Abstract:
A double acting, miller cycle, reciprocating piston with dual rotary displacer, stirling engine is provided. Configurable as a heat pump, a heat engine, or as a combination with one side driving the other, the engine is completely closed, sealed and pressurized with the piston ring as the only internal seal. A miller cycle is created by allowing transfer of the working fluid (typically hydrogen gas) past the piston to balance working fluid pressure only at the extremes of the piston stroke. Two coordinated rotating displacers service opposite sides of one piston. Each displacer manages heat flow, according it its length and shape, through one side of the length of its encasing tube into and out of the working fluid through the other side of the length of its encasing tube. The dead space between the piston and the displacer holds regenerator material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in part of U.S. patent application Ser. No. 13/411,630, titled “Stirling Engine,” filed 2 May 2012, published as U.S. Pat. App. Pub. No. 2014/0238012, the entire contents of which application are incorporated herein by reference. It is to be understood, however, that in the event of any inconsistency between this specification and any information incorporated by reference in this specification, this specification shall govern. 
     
    
     BACKGROUND 
       [0002]    The concept of mechanically manipulating the ideal gas laws to convert heat into motion or vice-versa was first patented by Robert Stirling in 1817. Since that time several designs, most utilizing multiple pistons, have emerged including some designs utilizing pressure waves in lieu of a displacer with only a single piston. 
         [0003]    The basic Stirling engine includes a trapped gas that is heated or cooled which then expands or contracts (according to the ideal gas laws) which pushes or pulls on a piston which then drives a crankshaft. The crankshaft is typically coupled to a flywheel and an output shaft. The output shaft delivers usable mechanical force relative to the initial temperature differential and amount of heat transferred. 
         [0004]    Current commercial designs utilize a piston style displacer to move the working gas from a heating chamber to a cooling chamber and back. Common designs use multiple internal seals and two or more pistons. Current designs are complex and difficult to manufacture making them relatively high cost. The greater efficiency, reliability, lifespan, cleanliness, and flexibility that Stirling engines demonstrate compared to internal combustion engines has previously been sacrificed in favor of the faster start up, control response, greater power density, and ease of manufacture of competing engines. However, the inherent advantages of the Stirling engine allows it to compete successfully in various specialty niches of the engine market, such as satellite power production, waste heat recovery, cryogenics, solar power conversion, space craft, and submarines, where faster start up, control response, greater power density, and ease of manufacture are not the critical criteria in engine selection. 
         [0005]    The Stirling engine has many advantages such that it could displace internal combustion engines in many applications if a few of the Stirling engine&#39;s drawbacks could be addressed. For example the Stirling engine has fewer moving parts, no need for expensive sound deadening or exhaust gas treatment, nor complex ignition, timing, and fuel handling requirements. Furthermore, the Stirling engine benefits from a large menu of energy sources and fuels to choose from and the use of non-polluting gasses when used in refrigeration. 
         [0006]    Accordingly, there is a need for a Stirling engine with lower cost, and higher power density. Such an improved Stirling engine could become the mainstream choice in such applications as hybrid automobiles, aircraft, and boats, as well as electric generators, refrigerators and water heaters. In other words, applications in which costs, simplicity and power density are the primary consideration and where start up speed and control response are ancillary considerations. 
     
    
     
       DRAWINGS 
         [0007]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of an improved Stirling engine and together with the description, serve to explain the principles and operation thereof. 
           [0008]      FIG. 1  is a hidden line perspective side view of a Stirling engine according to an exemplary embodiment with the piston at the end of a power stroke. 
           [0009]      FIG. 2  is a hidden line end view of the Stirling engine shown in  FIG. 1  with the piston approximately half-way through a power stroke. 
           [0010]      FIGS. 3 and 9  are hidden line perspective top views of the Stirling engine shown in  FIG. 1 . 
           [0011]      FIGS. 4-5  are hidden line perspective end views of the Stirling engine shown in  FIG. 2 . 
           [0012]      FIG. 6  is a hidden line end view of the Stirling engine shown in  FIG. 2 . 
           [0013]      FIG. 7  is a hidden line top view of the Stirling engine shown in  FIG. 2 . 
           [0014]      FIG. 8  is a partially exploded end view of the Stirling engine shown in  FIG. 1 . 
           [0015]      FIG. 10  is a hidden line top view of the Stirling engine shown in  FIG. 1 . 
