Patent Publication Number: US-8109086-B2

Title: External combustion engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an external combustion engine using the change of volume of a working fluid accompanying generation and liquefaction of steam of the working fluid to cause displacement of a liquid part of the working fluid and converting this to mechanical energy for output. 
     2. Description of the Related Art 
     In the past, this type of external combustion engine was described in Japanese Unexamined Patent Publication No. 2007-255259. In this prior art, the average pressure of the internal pressure of the main container was made to approach a target pressure for the purpose of improving the output and efficiency of the external combustion engine. 
     Explaining this in brief, liquid is sealed in an auxiliary container separate from the main container in which the working fluid is sealed, this auxiliary container and main container are communicated through a venturi means, and the liquid in the auxiliary container is heated by an auxiliary heater to vaporize it. 
     The auxiliary container and the auxiliary heater are configured so that the internal pressure of the auxiliary container becomes close to the target pressure. Due to this, the average pressure of the internal pressure of the main container is made to change tracking the internal pressure of the auxiliary container and the average pressure of the internal pressure of the main container is made to approach the target pressure. 
     According to this prior art, it is possible to maintain the average pressure of the internal pressure of the main container at substantially the target pressure without using a control device or various types of sensors etc., so the output and efficiency of the external combustion engine can be improved by a simplified configuration. 
     SUMMARY OF THE INVENTION 
     The inventors studied using the high temperature exhaust gas of another heat engine (for example, an automobile engine) as a heat source of the auxiliary heater so as to raise the efficiency of energy utilization. 
     In this studied comparative example, for example, when the other heat engine is being operated in its maximum output state etc., the temperature of the exhaust gas becomes extremely high. As a result, the temperature of the auxiliary heater ends up excessively rising beyond the normally envisioned temperature. When the internal pressure of the auxiliary container also ends up excessively rising beyond the normally envisioned pressure, measures have to be taken to prevent the auxiliary container etc. from breaking. 
     Even when using something other than the exhaust gas of another heat engine as the heat source of the auxiliary heater (for example, a heating element etc.), a similar situation occurs if the temperature of the heat source of the auxiliary heater becomes extremely high and the temperature of the auxiliary heater excessively rises. 
     The present invention was made in consideration of the above problem and has as its object the suppression of the rise of the internal pressure of the auxiliary container in emergencies when the temperature of the auxiliary heater excessively rises. 
     To achieve the above object, in the invention as set forth in claim  1 , there is provided an external combustion engine provided with a main container in which a working fluid is sealed flowable in a liquid phase state, a heater heating part of the liquid phase state working fluid in the main container to make it vaporize, a cooler cooling steam of the working fluid heated and vaporized by the heater so as to make it liquefy, an output part converting displacement of the liquid part of the working fluid caused by a change of volume of the steam into mechanical energy and outputting the energy, an auxiliary container communicated with the main container through a venturi means and having a liquid sealed inside it, an auxiliary heater heating the liquid in the auxiliary container to make it vaporize, a storage container communicated with the auxiliary container and storing the liquid, and a liquid draining means for draining liquid in the auxiliary container into the storage container when the internal pressure of the auxiliary container becomes a first predetermined pressure or more. 
     According to this, by draining the liquid in the auxiliary container into the storage container, the internal pressure of the auxiliary container can be lowered, so at times of emergencies where the temperature of the auxiliary heater excessively rises, a rise of the internal pressure of the auxiliary container can be suppressed. 
     Note that, “the internal pressure of the auxiliary container becomes a first (second) predetermined pressure or more (or less)” in the present invention includes in meaning when the differential pressure between the internal pressure of the auxiliary container and the internal pressure of the storage container becomes a first (second) predetermined pressure or more (or less). 
     In the invention as set forth in claim  2 , there is provided the external combustion engine as set forth in claim  1 , wherein the auxiliary container and the storage container are communicated via a first valve, the first valve opens when the internal pressure of the auxiliary container becomes a first predetermined pressure or more, and the liquid draining means is the first valve. 
