it prevents an accumulation of amplitude efiect under the influ-
ence of periodic torques, which would otherwise tend to cause
synchronous deflection effects of marked magnitude.
Torque Diagrams for Different Types of Engine.
It is now proposed to consider a few of the more important cases
of the application of crank-effort or torque curves to examples
occurring in practice.
For the purposes of comparison, it will be more convenient to
assume that all the types of engine have the same sized cylinder,
the engine speed being constant in each case.
In the examples considered, the bore and stroke have been
taken as 3 and 4 inches respectively, and the engines to be running
at 1,000 revolutions per minute.
Further, a connecting rod crank ratio of 4 ( = n) has been assumed,
and the weight of the reciprocating parts to be 4 lbs.
A standard example of indicator diagram has been taken,
plotted out on a crank angle base, and corrected for inertia effects
in the manner previously explained.
The equivalent inertia pressures in lbs. per square inch have been
estimated to be 59 and 36 for the in- and out-centres respectively.
In each case the mean value of the torque for one complete



THE MECHANICS OF THE ENGINE



287



cycle of operations of a single cylinder or two crank revolutions
has been obtained from the mean height of the torque diagram,
and further, the ratio of the maximum to the mean torque is given
in each case.
Case I. — The single-cylinder type, as illustrated diagrammati-




FiG. 165a.-



360
Crank Angle.
-The Single Cylinder Engine Torque Curve.
cally in Figs. 165 and 165a, gives a torque diagram as illustrated in
the upper part of the same figure.
