Improvements in or relating to Cranks of Bicycles and other Velocipedes.
Year: 1888

page_text: COMPLETE SPECIFICATION.
Improvements in or relating to Cranks of Bicycles and other
Velocipedes.
I, ALFRED JÖRGENSEN of Helsingfors, Finland, Engineer do hereby declare the
nature of the said invention and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement
The object of this invention is to produce a periodical change of the position of the
cranks in a bicycle or other velocipede so that under the running of the bicycle the
one crank always passes the dead point immediately before or after the passage of
the other crank by the same point, by which the treading acts more uniformly and
becomes less fatiguing. This result is effected by means of two centres, secured on
the shaft of the wheel of the bicycle one for each crank.
On the drawing Figure 1 represents such a centre in section. Figures 2 to 6 are:
detail views.
A is the shaft of the bicycle's wheel. This shaft is provided with a flange B keyed
or otherwise fixed to it. In the flange B are two helix-shaped inverse grooves C, in
which are running two screw thread parts D being of the same thickness as the width
of the grooves in the flange. On the outside of the thread segments D there are
other screw thread parts E crossing the former and solidly united or in one piece with
the screw thread parts D. In Figure 3 the flange B is visible viewed from the end
with the one couple of screw thread parts DE, the other pair of the screw thread
parts is left out, so that the groove C for the inner thread of this pair of screw thread
parts is open. In Figure 4 a pair of screw thread parts is shown introduced in the
Hange, viewed from without and in Figure 5 the flange. B.alone and its. one thread
groove is visible.
The outer thread parts E are thus situated outside of the circumference of the
flange B. The flange B as well as the thread parts are surrounded by a socket F
provided with a bottom. From this end of the socket F projects a centre F' to which
the crank is secured. Inside of the socket F are grooves G for the outer screw thread
parts E and in its bottom are holes H through which the one end of the inner screw
thread parts D can be passed. The screw thread parts E. are thus sunk into the
socket in the same manner as the screw thread parts D'are sunk into the flange B.
In Figure 6 the socket F is visible from the open end. The length of the screw thread
D

page_text: parts is somewhat greater than the thickness of the flange B and the bottom of the
socket F together.
In the event of a longitudinal displacement of the thread parts D in their grooves
in the flange B the socket F is turned in relation to the flange B. If there were only
the screw thread parts B and if the socket F were attached to the latter by means of
screws or the like. The socket F would at the displacement of the same screw thread
parts turn in accordance with the pitch of the same screw thread parts. In order that
the turning of the socket F shall become so much the greater I provide the outer screw
thread parts E which by their engaging in grooves in the socket put the latter under
the influence of the motion between the thread E and the flange B. The same result
would also be obtained by means of only one pair of thread parts but in order to
divide the strain there are two sets of thread parts. As further the grooves in the
flange B are not crossing one another as on a common scrow, the one pair must in
order to have the thread parts to turn in the same direction be displaced to the left of
the flange B (fig. 4 or 5) when the other pair is displaced to the right or vice versa.
In order to impart such a motion to the screw thread parts the socket F and the
flange B are surrounded by a box consisting of two parts I and K and provided in its
bottom with circular grooves O and P the bottom surfaces of which are parallel one
with another but form inclined planes to the vertical plane soo fig. 1 and 2 which latter
figure shows the part K and its groove P. The box is by means of Ings L projecting
from the part K and an intermediate lug on the frame of the bicycle and a pin through
the said lugs united to the said frame so as not to be able to turn round. The ends of
the thread parts enter into the grooves O and P and have thus an alternato motion in
their own longitudinal direction at the same time as they are turning round with the
flange B or the shaft A.
At each revolution of the shaft A the screw thread parts will owing to the influence
of the grooves O and P obtain an alternate motion which as before said effects that
the socket F during one half revolution has a slower motion and during the other half
revolution a more rapid motion than the shaft A depending upon the direction in which
the screw thread parts are displaced. The centres one for each crank are disposed so
that the crank has a quicker motion at the up stroke and a slower one at the down-
stroke, from which results that when the one crank is passing the dead point in the
lower position, the other crank has already passed this point at the top position. In
this way the treading is facilitated and the bicycle obtains a more uniform run.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed I declare that what I claim is.
First. Centres for a movable fixing of the cranks in a bicycle or other velocipede
each consisting of a flange arranged on the shaft of the driving wheel and of a socket
surrounding this flange in which box the crank is secured and which by means of two
crossed and connected screw threads or several pairs of such crossed threads working
in grooves on the flange and on the socket and brought in an alternate motion by
inclined planes at their ends obtain a periodical accelerating and slackening motion
when the shaft of the wheel is turning round substantially as set forth.
Second. The construction of bicycle or other velocipede crank centre as described
and shown.