US1937541A - Compressor piston or the like - Google Patents

Description

Dec. 5, 1933. B. s, A|KMAN 1,937,541

COMPRESSOR PISTON OR THE LIKE Filed May 6, 1932 3 Sheets-Sheet 1 ,'59 7`\\\ 99A FQ WWW@ Dec. 5, 1933. B, s' A|KMAN i COMPRESSOR PISTON 0R THE LIKE Filed May 6, 1932 F Sheets-Sheet 2 Dec. 5, 1933. B. s. AIKMAN 1,937,541

COMPRESSOR PISTON OR THE LIKE Filed May 6, 1952 3 Sheets-Sheet 3 Patented Dec. 5, 1933 Y 1,937,541 A cowieassson risroN 'on Tini Linn Burton S. Aikman, Milwaukee, Wis., assigner to National Brake & Electric Company, Milwaulice, Wis., a corporation oi Wisconsin Application May 6, i932. Serial No. 609,652

19 Claims.

This application is a continuation in part of my co-pending application Serial No. 443,317, led April 1l, 1930, which V'relates to a method of and means for compressing gases and which disclosed, by way of illustration only, an air compressor capable of efcient operation at high speed without overheating. As more clearly pointed out rin my copending application but Vwhich is mentioned here for emphasis, a number of factors are'present in my compressor which contribute to this high eiicienoy, among them seing the intake, valve construction, which is simple, of exceeding rapidity of operation, providing a large inlet opening, with rapid opening and closing to the full` extent in a minute fraction of the cycle oi operation. Another feature is the unusually small clearance space and the extremely short passage between the valve and the interior of the cylinder. Another feature is the character of the lubricating system, no appreciable oil being passed by the piston and hence, fouling of the discharge valve being prevented, with consequent minimum leakage of the discharge checl; valve. Due to non-interference of the lubrication requirements with the valve action, the valves-that is, both the in-` take and the discharge valves-stay tight, and the aforesaid high eciency may be maintained over` Another feature is the novel tremely light weight reciprocating parts, togetherV with other features, for the specific details of which reference may he had to the disclosure in my copending application.'

The present invention is principally concerned with the construction and arrangement of the piston and associated parts, and has for its primary purpose the provision of a piston structure which is particularly adapted for high speed work and high volumetric emciency. To this end there are a number of specific features ci novelty in the structure to attention will be more fully called later, out some of which may be referred to herein generally, namely, the double use of the piston ring groove clearance', the

double use of the piston skirt clearance, the ther# mal separation of the two parts of the piston,

(ci. 23o-'221) to claim Ythe same broadly.

Now, in order tofacquaintthose skilled in the art with themanner of constructing and operat ing a device embodying my invention, ,IV shall meer f describe, in connection with the accompanying.4

drawings, a specic embodiment of thesame.-y

Vln the accompanying drawings, in which like reference numerals refer to like parts throughs"` out: 7

iFigure i is. a *vertical longitudinal sectiony through aconipressor of my invention;

Figure 2 is afvertical elevation 'ofmyimpr(fivedr piston structure embodying the lprinciiziles of the,

present invention and preferably` vutilized i'nftlie compressor illustrated in Figure 1;k l

Figure 3 is a longitudinal crossvsectional view through the pistonfshown in Figure 2 and-cor v responding to a section taken along vtheline 3%-,3 of Figurez; v

Figure 4 is a Vtop in Figure 2;V n y I I .c

Figure 5 is a section taken alongthe line5-5 of Figure 3; 1 Y

planiviewY of thefpiston Vshown Figure 6 isl a kfragmentary,sectional viewfillus'- trating the position ofthe ring valve with respect to vthe piston duringY the compression stroke thereof; I y

`Figure 7 is asimilar fragmentary sectional view showing the position-of the ring valvewon'v the suction stroke :of thep'iston; Y u, f

Figure 8 shows a modified form, of piston 4structure illustrating `another method of'A lubrication control and Vprovided with means :whereby excess oil is removed, partly mechanicallyfand partly4 pneumatically; from the wallsgof the cylinder;

Figure 9 is a vertical sectional view taken along:

the line 9-9 of'Figure 8; Y f g Figure lov is across section taken along thev line 10-10 of Figure 8; f Figures 1l to 15, inclusive, illustratevarious,v

modied forms of the intake Valve-structure Vand, I

different installations in which the features ofA Y. the present invention may be utilized.

Referring now more particularly to Figure 1, the main frame ci the machine comprises a crank caserandcylinder casting 1, the upper end of which comprises an integral cylinder section 2 and the lower part of kwhich comprises a crankcase section 3, integral with the cylinder 2 and havingat its base a suitable oil sump 4, formed in an enlargement of the lower end of the crank case.l The base 3 thus provides a relatively large volume of lubricating oil for operation of the compressor over extended periods of time.

The case 3 is provided on one or both sides with a suitable hand hole 12 covered by a plate or cover member 13, this plate or cover member being removable for inspection of the lower end of the connecting rod 14 and its bearing upon the crank pin 15 The crank shaft 16, which is adapted to be driven by any suitable means, is mounted as shown in bearings of the roller type 17 and 18, having their inner races mounted upon the ends of the crank shaft 16 and their outer racesv mounted in circular end plates 19 and 20, which end plates are bolted by meansv of suitable anges upon the ends of the crank casesectionr 3. The end plates 19 and 2G are suitably piloted into cylindrical bores in the end walls of the chamber 3 and are located angularly by means of dowel pins 22. Suitable packing,

vsuch as 24, is clamped between the plate and the crank casing to provide a tight joint. Cap screws such asl 25 extend through the flanges l of the end plates and are threaded into the metal ofthe case 3 surrounding the cylindrical bores'in the end walls.` rlihe crank shaft 16 is highv speed operation.

The connecting rod cap 32 is provided with afdippergor oil thrower 33 for causing oil to be carried upwardly to lubricate the crank-shaft bearing, the connecting Vrod bearing and ther piston with its guiding cylinder. The connecting rod `is' provided with lubricating passageways 34-34, to provide suitable lubrication for the connecting rod 14 and crank 15.

A`suitableliner Voi? bearing metal is provided onl thev connecting'rod crank bearing according to .known gas engine practice. The upperend 1 pin is preferably gripped by the piston, being Vheld therein by a Cotter pin orthe like, solthat Arelative"bearing motion between the pin 36 and the liner 35 occurs. Lubrication for this bearing i'sprovided by an oil-duct 37 extending through the upper end ofthe connecting rod and through the liner 35.

Piston construction The piston 38 is a compound structure or it maybe considered as consisting oi' two ,functionallydifferent parts. The lower part 39 of the piston 38 immediately adjacent the Wrist pin 36 'comprises a guiding memberin the nature of a crosshead.

While the piston structure 38 is in reality a The connecting rod 14 and the piston may' trunk piston, forming both a guide member and a working orr displacement member, the upper part or head portion Y40, which performs the actual service of acting as a moving wall for the working chamber 42 of the cylinder, has substantially no guiding function, whereas the lower portion 39 has substantially no displacement function. In fact, the portion 39 does not enter the working .chamber 42 of the cylinder 2. The headportion 40, which really becomes thel working piston or plunger, comprises a circular disc having the frustro-conical dome 43 adapted to enter the discharge passageway V44 oi the compressor for minimizing the volumetricclearance. The passageway 44 is formed centrally of the head 45 of the working cylinder 46. The bottom surface of the head 45 is carefully machined, as is the discharge passageway 44, and

the cylinder head 4G and its boss43 are like-` wise carefully machined, and the throw of the crank is such that the head 40 approaches the cylinder head 45 almost toi-actual contact in order to minimize the loss in volumetric eiciency which ani/'clearance at the end of the stroke entails.

As stated, the present invention is primarily concerned with the structure of the piston and associated parts. The working piston or head 401s joined to the guiding portion 39 through a vrigid crossed web connection 48, which supports the head 40 substantially out of contact with the Awalls of the cylinder 4G, the guiding action being secured mainlyby the'lower portion 39, and to some extent, if desired, by the oil wiper or oil distributor 47, which comprises a'circular disc or wall, cast integral with webs 48 and 49 joining the head portion 40 and with the lower portion 39.Y The disc 47 has, in one air cooled compressor which is of a capacity of 3.13 cubic feet per minute free air displacement at 160Q to to 1760 Pt. P. M. with two inch bore and one inch stroke, aclearance of approximatelyl inch in the cylinder. n Y

Bil f The lower surface of the disc 47 is dished in at the edges in order to provide alrelatively sharp circular edge 47a, tending to scrape inwardly and to. carry downwardly any excess of lubricantY .which may lodge upon the inner wall of the guid- The skirt or bottom to the disc 47 by the four webs 49 which'rnay be considered as continuations of the webs 48. The webs 49 are interrupted at the'center in order to provide clearance space aty 50 for the upperv end of the connecting rod 14. This structure is shown more clearly in the'section of Figure 3.

