Abstract:
An external combustion engine comprising a pipe-shaped main container in which a working fluid is sealed flowably in a liquid state, a heated part formed at a location of one end of the main container and heating part of the working fluid in the main container in order to make it evaporate, a cooled part formed at a location next to the heated part toward the other end of the main container and cooling the vapor of the working fluid evaporated at the heated part in order to make it condense, an output unit communicated with the other end of the main container and converting the displacement of the liquid phase part of the working fluid to mechanical energy for output, and a controller alternately performing a heat storage mode making displacement of the liquid phase part of the working fluid stop in order to make the heated part store heat and an output mode allowing displacement of the liquid phase part of the working fluid and taking output from the output unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an external combustion engine using evaporation and condensation of a working fluid to cause a liquid phase part of a working fluid to displace, and converting the displacement of the liquid phase part of the working fluid to mechanical energy for output. 
         [0003]    2. Description of the Related Art 
         [0004]    This type of external combustion engine is called a “liquid piston steam engine”. In this conventional type of engine, a pipe-shaped container is sealed with a working fluid flowable in a liquid state, a heated part formed at one end of the container is used to heat part of the liquid state working fluid to cause it to evaporate, and a cooled part formed at the middle of the container is used to cool the vapor of the working fluid to cause it to condense. By alternately repeating evaporation and condensation of this working fluid, the liquid phase part of the working fluid is cyclically made to displace (so-called “self-excited vibration”), then this self-excited vibration of the liquid phase part of the working fluid is taken out at an output unit as mechanical energy. (For example, see Japanese Patent Publication (A) No. 2004-84523 and Japanese Patent Publication (A) No. 2007-255259). 
         [0005]    In the engine disclosed in Japanese Patent Publication (A) No. 2007-255259, the internal pressure of the container is regulated in accordance with the temperature of the heated part to improve the efficiency of the liquid piston steam engine. Note that in the engine disclosed in Japanese Patent Publication (A) No. 2004-84523, the internal pressure of the container is not regulated. 
       SUMMARY OF THE INVENTION 
       [0006]    According to detailed studies by the inventors, it was learned that in the engine disclosed in the above Japanese Patent Publication (A) No. 2007-255259, the heated part temperature Th and the efficiency η of the liquid piston steam engine are in the relationship shown by the graph of  FIG. 7 . That is, in the above engine, the lower the heated part temperature Th ends up becoming, the lower the efficiency η ends up becoming. 
         [0007]    Therefore, in the above engine, for example, in the region of the heated part temperature T 0  to T 1  shown in  FIG. 7  (high efficiency region), it is preferable to raise the heated part temperature Th in order to raise the efficiency η and obtain the desired efficiency η. 
         [0008]    For example, in the case of utilizing the waste heat of another heat engine (exhaust gas of internal combustion engine etc.) as the heating source of the heater to heat the working fluid, the amount of heat given to the heated part fluctuates. In this case, if the amount of heat given to the heated part is small, there is a possibility that the heated part temperature Th ends up becoming lower and efficiency η ends up becoming lower. 
         [0009]    Even in a liquid piston steam engine such as disclosed in the above Japanese Patent Publication (A) No. 2004-84523 where the internal pressure of the container is not regulated, in the same way as the engine disclosed in the above Japanese Patent Publication (A) No. 2007-255259, there is a possibility that if the amount of heat given to the heated part is small, the efficiency η ends up falling. That is, this is because when the amount of heat given to the heated part is small, the heating efficiency of the working fluid (evaporation efficiency) ends up deteriorating and a drop in the efficiency η is invited. 
         [0010]    The present invention, in view of the above point, has the improvement of the efficiency as its object, when the amount of heat given to the heater is small. 
