Abstract:
An external combustion engine alternately repeating a first stroke of making a working fluid evaporate at a plurality of heating portions and making a liquid phase part of the working fluid displace toward an output part side and a second stroke of making the working fluid evaporated at the first stroke condense at the plurality of cooling portions and making the liquid phase part of the working fluid displace toward the side of the plurality of the heating portions and provided with inflow adjusting means for reducing differences in inflows among the plurality of the heating portions, wherein the inflow is defined as the amount of a liquid phase part of the working fluid flowing into the heating portions when the liquid phase part of the working fluid displaces from the output part side to the side of the plurality of the heating portions in the second stroke.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an external combustion engine using evaporation and condensation of a working fluid to cause a liquid phase part of the working fluid to displace, and converting the displacement of the liquid phase part of the working fluid to mechanical energy for output. 
     2. Description of the Related Art 
     In the past, one external combustion engine was disclosed in Japanese Patent Publication (A) No. 2005-330885. In such an external combustion engine, a container in which a working fluid is sealed flowable in the liquid phase state, is formed with a heating portion heating part of the liquid phase state working fluid to evaporate it, and a cooling portion cooling the working fluid evaporated at the heating portion to condense it. 
     By alternately repeating this evaporation and condensation of the working fluid, the liquid phase part of the working fluid is made to cyclically displace, and the vibration of the liquid phase part of the working fluid is taken out at the output part as mechanical energy. 
     In the prior art, the part of the container at the output part side is formed by a single merging pipe and the parts of the container forming the heating portion and cooling portion are formed by large numbers of branch pipes so as to increase the heat conduction areas of the heating portion and cooling portion. Due to this, the heating efficiency (evaporation efficiency) and cooling efficiency (condensation efficiency) of the working fluid are improved to increase the output of the external combustion engine. 
     In the above prior art, when the liquid phase state working fluid did not sufficiently reach the heating portion, the heating efficiency (evaporation efficiency) of the working fluid could fall and in turn the output of the external combustion engine could fall. 
     In the above prior art, the part of the container at the output part side was formed by a single merging pipe, while the parts of the container forming the heating portion and cooling portion were formed by large numbers of branch pipes. According to detailed studies of the inventors, branch pipes where the liquid phase state working fluid will easily reach the heating portion and branch pipes where the liquid phase state working fluid will have a hard time reaching the heating portion end up being formed and, as a result, the output of the external combustion engine can be lowered. Such a state occurs not only when there are large numbers of branch pipes, but also when there are two branch pipes. 
     SUMMARY OF THE INVENTION 
     An object of the present invention, in view of this point, is to improve the heating efficiency of a working fluid by a plurality of heating portions. 
     To achieve the above object, in the external combustion engine as set forth in claim  1 , there is provided an external combustion engine comprising a container having one merging pipe, a plurality of branch pipes, and a branched part branching from said merging pipe toward said plurality of branch pipes and having a working fluid sealed inside it flowable in the liquid phase state, a plurality of heating portions heating and evaporating part of said working fluid in a liquid phase state, formed at said container to correspond to said plurality of branch pipes, and communicated with the ends of said plurality of branch pipes at the sides opposite to said branched part, a plurality of cooling portions cooling and condensing said working fluid evaporated at said heating portions, formed at said plurality of branch pipes, and an output part converting displacement of the liquid phase part of said working fluid to mechanical energy, communicated with an end of said merging pipe at a side opposite to said branched part, said external combustion engine alternately repeating a first stroke of making said working fluid evaporate at said plurality of heating portions and making the liquid phase part of said working fluid displace toward said output part side and a second stroke of making said working fluid evaporated at said first stroke condense at said plurality of cooling portions and making the liquid phase part of said working fluid displace toward the side of said plurality of the heating portions, and further comprising inflow adjusting means for reducing differences in inflows among said plurality of the heating portions, wherein the inflow is defined as the amount of a liquid phase part of said working fluid flowing into the heating portions when the liquid phase part of said working fluid displaces from said output part side to the side of said plurality of the heating portions in said second stroke. 
     Due to this, it is possible to equalize the inflow of the liquid phase state working fluid to the plurality of the heating portions, so it is possible to improve the heating efficiency (evaporation efficiency) of the working fluid and possible to increase the output of the external combustion engine. 
