Abstract:
A Rankine cycle system includes a boiler configured to apply waste heat to refrigerant circulating in an internal-combustion engine to vaporize the refrigerant; a gas-liquid separator configured to separate gas-liquid two-phase refrigerant, sent from the boiler, into gas phase fluid and liquid phase fluid; a superheater configured to superheat the gas phase fluid, sent from the gas-liquid separator, through heat exchange with exhaust gas of the internal-combustion engine; an expander configured to expand the gas phase fluid, passing through the superheater, to recover thermal energy, and a condenser configured to condense the gas phase fluid, passing through the expander, to return the gas phase fluid to liquid phase fluid. The gas-liquid separator is fixed to a cylinder head of the internal-combustion engine. It is preferable that the gas-liquid separator is configured to include a bracket, and is fixed to the cylinder head via the bracket.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the present invention relate to a Rankine cycle system for vehicle, and in particular, to a structure of mounting a Rankine cycle system on a vehicle. 
       BACKGROUND 
       [0002]    Patent Literature 1 discloses a technology relating to a Rankine cycle system mounted on a vehicle. In this Rankine cycle system, liquid phase fluid is boiled by waste heat of an engine and is changed to gas phase fluid. The gas phase fluid is expanded whereby work is taken out, and then the expanded gas phase fluid is condensed to be returned to liquid phase fluid. 
         [0003]    Following is a list of patent literatures which the applicant has noticed as related arts of embodiments the present invention. 
         [0004]    Patent Literature 1: JP 2015-94271 A 
         [0005]    Patent Literature 2: JP 2002-316530 A 
         [0006]    Patent Literature 3: JP 2011-189824 A 
       SUMMARY 
       [0007]    In the case of mounting a Rankine cycle system on a moving body such as a vehicle or the like as in the conventional art described above, the environment surrounding the Rankine cycle system is always changing due to traveling air, a pressure change, or the like. In particular, as a gas-liquid separator which is a constituting element of a Rankine cycle system does not have a heat source, it may be largely affected by a low-temperature environment so that the amount of heat rejection may increase. When the amount of heat rejection increases, the gas phase fluid (vapor) stored inside is condensed. In that case, as the vapor amount sent to an expander decreases, the heat recovery efficiency of the system is lowered. In the conventional art described above, consideration is not given on suppression of a temperature drop of the gas-liquid separator. As such, there is still room for improving the heat recovery efficiency. 
         [0008]    The present invention has been made in view of the aforementioned problem. An object of the present invention is to provide a Rankine cycle system for vehicle capable of improving heat recovery efficiency of the Rankine cycle system while suppressing a temperature drop of a gas-liquid separator. 
         [0009]    In order to achieve the above described object, a first embodiment of the present invention is a Rankine cycle system for vehicle including 
         [0010]    a boiler configured to apply waste heat to refrigerant circulating in an internal-combustion engine to vaporize the refrigerant; 
         [0011]    a gas-liquid separator configured to separate gas-liquid two-phase refrigerant, sent from the boiler, into gas phase fluid and liquid phase fluid; 
         [0012]    a superheater configured to superheat the gas phase fluid, sent from the gas-liquid separator, through heat exchange with exhaust gas of the internal-combustion engine; 
         [0013]    an expander configured to expand the gas phase fluid, passing through the superheater, to recover thermal energy, and 
         [0014]    a condenser configured to condense the gas phase fluid, passing through the expander, to return the gas phase fluid to liquid phase fluid, wherein 
         [0015]    the gas-liquid separator is fixed to a cylinder head of the internal-combustion engine. 
         [0016]    A second embodiment of the present invention is the Rankine cycle system for vehicle according to the first embodiment, wherein 
         [0017]    the gas-liquid separator includes a bracket made of metal, and 
         [0018]    the gas-liquid separator is fixed to the cylinder head via the bracket. 
         [0019]    A third embodiment of the present invention is the Rankine cycle system for vehicle according to the first embodiment, wherein 
         [0020]    the condenser is arranged on a vehicle front side with respect to the gas-liquid separator, and 
         [0021]    the gas-liquid separator is arranged at a position where a part of the gas-liquid separator overlaps the condenser when seen from the front of the vehicle. 
         [0022]    A fourth embodiment of the present invention is the Rankine cycle system for vehicle according to the first embodiment, wherein 
         [0023]    the internal-combustion engine includes a plurality of cylinders arranged in series, and 
         [0024]    the gas-liquid separator is fixed on an exhaust side with respect to a plane including a central axis of the cylinders, the plane being in parallel with a row direction of the cylinders. 
