Improvements in Steam Engines.
Year: 1893

page_text: Date of Application, 11th July, 1893
Complete Specification Left, 11th Apr., 1894-Accepted, 2nd June, 1894
PROVISIONAL SPECIFICATION.
Improvements in Steam Engines.
1, JOHN ISAAC THORNYCROFT of the Firm of John I. Thornycroft & Co. of
Church Wharf, Chiswick, in the County of Middlesex, Steam Yacht and Launch
Builders, do hereby declare the nature of this invention to be as follows:-
My invention has reference to an improved construction and arrangement of
steam engines for driving screw propeller shafts.
It was long since proposed to reduce the friction of engines by using cranks
opposite and adjacent with cylinders overlapping but in the same plane. This
arrangement involves an inconvenient height of engine and adds considerably to
the weight. Now I propose to get the same advantage and avoid the increased
height by making sufficient angle between the cylinders to cause them to clear
each other and by putting the cranks at an angle differing from two right
angles by the angle between the cylinders. I provide four cylinders arranged
in pairs; their pistons work on to four cranks in a shaft carried by four
bearings; the two cranks for each pair of cylinders are juxtaposed and
connected by a common arm without any intervening bearing; there are two
bearings between the two pairs of cranks. The two cranks forming each pair are
arranged at such an angle that when one piston is at the end of its inward
stroke the other will be at the end of its outward stroke and a projection of
the axis of either piston rod will-pass through the axes of its crank pin and of the
shaft. The caps of the propeller shaft bearings are secured in position by
extensions of the pillars that carry the engine cylinders. By my improved
arrangement the weight of an engine of given power may be appreciably reduced
without diminution of strength and by the described relative arrangement of the
cranks and cylinders the weight upon the main bearings due to the pressure on the
pistons is very greatly reduced.
Triple expansion and other engines may be constructed according to my
invention.
A triple expansion engine is made to consist of two pairs of cylinders related to
cranks in the way described, the first pair forming the high and intermediate
cylinders whilst the third and fourth cylinders take the place of the one low
pressure cylinder found in an ordinary triple expansion engine.
Dated this Tenth day of July 1893.
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant

page_text: Improvements in Steam Engines.
I, JOHN ISAAC THORNYCROFT of the Firm of J. I. Thornycroft & Co. of
Church Wharf, Chiswick, in the County of Middlesex, Steam Yacht and Launch
Builders, 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 has reference to an improved construction and arrangement of
steam engines for driving shafts such as screw propeller shafts.
It was long since proposed to reduce the friction of engines by using cranks
opposite and adjacent with cylinders overlapping but having their axes in a
common plane. This arrangement involves an inconvenient height of engine anl
adds considerably to the weight. The use of cylinders inclined towards each other
with their axes in parallel planes, and with pistons working onto oppositely
arranged and adjacent cranks has also been proposed but in this arrangement the
moving parts are not in all their positions effectually balanced.
Now with the view of securing the advantages of the known arrangement;
just above mentioned whilst at the same time avoiding the increased height I
according to my invention construct an engine in which I make sufficient angle
between the cylinders to cause them to clear each other and place the cranks
at an angle differing from two right angles by the angle between the cylinders.
I provide. four cylinders arranged in pairs; their pistons work on to four cranks
in a shaft carried by four bearings; the two cranks for each pair of cylinders
are juxtaposed and connected by a common arm without any intervening
bearing, and there are two bearings between the two pairs of cranks. The two
cranks forming each pair are arranged at such an angle that when one piston
is at the end of its inward stroke the other will be at the end of its outward
stroke and a projection of the axis of either piston rod will pass through the axes
of its crank pin and of the shaft. The caps of the crank shaft bearings are secured
in position by extensions of the pillars that carry the engine cylinders. By my
improved arrangement, the weight of an engine of given power may be appreciably
reduced without diminution of strength, and by the described relative arrange-
ment of the cranks and cylinders, the weight upon the main bearings, due to the
pressure on the pistons, and also the vibration of the engine, are very greatly
reduced.
Triple expansion and other engines may be constructed according to my
invention.
In the accompanying drawings,
Fig. 1 is a side elevation, partly in section;
Fig. 2 a plan; and
Fig. 3 a cross-section on the line of Fig. 1, showing so much of a four-
cylinder triple expansion double acting engine as is necessary to illustrate the
nature of my invention.
Figs. 4, 5, 6 and 7 are detail views drawn to a larger scale.
Fig. 8 is a central vertical section showing an automatic steam valve hereinafter
referred to.
Figs. 1, 2 and 3 are drawn to a smaller scale than the remaining figures.
The triple expansion engine shown, consists of two pairs of cylinders, the first
pair 1 and 2 forming the high and intermediate pressure cylinders, whilst the
second pair 3 and 4, which are low pressure cylinders, take the place of the one
low pressure cylinder found in ordinary triple expansion engines. The cylinders
Fig. 3 a cross-section on the line of Fig. 1, showing so much of a four-
cylinder triple expansion double acting engine as is necessary to illustrate the
nature of my invention.
Figs. 4, 5, 6 and 7 are detail views drawn to a larger scale.
Fig. 8 is a central vertical section showing an automatic steam valve hereinafter
referred to.
Figs. 1, 2 and 3 are drawn to a smaller scale than the remaining figures.
The triple expansion engine shown, consists of two pairs of cylinders, the first
pair 1 and 2 forming the high and intermediate pressure cylinders, whilst the
second pair 3 and 4, which are low pressure cylinders, take the place of the one
low pressure cylinder found in ordinary triple expansion engines. The cylinders
of each pair are arranged at an angle & to each other, as seen in end view, with
:

