Improvements in Rotary Steam Engines.
Year: 1899

page_text: Date of Application, 27th May, 1899-Accepted, 29th July, 1899
COMPLETE SPECIFICATION.
Improvements in Rotary Steam Engines.
We, FERDINAND KRUGER, Civil Engineer, and JULIUS KROST, Architect, both
of Taubenstrasse 54, Berlin, Germany, 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:-
Our invention relates to rotary steam engines, in which a revolving piston is
carried by a piston disc mounted on a shaft, the said piston, piston disc and shaft
being enclosed in a circular casing: and the objects of our improvements are, first,
to provide perfect and reliable packings between the revolving parts and the
casing so as to avoid escape of steam; second, to provide means for protecting
the said packings against wear in order to permanently maintain the machine
in a perfect working condition; and third, to simplify its construction.
We attain these objects by the means illustrated in the accompanying draw-
ings, in which Figure 1 is a side view of the entire machine, some of its parts
being partially broken.
Figure 2 a vertical section thereof on the line, r, of Figure 1, looking from
the left; and Figure 3a front view of Figure 1 likewise from the left.
Figures 4 to 7 inclusive are detail and diagrammatical views hereinafter ex-
plained.
Similar letters refer to similar parts throughout the several views.
The casing consists of two semi-annular parts 1, 2, forming hollow spaces 3, 4,
and of two circular covers 5, 6, connected to the parts 1, 2. A main driving shaft 7
passes through the centre of the casing, and a piston disc 8 is mounted thereon
and provided with a projecting arm 9 carrying a piston 10, 11, 12, plainly repre-
sented in the detached view, Figure 4. The casing is mounted upon a base
plate 13 carrying at the same time supports 14 for the main driving shaft.
The packing of the piston consists of a spring ring 15 split at 16 in the well
known Z shaped form, surrounding with play the middle reduced portion 11 of
the piston and kept in position by collars 10, 12, allowing likewise of a slight
play of the ring, so that steam can enter between collar 10 and ring 15 as well
as between stem 11 and the ring. The latter is provided with a stud 17, Figures 1,
2, engaging with a groove of a projecting part 18 of disc 8, a turning displacement
of ring 15 on stem 11 and with respect to the hollow space 3 of the casing thus
being prevented. Any other means may be provided for accomplishing this pur-
pose without departure from our invention. Ring 15 is preferably covered with
à laver 19 of soft metal applied to its outer surface.
By these means, when pressure of steam is applied to the piston and the latter
revolved in the direction of arrow f, Figure 1, ring 15 will be closely pressed
against collar 12 and at the same time expanded so as to closely fit in the hollow
space 3 of the casing, provided that the outer surface of ring 15 exactly conforms
to the curvature of the hollow space 3, the latter gradually changing from con-
cavity on its outer portion 20 to convexity on its inner portion 21.
To attain this, the ring will be conformed as much as possible to the peculiar

page_text: inner surface form of space 3 when casting the soft metal around it and then
fitted therein by grinding. In order to permanently maintain a close fitting
of the ring and a perfect working condition of the machine we have secured ring 15
against turning in its revolving movement by the above mentioned stud 17. For
the geometrical condition of a smooth and free movement of the ring within the
space 3 consisting in that the ring be deprived of any tendency to turn, if there
were not provided means to prevent this, clamping and wear by friction should
take place so as to deform the close contact surface of the ring and loosen the
packing.
There is another tendency to destroy the piston packing in rotary steam
engines of this kind, resulting from the usual arrangement of the slide valve
for periodically closing the steam chamber 3 of the casing. In the drawings, the
said slide valve 22 is controlled by a cam disc 23 provided with a cam 26 and
mounted on shaft 7, and by a spring actuated lever 24 bearing with a roller 25
against the cam surface of cam disc 23.
Slide valve 22 is guided in a slot penetrating the chamber walls, 1, 2, and in a
box 28 screwed to the casing, as represented, Figure 1, box 28 being removed in
this figure, and Figure 3 in dotted lines.
The inner edge 34 of the slide valve is slightly excavated so as to closely bear
against the edge of piston dise 8 under the pressure of a flat spring 38.
A rod 31 passes loosely through a longitudinal slot of the slide body taking
along with it the slide by means of collars 29, 30.
Rod 31 is connected to lever 24 by a link 32.
By these means, slide 22 will be periodically shifted towards the right of
Figure 3 in order to allow of the passage of arm 9 and the piston, and at once
driven towards the left by spring 27 in order to close again the steam chamber.
At the same time the usual steam admitting valve provided in a steam chest 35
is shifted, and live steam supplied through opening 36 to chamber 3; and as
the latter is closed by slide 22 the pressure of the steam causes the piston to
travel round. The exhaust steam is discharged through an opening 37 and a
pipe 38.
At each revolution, piston ring 15 will therefore pass once the guide slot of the
slide penetrating the chamber walls 1, 2. If now, as usually and represented in
the diagram Figure 5, slot 39 is radially directed towards the centre of revolution,
ring 15 when passing the slot will momentarily register with the latter and
therefore be caught by the slot, as the ring expands by elasticity. A shock will
therefore arise, whenever the ring passes the slot, and a perfect working con-
dition can never be attained.
On the other hand, by the repeated shocks, the ring will be shortly deformed
and worn out, so as to reduce the efficiency by escape of steam.
In order to overcome these inconveniences, we have disposed the said slot
obliquely, that is, at an angle to a radial line, as represented, Figure 1, and diagram-
matically shown, Figure 6. From the latter figure it will appear that even
though the ring 151 should be of smaller size than the width of slot 391, it could
never be caught by the slot .but will cross the same during its whole passage, so
that there would be no moment in which the ring should be fully released from
the surrounding wall of the casing. By this feature of our invention we therefore
attain and permanently maintain a smooth and uniform working of the machine,
any shock being avoided and the piston packing protected against wearing out
and being destroyed.
The above mentioned inconveniences could be partially overcome by enlarging
ring 15, Figure 5, beyond the width of slot 39. But as slide 22 should pre-
ferably be made of a comparatively large width in order to present a large pack-
ing surface 34 to the edge of piston dise 8 and in consequence thereof the slot
likewise should be made as wide as possible, a still larger size of the ring should
be required. On the contrary, there are important reasons for making the ring
as narrow as possible, first, in order to reduce the resistance by friction, and

