Improvements in Rotary Steam Engines.
Year: 1896

page_text: Date of Application, 15th Dec., 1896
Complete Specification Left. 15th Sept. 1897-Accepted. 16th Oct. 1897
PROVISIONAL SPECIFICATION.
Improvements in Rotary Steam Engines.
I, CHARLES AXEL BACKSTROM, c/o George Westinghouse Pittsburg, County of
Allegheny and State of Pennsylvania, United States of America Engineer do
hereby declare the nature of this invention to be as follows:
My, invention relates to rotary steam engines and has for its object to provide
an engine which shall be simple and compact in its construction, which shall
have great economy in its comsumption of steam, and which may be easily operated
and governed.
With these ends in view I have devised an engine in which a plurality of
cylinders or drums, provided with zig-zag gear teeth and corresponding grooves,
are arranged in a closely fitting casing so that the teeth and grooves of the adjacent
drums or cylinders intermesh. By this construction a body of steam introduced
under suitable pressure between such drums or cylinders into the grooves
successively and then cut off, acts expansively upon the teeth and causes the
drums to rotate in opposite directions, the steam being exhausted after it has
become expanded to such a degree as to preclude it from performing further
effective work.
My invention is illustrated in the accompanying drawings, in which Figure 1
is a plan view of the engine, a portion of the casing being removed. Figure 2
is a transverse section on the line - Figure 1, and Figure 3 is a longitudinal
vertical section through the casing, the drums and the ends of the casing being
omitted. Figure 4 is a development of one of the drums.
Referring to the drawings in detail, 1 and 2 are the cylinders or drums which
are exact duplicates of each other and which are preferably built up of plates
or discs 3, as indicated most clearly in Figure 2. As shewn in Figures 1 and 4,
these plates or discs 3 vary in thickness, the thickest plates being at the ends
of the drums and the thinnest ones at the middle, the decrease in thickness from
the ends to the middle being a gradual one. By reason of this construction,
the expansion of the steam, and consequently the work done by it, is effected
in the shortest possible time, and, furthermore, the smallest possible portion of
the cylinders or drums is unbalanced at any time by unequal pressures. This
construction of the drums is not essential to the operation of my invention how-
ever, and in practice it may sometimes be found desirable to make all of the
plates or discs of the same thickness as well as of the same contour. I have also
shewn each plate as provided with five gear teeth 4, and five spaces 5, alternating
therewith, but this number may be more or less than five if desired.
The drums or cylinders are built up to form a perfect gear of a certain number
of teeth depending upon the number of plates and the number of teeth in each
plate, each successive plate being placed in advance of the preceding plate so
as to form an element of the completed gear. In the example shewn in the
drawing, fourteen plates are employed in building up each drum, each of said
plates having five teeth. It will be seen that the plates on each drum may be
regarded as forming two sets or gears each of which sets or gears has thirty-five

page_text: elements or teeth those of one set.or gear being substantially a half tooth in
advance of the other and the two gears being pitched in opposite directions from
the central plane of the drum. The plates' thus assembled upon a suitable shaft,
are rigidly clamped together. 6 and 7 are the rows of zig-zag gear teeth which
constitute pistons and which will be hereinafter designated as gear tooth pistons,
and 8 and 9 the corresponding rows of zig-zag grooves which, in conjunction
with the contiguous portions of the casing, constitute expansion chambers. The
gear tooth pistons 6 and grooves S extend in helical lines from the central plane
of the drum to one end, and the gear tooth pistons 7 and grooves 9 in the same
manner from the central plane to the other end of the drum. The two drums
are constructed exactly alike, and when placed side by side in contact, the gear
tooth pistons 6, 7 of one drum will engage with the grooves 8, 9 of the other
drum, as will be readily understood.
While I prefer to place the drums side by side so that their axes shall lie
in the same horizontal plane, it will be understood that they may be otherwise
arranged if desired.
In the construction shewn, each of the sets of pistons and grooves extends over
a little more than one-third of the circumference of the drum, and this has
been found a desirable and satisfactory arrangement in practice, but it is obvious
that this length may be varied within considerable limits if desired. I have
also shewn each of the drums as made up of fourteen toothed plates, but. it is
obvious that a greater or less number may be employed without departing from
the invention.