         [0011]    To achieve the above object, in the aspect of the invention as set forth in claim  1 , there are provided: 
         [0012]    an external combustion engine comprising:
       a pipe-shaped main container in which a working fluid is sealed flowably in a liquid state,   a heated part formed at a location of one end of the main container, and heating a part of the working fluid in the main container in order to make it evaporate,   a cooled part formed at a location next to the heated part toward the other end of the main container, and cooling the vapor of the working fluid evaporated at the heated part in order to make it condense,   an output unit communicated with the other end of the main container, and converting the displacement of the liquid phase part of the working fluid to mechanical energy for output, and   a controller alternately performing
           a heat storage mode making displacement of the liquid phase part stop in order to make the heated part store heat and   an output mode allowing displacement of the liquid phase part and taking output from the output unit.   
               
 
         [0020]    According to this, after the heat storage mode is used to store heat in the heated part, the output mode is performed in order to take output from the output unit. 
         [0021]    Compared with the case of constantly taking output from the output unit, it is possible to raise the temperature of the heated part. 
         [0022]    Even when the amount of heat given to the heater is small, the heat exchange amount between the heated part and the working fluid can be increased. Therefore, it is possible to improve the efficiency when the amount of heat given to the heater is small. 
         [0023]    In the aspect of the invention as set forth in claim  2 , there is provided the external combustion engine as set forth in claim  1  wherein the controller only performs the output mode when the amount of heat given to the heated part is large. 
         [0024]    When the amount of heat given to the heated part is small, the heat storage mode and the output mode are alternately performed. 
         [0025]    Due to this, the efficiency when the amount of heat given to the heated part is small can be made to approach the efficiency when the amount of heat given to the heated part is large. 
         [0026]    In the aspect of the invention as set forth in claim  3 , there is provided the external combustion engine as set forth in claim  1  wherein the controller decides on the switching between the heat storage mode and the output mode based on the temperature of the heated part. 
         [0027]    Due to this, it is possible to efficiently switch between the heat storage mode and the output mode. 
         [0028]    In the aspect of the invention as set forth in claim  4 , there is provided the external combustion engine as set forth in claim  3  wherein the controller 
         [0029]    performs the heat storage mode when the temperature of the heated part is less than the first predetermined temperature, 
         [0030]    switches from the heat storage mode to the output mode when the temperature of the heated part becomes a second predetermined temperature or more in the heat storage mode, and 
         [0031]    switches from the output mode to the heat storage mode when the temperature of the heated part becomes less than the first predetermined temperature in the output mode. 
         [0032]    Due to this, it is possible to effectively improve the efficiency. 
         [0033]    In the aspect of the invention as set forth in claim  5 , there is provided the external combustion engine as set forth in claim  4  wherein the second predetermined temperature is the first predetermined temperature or more. 
         [0034]    In the aspect of the invention as set forth in claim  6 , there is provided the external combustion engine as set forth in claim  4  wherein the controller performs a start-up mode driving the output unit from the outside to make the displacement of the liquid phase part of the working fluid start when shifting from the heat storage mode to the output mode. 
         [0035]    In the aspect of the invention as set forth in claim  7 , there is provided the external combustion engine as set forth in claim  6  wherein the controller performs the start-up mode for a predetermined time. 
         [0036]    Due to this, it is possible to easily execute the start-up mode. 
         [0037]    In the aspect of the invention as set forth in claim  8 , there is provided the external combustion engine as set forth in claim  6  wherein the controller determines the end of the start-up mode based on the output from the output unit and the revolution speed of the output unit. 
         [0038]    Due to this, it is possible to shorten the execution time of the start-up mode. 
         [0039]    In the aspect of the invention as set forth in claim  9 , there are provided: 
         [0040]    an external combustion engine comprising:
       a pipe-shaped main container in which a working fluid is sealed flowably in a liquid state,   a heated part formed at a location of one end of the main container, and heating a part of the working fluid in the main container in order to make it evaporate,   a cooled part formed at a location next to the heated part toward the other end of the main container, and cooling the vapor of the working fluid evaporated at the heated part to make it condense,   an output unit communicated with the other end of the main container and converting the displacement of the liquid phase part of the working fluid to mechanical energy for output, and   a displacement speed regulator for reducing the speed of displacement of the liquid phase part, when the amount of heat given to the heated part is small compared with when the amount of heat given to the heated part is large.       
