Valve Gear for Engines.
Year: 1888

page_text: COMPLETE SPECIFICATION.
Valve Gear for Engines.
1, GEORGE FREDERICK REDFERN, of the firm of G. F. Redfern & Co., the
General Patent Office, No. 4 South Street, Finsbury, in the County of Middlesex,
Patent Agents, do hereby declare the nature of this invention (a communication
from abroad by Ellis James Woolf and James Franklyn Williamson, both of
Minneapolis, in the State of Minnesota, United States of America,) 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 that class of valve gear in which the valves are
actuated from a single eccentric and is in the nature of a radical improvement on
the mechanism illustrated in United States Letters Patent granted to John Grime,
under dates of February 9th and November 2nd 1886, numbered 335578 and
351912, respectively.
The general object of my invention is to obtain the nearest possible approxi-
mation to an absolutely perfect valve movement. Or, in other words, I seek to
obtain a valve motion which will correspond absolutely to the motion of the
piston, or be the nearest practicable approximation to that perfect correspondence
which is theoretically required between the two.
More specifically, I aim to obtain the following results, viz.: (1) a variable cut
off which will take effect at equidistant points from the opposite ends of the
cylinder on the in and out strokes throughout a long range of variation and for
both forward and back movements of the engine; (2) comparatively uniform
exhaust and uniform compression; (3) a quick full port opening quick cut off
avoiding wire drawing of the steam; (4) the admission of equal volumes of steam
behind the piston on the in and out stroke, even in the cases where the cut off
is not uniform, in virtue of the compensation afforded by the inversely related
time of full port opening, or in other words, the port cut off at the shortest
distance is first wide open; (5) a comparatively late exhaust for any given cut
off, thereby using steam very expansively.
These results, I seek to accomplish by the simplest possible construction.

page_text: To these ends, my invention consists of the mechanism hereinafter full described
and particularly pointed out in the claims.
Though of general application to various kinds of engines, my invention is especially
well adapted for use on locomotives and I have, in the drawings, shown it
so applied.
Like references referring to like parts throughout, figure I is a side elevation
of a part of a locomotive embodying my invention; figure II is a rear view of
the same, partly in elevation, and partly in section, and some of the parts being
broken away figures III, IV and V are details of the pivoted guide and its
slide detached figure VI is a view, in side elevation, of the standard for
supporting the pivoted guide from the driver axle detached, figures VII and VIII
are details showing points of attachment of radius bar and eccentric rod; and
figures IX and X are diagrams illustrative of the action of the mechanism.
1 is the main driving axle, 2 one of the main driving wheels, 3 one of the
forward truck wheels, 4 part of the forward truck frame, 5 one of the cylinders
and 6 its steam chest, 7 its valve, a part of the boiler, 9 a part of the main
supporting frame, 10 the crank pin, 11 the connecting rod, 12 the cross head
guides, and 26 the piston rod of an ordinary locomotive 13 is an eccentric on
the axle 1, lying directly together with the crank; 14 is the eccentric strap and
is provided with an extended arm 15 having in its outer end a bearing for a
pivot pin 16 is a standard mounted loosely on the axle adjacent to the eccentric
and provided at its outer end with a bearing for a rock shaft; 17 is a rock shaft
supported at its opposite ends in the standards 16 and extending through the
saine outward toward the arms of the eccentric straps; 18 is a crank lever rigidly
secured to the shaft 17, and is provided with suitable connections (not shown)
extending to the engineer's cab; 19 is a slide block guide rigidly secured to the
outer end of the rock shaft at a point in the guide offsett toward the cylinder
from its longitudinal axis.
This point is hereinafter designated K' and constitutes the point of suspension
in this valve gear. The fact that this point of suspension is offsett from the
longitudinal axis is of great importance as will be hereinafter made clear.
20 is a slide block working in the guide 19 and provided at its center with
an outwardly projecting pivot pin 21, which rests in the bearing on the outer
end of the eccentric arm 15 and pivotally connects said slide block and the
eccentric strap. This point, in the diagram, is designated 0; 22 is the valve stem
of the ordinary slide valve 7.
In a suitable bearing 23, on the main frame is journalled a rock shaft 24
provided with the rocker arms m' and ' rigidly attached thereto.
To the rocker arm is attached the valve rod Q in such manner that they
are at right angles or about at right angles to each other when the valve is in
its mid position.
