Year: 1887

page_text: Date of Application, 26th May, 1887
Complete Left, 27th Feb., 1888
Complete Accepted, 13th Apr., 1888
I CHARLES DAVY of 30 Whitworth Road Sheffield in the County of York, Engineer
do hereby declare the nature of this invention to be as follows:-
.
My invention relates to an improved gas engine, and it has for its object to obtain
a ratio of expansion of the ignited gases greater than that of their previous com-
pression and to effect the complete expulsion of the residual or waste gases after they
have done their work in the cylinder.
These results are accomplished by causing the piston to make strokes of unequal
length and at different positions in the cylinder, the length of the inhaling and
working strokes being normal, whilst that of the compression stroke is less and that
of the exhaust stroke is greater than the normal length (i.e. the diameter of the orbit
of the crank,) the one being as much greater as the other is less.
The length of the exhaust stroke exceeds that of the working stroke by the extent
the piston is distant from the end of its cylinder at the commencement of the working
stroke so that the piston will travel to the extreme end of the cylinder on the exhaust
stroke, thereby completely expelling the waste gases, and the length of the com-
pressing stroke being so much less than that of the working stroke, the ratio of
compression is less than the ratio of expansion.
In carrying out the invention I use two cylinders having their pistons coupled on
to the same crank and both working on the four cycle principle but so timed as to
make the first and third and second and fourth strokes of the cycle together, that
is to say, when one is making its working stroke, (or is being propelled by the
reexpansion of compressed air, if fresh gas has not been admitted) the other is inhaling
a fresh charge and when one is making its exhaust stroke, the other is compressing
the charge previously inhaled, and reciprocally. The piston connecting rods are
coupled to the crank through the medium of an equal armed tumbler or elbow lever
whereby at certain points of the revolution of the crank the position of the pistons
relatively to each other and to the cylinders in which they work is changed so as to
cause them to make strokes of different lengths at different stages of the four cycle
operation, and so produce the results above described, this change in the relative

page_text: positions of the pistons being brought about by the resistance to compression of the
charge contained in one of the cylinders unbalanced by any corresponding resistance
in the other cylinder. The tumbler or elbow lever may be pivoted directly on the
crank pin or upon a rod coupled to the crank pin in the manner of an ordinary con-
necting rod, and supported at the other end by a radius link or slides. Instead of an
elbow lever or tumbler, a tumbler shaft with lever arms at its opposite ends may be
used.
C. DAVY.
By A. M. & Wm. Clark,
53. Chancery Lane, London,
Patent Agents.

page_text: 1, CHARLES DAVY, of 30, Whitworth Road, Sheffield, in the County of York,
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 gas engine; and it has for its object to obtain
a ratio of expansion of the ignited gases greater than that of their previous
compression, and to effect the complete expulsion of the residual or waste gases from
the cylinder.
These results are accomplished by causing the piston to make strokes of unequal
length and at different positions in the cylinder, the length of the inhaling
and working strokes being normal, whilst that of the compression stroke is less, and
that of the exhaust stroke greater than, the normal length (i.e. the diameter of the
orbit of the crank) the one being as much greater as the other is less.
The length of the exhaust stroke exceeds that of the working stroke by the distance
of the piston from the end of its cylinder at the commencement of the working stroke,
so that the piston will travel to the extreme end of the cylinder on the exhaust stroke,
thereby completely expelling the waste gases, and the length of the compressing
stroke being so much less than that of the working stroke, the ratio of compression is
less than the ratio of expansion.
The desired object is accomplished by causing the distance between the crank pin
and the working face of the piston, to be varied automatically during the different
phases or strokes of the four cycle system of working, this being effected by the
introduction, at the joint between the connecting rod and crank pin or between the
connecting rod and piston trunk or rod, of what I term a rocking rank or tumbler,
whereby the length of stroke of the piston and its position in the cylinder, are
controlled, as hereafter described.
By the employment of a rocking crank or tumbler, the outward motion of the
piston is controlled, so that the piston, when completing its compression stroke, is
arrested in a gradual and silent manner upon the arrival of the tuinbler or crank at
its dead point.
Reference is to be had to the accompanying drawings forming part of this
specification, wherein I have represented examples of the application of my invention
to a single cylinder and twin cylinder engine respectively.
I will first describe the invention as applied to a single cylinder engine. Figure 1
is a longitudinal vertical section of the engine, the piston being in the position it
occupies at the end of the exhaust stroke. Figure 2 is a similar view of the engine,
the piston being in the position it occupies at the end of the compression stroke.
Figure 3 is a horizontal longitudinal section corresponding to figure 2. A is the
cylinder, and Bits water jacket, as usual. is the working piston, D its connecting
rod, and E the crank.

