US2126376A - Two-cycle diesel engine - Google Patents

Description

Aug. 9, 1938. c. e. CURTIS TWO-CYCLE DIESEL ENGINE Filed Feb. 1, 1935 2 Sheets-Sheet 1 s- 9, 9 c. G. cUBTIs 2,126,376

' TWO-CYCLE DIESEL ENGINE Filed Feb. 1, 1935 2 Sheets-Sheet? 7 mum mm 000 F; 8

w ATTORNEY "til i a elects 0=-CYCLE omsar. ENGINE t G. @nrtis, New York, N. Y. Application February 1, i935, Serial No.

This iuvehtiou applies particularly to two-c rcle engines operating with uniflow scavenaihe and the main ohiect is to provide exhaust valve mechahism which will hive emclent scaveneine and a larae weiaht ol air in. the cylinder and will operate satisfactorily at high speeds and which will he at sole and rus ed construction. The meclhc object is to provide a form of valve which requires no adjustment and will remain tight, but which will haveadeauate area, will open and close auichlv, and which will derive its motion from crahhshait operation.

ll'o accomplish this result It use a piston valve or valves in the combustion end oi the cylinder,

and l. have succeeded in operating this valve or valves he a roclriha eranh motion, connecting rods ahd a lav craulishatt in such a way as to obtain a large port ***e with a comparatively small total movement of the valve, and to have the period durina which the valve remains open suitahle tor eliectine the necessarv pressure drop to aether with the scavenging. in other words, the valve remains open lone enough to drop the pressure and scavenge ehlcieatlv. This results in an extremely simple and rugged type at mechanism. which can he operated at verv much hleher speeds than is permissihle with poppet valves which reeture frequent adjustment and re 'a'rihclihe.

hi the accolripauvihe drawings, li igate l. is a sectional view through the centre oi a Diesel ellelhe cylinder with an exhaust piston valve in the head and with the operatives mechanism which it provide. This view shows the piston valve shout to open.

the. it shows the piston valve in the mpeapcai tioa.

the. 3 shows the piston valve in the closed posttion at the lowest point oi the strolre.

lite. t shows my invention as applied to two piston valves in the head instead off one, this view being a side view to elevation.

Fig. 5 is a top view of the same arraneemeht and Fla. 6 is a sectional top view talren on the plane (til. I t

led by two headers it and it, oneon each side oi the engine. so as to have ample volume of air in the immediate neighborhood of the ports when scavenging takes place. The exhaust ports it of the valve are uncovered by the piston as it moves upward, the piston itself being packed with a. sumclent aumher of rings. to be perfectly gas tight in its lower position. These exhaust ports reach all the way around the cylinder of the piston valve and discharge into a header or annular passage which leads through to theerhaust opening it; The piston valve is also provided with piston rings at its upper end so that if there is any pressure in the exhaust hell; it the gas cannot leals: out into the engine roora. The piston this operated by a trunk piston rod it provided with a wrlstpin it operating in the usual manner. The upper end of the connecting rod is pivoted to a reciting hell crash it hv a pin til. the rocking hell crank it turns on a fixed pivot ll I place the pivot ti in such a position that when the piston valve is in its lower position the piston rod lssubstantialiv in the position shown to 3 and the heavy thrust due to the maximiurl gaspressure during the cycle is taken on the plus it and ill, which plus may he large and provide ample working surface. in other words, the connecting rod is practically on the dead center shown in Fig. 3. hell crack I operate hp a connecting rod it h pivoted to the hell crahh by the pin. it, the lower ehd of the rod connected to a eranltpih on a lav-crankshaft which is driven hv gear or other means directly from the math crahhshait lit: as shown in the'drawings. The ohlect of this mechanical arrangement is to enahle the exhaust ports it to he made as long as possible and yet to have the total strolte of the piston valve as small as possible. its shown in the drawings I have made the portion of the strolte oi the valve which is required to open the 40 ports about halt the total valve throw, and I secure this ample movement by an arc of movement or the crankshaft which in a two-cycle englue should occupy much less than half the total circular movement. The effect of this mechanism is to greatly intensify the relative port opening movement of the valve compared with the rest of the movement of the valve and to derive this movement from a simple crankshaft.

It also accomplishes the result of taking a large part of the strain oil the connecting rod 22 and the crankshaft 25 by having the combustion in the cylinder take place when the connecting rod l! is on or nearly on the dead-centre; By using the upper part of the arc travelled by the lay-crankpin and by the arrangement shown the movement of the valve at the time of opening or at the time of closing is comparatively rapid, while its movement towards the lower end of the stroke is very much slower.

Inthedrawingsthemaincrankisshownas about 95 back of the lower dead center and at some such point as this-possibly considerably later-I propose to begin opening the exhaust valve so as to let down the gas pressure in the cylinder in ample time before the inlet ports are exposed by the piston and before scavenging should begin. I therefore set the crankpin of the lay-shaft 26 in position a as shown, the bell crank 20 being in the position shown and the lower edge of the piston valve being even with the lower edge of the exhaust ports as shown in Fig. i so that the valve is just about to open.