     In the invention described in claim  2 , there is provided the external combustion engine as set forth in claim  1 , wherein said inflow adjusting means are formed so that flow resistances of the plurality of flow paths from the end of said blanched part at said merging pipe side to the end thereof at the side of said plurality of branch pipes respectively become the same. 
     The description “flow resistances of the plurality of flow paths become the same” in this specification does not mean only the flow resistances of the plurality of flow paths strictly becoming the same and is used in the sense including cases where manufacturing error etc. results in the flow resistances of the plurality of flow paths slightly differing. 
     In the invention described in claim  3 , there is provided the external combustion engine as set forth in claim  2 , wherein said plurality of flow paths of said branched part become mutually symmetric shapes so that the flow resistances of said plurality of flow paths respectively become the same. 
     In the invention described in claim  4 , there is provided the external combustion engine as set forth in claim  1 , wherein said inflow adjusting means are formed so that the flow resistance of said branched part is made smaller than the flow resistances of said cooling portions. 
     In the invention described in claim  5 , there is provided the external combustion engine as set forth in claim  4 , wherein a length l in  of the branched part, a hydraulic diameter d in  of a flow path of the branched part, a length l r  of the cooling portions, and a hydraulic diameter d r  of a flow path of the cooling portions satisfy the following relationship:
 
 l   in   /d   in   &lt;l   r   /d   r  
         where,   l in : length of branched part   d in : hydraulic diameter of flow path of branched part   l r : length of cooling portions   d r : hydraulic diameter of flow paths of cooling portions.       

     In the invention described in claim  6 , there is provided the external combustion engine as set forth in claim  1 , wherein said plurality of branch pipes are provided with flow resistance adjusting means for making a flow resistance of a branch pipe at the side close to said output part larger than a flow resistance of a branch pipe at the side far from said output part, and said inflow adjusting means are said flow resistance adjusting means. 
     In the invention described in claim  7 , there is provided the external combustion engine as set forth in claim  6 , wherein said plurality of branch pipes are provided with venturi, a resistance value of a venturi provided in a branch pipe at the side close to said output part is made larger than a resistance value of a venturi provided in a branch pipe at the side far from said output part, and said flow resistance adjusting means are said venturi. 
     In the invention described in claim  8 , there is provided the external combustion engine as set forth in claim  1 , wherein at said plurality of heating portions, said inflow adjusting means are formed so that a heating portion at the side close to said output part is positioned above a heating portion at the side far from said output part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein: 
         FIG. 1  is a cross-sectional view showing the schematic configuration of an external combustion engine according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view showing the schematic configuration of an external combustion engine according to a second embodiment of the present invention; 
         FIG. 3  is a cross-sectional view showing the schematic configuration of an external combustion engine according to a third embodiment of the present invention; 
         FIG. 4A  is an enlarged view of part A of  FIG. 3 , while  FIG. 4B  is a cross-sectional view along the line B-B of  FIG. 4A ; and 
         FIG. 5  is a cross-sectional view showing the schematic configuration of an external combustion engine according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Below, a first embodiment of the present invention will be explained based on  FIG. 1 . The external combustion engine according to the present invention is also called a “liquid piston type steam engine”. This engine is, for example, used as a drive source for an electrical generator.  FIG. 1  is a view showing the schematic configuration of an external combustion engine according to the present embodiment. The up and down arrows in  FIG. 1  show the up-down directions in the installed state of the external combustion engine. 
     The container  10  is a pipe-shaped pressure container in which the working fluid (in the present embodiment, water)  11  is sealed flowable in the liquid phase state and has one merging pipe  12  positioned at one end side of the container  10 , four branch pipes  131  to  134  positioned at the other end side of the container  10 , and a branched part  14  branching from the merging pipe  12  to the four branch pipes  131  to  134 . In the present embodiment, the merging pipe  12 , branch pipes  131  to  134 , and branched part  14  are formed by stainless steel. 