     In the invention as set forth in claim  3 , there is provided the external combustion engine as set forth in claim  2 , wherein the auxiliary container and the storage container are communicated via a first pipe, the first valve is arranged in the first pipe, and an end of the first pipe at the auxiliary container side is arranged to be lower than a level of a liquid in the auxiliary container. 
     In the invention as set forth in claim  4 , there is provided the external combustion engine as set forth in claim  1 , further provided with a liquid returning means for returning the liquid in the storage container to the auxiliary container when the internal pressure of the auxiliary container becomes a second predetermined pressure which is smaller than first predetermined pressure, or less. 
     Due to this, after the liquid draining means drains the liquid from the auxiliary container to the storage container, the liquid can be easily returned from the storage container to the auxiliary container. 
     In the invention as set forth in claim  5 , there is provided the external combustion engine as set forth in claim  4 , wherein the auxiliary container and the storage container are communicated via a second valve, the second valve opens when the internal pressure of the auxiliary container becomes a second predetermined pressure or less, and the liquid returning means is the second valve. 
     In the invention as set forth in claim  6 , there is provided the external combustion engine as set forth in claim  5 , wherein the auxiliary container and the storage container are communicated via a second pipe, the second valve is arranged in the second pipe, and an end of the second pipe at the storage container side is arranged to be lower than a level of the liquid in the storage container. 
     In the invention as set forth in claim  7 , there is provided the external combustion engine as set forth in claim  5 , wherein the auxiliary container and the storage container are communicated via a second pipe, the second valve is arranged in the second pipe, an end of the second pipe at the storage container side is arranged to be lower than a level of the liquid in the storage container, and the second pipe as a whole is arranged lower than the first pipe. 
     In the invention as set forth in claim  8 , there is provided the external combustion engine as set forth in claim  1 , wherein the storage container is opened to the atmosphere. 
     In the invention as set forth in claim  9 , there is provided the external combustion engine as set forth in claim  1 , wherein the storage container is sealed and gas is sealed in the storage container. 
     In the invention as set forth in claim  10 , there is provided the external combustion engine as set forth in claim  9 , wherein the storage container is formed by a soft bag deforming due to the differential pressure between the inside and outside. 
     Due to this, when the amount of the liquid in the storage container fluctuates, the inside volume of the storage container changes in accordance with the fluctuations in the amount of liquid, so it is possible to suppress fluctuations in the internal pressure of the storage container accompanying fluctuations in the amount of liquid in the storage container. Further, by forming the storage container by a soft bag, it is possible to change the inside volume of the storage container. 
    
    
     
       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 schematic view of an electric power generation system showing a first embodiment of the present invention; 
         FIG. 2  is a graph showing a temperature gradient in an auxiliary container of  FIG. 1 ; 
         FIG. 3  is a view of a heat resistance model of an auxiliary container of  FIG. 1 ; 
         FIG. 4  is a schematic view of an electric power generation system showing a second embodiment of the present invention; 
         FIG. 5  is a schematic view of an electric power generation system showing a third embodiment of the present invention; and 
         FIG. 6  is a schematic view of an electric power generation system showing 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  to  FIG. 3 . The external combustion engine of the present invention is also called a “liquid piston type steam engine”. This embodiment applies the external combustion engine of the present invention to a drive source of an electric power generation system mounted in an automobile.  FIG. 1  is a view of the configuration showing the schematic configuration of an external combustion engine in the present embodiment. The up and down arrows at the top of  FIG. 1  show the up-down directions in the mounted state of the external combustion engine. 
     The main 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. The main container  10  has one merging pipe  12  positioned at one end side of the main container  10  and a plurality of (four in the present embodiment) branch pipes  131  to  134  branching from the merging pipe  12  at the other end side of the main container  10 . 
     In the present embodiment, the merging pipe  12  and branch pipes  131  to  134  are made from stainless steel. In the present embodiment, the cross-sectional shapes of the flow paths of the merging pipe  12  and branch pipes  131  to  134  are circular. The invention is not necessarily limited to circular shapes and may also be non-circular shapes. 
