US2796216A - Piston-type machine - Google Patents

Description

June 18, 1957 Filed" Aug 4, 1953 1 FIG. I, 2 T5 T G. E. MALLINCKRODT PISTON-TYPE MACHINE 3 Sheets-She" 6t 1 June 18, 1 57 e. E. MALLINCKRO DT PISTON-TYPE MACHINE I5 Sheets-Sheet 2 Filed Aug. 4, 1953 G. EJMALLINCKRODT June 18, 1957 PISTON-TYPE MACHINE 3 Sheets-Sheet 3 Filed Aug. 4, 1953 PISTON -TYPE MACHINE George E. Mallinckrodt, St. Louis, Mo. Application August 4, 1953, Serial No. 372,222

34 Claims. (Cl. 230-144) This invention relates to piston-type machines, including machines such as engines and pumps capable of operation by or upon gaseous or vapor mediums, and preferably employing several rotors having alternating pistons interdigitated and operative in an annular or toroidal cylinder and having torsional spring connections with a power shaft. The invention is an improvement upon the construction disclosed in my copending United States patent application Serial No. 273,392, filed February 26, 1952, now Patent 2,736,328, for Rotary Machine.

Among the several objects of the invention may be noted the provision of means for improving the pistons and associated parts of apparatus of the class described so as to minimize leak-age past the pistons; the provision of means for improving piston and piston ring geometry, structure and sealing effects thereof; and the provision of improved means for coupling the rotors with the drive shaft. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of which will be indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

Fig. l is an ideal axial section illustrating various features of the invention;

Fig. 2 is an ideal cross section taken on line 2-2 of Fig. 1;

Fig. 3 is a cross section taken on line 3-3 of Fig. 1, partly in elevation;

Fig. 4 is a separated view showing certain piston ring elements;

Fig. 5 is an enlarged end view of a pair of cooperating wing pistons, the view being taken on line 5-5 of Fig. l but showing certain pistons in an approach position; and,

Fig. 6 is an enlarged detail cross section of a piston, being taken on line 6-6 of Fig. 5.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Briefly, a preferable (though not the only) form of machine embodying the invention is constituted by two rotors, a drive shaft and a surrounding annular or toroidal cylinder. Each rotor carries several cantilever type pistons within the cylinder, in the present example there being four pistons on each rotor which interdigitate. Each rotor has a spring power connection to the shaft. The stationary frame, of which the cylinder forms a part, carries cam tracks. Each rotor carries four swinging follower arms which are spring biased outward toward the respective cam track. (The ends of the arms have suitable follower rollers riding the track. Relationship between the track shape and follower arms is such that in certain positions of the rotor the followers assume positions preventing reverse movement of the respective rotor. If the machine constitutes an engine, each rotor "nits States Patent O in response to certain intake, compression, expansion and exhaust events is caused to rotate, the rotors alternating in delivering power through torsion springs to the shaft. The cam track and followers constitute reverselocking means to permit each rotor alternately to assume the reverse-locking position with respect to the frame, the latter functioning as a reaction member for driving the other rotor upon expansion of gas between interdigitated pistons. Further details of the above-mentioned parts and their operation may be found in said application Serial No. 273,392. Hereinafter only such details regarding them will be set forth as are required to understand the points of departure constituted by the present invention.

Referring now more particularly to the drawings, there is shown in general at numeral 1 a stationary assembly or casing consisting of a ring 3 to which are attached checks 5 forming an annular or toroidal cylinder 7. Extensions 6 from the checks 5 carry housing 8 for cam tracks 9 and 11. Head assemblies 13 form parts of the housing and support bearings 15 for relatively movable rotors -F and S. The rotors in part form inside closures 18 and 19 for the cylinder 7. Rotor F carries wingtype pistons A, -B, C, D (Fig. 2), and rotor S carries interdigitated wing-type pistons W, X, Y, Z. The forms of the pistons A, .B, C, D, and how these pistons lap the adjacent rotor parts 18 and 20, will be clear from Figs. 1, 2, S and 6. Pistons W, X, Y, Z overlap the adjacent end of rotor F in the same way but in the opposite axial direction. The adjacent closure ends 18 and 19 of the rotors F and S are sealed by a ring -10.

A power shaft P is supported upon bearings 17 within the rotors F and S, and includes extensions 19 which pass out of the casing 1 through quills 21 and 23 of the rotors. A torsion spring 25 connects quill 21 and one shaft extension 19, to form a driving connection between the rotor -F and the shaft P. A torsion spring 27 also connects quill 23 to form a driving connection between the rotor S and the shaft P. The springs 25 and 27 are torsionally unstressed when thepistons assume the positions shown in Fig. 2, although they are under axial compression.

Keyed to the quills of the rotors are hubs 12 carrying radial arms 14. The arms in turn have clamps 42 fastening them to pivot pins 31 which are pivoted on needle bearings 40 for pivoting clamped follower arms 33. On the ends of arms 33 are rollers 34 engaging the cam track 9 under action of bail-type springs 37. The springs may be variably tensioned by adjusting the angular positions of the pins 31 in the clamps 42. In Fig. 3 the dotted skeleton lines indicate the reverse-locking positions of the arms and rollers relative to one cam track. At I-1 and I-2 on Fig. 2 are shown fuel inlet ports, and at E-l and E2 exhaust ports. Numeral 41 indicates recessed ignition plugs of the glow type for high-speed operation, plugs 43 being for low-speed operation and plugs 45 for starting the device with the priming of fuel. Further details will be unnecessary, but if desired may be found in said application Serial No. 273,392. 1

it will here suflice to state that in Fig. 2 the rotors and their pistons move clockwise. An expansion event may be assumed to be occurring between pistons D and Z; also between B and X. Reaction occurs against pistons D and B, the rotor F being at this time reverse locked by action of its follower rollers 34 on the cam track 9. Exhaust events are occurring between pistons X and C; also between A and Z (see ports 13-2 and E-l). Suction events draw fuel in at ports I-1 and I-2 between pistons A and W, and between pistons C and Y, respec-v tively. A compression event is occurring between pistons Y and D; also between pistons W and B. Under these conditions the unit pressure of expansion is greater than the unit pressure of compression. As stated, the arms 33 of the rollers 34 of rotor F are reverse locked. After a cycle of event is completed, the angular positions of rotors S and F become interchanged. The cycle then starts over, with the other rotor receiving the thrust. Each rotor, while receiving thrust, delivers energy to the shaft P by winding of its respective spring 25 or 27, as the case may be.

A first'feature of the present invention will now be described. Each of the pistons A-D and WZ has radial front and back faces 47 (Figs. 2 and The parts of these faces that overhang the adjacent rotor for interdigitation are angled inward from the radial direction by bevels, as shown at 49. The remaining parts of these faces are formed as fillets 51 in the regions of attachment of the pistons to their respective rotors. As one piston approaches another, the fillets 51 may interdigitate with the spaces left by the bevels 49. This construction provides the fillets 51 for buttressing the pistons where they are joinedto their respective rotors, while at the same time allowing opposite faces of adjacent pistons to approach one another closely during the compression event. It will of course be obvious that other shapes may be used at 49 and 51, provided the space left by whatever shape is given to 49 will accommodate the fillet 51. Preferably the spaces and fillets should be complementary inshape, i. e., the same in shape but one hollow and the other solid. The fillets form strengthening buttresses.

