IMPROVEMENTS' IN HOT-AIR-ENGINES, PARTLY APPLICABLE TO OTHER FLUID PRESSURE ENGINES
Year: 1883

page_text: LETTERS PATENT to Wilhelm Schmidt of Wolfenbüttel, Germany for an
Invention of IMPROVEMENTS' IN HOT-AIR-ENGINES, PARTLY APPLICABLE TO
OTHER FLUID PRESSURE ENGINES
PROVISIONAL SPECIFICATION left by the said Wilhelm Schmidt at the
Office of the Commissioners of Patents on the 10th November 1883.
"
WILHELM SCHMIDT of Wolfenbüttel, Germany, IMPROVEMENTS IN HOT-AIR-
ENGINES, PARTLY APPLICABLE TO OTHER FLUID PRESSURE ENGINES
"
This invention relates chiefly to closed hot air engines working with high-pressure.
It comprises a double-acting air pump adapted to act both as a compression
pump proper and as a pump for replacing the escaped air, this effect being obtained
by completely shutting off the air contained in the waste space at the reversal
of the stroke, so that the air may expand to a pressure below that of the atmosphere,
any loss of air may be replaced through a suction valve operated by the excess of
pressure of the atmosphere.
Also a connecting rod adapted to be longthened by means of an eccentric
for the purpose of varying the size of the waste space and thereby also the pressure
in the engine.
Also an extensible valve-rod or eccentric-rod for the purpose of stopping the
engine.
Also a liquid receptacle heated by the heating apparatus of the engine or by
the heat of the working air, and filled with liquid at the boiling point, so that any
rise of temperature beyond the limit fixed for the heating apparatus, or for the
working air causes the evaporation of liquid and thereby a mechanical regulation
of the quantity of air admitted to the grate.
Also an air moistening apparatus placed in the air conduit, and filled with liquid
having a high boiling point, for the purpose of charging the air with unevaporated
particles of liquid adapted to preserve the packing, lubricant and joints.
Also the combination of a heating apparatus with a preliminary heater, in
which the exhaust from the cylinder serves to heat the frosh or cold air, by flowing
along the latter but in opposite direction, preferably through a pipe coil surrounding

page_text: that part of the heating coil of the heating apparatus in which the air has not yet
been raised to a high temperature.
Also a double acting power and compression cylinder bored to the same width,
the excessive size of the compression cylinder being compensated for by carrying
back a portion of the air sucked in.
Also the use of an ordinary distribution slide valve against which the crank
has an angular lead of 90° and which contains lateral ports or channels carrying
pressure valves, for the purpose of controlling a double-acting compression pump.
Also the use of cavities or notches between the lower or main valve and the
expansion or auxiliary valve of hot-air, gas or steam-engines, in order to produce
a difference of pressure botween the two valves and the valve chest, by means
of the pressure of expansion which periodically exists in the said hollows, whereby
the lower valve or main valve is periodically coupled to or detached from the upper
valve (connected with the eccentric).
Also the use of a second suction appliance in the compression cylinder, in
combination with a cut-off or closing appliance controlled by the governor, both
appliances being connected by a pipe leading to the suction pipe, for the purposo
of temporarily setting out of action the atmospheric suction valve in the compression
cylinder.
Also the use of a valve with adjustable load, placed between the two slide-
valve-chests, in combination with a throttle valve in the pipe conduit controlled by
the governor, for the purpose of admitting cold air direct into the working cylinder
thereby regulating the effect of the engine.
Also the adoption of the improvements described for open hot air engines, by
the use of an open suction pipe into which water is sucked by a closing device
controlled by the governor,

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Wilhelm Schmidt in the Patent Office on the 9th May 1884.
WILHELM SCHMIDT, of Wolfenbüttel, Germany, "IMPROVEMENTS IN HOT-AIR-
ENGINES, PARTLY APPLICABLE TO OTHER FLUID PRESSURE ENGINES,"
This invention chiefly relates to hot air engines working with high pressure and
using repeatedly the same quantity of air,
In describing this invention reference will be made to the accompanying
drawings of which Fig I is a longitudinal vertical section, Fig II a horizontal
section and Fig III a half elevation and half cross section of an engine embodying
my invention, while the remaining Figures illustrato details and modifications.
