Abstract:
Axially protruding, centrally cooled pistons rotate around a stationary primary rotation axis within a cylindrical piston chamber. The pistons are held on both of their axial ends by concentrically rotating crank disks as intertwined rotary assemblies. On the outside of each crank disk is hinged a driving piston that slides in a radial guide of two flywheels oppositely axially adjacent the piston chamber and crank disks. The flywheels rotate around an offset secondary rotation axis. As a result. The pistons are individually and oppositely alternately accelerated and decelerated. Volumes between them angularly expand and contract. Inlets and outlets are positioned along the piston chamber circumference in correspondence with expansion and contraction phases of the rotating volumes. A low number of moving parts, area sealed volumes, no valves, no dead volume, balanced mass forces, vibration free rotation and short force transmission paths provide for lightweight construction and high rotational speeds.

Description:
FIELD OF INVENTION 
     The present invention relates to pumps, compressors and engines with circumferential undulating, area sealed rotating pistons. 
     BACKGROUND OF INVENTION 
     Piston devices are preferably used where a large fluid pressure difference needs to be induced or utilized. Commonly employed linearly oscillating piston pumps, compressors and engines are well known for their mechanical friction losses, fluid friction losses and thermodynamic losses. Mechanical friction losses particularly in engines are attributed to the commonly large number of valves, pistons and their driving and linking mechanisms and the friction in between them. Fluid friction losses occur predominantly across intake and exhaust valves. Thermodynamic losses are contributed by the initial fluid compression taking place in the hot combustion chamber where the working fluid under compression is additionally heated from outside. As the working fluid also heats up internally during its compression, the compression ratio is reduced by the external heating in a gasoline engine by the self ignition temperature of the gasoline vapors. In a diesel engine well known chemical reaction temperatures limit the maximum compression ratio. Thermodynamic efficiency is directly related to compression ratio as is well known in the art. Therefore there exists a need for a piston device that may be utilized as a pump, compressor and/or in a combustion engine and that provides reduced mechanical friction losses due to a reduced number of moving parts, reduced fluid friction losses due to a fluid exchange control without valves and in case of a combustion engine reduced thermodynamic losses due to a compression stage that is structurally separated from combustion heated structures. The present invention addresses these needs. 
     The concept of a rotating volume that contracts and expands while moving in a loop has been considered in the prior art to provide fluid exchange without valves. The well known Wankel engine is the only mass produced rotating piston combustion engine to date. Despite its compact design without valves, it has the fundamental flaw of a line contact seal that slides along an abruptly changing peripheral surface with high velocity. This limits live time as well as compression ratio. Therefore, there exists a need for a rotating piston engine that provides area sealing in between continuously shaped sealing surfaces for a reliable lasting operation. The present invention addresses also this need. 
     Other rotating piston engine concepts in the prior art provide work volumes that expand and contract while rotating. On the one hand, these engine concepts fail to address the particular needs for a simple mechanical drive with a low number of joints and the shortest mechanical force transmitting paths that can be designed with sufficient strength and stiffness and yet with minimal moving mass and mass forces. Also it is desirable to have all moving masses at a minimum and substantially balanced to minimize vibration and bearing loads at high rotational speeds. This is one well known prerequisite to drive such devices with sufficiently high rotational speeds in order to obtain a power-to-weight ratio of such an engine that is at least comparable with that of a modern oscillating piston engine. Therefore, there exists a need for a rotating piston device that is mechanically simple with a low number of lightweight moving parts and with substantially balanced rotating masses for high rotational speeds and consequently for a high power-to-weight ratio. The present invention addresses also this need. 
     On the other hand, to employ a rotary piston device in conjunction with hot combusting fluids, there is a need to provide the pistons particularly with a sufficiently loose connection, cooling and lubrication so that they their thermal expansion and sliding friction may be conveniently controlled. At the same time pistons and other parts contributing in encapsulating the work volumes are desired to have area contact in the sliding seal interfaces. This is another prerequisite for reliable sealing at high pressures, minimized wear and optimized heat transfer in the sliding seal interfaces. The present invention addresses also these needs. 