A second feature of the invention is that each piston is axially'double-gashed from one end to the other and from its outside to its point of inside attachment to its rotor. The two slots or gashes are indicated at 53 and 55, separating three wings 22, 24 and 26 (see Fig. 5). Each piston is also provided with transverse openings 57 through its wings for accommodating a draw bolt 59, the head and the nut of which are contained in endwise counterbores-61 in the piston faces 47. Around each bolt 59 and in each respective gash is a washer 63, preferably composed of a material which galls relative to the material .of which the piston is formed. Thus, for example, if the piston is formed of SAE 1020 steel, a suitable galling'material for each washer might be preferably SAE 316 steel. Other suitable steels for the washers might be SAE- 302, 304. The purpose of the stated galling characteristic is that when the three relatively thin wing parts of the piston formed by the gashes 53 and 55 are drawing together against the galling washers 63, there Will be no tendency for these three parts under pressure loading (caused by power thrust) to have any substantial shearing movement relative to one another. It will be noted in this connection that the pistons function as cantilevers in supporting their loads, and the stated shearing movement tends to occur. By preventing such movements piston rigidity is obtained, despite the gashes through them.

A third feature of the invention consists in the piston rings employed in the gashes. In each gash 53 and 55 are employed four ring parts such as shown separated into pairs in Fig. 4. There are shown two layers of ring elements side by side in said Fig. 4, but it is to be understood that each layer is stacked on the other when the ring parts are in assembled position in a piston gash. Each ring in each gash therefore constitutes four L-shaped parts whichare identical and arranged relatively as shown in Figs. 1 and 4. Each part is preferably identical to the others and constitutes a thin, flat L-shaped member 65 73 and the adjacent leg 67.

the left, and those for the other layer in the same gash are shown at the right. The right and left layers of Fig. 4 are superimposed before insertion into a respective gash. Assembly is accomplished before the washers 63 and bolts 59 are inserted. At the time that the ring parts are inserted into their respective gashes, there is inserted a nest of concentric circular spring steel rings 81. These are of such a size that upon assembly they are deformed from their circular shape to exert radial pressure on the L-shaped ring parts 65, which forces these parts into radial engagement with the cylinder wall. At the same time there is a springing engagement between each tongue The forms and arrangements described favor compensation of ring and cylinder shapes for small inaccuracies of machining. Thus under inside pressure from rings 81, and certain oil pressure within the rings (to be described below) the ring elementsmove radially outward resiliently and sealingly 1-1 and n2 (Fig. 2

to fit the cylinder walls while resiliently maintaining sealing contact with one another at the tongues 73.

A fourth feature of the invention solves a problem arising from conditions occurring in certain engines, particularly of the alternating-piston type. These conditions are that during a certain part of the cycle one side of a piston will be under compression (superatmospheric pressure) and the other side under a partial vacuum (subatmospheric pressure). This condition magnifies leakage of gas and oil from the compression side to the partial vacuum side of the piston, more so than if the latter side of the piston were under atmospheric pressure. To minimize the leakage due to this pressure drop and to provide for optimum conditions of piston and ring lubrication, the following arrangement is employed:

A passage 83 is drilled from an interior part of each leading gash 53 to the interior of its respective rotor. This is not done in the case of the trailing gashes 55. The adjectives leading and trailing refer to the relationships of the gashes relative to the piston movements, which are clockwise (Fig. 2). in each piston a second opening 85 is drilled in the central wing 24 of the piston between the gashes. The outer end 28 of each opening 85 in one rotor communicates with a slight clearance between the respective central piston parts 24 and the outer cylinder wall.

The inner ends 30 of openings 85 on a given rotor communicate with a circular groove 89 cut in part 5',

which is not swept by the pistons and is adjacent thev respective rotor. Each groove 89, through a suitable drill hole '91, is in communication with a pipe 93 that may lead simply to atmosphere or a suitable sump (not shown) which is under atmospheric pressure. Each groove 89 is interrupted as indicated at two regions 90 on a diameter passing through the centers of intake ports A second drill hole 95 is in communication with a lubricant pressure line 97. Pressure may be maintained in this line by a suitable lubricant pump (not shown) which may receive as all or part of its supply lubricant from the sump (not shown) with which line 93 communicates. The hole 95 communicates with a circular groove 99 in rotor F. In the rotor F this groove is in communication through a port 101 with the space between rotors. By this means pressure is supplied to the confined space between the rotors. Confinement is due to the sealing ring 10 and end seals 103 having legs 67 and 69. The end of each leg 69 is slotted I at a small angle (3, for example) as indicated at 71, leaving a flexible tongue 73 for engagement with the inside end of the unslotted adjacent leg 67 when it is assembled as in Fig. 4. Each member is provided with an opening 75 at its corner, which includes a throat 77 extending to the inside of the L-shape, thus leaving a springy area 79. In Fig. 4 the two ring members for one layer of these in a gash such as 53 are shown at and 105. The resulting pressure internal to the rotors tends axially to separate them, this tendency being rcsisted by the initial compression in the springs 2'7. Thus rotor end-thrusts are substantially balanced.

