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Description: |
| Abstract:
The valve-motion is intended to work with an ordinary single slide-valve proportioned for cutting off by the lap. An eccentric gives a smooth motion with no concussions; but when applied to such valve it opens and closes the passages for the induction and ed notion of the steam slowly. This occasions wire-drawing the obvious reduction of pressure of the steam in passing through a scantily-opened orifice in the early part of the opening motion and the last part of the closing motion. Such wire-drawing is a loss. Many efforts have been made to reduce it by providing liberal passages and opening and closing them rapidly and varying the point of cut-off to effect regulation. The present invention is an improvement in mechanism for attaining these ends.
The requirements for a perfect distribution of steam in the cylinder of a stationary engine are-first, at the beginning of each stroke of the piston the steam-port leading into the end of the cylinder behind the piston shall be amply opened to admit steam at as nearly as possible boiler-pressure, the port at the other end of the cylinder being at the same time fully opened to the exhaust-pipe to permit the free exit of the steam which has done work in the opposite stroke; second, these conditions to be maintained, so as to preserve the initial pressure, until the point of cut-off determined by the governor is reached; third, the admission -port to be closed sharply without arresting the exhaust from the opposite end of the cylinder; fourth, these last conditions to continue, allowing the steam to drive the piston by its elastic expansion, until near the end of the stroke; fifth, the exhaustion from the opposite end to be closed and the remaining exhaust-steam before the piston to be compressed (sometimes termed cushioned) to raise the pressure in the clearance-space and valve passage or passages, and, sixth, this to continue until just before the end of the stroke, when, seventh, the port to the first end of the cylinder is to be opened to the exhaust, so as to discharge from that end preparatory to the commencement of the return of the piston. The like succession of conditions will occur during the return stroke and will be repeated continuously While the engine is in operation, with the required changes in the position of the cut-off point to maintain uniform speed if the load or the steam -pressure varies. These requirements have been fairly Well met in engines having separate steam and exhaust valves for each end of the cylinder and have been approximated in single-slide valve engines having a separate cut-off valve but there are serious objections to such additional valve. To obtain such motion with simple mechanism and a single valve and which will allow of rapid revolutions without concussion and noise is the object of my invention.
Economical distribution of the steam can be effected by means of a properly-proportioned single valve alone by operating with a certain step-by-step motion which may be attained by a cam. The valve and valve-stem may be light, but the operating parts have necessarily much weight, and in ordinary valve-gears the action involves noise and concussions, so as to be seriously objectionable. I have discovered that it is practicable to give such motion by two cams, one fixed on the shaft and the other changeable, and two combined sets of parts operated thereby, with the changes of velocity divided between them, so that the full transitions from slow to rapid motion and back again, occurring during each stroke, shall be confined to the valve and valve-stem. The valve having a proper amount of lap moves rapidly at the several periods of opening and closing the passages and moves slowly at intermediate periods. The offsets in the cams are so gradual and the relatively heavy rollers, rods, and levers directly actuated thereby have so moderate changes of motion that the engine may serve at a high speed without concussion. The construction provides for rapidly changing the point of cutoff through a wide range, so that the action of the governor is peculiarly efficient. The combined levers make the valve move in the same direction as one cam and to twice the extent of motion, the motion being received through an arm which I term a rocker, doubled in extent by an additional part, the lever effect being what is sometimes termed a lever of the third order, while the portion of the motion of the valve due to the other cam is received through a further rocking motion of such additional part. This important part I term a rider. It is a lever of the second order, and in addition to its function of in creasing the effective length of the rocker receives and reverses the motion of the second cam without increasing it.
Claims:
1. In a steam-engine, a single slide-valve adapted to effect the distribution and exhaust from both ends of the cylinder and to cut off by the lap, the two cams I and K, contributing through connections including a rocker to give two quick motions in each stroke separated by a period of rest, the cam I and its rod J connected. to the rocker at a point nearer the center of motion than the valve connection, so that the arrangement multiplies the motion, all substantially as herein specified.
2. In a steam-engine, a single slide-valve adapted to effect the distribution and exhaust from both ends of the cylinder and to cut off by the lap, the two cams I and K, contributing through connections including a rocker and rider to give two quick motions in each stroke separated by a period of rest, the cam K and its rod L connected to an arm of the rocker of such length that while it is desired for the rider to be ineffective its end may coincide with the fixed center of the rocker, substantially as herein specified.
3. In valve-gear for steam-engines, a single slide-valve and ports proportioned for cutting off by the lap, the rocker G and the rider H pivoted thereon, the latter having widely divergent arms one of which is connected to the Valve, in combination with the cam I fast on the shaft, shaped for imparting a two-step reciprocating motion to the connected rocker and the loose governor controlled cam K shaped for imparting a single reciprocating motion to the connected rider and a fluid pressure cylinder and piston connected with the rider near the mid-length of the proper arm thereof, arranged to maintain a reliable but yielding contact of each rod with its cam, all substantially as herein specified.
4. In valve-gear for steam-engines, the rocker, a rider pivoted thereon and having widely-divergent arms one of which is connected to the valve, in combination with rods connected to the rocker and to the other arm of above set forth.
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