The Cat Electronic System is a complete electronic control system for gas engines. The following benefits are the most significant advantages of the electronic system:
- Air/Fuel ratio control
- Extensive system diagnostics
- Precise control of engine operation
- Protection from detonation
- Timing control of individual cylinders
- Knock sensors
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| Illustration 1 | g06243501 |
| (1) Junction box | |
Most of the functions of the electronic system are provided by the Engine Control Module (ECM). The ECM is a sealed unit that is located inside a junction box (1) at the rear of the engine.
Five primary functions are supported by the ECM:
- Governing of the engine rpm
- Control of ignition
- Control of the air/fuel ratio
- Start/stop control
- Monitoring and protection of the engine
The ECM receives a signal from the speed/timing sensor. The ECM maintains the desired engine rpm through electrical control of the engine throttle.
Each cylinder has an ignition transformer that is located under the top of each valve cover. To initiate combustion in each cylinder, the ECM sends a pulse to the primary coil of the ignition transformer at the correct time. The time is based on firing order and engine speed. The transformer increases the voltage which creates a spark across the spark plug electrode.
The transformers are grounded through the valve cover. Use caution when a valve cover is removed.
Always disconnect the ignition harness from the transformer when a valve cover is removed.
An ignition harness connects each transformer to the ECM.
The ECM determines the desired volumetric flow rate for fuel. The determination is based on the components: actual engine speed, actual load, MAP, MAT, and internal maps. Next, the ECM sends information on the desired fuel flow to the fuel metering valve via the CAN data link. The ECM adjusts the signal to the fuel metering valve to maintain emissions. The process is repeated continuously during engine operation.
The ECM contains the logic and the inputs for controlling the starting and stopping of the engine. The logic for starting and stopping can be programmed by the customer. The ECM supplies positive "+" battery voltage to the starting motor relay and the gas shutoff valve.
The engine uses an energize-to-run system. The gas shutoff valve must remain energized to supply fuel to the engine. If power is removed from the gas shutoff valve, the fuel is shut off. The gas shutoff valve may be controlled by the customer.
Sensors are used to monitor engine operation. Wiring harnesses connect the sensors to the ECM. The ECM uses the information from the sensors to monitor the engine. The ECM also uses the information from the sensors to control the engine. The information is also used to generate event codes, and diagnostic codes. The codes can be read with a Cat Electronic Technician (ET).
Event - An event is a result of abnormal engine operation. If abnormal engine operation is detected, the ECM generates an event code. The ECM can generate an alarm, a shutdown, or a warning of an impending shutdown for abnormal engine operation. These conditions are some examples of events: high inlet air temperature, low oil pressure, and engine overspeed.
Diagnostic - A diagnostic code is a result of a problem with the operating system or with the monitoring system. The ECM uses sensors and internal circuitry to monitor the system components. If a problem develops in a component or a wiring harness, the control system will sense the problem. The control system will notify the operator by creating a diagnostic code. Some examples of conditions that activate diagnostics are a short in a circuit for a sensor, an open circuit, or a noisy signal.
Note: For detailed information on event codes and diagnostic codes, refer to Troubleshooting.
Sensors provide information to the engine ECM and EMCP. The information enables the ECM to control the engine as efficiently as possible over a wide range of operating conditions. The information is used for monitoring engine and gearbox operation and for protecting the engine and gearbox.
Refer to the document, Troubleshooting, UENR0515 for additional information on sensors and component locations.
Sensors are used to monitor gearbox operation. Wiring harnesses connect the sensors to EMCP Analog Input 1 and 2. The EMCP uses the information from the sensors to monitor the gearbox. The information is also used to generate event and diagnostics codes. The codes can be read with Cat Electronic Technician (ET).
Integrated Sensing Module (ISM)
The ISM monitors thermocouples that are at the exhaust port of each cylinder. Thermocouples are also mounted at the inlet and the outlet to the turbocharger. The temperatures are broadcast over J1939 for use with other modules.
The ISM also monitors detonation sensors which are located between every other cylinder. The detonation values are relayed to the ECM and can be seen over CAT ET. Event codes are generated for conditions where the detonation signal exceeds a level that is recoverable through ignition retardation (Least Severe) and when an engine shutdown is required (Most Severe).
The ISM calculates the average temperature for each bank. Event codes are generated if the following conditions occur:
- The temperature is higher than the limit that is programmed.
- The temperature of a cylinder deviates significantly from the average temperature for all the cylinders.