Improvements relating to the Construction of Valve Gear for Steam Engines.
Year: 1893

page_text: Date of Application, 18th Dec., 1893-Accepted, 28th Apr.,
1894
COMPLETE SPECIFICATION.
Improvements relating to the Construction of Valve Gear for
Steam Engines.
A communication by ISAK ISAACHSEN, of 13, Tellstrasse, Winterthur, in the
Republic of Switzerland, Mechanical Engineer.
1, WILLIAM PHillips ThompsON F.C.S., M.I.M.E., of The Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool and 6, Bank Street, Manchester,
both in the County of Lancaster and 323 High Holborn, in the County of
Middlesex, Civil 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:-
that
This invention relates to the construction of valve gears for steam engines, and
the main object of the invention is to modify the valve motion in such a way, t
the same is more advantageous, when the admission of steam is small, that is to
say, when the engine is run with a high degree of expansion. It is well known
that with the valve gears commonly used it is not possible to obtain a high degree
of expansion without at the same time necessitating a comparatively long period
of compression and an early exhaust.
Now, comparing the diagrams Figure 1 and Figure 2 of the accompanying
drawing, in which Figure 1 represents the usual Zeuner diagram for a common
slide valve motion, and Figure 2 a similar diagram for the slide valve motion of
the improved gearing, it will be seen that in Figure 1 the admission of steam
commences in the crank position A' and is cut off in the crank position B¹.
At C' the compression begins, while at D' release takes place. In Figure 2, the
corresponding periods are marked A, B, C, D, and the diagram has been
designed so that the periods of steam admission and cut off commence at the same
crank position as in Figure 1; it will however be seen that the diagram, Figure 2,
has the following advantages:-
4
1. The compression, cominencing at C, takes place much later than in Figure 1.
2. The release, commencing at D*, also takes place later than in Figure 1.
3. The amount of opening of the steam port (E' F') is greater in Figure 2
than (EF) in Figure 1 with the same travel of the valve (O' E' = 0³ E³) from
its central position to the end of its stroke.
Now it is well known that most of the valve gears hitherto used have motion
curves that are not precisely a circle, but they are not therefore more suitable for
use with small degrees of admissions; this will be clearly seen from the diagram,
Figure 3, representing the valve motion of Heusinger von Waldegg. In this
figure is shown in dotted lines the true circle lines which give the same admission
of steam as the motion curves, but it will be seen that no advantages are gained
with this motion with regard to the compression and exhaust period.
Now the object of the present invention is to produce a valve motion, the motion
curve or polar diagram of which has the properties illustrated by Figure 2.
Such a curve of irregular shape may now be considered to be the result of the
combination of two curves of symmetric shape as illustrated in Figure 4. The
dotted lines L and M in Figure 4 represent the polar diagrams of two independent
valve motions, and if these two motions are combined in such a way with each
other, that in every crank position the travel of the valve (counted from its central
position) produced according to one of the curves, adds itself algebraically to the
travel of the valve according to the other curve, the result will be a travel repre-
sented by the diagram N: So for instance the travel O B is equal to O B¹ + O`B³.

page_text: In the same manner are the curves N drawn in Figures 5 and 6, in which P is a
circle representing the ordinary valve motion diagram giving the same periods
of admission, compression and release as the modified curves N, but it will be seen
that the cut off B for these circular curves occurs much later than for those drawn
according to this invention, namely, B².
As will be seen, the curves L in Figure 4 and M in Figure 6 are circles, and
the motion represented by these circles may be produced in the usual way by
means of an eccentric, crank, etcetera. The motion represented by the oblong
curves M in Figures 4 and 5 may also be produced by a similar mechanism in
conjunction with a device that increases the speed of the slide valve_relatively as
it is moved out of its central position. The heart shaped curves L (Figures 5
and 6) may be produced in a similar way but the device with which the usual
gear is combined must have the reverse effect, namely, retard the speed of the
slide valve the more the same is moved out of its central position.
