Abstract:
A motor, expander, compressor, or hydraulic device is formed with an oscillating rotating piston comprising a cylinder having an axis of rotation and end surfaces and defining an oscillating compression volume and an expansion volume. An axial sealing member separates the compression volume and the expansion volume, and seal members seal the end surfaces of the piston. Valves operate to close the compression volume and open the expansion volume at each oscillation of the piston. Means are provided for reversing the rotation of the cylinder at the end of a compression cycle of the piston. One or more pistons may be provided that contact other pistons along axial surfaces to form axial seal surfaces with rolling contacts that reduce friction energy losses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60,168,479, entitled “Apparatus Using Oscillating Rotating Piston,” filed on Dec. 1, 1999, and the specification thereof is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to piston operated devices, and, more particularly, to motors, expanders, compressors, and hydraulics having rotating cylinders. 
     2. Background Art 
     The world is running on internal combustion engines. For over a century, internal combustion gasoline and diesel engines, turbines, and Stirling engines have been used. More recently the Wankel engine was developed. 
     The response time of turbines and Stirling engines is too slow for automobile use. Wankel engines have fallen out of favor. Gasoline and diesel motors have been the mainstays of the auto industry in spite of low efficiency. Considering the combustion temperatures in these motors, the theoretical efficiency (Carnot efficiency) should be above 70%. Typically the efficiency of today&#39;s automobile motors is 25%. One of the chief reasons for the low efficiency is the high-energy losses due to sliding friction of the pistons against cylinder walls. This loss is turned into heat and carried away by the cooling water around the engine block. 
     Piston engines have been functioning since the early days of steam powered devices. Standard internal combustion engines are everywhere. Variations of the internal combustion engine are the Wankel motor and rotary piston engine such as that described in U.S. Pat. Nos. 3,741,694. 5,813,372 describes a rotary piston engine in which internal friction is reduced since the pistons do not touch the cylinder walls. Only piston rings touch the walls. The cylinders and pistons rotate around an axis and rely on a sliding valve arrangement to open ports for intake and exhaust. The difficulty with this device is that the large sliding surfaces of the head past the valve ports supply a large amount of friction. 
     U.S. Pat. No. 5,803,041 describes a rotary engine in which linear piston motion is translated into rotary motion of the cylinder. 
     U.S. Pat. No. 5,138,994 describes a rotary piston engine in which a rectangular piston rotates in an annular cavity. As the piston rotates continuously in one direction, a gate that blocks the annular cavity opens once during each revolution of the piston to allow the piston to pass. The piston is connected to a central shaft by a disk that penetrates the inner cylindrical wall of the cavity. The problem with this device is that large sliding friction forces occur all the way around the rotary piston as it rubs against cylinder walls. Additional friction occurs where the disk penetrates the cylindrical wall. 
     U.S. Pat. No. 4,938,668 shows a rotating piston design in which two sets of rotating pistons oscillate together and apart forming cavities that change in volume as the two sets of pistons rotate around a common shaft. A cam system provides the thrust that drives the shaft. The pistons slide against an end plate in which are located intake and exhaust ports. This device would also have large sliding friction as the rotating pistons rub against the outer cylinder and against the end plates where the ports are located. 
     U.S. Pat. No. 4,002,033 is a rotary displacer that has a rotary-abutment sealing rotor that rotates against the main rotary piston. However, there is a slight space between the sealing rotor and the rotary piston, since the surface speeds are different. They both rotate at the same angular velocity, but since their diameters are different, the abutting surface velocities are different. The rotary piston does not touch the walls of the cylinder to eliminate sliding friction. This allows for excessive blow-by. To reduce the blow-by, grooves are formed in the piston walls to create turbulence in the gas flow. Blow-by is still a problem with this design. 
     U.S. Pat. No. 4,099,448 shows, rotating vanes that have rotating gears about the axes that keep the vanes synchronous. Sliding friction is prominent in this design, since the outer tips of the vanes have seals that slide on the cylinder walls. 
     U.S. Pat. No. 3,282,513 describes an engine that has rotating vanes that have sliding seals at the end of the vanes, which slide on cylinder walls. Lubricating oil must be supplied to the seals from the central rotating shafts. This device has some features in common with our single cylinder engine, but our single-cylinder engine has the seals mounted in the wall of the cylinder rather than in the rotating piston, and lubricating oil can be supplied from outside the cylinder rather than through the shaft and piston. 
     U.S. Pat. No. 2,359,819 is a pump that has sliding seals at cylinder walls. Similarly, U.S. Pat. Nos. 5,228,414, 3,315,648, 3,181,513, 2,989,040, 2,786,455, 1,010,583, and 526,127 describe designs that have rotating members that have seals that slide on cylinder walls. 
     Since oil supplies are being depleted and the atmosphere is being polluted with greenhouse gases, it is long past time for today&#39;s gasoline engines to be replaced by a more efficient power plant. In accordance with the present invention, which is called “MECH”, (acronym for motor, expander, compressor, or hydraulics) a new fluid displacement machine is provided that, with appropriate modifications, can function as an internal combustion engine, an expander (analogous to a turbine), a compressor, a hydraulic motor, or a pump. MECH incorporates rolling friction rather than sliding friction. 
     Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention is a motor, expander, compressor, or hydraulic device having in one embodiment an oscillating rotating piston comprising a partial-cylindrical piston having an axis of rotation and end surfaces and defining an oscillating compression volume and expansion volume. An axial sealing member separates the compression volume and the expansion volume and radial seal members seal the end surfaces of the piston. Valves operate to close the compression volume and open the expansion volume at each oscillation of the piston. Means are provided for reversing the rotation of the piston at the end of each cycle of the piston. In advanced embodiments, one or more pistons may be provided that contact other pistons along axial surfaces to form axial seal surfaces with rolling contacts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is a radial cross-sectional view of a four-cycle engine according to one embodiment of the present invention. 
     FIG. 2 is an end view of one embodiment of the invention, showing a crank for converting oscillating motion to continuous rotary motion. 
     FIG. 3 is a radial cross-sectional view of a two-cycle engine according to another embodiment of the present invention. 
     FIG. 4 is a radial cross-sectional view of an expander according to one embodiment of the present invention. 
     FIG. 5 is an enlarged view of and more particularly depicts an exhaust valve arrangement for the expander shown in FIG.  4 . 
     FIG. 6 is a radial cross-sectional view of a compressor according to another embodiment of the present invention. 
     FIG. 7 is a radial cross-sectional view of a single rotary piston for use in various applications of the present invention. 
     FIG. 8 is radial cross-sectional view of a crank design for a four-piston configuration of the present invention. 
     FIG. 9 is a radial cross-section view of a four-piston configuration of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As used herein, the term “MECH” means a motor, expander, compressor, or hydraulics, including two-cycle and four-cycle gasoline and diesel engines. The present invention provides internal friction losses that are much less than those of standard engines. Thus, operating efficiencies and fuel economy are significantly better. 
     For the same volume of engine, the inventive MECH has four times the displacement of an ordinary gasoline motor, which translates to four times the power. But since MECH has less friction loss, it is projected that a MECH engine would have five times the power of the same size gasoline motor. Or conversely, a MECH engine would weigh about one-fifth the weight of a gasoline engine for the same power. 
     A MECH engine can be used as the power plant of a car or truck, or it can be used as the power source in a hybrid automobile. MECH engines can also be manufactured for lawn mowers, motorcycles, electric power generators. Their lightweight would make them attractive for chain saws and other handheld power equipment. Large MECH diesel or gasoline engines can used in electric power plants. Home or business self-generation units can be constructed using small MECH engines. 
     It is known that rolling friction is much less than sliding friction. Pistons sliding in cylinders have high friction losses. In the present invention, rolling friction is involved when two rotating pistons roll together, rather than slide along their longitudinal axes. Most people associate the word “piston” with a cylindrical object that slides axially in a cylinder. In the present description, a “rotating piston” is defined to be a partial cylinder that oscillates in a rotating manner about an axis. It does not translate axially. The rotating piston actually rotates within the cylinder in contrast to a “rotary piston” (described in some prior art) in which the piston and cylinder rotate about some external axis. “Cylinder” in this specification and claims is used in the general sense of a “piston chamber”, and may include chambers having other than a strictly cylindrical shape. 
