UNION 9S7754 - Caterpillar

Introduction
The Electronic Control Module (ECM) controls most of the functions of the engine. The ECM is an environmentally sealed unit that is mounted in a terminal box on the engine. The ECM monitors various inputs from sensors in order to activate relays, solenoids, etc at the appropriate levels. The ECM supports the following five primary functions:
Engine speed governing
Air/fuel ratio control
Start/stop sequencing
Engine monitoring and protection
Ignition controlAn auxiliary sensing module is optional. The auxiliary sensing module improves the genset's ability to maintain a consistent level of frequency and voltage.Engine Speed Governing
The ECM maintains the desired engine speed by controlling the actuator for the throttle. The actuator is located at the inlet to the aftercooler. The actuator is electrically controlled and electrically actuated.The ECM issues a throttle command that represents a percent of the level of electrical current. The output can be viewed on the Caterpillar Electronic Technician (ET).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 software. Actual engine speed is detected via a signal from the speed/timing sensor. Parameters such as governor gain can be programmed with Cat ET.Air/Fuel Ratio Control
The ECM provides control of the air/fuel mixture for performance and for efficiency at low emission levels. The system consists of an electronic fuel metering valve, output drivers in the ECM, and maps in the ECM. The control compensates for changes in the BTU of the fuel in order to maintain desired emission levels.The following steps describe the basic operation:
The ECM determines the desired flow rates for the air and for the fuel. The flow rates are determined by these factors:
Desired engine speed
Actual engine speed
Calculated engine load
The command for the flow of the fuel is sent to the electronic fuel metering valve via the CAN data link. This process is repeated continuously during engine operation.Start/Stop Sequencing
The ECM contains the logic and the outputs for control of starting and of shutdown. The customer programmable logic responds to signals from the following components: engine control, emergency stop switch, remote start switch, data link and 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 type of 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, refer to Troubleshooting, "Programming Parameters".Engine Monitoring and Protection
The ECM monitors both the engine operation and the electronic