     The part of the merging pipe  12  where the branch pipes  131  to  134  are connected extends in the horizontal direction. The branch pipes  131  to  134  extend upward from the merging pipe  12 . The top ends of the branch pipes  131  to  134  are connected by a heater  14  exchanging heat of the working fluid  11  with exhaust gas (high temperature gas) of another heat engine (in the present embodiment, the automobile engine) to heat the working fluid  11 . The heater  14  forms part of the main container  10 . In the present embodiment, it is formed from copper superior in heat conductivity. 
     The heater  14  is arranged in gas pipe  15  through which the exhaust gas flows. Inside the heater  14 , hollow parts are formed communicating with the four branch pipes  131  to  134 . Parts of the hollow parts form heating portions  161  to  164  heating part of the liquid phase state working fluid  11  to evaporate. These heating portions  161  to  164  are four disk-shaped spaces provided corresponding to the branch pipes  131  to  134  and are arranged coaxially with the branch pipes  131  to  134 . 
     Among the hollow parts inside the heater  14 , the parts positioned above the heating portions  161  to  164  form a steam reservoir  17  storing the steam of the working fluid  11  generated at the heating portions  161  to  164 . 
     The steam reservoir  17  extends in parallel to the direction of arrangement of the heating portions  161  to  164  (left-right direction of  FIG. 1 ) and is communicated through communicating paths  18  and  19  to heating portions  161  to  164 . The communicating paths  18  extend from the centers of the disk-shaped heating portions  161  to  164  upward, while the communicating paths  19  extend from the outer circumferential parts of the disk-shaped heating portions  161  to  164  upward. 
     The steam reservoir  17  has a gas sealed in it as an additional medium in exactly a predetermined volume. As the additional medium, it is possible to select a medium for maintaining a gas phase state under the operating conditions of the external combustion engine. The gas used as the additional medium may for example be the easily handling air and may be pure steam of the working fluid  11 . 
     While not shown, for molding purposes, the heater  14  is molded split into a plurality of parts, then the plurality of split parts are fastened together by screws or other fastening means. At this time, the seal can be secured by arranging seal members between the plurality of split parts. It is also possible to join the plurality of split parts together by welding, brazing, or other connecting means. 
     The branch pipes  131  to  134  are arranged so as to run through the inside of a cooler  20  in which cooling water is circulated. The parts of the branch pipes  131  to  134  positioned in the cooler  20  form cooling portions  211  to  214  cooling the working fluid  11  evaporated at the heating portions  161  to  164  and making it condense. By cooling water circulating through the cooler  20 , the cooling portions  211  to  214  are cooled, and the cooling portions  211  to  214  cool the working fluid  11 . 
     A cooling water inlet  20   a  and a cooling water outlet  20   b  of the cooler  20  are connected to a circulation circuit of the cooling water. Inside the circulation circuit of the cooling water, a radiator (not shown) is arranged. Due to this, heat which the cooling water robs from the steam of the working fluid  11  is radiated by the radiator to the atmosphere. 
     The external combustion engine of the present embodiment is mounted in an automobile, so heat which the cooling water robs from the steam of the working fluid  11  can be utilized for warming up the automobile engine or utilized as the heat source for a heat core of an automobile air-conditioning system. The parts of the branch pipes  131  to  134  which form the cooling portions  211  to  214  may be formed from the superior heat conductivity copper. 
     The end part of the main container  10  at the merging pipe  12  side is communicated with an output part  22 . In the case of the present embodiment, the main container  10  is bent at its intermediate part (merging pipe  12 ) into an L-shape. The end of the main container  10  at the merging pipe  12  side is directed downward. The end part of the main container  10  at the merging pipe  12  side may also be directed upward or in the horizontal direction. 
     The output part  22  is provided with a piston  22   a  displacing upon receiving pressure from the liquid phase part of the working fluid  11 , a cylinder  22   b  slidably supporting the piston  22   a , and a coil spring (not shown) generating an elastic force pressing the piston  22   a  to the main container  10  side (upward in  FIG. 1 ). Instead of a coil spring, a crank and flywheel may also be used. 
     Next, the operation in the above basic configuration will be simply explained. First, if the working fluid (water)  11  in the heating portions  161  to  164  is heated and evaporates, high temperature, high pressure steam of the working fluid  11  is stored in the steam reservoir  17  and in the heating portions  161  to  164  and pushes down the levels of the working fluid  11  in the branch pipes  131  to  134 . 
     This being the case, the liquid phase part of the working fluid  11  is pushed out from the heating portion  161  to  164  side to the output part  22  side and the piston  22   a  of the output part  22  is pushed down (first stroke). At this time, the piston  22   a  elastically compresses the not shown coil spring. 
     Next, the levels of the working fluid  11  in the branch pipes  131  to  134  fall to the cooling portions  211  to  214 . If steam of the working fluid enters the cooling portions  211  to  214 , the steam of the working fluid  11  is cooled and condensed by the cooling portions  211  to  214 . 
     For this reason, the force pushing down the level of the working fluid  11  is cancelled and the force pushing down the piston  22   a  is cancelled. The once pushed down piston  22   a  at the output part  22  side rises due to the elastic spring back force of the not shown coil spring, the liquid phase part of the working fluid  11  is pushed back from the output part  22  side toward the heating portion  161  to  164  side, and the level of the working fluid  11  rises to the heating portions  161  to  164  (second stroke). 
     When using a crank and flywheel instead of the coil spring, the pushed down piston  22   a  at the output part  22  side rises due to inertia of the flywheel, the liquid phase part of the working fluid  11  is pushed back from the output part  22  side toward the heating portion  161  to  164  side, and the level of the working fluid  11  rises to the heating portions  161  to  164 . 
     By repeating such an operation (first stroke and second stroke), the liquid phase part of the working fluid  11  in the main container  10  cyclically displaces (so-called “self vibration”) and makes the piston  22   a  of the output part  22  cyclically move up and down. 
     That is, the working fluid  11  is alternately repeatedly evaporated and condensed whereby the steam of the working fluid  11  changes in volume. Due to this, the liquid phase part of the working fluid  11  appears to displace 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  22 . 
     Next, the configuration for adjusting the internal pressure of the main container  11  will be explained. The auxiliary container  30  is communicated with the main container  11  via a venturi means  31 . In the present embodiment, the auxiliary container  30  is arranged above the merging pipe  12 , the bottom part of the auxiliary container  30  and the merging pipe  12  are connected by pipe  32 , and the venturi means  31  is formed in the pipe  32 . 
     Due to the venturi means  31 , the internal pressure of the auxiliary container  30  (hereinafter referred to as “the auxiliary container inside pressure”) does not cyclically fluctuate following the internal pressure of the main container  11 , but stabilizes at a pressure substantially equal to the average value of the internal pressure of the main container  11  (hereinafter referred to as the “average pressure in the main container”). In the present embodiment, as the venturi means  31 , a fixed venturi of a reduced diameter of the passage is used. 
     In the present embodiment, the auxiliary container  30  and pipe  32  are made of stainless steel. The inside volume of the auxiliary container  30  is smaller than the inside volume of the main container  11 . Inside the auxiliary container  30 , a liquid  33  and a gas  34  are sealed. It is also possible to fill the inside of the auxiliary container  30  with just a liquid  33 . 
     In the present embodiment, as the liquid  33 , a liquid the same as the working fluid  11  (in the present embodiment, water) is used. When using a liquid different from the working fluid  11  as the liquid  33 , in the present embodiment, since the auxiliary container  30  is arranged above the merging pipe  12 , it is preferable to use a liquid with a smaller specific gravity than the working fluid  11 . 
     As the gas  34 , it is preferable to use a gas exhibiting poor solubility in the working fluid  11 . As the gas  34  in the present embodiment, helium, which exhibits poor solubility in water, is used. 
     An auxiliary heater  35  for heating and vaporizing the liquid  33  in the auxiliary container  30  is arranged so as to cover the top of the auxiliary container  30 . This auxiliary heater  35  is connected to be able to conduct heat with the heater  14 . Specifically, the auxiliary heater  35  and the heater  14  are connected through a connection member  36  formed from a superior heat conductivity material (for example, copper). 
     Due to this, the auxiliary heater  35  is heated by heat conducted from the heater  14 , so the auxiliary heater  35  can heat the auxiliary container  30  and can heat the liquid  33  in the auxiliary container  30 . 
       FIG. 2  is a graph showing the temperature gradient of the auxiliary container  30  when the auxiliary container  30  is heated. As shown in  FIG. 2 , the auxiliary container  30  is provided with a heat conducting structure where, at a top high temperature part  30   a , the temperature gradient is small enough to be ignored and, at the bottom low temperature part  30   b , a temperature gradient is formed where the temperature falls the further from the high temperature part  30   a.    
     In  FIG. 2 , the temperature Tm is the temperature of the high temperature part  30   a  (below, this temperature called the “high temperature part temperature”). The temperature Tc is the temperature at the bottom end of the low temperature part  30   b  (below, this temperature called the “low temperature part temperature”). This low temperature part temperature Tc is a temperature substantially the same as the temperature of the cooling portions  211  to  214  (more accurately is a temperature slightly higher than the temperature of the cooling portions  211  to  214 ). Therefore, the low temperature part temperature Tc is a temperature of the boiling point of the liquid  33  or less. 
       FIG. 3  shows a heat resistance model in the auxiliary container  30 . In  FIG. 3 , Th is the temperature of the heater  14 , Rh is the heat resistance between the heater  14  and the high temperature part  30   a  of the auxiliary container  30 , and Rm is the heat resistance between the high temperature part  30   a  of the auxiliary container  30  and the bottom end of the low temperature part  30   b  (outlet part of auxiliary container  30 ). 
     As will be understood from  FIG. 3 , the auxiliary container  30  has a structure having heat resistance such that, if heated by the auxiliary heater  35 , the high temperature part temperature Tm becomes lower than the temperature Th of the heater  14  and higher than the low temperature part temperature Tc (Tc&lt;Tm&lt;Th). 
     Further, the auxiliary container  30  is heated by the heat conducted from the heater  14 , so the high temperature part temperature Tm becomes smaller than the temperature T 1  of the heating portions  161  to  164  of the main container  11  (below, called the “heating portion temperature”). On the other hand, as explained above, the low temperature part temperature Tc is a temperature slightly higher than the temperature T 2  of the cooling portions  211  to  214  (below, called the “cooling portion temperature”). For this reason, the high temperature part temperature Tm becomes lower than the heating portion temperature T 1  and higher than the cooling portion temperature T 2  (T 2 &lt;Tm&lt;T 1 ). 
     As shown in  FIG. 1 , the storage container  40  storing the liquid  33  is communicated with the auxiliary container  30  through the first and second pipes  41  and  42 . The storage container  40  is a container having a certain degree of rigidity (for example, a plastic container etc.). The internal pressure of the storage container  40  is about the atmospheric pressure. In the present embodiment, the storage container  40  is opened to the atmosphere, so the internal pressure of the storage container  40  becomes the same as the atmospheric pressure. 
     The first and second pipes  41  and  42  are arranged in parallel. In the present embodiment, the second pipe  42  as a whole is arranged below the first pipe  41 . The first pipe  41  is a pipe for draining the liquid  33  in the auxiliary container  30  to the storage container  40 . Inside the first pipe  41 , a first valve (liquid draining means)  43  is arranged. 
     The second pipe  42  is a pipe for returning the liquid drained from the auxiliary container  30  through the first pipe  41  to the storage container  40 , to the auxiliary container  30 . In the second pipe  42 , a second valve (liquid returning means)  44  is arranged. In the present embodiment, one-way valves are used as the first and second valves  43  and  44 . 
     The first valve  43  opens when the differential pressure between the auxiliary container inside pressure and the internal pressure of the storage container  40  becomes a first predetermined pressure ΔP 1  or more. Here, the first predetermined pressure ΔP 1  is a pressure greater than the later explained target pressure. The second valve  44  opens when the differential pressure between the auxiliary container inside pressure and the internal pressure of the storage container  40  becomes a second predetermined pressure ΔP 2  smaller than the first predetermined pressure ΔP 1  or less. 
     The ends of the first and second pipes  41  and  42  at the auxiliary container  30  sides are arranged below the level of the liquid  33  in the auxiliary container  30 . In the present embodiment, the ends of the first and second pipes  41  and  42  at the auxiliary container  30  sides are arranged in a pipe  32  connecting the bottom of the auxiliary container  30  and the merging pipe  12 . 
     The ends of the first and second pipes  41  and  42  at the storage container  40  sides are arranged below the level of the liquid  33  in the storage container  40 . In the present embodiment, the ends of the first and second pipes  41  and  42  at the storage container  40  sides are arranged at the bottom part of the storage container  40 . 
     Next, the operation for adjusting the internal pressure of the main container  11  by the above configuration will be explained. If heat conducted from the heater  14  causes the liquid  33  in the high temperature part  30   a  to be heated and vaporized, steam at high temperature and high pressure is stored at the high temperature part  30   a . The auxiliary container  30  is configured so that, at this time, the level of the liquid  33  will not be pushed down to the low temperature part  30   b , but will be positioned in the high temperature part  30   a.    
     Due to this, the liquid  33  continues to contact the high temperature part  30   a , so the liquid  33  in the auxiliary container  30  is maintained in the boiling state. For this reason, the auxiliary container inside pressure can be maintained at the same pressure as the saturated steam pressure of the liquid  33  in the high temperature part temperature Tm. 
     The above-mentioned heat resistance Rh and heat resistance Rm are set so that when making the temperature of the liquid  33  in the case where the saturated steam pressure of the liquid  33  becomes equal to the target value of the average pressure in the main container (below, referred to as the “target pressure”) the target temperature, the high temperature part temperature Tm becomes substantially equal to the target temperature. For this reason, the auxiliary container inside pressure becomes substantially equal to the target pressure. In other words, the auxiliary container  30 , auxiliary heater  35 , and connection member  36  are configured so that the internal pressure of the auxiliary container  30  becomes substantially the target pressure. 
     Due to this, the internal pressure of the auxiliary container  30  is maintained at substantially the target pressure, so the average pressure in the main container changes tracking the auxiliary container inside pressure and approaches the target pressure. As a result, even if the heating portion temperature T 1  fluctuates, it is possible to maintain the average pressure in the main container at substantially the target pressure, so it is possible to prevent a drop in the performance (output and efficiency) due to fluctuations in the heating portion temperature T 1 . 
     The operation for adjusting the internal pressure of the main container  11  described here was the operation in the state where the temperature of the auxiliary heater  35  was the normally envisioned temperature (normal state). 
     However, when, for example, the temperature of the exhaust gas becomes extremely high like when the automobile engine is operating in its maximum output state, the temperature of the auxiliary heater  35  will excessively rise beyond the normally envisioned temperature. In this case, the high temperature part temperature Tm and low temperature part temperature Tc of the auxiliary container  30  will end up excessively rising beyond the normally envisioned temperature and the auxiliary container inside pressure will also end up excessively rising beyond the normally envisioned pressure. 
     In the present embodiment, in emergencies where the temperature of the auxiliary heater  35  excessively rises, when the differential pressure between the auxiliary container inside pressure and the internal pressure of the storage container  40  becomes a first predetermined pressure ΔP 1  or more, the first valve  43  opens, so the liquid  33  in the auxiliary container  30  drains to the storage container  40 . For this reason, the auxiliary container inside pressure can be lowered. 
