IMPROVEMENTS IN STEAM ENGINES
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
I, ALEXANDER MELVILLE CLARK, of the firm of A. M. and Wm. Clark, of
53, Chancery Lane, in the County of Middlesex, Fellow of the Institute of Patent
Agents, do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
STEAM ENGINES," a communication to me from abroad by William Saxon Arnold, of
Chatham, in the County of Kent, and Province of Ontario, Dominion of Canada,
Gentleman to be as follows:-
This Invention relates to improvements in steam engines in which steam is used
expansively and the crank is used as a medium for converting the reciprocating
motion of the piston into the rotary motion of the crank shaft. In engines using
steam expansively by cutting off early in their stroke, the pressure is greatly reduced
in the cylinder soon after cutting off and before the crank is in the best position for
work, and the objects of my improvements are, first, to apply the power which
is transmitted through the piston to the crank, when said crank is in a more
advantageous position to transmit power than with the present practice; secondly,
I avoid compression on the exhaust side of the cylinder and thereby prevent
accidents from the accumulation of water.
I attain these objects by the following mechanism.
The cylinder is open ended and is provided with three pistons, the centre one
being the working piston and transmitting power to the crank with the usual
connections, and the outer ones forming movable piston heads to the cylinder.
The movable piston heads are externally connected to each other by means of
piston rods cross heads and side bars.
The side bars are provided with wrist pins to which connecting rods are attached
that have a reciprocating motion adapted to the time and travel of the piston
heads.
The slide valve controls the admission of steam only, and is operated by any
suitable system of expansion gear.
The steam ports are situated at the inside of the innermost limit of travel of the
movable piston heads whilst the exhaust ports are so situated in the bottom of the
cylinder that the piston heads in their travel control the exit of steam,
Prins B11

page_text: In the centre of the one piston head is an ordinary stuffing box through which
the working piston rod passes.
When in operation the main piston makes a portion of its stroke before steam is
admitted to the cylinder, and the two piston heads simultaneously therewith travel
the same distance and in the same direction and are firmly held in place. The
exhaust port at the advancing side of the piston being uncovered by this motion
of the adjacent piston head and steam being then admitted, the main piston continues
the remainder of its stroke.
On the main crank shaft is fixed a disc on which is a segmental projection, and
against the face of disc and free to slide across the diameter of shaft is a slotted
plate which is provided with two segmental projections.
This sliding plate is elliptical and its two segments are respectively concentric
with the main shaft when the shaft is at the opposite end of the slot in the plate,
This sliding plate is connected by a rod with a pin at the upper end of a slotted
rocking lever, the lower end of which is pivoted on the bed plate of the engine.
Across the end of the engine bed plate furthest from the crank shaft is journalled a
small crank shaft provided at each end with cranks whose pins are connected by
rods with the wrist pins on the side bars by which the movable piston heads are
coupled together.
One of the crank pins is extended through a sliding block which is fitted to
slide in the slot of the rocking lever before mentioned.
When the main piston is at that end of the cylinder nearest the main shaft the
segmental projection on the revolving disc strikes the one projection on the sliding
plate thereby causing the said plate to move towards the cylinder. This motion is
transmitted to the rocking lever which through the medium of the sliding block
and crank pin throws the small crank shaft one half revolution, and thus gives
proper motion to the piston heads.
When in consequence of the rotary motion of the one and the sliding motion of
the other the end of the projection on the disc slides off the end of the projection
on the plate the outer circumference of the projection on the disc revolves against
the inner circumference of the projection on the plate and thereby prevents motion
in the plate until the projection on the disc comes in contact with the other projec-
tion on the plate. At the point where the segmental projection on the disc ceases
its contact with the end of the first mentioned projection on the plate the piston
heads have reached the extent of their travel and are held rigidly in place. It is at
this point that steam is admitted to the cylinder.
The return stroke is performed in a similar manner to the foregoing by the
segmental projection on the disc coming in contact with the other projection on the
plate.
100

