US254483A - John jambs - Google Patents

Description

(No Model.)

J. JAMES. GUT-OFF VALVE GEAR FOR STEAM ENGINES. No. 254,483.

Patented Mar. 7,1882.

N. PETERS. Plwmuxhogmphur, washngmn, DA C4 UNITED 'STATES YPATENT OFFICE.

JOHN JAMES, OF NEW YORK, N. Y.

CUT-OFF-VALVAE GEAR FOR STEAM-ENGINES.

SPECIFICATION forming part of Letters Patent No. 254,483, dated March 7, 1882.

Application filed April 9, 1881. (No model.)

To all whom it may concern:

Be it known that I, JOHN J AMES, of the city and county of New York, in the State of New York, have invented a certain new and useful Improvement in Gut-Off-Valve Gear for Engines, of which the following is a specification.

When a locomotive-engine is fitted with any of the ordinary forms of link-motion operating a main or distribution slide-valve the variation of the cut-oli' of the said main or distribution valve is eected by varying the relative positions oi the link and link-block. This variation is limited, however, on account of the en suing prejudicial distribution inherent to the link-motion operating a single valve when much linking-up is attempted. N otwithstanding this the link-motion, in conjunction with a single valve, is still almost universally applied to locomotives, and mainly on account of the simplicity of such arrangement. If, however, a separate cut-off slide-valve could be applied to a locomotive-engine which did not entail the usual amount and complexity of mechanism for varying the point of cut-off, the advantages would be evident. This is the object ot' myinvention. I apply a separate cut-off slidevalve, consisting of a single plate driven by a lever from some of the reciprocating partssuch as the piston-rod or cross-head-of the engine, and having an invariable movement or travel relatively to the engine-piston'. Such .cut-oil valve has a fixed (instead of a variable) travel, and a fixed (instead of a variable) length. Ordinarily the cut-off of a cut-0E valve is varied by varying the travel of the cut-0E valve, or by varying the length or lap of the cut-oft' valve, or by varying the angle between the special cut-off' eccentric and the crank. My method of varying the cutting-ofi' action of the cut-ofi' valve is to vary the travel of the main valve by altering the relative positions ot' the link and link-block in the ordinary linkmotion. This arrangement is advantageous, because of its simplicity and paucity of parts, and because by it can be secured both an earlier and agreater variation of cut-oli' with better distribution than is possible when the linklnoiou operating a single slide-valve alone is use In the accompanying drawings, Figure 1 represents a longitudinal vertical section through Referring first to Fig. 1, A designates an engine-cylinder, and B the piston thereof.

O designates the crank-shaft, and motion is transmitted from the piston to said crank-shaft through the pistou-rod B', cross-head D, and connecting-rod D' in the ordinary way. Upon the cylinder is the valve-chest A', in which is theusual main or distribution slidevalve, vE, which is secured to the valve-rod E', connected With an arm of the rock-shaft F. The other arm of the rock-shaft carries a block, a, which'lfits in a link, G, operated by the eccentrics G G2.

H designates the reversing or link-adj usting lever, which is connected with the link G by the rod I, the bell-crank J, and the suspensionlink J So far as described the en gine is like engines in common use, and as the operation of the link-motion is Well understood, further description thereot1 is unnecessary.

Upon the back of the main or distribution slide-valve E is mounted a cut-ofi' slide-valve, K, consisting of a single plate, which is of fixed length, and controls the passage of steam or other motive agent through the ports b of the main valve.

L designatesa rock-shaft supported in suitable bearings, and having arms projecting in opposite directions from it. To one of said arms is connected the valverod K' of the cutod' slide-valve K, and to the other armis connected a rod, L', which is connected with the cross-head D, and imparts an oscillating motion to the rock-shaft L, and edects the operation of the cut-oft' valve.

It will be clearly seen that the cut-off valve is not adjustable in its travel, and that therefore .its movement or travel is always the same relatively to the piston.

The principles on which my invention is based may be illustrated by the aid of diagrams Figs. 2 and 3, and in such diagrams I will suppose my inventionl applied to an ordinary doublecylinder steam or compressed-air locomotive with its cranks at right angles and fitted with the ordina-1y link-motion.. l take IOO the following dimensions respectively, first, for the case where the cut-off valve cuts oi with its inner edges and its motion is coincident with the piston, (diagram 1;) and, second, where the cut-off valve cuts off with its outer edges and its motion is reverse to the piston. These dimensions are chosen simply for illustration, and of course may be varied.

Fig. 2, maximum main-valve travel, Ytwo inches; cut-off-valve travel, one inch; mainvalve lap, five-sixteenths inch 5 cut-oif-valve lap, thirteen sixteenths inch; angular advance of eccentrics, twenty degrees; length of eccentric-rods, six times lift of link; open eecentric rods, (suppose.) Fig. 3, maximum main-valve travel, two inches; cut-off valve travel, one and one-fourth inch; main-valve lap, one-fourth inch; cut-odvalve clearance, three-eighths inch; angular advance of eccentrics, twenty degrees; length of eccentricrods, six times lift of link; crossed eccentricrods, (suppose.)

