IMPROVEMENTS IN AND CONNECTED WITH GAS ENGINES
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by James Arthur Drake and Richard
Muirhead at the Office of the Commissioners of Patents on the 11th October
1881.
JAMES ARTHUR DRAKE and RICHARD MUIRHEAD, both of Maidstone, in the
County of Kent, Mechanical Engineers. "IMPROVEMENTS IN AND CONNECTED
WITH GAS ENGINES."
Our Invention relates to motor engines of the kind in which a piston moving in
a cylinder and coupled by a connecting rod direct on to a crank, as in a steam
engine, is worked by the expansive force resulting from the rapid combustion of
an intimate mixture of inflammable gas and atmospheric air introduced into the
cylinder in a compressed state or compressed therein.
Hitherto engines of this kind have generally been constructed with a slide valve
for controlling the admission and ignition of the combustible charge, such slide
being faced on both sides and working between the cylinder face and a cover held
up constantly against it by bolts and nuts provided with springs, clips, or other
contrivances, having sufficient strength to resist the maximum internal pressure.
Slides so constructed require a large amount of power to work them, which in
engines of small size represents a very large percentage of the gross indicated
power, besides which the friction being constant the wear and tear is considerable,
necessitating frequent refacing. To obviate this we dispense with the "cover
altogether, and in place thereof we substitute a cross bar, between which and the
back of the valve we interpose a toothed sector shaped rocking piece. The arc of
this sector is placed next the back of the valve and the centre (or apex) against
the cross bar. Thus the reciprocating motion of the slide is imparted to the
sector and rolling substituted for sliding friction.
"
In order to relieve the valve of all unnecessary friction when there is a little or
no pressure in the cylinder, the ark of the sector is made slightly eliptical, or in
other words, the radius of one end of the arc is greater than that of the other.
Consequently as the sector rolls to and fro a slightly reciprocating movement is
imparted to the cross bar against which the apex of the sector bears. The cross
bar is held up by springs compressed and released as the slide reciprocates, and the
springs are so arranged that the greatest compression takes place at the time when

page_text: the charge is ignited, and as the pressure in the cylinder decreases the motion of
the slide becomes reversed, the pressure exerted by the springs against the back
of the slide is also diminished, and thus during the time when there is little or no
pressure in the cylinder the slide is worked with very little friction and excessive
wear and tear thereby prevented.
Instead of making the arc of the sector eliptical (or eccentric) the same object
may be attained by making the are truly circular and concentric, and the back of
the slide on which it rolls in the form of an inclined plane, the inclination of which
can be graduated so as to compress the springs in exact accordance with the
resistance they are required to exert. By adding another cross bar containing a
third spring or rigid stop to come into operation at the moment when the greatest
resistance is required, the two other springs may be made still lighter and the
constant pressure by which the slide is held up still further reduced.
The slide valve is worked by an eccentric or small crank on a second
motion shaft placed parallel to the crank shaft and driven by spur gearing or
pitched chain in the ratio of 1 to 4, that is to say, the second motion shaft makes
only one revolution to four of the crank shaft, and according to one method of
working the piston would receive only one impulse for every four revolutions.
When an impulse is required for every two revolutions of the crank shaft the
ignition chambers and lighting jets for firing the charge are made in duplicate and
come into operation alternately, one charging D valve being situated between
them allows one charge to be drawn into the cylinder during its forward stroke
and another charge when returning.
Several advantages are derived from this 1 to 4 arrangement. Thus according to
the first method of working with one impulse for every four revolutions as a
maximum the possibility of false explosions, i.e., the firing of the incoming charge
by flame or sparks left in the cylinder from the previous explosion is entirely
obviated. Another advantage is that as the speed of the slide is relatively slow
the time allowed for the clearing of the ignition chambers and relighting of the
intermediate jets is relatively longer, and thus the ignition is more certain even at
much higher velocity than has hitherto been obtained. This applies equally to
both methods of working. By adopting this arrangement also less power is
required to work the slide.
The ignition of the charge is effected by an intermediate flame or flames lighted
by a standing jet or jets, according as the slide is single or double acting, carried
to the cylinder port in a cavity or cavities of the slide in the usual way.
In engines of the kind under description in which the inflammable charge
is compressed previous to explosion, it has been usual to establish a communi-
cation between the ignition chamber of the slide and the interior of the cylinder
by means of a small hole bored into the cylinder or by a groove or chase formed
in the face of the slide in order that the pressure of the gas in the cylinder
may be transmitted to the flame in the ignition chamber behind the latter as to
prevent the flame from being extinguished. The holes and grooves alluded to are
very apt to become choked up with soot and burnt oil, and their action thus
destroyed, in order to obviate which defect we dispense with the above named
small holes or grooves altogether, and instead thereof we so arrange the hole in
the face of the slide which supplies the gas to the intermediate flame in the
ignition chamber (and which exists as a necessity) relatively to the cavity of the
ignition chamber itself, that the former communicates with the cylinder port a little
before the edge of the ignition chamber is presented to it, and thus the liability of
the igniting flame to be extinguished or forced back into the supply pipe is obviated
without having any additional holes or grooves in the cylinder face or face of the
slide.
The admission and cut off of the gas is effected by an ordinary hinged or flap
valve which covers the orifices of both gas and air inlets. The gas is by preference
admitted by a row of holes situated at the rear of the air port, i.e., between the air
inlet and the hinge of the flap valve and is conducted by a groove or grooves on

page_text: each side of the air inlet to the frout part of the valve, so that when the valve
is lifted by the suction of the piston, the gas and air are drawn in in proper
proportions and thoroughly incorporated so as to form a combustible mixture.
The regulation of the speed of the engine is effected as follows:-The exhaust
valve, which is a spindle valve of the usual kind held down by a spring and
opened by a cam on the second motion shaft in the usual way, is held open by the
governors when the normal speed of the engine is exceeded. The area of the
exhaust valve being considerably more than that of the combined air and gas
inlets, the lift valve covering these will not be opened by the suction of the piston
so long as the exhaust valve is held open by the governors.
Our improvements also relate to the means adopted for cooling the slide and
cylinder. In order to effect this the foundation on which the engine is mounted
is made in the form of a hollow box, a cistern to contain water, which is caused to
circulate round the cylinder by a pump actuated by a pin in the end of the counter
shaft. The water is caused to enter by a pipe situated immediately below and
behind the port leading into the cylinder; it is then conducted by suitably
arranged passages around the said port, and is then discharged into the jacket
surrounding the working cylinder. It is to be understood that the back part of
the cylinder constituting the combustion chamber is not itself surrounded by
water but only the mouth of the port leading into the same. After having
circulated round the part of the cylinder in which the piston works the water
is returned to the cistern by a channel formed in the casting of the cylinder
casing.