Of such devices there exist a great many, but, as those that are combined with
the use of eccentrics are disadvantageous because of the great friction in the
bearings, it is preferred to take the motion from any moving part of the engine
having the requisite travel, for instance, the crosshead. In Figure 7, B represents
the crosshead of an engine, and a pivoted sleeve for an oscillating rod or lever u
which is connected with the crosshead. The reciprocation of the crosshead,
besides operating the point A, will also oscillate the sleeve bon the pivot D, and
the motion curve of a slide connected with the point A, as shown, will have the
shape of the curve M in Figures 4 and 5, while the point A' will give the motion
curve L, Figures 5 and 6.
In Figure 8 is shown a manner of combining the two motions represented by
the circular curve L and the oblong curve M, Figure 4, with each other, namely,
the ordinary slide valve motion with the one illustrated in Figure 7. At the
point A on the lever a is mounted a bell crank e, one end of which is coupled by
a rode to the connecting rod, so that a, e, c, d, will form a parallelogram, while to
the other end C of the bell crank the valve rod is connected. The resulting travel
of the slide valve will then be the algebraic sum of the movement of the point A
and of the movement imparted to the point C from the connecting rod by the
link e and bell crank e.
In Figure 8ª the polar diagrams of this valve gear are shown. Underneath
the diagrams the main positions of. the piston are shown, the same letters being
used to designate the different positions of the crank in the polar diagrams and
the corresponding positions of the piston.
Figure 9 shows a valve gear similar to that in Figure 8, the difference being
that a vertical motion is imparted to the guide sleeve itself by the eccentric E
through the rocking lever D F G. The resulting polar diagrams are shown in
Figure 94 and do not materially differ from those shown in Figure 8ª.
Figure 10 is the same device as shown in Figure 9, but the lever a is in this
case connected to the end of a lever N, being supposed to be connected with the
crosshead for the purpose of driving a pump or the like..
Figure 10 shows the corresponding diagrams.
In Figure 11 is shown how a compound engine or twin engine may be provided
with valve gear according to this invention. The diagram is shown in Figure 11^
and conforms with the one shown in, Figure 5, the point B having a movement.
represented by the oblong curve M and the point C a movement represented by
the heart shaped curve L (see also Figure 7).
Figures 12 and 13 show the valve gear combined with oscillatory engines, and
Figures 12 and 134 the corresponding diagrams.
Figure 14 shows a modification of Figure 11, the difference being that the
point A', instead of being placed on the sliding lever a, is arranged on the oscillating
guide sleeve of the said lever; as will be seen from Figure 144 the motion curve
of the slide valve will thereby be somewhat altered..
In all these cases there has been used an oscillating lever alsliding through

page_text: a sleeve that is capable of an oscillating motion. This device may also be
arranged in other ways, for instance, as shown in Figure 15, where the valve
rod is connected to the sleeve, while the bearing for the swinging rod is formed
by a link or rod m. This arrangement gives a motion-curve as shown in Figure 15ª
(compare Figure 4, curve M).
Figure 16 shows this arrangement applied to the valve gear of Figure 8, and 16ª
the corresponding diagram. The other valve gears shown may also be arranged in
this manner.
As will be understood from Figure 17, the reversement of this kind of valve gear
may be done simply by reversing one of the two movements constituting the com-
bined motion of the slide valve. From Figure 18 it will also be seen that increasing
one of the curves L will result in an increase of the admission of the steam. Any
of the described valve gears may therefore be provided with a reversing mechanism
without any difficulty.
Figure 19 shows the valve gear Figure 9 provided with a reversing mechanism
consisting of a link H, pivotally connected with the lever I, handle K and a
block G, the latter sliding in the link and pivotally connected with that end of the
lever F to which the eccentric rod is connected in Figure 9, while the latter in this
case is connected to one end of the link. In this way the engine may be reversed
and the admission of steam varied simply by manipulating the reversing lever K in
different positions.
