Abstract:
A gear set is disclosed having a guide, such as a cam, engaging the output shaft of the gear shaft and being indexed thereby. The guide drives one or more followers which in turn drive one or more interfaces of a differential gear set. The output shaft may be driven by a third interface of the differential gear set. The followers may likewise engage piston assemblies in order to control the piston assemblies during execution of a process such as a four stroke combustion process, or other process involving compression or expansion of a gas. The piston assemblies are enclosed within a housing defining an annular chamber, such as a toroid. Apertures formed in the housing allow exhaust gases to leave and air to be taken in. In one embodiment, a hyper expansion port is formed in the housing to release a portion of the air during the compression stroke in order to decrease the pressure of combustion gases.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/670,567 entitled “DIFFERENTIAL WITH GUIDED FEEDBACK CONTROL FOR ROTARY OPPOSED-PISTON ENGINE” and filed on Apr. 12, 2005 for Dan K. McCoin and Mark D. McCoin, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates generally to rotary engines and more particularly to rotary opposed-piston engines.  
         [0004]     2. Description of the Related Art  
         [0005]     The vast majority of internal combustion engines currently in use are reciprocating engines in which a piston moves up and down within a cylinder. The linear motion of the piston is translated into rotary motion by a crankshaft connected to the piston by a piston rod. In a typical engine, due to the large forces involved, the coupling between the crankshaft and the piston rod and between the piston and the piston rod, is a simple journal bearing. Accordingly, significant friction is introduced when converting the reciprocating motion of the piston to rotary motion. Furthermore, the power output on the crankshaft is not constant. As the piston drives the crankshaft, the crankshaft rotates and changes the effective length of the lever arm between the piston and the crankshaft.  
         [0006]     Current internal combustion engines further require complicated valving mechanisms in order to introduce fuel and air into the cylinder and to release exhaust gases. Typically such mechanisms involve spring loaded valves that are biased toward the closed position. Cams, driven by the crankshaft open and close the valves at appropriate times by pushing against valve stems attached to the valves. The contact between the cam and the valve stems is typically a sliding contact introducing a great deal of friction just to open the valve.  
         [0007]     Rotary engines eliminate many of these problems. In one type of rotary engine, the pistons move within a donut shaped chamber, or toroid, and are attached to an output shaft at the center of the toroid. The piston moves along an arcuate path, defined by the toroidal chamber, directly causing the output shaft to rotate. Accordingly, no translation from reciprocating to rotary motion is required.  
         [0008]     The complicated valving systems of the reciprocating engine may be replaced in a rotary engine by simple apertures in the toroidal chamber. As the pistons move along the toroidal chamber, they move past the apertures drawing in air and expelling exhaust. A sealed combustion chamber is achieved by simply combusting the fuel air mixture in a portion of the toroidal chamber in which no apertures are formed.  
         [0009]     What is currently lacking in the art is a practical rotary engine. Prior attempts have not been commercially viable and do not overcome critical challenges. The primary obstacle to achieving a practical rotary engine lies in the shape of the chamber itself. In a reciprocating engine a combustion chamber is defined by the top surface of the cylinder, the wall of the cylinder, and the piston. The combustion chamber traps expanding gases, forcing the piston to move. In a rotary engine, one must find a way to define a combustion chamber within a toroidal chamber with no top surface, as in a cylinder.  
         [0010]     Two possible solutions to this problem exist. First, one may place a fixed barrier within the toroidal chamber. Accordingly, the piston, the barrier, and the walls of the toroid define a combustion chamber. Second, one may use two opposed pistons, fixing a first piston and allowing a second piston to move, then fixing the second piston and allowing the first piston to move. Thus a combustion chamber is defined by the two pistons and the walls of the toroid.  
         [0011]     Defining a fixed barrier is problematic because the piston must constantly change direction once it reaches the barrier. Opposed pistons do not have this problem, in as much as both pistons can be allowed to move within the toroid. However, both types of rotary engine must have some mechanism to control the movement of the piston, whether to reverse direction when needed or to fix the position of the piston in order to define a combustion chamber. Both types must also translate the discontinuous velocity of a piston into a substantially constant rotation of an output shaft. Prior systems provide no adequate means to control the pistons providing a smooth output at high output torques.  
         [0012]     Some designs, for example, use mechanisms to obstruct the movement of the piston in order to fix its position. In one system, stop pins are moved into place to stop the piston. However, such systems simply obstruct the motion of the piston. Accordingly, at high angular velocities the piston will repeatedly strike the stopping mechanism at high speeds causing premature breakage. Prior designs also provide no blending of motion to give a smooth output torque. Motion of the piston in prior systems is simply rectified to the correct rotational direction but is not controlled to provide a smooth angular velocity output. In addition to providing a low quality output, such systems are subject to a great deal of mechanical shock, clatter, wear, and breakage, regardless of load, resulting in a very short useful life.  
         [0013]     Accordingly, it would be an advancement in the art to provide a rotary opposed-piston engine providing a substantially constant output. Such a system should control the motion of the pistons to define a combustion chamber while reducing mechanical shock to the components thereof.  
       SUMMARY OF THE INVENTION  
       [0014]     Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.  
         [0015]     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.  
         [0016]     A system is disclosed for converting power between two power devices, one device continuous and the other intermittent. Power may flow from the continuous to the intermittent device, or from the intermittent to the continuous device. In one embodiment, the system is a main power conduit—for example a shaft and a flywheel—and the system includes a gear case to allow smooth power transfer. The gear case may include a differential which allows the power elements on the intermittent side to move at variable rates. The differential may be, for example, an exploded planetary gear set or an epicyclic planetary gear set.  
         [0017]     The system may also include a locking device which controls the velocity and position of the power elements of the intermittent side. The locking device may be a follower arm corresponding to each power element, where the position of the follower arm correlates to the position of the corresponding power element. The locking device may further include a cam configured to guide each of the follower arms and thereby control the position of each power element.  
