Patent Publication Number: US-6212994-B1

Title: Positive displacement rotary machine

Description:
FIELD OF INVENTION 
     This invention relates to a new and improved positive displacement rotary machine, and more particularly to such a machine which operates at uniform angular velocity, is inherently statically and dynamically balanced and is adaptable as, e.g., a pump, fluid motor, engine, compressor, expandor, vacuum pump. 
     BACKGROUND OF INVENTION 
     Conventional positive displacement rotary machines such as piston, gear, and vane type suffer from high impact forces due to engagement of the parts and unbalanced vane and piston inertia forces. This results in excessive noise and wear. Gear and vane devices also have inherently high leakage flow because of the line contact sealing. Although radial and axial piston types have surface contact sealing, much lower leakage flow, and no impact forces, their unbalanced inertia forces tend to make them noisy and produce vibrations particularly at high speeds. In addition, piston machines have higher weight to power ratio than rotary gear and vane devices. 
     SUMMARY OF INVENTION 
     It is therefore an object of this invention to provide a new improved positive displacement rotary machine. 
     It is a further object of this invention to provide such a machine which is operable in a variety of applications, e.g., fluid motor, fluid pump, compressor, expandor, vacuum pump, and engine. 
     It is a further object of this invention to provide such a machine in which all moving parts including pistons rotate at uniform angular velocity. 
     It is a further object of this invention to provide such a machine which is inherently statically and dynamically balanced. 
     It is a further object of this invention to provide such a machine which is capable of efficient high speed and high pressure fluid power operation. 
     It is a further object of this invention to provide such a machine in which pistons rotate uniformly without impact, with continuous sinusoidal sliding surface contact, complete mechanical balance and with very quiet operation. 
     It is a further object of this invention to provide such a machine in which rotary pistons are coupled with only two uniformly rotating mechanical elements resulting in simple linear design, and low cost piston machine that can be manufactured with common and conventional techniques. 
     It is a further object of this invention to provide such a machine which is very compact with high displacement per unit volume. 
     It is a further object of this invention to provide such a machine which permits of large intake/exhaust ports with low shear and unobstructed flow. 
     It is a further object of this invention to provide such a machine which has high volumetric efficiency at minimum clearance, very low leakage flow, and low friction hydrodynamic fluid bearing surface piston sealing. 
     It is a further object of this invention to provide such a machine which has improved energy efficiency. 
     The invention results from the realization that a new and improved positive displacement rotary machine which provides uniform angular velocity and inherent static and dynamic balance with good volumetric efficiency and low weight to power ratio can be effected using a piston rotor rotatable about a first axis and having a number of rotatable pistons engaged with a guide track on a chamber rotor rotatable about a second axis to travel through a central common chamber between pairs of aligned diametrically opposed radial fluid chambers so that the pistons are kinematically constrained to move with sinusoidal motion between their associated radial chambers smoothly, quietly and without impact while the rotors and pistons move with pure rotary motion. 
     This invention features a positive displacement rotary machine. There is a piston rotor uniformly rotatable about a first axis and including a number of pistons equally spaced about the first axis and uniformly rotatably mounted about their axes on the piston rotor. There is a chamber rotor uniformly rotatable about a second axis spaced from the first axis, for relative rotation in 2/1 respectively between the piston and chamber rotor, including a central common chamber and a number of radial fluid chambers arranged in diametrically opposed pairs across the common chamber, and a guide track extending between opposing pairs of radial chambers across the common chamber for kinematically constraining each of the pistons as they move from one of their associated radial chambers to the other through the common chamber. There are intake and exhaust ports for introducing and exhausting fluid from the radial chambers. 
     In a preferred embodiment each of the pistons and its associated radial chambers may have the same cross-sectional shape. The guide tracks may be continuous through the common chamber. The guide tracks may form a part of their associated pairs of radial chambers. The pistons may have their positions which engage their associated guide tracks conforming in shape to the shape of the guide tracks. The pistons in the radial chambers may be all in the same plane. The guide tracks may be generally triangular in cross-section shape. The triangular guide tracks may have an apex of approximately 90° or less. For maximum displacement, the ratio of the radius of the radial chambers to that of the common chamber may be twice the cosine of φ where φ=90°/N where N is the number of pistons. The length of the piston and the width of the piston may be determined for maximum displacement for a given number of pistons N and the diameter of chamber rotor, 2·Rm. 