From some point on the arm 15 of the eccentric strap either below or beyond
the pivot pin 21, to the other rocker arm me extends the eccentric rod R, said
rocker arm and eccentric rod being always so attached to each other that they
form with each other an oblique angle in mid position of the valve. This feature
has important functions, as hereinafter stated.
A radius bar 25 is pivotally attached to the standard 16 and to some part of the
main frame parallel to the eccentric rod.
As shown the respective pivot pins attaching the eccentric rod to the arm 15, and
the radius bar to the standard 16 are in the same axial line, and the respective pivot
pins attaching the radius bar to the main frame and the eccentric rod R to the rocker
arm mare in the same axial line when the valve or said rocker arm is in its mid
position. All that is necessary, however, is that the radius bar and eccentric rod be
substantially parallel.
The object of this feature is to avoid distortions in the valve movement which would
otherwise be produced by the movements of the main frame with reference to the
driving axle.
As the point of suspension, on the standard 16, is mounted on the axle,

page_text: and the support 23 for the rocker arm shaft 24 is mounted on the main frame 9, the
latter will rise and fall independently of the former and would vary the relative
position of the two, were it not for the radius bar 25. In virtue of this radius bar
and its points of attachment, the centers of the eccentric rod and the radius bar are
made to move in equal arcs, so far as the rising and falling of the frame with
reference to the axle is concerned, and the point of suspension and the point of
attachment of the eccentric rod to the rocker arm are kept in a constant relative
position, regardless of the uneveness of the track and the rising and falling of
the frame.
Operation. Having now described my construction as applied to a locomotive, I
will endeavor to make clear the functions of my mechanisin as applied to engines
generally, reference being had to the diagrams.
In brief, it may be stated that the function of connecting the rocker armi mand
the eccentric rod R so that they form with each other always an oblique angle (acute
in construction shown) is to overcome the obliquity of the connecting rod and effect a
rate of valve movement in opposite direction in unison with the rate of piston move-
ments in the opposite parts of its stroke; and the function of the offsett point of
suspension, or pivoting the guide 19 at the point K, is to correct an error or distortion
which would, otherwise, he introduced at the extremes of the valve movements in
opposite directions from mid position, and the beauty of the construction is that the
quality of this correction various in conformity to the error introduced (otherwise) by
varying the length of the throw of the valve."
In other words, the offsett point of suspension is a constant corrective for a variable
cut off.
That these are the functions of these features of construction may, perhaps, be
rendered more explicit by the following considerations.
It is a well known fact that the motion of a piston does not correspond to the motion
of the crank. The piston moves more rapidly in the half of the cylinder farthest
from the crank shaft, on both the in and out strokes. That is owing to the obliquity
of the connecting rod. The motion of the crank being uniform, the crank pin moves
through like ares in like times; but a greater are must be described to move the
piston through the half of the cylinder nearest to the crank shaft on both the in and
out strokes. In other words, the half strokes farthest from the crank shaft are made
in the least time.
The general principle involved is this, viz. In the movement of a point on the are
of a circle the horizontal movement, except at the limit and when exactly at right
angles to the radius drawn from the point, does not correspond in length to the angular
movement but the two have an inverse relation dependent on the part of the circle
and the direction of the movement. In other words, in all parts of the circle, with
the exceptions stated, a constant angular travel will produce a variable horizontal
travel and, conversely, a constant horizontal movement will produce a variable
angular movement.
In this valve gear, the above principle is employed to overcome the obliquity of the
connecting rod.
The rocker arms n' and m' are rigidly attached to the rock shaft 24. Hence what-
ever angular movement is given to the rocker arm m¹ will also be given to the rocker
arm n' and as the valve rod Q is attached to the rocker n', exactly at right angles,
when the valve is in mil position, the length of valve movement will correspond very
nearly to the angular movement of the rocker n'. Now, in virtue of the principle
hereinhefore stated, the rocker m' may be given such a position with reference to the
eccentric rod R that equidistant throws of the rocker n', in the opposite directions
from its mid position, will be made in unequal times. As shown, the two form with
each other an acute angle, when at mid position; and as the rocker m² is moved up
the arc, m,
the acuteness of this angle is increased and the amount of angular move-
ment for any given horizontal movement is correspondingly increased; and on the
movement of m' down the arc m, the reverse is true. In other words, the valve is
made to move more rapidly toward S than toward T. But when the valve is moving

page_text: toward S, the piston is moving in the part of its stroke which is most rapid; and
when the valve is moving toward T, the piston is moving in the part of the cylinder
nearest the crank shaft, or in that part of its stroke where it moves most slowly.
