD display. The display shows the operating status, the engine rpm, the secondary spark energy levels, and if the system is in single or double-strike mode.
Mount the display at a convenient viewing height. Mount the display within 15 m (50 ft) of the engine mounted ignition control module. The display can be mounted inside a control panel. The display can be mounted on a suitable flat surface that is preferable off the engine. The display should be mounted in order to minimize exposure to vibration.
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 CIS electronics.
Detonation Sensors
The detonation sensor is a powered device that outputs a filtered electrical signal and a amplified electrical signal of the engine's mechanical vibrations. There are three detonation sensors that are located on the right hand side of the engine. Each sensor is placed between two cylinders. This allows the detonation detection control strategy to better interpret a true detonation occurrence. 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 CIS
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| Illustration 3 | g00494466 |
Ignition Timing System | |
The Timing Control provides three signals to the Caterpillar Ignition System Interface Box 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 CIS 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 CIS.
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| Illustration 4 | g00329509 |
Relationship Between Speed Sensor And Clock Signals | |
Sent from Timing Control (pin-G) to CIS (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 CIS the ignition timing desired by the Timing Control. The pulse is sent once from TC to TC.
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| Illustration 5 | g00329510 |
Interface Reset Pulse Signal Relative To Crank Angle TC Signal | |
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| Illustration 6 | g00329512 |
Close up Of Interface Reset Pulse Signal Relative To Crank Angle TC Signal | |
Sent from Timing Control (pin-H) to CIS (pin-G, 10 pin Connector).
The Interface Reset Pulse signal is normally below 1 V. The Reset Pulse goes high to about 2.5 V. This signal should go high once from Top Center (TC) to TC.
Manual Override ("Mag Cal" Mode As Seen In DDT)
The Manual Override signal tells the CIS to control fully advanced ignition timing.
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| Illustration 7 | g00329513 |
Manual Override Signal, Timing Control In Electronic Timing Mode | |
Sent from Timing Control (pin-e) to CIS (pin-C, 10 pin Connector).
The manual override signal should remain below 1 V when the system is in Electronic Timing Control mode. A 5 V signal on this line will tell the CIS to run the ignition at fully advanced timing.
Ignition Pulses
The Ignition Pulse signal is the odd number bank's capacitor charge. The signals waveform indicates the discharge of the CIS and firing of cylinders. One pulse is shown for each number cylinder. This signal is used by the TCM to calculate ignition timing and some ignition diagnostics.
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| Illustration 8 | g00479636 |
Ignition Pulses Relative To Crank Angle TC Signal (Six Cylinder Engine) | |
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| Illustration 9 | g00479637 |
Close up Of Ignition Pulses Relative To Crank Angle TC Signal (Six Cylinder Engine) | |
Sent from CIS (pin-A, 10 pin Connector) to Timing Control (pin-c).
From TC to TC, this waveform should show one pulse for each number cylinder. The pulse is normally at 5 V and goes below 2 V when the CIS detects the ignition firing.
Interaction Of The Interface Signals
The manual override signal is held below one volt, the CIS is placed in "Mag Cal" Mode. The TCM generates the Clock signal by squaring the Speed Sensor (TCMPU) signal. This clock signal is used by the CIS electronics in order to keep track of the rotational position. When the the Reset pulse is received from the TCM, the CIS counts nine Clock signal edges. The CIS will then signal to fire Cylinder Number One. The CIS continues to monitor the Clock. The CIS signals to fire the remaining cylinders through the rotation. When the CIS discharges to fire the cylinder, an ignition pulse is generated. The Ignition Pulse signal is a reduced voltage signal of the odd number bank's capacitor voltage. Ignition Timing is calculated by comparing the timing offset between TC from the Crank Angle Sensor and the Ignition Pulse for Cylinder Number One.
When the Manual Override signal goes above one volt, the CIS operates in Manual (Standard) Mode. The CIS will no longer control ignition firing. The CIS will generate an ignition pulse at the most advanced ignition timing.The Ignition Timing is calculated in the same manner as in Electronic Timing Mode.
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| Illustration 10 | g00329517 |
Interaction Of Reset, Clock, Ignition Pulse And TC Signal | |
When the CIS receives the Reset Pulse, the CIS generates a ignition pulse after 9 Clock Signal edges (both rising and falling edges). The CIS generates the Ignition Pulse for Cylinder Number One. This should occur before the TC signal of the engine.
Ignition Pulse Firings
From TC to TC, this waveform should show one pulse for each cylinder. The pulses should go from 190 V to ground when the cylinder is signaled to fire.
CIS Wiring Diagram
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| Illustration 11 | g00492678 |
G3612 Engine CIS Wiring | |
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| Illustration 12 | g00492679 |
G3616 Engine CIS Wiring | |
Engine Start-up
At engine start-up, the Timing Control performs some system checks not done once the engine is running. The Manual Override signal places the CIS in Manual Mode until the engine speed is above 500 rpm. The Timing Control checks the Ignition Pulses signal for Cylinder No. 1 firing while the engine speed is between 120 and 300 rpm. If this ignition pulse is not present, the Timing Control will display the "No Magneto Interface Signal" fault. Once the engine speed increases between 300 and 500 rpm, the Timing Control will compare the timing of Cylinder No. 1 firing to the "Mag Cal" Timing stored in internal memory. If the two timing values do not match, the Timing Control will display the "Magneto Out Of Calibration" fault.
Detonation Mixing Control (DMC)
The purpose of the Detonation Mixing Control (DMC) is to expand the detonation protection system that is offered by the Timing Control Module (TCM) and the Electronic Ignition System (EIS) on the Caterpillar gas engines. The DMC allows up to 8 detonation sensors to be monitored on an engine.
The Detonation Mixing Control is designed to be sold as an attachment to existing G3500 and G3600 gas engines. The Detonation Mixing Control will be sold as a standard control on future G3500 and G3600 gas engines. The Detonation Mixing Control is compatible with the Timing Control Module in standalone applications. The Detonation Mixing Control is compatible with the Electronic Ignition System Control in standalone applications. The Detonation Mixing Control is compatible with the Timing Control with the G3600 Engine Control in the Engine Supervisory System arrangement. The Detonation Mixing Control is compatible with the G3500 Air/Fuel Ratio Control with Electronic Ignition System Control. Future expansion may include the G3300 gas engines and the G3400 gas engines
The Detonation Mixing Control performs the following functions:
Detonation Signal Mixing - Combines selected segments from each detonation sensor signal, based on engine type and firing order, for output to the detonation protection control.
Rotation Position Control - Monitors the rotational position of the engine. Monitors position in the firing order.
DC Voltage Monitoring - Monitors DC voltage level of detonation sensors.
Diagnostics - Generates sensor diagnostics. Display diagnostics on DDT. Takes appropriate action when diagnostics occur.
Communicate Information Over CAT Data LInk - Receive and send information to DDT. Request and receive information from EIS. Receive and send information from ECM.
Detonation Signal Mixing
The purpose of the Detonation Signal Mixing function is to provide accurate engine detonation information from all cylinders to the detonation protection system. This enhances the existing system by expanding the protection from the four center cylinders to all engine cylinders.
The Detonation Signal Mixing controls which segments of each detonation sensor signal are used to create the detonation signal output to the detonation protection system. The microprocessor controls two 1-of-4 analog switches to select which sensor signal segments are used. The signal from the detonation sensor closest to the combusting cylinder is selected and passed to the protection system. As the combusting cylinder changes, the selected sensor signal will also change.