Year: 1887

page_text: Date of Application, 13th Oct., 1887
Complete Specification Left, 13th July, 1888
Complete Specification Accepted, 31st Aug., 1888
I CHARLES DAVY of 30 Whitworth Road, Ranmoor, Sheffield, in the County of
York, Engineer, do hereby declare the nature of this invention to be as follows:-
My Invention relates to improvements in gas engines whether single ar twin
cylinder engines using a homogeneous mixture of air and gas and working on the
four cycle principle, and has for its object first, to enable the residual gases of com-
bustion to be wholly (or nearly so) swept out of the working cylinder by a scavenger
charge of pure air whilst the working piston is making its exhaust stroke.
To this end the invention consists in the combination with the working cylinder of
an air pump worked in such manner that the delivery of air therefrom takes place
coincidentally with the discharge of waste gases during the exhaust stroke of the
working piston. The air pump cylinder is in connection with the working cylinder
through an ordinary lift discharge valve (or a suitable slide valve) which may either
be lightly loaded and open automatically or be worked by suitable gear. The scavenger
charge of air is forced under slight pressure into the working cylinder preferably
through the working piston which has for that purpose a suitably formed passage
through its back end in communication by a longitudinal groove in its side with the
port leading from the air pump discharge valve.
By this means the gases of combustion will be expelled through the exhaust valve
of the working cylinder, partly by the working piston, and partly by the scavenger
charge which is forced into the working cylinder during the exhaust stroke, so that
at the end of the exhaust stroke the combustion chamber will contain a charge of
nearly pure air instead of gases of combustion. The capacity of the air should
be sufficiently great to ensure practically the whole of the residual gases being
blown out.
pump
To ensure the intimate and homogeneous mixture of the inhaled charge of com-
bustible gas and air, with the air remaining in the combustion chamber from the
previous scavenger charge, I cover the inlet port of the combustion chamber with
a fine rose through which the charge passes at a high velocity in fine jets directed
towards all parts of the combustion chamber.

page_text: The invention has secondly for its object to regulate the speed of the engine in
which a scavenger charge of pure air is used as above described.
As the combustion chamber contains only pure air or nearly pure air at the com-
mencement of the inhaling stroke the inhaled combustible charge must be very rich
in gas. When the maximum power of the engine is required the homogeneous
mixture is relatively rich and in order that the speed may be regulated within certain
limits, the engine is made to automatically reduce the quantity of gas only or air and
gas inhaled. Before however the homogeneous mixture becomes so impoverished
that it will not fire with good effect the engine is made to cut off the gas supply
entirely and the engine will then, without loss of gas, miss fire until the speed of the
engine is reduced sufficiently when the normal working of the engine is resumed.
Dated this 13th day of October 1887.
CHAS.
DAVY.
By A. M. & Wm. Clark,
53, Chancery Lane, London,
Patent Agents.

page_text: COMPLETE SPECIFICATION.
Improvements in Gas Engines.
I, CHARLES DAVY, at 30 Whitworth Road, Ranmoor, 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 improvements in gas engines whether of the single or twin-
cylinder type using a practically homogeneous mixture of air and gas and working
on what is known as the four-cycle principle; and my invention has for its object
first to enable the residual gases of combustion to be wholly (or nearly so) swept out
of the working cylinder by a scavenger charge of pure air whilst the working piston
is making its exhaust stroke.
For this purpose, the invention consists in the combination with the working
cylinder, of an air pump working in such manner that the delivery of air therefrom
to the working cylinder takes place coincidentally with the discharge of waste gases
during the exhaust stroke of the working piston, the air being delivered from the
pump to the cylinder directly in front of the working piston in such a direction as to
displace and force out of the working cylinder as much as possible of the residual
gases of the previous explosion so that there shall only remain in the cylinder pure
air to be mixed with the next incoming charge of gas and air. To this end the air
pump cylinder is in connection with the working cylinder through an ordinary lift
discharge valve (or a suitable slide valve) which may either be lightly loaded and
open automatically or be worked by suitable gear. The scavenger charge of air is
forced under slight pressure into the working cylinder preferably through the
working piston itself which has for that purpose a suitably formed passage through
its back end in communication, by a longitudinal groove in its side, with the port
leading from the air pump discharge valve.
By this means, the gases of combustion will be expelled through the exhaust valve
of the working cylinder partly by the working piston and partly by the scavenger
charge which is forced into the working cylinder during the exhaust stroke in such a
way as to carry before it and expel from the cylinder the residual gases from the
previous explosion. By this means the combustion chamber will contain at the end
of the exhaust stroke nearly pure air instead of gases of combustion.
The capacity of the air pump should be sufficiently great to ensure practically the
whole of the residual gases being blown out.
To ensure the intimate and homogeneous mixture of the inhaled charge of com-
bustible gas and air with the air remaining in the combustion chamber from the
previous scavenger charge, the inlet port of the combustion chamber is covered with
a fine rose through which the charge passes at a high velocity in fine jets directed
towards different parts of the combustion chamber the resulting explosive mixture
being practically homogeneous.
The Invention has secondly for its object to regulate the speed of the engine in
which a scavenger charge of pure air is used, as above described.