     The merging pipe  12  is formed into a substantial U-shape. It is arranged so that the two ends face upward. The four branch pipes  131  to  134  are formed into straight shapes. The branch pipes are arranged so that their longitudinal directions are parallel with the direction of gravity (up-down direction). The four branch pipes  131  to  134  have the same shapes and same dimensions. In the present embodiment, they are pipes of the same lengths and same inside diameters. 
     The branched part  14  is branched symmetrically into two limbs from one end of the merging pipe  12 , then is further branched symmetrically into two limbs at each limb and is connected to the bottom ends of the branch pipes  131  to  134 . The branched part  14  is shaped geometrically symmetric. That is, the four flow paths from the single end of the merging pipe  12  to the four bottom ends of the branch pipes  131  to  134  are shaped symmetrically. Therefore, the flow resistances of the four flow paths become the same. 
     The top ends of the branch pipes  131  to  134  are connected to a heat exchanger  15  exchanging heat between the working fluid  11  and the high temperature gas. The heat exchanger  15  is comprised of a box-shaped block member  16  and a case  17  housing the block member  16 . 
     The block member  16  forms part of the container  10  and is formed by copper, aluminum, or other material superior in coefficient of thermal conductivity. The longitudinal direction of the block member  16  faces the direction of arrangement of the four branch pipes  131  to  134  (lateral direction of  FIG. 1 ). 
     While not shown, for convenience in molding, the block member  16  is divided into a plurality of mating parts, then the plurality of mating parts are fastened together by screws or other fastening means. 
     Inside the block member  16 , the hollow parts are formed in communication with the four branch pipes  131  to  134 . Parts of the hollow parts form four heating portions  181  to  184 , which heat and evaporate part of the liquid phase state working fluid  11 . 
     The four heating portions  181  to  184  are disk-shaped spaces, which are provided corresponding to the four branch pipes  131  to  134 . The axial centers of the disk-shaped heating portions  181  to  184  and the axial centers of the branch pipes  131  to  134  are arranged coaxially. 
     Among the hollow parts inside the block member  16 , the parts positioned above the heating portions  181  to  184  form a steam reservoir  19  storing the steam of the working fluid  11  generated at the heating portions  181  to  184 . 
     This steam reservoir  19  extends in parallel to the direction of arrangement of the heating portions  181  to  184  (lateral direction in  FIG. 1 ) and is communicated with the four heating portions  181  to  184  through communicating paths  20  and  21 . The communicating paths  20  extend from the centers of the disk-shaped heating portions  181  to  184  to the top direction, while the communicating paths  21  extend from the outer circumferences of the disk-shaped heating portions  181  to  184  to the top direction. 
     A gas serving as an additional medium is sealed inside the steam reservoir  19  in a predetermined volume. As the additional medium, it is possible to select a medium maintaining a gas phase state under the operating condition of the external combustion engine. Therefore, the gas serving as the additional medium may for example be the easy-to-handle air or pure steam of the working fluid  11 . 
     The case  17  extends in the longitudinal direction of the block member  16  (lateral direction of  FIG. 1 ). At the two ends of the case  17 , gas pipes (not shown) through which high temperature gas (high temperature fluid) serving as a heat source flows, are connected. The space formed between the outer surface of the block member  16  and the inside wall surface of the case  17  forms a gas flow path  22  through which the high temperature gas flows. 
     The gas flow path  22  inside the case  17  is provided with heat conduction fins (not shown) for increasing the heat conduction area between the block member  16  and the high temperature gas. 
     At the outer circumference of the bottom ends of the branch pipes  131  to  134 , a cooler  23  through which cooling water is circulated is arranged in contact with the pipes for heat conduction. The inside spaces of the branch pipes  131  to  134  in contact with the cooler  23  form cooling portions  241  to  244  for cooling and condensing the working fluid  11  evaporated at the heating portions  181  to  184 . 
     Therefore, by cooling water circulating in the cooler  23 , the portions of the branch pipes  131  to  134  in contact with the cooler  23  are cooled. Due to this, the working fluid  11  is cooled at the cooling portions  241  to  244 . 
