IMPROVEMENTS IN EXPANSION GEAR FOR STEAM-ENGINES
Year: 1881

page_text: LETTERS PATENT to John Bodington, of Harborne, near Birmingham, for an
Invention of "IMPROVEMENTS IN EXPANSION GEAR FOR STEAM-ENGINES."
PROVISIONAL SPECIFICATION left by the said John Bodington at the
Office of the Commissioners of Patents on the 4th January 1881.
"
JOHN BODINGTON, of Harborne, near Birmingham. IMPROVEMENTS IN
EXPANSION GEAR FOR STEAM ENGINES."
This Invention relates to a novel method of effecting the expansion of steam in
steam engine cylinders, whereby the steam is "cut off" automatically.
For this purpose I provide a vertical governor spindle, on the lower part of
which I mount two cams, one of which is keyed firmly on to the governor spindle
and controls the admission and exhaust; the other is loose and may be turned
round on the said spindle, this latter controlling the "cut off." The governor
spindle is provided with a slot, in which is a vertical toothed rack so fitted as to
slide up and down, into which gears one (the first and smallest of a connected
series of five toothed wheels, the fifth of the series of said toothed wheels engaging
in and actuating a worm which gears into a worm wheel either keyed on to the
loose cam or cast in one piece with it. The toothed rack series of five toothed
wheels and worm all rotate with the governor spindle. A small spindle, to the
upper end of which is fixed a hollow sphere, passes centrally down into the governor
spindle until its lower end bears on the top of the rack or part in which the rack
is placed. The hollow sphere may be weighted to balance the governor balls,
which are of the ordinary description.
The method of operation is as follows:-
When the governor balls rise by reason of an increase of speed in the engine
controlled by them the rack is raised, giving motion by means of the aforesaid
series of five toothed wheels to the worm and worm wheel, thereby turning the
loose "cut off" cam round on the governor spindle forward of the fixed cam
controlling the admission and exhaust. This latter by striking against a friction
roller which works on a pin fixed in a sliding part connected to the valve rod
pushes the valve until a port is full open, when the loose cam strikes against

page_text: another and similar friction roller at an opposite point of the sliding part of the
valve rod, and brings the valve back until the port is just closed, thus cutting off
steam. It operates at each end in like manner. Eccentrics may be employed
instead of cams.
The above arrangement refers to a case in which one slide valve only is employed.
When two valves are used, namely, an admission and exhaust valve and a "cut off"
valve, I may apply two eccentrics, fast and loose respectively, the cut off eccentric
being worked by the governors in exactly the same manner as the loose cam before
described. Between the two valves I place a fixed block with suitable ports cast
straight through. I lessen the pressure on the backs of the valves by means of a
plate which may be adjusted up to them by screws passing through the valve chest
cover.
The governor spindle and balls may be driven at the same speed as the crank
shaft by means of bevil gearing.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Bodingdon in the Great Seal Patent Office on the 4th July
1881.
JOHN BODINGTON, of Harborne, near Birmingham.
EXPANSION GEAR FOR STEAM ENGINES."
"IMPROVEMENTS IN
This Invention relates to a novel method of effecting the expansion of steam in
steam engine cylinders, whereby the steam is "cut off" automatically.
For this purpose I provide a vertical governor spindle, on the lower part of
which I mount two cams, one of which is keyed firmly on to the governor spindle
and controls the admission and exhaust, the other is loose and may be turned
round on the said spindle, this latter controlling the "cut off." The governor
spindle is provided with a slot, in which is a vertical toothed rack so fitted as to
slide up and down, into which gears one (the first and smallest of a connected
series of five toothed wheels, the fifth of the series of said toothed wheels engaging.
in and actuating a screw or worm which gears into a worm wheel either keyed on
to the loose cam or cast in one piece with it. The toothed rack series of five
toothed wheels, and screw or worm all rotate with the governor spindle. A
small spindle, to the upper end of which is fixed a hollow sphere, passes centrally
down into the governor spindle until its lower end bears on the top of the rack or
part in which the rack is placed. The hollow sphere may be weighted to balance
the governor balls, which are of the ordinary description.
The method of operation is as follows:-
When the governor balls rise by reason of an increase of speed in the engine to
be controlled by them the rack is raised, giving motion by means of the aforesaid
series of five toothed wheels to the screw or worm and worm wheel, thereby
turning the loose "cut off" cam round on the governor spindle forward of the fixed
cam controlling the admission and exhaust. This latter, by striking against a
friction roller which works on a pin fixed in a sliding part connected to the valve
rod pushes the valve until a port is full open, when the loose cam strikes against
another and similar friction roller at an opposite point of the sliding part of the
valve rod and brings the valve back until the port is just closed, thus cutting off
steam. It operates at each end in like manner. Eccentrics may be employed
instead of cams.
The above arrangement refers to a case in which one slide valve only is
employed. When two valves are used, namely, an admission and exhaust valve
and a "cut off" valve, I may apply two excentrics, fast and loose respectively, the
cut off excentric being worked by the governors in exactly the same manner as
the loose cam before described. Between the two valves I place a fixed block with
suitable ports cast straight through. I lessen the pressure on the backs of the
valves by means of a plate, which may be adjusted up to them by screws passing
through the valve chest cover.
The governor spindle and balls may be driven at the same speed as the crank
shaft by means of bevil gearing.
Referring to the accompanying Sheet of illustrative Drawings,
Figure 1 is an elevation of expansion apparatus according to this Invention, cams
and a single slide valve only being employed.
Figure 2 is a plan of the same partly in section, the position of the crank being
just over the centre.
Figure 3 is a plan of the cam arrangement of Figures 1 and 2, with worm and
worm wheel.
Figure 4 is a plan of the apparatus partly in section, in which arrangement