The pressure between the rotors is utilized to supply lubricant to the piston and cylinder walls. This is done by providing on the inside of each rotor a ring 1'97. Each ring is attached to its respective rotor and incorporates four ports 109, each communicating with one of the passages 83. A spring-pressed check valve 111 is usedin each port, its spring being backed by an adjustable threaded backstop nipple 113, so as to control the pressure which the valve will release for outward flow of lubricant to its respective passage 83. Lubricant is thus supplied to the leading ring sealing means in each piston. The above-described porting system then operates as follows during engine operation:

Lubricant pressure supplied over line 7 reaches the inside of the rotors, and as long as there is a suitable pressure drop across the valves 111, will find its way through passages 83 to the space within and surrounded by the group of piston ring elements in the leading gashes 53. This pressure internal to the ring elements, in addition to the internal pressure from the circular springs 81, tends to force outward the ring elements. The fit of the ring members 65 in the gashes 53 and 55, the sealing actions of tongues 73, and the springiness of the ring elements are designed to inhibit leakage into the cylinder; but some leakage will gradually occur as lubricant is used. As this leakage progresses, the pressure drop across valves 111 will gradually increase until they open to supply an additional amount of lubricant needed, after which the pressure drop will decrease and the valves 111 reclose. Considering a single piston, gas leakage that tends to occur from the front past the rings in the leading gash 53 will also enter the clearance between gashes outside of the central wing part 24. Thus leakage of both gas and oil in connection with each piston is dissipated through its passage 85, grooves 89, passage 91, line 93 and to the atmosphere or sump. Therefore, leakage will not pass to the rear of each piston across the rings in the trailing gash 55, because of the free outlet to the atmosphere or sump from the clearance between the sets of rings in the gashes 55 and 53. The purpose of the interruptions 90 in grooves 89 is to prevent leakage of oil under pressure Within the ring-s of the leading gash directly past these rings to the inlets I-1 and 14, as the respective pistons cross these inlets.

A fifth feature of the invention has already been alluded to with regard to the torsion springs 25 and 2.7. As stated, they have two functions, namely, to transmit torque from the respective rotors to the shaft P, and axially to counterbalance pressure within the rotors F and S. To this end they require effective anchoring means of a type to reduce the likelihood of spring breakage. The anchoring means for each is the same and the description of one will suffice, the reference numerals used being the same in connection with each spring. The anchoring means to each rotor is constituted by a nose ring 115 bolted to the rotor end, over which is slipped the inner end of the spring. Attached to the nose ring is a taperthreaded split ring 117 on which is threaded a nut 119. By threading down the nut 119 on the taper-threaded ring 117, the inner end of the spring is tightly frictionaliy anchored without introducing any undue local stresses at any one point of the spring coiling. At the other end of the spring is a second nose ring 121 which is held by set screws 123 to knurling 125 on the shaft extension 1%. Attached to the nose ring 121 is a second split taperthreaded nose ring 127, upon which is threaded a nut 129. When the nut 129 is threaded on the nose ring 127, the outer end of the spring 25 (or 27, as the case maybe) is frictionally anchored without introduction of undue local stresses.

The various features of the invention have been described in application to the alternating-piston engine described, but it is to be understood that such application is not limiting and that there may be analogous machines to which they are applicable.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative, andnot in a limiting sense.