     Further, when the differential pressure between the auxiliary container inside pressure and the internal pressure of the storage container  40  becomes a second predetermined pressure ΔP 2  smaller than the first predetermined pressure ΔP 1  or less, the second valve  44  opens, so the liquid  33  drained from the auxiliary container  30  to the storage container  40  can be returned to the auxiliary container  30 . 
     Due to the above, in emergencies where the temperature of the auxiliary heater  35  excessively rises, a rise in the auxiliary container inside pressure can be suppressed. As a result, it is possible to prevent the auxiliary container  30  etc. from breaking due to the rise in the auxiliary container inside pressure. 
     Showing an example of settings of the first and second predetermined pressure ΔP 1 , ΔP 2 , in this example, the auxiliary container inside pressure is usually 1 MPa or so, so the first predetermined pressure ΔP 1  is set to 1.5 MPa (ΔP 1 =1.5 MPa). That is, the first valve  43  opens when the auxiliary container inside pressure becomes 1.5 MPa or more higher than the internal pressure of the storage container  40 . 
     Further, the second predetermined pressure ΔP 2  is set to −0.05 MPa (ΔP 2 =−0.05 MPa). That is, the second valve  44  opens when the auxiliary container inside pressure becomes 0.05 MPa or more lower than the internal pressure of the storage container  40 . 
     Therefore, in this example, when the temperature of the auxiliary container  30  becomes extremely high, the first valve  43  opens, and the liquid  33  in the auxiliary container  30  is drained to the storage container  40 , and the heating of the auxiliary container  30  by the auxiliary heater  35  is stopped (specifically, the automobile engine is stopped). When the auxiliary container inside pressure falls to the internal pressure of the storage container  40  or less, the second valve  44  opens, and the liquid  33  in the storage container  40  is returned to the auxiliary container  30 . 
     As another example of setting, the second predetermined pressure ΔP 2  may also be set to about 1 MPa of course (ΔP 2 =1 MPa). 
     Second Embodiment 
     In the first embodiment, the ends of the first and second pipes  41  and  42  at the storage container  40  sides were arranged below the level of the liquid  33  in the storage container  40 . On the other hand, in the second embodiment, as shown in  FIG. 4 , the end of the first pipe  41  at the storage container  40  side is arranged higher than the level of the liquid  33  in the storage container  40 . 
     In the present embodiment as well, it is possible to obtain actions and effects similar to the first embodiment. According to the present embodiment, the end of the first pipe  41  at the storage container  40  side is arranged at the top part of the storage container  40 . Due to this, even if an obstruction in the pipe layout makes it impossible to arrange the end of the first pipe  41  at the storage container  40  side at the bottom part of the storage container  40 , the first pipe  41  can be arranged without hindrance. 
     As a modification of the present embodiment, it is also possible to arrange the end of the second pipe  42  at the auxiliary container  30  side above the level of the liquid  33  in the auxiliary container  30 . According to this modification, it is possible to arrange the end of the second pipe  42  at the auxiliary container  30  side in the auxiliary container  30 . Even if an obstruction in the pipe layout makes it impossible to arrange the end of the second pipe  42  at the auxiliary container  30  side at the pipe between the auxiliary container  30  and the merging pipe  12 , the second pipe  42  can be arranged without hindrance. 
     Third Embodiment 
     In the first embodiment, the storage container  40  was opened to the atmosphere to make the internal pressure of the storage container  40  the same as the atmospheric pressure. On the other hand, in the present third embodiment, as shown in  FIG. 5 , the storage container  40  is sealed and the liquid  33  and the gas  45  are sealed in the storage container  40 . 
     According to the present embodiment, by setting the sealed volumes of the liquid  33  and gas  45 , it is possible to freely set the internal pressure of the storage container  40 . For this reason, for example, by setting the internal pressure of the storage container  40  somewhat higher than the atmospheric pressure, it is possible to increase the amount of flow of the liquid  33  from the inside of the storage container  40  to the auxiliary container  30  when the second valve  44  opens and shorten the time required for returning the liquid  33 . 