     The intake and exhaust ports may each extend along the chamber rotor over the period when each piston moves between top dead center and bottom dead center in each of its associated pair of radial chambers. One of the rotors may be connected to a source of rotary power. The intake port may be connected to a source of fluid and the fluid may be provided pressurized at the exhaust port and the rotary machine may be operated as a fluid pump. The intake port may be connected to a source of pressurized fluid and one of the rotors may be connected to a drive device for providing output rotary power and the rotary machine may be operated as a fluid motor. The exhaust port may be connected to a container to be evacuated and may extend along the chamber rotor over the period when each piston approaches bottom dead center. One of the rotors may be connected to a drive device for providing rotary power and the rotary machine may be operated as a vacuum pump. The exhaust port may be connected to a compressor tank and the intake port may extend along the chamber rotor over the period when each piston approaches top dead center. One of the rotors may be connected to a drive device for providing rotary power and the rotary machine may be operated as a compressor or expandor. The intake and exhaustor ports may extend along the chamber rotor over the period when each piston moves from bottom dead center of its exhaust stroke in one of its associated radial chambers to bottom dead center of the intake stroke in the other of its associated radial chambers. A valve may be provided in the port area for varying the displacement. One of the rotors may be connected to a drive device for providing rotary output power and the rotary machine may be operated as a two-stroke scavenged intake and exhaust engine. 
     The chamber rotor may be connected to a source of rotary power or it may be connected to a drive device. Each of the pistons may include at least one circumferential seal for sealing between the piston and radial chamber. The radial chambers may extend through the chamber rotor to its outer periphery. A thrust washer or pressurized fluid may seal the piston and chamber rotor faces. The housing may have a peripheral wall for closing the outer periphery of the chamber rotor. Each of the radial chambers may include an annular seal for sealing between each radial chamber and the housing. The intake and exhaust ports may be in the peripheral wall and/or a side wall. The radial chambers may be open on opposite sides and the housing may have side walls for closing the open opposite sides. Each piston may include a piston pivot pin which is rotatably mounted in the piston rotor, integral with the piston, or the piston rotor may include a number of fixed pivot pins, one for rotatably mounting each of the pistons. The vacuum pump may include a vacuum valve for maintaining the vacuum at the intake port. The compressor may include a pressure valve for maintaining the pressure at the exhaust port. 
     This invention also features a positive displacement rotary fluid pump including a piston rotor rotatable about a first axis and including a number of pistons equally spaced about the first axis and rotatably mounted about their axes on the piston rotor. There is a chamber rotor rotatable about a second axis spaced from the first axis including a center common chamber and a number of radial fluid chambers arranged in diametrically opposed pairs across the common chamber, and guide tracks extending between opposing pairs of radial chambers across the common chamber for kinematically constraining each of the pistons as they move from one of their associated radial chambers to the other through the common chamber. There are intake and exhaust ports for introducing and exhausting fluid from the radial chambers. The intake and exhaust ports each extend along the chamber rotor over the period when each piston moves between top dead center and bottom dead center in each of its associated pair of radial chambers. One of the rotors is connected to a source of rotary input power. The intake port is connected to a source of fluid and the fluid is provided pressurized at the exhaust port. 
     The invention also features a positive displacement rotary fluid motor. There is a piston rotor rotatable about a first axis and including a number of pistons equally spaced about the first axis and rotatably mounted about their axes on the piston rotor. There is a chamber rotor rotatable about a second axis spaced from the first axis and including a central common chamber and a number of radial fluid chambers arranged in diametrically opposed pairs across the common chamber. There are guide tracks extending between opposing pairs of radial chambers across the common chamber for kinematically constraining each of the pistons as they move from one of their associated radial chambers to the other through the common chamber. There are intake and exhaust ports for introducing and exhausting fluid from the radial chambers. The intake and exhaust ports each extend along the chamber rotor over the period when each piston moves between top dead center and bottom dead center in each of its associated pair of radial chambers. The intake port is connected to a source of pressurized fluid and one of the rotors is connected to a drive device for providing output rotary power. 
