73-18
76-71
79-11
80-60



THE MECHANICS OF THE ENGINE



269



From these results it will be evident that the greater the obliquity
of the connecting rod, the earher in the stroke is the velocity of
the piston a maximum ; and the longer the connecting rod in rela-
tion to the crank, the nearer to its mid-position does the maximum
velocity of the piston occur — that is, the motion of the piston
approaches a simple harmonic one.
In an exactly similar manner the velocity at any point of the
stroke of the piston having an ofiset or " desaxe " cylinder can be
obtained.
It is only necessary to differentiate the expression for the
piston displacement in order to arrive at an expression for the
piston's velocity at any crank angle.
The Graphical Method for Piston Velocity.
With the notation employed in Fig. 154, let Vj, represent the
piston's velocity at any point P, and V„ the uniform crank pin
linear velocity.
Vo










c




F^






^j-^


--7


N^


\


P_^


■-r






^


\


Vp








)


1



Fig. 154.
It will be evident that at the crank pin C its direction of motion
will be tangential to the crank pin circle.
Further, the resolute of the piston's velocity along the connect-
ing rod must be equal to the resolute of the crank pin's velocity
along this rod, since it is a rigid mass.
