Improvements in the Driving Gear of Cycles and the like.
Year: 1896

page_text: COMPLETE SPECIFICATION.
Improvements in the Driving Gear of Cycles and the like.
1, THEODOOR HERMAN HELENES BODDE, of No. 63 van Marlestraat, The Hague,
Holland, Gentleman, 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 a construction and arrangement of the sprocket or chain
wheels of cycles and the like, the object being to better utilise the power applied to
the cranks.
In cycles provided with toothed chain wheels, a great part of the power exerted by
the rider is lost, because when the crank is in the vertical position, the power applied
to it, does not, or only to a very small extent, aid in propelling the cycle.
The arrangement and construction of the toothed chain wheels hereafter described,
serve to obviate that drawback, in a practically perfect manner, almost all of the
power applied to the crank acting to propel the cycle.
To clearly explain my invention I have illustrated in the accompanying drawing
some ways of carrying it into effect.
In the drawings, Figs. 1 to 4, are side elevations of the lower part of the frame
provided with my improved arrangement of wheels, with a part of the crank and (in
the case of Fig. 1) with a portion of the driving wheel.
Figs. 5 and 6 to 6 are diagrammatic views showing the progressive rotatory
movement of the crank at different points.
It is known that it is only that portion of the power exerted upon the crank at
right angles to the length or direction of the crank arm, which acts to propel the cycle;
the remainder of the power having an effect which is unfavourable to propulsion, by
reason of the friction on the bearings.
Referring first to Figs. 5 to 6. In the horizontal position of the crank K, the
operative power is at its maximum and the effect unfavourable to propulsion is nil.
In another position of the crank K, as for example, the position shown in Fig. 5,
in which the force a-b is resolved into two other forces a- and a-c, the force a-c
acts to propel the cycle, whilst the force a-d is unfavourable to propulsion.
The more the crank approaches the vertical position, the greater becomes the
force a-d which produces friction and corresponds to a loss of power, and the greater
is the diminution of the useful effect of the force applied to the crank; such force
becoming nil when the crank is in its vertical position.
Experienced and trained riders avoid this loss of power as far as possible, because
instinctively so to speak, they press upon the pedal only when the crank is at an
angle of less than 45° to the horizontal, but then they cannot exert any useful effort
during half a revolution of the crank.
My new arrangement and construction of parts obviates this drawback almost
completely as will be hereinafter described.
On considering that the positions of the crank, which make an angle of less than 45°
with the horizontal and therefore are situated in the arcs I and III of the circle, are
the positions that are favourable to propulsion of the cycle, whereas those positions of
the crank which make an angle greater than 45° with the horizontal, and are
therefore situated in the ares II and IV of the circle, are the positions that are
unfavourable to propulsion, I formed the idea of utilizing in the propulsion of
the cycle, the favourable positions of the crank during a longer period than the
unfavourable positions.

page_text: The greater this proportionate period of time, the smaller will be the loss of power
applied to the crank.
In Fig. 6 the sprocket wheel A is made of approximately elliptical form, such that
with a constant speed (as is the case when travelling during a relatively short time)
the wheel A, when the major axis of the ellipse is in a vertical position, takes a longer
time to move through the same angle of rotation than when the minor axis of the
ellipse is in the vertical position.
As the cranks are set at right angles to the major axis of the ellipse, they will
move more quickly through their vertical positions than through their horizontal
positions, that is to say, that during a determined period, the rider will pedal longer
with the favourable positions of the cranks than with the unfavourable positions of the
same.
Under these circumstances, a rational and accurately determined ratio between the
lengths of the major and minor axes of the ellipse will allow of reducing to a minimum
the loss of power during progression.
The use however of a sprocket wheel of the shape described will not allow the
desired tension to be maintained on the chain in both the inclined and horizontal
positions of the ellipse (Figs. 64-6); and therefore for the purpose of preserving the
tension, I provide above or below the small toothed chain wheel B of the driving
wheel, an auxiliary toothed wheel C.
This auxiliary toothed wheel C is approximately of the same dimensions as the
toothed wheel B.
Figs. 6 to 6 of the accompanying drawings illustrate the four positions of the
crank K and of the elliptical sprocket wheel A, during half a revolution of the axle.
The distance between the centres of the small toothed wheels B and C is made such
that the inclination of the chain between the wheels A and B, and between the
wheels A and C, in the position shown in Fig. 6, is the same as that between
the wheels A and C, and between the wheels A and B in the position shown in
Fig. CB.
°
In these figs., let
E be the major axis of the ellipse, e the minor axis of the ellipse, R the radius of
: the small toothed chain wheel B, and
r the radius of the auxiliary toothed wheel C, f the distance between the centres of
the toothed wheels B and C, and N the angle of the chain between the toothed
wheels A and B in Fig. 6; and between the toothed wheels A and C in Fig. 6B. The
dimensions of the toothed wheels must be determined as follows:-
N (Fig. 6) is N=ER, and thus is equal to N (Fig. 6B) which is
N=+e; whence follows: ER=f+r-
e
If these proportions be adopted for the dimensions, the chain will always have
a sufficient tension, as may also be seen from Figs. 6 to 6°, and in the case where
the ratio of length between the major and minor axes of the ellipse, is not too
large, the loss of power during progression becomes reduced to a minimum, and
consequently the arrangement allows the greatest possible useful effect to be
obtained.
Fig. 1 illustrates one method of applying in a practical manner toothed wheels to
the frame G of a safety bicycle.
The sprocket wheel A is mounted in the same manner as is the ordinary wheel,
and the crank K is carried similarly by the wheel and axle.
The frame is provided with a bracket G to receive the auxiliary pinion C mounted
on a stud on said bracket.
Fig. 2 illustrates a simpler arrangement of the auxiliary toothed wheel for
maintaining the tension of the chain.
In this modification, the auxiliary toothed wheel D may be of an oval or
eccentric form and mounted directly upon the frame G between the sprocket
wheel A and the toothed wheel on the axle of the driving wheel or the, wheel D
may be circular and be eccentrically mounted on a bracket D₁ as shown in
Fig. 2.