         [0025]    A fifth embodiment of the present invention is the Rankine cycle system for vehicle according to the first embodiment, further including a heat insulation tank that integrally covers the superheater and the gas-liquid separator. 
         [0026]    According to the first embodiment of the present invention, as the gas-liquid separator is fixed to the cylinder head, the heat of the cylinder head is transferred to the gas-liquid separator efficiently. As such, according to this embodiment, it is possible to suppress a temperature drop of the gas-liquid separator. Thus, it is possible to suppress lowering of the efficiency of the Rankine cycle. 
         [0027]    According to the second embodiment of the present invention, the gas-liquid separator is fixed to the cylinder head via a metal bracket. Thus, according to this embodiment, it is possible to fix the gas-liquid separator to the cylinder head reliably, and to transfer the heat of the cylinder head to the gas-liquid separator efficiently via the bracket. 
         [0028]    According to the third embodiment of the present invention, a part of the traveling air flowing toward the gas-liquid separator is blocked by the condenser. Thus, according to this embodiment, as heat rejection from the gas-liquid separator is suppressed, it is possible to suppress lowering of the efficiency of the Rankine cycle. 
         [0029]    According to the fourth embodiment of the present invention, as the gas-liquid separator is kept at a high temperature by the exhaust heat of the exhaust side, it is possible to suppress heat rejection from the gas-liquid separator effectively. 
         [0030]    According to the fifth embodiment of the present invention, as the temperature around the gas-liquid separator can be maintained by the heat insulation tank, it is possible to suppress heat rejection from the gas-liquid separator effectively. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0031]      FIG. 1  is a diagram illustrating a configuration of a Rankine cycle system according to a first embodiment of the present invention; 
           [0032]      FIGS. 2A and 2B  are schematic diagrams for explaining a structure of fixing a gas-liquid separator; 
           [0033]      FIG. 3  is a diagram for explaining a best positional relation between a transverse engine and a gas-liquid separator; 
           [0034]      FIG. 4  is a diagram for explaining a best positional relation between a transverse engine and a gas-liquid separator; 
           [0035]      FIG. 5  is a diagram for explaining a best positional relation between a longitudinal engine and a gas-liquid separator; 
           [0036]      FIGS. 6A and 6B  are diagrams for explaining a positional relation between a condenser and a gas-liquid separator; 
           [0037]      FIGS. 7A and 7B  are schematic diagrams for explaining a structure of fixing a gas-liquid separator in a Rankine cycle system according to a second embodiment of the present invention; 
           [0038]      FIG. 8  is a schematic diagram for explaining a structure of fixing a gas-liquid separator in a Rankine cycle system according to a third embodiment of the present invention; 
           [0039]      FIG. 9  is a schematic diagram for explaining a structure of fixing a gas-liquid separator f in the Rankine cycle system according to the third embodiment of the present invention; 
           [0040]      FIG. 10  is a schematic diagram for explaining a structure of fixing a gas-liquid separator in a Rankine cycle system according to a fourth embodiment of the present invention; 
           [0041]      FIG. 11  is a schematic diagram for explaining a structure of fixing a gas-liquid separator in the Rankine cycle system according to the fourth embodiment of the present invention; 
           [0042]      FIG. 12  is a schematic diagram for explaining a structure of fixing a gas-liquid separator in a Rankine cycle system according to a fifth embodiment of the present invention; 
           [0043]      FIG. 13  is a schematic diagram for explaining a structure of fixing a gas-liquid separator in a Rankine cycle system according to the fifth embodiment of the present invention; 
           [0044]      FIG. 14  is a diagram for explaining the shape of a bracket  6   a;    
           [0045]      FIG. 15  is a diagram for explaining the shape of a bracket  6   b;  and 
           [0046]      FIGS. 16A and 16B  are diagrams illustrating a configuration of a Rankine cycle system according to a sixth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0047]    Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, common elements are denoted by the same reference numerals and are not repeatedly described herein. It should be noted that in the case of referring to the numbers such as the number, amount, volume, range, and the like of each element in the embodiments provided below, the present invention is not limited to such numbers referred to, unless it is described specifically or apparently specified to such numbers in principle. Further, the structures described in the following embodiments are not indispensable for the present invention unless it is described specifically or apparently specified in principle. 
