Abstract:
An external combustion engine comprising a container ( 11 ) sealed with a working liquid ( 12 ) in a way adapted to allow the liquid to flow therein, a heating unit ( 13, 30 ) for heating and vaporizing the working liquid ( 12 ) in the container ( 11 ), and a cooling unit ( 14 ) for cooling and liquefying the vapor of the working liquid ( 12 ) heated and vaporized by the heating unit ( 13, 30 ) is disclosed, wherein the displacement of the working liquid ( 12 ) caused by the volume change of the vapor is output by being converted into mechanical energy. A pressure regulating unit ( 16, 60, 63 ) regulates the internal pressure (Pc) of the container ( 11 ). A control unit ( 21 ) controls the pressure regulating unit ( 16, 60, 63 ) based on at least the temperature (T 1 ) of the heated portion ( 11   a ) of the container ( 11 ) for vaporizing the working liquid ( 12 ). The control unit ( 21 ) calculates the temperature (T 1 ) based on at least the heat quantity (Q) applied from the heating unit ( 13 30 ) to the working liquid ( 12 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to an external combustion engine for outputting mechanical energy by converting the displacement of a working liquid, caused by the volume change of the vapor of the working liquid, into mechanical energy. 
         [0003]    2. Description of the Related Art 
         [0004]    In the prior art, an external combustion engine, in which a working liquid is sealed in a container, is disclosed in Japanese Unexamined Patent Publication No. 2005-330910. Part of the working liquid in the container is heated and vaporized by a heater and the vapor of the working liquid thus vaporized is cooled and liquefied by a cooler thereby to output energy by converting the displacement of the working liquid, caused by the volume change of the vapor of the working liquid, into mechanical energy. 
         [0005]    This prior art comprises a pressure sensor for detecting the internal pressure of the container, a temperature sensor for detecting the temperature of the heated portion of the container for vaporizing the working liquid, a valve for discharging the working liquid in the container into the atmosphere and a control unit for controlling the on/off operation of the valve. 
         [0006]    By reducing the volume of the working liquid by discharging part thereof in the container into the atmosphere when the internal pressure of the container increases to not lower than the saturated vapor pressure of the working liquid at the temperature of the heated portion, the internal pressure of the container is controlled not to exceed the saturated vapor pressure of the working liquid. 
         [0007]    As a result, the condensation and liquefaction of part of the vapor with the internal pressure of the container exceeding the saturated vapor pressure of the working liquid is suppressed to thereby suppress the output and efficiency reduction of the external combustion engine. 
       SUMMARY OF THE INVENTION 
       [0008]    In this conventional technique, however, the temperature of the heated portion is detected directly by a temperature sensor, and therefore, the temperature sensor is required to be arranged in contact with the heated portion. As a result, the problem is posed that the temperature sensor is liable to be damaged by the high temperature of the heated portion. 
         [0009]    In view of this point, a first object of this invention is to suppress the reduction in output and efficiency of the external combustion engine without detecting the temperature of the heated portion directly. 
         [0010]    In view of the point described above, a second object of the invention is to estimate the temperature of the heated portion without detecting the temperature thereof directly. 
         [0011]    This invention has been conceived to achieve the objects described above and provides an external combustion engine for outputting mechanical energy by converting the displacement of a working liquid ( 12 ) caused by the volume change of the vapor into mechanical energy, comprising: 
         [0012]    a container ( 11 ) sealed with the working liquid ( 12 ) in a way adapted to allow the liquid to flow therein; 
         [0013]    a heating means ( 13 ,  30 ) for heating and vaporizing the working liquid ( 12 ) in the container ( 11 ); 
         [0014]    a cooling means ( 14 ) for cooling and liquefying the vapor of the working liquid ( 12 ) heated and vaporized by the heating means ( 13 ,  30 ); 
         [0015]    a pressure regulating means ( 16 ,  60 ,  63 ) for regulating the internal pressure (Pc) of the container ( 11 ); and 
         [0016]    a control means ( 21 ) for controlling the pressure regulating means ( 16 ,  60 ,  63 ) based on at least the temperature (T 1 ) of the heated portion ( 11   a ) of the container ( 11 ) for vaporizing the working liquid ( 12 ); 
         [0017]    wherein the control means ( 21 ) calculates the temperature (T 1 ) based on at least the heat quantity (Q) applied to the working liquid ( 12 ) from the heating means ( 13 ,  30 ). 
         [0018]    In this configuration, the temperature (T 1 ) of the heated portion ( 11   a ) is calculated by the control means ( 21 ) based on at least the heat quantity (Q) applied to the working liquid ( 12 ) from the heating means ( 13 ,  30 ), and therefore, the temperature (T 1 ) of the heated portion ( 11   a ) can be estimated without detecting the temperature (T 1 ) of the heated portion ( 11   a ) directly. 
         [0019]    Based on the temperature (T 1 ) of the heated portion ( 21 ) thus estimated, the pressure regulating means ( 16 ,  60 ,  63 ) is controlled, and therefore, the reduction in output and efficiency of the external combustion engine ( 10 ) can be suppressed. As a result, the reduction in output and efficiency of the external combustion engine ( 10 ) can be suppressed without detecting the temperature (T 1 ) of the heated portion ( 11   a ) directly. 
         [0020]    According to this invention, specifically, the control means ( 21 ) calculates the saturated vapor pressure (Ps 1 ) of the working liquid ( 12 ) at the temperature (T 1 ) based on the temperature (T 1 ) and the vapor pressure curve of the working liquid ( 12 ). 
         [0021]    According to this invention, more specifically, the control means ( 21 ) controls the pressure regulating means ( 63 ) in such a manner as to reduce the internal pressure (Pc), if not lower than the saturated vapor pressure (Ps 1 ). 
         [0022]    Also, according to this invention, more specifically, the control means ( 21 ) may control the pressure regulating means ( 16 ,  60 ) in such a manner that the internal pressure (Pc) is decreased if not lower than the saturated vapor pressure (Ps 1 ) and increased if not higher than the saturated vapor pressure (Ps 1 ). 
         [0023]    Also, according to this invention, more specifically, the control means ( 21 ) may control the pressure regulating means ( 16 ) in such a manner that the internal pressure (Pc) is decreased in the case where the average value (Pca) of the internal pressure (Pc) is not lower than a target value (Pc 0 ) calculated based on at least the saturated vapor pressure (Ps 1 ) and the internal pressure (Pc) is increased in the case where the average value (Pca) is not higher than the target value (Pc 0 ). 
         [0024]    Also, according to this invention, there is provided a temperature calculating device used with an external combustion engine for outputting mechanical energy by converting the displacement of the working liquid ( 12 ) caused by the vapor volume change into mechanical energy, comprising a container ( 11 ) sealed with the working liquid ( 12 ) adapted to allow the liquid to flow therein, a heating means ( 13 ,  30 ) for heating and vaporizing the working liquid ( 12 ) in the container ( 11 ) and a cooling means ( 14 ) for cooling and liquefying the vapor of the working liquid ( 12 ) heated and vaporized by the heating means ( 13 ,  30 ), 
         [0025]    wherein the temperature (T 1 ) of the heated portion ( 11   a ) of the container ( 11 ) for vaporizing the working liquid ( 12 ) is calculated based on at least the heat quantity (Q) applied to the working liquid ( 12 ) from the heating means ( 13 ,  30 ). 
         [0026]    As a result, the temperature of the heated portion can be estimated without detecting the temperature of the heated portion directly. 