Relatively, therefore the fast motions and slow motions of the piston and valve, take
place at corresponding parts of their travel.
Now the ratio of the mean velocities of the piston in the two parts of its stroke
may be mathematically determined, inasmuch as they are to each other inversely as
the ares passed through by the crank, which are known quantities. Hence the mean
ratio from mid position to its limit of travel in opposite directions may be given the
same ratio as the mean velocities of the piston, by simply varying the angle of the
rocker m' to the eccentric rod R.
Hence the valve not only moves fast when the piston moves fast, and conversely,
but the two move at substantially the same rate. Or in other words, the two are in
unison.
But this is only true of the mean rates of motion-and the two would correspond
only at certain parts of their respective paths. At the extremes the valve would be
thrown a little too far in one direction and not quite far enough in the other and the
actions, cut off, exhaust and compression, would take place a little too soon in one
direction and a little too late in the other. For very short valve motions this error
might not be material; but it is magnified as the travel of the valve is increased.
For the length of valve travel is increased by increasing the horizontal movement
of the eccentric rod (as hereinafter explained) while the angle of the rocker m' to the
eccentric rod, at mid position remains substantially constant. Hence, as the angular
movement corresponding to a given horizontal movement of the rod, is greater the
farther the point moves the arc, the rocker would be moved too far toward m¹l and
not far enough toward mil.
Now the offsett point of suspension corrects this error by substracting from the
valve motion at one end and adding to it at the other.
It should be noted that in the construction as shown in the drawings the eccentric,
the crank and the axis of the crank shaft always lie in the same line either on the
same side of the shaft (as shown) or at opposite sides of the same. Hence the eccentric
and crank may be treated as moving in the same circle, if we conceive the crank to be
shortened to the throw of the eccentric.
It must be further noted that, inasmuch as the eccentric strap 13 rotates about the
axis of the crank shaft and the outer end of its extended arm 15 is constrained to
follow a straight line, i.e. the guide 19, any point as d, on said arm will have a
motion derived from said two motions. The eccuntric rod R is attached at such a
point and takes such a motion, and its path (i.e. of point d), when the guide is in
position shown in figure IX is the ellipse D.
This would be back gear for a locomotive. In figure X the ellipses D1 and D" in
oppositely inclined planes, would represent the path of the point d in forward and
backward gear respectively for a locomotive.
The full lines in both figures represent the respective positions taken by the axis of
the guide, the point d, and the point e; and the dotted lines show the corresponding
positions which these same parts would occupy if the guide were pivoted at K, some
point in its longitudinal axis.
On inspection, it is evident that whether the point of suspension be at K or K' the
distance which the point d will be thrown, to the opposite sides of the vertical Y Y¹
through the axis of the crank, depends on the angle of the axis of the guide to the
line in other words this angle determines the horizontal motion given the
eccentric rod, and it is by varying the angle and horizontal motion that the valve
travel is varied. But it is equally evident that in all positions of the guide, except the
vertical position, the point d'is thrown farther to the left or away from the cylinder
when the guide is pivoted at K'.
The effect is to restrain the rocker m² from moving as far up the arc m as it other-
wise would and to make it move farther in the direction m¹, subtracting from the
valve travel toward S and adding to its travel toward T.

page_text: Now it can be readily shown that the distance which d is thrown farther to the left
or away from the cylinder in virtue of this offsett point of suspension varies in propor-
tion to the angle of the axis of the guide to the vertical Y Y
This is evident from the fact that when the axis is vertical the point c and hence
also the point d, is in exactly the same position as if the aide were pivoted on K, bui
as the guide is swung from the vertical, the position which it does occupy is separated
from the position it would occupy if the guide pivoted on K, by an increasing distance
measured on a horizontal line. When the guide is horizontal, for example, the two
would be separated by an infinite distance. The possible variation in separation is
therefore from zero to infinity.
This is true for backward and forward gear, and is well shown in figure X, wherein
the angles between the axis of the guides and the distance between K and K are
greatly magnified. In the figure V Vi represent the position of the guide for forward
(locomotive) motion and WW for backward; while the dotted lines and we w
represent corresponding positions, which the guide would occupy if pivoted at K.
