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| Illustration 1 | g01913607 |
Typical view of the ECM (1) J1/P1 ECM connector (2) J2/P2 ECM connector | |
The ECM has two connectors. The J1/P1 connector (1) and the J2/P2 connector (2) are 64-pin connectors. Each pin provides a connection point for a signal interface for the ECM.
Overview of the Electronic Control System
The electronic control system is designed to control the engine operation for optimum performance with minimal emissions.
The ECM is the engine control computer for the electronic control system. The ECM provides the capacity for the input/output functions, the control functions, the data link communications, and the computational functionality for the system. This functionality is detailed below:
Input/Output Functions
The ECM relies on several different types of input devices in order to gather information that is related to the current state of engine operation. The ECM receives the status information from the input devices. The information is used to calculate the correct output action that is needed in order to control engine operation. These output actions are based on calculations that are made on cumulative data from other system components, software parameters, and information. The actions taken by the ECM are related to desired operation. The ECM utilizes switch inputs, sensor inputs, and data link communications to provide input information from the engine components.
The ECM provides the following output functions:
- Power supply control for related components
- Controller circuits for engine operation
- Communications ports for the communication medium
The ECM utilizes outputs as power supplies, high side ECM drivers (switch to battery circuits), and low side ECM drivers (switch to ground circuits). the ECM also utilizes data link communications to output command signals to other engine controllers.
Control Functions
Control functions are typically commands that are derived internally to the ECM circuitry. Control functions are used in order to calculate the necessary effect on the signal status for the output circuits that control the engine operation. The ECM utilizes the output drivers and data link communications to implement control over engine operation.
Data Link Communications
The ECM utilizes the CAN data link exclusively for communications on this engine. This data link adheres to SAE J1939 communication protocols for all data link communications.
The CAN data link is used for communications between the ECM, controllers, and displays. The CAN data link is also used for communications with an electronic service tool.
Computational Functionality
The computational functionality of the ECM is dedicated to all aspects of engine operation and engine monitoring. The ECM is continuously evaluating the current state of operation. The results are compared by the ECM to the desired state of operation. The ECM evaluates the difference between these two states in order to calculate the necessary control command signals. The ECM then modifies output signals in order to bring the current state of operation closer to the desired state of operation. The ECM also compares the current state of operation to an acceptable range of operation. If the status of any parameter is not within the acceptable range of operation, the ECM communicates the adverse condition to the operator.
Emissions Control System
The G3306B Engine is designed to operate within regulated emissions levels under all engine operating conditions. The electronic control system provides for monitoring and control of the engine emissions levels.
Note: From the prospective of air/fuel control, the carburetor on the engine is used to mix the inlet air with a metered gas quantity. The load control valve for the carburetor must be adjusted to the full open (fully rich) position.
The fuel actuator is used to control the air/fuel ratio by controlling the amount of fuel that is mixed with the air entering the carburetor. Two oxygen sensors are mounted in the engine exhaust piping in order that the ECM can continuously monitor emissions levels. A throttle actuator is utilized by the ECM to control engine speed.
Note: The correct regulator output gas pressure must be established prior to operating the engine. Refer to Testing and Adjusting, "Gas Pressure - Check and Adjust" for information relating to the differential pressure setting for the correct air/fuel ratio. Correctly setting the gas pressure regulator for the engine allows for optimum engine start-up and stable engine operation with no engine load.
Closed Loop Fuel Control
Emissions control is provided by continuously monitoring engine exhaust and adjusting the air/fuel ratio. This control strategy is called a closed loop control system. In this system, the ECM utilizes a feedback loop to determine air/fuel ratio. The ECM monitors the exhaust oxygen sensors, the exhaust temperature sensors, and other engine operating conditions to determine the current emissions. The ECM then uses this information to calculate a desired fuel valve position in order to adjust or maintain the emission levels. If the ECM is unable to establish an acceptable level of emissions for the engine, a diagnostic trouble code is activated. If the condition is severe, the engine may be shut down.
Control System Components
The following control system components provide for monitoring and control of engine emissions:
Electronic Control Module (ECM) - The ECM monitors engine sensors, compares data, and adjusts the actuator valve signals in order to maintain engine emissions. Sensor input data is collected used to compare current operating conditions to the desired operating conditions. Output control for the various actuators and ignition transformers is initiated in order to maintain the desired emissions level.
Oxygen Level Sensors - The oxygen level sensors are monitored by the ECM in order to determine the emissions output of the engine and catalytic convertor performance. The ECM uses the data that is collected from these sensors to help calculate air/fuel ratio control and determine desired control strategy. The ECM also uses the oxygen sensors to monitor the performance of the catalytic convertor.
Fuel Valve Actuator - The fuel valve actuator is used to control the amount of fuel that is allowed to mix with the inlet air. The fuel valve actuator operates a mechanical butterfly valve in the fuel piping to the engine. As the fuel actuator reacts to the control signal from the ECM, the butterfly valve is adjusted to modify fuel delivery to the engine. The air/fuel ratio for the engine is directly proportional to fuel valve adjustment.
Catalytic Convertor - The catalytic converter utilizes a chemical reaction to convert emissions that are harmful to the environment to less harmful compounds. The catalyst converts Nitrogen Oxide (NOX), Carbon Monoxide (CO), and Hydrocarbons (CXHY) in the exhaust gasses into less harmful compounds. The exhaust emissions are converted to Nitrogen (N2), Carbon Dioxide (CO2), and Water ((H2O)). The ECM also monitors the temperature of the exhaust gasses at the inlet and outlet of the catalytic convertor.
Open Loop Fuel Control
Open loop mode is initiated by the ECM during a failure of one of the oxygen sensors. In this mode, the fuel position based on a fuel map that is stored in the ECM. A diagnostic trouble code is generated for this mode of operation.
Emissions System Calibration
As the oxygen sensor ages, the performance of the sensing element degrades. Periodically, Caterpillar Electronic Technician (ET) must be used to calibrate these sensors. Refer to Operation and Maintenance, "Carburetor Air/Fuel Ratio - Check/Adjust" for service interval information. Refer to Testing and Adjusting, "Air/Fuel Ratio Control - Adjust" for information related to adjusting the air/fuel ratio using Cat ET.
ECM Software
The ECM software is typically called a flash file. The flash file is a data file that is installed into the ECM. This data file provides the ECM with the software and the data that is needed to run the engine. Occasional updates to the flash file are provided by Caterpillar. The new software files can be downloaded from the Service Information System (SIS) web site. Use Cat ET to download the flash file to the ECM. Refer to Testing and Adjusting, "ECM Software - Install" for details.