     The cooling water inlet  23   a  and cooling water outlet  23   b  of the cooler  23  are connected to a circulation path of cooling water. A radiator (not shown) is arranged in the circulation path of the cooling water. Due to this, the heat which the cooling water robs from the steam of the working fluid  11  is radiated by the radiator into the atmosphere. The portions of the branch pipes  131  to  134  in contact with the cooler  23  may be formed by copper or aluminum superior in coefficient of thermal conductivity. 
     The other end of the merging pipe  12  is communicated with the output part  25 . The output part  25  has a piston  26  displacing upon receiving pressure from the liquid phase part of the working fluid  11  and a cylinder  27  supporting the piston  26  in a slidable manner. 
     Next, the operation in the above configuration will be briefly explained. 
     First, when the working fluid (water)  11  in the heating portions  181  to  184  is heated and vaporized, high temperature and high pressure steam of the working fluid  11  is built up in the steam reservoir  19  and the heating portions  181  to  184  and the level of the working fluid  11  is pushed down in the branch pipes  131  to  134 . 
     This being the case, the liquid phase part of the working fluid  11  is pushed from the side of the heating portions  181  to  184  to the side of the output part  25  and the piston  26  of the output part  25  is pushed up (first stroke). 
     Next, when the level of the working fluid  11  in the branch pipes  131  to  134  falls to the cooling portions  241  to  244  and steam of the working fluid  11  enters the cooling portions  241  to  244 , the steam of the working fluid  11  is cooled by the cooling portions  241  to  244  and condensed. For this reason, the force pushing down the level of the working fluid  11  is eliminated and the force pushing up the piston  26  is also eliminated. 
     The pushed up piston  26  at the output part  25  side descends, the liquid phase part of the working fluid  11  is pushed back from the output part  25  side to the heating portion  181  to  184  side, and the level of the working fluid  11  rises to the heating portions  181  to  184  (second stroke). 
     By repetition of this operation, the liquid phase part of the working fluid  11  in the container  10  cyclically displaces (so-called self excited vibration) and the piston  26  of the output part  25  is made to cyclically move up and down. 
     That is, by alternately repeating the evaporation and condensation of the working fluid  11 , the liquid phase part of the working fluid  11  displaces like a piston. This displacement of the liquid phase part of the working fluid  11  is converted to mechanical energy and output at the output part  25 . 
     In the present embodiment, the branched part  14  is made geometrically symmetric and the flow resistances of the four flow paths from the single end of the merging pipe  12  to the four ends of the branch pipes  131  to  134  at the branched part  14  are made the same. 
     For this reason, the liquid phase state working fluid  11  can be made to equally reach the four heating portions  181  to  184 , so the heating performance (evaporation performance) of the working fluid  11  can be improved and in turn the output of the external combustion engine can be increased. 
     As will be understood from the above explanation, the present embodiment forms the branched part  14  to be geometrically symmetrical. Due to this, the inflow adjusting means of the present invention is formed by making the flow resistances of the four flow paths from the single end of the merging pipe  12  to the four ends of the branch pipes  131  to  134  at the branched part  14  the same. 
     Second Embodiment 
     The first embodiment forms the branched part  14  to be geometrically symmetric, but in the second embodiment, as shown in  FIG. 2 , the flow resistance of the branched part  14  is made smaller than the flow resistance of the cooling portions  241  to  244 . 
     In the present embodiment, the merging pipe  12  is formed into a substantially L-shape. The end of the merging pipe  12  at the output part  25  side faces upward, while the other end thereof is arranged to face the direction of arrangement of the branch pipes  131  to  134  (lateral direction of  FIG. 1 ). 
     The branched part  14  is formed in a straight shape and is arranged so that its longitudinal direction becomes parallel to the direction of arrangement of the branch pipes  131  to  134  (lateral direction of  FIG. 1 ). In the present embodiment, the cross-sectional shape of the flow path of the branched part  14  is circular, but it is not necessarily limited to a circular shape and may also be noncircular. 
     Further, the length l in  of the branched part  14 , the hydraulic diameter d in  of the flow path of the branched part  14 , the length l r  of the cooling portions  241  to  244 , and the hydraulic diameter d r  of the flow path of the cooling portions  241  to  244  satisfy the following relationship:
 
 l   in   /d   in   &lt;l   r   /d   r  
 
     The hydraulic diameter of the flow path is the diameter when converting the cross-sectional shape of the flow path to a circle and is expressed by the following formula:
 
 d   e =4 ×S/L  
 
     where, d e  is the hydraulic diameter, S is the sectional area of the flow path (corresponding to sectional area of circle), L is the length of the wetted perimeter (corresponding to circumference). 
     In the present embodiment, the cross-sectional shape of the flow path of the branched part  14  is circular, so the hydraulic diameter d in  of the flow path of the branched part  14  is the same as the inside diameter of the branched part  14 . The hydraulic diameters d r  of the flow paths of the cooling portions  241  to  244  are the same as the inside diameters of the cooling portions  241  to  244 . 
     According to the present embodiment, the flow resistance of the branched part  14  becomes smaller than the flow resistances of the cooling portions  241  to  244 , so compared with the case where the flow resistance of the branched part  14  is the same as the flow resistances of the cooling portions  241  to  244 , it is possible to equalize the inflow of the liquid phase state working fluid  11  to the cooling portions  241  to  244 . 
     As a result, in the same way as the above first embodiment, it is possible to equalize the inflow of the working fluid  11  in the liquid phase state to the four heating portions  181  to  184  and, in turn, increase the output of the external combustion engine. 
     Third Embodiment 
     In the above second embodiment, the flow resistance of the branched part  14  is made smaller than the flow resistances of the cooling portions  241  to  244 , but in the third embodiment, as shown in  FIG. 3 ,  FIG. 4A  and  FIG. 4B , among the branch pipes  131  to  134 , a flow resistance of a branch pipe at the side close to the output part  25  is made larger than a flow resistance of a branch pipe at the side far from the output part  25 . 
     Specifically, the bottom ends of the branch pipes  131  to  134  are provided with venturi  301  to  304 . The resistance values of the venturi  301  to  304  are set to become larger the further from the venturi  301  farthest from the output part  25  toward the venturi closest to the output part  25 . The venturi  301  to  304  correspond to the flow resistance adjusting means in the present invention. 
     In the present embodiment, fixed venturi are used as the venturi  301  to  304 , so the venturi diameters of the venturi  301  to  304  are set to become smaller along the flow path of the branched part  14  from the venturi  301  farthest from the output part  25  toward the venturi  304  closest to the output part  25 . 
     In the present embodiment, the flow resistance of the branched part  14  becomes substantially the same as the flow resistances of the cooling portions  241  to  244 . 
     According to the present embodiment, at the branch pipes  131  to  134 , a flow resistance of a branch pipe at the side close to the output part  25  becomes larger than a flow resistance of a branch pipe at the side far from the output part  25 , so inflow of the liquid phase state working fluid  11  to a branch pipe at the side close to the output part  25  is suppressed. 
     For this reason, compared with the case where the flow resistances of the branch pipes  131  to  134  are the same as each other, it is possible to equalize the inflow of the liquid phase state working fluid  11  to the branch pipes  131  to  134 . 
     As a result, in the same way as the above first embodiment, it is possible to equalize the inflow of the liquid phase state working fluid  11  to the four heating portions  181  to  184  and in turn possible to increase the output of the external combustion engine. 
     The higher the drive frequency of the external combustion engine becomes, the greater the difference between the inflow of the working fluid  11  to a branch pipe at the side close to the output part  25 , and the inflow of the working fluid  11  to a branch pipe at the side far from the output part  25  becomes. 
     In consideration of this point, for external combustion engines set with high drive frequencies, the difference between a resistance value of a venturi of the side close to the output part  25  and a resistance value of a venturi of the side far from the output part  25  is preferably set large. 
     In the present embodiment, fixed venturi are used as the venturi  301  to  304 , but it is also possible to use variable venturi as the venturi  301  to  304 . 
     When using variable venturi as the venturi  301  to  304 , the difference between a resistance value of a venturi of the side close to the output part  25  and a resistance value of a venturi of the side far from the output part  25  can be changed in accordance with fluctuation of the drive frequency of the external combustion engine accompanying load fluctuations at the output part  25  side. 