When the eccentric is at a, the upper end of the arm 15, is at cl for forward motion
and ate for backward motion; and when the eccentric is at a¹, the upper end of the
arm 15 is at c for forward and at for backward motion; while if the guide had
been pivoted at K, the corresponding positions of the outer end of the arm 15, when
the eccentric was at a would have been for forward and for backward motion:
and when the eccentric was at a', the outer end of the arm would have been at for
forward and for backward gear. Bute and care much farther to the left than
and f
As d is a point on the arm 15, it is also moved farther to the left.
In other words, as the error introduced by increasing the horizontal movement of
the eccentric rod to secure greater valve travel is increased, the correction is increased
in like proportion. The correction varies as the error varies.
Pivoting the point of suspension at K connecting the rocker arm m² and eccentric
rod at an oblique angle to each other, and connecting the rod to the rocker at a point
below the point of attachment of the rod to the eccentric arm, d, taken all together,
have an additional function, of advantage in preserving uniformity, in a reversing
engine. This combined function comes into play in shifting from forward to
backward motion. As the tracing of this function is very difficult, requiring an
abstruse mathematical discussion, it is not deemed essential in this specification.
There is a limit to the distance between K and K'; and better and worse positions
for this offsett point of suspension to occupy. Its proper position for any given
dimensions of all the cooperative parts of the valve gear may be determined mathe-
matically within a sufficiently near approximation for practical purposes.
The proper proportions and positions of the respective parts having been once
determined, the importance of maintaining them in these relations is self evident, in
view of the foregoing discussion. The radius bar 25 accomplishes this function, as
herein before stated.
When all the parts are properly proportioned, this valve gear gives a valve motion
which is almost perfect, the actions, cut off, exhaust, and compression being very
nearly uniform.
Modifications can be made in this construction without parting from the spirit
of my invention.
Having now particularly described and ascertained the nature of my inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1 In a valve gear the combination with an eccentric of an eccentric strap pro-
vided with an extended arm, a guide for the outer end of said arm, constraining
it to move in a definite path, a rocker provided with a pair of rigid arms, a valve
rod connected to one of said arms at or about right angles when the valve is in
mid position and an eccentric rod having one end attached to the extended arm of
said eccentric strap, and the other end attached to the other rocker arm at an

page_text: oblique angle when the valve is in mid position, substantially as and for the
purpose set forth.
2. In a valve gear, the combination with an eccentric strap having an extended
arm of a guide for the outer end of said arm pivoted at a point offsett from its
longitudinal axis and an eccentric rod for driving the valve, attached to said arm,
substantially as and for the purpose set forth.
3. In a valve gear, in combination, an eccentric strap having an extended arm, a
guide for the outer end of said arm pivoted at a point offsett from its longitudinal
axis, a rock shaft provided with a pair of rocker arms, a valve rod attached, at or about
right angles, to one of said rocker arms, when the valve is at mid position, and an
eccentric rod having one end attached to the other rocker arm at an oblique angle,
when the valve is in mid position and its other end attached to the extended arm of the
eccentric strap, substantially as and for the purpose set forth.
4. In a locomotive, an automatically adjustable support for the point of suspension
of a valve gear, consisting of a standard boxed on the main driving axle in com-
bination with a radius bar attached at one end to said standard and at the other to a
part of the main frame, as and for the purpose set forth.
5. In a valve gear for locomotives, in combination with an eccentric on the main
driving axle and an eccentric strap provided with an extended arm, a standard boxed
on said axle, a guide for the outer end of said arm pivoted to said standard, a rocker
mounted on the main frame for communicating motion to the valve, an eccentric rod
from said arm to said rocker, and a radius bar parallel to the eccentric rod attached
to the standard and to a part of the main frame, substantially as and for the purpose
set forth.
6. In combination with the driving axle 1, the eccentric 13, the strap 14 having
the arm 15, the standard 16, the rock shaft 17, the guide 19 rigidly secured to said
rock shaft at a point offsett from the longitudinal axis of the guide, the slide block 20
to which the arm 15 is attached by pivot 21, the rocker shaft 24, having rocker arms m
and n', the valve rod 0, attached to n' at right angles and the eccentric rod R attached
to m at an oblique angle and having its other end attached to the arm 15, all
substantially as described.
Dated the 24th day of September 1800