The main engine crank turns in a direction clockwise as shown by the arrows, and the lay-crank turns in the opposite direction, so that by the time the main crank has reached the position b, the lay-crank has reached a corresponding position b' and the piston valve has been drawn up sufllciently. to open the exhaust port fully. As the main crank moves from the position b to the position which causes the piston to cover and close the inlet ports the lay-crank moves to a corresponding position 0' and this brings 'the valve back into the position shown in Fig. 1

just closing it. Cylinder compression therefore begins at this point and the cylinder pressure is equal to the scavena'ln8 pressure or approximates it. As the main crank moves from position c to position d the lay-crank moves to the corresponding position 01 and brings the valve to its bottom position with all the piston rings resting on the solid part of the valve cylinder so that the valve is gas tight in,this position. This position of the valve is shown in Fig. 3. As the main crank passes over the upperdead center combustion takes place and the maximumpressure at that time or soon thereafter comes on the main piston and also on the piston valve, but while the lay-crank has moved up through a considerable are this has produced only a little movement of the bell crank 7.0 and as the connecting rod I1 is still operating at practically the dead center, the valve has not gone up materially. The valve does not move materially until the pressure in the main cylinder has very substantially declined.

In order to reduce the stresses on the valve and valve-operating mechanism as much as possible, I arrange the relative areas of the inlet ports and the exhaust ports so that only a small part of the total pressure drop takes place in passing through the inlet port leaving a large proportion of the total pressure drop to be available for causing the flow through the exhaust ports. This not only increases the velocity through the exhaust valve but it enables a smaller piston and smaller exhaust ports to be used. It also results in a higher pressure in the cylinder during scavenging and an increased supercharge at the end of the stroke, provided the exhaust valve is closed in time to permit the scavenging air to flow in as fast or faster than it can flow out through the exhaust valve as the inlet ports are being closed by the piston.

My exhaust piston valve and operating mechanism has also the great advantage that it can be operated at very high speed-much higher than is possible with poppet valvcsrpartioularly in a two-cycle engine, and the mechanism is extremely simple and rugged. The closing movement of amasve the piston valve also increases the compression in the cylinder and adds several per cent to the power of the engine. It is also quite important in a high speed engine to have ample scavenging air reservoir capacity for all the inlet ports so that during the period of scavenging, which may not be more than 1/50th of a second, the volume of air surrounding the scavenging ports will be suflicient to feed these ports promptly. For this purpose I provide an air belt I4 and It on each side of the cylinder so as to feed the ports on both sides effectively and these air belts or headers are connected by air passages through between the cylinders so as to feed the ports lying between the cylinders.

In the operation of the mechanism in some cases I prefer to use two exhaust piston valves l2, II, somewhat smaller than the single exhaust valve in the centre. These are shown in top view (Fig. 6) and the operation of the actuating mechanism (which is similar to that already described) will be readily understood by examination of Figs. (and 5, the bell crank 20 being forked to take care of the two connecting rods l1, l1 and being driven by a single long connecting rod 22 reaching down to the lay-shaft 25, as shown.

In Figs. 7 and 8, the latter of which is a section taken on the plane 8-8 Fig. '1, I show an arrangement of two headers and cross passages for feeding the air effectually and promptly to the cylinder inlet ports. I 4ll are the two headers. "-IHII are openings in the housing walls to permit the air to flow from the headers to the outer walls of the cylinder. The upper wall 82 and the lower wall ll are carried right across the cylinder so as to make a passage connecting the two headers. To enable the cylinder liners to be close together so as to make as short an engine as possible, I provide openings in the wall of the housing II which permits the air to flow from either side into the space surrounding the liner. I also provide openings in the cross wall of the housing so as to permit air to flow from both sides of the wall into the liner which is drawing scavenging air at that instant.

What I claim as new and desire to secure by Letters Patent of the United States is: v

l. A two-stroke cycle engine comprising a cylinder and piston, a crank and connections for transmitting the reciprocatory movements of said piston to said crank, an inlet port and an exhaust port, and a port-controlling means comprising a piston valve, a bell-crank, a rod connecting an arm of said bell-crank and piston valve, a crank turning at the same speed of revolution as said engine-crank, and a rod connecting the secondnamed crank and an arm of said bell crank, the arrangement of said'cranks and connections being such that the rod connected to said pistonvalve and the arm of the bell crank to which it is connected are approximately on dead center at the same time that the engine-crank and its connecting-rod are on dead-center.

2. A two stroke cycle engine according to claim 1, wherein the piston-valve, the port controlled thereby, and the crank-arm which is attached to the piston-valve connecting-rod are so constructed and arranged that the port is opened and closed in that part of the arc of movement of the aforesaid arm inwhich it is generally at right- 3. A two stroke cycle engine comprising a cylinder and piston a crank and connections for transmitting the reciprocatory movements of said piston to said crank. an inlet port and an exhaust-port, and port-controlling means comprising a piston-valve, a hell-crank, and means timed with the speed oi. revolution of said englue-crank for oscillating said bell-crank to move said piston-valve to open and close the port controlled thereby. the arrangement of the parts bein: such that the arm 0! the bell-crank which is connected to the piston-valve is approximately on dead-center at the same time that the enginecrank and connecting-rod are on dead-center,

and such that the piston-valve opens and closes said port in that part of the arc of movement of said arm in which it is generally at right-angles to its dead-center position and moves said piston-valve rapidly, the movement of the pistonvalve after the port is closed being effected inthat part of the movement 0! the aforesaid arm in which it approaches dead-center and moves the piston-valve most slowly.

CHARLES G. CURTIS.

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