     This invention also features a positive displacement rotary vacuum pump including a piston rotor rotatable about a first axis and including a number of pistons equally spaced about the first axis and rotatably mounted about their axis on the piston rotor. There is a chamber rotor rotatable about a second axis spaced from the first axis including a central common chamber and a number of radial fluid chambers arranged in radially opposed pairs across the common chamber, and guide tracks extending between opposing pairs of radial chambers across the common chamber for kinematically constraining each of the pistons as they move from one of the associated radial chambers to the other through the common chamber. There are intake and exhaust ports for introducing and exhausting fluid from the radial chambers. The exhaust port is connected to a container to be evacuated and extends along the chamber rotor over the period when each piston approaches bottom dead center. One of the rotors is connected to a drive device for providing rotary input power. 
     This invention also features a positive displacement rotary compressor. There is a piston rotor rotatable about a first axis and including a number of pistons equally spaced about the first axis and rotatably mounted about their axes on the piston rotor. There is a chamber rotor rotatable about a second axis spaced from the first axis including a central common chamber and a number of radial fluid chambers arranged in diametrically opposed pairs across the common chamber. There are guide tracks extending between opposing pairs of radial chambers across the common chamber for kinematically constraining each of the pistons as they move from one of their associated radial chambers to the other through the common chamber. There are intake and exhaust ports for introducing and exhausting fluid from the radial chambers. The exhaust port is connected to a compressor tank. The intake port extends along the chamber rotor over the period when each piston approaches top dead center and one of the rotors is connected a drive device for providing rotary input power. 
     This invention also features a positive displacement rotary two-stroke intake and exhaust scavenged engine. There is a piston rotor rotatable about a first axis and including a number of pistons equally spaced about the first axis and rotatably mounted about the axis on the piston rotor. There is a chamber rotor rotatable about a second axis spaced from the first axis including a central common chamber and a number of radial fluid chambers arranged in diametrically opposed pairs across the common chamber. There are guide tracks extending between opposing pairs of radial chambers across the common chamber for kinematically constraining each of the pistons as they move from one of their associated radial chambers to the other through the common chamber. There are intake and exhaust ports for introducing and exhausting fluid from the radial chambers. The intake and exhaust ports extend along the chamber rotor over the period when each piston moves from bottom dead center of its exhaust stroke in one of its associated radial chambers to bottom dead center of its intake stroke in the other of its associated radial chambers. One of the rotors is connected to a drive device for providing rotary output power. 
    
    
     DISCLOSURE OF PREFERRED EMBODIMENT 
     Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: 
     FIGS. 1-4 are illustrative schematic plan views of a sequence of operation of a positive displacement rotary machine according to this invention using three pistons and six radial chambers; 
     FIG. 5 is a schematic three-dimensional view of a chamber rotor according to this invention with ten radial chambers for accommodating five pistons; 
     FIG. 6 is a schematic three-dimensional view of five pistons for engagement with the rotor for assembly with the chamber rotor of FIG. 5; 
     FIG. 7 is a schematic plan view of the base of the piston rotor which mounts the pistons of FIG. 6; 
     FIGS. 8A-C are schematic end elevational views of various piston and radial fluid chamber cross-sections; 
     FIG. 9 is a schematic sectional front elevational view of a positive displacement rotary machine according to this invention ported for operation as a fluid pump/motor; 
     FIG. 10 is a view similar to FIG. 9 of another construction of a fluid pump/motor using the positive displacement rotary machine of this invention; 
     FIG. 11 is a side elevational sectional view of the fluid pump/motor of FIG. 10; 
     FIG. 12 is a schematic sectional front elevational view of a positive displacement rotary machine according to this invention ported for operation as a vacuum pump; 
     FIG. 13 is a side elevational sectional view of the vacuum pump of FIG. 12; 
     FIG. 14 is a schematic sectional front elevational view of a positive displacement rotary machine according to this invention ported for operation as an air compressor, 
     FIG. 15 is a schematic top view of the chamber and piston rotors of FIG. 14; 
     FIG. 16 is a side elevational sectional view of the air compressor of FIG. 14; 
     FIG. 17 is a schematic sectional front elevational view of a positive displacement rotary machine according to this invention ported for operation as an engine; 
     FIG. 18 is a schematic top view of the chamber and piston rotors of FIG. 17; 
     FIG. 19 is a side elevational sectional view of the engine of FIG. 17; 
     FIGS. 20,  21  and  22  are diagrammatic views illustrating certain lengths and angles of the rotary machine; and 
     FIG. 23 is a schematic sectional front elevational view of a positive displacement rotary machine according to this invention with a sliding valve for variable displacement. 
