Year: 1897

page_text: Chain Gear.
GEORGE FREDERICK STURGESS, The Ingle-nook, Leicester, in the County of
Leicester, Hosier's Engineer, do hereby declare the nature of this invention to be as
follows:-
Chain Gear. A compound variable speed and reversing gear, consisting of a disc
with a seginent flange, a gear wheel within the flange of the disc, and an endless
chain encircling the flange and gear wheel all mounted to rotate round a common
centre of action on a shaft. The roller teeth of the endless chain are free to run on
the flange of the disc and mesh with the teeth of the gear wheel. The rollers can
advance with or without the flange, or faster or slower than the flange of the disc;
or go forward or backward to one direction of the disc. For illustration, assuming
the flange to equal 21, and the gear wheel 7 roller teeth in circumference; the endless
chain meshing with the gear wheel at a tangent to each revolution of the disc and
gear wheel forward, the rate of passage of the roller teeth forward equals 21.7 when
the gear wheel only revolves forward, and 14 when the disc only revolves forward.
That is to say, the maximum speed when the disc and wheel revolve together,.
and the minimum speed when the disc only is stopped and the wheel
revolves, and the medium speed when the gear wheel only is stopped and the disc
only revolves; namely, 21 teeth less 7 teeth retarded by the stopping of the gear
wheel, leaving 14 roller teeth only advanced or passed. When the endless chain is
doubled back and passed around the gear wheel, the direction of the chain is
reversed & the proportion of the number of roller teeth passed varied. To transmit
the motion from the endless chain, an internally cut gear wheel or belt pulley is
fitted over the disc, into the teeth of which the roller teeth of the endless chain fit;
or a sprocket chain runs over the flange of the disc and meshes with the roller teeth
of the endless chain.
Dated this Ninth day of August 1897.
GEORGE FREDERICK STURGESS, of The Inglenook, Leicester, in the County of
Leicester, Hosier's Engineer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
This invention has for its object to provide a differential gear, more simple and
efficient and more readily applied than those used 'heretofore, and it consists of

page_text: internal and external sprocket wheels, meshed together by an endless roller chain of
a given number of links differing from the number of teeth in the sprocket wheels
by at least one tooth or link and a chain holder the construction of which allows of
the use of a chain having the minimum difference in number of links, mounted
round a common centre of motion, in a manner that the parts can rotate together
or independently, and at different times and in opposite directions as required.
Fig. 1 is an elevation partly in section, and Fig. 2 is a cross-section of the chain
gear complete.
I might here say, that either of the sprocket wheels is dispensed with as required,
according to the uses to which the gear is put, and the gear can be rotated in either
direction.
Referring to said figs. the chain holder consists of a flanged disc 1 having
apertures 3 and 3* cut in the flange making an arc of a circle 2 on one side and an
arc of a circle 2ª on the other side of the central boss 8. Arc 2 has a groove or
race 6 in its outer face, and are 2" has a similar race 7 in its inner face, in which the
rollers 9 of the chain 11 run, whereby the chain 11 is allowed to run upon the out-
side of the are 2 and mesh with wheel 12 and upon the inside of the arc 2ª and
mesh with wheel 10. Either of the arcs may be dispensed with according to the
uses to which the gear is put. Although in the drawings the arcs are made con-
centric to the boss 8, (in order to accomodate the dimensions of the other parts)
their extremities are eccentric and they impart to the chain an eccentric movement
to the axis of the gear. The size and shape of the arcs are determined by the
distance between the sprockets and the length of chain used. For instance when
the external sprocket is enlarged the inclines of the extremities of are 2 are con-
tinued to carry the chain into engagement with the external sprocket making the
arc 2 more eccentric to the axis of the gear, and the chain passes in and out of the
chain holder, which serves to impart an eccentric movement to the chain in any case.
The sprocket wheels and the chain may have any number of teeth, providing the
chain differs from one of the sprocket wheels by at least one tooth or link.
For the purpose of this specification the chain 11 has eleven links and roller stop 4
and engages the internal sprocket wheel 10 which has ten teeth and stop pin 5 and
engages the external sprocket wheel 12 which has twelve teeth and stop pin 13. The
whole gear is mounted round the hoss 8 of the eccentric cam or disc 1 and by the
construction of the eccentric cam the minimum difference between the sprocket
wheels 10 and 12 and chain 11 viz. a variation of one tooth or link is obtained. It
is understood that any part of this gear can be connected up or attached to any part
of machinery. Assuming the gear was applied to hoisting, windlass or other
machinery in which slow advancement or great power is required, then the chain 11
is retarded or held stationary by suitable stop means being thrown in the way of
roller stop 4 and the cam track 1 revolves causing each link of the chain to engage
with the sprocket wheels alternately, with the result that to every rotation of the
eccentric cam track 1 the internal sprocket 10 recedes one tooth, and the external
sprocket 12 advances one tooth in relation to the chain owing to the latter having
one tooth more, and the former one tooth less than the total number of links in the
chain 11. If the difference between the chain & sprockets was three teeth, the
sprocket would advance at a corresponding distance or speed and so forth. In
the rotation of the eccentric cam track 1 the links of the chain 11 undulate like a
snake as it were, each link engaging the sprockets alternately. The stop means
allow the roller stop 4 to reciprocate radially. The sprocket wheels have an inter-
mittent movement, advancing one tooth each time the arc 2 of the eccentric cam
track passes the roller stop 4. This motion will be better understood when I say
that if the chain and sprocket wheels corresponded in number of teeth and links
neither sprocket wheel would advance as the links would simply register with the
same teeth at every rotation of the cam track.
When a regular motion is required, the external or internal sprocket wheel is
stopped the chain liberated aud the eccentric cam driven causing the other sprocket
wheel to move two teeth, but when it is desirable for one sprocket to move only one