         [0027]    According to this invention, specifically, the control means ( 21 ) can calculate the temperature (T 1 ) using Equation (1) below: 
         [0000]        T 1= Q /( m·Cp )− T 0   (1) 
         [0028]    where m is the mass of the heated portion ( 11   a ), Cp the specific heat of the heated portion ( 11   a ), and T 0  the temperature of the heated portion ( 11   a ) before being heated by the heating means ( 13 ,  30 ). 
         [0029]    Also, according to this invention, specifically, the heating means is an electric heater ( 13 ), the external combustion engine further comprising a wattage detecting means ( 22 ) for detecting the wattage (Q 1 ) input to the electric heater ( 13 ), and 
         [0030]    the control means ( 21 ) can calculate the temperature (T 1 ) using the wattage (Q 1 ) in place of the heat quantity (Q). 
         [0031]    Also, according to this invention, specifically, the heating means is a heater ( 30 ) for exchanging heat with a high-temperature gas, the external combustion engine comprising: 
         [0032]    a first temperature detecting means ( 34 ) for detecting the temperature (Tgi) of the high-temperature gas before exchanging heat with the heated portion ( 11   a ); 
         [0033]    a second temperature detecting means ( 35 ) for detecting the temperature (Tgo) of the high-temperature gas after exchanging heat with the heated portion ( 11   a ); and 
         [0034]    a flow rate detecting means ( 33 ) for detecting the flow rate (mg) of the high-temperature gas; 
         [0035]    wherein the control means ( 21 ) may calculate the heat quantity (Q) based on at least the temperature (Tgi) of the high-temperature gas before exchanging heat with the heated portion ( 11   a ), the temperature (Tgo) of the high-temperature gas after exchanging heat with the heated portion ( 11   a ) and the flow rate (mg). 
         [0036]    According to this invention, more specifically, the control means ( 21 ) can calculate the heat quantity (Q) using Equation (2) below. 
         [0000]        Q=mg·Cgp· ( Tgi−Tgo )   (Equation (2)) 
         [0000]    where Cgp is the specific heat of the high-temperature gas. 
         [0037]    Incidentally, the reference numerals inserted in the parentheses following the name of each means described in this column and the claims indicate the correspondence with the specific means described in the embodiments explained later. 
         [0038]    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 
         [0039]      FIG. 1  is a diagram showing a general configuration of a power generating device according to a first embodiment of the invention. 
           [0040]      FIG. 2  is a diagram for explaining the operation characteristics of an external combustion engine according to the first embodiment of the invention. 
           [0041]      FIG. 3A  is a PV diagram for the external combustion engine according to the first embodiment, showing an ideal state. 
           [0042]      FIG. 3B  is a PV diagram for the external combustion engine according to the first embodiment, showing a state in which the peak value of the internal pressure of the container is lower than the saturated vapor pressure. 
           [0043]      FIG. 3C  is a PV diagram for the external combustion engine according to the first embodiment, showing a state in which the peak value of the internal pressure of the container is higher than the saturated vapor pressure. 
           [0044]      FIG. 4A  is a diagram for explaining the problem posed by the conventional steam engine, showing a state in which the volume of the working liquid  12  is reduced. 
           [0045]      FIG. 4B  is a diagram for explaining the problem posed by the conventional steam engine, showing a state in which the volume of the working liquid  12  is increased. 
           [0046]      FIG. 5  is a graph showing the relation between the volume of the working liquid and the efficiency of the external combustion engine. 
           [0047]      FIG. 6  is a block diagram showing a general control operation according to the first embodiment. 
           [0048]      FIG. 7  is a graph showing the vapor pressure curve of the working liquid. 
           [0049]      FIG. 8  is a diagram showing a general configuration of the power generating device according to a second embodiment of the invention. 
           [0050]      FIG. 9  is a diagram showing a general configuration of the power generating device according to a third embodiment of the invention. 
           [0051]      FIG. 10  is a block diagram showing a general control operation according to the third embodiment. 
           [0052]      FIG. 11  is a diagram showing a general configuration of the power generating device according to a fourth embodiment of the invention. 
           [0053]      FIG. 12  is a block diagram showing a general control operation according to the fourth embodiment. 
           [0054]      FIG. 13  is a diagram showing a general configuration of the power generating device according to a fifth embodiment of the invention. 
           [0055]      FIG. 14  is a block diagram showing a general control operation according to the fifth embodiment. 
           [0056]      FIG. 15  is a diagram showing a general configuration of the power generating device according to a sixth embodiment of the invention. 
           [0057]      FIG. 16  is a graph showing the temperature gradient of a regulating container according to the sixth embodiment of the invention. 
           [0058]      FIG. 17  is a block diagram showing a general control operation according to the sixth embodiment. 
           [0059]      FIG. 18  is a diagram showing a general configuration of the power generating device according to a seventh embodiment of the invention. 
           [0060]      FIG. 19  is a block diagram showing a general control operation according to the seventh embodiment. 
           [0061]      FIG. 20  is a diagram showing a general configuration of the power generating device according to an eighth embodiment of the invention. 
           [0062]      FIG. 21  is a block diagram showing a general control operation according to the eighth embodiment. 
           [0063]      FIG. 22  is a diagram showing a general configuration of the power generating device according to a ninth embodiment of the invention. 
           [0064]      FIG. 23  is a time chart for explaining the operation of a control unit according to the ninth embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
       [0065]    A first embodiment of the invention is explained below with reference to  FIGS. 1 to 7 .  FIG. 1  is a diagram showing a general configuration of a power generating device including an external combustion engine  10  and a power generator  1  according to this invention. 
         [0066]    As shown in  FIG. 1 , the external combustion engine  10  according to this invention, which is for driving a generator  1  to generate the electromotive force by vibrating and displacing a movable element  2  with a permanent magnet embedded therein, comprises a container  11  sealed with a working liquid (water in this embodiment)  12  adapted to allow the liquid to flow therein, an electric heater  13  making up a heating means for heating and vaporizing the working liquid  12  in the container  11 , and a cooler  14  making up a cooling means for cooling the vapor of the working liquid  12  heated and vaporized by the electric heater  13 . 
         [0067]    The temperature of this electric heater  13  is regulated by a temperature controller  13   a . Also, the cooling water is circulated in the cooler  14  according to this embodiment. Though not shown, a radiator for radiating the heat taken away from the vapor of the working liquid  12  by the cooling water is arranged in the cooling water circulating circuit. 
         [0068]    According to this embodiment, the heated portion  11   a  making up a portion of the container  11  in contact with the electric heater  13  and the cooled portion  11   b  making up a portion of the container  11  in contact with the cooler  14  are formed of copper or aluminum high in heat conductivity. 
         [0069]    An intermediate portion  11   c  of the container  11  between the heated portion  11   a  and the cooled portion  11   b , on the other hand, is formed of stainless steel high in heat insulation property. Incidentally, the portion of the container  11  nearer to the generator  1  than the cooled portion  11   b  is also formed of stainless steel high in heat insulating property. 
         [0070]    The container  11  is a pipe-like pressure vessel formed substantially in the shape of U having first and second linear portions  11   e ,  11   f  with a bent portion lid at the lowest position. The electric heater  13  and the cooler  14  are arranged, with the electric heater  13  above the cooler  14 , in the first linear portion  11   e  at one horizontal end of the container  11  (right side on the page) with the bent portion  11   d  therebetween. 