     SUMMARY 
     Preferably two axially protruding rotary pistons are commonly rotationally guided and individually angularly accelerated within a common cylindrical piston chamber. As the rotary pistons individually and alternately accelerate and decelerate during their rotation around a stationary primary rotation axis, work volumes between them angularly expand and contract. Inlets along the piston chamber provide peripheral access of a work fluid to the work volumes as the expanding work volumes pass by the inlets. As the contracting work volumes pass by the outlets, the contained work fluid is vacated into the outlets. Angular position and extension of the inlet(s) and outlet(s) are selected in conjunction with the intended use of the rotary piston device as a pump, compressor or as a motor as may be well appreciated by anyone skilled in the art. 
     Each rotary piston is part of a rotary assembly that includes crank disks axially coupled to the rotary pistons at both their axial ends. Each crank disk has a crank joint with a tertiary rotation axis fixed with respect to their rotary piston and in a secondary offset to the primary rotation axis. Joined at the crank joints are driving pistons that rotate freely around their respective tertiary rotation axes and, together with their rotary assembly, around the primary rotation axis. Each driving piston in turn is radial free guided in a radial sliding guide of flywheels outward and immediately adjacent to both crank disks. The flywheels with their sliding guides rotate around a stationary secondary rotation axis that is in a primary offset to the primary rotation axis. Due to the primary offset, the driving pistons are forced radial inward and outward in their radial sliding guides as they are rotated by the radial sliding guides around the secondary rotation axis. The changing distance of the driving pistons to the secondary rotation axis results in a varying rotational speed of them together with the joined rotary assemblies around the primary rotation axis while the flywheels rotate at a substantially constant speed. The tertiary rotation axes compensate for a periodically changing angle of the driving pistons relative to their respective rotary assemblies. 
     The sliding guides of opposite flywheels are aligned with each other and each of them extends preferably continuous across the secondary rotation axis. Driving pistons belonging to separate rotary assemblies are guided in the radial sliding guides on opposite sides of the secondary rotation axis. Thus, the two rotary assemblies and their driving pistons are accelerated and decelerated individually and in an alternating fashion. As a favorable result, the angular mass forces resulting from angular acceleration and deceleration of the two rotary assemblies and their joined driving pistons are substantially cancelled out in the radial sliding guides and have no substantial effect on the continuous rotation of the flywheels. 
     The driving pistons may be joined with their crank disks diametrically opposite the rotary piston with respect to the primary rotation axis. Consequently, a combined mass center of each rotary assembly and its respective driving pistons may be positioned coinciding with the primary rotation axis. Centrifugal mass forces of individual rotary assembly components and their respective driving pistons may thereby cancel themselves out. 
     The rotary piston device provides a low number of rotating parts, area sealing interfaces between pistons and their contacting faces, fluid exchange without valves, balanced centrifugal and angular mass forces, short force transmission paths between joined and coupled components of individually opposing mass forces and smooth rotation. As a consequence, the rotary piston device may be operated reliably and efficiently at high rotational speeds, which in turn provide for a high power-to-weight ratio. 
     The rotary piston device may be part of a combustion engine providing compression of air and/or air/fuel mixture and, in an additional separate stage, a motor that is harvesting pressure energy and, eventually, also the kinetic energy of the pressurized combusted and/or combusting air and/or air fuel mixture. The rotary piston device may also be operated as a pump or motor of incompressible fluid, and/or as a compressor or motor for compressible fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a first perspective view of rotary piston device of a first embodiment of the invention. 
         FIG. 2  is the first perspective view of the rotary piston device of  FIG. 1  cut along a vertical mid side plane. 
         FIG. 3  is the first perspective view of the rotary piston device of  FIG. 1  with the housing cut along a vertical mid front plane. 
         FIG. 4  is the first perspective view of rotary pistons of a first embodiment of the rotary piston device as in  FIGS. 1 ,  2 ,  3 . 
         FIG. 5  is the first perspective view of a rotary assembly including one rotary piston of  FIG. 4 . 
         FIG. 6  is the first perspective view of the rotary assembly of  FIG. 5  with drive pistons and fly wheels as in  FIG. 3  in angled cut view. 
         FIG. 7  is a second perspective view of the rotary assembly, one drive piston and one fly wheel as in  FIG. 6 . The rotary piston is cut along the vertical mid side plane and the vertical mid front plane. 