page_text: In the case of a single cylinder engine, the invention consists in connecting the
working piston C to its connecting rod D through the medium of the rocking crank
or tumbler F, in such a manner that the effective length of the connecting rod D is
at certain periods in the cycle of operation, increased and decreased according to the
position occupied by the said crank or tumbler, with the result that the piston is
caused to make strokes of different lengths and positions in the cylinder, as hereafter
described.
The tumbler F is a double crank pivoted on gudgeons within an extension C* of the
piston, and the connecting rod D takes hold of its crank pin f¹. The crank arms have
extensions making an angle of about 120° to the said arms and terminating in pins f
which are taken hold of by a pair of links h to which are connected springs H whose
other ends are attached by links ¹, to fixed points of the piston. The tendency of
these springs is to throw the tumbler into the position it occupies in figure 1, and
thereby to increase the effective length of the connecting rod D. This they are free to
do during the exhaust stroke, when little resistance is offered by the gases to the inward
motion of the piston, the extent to which the effective length of the connecting rod is
increased, being sufficient to cause the piston to advance quite up to the inner end of
the cylinder and thus expel the whole of the products of combustion therefrom. The
relative position of the parts remains unchanged during the next following outward
or inhaling stroke, but on the next inward or compression stroke, the power of the
springs is overcome by the resistance to compression offered by the gaseous charge in
the cylinder, the consequence being that the tumbler is thrown over to the position
shewn in figure 2 thereby shortening the combined effective length of the piston
and connecting rod, so that the piston does not advance to the inner end of the
cylinder.
.
It will be observed that the crank or tumbler F is at its dead point in figure 2, the
crank pin, centre f, and the driving crank E, being in the same straight line. The
relative position of the parts remains unchanged during the ignition or working
stroke, until on the opening of the exhaust the springs H are free to act and return
the tumbler to the position shewn in figure 1.
I will now describe the application of the invention to the pistons of a twin cylinder
engine. Figure 4 is a longitudinal section of so much of the engine as is necessary
to illustrate the invention. Figure 5 is a similar view of a modification. Figure 6
is a section through the tumbler, the section being taken through the two crank
pins fl and the centre gudgeons f. Figure 7 is a plan of another modification.
Figure 8 is a diagram illustrating the varying strokes of the pistons.
The two twin cylinders A A' are placed the one above the other, and their
pistons CC are coupled by connecting rods D D to the same driving crank E, of
which only the pin and the orbit in which it revolves are represented in figure 4, the
crank shaft being omitted. Both cylinders work on the four cycle principle, but the
pistons are so timed that when one is making the first or inhaling stroke, the other
is making the third or working stroke, and when one is making the second or
compression stroke, the other is making the fourth or exhaust stroke, and
reciprocally.
The connecting rods D D¹ are coupled to the said driving crank pin E through
the medium of an equal armed elbow lever or tumbler F, the connecting rods taking
hold of the tumbler crank pins f¹ and the tumbler oscillating at certain points in the
revolution of the main driving crank E on the said crank pin as, a centre. By the
oscillation of this tumbler, the position of the pistons CC relatively to each other
and to their cylinders is changed so that they make strokes of different lengths at
different stages of the four cycle operation, this change in the relative positions of the
pistons being brought about by the resistance to compression of the gaseous charge
contained in one of the cylinders unbalanced by any corresponding resistance in the
other cylinder, and the extent of the relative motion of the pistons is limited by one
of the tumbler crank pins farriving at its dead point.
In figure 4, the piston Chas just completed its compression stroke, and the piston ()
has just completed its exhaust stroke.

