Improvements in Gas Engines having Two Pistons in the same Cylinder.
Year: 1886

page_text: PROVISIONAL SPECIFICATION.
Improvements in Gas Engines having Two Pistons in the same
Cylinder.
I, JOHN ROBERT NIXON of Heathcote House, York Road West Hartlepool, in the
County of Durham, Engineer do hereby declare the nature of this invention to be
as follows:-
My invention relates to that class of gas engines in which two pistons work in one
cylinder and the crank receives an impulse once during each revolution and consists
in improved arrangements of links and slides or combinations of mechanism for causing
the two pistons to move in the manner required for drawing in, compressing, expanding
and expelling the charge of gas and air and for making the volume of the charge
drawn in and the ratio of expanion variable.
My improved gas engine may be arranged as a vertical or inclined engine but is
preferably made horizontal and the description of my improvements applies to an
engine arranged in this position.
"
are
To the end of a suitable frame or bed plate provided with pedestals for the crank-
shaft I attach an open ended cylinder in which two pistons are fitted, one in the front
part and one in the back part of the cylinder. The words "front" and "back
applied to the cylinder and other parts hereinafter described as looked at from the
crankshaft end of the engine. To the crankpin two short links are coupled leading in
opposite directions. The other ends of these links are fitted or formed with pins or
gudgeons which are guided as hereinafter described so that one of them moves in
front of the crankshaft and one behind it at or about the level of the crankshaft centre.
Instead of the single links, in some cases I use one or two pairs of links. The back
gudgeon is connected by a connecting rod to the front piston. The front gudgeon is
made solid with or rigidly fixed in its link or links and carries at or near its outer
ends two slotted cross pieces fixed on it the slots being at right angles to the centre
line of the link, or the link or links may be made of T shape and the cross slots
formed in them. A sliding block carrying a pin is fitted in each slot so that it can
be traversed in the slot and fixed in any position. The pins are connected to the back
piston by two side rods which pass backwards above or below the crank shaft on each

page_text: side of the cylinder and may be bent or curved to clear the crank shaft. The motion
of each gudgeon is controlled either by straight guides or slide-bars, in which case the
gudgeon may be fitted with slide blocks or rollers, or by an arm vibrating on a pivot
near the base of the bedplate, in which case the gudgeons will have a reciprocating
motion in a slightly curved path. The guides for the front gudgeon are so arranged
that its centre moves in the centreline of the cylinder or approximately in this centre-
line, and the guides for the back gudgeon may be so arranged that its centre moves
quite or approximately in the same centreline or the guides may be made adjustable
so that its path may be inclined to this centreline or not, as may be preferred.
In the front part of the cylinder ports are arranged for the admission of the charge
of gas and air and for the exhaustion of the products of combustion. These ports are
provided with valves for opening and closing the admission and exhaust and these
valves may be actuated by the pressure in the cylinder or controlled by means of
gearing or mechanisin in any suitable ordinary manner. In the back part of the
cylinder beyond the extreme backward position of the front piston a small port is
arranged through which the charge is ignited by any convenient ordinary method.
As the crank revolves, the two pistons move in the cylinder and alternately approach
to and recede from each other. They are nearest together at the ends of the stroke
and furthest apart when the crank pin is passing the top and bottom centres or is near
these positions.
I shall first describe the action of the combination of links on the motion of the
pistons as it takes place when the slide blocks and pins to which the side rods are
attached are so fixed that the axes of the pins coincide with that of the gudgeon.
When the crankpin is on the forward centre, the two links, connecting and side
rods are all in a horizontal position and the pistons are drawn close together, while
the space between them communicates with the admission and exhaust ports. As the
crank moves, say, downwards, the links will assume an oblique position, whereby
the motion of the front piston is reduced and that of the back piston increased, so that
their distance from each other increases and the charge of air and gas is drawn in.
