Speed Oscillation (Governor Hunting)
Hunting is the engine speed continuously going up and down even at a constant load: the governor cannot hold the fuel quantity at a stable point and swings between below and above the target. It is heard as a regular rise and fall in sound, and frequency on a generator or flow on a pump fluctuates accordingly.
At the root of the oscillation there is usually one of three things:
- Mechanical: binding in the throttle linkage joint, slack or friction in the cable; the controller gives a command, the mechanics respond with a delay, then move too far.
- Control setting: the gain has been set too high. The tuning rule is to sharpen it until oscillation begins and then back it off a little.
- Signal: noisy or intermittent pulses from the speed sensor, or fluctuation of the supply voltage.
The first step in diagnosis is to rule out the mechanics: stop the engine and move the throttle lever by hand from idle to full throttle; if you feel binding or play, eliminate that before adjusting the control. The GS740-3P's soft ramp exists precisely to reduce this risk; it applies the position command as a ramp instead of a step, so no shock or overshoot occurs in the mechanics.
Context in which this term is used: Electronic speed and throttle control on a diesel engine