page_text: I
As the combustion chamber contains only pure air or nearly pure air at the com-
mencement of the inhaling stroke, the inhaled combustible charge must be more than
usually rich in gas in order that the gas and air (including the residual scavenger
charge) may be present in the proper proportions in the cylinder to constitute an
efficient firing mixture. When the maximum power of the engine is required, the
explosive mixture is relatively rich, and in order that the speed may be regulated
within certain limits, the engine is made to automatically reduce the quantity of gas,
or of air and gas, inhaled. Before however the mixture in the cylinder becomes so
impoverished that it will not fire with good effect, the engine is made to cut off the
gas supply entirely and the engine will then miss fire without loss by the exhaustion
of unexploded gas, until the speed of the engine is reduced sufficiently, whereupon
the normal working of the engine will be resumed.
Reference is to be had to the accompanying drawings forming part of this speci-
fication which illustrate, in figures 1 and 4 examples of two modes of introducing the
scavenger charge of pure air as applied to a twin cylinder engine.
Figure 1 represents a horizontal section of the engine taken through the working
and air pump cylinders, one of the working pistons being shewn in section and the
other in plan. A, A', are the working cylinders and B B₁ are the working pistons
coupled to a crank shaft C by the usual connecting rods. The working cylinders
may be provided with valves and valve gear of any suitable type for the admission of
air and gas, for igniting the explosive charge, and for exhausting the products of
combustion on the well-known. four-cycle principle. The valve gear is so timed that
the pistons 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 re-expansion 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.
Between the working cylinders (or in any other convenient position) there is an air
pump cylinder D the piston E of which makes its discharge stroke at the same time
that the working pistons B B₁ are making their inward strokes, the one making an
exhaust and the other a compressing stroke, as above mentioned. The cylinder D is
provided with two outlet valves a a¹ communicating respectively with the working
cylinders A A' through the ports c c¹. The cylinder is provided with one or two
inlet or suction valves b, seen in figure 2 which is a vertical section on line 1-1
figure 1, shewing the valve a and beneath it the valve b. In order that the scavenger
charge may enter the working cylinders throughout the exhaust stroke, the pistons B B¹
have each a longitudinal groove d or d¹ cut along the side next to, and coinciding
throughout the whole of the piston stroke with, the port c or c¹ and opening out in
the form of a bell mouth dx at the inner or working face of the piston.
It will be understood that, although the air pump makes its inward or discharging
stroke concurrently with the inward strokes of the two working pistons, the scavenger
charge of pure air always passes through that one of the working cylinders (as for
instance A) which may be at the time discharging the products of combustion since
the pressure of the gas and air (or of air only as the case may be) then undergoing
compression in the other cylinder (as in A¹) is superior to the pressure existing in the
air pump and therefore keeps the outlet valve a' leading to that cylinder closed. The
outlet valves a a' and the inlet valves are preferably ordinary automatic lift
valves but they may be lifted by mechanism or I may employ mechanically moved
slide valves.
Figure 3 is a vertical section through the combustion chamber of one of the working
cylinders.. F is the inlet valve for air and gas, G is the exhaust valve and H is the
igniting valve, these three valves being of any ordinary or suitable type.
To ensure as far as possible, homogeneity in the gaseous mixture I cover the inlet
valve F, figure 3, with a fine rose. I by which the inhaled charge, is dispersed amongst
the pure, or nearly pure, residual charge of air remaining in the combustion chamber
at the termination of the exhaust stroke.
Instead of causing the scavenger charge to pass through the working pistons B B¹,

