Understanding Governor Sensitivity and Stability

A governor is a device used to regulate the mean speed of an engine when there are variations in the load. It does this by controlling the fuel supply to the engine. Two important characteristics of a governor are sensitivity and stability.

What is Governor Sensitivity?

Sensitivity in a governor refers to its ability to respond quickly to small changes in speed. A highly sensitive governor will have a large movement of the sleeve for a small percentage change in speed.

• High sensitivity means a large change in sleeve position for a small change in engine speed.
• Mathematically, sensitivity is often related to the range of speed change needed to move the sleeve from one extreme position to the other.
• A sensitive governor can detect and react to even slight speed fluctuations.

What is Governor Stability?

Stability in a governor refers to its ability to maintain a steady speed without excessive oscillations (hunting) or fluctuations. A stable governor will bring the engine speed to the required value and maintain it there under varying load conditions, without continuous up-and-down variations in speed.

• A stable governor prevents hunting, which is the oscillation of the sleeve and engine speed above and below the mean speed.
• If a governor is unstable, it might overcorrect speed changes, leading to continuous fluctuations.

Relationship Between Sensitivity and Stability

There is an important relationship between the sensitivity and stability of a governor. Generally, a highly sensitive governor tends to be less stable, and a stable governor tends to be less sensitive.

• If a governor is too sensitive, a very small change in speed causes a large movement of the sleeve, leading to a large change in fuel supply. This large change in fuel supply might cause the engine speed to overshoot the desired value.
• Once the speed overshoots, the governor acts again, but might again overcorrect, leading to oscillations or hunting.
• This hunting is a sign of instability. Therefore, high sensitivity can lead to instability.
• Conversely, if a governor is not very sensitive (low sensitivity), it might not respond quickly or sufficiently to small speed changes, making it more stable (less prone to hunting) but less precise in maintaining a constant speed under minor load variations.

Thus, sensitivity and stability are inversely related. Increasing the sensitivity of a governor can decrease its stability, and improving stability might require reducing sensitivity to some extent.

In summary:

High Sensitivity → Tendency towards Instability (Hunting)

Low Sensitivity → Tendency towards Stability (Less Hunting)

The design of a good governor involves finding a balance between achieving acceptable sensitivity for speed regulation and ensuring sufficient stability to prevent hunting.