           [0016]      FIG. 11  is an end view of the piston, connecting rod, and crankshafts of the Stirling engine shown in  FIG. 2 . 
           [0017]      FIG. 12  is a hidden line perspective top view of the Stirling engine shown in  FIG. 1  having a radiator coupled to the displacer housings and a heat source positioned underneath the displacer housings. 
           [0018]      FIG. 13  is a hidden line perspective bottom view of the Stirling engine shown in  FIG. 1  having a radiator coupled to the displacer housings and a heat source positioned underneath the displacer housings. 
           [0019]      FIG. 14  is a hidden line perspective end view of the Stirling engine shown in  FIG. 1 . 
           [0020]      FIG. 15  is a hidden line perspective bottom view of the Stirling engine shown in  FIG. 1 . 
           [0021]      FIG. 16  is an exploded perspective view of the Stirling engine shown in  FIG. 13 . 
           [0022]      FIG. 17  is a hidden line perspective bottom view of the Stirling engine shown in  FIG. 2  having a radiator coupled to the displacer housings and a heat source positioned underneath the displacer housings. The displacers and piston are shown in a different position compared to  FIG. 13 . 
           [0023]      FIG. 18  is a hidden line end view of the Stirling engine shown in  FIG. 17 . 
           [0024]      FIG. 19  is an exploded perspective view of the Stirling engine shown in  FIG. 17 . 
           [0025]      FIG. 20  is an exploded perspective view of the piston, connecting rods, and crankshafts in the Stirling engine shown in  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Provided herein is an improved Stirling engine  10 , and methods of operation and use, that address the difficulties and maximizes the advantages of the Stirling cycle engine. Lower production and maintenance costs are possible due to the elimination of all but one internal seal (on the piston  14 ) sealing all moving parts within the pressure vessel (isolating them from heat and corrosive gasses or liquids) and fewer, simpler parts manufactured with less precision. 
         [0027]    Greater power density is achieved by using two displacers  12  with one on either side of the piston  14  to produce power in each direction of every stroke similar to the Stanley steamer engine. Working gas is transferred at the end of the power stroke, similar to the Miller cycle engine, to prevent counter pressure, pre-load the coming power stroke, and simplify initial pressurization. Greater initial pressurization, possible due to the elimination of external seals, makes more gas molecules available to transfer heat. 
         [0028]    Smoother quieter operation is achieved with a lighter flywheel by means of reshaping and rotating rather than reciprocating the displacer  12 . Using a single piston  14  with both sides driven reduces complexity, compared to multiple cylinder engines of similar power output. 
         [0029]    Rotating instead of reciprocating the displacer  12  eliminates the counter action of gas pressure on the displacer piston during the power stroke as well as the extra friction. The working gas is guided into a vortex that efficiently transfers heat between a wall of the heat exchanger  16  and the working gas. Adjusting the relative position of the displacer  12  and the piston  14  allows flexibility in where the heating and cooling areas are on the housing  18  of the heat exchanger  16 . 
         [0030]    Rotating at 90 degrees to the piston  14 , unless connected through a constant velocity joint or powered by separate motor or timing belt, the displacer  12  provides precise control over the heating and cooling of the working gas. The displacer  12  may be formed of a lightweight, insulating, and heat resistant, inflexible compound of either graphite carbon or silicon. The displacer  12  may be coated with a pattern of insulator such as Aerogel and regenerator material (such as nickel foam) to appropriately guide heat flow and have a shape that creates and controls the turbulence of the working gas. 
         [0031]    Working gas turbulence is controlled both by the cam shape of the displacer  12  which compresses and releases the working gas in the desired direction and place, and by the shape of the chamber  40  it creates as it directs the gas movement out of and into the piston cylinder  20 . The working gas can be trapped in the displacer  12  for a few degrees and released suddenly by creating a rotating valve at the intersection of the displacer  12  and piston cylinder  20 , for greater power. In an embodiment, a constantly rotating vortex is formed as the displacer  12  turns and the working gas expands and contracts. In another embodiment, further control of turbulence may be achieved by placing storage pockets in the displacer  12  that will pressurize during the heating cycle and release the pressure in a specific direction through a nozzle during the cooling cycle. The displacer  12  shape and relative motion creates a constant sized area in which a mechanical means of directing turbulence, such as a fan, can be inserted if desired. 
