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| Illustration 1 | g02425242 |
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Engine mounted ECM junction box (front side engine view) | |
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| Illustration 2 | g02425303 |
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Location of the primary and secondary control modules (1) Primary ECM (2) Secondary ECM (3) Control assembly (diode box) | |
The electronic control system for this engine utilizes primary ECM (1) and secondary ECM (2). The primary ECM provides engine control under normal operating conditions. The secondary ECM provides a redundant function in the case that the primary ECM fails. Using circuit diodes, control assembly (3) provides isolation of the control circuits for each ECM during both modes of operation.
The ECM utilizes two connectors. The J1/P1 connector is a 70-pin connector, while the J2/P2 connector is a 120-pin connector. 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 engine operation for optimum performance with minimal emissions.
The ECM is the engine control computer for the engine 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
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 status information from the input devices for the engine. The ECM uses this information to calculate the correct output action that is needed to control engine operation. These output actions are based on calculations made on cumulative data from the following:
- Engine system components
- Software parameters
- Information related to desired operation
The ECM utilizes switch inputs, sensor inputs, and data link communications to provide input information from the engine system components.
The ECM provides the following output functions:
- Power supply control for related components
- Controller circuits for engine operation
- Communications ports for communication medium
The ECM utilizes the following outputs for engine control:
- Outputs used as power supplies
- Injector drivers (108 V outputs)
- High side ECM drivers (switch to battery circuits)
- Low side ECM drivers (switch to ground circuits)
- Data link communications to output command signals to other engine controllers
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.
The ECM uses two different communication protocols for data link communications:
- Cat Data Link
- CAN data link (SAE J1939)
These two types of data links are the main structure for communication between all of the controllers on the engine and on the machine.
The CAN data link is used for communications between the engine ECM and controllers and displays that are on the engine and application. The CAN data link may also be used for communications with Caterpillar Electronic Technician (ET).
Communications on the Cat Data Link utilize a Caterpillar proprietary language that is used for communications between Caterpillar proprietary controllers and displays. The Cat Data Link is also used for communications with Cat ET.
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 engine operation. The results are compared by the ECM to the desired state of engine 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.
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.