     FIG. 1 shows the concept of a MECH four-cycle internal combustion engine. In engine block  1 , rotating pistons  2  and  3  rotate in an oscillating manner about shafts  6  and  7  in cylinders  4  and  5  and roll together at contact point  15  (actually a “contact line”). This rolling contact point forms an axial rolling seal that prevents gases from passing between the lower chambers  26 ,  27  and upper chambers  24 ,  25 . This rolling seal has much less friction than a sliding seal. Note that the pressure in upper chamber  24  is about the same as that in upper chamber  25 , and the pressure in lower chamber  26  is about the same as the pressure in lower chamber  27 , so that there would be little tendency for gas to flow through gap  22 . It is seen therefore, that the shafts  6 ,  7  are coaxial with the axes of the cylinders, and the pistons pivot eccentrically about an axis of rotation defined by, and essentially coaxial with, the shafts. 
     In this specification and in the claims, “eccentric” refers to a piston having its axis of rotation—or more specifically to this application, its pivotal axis—displaced from its center of gravity so that it is capable of imparting reciprocating motion. Ordinarily in the invention, a piston&#39;s pivotal axis is parallel to, but offset from, the piston&#39;s longitudinal axis running through its center of gravity. Thus, as a piston pivots “eccentrically,” the bulk of its mass is always offset from its pivotal axis, although the piston&#39;s center of gravity reciprocates along an arc concentric to the pivotal axis. 
     The rotating pistons shown in the FIG. 1 are hemi-cylindrical. That is, the angle drawn from one face to the other is 180 degrees. This angle can be varied to suit the application, and while 180 degrees is preferable for some applications the hemi-cylindrical shape shown in the figures is by way of example rather than limitation. The wedges  8  and  9  can also be varied in angle for different applications. Gap  22  between the rotating pistons  2 ,  3  and the cylinder walls should be large enough so that the rotating pistons do not rub the walls. The gap  22  should be large enough to prevent the quenching of combustion, which would lead to hydrocarbon emissions. 
     End plates (not shown in FIG. 1) cover the ends of the rotating pistons  2 ,  3  and are secured to the engine block  1 . Sliding friction occurs between the ends of the rotating pistons and the end plates, but this friction is relatively small since the rotating pistons  2 ,  3  can be very long compared to their diameter. For example, the cylinder diameter might be four inches, while the length might be two or three feet. Installing radial end seals  20  in grooves in the end plates can reduce this sliding friction further by eliminating the need to have the pistons tightly pressed against the end plates. These seals  20  are similar to piston rings in ordinary motors. End seals  20  are “U” shaped with the bottom ends abutted and the opposite ends pressed against the shafts  6  and  7 . Oil can be injected between the end seals. Springs (not shown) within the end plate grooves bias the seals  22  against the ends of the rotating pistons. 
     In operation, as rotating piston  3  rotates clockwise, piston  2  rotates counterclockwise, and the fuel-air mixtures in upper chambers  24  and  25  are compressed. When compression is complete, a spark plug (not shown) fires and ignites the fuel-air mixture. The explosive pressure reverses the direction of rotation of the rotating pistons  2 ,  3 . The counter-rotating pistons compress the fuel-air mixtures in lower chambers  26  and  27 . Ignition in chambers  26  and  27  then again reverses the direction of the rotating pistons  2 ,  3 . Valve rods  11 , actuated by cams (not shown) open upper valves  10  and allow exhaust gases to escape from upper chambers  24  and  25  through upper channels  12  and past upper valves  10 . (By “upper” and “lower” in this description, we mean the upper and lower parts of the drawing, not necessarily upper and lower parts of a physical machine). If a piston is very long, more than one intake and exhaust valve and spark plug may be advantageous; all embodiments of the invention functioning as an internal combustion engine may optionally feature more than one spark plug, more than one intake valve, and more than one exhaust valve per chamber. 
     During the next cycle, rods  14  open lower valves  13  to allow exhaust gases to escape from lower chambers  26  and  27  via lower channels  12 ′ while a new fuel-air mixture is drawn into upper chambers  24  and  25  through intake valves. These intake valves are located directly behind the exhaust valves  10  (further into the page) and are thus not shown. Similar intake valves are located behind lower valves  13 . The cycles repeat. 