     In this case, as the venturi  301  to  30 , electrical type variable venturi are used. When the drive frequency of the external combustion engine is low, the difference between a resistance value of a venturi of the side close to the output part  25  and a resistance value of a venturi of the side far from the output part  25  is controlled to become smaller, while when the drive frequency of the external combustion engine is high, the difference between a resistance value of a venturi of the side close to the output part  25  and a resistance value of a venturi of the side far from the output part  25  is controlled to become larger. 
     Further, in the present embodiment, the venturi  301  to  304  are arranged at the bottom ends of the branch pipes  131  to  134 , but it is not necessary required that they be arranged at the bottom ends. It is possible to arrange the venturi  301  to  304  at any locations of the branch pipes  131  to  134 . 
     Further, in the present embodiment, all branch pipes  131  to  134  are provided with venturi  301  to  304 . The venturi  301  to  304  form the flow resistance adjusting means in the present invention, but it is not necessarily required that all branch pipes  131  to  134  be provided with venturi. It is also possible to have only the branch pipe at the side close to the output part  25  provided with a venturi and have the branch pipe at the side far from the output part  25  not provided with a venturi so as to form the flow resistance adjusting means in the present invention. 
     Fourth Embodiment 
     In the above third embodiment, among the branch pipes  131  to  134 , a flow resistance of a branch pipe at the side close to the output part  25  is made larger than a flow resistance of a branch pipe at the side far from the output part  25 . 
     On the other hand, in the fourth embodiment, as shown in  FIG. 5 , among the heating portions  181  to  184 , a heating portion at the side close to the output part  25  is arranged at a position higher than a heating portion at the side far from the output part  25 . In  FIG. 5 , the dimension AH shows the difference in heights of the arrangement positions between the heating portion  181  farthest from the output part  25  and the heating portion  184  closest to the output part  25 . 
     In the present embodiment, the placement heights of the heating portions  181  to  184  become higher from the heating portion  181  farthest from the output part  25  toward the heat portion  184  closest to the output part  25 . 
     Due to this, compared with the case where the placement heights of the four heating portions  181  to  184  are made the same, it is possible to equalize the inflow of the liquid phase state working fluid  11  to the four heating portions  181  to  184  and, in turn, increase the output of the external combustion engine. 
     Preferably, by changing the heights of the heating portions  181  to  184  by exactly the difference in flow resistance at the branched part  14 , the liquid phase state working fluid  11  may be made to flow equally to the four heating portions  181  to  184  and, in turn, possible to increase the output of the external combustion engine more. 
     Other Embodiments 
     (1) In the above embodiments, the heating portions  181  to  184  are formed in disk shapes expanding in the horizontal direction with respect to the branch pipes  131  to  134 , but the heating portions  181  to  184  can be changed in shape in various ways. For example, they may also be formed into cylindrical shapes extending upward with the same inside diameters as the branch pipes  131  to  134 . 
     (2) In the above embodiments, four each of the branch pipes  131  to  134  and the heating portions  181  to  184  are formed, but it is also possible to provide any number of branch pipes and heating portions so long as two or more. 
     Further, in the above embodiments, the branch pipes  131  to  134  and the heating portions  181  to  184  are arranged in only the flow direction of the high temperature gas (lateral direction of  FIG. 1  to  FIG. 3  and  FIG. 5 ), but it is also possible to arrange the branch pipes and the heating portions in not only the flow direction of the high temperature gas, but also the direction perpendicular to the flow direction of the high temperature gas (direction vertical to paper surface of  FIG. 1  to  FIG. 3  and  FIG. 5 ). Due to this, it is possible to suppress the increase the volume of the external combustion engine, so it is possible to increase the number of the branch pipes and the heating portions. 
     (3) In the above embodiments, high temperature gas is used as the heat sources of the heating portions  181  to  184 , but it is also possible to use various high temperature fluids as the heat sources of the heating portions  181  to  184 . 
     Further, heating elements may also be used as the heat sources of the heating portions  181  to  184 . In this case, the heating elements may be brought into contact with the block member  16  in a heat conductible manner, or the heating elements may be arranged in proximity at predetermined distances from the block member  16 . 
     (4) The external combustion engine according to the present invention can be applied to not only the drive source of an electrical generator, but also the drive source of various other apparatuses. 
     While the invention has been described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.