page_text: tooth, then the teeth of the other sprocket must be of corresponding number to the
links of the chain assuming the internal sprocket 10 to be retarded by suitable stop
means engaging the stop pin 5 to every rotation of the eccentric cam track 1 the
chain 11 will advance one link in the direction of travel of the cam track 1 and the
external sprocket 12 two teeth in relation to the internal sprocket with a continuous
and regular movement. Assuming the external sprocket 12 to be retarded by
suitable stop means engaging the stop pin 13 to every rotation of the cam track 1
the chain 1 will recede one link and the internal sprocket 10 two teeth in the
opposite direction to the cam track 1 in relation to the external sprocket and when
one sprocket is driven and the eccentric cam track is retarded the other sprocket
wheel advances at a greater speed than when the chain is retarded and the eccentric
cam track driven. Assuming the cam track 1 to be retarded and the internal
sprocket 10 to be driven for every rotation of the internal sprocket 10 the external
sprocket 12 would advance ten teeth and by liberating the cam track 1 whilst the
internal sprocket is still rotating, the whole gear would rotate in unison. Assuming
the eccentric cam track 1 to be retarded and the external sprocket 12 to be driven to
every rotation of the external sprocket the internal sprocket would rotate or advance
twelve teeth, that is one complete rotation and two teeth, and by releasing the
eccentric cam track 1 the whole gear would advance in unison, the internal sprocket
going slower or keeping time with the external sprocket. Therefore taking the
internal sprocket 10 to be the sprocket on the driving wheel of a cycle, motor car,
counter-shaft, lathe or other moving machinery and the external sprocket 12 to be
the driven part, it will be seen that the said moving machinery can be driven at a
slow speed when the eccentric cam track 1 is allowed to rotate, and at a faster speed
when the eccentric can track 1 is stopped. By using a roller chain the friction of
the chain over the cam track is greatly reduced, and the gear made so compact, as
to be of practical application and utility to mechanics generally. I have shewn
one form without attempting to shew the many ways of making, applying and
using my invention.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is
1. A differential gear comprised of a roller chain sprocket wheels, and a chain
holder or eccentric cam track serving to impart an eccentric movement to the chain,
to engage it with the sprocket wheels, mounted to operate round a common centre of
action so as to rotate in unison or at different speeds, and means whereby one sprocket
travels at the minimum difference of speed in relation to the other sprocket wheel
such means comprised of a chain differing from the sprocket wheels by one tooth or
link and a chain holder the construction of which allows of this minimum variation
substantially as and for the purposes set forth.
2. A differential gear comprised of a chain, sprocket wheels and an eccentric cam
track serving to engage the chain with the sprocket wheels, mounted to operate
round a common centre of motion, the chain provided with rollers to reduce friction,
the eccentric cam track provided with a race to receive the rollers, and hold them in
engagement with the sprocket wheels, and means operating to impart a plurality of
speeds, substantially as and for the purposes set forth.
3. A differential gear comprised of a chain, sprocket wheels and an eccentric cam
track, serving to connect the sprocket wheels mounted to operate round a common
centre of motion, means whereby the chain rides upon the inside of the eccentric cam
track, on one side the common centre of motion so as to engage one sprocket
wheel, and upon the outside of the eccentric cam track on the other side of the.
common centre of motion as to engage the other sprocket wheel, and means operating
to impart a plurality of speeds, substantially as and for the purposes set forth.
4. A differential gear comprised of a chain, a sprocket wheel and an eccentric cam
track, or chain holder serving to engage the chain with the sprocket wheel, mounted
to operate round a common centre of action, having provisions whereby the chain is

page_text: retarded, whilst the cam track is driven causing the sprocket to move at a different
speed to the cam track, substantially as and for the purposes set forth.
5. A differential gear comprised of a chain, sprocket wheels and an eccentric cam
track or chain holder serving to engage the chain with the sprocket wheels, mounted
to operate round a common centre of action, having provisions whereby one sprocket
wheel is retarded whilst the cam is driven causing the other sprocket to move at a
different speed and in the opposite direction to the eccentric cam track, substantially
as and for the purposes set forth.
6. A differential gear comprised of a chain, a plurality of sprocket wheels and an
eccentric cain track, or chain holder serving to engage the chain with the sprocket
wheels mounted round a common centre of action and capable of independent
movement, having provisions whereby the chain, internal sprocket wheel external
sprocket wheel and cam track adapted to be independently retarded and means.
operating to give a plurality of speeds, substantially as and for the purposes set
forth.
7. A differential gear comprised of a chain an internal and an external sprocket
wheel and an eccentric cam track or chain holder mounted round a common centre
of action so as to rotate in unison the chain adapted to ride upon one side of the
cam track so as to engage one sprocket wheel and upon the other side so as to engage
the other sprocket wheel, whilst the cam track is retarded, causing the driven sprocket
wheel to rotate at a different speed to the driving sprocket wheel, the eccentric cam
track or chain holder being of such construction as to admit the minimum length of
chain relative to the size of the sprocket wheels, that is, one tooth or link more in
the chain than the number of teeth in the internal sprocket wheel substantially as
& for the purposes set forth.
8. A differential gear comprised of a chain, an external and: an internal sprocket
wheel and and an eccentric cam track or chain holder serving to engage the chain with
the sprocket wheels, mounted to operate. round a common.centre of action having
provisions whereby the chain is retarded so as to cause the sprockets to rotate in
opposite directions the external sprocket advancing and the internal sprocket
receeding in relation to the chain substantially as and for the purposes set forth.
9. A differential gear consisting of the parts constructed arranged and operating
substantially as and for the purposes set forth.