Improvements in Crank and Slotted Crosshead Mechanism.
Year: 1891

page_text: Date of Application, 2nd June, 1891-Accepted, 4th July, 1397
COMPLETE SPECIFICATION.
[Communicated from abroad by THE LAFORGE ENGINE COMPANY, doing business
in Jersey City, County of Hudson, New Jersey, United States of America.]
Improvements in Crank and Slotted Crosshead Mechanism.
1, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents,
45 Southampton Buildings in the County of Middlesex, 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 :—
In the accompanying drawings forming part of this Specification and in which
Figure 1 represents a side view in partial longitudinal vertical section of the
yoke and the crank-block as applied to a steam engine.
Figure 2 face view of the guide C.
This invention relates to an improvement in a device through which recipro-
cating movement is converted into the rotary movement of a crank, or vice-
versa, the said device consisting of a yoke in the form of a pair of parallel
guides at substantially right angles to the path of the reciprocating movement,
between which guides a block sl'des, and in which block the crank-pin of a
crank-shaft is arranged, so that the said yoke reciprocating at right angles to
the axis of the crank will impart rotary movement to the crank, or vice-versa,
the crank-pin and the block it carries travelling between the said guides, this
device being commonly called a "Scotch Yoke," the said yoke being specially
adapted to that class of steam-engines in which a pair of cylinders are arranged
in line with each other, the adjacent ends open, a cylindrical piston arranged
in each cylinder the two pistons connected between the cylinders, forming a
guide in which the crank-block operates, so that a reciprocating movement
imparted to the pistons, will through said block, convert said reciprocating
movement of the pistons into rotary movement of the crank, and is an improve-
ment upon the yoke of the steam-engine for which British Letters Patent
No. 2948 of 1889, dated February 19th 1889 were granted.
In the usual construction of such yokes, the two parallel guides between which
the crank-block or slide operates, are rigidly connected.
In the construction of this engine it has been found difficult to make so perfect a
fit between the slide or block and the guides as to prevent possible play, such play,
however slight, owing to the great rapidity with which the engine is operated,
unavoidably produces a thump at each reversal of the stroke.
The object of the present invention is to construct the yoke so as to avoid all
possible play between the parallel guides.
In operation in the said engine the thrust of the piston in imparting movement to
the crank, is alternately first one piston upon the guide it carries, then the other
piston upon the guide it carries, so that the tendency of the two pistons in operation
is to press the guides toward each other. Taking advantage of this fact, the
invention consists in uniting the two guides by a yielding connection, whereby the
guides may approach each other under the pressure of the respective pistons, and
so that they will always bear firmly against the block irrespective of imperfection
of fit or wear of the block, and as more fully hereinafter described.
In illustrating the invention it is shown as adapted to the said engine, but show
only so much of the engine as necessary to the understanding of the invention.
A, represents the piston-rod from one cylinder, and B, the piston-rod from the
other cylinder. To the piston-rod A, the guide C, is attached, which as in the
previous Patent is at right angles to the axis of the piston-rod A; and to the piston-
rod B, is a like guide D, parallel to the guide C; these guides are connected at

page_text: their ends by studs E E, so as to hold them always in the same longitudinal plane
with each other. The crank-block or slide, as here represented, is made in two
parts FG, divided in a plane parallel with the plane of the face of the two guides,
and adapted to receive the crank-pin, the block being constructed with an
opening H through it at right angles to the axis of the piston-rods, and in which
the crank-pin operates, as in the previous Patent. The parts F G are constructed
so as to leave a slight space I, between them, the parts being connected by steady-
pins J, and so that while the two parts will properly embrace the crank-pin, the
space between them will allow of a contraction of the block under the wear of the
crank-pin.
Instead of rigidly connecting the two guides C D so that they unyieldingly
stand at the same distance from each other, the studs E, are made fast in one of the
guides as C, and pass freely through the other guide D, and so as to allow the
guide D and studs to play the one upon the other. Outside the guide D, the two
studs are provided with heads K, between which and the back of the guide D,
suitably springs L, are arranged, the tendency of which is to force the two guides
toward each other, or yieldingly hold them at any position in which they may
stand.
The face of one or both of the guides is constructed with a cam-groove M, in
which a stud N, on the crank-slide works up and down as the slide so moves under
the action of the crank, the same as in the previous Patent, this cam-groove
imparting to the guides and pistons an oscillatory movement, whereby the pistons
may serve as valves, this feature, however does not enter into the present invention,
but is illustrated in Fig. 2, the groove being of the same shape as in the said
previous Patent.
The thrust of the pistons being against each other, that is to say, the thrust of
the piston of the rod A is against the guide C, when running in one direction and
the thrust of the piston of the rod B is against the other guide D when running
in the opposite direction, the two pistons thus being opposed to each other, the
tendency of the force is to press the two toward cach other and against the crank-
block between them. The springs L yieldingly hold the guides in these positions
against the block, consequently the guides will bear against the block at all times,
and so as to prevent any possible play between the block and guides, and will take
up whatever wear may occur between the crank and block, or between the block
and guides.
The crank-block is represented as divided, and this preferred in order to
readily take up the wear of the crank, but the block may be solid if desirable.
In case the action is always in a direction tending to force the guides toward
each other, the springs L may be omitted, but it is preferred to employ them to
avoid any possible rattle or play of the parts which might otherwise occur.
While this invention is specially applicable to engines of the class of the Patent
before referred to, it will be understood that it is also applicable to yokes of this
character employed for other purposes.
Having now particularly described and ascertained the nature of the said.inven-
tion and in what manner the same is to be performed as communicated to me by my
foreign correspondent I declare that what I claim is :-
First. In a combined yoke and crank for converting reciprocating into rotary
motion or vice-versa, the yoke composed of two parallel guides at substantially right
angles to the line of reciprocating movement, combined with a crank-block
arranged between said guides and so as to slide therein under the rotation of the
crank, the said guides yieldingly connected and so as to bear with yielding
pressure upon the opposite sides of said block, substantially as described.
Second. In a combined yoke and crank for converting reciprocating into
rotary motion or vice-versa, the combination of two guides CD, the said guides
being parallel, studs E E connecting said guides, but passing freely through one of

page_text: said guides, with springs between said studs and the guides tending to yieldingly
force the guides toward each other, with a crank-block arranged between said
guides and adapted to slide therein under the rotation of the crank, substantially
as described.
Dated this 2nd day of June 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicants.