US2051469A - Scavenging of two-cycle engines - Google Patents

Description

Aug 18, 1936.. i E. s. DENNISON 2,053,459

SCAVENGING OF TWO-CYCLE ENGINE Filed Dec. 14, 1935 2 Sheets-Sheet 1 INVENTOR EDWARD $.DENNISON.

BY allabl M ATTORNEY Patented Aug. 18, 1936 UNITED Y STATES PATENT OFFICE.-

. 1 2,051,409 SCAVENGING or TWO-CYCLE enemas of Pennsylvania a Application December 14, 1933, Serial 110,702,403

2 Claims. (Cl. 123-65) My invention relates to two-cycle engines and it has for an object to provide for an improved exhaust and scavenging arrangementso that effective scavenging may be had with a. relatively large effective working stroke of the engine.

Itis old tohave a two-cycle engine cylinder provided with opposed scavenge air and exhaust ports; however, this simple arrangementis not very effective unless the piston is modified to provide for deflection of the air in order to prevent transverse passage of the air directly across the cylinder and out the exhaust ports. A second arrangement has been used wherein a partial belt of scavenge air ports is arranged below a similar partial belt of exhaust ports, the air crossing the cylinder and being. deflected by the opposite imperforate cylinder wall upwardlyuntil deflected by the head soas to pass downwardly to the exhaust ports, the air path being substantially a loop wherein the outlet is super-. posed with respect to the inlet. An objection to the second arrangement is that the provision of an imperforate cylinder wall to deflect the air upwardly necessitates partial port belts with the result that the ports have to be made higher than would be the case if they extended completely around the cylinder, and, therefore, to the extent that they have to be made higher, to that extent is the working stroke lessened. A third arrangement has been proposed which constitutes an improvement over the first type in that the air ports are directed radially toward a center disposed eccentrically with respect to the cylinder axis and variously inclined to secure upward travel of the air at one. side of the cylinder, the air being deflected downwardly to the other side by the cylinder head and passing downwardly at the latter side to exhaust ,ports disposed in opposed relation with respect to the air ports;

however this type of construction is also objec tionable because of the necessary port heightfand the consequent lessened efiective engine stroke .as' compared to an arrangement wherein come,

plete belts or ports are provided.

'llt is "also old to have both scavenge and1ex=f haust' ports extend around the full perimeter of the-cylinder, the scavenge ports radiating from the 'cylinder axis. 'By thismeans, it. is intended. to produce'a central iountain'of airmoving up-'. wardly, while th e exhaust gasesfare forced down wardly in the annular spacebetween the air Tool-Q uinn and the cylinder wall however, this 'a' rangementfsufi ers'from instability unlessthe m f i u m ac lnor s ident c l wh fi f efaet iel i-sflfl be; wit t re ult that, the-,1.

air column is thrown ofl center in an irregular and indeterminate way and undesirable mixing of air and exhaust gases results.

In accordance with my inventiom-I provide a complete belt of exhaust ports and a complete belt of scavenge air ports arranged immediately below the'exhaust ports, with the result that a minimum height of ports is involved and a large efiective working stroke is preserved; and, to impartthe desired directional effect to the air, the air ports radiate from a center which is eccentric to the cylinder axis so that the resultant velocity effect of the entering air produces an up- .wardly moving eccentric column of air disposed toward the side of the cylinder nearest to the eccentric center, the air passing upwardly and being deflected downwardly to push products of combustion out the exhaust ports. By directing Y the air to a locus near one wall, the'upward moving column is caused to occupy roughly one half of the cylinder section while exhaust gases occupy the other half and any difilculty because of inport height and ,imper'forateness of a'cylinderwall and the advantage, ofminimum cylinder lengthrequiredfqr-the ports without the disadvantage of instability of the fourth arrangement;

Therefore, a further object ofrmy. invention is: to provide a tworcycle cylinderawith complete belts of exhaust and scavenge air ports, with the scavenge air portsarranged immediately below the. exhaustpOrtsand radiating from a'zc-enter eccentric totheeylinder axis to secure suchifio'w of air as. to efiectively evict products. of combus-- tion from'th cylinder. if If it is resultant air column with respect tothe interior f hefiylii d thi m y. b achieved; by. relay-w esired to change; thelocation; of the tiveIin'clination of the air; ports; forexample, if v the air port or ports; at. minimumrradius' with respect .to vth eccentriccenter are-.inclined upwardly, the,-.a 1 r,.entering ,through the. remainder of the; ports, is rendered more'eifective' toposltion the resultant ;eolumn nearer, :to" the; side-1 or "the cylinder 1 at -the; upwardly inclinedyportsi fincengine so as to obtain the most effective opera-- tion, this being done by having the eccentric centers of the scavenge ports arranged in the plane of the crank shaft axis.

These and other objects are effected by my invention as will be apparent from the following description and claims taken in connection with the accompanying drawings forming a part of this application, in which:

Fig. l is a vertical sectional view showing my improved scavenging arrangement;

Fig. 2 is a horizontal sectional view taken along the line 1III of Fig. 1 and showing the scavenge air ports;

Fig. 3 is a sectional view taken along the line III-III of Fig. 1 and showing the exhaust ports;

Fig. 4 is a sectional view of a modified arrangement wherein one or more air ports are inclined inwardly and upwardly;

Fig. 5 shows a plurality of cylinders grouped so that the scavenge port eccentric centers are in a plane of the longitudinal center line of the engine;

Fig. 6 is a view similar to Fig. 2' but showing a modified arrangement of scavenge ports;

Fig. 7 shows a further modified scavenge port arrangement;

Fig. 8 shows a further modified arrangement of exhaust ports; and Fig. 9 is a diagrammatic view illustrative of a fiow principle involved.

Before taking up a description of features of the invention in detail, certain principles and objectives will be considered. A full perimeterof both scavenge and exhaust ports is desirable to avoiddead spaces and to increase the eflective stroke of the engine, this arrangement minimizing the portion of the stroke used for the exhaust and scavenging process. Also, the air should be so controlled that it flows up at one side of the cylinder and down at the other, as this produces more orderly scavenging and provides a minimum area of contact of the upwardly and downwardlymoving columns, and, therefore, minimizes the admixture of air and exhaust gases. The latter point will be clear from diagrammatic Fig. 9. If the air is assumed to move upwardly as a central column, then the downwardly moving column would be a cylinder thereabout, the contact being a circle indicated at a. 0n the other hand,

where the upwardly columnmoves up at one side of the diametral plane b and down at the other, the area of contact of the columns is very much less and is a minimum. In the first case. the cylindrical contact a would be 2.22 times the diametral contact b. In my improved scavenging arrangement, the operation is such that low, or substantially diametral, contact occurs.

In Figs. 1- and 2, I show an engine cylinder Ill having a piston ll therein, the cylinder ll having a head construction I! provided with a fuel injection device ll of any suitable type.

' The cylinder is provided with a complete belt of exhaust ports I! which are radially disposed with respect to the cylinder axis I. Immediately below the ports It, the cylinder isrprovided with a complete belt of scavenge air ports II which are disposed substantially radially with respect to a center It which is eccentric to the cylinder I 6.

An exhaust manifold 20 receives products of combustion leaving the ports i5 and a scavenge air manifold 2i supplies scavenge air through the ports I! to evict products of combustion-from the cylinder. In operation, and near the end of a power or working stroke, the piston ll first uncovers the exhaust ports l5, whereupon there follows a'drop in pressure of the combustion gases and outflow at high velocity of products of combustion through all of the'ports IS, the complete belt of exhaust ports providing. for

' highly effective action of this kind, while, at the same time, requiring minimum cylinder length for accommodation of the ports. As soon as the scavengeair ports l'l begin to become uncovered, then the scavenging air is eifective to drive products of combustion out through the exhaust ports.

As the exhaust ports 15 and the scavenge air ports I! are arranged as annular belts extending completely around the cylinder andas the ports of each belt are arranged as close together as possible consistent with strength of the cylinder and cooling thereof and as the belts are arranged close together, it will be apparent that a minimum extent of cylinder height or length is used to provide the ports, with the result that the effective working stroke is maintained at a maxi,-

mum. 1

As will be seen from Fig. 3, the annular belt of exhaust ports radiate from the cylinder axis, thereby providing for maximum discharge area, minimum cylinder length for their accommodation and efi'ective discharge. 0n the other hand, as may be seen from Fig. 2, the scavenge air ports I I radiate from an eccentric center ll so as to secure, due to the resultant velocity of air' entering through the ports 11, a column of air which moves upwardly at or toward the side of the cylinder having ports of minimum radius with respect to the eccentric center, the column of air moving upwardLv and being deflected by the head I! for movement downwardly at or toward the other side of the cylinder to evict products of combustion through the exhaust ports.

While all of the scavenge air ports may be disposed horizontally, the arrangement thereof radially with respect to an eccentric center providing for the aforementioned fiow eflects given to the air, as shown in Fig. 4, the column of air may be caused to move upwardly more closely bunched to the side of the cylinder by inclining inwardly and upwardly one or more air ports, indicated at lla. Also, the inclined ports are advantageous in a directive sense.

In Fig. 5, I show a preferable arrangement of cylinders IO and an air manifold or box 2!, which communicates with the scavenge ports H of each cylinder, the cylinders being so disposed that the eccentric unters ll fall on the longitudinal center line of the engine. Some throttling occurs in the regions 28 between adjacent cylinders; and, to avoid any injurious eifect because of lack of flow balance, as would be the case if'the cylinders were placed so that the relation of the port to the manifold was a random one, the cylinders are placed so that the eccentric centers ll fall on the longitudinal center line of the engine. whereby the flow from each side toward the eccentric centers issymmetrical and upward flow -of air in eachcylinder 'isbettercontrolledto minimizethesdmixtureofscavenl eairwith'li gasesf. The symmetrical flow of air into the cylinders on this account is further assisted by the provision of equal flow areas 24 at each side of each cylinder.

Fig. 6 shows an ,arrangement wherein the scavenge ports I'll) have their center lines tangent to a circle 26, the effect of this arrangement being to givea swirling motion to the air to aid in combustion.

' Fig. 5 may be employed, the eccentric centers being in the engine longitudinal center line and the cylinders being left sufliciently blank to either side of the center line, as shown in Fig. 7 at 21 and 28, to avoid any by-passing efiect of the wrist pin bore indicated in dotted lines at 29, the two sets of scavenge ports He, "c of each cylinder being directed toward a common center l8; and, as the centers it are, as in Fig. 5, in the plane of the longitudinal center line of the engine,- air will flow in symmetrically from each side toward the centers 18 and upward flow will be better controlled, as heretofore pointed out.

While the arrangements of scavenge air ports are effective to secure the operations pointed out, nevertheless, it may be desirable in some cases to prevent the possibility of short-circuiting of scavenging air directly from the scavenge ports to the exhaust-ports at the arcuate region of the cylinder nearest to the eccentric center l8. Accordingly, in Fig. 8, I show an alternative form of .my invention wherein the circumferentially-exest to the eccentric center l8 being omitted. The

scavenge ports are radially disposed with the eccentric center I8 as described in connection with Fig. 2.

From the foregoing, it will be apparent that I have provided an arrangement which gives effective and eflicie'nt scavenging with maximum eflective working stroke of the engine. As shown the scavenge air and exhaust ports are each arranged as a complete annular belt of closely spaced ports, whereby minimum cylinder length is required for their accommodation; and the complete belts or ports facilitate the maintenance of adequate strength in the cylinder and provide for a more symmetrical structure. The complete annular belt of exhaust ports provides for effective discharge at high velocity all the way around the cylinder as soon as such ports are uncovered by the piston, this annular discharge of pf'ifiducts of combustion induced by the pressure dfiip between the interior of the cylinder and the exhaust manifold continuing even after the scavenge air ports begin to open. a

The scavenge-air ports are arranged to promote eii'ective scavenging, they being directed radially toward an eccentric center so as to secure bunching of the air at the side of the cylinder adjacent to the eccentric center, the air moving upwardly as a column due to the resultant effect of its velocity energy, and the upwardly moving column is deflected by the cylinder head for movement downwardly in a bunched manner at the other side'to evict products of combustion through the exhaust ports. Thus, it will be seen that, by having the scavenge air ports directed toward an eccentric center, the kinetic energy of the enter- .ing air is not dissipated in a turbulent manner without effectively scavenging the cylinder, but

the preponderating effect of the velocii'jegergy toward the side of the cylinder at the eccentric center provides an upwardly moving current of air at the latter side. If desired, the directive tendency of the air may be aided by inclining upwardly or inwardly one or more of the scavenge air ports at the eccentric center side of the cylinder. It will also be seen that, by having the eccentric centers in the plane of the engine center line, symmetrical fiow of air into the cylinders and consequent better control of the upwardly moving air columns are provided for.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

What I claim is:

1. In a two-cycle engine, a cylinder, complete and superposed annular belts of exhaust and scavange ports extending through the cylinder wall and a piston uncovering the exhaust and scavenge ports=-successively at the. end of each working stroke, the scavenge ports being disposed EDWARD s. DENNISON.

Images