         [0071]    Though not shown, in order to secure the space to vaporize the working liquid  12 , a gas of a predetermined volume is sealed at the upper end portion of the first linear portion  11   e . This gas may be air, for example, or the pure vapor of the working liquid  12 . 
         [0072]    At the upper end of the second linear portion  11   f  of the container  11  at the other horizontal end (left side on the page) with the bent portion  11   d  therebetween, on the other hand, a piston  15  adapted to be displaced under the pressure from the working liquid is arranged slidably in a cylinder portion  15   a.    
         [0073]    The piston  15  is coupled to the shaft  2   a  of a movable element  2 , and a spring  3  making up an elastic means for generating the elastic force to press the movable element  2  toward the piston  15  is arranged on the side of the movable element  2  far from the piston  15 . 
         [0074]    The bent portion  11   d  of the container  11  is connected with a pressure regulating means  16  for regulating the internal pressure (hereinafter referred to as the in-container pressure) Pc of the container  11 . This pressure regulating means  16  is comprised of a pressure regulating container  17  and a piston mechanism  18 . The pressure regulating container  17  communicates with the bent portion  11   d  through a connecting pipe  19 . The pressure regulating container  17  is filled up with a pressure regulating liquid  20 . According to this embodiment, the pressure regulating container  17  is arranged above the bent portion lid, and the pressure regulating liquid  20  is water as is the working liquid  12 . 
         [0075]    The pressure regulating container  17  and the connecting pipe  19  are desirably formed of a material high in heat insulating property. According to this embodiment, the pressure regulating liquid  20  being water, the pressure regulating container  17  and the connecting pipe  19  are formed of stainless steel. 
         [0076]    The piston mechanism  18  is for regulating the internal pressure (hereinafter referred to as the regulating container internal pressure) Pt of the pressure regulating container  17 , and comprised of a pressure regulating piston  18   a  and an electrically-operated actuator  18   b.    
         [0077]    The pressure regulating piston  18   a  is arranged at the upper end portion in the pressure regulating container  17  and adapted to be reciprocated vertically by the electrically-operated actuator  18  external to the pressure regulating container  17 . 
         [0078]    Next, an electronic control unit according to this embodiment is briefly explained. The control unit  21  includes a well-known microcomputer having a CPU, a ROM, a RAM, etc. and a peripheral circuit thereof and corresponds to the control means according to this invention. 
         [0079]    The control unit  21 , in order to control the pressure regulating means  16 , is supplied with the detection signals from a wattage sensor  22  for detecting the wattage Q 1  input to the electric heater  13 , a cooled portion temperature sensor  23  for detecting the temperature (hereinafter referred to as the cooled portion temperature) T 2  of the cooled portion  11   b  and an regulating container internal pressure sensor  24  for detecting the regulating container internal pressure Pt. Incidentally, the wattage sensor  22  corresponds to the wattage detecting means according to the invention. 
         [0080]    The control unit  21  controls the drive of the electrically-operated actuator  18   b  based on the detection signals from the sensors  22  to  24 . 
         [0081]    Next, the operation with this configuration is explained with reference to  FIG. 2 . With the activation of the electric heater  13  and the cooler  14 , the working liquid (water)  12  in the heated portion  11   a  is heated and vaporized by the electric heater  13 , and the high-temperature high-pressure vapor of the working liquid  12  is accumulated in the heated portion  11   a  thereby to push down the liquid level of the working liquid  12  in the first linear portion  11   e . Then, the working liquid  12  sealed in the container  11  is displaced from the first linear portion  11   e  toward the second linear portion  11   f  and pushes up the piston  15  on the generator  1  side. 
         [0082]    In the case where the liquid level of the working liquid  12  in the first linear portion  11   e  of the container  11  falls to the cooled portion  11   b  and the vapor of the working liquid  12  advances into the cooled portion  11   b , then the vapor of the working liquid  12  is cooled and liquefied by the cooler  14 . Thus, the force to push down the liquid level of the working liquid  12  in the first linear portion  11   e  is extinguished and the liquid level in the first linear portion  11   e  rises. As a result, the vapor of the working liquid  12  is expanded, and the piston  15  on the generator  1  side which has been pushed up moves down. 
         [0083]    This operation is repeatedly executed until the electric heater  13  and the cooler  14  are deactivated. In the meantime, the working liquid  12  in the container  11  is periodically displaced (by what is called the self vibration) thereby to move the movable element  2  of the generator  1  vertically. 
         [0084]    The present inventor has acquired, through experiment and analysis, the following knowledge about the relation between the peak value Pc of the in-container pressure Pc and the performance (output and efficiency) of the external combustion engine  10 . 
         [0085]      FIG. 3A  shows the PV diagram in a given state of the external combustion engine  10 . The abscissa of this PV diagram represents the volume (hereinafter referred to as the piston volume) of the space defined by the container  11  and the piston  15 , and the piston volume changes with the reciprocal motion of the piston  15 . This is also the case with the abscissa of the PV diagram shown in  FIGS. 3B ,  3 C. 
         [0086]      FIG. 3A  shows a PV diagram showing a state in which the peak value Pc 1  of the in-container pressure Pc is lower than the saturated vapor pressure Ps 1  of the working liquid  12  at the temperature (hereinafter referred to as the heated portion temperature) T 1  of the heated portion  11   a  and nearest to the saturated vapor pressure Ps 1 . In the process, an ideal state prevails in which the work done per period of the external combustion engine  10  is largest and the performance (output and efficiency) of the external combustion engine  10  is highest. 
         [0087]      FIG. 3B , on the other hand, is a PV diagram with the peak value Pc 1  extremely lower than the saturated vapor pressure Ps 1 . Under this condition, the work done per period is so small that the performance (output and efficiency) of the external combustion engine  10  is reduced. 
         [0088]      FIG. 3C  shows a PV diagram with the peak value Pc 1  higher than the saturated vapor pressure Ps 1 . Specifically, with the increase in the heated portion temperature T 1 , the high-temperature vapor exists in the heater  12  even in the case where the piston volume is largest with the piston  15  located at the bottom dead center (the highest position in  FIG. 1 ). 
         [0089]    In the process, the piston  15  moves from the bottom dead center toward the top dead center (lowest position in  FIG. 1 ). With the reduction in the piston-controlled volume, the vapor of the working liquid  12  is compressed and the in-container temperature P rises. Also, the working liquid  12 , advancing into the heated portion  11   a , is heated and vaporized, and therefore, the in-container pressure Pc further increases. As a result, the peak value Pc 1  exceeds the saturated vapor pressure Ps 1 . 
         [0090]    As long as the peak value Pc 1  is higher than the saturated vapor pressure Ps 1  as described above, the peak value Pc 1  exceeds the saturated vapor pressure Ps 1 . Therefore, part of the vapor of the working liquid  12  is condensed and liquefied. As a result, the negative work for moving the piston  15  downwardly is done, thereby reducing the performance (output and efficiency) of the external combustion engine  10 . 
         [0091]    In order to achieve the highest performance (output and efficiency) of the external combustion engine  10 , therefore, a state should be maintained in which the peak value Pc 1  of the in-container pressure Pc is kept lower than the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  and as near to the saturated vapor pressure Ps 1  as possible. 
         [0092]    As is well known, however, the saturated vapor pressure Ps 1  of the working liquid  12  changes with the heated portion temperature T 1  (see  FIG. 7  described later). Also, the peak value Pc 1  of the in-container pressure Pc changes with the change in the heated portion temperature T 1  and the temperature (hereinafter referred to as the cooled portion temperature) T 2  of the cooled portion  11   b  and the leakage of the working liquid  12  from the container  11 . 