The drum 1 is mounted upon and keyed to a shaft 10 and the drum 2 is
similarly mounted upon and keyed to a shaft 11. The longitudinal portion of
the casing for the drums I and 2 is made in two parts, 12 and 13, provided
respectively with a semicircular flange 14 and 15 at each end and with side
flanges 16 and 17, the latter being fastened together by bolts as shewn. The
inner contour of the casing is such as to exactly fit the drums, the two chambers
thus formed communicating at their adjacent sides as shewn in Figure 2. The
size of this communicating opening will obviously be dependent upon the depth
of the teeth upon the drum.
Extending longitudinally of the casing and centrally below the two drums,
is a chamber 18, into which steam is admitted through a conduit 19.extending
through the base 20. An inlet port 21 is located at the middle of the chamber 18,
this location being such as to admit the steam into the space formed between
the teeth on the two cylinders located midway between their ends. Located
in the opposite side of the casing is an exhaust chamber 22 with which com-
municate two exhaust ports 23 located respectively near the ends of the drums.
The exhaust from the chamber 22 is through a centrally located outlet 24. The
arrangement of these ports and chambers may be considerably varied in practice
and the chambers 18 and 22 may be omitted altogether if desired. The shafts 10
and 11 are journaled in heads 25 bolted to the flanges 14 and 15, these heads
being provided with the usual boxes and oiling devices which, as they form no
part of my invention, need not be further described.
In the present invention, I have shewn the shaft 10 as longer than the shaft 11,
this longer shaft being intended for the application of a pulley or other suitable
power transmitting device. It will be readily understood, however, that power might
be transmitted from either or both of the shafts, if desired. It should be stated
that the central portion 26 of the part 12 of the casing is or may be extended
downward between the two drums in order to ensure a slight compression of
steam sufficient to properly balance the drums. If this or some other provision
were not made, the upward pressure of the steam entering through the port 21
might cause binding and frictional wear between the drums and the contiguous
upper side of the casing.
While I have shewn the inlet port located at the bottom of the casing and the
exhaust ports at the top, it will be understood that this arrangement, may be

page_text: reversed if desired in practice, the operation being the same in both cases, except
that in the form shewn, the upward pressure of the steam will serve to counter-
balance the weight of the drums.
At each end of each cylinder or drum, a ring or plate 27 is located, as shewfi
in Figure 1. This plate may be provided with suitable packing 28 as indicated;
or the packing may be dispensed with. These rings or plates 27 serve as a
means for retaining the steam until a complete turn of the drum takes place:
The operation of the engine may be briefly stated as follows:-When the steam
is introduced through the inlet port 21, it enters the expansion chamber formed
by the teeth adjacent to the port and the contiguous portion of the casing, and,
as the teeth constitute pistons against which the steam acts, the drums are caused
to rotate in opposite directions as shewn by the arrows in Figure 2. As the
rotation continues, the steam is cut off and a progressively increasing space is
afforded for the expansion of the body of steam admitted and a constantly
increasing effective piston area is provided until the steam reaches the ends of
the drums, when on account of the end plates 27 it will be carried as dead steam
until the exhaust ports 23 are reached, when it will be exhausted into the
chamber 22. This operation is continuous, for as soon as one of the drums has
rotated a very short distance after the first introduction of the steam, the other
drum will receive steam, which in turn will be cut off. The central space between
the next adjacent pistons of the first drum will then come beneath the, inlet
port and a supply of steam will be admitted to that space and then cut off and
expanded to the ends of the drum as the rotation continues. This introduction
ani expansion of steam successively into one space or groove after another will
be repeated and the rotation of the drums be thus rendered continuous.
With this arrangement of zig-zag gear tooth pistons and grooves, the rotation
of the two drums exactly in unison and without any slip is ensured, said pistons
and grooves constituting a perfect gear. It thus appears that the entire expansive
force of the steam is utilized without waste, and in such a manner as to produce
the most desirable results.
While I have shewn an engine comprising two drums provided with a specific
number of teeth forming pistons and intermediate expansion chambers and a
casing provided with two exhaust ports located opposite the inlet port, I desire
it to be understood that my invention is not limited as regards the number,
dimensions or arrangement of the said parts.
Dated this 15th dox of December 1896
W. P. THOMPSON & Co.,
322 High Holborn, W.C., Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Rotary Steam Engines.
I, CHARLES AXEL BACKSTROM, c/o George Westinghouse, Pittsburg, County of
Allegheny and State of Pennsylvania, United States of America, 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 rotary steam engines and has for its object to provide
an engine which shall be simple and compact in its construction, which shall
have great economy in its comsumption of steam, and which may be easily operated
and governed.