       First Embodiment 
     1. Configuration of Rankine Cycle System 
       [0048]      FIG. 1  is a diagram illustrating a configuration of a Rankine cycle system  100  of a first embodiment. The Rankine cycle system  100  of the first embodiment is configured as a Rankine cycle system for vehicle which includes an internal-combustion engine (engine)  10  and is mounted on a vehicle. The type and the structure of the engine  10  are not limited. However, a cylinder block and a cylinder head of the engine  10  are provided with a refrigerant flow path  12  through which refrigerant circulating in the engine  10  flows. The refrigerant flow path  12  includes a water jacket surrounding the cylinder. The engine  10  is cooled through heat exchange with the refrigerant flowing in the refrigerant flow path  12 . In the present embodiment, water is used as refrigerant. 
         [0049]    The engine  10  is cooled in such a manner that the refrigerant flowing in the refrigerant flow path  12  is boiled by the waste heat of the engine  10  and a part thereof is vaporized. This means that the refrigerant flow path  12  functions as a boiler for boiling the refrigerant in a liquid phase flowing inside by the heat of the engine  10 . It should be noted that the configuration of the refrigerant flow path  12  is not limited particularly if it is a path through which the refrigerant is able to flow inside the engine  10 . Further, the refrigerant flowing in the refrigerant flow path  12  is not limited to water. Any refrigerant may be used if it is liquid phase fluid at room temperature and is changed to gas phase fluid when boiled by the heat of the engine  10 . 
         [0050]    The refrigerant flow path  12  of the engine  10  is connected with a gas-liquid separator  16  via a refrigerant pipe  14 . When the refrigerant is boiled by the heat of the engine  10 , liquid phase fluid is discharged from the refrigerant flow path  12 , along with gas phase fluid. The gas-liquid separator  16  separates the gas-liquid two-phase refrigerant, flowing into the gas-liquid separator  16 , into liquid phase fluid and gas phase fluid. The gas-liquid separator  16  is connected with a first water pump  20  via a refrigerant pipe  18 . The liquid phase fluid, separated by the gas-liquid separator  16 , flows into the first water pump  20  via the refrigerant pipe  18 , and is sent to the refrigerant flow path  12  by the first water pump  20 . 
         [0051]    The gas-liquid separator  16  is connected with a superheater  30  via a refrigerant pipe  28 . The superheater  30  is provided upstream of the catalyst  24  in an exhaust passage  22  of the engine  10 . More specifically, the superheater  30  is provided so as to cover the periphery of an exhaust manifold  26  and is integrated with the exhaust manifold  26 . A space surrounded by the inner wall surface of the superheater  30  and the external wall surface of the exhaust manifold  26  forms a flow path in which gas phase fluid sent from the gas-liquid separator  16  flows. As both gas phase fluid and liquid phase fluid exist in the gas-liquid separator  16 , the gas-phase fluid is in a state of saturated vapor. The gas phase fluid flowing into the superheater  30  becomes superheated vapor by absorbing exhaust heat transferred from the wall surface of the exhaust manifold  26 . It should be noted that the superheater  30  is not necessarily integrated with the exhaust manifold  26 . The superheater  30  may be integrated with another part (catalyst  24 , for example) of the exhaust passage  22 , if the superheater  30  is configured to be able to absorb exhaust heat. 
         [0052]    The superheater  30  is connected with a turbine  34  which is an expander, via a refrigerant pipe  32 . In the turbine  34 , gas phase fluid (superheated vapor) sent from the superheater  30  is expanded, and heat energy is recovered. A connecting portion between the refrigerant pipe  32  and the turbine  34  is provided with a supersonic nozzle not shown. The gas phase fluid is jetted from the supersonic nozzle to the turbine  34  to thereby rotate the turbine  34 . Rotation of the turbine  34  is transmitted to an output shaft of the engine  10  via a reduction device not shown. This means that the heat energy recovered by the turbine  34  is used for assisting the engine  10 . However, it is also possible to have a configuration in which a power generator is driven by the turbine  34  and the generated electricity is stored in a storage battery. 