         [0093]    Specifically, in the case where the heated portion temperature T 1  and the cooled portion temperature T 2  decrease with the decrease in the temperature of the electric heater  13  and the temperature of the cooling water circulating in the cooler  14 , accompanied by the temperature reduction of the working liquid  12 , then the working liquid  12  is thermally compressed and the volume thereof is reduced. Also, the leakage of the working liquid  12  from the container  11 , even in a small amount at a time, reduces the volume of the working liquid  12 . 
         [0094]    Once the volume of the working liquid  12  is reduced, as shown in  FIG. 4A , the working liquid  12  fails to advance sufficiently into the heated portion  11   a  even in the case where the piston  15  is located at the top dead center (lowest position in  FIG. 1 ) and the piston volume is minimum. 
         [0095]    As a result, the vaporization of the working liquid  12  in the heated portion  11   a  is suppressed, thereby reducing the peak value Pc 1  of the in-container pressure Pc. 
         [0096]    In the case where the heated portion temperature T 1  and the cooled portion temperature T 2  increase and hence the volume of the working liquid  12  increases, on the other hand, as shown in  FIG. 4B , the vapor fails to advance sufficiently into the cooled portion  11   b  even in the case where the piston  15  is located at the bottom dead center (highest position in  FIG. 1 ) and the piston volume is maximum. 
         [0097]    As a result, the liquefaction of the vapor in the cooled portion  11   b  is suppressed, thereby increasing the peak value Pc 1  of the in-container pressure Pc. 
         [0098]      FIG. 5  is a graph showing the relation between the volume of the working liquid  12  and the efficiency of the external combustion engine  10 . Though not shown, the relation between the volume of the working liquid  12  and the output of the external combustion engine  10  is similar to the relation shown in  FIG. 5 . 
         [0099]    As can be understood from  FIG. 5 , in the case where the volume of the working liquid  12  is a predetermined value V 1 , the performance (output and efficiency) of the external combustion engine  10  is highest. Under this condition, the PV diagram is plotted as shown in  FIG. 3A . 
         [0100]    In the case where the volume of the working liquid  12  assumes the value V 2  smaller than a predetermined volume V 1 , on the other hand, the PV diagram is as shown in  FIG. 3B , and the performance (output and efficiency) of the external combustion engine  10  is decreased. In the case where the volume of the working liquid  12  is V 3  and larger than the predetermined volume V 1 , on the other hand, the PV diagram as shown in  FIG. 3C  is plotted, and the performance (output and efficiency) of the external combustion engine  10  is decreased. 
         [0101]    In view of this, according to this embodiment, while the external combustion engine  10  is in operation, the in-container pressure Pc is regulated in such a manner that the peak value Pc 1  of the in-container pressure Pc is lower than the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  and as near to the saturated vapor pressure Ps 1  as possible. In this way, the reduction in the performance (output and efficiency) of the external combustion engine  10  due to the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc is suppressed. 
         [0102]      FIG. 6  is a block diagram showing a general control operation according to this embodiment. First, the heated portion temperature T 1  is calculated according to Equation (1) below. 
         [0000]        T 1= Q/ ( m·Cp ) −T 0   (1) 
         [0000]    where Q is the heat quantity (kJ) applied to the working liquid  12  from the heating means (electric heater  13  in this case), m the mass (kg) of the heated portion  11   a , Cp the specific heat (kJ/kg·K) of the heated portion  11   a  and T 0  the temperature (K) of the heated portion  11   a  before being heated by the heating means. 
         [0103]    According to this embodiment, the heat quantity Q applied from the electric heater  13  to the working liquid  12  is substantially equal to the wattage Q 1  input to the electric heater  13 , and the temperature T 0  of the heated portion  11   a  before being heated is substantially equal to the cooled portion temperature T 2 . 
         [0104]    According to this embodiment, therefore, the heated portion temperature T 1  is calculated from Equation (1) using the wattage Q 1  input to the electric heater  13  in place of the heat quantity Q applied from the electric heater  13  to the working liquid  12  and the cooled portion temperature T 2  in place of the temperature T 0  of the heated portion  11   a  before being heated. 
         [0105]    Incidentally, in place of the temperature T 0  of the heated portion  11   a  before being heated, the cooled portion temperature T 2  is not necessarily used, but the temperature of the portion of the container  11  other than the heated portion  11   a  and the cooled portion  11   b , the ambient temperature in the neighborhood of the heated portion  11   a  or other temperature approximate to the temperature T 0  of the heated portion  11   a  before being heated, may be used in place of the temperature T 0  of the heated portion  11   a  before being heated. 
         [0106]    Next, based on the heated portion temperature T 1  calculated by Equation (1) and the vapor pressure curve of the working liquid  12  shown in  FIG. 7 , the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  is calculated. 
         [0107]    In the case where the peak value Pt 1  of the regulating container internal pressure Pt is lower than the saturated vapor pressure Ps 1 , the electrically-operated actuator  18   b  pushes out the pressure regulating piston  18   a  thereby to reduce the volume of the pressure regulating container  17 . As a result, the pressure regulating liquid  20  is compressed and the regulating container internal pressure Pt rises, while at the same time increasing the peak value Pt 1  of the regulating container internal pressure Pt. 
         [0108]    In the case where the peak value Pt 1  of the regulating container internal pressure Pt is higher than the saturated vapor pressure Ps 1 , on the other hand, the electrically-operated actuator  18   b  pulls in the pressure regulating piston  18   a  and increases the volume of the pressure regulating container  17 . As a result, the pressure regulating liquid  20  is expanded and the regulating container internal pressure Pt decreases, thereby decreasing the peak value Pt 1 . 
         [0109]    The container  11  communicates with the pressure regulating container  17  through the connecting pipe  19 , and therefore the in-container pressure Pc follows the regulating container internal pressure Pt. As a result, the peak value Pc 1  of the in-container pressure Pc can be rendered to approach the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1 . 
         [0110]    Therefore, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state. Thus, the reduction in the performance (output and efficiency) of the external combustion engine  10  which otherwise would occur due to the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc can be suppressed. 
         [0111]    According to this embodiment, the heated portion temperature T 1  is calculated from the wattage Q 1 , etc. input to the electric heater  13 . As a result, the heated portion temperature T 1  can be estimated without detecting it directly, and therefore, the performance reduction of the external combustion engine  10  can be suppressed without detecting the heated portion temperature T 1  directly. 
         [0112]    The sensors  22  to  24  used in this embodiment can be arranged at other than the heated portion  11   a . Thus, the trouble such as the damage to the sensors  22  to  24  which otherwise might be caused by the high temperature of the heated portion  11   a  can be avoided. 
         [0113]    According to this embodiment, the pressure regulating liquid  20  in the pressure regulating container  17  is identical with the working liquid  12 . Nevertheless, a liquid such as a liquid metal, higher in compressibility than the working liquid  12 , may be used as the pressure regulating liquid  20 . As a result, the displacement amount of the pressure regulating piston  18   a  can be reduced as compared with a case in which the pressure regulating liquid  20  is identical with the working liquid  12 , thereby making it possible to reduce the size of the external combustion engine  10 . 
         [0114]    Incidentally, in the case where a liquid metal is used as the pressure regulating liquid  20 , it is recommended that, as the specific gravity of the liquid metal is larger than that of the working liquid  12 , the pressure regulating container  17  should be arranged under the bent portion  11   d  to prevent,the pressure regulating liquid  20  from mixing with the working liquid  12 . 
       Second Embodiment 
       [0115]    According to the first embodiment described above, the working liquid  12  is heated by the electric heater  13 . According to the second embodiment, on the other hand, as shown in  FIG. 8 , the working liquid  12  is heated by a high-temperature gas (such as the exhaust gas of an automobile). 
         [0116]      FIG. 8  is a diagram showing a general configuration of the power generating device according to this embodiment. According to this embodiment, as compared with the first embodiment, the electric heater  13 , the temperature controller  13   a  and the wattage sensor  22  are eliminated. According to this embodiment, on the other hand, a heater  30  for exchanging heat with a high-temperature gas is arranged to cover the heated portion  11   a . This heater  30  corresponds to the heating means according to this invention. 
         [0117]    The heater  30  is inserted into a gas pipe  31  in which the high-temperature gas flows. A bypass pipe  31   a  branching from the gas pipe  31  is arranged in the portion of the gas pipe  31  upstream of the heated portion  11   a  in the high-temperature gas flow. 
         [0118]    This branch of the bypass pipe  31   a  includes a regulating valve  32  for regulating the ratio of flow rate between the high-temperature gas flowing in the heated portion  11   a  and the high-temperature gas flowing in the bypass pipe  31   a . The opening degree of the regulating valve  32  is controlled by the control unit  21 . 
         [0119]    Also, according to this embodiment, in order to calculate the heated portion temperature T 1 , the detection signals are input to the control unit  21  from a flow rate sensor  33  for detecting the flow rate (mass flow rate) mg of the high-temperature gas flowing in the heated portion  11   a , a pre-heating gas temperature sensor  34  for detecting the high-temperature gas temperature Tgi before heating the heated portion  11   a  and a post-heating gas temperature sensor  35  for detecting the high-temperature gas temperature Tgo after heating the heated portion  11   a.    
         [0120]    Incidentally, the flow rate sensor  33  corresponds to the flow rate detecting means according to the invention, the pre-heating gas temperature sensor  34  to the first temperature detecting means according to the invention, and the post-heating gas temperature sensor  35  to the second temperature detecting means according to the invention. 
         [0121]    According to this embodiment, the heat quantity Q applied to the working liquid  12  from the heating means (the heater  30  in this embodiment) is calculated from Equation (2) below. 
         [0000]        Q=mg·Cgp· ( Tgi−Tgo )   (2) 
         [0000]    where Cgp is the specific heat (kJ/kg·K) of the high-temperature gas. The heated portion temperature T 1  is calculated from the heat quantity Q and Equation (1). 
         [0122]    As a result, like in the first embodiment, the heated portion temperature T 1  can be estimated without detecting the heated portion temperature T 1  directly. 
       Third Embodiment 
       [0123]    According to the first embodiment described above, the deterioration of the performance of the external combustion engine  10 , which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc, is prevented by rendering the peak value Pc 1  of the in-container pressure Pc to decrease below the saturated vapor pressure Ps 1  and approach the saturated vapor pressure Ps 1  as far as possible. According to the third embodiment, on the other hand, the deterioration of the performance of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc is suppressed by rendering the average value Pca of the in-container pressure Pc to approach a target value Pc 0 . 
         [0124]    The average value Pca of the in-container pressure Pc is defined as the one during one period of self vibration of the working liquid  12 , and the target value Pc 0  as a value approximate to the average value (hereinafter referred to as the ideal average value ( FIG. 3A )) Pci of the in-container pressure Pc in the ideal state in which the performance (output and efficiency) of the external combustion engine  10  reaches maximum. 
         [0125]      FIG. 9  is a diagram showing a general configuration of a power generating device according to this embodiment. According to this embodiment, as compared with the first embodiment, a restrictor  36  for suppressing the propagation of the in-container pressure Pc into the pressure regulating container  17  is formed in the connecting pipe  19 . In this restrictor  36 , the path diameter of the connecting pipe  19  is reduced. As a result, the regulating container internal pressure Pt is prevented from changing following the periodic change of the in-container pressure Pc, and therefore, settled at a level substantially equal to the average value Pca of the in-container pressure Pc. 
         [0126]      FIG. 10  is a block diagram showing a general operation to control the in-container pressure Pc according to this embodiment. First, like in the first embodiment, the heated portion temperature T 1  is calculated by Equation (1) described above. Next, according to this embodiment, the saturated vapor pressure Ps 2  of the working liquid  12  at the cooled portion temperature T 2  is calculated based on the cooled portion temperature T 2  and the vapor pressure curve of the working liquid  12  shown in  FIG. 7 . Incidentally, the saturated vapor pressure Ps 2  of the working liquid  12  at the cooled portion temperature T 2  is equal to the minimum value Pc 2  ( FIGS. 3A to 3C ) during one period of the in-container pressure Pc. 
         [0127]    Next, the target value Pc 0  is calculated based on the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  and the saturated vapor pressure Ps 2  of the working liquid  12  at the cooled portion temperature T 2 . According to this embodiment, the target value Pc 0  is set to an intermediate value, or more specifically about an average value, between the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  and the saturated vapor pressure Ps 2  of the working liquid  12  at the cooled portion temperature T 2 . 
         [0128]    In the case where the regulating container internal pressure Pt is lower than the target value Pc 0 , the electrically-operated actuator  18   b  pushes out the pressure regulating piston  18   a  and reduces the volume of the pressure regulating container  17 . As a result, the pressure regulating liquid  20  is compressed and the regulating container internal pressure Pt rises. 
         [0129]    In the case where the regulating container internal pressure Pt is higher than the target value Pc 0 , on the other hand, the pressure regulating piston  18   a  is pulled in to reduce the volume of the pressure regulating container  17 . As a result, the pressure regulating liquid  20  is expanded and the regulating container internal pressure Pt is reduced. 
         [0130]    Then, the average value Pca of the in-container pressure Pc, which also follows the regulating container internal pressure Pt, approaches the target value Pc 0 . In other words, the average value Pca of the in-container pressure Pc approaches the ideal average value Pci. 
         [0131]    As a result, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state, and therefore, the reduction in the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc can be prevented. 
         [0132]    According to the first embodiment, the peak value Pt 1  of the regulating container internal pressure Pt is detected. In view of the fact that the regulating container internal pressure Pt reaches the peak value Pt 1  within a very short time, the sensing period of the regulating container internal pressure sensor  24  for detecting the regulating container internal pressure Pt is greatly shortened. 
         [0133]    According to this embodiment, in contrast, as described above, the regulating container internal pressure Pt is settled at a pressure substantially equal to the average value Pca of the in-container pressure Pc without changing following the in-container pressure Pc. As a result, the sensing period of the regulating container internal pressure sensor  24  for detecting the regulating container internal pressure Pt can be set longer than in the first embodiment described above. 
         [0134]    Consequently, the detection of the regulating container internal pressure Pt is facilitated as compared with the first embodiment and, therefore, the performance (output and efficiency) of the external combustion engine  10  can be easily improved as compared with the first embodiment. 
         [0135]    Incidentally, according to this embodiment, the electric heater  13  is used as a heating means for heating and vaporizing the working liquid  12 , and therefore, the heated portion temperature T 1  is calculated by Equation (1) described above. As in the second embodiment described above, however, the heated portion temperature T 1  may be calculated by Equations (1) and (2) using the heater  30  for exchanging heat with the high-temperature gas as a heating means. 