It will be understood from the above that the leading principle in all the valve
gears described herein as examples is simply adding to any of the valve gears used
at present, an oscillating lever that transforms the regular or symmetric movement
imparted to the slide valve from a rotating oscillating or reciprocating part of the
engine to an irregular movement, being the algebraic sum of two separate move-
ments, the result of which is more advantageous for engines run with small
admissions of steam. This said oscillating lever may be arranged in any suitable
way. It is not limited to the examples shown in the drawing, but may be combined
with the valve rod, and the part from which the same receives its motion in any
other way so that the distance from the pivot of the oscillating lever to its point of
connection with the valve rod varies during the travel of the valve, or in other
words, that the leverage of the oscillating lever will vary during its oscillation
relatively to the valve rod.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is-
1. In a valve gear, the combination, with the valve rod and the part or parts
moving the same, of an oscillating lever the movement of which is governed not
only by the part or parts, that imparts to the same its rocking or swinging motion,
but also by a guide, relatively to which the lever has a sliding motion, in such a
way that the point of the said lever, from which the slide valve receives its move-
ment has a varying radius of oscillation during the travel of the valve whereby the
motion of the slide valve is modified so that it will be more advantageous for small
admissions of steam, at the same time retarding the point of compression and
release and giving a larger steam port opening, substantially as described.
2. In a valve gear as described, the combination, with the valve rod and the
cross head of the engine, of an oscillating lever a pivoted to the crosshead or a part
moving with the same or another reciprocating part of the engine and being guided
in a bearing that admits of a sliding movement of the said lever relatively to the
bearing.
3. In a valve gear as described, the combination, with the valve rod and the
crosshead of the engine, of an oscillating lever a pivoted to the crosshead or a part
moving with the same and guided in a bearing that admits of a sliding movement of
the said lever relatively to the bearing, said oscillating lever having pivotally
connected with it a bell crank, one end of which is connected with the valve rod,

page_text: and the other end of which is connected with the connecting rod of the engine by
means of a link substantially as described with reference to Figure 8.
4. In the valve gear set forth in Claim 3, the modification described with
reference to Figure 16 in which the valve rod is connected to the guide for the
oscillating lever, the bell crank instead of being connected to the valve rod being
coupled to a link m having its pivot on a fixed point.
5. In a valve gear substantially as described with reference to Figures 9, 10
and 12, the combination, with the valve rod and the crosshead of the engine, of an
Oscillating lever a pivoted to the crosshead or a part moving with the same and
guided in a bearing that admits of a sliding movement of the said lever relatively
to the bearing, said guide for the oscillating lever being connected with an eccentric
rod or other part of the engine imparting to the same a reciprocating motion.
6. The arrangement of valve gear for oscillating engines substantially as described
with reference to Figure 12 in which the oscillating lever is connected with the
piston rod of the engine.
7. The arrangement of valve gear for oscillating engines (substantially as described,
Figure 13,) in such manner that the guide for the oscillating lever is mounted on
the cylinder or other oscillating part of the engine, the said lever a having a pivot
on the framework of the engine and at another point connected through a link with
a lever carrying the valve rod and also with the piston rod of the engine.
8. The arrangement of valve gear for compound and twin engines substantially
as described (Figures 11 and 14) in such manner that each of the crossheads of the
engine is connected with an oscillating lever of the kind set forth, each of the valve
rods carrying a lever, one end of which is connected through a link with one of the
said oscillating levers at one side of its guide, and the other end of which is
connected through a link with the other oscillating lever at a point outside its
guide or with the guide itself.
9. The arrangement of reversing mechanism for the valve gear substantially as
described with reference to Figure 19.
10. The several combined arrangements and construction of parts forming the
improved valve gear for steam engines.
Dated this 16th day of December 1893.
WM. P. THOMPSON & Co.,
Agents for the Applicant.