Improvements in Valve Gear for Steam Engines.
Year: 1894

page_text: Date of Application, 22nd Mar., 1894
Complete Specification Left, 21st Dec., 1894-Accepted, 2nd Feb., 1895
PROVISIONAL SPECIFICATION.
Improvements in Valve Gear for Steam Engines.
I THOMAS COOPER of Great Ryburgh in the County of Norfolk, Engineer, do
hereby declare the nature of this invention to be as follows:-
This invention relates to improvements in that class of reversing gear for steam
engines, wherein only one excentric is employed to drive the slide valve for each
cylinder. Such gears have, for many years, been constructed with a single
excentric mounted on the crank shaft, suitable means being provided for driving
the excentric, and also for moving it partially round on the shaft, from the proper
position for forward running, to that for backward running, and vice versa.
This class of gear, which is described in the Specification of my Patent
No. 16468, 1886, has the great merit of simplicity, but it also has this disadvantage,
viz., that with it the engine cannot be worked with various degrees of expansion, as
with a link motion, because as the excentric has to rotate on the shaft, any inter-
mediate position between full gear either way, displaces the slide valve, so that it
does not then admit steam to the cylinder at the proper point of stroke of piston.
The object of the present invention is to overcome this defect, while the simplicity
of a single excentric is maintained.
To this end, the valve-actuating excentric is so arranged that in being moved
from full gear backward or forward, the path of its centre is across the crank
shaft, and not round it, and thus the length of the travel of the slide valves may
be regulated, without the proper position of the valves being altered. The engine
can therefore, according to my invention, be worked with any desired degree of
expansion.
Simple means are also provided for driving the excentric, so that when working
in any desired position, there is no friction or wear or any part of the gear, except
as between the excentrics and their bands or straps.
An improved arrangement for moving the excentrics, for reversing the engine, is
also provided.
It will be understood that the gear is equally applicable to single and double
cylinder engines, and that details of construction may be modified to suit different
designs of engines, the main features remaining the same.
In carrying out my invention, I employ upon the crank shaft for each cylinder,
an excentiie made with a tail piece on one side, which is pivotted on a stud carried
by the dip of the crank shaft, or by a disc or arm attached to the shaft. At the
opposite side of the excentric is a slotted hole, in which is a stud provided with a
flat-sided die fitting the side of the slotted hole, so as to give a proper wearing
surface. The stud just mentioned is secured to a driving disc, which disc, in a
double cylinder engine, forms one of a pair carried at either end of a sleeve fitting
snugly on the crank shaft, and being capable of partial rotation thereon. If the
disc be rotated on the crank shaft, it will, by means of a driving stud engaging
with the slot in the excentric, carry one side of the latter with it, but the other
side of the excentric is pivotted to the dip of the crank, and therefore the centre of
the excentric moves across the shaft, describing the are of a circle with its pivot
as centre, and thus at any point, from full gear forward to full gear backward, the
position or setting of the slide valve is not altered, save to the small extent of the
versed sine of the arc of the circle named, which, in practice, is inappreciable. In
he sleeve which carries the disc or discs, is a straight slot extending the whole

page_text: length, and in the shaft within the sleeve is a spiral groove. In the slot fits a key,
which, on its underside, has a projection fitting in the spiral groove, and on the
top of the key is a projecting part which fits into a strap circumferentially grooved
internally for said projection to revolve in. This key engaging in the groove,
drives the sleeve round with the shaft, and if the key is moved either to right or
left by means of the strap. the sleeve will be rotated on the shaft, and will carry
the excentric with it, so as to change its position thereon, thereby either causing
the reversal of the engine, or variation in the expansion, by regulating the travel
of the slide valves. In order to relieve the key and strap of any friction, except
when being moved, the excentrics are provided with projecting lugs in such a
position as to come in contact with adjustable screw pins inserted in the crank
shaft, which screw pins, set at the proper length, take the strain in driving the
excentrics.
When the design of the engine admits of the strap being of considerable length,
say, equal to the diameter, it can be moved on the shaft with an ordinary fork
lever, but when it is desirable to get the excentrics as close together as possible,
the strap is made narrow, and it is then necessary to provide means for holding it
rigidly in proper position with regard to shaft, otherwise it would wobble about,
and jam on the shaft from the pressure of key not being equal all round.
To get over this difficulty without using more than one key, and at same time to
provide a simple and efficient means for moving the strap sideways, a cross bar is
mounted parallel to the crank shaft, and attached to side bracket plates, or to other
suitable part of the engine. On this cross bar is carried a sliding bracket fitted
with a small cog pinion and spindle, and a handle for turning same.
This cog
pinion engages with a cog rack carried on the cross bar. By moving handle, the
bracket is moved sideways in lines perfectly parallel with crank shaft.
Strap before mentioned is made with tail piece, which fits in a suitable recess in
the bracket, and thus is kept rigidly at right angles to crank shaft, although free
to be moved sideways by hand lever.
Dated this 22nd day of March 1894.
NEWTON & SON,
Agents for the Applicant.
Improvements in valve Gear for Steam Engines.
I THOMAS COOPER of Great Ryburgh, in the County of Norfolk, 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 :-
This invention relates to improvements in that class of reversing gear for steam
engines, wherein only one excentric is employed to drive the slide valve for each
cylinder. Such gears have for many years been constructed with a single excentric
mounted on the crank shaft, suitable means being provided for driving the
excentric, and also for moving it partially round on the shaft, from the proper
position for forward running, to that for backward running, and vice versa.
This class of gear, which is described in the Specification of my Patent
No. 16468 (1886), has the great merit of simplicity, but it also has this dis-
advantage, viz., that with it the engine cannot be worked with various degrees of
expansion, as with a link motion, because, as the excentric has to rotate on the
shaft, any intermediate position between full gear either way, displaces the slide
valve, so that it does not then admit steam to the cylinder at the proper point of
the stroke of the piston.
The object of the present invention is to overcome this defect, while the simplicity
of a single excentric is maintained.