       Fourth Embodiment 
       [0136]    In the third embodiment described above, the pressure regulating means  16  is comprised of the pressure regulating container  17  and the piston mechanism  18 . In the fourth embodiment, on the other hand, as shown in  FIG. 11 , the pressure regulating means  16  is comprised of a pressure regulating container  17  and a pump mechanism  37 . 
         [0137]      FIG. 11  is a diagram showing a general configuration of a power generating device according to this embodiment. The pump mechanism  37  includes a pump  38 , an intake pipe  39 , a discharge pipe  40 , an intake on/off valve  41  and a discharge on/off valve  42 . 
         [0138]    The pump  38  for sucking in and storing therein the pressure regulating liquid  20  in the pressure regulating container  17  and discharging the stored pressure regulating liquid  20  to the pressure regulating container  17  is connected to the pressure regulating container  17  through the intake pipe  39  and the discharge pipe  40 . 
         [0139]    The intake on/off valve  41  is arranged in the intake pipe  39 , and once the intake on/off valve  41  is opened, the pressure regulating liquid  20  in the pressure regulating container  17  is sucked in by the pump  38  and stored therein. 
         [0140]    The discharge on/off valve  42  is arranged in the discharge pipe  40 , and once the discharge on/off valve  42  is opened, the pressure regulating liquid  20  stored in the pump  38  is discharged to the pressure regulating container  17 . The operation of the on/off valves  41 ,  42  is controlled by the control unit  21 . 
         [0141]      FIG. 12  is a block diagram showing a general operation to control the in-container pressure Pc according to this embodiment. According to this embodiment, in the case where the regulating container internal pressure Pt is lower than the target value Pc 0 , the intake on/off valve  41  is closed and the discharge on/off valve  42  is opened thereby to increase the volume of the working liquid  12 . As a result, the regulating container internal pressure Pt increases. 
         [0142]    In the case where the regulating container internal pressure Pt is higher than the target value Pc 0 , on the other hand, the intake on/off valve  41  is opened while the discharge on/off valve  42  is closed thereby to reduce the volume of the pressure regulating liquid  20  in the pressure regulating container  17 . As a result, the regulating container internal pressure Pt is decreased. 
         [0143]    Then, like in the second embodiment, the average value Pca of the in-container pressure Pc approaches the target value Pc 0 . As a result, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state. Thus, the reduction of the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the peak value Pc 1  of the in-container pressure Pc can be prevented. 
         [0144]    According to this embodiment, and as in the second embodiment, the reduction of the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the peak value Pc 1  of the in-container pressure Pc is prevented by rendering the average value Pca of the in-container pressure Pc to approach the target value Pc 0 . As in the first embodiment, however, the restrictor  36  may be eliminated, and the reduction in the performance (output and efficiency) of the external combustion engine  10 , which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the peak value Pc 1  of the in-container pressure Pc, may be prevented by setting the peak value Pc 1  of the in-container pressure Pc to a level lower than the saturated vapor pressure Ps 1  and rendered to approach the saturated vapor pressure Ps 1  as far as possible. 
         [0145]    According to this embodiment, the electric heater  13  is used as a heating means for heating and vaporizing the working liquid  12  and, therefore, the heated portion temperature T 1  is calculated using Equation (1). As in the second embodiment, however, the heater  30  for exchanging heat with the high-temperature gas may be used as a heating means, and the heated portion temperature T 1  may be calculated according to Equations (1) and (2) described above. 
       Fifth Embodiment 
       [0146]    In the fourth embodiment described above, the in-container pressure Pc is regulated using one pressure regulating container  17 . In the fifth embodiment, in contrast, as shown in  FIG. 13 , the in-container pressure Pc is controlled using two regulating containers  43 ,  44 . 
         [0147]      FIG. 13  is a diagram showing a general configuration of a power generating device according to this embodiment. According to this embodiment, the pressure regulating means  16  is comprised of two regulating containers  43 ,  44 , two pumps  45 ,  46  and two on/off valves  47 ,  48 . 
         [0148]    The two regulating containers  43 ,  44  communicate with a bent portion lid through the connecting pipes  49 ,  50 , respectively. The two regulating containers  43 ,  44  are kept at different levels of pressure by the pumps  45 ,  46 , respectively. The two on/off valves  47 ,  48  are arranged in the two connecting pipes  49 ,  50 , respectively, and the on/off operation of the two on/off valves  47 ,  48  is controlled independently of each other by the control unit  21 . 
         [0149]    Also, according to this embodiment, the regulating container internal pressure sensor  24  for detecting the regulating container internal pressure Pt is eliminated, and, in its place, the detection signal from the in-container pressure sensor  51  for detecting the in-container pressure Pc is input to the control unit  21 . 
         [0150]    The internal pressure of the regulating container  43  is always kept at a level higher than the target value Pc 0  by the pump  45 , while the internal pressure of the other regulating container  44  maintained at a level lower than the target value Pc 0  by the pump  46 . 
         [0151]      FIG. 14  is a block diagram showing a general operation to control the in-container pressure Pc according to this embodiment. In this embodiment, as long as the average value Pca of the in-container pressure Pc is lower than the target value Pc 0 , the on/off valve  47  of the regulating container  43  is opened, while the on/off valve  48  of the other regulating container  44  is closed. As a result, the in-container pressure Pc increases. 
         [0152]    In the case where the average value Pca of the in-container pressure Pc is higher than the target value Pc 0 , on the other hand, the on/off valve  47  of the regulating container  43  is closed while opening the on/off valve  48  of the other regulating container  44 . As a result, the in-container pressure Pc is decreased. 
         [0153]    Then, like in the third embodiment, the average value Pca of the in-container pressure Pc approaches the target value Pc 0 . As a result, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state and, therefore, the reduction in the performance (output and efficiency) of the external combustion engine  10 , which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc, can be prevented. 
         [0154]    Although this embodiment uses the two pumps  45 ,  46  to apply pressure into the two regulating containers  43 ,  44  differently from each other, the interior of the two regulating containers  43 ,  44  may alternatively be kept at different pressure levels by use of a common pump. 
         [0155]    Also, instead of using the two regulating containers  43 ,  44  set to different pressures as in this embodiment, three or more regulating containers may be used to set different pressures. 
         [0156]    In this case, three or more regulating containers are each equipped with an on/off valve, and in the case where the average value Pca of the in-container pressure Pc is lower than the target value Pc 0 , the on/off valve of only one of the three regulating containers of which the regulating container internal pressure is lower than and nearest to the target value Pc 0  is opened, while in the case where the average value Pca of the in-container pressure Pc is lower than the target value Pc 0 , on the other hand, the on/off valve of only one of the three regulating-containers, of which the regulating container internal pressure is higher than and nearest to the target value Pc 0 , is opened. 
         [0157]    According to this embodiment, the electric heater  13  is used as a heating means for heating and vaporizing the working liquid  12 , and therefore, the heated portion temperature T 1  is calculated using Equation (1). As in the second embodiment, however, the heated portion temperature T 1  may be calculated according to Equations (1), (2) using the heater  30  for exchanging heat with the high-temperature gas as a heating means. 
       Sixth Embodiment 
       [0158]    According to the third embodiment described above, the pressure regulating means  16  includes the pressure regulating container  17  and the piston mechanism  18 , while in the fourth embodiment, the pressure regulating means  16  is comprised of the pressure regulating container  17  and the pump mechanism  37 . According to the sixth embodiment, on the other hand, as shown in  FIG. 15 , the pressure regulating means  16  is comprised of the pressure regulating container  17  and the pressure-regulating heating device  52 . 
