Test: Governors - 3 - Mechanical Engineering MCQ

A Governor is said to be sensitive when it readily responds to a small change of speed. The movement of the sleeve for a fractional change of speed is measure of sensitivity.

Friction at the sleeve makes the governor less sensitive.

The effort of a governor is the mean force exerted at the sleeve for a given percentage change of speed.

For stable governor
F = Ar - B
and F = mrω²
∴ 

When governor is running at constant speed, then the net force acting of sleeve is zero.

Sensitiveness of a governor is a desirable quality. However, if a governor is too sensitive, it may fluctuate continuously above and below the mean position, it is called hunting of governor.

For isochronous governor
f = ar
Hence plot will be

Controlling force curve is plotted between controlling force at y-axis and radius of rotation at x-axis.

where, h = height of governor
N = RPM

The controlling force curve of a spring controlled governor is straight line and thus can be expressed as
f = ar+ b
when f = 1600 N, r = 400 mm
when f = 800 N, r = 240 mm
1600 = a(0.4) + b ...(i)
800 = a(0.24) + b ...(ii)
By solving (i) and (ii) we get
a = 5000 N/m
b = -400 N

To make the governor isochronous, the controlling force line must pass through the origin. This is possible only if the initial tension is increased by 400 N.