Abstract:
A heat engine enclosed in a housing has two chambers maintained at different temperatures. The first chamber (“hot chamber”) receives heat energy from an external power source. The second chamber (“cold chamber”) is connected to the hot chamber by two conduits, such that a fluid (e.g., air, water, or any other gas or liquid) filling the two chambers can circulate between the two chambers. The expansion of the fluid in the hot chamber and the compression of the fluid in the cold chamber drive a turbine to provide a power output. The fluid may be pressurized to enhance efficiency. In one embodiment, the turbine propels an axle in a rotational motion to transmit the power output of the heat engine to an electrical generator outside of the heat engine&#39;s housing. In one embodiment, the turbine includes a first set of blades and a second set of blades located in the hot chamber and the cold chamber, respectively. The blades may each have a flat profile having two unequal surfaces, such that the turbine rotates in preferentially in one direction.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to applying Stirling engine principles to the design and use for power conversion equipment. In particular, the present invention relates to applying Stirling engine principles for electrical and mechanical power generation, especially in the direct current (DC) mode or in the alternating current (AC) modes.  
         [0003]     2. Discussion of the Related Art  
         [0004]     The Stirling engine is a heat engine that operates by converting the heat energy which flows between two portions of the heat engine having different temperatures into mechanical power. A typical Stirling engine uses the heat energy to drive a coordinated and reciprocating motion of a set of pistons. Numerous designs of Stirling engines can be found in the prior art, including: U.S. Pat. Nos. 6,578,359, 6,050,092, 6,195,992, 6,735,946 and 6,164,263. The designs of these Stirling engine are typically complex and include numerous moving parts. Consequently, these designs are costly to manufacture and their efficiencies are low.  
       SUMMARY  
       [0005]     The present invention provides a heat engine enclosed in a housing having two zones maintained at different temperatures. The first zone (“hot zone”) receives heat energy from an external power source. The second zone (“cold zone”) is connected to the hot zone, such that a fluid (e.g., air, water, or any other gas or liquid) filling the two zones can circulate between the two zones. The expansion of the fluid in the hot zone and the compression of the fluid in the cold zone provide a symmetrical thermodynamic cycle to drive a turbine to provide a power output. The fluid may be pressurized to enhance efficiency.  
         [0006]     In one embodiment, the turbine propels an axle in a rotational motion to transmit the mechanical power output of the heat engine. In one embodiment, the turbine propels an axle in a rotational motion to transmit the power output of the heat engine to an electrical generator outside of the heat engine&#39;s housing. In one embodiment, the turbine includes a first set of blades attached to a plate located in the hot zone and a second set of blades attached to a plate located in the cold zone. The blades may each have a flat profile having two unequal surfaces, such that the turbine rotates in preferentially in one direction. In one embodiment, the electrical generator includes one or more magnets in rotational motion according to the rotational motion of the axle, and one or more conductive coils coupled to the magnetic fields of the one or more magnets. The amount of coupling between the magnets and the coils may be controlled by a step motor moving the coils into different positions relative to the magnets. In one embodiment, the electrical generator delivers AC power. Alternatively, DC power may be provided by either rectifying the AC power, or by selectively coupling those coils that have an instantaneous positive voltage relative to a ground terminal. To synchronize the coil selection, a position sensor may be provided to sense the positions of the magnets. In one embodiment, the position sensor includes a light sensitive sensor, a light emitting diode and a light reflector.  
         [0007]     According to one embodiment of the present invention, a temperature sensor may be used to control the power output of the heat engine. A signal output of the temperature sensor indicates a temperature difference between the hot and cold chambers. Based on this output signal of the temperature sensor, a control circuit adjusts the coupling between the magnets and the coils in the electrical generator. In an AC power generation application, a control circuit senses to the frequency of the electrical generator&#39;s output power to control the output power of the electrical generator.  
         [0008]     In one embodiment, adding power output is achieved using thermal couples and thermionic devices. The thermal couple takes advantage of the temperature difference between the hot and cold chambers. The thermionic devices extract heat from the housing of the heat engine. These devices may be stored in an insulated chamber between two plates separating the hot and cold zones.  