         [0159]      FIG. 15  is a diagram showing a general configuration of a power generating device according to this embodiment. The pressure-regulating heating device  52  is comprised of a pressure-regulating electric heater  53  closely arranged at a portion of the pressure regulating container  17  far from the connecting pipe  19  (upper end in  FIG. 15 ) and a pressure-regulating temperature controller  54  for regulating the temperature of the pressure-regulating electric heater  53 . 
         [0160]    The control unit  21  controls the pressure-regulating temperature controller  54  thereby to regulate the heat quantity supplied from the pressure-regulating electric heater  53  to the pressure regulating container  17 . 
         [0161]      FIG. 16  is a graph showing the temperature gradient of the pressure regulating container  17  heated by the pressure-regulating electric heater  53 . As shown in  FIG. 16 , the pressure regulating container  17  has such a heat conducting structure that the temperature gradient of the high-temperature portion  55  far from the connecting pipe  19  is negligibly small, while the temperature of the low-temperature portion  56  near to the connecting pipe  19  decreases progressively with the increase in the distance from the high-temperature portion  55 . In  FIG. 16 , the temperature Th is that of the high-temperature portion  55  (hereinafter referred to as the high-temperature portion temperature). 
         [0162]    Also, the temperature Tc is that of the end portion of the low-temperature portion  56  near to the connecting pipe  19  (hereinafter referred to as the low-temperature portion temperature) and substantially equal to the cooled portion temperature T 2  (accurately, slightly higher than the cooled portion temperature T 2 ). The cooled portion temperature T 2 , therefore, is not higher than the boiling point of the pressure regulating liquid  20 . 
         [0163]    The pressure regulating liquid  20  in the high-temperature portion  55  is heated and vaporized by the pressure-regulating electric heater  53 , and the high-temperature high-pressure vapor  57  is accumulated in the high-temperature portion  55  thereby to push down the liquid level of the pressure regulating liquid  20  in the high-temperature portion  55 . 
         [0164]    The temperature of the low-temperature portion  56 , on the other hand, decreases progressively with the increase in the distance from the high-temperature portion  55 , and therefore, the liquid level of the pressure regulating liquid  20  is kept located in the high-temperature portion  55  without being pushed down to the low-temperature portion  56 . As a result, the pressure regulating liquid  20  is kept in contact with the high-temperature portion  55  and, therefore, the pressure regulating container  17  is kept in boiling state. Thus, the regulating container internal pressure Pt can be kept at the same level as the saturated vapor pressure of the pressure regulating liquid  20  at the high-temperature portion temperature Th of the pressure regulating container  17 . 
         [0165]      FIG. 13  is a block diagram showing a general operation to control the in-container pressure Pc according to this embodiment. According to this embodiment, in the case where the regulating container internal pressure Pt is lower than the target value Pc 0 , the pressure-regulating temperature controller  54  increases the temperature of the pressure-regulating electric heater  53  and hence the high-temperature portion temperature Th of the pressure regulating container  17 . As a result, the saturated vapor pressure of the pressure regulating liquid  20  increases and so does the regulating container internal pressure Pt. 
         [0166]    In the case where the regulating container internal pressure Pt is higher than the target value Pc 0 , on the other hand, the pressure-regulating temperature controller  54  decreases the temperature of the pressure-regulating electric heater  53  thereby to reduce the high-temperature portion temperature Th of the pressure regulating container  17 . As a result, the saturated vapor pressure of the pressure regulating liquid  20  is decreased and so is the regulating container internal pressure Pt. 
         [0167]    Then, as in the second and third embodiments, the average value Pca of the in-container pressure Pc approaches the target value Pc 0 . As a result, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state, and therefore, the deterioration of the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc can be prevented. 
         [0168]    The vapor  57  in the high-temperature portion  55  may be either the pure vapor of the pressure regulating liquid  20  or a mixture of the vapor of the pressure regulating liquid  20  and another gas (such as air). 
         [0169]    According to this embodiment, the electric heater  13  is used as the heating means for heating and vaporizing the working liquid  12 , and therefore, the heated portion temperature T 1  is calculated according to Equation (1). Like in the second embodiment, however, the heated portion temperature T 1  may alternatively be calculated by Equations (1) and (2) using the heater  30  for exchanging heat with the high-temperature gas as a heating means. 
         [0170]    Also, according to this embodiment, the pressure regulating liquid  20  in the pressure regulating container  17  is vaporized by the pressure-regulating electric heater  53 . Nevertheless, the pressure regulating liquid  20  in the pressure regulating container  17  may alternatively be vaporized using a high-temperature gas as a heat source. 
       Seventh Embodiment 
       [0171]    According to the third, fourth and sixth embodiments described above, the in-container pressure Pc is regulated by arranging the pressure regulating container  17  and regulating the regulating container internal pressure Pt. According to the seventh embodiment, however, as shown in  FIG. 18 , the pressure regulating container  17  is eliminated, and the in-container pressure Pc is regulated by regulating the volume of the container  11 . 
         [0172]      FIG. 18  is a diagram showing a general configuration of a power generating device according to this embodiment. According to this embodiment, the pressure-regulating means  16  is comprised of an expansion and contraction portion  58  of the container  11  and an electrically-operated actuator  59 . The expansion and contraction portion  58  is formed as a bellows on the bent portion lid of the container  11  in a way adapted to extend and contract in horizontal direction. The electrically-operated actuator  59  for expanding and contracting the expansion and contraction portion  58  is coupled to the container  11 . 
         [0173]    The electrically-operated actuator  59  is controlled by the control unit  21  based on the heated portion temperature T 1  calculated according to Equation (1), the cooled portion temperature T 2  detected by the cooled portion temperature sensor  23  and the in-container pressure Pc detected by the in-container pressure sensor  51 . 
         [0174]      FIG. 19  is a block diagram showing a general operation to control the in-container pressure Pc according to this embodiment. First, as in the third embodiment, the heated portion temperature T 1  is calculated according to Equation (1) described above, after which the target value Pc 0  is calculated based on the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  and the saturated vapor pressure Ps 2  of the working liquid  12  at the cooled portion temperature T 2 . 
         [0175]    According to this embodiment, in the case where the average value Pca of the in-container pressure Pc is lower than the target value Pc 0 , the in-container pressure Pc is increased by controlling the electrically-operated actuator  59  in such a manner as to contract the expansion and contraction portion  58 . 
         [0176]    In the case where the average value Pca of the in-container pressure Pc is higher than the target value Pc 0 , on the other hand, the in-container pressure Pc is decreased by controlling the electrically-operated actuator  59  in such a manner as to expand the expansion and contraction portion  58 . 
         [0177]    As a result, the average value Pca of the in-container pressure Pc approaches the target value Pc 0 . Thus, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state, and therefore, the deterioration of the performance (output and efficiency), which otherwise might be caused by the change in the saturated vapor pressure Ps 1  or the change in the peak value Pc 1  of the in-container pressure Pc, can be prevented. 
         [0178]    Incidentally, according to this embodiment, the average value Pca of the in-container pressure Pc is rendered to approach the target value Pc 0 . As an alternative, however, the peak value Pc 1  of the in-container pressure Pc may be rendered to approach the saturated vapor pressure Ps 1 . 