         [0018]     A rotary engine is also disclosed. The rotary engine may comprise a plurality of pistons secured to a hub, and a housing enclosing the pistons. The housing and piston hubs may define a toriodal chamber within which the pistons rotate. The engine may have a differential and a locking device to provide a smooth power output to a main shaft from the intermittent power inputs of the pistons operating in a combustion cycle.  
         [0019]     The rotary engine may be, for example, a pneumatic motor, a spark ignited engine, or a diesel cycle engine. The rotary engine may also be a heat engine such as, for example, a steam engine. In one embodiment, the rotary engine can be configured to perform a constant volume combustion cycle for at least a portion of the combustion event, allowing the engine to achieve greater efficiencies through higher cylinder pressures than conventional engines. Also, the engine can be configured to operate on a hyper-expansion cycle, allowing the engine to achieve greater efficiencies than in conventional engines. The rotary engine may be configured with scalloped pistons to make the combustion chambers of the engine more favorable for combustion. The engine may also be configured to start without an external starting device through manipulation of the hyper-expansion capability.  
         [0020]     An energy conversion device is also disclosed. The energy conversion device may be configured to run on an Alpha-cycle which provides power to a main shaft, or on a Beta-cycle which takes power from a main shaft. The energy conversion device may contain a plurality of compression-expansion chambers. The device may be configured to take a high energy fluid and convert it to a low energy fluid thereby supplying power to the main shaft, or to take a low energy fluid and convert it to a high energy fluid, while taking power from the main shaft. The energy conversion device can thereby act as a pump, air compressor, combustion engine, heat engine, or any other device consistent with the operations described. The energy conversion devices may be added to the same main shaft. The devices can therefore act as stages in supplying power to the main shaft, or one energy conversion device may be configured to supply power to another energy conversion device through the main shaft.  
         [0021]     These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:  
         [0023]      FIG. 1A  illustrates one embodiment of a system for converting intermittent power inputs to a constant power output in accordance with the present invention;  
         [0024]      FIG. 1B  illustrates one embodiment of an energy conversion device in accordance with the present invention;  
         [0025]      FIG. 2  is an exploded perspective view of an energy conversion device in accordance with the present invention;  
         [0026]      FIG. 3  is a cutaway side view of a housing and a piston assembly, in accordance with the present invention;  
         [0027]      FIG. 4A  is a side view of opposing pistons forming a compression-expansion chamber in accordance with the present invention;  
         [0028]      FIG. 4B  is a side view of opposing pistons with scalloped faces forming a compression-expansion chamber in accordance with the present invention;  
         [0029]      FIG. 5A  is a schematic illustration of four compression-expansion chambers formed within a toroidal chamber in accordance with the present invention;  
         [0030]      FIG. 5B  is a schematic illustration of another embodiment with four compression-expansion chambers formed within a toroidal chamber in accordance with the present invention;  
         [0031]      FIGS. 6A-6C  are schematic illustrations illustrating the movement of piston assemblies executing a four-cycle combustion process;  
         [0032]      FIG. 7  is a schematic representation of the angular regions corresponding to stroke and dwell movements of the piston assemblies, in accordance with the present invention;  
         [0033]      FIG. 8  is a pressure-volume plot of a conventional engine and a rotary opposed-piston engine, in accordance with the present invention  
         [0034]      FIG. 9  is a schematic representation of a chamber having a hyper-expansion port, in accordance with the present invention;  
         [0035]      FIG. 10  is a schematic representation of a differential having exploded planetary gearing, in accordance with the present invention;  
         [0036]      FIG. 11  is a schematic representation of a differential having epicyclic planetary gearing, in accordance with the present invention;  
         [0037]      FIG. 12  is a schematic illustration of a carrier and epicyclic planetary gear, in accordance with the present invention;  
         [0038]      FIG. 13  is a graph of velocity profiles of piston assemblies, in accordance with the present invention;  
         [0039]      FIG. 14  is a schematic representation of a cam profile suitable for use in the present invention;  
         [0040]      FIG. 15  is a schematic representation of a cam profile having two lobes, in accordance with the present invention;  
         [0041]      FIG. 16  is a front and side view of a cam follower, in accordance with the present invention; and  
         [0042]      FIG. 17  is a side view of an alternative embodiment of a cam follower in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.  
         [0044]     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.  
         [0045]      FIG. 1  illustrates one embodiment of a system  100  for converting power, with intermittent power on one side of the system  100  and continuous power on the other. The system  100  may comprise a first power device (not shown) coupled to a main power conduit. The first power device may be a continuous power device, which means the power device may supply continuous power to the main power conduit, or it may be configured to take continuous power from the main power conduit. The main power conduit may comprise a flywheel and a main shaft  132 . The main power conduit  132  may be coupled to a second power device  22 , which may be an intermittent power device. The second power device  22  may supply intermittent power to the main power conduit  132 , or it may use the power from the main power conduit  132  intermittently.  
         [0046]     In one embodiment, the second power device  22  is an internal combustion engine, and intermittently supplies power to the main power conduit  132 . In this manner, the power may flow from the second power device  22  to the first power device. In another embodiment, the second power device  22  is a pump or compressor, and takes power from the main power conduit  132  intermittently to compress gas and supply the gas through a port  62 ,  66 ,  74 ,  174  to some other device. In this manner, power may flow from the first power device to the second power device  22 , and the second power device  22  may output power as an intermittent stream of compressed gas.  
         [0047]     The system  100  may further include a gear case  28  coupled to the main power conduit. The gear case  28  may transfer power between the main power conduit  132  and the second power device  22 . As indicated above, the power can transfer through the gear case  28  in either direction—either from the main power conduit  132  to the second power device  22 , or from the second power device  22  to the main power conduit  132 . The gear case  28  thereby transfers power between the first power device and the second power device.  
         [0048]     The gear case  28  may include a differential. The differential may be configured to allow multiple power elements within the second power device  22  to rotate at a variable rate. Rotating at a variable rate in this embodiment may mean allowing power elements within the second power device  22  to change rotational speeds relative to each other, including allowing power elements to stop, while allowing the main power conduit  132  to maintain a smooth continuous rotation. The differential may comprise an exploded planetary gear set, or an epicyclic planetary gear set.  
         [0049]     The gear case  28  may further include a locking device. The locking device may be configured to control the relative velocity and position of a plurality of power elements within the power device  22 . Dividing the second power device  22  into power elements allows the second power device  22  to have multiple intermittent contributors to the supply or receipt of power. In one example, the power elements of the second power device  22  may be a plurality of piston assemblies. Each piston assembly may comprise one or more pistons, and the piston assemblies may be within the housing  22 . In one embodiment, the locking device may comprise a follower for each power element. The position of each follower may correlate to the position of the corresponding power element. The locking device may further comprise a cam configured to guide each of the followers, thereby controlling the position of each power element.  
         [0050]     The system  100  may further comprise an electronic control module  5  (ECM) configured to communicate with various sensors and actuators in the system  100 . In one embodiment, the ECM  5  may communicate with an ambient air pressure sensor  15  configured to provide a signal readable by the ECM  5  to indicate the current ambient air pressure.  
         [0051]     The system  100  may further comprise a hyper expansion port  174 . A hyper expansion port  174  is a port that allows fluid to escape a combustion chamber during a time when a normal engine cycle would begin to compress air. An engine operating in a hyper expansion mode pulls work from combusted fluid until the fluid is down to a pressure at or near ambient air pressure. This allows the engine to derive a little more work out of the combustion event rather than just venting high pressure gas. A conventional engine cannot operate in a hyper expansion mode because of limitations in piston crank angles where power can be effectively applied to the crankshaft, and because hyper expansion reduces the power density of the engine. A rotary engine can be configured to derive work from the piston at any time, and naturally has a high power density, so hyper expansion can be performed in a rotary engine.  
         [0052]     The ECM  5  may be configured to manipulate the hyper expansion port  174  in response to the ambient air pressure sensor  15  such that a constant fluid mass remains in a combustion chamber within the housing  22  at the end of a fluid intake operating phase through a wide range of ambient operating pressures. The ECM  5  may thereby operate the system  100  as a rotary combustion engine with relatively constant power available at high altitudes. For example, the system  100  may comprise a rotary engine on an aircraft, allowing the engine to have about the same power available at flying altitudes as at sea level.  
         [0053]     The ECM  5  may be configured in one embodiment to manipulate an intake port  66 , an exhaust port  74 , and a combustion initiation device  62 . The combustion initiation device  62  may comprise a fuel injector, a spark initiator, or both. Additionally, there may be multiple combustion initiation devices  62  at various points on the housing  22 . For example, there may be a fuel injector  62  configured to inject fuel during an air intake event, and there may be a spark initiator  62  configured to initiate combustion at a desired time in the operation cycle of an engine. In another example, there may be a fuel injector  62  configured to inject fuel at a desired time in the operation cycle of an engine where the fluid in the combustion chamber is hot enough to ignite the fuel directly.  
         [0054]     In one embodiment, the ECM  5  may be configured to operate the system  100  as a hyper-expansion engine, and to manipulate the intake port  66 , exhaust port  74 , and/or combustion initiation device  62  in a manner such that the engine can be started without an external starting mechanism. Even where the engine is not normally operated as a hyper-expansion engine, the ECM  5  can be further configured to manipulate the hyper-expansion port  174  to start without an external starting mechanism. This starting mechanism works in an engine capable of hyper-expansion because the forces generated in combusting the air in a cylinder at ambient pressure can overcome the slight compression performed during a hyper-expansion cycle.  
         [0055]      FIG. 1B  illustrates one embodiment of a system  101  comprising an energy conversion device  22   b / 28   b  in accordance with the present invention. The system  101  may further comprise a second energy conversion device  22   a / 28   a , and the first and second energy conversion devices  22   a / 28   a - 22   b / 28   b  may share a flywheel  140 . The system  101  may comprise a power conduit  132  which may be a main shaft  132  coupled to the flywheel  140 . Each energy conversion device  22   a / 28   a - 22   b / 28   b  may comprise at least one expansion-compression chamber configured to sequentially compress and expand.  
         [0056]     Each energy conversion device  22   a / 28   a - 22   b / 28   b  may be configured to receive a high energy fluid before an expansion phase of the expansion-compression chamber, to allow expansion of the high energy fluid and transfer power to the main shaft  132 , then to release the residual low energy fluid from the expansion-compression chamber. This is referred to herein as an Alpha cycle. An energy conversion device  22   a / 28   a - 22   b / 28   b  may intermittently take energy from the main shaft  132  during an Alpha cycle, for example to compress air before a fuel injection event, while the Alpha cycle nets a transfer of energy to the main shaft  132 .  
         [0057]     Each energy conversion device  22   a / 28   a - 22   b / 28   b  may be configured to receive a low energy fluid before a compression phase of the expansion-compression chamber, to compress the low energy fluid by taking power from the main shaft  132 , then to release the residual high energy fluid from the expansion-compression chamber. This is referred to herein as a Beta cycle.  
         [0058]     The high energy fluid may be compressed air, steam, or a fluid with high chemical potential energy like hydrogen, diesel fuel, or gasoline. The low energy fluid may be a fluid that has expended a portion of the stored chemical or thermal energy in the fluid. Therefore, the energy conversion device may be, without limitation, an internal combustion engine, a heat engine, a steam engine, a pneumatic motor, or the like. The energy conversion device may also operate as an air compressor or a fluid pump.  
         [0059]     In one embodiment, each energy conversion device  22   a / 28   a - 22   b / 28   b  operates on an Alpha cycle and contributes net energy to the power conduit  132 . In another embodiment, one energy conversion device  22   a / 28   a  operates on the Alpha cycle and contributes net energy to the power conduit  132 , while the other energy conversion device  22   b / 28   b  operates on the Beta cycle and receives net energy from the power conduit  132 .  
         [0060]      FIG. 2  is an exploded perspective view of an energy conversion device  10  in accordance with the present invention. The energy conversion device  10  may comprise a first piston A coupled to a first hub  14 , and a second piston B coupled to a second hub  14 . The piston A, counter-piston A′, and hub  14  may be a first power input  12   a , or a first piston assembly  12   a . Likewise, the piston B, counter-piston B′, and hub  14  may be a second power input  12   b , or a second piston assembly  12   b . For the sake of clarity, the piston and counter piston of piston assembly  12   a  shall be referred to as A and A′, respectively. The piston and counter piston of piston assembly  12   b  shall be referred to as B and B′, respectively.  
         [0061]     The energy conversion device  10  may further comprise a power conduit  132 , a gear case  28 , one or more combustion initiation devices  62 , an intake port  66 , and an exhaust port  74 . The energy conversion device  10  may further comprise a hyper expansion port  174  (not shown).  
         [0062]      FIG. 3  is a cutaway side view of a housing  22  and piston assemblies  12   a ,  12   b . The hub  14  may include a groove  20 , which together with a housing  22  forms a toroidal chamber, with a circular cross-section in one embodiment, within which the pistons A,A′,B,B′ move. Alternatively, the groove  20  and housing  22  may form chambers having other shapes, such as a toroid having a square, elliptical, or rectangular cross-section. As used herein, a toroidal chamber describes the chamber required to accommodate a piston of any shape rotating about the hub  14 . The housing  22  may have a cover  24  and a base  26 . The base  26  may secure to a gear box  28  housing gears controlling the movement of the piston assemblies  12   a , 12   b . A cover  24  may secure to the base  26  by means of bolts or other securement means. In some embodiments, the base  26  may be integrally or monolithically formed with the gear case  28 , or a portion of the gear case  28 .  
         [0063]     Piston assembly  12   a  may secure to a shaft  30  extending into the gear box  28 . Piston assembly  12   b  may secure to a shaft  118 . In some embodiments, the shaft  30  is hollow and the shaft  118  extends therethrough. In others, the shaft  118  is hollow and the shaft  30  extends therethrough. In some embodiments, both shafts  30 ,  118  are hollow and a power output shaft  132  may extend therethrough in order to exchange power with the energy conversion device  10 .  
         [0064]      FIG. 4A  illustrates a side view of opposing pistons A,B and a resulting combustion chamber  54 . Each piston A, A′, B, B′ may include two faces  40 ,  42  separatedby an angle  44 . The angle  44  may be chosen to maximize the compression ratio of the engine  10  while providing a sufficiently strong base  46 . A key  48  may be formed monolithically with the piston A, A′, B, B′ and fit into a corresponding slot in the hub  14 . A set screw or like fastener may retain the key  48  within the hub  14 . Alternatively, a piston A, A′, B, B′ may be fastened integrally or monolithically to the hub  14 .  
         [0065]     Referring to  FIG. 4B , in some embodiments, the faces  40 , 42  have scallops  50  formed thereon in order to improve characteristics of the combustion chamber. In a combustion chamber, the air-fuel mixture near the walls of the chamber is cooler than the air in the center of the chamber. Accordingly, the fuel near the walls of the chamber may not fully combust, causing efficiency loss and increased pollution. Further, heat transfer from the walls to the environment reduces the efficiency of combustion. To minimize this effect, the surface area to volume ratio must be reduced. The shape having the largest surface area to volume ratio is the sphere. By forming scallops  50  in the faces  40 , 42  of the pistons A,A′,B,B′, a combustion chamber approaching spherical is produced. Compare the combustion chamber  54  in  FIG. 4A  formed by flat piston faces  40 , 42  with the combustion chamber  56 . Note that any degree of scalloping improves the shape of the combustion chamber, and scalloping as used here is intended to cover any incremental changes beyond a flat piston face.  
         [0066]     Scalloping the pistons A,A′,B,B′ may also enable the angle  44  and base  46  of the piston A,A′,B,B′ to be made larger. Where the faces  40 , 42  are flat, the separation between the faces  40 , 42  must be sufficiently large to define a suitable combustion chamber during the combustion stroke. However, where the faces  40 , 42  are scalloped the angular separation between the pistons A,A′,B,B′ can be made smaller. Accordingly, the angle  44  and base  46  of the pistons A,A′,B,B′ may be made larger ratio while still creating a combustion chamber having the correct volume.  
         [0067]      FIG. 5A  is a schematic illustration of four combustion chambers  60 ,  72 ,  68 ,  70  formed within a toroidal chamber in accordance with the present invention. In the example, the chamber  72  has just experienced combustion and is ready to exhaust, chamber  68  has just exhausted and is ready to intake fresh air, chamber  70  is just completing the intake cycle and is ready to compress the air, and chamber  60  has just compressed air and is ready for the combustion cycle. Pistons A, A′ are counter pistons, and are physically attached to the same hub  14  of piston assembly  12   a . Likewise, Pistons B,B′ are counter pistons and are physically attached to the same hub  14  of piston assembly  12   b.    
         [0068]      FIG. 5B  is a schematic illustration of four combustion chambers  60 ,  73 ,  68 ,  70  formed within a toroidal chamber in accordance with the present invention. In the example, the pistons A,A′,B,B′ have scalloped faces  50 , and the combustion chambers are in approximately the same relative positions as those in  FIG. 5A .  
         [0069]      FIGS. 6A-6C  illustrate one possible series of motions of the pistons A, A′, B, B′ accomplishing a four-stroke combustion process. Referring to  FIG. 6A , the combustion stroke begins with piston assemblies  12   a ,  12   b  positioned as shown. Volume  60  typically contains compressed air. In some embodiments, fuel may be injected through combustion initiation device  62  as part of a diesel cycle or fuel injected four stroke cycle. Alternatively, a fuel air mixture may be taken in during the intake stroke discussed below, and the use of combustion initiation device  62  as a fuel injector may be unnecessary.  