         [0053]    The gas phase fluid, expanded by the turbine  34 , is sent to the condenser  40  via a refrigerant pipe  36 . The gas phase fluid, sent to the condenser  40 , is cooled and condensed by the condenser  40  to be returned to liquid phase fluid. The liquid phase fluid generated by condensation of the gas phase fluid is sent from the condenser  40  to a catch tank  44  via a refrigerant pipe  42 , and is temporarily stored in the catch tank  44 . The catch tank  44  is connected with the gas-liquid separator  16  via a refrigerant pipe  46 . The refrigerant pipe  46  is provided with a second water pump  48 . The second water pump  48  is a pump for sending liquid phase fluid, stored in the catch tank  44 , to the gas-liquid separator  16 . A check valve, not shown, is provided between the second water pump  48  and the gas-liquid separator  16 . The check valve is used for preventing backflow of liquid phase fluid from the gas-liquid separator  16  to the catch tank  44 . It should be noted that the refrigerant pipe  46  may be configured to connect the catch tank  44  and an intermediate portion of the refrigerant pipe  18 . With such a configuration, when the second water pump  48  is driven, the liquid phase fluid stored in the catch tank  44  is sent to the gas-liquid separator  16  and the engine  10 . 
         [0054]    The Rankine cycle system  100  further includes an electronic control unit (ECU)  70  as a control device. The ECU  70  includes at least an input/output interface, a memory, and a central processing unit (CPU). The input/output interface is provided to take in sensor signals from various sensors provided to the Rankine cycle system  100  or the engine  10  on which the Rankine cycle system  100  is mounted, and also output operation signals to various actuators provided to the Rankine cycle system  100 . The memory stores various control programs, maps, and the like. The CPU reads, from the memory, and executes control programs or the like, and generates operation signals of various actuators based on the sensor signals taken in. 
       2. Structure of Mounting Rankine Cycle System on Vehicle 
       [0055]    The Rankine cycle system  100  is mounted in an engine compartment of a vehicle for accommodating the engine  10 . As the mounting space inside the engine compartment is limited, various restrictions may be placed on the arrangement of the respective components of the Rankine cycle system  100 . Further, as the gas-liquid separator  16  which is one component of the Rankine cycle system  100  does not have a heat source, it is susceptible to the surrounding temperature. As such, when the gas-liquid separator  16  is arranged in a low temperature region, condensation of the gas phase fluid (vapor) inside thereof progresses by heat rejection from the gas-liquid separator  16 . As such, the inventor of the present application has carried out intensive studies on the structure of mounting the gas-liquid separator  16  on a vehicle to suppress lowering of the heat recovery efficiency of the Rankine cycle system  100  caused by heat rejection from the gas-liquid separator  16 . As a result, the inventor of the present application has found out a structure of mounting the gas-liquid separator  16  on a vehicle described below. 
       2-1. Gas-liquid Separator Fixing Structure 
       [0056]      FIGS. 2A and 2B  are schematic diagrams for explaining a structure of fixing a gas-liquid separator, in which  FIG. 2A  illustrates the Rankine cycle system when seen from the top of the vehicle, and  FIG. 2B  illustrates the Rankine cycle system when seen from the front of the vehicle, respectively. Further, in  FIGS. 2A and 2B , configurations of the Rankine cycle system  100  other than the main components thereof are omitted. As illustrated in  FIGS. 2A and 2B , the Rankine cycle system  100  is mounted in an engine compartment  1  of a vehicle. The engine  10  is mounted on an engine mount (not shown) provided in the engine compartment  1 . The gas-liquid separator  16  is fixed to the engine  10  via brackets  2   a  and  2   b.  More specifically, one end of the bracket  2   a  is fixed to an upper portion of the gas-liquid separator  16 , and the other end thereof is fixed to an upper face of a cylinder head  101  of the engine  10 . Further, one end of the bracket  2   b  is fixed to a lower portion of the gas-liquid separator  16 , and the other end thereof is fixed to a side face of a cylinder block  102  of the engine  10 . It should be noted that each of the brackets  2   a  and  2   b  is formed by processing a plate material made of metal, and is in a shape capable of securing strength necessary for fixing the gas-liquid separator  16 . Further, a plurality of bolts is used for fixing between the brackets  2   a  and  2   b  and the engine  10  and between the brackets  2   a  and  2   b  and the gas-liquid separator  16 , respectively. 
         [0057]    According to the structure of fixing the gas-liquid separator  16 , the gas-liquid separator  16  is fixed to the engine  10  via the metal brackets  2   a  and  2   b.  Thereby the heat generated in the engine  10  is transferred to the gas-liquid separator  16  via the brackets  2   a  and  2   b.  In the gas-liquid separator  16 , vapor condensation due to a temperature drop can be suppressed by the heat received from the engine  10 . As such, lowering of heat recovery efficiency of the Rankine cycle system  100  can be suppressed. 