When the crank pin has reached its bottom centre, the pistons are farthest apart and
the lengths of the admission and exhaust ports are such that they are covered or closed
by the front piston when this position is reached. During the next quarter revolution
the effect of the obliquity of the links is reversed and the motion of the front piston
is accelerated while that of the back piston is retarded thereby, and when the crank
pin has reached its back dead centre, the pistons are close together again and the
charge between them is compressed. If the back gudgeon is guided in a path coinciding
with the centre line of the cylinder the distance of the pistons from each other at the
back and front end of the stroke is the same, but if the path is so adjusted that the
centre of the back gudgeon is on or nearer the centre line of the cylinder at the front
end of the stroke and above or below and farther from this centreline at the back end
of the stroke, then the pistons will be farther apart in their backmost positions by the
difference between the horizontal projections of the connecting rod in these extreme
positions, and the space into which the charge is compressed is larger. During the
third quarter of the revolution the obliquity of the links accelerates the front piston
and retards the back piston, so that the charge which is ignited when the crank pin
passes its back dead centre or is near this position, expands and propels the front
piston. When the crank pin arrives at the top centre, the exhaust port is uncovered
by the front piston, whose motion is retarded by the obliquity of the links while that
of the back piston is accelerated, so that the contents of the cylinder are expelled and
the pistons brought again into their most proximate position when the crank pin
reaches its front dead centre.
When arranged in this manner with the axes of the side rod pins and front gudgeon
coinciding, the pistons occupy the same positions when the crank pin is at the top and
bottom centre, so that the charge is expanded after ignition to the same volume it
occupied before compression. By shifting the side rod pins and slide blocks in the
slots of the cross pieces, say downwards, these volumes are made different. The front
link and slot then form a bellerank lever with its fulcrum on the gudgeon. With the

page_text: crank pin on the front and back dead centres, the pins will occupy a position vertically
below the gudgeon, and the position of the back piston will not be perceptibly affected
by the pins being shifted, as the side rods are of great comparative length. With the
crank on the down centre, the front link will slant from the gudgeon to the crank pin
in a backward and downward direction, and the slot in the cross pin at right angles to
the link in a downward and forward direction, so that the back piston is drawn
forward for a distance equal to the horizontal projection of the excentricity of the side
rod pin as compared with the position it occupied with concentric pins and gudgeon.
The distance between the pistons is thereby reduced by this length and the volume of
the admitted charge by a corresponding quantity. When the crank is on its top
centre, the front link will slant from the gudgeon in a backward and upward direction
and the slot in a downward and backward direction, so that the back piston is shifted
towards the back by a distance equal to the horizontal projection of the excentricity of
the side rod pin, as compared with the position it occupied with concentric pins
and gudgeon. The distance between the pistons is thereby increased by this length
and the volume to which the ignited charge expands increased correspondingly. By
varying the excentricity of the side rod pins the volume of gas and air admitted, and
the compression and expansion of the charge can be varied as may appear desirable for
the best utilisation of the gas or engine.
EMMOTT & Co.,
Agents for the Applicant.

page_text: COMPLETE SPECIFICATION.
Improvements in Gas Engines having Two Pistons in the same
Cylinder.
I JOHN ROBERT NIXON of Heathcote House, York Road, West Hartlepool in
the County of Durham, 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 that class of Gas engines in which two pistons work in one
cylinder and the crank receives an impulse once during each revolution Letters
Patent for which have been granted to James Atkinson Nod. 2712 and dated the
28th February 1885 and consists in improved arrangements of links and slides or
combinations of mechanism for causing the two pistons to move in the manner required
for drawing in, compressing, expanding and expelling the charge of gas and air and
for making the charge drawn in and the ratio of expansion variable.
My improved gas engine may be arranged as a vertical or inclined engine, but is
preferably made horizontal and the description of my improvements applies to an
engine arranged in this position.