         [0070]     As the pistons reach the positions illustrated in  6 A, combustion initiation device  62 , for example a spark plug, may fire causing the fuel and air in the volume  60  to explode, driving piston B away from piston A. Driving piston B away from piston A simultaneously powers an intake stroke inasmuch as it causes piston B′ to rotate toward piston A, thereby drawing air, or a fuel air mixture, through the intake port  66  into volume  68 . The rotation of piston B′ toward piston A also powers a compression stroke as the air, or fuel-air mixture, in volume  70  is compressed. An exhaust stroke likewise occurs simultaneously, as piston B is toward piston A′, expelling combustion gases from volume  72  through the exhaust port  74 .  
         [0071]     Referring to  FIG. 6B , as piston B′ approaches piston A, piston A slows and piston B′ begins to accelerate. For a few degrees of rotation piston assemblies  12   a  and  12   b  may move at the same velocity. As the piston assemblies  12   a  and  12   b  approach the positions illustrated in  6 C, the air in volume  70  is ignited and the cycle is repeated.  
         [0072]     The engine  10  may be used to perform other processes such as the diesel cycle, compressing gas, or serving as a pneumatic motor. For example, in order to perform the diesel cycle, diesel fuel may be injected into volume  60  at the end of the compression stroke through a combustion initiation device  62  comprising a fuel injector. In order to function as an air compressor, a port may be added such that at the point where ignition occurs in the four-stroke cycle, the air is released into a holding tank. In order to achieve a pneumatic motor, a port may be added such that at the point where combustion occurs in the four-stroke cycle, compressed gas is allowed to enter the chamber and drive the piston.  
         [0073]      FIG. 7  illustrates the angular regions corresponding to each part of one embodiment of the four-stroke cycle. The angular regions may be described as a dwell region  80 , a combustion/exhaust region  82 , a second dwell region  84 , and an intake/compression region  86 . The dwell portion  80 ,  84  corresponds to the portion of the cycle where the piston assemblies  12   a ,  12   b  move in unison, typically at constant velocity. The dwell portion of the cycle may serve to position the piston assemblies  12   a ,  12   b  in preparation for the next cycle. In some embodiments, the dwell portions  80 ,  84  may also enable a “burn dwell” in which the fuel is ignited near the beginning of the dwell portion  80 , thereby causing a constant volume combustion event as the piston assemblies  12   a ,  12   b  move through the dwell region  80 ,  84 .  
         [0074]     Referring to  FIG. 8 , a pressure-volume (PV) plot of the four-stroke cycle illustrates the improved thermodynamic efficiency resulting from a burn dwell. Those of skill in the art will recognize that the area of the PV plot circumnavigated by the engine  10  during a combustion event correlates to the amount of work extracted from the combustion event. Plot area  90  represents the combustion cycle of a conventional four-stroke engine. Plot  92  represents the PV trajectory for an engine performing a constant volume burn dwell combustion event. The plot area  94  represents the opportunity for additional work recovery from an engine utilizing a burn dwell. A particular embodiment of an engine  10  using a burn dwell may utilize some or all of the plot area  94  depending upon the maximum allowable pressures, combustion rates, heat losses to the environment, and other variables understood by one of skill in the art.  
         [0075]     Additional efficiency gains may be captured by using hyper-expansion (expansion of combustion gases to a volume larger than that of the intake air). Plot area  96  represents the potential additional work that can be captured by allowing the combustion gases to expand to atmospheric pressure. During the combustion process, the amount of gas in the combustion chamber increases. The air and gasoline that went into the combustion cycle is converted into a much larger amount of inert gases, left over oxygen, and combustion byproducts such as CO 2 . Combustion gases also have increased pressure due to their higher temperature as a result of combustion. Accordingly, in order for the combustion gases to expand until they reach atmospheric pressure, the combustion chamber must expand to a volume significantly larger than the volume of the air going into the combustion process. In a conventional engine, because the cylinder has a fixed size, combustion gases cannot expand further and perform more useful work. Accordingly, exhaust gases are simply released and the potential work is wasted.  
         [0076]     Referring to  FIG. 9 , in one embodiment of an engine  10  hyper-expansion is made possible by decreasing the volume of air taken in during the intake stroke. A hyper-expansion port  174  is provided such that as a piston moves through the compression stroke, air is allowed to escape through the hyper-expansion port  174 . The released air may be vented to the exhaust to assist in pumping exhaust air out. Once the piston moves across the port  174 , captured air is compressed for the remaining portion  102  of the compression stroke. In this manner, the volume of combustion gases is also reduced and achieves a lower pressure at the end of the combustion stroke.  
         [0077]     The hyper-expansion port  174  need not be a separate port and could be shared with the intake port  66 . For example, hyper-expansion can be achieved by the ECM  5  modulating the intake port  66  to achieve the same effect by closing the intake port  66  before the intake cycle would otherwise be complete. All of these variations of the hyper expansion cycle are considered within the scope of the present invention.  
         [0078]     Although hyper expansion improves efficiency, it also reduces power output. The compression ratio of the engine is effectively reduced due to the decrease in the volume of air compressed during the compression stroke. Accordingly, in some embodiments, the hyper-expansion port  174  may be opened and closed according to the power demanded at a given moment. For example, in an automobile, when moving at constant velocity the port  174  may be opened to increase engine efficiency. When the automobile is accelerating, the port  174  may be closed to increase power.  
         [0079]     In aeronautical applications, for example, the port  174  may be opened or closed to compensate for the decrease in pressure of intake air with increasing altitude. For example, when an aircraft flies in the rarified air of the upper atmosphere, the port  174  may be closed to increase the amount of intake air. At lower altitudes, the port  174  may be opened inasmuch as the air pressure is greater.  
         [0080]     In some embodiments, a pressure sensor may control opening and closing of the port  174  such that a constant, or near constant compression ratio is achieved. For example, a pressure sensor in the toroidal chamber may detect that the compression ratio is lower than some value and close the port  174 . Alternatively, a port  174  may be manually operated, such that when the driver of a vehicle needs more power the port  174  can be closed. Similarly, an ambient air pressure sensor, mass air flow sensor, and other methods of determining the air mass in the cylinder can be used to control the hyper-expansion port  174 .  
         [0081]     Referring to  FIG. 10 , a gear case  28  may contain a differential  116   a - 116   d  and a locking device. The differential  116   a - 116   d  may be configured to allow the power inputs  12   a ,  12   b  to rotate at variable rates. The differential  116   a - 116   d  shown in  FIG. 10  comprises an exploded planetary gear set  116   a - 116   d.    
         [0082]     The locking device may be configured to control the relative velocity and position of the power inputs  12   a , 12   b . The locking device may comprise a plurality of followers  142   a ,  142   b , where each follower corresponds to one of the power inputs  12   a , 12   b . The locking device may further comprise a cam  136  configured to guide each of the plurality of followers  142   a ,  142   b . The followers  142   a ,  142   b  shown in  FIG. 10  comprise cam followers coupled to a follower shaft  122   a ,  122   b . The cam  136  may be a groove defining a closed path. The cam  136  may be a groove in the flywheel  140 , wherein the position of the groove in the flywheel  140  fixes the corresponding positions of the follower arm  122   a ,  122   b , follower coupling gear  126 ,  146 , piston driving gear  128 ,  148 , and therefore the piston  12   a ,  12   b.    
         [0083]     Power inputs  12   a ,  12   b  in  FIG. 10  rotate within the toroidal chamber  23  as shown. Power inputs  12   a , 12   b  will not be at 180 degrees apart in an engine  10  with 4 pistons A,A′,B,B′ because the counter pistons are at 180 degrees. However,  12   a , 12   b  are shown at 180 degress in  FIG. 10  for clarity.  
         [0084]     The power input  12   a  operates in the example as follows. Power input  12   a  is coupled  30  to the piston driving gear  128  and differential gear  116   d . The coupler  30  may comprise a hollow shaft  30  such that power input  12   a  directly drives the gears  128 ,  116   d , and allows the main shaft  132  to pass therethrough. When power input  12   a  provides power and power input  12   b  is locked by the cam  136 , power input  12   a  turns the differential gear  116   b , causing a ring gear  114  to rotate as the differential gear  116   a  is in one embodiment locked. The ring gear  114  may be configured to transfer power to the main shaft  132  through a jack shaft  115  and drive gear  130 . The piston driving gear  128  turns the follower coupling gear  126 , causing the follower arm  144   a  to rotate about the follower shaft  122   a , whereupon the cam follower  142   a  may roll unconstrained in the cam groove  136 . During a designed burn dwell, the cam groove  136  constrains the cam follower  142   a  to reduce the relative expansion rate of the combustion chamber  72 , or to hold the combustion chamber  72  volume constant. Note that during a burn dwell, the cam  36  may be configured to move the power input  12   b  at a speed up to the same speed as the power input  12   a.    
         [0085]     Note that the jack shaft  115  is given by way of example of a power transfer mechanism from the differential  116   a - 116   d  to the main shaft  132 . In another example, a pinion shaft may be placed between the differential gears  116   c - 116   d , and coupled to the main shaft  32  such that when the exploded planetary gears rotate about the main shaft  32  power is supplied to the main shaft. Without limitation this method is also considered within the scope of the present invention.  
         [0086]     The power input  12   b  operates in the example as follows. Power input  12   b  is coupled  118  to the piston driving gear  148  and differential gear  116   a . The coupler  118  may comprise a hollow shaft  118  such that power input  12   b  directly drives the gears  148 ,  116   a , and allows the main shaft  132  to pass therethrough. When power input  12   b  provides power and power input  12   a  may be locked by the cam  136 , power input  12   b  turns the differential gear  116   a , causing the ring gear  114  to rotate as the differential gear  116   b  may be locked. Ring gear  114  may be configured to transfer power to the main shaft  132  through a jack shaft  115  and drive gear  130 . The piston driving gear  148  will turn the follower coupling gear  146 , causing the follower arm  144   b  to rotate about the follower shaft  122   b , whereupon the cam follower  142   b  may roll unconstrained in the cam groove  136 . During a designed burn dwell, the cam groove  136  will constrain the cam follower  142   b  to reduce the relative expansion rate of the combustion chamber  60 , or to hold the combustion chamber  60  volume constant. Note that during a burn dwell, the cam  36  may be configured to move the power input  12   a  at a speed up to the same speed as the power input  12   b.    
         [0087]     A flywheel  140  may also have a geared starter ring  150  secured thereto, or monolithically formed therewith, for engaging a starter motor or the like. In some embodiments, magnets may mount to the flywheel  140  and serve as the rotator of an alternator. In some embodiments, magnets may be configures such that the flywheel  140  also serves as the armature of a motor used to start the engine  10 , in which case a separate starter motor would be unnecessary. A flywheel  140  may also have vanes thereon and serve to cool the engine  10 .  
         [0088]     Referring to  FIG. 11 , in some embodiments, the differential may be embodied as an epicyclic planetary gear set  194 ,  182 .  
         [0089]     The embodiment shown in  FIG. 11  functions as follows. When the power input A is providing power, power input A is coupled  30  to rim gear  214  and sun gear  180 . While cam follower  142   b  is locked, the linking gear  202  is locked, and therefore rim gear  190  is locked, preventing the carrier  191  from rotating and allowing planetary gears  182  to orbit sun gear  180 . Therefore, planetary gears  182  must rotate in place, forcing ring gear  186  to rotate, which is coupled to the flywheel  140  and the main shaft  132 . Rim gear  214  drives stationary gear  212  which drives follower gear  210 . The follower arm  122   a  therefore turns causing the follower  144   a  to rotate freely in the cam  136  except during a burn dwell as described above under  FIG. 10 .  
