An Improved Crank.
Year: 1896

page_text: An Improved Crank.
THOMAS SPENCER JAMES 172 Camden Grove Peckham S.E. Engineer
do hereby declare the nature of this invention to be as follows:-
An arm having at its free end a slot, is made fast to the crank shaft; at the
side of this arm, is a secondary arm, having an extending piece jointed to it; &
which piece carries the crank pin & also a pin & roller, which engages in the slot
aforesaid; the arms are kept in position by a spring or springs & so forms what I
term a spring crank & according to the angle or position of the slot, may be used
as an ordinary crank with regular throw, by making fast the arms; or by leaving
the arms free; as a crank with regular throw but with spring action; or again, as
a variable throw crank according to the pressure or load put upon the crank pin.
Dated this 6th day of February 1896.
THOS. S. JAMES.
I, THOMAS SPENCER JAMES, of 172 Camden Grove, Peckham, London,
Engineer, 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 an improved construction of cranks whereby the length
of leverage of the crank is automatically increased or diminished in proportion as
the propelling force applied to the crank pin is varied to overcome a varying
resistance. It consists in combining with the crank arm a lever connected to it
by a pivotted link or links and also engaged with it by one or more pins or rollers
which lever is acted upon by a spring in such manner that when the crank pin is
only subject to a moderate pressure, the spring holds the arm in a retracted position
in which the crank pin is at a comparatively short radius from the crank shaft,
while when it is subject to increased pressure the lever arm moves outwards, so as
to increase the radius at which the crank pin acts.
The said improved construction of cranks is shewn on the accompanying
drawings in which
Fig. 1 shews a side view and Fig. 2 an end view of one construction.
Fig. 3 shews a view of the crank arm separate from the lever arm.
A is the crank arm fixed at a' to the crank shaft and having its front end formed
with an upward inclined slot a while at a it has pivotted to it a link B, to the
other end of which is pivotted the looped or slotted lever arm_C, through the
opening of which the crank arm A passes, and which has a pin D (which may if
necessary carry a roller) working in the slot of A. The upper end of the lever
arm C carries the crank pin E. A strong looped spring F is made to act upon
the crank arm and link B in such manner, that when the crank pin is only subject

page_text: to a certain strain for overcoming a moderate resistance, the lever C will be held
in the position shewn in full lines at Fig. 1, in which the crank pin E will be at
minimum length of radius from the crank shaft at a.
When, on the other hand the crank pin is subject to an increased strain, it will,
in overcoming the spring F, cause the lever E to move forward and upward in the
slot a, the link B turning on its pivot in following this motion, until, when the
crank pin is subject to the maximum strain, the parts will assume the extreme
position shewn in dotted lines at Fig. 1, in which position it will be seen that the
radius or length of leverage at which the crank pin works is considerably longer
than that at which it works when only overcoming a minimum resistance, and
consequently, assuming the construction to be applied to a cycle crank, the
propelling power will be exercised at a much greater advantage when the resistance
to propulsion is increased, as when going up hill.
At the same time it will be seen that when the propelling power is applied by
pedal motion, where a certain portion of each revolution is ineffective, the spring,
in overcoming the decreasing pressure of the foot, will force the lever C back into
its original position, so that during the ineffective part of the revolution, the
crank pin will be at the minimum distance from the crank shaft, and consequently
the motion of the rider's feet will be correspondingly reduced during that part of
the revolution.
As this reduction of the motion of the feet is of considerable advantage, it will
be seen that my invention may also be employed for effecting this purpose only,
that is to say, that the spring F can be made of such strength that when applying
only moderate pressure on the pedals for ordinary propulsion, the lever will at
once be moved forward as described so as to afford the maximum leverage, while
during the ineffective part of the revolution it will be retracted to a very short
leverage.
Fig. 4 shews a side elevation of a modification of the above construction;
Fig. 5 shews an end view, and Fig. 6 shews a view of the crank arm detached.
This arrangement only differs from the foregoing. one in that instead of making
the end of the lever arm A with a slot in which works a pin on the lever C, the
latter is provided with two rollers D D working respectively on the upper and
under surfaces of the upward inclined part a of the crank arm; also instead of
acting upon the lever by a looped spring as the first arrangement, it is acted upon
by a helical spring F, connected to it by a link G.
The underside of the crank arm is by preference formed with a series of hollow
curves as shewn, which will have a ratchet like action in tending to hold the lever C
in different forward positions corresponding to different degrees of pressure put-
upon the crank pin.
The action is otherwise precisely the same as at Figs. 1 to 3, the dotted lines
shewing the position of the lever and links when the maximum force is applied.
Fig. 7 shews a side view of another modification which is similar to that first
described with the exception that the link B connecting the lever C to the crank-
arm A is pivotted to an intermediate part of the latter, instead of at the front end,
the slot a of the crank arm being inclined downward instead of upward and the
lever being acted upon by a helical spring F connected respectively to its outer end
and to the link B. In the arrangement shewn at Figs. 8 and 9 the links B instead
of being pivotted to the levers C, are passed through eyes on the ends of the
latter, and may be provided with caoutchouc washers 6' between collars b, which
assist the action of the springs F; Fig. 8 is otherwise similar to Fig. 1, and Fig. 9
is similar to Fig. 4.
In all the above described constructions the lever C may if desired be made
rigid with the crank so as to act in the ordinary way by securing it by means of
a screw or other stop. In some cases I make the crank A with two holes for
fitting on the crank shaft, as shewn at Fig. 10, so that the length of the crank
arm can be made longer or shorter, to suit the convenience of riders, according as
it is fitted with the one or the other hole on the shaft.

page_text: Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. In a crank, the combination with a crank arm fixed to the crank shaft of a
lever arm carrying the crank pin at one end while at the other end it is connected
to the crank arm by a link, and at an intermediate point it bears upon the crank
arm by one or more pins or rollers, such lever arm being acted upon by a spring in
such manner that when the crank pin is only subject to a moderate pressure the
spring holds the arm in a retracted position in which the crank pin is at a com-
paratively short radius from the crank shaft while when it is subject to increased
pressure, the lever arm is moved outwards against the action of the spring so as
to extend the leverage of the crank pin, substantially as described.
2. In a crank, the combination of a slotted crank arm A, a lever C carrying the
crank pin E and having a pin or roller D engaged with the slot of the crank arm,
a link B connected to the crank arm and to the lever arm, and a spring F acting
upon the lever arm so as to tend to hold it in a retracted position, substantially
as described with reference to Figs. 1, 2, 3, 7 and 8 of the drawings.
3. In a crank, the combination of a crank arm A a looped or slotted lever C
carrying the crank pin E through which lever the crank arm passes, pins or
rollers D on the lever bearing upon the crank arm, links B connected to the crank
arm and to the lever and a spring F acting on the lever so as to tend to hold it in
a retracted position, substantially as described with reference to Figs. 4, 5, 6
and 9 of the drawings.
Dated this 6th day of November 1806
ABEL & IMRAY,
Agents for the Applicant.