In order that my invention may be more readily understood and carried into effect,
I have hereunto appended three sheets of drawings marked with letters of reference,
similar letters denoting similar parts on the differont figures.
Figure 1 shows a sectional elevation and figure 2 an end view of the engine
figure 3 sheet 2 shows a plan, partly in section; figures 4 and 5 enlarged views of
the sliding block; figures 6 and 7 show a modification of the arrangements for
varying the rate of expansion; figures 8 to 13 sheet 3 show diagrams of the positions
the parts occupy at different positions of the crank and sliding block.
""
To the end of a suitable frame or bed plate a provided with pedestals bb for the
crank shaft c I attach an open ended cylinder d in which two pistons e and fare
fitted, e in the front part and f in the back part. The words "front" and "back
are applied to the cylinder and other parts herein after described as looked at from
the crank shaft end of the engine. To the crank pin c¹ a short link with brasses g¹
is coupled, and connected at its other end by a gudgeon or pin g³ to a connecting
rod g³ attached by a pin e¹ to the front piston e. The gudgeon g² is guided by means
of two swing links or rocking arms g vibrating on a pivot or pin g passed through
the sides of the bed plate a. Instead of being guided by swing links, the gudgeon
may be fitted with slide blocks and guided in horizontal or inclined guides formed on
or attached to the bed plate.
To the crank pin c¹ another pair of links h h fitted with brasses h¹ h³ is coupled and
formed with gudgeons or pins h h at their other ends, which are supported by swing
links vibrating freely on the gudgeon A supported in two brackets 12 12 fixed to the
bed plate. The links are made T shaped at their outer ends and cross grooves or
slides h³ ³ are formed in them, in which a sliding block is fitted. This block is
shewn in detail by figures 4 and 5 on an enlarged scale and is formed as shewn solid

page_text: with a pin * between the cheeks he he. A pin h² is passed through the cheeks by
means of which the slide block is suspended from the gudgeon by a screwed
link. The gudgeon is formed with a thicker part in its middle portion, which is
bored out so that a nut can be rotated in it, the nut being formed with a hand
wheel on the top and held in its place by a nut being screwed upon it or by
equivalent means. By turning the nut, the slide block * can be moved up or down
in the slides or grooves in the links h, and is held by the screwed link in the
cross slides formed in the ends of the links hh during their movement, 13 and
the gudgeon l' vibrating in the brackets during this movement.
The back piston is connected by the pin or gudgeon working through
openings formed in the sides of the cylinder d to two side rods k k forged solid
at their other ends with the cross piece which is turned backwards as shewn at the
middle and has brasses einbracing the pin of the slide block * fastened to it or is
connected to the pin in any other suitable manner. This arrangement is adopted for
the purpose of clearing the sweeps of the crank shaft by the side rods while keeping
the links short and permitting the pin 4 to be brought into the same centre
as the gudgeons h³ ³. I do not however confine myself to the details of the
arrangements shewn, but these may be varied. Instead of guiding the gudgeons h² h²
by means of swing links they may be fitted with slide blocks and guided by guides
formed on or attached to the bed plate, or the swing link may vibrate on a pin
arranged near the bottom of the base plate instead of being supported in brackets.
The cross slides instead of being solid with the links may be formed or keyed
upon the outer ends of gudgeons fixed in the links, and slide blocks with projecting
pins to which the side rods are directly connected may be used. Instead of the
slide block being supported from the gudgeon by a vibrating link, the cross
slides of the links hh may be connected as shewn on figures 6 and 7 by a
cross piece m bolted to them and a nut m' with hand wheel arranged in this cross
piece as shewn, while the block is connected to a screw m³ and raised or lowered by
this arrangement. Instead of the pin 4 being formed centrally with the slide block *
and the side rods with a return tail, the block may have a projection with a pin or
gudgeon passed through it or pins formed on it and the side rods may have bosses to
fit on the pin or gudgeon or these pins. Obviously double or forked links may be
used in places instead of single links and vice versa, and the details generally may
be varied while preserving the essential points of the arrangement for actuating the
pistons, which are that the front piston directly actuates the crank or is actuated by
the crank through a short back link, while the back piston is actuated through side
rods connected to pins or their equivalent attached to blocks adjustable in cross slides
rigidly connected to a short front link or to short front links.