page_text: With these ends in view I have devised an engine in which a plurality of
cylinders or drums, provided with zig-zag gear teeth and corresponding grooves,
are arranged in a closely fitting casing so that the teeth and grooves of the adjacent
drums or cylinders intermesh. By this construction a body of steam introduced
under suitable pressure between such drums or cylinders into the grooves
successively and then cut off, acts expansively upon the teeth and causes the
drums to rotate in opposite directions, the steam being exhausted after it has
become expanded to such a degree as to preclude it from performing further
effective work.
My invention is illustrated in the drawings, filed with my Provisional Specifi-
cation in which Figure 1 is a plan view of the engine, a portion of the casing
being removed. Figure 2 is a transverse section on the line - Figure 1, and
Figure 3 is a longitudinal vertical section through the casing, the drums and
the ends of the casing being omitted. Figure 4 is a development of one of
the drums.
Referring to the drawings in detail, 1 and 2 are the cylinders or drums which
are exact duplicates of each other and which are preferably built up of plates
or discs 3, as indicated most clearly in Figure 2. As shewn in Figures 1 and 4,
these plates or discs 3 vary in thickness, the thickest plates being at the ends
of the drums and the thinnest ones at the middle, the decrease in thickness from
the ends to the middle being a gradual one. By reason of this construction,
the expansion of the steam, and consequently the work done by it, is effected
in the shortest possible time, and, furthermore, the smallest possible portion of
the cylinders or drums is unbalanced at any time by unequal pressures. This
construction of the drums is not essential to the operation of my invention how-
ever, and in practice it may sometimes be found desirable to make all of the
plates or discs of the same thickness as well as of the same contour. I have also
shewn each plate as provided with five gear teeth 4, and five spaces 5, alternating
therewith, but this number may be more or less than five if desired.
The drums or cylinders are built up to form a perfect gear of a certain number
of teeth depending upon the number of plates and the number of teeth in each
plate, each successive plate being placed in advance of the preceding plate so
as to form an element of the completed gear. In the example shewn in the
. drawing, fourteen plates are employed in building up each drum, each of said
plates having five teeth. It will be seen that the plates on each drum may be
regarded as forming two sets or gears each of which sets or gears has thirty-five
elements or teeth those of one set or gear being substantially a half tooth in
advance of the other and the two gears being pitched in opposite directions from
the central plane of the drum. The plates thus assembled upon a suitable shaft,
are rigidly clamped together. 6 and 7 are the rows of zig-zag gear teeth which
constitute pistons and which will be hereinafter designated as gear tooth pistons,
and 8 and 9 the corresponding rows of zig-zag grooves which, in conjunction
with the contiguous portions of the casing, constitute expansion chambers. The
gear tooth pistons 6 and grooves 8 extend in helical lines from the central plane
of the drum to one end, and the gear tooth pistons 7 and grooves 9 in the same
manner from the central plane to the other end of the drum. The two drums
are constructed exactly alike, and when placed side by side in contact, the gear
tooth pistons 6, 7 of one drum will engage with the grooves 8, 9 of the other
drum, as will be readily understood.
While I prefer to place the drums side by side so that their axes shall lie.
in the same horizontal plane, it will be understood that they may be otherwise
arranged if desired.
In the construction shewn, each of the sets of pistons and grooves extends over
a little more than one-third of the circumference of the drum, and this has
been found a desirable and satisfactory arrangement in practice, but it is obvious
that this length may he varied within considerable limits if desired. I have
also shewn each of the drums as made up of fourteen toothed plates, but it is

page_text: obvious that a greater or less number may be employed without departing from
the invention.
The drum 1 is mounted upon and keyed to a shaft 10 and the drum 2 is
similarly mounted upon and keyed to a shaft 11. The longitudinal portion of
the casing for the drums 1 and 2 is made in two parts, 12 and 13, provided
respectively with a semicircular flange 14 and 15 at each end and with side
flanges 16 and 17, the latter being fastened together by bolts as shewn. The
inner contour of the casing is such as to exactly fit the drums, the two chambers
thus formed communicating at their adjacent sides as shewn in Figure 2. The
size of this communicating opening will obviously bo dependent upon the depth
of the teeth upon the drums.
