IMPROVEMENTS IN VARIABLE EXPANSION GEAR FOR LINK MOTION ENGINES "
Year: 1882

page_text: LETTERS PATENT to Thomas English of Hawley near Dartford in the County
of Kent, for an invention of "IMPROVEMENTS IN VARIABLE EXPANSION
GEAR FOR LINK MOTION ENGINES
"
PROVISIONAL SPECIFICATION left by the said Thomas English at the
Office of the Commissioners of Patents on the 24th March 1882.
THOMAS ENGLISH of Hawley near Dartford in the County of Kent.
"IMPROVEMENTS IN VARIABLE EXPANSION GEAR FOR LINK MOTION ENGINES"
This Invention has for its object improvements in variable expansion gear for
link motion engines and applies to a link motion of the type in which the travel of
the slide valve is regulated by shifting the link block along the link-The central
point or point of least motion in the link is controlled so that it can have a
rectilinear or approximately rectilinear reciprocating movement only; and this
movement, which is due to the angular advance of the eccentrics after having
been reversed in direction (by an interposed lever or rocker or equivalent means).
is imparted to a separate expansion valve with or without variable lap mounted
on the back of the mainslide valve
This arrangement provides for an earlier and better cut off of the steam or
other fluid than can be given by the link motion alone, whilst it does not interfere
with the use of the link in the ordinary way, for varying the cut off, for starting,
stopping, and reversing the engine.
Or the same result may be obtained by shifting each of the eccentrics half way
round the shaft and interposing a rocker between the link block and the main.
valve in such manner as to reverse their respective movements; the expansion
valve then receiving directly the movement of the central point, or point of least.
motion, in the link.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Thomas English in the Great Seal Patent Office on the
23rd September 1882.
THOMAS ENGLISH of Hawley near Dartford in the County of Kent
"IMPROVEMENTS IN VARIABLE EXPANSION GEAR FOR LINK MOTION ENGINES
"
This Invention has for its object improvements in variable expansion gear for
link motion engines and applies to a link motion of the type in which the travel of
the slide valve is regulated by shifting the link block along the link. The central
point or point of least motion, in the link is controlled so that it can have a
rectilinear or approximately rectilinear reciprocating movement only, and this
movement, which is due to the angular advance of the eccentrics, after having.
been reversed in direction (by an interposed lever or rocker or equivalent
means) is imparted to a separate expansion valve furnished with one or more
ports with or without variable lap and mounted on the back of the main slide
valve..
'
This arrangement provides for an earlier and better cut off of the steam or other
fluid than can be given by the link motion alone, whilst it does not interfere with
the use of the link, in the ordinary way, for varying the cut off, for starting,
stopping and reversing the engine.
Or the same result may be obtained by shifting each of the eccentrics half way
round the shaft, and interposing a rocker between the link block and the main
valve in such manner as to reverse their respectivė movements, the expansion
valve then receiving directly the movement of the central point or point of least
motion in the link.
Figure 1 is a plan and Figure 2 is a side elevation of valve gear constructed in
accordance with my invention.
A is the crank shaft and B, B, are two eccentrics upon it, they are fixed at an
obtuse angle to the crank, the excess over the right angle being the angular advance
of the eccentric.
C is the link jointed to the eccentric rods at C₁, C. This link at its central
point, or point of least movement is provided with pivots C², C2, and these pivots
have their bearings in blocks C*, C*, which are capable of sliding towards or away
from the crank shaft in the rectilinear guides D. D. E is the link block and its
position in the link C can be varied by levers and rods in the usual way to alter
the cut off, or to start, stop or reverse the engine.
F is the connecting rod by which the link block E is connected with the rod G
of the main slide valve H. This valve slides upon a valve seat of the ordinary
description and through it are formed two steam ports, over which the expansion
valve K works. The point of cut off is determined by the amount of lap given to
the edges of the port of the expansion valve K. The rod K' of this valve is
connected by a link L with the lower arm of the rocker M, which has its fulcrum
at M' carried in stationary bearings. The upper arm of the rocker M, is connected
by a link N with one of the blocks C* which receive the pivots C², of the link C
so that the movement of the block C, (which is that of the point of least
movement of the link C) is after reversal in direction, transmitted to the expansion
valve.
Figures 3 and 4 shew a like arrangement excepting that the pivots 03, 0%, are
not received into blocks sliding in guides but are suspended by links D**, so that
in this case the motion of the pivots is only approximately rectilinear.
As before stated the same result may be obtained by shifting each of the

page_text: eccentrics half way round the shaft A (thereby making their angles with the crank
acute by the same amount as they are at present obtuse) by reversing the
movement from the link block to the main slide, and by directly connecting the
expansion valve rod K' with the block C*.
Figures 5 and 6 illustrate this modification.
For the purposes of this mechanism the eccentrics need not necessarily be
attached to the link at equal distances from its centre if their throws and positions
relatively to the crank are so adjusted as to give a movement to the point of the
link at which the expansion valve spindle is attached, approximately the same as
would be given to it as above described.
Having thus described the nature of my said Invention and the manner of
performing the same I would have it understood that I claim :-
First. The method of adapting a link motion to work both a main slide valve
and an expansion valve, by taking the movement for the former from the link block,
and for the latter from the centre of the link or point of least movement, or point
in the link where its motion is due only to the angular advance of the eccentrics,
and by reversing one or other of these movements before imparting it to main or
to the expansion valve substantially as described.
Second. The method of adapting a link motion to work both a main slide valve
and an expansion valve, by taking the movement for the latter from the pivots by
which the link is supported, and reversing this movement before imparting it to
the expansion valve substantially as described.
Third. My improved variable expansion gear for link motion engines substantially
as described.
'
In witness whereof I the said Thomas English have hereunto set my hand
and seal this eighteenth day of September in the year of our Lord One
thousand eight hundred and eighty two.
THU ENGLISH (LS.)