         [0179]    Also, according to this embodiment, the electric heater  13  is used as a heating means for heating and vaporizing the working liquid  12 , and the heated portion temperature T 1  is calculated according to Equation (1). As an alternative, as in the second embodiment, the heated portion temperature T 1  may be calculated by Equations (1), (2) using the heater  30  for exchanging heat with the high-temperature gas as a heating means. (Eighth embodiment) In the seventh embodiment described above, the in-container pressure Pc is regulated by regulating the volume of the container  11 . According to the eighth embodiment, in contrast, as shown in  FIG. 20 , the in-container pressure Pc is regulated by controlling the temperature of the working liquid  12 . 
         [0180]      FIG. 20  is a diagram showing a general configuration of the power generating device according to this embodiment. The pressure regulating means  60  according to this embodiment is comprised of a temperature controller for maintaining the temperature of the working liquid  12  at a constant level. 
         [0181]    This temperature controller  60  is arranged at a portion of the container  11  other than the heated portion  11   a  and the cooled portion  11   b , and includes a heater unit  61  for heating the working liquid  12  and a cooler unit  62  for cooing the working liquid  12 . 
         [0182]    The on/off control operation of the heater unit  61  and the cooler unit  62  of the temperature controller  60  is performed by the control unit  21  based on the heated portion temperature T 1  calculated by Equation (1) and the in-container pressure Pc detected by the in-container pressure sensor  51 . 
         [0183]      FIG. 21  is a block diagram showing a general operation to control the in-container pressure Pc according to this embodiment. According to this embodiment, the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  is calculated based on the heated portion temperature T 1  calculated by Equation (1) and the vapor pressure curve of the working liquid  12  shown in  FIG. 7 . 
         [0184]    In the case where the peak value Pc 1  of the in-container pressure Pc is higher than the saturated vapor pressure Ps 1 , the cooler unit  62  is activated and cools the working liquid  12 . As a result, the working liquid  12  is thermally contracted, and therefore, the in-container pressure Pc decreases, thereby decreasing the peak value Pc 1  of the in-container pressure Pc. 
         [0185]    In the case where the peak value Pc 1  of the in-container pressure Pc is lower than the saturated vapor pressure Ps 1 , on the other hand, the heater unit  61  is activated and heats the working liquid  12 . As a result, the working liquid  12  is thermally expanded, and the in-container pressure Pc increases, thereby increasing the peak value Pc 1  of the in-container pressure Pc. 
         [0186]    In this way, the peak value Pc 1  of the in-container pressure Pc approaches the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1 . As a result, the operating condition of the external combustion engine  10  can always be rendered to approach the ideal state. Thus, the deterioration of the performance (output and efficiency) which otherwise might be caused by the change in the saturated vapor pressure Ps 1  and the change in the peak value Pc 1  of the in-container pressure Pc can be prevented. 
         [0187]    According to this embodiment, the electric heater  13  is used as a heating means for heating and vaporizing the working liquid  12  and the heated portion temperature T 1  is calculated by Equation (1). Like in the second embodiment, however, the heated portion temperature T 1  may be calculated by Equations (1) and (2) using the heater  30  for exchanging heat with the high-temperature gas as a heating means. 
       Ninth Embodiment 
       [0188]    In the first, second and eighth embodiments described above, the deterioration of the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  and the change in the peak value Pc 1  of the in-container pressure Pc can be prevented by reducing the peak value Pc 1  of the in-container pressure Pc below the saturated vapor pressure Ps 1  and rendering the peak value Pc 1  to approach the saturated vapor pressure Ps 1  as far as possible. Also, in the third, fourth, fifth, sixth and seventh embodiments described above, the deterioration of the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the saturated vapor pressure Ps 1  and the change in the peak value Pc 1  of the in-container pressure Pc can be prevented by rendering the average value Pca of the in-container pressure Pc to approach the target value Pc 0 . 
         [0189]    According to the ninth embodiment, in contrast, the deterioration of the performance (output and efficiency) of the external combustion engine  10  which otherwise might be caused by the change in the peak value Pc 1  of the in-container pressure Pc can be prevented by discharging the working liquid  12  outside in an amount by which the in-container pressure Pc exceeds the saturated vapor pressure Ps 1 . 
         [0190]      FIG. 22  is a diagram showing a general configuration of the power generating device according to this embodiment. This embodiment represents an application of the invention to the conventional technique described above (Japanese Unexamined Patent Publication No. 2005-330910). Specifically, in the prior art described above, the heated portion temperature T 1  is detected directly, while according to this embodiment, the heated portion temperature T 1  is calculated based on the wattage Q 1  input to the electric heater  13 . The other parts of the configuration are similar to those of the prior art described above. 
         [0191]    The pressure regulating means  63  according to this embodiment is comprised of a valve  63  for establishing communication between the interior of the container  11  and the atmosphere. 
         [0192]    The on/off control operation of the valve  63  is performed by the control unit  21  based on the heated portion temperature T 1  calculated by Equation (1) and the in-container pressure Pc detected by the in-container pressure sensor  51 . 
         [0193]    Specifically, the saturated vapor pressure Ps 1  of the working liquid  12  at the heated portion temperature T 1  is calculated based on the heated portion temperature T 1  calculated by Equation (1) and the vapor pressure curve of the working liquid  12  shown in  FIG. 7 . 
         [0194]    Next, in the case where the in-container pressure Pc is not lower than the saturated vapor pressure Ps 1 , as shown in  FIG. 23 , the valve  63  is opened and the working liquid  12  in the container  11  is discharged into the atmosphere, while in the case where the in-container pressure Pc is lower than the saturated vapor pressure Ps 1 , on the other hand, the valve  63  is closed. 
         [0195]    As a result, the internal pressure of the container  11  is prevented from exceeding the saturated vapor pressure of the working liquid  12  during the operation of the external combustion engine  10 . 
         [0196]    Incidentally, during the operation of the external combustion engine  10 , the internal pressure of the container  11  reaches a maximum when the piston  15  is located at the top dead center (lowest position in  FIG. 22 ) where the piston volume is smallest. As indicated by two-dot chain in  FIG. 22 , therefore, a position sensor  64  for detecting the position of the piston  15  is arranged, and the timing at which the piston  15  is located at the bottom dead center is detected through the position sensor  64 , and in synchronism with the particular detection timing, the on/off control operation of the valve  63  may be performed. 
         [0197]    In this case, the on/off control operation of the valve  63  is performed in such a manner that once the internal pressure of the container  11  retrieved from the pressure sensor  36  with the piston  15  at the bottom dead center increases to or higher than the saturated vapor pressure, the valve  63  is opened for a predetermined period of time shorter than the reciprocation period of the piston  15 . In this way, the working liquid in the container  11  is discharged stepwise. 
         [0198]    According to this embodiment, the electric heater  13  is used as a heating means for heating and vaporizing the working liquid  12 , and therefore, the heated portion temperature T 1  is calculated by Equation (1). As in the second embodiment, however, the heated portion temperature T 1  may be calculated by Equations (1) and (2) using the heater  30  for exchanging heat with the high-temperature gas as a heating means. 
       Other Embodiments 
       [0199]    According to each embodiment described above, the heated portion temperature T 1  is calculated by Equation (1). As an alternative, the heated portion temperature T 1  may be calculated by correcting Equation (1) using an appropriate coefficient. 
         [0200]    Also, although the heat quantity Q applied from the high-temperature gas to the electric heater  13  is calculated by Equation (2), the heated portion temperature T 1  may be calculated by correcting Equation (2) using an appropriate coefficient. 
         [0201]    Further, although this embodiment represents an application of the invention to a drive source of the power generating device. Nevertheless, the external combustion engine according to this invention can be used also as a drive source other than the power generating device. 
         [0202]    While the invention has been described by reference 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.