page_text: In figure 5, the tumbler F, instead of being pivoted directly on the crank pin E, is
pivoted by gudgeons f on a forked rod I coupled to the crank. pin E in the manner
of an ordinary connecting rod, and supported at the other end by a radius link i or
by slides. The tumbler in this case, is in the form of a pair of discs turning together
as one, in which the crank pins flare fixed, and in order to check oscillation and
avoid shock, a brake shoe K fitted in the head of the rod 1 is pressed by a spring
behind it, against the periphery of the discs.
It will be obvious, without illustration, that instead of an elbow lever or tumbler, a
tumbler shaft with cranks at its opposite ends, may be used, in which case the
cylinders may be placed side by side. Such an arrangement is represented in
Figure 7, which represents a plan of the engine. The same letters of reference
represent parts performing the same functions as those in the previous figures.
In this arrangement, the centres f' to which the connecting rods D D¹ are attached,
are the crank pins of a pair of double cranks on the tumbler shaft F, and this shaft is
journaled at its outer ends, in two rods I coupled to the main crank E, which may
either extend across, as shown, or may consist of two cranks in line, with a bearing
between them. In this case, the other ends of the rods I work in slides i formed on
the trunks C✶ of the pistons. The brake to check the oscillation of the tumbler past
the dead centres of its cranks, consists of a disc F* fast on the tumbler shaft, or
forming one of the members of one of the cranks f¹ embraced by a strap K pressed
against the disc by a spring whose other abutment is fixed to the rod I, as shewn, the
periphery of the disc being eccentric to the shaft, to cause the brake to act most
effectually on the arrival of either pin f' at its dead point.
The diagram, figure 8, which applies indifferently to all the figures, illustrates
particularly the approximate path or orbit described by the pin f¹ to which is con-
nected the upper piston C, in figure 4. From 1 to 2 is the inhaling stroke, of normal
length; from 2 to 3 is the compression stroke, by which the gases represented by
volume W X, are compressed to the volume represented by W Y, ready for ignition.
From 3 to 4 is the working or propelling stroke, also of normal length, during which
the gases expand from the volume W Y to the volume W Z; and from 4 to I is the
exhaust stroke by which the products of combustion are completely expelled, except
of course from the clearance spaces. The phases represented by lines W, X, Y, Z,
are similar for the other cylinder.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is ;-
1st. In a gas engine, the combination with the working piston, connecting rod, and
crank, of a rocking tumbler, elbow lever, or crank, so applied as at certain periods in
the cycle of operation, to increase and decrease the distance between the working face
of the piston and the main crank pin so as to cause the piston to perform strokes of
different lengths and positions in the cylinder, the change in the relative position of
the piston being limited by the arrival of the tumbler at its dead point, substantially
as and for the purpose specified.
2nd. In a gas engine, the combination with the piston and its connecting rod, of a
rocking tumbler, elbow lever, or crank, applied substantially as herein described and
illustrated in Figures 1 to 3 of the drawings, so as to increase and decrease the
effective length of the connecting rod at certain periods in the cycle of operation, the
motion of the tumbler in one direction being produced by the resistance of the gases
to compression and in the other direction by spring power, as specified.
3rd. In a twin cylinder gas engine, the combination with the two pistons and their
connecting rods, of a tumbler or rocking elbow lever whereby the two pistons are
connected with one another and with the same crank and whereby the resistance of
the gases opposed to the one piston when making its compression stroke, is caused to
move the other piston close up to the back end of its cylinder, so as to effect the
almost complete expulsion of the residual gases from said cylinder and reciprocally,

page_text: and whereby the aforesaid change in the relative positions of the pistons is limited by
the arrival of the tumbler at its dead point, as specified.
4th. The three several combinations and arrangements of parts of a twin cylinder
gas engine, in which the two pistons are connected with one another and with the
same crank shaft through the medium of a tumbler, substantially as herein described
and represented in Figures 4, 5, and 7, of the drawings.
Dated this 97th day of Februa 1888
CHAS. DAVY.
By A. M. & Wm. Clark,
53, Chancery Lane, London,
Patent Agents.