         [0058]    It should be noted that the brackets are able to efficiently transfer heat near the cylinder  104  having a high temperature to the gas-liquid separator  16 , if at least the bracket  2   a  for fixing the gas-liquid separator  16  to the cylinder head  101  is included. As such, it is only necessary that at least the bracket  2   a  is included. There is no limitation on the necessity of other brackets including the bracket  2   b  and the fixing structure thereof. Further, the material of the brackets  2   a  and  2   b  is not limited to metal. However, it is preferable to use a material having high heat conductivity and high strength. 
       2-2. Arrangement of Gas-liquid Separator 
       [0059]    By fixing the gas-liquid separator  16  to the engine  10  via the brackets  2   a  and  2   b  as described above, a temperature drop of the gas-liquid separator  16  can be suppressed. It is also possible to further suppress a temperature drop depending on the arrangement of the gas-liquid separator  16 . Hereinafter, description will be given on a structure for further improving heat recovery efficiency of the Rankine cycle system  100 , while focusing on the positional relations between the gas-liquid separator  16  and other components. 
       2-2-1. Positional Relation Between Gas-liquid Separator and Engine 
       [0060]    A reference character S 1  in  FIG. 2A  denotes a plane including a central axis L 1  of the cylinder  104 , and the plane is in parallel with a row direction of the cylinders  104  provided in series along the longitudinal direction of the cylinder block  102 . Further, a reference character S 2  in  FIG. 2B  denotes a mating face with the cylinder block  102  of the cylinder head  101 . In the below description, an “exhaust side” indicates an exhaust side where the exhaust passage  22  of the engine  10  is provided with respect to the plane S 1 , and an “air intake side” indicates an air intake side where an air intake passage, not shown, of the engine  10  is provided with respect to the plane S 1 . 
         [0061]    In the fixing structure illustrated in  FIGS. 2A and 2B , a transmission  103  is fixed to a side face of the cylinder block  102 . The gas-liquid separator  16  is arranged in a space of the exhaust side above the transmission  103  (that is, an exhaust passage  22  side of the engine  10 ). The region of the exhaust side of the engine  10  is in a higher temperature than that of the air intake side of the engine  10  due to an effect of the exhaust heat. As such, according to the arrangement of the gas-liquid separator  16  illustrated in  FIGS. 2A and 2B , the gas-liquid separator  16  can be arranged in a high temperature region in the engine compartment  1 . Thus, a temperature drop of the gas-liquid separator  16  can be suppressed effectively. 
         [0062]    Further, in the fixing structure illustrated in  FIGS. 2A and 2B , the gas-liquid separator  16  is arranged on the cylinder head  101  side of the engine  10  with respect to the plane S 2 . In the engine compartment  1  of the vehicle, the temperature becomes higher upward. As such, according to the arrangement of the gas-liquid separator  16  illustrated in  FIGS. 2A and 2B , the gas-liquid separator  16  can be arranged in a high temperature region in the engine compartment  1 . Thus, a temperature drop of the gas-liquid separator  16  is suppressed effectively. 
         [0063]    Further, in the fixing structure illustrated in  FIGS. 2A and 2B , the gas-liquid separator  16  is arranged near the superheater  30 . Thereby, the pipe length of the refrigerant pipe  28  can be shortened. As such, heat rejection from the refrigerant pipe  28  can be suppressed. Thus, heat recovery efficiency of the Rankine cycle system  100  can be further improved. 
         [0064]      FIGS. 3 to 5  illustrate specific arrangements of the gas-liquid separator  16  with respect to the engine  10  according to the engine type. Each of the drawings shows six positions in arrangements P 1  to P 6  as exemplary arrangements of the gas-liquid separator  16 . More specifically, the arrangements P 1  and P 2  show positions opposite to the transmission  103  with respect to the engine  10 . The arrangement P 1  shows a position on the air intake side, and the arrangement P 2  shows a position on the exhaust side, respectively. The arrangements P 3  and P 4  show positions above the engine  10 . The arrangement P 3  indicates a position on the air intake side, and the arrangement P 4  indicates a position on the exhaust side, respectively. Further, the arrangements P 5  and P 6  indicate positions above the transmission  103 . The arrangement P 5  shows a position on the air intake side, and the arrangement P 6  shows a position on the exhaust side, respectively. 