    
    
     This invention relates to a positive displacement rotary machine which employs two rotors that rotate eccentric to one another with pure rotational motion yet provide linear sinusoidal motion between the pistons on one of the rotors, the piston rotor, and the chambers on the other of the rotors, the chamber rotor. Each piston is rotatably mounted on the piston rotor and cooperates with a pair of diametrically opposed radial fluid chambers on the chamber rotor by means of a guide track that kinematically constrains the piston as it moves from one of its radial chambers to the other through a central common chamber. 
     The result is an improved rotary machine which may be used for any manner of applications, for example, as a positive displacement device such as a fluid motor, fluid pump, compressor, expandor, vacuum pump or engine. Because all of the moving parts including the pistons rotate at a uniform angular velocity, the machine is statically and dynamically balanced and is capable of quiet and high-speed operation without impact. Furthermore, the machine admits of a high displacement per unit volume in a very compact package with improved energy efficiency. In addition, the design allows large intake and exhaust ports with low shear and unobstructed flow with high volumetric efficiency at minimum clearance and very low leakage flow. The operation of the machine may best be understood with reference to FIGS. 1-4 which show a top plan view with the piston rotor and housing omitted and the pistons engaged with their radial chambers on the chamber rotor. Although in these figures the number of pistons is chosen to be three, this is for illustrative purposes only as any number of pistons can be used. 
     There is shown in FIG. 1 a rotary machine  10  according to this invention including three pistons  12 ,  14  and  16  each of which is rotatably mounted to a piston rotor  120 , not shown in FIG. 7, by means of pivot pins  18 ,  20 ,  22 , force fitted or integral with the piston rotor, so that each piston can rotate about its own axis  24 ,  26 ,  28  in the direction indicated by arrows  30 ,  32 ,  34  as the entire rotor and all three pistons rotate about the piston rotor axis  36  at the same speed but opposite to the rotor in the direction of arrow  38 . Chamber rotor  40  rotates at half the piston rotor speed in the same direction indicated by arrow  42  and includes three pairs of diametrically opposed radial fluid chambers  44 ,  46 ;  48 ,  50 ;  52 ,  54  which are associated with pistons  12 ,  14  and  16 , respectively. Each piston has associated with it a pair of radially opposed chambers. There are twice the number of radial chambers as there are pistons. All of the radial chambers communicate with a central common chamber  56 . The radial fluid chambers are separated by lands  58 ,  60 ,  62 ,  64 ,  66  and  68 . 
     Each pair of radial chambers, as exemplified by chambers  52  and  54 , share a guide track  70  which extends from one to the other through the common chamber  56 . The shape of guide track  70  is such that it kinematically constrains the piston, in this case, the piston  16 , as it moves between radial chambers  52  and  54  through the common chamber  56 . All of the guide tracks  70 ,  72  and  74  pass through the center of rotation  76  of chamber rotor  40 . Each radial chamber  40 , again exemplified by chamber  54 , includes two downward sloping sides  80 ,  82  which meet at a lower apex  84  and two side walls  86  and  88  perpendicular to the paper. The top of chamber  54  in the plane of the paper and its outer end  90  are closed by a housing, not shown. The piston rotor, not shown in FIG. 1, rotates in the direction of arrow  38  about its axis  36  and the chamber rotor  40  rotates about its axis  76  in the same direction at one-half the speed of the piston rotor. The pistons  12 ,  14  and  16  move back and forth in their associated respective radial chambers and rotate on their pivot pins  24 ,  26  and  28  as necessary to remain aligned as constrained by their respective guide tracks  72 ,  70  and  74 . 