     FIG. 2 shows end plate  50  and the mechanism that is located on the end plate. This end plate attaches to the end of the engine block  1  and abuts the ends of the rotating pistons  2 ,  3 . Shafts  6  and  7  from FIG. 1 extend through the end plate  50  and are attached to gearwheel  60  and gearwheel  61 . These gearwheels have gear teeth on their circumferences that mesh to maintain gearwheels in  60  and  61  in proper mutual orientation. The purpose of this gear meshing is to prevent slippage of the rotating pistons  2  and  3  as they roll together. The gears also transmit energy from gearwheel  60  to gearwheel  61  so that this energy can be transmitted to the crank rod  51 , which is pivotally attached to gearwheel  61  by shaft  52 . Crank rod  51  then drives flywheel  54  by pivoting shaft  53 . (The phantom lines of  53  and the end of the crank rod  51  mean that these parts are beneath the flywheel  54  from the viewer&#39;s perspective.) Crankshaft  55  is connected to flywheel  54  and carries power from the engine to the exterior. The crankshaft  55  exits through the engine housing (not shown) that is on the viewer&#39;s side of FIG.  2 . 
     The oil pump consists of a plunger  75  (a curved rod) and curved chamber  76 . Plunger  75  is attached to one of the gearwheels. As the gearwheel oscillates, plunger  75  plunges into chamber  76  and forces oil (which rests in the housing in which the gearwheels are located) to flow through the check valve  78 . The oil is piped to wherever it is needed. Check valve  77  allows oil to flow into chamber  76 . 
     The end plate on the opposite end of the engine block  1  may have a similar gear mechanism, but it is not required. That end plate provides bearings for shafts  6  and  7  and end seals  20 . The engine needs a starter, intake and exhaust manifold, ignition wiring, timing chain, valve cams, and other items common to gasoline or diesel motors. For clarity, these items are not added to the figures. Water flowing through channels in the engine block  1  can cool the engine. These channels are not shown. They can be added by those skilled in the art. 
     One of the important advantages of the MECH engine is that the cylinder walls and the rotating pistons can be very hot, since the rotating pistons do not touch the cylinder walls and no lubrication is required there. If the surfaces are very hot, less heat will be lost from the burning gases to the surfaces. This will provide greater fuel economy. In ordinary internal combustion engines, a large fraction of the fuel energy is lost to the cylinder walls and carried away by cooling water to the radiator. In MECH, the end plates will require cooling, since lubrication is applied there. Internal gaps in the walls can provide insulation between the hot cylinder walls and the end plates. Heat from the gases will be lost to the end plates, but if the cylinders are long compared to the diameter, this loss will be relatively small. 
     In FIG. 3, showing a two-cycle engine, fuel-air mixture is drawn through tubes  106  and  116  in engine block  100 , past reed valves  117  (or other type of check valve) into lower chambers  126  and  127  as rotating piston  102  rotates counterclockwise and rotating piston  103  rotates clockwise. Fuel-air mixtures in upper chambers  124  and  125  are compressed. At the completion of compression, spark plugs (not shown) fire, and the explosion forces the rotating pistons  102 ,  103  to reverse directions. Reed valves  117  close and the gases in lower chambers  126  and  127  are compressed. 
     When the rotating pistons approach the end of a cycle, they contact the ends of shafts  111  at points  122 , which are cutouts in the face of the pistons to provide near-normal contact. This forces valves  110  to open allowing exhaust gases from upper chambers  124  and  125  to exit through tubes  115 . Reduction of pressure in upper chambers  124  and  125  allows compressed gases in lower chambers  126  and  127  to pass through interior channels  120  through reed valves (or other types of check valves)  121  into upper chambers  124  and  125 . By having valves  121  at one end of the cylinders defined in the engine block  100  and exhaust valves  110  at the other end, the gas flowing in through  121  will tend to purge the exhaust gases and fill the upper chambers  124  and  125  with fresh fuel-air mixtures. Thus, the channels  120  and valves  121  preferably are located in the wedge  108  near the periphery of the cylinder (behind the exhaust valve  110  in the drawing), but for the sake of clarity of illustration, it is shown in the narrower part of the wedge  108  as though the channels  120  and valves  121  were at the same end of the cylinder. 