         [0065]      FIGS. 3 and 4  are diagrams for explaining a good positional relation between a gas-liquid separator and a transverse engine. A transverse engine in this context means an engine arranged such that the row direction of the cylinders  104  is in a vertical direction with respect to the traveling direction of the vehicle. Further,  FIG. 3  illustrates an exemplary arrangement in which the front side of the vehicle is the exhaust side, and  FIG. 4  illustrates an exemplary arrangement in which the rear side of the vehicle is the exhaust side. 
         [0066]    In the case where the engine  10  is a transverse engine, as shown in  FIGS. 3 and 4 , it is preferable to arrange the gas-liquid separator  16  at the position of the arrangement P 2 , P 4 , or P 6  where it is on the exhaust side with respect to the plane S 1  of the engine  10 . It is particularly preferable to arrange the gas-liquid separator  16  at the position of the arrangement P 4  where the gas-liquid separator  16  positively receives the heat of the exhaust manifold  26  and the superheater  30 . 
         [0067]      FIG. 5  is a diagram for explaining a best positional relation between a gas-liquid separator and a longitudinal engine. A longitudinal engine in this context means an engine arranged such that the row direction of the cylinders  104  is in parallel with the travelling direction of the vehicle. Even in the case where the engine  10  is a longitudinal engine, it is preferable to arrange the gas-liquid separator  16  at the position of the arrangement P 2 , P 4 , or P 6  which is on the exhaust side with respect to the plane S 1  of the engine  10 , similar to the case where the engine  10  is a transverse engine. It is more preferable to arrange the gas-liquid separator  16  at the position of the arrangement P 4  where it positively receives heat of the exhaust manifold  26  and the superheater  30 . 
       2-2-2. Positional Relation Between Gas-liquid Separator and Condenser 
       [0068]      FIGS. 6A and 6B  are diagrams for explaining a positional relation between a gas-liquid separator and a condenser, in which  FIG. 6A  is a schematic perspective view of the inside of the engine compartment  1  seen from a side face side of the vehicle, and  FIG. 6B  is a schematic perspective view of the inside of the engine compartment  1  seen from the front of the vehicle, that is, in a direction B shown in  FIG. 6A . 
         [0069]    As illustrated in  FIG. 6A , the condenser  40  is arranged on the vehicle front side with respect to the gas-liquid separator  16 . Further, a grille  3  for taking traveling air into the engine compartment  1  is arranged in front of the condenser  40 . Further, as illustrated in  FIG. 6B , the gas-liquid separator  16  is arranged at a position where a portion thereof overlaps the condenser  40  when seen from the front of the vehicle. According to the arrangement of the gas-liquid separator  16  as illustrated in  FIGS. 6A and 6B , a portion of the traveling air from the grille  3  blowing through around the gas-liquid separator  16  is blocked by the condenser  40 . Thereby, a temperature drop of the gas-liquid separator  16  due to the travelling air can be reduced. 
         [0070]    While a lower portion of the gas-liquid separator  16  overlaps the condenser  40  when seen from the front of the vehicle in the example described above, the positioning relation between the gas-liquid separator  16  and the condenser  40  is not limited to this relation. It is only necessary that at least a portion of the gas-liquid separator  16  overlaps the condenser  40  when seen from the front of the vehicle. With this configuration, a temperature drop of the gas-liquid separator  16  caused by the travelling air can be reduced. 
       Second Embodiment 
       [0071]    Next, a Rankine cycle system  110  of a second embodiment will be described.  FIGS. 7A and 7B  are schematic diagrams for explaining a structure of fixing the gas-liquid separator  16  in the Rankine cycle system  110  of the second embodiment, in which  FIG. 7A  illustrates the Rankine cycle system when seen from the top of the vehicle, and FIG.  7 B illustrates the Rankine cycle system mounted on the vehicle when seen from the front of the vehicle, respectively. Further, in  FIGS. 7A and 7B , the same elements as those of the Rankine cycle system  100  of the first embodiment illustrated in  FIGS. 2A and 2B  are denoted by the same reference numerals. 
         [0072]    The Rankine cycle system  110  of the second embodiment is arranged at a position where the gas-liquid separator  16  overlaps the superheater  30  or the exhaust manifold  26  in a region above the exhaust side of the engine  10  when seen from the top of the vehicle. The gas-liquid separator  16  is fixed to the engine  10  via brackets  4   a  and  4   b.  The respective brackets  4   a  and  4   b  are fixed to an upper surface of the cylinder head  101 , and are arranged to extend from the upper surface in the horizontal direction of the exhaust side. The gas-liquid separator  16  is interposed and fixed between the brackets  4   a  and  4   b.  Thereby, the upper surface of the superheater  30  is covered with the gas-liquid separator  16  and the brackets  4   a  and  4   b.  It should be noted that each of the brackets  4   a  and  4   b  is formed by processing a plate material made of metal, and is in a shape capable of securing strength necessary for fixing the gas-liquid separator  16 . Further, a plurality of bolts is used for fixing between the brackets  4   a  and  4   b  and the engine  10  and between the brackets  4   a  and  4   b  and the gas-liquid separator  16 , respectively. 
