An Electronic Control Module (ECM) controls most of the functions of the engine. The ECM is an electronic engine control that is mounted on the side of the engine. The ECM monitors inputs from various sensors in order to activate relays, solenoids, actuators, etc at the appropriate levels. The ECM supports the following four functions:
- Start/stop sequencing
- Ignition control
- Engine speed governing
- Engine monitoring and protection
The following functions are optional:
- Air/fuel ratio control
- Prelubrication and post lubrication
The ECM contains the logic and the outputs for control of engine starting and of engine shutdown. The logic can be programmed by the customer. The logic responds to signals from the following components:
- Engine control switch
- Emergency stop switch
- Remote start switch
- Data link
- Prelubrication system
- Other inputs
When the programmable logic determines that it is necessary to crank the engine, the ECM supplies +Battery voltage to the relay for the starting motor. The ECM removes the voltage when the programmable crank terminate speed is reached or when a programmable cycle crank time has expired.
The engine must be equipped with an energize-to-run Gas Shutoff Valve (GSOV). The source of the voltage to the GSOV depends on the engine's configuration. The GSOV may be energized by the customer's equipment or by the engine's control system.
If the engine's control system controls the GSOV, the ECM supplies +Battery voltage to the GSOV whenever the programmable logic determines that fuel is required to operate the engine.
For more information on programmable parameters, see Troubleshooting, "Programming Parameters".
The ECM provides variable ignition timing that is sensitive to detonation.
Each cylinder has an ignition transformer that is located under the valve cover for the cylinder. To initiate combustion, the ECM sends a pulse of approximately 100 volts to the primary coil of each ignition transformer at the appropriate time and for the appropriate duration. The transformers step up the voltage in order to create a spark across the spark plug electrode.
Detonation sensors monitor the engine for excessive detonation. The engine has two detonation sensors. Each sensor monitors a cylinder bank. The sensors generate data on vibration that is processed by the ECM in order to determine detonation levels. If detonation reaches an unacceptable level, the ECM retards the ignition timing of the engine. If retarding the timing does not limit detonation to an acceptable level, the ECM shuts down the engine.
The ECM provides extensive diagnostics for the ignition system. The ECM also contains an input for ignition timing in order to allow operation with alternate fuels such as propane that require a timing offset.
The ECM maintains the desired engine speed by controlling the electronic actuator for the throttle. The actuator is located above the air inlet manifold.
The actuator is electrically controlled and electrically actuated. The ECM sends a throttle command to the actuator via the CAN data link. The actual throttle position can be determined by comparing a scribe mark on the throttle shaft with the increments on a protractor.
Desired engine speed is determined by the status of the idle/rated switch, the desired speed input (analog voltage or 4 to 20 mA), and parameters such as maximum engine high idle speed that are programmed into the ECM. Actual engine speed is detected via a signal from the speed/timing sensor. Parameters such as governor gain that controls the engine stability can be programmed with Caterpillar Electronic Technician (ET).
Engine Monitoring and Protection
The ECM monitors both the engine operation and the electronic control system.
Problems with engine operation such as low oil pressure produce an event code. The ECM can issue a warning or a shutdown for a low oil pressure event. This depends on the severity of the condition. For more information, refer to Troubleshooting, "Event Code List".
Problems with the electronic control system such as an open circuit produce a diagnostic code. For more information, refer to Troubleshooting, "Diagnostic Code List".
Optional Air/Fuel Ratio Control
This system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The ECM compensates for changes in the BTU of the fuel in order to maintain desired emission levels. The ECM provides control of the air/fuel mixture for maximum performance and for efficiency at low emission levels. The system is dependent on information from the following inputs:
- Status of various sensors
- Status of some output drivers in the ECM
- Control maps in the ECM
- Parameter settings that have been entered via Cat ET
There are two types of Air/Fuel Ratio Control that are available for these G3500 (A3) Engines:
The ECM compensates for changes in the concentration of oxygen that is in the exhaust in order to maintain desired emission levels. Illustration 1 is a diagram of the system's main components.
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| Illustration 1 | g01247129 |
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Diagram of the system for the air/fuel ratio control that is for the oxygen feedback | |
To accurately control the air/fuel ratio, the ECM depends on the following parameters that are programmed via the "Configuration" screen of Cat ET. For details on these parameters, refer to Systems Operation/Testing and Adjusting, "Electronic Control System Parameters".
- "Desired Oxygen At Full Load"
- "Oxygen Feedback Feature Enabled Status"
- "Air/Fuel Proportional Gain"
- "Air/Fuel Integral Gain"
- "Fuel Ratio"
- "Desired Fuel Valve Position Offset"
The air/fuel ratio is controlled whenever the air/fuel ratio control is enabled via the "Oxygen Feedback Enable Status" parameter.
The following steps describe the basic operation of the system:
- The ECM uses the following factors in order to determine the desired fuel flow rate:
- Desired engine speed
- Actual engine speed
- Calculated engine load
- The amount of oxygen in the exhaust
The ECM monitors the status of the oxygen sensor via a Pulse Width Modulated signal (PWM) in order to determine the amount of oxygen in the exhaust.
- The ECM determines the rate of fuel flow that is required in order to achieve the desired level of oxygen that is in the exhaust. The ECM develops a command signal for the fuel flow to the engine. The signal is sent to the electronic fuel metering valve via the CAN data link.
The ECM compensates for changes in the concentration of NOX and oxygen that is in the exhaust in order to maintain desired emission levels. Illustration 2 is a diagram of the system's main components.
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| Illustration 2 | g01389952 |
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Diagram of the system for the air/fuel ratio control that is for the NOX feedback | |
To accurately control the air/fuel ratio, the ECM depends on the following parameters that are programmed via the "Configuration" screen of Cat ET. For details on these parameters, refer to Systems Operation/Testing and Adjusting, "Electronic Control System Parameters".
- "Emissions Feedback Mode configuration"
- "Desired Engine Exhaust NOx Level Setting"
- "Air/Fuel Proportional Gain"
- "Air/Fuel Integral Gain"
- "Desired Fuel Valve Position"
The system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The ECM compensates for changes in the BTU of the fuel in order to maintain desired emission levels.
The air/fuel ratio is controlled whenever the air/fuel ratio control is enabled via the "Emissions Feedback Mode" configuration.
The following steps describe the basic operation:
- The ECM uses the following factors in order to determine the desired fuel flow rate:
- Desired engine speed
- Actual engine speed
- Calculated engine load
- The amount of NOX and of oxygen in the exhaust
The ECM monitors the status of the NOX sensor via the CAN data link in order to determine the amount of oxygen in the exhaust.
- The ECM determines the rate of fuel flow that is required in order to achieve the desired level of NOX and oxygen that is in the exhaust. The ECM develops a command signal for the fuel flow. The signal is sent to the electronic fuel metering valve via the CAN data link.
Optional Prelubrication and Post Lubrication
The prelubrication system consists of an oil pressure sensing switch and a prelubrication pump. The ECM controls the prelubrication pump in order to raise the oil pressure to a sufficient level prior to cranking the engine.
The strategy for post lubrication operates after shutdown. This ensures that the turbocharger has adequate lubrication during the engine deceleration after the fuel has been shut off. When the engine reaches 0 rpm, the output for the prelube pump will operate for three minutes.