In the front part of the cylinder a port n is arranged for the admission of the
charge of gas and air and a port o for the discharge of the products of combustion.
The port n is provided with a valve n opening inwards against the pressure of the
spring n when a vacuum is formed between the pistons and admitting the charge,
the gas for which is drawn through the passage n³ communicating with the orifice n*,
while the air is drawn in through the orifice n°. The exhaust port o is fitted with a
valve o' opening outwards against spring pressure. These valves may be arranged in
any ordinary manner suitable for being actuated by the pressure within the cylinder
or controlled by gearing or mechanism in any ordinary manner, and forin no part of
my invention. Instead of a combined air and gas valve, separate valves for the
admission of the air and gas may be used, and the gas supply controlled by a governor
in any ordinary manner, or an additional gas valve so controlled may be used with
the combined air and gas valve. In the back part of the cylinder beyond the extreme
backward position of the front piston a small port is arranged upon which an igniter p
is fixed which may be actuated from one of the side rods & by a link p' and lever p³,
or may be otherwise arranged in any ordinary convenient manner for igniting the
charge at the required period of the revolution of the crank. The cylinder may be
jacketed with water at the part in which the pistons work.

page_text: As the crank revolves, the two pistons move in the cylinder and alternately approach
to and recede from each other.
They are nearest together at the ends of the stroke and furthest apart when the
crank pin is passing the top and bottom centres or is near these positions. I shall
first describe the action of the combination of links on the motion of the pistons as it
takes place when the slide blocks and pins to which the side rods are attached are so
fixed or held that the axes of the pins coincide with those of the gudgeons. The
positions of the pistons are shewn on the diagrams figures 8, 9, 10 and 11 sheet 3
corresponding to different positions of the crank pin. When the crank pin is on the
forward centre as shewn on figures 1, 3 and 8 the two links 9 and 7, connecting rod g³
and side rods k are all in a horizontal position and the pistons e and fare drawn close
together, while the space between them communicates with the admission and exhaust
ports. As the crank moves, say, downwards, the links will assume an oblique position,
whereby the motion of the front piston is reduced and that of the back pistou increased
so that their distance from each other increases and, the charge of air and gas is
drawn in.
When the crank pin has reached its bottom centre, as shewn on figure 9, the pistons
are farthest apart and the lengths of the admission and exhaust ports are such that
they are covered or closed by the front piston when this position is reached. During
the next quarter revolution the effect of the obliquity of the links is reversed and the
motion of the front piston is accelerated while that of the back piston is retarded
thereby, and when the crank pin has reached its back dead centre, as shewn on
figure 10, the pistons are close together again and the charge between them is
compressed. If the back gudgeon is guided in a path coinciding with the centre line
of the cylinder the distance of the pistons from each other at the back and front end of
the stroke is the same, but if the path is so adjusted that the centre of the back
gudgeon is on or nearer the centre line of the cylinder at the front end of the stroke
and above or below and farther from this centre line at the back end of the stroke, then
the pistons will be farther apart in their backmost positions by the difference between
the horizontal projections of the connecting rod and link in these extreme positions
and their full lengths, and the space into which the charge is compressed is larger.
For the purpose of reducing the compression I prefer to place the pin g on which the
swing links g* vibrate under the gudgeon g² or nearly under it when in the position it
occupies when the crank is on its forward centro, as shewn on the drawings. During
the third quarter of the revolution the obliquity of the links accelerates the front
piston and retards the back piston, so that the charge, which is ignited when the
crank pin passes its back dead contre or is near this position, expands and propels
the front piston. When the crank arrives at the top centre as shewn on figure 11 the
exhaust port is uncovered by the front piston, whose motion is retarded by the
obliquity of the links while that of the back piston is accelerated, so that the contents
of the cylinder are expelled and the pistons brought again into their most proximate
position when the crank pin reaches its front dead centre.