     When the rotating pistons  102 ,  103  again reverse direction, springs  112  cause valves  110  to close so that the trapped gases in upper chambers  124  and  125  will again be compressed. The cycles are repeated. 
     A two-cycle MECH engine will be similar to the four-cycle MECH engine in other respects. That is, it will have a mechanism similar to that of FIG. 2 on one end plate, and it will have end seals  20  as seen in FIG. 1, but which are not seen in FIG.  3 . Rolling contact point  15  provides a seal to prevent gas flow from high-pressure chambers to low-pressure chambers. 
     When a high-pressure gas (such as steam, air, refrigerant vapor, etc.) is available, an expander can extract energy from the expansion of the gas to a lower pressure. Turbines are typically regarded as the expanders in steam power plants. MECH units with the appropriate construction can also serve as expanders. 
     Industry has used rotary vane, geroter, gear motor, and screw expanders for various applications. These devices typically have high internal friction and excessive blow-by. This leads to low volumetric efficiency. MECH expanders would have low internal friction and much lower blow-by. 
     MECH expanders would be much less expensive to build than turbines and could be used for steam, compressed air, and low-boiling point fluids. A similar configuration can be used as a hydraulic motor. For applications such as driving irrigation pumps or other pump applications, the MECH expander can be coupled directly to a MECH pump without having to have a generator and electric motor to drive a pump. When an expander drives a generator, which drives a motor, which drives a pump, the inefficiencies of this series of the devices are multiplied together. 
     FIG. 4 shows a MECH expander. Steam, air, or other high-pressure gas enters the intake tubes  216 , passes through valve assemblies  220 , and flows into lower chambers  226 ,  227 , when valves  214  are open, and drives rotating pistons  202  and  203  in opposite directions about shafts  206 ,  207 . When pistons  202  and  203  approach the end of their stroke, valve shifters  222  strike valves  213  and force valves  214  to close and valves  213  to open. High-pressure gas then enters upper chambers  224 ,  225  via intake tubes  116  and reverses the direction of rotation of the rotating pistons  202 ,  203 . The valve assemblies  220  are located in wedges  209  that separate upper chambers  224 ,  225  from lower chambers  226 ,  227 . High-pressure gas tends to hold the valves  211  in one position until the rotating pistons  202 ,  203  shift them to the other positions. 
     FIG. 5 shows an exhaust valve assembly  230 , which is located behind valve assembly  220  in FIG.  4 . When high-pressure gas is entering lower chamber  227 , gas is exhausting from upper chamber  225  through exhaust valve assembly  230  past valve  233  and into exhaust tube  236 . Valve shifters like  222  (FIG. 4) strike the exhaust valves  231  at the end of each stroke to alternately open and close valves  233  and  234  by rod  231 . 
     The MECH expander has an end assembly like that of FIG.  2  and has other similarities to the MECH internal combustion engine. 
     The MECH expander of FIG. 4 can also function as a hydraulic motor. For an expander engine such as this, there is the possibility that when the high pressure gas supply is shut off, the pistons or the valves might stop in such a position that the engine would not start when the pressure is turned on again. A starter may be required. 
     An alternative valve system for the expander would be a crankshaft-driven cam that opens spring-loaded valves. This method would allow the intake valve to close before the piston reached the end of its stroke to allow adiabatic expansion of the gas for better efficiency. 
     The people of China, India, and other developing nations increasingly seek the benefits of air conditioning. Factories cannot keep up with the demand. A major problem is that the power grids and power plants in those countries do not have the capacity to provide the necessary power for all the new air conditioners. Even in the U.S., power brownouts have occurred in California and New York on hot days. A more efficient air conditioner would alleviate these problems. 
     Refrigerant compressors are the main energy consumers in refrigeration equipment and air conditioners. Piston compressors have high internal friction. Scroll, rotary vane, and screw compressors have high friction and excessive blow-by. The inventive MECH compressors would solve these difficulties. Small, compact, MECH compressors can be built for refrigerators, while large units can be manufactured for large air conditioners. 