I claim:

1. In apparatus of the class described, a stationary casing comprising a cylinder, a movable power member movably cooperating with said stationary casing and carrying a piston movable in the cylinder, spaced annular sealing means on the piston, a channel in the piston communicating through a wall of the piston and with the space between the annular sealing means, said wall and said cylinder, said casing having a relief port therethrough communicating with said channel and so'formed relative to it that they remain in communication during movement of the piston.

2. in apparatus of the class described, a stationary member, a cylinder connected thereto, said cylinder being open on one side where it is closed by a movable closure member having an outlet opening, a piston attached to the closure member and extending into the cylinder for movement therein, spaced sealing means operative between the piston and cylinder, said piston having a channel connecting that part of the space between the surface of the piston and cylinder which is between said spaced sealing means, said piston channel leading to said outlet opening in said closure member, said stationary member having a relief passage therethrough so formed relative to said outlet opening in the closure member that the passage and the channel remain in communication during movement of the closure member.

3. In apparatus of the class described, a stationary member,'a cylinder connected thereto, said cylinder being open on one side where it is closed by a movable closure member, a piston attached to the closure member and extending into the cylinder for movement therein, expansible annular ring sealing means operative between the piston and cylinder, said piston having a passage extending from within the expansiblc sealing ring through said closure member, said stationary member having a pressure inlet adapted to maintain a connection with said passage during movement of the closure member.

4. Apparatus made according to claim 2, wherein the cylinder is of annular form and said closure member is rotary, whereby the piston has rotary movement in the cylinder.

5. Apparatus made according to claim 2, wherein each of said spaced sealing means is of hollow expansible ring form surrounding the piston and including another inlet passage through said closure means and connecting with the hollow portion within at least one of said ring sealing means.

6. Apparatus made according to claim 2, wherein each of said spaced sealing means is of hollow expansible ring for-m surrounding the piston and including a second passage having an inlet in said closure and an outlet in the hollow portion within at least one of said ring sealing means, said stationary member having also a lubricant pressure inlet adapted to maintain a connection with said second passage during movement of said closure member. 7. A rotary alternating-piston machine comprising an annular cylinder open on its inside, a pair of rotors closing said inside, at least one piston on each rotor and operative with relative movements in the cylinder, spaced sets of peripheral sealing means on each piston, each piston having a relief passage extending from an inlet point on the surface of the piston between said spaced sealing means to an outlet point, and means operative during rotor movement providing a connection to atmosphere from said outlet point.

8. Apparatus made according to claim 7, wherein said stationary member has at least one pressure inlet, said rotors having pressure passages connecting with said pressure inlet during rotor movement and communicating with points within certain of the piston sealing means that are foremost during piston movement.

'9. Apparatus made according to claim 8, including check valves in the last-named pressure passages adapted to open for flow fromflthe rotor to the piston.

10. In a rotary alternating piston machine, an annular cylinder, rotors abutting within the plane of the cylinder, at least one piston on each rotor operative in the cylinder, eachpiston being attached to one rotor and axially overlapping the other rotor so as to interdigitate in the cylinder, each piston having a front and a rear wall, fillet means forming buttresses from the front and rear walls of each piston and extending to its respective rotor, the front and rear Walls of each piston being shaped in the. region of rotor overlap to accommodate the fillet means on the adjacent piston.

11. Apparatus made according to claim 10, wherein the forms of said fillets and of said accommodating shapes are complementary.

12. A ring sealing element for rectangular pistons comprising an L-shaped member having an opening within its corner portion including an extension of the opening to an inside angle of the L.

13.A ring sealing element made according to claim 12, wherein said opening is circular and the extension is constituted by a slot.

14. A ring sealing element for rectangular pistons comprising an L-shaped member, the end of at least one leg of which is laterally relieved on its inside a sufficiently short distance from its end to provide an endwise springy tongue.

15. A ring sealing element for rectangular pistons comprising an L-shaped member, the end of at least one leg of which is laterally slotted on its inside a sufliciently short distance from its end to provide an endwise springy tongue.