         [0032]    Greater heat input and therefore power as well as reduced complexity is made possible through utilizing the entire length of the displacer housing  18  as opposed to heating only one end of the housing  18  as in current designs (a wider path allows more heat to flow). More efficient heat transfer is achieved by means of greater control of working gas turbulence, optimization of the displacer chamber  40  volume to surface ratio, shape, surface roughness and corrugation, direct control of heat transfer from heat source, adjustable displacer to piston ratio and minimization of dead space. The passage  24  between the displacer  12  and the piston  14  may be filled with a mesh of nickel foam that acts as a regenerator  64 . 
         [0033]    The use of a through-the-piston  14  connecting rod  26  creates accurately timed coordination and counter rotation of the opposing displacer  12 . In addition to eliminating possible frozen states on startup, the counter rotation of the displacers  12 , with the flywheel turning opposite the direction of the output shaft  28 , reduces gyroscopic progression that may be an issue in some applications. In most applications putting the flywheel on the output shaft  28  will reduce total weight. Some configurations may disallow the use of a one piece through the piston  14  connecting rod  26  and require either two standard mirror image connecting rods or a timing belt or electronic means of coordinating the rotation of the two displacers  12 . Since the displacers  12  regulate and time the heat transfer from the exchanger  16  to the working gas which then pushes on the piston  14 , as long as the displacers  12  are coordinated, no mechanical connection is required between the piston  14  and displacers  12 . A constant speed can be obtained by turning the displacers  12  electronically to control the piston  14  and crankshaft  30 . 
         [0034]    The piston  14  is designed as a two identical piece part that is bolted together and houses a piston pin  32  on bearings  74  and provides for easy assembly of two opposing continuous oil-less piston rings  34 . The concave shape of the piston face  36  provides clearance for the crankshaft  30 , strength for the power stroke and brings the displacers  12  closer together without additional mechanical parts. Controlled leakage at the extreme of the piston stroke, similar to the Miller cycle, eliminates counter pressure when pressure is left over from the power stoke. 
         [0035]    The piston cylinder  20  doubles as the crankshaft housing and provides the fulcrum against which the crankshaft pushes. Since the entire engine  10  is a pressure vessel, containing it within standard tubing reduces weight and complexity. The openings  38  from the cylinder  20  to the displacer chamber  40  are shaped to minimize the loss of support against the pressure while providing adequate gas flow. Dead space is minimized by filling it with packing material to displace the gas. The bearing mounts  42  are the same distance apart as the length of the connecting rod  26 , measured from bearing center to bearing center on the connecting rod  26  and the cylinder  20 . Maintenance free bearings are located well away and shielded from heat sources for maximum maintenance free life. The lack of lubricating fluid eliminates the oil pump, tubing, machined channels oil filter and lightens the engine  10 . 
         [0036]    The displacer housing  18  functions as the heat exchanger. Essentially a long tube, strong enough to contain the pressure while heated on one side  44  and cooled on the other side  46 . The displacer housing  18  has a welded cap  48  at one end  50  and is bolted or welded to the piston cylinder at the other end  52 . While the points of assembly are shown in the figures as flanges, a high pressure model would use a stronger means of joining the pieces such as an interrupted thread design similar to a cannon breech, or a threaded pipe design or welding. 
         [0037]    A rough finish and possibly corrugation interleaving with the displacer  12 , to facilitate heat transfer, may be applied by chemical or mechanical means. When used with combustible fuels the heated side  44  can be coated with catalyst to maximize the chemical reaction of the fuel with the oxidizer. The ideal material would be pure carbon in crystal form with a nano-scale fractal pattern finish to facilitate heat transfer from the source through the wall and into the working gas. Less ideal but still functional materials would be titanium or commercial steel tubing. Greater efficiency can be gained by constructing the displacer housing  18  in a multi-part clam shell design separating the sides with insulation so the heat travels through the working gas instead of circumferentially through the shell. This may increase manufacturing costs; however, with the extended life span of the Stirling engine  10 , the added efficiency of this option may be desired. 