When arranged in this manner, with the axes of the side rod pin ³ and front
gudgeon coinciding, the pistons occupy the same positions when the crank pin is at
the top and bottom centro, if the front gudgeon is guided in slides in the centre line
of the cylinder, so that the charge is expanded after ignition to the same volume it
occupies before compression. When swing links are used as shown on the drawings
and the centre of the side rod pin h coincides with the centre of the gudgeon h², the
volumes between the pistons at the end of adınission and expansion differ slightly, as
is seen from the diagrams figures 9 and 11. By moving the sliding block with pin
a little upwards so that the pin his above the gudgeons h³, these volumes can be
made equal, if desired. On the other hand by shifting the side rod pin 7º and
block downwards, the difference between these volumes is increased. The front
links and slide h³ then form a bell crank lever having its fulcrum on the gudgeon
and a reciprocating motion as well as a vibrating one. With the crank pin on the
front and back dead centres, the pin 4 will occupy a position vertically below the

page_text: gudgeons or pins A³, as indicated by dotted lines on figures 8 and 10, and the position
of the back piston will not be perceptibly affected thereby, as the side rods are of
great comparative length. With the crank on the down centre, as shewn on figure 12,
the front link will slant from the gudgeon to the crank pin in a backward and
downward direction, and the cross slide at right angles to the link in a downward
and forward direction, so that the back piston is drawn forward for a distance equal
to the horizontal projection of the excentricity of the side rod pin h³ as compared
with the position it occupied with concentric pins and gudgeons. The distanco
between the pistons is thereby reduced by this length and the volume of the admitted
charge by a corresponding quantity. When the crank is on its top centre, as shewn
on figure 13, the front link will slant from the gudgeons or pins h² in a backward
and upward direction and the cross slide in a downward and backward direction,
so that the back piston is shifted towards the back by a distance equal to the horizontal
projection of the excentricity of the side rod pin, as compared with the position it
occupied with concentric pins and gudgeons. The distance between the pistons is
thereby increased by this length and the volume to which the ignited charge expands
increased correspondingly. By varying the excentricity of the side rod pin 4* or its
equivalent the volume of gas and air admitted, and expansion of the charge can be
varied as may appear desirable for the best utilisation of the gas or engine.
I am aware that gas engines with two pistons in the same cylinder working with a
differential motion and with ports covered and uncovered by the pistons have been
made before, by James Atkinson under his Patent No. 2712 of 1885 but in these the
centre of the crank shaft does not lie in the centre line of the cylinder and the pistons
are actuated from or connected to the crank pin by rods and beams. or two-armed
levers vibrating on fixed fulcra, and they have not been provided with arrangements
for varying the admission and rate of expansion.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to bo performed, I declare that what I claim is
Firstly, the general arrangement of gas engines, substantially as herein before
described and shewn by the drawings.
Secondly, in gas engines with two pistons working in the same cylinder, tho
arrangement of placing the centre of the crank shaft in the centro line of the cylinder
and producing the differential motion of the pistons by coupling the front piston
directly to the crank pin by a link or links and connecting rod and actuating the back
piston by side rods attached to a pin on a block or to pins on blocks adjustable in
cross slides formed on or rigidly connected to a link or links coupled to the crank pin,
substantially as herein before described and illustrated by the drawings.
Thirdly, in gas engines with two pistons working with differential motions in the
same cylinder, the arrangement of making the volumes at the end of admission and
expansion variable by means of adjustable sliding blocks, with pins actuating the back
piston, substantially as herein before described and illustrated.
EMMOTT & Co.,
Agents for the Applicant.