The head or working piston member 40 has a relatively thin central portion and at the margins the head is thicker in order to provide for the location of a piston ring groove 52. The groove 52 receives the piston ring 53, which may Vbe av 'standard concentric ring having a step joint or other suitable tight connection between the ends thereof, but which is preferably of the double stroke. The groove 52 is of a depth great enough to providea clearance back of the ring 53'as shown on an enlarged scale in Figures 6 and 7. This clearance is .indicated at 54 in Figures 6 and 7 and it serves the dual function of clearance for the ring 53 and also as an inlet passageway for the working chamber 42as clearly set forth in my copending application.r 1 j The upper and lower surfaces oi the groove 52 are flat, that is, these surfaces are planes lying at right angles to the axis lof the pistonlil, so that they are parallel'to each other. Likewise, the upper and lower surfaces of the ring 53 are parallel to each other and adapted to-t flat against the upper and lower end surfacescf the groove Y52 and to form airtight contacts therewith.

The anges 55 and 56 ,which denne the end permit the entry of air into the working chamber.

42 on the intake stroke of the compressor. That is to say, the space between the lower flange 56 and the cylinder wall 45 is a part of the intake passageway of the compressor.V This does noty need to be uniform all the way around. There might be shallow grooves across the end of the flange 56 instead of a uniform clearance.

A series of holes 57Vare drilled in the upper surface of the piston head 40 in the flange 55, so as to intersect and communicate withthe clearance 54 between the ring 53 and the groove 52. The ring 53 makes a tight t with the cylinder 46. This fit is a peripheral, or cylindrical fit. The ring 53 also makes a tight t withthe ange 56 during the compression stroke by press-- ing against the same in an axial direction and making a flat orplanar it therewith. The ring 53 hassufcient friction with the wallsof the cylinder 46 to cause it to tend to remain in any' position in which it is placed in the cylinder bore, said ring fitting inthe groove so freely that' the piston tends to move with respect to the ring upon each reversal of motion of the piston. The piston and ring thus have lost motion between them to the extent offlfteen .or twenty thousandths o1"- an inch in the particular embodiment hereinshown. This, obviously, maybe greater or less, as maybe desired.

As clearly disclosed in my copending application, the compression cylinder 46 is functionally disassociated from the guiding cylinder 2, although it is of the same diameter and structurally is rigidly connected to the same by virtue of the flange 6 2 of the working cylinder Liti-being connected with the ange 60 Vformed at the.V

upper end of vthe guiding `cylinder 2 by means such as the cap screws 64. Itis to be noted that the flange 60 is provided with athreaded opening leading into the intake chamber 66v formed between the flanges 60 and 62. The chamber 66 communicates with the atmosphere through the opening 65. The upper end of Athe working cylinder 46 is provided with a discharge check valve chamber 68 which communicates with vthe interior of the cylinder 46 through thel discharge passageway 44v mentioned above. The chamber 68 discharges through a cored passageway 69 and the communication between the `cyl- `oi the piston. Vcompressed air isadmitted back of the ring 53, it tends to expand outwardly'against thecylinder starts on its-downward travel.

inder V46 and the discharge chamber .68risv controlled by a spring pressed check valve 73 inthe` forrnof arelatively thin disc vof metal or other suitable material.l f `x Y Y.

The operation of the structure thus far described is as follows: When the shaft 16 sturned, the

crank and connecting rodjwill reciprocate' the ypiston structure 38 in well known manner.

shown in Figure 1, the piston-is at tliebottomv of its travel, the crank being in its'lowermost throw. It will loe-observed that vthe ring 53 en gages the top of the groove 52, that is, under the flange-55.

held by said friction of motion Vagainst the flange 55 during the downward stroke of the piston' The` ring 53,l having suflicient friction to drag along Athe cylinder walls, will be' until the latter reaches the position shownin he ring 53 stands still, temporarilybut the"A piston. rises, bringing thelower ilang'e 56 against the ring 53 andyas soon as said lost motionthat is, the minute space between the ring and the end wall of the groovehasbeen 'taken up,

the ring 53 is held against'the lowerl flange56 and is compelled to follow the upward motion of the piston, as shown in Figure 6. Thus the passage which was previously wide open is com-V pletely closed off in exceedingly small part of the angular cycreof the crank shaft.l