         FIG. 8  is the second perspective view of the rotary assembly with a rotary piston of a second embodiment of the invention. The rotary assembly is cut along the vertical mid side plane. 
         FIG. 9  is the second perspective view of the rotary assembly of  FIG. 8  depicting the entire rotary piston. 
         FIG. 10  is the second perspective view of a doubled rotary assembly of a third embodiment of the invention. 
         FIG. 11  is the second perspective view of the third embodiment rotary piston device with the housing and flywheels cut along the vertical mid front plane. Depicted as solids are also work volumes and fluid accesses and a combustion volume as provided in the third embodiment. 
         FIG. 12  is the first perspective view of the third embodiment as in  FIG. 11  without doubled rotary assemblies and without driving pistons. 
         FIG. 13  is a third perspective view of the work fluid volumes and channels at a first angular flywheel position. The doubled rotary assemblies are cut along a rear vertical mid side plane. 
         FIG. 14  is the third perspective view as in  FIG. 13  at a second angular flywheel position in a 30 deg angle to the first angular flywheel position. 
         FIG. 15  is the third perspective view as in  FIG. 13  at a third angular flywheel position in a 30 deg angle to the second angular flywheel position. 
         FIG. 16  is the third perspective view as in  FIG. 13  at a fourth angular flywheel position in a 30 deg angle to the third angular flywheel position. 
         FIG. 17  is the third perspective view as in  FIG. 13  at a fifth angular flywheel position in a 30 deg angle to the fourth angular flywheel position. 
         FIG. 18  is the third perspective view as in  FIG. 13  at a sixth angular flywheel position in a 30 deg angle to the fifth angular flywheel position. 
         FIG. 19A  depicts an operation schematic of a single stage engine configuration of the rotary piston device. 
         FIG. 19B  depicts an operation schematic of a dual stage engine configuration of the rotary piston device. 
     
    
    
     DETAILED DESCRIPTION 
     As in  FIGS. 1-6 , a rotary piston device  100  of a first embodiment of the invention includes a housing  110  having inside a primary piston chamber  114 . The primary piston chamber  114  is rotationally symmetric with respect to a primary rotation axis AP, which is stationary with respect to the housing  110 . The primary piston chamber  114  is preferably cylindrical. Also part of the rotary piston device  100  are preferably two rotary assemblies  200 A,  200 B suspended concentrically to each other, two opposing flywheels  181 ,  182 , and two opposing driving pistons  191 ,  192  at each of the rotary assemblies  200 A,  200 B. The rotary assembly  200 A,  200 B are rotationally suspended with respect to the primary rotation axis AP within the primary piston chamber  114 . Part of each rotary assembly  200  is a rotary piston  161 A/ 161 B axially extending along the primary rotation axis AP between two opposing axial piston ends  1691 ,  1692  and two opposing crank disks  211 , 212 . Each of the crank disks  211 / 212  has an axial piston coupling  215 / 216 , a crank joint  231 / 232  and a bearing disk  213 / 214  that is in between a respective axial piston coupling  215 / 216  and a respective crank joint  231 / 232 . Each bearing disk  213 / 214  has a chamber seal face  217 / 218  that contributes in axially sealing the primary piston chamber  114  and that is in a sliding seal contact with an opposite piston coupling back face  220 / 219 . The axial piston couplings  215 , 216  are axially engaging with a respective one of the opposing piston ends  1691 / 1692  such that torque, fluid pressure on the rotary pistons  161 A,  161 B as well as mass forces of the rotary pistons  161 A,  161 B are transferred onto the adjacent crank disks  211 ,  212  while the rotary pistons  161 A,  161 B remain preferably axially loose in between the opposing axial piston couplings  215 ,  216 . In that way, the rotary pistons  161 A,  161  B may freely axially expand when heated by a compressed and/or combusting fluid in the adjacent work volumes  111 A,  111 B. Each of the crank joints  231 , 232  provides a tertiary rotation axis AT that is fixed with respect to the respective rotary assembly  200 . The tertiary rotation axes AT are in a secondary offset to the primary rotation axis AP. The rotary pistons  161 A,  161 B are axially flush with each other. A secondary bearing disk  214  of one the two rotary assemblies  200 A,  200 B is rotationally suspended inside a primary bearing disk  213  of one other of the two rotary assemblies  200 A,  200 B preferably via a disk interconnect bearing  241 . The bearing disks  213 ,  214  have radial seal faces  223 ,  224  in rotating seal contact with each other. The primary bearing disk  213  has also peripheral seal face  225  in rotating seal contact with the housing  100 . Seal faces  223 ,  224 ,  225  contribute in axially sealing the primary piston chamber  114 . 
