IMPROVEMENTS IN THE VALVE GEAR OF STEAM ENGINES
Year: 1884

page_text: COMPLETE SPECIFICATION.
We, JOHN TWEEDY, Engineer of West Lodge, Walker, in the County of
Northumberland and JAMES PATTERSON Junior, Engineer of 19 Hawthorn Street,
in the City and County of Newcastle upon Tyne, do hereby declare the nature of
our said invention for "IMPROVEMENTS IN THE VALVE GEAR OF STEAM ENGINES
and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement :-
"
Our invention relates to certain improvements in construction and arrangement
of the valve gear of steam engines affording great control over the functions of the
valve with simplicity and accessibility of working parts and is applicable more
particularly to the type of gear commonly known as Hackworth's gear.
And in order that our said invention and the manner of performing the same
may be properly understood, we hereto append a sheet of explanatory drawings.
In these drawings the same reference numerals are used to point out the same
parts wherever these are repeated, the general features only of the arrangement are
drawn and it is to be understood that any parts or details not delineated or
described are to be arranged and constructed as in existing engines or in analogous
manner.
The invention is shewn as applied to an inverted direct acting marine engine but
we do not restrict ourselves to the precise arrangement of the essential parts which
may be varied to suit special requirements without affecting the principle upon
which it operates.
On the engine shaft 1-Figures 1. 2 and 3-an eccentric sheave 2, is formed or
secured, (in this arrangement of the levers immediately or nearly in line with the
crank,) embracing this sheave is an eccentric strap 3 having formed on or secured
to it, a rod 4 of any convenient length. At some point in this rod, depending on
the proportion of the different parts and the motion desired to be given to the valve
a link 5 is introduced or a guide as shewn in Figure 3. On the shaft being turned,
the end of the eccentric rod 4 will describe a path more or less truly circular or
elliptic as may be required and governed by the point of attachment of the link 5
or equivalent guide. From this point any modification of Hackworth's or Finks
valve gears may be used to transmit the motion, which is capable of being con-
siderably modified (as to the path described) by the influence of the link 5, to the
valve spindle. The modification shewn is of what is called Hackworth's gear and

page_text: consists of a lever 7 articulated at one end to the eccentric rod at 6: another point S
in the lever is guided in a reversible guide 9 (or reversible link 9 as shewn in
Figure 3) and another point 10 is joined to the valve spindle by a link 11.
Figures 4. 5. 6 and 7 shew diagrams of some of the varying paths described by
the end 6 of eccentric rod 4 at different points of attachment of the link or guide 5.
These diagrams illustrate how widely the movements to be communicated to the
valve, by the intervening gear, are capable of being varied by the attachment of
the link or guide to eccentric rod.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is:
First Controlling the movement of the end of an eccentric rod by a fixed link, or
equivalent device, so as to make it describe paths of varying form, according to the
point of attachment of said link, substantially as shewn and described.
Second The combination of parts constituting the valve gear arranged constructed
and operating substantially as shewn and described.
2011
LNThan 1001