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| Illustration 1 | g01399035 |
Diagram of the governing system | |
The Electronic Control Module (ECM) continuously strives to achieve the engine speed that is desired for the operating condition.
The desired engine speed is determined by these factors:
Desired Speed Input - A signal of either 0 to 5 VDC or 4 to 20 mA can provide this input. The "Desired Speed Input Configuration" determines the input that is used by the ECM. This input can be provided by a potentiometer or a programmable logic controller.
Programmable Parameters - The Caterpillar Electronic Technician (ET) is used to program these parameters that affect the desired engine speed: "Low Idle Speed", "Minimum High Idle Speed" and "Maximum High Idle Speed". The programmable "Engine Accel. Rate" determines the rate of acceleration and of deceleration. The "Governor Type Setting" parameter can be set to "Droop" or to "Isochronous". Refer to Systems Operation/Testing and Adjusting, "Electronic Control System Parameters" for additional information on these parameters.
Idle/Rated Switch - The idle/rated switch is used to select low idle speed or actual high idle speed. One of the two speeds is selected by the position of the idle/rated switch and the current oil pressure.
- If the idle/rated switch is in the idle position, the ECM will always select the low idle speed.
- If the engine oil pressure is less than the setpoint for the low oil pressure alarm level, the ECM will always select the low idle speed.
- If the engine oil pressure is greater than the setpoint for the low oil pressure alarm level and the idle/rated switch is in the rated position, the ECM will select the actual high idle speed.
The actual engine speed is detected via a signal from the engine speed/timing sensor. The ECM compares the actual engine speed to the desired engine speed. The ECM functions as an electronic governor in order to develop a throttle command.
The electronic governor uses gains in order to provide stable operation.
The governor's throttle command is a percent of the maximum position of the throttle. The throttle command is sent to the throttle actuator. The throttle actuator is mechanically connected to the throttle body.
The value of the throttle command can be viewed on Cat ET.