 
         [0046]    According to this, when the amount of heat given to the heated part is small, it is possible to make the temperature of the heated part close to the temperature of the heated part when the amount of heat given to the heated part is large. 
         [0047]    For this reason, the efficiency when the amount of heat given to the heater is small can be improved. 
         [0048]    In the aspect of the invention as set forth in claim  10 , there is provided the external combustion engine as set forth in claim  9  wherein the displacement speed regulator increases the external load of the output unit in order to reduce the speed of displacement of the liquid phase part of the working fluid. 
         [0049]    In the aspect of the invention as set forth in claim  11 , there is provided the external combustion engine as set forth in claim  1  further comprising
       an auxiliary container communicated with a part of the main container between the cooled part and output unit, and sealed with a liquid, and   a pressure regulator for regulating an internal pressure of the auxiliary container based on the temperature of the heated part.       
 
         [0052]    According to this, it is possible to adjust the internal pressure of the main container in accordance with the temperature of the heated part, so that a higher efficiency can be obtained. 
         [0053]    The present invention may be more fully understood from the description of preferred embodiments of the invention, as set forth below, together with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0054]      FIG. 1  is a schematic view summarizing the external combustion engine in a first embodiment of the present invention. 
           [0055]      FIG. 2  is a flow chart summarizing mode switching control processing executed by the control device of  FIG. 1 . 
           [0056]      FIG. 3  is a timing chart showing an example of mode switching control in a first embodiment. 
           [0057]      FIG. 4  is a schematic view summarizing the external combustion engine in a second embodiment of the present invention. 
           [0058]      FIG. 5  is a flow chart summarizing mode switching control processing executed by the control device in the second embodiment. 
           [0059]      FIG. 6  is a graph showing the relationship between a heated part heat capacity Q and a heated part temperature Th in a third embodiment operated by two different frequencies N 1 , N 2 . 
           [0060]      FIG. 7  is a graph showing the relationship between the heated part temperature Th and efficiency η of the liquid piston steam engine in the related art. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0061]    Below, a first embodiment of the present invention will be explained based on  FIG. 1  to  FIG. 3 .  FIG. 1  is a schematic view summarizing the external combustion engine (liquid piston steam engine)  10  in the present embodiment. The up/down arrow in  FIG. 1  shows the up/down direction in the state of installation of the liquid piston steam engine  10 . 
         [0062]    The liquid piston steam engine  10  has a main container  11  and a generator  12  forming an output unit. Inside a casing of the generator  12 , a moving element  14  in which permanent magnets are embedded is housed. If this moving element  14  displaces due to vibration, electromotive force is generated. 
         [0063]    The main container  11  is a pipe-shaped pressure container. This has sealed inside it a working fluid (in the present embodiment, steam)  15  flowably in a liquid state. At the outer circumference of the main container  11 , a heater  16  for heating part of the liquid state working fluid  15  inside the main container  11  to cause it to evaporate and a cooler  17  for cooling to condense the working fluid  15  heated to evaporate by the heater  16  are arranged in contact. 
         [0064]    The main container  11  is formed into an approximately U-shape and is arranged so that its bent part is positioned at its bottom most part and its two ends are positioned at its topmost part. The heater  16  and the cooler  17  are provided at one end side of the main container  11 . The heater  16  is arranged so as to be positioned above the cooler  17 . 
         [0065]    In the present embodiment, the heater  16  exchanges heat with a high temperature gas (for example, automobile exhaust gas) to heat the working fluid  15 . The heater  16  may also be constituted by an electric heater. Further, the cooler  17  has cooling water circulated inside it. While not shown, the heat which the cooling water robs from the steam of the working fluid  15  is designed to be radiated to the outside (into the atmosphere) in a radiator arranged in a circulating circuit of the cooling water. 