     In operation, FIG. 2, with a small clockwise motion of the piston rotor in the direction of arrow  38  and the chamber rotor in the direction of arrow  42 , piston  12  has moved outwardly to top dead center while piston  14  has moved inwardly towards bottom dead center and piston  16  has moved outwardly from a position in common chamber  16  in FIG. 1 to a position just above bottom dead center in FIG.  2 . With continued motion, as shown in FIG. 3, piston  12  recedes from top dead center, piston  14  moves further into the common chamber  56 , and piston  16  moves further outwardly in its radial chamber, and in FIG. 4 piston  12  has withdrawn even further in its radial chamber, piston  14  has now moved to the halfway point between its radial chambers  54  and  52  where it is right at the center of common chamber  56  and piston  16  has moved closer to the top dead center position in its radial chamber  44 . 
     The construction of a chamber rotor is shown in more detail in FIG.  5 . In FIG.  5  and the following figures, like parts have been given like numbers and similar parts have been given like numbers accompanied by a lower case letter or a prime. Chamber rotor  40   a,  FIG. 5, differs somewhat from chamber rotor  40  shown in FIGS. 1-4 in that it has ten radial fluid chambers to cooperate with five pistons as opposed to the device in FIGS. 1-4 where only three pistons are cooperating with six radial fluid chambers. Chamber rotor  40   a,  FIG. 5, however, illustrates more clearly one particular embodiment of the chambers. Here can be seen clearly the shape of the chambers as illustrated by radial fluid chamber  54   a,  where the sloping sides  80   a  and  82   a  meet at an apex or a point to form track  70   a.  In FIG. 15 sides  80   a  and  82   a  meet preferably at a 75° to 90° angle. Although the track is generally pointed, a small radius  100  may be used for easier machining, control of leakage flow and smoother operation. However, any manner of guide track which constrains the movement of the pistons from one of its radial fluid chambers to the other across the common chamber  56  will satisfy the invention. Without the open area provided by the common chamber  56 , the pistons would be unable to move back and forth between their radial chambers, but without the continuous guide tracks the pistons would not move smoothly through that open common chamber  56 . 
     The five pistons which engage with the ten radial fluid chambers of chamber rotor  40   a,  FIG. 5, are shown in FIG.  6 . Each piston, as exemplified for example by piston  14   a,  has flat sides  102 ,  104 , flat ends  106  and  108 , not visible, and a lower portion which has sloping sides  110  and  112  to form a triangular apex  114  including a small radius which nicely conforms with the contours of the radial chambers in FIG. 5 to control leakage flow. The pivot pins including  18   a,    20   a  and  22   a  on which pistons  12   a,    14   a  and  16   a,  respectively, are free to rotate about their own axes, are mounted in piston rotor base  120 , FIG. 7, which includes five bores such as bores  122 ,  124  and  126  for receiving pivot pins  18   a,    20   a  and  22   a.  Although the pistons in FIG. 1 have been shown as pivotally mounted for rotation about their pins  18 ,  20  and  22 , this is not a necessary limitation of the invention. For example, the pins may be force fitted into the pistons and rotatably mounted in the base  120  or the pistons may have the pins an integral part of their design as shown in FIG.  6 . This is a matter of design choice for cost and strength considerations. 
     The piston and piston rotor and the radial chambers and chamber rotor are all rotatable in the same plane for perfect balance. Either rotor can be the driven or driver: either one can provide the output rotary power or accept the input rotary power. Often the chamber rotor is chosen as the input/output because it moves at half the speed of the piston rotor. The guide track is generally continuous in the radial chambers and across the common chamber to facilitate smooth operation. Discontinuities can be tolerated, though are not preferred. 