The ring 53, bearing againstthe lower ilangev 56 and simultaneously bearing against the iiiside of Vthe cylinder wall 46, -forms a iluid tight connection between the working piston40 and the cylinder 46. The ring is held against said bottom end wall ofthe groove by two forces, first, vthe irictional resistance ofthe ring sliding along the cylinder walls 46 and, second, by the 'down`` wardor outward pressure of the air compressed in the working chamber 42 by the-upward stroke 1n the present instance, since walls 46, as well as to be held downwardly against the flange 56, ,thereby securing anexcellerit'seal gas is Y discharged past the valve 73 into the` chamber 68 until the stroke is completed, where-v upon the check valve 73 closes. The pisto'n then upward stroke the position.r or" thering 53 with respect'to its groove was asV shown in Figure 6, as soon as the piston starts downward and moves a distance equal to the clearancebetween `the that the piston beginsto move downwardly,thef

ring 53 leaves its lowerseat, which`is,`in fact, thek intake valve seat, and cornrmmication is thereupon opened between the working chamber 42 and the intakecliamber 56, by a passageway of ample size tov permit the flow jof air into the working chamber 42 to occur'ireely. y

between the piston and cylinder wall. VSlo Afar Whereas, on the The spaceradially'between the flange 56 andV the cylinder wall 46, while small in radial di mansion, is relatively large in circumference andtherefore. permits of a relativelylarger total, in-.

' comprises the radial clearance 77 (Figure. 7)

YlO

ffl

Vcylinder head pleted. The tendency of the inertia of the ringl between the ange 56 of -the piston and the cylinder wall, the clearance 78 between the ring 53 in its'fupper position and the lower end wall of the groove 52, the clearance space 54 between thering 53 and the bottom of the groove 52 and the drilled openings 57. The yvalve controlling this passageway is the packing ring 53, anditl seats against the lower end wall of the groove 52 to close off said intake passageway.

When the compressor is operated at high speed the inertia oi the ring acts `to help the valve action, rather than to hinder it. Consider, for example, that the piston is moving inward on its compression stroke-that is, toward the and the stroke is being comis to throw it ahead with respect to the piston 40. So long as the pressure of the gas upon the ring exceeds the inertia of the ring, the ring will not tendto leave the valve seat. However, the tendency is there and operates in thek right direction. Likewise, Vwhen the piston moves 'downwardly to the bottom of its suction stroke,

the tendency is to throw the ring 53 downwardly against its seat, tending thereby to close the valve morek quickly, so that the initial motion of the piston 40 will not be lost. This inertia tendency of the ring is relatively inconsequential in the size I have illustrated but it may, under certain circumstances, be important and I am calling attention to thesame l. The clearance introduced by these minute intake passageways constitutes a very small fraction of the cylinder volume. The intake passageway, while it is of ample size, is exceedingly short. t is possible, of course, to further reduce .the length of the intake passageway slightly by @reducing the width of the ring 53, but the ring 3 should have'sufiicientbearing surface upon the inside of the cylinder wall, considering its diameter, to cause it to guide itself within the 4small limits of the clearance oi the groove and' the ring.

The dome 43 of the piston 40 substantially fills the discharge passageway 44, thereby reducing the clearance at that point. I may employ a peripheral discharge check valve under certain circumstances, but l rind the disu charge check valve herein shown to be satisfacn tory. The of air through the intake Ypas-- sageway keeps metal particles carbon the like from depositing in the groove and thereby 'maintams' the ring and the groove clear and in prime operating condition.

` I have described above the pneumatic function oi rthe packing ring, carried by the specially formed groove 52 in the piston 49, as a suitable intakevalve. The piston is also provided with suitable lubrication carriers or wipers which serve a useful function in connection with the lubrication of the compressor.

The guiding cylinder 2 and' the lower portion 39 of the piston are copiously lubricated by splash lubrication from the crank case. The piston structure 38 is so proportioned that the piston member or'head 40, which is the working piston for the working cylinder 42, travels solely with-A in said working chamber. Likewise, the guiding portion 39 of the piston structure operates solely within the guiding cylinder 2. The wiper, or lubrisant distributor-47, however, works in both cylinders, namely, the cylinder 2 and the cylinder 46. While its chief function is to prevent the :escape of lubricant from the crank case by forming a seal over the guiding structure i33, it/performs, also, the equally'irnportant functiony of transferring a minute quantity of lubricant from the guidingcylinder 2`to the working cylinder 46.