         [0066]    The working fluid  15  is water, so the main container  11  is formed by stainless steel. In the main container  11 , the part contacting the heater  16  and making the working fluid  15  evaporate, that is, a heated part  11   a , and the part contacting cooler  17  and making the working fluid  15  condense, that is, a cooled part  11   b , may also be formed from copper, aluminum, etc. superior in heat conductivity. 
         [0067]    To secure the space in which the working fluid  15  evaporates, a predetermined volume of a gas is sealed above the heated part  11   a . This gas may for example be air or pure steam of the working fluid  15 . 
         [0068]    At the other end of the main container  11 , a piston  18  displacing by pressure received from the working fluid is arranged slidably in a cylinder part  19 . The piston  18  is coupled with a shaft  14   a  of the moving element  14  of the generator  12 . At the opposite side of the moving element  14  from the piston  18 , a coil spring  20  for pushing the moving element  14  to the piston  18  side is provided. 
         [0069]    The generator  12  functions as a so-called motor generator. At the time of normal operation of the liquid piston steam engine  10 , power is generated due to the displacement of the piston  18 . On the other hand, at the time of start-up of the liquid piston steam engine  10 , the piston  18  is driven by power supplied from the outside and this piston  18  acts as a starter motor. 
         [0070]    The mechanism for regulating the internal pressure of the main container  11  (below, referred to as the “main container internal pressure”) will be explained below. The auxiliary container  21  communicates with the main container  11  through a pipe-shaped communicating part  22 . In the present embodiment, the auxiliary container  21  is arranged above the bent part of the main container  11 . 
         [0071]    The auxiliary container  21  has sealed inside it a liquid  23  and gas  24 . In the present embodiment, the liquid  23 , like the working fluid  13 , is made of water. As the gas  24 , a gas exhibiting insolubility in the liquid  23  is preferably used. As the gas  24 , helium exhibiting insolubility in water is used. It is also possible to seal only the liquid  23  inside the auxiliary container  21 . 
         [0072]    The auxiliary container  21  and communicating part  22  are preferably made of materials superior in heat insulating property. In the present embodiment, the liquid  23  is made of water, so the auxiliary container  21  and communicating part  22  are made of stainless steel. The communicating part  22  has a throttling mechanism  25  arranged in it. In the present embodiment, a fixed throttle is used as the throttling mechanism  25 . As the throttling mechanism  25 , a variable throttle may also be used. 
         [0073]    The pressure regulator  26  for regulating the internal pressure Pt of the auxiliary container  21  (below, referred to as the “auxiliary container internal pressure”) comprises a pressure regulating piston  26   a  and a power actuator  26   b . The pressure regulating piston  26   a  is arranged slidably in the vertical direction at the top end side of the auxiliary container  21 . The power actuator  26   b  is arranged above the auxiliary container  21  and drives the pressure regulating piston  26   a  in the vertical direction. 
         [0074]    The electronic control part in the present embodiment will be summarized below. A control device  27  comprises a known microprocessor including a CPU, ROM, RAM, etc. and its peripheral circuits. The control device  27 , a later explained DC/DC converter  33 , and a later explained sub-controller  35  constitute the controller in the present invention. 
         [0075]    The control device  27  receives as input detection signals of a temperature sensor  28  detecting a temperature Th of the heated part  11   a  (below, referred to as the “heated part temperature”) and a pressure sensor  29  detecting the auxiliary container internal pressure Pt for controlling the pressure regulator  26 . The control device  27  controls the power actuator  26   b  based on the detection signals of the sensors  28  and  29 . 
         [0076]    The control device  27  controls the relay  31  to switch between a charging circuit for being charged with the power generated at the generator  12  and the drive circuit for driving the generator  12  as a starter motor. 
         [0077]    The charging circuit is comprised of a rectifier  32  rectifying the current generated at the generator  12 , a DC/DC converter  33  converting the voltage of the current I rectified at the rectifier  32 , and a battery  34  for being charged with the power output from the DC/DC converter  33 , which are all connected in series. 
         [0078]    The drive circuit is comprised of a sub-controller  35  for controlling the drive of the generator  12  and the battery  34  connected in series. The DC/DC converter  33  and sub-controller  35  are controlled by the control device  27 . 
         [0079]    The basic operation of the above configuration (normal operation) will be explained below. If operating the heater  16  and cooler  17 , a first stroke making the liquid phase part of the working fluid  15  displace toward the generator  12  side is performed. In this first stroke, the liquid state working fluid  15  in the heated part  11   a  is heated to evaporate by the heater  16 , steam of the high temperature and high pressure working fluid  15  builds up in the heated part  11   a , and the liquid surface of the working fluid  15  is pushed down inside the heated part  11   a.    
         [0080]    This being so, the liquid part of the working fluid  15  sealed in the main container  11  displaces from the heated part  11   a  side to the generator  12  side and pushes up the piston  18  of the generator  12 , whereby the coil spring  20  is elastically compressed. 
         [0081]    After a while, when the liquid surface of the pushed down working fluid  15  reaches the cooled part  11   b  and the steam of the working fluid  15  enters the cooled part  11   b , a second stroke for making the liquid phase part of the working fluid  15  displace toward the heated part  11   a  side is started. 
         [0082]    In this second stroke, the steam of the working fluid  15  entering the cooled part  11   b  is cooled to condense by the cooler  17 , so the force pushing down the liquid surface of the working fluid  15  is eliminated. This being so, the piston  18  at the generator  12  side descends due to the elastic recovery force of the coil spring  20 . 
         [0083]    For this reason, the liquid phase part of the working fluid  15  displaces from the generator  12  side to the heated part  11   a  side, the liquid surface of the working fluid  15  rises to the heated part  11   a , and the liquid state working fluid  15  is again heated to evaporate at the heated part  11   a.    
         [0084]    The first stroke and second stroke are repeatedly performed until making the operations of the heater  16  and cooler  17  stop. During that time, the liquid phase part of the working fluid  15  in the main container  11  cyclically displaces (so-called “self-excited vibration”) and makes the moving element  14  of the generator  12  move up and down. 
         [0085]    That is, by the alternately repeating evaporation and condensation of the working fluid  15 , the liquid phase part of the working fluid  15  vibrates by self-excited vibration as a liquid piston. This self-excited vibration of the liquid piston is taken out as output. 
         [0086]    The control for regulating the main container internal pressure is described in detail in the above Japanese Patent Publication (A) No. 2007-255259, so it will only be summarized. The control device  27  uses the heated part temperature Th and a steam pressure curve of the working fluid  15  stored in advance in the control device  27  to calculate the saturated steam pressure of the working fluid  15  at the heated part temperature Th. 
         [0087]    The target value for the average value of the main container internal pressure (below, referred to as the “main container internal average pressure”) is made the average value of the saturated steam pressure of the working fluid  15  at the heated part temperature Th and the atmospheric pressure (0.1 MPa). In the present embodiment, as an approximation of the saturated steam pressure of the working fluid  15  at the temperature of the cooled part  11   b , the atmospheric pressure (0.1 MPa) is used. Note that it is also possible to make the above average value suitably adjusted in value the target value. 
         [0088]    Furthermore, when the auxiliary container internal pressure Pt is lower than the target value, the power actuator  26   b  pushes out the pressure regulating piston  26   a  to reduce the volume of the auxiliary container  21 . Due to this, the liquid  23  is compressed and the auxiliary container internal pressure Pt rises. 
         [0089]    On the other hand, when the auxiliary container internal pressure Pt is higher than the target value, the pressure regulating piston  26   a  is retracted and the volume of the auxiliary container  21  is reduced. Due to this, the liquid  23  expands and the auxiliary container internal pressure Pt falls. 
         [0090]    This being so, the main container internal average pressure changes tracking the auxiliary container internal pressure Pt and as a result approaches the target value. Due to this, even if the heated part temperature Th fluctuates, the main container internal average pressure can be maintained at substantially the target value. For this reason, a suitable main container internal pressure for the heated part temperature Th can be maintained and a drop in performance (output and efficiency) can be prevented. 
         [0091]    The characterizing operation in the above configuration will be explained below. The operation of the liquid piston steam engine  10  may be roughly divided into the output mode taking output from the output unit  12 , the heat storage mode where heat is stored in the heated part  11   a , and the start-up mode performed when shifting from the heat storage mode to the output mode. The output mode performs the above basic operation (ordinary operation). 
         [0092]    The “heat storage mode” is the mode performed when the heated part temperature Th (° C.) becomes lower in the output mode. In this mode, the control device  27  switches the relay  31  to the rectifier  32  side as shown by the solid line position of  FIG. 1  and the DC/DC converter  33  increases the current value. 
         [0093]    If the DC/DC converter  33  increases the current value, the generator  12  becomes larger in load, so the speed (displacement speed) of the self-excited vibration of the liquid piston falls and the self-excited vibration of the liquid piston stops. 
         [0094]    When the self-excited vibration of the liquid piston stops, the heat exchange amount between the heated part  11   a  and the working fluid  15  remarkably decreases, so the heated part  11   a  stores heat and the heated part temperature Th rises. 
         [0095]    The start-up mode is performed in the state where the self-excited vibration of the liquid piston has stopped. In the start-up mode, the control device  27  switches the relay  31  to the sub-controller  35  side as shown by the two-dot chain line position of  FIG. 1 . Furthermore, the sub-controller  35  drives the generator  12  for exactly a predetermined time (for example, several seconds or so). That is, it is possible to make the generator  12  function as a starter motor and as a result make the liquid piston start self-excited vibration and shift to the output mode. 
         [0096]    The output mode, heat storage mode, or start-up mode is switched to by the control device  27 .  FIG. 2  is a flow chart summarizing the mode switching control processing executed by the control device  27 . 
         [0097]    When the self-excited vibration of the liquid piston is detected to stop, the control processing as shown in  FIG. 2  is started. First, at step S 100 , it is judged if the heated part temperature Th is a predetermined temperature T 1  or more. The predetermined temperature T 1  corresponds to the second predetermined temperature in the aspect of the invention of claim  4  and is a freely determined temperature. 
         [0098]    When it is judged at step S 100  that the heated part temperature Th is the predetermined temperature T 1  or more, the routine proceeds to step S 110  where the above-mentioned start-up mode is performed. When at step S 110  the start-up mode ends, the routine proceeds to step S 120  where it is judged if the heated part temperature Th is at least the predetermined temperature T 0 . 
         [0099]    The predetermined temperature T 0  corresponds to the first predetermined temperature in the aspect of the invention of claim  4  and is a freely determined temperature. In the present embodiment, the relationship between the predetermined temperature T 0  and the predetermined temperature T 1  is T 0 ≦TL. 
         [0100]    When it is judged at step S 120  that the heated part temperature Th is the predetermined temperature T 0  or more, the routine proceeds to step S 130  where the above-mentioned output mode is performed to generate power. 
         [0101]    When it is judged at step S 130  that the heated part temperature Th is less than the predetermined temperature T 0 , the routine proceeds to step S 140  where the above-mentioned heat storage mode is performed to make the self-excited vibration of the liquid piston stop. 
         [0102]    When it is judged at step S 100  that the heated part temperature Th is less than the predetermined temperature T 1 , the routine proceeds to step S 140  where the heat storage mode is performed to make the self-excited vibration of the liquid piston stop. 
         [0103]    As specific examples of the predetermined temperatures T 0  and T 1 , when using water as the working fluid  15  and setting the operating pressure at 1 MPa to 10 MPa, the predetermined temperature T 0  is set to 180° C. to 331° C. and the predetermined temperature T 1  is set to 180° C. to 331° C. in accordance with the predetermined temperature T 0 . 
         [0104]      FIG. 3  is a timing chart showing an example of the mode switching control in the present embodiment. The heated part temperatures T 0  and T 1  of  FIG. 3  correspond to the heated part temperatures T 0  and T 1  of  FIG. 7 .  FIG. 3  shows an example of the case where the amount of heat given to the heated part  11   a  (below, referred to as “the heated part heat capacity”) Q(W) is small. 
         [0105]    As shown in  FIG. 3 , if the heated part temperature Th is less than a predetermined temperature T 0 , the heat storage mode is performed to make the heated part temperature Th rise to a predetermined temperature T 1 . In the heat storage mode, the heat exchange amount q between the heated part  11   a  and the working fluid  15  is substantially zero. 
         [0106]    If the heated part temperature Th becomes a predetermined temperature T 1  or more, the start-up mode is shifted to. In the start-up mode, the heat exchange amount q between the heated part  11   a  and the working fluid  15  gradually increases. At this time, the heated part temperature Th rises somewhat from the predetermined temperature T 1 . 
         [0107]    When the start-up mode ends and the output mode is shifted to, the heated part temperature Th also gradually falls. Furthermore, if the heated part temperature Th becomes less than the predetermined temperature T 0 , the heat storage mode is again performed. 
         [0108]    In this way, in the present embodiment, the ordinary operation (power generation) is performed intermittently, so even when the heated part heat capacity Q is small, it is possible to raise the heated part temperature Th and increase the heat exchange amount q between the heated part  11   a  and the working fluid  15 . For this reason, it is possible to improve the efficiency when the heated part heat capacity Q is small. 
         [0109]    As shown in  FIG. 3 , in output mode, the heated part temperature Th gradually falls because the heated part  11   a  and the working fluid  15  exchange heat and the heat stored in the heated part  11   a  is robbed by the working fluid  15 . Furthermore, in the output mode, the heat exchange amount q between the heated part  11   a  and the working fluid  15  is maintained substantially constant to make the auxiliary container internal pressure Pt constant. The main container internal pressure may also be regulated in accordance with fluctuation in the heated part temperature Th. If maintaining the auxiliary container internal pressure Pt constant, the pressure regulator  26  becomes unnecessary. 
       Second Embodiment 
       [0110]    In the second embodiment, the time for performing the start-up mode is shortened, compared with the above first embodiment.  FIG. 4  is a schematic view of an outline of a liquid piston steam engine  10  in the present embodiment. 
         [0111]    The control device  27  receives as input a detection signal from a sensor  40  detecting a frequency N and generated power value W of the generator  12 . As the sensor  40 , a frequency sensor detecting the frequency N and a power sensor detecting a generated power value W can be used. 
         [0112]    As the sensor  40 , only a current sensor detecting the current value of the power generated by the generator  12  is used. The control device  27  may use the current value of the power generated by the generator  12  to calculate the generated power value W and frequency N of the generator  12 . 
         [0113]      FIG. 5  is a flow chart showing an outline of the control processing performed by the control device  27  in the present embodiment. 
         [0114]    First, at step S 200 , it is judged if the frequency N and generated power value W of the generator  12  are larger than 0. 
         [0115]    When it is judged at step S 200  that the frequency N and generated power value W of the generator  12  are larger than 0, the routine proceeds to step S 210  where the output mode is performed to generate power. When at step S 200  the frequency N and generated power value W of the generator  12  are 0 or less, the routine proceeds to step S 220  where it is judged if the heated part temperature Th is the predetermined temperature T 1  or more. 
         [0116]    When it is judged at step S 220  that the heated part temperature Th is the predetermined temperature T 1  or more, the routine proceeds to step S 230  where the start-up mode is performed. When it is judged at step S 220  that the heated part temperature Th is less than the predetermined temperature T 1 , the routine proceeds to step S 240  where the heat storage mode is performed and the self-excited vibration of the liquid piston is made to stop. 