The combined hot and cold cylinder a contains two pistons b, b¹ at such a
distance from each other that the cold air is prevented from coming in contact
with the walls of the cylindrical hot air space a', hereinafter called hot air cylinder
or power cylinder, and that the hot air is prevented from coming in contact with
the walls of the cylindrical cold air space a, hereinafter called cold air cylinder or
compression cylinder.
The two cylinders are provided with slide valves s and s¹, and the valve motion
of the hot air or power cylinder a is exactly the same as that of a single acting
steam engine working with steam cut off at 3 stroke, the eccentric being
120 degrees in advance of the crank.
The valve gear of the compression cylinder a¹¹ is arranged in such manner that
at the end of the suction period (that is to say when the crank is in one of its
dead centres) the piston b during its back stroke or compression stroke first
forces 1% or 1 of the air which has been sucked in, back into the suction
chamber connected with the cooling pipe g placed in a cold water tank.
Subsequently the piston compresses the air still contained in the cylinder and
finally forces the compressed air into the compression chamber d'. During the
compression the valve 8' shuts off the cylinder all from the compression chamber d¹.
The cold air which has been sucked in from the worm g, subsequently compressed
in the cylinder a" and then conducted into the chamber d', passes through pipe d"
into the bell shaped air moistening apparatus h, where it flows around the
receptacle e" in the direction of the arrows, during which time the air is saturated
with water, oil or any other substance contained in the receptacle e¹¹.
Afterwards the cold air passes through piper dil into the heating vessel q
containing a pipe coils, made of wrought iron (or other suitable material) and
cast into the body q; during the passage through the coil the air is heated
and passes at the lowest point of the coil through pipe d' into the valve
chamber d, after which it flows into the chamber a¹ in order to act on the power
piston b.
The cast iron jacket g protect the heating coil from burning, and serves for
transmitting and storing heat.
It should be observed, that when the piston is in its extreme position to the
right, the chamber all is completely closed by the lap of the valve, so that the
compressed air contained in the chamber all may be expanded to one ritmosphere
during the first part of the subsequent stroke, and if the machine is short of air, so
as to allow the pressure to fall below one atmosphere, atmospheric air is sucked in
through valve v. (whereby the normal state of the machine, as regards the supply
of air, is maintained.). When the piston moves further towards the left the
chamber a communicates, with the pipe coil g, and cold air flows in from the
latter, to be compressed during the back stroke in the manner as described above:

page_text: By means of this suction valve v, the air lost through leakages is therefore
replaced. In the meantime the air has had the following effect on the other
piston b.
The hot air from the valve chamber & acts on the piston b and presses the same
towards the right; when the stroke of the piston towards the right is terminated
(the communication between a¹ and d having been cut off by means of the valvo 8
already at 10 of the stroke) the chamber a¹ is set in connection with the
chamber-i, so that the expanded air passes- during the return stroke (towards the
_left) of the piston, from chamber a' into chamber i and from the latter through
pipe into the coil pipe which encloses the heating coil z. The air in the
coil ¹, being still hot, heats the coil from without, as it comes in contact with
those parts. of the coil in which the air has a comparatively low temperature.
As it rises in a helical line around the heating coil the exhaust air becomes
gradually colder and comes in contact with still colder sections of the coils and
escapes above through pipe m. The pipe m leads directly to the worm g in which
the air is completely cooled before it begins again to circulate through the engine.
The machine is otherwise constructed as follows:
2
a.) The apparatus for moistening the air comprises a liquid receptacle e", the
upper edge of which is turned inward and which is provided at the bottom with
lateral holes. The liquid is kept in constant circulation by escaping through the 1
bottom and being brought back into the receptacle from above by the air current.
The receptacle is filled with liquid of a high boiling point.
b. The machine may be set in motion or stopped by lengthening, respectively
shortening, the valve rod connected with the eccentric, the two rods being
connected with each other by means of a pin or bolt which has an eccentric bearing
and is provided with a spring and a handle adapted to be turned and adjusted as
required. If the valve rod is lengthened, the valve no longer opens the port
between d and a¹, whereby the engine is stopped.
c) To prevent the excessive heating of the heating coils and to prevent the air
in the working cylinder from exceeding a given maximum temperature, the cast
iron body q is surrounded by a closed circular vessel f filled with liquid of a
certain boiling point (for instance oil of a boiling point corresponding to the desired
temperature of the air working the machine or of the heating apparatus.)
