Some installations require that engine speed
CONTROL OF ENGINE SPEED AND POWER
remain constant from a no-load to a full-load condition.
In a gasoline engine, speed and output are
Governors that function to maintain a constant speed,
controlled by regulating the amount of air flowing into
regardless of load, are called "constant-speed"
the cylinders of the engine. The carburetor is designed
governors. Governors that maintain any desired engine
to control the airflow. The amount of air and its
speed between idle and maximum speeds are classified
velocity, in turn, control the quantity of fuel with
as "variable-speed" governors. Speed-control devices
which the air is mixed before the mixture enters the
designed to keep an engine from exceeding a specified
cylinders.
maximum speed and from dropping below a specified
minimum speed are classified as "speed-limiting"
The throttle valve controls the quantity and velocity
governors. (In some cases, speed-limiting governors
of air flowing to the cylinders. By operating the valve,
function only to limit maximum speed.) Some engine
you admit more or less air to the engine, and the
installations require a control device that limits the load
carburetor automatically supplies the gasoline
that the engine will handle at various speeds. Such
necessary to maintain the correct fuel-air ratio.
devices are called "load-limiting" governors.
Regulation of fuel or air supply by manual throttle
control is adequate when engine speed and output re-
A governor may also be designed to perform two or
quirements remain constant. However, the re-
more of these functions. In this case, the operating
quirements of most engines used by the Navy vary
mechanisms that perform the various functions are
because of fluctuating loads. The conditions under
combined in a single unit.
which aviation support equipment engines and the
SPRING-LOADED CENTRIFUGAL
engine of a generating unit operate are examples of
GOVERNORS
fluctuating loads. Tow tractors, weapon loaders, and
forklifts alternate between heavy loads and no loads. In
In most of the governors installed on diesel engines
the case of a generating unit, the demands for electricity
used by the Navy, the centrifugal force of rotating
are variable. Manual throttle control is not adequate to
weights (flyballs) and the tension of a helical coil
hold engine speed reasonably constant during such
spring (or springs) are used in governor operation. On
fluctuations in load. For this reason, a speed control
this basis, most of the governors used on diesel en-
device, or governor, is provided to prevent the engine
gines are generally called "spring-loaded centrifugal
from overspeeding and to allow the engine to meet
governors."
changing load conditions.
In spring-loaded centrifugal governors, two forces
SPEED-REGULATING GOVERNORS FOR
oppose each other. One of these forces is the tension of
DIESEL ENGINES
a spring (or springs), which may be varied either by an
adjusting device or by movement of the manual throttle.
The type of load and the degree of control desired
The other force is produced by the engine. Weights
determine the kind of governor to be used on a diesel
attached to the governor's drive shaft are rotated, and a
engine. Since all governors used on diesel engines
centrifugal force is created when the shaft is driven by
control engine speed through the regulation of the
the engine. The centrifugal force varies directly with
quantity of fuel delivered to the cylinders, these
the speed of the engine.
governors may be classified under the general heading
The tension of the spring(s) is transmitted to the
of speed-regulating governors. Governors used on
fuel system through a connecting linkage, and tends to
diesel engines may also be classified in various other
increase the amount of fuel delivered to the cylinders.
ways, such as the function or functions performed, the
On the other hand, the centrifugal force of the rotating
forces used in operation, and the means by which the
weights, through connecting linkage, tends to reduce
governor operates the fuel-control mechanism.
the quantity of fuel injected. When the two opposing
Governors are designed to control engine speed
forces are equal, or balanced, the speed of the engine
under varying load conditions. Since the type of load
remains constant.
and the degree of control desired vary from one type of
To illustrate how the centrifugal governor works,
installation to another, the primary function of a
let us assume that an engine operates under load, and
governor depends upon the requirements of a particular
that the opposing forces in the governor are balanced,
installation.
so that the engine speed is constant. If the load is
4-23