     Each of the rotary pistons  161 A/ 161 B features angled piston faces  165 , a center face  164 , and a peripheral face  166  with optional lubrication grooves  168 . The peripheral face  166  provides preferably circumferential area contact sealing with a primary peripheral wall  116  of the primary piston chamber  114 . Nevertheless and as may be well appreciated by anyone skilled in the art, the peripheral face  166  may feature other well known sealing features. Likewise, the center face  164  may be in a circumferential area contact sealing with a central seal wall  144  provided by a center tube  140 . Optional well known seal features may also be employed on the center face  164 . 
     Axial piston holes  1681  may serve as part of a lubricant supply channel to supply lubricant to the circumferential lubrication grooves  168 . Each rotary piston  161 A,  161 B is preferably of an axially substantially continuous profile that may be fabricated by well known extrusion techniques. Axially substantially continuous means in the context of the present invention that axial discontinuities such as circumferential lubrication grooves  168 , piston end seal lips  1693  and radial lubrication groove access holes  1681  are fabricated into the rotary pistons  161 A/ 161 B by material removal processes. The axial piston holes  1612 ,  167  are preferably through holes optionally also serving as part of a coolant transfer channel  251 ,  167 ,  252  as shown in  FIG. 6 . 
     In a second embodiment of the invention as depicted in  FIGS. 8 ,  9 , the rotary pistons  161 A,  161 B may each feature a peripheral seal profile  160  and center seal profile  163  that are both axially substantially flush with the respective rotary piston  161 A/ 161 B. Each peripheral seal profile  160  is radial outward sliding engaging with the respective rotary piston  161 A/ 161 B and features the peripheral contact face  166  configured for a snug sliding sealing contact with the primary peripheral wall  116 . The center seal profile  163  may provide the center face  164  that is configured for a snug sliding sealing contact with the central seal wall  144 . A radial spring profile  169  is springily interposed preferably between the respective rotary piston  161 A/ 161 B and the center seal profile  163  to resiliently press the center face  164  into contact with the central seal wall  144  in opposition to centrifugal forces. Nevertheless, the radial spring profile  169  and/or the like may be similarly springily interposed between the respective rotary piston  161 A/ 161 B and the peripheral seal profile  160 . The peripheral seal profile  160  may be axially sliding interlocked at its axial ends with a stiffening rib  1601  that in turn may be radial coupled via radial pin holes  1602  with respective axial piston couplings  215 ,  216 . 
     Center seal profile  163  and peripheral seal profile  160  provide area sealing irrespective eventual elastic radial deformation of the rotary piston  161 A/ 161 B due to centrifugal mass forces at high rotational speeds while the rotary pistons  161 A/ 161 B are radial fixed by the opposing axial piston coupling  215 ,  216  and while they are substantially free suspended in between them. The radial substantially free suspending of the rotary pistons  161 A,  161 B may contribute in transferring centrifugal mass forces of the rotary pistons  161 A,  161 B directly onto the respective crank disks  211 ,  212 . Moreover and in the preferred case of the respective crank joints  231 ,  232  being diametrically opposite the axial piston couplings  215 ,  216  with respect to the primary rotation axis AP, a combined mass center MC of an individually driving rotary assemblies  200 A/ 200 B and its respective driving pistons  191 ,  192  may be predetermined to coincide with the primary rotation axis AP. In the second embodiment with the radial substantially free suspended rotary pistons  161 A,  161 B in conjunction with the combined mass center MC coinciding with the primary rotation axis AP, centrifugal mass forces of the rotary assembly  200  and the respective driving pistons  191 ,  192  may be substantially cancelled out within the rotary assembly  200 . Only the centrifugal mass forces of the optional peripheral seal profile  160  and the optional stiffening rib  1601  may be transferred onto the housing  100 . This may substantially reduce bearing loads on the disk interconnect bearings  241  and disk housing bearings  242  as well as vibration of the rotary piston device  100  at high rotational speeds. Disk housing bearings  242  are held in the housing  110  thereby defining the primary rotation axis AP for the rotary assemblies  200 A,  200 B,  200 BA,  200 BB of all three embodiments. 