         [0009]     The present invention provides a heat engine in which the gas or fluid transferring heat between the hot and cold zones is used to drive the turbine, resulting in low power loss in the energy conversion process. In addition, the housing provides air flow between the hot zone and the cold zone through a center shaft and a peripheral space so as to allow 100% component use with no dead time. The cylindrical symmetry of the heat engine provides stability with minimum vibration and an absence of drag during operation. The heat engine of the present invention has a simple design with few moving parts, without the requirements of a displacer, a piston or a regenerator. Thus, the heat engine of the present invention is light weight, low component cost and easy to maintain.  
         [0010]     A heat engine of the present invention may be used to power an automobile or another vehicle. It can also be incorporated, for example, in any application in which a source of heat energy is provided (e.g., fuel cells or energy recovery from combustion of waste).  
         [0011]     In addition, the control system of the present invention provides a consistent output power to enhance fuel efficiency.  
         [0012]     The present invention is better understood upon consideration of the detailed description below and the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows heat engine  100  receiving solar energy from a solar reflector  160 , in accordance one embodiment of the present invention.  
         [0014]      FIG. 2  shows one implementation of heat engine  100  of  FIG. 1  in a cross-sectional view.  
         [0015]      FIG. 3  represents both the cross-sectional view of heat engine  100  along line B-B′, viewed from top, and the cross-sectional view of heat engine  100  along line C-C′, viewed from the bottom.  
         [0016]      FIG. 4  is a cross section view of heat engine  100  along line D-D′, showing center axle  101 , magnets  108  and coils  109 .  
         [0017]      FIG. 5  shows control circuit  501  capable of controlling the output power based on an operating temperature difference.  
         [0018]      FIG. 6  shows multiplexing switch  601  provided to selectively couple each of terminal x to output terminal y. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     The present invention provides a heat engine, operating under Stirling engine principles, for converting heat energy into mechanical and electrical energy. The electrical energy derived using a heat engine of the present invention may be in the form of alternating current (AC) power, for immediate distribution, or in the form of direct current (DC) to allow storage or other applications.  
         [0020]     The heat engine of the present invention may operate with any source of heat energy, including solar, geothermal, fossil, landfill recovered or other fuels.  FIG. 1  shows heat engine  100  receiving solar energy from a solar reflector  160 , in accordance one embodiment of the present invention. One embodiment of heat engine  100  of  FIG. 1  is shown in a cross section view in  FIG. 2 . As shown in  FIG. 2 , heat energy  100  includes an external housing  107  which seals a hot portion or zone  107   a  and a cold portion or zone  107   b . In this detailed description, the terms “hot” and “cold” are relative. A heat engine of the present invention will operate as long as there is a sufficient temperature difference between the hot portion and the cold portion. Further, the upper and lower portions of  FIG. 2  are labeled “top” and “bottom”, respectively, merely to facilitate reference in this detailed description. A heat engine of the present invention is not limited by its position in any orientation.  
         [0021]     Hot portion  107   a  (“hot zone”) and cold portion  107   b  (“cold zone”) are insulated from each other by insulating zone  106 . Except for insulating zone  106 , housing  107  may be metallic (e.g., steel) to allow rapid and even heat distribution. Heat engine  100  includes turbine  103 ; in the implementation shown in  FIG. 2 , turbine  103  includes two sets of blades, labeled  103   a  and  103   b , respectively, which are connected by center axle  101 . Blade set  103   a  and blade set  103   b  are housed within the hot and cold zones, respectively. Blade sets  103   a  and  103   b  are preferably made of metal to allow even and rapid heat distribution. In this embodiment, blade sets  103   a  and  103   b  are provided on support plates  114  and  115  respectively.  