One of the greatest difculties in air compression is with lubrication. The ordinary trunk piston of an air compressor must'be lubricated sufficiently well to withstand the. mechanical thrust and wear to which it is subjected as a machine element, in-dependentof its pneumatic function. in the present'piston constructionl have separated the two functions, namely, the mechanical function and the pneumatic function, since'the upper or working piston 40 has little or no guiding function in thevcylinder 46 and the portion 39 has substantially no pneumatic function. It is, however, desirable to reduce the ring friction, that is, the friction between thering 53 and the walls ofthe cylinder 46, and on thataccount it is desirable to provide a small amount ci lubrication in the working cylinder.

About all the oil that is necessary in the working cylinder of Vthis compressor is the equivalent of one or two drops an hour for lubricating the ring 53. Anything more than that is unnecessary the ring does not become gummed with carbonized oil in case of excessive temperature. Likewise, the oil does not accumulate on the discharge check valve and carbonize and cause the valve to leak.

It also wainimizes any danger of any possible explosion dus vto oil in theinter-cooler in the caser of a compound compressor.V There are numerou other advantages in sparse lubrication.

As an aid to the maintenance of sparse lubrication in the working or-compressing cylinder the piston structure shown particularly in'Figures lv to E 'is provided with inclined walls or surfaces.

' The underside of the flange or wiper 47 is inclined or-ilared, see Figures l and 3, andthe same is true ofthe upper marginal portion of the guiding crosshead 39 disposed just underneath the ange 47, being the portion of Athe piston struc-Y ture adjacent wherethe arrow line 38 terminates inFigure l By virtueof this construction, in

the'upwardmovement ofthe' piston 3S any oil deposited on this member from the guiding or lower cylinder l2 will be moved toward the 'central portion ofthe piston-when thelatter reachesv its top dead center by virtue of the inertia of the oil,'and on the downward strolre any oil that may be deposited on the undersideof the ledge or flange 47 will be accordingly moved toward the center of the piston structure There is vthus av constant tendency to remove excess oil from the walls ofthe guiding cylinder and to direct the same toward the center of the piston structure from whence it returns tothe crank case. v

It is to be observedthat not only does the compressing functicnand the mechanical driving function occur in parts ofthe compressor cylinder structure which are thermally separated, but also the same principles are utilized in constructing the piston. Actually, the piston con 48 which vare freelyiin contact with the air inv the intake chamber 66.` Thehead 40 is lcomposed of a relatively thin wall, the bottom s ur- Qface of which is freely in-contact with vthe air A stratification and a consequent selective expuln sion of the highly heated air at the beginning of the stroke, followed by the expulsionof 'the cooler air which is introduced into the working 'chamber L12 at the last part of the intake stroke.

Thus, not only is the highly heated air drawn away frornthe compressing piston 40, the piston part subjected to the high temperature, but also the walls 48 act as radiating fins and serve to dissipate heat from the compressing piston head 4.0. Due to this thermal separation of the parts, both as regards the cylinder constructionand the piston constructionrvery satisfactory lubrication oi the mechanical operating parts can be maintained under conditions where the compressorsv of the prior art would fail.

I do not intend to limit the piston structure and the .associated inlet valve construction to that illustrated by way of example in Figures 6 and 7. In Figures 11 to 15, inclusive, I have shown dif'- ferent modified forms of piston head constructions to correspond to different forms of inlet valve rings. They do not exhaust by any means the variations which are possible withinl the principles taught herein.

In Figure 11 the ring 53 is provided' with an upwardly extending flange which is engaged by the upper nange 55 of the piston 40on the downward stroke, the main body of the ring 53 being held away from thedrilled passageways 57 during the intake stroke and the air entering by way of drilled passageways 82 under the ring 53, through the clearance between the bottom ofthe groove and the ring 53 and the space between the body of the ring 53 and the flange 55, and up through the'drilled passagewaysl. The drilled passageways 57 and 82'rnay be aligned, thatis, formed by a through drilling. The action is the same as described in connection with Figures 6 and. L l

In Figure 12 I have shown the ring53 as provided with a series of drilled passageways 84 which are obstructed by Vthe lower flange 56 on the compression stroke, but the upper flange 55 of `the piston is beveled, as at 55a, so that when the ring 53 is seatedagainst the upper ange, as .on the suction stroke, the passageways Vall are not obstructed. The inlet passageway in that case comprises the clearance between the flange 56Vand the cylinder wall 46, the drilled passageways Se and the clearance between the flange 55 and the cylinder wall e6. The operation is substantially the saine as that described in connection with Figures 6 and 7. f l

