Improvement in Engine Valve Gears.
Year: 1898

page_text: Date of Application, 12th July, 1898-Accepted, 27th Aug., 1898
COMPLETE SPECIFICATION.
Improvement in Engine Valve Gears.
I, CHARLES ARTHUR ALLISON, of 52, Chancery Lane, London, in the County
of Middlesex, Patent Agent, do hereby declare the nature of this invention,
(which has been communicated to me from abroad by Lincoln Alexander Lang,
of Yule, Billings County, North Dakota, United States of America, Capitalist,
and Edward Freeman Walsh, of Endicott Arcade, St. Paul, Ramsey County,
Minnesota, United States of America, Physician), and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement:―
This invention, pertaining to improvements in valve gears of link type, will
be readily understood from the following description taken in connection with
the accompanying drawings in which:
Fig. 1 is a side elevation of a valve gear exemplifying my invention; and
Fig. 2, a perspective view thereof.
In the drawings:-
1, indicates the main shaft of an engine:
2, an eccentric fast thereon:
3, the eccentric strap, which is entirely without the usual rigid eccentric rod:
4, the valve rod whose reciprocations are to be transmitted to the valve:
5, that end of the valve rod distant from the shaft and adapted for any of the
usual systems of connections with the valve stem or valve stem rocker:
6, a link, having a mean radius equal to the length of the valve rod, the link
lying in the plane of the eccentric strap and the back of the link being as close
to the eccentric strap as is consistent with non-interference of the parts as they
move:
7, the block of the link, the same sliding in the link, as usual, the inner end
of the valve rod being pivotted to the block:
8, a pivot in a fixed position in the plane of the mean tangent of the link:
9, an arm free to oscillate on pivot 8 and lying alongside the link:
10, link-supporting pivot carried by the free end of arm 9 and engaging an
intermediate portion of the link, the link block 7 to be capable of adjustment in
the link to one side and the other of supporting pivot 10, by any usual or suitable
adjusting mechanism:
11, a pivot carried by eccentric strap 3 as far inwardly upon the strap as is
practicable:
12, an arm rigid with arm 9 and having its outer end connected with pivot 11:
13, the hell-crank thus formed by rigidly connected arms 9 and 12, these arms
being at such an angle to each other as the expediency of construction brings
about:
14, a pivot carried by the eccentric strap on that side of the shaft opposite
pivot 11:
15, a pivot carried by one end of the link:

page_text: 16, a coupling bar connecting pivots 14 and 15: and
17, an exemplifying suspender for adjusting and supporting the valve-rod.
Referring to Fig. 1, it is obvious that one effect of the motion of the eccentric
strap is to oscillate the bell-crank and shift pivot 10 and the link to and from
the shaft thus giving reciprocating motion to the valve rod. Arm 12 restrains
the rotation of the eccentric strap and limits the movement, of pivot 11. to that
of an arc toward and from the shaft. Pivot 14 describes a distorted ellipse whose
major axis represents the degree of oscillation of the link upon pivot 10. The
movement of pivot 10 toward and from the shaft is to be equal to twice the lap
plus twice the lead of the valve -and the bell crank and the throw of the
eccentric are to be constructed accordingly. Pivots 14 and 15 are to be so related
to the strap and link as to give to the link the oscillation proper for the desired
maximum port opening when the block is at full gear.
When the eccentric centre crosses a line joining the shaft-centre and pivot 11,
then pivot 10 will be at one extreme of its movement and the mean tangent of the
link will be perpendicular to the mean plane of the valve rod 4 and the valve rod
may then be moved to sweep the block throughout the length of the link with-
out changing the position of the valve. Give to the eccentric a half turn and
pivot 10 will be thrown to its other extreme of motion, and again the block can
sweep the length of the link without changing the position of the valve. Pivot 14
effects the oscillation of the link upon pivot 10 while pivot 11 causes the move-
ment of pivot 10 and the link, the resulting functional movement of the link-
block and valve being sharply concentrated at opposite points of the cycle of
movements, leaving long dwells in the intervals between those movements. The
functional results are extraordinary, as will be hereafter indicated.
A mere survey of Fig. 1 shows that the entire system which reciprocates the
valve-rod is concentrated close to the main shaft, thus permitting of the use of a
long valve-rod and permitting the system of mechanism to be kept within a
small field near the shaft. The entire system may be disposed at any angular
position about the shaft, thus permitting the valve rod to lead off in any desired
direction for connection to the valve-stem or valve-rod, the system being. thus
peculiarly adapted for use under conditions where there is but limited room and
where obstructions may prevent leading the valve rod directly toward the valve.
The construction also permits the link to lie in the plane of the eccentric, thus
permitting the direct transmission of the working strains. It is obvious, without
analysis, that the device, with a single eccentric, has all of the capacities of the
ordinary double-eccentric link motion, so far as variability of cut-off and reversi-
bility of engine is concerned; that the comparatively long valve-rod permits of
a correspondingly straight link; that the transmission of strains is peculiarly
direct and the mechanisms comparatively free from joints and offset connections
productive of side strains; that a light valve-rod instead of a heavy link needs to
be adjusted; that the block is practically free from slip; that the strap friction
of but one eccentric is involved; that the eccentric needs but short throw; and that
evils of rod-angularity are nullified.
An analysis of the system by those skilled in the art will develop the following
extraordinary qualities:-First, an extremely rapid opening and closing of ports
at all gears, back or forward, the motion being so prompt as to be completed in
say two inches of piston travel where the latter is twenty-four inches; second,
such prompt action in opening and closing gives long periods for entry and ex-
haust of steam and thus permits of less port opening, and consequently, of less
valve travel, with consequent economy in valve-moving energy; third, such
prompt action avoids exhaust lead if desired, and avoids back pressure and com-
pression evils; fourth, the lead is constant and; what is of the highest importance,
this constancy of lead is secured without any sacrifice of port-opening fifth, a
sharp cut-off is secured within any practical desires, it being practicable to cut
off at any point within two inches of each end of the stroke in the case 'of an
engine having twenty-four inches stroke, and without any concomitant sacrifices in

