Governors

1. Mechanism of machinery
Chapter 7
Governors
Pr.by. Mr. TESFAYE MENGESHA
3/15/2023 1

2. 7.1 Introduction
The function of a governor is to regulate the mean speed of an engine, when there are
variations in the load e.g., when the load on an engine increase, its speed decreases,
therefore it becomes necessary to increase the supply of working fluid. On the other
hand, when the load on the engine decreases, its speed increases and thus less
working fluid is required.
The governor automatically controls the supply of working fluid to the engine with
the varying load conditions and keeps the mean speed within certain limits.

3. 7.2 Classification of Governors
The governors may, broadly, be classified depending on the controlling force acting on
the governor as
1. Centrifugal governors, and 2. Inertia governors.
The centrifugal governors, may further be classified as follows:

4. 7.2.1 Centrifugal Governors
The centrifugal governors are based on the balancing
of centrifugal force on the rotating balls by an equal
and opposite radial force, known as the controlling
force. It consists of two balls of equal mass, which are
attached to the arms as shown in Fig. below. These
balls are known as governor balls or fly balls. The
balls revolve with a spindle, which is driven by the
engine through bevel gears. The upper ends of the
arms are pivoted to the spindle, so that the balls may
rise up or fall down as they revolve about the vertical
axis. The arms are connected by the links to a sleeve,
which is keyed to the spindle. This sleeve revolves
with the spindle; but can slide up and down. The balls
and the sleeve rises when the spindle speed increases,
and falls when the speed decreases. In order to limit
the travel of the sleeve in upward and downward
directions, two stops S, S are provided on the spindle.
The sleeve is connected by a bell crank lever to a
throttle valve. The supply of the working fluid
decreases when the sleeve rises and increases when it
falls.

5. 7.2.2 Governor characteristics
The characteristics that are related to the proper functioning of a governor are stability and
sensitivity. These characteristics affect the controlling force of the governor.
Controlling Force of governor
The controlling force in centrifugal governors is the equivalent inward radial force that
controls ball movement. The controlling force, which is due to sleeve weight, spring force,
etc., is the constraining force acting on the balls thereby controlling ball movement. The
controlling force depends on the horizontal radial position of the balls and it may be
expressed as
F =f(r)
• Neglecting the effect of friction and the inertia forces of the links, the centripetal force
acting on the ball is
𝐹𝑐 = 𝑚𝑟𝜔2

6. Stability of governor
A governor is said to be stable when for every speed within the working range there is a definite
configuration i.e. there is only one radius of rotation of the governor balls at which the governor is in
equilibrium. For a stable governor, if the equilibrium speed increases, the radius of governor balls must also
increase. A governor is said to be unstable, if the radius of rotation decreases as the speed increases.
Sensitiveness of governor
Consider two governors A and B running at the same speed. When this speed increases or decreases by a
certain amount, the lift of the sleeve of governor A is greater than the lift of the sleeve of governor B. It is
then said that the governor A is more sensitive than the governor B. Sensitivity of a governor is defined as
the change in level of the revolving balls corresponding to a change of speed. For maximum and minimum
governor speeds, 𝜔1 and 𝜔2, respectively, the coefficient of sensitivity of a governor is defined as

7. Isochronous Governors
A governor is said to be isochronous when it is infinitely sensitive. This condition is obtained
when 𝜔1 = 𝜔2. For this case, the controlling force curve becomes a straight-line coinciding with
the centripetal force.
Power of a Governor
Power of a governor is the work done at the sleeve for a given change in speed. When the speed
of the governor rises from the minimum to its maximum position, the work the governor can do
against the external forces is the capacity or power of the governor.
𝑃𝑜𝑤𝑒𝑟 = 𝑡𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦
Or
𝑃𝑜𝑤𝑒𝑟 = 𝑚𝑒𝑎𝑛 𝑒𝑓𝑓𝑜𝑟𝑡 × 𝑠𝑙𝑒𝑒𝑣𝑒 𝑚𝑜𝑣𝑒𝑚𝑒𝑛𝑡

8. 7.3 The Porter Governor
The Porter governor is a dead weight governor and is illustrated in Fig. below. As the speed
of the shaft increases, the balls move outward raising the sleeve height, and vice versa. The
controlling load is attached to the sleeve.
Consider the forces acting on one-half of the governor as
shown on figure
Again, considering the equilibrium of the forces acting
on B. The point B is in equilibrium under the action of
the following forces,
(i) The weight of ball (w = m.g),
(ii) The centrifugal force (FC),
(iii) The tension in the arm (T1), and
(iv) The tension in the link (T2).