         [0022]      FIG. 3  represents both the cross-sectional view of heat engine  100  along line B-B′, viewed from top, and the cross-sectional view of heat engine  100  along line C-C′, viewed from the bottom. In relation, the cross-sectional view of  FIG. 2  represents a cross-section along line A-A′ of  FIG. 3 . Blade sets  103   a  and  103   b  are each provided a rounded contour, such that one side of the blade has a larger cross-section than the other, to allow the blades to rotate in a predetermined direction. The difference in surface area is not necessary, but may provide some advantage in some applications, such as ease in starting up. Blade sets  103   a  and  103   b  provide large surface areas for heat transfer. Thus, heat engine  100  has a high surface to volume ratio to enhance efficiency.  
         [0023]     Center axle  101  is unsheathed in air shaft  102  that runs from top to bottom along the entire lengths of hot portion  107   a  and cold portion  107   b  of housing  107 , connecting the hot and cold chambers. The hot and cold zones are also connected by annular space  104  along the circumference of the outer wall of housing  104 . Center axle  102  is held by bearings  105 , which allow center axle  101 —and thus blade sets  103   a  and  103   b  also—to rotate about its center axis. Because the contact points between bearings  105  and center axle  103  are the only locations in heat engine  100  which experience mechanical wear and tear, heat engine  100  has a long service life and a low service requirement and thus easily maintained. A portion of center axle  101  extends outside of housing  107 . Cylindrical magnet  108  attaches to and rotates with this portion of center axle  101  which extends outside of housing  107 . One or more coils  109  surround magnet  108 . Coils  109  may be driven by step motor  110  in an up and down motion to vary the amount of magnet flux coupling the magnetic field of magnet  108 .  FIG. 4  is a cross sectional view of heat engine  100  along line D-D′, showing center axle  101 , magnet  108  and coils  109 . As shown in  FIG. 4 , coils  109  may include one or more coils with their respective output terminals (labeled “x”) and a common ground terminal.  FIG. 2  also shows reflector  111  provided with magnet  108 , and a position sensor  112 . Position sensor  112  includes a light emitting diode (LED) and a sensor sensitive to light reflected from reflector  111 . Each of coils  109  may be provided with a position sensor, so that a control circuit may be able to determine the frequency and the phase of the alternating electrical current induced in the coil by the magnet.  
         [0024]     In this embodiment, when coils  109  includes more than one coil (as may be desirable for DC power generation), a multiplexing switch  601  may be provided, as shown in  FIG. 6 , to selectively couple each of terminal x to output terminal y according to the phase of the alternating electrical current in each coil. If only one coil is present in coils  109 , the single output terminal x of coils  109  is directly coupled to terminally.  
         [0025]     During operation, as heat builds up in hot portion  107   a  of housing  107 , the expanding air in the hot zone rises and pushes against blade set  103   a  on support plate  114 . Thus, turbine  103  begins to rotate about the axis of center axle  101  due to the torque of the expanding air. The expanding air moves radially outward towards the periphery and into the cold zone via annular air space  104 . As the expanding air enters into cold zone  107   b , the air in cold zone  107   b  contracts by a cooling mechanism (e.g., the walls of housing  107  in cold zone  107   b  may include pipes circulating a cooling fluid). The contracting air draws the expanding air into cold zone  107   b . As blade set  103   b  on support plate  115  in cold zone  107   b  is connected by center axle  101  to rotating blade set  103   a  on support plate  114 , blade set  103   b  rotates at the same angular speed as blade set  103   a , thereby contributing to the torque rotating turbine  103 . The cooled air in cold zone  107   b  is drawn by convection radially towards center axle  101  and is forced into hot zone  107   a  via air shaft  102 . Thus, a circulation of air is established which flows radially outwards in hot zone  107   a , enters cold zone  107   b  via annular airspace  104 , flows radially inwards in cold zone  107   b  and returns to hot zone  107   a  through air shaft  102 . In this process, the relatively hot air from hot zone  107   a  that expands and flows into cold zone  107   b  is cooled in cold zone  107   b , while the relatively cold air from cold zone  107   b  is heated in hot zone  107   a . As magnet  108  rotates with center axle  101 , the result varying magnetic field induces one or more electrical currents in coils  109 . This electric current can be used to generate AC or DC electrical power, as discussed in further detail below. A temperature difference between hot zone  107   a  and cold zone  107   b  may be established, such that the output power and the heat dissipated from housing  107  equals the input power. Cold zone  107   b  may be cooled and maintained at a pre-determined temperature by fluid (e.g., air). Such fluid may flow in channels provided in walls of housing  107   b , or by other means known to those skilled in the art. Efficiency for the heat transfer may be enhanced by pressurizing the hot and cold zones. Alternatively, rather than using air, other gases may also be used.  
