An improved Hot Air Motor
Year: 1895

page_text: Date of Application 6th May 1895-Accepted 8th June, 1895
An improved Hot Air Motor
I, GEORGE FREDERICK REDE FR, of the Firm of G F Redfein & Co, The
General Patent Office, No 4, South Street, Finsbury, in the County of London
Patent Agents, do hereby declare the nature of this invention (a communication
to me by The Tientham Engineering Company, Limited, whose registered office
at The Trentham Engineering Works, Tientham in the Colony of Victoria)
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement
I he object of this invention is to provide a durable hot air motor which will
be simple in its construction
It consists in a hot an engine constructed as follows
A cylinder open at one end (termed the cool end) and closed at the other
(termed the hot end), is fitted with two piston, and at the hot end it may be
lined with non-conducting material, and is adapted to receive a fire
The pistons
are arranged as follows One near the mouth or open end of the cylinder
(termed the working piston) is designed to be reciprocated by the intermittent
expansion of the air within the cylinder, whilst the other (the distributing or
displacer piston) divides the hot end of the cvlinder from the cool end and by
its motion moves the air from the cool end to the hot end and expels the heated
and burnt air and draws fresh charges These two pistons are connected
with a main crank shaft by rods and levers in such a manner that the space
between them is continually varying, the movement of the distributing or displacer
piston being in advance of the other
The space between the two pistons is connected with the outer air through a
valve which allows air to enter but prevents its exit, and is connected with the
hot end of the cylinder by a pas age which may be stopped by a valve operated
by the working of the engine, whilst the hot end of the cylinder is connected
with the outer air through a valve also operated by the engine, or one valve
may be made to regulate these three openings
To prevent as much as possible the passage of heat from one end of the
cylinder to the other, the distributing or displacer piston is made longer than
its stroke, so that any point in the wall of the cylinder cannot become exposed
to both the hot and the cold air
The pistons are connected to the crank shaft of the engine in such a way that
they move relatively to each other, as hereinafter described, so as to diaw air
into the space between said pistons at one part of the stroke and afterwards force
it into the hot end of the cylinder at another part, as will be understood from
the following description, reference being had to the accompanying diawings
wherein
Figure 1 is a vertical central section of a hot air motor constructed according to
this invention,
Figure 2 is a transverse section on line 2 2, Figure 1, and
Figure 3 is a plan of said motor, whilst
Figures 4 and ɔ are respectively a side elevation and a section of the governor

page_text: Figure 6 is a diagramatic view illustrating the operation of this invention,
whilst
Figure 7 is a side elevation of part of the cylinder of the motor illustrating the
connection of a starting reservoir thereto
The same letters of reference indicate the same parts in all the figures
A A represent the distributing or displacer and power pi tons respectively and
B the cylinder in which ther work, the first-mentioned piston being used to force
the an from the space between the two pistons into the hot end of the cylinder,
whilst the other tran mit- the force of the pressure caused by the expansion of the
air to the crank shaft of the engine
In engines of this class as hitherto usually made a given quantity of air is
contained in the cylinder, one end of which is closed and is kept hot by means of a
fire under or around it, whilst the other end is clo ed by the working piston, and is
kept cool by being surrounded with water A portion of this ur is moved
backward and forward from one end of the evlinder to the other by means of the
distributing on displacer piston working, between the power piston and the hot end
of the cylinder, passin usually through a regenerator on its way becoming heated
and expanded in the hot end and cooled and contracted in the cool end, which
expan ion and conti action is tran mitted through the power piston to the mechani m
Now, as the in passing into the hot end cannot attain to the temperature of
the cylinder, noi in pa sing to the cool end can it be cooled to the temperature
of the water surrounding that end, it follows that its range of temperature is small
whilst some air is retained in the regenerator at each stroke which has not been
heated to the highest temperature in the one case nor cooled to the lowest
temperature in the othe
In order to obviate these defects the present invention has been devised
In tead of using the ime an continually, a fresh charge is taken in between
the two pistons A A¹ at each revolution of the engine and after passing it, or
at any rate the major part of it, through the regenerator C to the hot end of
the cylinder B, it is allowed to exhaut buck through the regenerator into the
atmosphere, thus en uring that the air initially is at the atmospheric temperature
In order to reduce the loss through air remaining in the tegenerator (at each
stroke, it is according to this invention made of a mass of loose rounded particles,
such as waterworn gravel, sand oi metallic spheres which, as they expose a large
surface and thoroughly bak up the currents of air passing through them have a
large heating and coolin effect, whilst the capacity of the spaces between the
particles is sin ill Moreover should these spaces he ome choked by dust or other
matter, the whole mass may be ens ly and quickly taken out cleaned and replaced,
and thus the particles (and consequently the interstices) may be finer than would
otherwise be practicable
The fuel is placed within the hot end of the cylinder, and the air, forced into
such hot end by the action of the two pistons, is caused to pass through such fuel,
thus increasing the temperature of the air to the highest possible point
Hitherto the motion of the two pistons in the cylinder has been controlled by
means of two cranks on the main shaft set approximately at right angles to one
another This arrangement, however, has the defect that the two pistons do not
come together until a large portion of the out stroke of the power piston has
taken place, when they iminediately commence to separate, and continue to do so
for the remainder of the stroke The effect of this is that some of the air is not
forced into the hot end at its highest pressure and some of it is withdrawn before
it has exerted its full power by expansion To secure a better relative motion of
the pistons the following combination of levers and rods has been devised in
connection with a single crink
D represents the cran! shaft, which is mounted in suitable bearings d at one side
of the cylinder B, while two levers EF are pivoted upon a convenient support
(preferably arranged on the other side of said cylinder), one above and the other
below the level of the crank shaft D The low lever I my be made into

page_text: parts arranged one on either side of the cylinder as shown, in order to reduce the
length of the engine The upper lever E is corne-ted by a rod e with the lower or
distributing piston A, whilst the lower level F is connected by rods for other
suitable means with the upper or power piston A¹ Both levers CF are connected
with the crank d¹ by connecting rods e¹¹ either directly or by means of a joint
on the end of one of the rods as shown
These connecting rods are pivoted to the working lever, at such points that
during the greater part of the up stroke of the pistons A both connecting
rods e¹¹are nearly in a straight line, thus keeping the working lever, about the
same distance part and the two pistons piactically together as illustrated
diagramatically by the numerals to 5 mn Figure 6 whilst on the down stroke
they form more acute angle with one another, binging the levers E F closer
together and widening the space between the pistons A A', as indicated by the
numerals 6 to 12 in said Figure 6 it being seen that the pistons gradually move
further apart until they reach that part of the stroke which is indicated by the
numeral 9 where they will be furthest away from each other after which they
again approach until they reach the points marked 1 when they are practically
together, being quite clo e at the points marked 2 The space between the pistons
may be adjusted as found desirable by altering the length of the connecting
rods ef and the position at which they are pivoted to the levers Eas will be
readily understood
Although the principle of using a distributing or displacer piston between the
power piston and the hot end of the cylinder is peculiarly ad ipted to the burning of
fuel within the cylinder (because it interposes a screen between the fire and the power
piston, and also draws in a chuige of cold an below the power piston each
revolution), its efficiency may be increased by allowing either the whole or a portion
of the air passing from the space between the two pistons to the hot end of the
cylinder to pass through a passage G or passages in the upper portion a of the
distributing piston (said upper portion closely fitting the cylinder) into an annular
space g surrounding the lower part of said distributing or displacer piston and down
through the space into the file, the return of such an being prevented by a valve g¹
in the passage G In order that the an which goes through this passage into the
hot end of the cylinder B may come in contact with the burning fuel, the bottom
of said cylinder is made hemispherical, as shown at b, or of such a curve that the
air may pass into the fuel without meeting any abrupt turnings or angles The
remainder of the air drawn into the space between the two pistons is forced into the
hot end of the cylinder B through a pipe 2 leiding from about the centre of
the cylinder B to below the regenerator C as shown in Figures 1 and 2
Usually these two methods of leading the au into the hot end of the cylinder
will be used conjointly as shown, but in certain circumstances such as in engines of
moderate power, cather may be used separately the arrangement of parts being
similar, except that when the whole of the air enters through the passage ground
the distributing or displacer piston, the exhaust valve H with its casing will be on
the side of the cylinder B above the fire instead of beneath it
the
In order to govern the peed of the engine automatically the device illustrated
in Figures 4 and 5 is used On the mun shaft D of the engine (or on a shaft
driven by suitable gearing from the main shaft) are two cams II' close together
and arranged to operate a lever or rod which operates the exhaust valve H
end of said lever being wide enough to bear upon both cams One of these cams I
opens the exhaust valve, and is rigidly fixed on the shaft D, whilst the other keeps
d valve open until the proper point for it to be closed, the closing being done by
spring or a weight The other cam I¹ is loose on the shalt D, but is carried
ound with it by being attached to pivoted weighted arms, forming a centri-
ugal governor and revolving with the shaft D, being normally retained in about
he positions shown by spiral or other springs Should the centrifugal force
the weighted aims be increased by an Increase in the speed of the
ngine, the loose cam I will be moved backward in relation to the shaft D

page_text: closing the exhaust valve H later and allowing more air to escape without passing
into the hot end of the cylinder B, and consequently reducing the resultant pressure
on the piston
When working at full power this closing should take place at about two-thirds
of the down stroke of the power piston A', the remainder of the stroke being devoted
to the compression of the air in the cylinder but should the speed of the engine
become too great, the centrifugal force of the weighted arms will overcome the
tension of the springs 2 and will cause said arms to fly outwards, moving the
cam I backward in relation to the shaft D and consequently allowing the exhaust
valve H to close later, thereby causing some of the fresh in the cylinder to pass
away in the exhaust and thus reducing the compression I he reverse operation
will take place when the speed is reduced
It will be readily understood that many different mechanical arrangements
might be used instead of the cams II weighted arms and other puts of the
governor shown which would effect the desired object of closing the exhaust
valve at an earlier or later part of the revolution in order to regulate the speed of
the motor
In order to feed fuel (such as charcoal or coke) into the furnace, or lower end
of the cylinder B, of the engine without stopping it, the following arrangement
may be used A short cylindrical barrel or drum L is caused to revolve slowly
in a curved seating attached to the side of the cylinder B above the fire, said
drum being in ide to fit in an air-tight manner in the sciting l, which extends about
half way round said dium as shown itted around the other half of the circum-
ference of the drum is a hopper to hold the fuel, the side of the hopper towards
the drum being open so that the fuel rests against the drum From the centre of
the seating and leading into the furnace of the engine is a passage 12, and
round the circumference of the drum are formed a number of pockets ³, which
become filled with fuel in passing the hopper and discharge same into the furnace
through the passage
This revolving feed drum is driven by belt, spur, worm, sprocket, or other
suitable gearing, from the main shaft or other moving part of the engine, its speed
being regulated according to the amount of fuel required to be fed into the furnace
in a certain time
In starting the engine the following arrangement may be used, supposing the
engine to be a small one The fly-wheel is turned to such a position that the
pistons A A' are near their highest point and the exhaust valve 11 open
The fire
is lighted through an opening M provided for the purpose in the side of the lower
end of the cylinder, and is blown up by any suitable bellows or blower held to
the said opening, the smoke pa sing away through the exhaust When the fire is
propcils lihted and the interior of the furnace is warm, this opening is clo ed by
à door m and the fly-wheel d on the crank shaft D is pulled round until the engine
starts
Supposing the engine to be too large to be conveniently started by hand, the
apparatus illustrated in Figure 7 may be added It comprises a reservou N
adapted to contain compressed air and connected with the space between the
pistons A A¹ by a passage n, fitted with a valve n', which may be set to allow air
to pass into the reservoir N and prevent its return, or it may be entirely closed,
while a passage n² leading from said reservoir N to the lower end of the cylinder
may be opened and closed at will by a valve n³ operated by hand or by the working
of the engine
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
-
1 A hot air engine having a power piston and a distributing or displacer piston
in a cylinder, in one end of which the fuel is burnt substantially as specified
2 In a hot air motor having a power piston and a distributing or displacer

page_text: piston in the same cylinder, the arrangement of levers and rods herein described
for controlling the relative motions of the two pistons and crank, said levers and
rods being arranged, constructed and operating substantially as and for the purposes
specified
3 In a hot air motor the use of a mass of rounded part cles of gravel, sand
or other suitable material as a regenerator substantially as and for the purposes
specified
4 In a hot air motor, mechanism for regulating the speed of the motor by allowing
the exhaust valve to close at an earlier or later point of the revolution substantially
as specified
5 In a hot air motor having the fire within the cylinder, the use of a hemispherical
or curved bottom or hot end to the cylinder for the purpose of causing a current
of air passing downward round the piston to converge into the fire substantially as
specified
In a hot air engine having a fire within the cylinder, the use of a receiver
(such as N) adapted to be charged with compressed air from the engine when
working and fitted with suitable valves and passages for allowing some of said
compressed air to enter the furnace for the purpose of starting the engine
substantially as specified and as illustrated in Figure 7 of the accompanying
drawings
7 The combination and arrangement of parts constituting the hot air motor
herein described, said parts being constructed, arranged and operating substantially
as and for the purposes herein described and explained and as illustrated in he
accompanying drawings
Dated this Sixth day of May One thousand eight hundied and ninety-five
G F REDFERN & Co,
4, South Street, Finsbury, London, Agents for the Applicant