page_text: excentrics and two slide valves are employed, the position of crank being barely on
centre.
Figure 5 is a plan of the excentric arrangement of Figure 4, with worm and
worm wheel.
Figure 6 is a section of steam chest cover and plate for taking pressure off slide
valve.
In the whole of these Figures similar letters and figures of reference indicate
like parts, a being the vertical governor spindle; b, the fixed cam; c, the loose
cam; d, slot in which is fitted the rack e; 1, 2, 3, 4, 5, the series of five toothed
wheels, the toothed wheel 5 engaging in and actuating the screw or worm f, which
gears into and operates the worm wheel g on the loose cam c; i, spindle; j, hollow
sphere; k, k¹, governor balls; 1, 1, friction rollers working on pins m, m³, fixed in
the sliding part n; o is the, slide.valve (Figure 1); p is an admission and exhaust
valve, and p a cut off valve; -q and q¹ are respectively the main and cut off
eccentrics; r, fixed block.
Having now described the method of carrying my Invention into practical
effect, I would observe that I do not bind myself to the exact means hereinabove
set forth, as it is obvious that various modifications may be made without affecting
the principle of the Invention; notably I do not bind myself to the exact method
of turning the "cut off" eccentric or cam round. I may employ a longer lift to
the rack and fewer toothed wheels; nor do I confine myself to placing the cams or
excentrics on a line with the valve spindle, as I may place them away from the
centre and use a rocking lever or levers connecting the sliding part with the valve
rod or the excentrics with the valve rods, as the case may be. When a rocking
lever is or rocking levers are employed the cams or excentrics need have only half
the throw required in, the former case, and instead of the spindle i and hollow
sphere I may employ a spiral spring passing centrally down the governor spindle
with a screw on the top to regulate the tension of said spiral spring. The fixed
block between the two valves may be made parallel, the governor spindle
being brought out centrally between the two valve spindles and the straps with
the rods fixed thereto being excentric to the governor spindle.
What I claim as secured to me under the Letters Patent hereinbefore in part
recited is,―
1. In expansion gear for steam engines the method of turning the "cut off"
excentric or cam round on its spindle, substantially as described and illustrated in
the Drawing.
2. The arrangement of the fixed block between the main and "cut off" valves,
substantially as described and illustrated in Figure 4 of the Drawing.
3. The method of lessening the steam pressure on the backs of slide valves by
means of a plate, which may be adjusted up to them by screws passing through the
valve chest cover, substantially as described and illustrated in Figures 2 and 6 of
the Drawing.
4, The general combination of parts constituting the expansion gear for steam
engines, substantially as herein before described and illustrated in the accompanying
Drawing.
In witness whereof, I, the said John Bodington, have hereunto set my hand
and seal, this Twenty ninth day of June, in the year of our Lord One
thousand eight hundred and eighty one.
JOHN BODINGTON. (L.S.)