From the bottom of the vessel fa pipe leads to the vessel U provided with a
float h¹¹ connected by means of rod g¹ with a throttle valve d³ situated in the air
pipe, which serves to supply the air for entertaining the combustion. If the
heat in the heating coil and consequently also in the cast iron body, exceeds tho
boiling point of the liquid in the vessel f, vapours are generated in the latter which
force liquid from the vesself into the vessel ", this causes the float h² to rise which
diminishes or cuts off the supply of air to the fire place, so that the combustion
decreases or ceases.
For the purpose of working the machine at a bigher or lower pressure according
to requirements, that is to say, to obtain more or less power, the cross-head is
provided with an appliance by means of which the waste space or clearance
between the cylinder cover and the piston b' may be increased or decreased. This
appliance for altering the clearance consists of a piston rod pin (or connecting rod
pin) p, mounted in eccentric bearings, and which may be turned by means of a
lever p¹, adapted to be moved and fixed on a sector like the hand lever of a link
motion. By turning the pin the piston in the cylinder is displaced and thereby
the waste space altered.
The following will serve to explain how far the adjustment of the piston causes
an alteration in the expansion of air in the machine and in the power of the same.
Supposing the waste space to be equal to a unit of volume and the pressure of
the air in the machine equal to 5 atmospheres, the air contained in the waste space
which is cut off by the valve s¹ expands until it communicates with the suction
space e and pipe g, during which expansion period any air lost through leakages
is replaced by means of the suction valve v.

page_text: If by adjusting the lever p¹, the waste space is increased, a larger quantity of
air will be expanded in the same and the cut off towards the suction space being:
constantly the same, that is to say remaining exactly the same, as with one volume
of waste space, the expansion of air which was previously from one volume to five
volumes will consequently decrease according to the increase of the waste space,
the pressure cannot fall as far as one atmosphere, so that no air will be sucked in
through valve v, the loss of air in the machine will not be replaced, the pressure of
the air decreases and the machine works at a lower pressure.
To influence and regulate the generation of power by means of the governor x,
the cylinder cover (Fig X) is provided with a second suction valve v connected
with the suction space g through pipe 73. This suction pipe is provided with a
valve a³ which may be opened or closed by the governor (represented in the drawing
by the lifting rod x of a centrifugal governor).
As long as the engine has not reached or exceeded its mean speed, the valve a³
remains closed, and air is constantly sucked in through valve v, and the pressure of
air in the machine is increased. If the mean speed of the machine is exceeded the
governor opens the valve a³, and air flows from the suction space g through:
valve into the cylinder, before the valve through which atmospheric air is
admitted, commences to act. In consequence of this, no fresh air is admitted, the
machine retains its speed, till through the escape of air the pressure in the ongine
and consequently the number of strokes decreases until the governor finally closes
the valve a. This regulator which thus influences the speed of the engine, acts.
but gradually, it may, however, occur that the engine is suddenly disconnected
from the machine set in motion by the same, the result being a sudden increase in
the number of strokes. This result is prevented by connecting the governor with
a throttle valve placed in the pressure pipe d'. This arrangement in combination
with a valve between chamber d and d' has the following effect:
If the speed of the engine is too great, the narrowing of the air passage in d
(throttle valve) creates a resistance which causes an increase of pressure behind the
throttle valve, and also in the chamber d¹.
Owing to this the valve ³ which is but slightly loaded by means of the helical
spring, opens towards the chamber d, whereby, besides hot air from the
heating coil, cold air from the chamber d' flows into d and from there into the
cylinder a¹.
The above described hot air engines with a closed circulation of air, as well as
those which will be described below, may be employed as open hot air engines by
omitting the worm g and introducing into the suction pipe g¹ a water pipe w, as
shown in Fig. V. The supply of water is influenced by the governor so that
when the speed of the engine is too great, less water is supplied to the engine and
evaporated by the same.
•
Fig. VI represents part of a double acting engine of the system above described
and illustrated by Figs I, II, III.