     FIG. 6 is a schematic of a MECH compressor. The rotating pistons are shown as quadrants of cylinders with the angle from face-to-face of about 90 degrees. The face-to-face angle could be 180 degrees as shown in the previous figures, or some other angle, but it is depicted in FIG. 6 at 90 degrees to demonstrate the flexibility of design parameters for MECH geometries. 
     In block  300 , rotating piston  302  alternately compresses gas in chambers  324  and  326 , while rotating piston  303  alternately compresses gas in chambers  325  and  327 . When a particular piston face is receding, gas is drawn into the corresponding chamber past reed valves  310  (or other type of check valve) through tubes  313 . When the gas is compressed, valves  310  close, and the gas is forced out past reed valves  311  and through tubes  312 . 
     The gear mechanism on the end plate is similar to that shown in FIG. 2, but the gear wheels  60  and  61  could be only half-wheels (that is, 180 degrees) if the rotating pistons  302 ,  303  are only quadrants of a cylinder, and the stroke length of the crankshaft would be less. In this case, power is input to the crankshaft, and the crankshaft drives the rotating pistons to compress the gas. 
     This design also serves as a liquid pump. For liquids, gap  322  is not excessively small so that resistance to piston motion would not be large. The intake and exhaust tubes could be larger. 
     For a compressor or liquid pump, a MECH motor or expander can be used to drive a MECH compressor or pump directly. For example, if an expander is the driver, shafts  206  and  207  of FIG. 4 extend into the compressor and become shafts  306  and  307  of FIG. 6. A crank rod and crankshaft are not necessary. 
     FIG. 7 shows a single piston embodiment of a MECH useful for a motor, expander, or compressor. Rather than have two pistons that roll together, one rotating piston  403  in block  400  has seals  433  to prevent gases from flowing from one chamber  460  to the other  462 . These seals are similar to the piston rings in a car engine, but are straight. Seals  433  are free to slide in slots  434  and are forced by serpentine strip springs  435  to press radially inward against the rotating piston. Oil can be injected between the two seals for lubrication. The ends of these seals  433  are placed next to the ends of seals  444  that are in slots in the end plates (not shown). This design does not exploit the advantage of rolling friction, but does provide a compact engine of high power density. 
     A similar seal  430  in slot  431  in wedge  409  prevents blow-by past the shaft  407 . Serpentine spring  432  presses the seal against the shaft. Valves are not shown in this figure, since the design is applicable to the different configurations of MECH. This design can be adapted to multiple rotating pistons in a single block, but each rotating piston and its cylinder would be separated from the others. 
     Counterweights may be attached to the gear wheels  60  and  61  in FIG. 2 (and their counter parts in other embodiments) to reduce vibration of the engine due to the motion of the rotating pistons. Being made hollow can make the pistons lighter. If the motor is a four-cylinder design (constructed by duplicating the two-cylinder design and attaching them side-by-side) with the sets of pistons rotating 180 degrees out of phase, vibration would be cancelled, and the counterweights would be unnecessary. This can be accomplished by having all four rotating pistons drive a single flywheel as shown in FIG.  8 . In this case, the upper pistons are not exactly 180 degrees out of phase with the lower ones, but are close to 180 An alternative method would be to have two flywheels and crankshafts, and the two flywheels would have gear teeth on the circumference that would mesh with each other. This provides a very smooth running motor. 
     An alternative geometry to cancel vibration is shown in FIG. 9, which is a cross section through the rotating pistons and engine block. Four rotating pistons  501 ,  502 ,  503 , and  504  are mounted in engine block  500 . On the end plate of this design, all four gear wheels (not shown) would mesh to keep the rotating pistons appropriately aligned. Note that the center of mass of the upper pistons moves downward as the center of mass of the lower ones moves upward. 
     Left and right pistons roll together at contact point  515 . During part of the cycle, the upper and lower pistons roll together at contact points  516 . It is not really necessary that the pistons touch at point  516  for proper function of the engine, but since all four gear wheels must mesh, the pistons will touch there. The body  520  occupies the space between the pistons to prevent unused gas from occupying that space. This body is held in place by attachment to the end plates. It could contain channels for cooling water. These methods of reducing vibration apply to all versions of MECH. 
     The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.