Extending longitudinally of the casing and centrally below the two drums,
is a chamber 18, into which steam is admitted through a conduit 19 extending
through the base 20. An inlet port 21 is located at the middle of the chamber 18,
this location being such as to admit the steam into the space formed between
the teeth on the two cylinders located midway between their ends. Located
in the opposite side of the casing is an exhaust chamber 22 with which com-
municate two exhaust ports 23 located respectively near the ends of the drums.
The exhaust from the chamber 22 is through a centrally located outlet 24. The
arrangement of these ports and chambers may be considerably varied in practice
and the chambers 18 and 22 may be omitted altogether if desired. The shafts 10
and 11 are journaled in heads 25 bolted to the flanges 14 and 15, these heads
being provided with the usual boxes and oiling devices which, as they form no
part of my invention, need not be further described.
In the present invention, I have shewn the shaft 10 as longer than the shaft 11,
this longer shaft being intended for the application of a pulley or other suitable
power transmitting device. It will be readily understood, however, that power might
be transmitted from either or both of the shafts, if desired. It should be stated
that the central portion 26 of the part 12 of the casing is or may be extended
downward between the two drums in order to ensure a slight compression of
steam sufficient to properly balance the drums. If this or some other provision
were not made, the upward pressure of the steam entering through the port 21
might cause binding and frictional wear between the drums and the contiguous
upper side of the casing.
While I have shewn the inlet port located at the bottom of the casing and the
exhaust ports at the top, it will be understood that this arrangement may be
reversed if desired in practice, the operation being the same in both case, except
that in the form shewn, the upward pressure of the steam will serve to counter-
balance the weight of the drums.
At each end of each cylinder or drum, a ring or plate 27 is located, as shewn
in Figure 1. This plate may be provided with suitable packing 28 as indicated,
or the packing may be dispensed with. These rings or plates 27 serve as a
means for retaining the steam until a complete turn of the drum takes place.
The operation of the engine may be briefly stated as follows:-When the steam
is introduced through the inlet port 21, it enters the expansion chamber formed
by the teeth adjacent to the port and the contiguous portion of the casing, and,
as the teeth constitute pistons against which the steam acts, the drums are caused
to rotate in opposite directions as shewn by the arrows in Figure 2. As the
rotation continues, the steam is cut off and a progressively increasing space is
afforded for the expansion of the body of steam admitted and a constantly.
increasing effective piston area is provided until the steam reaches the ends of
the drums, when on account of the end plates 27 it will be carried as dead steam
until the exhaust ports 23 are reached, when it will be exhausted into the
chamber 22. This operation is continuous, for as soon as one of the drums has
rotated a very short distance after the first introduction of the steam, the other
drum will receive steam, which in turn will be cut off. The central space between
the next adjacent pistons of the first drum will then come beneath the inlet

page_text: port and a supply of steam will be admitted to that space and then cut off and
expanded to the ends of the drum as the rotation continues. This introduction
and expansion of steam successively into one space or groove after another.;will
be repeated and the rotation of the drums be thus rendered continuous....
With this arrangement of zig-zag gear tooth pistons and grooves, the rotation
of the two drums exactly in unison and without any slip is ensured, said pistons
and grooves constituting a perfect gear. It thus appears that the entire. expansive
force of the steam is utilized without waste, and in such a manner as to produce
the most desirable results.
While I have shewn an engine comprising two drums provided with a specific
number of teeth forming pistons and intermediate expansion chambers and a
casing provided with two exhaust ports located opposite the inlet port, I desire
it to be understood that my invention is not limited as regards the number,
dimensions or arrangement of the said parts.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. A rotary steam engine in which the moving parts consist of two or more
drums enclosed in a casing, each said drum being provided with a number of
stepped helical grooves formed by projecting gear teeth disposed in a spiral or
spirals round the curved periphery, said drums being so located in the casing
that the teeth thereof intermesh, substantially as described.
2. The modification of the invention wherein the teeth of each drum are
arranged in two sets of spirals diverging in opposite directions from the central
plane of the drum substantially as described.
3. The modification of the invention wherein each drum is constructed of a
number of toothed discs either of the same thickness or of different thicknesses
secured upon a shaft each disc being displaced relatively to the neighbouring
discs so that stepped helical grooves are formed, substantially as described.
4. A rotary engine constructed and operating substantially as described.
Doted thin 15th dor of Santambar 1897
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham,
Patent Agents for the Applicant.