US2076976A - Scavenge pumping means for internal combustion engines - Google Patents

Description

April 13, 1937. Q w 5 BURN I 2,076,976

SCAVENGE PUMPING MEANS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 15, 1955 '5 Sheets-Sheet 1 PM 7 in renter April 13, 1937. w 5 BURN 2,076,976

SCAVENGE PUMPING MEANS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 1 5, 1935 3 Sheets-Sheet 2 Lye/22hr V a ile/wary!) April 13, 1937. w. s. BURN ,9

- SCAVENGE PiJMPING MEANS FOR INTERNAL CQMBUSTIOIL ENGINES Filed Nov. 15, 1955 s Sheets-Sheet s nren or zuwma am y JQfnrnQyS Patented Apr. 13, 1937 SCAVEN GE PUIVIPIN G MEANS FOR INTERNAL COMBUSTION ENGINES Walter Scott Burn, Hartlepool, England, assignor to The National Gas andOil Engine Company Limited, and Alfred Bickerton Balmford, Ashton-under-Lyne, England, and. Walter Scott Burn, Hartlepool, England Application November 13,1935, Serial- Nof49634 In Great'Britain November. 1 3,193i

.10 Claims. (Cl. mi -e) This invention relates to the scavenging arrangements of two stroke oil engines and has for its primary object to provide an improvedcon structional form of pump andassemblage' of valve and operating gear which will be "particularly compact and eflicient when compared with arrangements heretofore proposed.

Another object is toprovide a simple and highly efiicient scavenge air pump that is capa ble of being placed immediately adjacenttothe cylinder of a two stroke cycle internal combustion engine without the usual delivery pipes or air receivers, and capable of being precisely timed and given the proper amount and: rate of movement-to deliver'iirst scavenging air and then supercharging air .at any predetermined time relative to the exhaust and scavenging periods of the main cylinder and at the requisite rate and pressure, thus entailing a minimum of work incompressing and delivering the air and, because ofthis cooperative actio'nwiththe port openings, causing :a reduction in the excess-air ratio required for accomplishingthe scavenging operation; 3

The pump of this inventioncomprises a vanelike .displacer pivoted at one extremity =for angu+ lar movement within a sector-shaped casing communicating through ports with an air source and with the scavenging 1 and supercharging air inlet of the engine cylinderymeansi driven' by thetengine for oscillating said sdisplacer to draw air into said sector-shaped casing :from' the: air source-and to expel such. air into thewengine icylinderw and valve means; also driven by 1 the engine; "controling-the opening 1 and closing of saidporfbs," 1: 0:: i The operating .mechanism for imparting angular. movement 'to the displacer may; :be an ec centric gear or a cam;ro1ler.:and returnspring,

or return mechanism; but inaany: case it ispresferred. to: arrange this operatirig mechanismnto act on thedisplacer in the :vicinity of the pivot or hinge of the latter in such manner. as tokeep the I travel .of the 2 operating mechanism. within relatively small dimensions; 1 This arrangement and @the angular form of the 1 pump-ensure that, .while' utilizing ancperatinggear of small dimen sions possessing also only small movementya large total displacement shall be obtainable, the pump beingiprimarily. intendedfor usezwith relatively large air displacements atvlo-w pressures. For air :sealing purposes, labyrinth "grooves rare formed. around 'the outside of the; dis'placn and onlyi a. small running clearance'is allowedi' .Pump suctionand discharge iarerpreferably to enableit' to be withdrawn from controlled by single 1 valve which may He a semi-rotary valve oscillatingin a sector shaped casingand suitably operated by'cam}; roller-spring and-lever mechanism *whieh enables it to serve firstas suction valve to connect the pump to the scavenging" a'ir source 'while cutting oii delivery to theenginecylinder and then as scavengepui'np delivery valveto scavenge and 'supercharge the engine cylinder while cutting off the suction port. I

Cam operation -of the"displacer is preferred 'as 'thisenabl'es a precise control of air delivery "to b Obtained. J

In the case of unidirectional enginesthe'dis 'placenoperatingfcain profile can be made to give the requisite relativelyouick delivery to coincidewith theicylinder scavenging and superchargingperiods as controlled by the piston and cylinderports;whilethe return or suction strokecan "be made more slowly over the remaining" greater period} thereby reducing the suctionor negative pressure. V v I Tofmake the pump reversible, the ,cam op eratingthe displacerand that operatingfythe valve can be symmetrical and suitablelost ino tion arranged in the j shaft driving coupling to give thecorrect relative timings for either direction of rotation;

[It is preferred to have aseparate pump associated'with eachcylinderfeach with its required cperatingmechanism, operated from a shaft running parallel tothe displacer and parallel toqandfdriven from the main engine crankshaft.

The driving shaftean be used for operating other service pumps such as 'thefuel pump etc. The

mnp casing is attached directly ontow h Side. e

of the cylinder, the general arrangement being such as to cause a' minimum Ofclearance vol,- ume. and changes of direction of the incoming or out-going air etween the scavenge pump air inlet n ain thecylinder ports.

l e construction di'the'control valve; is such as to give a'goodzficw of air into the scavenge pump fromjth'e air source (which may bean fair' suctionbelt embodiedin the 'rnain cylinder casing) and a1so' to facilitate the discharge of air intothe scavenge belt of the main cylinder. "Ihevalveconstruction'is, furthermore; such as i i itscasing withutdi smantling the sameby having detachable beari'ngpivotsw "9' 'Thef shaft operating the scavenge pump valve may be that ivhich drivesthe scavenge pump flap or it may be a separate shaft. v an alternative construction the suction and discharge or' control" valve may be a flat valve operated by suitable rockers controlling a port to the cylinder belt and one to the suction chamber. This arrangement gives reduced clearance volume.

If required, the pump can be made double acting, with two valves for supplying either two single acting cylinders or one double acting cylinder.

In order to obtain a high volumetric eflicency from the aforesaid scavenge pump and to eliminate any negative suction pressure in the pump which may cause oil to be drawn into the pump from the region of the operating mechanism, the aforesaid pump or pumps may be charged by a primary blower separately or independently driven.

as to enable the flap to be removed=without disturbing the casing. This is aided by fixing the flap by studs to the pivot shaft.

The accompanying drawings illustrate one way of carrying the invention into effect.

In said drawings: j Fig. 1 is a sectional elevation viewed as .if taken on the line of Fig. 2;

Fig. 2 is a view at right angles to Fig. 1,1ooking in the direction of the arrow :1: thereof and with one half in section upon the line 2-2 of Fig. 1;

Fig. 3 is a diagram of the cam associated with the scavenge air control valve, indicating how the valve positions illustrated in Figs. 4, 5, 6 and '1 are derived;

Figs. 4, 5, 6 and '1 represent different cycle positions of the control valve; and

Figs. 8, 9 and 10 are diagrams showing how certain valve and piston positions are related,

Referring first to Figs. 1 and 2, the air pumping element or displacer comprises a flat flap portion 3 adapted, in the position shown, to lie close to the engine frame 4 which carries the cylinder 5 of which a part only is illustrated. This cylinder is preferably, though not necessarily, adapted to be scavenged in the manner described in my copending application Serial No.

49,632 filed November 13, 1935 for Internal combustion engines. The flap part 3 is curved at its lower end as indicated at 6 to carry an offset portion 1 which is removably connected by studs 8 to the flattened surface of a rock shaft 9.

The shaft 9 is supported at each end in a roller bearing |ll mounted in the side walls ll of a casing having a top wall I! concentric with the shaft. The upper end of the flap portion 3 has a flange |3 curved to suit the casing wall l2 and there are also side flanges M to engage the casing side walls H, the whole being stiffened by webs |5. The flap flange i3 is shown to have a set of grooves or channels I6 to serve as a packing, said grooves being extended downwards along the side flanges I4 for the same purpose. Labyrinth packing |1 secures airtightness at the bearings l0 and a packing strip I8 adjustably' attached to the casing by studs I9 engages the shaft 9-for a similar purpose.

The flap as a whole; is adapted to be moved inwardly (toward the cylinder) to the extreme position shown aganst the returning action of springs 29, the floating abutments 2| of which are coupled by links 221to lugs-23 on the flap. These lugs and the links 22 are spaced suflicient ly far apart to permit a cam 24 to engage a roller 25 carriedupon a roller bearing 26 by a shaft (not numbered) which is v.stationarily the frame 4 and easing wall The detail construction of the pump is such mounted in bosses 21 formed in the flap. Said cam 24 is carried on a cam shaft 28 which is driven from the engine in any suitable way. At the upper end of the flap is a pocket 29 in communication with the flap casing, having a spring loaded relief cover 30. Below said pocket level is a semi-rotary valve 3| adapted to cover i and uncover a suction port 32 leading to an air belt 33 around the engine cylinder and also to cover and uncover a port 34 leading to the cylinder- This valve 3| operates in a cavity 35 provided in the engine frame 4 and has arms 36 detachably fixed as by a nut 31 to a pivot 39 itself attached to a ball bearing 39 removably secured to One end of onev of the pivots 38 is extended and formed as a crank 38a: connected by a rod 40 to a lever 4| free to rock about a shaft 42. Compression springs 43 react between a stationary abutment 44 and an abutment 45 pivotally connected by a fork 46 to the lever 4|, and a cam 41 on a shaft 48 acting through a roller 49 serves to rock the lever 4| against the spring action.

The cams 24 and 41 rotate at engine speed.

The timing of the scavenge air displacer 3 and control valve 3| will be understood from a consideration of the diagrams shown in Figs. 3 to 10.

As indicated in Fig. 8, when the time for exhaust lead is completed the engine crank is 20 from the bottom dead centre and the scavenge air displacer 3 commences movement towards its opposite extreme position shown in Fig. 10, where the whole of the air previously drawn into the casing is discharged. The cam 24 in doing this has moved angularly through 90 or thereabouts. Approximately %,0f the air is discharged when the cam 24 has moved angularly through 70 or thereabout, corresponding to exhaust cut off which is the condition shown in Fig. 9. In passing from the position of Fig. 9 to position of Fig. 10, air is admitted for supercharging, the exhaust being already closed.

Referring now to Fig. 3 it is therein shown the position which the roller 49 for operating the semi-rotary valve 3| assumes in relation to the cam 41 at four angular intervals designated A, B, C and D, producing the valve conditions correspondingly designated A, B, C and D in Figs. 4, 5, 6 and '1. While the cam 41 is in position such that its circular portion of smaller radius engages said rotary valve roller 49, the valve 3|, as shown in Fig. 4, keeps the suction port closed and the inlet port 34 to the cylinder full open.-

This condition exists while the piston is passing from position Fig. 9 to position Fig. 10. During upward travel of the piston from the position of Fig. 10 i. e. through the real compression period of the cycle-the valve 3| remains quiescent, covering the suction port, but later, in the vicinity of the firing point, the roller 49 is gradually moved, as shown'in Fig. 3, from position A to positions B, C and D, the valve conditions produced being shown in Figs. 4, 5, 6 and 7. As will be understood, the valve 3| thus gradually uncovers the suction port 32 and covers the delivery port 34, the latter being, however, independently closed by the piston while the valve 3| is closing. During the exhaust portion of the outward, or downward, stroke of the piston, the delivery port 34 is kept closed by that cylindrical portion of the cam 41 which is of larger radius, until the position of Fig. 8 is reached, whereupon the roller 49 passing through its cycle positions D C B A in movement off the cam portion of larger radius onto the portion of smaller radius causes the valve 3| to gradually cover the suction port 32 and to uncover the delivery port 34, which are the conditions requisite for operation as represented by Figs. 8, 9 and 10.

What I claim is:

1. A scavenge pump for two'stroke internal combustion engines, comprising in combination with an engine, a vane-like displacer pivoted at one extremity for angular movement within a sector-shaped casing attached at the side of the engine cylinder, said casing having communication through ports with an air source and with the scavenging and supercharging air inlet of the engine cylinder, means including an outside separate shaft driven by the engine for oscillating said displacer to draw air into said sector-shaped casing from the air source and to expel such air into the engine cylinder, and valve means also outside and driven by the engine to control the opening and closing of said communication ports according to the timing with the cylinders cycle of engine operation.

2. A scavenge pump according to claim 1, wherein the air displacer is oscillated by operating mechanism including a cam acting thereon in the vicinity of its oscillation pivot.

3. A scavenge pump according to claim 1, wherein a single valve is operated to control the alternate intake and expulsion of air to and from the sector-shaped casing.

4. A scavenge pump according to claim 1 wherein the valve means comprises a semi-rotary valve which is oscillated in a sector shaped recess forming an extension of the displacer casing and having in its arcuate face valve ports communicating with the air source and the engine cylinder, respectively, said ports being alternately opened and closed by the oscillation of said valve so that it alone controls both the intake and expulsion of air to the displacer casing.

5. A scavenge pump according to claim 1 characterized by the fact that the valve means .45 includes an oscillating member mounted in a receiver space upon detachable bearing pivots which permit of its withdrawal from the casing without dismantling, and said member alone serves to control both the intake and expulsion 50 of air to the displacer casing.

6. A scavenger pump according to claim 1,

sides and top.

8. A scavenge pump according to claim 1, characterized by the fact that the mechanism for operating the displacer vane and the mechanism for actuating the valve means comprises means adjustable as to timing so as to permit the pump to be operated in either direction of rotation of the motor.

9. A scavenge pump for internal combustion engines, comprising a sector-shaped casing fastened to the side of the engine cylinder, a vanelike displacer mounted to oscillate in said casing, a passage for air to be drawn from a supply source into the displacer casing, a passage for air to be discharged from said casing into the cylinder, a valve controlling both of said passages so as to alternate the opening thereof according to the movement of the displacer within the casing, a shaft outside the cylinder driven by the engine crank shaft and carrying a cam for oscillating the displacer member, and means coordinated with said outside shaft for operating the said passage control valve.

10. A scavenge pump for internal combustion engines, comprising, in combination with an engine cylinder, 2. sector-shaped casing fixed on the outer side of the cylinder, a flap form of displacer mounted to oscillate in said casing, a passage for air to be drawn from a supply source into the displacer casing, a passage for air to be discharged from the easing into the cylinder, an oscillating valve controlling both of said passages so as to alternately open and close the same, a shaft supported on the casing outside the cylinder and carrying a cam for oscillating the displacer member, and another shaft mounted on the casing also outside the cylinder for actuating said passage control valve through linkage members; both of said outside shafts being driven by and in timing with the crank shaft of the engine.

WALTER SCO'I'I BURN.

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