page_text: Or for the purpose of maintaining the tension of the chain the small toothed
chain wheel on the driving wheel may also be made of oval or similar form, or
as shown in Fig 4 a circular wheel F eccentrically mounted may be employed.
As a very slight eccentricity of the small chain wheel F is sufficient to maintain a
constant tension on the chain, this eccentricity will affect only in a small degree the
action of the elliptical sprocket wheel A. It is only necessary that the small chain
wheel F shall have one half of the number of teeth of the elliptical wheel A. so that
only one single ratio of gearing can be used in this arrangement.
Instead of making the wheel A of elliptical form, this form may be given to the
small chain wheel B on the driving wheel.
In this arrangement which is shewn in Fig. 3, the sprocket wheel H on the crank
axle retains its ordinary round shape, and the advantage of passing rapidly through
the unfavourable positions of the cranks is obtained by an oval or eccentric wheel or
a circular wheel L eccentrically carried by the driving wheel as shown.
In order to maintain a constant tension of the chain, an auxiliary eccentric toothed
wheel or a circular wheel M eccentrically carried is mounted directly on the frame
above the sprocket wheel H.
In the modification shown in Fig. 3, as in that shown in Fig. 4. the chain wheel on
the driving wheel can also have only one half of the number of the teeth of the large
wheel H. It is therefore only suitable for a single ratio of gearing.
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. In the driving gear of cycles and the like, the employment of an elliptical
approximately elliptical sprocket wheel or the like together with means for
serving the tension of the chain or the like passing over same, the shape of the
sprocket wheel enabling the crank to pass rapidly through the positions unfavourable
to developing power substantially as described.
2. In the driving gear of cycles and the like the employment of an elliptical or
approximately elliptical sprocket wheel or the like and of an auxiliary toothed
wheel or the like supported above or below the wheel on the axle of the driving
wheel, whereby the tension of the chain or the like may be preserved substantially
as described.
3. In the driving gear of cycles and the like the employment of an elliptical
or approximately elliptical sprocket wheel or the like and of a wheel of an oval or
similar form or a wheel eccentrically mounted on the axle of the driving wheel
for the purpose among others of preserving the tension of the chain substantially
as described.
4. In the driving gear of cycles and the like the employment of an elliptical
or approximately elliptical sprocket wheel or the like and of an auxiliary toothed
wheel or the like either oval or of similar form or eccentrically hung, mounted
between the sprocket wheel and the wheel on the axle of the driving wheel for the
purpose of preserving the tension of the chain substantially as described.
5. In the driving gear of cycles and the like the employment with an ordinary
procket wheel or the like and an oval or eccentric wheel or a wheel eccentrically
mounted on the axle of the driving wheel of an auxiliary oval or eccentric wheel
or a wheel eccentrically hung mounted near the sprocket wheel and receiving the
chain or the like partially passing round same, the whole being adapted to enable
he cranks to pass rapidly through the positions unfavourable to developing power and
o maintain a tension on the chain substantially as described.
Dated this 21st dow of T... 1900
PHILIP M. JUSTICE,
Chartered Patent Agent, London,
For the Applicant.