16. A ring sealing element for rectangular pistons comprising an L-shaped member, the end of at least one leg of which has a lateral slot on its inside a sufiiciently short distance from its end to provide an endwise springy tongue, said slot being angled relative to the leg end.

17. A ring sealing element made according to claim 12, wherein the end of at least one leg of the L-shaped member is laterally slotted a sufiiciently short distance from the inside of its end to provide a springy tongue.

18. Ring sealing means for rectangular pistons comprising a group of two sealing elements arranged together to form a rectangle in a plane and each comprising an L-shaped member having an opening within its corner portion communicating with an inside angle of the L, the end of one leg of each L-sh'aped element abutting the inside of a leg of the other.

19. Ring sealing means for rectangular pistons comprising a group of two sealing elements arranged together to form a rectangle in a plane, each element comprising :an L-shaped member having an opening within its corner end of at least one leg of an element being slotted a sufficiently short distance from its end to provide a springy tongue, the springy-tongue-end of each element abutting the inside of an unslotted leg of the adjacent element.

20. Ring sealing means made according to claim 19,

wherein groups as described are layered so that the corner portions of each element lie over the abutting leg portions of adjacent elements.

21. An alternating-piston engine comprising an annular cylinder, a pair of rotors, pistons on the rotors interdigitating in said cylinder and having relative movements therein, a power shaft surrounded by said rotors and extending therefrom, a torsional spring coupling each rotor with the power shaft, said rotors being hollow and sealed with respect to the shaft and being sealed axially relative to one another to form an enclosure, means for introducing a pressure medium within said enclosure tending axially to separate said rotors, said springs being installed with sufiicient compression effective between the shaft and their respective rotors to offset a substantial amount of pressure tending to separate said rotors.

22. In apparatus of the class described, a toroidal cylinder, said cylinder having an opening on the inside which is closed by relatively movable closure members constituting rotors, each rotor having pistons in the cylinder ii I) interdigitating with the pistons of the other, pressure-* responsive expansible means on the pistons sealing them with respect to the cylinder, a power shaft, drive meansconnecting each rotor with the shaft adapted to afford relative rotary movements between the rotors as they drive, said rotors being hollow to form pressure compartments, and means for introducing oil under pressure into the compartments, said rotors having passages leading from said compartments to said expansible means on said pistons.

23. Apparatus made according to claim 22, wherein said passages in the rotors include check valves adapted to open in response to such a predetermined reduction in pressure upon the expansible means as may be caused by leakage.

24. Apparatus made according to claim 22, wherein each rotor has additional pressure relief passages which respectively extend to the surfaces on the respective'pistons of the rotor which are adjacent said expansible means.

25. Apparatus made according to claim 22, wherein said toroidal cylinder includes a relief passage, and wherein said pistons include passages leading to said relief passages from parts of their faces facing the cylinder and adapted to carry off oil and gas leakage.

26. In apparatus of the class described, a toroidal cylinder, said cylinder havingan opening on the inside where where it is closed by relatively movable closure members constituting rotors having a sealing abutment, each rotor having pistons in the cylinder interdigitating with the pistons of the other, pressure-responsive expansible means on the pistons sealing them with respect to the cylinder, a power shaft, drive means connecting each rotor with the shaft adapted to afford relative rotary movement between the rotors, sealing means between the rotors and the shaft, whereby a chamber is formed within the rotors, means for introducing liquid under pressure into said chamber, said rotors having liquid passages leading from said chamber to said expansible means on said pistons and adapted under pressure to actuate s'aid expansible means.

27. In apparatus of the class described, a toroidal cylinder, said cylinder having an opening on the inside where it is closed by abutting relatively movable closure members constituting rotors having an axial sealing abutment, each rotor having pistons in the cylinder interdigitating with the pistons of the other, pressure-responsive expan sible means on the pistons sealing them with respect to the cylinder, a power shaft, an axially compressed spring connecting each rotor with the shaft adapted to afford portion communicating with an inside angle of the L the 5; relative rotary movements between the rotors and tending axially to abut them, sealing means between the rotors and the shaft, whereby a pressure compartment is formed between them, means for introducing oil under pressure in said compartment, said rotors having passages leading from said compartments to said expansiblc means on said pistons, the pressure in said compartment tending to force the oil to said passages and to counterbalance the abutting forces of said springs.