     The two opposing flywheels  181 ,  182  are each positioned immediately outside and adjacent a respective bearing disk  213 ,  214 . They are rotationally suspended via flywheel bearings  184  in the housing  110  thereby defining a secondary rotation axis AS for the flywheels  181 ,  182 . The secondary rotation axis AS is stationary with respect to the housing  110  and in a primary offset OP to the primary rotation axis AP. Each of the two opposing flywheels  181 / 182  has a radial guide  185 / 186  in which two driving pistons  191 / 192  each belonging to a separate rotary assemblies  200 A/ 200 B are radial guided. The two opposing driving pistons  191 , 192  are joined with a respective crank joint  231 , 232  and rotationally suspended with respect to the tertiary rotation axis AT. 
     The flywheels  181 ,  182  rotate with a substantially constant secondary angular velocity together with the driving pistons  191 ,  192 , which are radial held in constant distance to the primary rotation axis AP via the crank joints  231 ,  232 . Hence, the driving pistons  191 ,  192  are once forced towards the secondary rotation axis AS and once forced back outwards during a single rotation of the flywheels  181 ,  182 . As the driving pistons  191 ,  192  move radial back and forth, their primary angular velocities with respect to the primary rotation axis AP changes together with their respective joined rotary assembly  200 A/ 200 B. When the driving pistons  191 ,  192  are closest to the secondary rotation axis AS, the primary angular velocity of the rotary assembly  200  is at a minimum. When the driving pistons  191 ,  192  are at a maximum distance to the secondary rotation axis AS, their primary angular velocity of the rotary assembly is at a maximum. 
     Between their maximum and minimum primary angular velocities, the rotary assemblies  200 A,  200 B are once accelerated and once decelerated in an alternating fashion during a single flywheel  181 ,  182  rotation. This in turn results in alternating circumferential expansion and contraction of work volumes  111 A,  111 B that are encapsulated inside the primary piston chamber  114  in between the piston faces  165  and chamber seal faces  217 ,  218 . Also, since one of the two rotary assemblies  200 A,  200 B together with its driving pistons  191 ,  192  is accelerated substantially at the same rate as the other one of the two rotary assemblies  200 A,  200 B with its driving pistons  191 ,  192  is decelerated, their respective angular mass forces substantially cancel each other out at radial guides  185 ,  186 . This contributes to a steady rotational speed of the flywheels  181 ,  182  as may be well appreciated by anyone skilled in the art. 
     The two opposing crank disks  213 ,  214  are preferably torque coupled across rotary pistons  161 A,  161 B and consequently the opposing flywheels  181 ,  182  are also rotationally coupled across the driving pistons  191 ,  192  and across the rotary assemblies  200 A,  200 B. As depicted in  FIG. 7 , torque coupling of the rotary pistons  161 A,  161 B with the axial piston couplings  215 ,  216  is accomplished by coupling protrusions  2161  that preferably axially loose interlock with through holes  1612 ,  167  of the rotary pistons  161 A,  161 B. The interlocking of the coupling protrusions  2161  with the through holes  1612 ,  167  may be rigid in radial direction in the second embodiment and may be radial rigid or loose in the first embodiment by predetermined radial interlock tolerances as may be well appreciated by anyone skilled in the art. 
