IMPROVEMENTS IN ELLIPTIC AND SEMI-ELLIPTIC SPRINGS FOR VEHICLES AND FOR OTHER USES."
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by Philip Middleton Justice at the Office
of the Commissioners of Patents on the 3rd August 1881. A communication
from abroad by William Davison, of Hoboken, in the County of Hudson and
State of New Jersey, United States of America.
"
PHILIP MIDDLETON JUSTICE, of 14, Southampton Buildings, in the County of
Middlesex, Patent Agent. 'IMPROVEMENTS IN ELLIPTIC AND SEMI-ELLIPTIC
SPRINGS FOR VEHICLES AND FOR OTHER USES." A communication from abroad
by William Davison, of Hoboken, in the County of Hudson and State of New
Jersey, United States of America.
This Invention relates to vehicle springs of the elliptic or the half elliptic form,
the plate or plates of which are concavo-convex in cross section, and so disposed or
arranged in the spring and with reference to their connection with the vehicle or
other object with which the springs are to be used, that the edges of the plate are
subject to compression only in service, while the tension is expended wholly on
the web between said edges or a portion of it, said form and arrangement having
been found in practice to add very greatly to the power or capacity of the spring
as compared with that in which the edges of the plates of such form sustain the
tension, because the cracks and fissures which exist in the edges of the plates,
more or less, no matter how well they may be made, are in this case not only
relieved of strain but pressed so as to close or tend to close, while on the web on
which the tension is borne there are no such cracks and fissures to favour the
breaking of the metal, or if any they are much less in degree.
The first part of the Invention consists in making the plates of such springs of
greater thickness in the said middle or intervening web which sustains the tension
than the said edges whereon the compression is sustained, and also (when two or
more plates are used in the spring) inaking both sides upon one and the same
radius and consequently the same curvature, the objects being first to so dispose
the metal that the larger portion is given to the part where the tension is sustained,
and the lesser to the parts subject to compression in proportion to their respective
requirements, and, second, to enable the plates to bear alike upon each other
throughout their whole area, thus in the first place making springs of greater
power from a given quantity of metal, and in the second place rendering them
more durable and also increasing their sustaining power. The second part of the
Invention consists in making the studs that are employed for keeping the respective
plates in position to project from the convex side of the plates, the indentations in
the plates being in the concave side, the studs thus conforming to the convexity of

page_text: the plates and the indentations to the concavity, and preserving the continuity of
both surfaces better than if the studs were struck up from the other side, in which
case the convex surface would be broken by the indentations, and abrupt angles
favourable to cracks would be formed. The third part of the Invention consists of
making the outside or short plate of a spring composed of two or more plates
convex on the inside, or the side bearing on the other plate, and flat on the top or
outside that is to fit the band, or be connected to or bear against the carriage or
other object, and in the case of springs composed only of one plate making a
short portion flat on the top at the middle for the same purpose, the underside
being convex as before.
The plates of the springs being made in concavo convex form and arranged with
the convex sides towards the chord of the arc formed by the longitudial bend, it is
plain that the effect of the load on the springs is to produce tension on the middle
web and compression on the edges.
The edges then where the cracks and fissures exist that favour breaking under
tension need not be as thick as they would otherwise require to be if arranged the
reverse way and subject to tension, hence I propose to make such plates thinner at
and near the edges, and thicker at and towards the middle where the tension
comes, and thus so arrange the metal that for equal quantities I secure much
greater power than when the plates are made of uniform thickness, as commonly
done, or of greater thickness at the edges, as has also been done, for as the effect of
compression is much less destructive to the metal than that of tension, it follows
of course that less metal will serve in the place of compression, which allows more
in the place of tension where more is demanded.
$
By this arrangement I secure the greatest power of which the metal is capable,
and thus economise both in the amount of metal used and in labour and power of
making as well, for the lighter the spring the less the cost of making, and there is
also an economy in use too in vehicles in which lightness is important.
The variation in the thickness or taper from the middle, to the edges may be as
preferred or found best in practice, particularly for springs of one plate only, but
for springs of two or more plates, the preferred arrangement is that which is. due
to tlie curvatures of both sides of the plates, being formed. on one and the same
radius and thus being alike, the preferred curvature however being that in which
the chord of the concave side of the plate equals the radius of the circle, but it may
be varied at will. By thus curving both sides of the plates upon one and the
same radius, they bear alike all over one another, and thus sustain each other to
the best advantage, and-also-wear-uniformly,-and-thus become more lasting. The
concavities or indentations are formed in the concave side in conformity therewith,
and the resulting studs are thrust up on the convex side also in conformity thereto,
as before mentioned, thus favouring the strength of the plates instead of detracting
from them, as would be the case if formed reversely on said plates.
When springs of two or more plates are used, a band is employed which also has
or may have a cavity to receive the stud of the bottom plate, which band may be
so expanded by heat when applied as to allow the plates to enter with the stud
and then shrink tight in cooling. The short.or top plate of the compound spring
has its upper side made flat as before described to fit the band or the carriage or
other object to which it is to be attached in case the band embraces them both, the
under side being convex the same as the others, and the single plate spring has a
corresponding flat portion at the middle of the top when desired for the same
purpose, the place of the concavity being made full in the shaping of the
plate.