Los Angeles herald. [microfilm reel] (Los Angeles [Calif.]) 1900-1911, 1910-07-10
ON CARS DRIVER
DEPENDS ITS LIFE
Designers Make Provision in the
Plans for Everything but
Care of Chauffeur
SLOW SPEED lessons RISKS
Succession of JoItS Often Causes
Fractures Which Show
Up at Later Date
SLOW SPEED lessons RISKS
BY DIR. CHARLES w. SNYDER,
Local Agent AIiddIeby Cars

In designing the parts of an automo-
bile one of the chief things to be COM
sidered is the strength of the materials.
Let us take a gas engine as an in
stance. The cylinders are subject to a
tension of about 300 pounds per square
inch at the time of each ordinary ex-
plosion, but under exceptional in
stances this might be increased to sixty
pounds per square inch, so we must
base our calculations on the latter.
Good gray cast iron has an ultimate
tensile strength of about 10000 pounds
per square inch. That is, piece one
inch on all sides will stand stress of
10000 pounds before breaking.
Calculating from this, our cylinder
walls need be only 1-32 of an inch thick
to stand the explosive pressure-but
Cast iron is never perfect, and there
would be spots which would not stand
the pressure. Again, if the iron was so
thin Coast iron being very brittle)
slight blow would fracture the cylinder.
Therefore when the cylinder is de-
signed these things must be taken into
consideration. The necessary thickness
is determined, and this thickness null
tiplied by what is known as "the factor
of safety" which in cast iron is usually
considered as being from seven to nine,
therefore your cylinder walls are from
seven to nine times as thick as is abso-
lutely required.
In the same manner the connecting
rods are calculated, though they are
subject to compression istead of ten
sion. The compression strength of the
material is known, and the necessary
size of the connecting rod determined
so that it will stand the full power of
the explosion without bending. This
pressure in a 4x4-inch cylinder, with q
full throttle, is from two to two and a
L. OF oyn1nsinY1
ON CRANK SHAFT
On the crank shaft there is another
series of stresses. Tensile strength and
strength of compression need hardly be
considered, because if the shaft will
stand the stresses of torsion and f1exure
it can take care of any other stress
which may be applied. The bending
moment is determined, i. e., the forces
tending to twist" the shaft. and which
consist of the power applied by the
connecting rod at each point in the
crank circle and the resistance Of
fered by the inertia of the shaft, fly
wheel, car, ETC., against this turning
effect. These forces must be calculated
and the proper factor of safety allowed.
usually about ten. Then all the forces
which tend to bend the shaft must be
considered and allowed for
In a like manner the whole car must
be gone over and calculated to nicely,
because you don't want an automobile
of excessive weight, and on the other
hand you insist that it must "stand
up" and to secure both of these con-
ditions all the weight must be removed
that is possible without sacrificing
strength.
If any material be continually sub
iected to constant stresses which are
near it's limit of ultimate strength. u
point arrives where it can no longer
stand these stresses, and it necessarily
yields, and finally breaks. In calculat-
ing the strength Of materials for auto
biles, there is an unknown factor al
ways appearing, l. e., the driver, he is
purely a guess, but most important in
the life of the car.
The designer calculated his details
as near as he could, assuming the
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