         [0073]    With this configuration, the brackets  4   a  and  4   b  function as heat transfer members that efficiently receive the heat of the superheater  30  and transfer the heat to the gas-liquid separator  16 . Thereby, as the gas-liquid separator  16  is able to efficiently receive the heat of the superheater  30 , a temperature drop is suppressed. 
         [0074]    It should be noted that in the Rankine cycle system  110  of the second embodiment, the shape of the brackets  4   a  and  4   b  is not limited. The brackets  4   a  and  4   b  may be in a shape covering at least the upper surface side of the superheater  30  or the exhaust manifold  26 . Further, the material of the brackets  4   a  and  4   b  is not limited to metal. However, it is preferable to use a material having high heat conductivity and high strength. 
       Third Embodiment 
       [0075]    Next, a Rankine cycle system  120  of a third embodiment will be described. The Rankine cycle system  120  of the third embodiment is characterized in a structure in which the cylinder head  101  and the gas-liquid separator  160  are integrally formed.  FIGS. 8 and 9  are schematic diagrams for explaining a structure of fixing a gas-liquid separator in the Rankine cycle system  120  of the third embodiment.  FIG. 8  illustrates a state where the gas-liquid separator  160  and the cylinder head  101  are integrated when seen from the exhaust side, and  FIG. 9  illustrates a state where the gas-liquid separator  160  and the cylinder head  101  are disassembled when seen from the air intake side, respectively. 
         [0076]    As illustrated in  FIGS. 8 and 9 , the gas-liquid separator  160  is provided with an inlet port  161  for refrigerant. The inlet port  161  is used for introducing refrigerant from the refrigerant flow path  12  of the engine  10  to the gas-liquid separator  160 . The inlet port  161  of the gas-liquid separator  160  is joined to an outlet port  121  of the refrigerant flow path  12  of the cylinder head  101  by welding or the like, whereby the gas-liquid separator  16  and the cylinder head  101  are integrated. 
         [0077]    With this configuration, as the gas-liquid separator  160  and the cylinder head  101  are integrally fixed, a temperature drop is suppressed by an action of heat transfer from the cylinder head  101 . Further, as the gas-liquid separator  160  and the cylinder head  101  are integrated, heat transfer property can be improved and the number of components such as refrigerant pipes and brackets can be reduced. 
       Fourth Embodiment 
       [0078]    Next, a Rankine cycle system  130  of a fourth embodiment will be described. The Rankine cycle system  130  of the fourth embodiment is characterized in that a bracket  163  for mounting a gas-liquid separator  162  to the cylinder head is integrally formed with the gas-liquid separator  162 .  FIGS. 10 and 11  are schematic diagrams for explaining a structure of fixing the gas-liquid separator  162  in the Rankine cycle system  130  of the fourth embodiment.  FIG. 10  is a perspective view of a state where the gas-liquid separator  162  is mounted on the cylinder head  101  when seen from the air intake side, and  FIG. 11  is a perspective view of a state where the gas-liquid separator  162  is mounted on the cylinder head  101  when seen from the exhaust side, respectively. 
         [0079]    As illustrated in  FIGS. 10 and 11 , the gas-liquid separator  162  is provided with the bracket  163  integrally. The bracket  163  is configured such that one end side thereof is directly joined to the main body of the gas-liquid separator  162  by welding or the like, and the other end side thereof is fixed to a side face of the cylinder head  101  with bolts or the like. The gas-liquid separator  162  is also provided with an inlet port  164  for refrigerant. The inlet port  164  is connected with an outlet port (not shown) of the refrigerant flow path  12  of the cylinder head  101 . 
         [0080]    With this configuration, as the gas-liquid separator  162  is fixed to the cylinder head  101 , a temperature drop is suppressed by an action of heat transfer from the cylinder head  101 . Further, as the bracket  163  is integrated with the gas-liquid separator  162 , heat conductive property can be improved and the number of components can be reduced. 