         [0090]     When the power input B is providing power, power input B is coupled  118  to sun gear  192  which drives planetary gears  194 , rim gear  196 , ring gear  198  and therefore follower gear  200 . The linking gear  202  is unlocked, therefore the rim gear  190  rotates causing the carrier  191  to rotate. While cam follower  142   a  is locked, follower gear  210 , stationary gear  202 , and rim gear  214  are likewise locked. Therefore, sun gear  180  is locked, and the rotating carrier  191  drives the planetary gears  182 , ring gear  186 , and therefore the flywheel  140 . The follower arm  122   b  turns and causes the follower  142   b  to rotate freely in the cam  136  except during a burn dwell as described above under  FIG. 10 .  
         [0091]     Some embodiments of the engine  10  may have multiple stages. That is to say, multiple toroidal chambers, each with a corresponding piston assemblies  12   a , 12   b , differential, guides  136 , and followers  134   a ,  134   b , may drive a single output shaft  132 . In some embodiments, a second guide  220  may be formed in a face of the flywheel  140  opposite the first guide  136 . In such an embodiment, the differential, followers  134   a ,  134   b , and piston assemblies  12   a ,  12   b  of the second stage may simply be a mirror image of the first stage positioned next to the second guide  220 . The second guide  220  may be a mirror image of the first guide  136 . In one embodiment, the second guide  220  is rotated 45 degrees about the output shaft  132 . In the some embodiments of the engine  10 , a combustion stroke will occur in the toroidal chamber once for every 90 degree rotation of the flywheel  140 . Accordingly, shifting the guide  220  of the second stage 45 degrees ensures that a combustion stroke will occur for every 45 degree rotation of the flywheel, resulting in a more constant output torque and reduced vibration.  
         [0092]     In some embodiments, the engine  10  may have a first stage operating on an Alpha cycle, connected to a first guide  136 , and a second stage operating on a Beta cycle, connected to a second guide  220 . In such a configuration, the first stage of the engine  10  provides power, and the second stage of the engine  10  performs work—for example by compressing air.  
         [0093]      FIG. 12  is a schematic illustration of a carrier  191  and epicyclic planetary gear  182 , in accordance with the present invention to clarify aspects of the embodiment of  FIG. 11 . When piston A powers, piston A is coupled  30  to a sun gear  180 . The carrier  191  is locked when piston B is locked, and therefore the planetary gears  182  rotate in place, and force the ring gear  186  to rotate in the opposite direction of the sun gear  180 .  
         [0094]     When piston B powers, piston B rotates the carrier  191  (see  FIG. 11  description). When piston A is locked, the sun gear  180  is locked, and the planetary gears  182  revolve around the sun gear  180  with the carrier  191 . Therefore, the ring gear  186  rotates in the same direction as the carrier  191 .  
         [0095]     The ring, planetary, and sun gears are related as shown in Equation 1. As used below, Ω s , Ω r , and Ω c  represent the rotation speeds of the sun, ring, and carrier, while r s , r r , and r c  are the radii of the sun, ring, and carrier gears. It is understood that use of the radius works when the gear teeth are configured to provide similar linear displacements with each tooth engagement, but that gear tooth ratios could be used if desired. 
 
Ω s   r   s =Ω r   r   r ±2Ω c   r   c   Equation 1. 
 
         [0096]      FIG. 13  illustrates a plot of the angular velocity of the piston assemblies  12   a ,  12   b  versus angular position. Plots  290   a - 290   c  represent various possible velocity profiles for the first 180 degrees of rotation of piston assembly  12   a . Plots  292   a - 292   c  represent various possible velocity profiles for piston assembly  12   b . Plots  292   a - 292   c  also reflect possible velocity profile of piston assembly  12   a  during the second 180 degrees of its rotation, just as plots  290   a - 290   c  also represents possible velocity profiles for piston assembly  12   b  during the second 180 degrees of its rotation. A velocity profile may be generated by the considerations of the mechanical parts of an embodiment, as well as the desired combustion characteristics.  
         [0097]     The plots  290   a - 290   c  and plots  292   a - 292   c  illustrate velocity profiles utilizing a continuous function and having pseudo-dwells of differing duration. The flat area where both  12   a ,  12   b  have nearly identical velocities represent the pseudo-dwell location. In some embodiments, Equations 2 and 3 may be utilized to develop a velocity profile. 
 
Ω b (relative)=( PMRR *(1+( ABS (Cos( Dx )))ˆ K )/2)  Equation 2. 
 
Ω a (relative)=( PMRR−Ω   b )  Equation 3. 
 
         [0098]     In the equations, Ω represents the relative angular velocity of  12   a  or  12   b , Dx represents the current angular displacement of the power input  12   a  or  12   b , and PMRR is the piston to main rotation ratio, or the number of times a piston A,B,A′,B′ completes a revolution per turn of the flywheel  140 . K represents an arbitrary value, where values of K at 1 or below do not have a dwell time, and values of K above 1 have a pseudo-dwell. The velocity profiles of Equation 2 and 3 only produce a pseudo-dwell because they do not literally bring the power inputs  12   a ,  12   b  to identical speeds. However, with a K value of 2, and PMRR=2 (curve  292   c ), the velocities of  12   a ,  12   b  are within about 1% of each other from 85 to 95 degrees, and within about 6% of each other from 80 to 100 degrees.  