     Each of the two assemblies  200 A,  200 B preferably features one primary bearing disk  213  and one secondary bearing disk  214  such that the two rotary assemblies  200 A,  200 B are intertwined around the primary rotation axis AP. In that case, a radial supply channel  251  may extend radial outward inside the secondary bearing disk  214  from a center tube hole  2121  up to an axial piston hole  167 . A radial supply channel such as depicted supply channel  251  and an axial piston hole such as piston hole  167  may be part of a lubricant supply channel that supplies lubricant to the lubrication grooves  168  on the peripheral piston face  166 . Radial lubrication groove access holes  1681  may be connecting for that purpose the outside lubrication grooves  168  with the inside of a corresponding axial piston hole. The axial piston hole  167  may be a through hole and connected with a radial drain channel  252  extending outward from the axial piston hole  167  in the primary bearing disk  213 . Radial supply channel  251 , axial through hole  167  and radial drain channel  252  may be part of a coolant transfer channel through which coolant may be transferred through the rotary pistons  161 A,  161 B. The axial coolant through holes  167  are preferably in proximity to the peripheral edges of the piston faces  165  where maximum heat transfer with the work fluid during its intake and/or exhaust may occur. Coolant and/or lubricant exiting the rotary assemblies  200 A,  200 B may be captured by drain grooves in the peripheral wall  116  as may be well appreciated by anyone skilled in the art. 
     A piston slider  170  axially extending along the primary rotation axis AP and substantially flush with the rotary pistons  161 A,  161 B may be circumferential positioned at the primary piston chamber  114 , where the rotary pistons  161 A,  161 B pass by in closest proximity and where the work volumes  111 A/ 111 B are at a minimum. The piston slider  170  may skim the peripheral piston faces  166  from lubricant and/or coolant while at the same time providing a sealing barrier between oppositely adjacent high pressure fluid access  130  and low pressure fluid access  120 . 
     Also held in the housing  110  is a center tube  140  that is concentric with respect to and axially extending along the primary rotation axis AP. The center tube  140  is inserted from at one side of the housing  110  and extends through the opposing flywheels  181 ,  182 , through center tube holes  2121  in the secondary bearing disks all the way across the rotary assemblies  200 A,  200 B. The center tube  140  has an axial service fluid channel  142  in communication with circumferential assembly supply holes  145 , which in turn are axially aligned and in rotationally free communication with the service fluid channel  251 ,  167 ,  252  and the like lubrication channel. Likewise, the center tube  140  may feature driving piston supply holes  148 , that supply the interfaces between driving pistons  191 ,  192  and radial guides  185  as well as crank joints  231 ,  231  with lubricant and/or coolant. Since the flywheels  181 ,  182  are torque coupled via driving pistons  191 ,  192  and rotary assemblies  200 A,  200 B, the center tube  140  may be conveniently utilized for coolant and lubricant supply at the location otherwise occupied by central torque transmitting shafts well known in the prior art. 
     Referring to  FIGS. 10-18  and in accordance with a third embodiment of the invention, secondary rotary assemblies  200 BA,  200 BB may be axially connected with each of the rotary assemblies  200 A,  200 B at one of the crank joints  231 ,  232  combined in a central crank joint  233 . A central driving piston  195  may be joined to the central crank joint  233 . The connection is preferably such that a primary bearing disk  213  is facing a secondary bearing disk  214  at the central crank joints  233 . The crank joints  231 ,  232 ,  233  may be preferably configured with spherical bearing surfaces such that elastic angular deformation in the crank joints  231 ,  232 ,  233  due to torque transfer, angular mass force cancellation, and local centrifugal mass forces is not transferred onto the driving pistons  191 ,  192 ,  195 . Thereby peak contact pressures in the bearing interfaces between driving pistons  191 ,  192 ,  195  and crank joints  231 ,  232 ,  233  as well as between driving pistons  191 ,  192 ,  195  and radial guides  185 ,  186  may be substantially avoided. The central driving pistons  195  may be axially segmented such that the central crank joint  233  may be sandwiched in between the axial segments of the central driving piston  195 . 