page_text: distribution. So far as known to me, these results have not heretofore been
attained in link motion valve gears.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:-
1. In a valve gear, the combination, substantially as set forth, of a single
eccentric, a rodless strap therefor, a first pivot and a second pivot carried by said
strap, a pivot fixed near the eccentric, a link supporting arm mounted thereon,
a link pivot carried by the free end of said arm, a link pivotted on said link-
pivot, a block adjustable in said link, a connecting bar pivotted to the link and to
the first pivot of the eccentric strap, a connection from the second pivot of the
eccentric strap to said fixed pivot to restrain the turning of the eccentric strap,
and a connection between the second pivot of the eccentric strap and said link
pivot whereby said link pivot is moved toward and from the eccentric.
2. In a valve gear, the combination, substantially as set forth, of a single
eccentric, a rodless strap therefor, a first pivot and a second pivot carried by said
strap, a pivot fixed near the eccentric, a link supporting arm mounted thereon,
a link pivot carried by the free end of said arm, a link pivotted on said link-pivot,
a block adjustable in said link, a connecting bar pivotted to the link and to the
first pivot of the eccentric strap, and an arm mounted on said fixed pivot and
connected with the second pivot of the eccentric strap and rigidly connected with
said link supporting arm.
3. In a valve gear, the combination, substantially as set forth, of a single
eccentric, a rodless strap therefor, a first pivot and a second pivot carried by said
strap, a pivot fixed near the eccentric, a bell-crank mounted on said fixed pivot and
having one of its arms connected with the second pivot of the eccentric strap, a
link pivotted to the other arm of the bell-crank, a link-block adjustable in said
link, and a connecting bar pivotted to said link and to the first pivot of the
eccentric strap.
4. In a valve gear, the combination, substantially as set forth, of a single
eccentric, a rodless strap, a link, a link-block adjustable therein, a connection
pivotted to the link and to the eccentric strap to impart an oscillating movement
to the link, and a bell-crank interposed between the link and eccentric and serving
to reciprocate the link and to restrain the turning of the eccentric strap
5. In a valve gear, the combination, substantially as set forth, of a single
eccentric, a rodless strap therefor, a link-supporting pivot mounted near the
eccentric and capable of movement to and from the eccentric, mechanical connec-
tions between such pivot and strap for causing said pivot to move toward and
from the eccentric, a link mounted on said pivot, a block adjustable in said link,
and a connection pivotted to said strap and link for oscillating the link upon
said supporting pivot.