The engine is provided with compression and working cylinders of different
diameters, whereby the arrangement by means of which the air sucked in is partly
forced back into the suction space l, may be omitted.
In the modification represented by Fig.. VII this difference in the diameter
of the cylinders is omitted, and the arrangement resembles that represented
by Fig. I.
The above described systems of engines with single valves permit only a
moderate compression, respectively expansion in the compression and working
cylinder.
To obtain a higher compression and expansion, double valves could be employed
which may be advantageously replaced by the molification illustrated by Figs. XI,
XII and XIII.
The valve gear for the compression cylinder a consists of the ordinary main
slide valve, set in motion by means of a separate eccentric e' at right angles to the

page_text: main crank, and having side channels c¹ c¹¹ closed by means of valves c³ c. This
main slide valve works as follows:
The piston g' is in its extreme position towards the right and on the point of
moving towards the left, while the valve g³ on the contrary is on the point of
moving towards the right, whereby, owing to the large inner lap of the valve, the
cylinder a is closed from the suction space e at the beginning of the stroke in the
same manner as in the single acting system, consequently the supply of air is
regulated through valve v, and the speed by means of the governor in the same
manner as above described see Fig. X.
While on the right at the beginning of the suction period the cylinder is cut off
from the suction space e (during the continued motion of the piston the opening as
described above takes place so that air is sucked in from the suction space)
compression takes place on the other side of the compression cylinder.
The side channel c' and the valve c³ permit the influx of compressed air into the
valve box d by the lifting of the valve c³ only when the air, is at full pressure.
For the working cylinder a¹ the valve motion controlled by the eccentric is
arranged in the following manner.
The valve motion comprises an ordinary main valve gʻ (Meyer's system) provided
on the left and on the right with prolonged laps g, g. On this valve rests a
second valve having recesses o o¹, the object of which will be hereinafter explained
and which valve is alternately coupled and uncoupled with the lower valve. This
coupling is automatic and is caused by the pressure in the valve box, as soon as
one of the ports 133 of the main valve g' is closed by the upper valve g³.
(It will be observed that the lower valve is not connected with an eccentric)
Owing to the recesses o o¹ the upper valve is pressed against the lower valve
with a pressure corresponding to the surfaces of the recesses o o', the upper valve
is therefore held against the lower valve and follows the motion of the same by
friction. The following effects are obtained by this arrangement:
In the position represented by Fig XI, (the crank being in its dead centre on
the right) the valve is in its central position (the eccentric e³ is from 40 to 60° in
advance of the crank according to the cut off required).
During the motion of the piston towards the left, the left channel * being
covered by the upper valve, and the upper valve being consequently pressed
against the lower valve, the latter is taken towards the left by the upper valve
(both valves being at this moment coupled by friction) until during the motion
towards the left the channel i communicates from below with the valve box. At
this moment the pressure censes, compensation takes place, and the dimensions are
Buch, that at the moment of this uncoupling the channel is on the other side of
the valve is completely open. The lower uncoupled valve now stops, while the
upper valve on the contrary continues to move to the left and during its continued
motion cuts off the communication of the channel with the interior of the valve
box, whereby the supply of steam ceases. Fig. XIII.
The expansion now begins and is communicated to the air contained in the
recess on the right, so as to cause a difference of pressure between the lower
surface and the upper surface of the upper valve.
This difference of pressure is increased by the continued expansion of the steam
in the cylinder, so that, when the eccentric is in its dead centre, and on the point
to begin its motion towards the right, the excess of pressure on the top is strong
enough to cause a renewed coupling of the valves and to cause the upper valve to
take the lower valve back into the central position. At this moment (in the
central position) the recess o¹ on the right and the channel 3 are cut off from
the cylinder a¹, so that even after the expansion in the cylinder is terminated, a
diminished pressure remains in the recess, owing to which the upper valve continues
to take along the lower valve.
After this the same operation takes place on the left side.

page_text: Small stops t are provided for the lower valve, and a brake spring is applied, at
the top for the case that the machine runs empty. The longer or shorter lead of
this valve influences the cut off at which the machine works.
The cut off may be made variable in the manner of Meyer's valve-motion, by
composing the upper valve of two parts and coupling the same with the valve rod
by means of left and right handed screw threads.