         [0117]    According to this control processing, at the time of the start-up mode, when the frequency N and generated power value W of the generator  12  exceed 0, the start-up mode is immediately ended and the output mode shifted to. Therefore, compared with when performing the start-up mode for a predetermined time like in the above first embodiment, the time for performing the start-up mode can be shortened. 
       Third Embodiment 
       [0118]    In the above first and second embodiments, by making the self-excited vibration of the liquid piston stop, the heated part temperature Th is made to rise. On the other hand, in the third embodiment, the speed (displacement speed) of the self-excited vibration of the liquid piston is reduced to make the heated part temperature Th rise. 
         [0119]    The configuration of the liquid piston steam engine  10  in the present embodiment is the same as that in the above first and second embodiments. Only the control processing executed by the control device  27  differs from the above first and second embodiments. 
         [0120]      FIG. 6  is a graph showing the relationship between the heated part heat capacity Q and the heated part temperature Th in the two different operation frequencies N 1  and N 2 . The “operation frequency” means the frequency of the self-excited vibration of the liquid piston. The faster the displacement speed of the liquid piston becomes, the larger the operation frequency becomes, while the slower the displacement speed of the liquid piston becomes, the smaller the operation frequency becomes. 
         [0121]    The relative magnitude of the operation frequencies N 1  and N 2  in  FIG. 6  is N 1 &gt;N 2 . As will be understood from  FIG. 6 , if the heated part heat capacity Q is constant, the smaller the operation frequency becomes, the higher the heated part temperature Th becomes. This is because the smaller the operation frequency, in other words, the slower the displacement speed of the liquid piston becomes, the smaller the heat exchange amount between the heated part  11   a  and the working fluid  15  becomes. 
         [0122]    In the present embodiment, when the heated part heat capacity Q is small, the control device  27  performs control processing so that the DC/DC converter  33  increases the current value and increases the load of the generator  12 . 
         [0123]    Due to this, when the heated part heat capacity Q is small, the operation frequency may be lowered to make the heated part temperature Th a high temperature, so it is possible to improve the efficiency when the heated part heat capacity Q is small. The control device  27  and the DC/DC converter  33  correspond to the displacement speed regulator in the present invention. 
       Other Embodiments 
       [0124]    The above first to third embodiments only show examples of the specific configurations of the controller and displacement speed regulator in the present invention. As the specific configurations of the controller and displacement speed regulator, it is of course possible to use various configurations enabling similar operations as with the above first to third embodiments. 
         [0125]    In the above embodiments, the pressure regulator  26  for regulating the auxiliary container internal pressure Pt is comprised of the pressure regulating piston  26   a  and the power actuator  26   b , but the invention is not limited to this. For example, it is possible to use the various pressure regulator disclosed in the above Japanese Patent Publication (A) No. 2007-255259. 
         [0126]    In the above embodiments, the example of application of the present invention to a so-called single cylinder type liquid piston steam engine  10 , where the main container  11  as a whole is formed into a single pipe shape, is shown, but the invention is not limited to this. The present invention may also be applied to a liquid piston steam engine, where the part of the main container  11  at the heated part  11   a  side is comprised of a plurality of branch pipes, and the remaining part of the main container  11  is comprised of a single header pipe. 
         [0127]    In the above embodiments, the example of application of the present invention to a liquid piston steam engine  10 , provided with only one main container  11 , was shown. However, the invention is not limited to this. The present invention may also be applied to a liquid piston steam engine, provided with a plurality of main containers  11  and linking the main containers  11  by a single output unit. 
         [0128]    In the above embodiments, the case of application of the external combustion engine of the present invention to a drive source of a generating system was explained, but the invention is not limited to this. 
         [0129]    The external combustion engine of the present invention may also be utilized as a drive source of other than a generating system. 
         [0130]    While the invention has been described by references to specific embodiments chosen for purposes 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