         [0026]     The operating temperature difference between hot zone  107   a  and cold zone  107   b  either by the cooling method discussed above, by controlling the output power, or both. The output power can be controlled by increasing or decreasing the magnetic field coupling between magnet  108  and coils  109  by motor  110  driving coils  109  up or down. A temperature sensor (not shown) sensitive to the temperature difference between hot zone  107   a  and cold zone  107   b  may be provided to sense the operating temperature difference.  FIG. 5  shows control circuit  501  capable of controlling the output power based on the operating temperature difference. The control scheme may be implemented using digital or analog techniques, as known to those skilled in the art. As shown in  FIG. 5 , a signal v representing the operating temperature difference is received from the temperature sensor and provided to control circuit  501 . Based on the value of signal v, output control signal w drives step motor  110  up or down to vary the magnetic coupling between magnet  108  and coils  109 , as appropriate.  
         [0027]     For generating AC electrical power, position sensor  112  may be used to detect the rotational frequency of axle  101 . Positional sensor  112  asserts a control signal (e.g., control signal t) to control circuit  501  whenever reflector  111  comes into the detection field of positional sensor  112 . The time difference between successive assertions of the control signal allows control circuit  501  to determine the frequency of the rotating magnetic field of magnet  108 , and thus the frequency of the output AC power.  
         [0028]     As mentioned above, for AC power generation, coils  110  need only be a single coil, output terminal y is a single output. Without further processing, the output power is delivered in the form of an AC current flowing between terminal y and the ground terminal, whose frequency is proportional to central axle  101 &#39;s angular speed of rotation. Because the amount of output power is a load on center axle  101 , increasing the amount of magnetic coupling between magnet  108  and coils  109  increases the load on center axle  101 , thereby affecting the angular speed of rotation. Accordingly, the output terminal y may be coupled into a high impedance input terminal of control circuit  501 , which may be provided a frequency sensing circuit (e.g., a trigger circuit). The detected frequency of the output AC current is used to adjusted through step motor  110 , which drives coils  109  up or down according to output control signal w. This control scheme may thus be used to provide an output power from heat engine  110  which is compatible with 50 or 60 Hz household AC power.  
         [0029]     In DC power generation, coils  110  may include multiple coils. At any given time, some of terminals x have positive voltages relative to the ground terminal, and others of terminals x have negative voltages relative to the ground terminal. During DC power generation, the position sensor associated with each of coils  109  provides to control circuit  501  control signal t which indicates when the associated reflector comes into the detection field of the position sensor. Once the particular coil of coils  109  is identified as having the desired positive voltage phase, control circuit  501  provides control signals z to switch  601  ( FIG. 6 ) which selectively couples output terminal x of the particular coil to output terminal y. In this manner, DC power generation is accomplished. The signal in output terminal y may be shaped to a constant voltage using, for example, a low-pass filter or a voltage regulator.  
         [0030]     Alternatively, the AC output power generated according to discussion above may be rectified to provide a DC power output, using any suitable rectifier circuits known to those skilled in the art.  
         [0031]     Additional energy conversion may be accomplished using thermal couples that provide output signals according to the temperature difference between hot zone  107   a  and cold zone  107   b . Alternatively, the walls of housing  107  at hot zone  107   a  may be used to generate power using thermionic principles. The thermal couples or thermionic components can be housed insulating zone  106  of  FIG. 1 , for example.  
         [0032]     The above detailed description is provided to illustrate the specific embodiments of the present invention and is not intended to be limiting. Numerous modifications and variations with in the scope of the present invention are possible. The present invention is set forth in the following claims.