page_text: their axes in two vertical parallel planes so that the centres of the crank pins can
be brought closer together than would be possible if the cylinders were arranged
in line with each other, the amount of such inclination being made as small as
possible consistent with the attainment of this object. The pistons of the
cylinders 1 and 2 work through connecting rods in the usual way onto two
cranks 6, 6 and the pistons of the cylinders 3 and 4 work onto two similar
cranks 6, 6, the crank shaft 7 being supported in four main bearings 8, 8; 8b, 8°.
The two cranks 6, 6ª are inclined at an angle ẞ to each other equal to 180 degrees
less the angle & at which the two cylinders 1 and 2 are inclined to each other,
so that when one piston is at the end of its upstroke the other will be at the end of
its downstroke, and the projection of each piston rod will pass through the axes of
its crank pin and of the crank shaft. The cranks 6, 6° connected to the pistons
of the second pair of cylinders 3 and 4, are similarly arranged, the crank 6b being
at right angles to crank 6 and crank 6c being at right angles to crank 6. By this
construction the pressure of the pistons on the two crank pins can be made to
practically balance each other, thereby enabling the engine to run at high speeds
with little or no vibration, and reducing the friction of the crank shaft in its
bearings. The two cranks forming each pair are connected by a common arm 9 so
that there is no bearing between them, the bearings 8 and 8b being arranged
between two pairs of cranks as shown, and the others, 8 and 8°, being at the
respective ends of the crank shaft. Obviously instead of using two bearings 8ª
and 8', a single bearing of equivalent length may be used. Each arm 9 may
advantageously be provided with a balance weight 9a as shown in Fig. 4. The
said main bearings may, as shown, each consist of a separate casting, the several
castings being connected on one side by a deep angle bar 10 and on the other side
by a flat steel base plate 10" as shown in Fig. 5.
The cylinders of each pair are connected together and carried by two pairs of
pillars 11 the pillars of each pair being brought so close together that they can be
used as keep bolts for the caps or keeps 12 of the main bearings, thereby reducing
the weight of the engine. For this purpose the lower ends of the pillars are made
to pass through the keeps and are screwed into the corresponding main bearing,
and these ends are enlarged so that the nuts 13, which screw over them, can, when
necessary, be slipped up the plain parts of the pillars to enable the keeps to be
raised. Each nut may be locked in place, when screwed down, by a set screw 12ª.
To enable the keeps to be easily removed from the pillars, each keep whilst these
are in position, may advantageously be formed at each end with a slot 14 and
recess 15 as shown in Fig. 6, so that when the corresponding nuts 13 are screwed
down, the circular extensions 13ª of such nuts will enter the recesses 15 and
securely hold the keep in place, and when the nuts are raised, the keep can be
turned upward so that the pillars will then pass through the slots 14 and enable the
keep to be readily removed. This mode of utilising the pillars that carry the
cylinders, as keep bolts may advantageously be used in engines other than those
the cylinders and cranks of which are arranged in the peculiar manner hereinabove
explained.
To lock the lower end of each pillar firmly in place and prevent it working
loose, a cottar or wedge shaped bolt 15 (Fig. 7) is arranged in an inclined hole 15ª
in the corresponding main bearing in such a manner that it can be adjusted in an
end ways direction and caused to bear against the bottom of the pillar and thus
prevent any play between the screw threads on the pillar and those in the hole into
which the pillar is screwed.
The pillars constituting each pair of pillars are in the example shown, connected
by a stay 17 that forms a guide for the valve rod, and the two pairs of pillars of
each pair of cylinders are connected by a table or frame 18 that serves to stay the
lower portions of the cross head guides 19.
Suitable stays such as 20 and 21 are provided to steady the engine. Some of
these stays viz. 20, go direct to the sides of the vessel, whilst the others, viz. 21, are
attached to bosses 22 cast on prolongations of the castings forming the main