page_text: second, to reduce the weight of the ring, of the piston and of arm 9, as these
parts must be counterbalanced and care is to be taken to reduce as much as
Whilst these conditions are
possible the weights of the parts in any machine.
at variance with each other in the arrangement represented, Figure 5, they fully
harmonise in our invention.
We will now describe the packing between the edge of piston disc 8 and the
corresponding parts of the casing. For this purpose annular grooves 40, 41, are
provided between the parts 1, 2, of the casing and either of the covers 5, 6. The
insides of the said grooves formed by the parts 1, 2, and 5, 6, are smooth, and
rigid rings 42, 43, fit in the said grooves so as to lie with their cylindrical outer
surfaces in close contact with the smooth sides of the grooves and with their
smooth inner edges in close contact with the outer faces of the piston disc 8.
There are annular spaces left between the outer edges of the rings and the opposite
sides of parts 1, 2.
Rings 42, 43, perform therefore fully the function of ring shaped pistons and
may be provided too with packing spring rings as usual in pistons for steam
engines. There are a plurality of springs 46, 47, disposed along and bearing
against the rings 42, 43, and slightly pressing the sanie against piston disc 8, the
pressure of the said springs being only sufficient to overcome the friction of
rings 42, 43, in their grooves 40, 41, and not establish heavy friction between
rings 42, 43, and piston disc 8.
By these means, the rings 42, 43, although always remaining in close con-
tact with the outer cylindrical sides of channels 40, 41, and with the piston disc 8,
are yet capable of slight oscillations, following any slight lateral oscillation of
disc 8 in its revolving movement.
In order to prevent escape of steam between the inside edges of the rings 42, 43,
and disc 8, for which purpose the slight pressure of springs 46, 47, might not
suffice, the hollow space 3 is brought into communication with the space behind
the rings 42, 43, by means of narrow channels 48, 49, Figure 7, provided in the
parts 1, 2, and in proximity to the steam supplying opening 36, Figure 7 repre-
senting a partial section through the casing taken on line y, y, of Figure 1, look-
ing as indicated by the arrow.
By these means, the steam is likewise allowed of entering the space behind
the rings 42, 43 in which space therefore always the same pressure will be main-
tained as in the hollow space 3. But as the rings are rigid and solid, the steam
pressure cannot expand them to increase the friction on their outer cylindrical
surfaces, but only actuate them in the direction they are free to move, giving
way, i.e. towards the piston disc 8. But as the steam is forced by the same pres-
sure to enter between disc 8 and the inner edges of the rings 42, 43, the latter
will be actuated from opposite sides by nearly the same pressure.
In consequence thereof, the rings 42, 43, are practically released from the steam
pressure and subjected only to the slight pressure of springs 46, 47, whatever
pressure there may be maintained in the hollow space 3 of the casing.
By these means, we attain a perfect and permanent packing of but little
resistance. The escape of steam entering the space behind rings 42, 43, between
the covers 5, 6, and disc 8 is prevented by stuffing boxes surrounding shaft 7,
whilst cocks or valves may be provided for removing from time to time the water
condensed therein.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed we declare that what we
claim is:-
1. In a rotary steam engine, the combination of a casing containing an annular
hollow space, a piston revolving in the said hollow space and provided with an
elastic packing ring, the outer surface of the latter conforming to the inner
surface of the hollow space, means for preventing the ring from turning on the
piston, a reciprocating slide valve extending through the wall of the hollow space

page_text: and placed out of line with the centre of the casing, and means for reciprocating
the slide valve, substantially as and for the purposes described.
2. In a rotary steam engine, the combination of a casing containing an annular
hollow space, a piston revolving in the said hollow space and provided with an
elastic packing ring, the outer surface of the latter consisting of a layer of soft
material and conforming to the inner surface of the hollow space, means for pre-
venting the ring from turning on the piston, a reciprocating slide valve extending
through the wall of the hollow space and placed out of line with the centre of
the casing, and means for reciprocating the slide valve, substantially as and for
the purposes described.
3. In a rotary steam engine, the combination of a casing, a disc revolving in the
casing, a piston provided at the edge of the said disc, annular grooves provided
in the casing opposite to the two faces of the revolving disc, packing rings guided
in the said grooves, springs for pressing the said packing rings against the faces
of the revolving disc. so as to form two separate sections or chambers in the
casing, and channels passing from one to the other of the said separate sections
or chambers, and provided in proximity to the steam inlet, substantially as and
for the purposes described.
H. GARDNER,
Patent Agent, 166, Fleet Street, London,
Agent for the said Ferdinand Kruger and Julius Krost.