page_text: To this end, the valve-actuating excentric is so arranged, that in being moved
from full gear backward or forward, the path of its centre is across the crank
shaft, and not round it, and thus the length of the travel of the slide_valves may be
regulated without the proper position of the valves being altered. The engine can
therefore, according to my invention, be worked with any desired degree of
expansion.
It will be understood that the gear is equally applicable to single and double-
cylinder engines, and that details of construction may be modified, to suit different
designs of engines, the main features remaining the same.
In the accompanying drawing I have shown my invention as applied to a double
cylinder engine.
Fig. 1 is a plan view, partly in section ;
Fig. 2 is a section on the line 1. 2 of Fig. 1; and
Fig. 3 is a partial front view, partly in section.
A is the crank shaft, between the cranks a a¹ on which, are arranged the
excentrics B B', one for each cylinder. These excentrics are provided with
straps CC, connected to the valve rods c c in the ordinary manner.
The
excentrics, as illustrated, are threaded on to the crank shaft, being large enough
to pass over the dips of the cranks; they may, however, be made in two parts,
if desired. Each excentric is provided with a tail b, which is pivotted to the
dip of the crank, or to an arm or disc specially provided on the shaft, if more
convenient. On the other side of the excentric is a slotted hole 62, in which is
a stud d, carried by a disc D, which is one of a pair situated at either end of
the sleeve E, and forming part thereof. Upon the stud d, is a flat-sided die d³,
which fits the side of the slotted hole 62. The sleeve E, which is made in two
parts, secured together by bands e, fits snugly on the crank shaft A, and is capable
of partly rotating thereon. If the sleeve E be rotated on the crank shaft, it
will, by means of the stud d (carried by the disc D) engaging with the slot in
the excentric, carry the latter, which loosely encircles the shaft, with it; but
the other side of the excentric is pirotted to the dip of the crank, and therefore the
middle of the excentric, instead of moving round, moves across the shaft, describing
an arc of a circle, with its pivot as centre (as indicated at Fig. 2); and thus, at
any point from full gear forward to full gear backward, the position or setting
of the slide valve is not altered, save to the small extent of the versed sine of the
are of the circle named, which in practice is inappreciable.
In the sleeve E, which carries the discs D, is a straight slot e¹, extending the
whole length of the sleeve, and in the shaft A, within the sleeve, is a spiral.
groove a*.
In the slot fits a key F, which, on its underside, has a projection f
fitting the spiral groove a*, and on the top of the key F is a projection, which
fits into a strap G, provided with a circumferential internal groove, for the
projection f¹ to revolve in. The sleeve E is carried round with the shaft A by
means of the key F, and its position on the shaft can be changed by shifting the
key along the slot of the sleeve, by means of the strap G, while retaining the
projection in the spiral groove a*.
For moving the strap G sideways, to turn the sleeve E on the shaft A, for
the purpose of changing the position of the excentrics, the following arrangement
is provided.
H is a cross bar mounted parallel to the shaft A, and suitably supported by
plates h h, attached to the engine-framing. A sleeve I embraces the bar H, and is
rigidly connected to the strap G. The sleeve I is moved to and fro lengthwise on
the bar H by means of a pinion i, supported by the sleeve, engaging with a rack h¹
formed in the bar H. J is a handle for rotating the pinion i.
The position of the parts, as shewn in the drawing, is in mid-gear. For forward,
gear, the strap G is moved in the direction of the arrow (Fig. 1), and for back
gear in the opposite direction; the two extreme positions of the strap G are
indicated by dotted lines. Any intermediate position, to give any degree of
expansion, may, however, be provided for by rotating the sleeve E more or less on

page_text: the crank shaft A in the manner explained, thereby fixing the position of the
excentrics with regard to the said crank.
In order to take the strain of driving the excentrics, adjustable screw pins j¹
are provided on the cheeks of the crank dips a a¹, which engage with lugs d*
carried by the excentrics. These pins, as shewn in the drawing, are so placed as
to operate in contrary directions; j', which is indicated beneath the crank in
Fig. 1 by dotted lines, drives forward, while j drives backward. The means shewn
for moving the strap G is admirable for the purpose, on account of its rigidity, but
other arrangements may, under some circumstances, be employed.
From the above description it will be seen, that, without departing from the
simplicity of the single excentric, my invention provides for working the slide valve
in any position between full gear forward and full gear backward, so as to ensure
any desired degree of expansion.
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 :-
:-
Mounting the slide valve operating excentrics of steam engines in the manner
herein described with reference to the drawing, whereby any intermediate position
between full gear forward and full gear backward, can be secured, and any desired
degree of expansion attained, substantially as set forth.
Dated this 21st day of December 1894.
NEWTON & SON,
Agents for the Applicant.