In Figure 13 the 'ring'53 is provided with a series of diagonal drilled passageways 85, the lower ends of which passageways are obstructed by the lower flange 56 and the upper ends of such passageways 85 being not obstructed by the upper flange 55. The operation of this construction is substantially as described above in connection with Figures 6 and '7. In this construction it will be noted that the form of pistonhead is substantially the saine as in Figure l2. l

In Figure 14 the piston 40 is of somewhat difform-of valve ring. InFigurell the piston iQ-isA provided with the 'usualring groove `52 to accommodate the mainY body ofthe valvev ring86 and, communicating with the groove 52, anV auxiliary ring 'groove 52a is provided. This auxiliary groove accommodatesa fiat annular -valvemember 37 carried' by the ring iland whichserves to close, on thev discharge stroke, the drilled pas'- sageways' 88 but which does not obstruct atlan'y time the drilled passageways '89 in the upper flange 55. Preferably, and as in Figure 11,the drilled'passageways are aligned. ThisV modification operates substantially the same as described in connection with Figures 6 and 7, it being noted, however, that the4 actual-valve function is perforined by the. nat annular valve meinber-87v moved by the ring 85, insteadof 'combining-.the

two functions of valve and ring inthe'samestrucl f ture. f Thering 86 has a relatively slight lost motion with respect to the valvetl.: n ...Y

In Figure 15 I have-illustratedla' modified con`-r structionin which'the upper flange v55 ofthe piston head 40 is considerably Vvreduced andlthe ring groove V52 made somewhat more narrow. The lower flange 56 is, however, substantially the same form as is. disclosed in Figures `12 andx13. In Figure 15 the ring 901s not whollyV contained within Athe groove 52 but has a flange 92`v which is slotted, or notched, soas to provide, in-effect.- a'series of projections from the ring 90 into ,the narrow groove 52 fo'rmedin the piston,40.- The lower flange'56 cooperatesf with the ringfQO to seal the inletpassageways, that .is,.'the space be: tween' the piston .40 and the'cylinder wall..46, upon the upward orcompression stroke. On the downward, or. suction stroke, the'.v projections 92 are caught by the upper flangel 55,and air: passes L15, underthey ring 90 through the spacesfbetween the projections V92, between the ring 90, andthe Aferent construction to accommodate a different adjacentfwall of the head 40,:and' intoathe-vcyl inder.

In View ofthe high speed ofY operation ofthe compressor herein shown it is desirable to lstream ing. parts. For example, it is desirable to-round offvall sharp corners over which thexair'flowsto currents and the-friction offflow reduce the eddy the air. l Liz. .1 Figure 16 illustrates the type of steppedqjoint,

.line all constricted passageways and rapidly 'movi- l the'valverings 53, 86 and 90k are preferablyprovided with.- In this figure the reference numeral 53 indicates the valveringinrits entirety and the abutting means thereof are f complementarily' -forme'd in an `identical manner. Each labutting end of the ring 53 is provided with a vertical Aporgtion 150 terminating inA a projecting` tongue :.151

disposed in a` plane arranged at right angles to the general plane of the portion 150.' Theportion of thering 53 laterally'oppositef the portion'150 is provided with a slot 152 of substantially theA the other end.v Thus, the ring"k joint is inthe nature of a double steppedconstruction in which f the end portions of thering overlap in abutting relation, both in a horizontal and vertical plane as well as in a perpendicular plane.t 'In`th'is'man-- ner lateral leakage at the ends of the piston `ring .l u