page_text: "
COMPLETE SPECIFICATION.
I, ALEXANDER MELVILLE CLARK, of the firm of A. M. and Wm. Clark, of
53, Chancery Lane, in the County of Middlesex, Fellow of the Institute of Patent
Agents, do hereby declare the nature of the said Invention for "IMPROVEMENTS IN
STEAM ENGINES (a communication to me from abroad by William Saxon Arnold
of Chatham, Kent County, Province of Ontario, Canada, Gentleman,) 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 improvements in steam engines in which steam is used
expansively. In engines using steam expansively by cutting off early in their
stroke, the pressure is greatly reduced in the cylinder soon after cutting off and
before the crank is in the best position for work, and the objects of these improve-
ments are, first to apply the power which is transmitted through the piston to the
crank, when said crank is in a more advantageous position to transmit power than
with the present practice, second to avoid compression on the exhaust side of
cylinder and thereby prevent accidents from the accumulation of water.
I attain these objects by the mechanism illustrated in the accompanying in
which
Figure 1 is a longitudinal section of the cylinder, steam chest, and pistons.
Figure 2 is a top view of cylinder, steam chest, side bars, cross head and piston
rods the steam chest cover and valve being removed.
Figure 3, is a plan of the entire engine.
Figure 4 shows on an enlarged scale a side elevation of the cam-motion.
Figure 5 is an enlarged elevation of the slotted rocking lever with its sliding
block, wrist pins, and connecting rod.
Similar letters refer to similar parts throughout the several views.
The cylinder A is open ended and is provided with three pistons, the centre one"
being the main or working piston B connected to the main piston rod E which
transmits power to the crank with the usual connections.
The inovable piston heads C, and D, are externally connected to each other by
means of the end piston rods F F F, cross head G G, and side bars H H.
The side bars H H are provided with wrist pins I, I, to which connecting
rods m, m, are attached that have a reciprocating motion adapted to the time and
travel of the piston heads C, D.
The slide valve L controls the admission of steam only, and through its valve
rod, K, is operated by any suitable system of expansion gear.
The exhaust ports O, O, are so situated in the bottom of the cylinder that the
piston heads C D in their travel control the exit of steam.
In the centre of piston head C is an ordinary stuffing box U, through which the
main piston rod É passes.
When, in operation, the main piston B makes a portion of its stroke before steam
is admitted to the cylinder, the two piston heads C. D, having simultaneously
travelled the same distance and in the same direction and are firmly held in place;
this position is shown in the drawings Figure 1, the dotted lines designating the
reverse position of main piston and piston heads, The exhaust port O being

page_text: uncovered by piston head D and steam then admitted by the steam valve L, the
main piston B continues the remainder of its stroke.
On the main crank shaft a is secured the disc b, on which is a segmental projection c,
and against the face of the disc b, and free to slide transversely to the axis of shaft a,
is the plate d which is provided with two segmental projections e e¹¹.
To the plate d is attached one end of the rod g, the other end connecting with
the pin h. This pin h projects from the side of the upper end of a slotted rocking
lever i the lower end of said lever being pivotted from the bed plate of the engine
by the pivot n.
Across the end of the engine bed plate, furthest from the shaft a, is journalled
the small crank shaft k. Said crank shaft is provided at each end with cranks l
whose pins op, are connected by rods m, m with wrist pins I, I, on the side
bars H, H.
The wrist pin p is extended through the sliding block; the said block being free
to slide in the slot of the rocking lever i.
When the main piston B is at that end of the cylinder nearest the main shaft the
projection c on the disc b, comes in contact with the projection e¹¹ on the plate d,
thereby causing the plate d, to move towards the cylinder. This motion is trans-
mitted to the rocking lever i, by the connecting rod g; the said lever i will
therefore through the medium of the sliding block j, and extended wrist pin p
throw the crank shaft k one half revolution and thus (as the wrist pins o p and I I
are connected by the rods m, m) give proper motion to the piston heads C. D.
When in consequence of the rotary motion of the one and the sliding motion
of the other the end of the projection c on the disc b ceases its contact with
the end of the projection e¹¹ on the plate d, the outer circumference of the
projection c revolves against the inner circumference of the projection ell and
thereby prevents motion in the plate d until the projection c comes in contact with
the lower projection e on the plate d. At the point where the segmental projection c
on the disc b, ceases its contact with the end of the projection ell the cranks l, l,
have been thrown to their opposite extremes and the piston heads C, D, have reached
the extent of their travel and are held rigidly in place owing to the position of the
cranks 1, . It is at this point that steam is admitted to the cylinder.
The return stroke is performed in a similar manner to the foregoing by the
segmental projection c, on the disc b, coming in contact with the lower projection e
on the plate d.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is
The combination, in a steam engine, of the side bars H H provided with wrist
pins I I, of the cross heads G G carried by said bars, the piston rods F, F, F,
secured to cross heads G, G, the piston heads C, D, secured to piston rods F, F, F,
all having an intermitting reciprocating motion derived from and operated by the
mechanism consisting of disc b with its projection c said disc being secured to the
shaft a, the plate d with its projections e, ell, the rod g connecting the plate d to
the upper end of the slotted rocking lever i, the sliding block j, the wrist pins o, p
the cranks 1, l, the crank shaft k, and the connecting rods m, m, which connect the
wrist pins o, p, with the wrist pins I, I, on the side bars H, H, all substantially as
described for the purposes specified.