The cut-off may also be made variable in a manner similar to Rider's valve
motion, in which arrangement the upper valve, curved cylindrically at the bottom,
slides on the lower valve, while the channels of the lower and the recesses of the
upper valve are placed oblique.
To control the cut off by the governor, the parts described need only be connected
with the same in the well known manner. To obtain large heating surfaces,
several heating coils may be applied.
My invention is. also applicable to the regulation of the speed and pressure of
combined hot air and steam engines as illustrated by Figs. V, VIII, IX and XIV.
For preventing an excessive temperature of the air admitted to the power
cylinder, a special appliance operating through its expansion by heat is inserted into
the pipe-conduct leading to the valve chest of the power cylinder or in the valve
chest itself.
In the arrangement represented by Fig. VIII a pipe o connects the cold air
pipe d" with the hot air pipe d³, d' without touching the heating apparatus q,
and the said expansive appliance consists of a vessel containing a liquid of a
convenient boiling point, and a piston i³, adapted to act on a valve o' in the pipe o,
by means of a rod g³. If the temperature in the pipe d³ d' rises too high, vapours
are generated in the vessel ³, and act on the piston i³, so as to open the valve o¹
and admit cold air from the pipe d" to the pipe 11, in consequence of which the
temperature of the working gases falls.
The same regulation of temperature may be effected in the valve chest d, as
shown by Fig. XVI in which a metallic rod 20, preferably of zinc, is adapted.to act
on the valve v. If the temperaturo exceeds a given limit, the rod 20 expands,
thereby opening the valve v and admitting cold air from the valve chest d' of the
compression cylinder a¹¹ to the valve chest d.
The steam pressure may be increased or diminished by regulating the quantity of
water supplied by the pipe u, Fig IX, and thereby the quantity of steam introduced
into the engine.
J
For this purpose the valve a of the water supply pipe Fig V is connected, with
the governor and controlled by the same. The water supply may also be made
dependent on the steam pressuro, by means of a piston y see Fig IX or a membrane
movable in the cylinder y¹ which communicates with the inlet pipo of the engine,
the pressure of steam on the piston y being equilibrated by a weight or spring
acting on the top of the same. If the pressure in the pipe d' exceeds a given limit,
the piston y rises and allows steam and air to escape through the perforations L, in
consequence of which the steam pressure falls.
CLAIMS:

page_text: 4. A compression cylinder having an additional suction valve v³ in combination
with a closing device a³ controlled by the governor and inserted into the pipe 7+³
leading from the valve v¹ to the suction pipe.
5. A valve inserted between the two valve chests and provided with an
adjustable load, in combination with a throttle valve & controlled by the governor,
for admitting cold air direct into the power cylinder and thereby controlling the
effect of the engine.
6. The combination, with the pipe d' or valve chest d, of an apparatus controlled
by the temperature of the gases in the said pipe or valve chest and adapted to
admit cold gases from the branch pipe o or the cold air valve chest d¹ for
the purpose of regulating the temperature of such gases.
7. The combination, with the compressed air space and the suction pipe g¹
provided with water supply, of a loaded piston y or membrano communicating with
the said air space and adapted to control the said water supply.
8. The combination of the engine governor with a closing device in the water
supply pipe, and means for automatically controlling the said closing device by the
governor.
9. A liquid receptacle exposed to the heat of the working fluid or air and filled
with liquid of such a boiling point that vapours are formed as soon as the desired
maximum temperature of the working air is exceeded, in combination with means
for automatically cutting off the supply of air to the grate, by the generation or
pressure of such vapours.
10. An air moistening apparatus inserted into the pipe conduit and filled with
liquid of a high boiling point, for charging the air with liquid particles.
11. A pair of slide valves having recesses in the surface of contact adapted to
periodically communicate with the expansion or exhaust space for the purpose of
causing a difference between the pressures on the upper and lower side of the upper
valve thereby connecting and disconnecting the two valves.
12. A double acting power and compression cylinder of uniform bore, provided
with valve gear, adapted to return into the suction space a portion of the air
sucked in, in order to compensate for the excessive size of the compression cylinder.
The whole substantially as and for the purposes described.
In witness whereof I the said Wilhelm Schmidt have hereunto set my hand and
seal this first day of May A.D. 1884.