     Fourth Embodiment 
     In the third embodiment, the storage container  40  was formed by a plastic container etc. having a certain degree of rigidity, so the inside volume of the storage container  40  was constant. On the other hand, in the fourth embodiment, as shown in  FIG. 6 , the storage container  40  is formed by a soft bag which deforms due to the pressure difference of the inside and outside (for example, a plastic bag etc.), so the inside volume of the storage container  40  changes. 
     According to the third embodiment, the inside volume of the storage container  40  was constant, so movement of liquid  33  between the auxiliary container  30  and the storage container  40  caused the internal pressure of the storage container  40  to fluctuate. That is, if the liquid  33  in the auxiliary container  30  drains to the storage container  40 , the internal pressure of the storage container  40  rises, while if the liquid  33  returns from the storage container  40  to the auxiliary container  30 , the internal pressure of the storage container  40  falls. 
     For this reason, the amount of the liquid  33  in the storage container  40  causes the pressure difference between the auxiliary container inside pressure and the internal pressure of the storage container  40  to change, so there was the possibility of the reliability of the operations of the first and second valves  43  and  44  falling somewhat. 
     As opposed to this, according to the fourth embodiment, if the liquid  33  in the auxiliary container  30  drains to the storage container  40 , the storage container  40  formed by the soft bag swells and the inside volume of the storage container  40  increases. Due to this, a rise of the internal pressure of the storage container  40  is suppressed. If the liquid  33  returns from the storage container  40  to the auxiliary container  30 , the storage container  40  shrinks. By the reduction in the volume of the storage container  40 , the drop in the internal pressure of the storage container  40  is suppressed. 
     For this reason, fluctuation of the internal pressure of the storage container  40  caused by the fluctuations in the amount of the liquid  33  in the storage container  40  can be suppressed, so the first and second valves  43  and  44  can be reliably operated based on the differential pressure between the auxiliary container inside pressure and the internal pressure of the storage container  40 . 
     According to the present embodiment, the storage container  40  is formed by a soft bag, so the atmospheric pressure can be utilized to change the internal volume of the storage container  40 . For this reason, the configuration can be simplified compared with the case of using a mechanical mechanism to change the internal volume of the storage container  40 . 
     Other Embodiments 
     In the above embodiments, as the first and second valves  43  and  44 , one-way valves were used and the differential pressure between the auxiliary container inside pressure and the internal pressure of the storage container  40  was used to make the first and second valves  43  and  44  open. On the other hand, it is also possible to use solenoid valves as the first and second valves  43  and  44  and provide the auxiliary container  30  with a pressure sensor for detecting the auxiliary container inside pressure. In this case, if the auxiliary container inside pressure detected by the pressure sensor becomes the first predetermined pressure or more, the first valve  43  opens. Further, the second valve  44  may also be opened when the auxiliary container inside pressure detected by the pressure sensor falls to the second predetermined pressure or less. Instead of the first and second valves  43  and  44 , it is also possible to use a power pump etc. to drain and return the liquid  33 . 
     In the above embodiments, the storage container  40  and the auxiliary container  30  are connected through first and second pipes  41  and  42 . On the other hand, it is also possible to eliminate the first and second pipes  41  and  42 , arrange the storage container  40  and the auxiliary container  30  adjoining each other, and connect the two. 
     In the above embodiments, the exhaust gas of another heat engine is used as the heat source of the heater  14  and auxiliary heater  35 . On the other hand, it is of course also possible to use something other than the exhaust gas of another heat engine as the heat source of the heater  14  and auxiliary heater  35  (for example, a heating element etc.) 
     Further, the basic configuration of the external combustion engine in the embodiments is only shown as an example. The invention is not limited to this. The basic configuration of the external combustion engine of the present invention can be modified in various ways as shown in, for example, FIG. 14 to FIG. 25 of Japanese Unexamined Patent Publication No. 2007-255259. 
     In the above embodiments, the case of applying the present invention to a drive source of an electric power generation system mounted in an automobile was explained, but the external combustion engine of the present invention can also be utilized as a drive source for something other than an electric power generation system mounted in an automobile. 
     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.