     Although thus far the cross section of the pistons has been shown as rectangular with a triangular bottom, this is not a necessary limitation of the invention as any shape which provides the necessary displacement and adequately engages with the guide track to prevent rotation of the piston out of the track, particularly when crossing the center of chamber  56 , will suffice. The measure of the adequacy is the kinematic constraint imposed on the piston as it moves from one of its radial chambers to the other through the common chamber. For example, in FIGS. 8A-C, other cross-sections for a piston are suggested. In FIG. 8A the piston  12 ′ has an elliptical or parabolic preferred cross-section with a flat top and small track radius. Piston  12 ″, FIG. 8B, has a small radius teardrop shape. Piston  12 ′″, FIG. 8C, is generally rectangular with an apex at its lower end as shown in FIGS. 5 and 6. 
     The guide track may take any shape so long as it provides a kinematic constraint on the movement of the piston from radial chamber to radial chamber through the common chamber. While some discontinuity in the track may be permissible, the kinematic chaining or constraint should be constant to provide the smooth, impact-free operation between chambers that is desirable. 
     The relationships of the various parts may be better understood with reference to an explanation of the design for maximum pump or motor displacement per revolution for a given diameter and number of pistons as follows, where: 
     φ is the angle from chamber radial center to the chamber radial edge; 
     θ is the angle between the chamber radial edge and is equal to 2φ; 
     N is the number of pistons; 
     R rc  is the distance from the center of the chamber rotor to top dead center          (       R   rc     =         R   M   2     -     R   2           )     ;                   
     R m  is the radius of the chamber rotor; 
     R is one half the width of a piston; 
     P is the length of a piston; 
     Y is the effective length of the chamber; 
     Z is the length of the remainder of the chamber; 
     R cc  is the length of the chamber radial edge; 
     X is the distance between the center of the chamber rotor and the center of the piston rotor, X is also the distance between the center of the piston rotor        (     X   =         R   rc     -   P     Z       )                   
     as shown in FIGS. 20,  21  and  22 . 
     The pistons must not have contact interference during rotation. Once X and R rc  are determined P will be easily determined by the position of pistons X′ and X″ in FIG.  22 . 
     This relative piston location at the apex of L and Y′ can be determined graphically or analytically by known methods to determine the maximum value of P to prevent edge or corner interference of the pistons during relative rotation.          (     L   =         R   2     +     P   2           )     ,                   
     then        X   =         R   RC     -   P     2                     
     can be determined, where X is the eccentricity between the chamber and piston rotors. 
     Once this two-dimensional component of displacement is determined it need only be multiplied by the depth of the chamber along the direction of the rotational axes of the rotors to obtain full three-dimensional displacement volume.                φ   =     90   N       ;                  2      φ     =   θ             (   1   )                 R   rc     =         Rm   2         1   +       tan   2        φ       4                 (   2   )               R   =     2          R   rc     2        tan                 φ             (   3   )               Y   =     Z   =       R   rc     2               (   4   )                 R   cc     =       R   rc       2      cos                 φ               (   5   )               X   =         R   rc     -   P     2             (   6   )                         
     By selectively porting either through side walls or peripheral walls, the positive displacement rotary machine of this invention can be made to operate as a number of different types of machines, e.g., a fluid pump or motor, a vacuum pump, air compressor, expandor, or even an engine. 
     There is shown in FIG. 9 a device  200  which may be operated as either a fluid motor or a fluid pump which is enclosed in a housing  202  that has two ports  204  and  206 . Port  206  is indicated as the intake port and  204  as the exhaust port. However, these may be interchanged. If a fluid pressure is provided at the intake port then the device will be operated as a fluid motor. If the device itself provides pressurized fluid at the exhaust port then the device is operating as a fluid pump which must be driven by an external source of rotary power. With fluid pump/motor  200  the ports are peripheral and they extend over the period when each of the pistons moves between top dead center and bottom dead center in each of its associated pair of radial chambers. Here again the device includes five pistons  208 ,  210 ,  212 ,  214  and  216  rotatably mounted on pins  218 ,  220 ,  222 ,  224 ,  226  for rotation about their own rotational axis  228 ,  230 ,  232 ,  234  and  236 , respectively. All of the pistons are mounted on the piston rotor, not shown, which rotates in the direction of arrow  238  about the piston rotor axis  240 . Chamber rotor  242  rotates in the direction of arrow  244  about its axis  246 . And there are ten radial fluid chambers  248 ,  250 ,  252 ,  254 ,  256 ,  258 ,  260 ,  262 ,  264  and  266  in which the pistons move to and fro through common chamber  268  under the kinematic constraint of guide tracks  270 ,  272 ,  274 ,  276 ,  278 , respectively. 
     In another embodiment the hydraulic pump or motor  280 , FIGS. 10 and 11, includes but three pistons  282 ,  284  and  286  each of which is provided with circumferential sealing rings  288 ,  290 ,  292 ,  294 ,  296 ,  298 , to prevent side leakage as the pistons move between their associated radial chambers  296 ,  298 ,  300   302 ,  304  and  306  through common chamber  299  in chamber rotor  301  along guide tracks  308 ,  310  and  312 . In addition, each of the radial chambers is provided with end seals  314 ,  316 ,  318 ,  320 ,  322 ,  324  to prevent leakage between chamber rotor  326  and housing  328 . A thrust washer, or pressurize fluid spring may be provided to force the pistons and piston rotor against the chamber rotor to control leakage flow. Intake port  330  extends over the period where the pistons move from top dead center to bottom dead center or where the pistons leave the chamber, as the two rotors rotate in the direction as indicated by arrow  332 . A substantial portion of the remainder of the housing may be ported as the exhaust port. When the device is operated as a hydraulic motor, pressurized fluid is provided at intake port  330 . When it is operated as a pump the direction can be reversed so that the intake port becomes the exhaust port and pressurized fluid is provided there. The pressurized fluid to operate it as a hydraulic motor can be provided through conduit  334  and servo valve  336 . In addition, where it is desirable to vary the displacement of the fluid machine, a slide valve  335  may be utilized as shown in FIG.  23 . 
     In FIG. 11 it can be seen that the piston rotor includes base  336  mounted on axle  338  rotatable in bearings  340  and  342  in housing  328 . Base plate  336  mounts the three pistons  282 ,  284  and  286  which have teardrop shaped cross-sections and are pivotably mounted in base  336 . The end seals  314 ,  318  on radial chamber  292  are shown in FIG.  11 . Chamber rotor  301  is shown with portions removed and its axle  344  rotatably mounted in bearings  346  and  348 . 
     A vacuum pump as shown in FIGS. 12 and 13 can be implemented in the same fashion as the hydraulic motor/pump of FIGS. 10 and 11 with the exception that the conduit  334   a  is connected to a container to be evacuated and a vacuum valve  336   a  is used at the intake port instead of a servo valve. The pistons, the radial and common chambers, the housing and the porting are the same. In FIGS. 12 and 13 like numbers have been applied to like parts accompanied by a lower case a with respect to those parts in FIGS. 10 and 11. 
     For implementation as an air compressor, FIGS. 14,  15  and  16 , the rotary device according to this invention has a slightly smaller intake port  330   b  and the conduit  334   b  is connected to a tank for storing compressed fluid and a suitable valve  336   b  is employed in place of the vacuum valve  336   a.  In FIG. 15 the end seals, as exemplified by end seal  318   b  on radial chamber  292   b,  which is also used in FIGS. 10-13, is shown more clearly. 
     In a final example of the versatility of the rotary machine of this invention there is shown an implementation as a two-cycle, scavenged intake and exhaust, heat engine wherein a fuel injector  350  fires the charge at top dead center and the intake  330   c  and exhaust  331  ports are interconnected through common chamber  299   c  for complete scavenging. 
     The rotary machine of this invention may also serve as a variable volume device by adding a moving valve such as slide valve  335  at the intake, FIG.  23 . 
     Although specific features of this invention are shown in some drawings and not others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. 
     Other embodiments will occur to those skilled in the art and are within the following claims: