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| Illustration 1 | g01244910 |
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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, a load sharing unit, 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 optional. If the idle/rated switch is used, the engine speed can also be affected by the engine 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 pressure warning, the ECM will always select the low idle speed.
- If the engine oil pressure is greater than the setpoint for the low pressure warning and the idle/rated switch is in the rated position, the ECM will select the rated 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. On generator set engines, two sets of gains are available: Primary and Auxiliary. On industrial engines, only the Primary set of gains are available. On generator set engines, the ECM uses the value of the "Grid Status" parameter in order to determine the set of gains that is used. If the "Grid Status" is OFF, the ECM uses the gains for the primary governor. If the "Grid Status" is ON, the ECM uses the gains for the auxiliary governor.
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 engine uses a throttle actuator that is electrically actuated. The throttle actuator is mechanically connected to the throttle body.
The value of the throttle command can be viewed on Cat ET, and on the Advisor monitor display. The actual position of the throttle can be viewed on a mechanical pointer that is built into the mechanism of the throttle.