page_text: bearings. These latter stays 21 together with the bed plate and pillars, form a
series of triangles whereby a rigid structure is obtained.
In order to prevent the high pressure piston exerting an unbalanced bending
moment on the crank shaft at starting, and thus enabling the said shaft to be made
of lighter section than would otherwise be desirable, I consider it advantageous to
place an automatic steam valve 23 with pipe 23" between the main stop valve 24
(Figs. 1 and 2) and the steam pipe 25 connecting the steam chest of the inter-
mediate pressure cylinder with the exhaust of the high pressure cylinder 1, so that
at starting, live steam will be admitted simultaneously to both the high and
intermediate pressure cylinders. By this means the intermediate pressure piston
will, at starting, be caused to exert a force tending to counteract the bending
moment on the crank shaft produced by the high pressure piston, and the steam
thus admitted to the connecting pipe 25 will, by creating a back pressure in the
high pressure cylinder, further reduce the said bending moment.
n
Fig. 8 is a vertical section showing a construction of automatic steam valve that
may conveniently be used for the purpose mentioned. It comprises a valve
proper 26 formed by an annular flange on a stem 26" and arranged within a case
which is formed with a valve seat 27 and steam inlet and outlet branches 28 and 28°
respectively. As will be seen the valve is of differential type so that if the area
of the upper side of the valve exposed to steam pressure is n times the area of the
lower side of the valve exposed to pressure, the valve will close when the steam
pressure above the valve is more than th of that below the valve and will again
open if the pressure falls below that limit. Thus with the arrangement described,
the valve will take steam from the engine side of the main stop valve 24 and
deliver it, reduced to th of its initial pressure, to the connecting pipe 25 and
intermediate pressure cylinder 2 for the purpose hereinbefore explained, as soon as
steam is admitted to the high pressure cylinder 1, and when the engine is fairly at
work the said valve will be automatically put out of action provided that the
pressure of the exhaust steam from cylinder 1 be greater than -th that of the
initial steam pressure. The valve stem 26 is arranged to extend through a stuffing
box 29 and is adapted to be moved by hand to ascertain that it is in working order.
The gland 30 may advantageously be recessed at 31 and be provided with a drain
pipe 32 to lead away any water or steam that may escape past the packing in the
stuffing box.
n
n
A similar steam valve may, if desired, be placed between the connecting pipe 25
and the steam chests of the low pressure cylinders 3 and 4 whereby the low
pressure pistons will be enabled to start the engine should the cranks connected
to the high pressure and intermediate pressure pistons be on their dead centres.
As will be obvious an engine having a single pair of cylinders and cranks may
be constructed according to my invention and such an engine can be used for
driving a shaft other than a screw propeller shaft as for example, the armature
shaft of a dynamo.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
1. A steam engine wherein the cylinders constituting a pair and the cranks
connected to the pistons of those cylinders are so relatively arranged that there is
sufficient angle between the said cylinders to cause them to clear each other and
the said cranks are so arranged at an angle differing from two right angles by the
angle between the cylinders as described and illustrated, that when one piston is at
the end of its inward stroke the other will be at the end of its outward stroke and a
projection of the axis of either piston rod will pass through the axes of its 'crank pin
and of the shaft.

page_text: 2. My improved steam engine as described with reference to the drawings.
3. Securing the caps or keeps of the crank shaft bearings in position by means
of the pillars that carry the engine cylinders (or cylinder) as described.
•
Dated this 11th day of April 1894
JOHN ISAAC THORNYCROFT.
W. Lloyd Wise,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.