28. Apparatus made according to claim 27, wherein said passages in the rotors include check valves controlling flow therethrough.

29. In apparatus of the class described, a stationary frame comprising an annular cylinder, said cylinder having'an opening on the inside where it is closed by abutting relatively movable closure members constituting hollow rotors, each rotor having pistons in the cylinder interdigitating with the pistons of the other, peripherally spaced leading and trailing expansible means on each piston sealing it relative to the cylinder, a power shaft, drive means connecting each rotor with the shaft adapted to afford relative movements between the rotors, sealing means between the rotors and the shaft, whereby a pressure compartment is formed within them, means adapted to introduce oil under pressure in said compartment, said means comprising a pressure port in at least one rotor and a pres sure port in the frame with groove means in one of them maintaining connections therebetween during rotor movement, said rotors having passages leading from said compartment to the leading expansible means on the pistons, a relief passage in each piston leading from a point on its surface between said leading and trailing expansible means and having an outlet in the respective rotor, relief ports in the frame, and groove means connecting each relief passage with a relief port and adapted to maintain a relief connection during rotor movement.

30. Apparatus made according to claim 29, wherein said drive means are compression springs between the shaft and respective rotors adapted to compensate against any tendency of said rotors at the abutment to separate due to internal pressure in said pressure compartment.

31. In apparatus of the class described, a hollow circular rotor, a wing piston extending exteriorly therefrom, said piston having peripherally spaced radial and axially extending slots, radially expansive pressure-responsive sealing means in the respective slots, and a port extending from within the hollow rotor into communication with the leading slot and within the expansible means therein.

32. Apparatus made according to claim 26, wherein the piston has an additional relief port extending from a point on its surface between said slots to an outlet from the rotor, said outlet being out of communication with the hollow portion of the rotor.

33. In apparatus of the class described, a rotor, an integral rigid cantilever piston extending exteriorly therefrom, said piston having an axially extending slot separating the piston into spaced parts, said spaced parts having coaxial openings therethrough communicating with said slot, a flat washer in the slot coaxial with said openings, said washer having opposite highly frictional surfaces engaging said spaced parts around said openings, and tensioned means extending through said openings and forcing said spaced parts against opposite faces of said washer, whereby the rigidity of the piston as a cantilever element is maximized, said slot being adapted for the reception of radially movable sealing means surrounding the washer.

34. In apparatus of the class described, a rotor, an integral rigid cantilever piston extending exteriorly therefrom, said piston flaring outward but being attached to the rotor by means of inwardly flaring buttresses, a portion of said piston extending axially from said buttresses so as to overhang the end of the rotor, said piston having spaced axially extending slots separating the piston into three spaced axial cantilever elements, said spaced elements having coaxial openings therethrough communicating with said slots, a fiat Washer in each slot coaxial with said openings, said washers having opposite highly frictional surfaces engaging said spaced elements around said openings, and tensioned means extending through said openings and forcing said spaced elements against opposite faces of said washers, whereby rigidity of the piston as an overhanging cantilever element is provided, said slots being adapted for the reception of radially slidable sealing means surrounding the washers.

References Cited in the file of this patent UNITED STATES PATENTS 367,873 Walters Aug. 9, 1887 386,011 Holmgren July 10, 1888 1,737,355 Bogue Nov. 26, 1929 2,547,374 Carideo Apr. 3, 1951 2,570,832 Mercier et a1. Oct. 9, 1951 2,579,698 Phillips Dec. 25, 1951 2,613,121 Oishei et a1. Oct. 7, 1952 FOREIGN PATENTS 11,411 Great Britain 1906

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