page_text: it
may be made to enter at the back of the combustion chamber and in this case the
working pistons are constructed without longitudinal grooves and bell mouths. The
outlet valves a a¹ are in this case placed as far back as convenient, and to prevent
the scavenger charge passing directly to the exhaust valves G, the ports c c¹ leading
into the working cylinders are so formed as to direct the scavenger charge of air
towards the working face of the piston, as shewn in figure 4. The air pump valves
are precisely the same as described and illustrated in figures 1 and 2.
In order to apply this part of the invention to a single cylinder engine, the air
pump piston would have to make one stroke to every two strokes of the working
piston and, as in the former case, would be timed so as to make its discharge stroke
concurrently with the exhaust stroke of the working cylinder. The air pump piston
would not in this case be worked directly from the engine crank, as in the former
case, but through the intervention of a mechanical movement which will cause the air
pump piston to make one stroke to every two of the working piston, but as the motion
of the air pump piston during its discharge stroke should not be slower than that of
the working piston, this mechanical movement should be such as to cause the air pump
piston to pause a sufficient time at the end of its stroke or to make its suction stroke
slowly and its discharge stroke quickly. Such a motion would be obtained by working
the air pump piston by a suitably-shaped cam driven from the crank shaft by spur
gear giving one revolution of the cam to two of the crank shaft.
The governing of the engine is regulated either by varying the supply of gas
whilst the supply of air remains constant or by varying the supply of both air and
gas within such limits under ordinary variations of speed that the mixture of the rich
fresh charge of air and gas with the residual charge of air shall be neither too rich
nor too poor in gas to fire effectively.
I will first describe the method of governing as applied to a single cylinder engine.
Referring to figure 5, F is the inlet valve for air and gas the air being admitted to the
valve chamber by the port or orifice and the gas by the port h after passing through
the valve g. K is a shaft driven at half the speed of the crank shaft, L is an eccentric
giving motion by the rod M to the rock lever N which is pivotted at O. The motion
of the lever N is communicated to the valves F and g through pendent strikers P p
jointed to the lever N at points about in line vertically above the valve spindles, on the
ends of which the strikers act. The striker p is inclined on its lower edge in the
direction of its width, the incline being either straight or preferably curved to a
varying radius in such way that by the lateral shifting of the striker to a progressively
varying extent, the distance between its inclined face and the end of the valve spindle
will be varied proportionately so that it will strike the valve spindle sooner or later, as
the case may be; this inclined face being stepped or serrated to prevent slipping on
meeting the valve spindle.
The striker P is of greater width than the striker p but one portion of it is similar
in shape and dimensions thereto. The lower end of the remaining portion or excess
width may be concentric to the pin by which the striker is jointed to the lever N. The
striker is coupled to the lever 7 worked by the governor Q by a link q' and the
striker P is coupled to the striker p by a link q' whereby the centre lines of the similarly
shaped portions of the two strikers are at all times kept parallel. When the engine
is developing its full power and the governor is in its lowest position the lowest or
longest portions of the strikers act upon the valves F 9, so that the charge of air and
gas is admitted throughout the inhaling stroke and a relatively rich charge is formed
in the working cylinder. By the rise of the governor consequent on an increased
speed of the engine the strikers are shifted laterally so as to bring shorter portions of
the strikers over the spindles of the valves F and g and consequently cause the valves
to be opened later and to a less extent, and to be closed earlier, thus reducing the
strength or richness of the explosive charge in the working cylinder. When by a
further increase of speed the charge would become so weak as not to fire with good
effect, the striker p is moved to such an extent that the spindle of the valve g is no
longer in its path and the admission of gas is consequently stopped entirely; the
striker P however being of greater width than p still continues to act on and open

page_text: the valve Fadmitting air only until the speed is so reduced as to bring the striker p
into action again. A cock on the gas supply pipe is adjusted so that when the engine
is developing its full power the mixture formed in the combustion chamber cannot be
richer than say one of gas to nine of air. By the action of the governor above
described the proportions are varied up to, say one of gas to fifteen of air.
In some cases, I dispense with the striker P, as shewn in figure 6 and make the
end of the lever N act directly upon the spindle of the valve F which is then opened
to a definite and constant extent. In this case, the speed is regulated by admitting
more or less gas only within the limits of efficient combustion before mentioned.
Figure 7 shews a duplication of the mechanism represented in figure 5 for working
and controlling the valves F and g, of a twin cylinder engine by the governor. In
this case also, the valve F may have a constant lift while the valve has a variable
lift as before described with reference to figure 6.
g
In each case, the adjustment of the mechanism, so that the striker which opens the
gas valve shall cease to act altogether when the mixture in the cylinder becomes too
impoverished to fire effectually, will be determined by experiment or by calculation.
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 :-
1. A gas engine, working on the four cycle principle, wherein a scavenger charge
of pure air is delivered by an air pump worked by the engine into the working
cylinder or cylinders of the engine during the exhaust stroke or strokes of the working
piston or pistons in such a direction as to carry before it and sweep out the residual
gases of the previous explosion, substantially as specified.
2. In a gas engine in which an air pump is combined with the working cylinder or
cylinders in the manner and for the purposes described, the construction of the
working piston or pistons with a passage communicating throughout the exhaust
stroke with the pump and opening through the inner face of the piston, substantially
as specified.
3. A four cycle gas engine wherein the charge of gas and air is diluted by the
residue of a scavenger charge of pure air delivered to the working cylinder during
the exhaust stroke and wherein the admission of gas (or of gas and air) is so regulated
that the gas supply will be diminished as the speed increases and altogether cut
off when the speed becomes excessive and the engine is required to miss fire, as
specified.
4. The herein described regulating mechanism actuated by the governor and
acting on the gas or gas and air admission valves, in the manner and for the purpose
specified.