         [0038]    On the outside of the engine  10 , the improvements include controlling and directing the heat from whatever source  54  directly to the desired area on the exchanger  16  with no need of the commonly used heater assembly. The use of insulation and ducting would be tailored to the heat source  54 . The heat source  54  may be geothermal, solar, combustion, or other desired heat source. The radiator  56 , if used in home or business power generation may double as a water heater. The supporting structure of the engine  10  and intake and exhaust would simplify the stacking and use of multiple engines  10  to achieve higher required output. Waste heat from the radiator  56  and the combustion products can partially be recycled to preheat air when combustible fuels are used. When using combustible fuels, the combustion area can be optimized for maximum efficiency depending upon the fuel used. Materials are chosen to optimize recycling of engines  10  after their useful life. Maintenance is simplified with standard fasteners and bearings that are widely available. Standard tubing sizes and common piston sizes are purposely chosen, to simplify any repairs that may be needed in rural areas as well as reduce production costs. The entire engine  10  is considered to be a pressure vessel, but the extra weight is minimal considering the greater power density achieved, that all moving parts are safely hidden inside and protected from dust and moisture, and the elimination of all but one external dynamic seal around the output shaft  28 . 
         [0039]    In an embodiment one side  58  of the engine  10  is powered and the other side  60  is used as a heat pump for refrigeration or heating. While shown parallel and equal in the figures, the displacer tubes  18  are independent of each other and multiple configurations are possible. For example, one heat exchanger  16  could sit on the top of an insulated container and draw heat out of it forming a refrigerator. The heat would then be used to preheat the combustion process for the other heat exchanger  16  which would drive the system. Alternatively, one engine  10  could use fuel to drive a second engine  10  that was used as a heat pump to provide refrigeration of food or medicine or distillation of liquids such as drinking water. Distillation would use both the heated and cooled sides of either or both of the exchangers  16 . 
         [0040]    In the event of catastrophic failure due to external insult or internal defect, the high-pressure gas is released in a controlled manner by the use of materials that deform rather than break. The route of pressure relief at the end of piston  14  travel clears the working gas from the undamaged side of the engine  10  in a controlled manner. The radiator  56  also functions as a shrapnel catcher on the top while shrapnel directed downward is slowed by the heating duct work  62  and directed by installation design into the earth or a component of the installation and away from sensitive areas. If hydrogen is used as the working gas, mixing it with nitrogen or carbon dioxide should moderate the tendency to burn rapidly. 
         [0041]    Also, contemplated herein are methods for providing rotational power according to the present disclosure. The methods thus encompass the steps inherent in the above described mechanical structures and operation thereof. Broadly, one method could include heating a volume of working gas with a heat source  54 , directing the heated working gas to act on a piston  14 , and rotating at least one displacer  12  to displace the working gas away from the heat source  54  such that the volume of working gas may be cooled. 
         [0042]    Accordingly, the improved Stirling engine  10  has been described with some degree of particularity directed to the exemplary embodiments. It should be appreciated, though, that modifications or changes may be made to the exemplary embodiments without departing from the inventive concepts contained herein. 
       Illustrative Embodiments 
       [0043]    In one embodiment, a double acting Stirling engine  10  in which a working fluid exerts force against a reciprocating piston  14  comprises: an elongated cylindrical heat exchanger  16  connected at a right angle, through regenerator material  64 , to the piston cylinder  20  with an elongated rotating displacer  12 , of such mass as to serve as a flywheel, inside the heat exchanger  16 , coordinated with the piston  14 , that moves the working fluid from the heat input side  44 , at which time the working fluid expands and exerts an increase of force on the piston  14 , to the heat extraction side  46 , where the working fluid contracts and reduces the pressure exerted upon the piston  14 , thus completing one cycle while a similar though not necessarily identical heat exchanger  16  and displacer  12  perform the same sequence against the second side  68  of the piston  14  180 degrees out of phase such that each direction of the piston  14  is productive with said parts arranged according to  FIG. 1 . 
         [0044]    A valve  70  can be actuated by the angle of the piston rod  26  allowing the working fluid pressure to equalize across the piston  14  at the extremes of the stroke of the piston  14 . The device  10  can include only one displacer  12  and heat exchanger  16  and the engine  10  is single acting. The displacer  12  can be comprised of one half lengthwise of one cylinder and a smaller division of a second cylinder of a larger radius divided along its length on a chord of length less than or equal to the diameter of the first half cylinder such that when the displacer  12  is mounted in its heat exchanger  16  there exists a gap for the working fluid to fill of the desired moon shape on one half of the radius of the displacer  12  between the displacer  12  and the wall of the heat exchanger  16  for the working length of the displacer  12 . 