Let b a l e e l be travel-circle of eccentrics. Draw two diameters, c a, c b, at right angles. Make d c e equal to the angular advance, with the center on the diameter c b produced, and radius equal to three times the rectilineal distance between e and c. Describe the arc e e2 ea e, a line drawn from any point in which arc to the center is approximately the virtual eccentric radius for the relative position of the link and link-block corresponding to thatpoint.

- With the same radius (3 e e) and center on the same diameter, but one-half the cut-offvalve travel to the left in diagram Fig 2, or to the right in Fig. 3, describe the arc e4 e5 csf Divide the arc e e2 e3 e into a number ofpartssay the upper half into three equal partsand draw e e4 e2 e5 e3 e parallel to c b. Draw l land l Z2 Z3 parallel to and at distances from a c equal respectively to the lap of the main valve, and to the lap of thecut-of valve in Fig. 2, or the clearance thereof in Fig. 3. y Join c4 c e5 c e6 c with the center c and radii e4 c e5 c e6 c. Describe arcs intersectingtheline Z l2 L3 in l Z2 Z3, respectively, and join l c Z2 c L3 c. Then the angles e4 c l e5 c ZZ e o Z3 are the angles of the crank at which cut-off takes place corresponding respectively to the positions of the link relative to the link-block which correspond with e e2 e3.

Referring to Fig. 2, it will be noticed that as the link moves from full to mid gear the cut-off takes place earlier, and that with the dimensions chosen the latest cut-off is about three-fifths, and when the link is in the position corresponding to e3 that the cut-off takes place about one sixth of the piston stroke. N'ow when the link motion alone is applied and the dimensionsUap lead eccentric throw) usual to locomotives taken, the cut-off takes place, when the link is in a position corresponding to e3 at approximately half-stroke. Hence when my invention is applied I have both earlier and greater variation of cut-off with better distribution.

It ought to be remarked here that even alsition somewhat short of mid-gear, the cut-oit' 8o takes place later in the piston-stroke. With the dimensions chosen the earliest-cutoff takes place about onetenth, and when the link is in the position corresponding to about e3 the cutoff of both main and cut-off valves is simultaneous and takes place about three-fifths of the stroke. Hence with my invention we have earlier and greater variation of cut-offwith better distribution than with thelink-motion alone.

.It is evident, with the dimensions chosen, a cut-off at approximately three-fifths is the latest possible, as, if the link moves from the position where that cut-off is effected, either toward full or mid gear, the cut-ofi' takes place earlier, being effected in the latter instance by the main valve. In order that the engine may start at all points of the revolution, the latest cutoff must be at least later than half-stroke, and this is insured when the cutoff-valve clearance is taken greater than the main-valve lap. In both cases the range of cut-off depends on the dimensions chosen, and when, as will be usually desired, an early cut-oi is in conjunction with a cut-olil as late as or somewhat later than half-stroke, it will usually tend to a better distribution to give some over-travel to the main-valve when in full-gear, to have crossed eccentricrods and to take the angular advance small. Where my invention is applied there is not the same necessity for a considerable angular advance-at least so far as pre-release is concerned-because usually the workinguid will be expanded to a greater degree than when the link-motion only is applied, and consequently will exhaust at less pressure.l

It will be evident that if the cut-off valve were constructed to cut-.0E upon its inner edges it should travel with the piston instead of reversely thereto, and hence the valve-rod K' should be connected below the rock-shaft L instead of above, as here shown.

I am aware that it is old to employ, in connection with a main valve and link-motionfor operating the same, a cut-off valve composed of two plates or parts adapted to be adjusted nearer to or farther from each other for varying the point of cut-off by means ot' a valve-stem having right and left hand threads which engage with corresponding nuts in the two plates or partsofthe valve. Such cut-oivalve is not of fixed length, like mine, but of variable len gth, and its length is varied for the purpose of varying the point of cut-01T.

I do not claim the above as ofmy invention.

IOO

By driving the cut-oft valve in this combination by a connection with the piston-rod or cross head of the engine the movements of the said valve correspond exactly with the movements of the piston in both directions, whereas when the cut-off valve is driven by an eccentric the movements of the said valve, owing to the i changing angles of the connecting-rod of the eccentric, do not exactly correspond with the 1o movements of the piston in both directions.'

What I claim as my invention, and desire to secure by Letters Patent, is-

In an engine, the combination, with a main driven by a connection with the piston-rod or cross-head of the engine, so that it has an invariable travel andan invariable motion relatively to the piston, substantially as and forl the 2 purpose specified.

JOHN JAMES.

Witnesses:

FREDK. HAYNES, A. C. WEBB.

Images