       FIGS. 11 ,  12  depict the rotary piston device  100  of the third embodiment including the housing  110 . Primary piston volumes  111 A,  111 BA as well as low pressure accesses  120 A,  120 B, high pressure accesses  130 A,  130 B and fluid transfer volume  154  in the preferred configuration as a combustion volume are depicted as solids. The driving pistons  191 ,  192  may contribute with their radial piston faces  193 A,  193 B,  194 A,  194 B in encapsulating secondary work volumes  112 A,  112 B,  112 C in between the radial guides  185 ,  186 , the respective flywheels  181 ,  182  and within secondary piston chambers  115 A,  115 B,  115 C. The secondary piston chambers  115 A,  115 B,  115 C are concentric with respect to secondary rotation axis AS. The flywheels  181 ,  182  rotate within the secondary piston chambers  115 A,  115 B,  115 C. The bearing disks  213 ,  214  axially separate the primary piston chamber(s)  114 A,  114 B from the secondary piston chambers  115 A,  115 B,  115 C. Central piston faces  196  of the central driving pistons  195  may contribute to encapsulate central secondary work volumes  112 C as described for secondary work volumes  112 A,  112 B. The central work volumes  112 C may be preferably utilized to receive combusting fluid. 
     The rotary piston device  100  may be utilized to compress fluid or to derive mechanical energy from compressed fluid as a motor. In the third embodiment, a compression stage may be conveniently combined with a motor stage and the entire rotary device  100  may operate as a combustion engine in which compressed air and/or air/fuel mixture is thermally energized in a well known fashion after exiting primary work volumes  111 A,  111 B in a pressurized condition and before or while entering secondary work volumes  111 BA,  111 BB through secondary pressure fluid access  130 B. For that purpose, the fluid transfer housing  150  may be configured as a well known combustion chamber. The third embodiment rotary piston device  100  may be operated as single stage combustion engine as schematically depicted in  FIG. 19A  or as a dual stage combustion engine as schematically depicted in  FIG. 19B . In the single stage operation, work fluid such as air and/or air/fuel mixture is compressed in a single stage prior to combustion and expanded in a singe stage following and/or during combustion of the air/fuel mixture. In the dual stage operation, fluid compression may be performed initially in the circumferential changing work volumes  111 A,  111 B that are a multiple of the radial changing work volumes  112 A,  112 B while both are maximum expanded. In a fluid cooler  155  placed along a fluid transfer channel between initial compression stage and final compression stage, the initially compressed fluid may be cooled down before entering the secondary piston chamber(s)  115 A and/or  115 B and before being compressed a second time. Fluid expansion may also be separated into two stages with the initial high pressure expansion preferably taking place in the central secondary piston chamber  115 C, where double bearing disk support of each central crank joint  233  may handle higher fluid pressures. Breaking up the expansion of the combusting air/fuel mixture into two stages provides for additional combustion reaction time before entering the final expansion stage again in a primary combustion chamber  114 B. For that purpose, a reactor  156  may be placed along a fluid transfer channel between high pressure and low pressure expansion stages. 
     The scope of the invention is not limited to a particular dimensional relation of primary offset OP and secondary OS. Nevertheless and as depicted, the primary offset OP may be about half the secondary offset OS and the angular extension of the rotary pistons  161 A,  161 B around the primary rotation axis AP may be about 120 degrees. In that case, the rotary pistons  161 A,  161 B are in closest proximity to each other and the work volumes  111 A,  111 B,  111 BA,  111 BB may be about zero in an angular position of the radial guides  185  as depicted for work volumes  111 B,  111 BB in  FIG. 13 . A dead volume well known in the prior art may be thereby substantially avoided. At that angular flywheel  181 ,  182  orientation, the radial guides  185 ,  186  are about perpendicular to an axis plane PL that coincides with primary rotation axis AP and secondary rotation axis AS. Also at that angular orientation, both intertwined rotary assemblies  200 A,  200 BA and  200 B,  200 BB have maximum angular acceleration and deceleration respectively and the same angular velocity as the flywheels  181 ,  182 . The piston sliders  170  are positioned also such that they contact the piston faces  166  while coinciding with the axis plane PL. 
