Improvements in Sprocket-wheels.
Year: 1893

page_text: ate of Application, 5th Sept., 1893-Accepted, 28th Oct., 1893
Improvements in Sprocket-wheels.
A communication from abroad by JOSIAH QUINCY, Gentleman, of 13, School
Street, Boston, Massachusetts, United States of America.
I, WILLIAM LLOYD WISE of No. 46 Lincoln's Inn Fields, in the County of
London, Consulting Engineer and Patent Agent, do hereby declare the nature of
this invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
This invention relates to an improvement in sprocket-wheels, and has in view the
provision of a sprocket-wheel which will bring about a more efficient transmission
of power, and consequent increase of speed with a given application of power.
In an ordinary sprocket-wheel having rigid teeth, the teeth are spaced the same
distance apart as the corresponding bearing-points of the chain, and in action the
chain is in operative engagement with a plurality of teeth of the wheel. The effect
of such engagement of the chain with the teeth of the wheel is to produce a very
great strain on the bearings of the wheel and a large amount of friction in
consequence.
It is obvious that the transmission of power is most effectively accomplished
through the engagement of the chain with a single tooth while it is substantially in
a diametrical line of the wheel which is at right angles to the stretch of chain
extending tangentially from the wheel. Obviously, if the friction on the bearings
before mentioned is overcome, the same power can be applied more effectively. It
is therefore the chief object of my invention to so construct a sprocket-wheel that
in action only that tooth which is substantially in a diametrical line of the wheel at
right angles to the stretch of chain shall be in operative engagement with the chain,
the remaining teeth being allowed limited play in the links of the chain.
To this end, the invention may he said to consist essentially in a sprocket-wheel
having pivoted teeth, free to recede from a position of operative engagement with
the chain, and spaced in closer proximity than the corresponding engaging points
of the chain.
The invention also consists in certain features of construction and arrangement
of parts to be fully described hereinafter and pointed out in the claims.
+
The accompanying drawings illustrate a construction by which the invention may
be carried out.
Figure 1 shows a side elevation of a sprocket-wheel constructed in accordance
with my invention.
Figure 2 shows one side of the wheel removed and the chain partly in section.
Figure 3 shows a cross-section of the wheel.
The same letters of reference indicate the same parts in all the figures.
In the construction illustrated in the drawings, the circular body-portion or what
may be termed the disc of the wheel is composed of a pair of annular plates a
and a', of exactly the same size, so that, when their centres are coincident, their
peripheries a a³ are flush. Each of the plates a and a¹ is provided on one side with
a series of equidistant recesses b at its periphery. The two plates are placed
together, with the recesses coinciding, and they form shoulders b¹ which are
approximately radial with respect to the wheel.
Each tooth of the wheel is a separate piece, and its engaging portion c, which
projects from the periphery of the wheel-disc, has much the same shape as the tooth
of an ordinary sprocket-wheel. A tooth has position in each of the spaces which
are formed by the recesses b, and is pivoted at its inner end, at such a point that it
may squarely abut the shoulder 6' at the end of the space in which it is confined,

page_text: and hence, when abutting this shoulder, its end is projected as far as possible from
the centre of the wheel.
The position of operative engagement of a tooth of the wheel is that in which it
abuts the radial shoulder at the end of the space in which said tooth is confined.
The teeth are spaced nearer together than the corresponding bearing-points of the
chain; that is, when the teeth are in their operative position, bearing against the
radial shoulders, their points of engagement with the chain are nearer together than
the corresponding engaging points of the chain. This is best illustrated in Figure 2,
where the chain is represented as driving the sprocket-wheel.
The chain is of ordinary construction, and consists of blocks d, connected by
links d', so as to have a space between each two blocks with a link d' at each side
thereof.
It will be observed that the top tooth is abutting the shoulder 6' at the forward
end of the space in which said tooth is confined, and that one of the blocks d of the
chain is bearing against said tooth toward the said shoulder. It will also be
observed that this tooth is substantially in a diametrical line at right angles to the
tangential stretch of the chain, and hence the most direct and effective transmission
of power from the chain to the wheel is secured at this point. The next following
block of the chain will not be bearing the tooth in front of it against the shoulder 61
in front of said tooth, for the reason already stated, that the bearing-points of the
chain are a greater distance apart than the bearing-points of the teeth when the
latter are in their operative positions against the radial shoulder. Hence the tooth
is free to play in the space between the blocks of the chain. The same thing is
true of all the other teeth which are interlocked with the chain.
It will now be seen that the bearings of the wheel are relieved of the strain to
which they are subjected by the engagement of a chain with a plurality of the rigid
teeth of an ordinary sprocket-wheel, and only a single tooth is in operative engage-
ment with the chain at a time.
The combined effect of gravity and centrifugal force ensures the engagement of
each tooth with the chain. This engagement takes place on the lower side, as
illustrated in Figure 2, the teeth consecutively encountering the blocks of the
chain, and being projected into the spaces between said blocks.
As the chain leaves a tooth, it draws the following tooth to its operative position
against a radial shoulder, and the chain remains in engagement with one tooth
until it draws the next tooth to operative position, so that no lost motion occurs.
The chain is supported directly and at all times on the peripheral surfaces a² a³ of
the wheel, and the movements of the teeth on their pivots do not effect the pitch of
the chain. The teeth project through the chain, and have engagement only with the
ends of the blocks thereof.
By reason of the teeth being spaced nearer together than the engaging-points of
the chain, the disc may be provided with the same number of teeth as a sprocket-
wheel with rigid teeth, and be of smaller circumference than the latter, while the
same chain may be used as with such rigid wheel.
A sprocket-wheel of the construction described is of special advantage in bicycle-
gear, and in the manufacture the disc a a' may be provided with internal screw-
threads a as shown in Figure 3, so that it can be screwed on to the hub e of the
bicycle-wheel. This construction renders the sprocket applicable to a bicycle
without any change in the latter.
It is evident that the invention may be embodied in different form from that in
which I have here shown it, and hence it is to be understood that I do not limit
myself to this particular form in which I have chosen to illustrate it.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, it is declared that what is
claimed is-
1st. A sprocket-wheel having pivoted teeth and constructed to permit limited
play of said teeth, in combination with a chain bearing on the periphery of the

page_text: wheel and having its points of bearing against the teeth a greater distance apart
than the corresponding bearing-points of the teeth in their operative position at the
limit of their pivotal movement in one direction.
2nd. A sprocket-wheel having pivoted teeth and rigid shoulders which limit the
movement of said teeth, in combination with a chain whose points of bearing
against the teeth are a greater distance apart than the corresponding points of the
teeth in their operative position abutting the radial shoulders.
Dated this 5th day of September 1893.
W. LLOYD WISE,
Per F. J. Brougham.