         [0099]     Any substantially constant velocity between opposing pistons will create a burn-dwell and derive some of the Plot area  94  work (see  FIG. 8 ) from the combustion cycle, and will therefore suffice for the purposes of the invention. Substantially constant velocity will vary with the application, but at least values where the pistons have a velocity within 10% of each other should be considered substantially constant, but also any value that makes the Plot area  94  efficiency valuable compared to the cost of higher combustion pressures should also be considered a valuable burn-dwell and therefore would be a substantially constant velocity. A true dwell can be imposed, of course, but it would require a discontinuity in the velocity profiles which may introduce clatter, backlash, and wear in the physical gearing mechanisms and wear on the physical systems. K can be selected arbitrarily high to approach arbitrarily close to a true dwell.  
         [0100]     As discussed hereinabove, dwells are portions of the cycle in which both piston assemblies  12   a ,  12   b  move in unison in order to enable constant volume combustion of the fuel air mixture. The plots  290   a - 290   c  are identical to the plots  292   a - 292   c  shifted 180 degrees.  
         [0101]     Referring to plots  290   a - 290   c , at zero degrees piston  12   a  may begin at zero velocity, serving to define a combustion chamber as piston  12   b  moves at its maximum velocity during the combustion process, as shown in plots  292   a - 292   c . As piston assembly  12   b  decelerates from its maximum velocity at zero degrees to the dwell velocity at approximately 90 degrees, as shown in plots  292   a - 292   c , piston assembly  12   a  accelerates to the dwell velocity, as shown in plots  290   a - 290   c , such that at 90 degrees both piston assemblies  12   a ,  12   b  have the same velocity. For configurations having a dwell, the piston assemblies  12   a ,  12   b  will have substantially the same velocity from slightly before 90 degrees until slightly after as illustrated in plots  290   c ,  292   c.    
         [0102]     At the point where the piston assemblies achieve the same velocity, the fuel air mixture has been compressed and is prepared for ignition. Accordingly, at, or slightly after 90 degrees the fuel air mixture is ignited and piston  12   a  begins to accelerate as it moves toward the 180 degree position where it achieves its maximum velocity, as shown in plots  290   a - 290   c . Piston  12   b , on the other hand, at or slightly after 90 degrees, begins to decelerate until it reaches zero velocity at 180 degrees. At this point, the cycle repeats, except plots  290   a - 290   c  represent the velocity profile of piston  12   b  and plots  292   a - 292   c  represent the velocity profile of piston  12   a.    
         [0103]     Referring to  FIG. 14 , a guide  136  may be embodied as a cam  136 , such as a groove  136 , or raised rail  136 . The cam profile  300  may be chosen to cause the piston assemblies  12   a ,  12   b  to have the velocity profile of  FIG. 13 . As discussed in conjunction with  FIGS. 10-11 , followers  134   a ,  134   b  may be embodied as rollers  142   a ,  142   b  attached to arms  144   a ,  144   b , which drive follower shafts  122   a ,  122   b . As the flywheel  140  is rotated, the cam  136  causes the followers  134   a ,  134   b  to rotate. Due to the coupling between the followers  134   a ,  134   b  and the piston assemblies  12   a ,  12   b , as discussed in conjunction with  FIGS. 10-11 , the rotation of the followers  134   a ,  134   b  causes corresponding rotation of the pistons  12   a ,  12   b.    
         [0104]     The various portions of the cam  136  may be described as dwell portions  302 , in which the pistons  12   a ,  12   b  are made to move in unison at nearly constant velocity, and stroke portions  304 , in which the piston assembly  12   a ,  12   b  move accelerate and decelerate at different rates. The cam profile may be derived mathematically or numerically from the velocity profile described in  FIG. 11  by tracing back through the gearing to determine what positions and angular velocities of the followers  134   a ,  134   b  correspond to the desired positions and angular velocities of the piston assemblies  12   a ,  12   b.    
         [0105]     Referring to  FIG. 15 , in some embodiments, the flywheel may experience one complete revolution for every two revolutions of the piston assemblies  12   a ,  12   b . Accordingly, the cam profile may have two lobes  310   a ,  310   b , with each lobe controlling the piston assemblies  12   a ,  12   b  through an entire revolution thereof. A cam profile with two lobes provides the benefit that the flywheel  140  is more closely balanced than a cam profile with a single eccentric lobe such as the one in  FIG. 14 .  
         [0106]     Referring to  FIG. 16 , the cam  136  and followers  134   a ,  134   b  may have any configuration known in the art of machine design. In one embodiment, the followers  134   a ,  134   b  are embodied as rollers  142   a ,  142   b  rotatably secured to the follower arms  144   a ,  144   b . Alternatively, a cam  136  may be embodied as a rail  320  and the followers  134   a ,  134   b  may be embodied as two rollers  322   a , 322   b  rotatably mounted to an arm  324 . The arm  324  may be rotatably mounted to the follower arms  144   a ,  144   b.    
         [0107]     In some embodiments, the rollers  322  may mount to slider blocks  326   a ,  326   b  slidably mounted to the arm  324 . Biasing members  328   a , 328   b  may urge the rollers  322  into engagement with the rail  320 . In the illustrated embodiment, the biasing members  328   a , 328   b  are Bellville springs situated to push the slider blocks  326   a , 326   b  toward one another. Biasing the rollers  322   a , 322   b  toward the cam may ensure firm contact between the rollers  322   a , 322   b  and the rail  320  thereby reducing clatter and backlash.  
         [0108]     Referring to  FIG. 17 , a guide  136  may be embodied as a groove  330 . In some embodiments, the groove  330  may have a wide portion  332  and a narrow portion  334 . In such embodiments, a roller  142   a ,  142   b  may be substituted with a large roller  336  and a smaller roller  338  corresponding to the wide portion  332  and narrow portion  334  of the groove  330 , respectively. The wide portion  332  and narrow portion  334  of the groove  330  may be offset from one another such that opposite sides of the rollers  336 ,  338  are kept in contact with the walls of the groove  330 . In some embodiments, the shaft  340  to which the rollers  336 ,  338  secure may be compliant, biasing the rollers  336 ,  338  toward contact with opposite walls of the groove  330  in order to reduce clatter and backlash.  
         [0109]     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.