         [0045]    The displacer  12  can comprise one half lengthwise of a cylinder and a separate cylinder of larger diameter divided lengthwise along a chord in which the chord of the larger cylinder is less than or equal to the diameter of the first smaller cylinder diameter. The displacer  12  can be cylindrical and the working surface  72  can be along the length of the cylinder and the shape of the end closest to the piston  14  directs the flow of working fluid in a desired manner. The displacer  12  can be cylindrical and the working surface  72  can be along the length of the cylinder and the shape of the end closest to the piston  14  directs the flow of working fluid in manner supportive of the desired working fluid flow within the heat exchanger  16 . 
         [0046]    The displacer  12  can be cylindrical and regenerator material  64  can be attached to the displacer  12 . The displacer  12  can be cylindrical and a tube with regenerator material  64  can extend along the length of the displacer  12 . The displacer  12  can be cylindrical and attached to the displacer  12  in the gap are various fins and equipment for monitoring and directing fluid flow. The displacer  12  can be cylindrical and a fan blade can extend along the length of the displacer  12  for purpose of directing working fluid flow. 
         [0047]    The displacer  12  can be cylindrical and its rotation can be controlled by being mechanically attached to the crankshaft  30  for the piston  14 . The displacer  12  can be cylindrical and its rotation ca be controlled by external timing device or motor. The displacer  12  can be cylindrical and its rotation can be controlled by magnetic coupling to a timing device. The displacer  12  can be cylindrical and can be composed partially or wholly of an insulating material. The displacer  12  can be cylindrical and can be a sealed vessel. 
         [0048]    The Stirling engine  10  can include two displacers  12  and two heat exchangers  16  each coordinated with opposite sides of the piston  14 . The two displacers  12  and two heat exchangers  16  can each be coordinated with opposite sides  66 ,  68  of the piston  14  by means of a connecting rod  26  that extends through the piston  14  and forces counter rotation of each displacer  12 . The two displacers  12  and two heat exchangers  16  can each be coordinated with opposite sides  66 ,  68  of the piston  14  by means of two connecting rods  26  each attached to opposite sides  66 ,  68  of the piston  14  which allow coordinated yet same or opposite rotation of the displacers  12 . 
         [0049]    The connecting rod  26  can mount within 1 inch of the center of the height of the piston  14 . The connecting rod  26  can be sealed at its connection to the piston  14  so as to not allow transfer of the working fluid during the active phase of the stroke. The connecting rod  26  can extend through a piston pin  32  which is mounted in the piston  14 . 
         [0050]    A strategically placed hole in the piston pin  32  can be used as a valve  70  to allow transfer of the working fluid at the extremes of the piston stroke by means of channels cut in the piston  14  and the pin  32  that align at the extremes of the piston stroke. The Stirling engine  10  can include a means allowing transfer of the working fluid from one side of the piston  14  to the other only at the extremes of the piston stroke. The Stirling engine  10  can be configured with one side  58  converting heat differential, as from a heat source  54 , into mechanical motion then used to power the other side  60  used for converting mechanical motion into heat differential as might be used in refrigeration or distillation. 
         [0051]    The piston cylinder  20  can encompass part of the crankshaft  30 . The piston cylinder  20  can serve as support for the output shaft  28 . The displacer(s)  12  can be mounted at a right angle to the piston cylinder  20 . Regenerator material  64  can be located between the displacer  12  and the piston  14 . The displacers  12  and displacer housings  18  can be parallel to each other and can be mounted on the same side of the piston cylinder  20 . The displacers  12  and displacer housings  18  can be parallel to each other and mounted on opposite sides of the piston cylinder  20 . The displacers  12  can also not be mounted parallel to each other. 
         [0052]    The heat dissipating radiator  56  can function as a shrapnel catcher in the event of catastrophic failure of the pressurized heat exchanger  16 . The device  10  can provide power for electrical generation. The device  10  can provide power for use in an automobile. The device  10  can provide useable mechanical power. The device  10  can be used on an aircraft. The device  10  can be used in a structure or dwelling. The device  10  can be used to convert sunlight to electricity. The device  10  can be used to convert fuel into electricity. The device  10  can be used on watercraft of any kind. The device  10  can be used on a spacecraft. 
         [0053]    The piston  14  can comprise two identical discs  34  fastened together. The device  10  can be attached to an alternator or generator which serves as a starter. The device  10  can be attached to an alternator or generator and the alternator or generator can be in a pressurized container obviating the need for a seal on the output shaft  28 . The device  10  can include a flywheel within the pressurized area. The device  10  can include a flywheel placed on the output shaft  28 .