     As the flywheels  181 ,  182  continue to rotate, the depicted driving piston  192 B moves closer to the secondary rotation axis AS thereby reducing its primary angular velocity together with the rotary piston  161 B and its equivalent rotary assembly while the other intertwined rotary assembly with its depicted rotary piston  161 A is accelerated at the same rate. Consequently, work volumes  111 B,  111 BB expand, while work volumes  111 A,  111 BA contract. This is depicted in the  FIGS. 14-18  with 30 deg rotationally increments of the flywheels  181 ,  182 . In  FIG. 13 , the work volume  111 B just got out of access with high pressure access  130 A after its contained pressurized air and/or air/fuel mixture was transferred to the combustion volume  154 . Pressure rise due to combustion in the closed combustion volume  154  may occur. In  FIG. 14 , work volume  111 BB receives combusting air/fuel mixture via high pressure accesses  103 B while work volume  111 B opens up to low pressure access  120 A and receives low pressure ambient air and/or fuel air mixture. Work volume  111 A is contracting and pressurizing the contained air and/or air/fuel mixture. Work volume  111 BA is accessed by low pressure access  120 B and releasing the contained expanded combusted air/fuel mixture. In  FIGS. 15-18 , work volume  111 BB is out of access with high pressure access  130 B while work volume  111 B is still accessed by low pressure access  120 A and work volume  111 BA is still accessed by low pressure access  120 B. In  FIG. 18 , the work volume  111 A is about to release the contained air and/or air/fuel mixture into the high pressure access  130 A and the combustion chamber  154 . 
     In a best mode anticipated by the inventor at the time of filing this invention, a single stage rotary piston device  100  similar as depicted in the  FIGS. 10-12  may be designed with rotary pistons  161 A,  161 B being about 200 mm long with peripheral wall  116  diameter of about 100 mm and center tube  140  diameter of about 20 mm. The work volumes  111 A,  111 B at their maximum circumferential expansion measure about 0.5 liter such that during one full rotation of the flywheels  181 ,  182  about 1 liter of fluid transfer volume is provided. Crank joints  231 ,  232 ,  233  and crank joint adjacent portions of the bearing disks  231 ,  232  as well as bolts and sheer pins inside the flywheels  181 ,  182  and bearing disks  231   232  may be of alloy steel. The remaining parts may be of high strength aluminum alloy. The primary offset OP is about 17.5 mm and the secondary offset OS about 35 mm. Full complement ball bearings are used for bearings  241 ,  242 ,  184 . 
     The mass of each doubled rotary assembly  200 A+ 200 BA,  200 B+ 200 BB including its respective driving pistons  191 ,  192 ,  195  is about 2.3 kg with their respective combined mass centers MC substantially coinciding with the primary rotation axis AP. 
     The below nomenclature is included as reference. Numerals in the Specification and Figures may have a letter extension where multiples of the same numerically referenced components are identified.
       100  Rotary piston device     110  Housing     111  Circumferential changing work volumes     112  Radial changing work volumes     114 / 115  Primary/Secondary Piston chamber     116  Peripheral primary piston chamber wall     120  Low pressure fluid access     130  High pressure fluid access     140  Center tube     142  Axial service fluid channel     144  Central seal wall     145  Circumferential assembly supply holes     148  Driving piston supply holes     150  Fluid transfer housing     154  Fluid heating volume     155  Fluid cooler     156  Reactor     160  Peripheral seal profile     1601  Stiffening rib     1602  Radial pin holes     161 A,  161 B Rotary pistons     1612  Through holes     163  Center seal profile     164  Center face     165  Piston faces     166  Peripheral piston face     167  Axial fluid hole     168  Circumferential lubrication grooves     1681  Radial lubrication groove access holes     169  Radial spring profile     1691 ,  1692  Opposing axial piston ends     1693  Piston end seal lips     170  Piston slider     181 ,  182  Flywheels     184  Flywheel bearings     185 / 186  Radial guides     191 / 192  Driving pistons     195  Central driving piston     193 / 194  Radial piston faces     196  Central piston face     200  Rotary assembly     211 ,  212  Crank disks     2121  Center tube hole     213 ,  214  Primary/Secondary bearing disk     215 ,  216  Axial piston coupling     2161  Coupling protrusions     217 ,  218  Chamber seal faces     219 ,  220  Coupling back faces     223 ,  224  Radial seal faces     225  Peripheral seal face     226  Central disk seal face     231 ,  232  Crank joint     233  Central crank joint     241  Disk interconnect bearing     242  Disk housing bearing     251  Radial supply channel     252  Radial drain channel   AP Primary rotation axis   AS Secondary rotation axis   AT Tertiary rotation axis   PL Axis plane   MC Combined mass center   

     Accordingly, the scope of the invention as described in the Figures and the Specification above is set forth by the following claims and their legal equivalent: