MENTS IN THE MACHINERY FOR OBTAINING ROTARY MOTION BY THE ACTION OF TWO FORCES ON DIFFERENT CRANKS
Year: 1884

page_text: I, GEORGE SHANN, of 3 Park Row, Albert Gate, London, in the county of
Middlesex, Engineer, do hereby declare the nature of my invention for IMPROVE-
MENTS IN THE MACHINERY FOR OBTAINING ROTARY MOTION BY THE ACTION OF
TWO FORCES ON DIFFERENT CRANKS, to be as follows:-
The cranks on which the two forces act, are not rigidly fixed on the same Crank
shaft, but are so connected together by machinery for giving alternate quick and
slow motion, that while one crank is passing thro' that part of its revolution
during which it can be driven in the required direction by the action of that one
of the motive forces which more directly does work upon it, the other crank is
thereby made to revolve through an angle greater than two right angles. The
relative positions of the two cranks are so arranged that each is made to pass both
its dead centres in the time during which the motive force is acting directly on
the other.
The quick-&-slow-motion connection between the crank shafts can be arranged
in more than one way: I proceed to describe the particular arrangements for
which I now ask protection.
Each of the crank-shafts carries a toothed wheel whose pitch line is in the form
of an ellipse, and in each case the axis of the shaft passes through one of the foci of
the pitch-ellipse. These wheels are either geared into one another, or are connected
by being geared into two similar elliptic wheels both fixed on a single intermediate
shaft in such a way that each wheel has one of the foci of its pitch ellipse in the
axis of that shaft.
On each crank-shaft the longer diameter of the elliptic wheel must be so placed,
in relation to the crank, that when the force is acting directly on that crank, the
wheel shall be engaged at that part of its circumference which is farther away from
the axis of the crank-shaft; and that during the return stroke it shall be engaged
at that part which is nearer to the axis of the crank-shaft.
The invention above described is especially applicable to velocipedes, and to two-
cylinder engines which, like most gas-engines, have the power applied at one end
of the cylinder only.

page_text: I, GEORGE SHANN, of 3 Park Row, Albert Gate, London, in the county of
Middlesex, Engineer, do hereby declare the nature of my invention for IMPROVE-
MENTS IN THE MACHINERY FOR OBTAINING ROTARY MOTION BY THE ACTION OF
TWO FORCES ON DIFFERENT CRANKS and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
The cranks on which the two forces act are not rigidly fixed on the same crank
shaft, but are connected together by such mechanism that while one crank is
passing through that part of its revolution during which it can be driven in the
required direction by the action of the force which does work more directly upon
it, the other crank is thereby made to revolve through an angle greater than two
right angles.
In the drawings accompanying this specification Figures 1 and 2 show such a
connexion between the two crank shafts, which is made as follows; A, A' are the
two cranks, and B, B¹ are two toothed wheels whose pitch lines are in the form of
an ellipse. Such wheels are herein-after referred to as "Elliptic wheels."
Each of the wheels B, B', is fixed onto the corresponding crank-shaft and
revolves with it; the axis of the crank-shaft in each case passing through one of
the foci of the pitch ellipse. Again, D), D¹, are two elliptic wheels similar to B, B¹;
both D, and D, are fixed onto a single counter-shaft-C,-and-revolve-with-it;_the_
axis of the shaft passing through one focus of each pitch-ellipse. To make the
drawings simpler, no parts of the wheels B¹, and D¹, have been shown in the side
view, Figure 2.
The three shafts A, A¹, and C, are so hung that each wheel on the counter-shaft
gears into the wheel on one of the crank-shafts, and the longest diameters of the
olliptic wheels are so placed that when either crank is in the middle of that part of
its stroke during which it can be driven in the required direction by the action of
the force which does work more directly upon it, then the pair of elliptic wheels
appertaining to that crank are in gear with one another at those parts of their
circumferences which are farthest from the axis of the crank-shaft and nearest to
the axis of the counter-shaft, respectively. This is shown in the drawings, where
the crank A, is represented in the middle of the effective part of its stroke, and the
crank A¹, in the middle of its return stroke; the forces on the two cranks being
supposed to act in parallel lines and in the same direction.
The effect of this arrangement is that while either crank is passing through any
given angle in that part of its revolution during which it can be driven in the
required direction by the action of the force which does work more directly upon
it, the motion of that crank will cause the counter-shaft to revolve through a
greater angle; and again the revolution of the counter-shaft will cause the other
crank, which is performing its return stroke, to pass through a still greater angle:
so that each of the cranks in turn will be carried past both its dead-points by the
action of the force on the other crank.
To meet special cases modifications of the arrangement herein-before described
may be made in various ways; for instance, when the mechanism is applied to a
velocipede it may be advantageous that the wheels on the crank-shafts should not
gear directly into wheels fixed on a single counter-shaft, but should gear into
wheels revolving upon two separate shafts, these separate shafts being in their
turn connected with a common counter-shaft by means of toothed wheels. In this
way the said counter-shaft, which may serve as the main axle of the velocipede, is

page_text: caused to revolve in the same direction as the crank-shafts and the ratio of the
velocities of the crank-shafts to the velocity of the counter-shaft may be varied.
Such a modification is shown in Figure 3 where A, A1, are as before, the cranks;
B, B', the elliptic wheels revolving with them; D, D¹, the two elliptic wheels
gearing into B, B'; H, H', are toothed wheels revolving with D, D; C, is the
counter-shaft and K, K¹, are wheels fixed on C, and gearing into the wheels H,
and H¹, respectively.
If it be desired that the shaft C, should turn in the same direction as the crank
shafts and revolve once for each revolution of the cranks, then the wheels K, K¹, on
the counter-shaft may be elliptic wheels, similar to, and gearing into, the wheels B,
and B¹, respectively.
Another modification is that if the two forces act in parallel lines but in opposite
directions the elliptic wheels on the two crank shafts may be geared directly into
one-another, no counter-shaft being used in this case. Figure 1 would represent
such an arrangement if there were only one pair of elliptic wheels, B, and D, and
a crank Z, as shown by the dotted lines in the drawing, were fixed on the shaft
which carries the wheel D.
It may be mentioned that in practice, circular wheels revolving about excentric
axes may be used in place of accurately shaped elliptic wheels in the above-
described machinery, provided that the required excentricity be not great; but the
teeth of such circular wheels will engage with one another more deeply at some
parts of their revolution than at others.
The invention herein-before described is primarily adapted for velocipedes and
gas-engines, but can be used for any purpose to which it is or may be found
applicable.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is an arrangement substantially corresponding to the arrangement or
arrangements here-in-before described, whereby each of two cranks, connected
together for the purpose of obtaining rotary motion, is caused to pass both its dead-
points in the time during which the other crank can be turned in the required
direction by the action of the force which does work more directly upon it.
Dated this 24th day of November 1884