Improved Crank Mechanism.
Year: 1898

page_text: Date of Application, 25th Mar., 1898-Accepted, 30th Apr., 1898
Improved Crank Mechanism.
I, FRANZ GUMPERT, of No. 75, Hauptstrasse, Brandenburg a/H, in the German
Empire, Merchant, 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:--
My invention relates to crank mechanism and is an improvement on that type
of crank mechanism, the effective leverage length whereof alters automatically
during the revolution by eccentric displacement.
Referring to the accompanying drawings:-
Figure 1 shews an elevation of the invention.
Figure 2 the same in section.
Figure 3 shews a section of the adjustable joint employed.
Figure 4 shews a diagram of the crank motion.
Figures 5 and 6 are diagrams of the eccentric crank motions hitherto known.
The motive power is supposed in all the figures to be acting perpendicularly
from above.
All crank mechanisms hitherto known which alter automatically the effective
length of the lever arm by means of varying the eccentricity, rely upon the recti-
linear adjustable connection of the crank with the shaft to be driven or with the
eccentric guide organ, as for instance the adjustable bearing of a sliding piece fixed
upon the shaft and moving in a longitudinal slot of the crank arm or the converse
thereof.
The numerous constructional modifications of this principle which has been
hitherto known are divisible into two groups.
The first group comprises those devices in which the transmission point of the
power coincides with the eccentric guiding point, or which moves in the same
track (see Figure 5) whilst to the other group belong those modifications in which
the motor force attacks the crank directly (see Figure 6).
My invention has with these two groups only so much in common, that the
effective leverage length alters automatically during the revolution by eccentric
displacement. It differs, however, entirely from the principle which underlies
both of the aforesaid groups, namely, that of the rectilinear adjustable connection
of the two parts, because the crank K (see Figure 1) is firmly fixed upon the
driving shaft W, and is connected with the eccentric ring E by means of a double
arm lever H at F. The motive power acts upon the end of the other lever arm
of H at the point A. The eccentric disc S around which the guide ring E revolves
is secured stationary.
The new technical results which are obtained by this construction will be best
demonstrated by the diagram Figure 4 when the same is compared with the
diagrams Figures 5 and 6 which illustrate the constructions hitherto known. The
proportional dimensions are alike in all these diagrams, but Figures 5 and 6 are
drawn to one half the scale of Figure 4.
In the crank driving, in which the crank K is connected with rectilinear dis-
Price R71

page_text: placement of the eccentric guiding point F (see Figure 5) the difference between the
longest lever arm a and the shortest lever arm bis certainly a considerable one.
This construction has, however, a great drawback in as much as the track of the
point which receives the force A, and that of the guiding point F coincides because
the point is at the same time also the point A. The crank K must consequently
be made as long as the longest lever arm a and its end therefore describes a much
larger circuit than the point A' itself, in other words the crank K experiences no
extension in its most favourable position. This drawback does not appear in the
device illustrated diagrammatically in Figure 6, because in this the track of the
application point of the force is the greatest, but on the other hand in this system
there is only a very slight difference between the. longest lever arms a and the
shortest lever arm b, because motive power is applied at the end A of the crank K,
but its other end F is connected with the eccentric guiding ring. In consequence
of this the shortest lever arm b still remains considerably longer than the shortest
of the eccentric..
My. improved construction has none of these drawbacks, because the crank K is
still considerably prolonged by means of the double arm lever H just in its most
favourable position, and the difference between the shortest lever arm 6 and the
longest a is just as great as in the arrangement shewn in Figure 5. In other
words the application point of the force A describes a heart-shaped curve, which
on the forwards stroke of the crank K falls far outside the circuit track of the end of
the crank, and on the back stroke thereof falls far inside the same; or it may be
stated thus, the track of the application point of the force lies not only as hereto-
fore eccentrically to the shaft driven but also eccentrically to the centre of the
eccentric.
For those machines in which human muscular power is the actuating' force it
will be advisable not to arrange the force to act as shown in Figure 4 in the direc-
tion cd, but rather in the direction e to g, because the other piece of the dead
joint will be rendered more easy in this manner.
My invention possesses many further advantages one of which is recognised in
the variable adjustability. In the construction hitherto known there is only pos-
sible the adjustability of the eccentricity, by means of a slot I (see Figure 1) in the
eccentric $ and the alteration of the lever arm length of the guiding point F by
means of a slot II, whereas in my construction it is possible to have a further
adjustment of the crank length by means of the slot III; moreover there may be
provided in the lever H adjusting slots IV, V, VI. By means of the two first the
lever arm lengths can be altered at will; by means of the last, the track of the
point of application of the force A can be considerably increased or diminished.
For this purpose it is necessary to make use of adjustable joints.
Figure 3 of the drawing shews by way of example such a joint in section and
this can as shewn in Figure 3 be conveniently arranged with ball bearings.
A further advantage of my construction may be recognised in completely avoid-
ing all the hitherto essential sliding frictional parts of the eccentric crank
mechanism. Moreover the play which constructors have at their disposal in the
direct carrying out of the invention, or in other words the adjustability of the
mechanism to the existing circumstances is however, considerably increased in
the present case by the circumstance that the length of the effective lever arm a is
quite independent of the diameter of the eccentric S, because the length of the
effective lever arm a, in addition to the various means of adjustment already
described can be altered. at will by the selection of a longer or shorter lever H.
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:
"
An improved crank mechanism the effective lever arm length whereof alters
automatically by eccentric displacement during the revolution, especially"charac-

page_text: terized by the double arm lever H adjustable in all directions, the point of
revolution whereof is at the same time the eccentric guiding point F, the said
lever having one of its lever arms jointed to the crank K rigidly fixed upon the
driving shaft W, while the motive power is applied to the end A of its other lever
arm, thus securing that the application point A of the power describes a heart-
shaped curve, which is not only eccentric to the driving shaft W but is also
eccentric to the guiding eccentric E.
Doted this 25th day of March 1898.
W. P. THOMPSON & Co.,
822, High Holborn, London, W.C., Patent Agents for the Applicant.