is effectivelyprevented. i

I have described above several Adifferent forms K 39 of the piston structure 38 is provided with an oil controlV ring 115, set in a'grocve 116, this groove being of a greater width than the width of the ring, t0 provide a clearance 11"! between the ring and the end walls ofthe groove. The Igroove communicates with a passageway 118A leading to theV central open space `V119 below the wall 120 of said, guiding'portionr 39 of the piston structure. The ring 115 may be a standard concentric piston ring having the usual step joint, but preferably is of the double stepped construction illustrated in Figure 16 like the ring 53 and it operates as a check valve, like the ring 53. Due to the splash of the oil thrower, or dipper 33, the walls of the guidingcylinder 2 are copiously lubricated. As the piston'rises from the position shown in Figure 9 to make the compression stroke, the natural tendency for the ring 115 is to lag, because of its frictional engagement with the walls ofthe guiding cylinder 2, behind the motionl of the piston.'V The result isv that the ring 115 engages the lower end wall of the groove, leaving the clearance 117 between the upper end wall of vthe groove and the ring 115. This provides, therefore, a passageway as follows, namely, from the space between'the vpiston headV 40 and the wall 120, through the clearance between the Wall 120 andv the.. cylinder walls'of the guiding cylinder 2, clearance 117 between the ring Vand the groove andthe radial clearance between the bottorn., of the groove rand therback of the ring 115,

passageway 118 to the open space 119, and there-` by to the crank chamber. Y

. 1 As the piston rises there -is thus a tendency to .45 vpreferably arrange to augment by a tight crank forma vacuumin the crank chamber and this I caseand cylinder. casting 1fas provided with a suitabler check valve indicated in its entirety by V`the reference numeral 122, but it is to be understood'thaty such a check valve construction need not be provided unless the piston structure indicated in Figures 8 and 9 is utilized in the compressor.

The operation of the structure so far described is substantially as follows: As the ring 115 moves upwardly in the guiding cylinder 2 itv tends to scrape lubricant onc the walls of the guiding cylindex Zand the same is then drawny through the aforementioned passageway into the crank chamber. The scraping from the walls is mechanical and the removal of the excess lubricant thus scraped is pneumatic. When the piston has reached the top of its stroke the ring 115 seizes the Walls with whatever friction it has, andas the piston descends the ring lags behind and engages the upper end wall of the groove 116, closing ofi communication be-V tween the bottom of the wall 120- and the top thereof. Any oil which is not scraped from` the walls by the ring 115 cannot be driven upwardly, as is the tendency in compressors as heretofore constructed, for two reasons. First, the ring 1.15 v

prevents discharge past the saine by such pneumatic pressure as is created in the crank chamber andsecond, I preferably make provision for releasing such pressure as might be generated in the crank chamber through the provision. ofv the automatic check valve 122 aforementioned, for

complete details or which reference may be made to my copending application mentioned above.

It is to be observed that atmospheric pressure prevails.r in the space between the head 40 land the intervening head 120, so that the formationv vwalls of the cylinder itself and toI a construction which ydoes not interpose atmospheric pressure between the guiding portion or the cylinder and the working, or pneumatic head of the piston.

Lubrication of the working cylinder 46in this case is effected' by a series of projections 123 on the webs 48 carried by the piston 33. These'projections Contact alternately with yboth cylinders and serve to carry across the gap between the cylinders suficient lubrication to keep the ring 53 inthe cylinder 46 sufficiently lubricated for satisfactory operation. As the piston descendsV there is a tendency to compress the'air in the crank case and to force the same out past the valve At that time the projections 123, which have a very slight clearance, possibly fifteen thousandths of an inch on one side, in the'bore oi the guiding cylinder 2, descend into the guiding cylinder Vand Contact with the oil on the walls of the cylinder. As the piston thereafter rises, the ring 115, engaging the lower end of its groove, opens apassageway for permitting air and the oil which is scraped from the walls or the guiding cylinder 2, to be drawn down into the crankcl1a.rnber as the piston rises. At the same time, `the projections 123 of the piston 40 transfer a lrn ofA oil to the walls of the compression cylinder 46, providing surcienti lubrication therefor.

While I have showny and describedabove certain novel details relative to the guiding piston and the thermally separatecornpressing piston, thevarious forms or piston heads arrangedto cooperate and accommodatethe various forms or" valve'rings, and the means Vcarried by the piston structure for securing the proper lubrication, it is to be understood that my invention `is not to be limited to the specicmeans shown and described, but that, in fact, widely different means may be employed `in' the practice of the broader aspects of my invention.

What I claim, therefore,l and desire to secure` by Letters Patent is:

1. A piston structure comprising aV cylindrical crosshead portion and a piston portion rof sub-` stantially the same diameter; said piston` and l crosshead being connected rigidly by integral webs, and an oil transfer member carriedby said connection.

2A piston structure comprising a cylindrical crosshead portion andra piston portion of sub- 'lli stantially the same diameter, said piston and crosshead being connected rigidly by integral webs, an oil transfer member carried by said connection, and means adapted to dissipate heat connecting the piston portion with said crosshead portion. v

4. A pistonv structure comprising a crosshead portion, a piston portion of substantially the Asame diameter as said crosshead portion, said piston vportion having aA groove therein and an intake passageway, and a piston ring controlling the opening and closing of said intake passageway.

5. A piston structure comprising a piston head having a pair of spaced flange members, and a piston ring member disposed between said flange members and movable to two positions therebetween, one of said members having yopenings formed therein and extending in a generally axial direction relative to the piston head, said openings being entirely closed olf by movement of the ring member to one of its positions.

6. A piston structure'comprising a piston head having a pair of spaced flange members, and a' piston ring member disposed between said flange members and movable to two positions therebetween, said ring member having openings formed therein and extending in a generally axial direction relative to the piston head, said open.

ings being entirely closed off by movement of the ring member to one of its positions.

7. A piston structure comprising a piston head having a pair of spaced iianges disposed in parallel relation, one of said flanges having bores therein extending in a generally axial direction, and a piston ring disposed between said anges andmovable to two positions therein, one entirely closing olf at least certain of said bores.

8. A piston structure comprising a piston head having a pair of spaced flanges, the lower of said flanges having bores therein extending in a generally axial direction, and a piston ring dis-l posed between said flanges and movable to two positions therein, one entirely closing on the bores in said lower flange.

9. A piston structure comprising a piston head having a pair of spaced flanges of unequal diameter, the upper flange being of larger diameter and having bores therethrough extending in a substantially axial direction relative to the piston head, and a piston ring, disposed between said flanges and movable to two positions therein, one against the lower ange of smaller diameter to close olf communication through said bores from the space above the pistonhead to the space below.

10. A piston structure comprising a crosshead portion, a piston portion including a headwall having a pair of spaced flanges, a piston ringtherein, webs joining the crosshead and piston portions, andY oil transferring means carried by from one cylinder surface to another.

12. A piston comprising a head having a relatively thin wall and a short cylindrical skirt, said skirt having a peripheral ring groove with planar radially extending walls, and a ring of less width than the groove disposed in said groove, the groove providing vclearance back of the ring-.communicating with the clearance between the'ring and the end walls of the groove and open communication being provided between the clearance back of the ring and the top of the piston.

13. Apiston structure comprising a head havy cal crosshead portion adapted to operate in one part of a vcylinder and a piston head portion adapted to voperate in another portion of thecylinder, integral webs connecting said piston!- so'y head portion with said crosshead portion, and a f flange supported between said portions and provided with an edge adapted to wipe oil from the portion of the cylinder engaged by said head portion.

15. A piston structure comprising a cylindri- -cal crossheadportion and a piston head portion, '1

said piston head portion having a relatively .thin

wall anda short cylindrical skirt with a periphn eral ring groove therein, a ring valve disposed in said groove, integral webs 'joining .said Vpiston head portion with said crosshead portion, oil 1; transfer means carried by said webs, and an oilscraping ring carried by said crosshead portion.v

16. A piston structure comprising a cylindrical crosshead portion and a piston head portion joined together by integral webs arranged tov prevent the excessive transfer ofk heat from the piston head portion to the crosshead portion, there being a transverse bore in said crosshead portion, anda wrist-pin disposed therein, said webs being 4vinterrupted adjacent said wrist-pin to accozmnodate a cooperating connecting rod.

1'7. A piston structure comprising aicylindri- .K

cal crosshead portion anda piston head portion,`

means comprising integral heat dissipating webs joining said crosshead portion "and said piston head'portion, there being a groove formed in each of said portions, and a ring/valve disposedV in each of said grooves. Y

18. A piston structure adapted for operation within the walls of a cylinder, said piston structure comprising a lower skirt portion terminating in `a head portion having a peripherally flared surface'inclined laway from the cylinder walls anda connected ange spaced therefrom andY provided with an undersurface also flared and inclined away fromthe walls of the cylinder.

L 19. A piston structure comprising a cylindrical v crosshead portionhaving at its upperend flared walls inclined toward the axial center of the piston and away from the walls of the cylinder,

and a separated anged portion carried on `the crosshead portion by integral webs, said flanged portion being also provided Vwith a flared surface inclined toward the center ofthe piston and away fromthe walls ofthe cylinder, whereby any oil deposited on said 'flared wallsl will by theirv j inertia be directed toward the center of theA pistony when the latter changes its direction of y movement.V

BURTQN S.AIKMAN.

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