       Fifth Embodiment 
       [0081]    Next, a Rankine cycle system  140  of a fifth embodiment will be described. The Rankine cycle system  140  of the fifth embodiment is characterized in the arrangement of the gas-liquid separator  16  and the punched shape of brackets  6   a  and  6   b.    FIG. 12  and  FIG. 13  are schematic diagrams for explaining a structure of fixing a gas-liquid separator  16  in the Rankine cycle system  140  of the fifth embodiment.  FIG. 12  illustrates a perspective view of a state where the gas-liquid separator  16  is mounted on the engine  10  when seen from the exhaust side, and  FIG. 13  is a diagram in which the gas-liquid separator  16  of  FIG. 12  is not shown. In  FIGS. 12 and 13 , the same elements as those of the Rankine cycle system  100  of the first embodiment illustrated in  FIGS. 2A and 2B  are denoted by the same reference numerals. 
         [0082]    As illustrated in  FIGS. 12 and 13 , the gas-liquid separator  16  is arranged at a position where it does not overlap the superheater  30  and the exhaust manifold  26  when seen from the top of the vehicle, that is, at a position away from the superheater  30  and the exhaust manifold  26  in a horizontal direction. The gas-liquid separator  16  is fixed with the brackets  6   a  and  6   b.  One end of the bracket  6   a  is fixed near an intermediate portion in the vertical direction of the gas-liquid separator  16 , and the other end thereof is fixed to an upper surface of the cylinder head  101  of the engine  10 . Further, one end of the bracket  6   b  is fixed to a lower portion of the gas-liquid separator  16 , and the other end thereof is fixed to a side face of the cylinder block  102  of the engine  10 . 
         [0083]      FIG. 14  is a diagram for explaining the shape of the bracket  6   a.    FIG. 15  is a diagram for explaining the shape of the bracket  6   b.  As shown in  FIG. 14 , the bracket  6   a  has a plurality of punched portions  61   a.  Similarly, the bracket  6   b  has a plurality of punched portions  61   b.  The shapes and the numbers of the punched portions  61   a  and  61   b  are not limited if they are within a range capable of securing the strength for fixing the gas-liquid separator  16 . 
         [0084]    With this configuration, heat of the engine  10  is transferred to the gas-liquid separator  16  via the brackets  6   a  and  6   b.  However, as the gas-liquid separator  16  is arranged at a position separated from the superheater  30  and the exhaust manifold  26 , there is a possibility that rejection of the heat from the brackets  6   a  and  6   b  to the surrounding, transferred from the engine  10 , may be increased due to an effect of traveling air or the like. According to the aforementioned structure of the brackets  6   a  and  6   b,  the surface areas of the brackets  6   a  and  6   b  are reduced due to the punched portions  61   a  and  61   b.  As such, a temperature drop of the gas-liquid separator  16  due to heat rejection from the brackets  6   a  and  6   b  is suppressed effectively. 
       Sixth Embodiment 
       [0085]      FIGS. 16A and 16B  are diagrams illustrating a configuration of a Rankine cycle system  150  of a sixth embodiment, in which  FIG. 16A  illustrates the Rankine cycle system when seen from the top of a vehicle, and  FIG. 16B  illustrates the Rankine cycle system mounted on the vehicle when seen from the front of the vehicle, respectively. Further, in  FIGS. 16A and 16B , the same elements as those of the Rankine cycle system  110  of the second embodiment illustrated in  FIGS. 7A and 7B  are denoted by the same reference numerals. 
         [0086]    The Rankine cycle system  150  of the sixth embodiment is configured such that the gas-liquid separator  16  is arranged in a region above the exhaust side of the engine  10  at a position where it overlaps the superheater  30  or the exhaust manifold  26 , when seen from the top of the vehicle, which is similar to the case of the Rankine cycle system  110  of the second embodiment illustrated in  FIGS. 7A and 7B . A heat insulation tank  50  is provided to cover at least the gas-liquid separator  16  and the superheater  30 . The heat insulation tank  50  is used for insulating the heat inside the tank by limiting heat transfer. 
         [0087]    With this configuration, a temperature drop of the gas-liquid separator  16  arranged inside is suppressed by the heat insulation function of the heat insulation tank  50 . Further, as the gas-liquid separator  16  is arranged immediately above the superheater  30 , a distance between the gas-liquid separator  16  and the superheater  30  is shortened. As such, it is possible to cover them with the heat insulation tank  50  having a relatively small capacity, which enables the thermal capacity of the heat insulation tank  50  to be reduced. Thereby, the heat insulation effect is improved.