Patent Publication Number: US-2015059569-A1

Title: Compression apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to compression apparatuses for compressing a gas. 
     2. Description of the Related Art 
     In recent years, hydrogen stations for supplying hydrogen gas to fuel-cell vehicles have been proposed. In hydrogen stations, a compression apparatus for supplying hydrogen gas in a compressed state is used to efficiently charge fuel-cell vehicles with hydrogen gas. The compression apparatus includes a compressor for compressing hydrogen gas, and a gas cooler for cooling hydrogen gas that is raised in temperature by being compressed by the compressor. For the gas cooler, use of a plate-type heat exchanger as described, for example, in JP 2000-283668 A has been proposed. 
     A plate-type heat exchanger includes a laminated body in which a large number of plates are stacked in layers. Between the stacked plates, flow channels for circulating fluids are individually formed. In the heat exchanger, heat exchange is performed between fluids flowing through their respective flow channels that are adjacent to each other in the plate stacking direction. 
     SUMMARY OF THE INVENTION 
     The above-described compression apparatus requires a large number of pipes to connect the compressor and the gas cooler, and thus requires the securement of a large installation space. 
     The present invention has been made to solve the above problem, and its object is to reduce the size of compression apparatuses. 
     In order to achieve the above object, a compression apparatus according to the present invention includes a compressor including a cylinder for compressing a gas, a heat exchanger for cooling the gas compressed in the cylinder, and a circulation passage for guiding the gas compressed in the cylinder into the heat exchanger, in which the heat exchanger is solid-phase bonded to the cylinder, the circulation passage extends through an area in which the heat exchanger and the cylinder face each other, and the area is surrounded by a surface at which the heat exchanger and the cylinder are solid-phase bonded. 
     In the present invention, the heat exchanger is solid-phase bonded to the cylinder. The circulation passage extends through an area in which the heat exchanger and the cylinder face each other, and the area is surrounded by a surface at which the heat exchanger and the cylinder are solid-phase bonded. Therefore, installation space for piping to connect the cylinder and the heat exchanger can be omitted, and the compression apparatus can be reduced in size. Further, piping can be omitted, which also contributes to a reduction in the number of components. Moreover, since the heat exchanger and the cylinder are in close contact by solid-phase bonding, the possibility of gas leakage can be reduced when a high-pressure gas discharged from the compressor flows through the circulation passage. 
     Here, the solid-phase bonding may be diffusion bonding. In this aspect, leakage of a high-pressure gas discharged from the compressor can be reduced more securely. 
     The circulation passage may extend through a flat surface at which the heat exchanger and the cylinder are solid-phase bonded. In this aspect, one surface of the cylinder facing the heat exchanger and one surface of the heat exchanger facing the cylinder contact each other on the entire surfaces. These surfaces facing each other are solid-phase bonded. This allows the surfaces to be bonded to be pressurized evenly during solid-phase bonding. Thus, the possibility of gas leakage can be reduced more securely. 
     The heat exchanger may have a structure in which a plurality of plates are stacked in layers so that cooling flow channels through which a cooling fluid for cooling the gas flows and gas flow channels through which the gas flows are formed alternately. In this case, a plate of the plurality of plates disposed at the end on the cylinder side may be solid-phase bonded to the cylinder. In this aspect, good efficiency of cooling the gas by the cooling fluid can be achieved. Further, the heat exchanger can be easily mounted to the compressor. 
     In this aspect, the plates adjacent to each other may be solid-phase bonded. In this aspect, since the adjacent plates are solid-phase bonded, the possibility of leakage of a gas or a cooling fluid from between the plates can be reduced. 
     According to the present invention, compression apparatuses can be reduced in size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a configuration of a compression apparatus (with a recovery header removed) according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of the compression apparatus taken in the position of arrows II-II in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the compression apparatus taken in the position of arrows III-III in  FIG. 1 . 
         FIG. 4  is a plan view of a hydrogen gas plate constituting a part of a gas cooler provided in the compression apparatus. 
         FIG. 5  is a plan view of a cooling water plate constituting a part of the gas cooler. 
         FIG. 6  is a diagram corresponding to  FIG. 1  in another embodiment of the present invention. 
         FIG. 7  is a diagram corresponding to  FIG. 2  in another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     A compression apparatus according to an embodiment of the present invention is a compression apparatus used, for example, in a hydrogen station for supplying hydrogen to fuel-cell vehicles. 
     As shown in  FIGS. 1 to 3 , the compression apparatus according to this embodiment includes a compressor  2  for compressing hydrogen gas, and a gas cooler  4  for cooling hydrogen gas after being compressed by the compressor  2 . The gas cooler  4  is a microchannel heat exchanger. 
     The compressor  2  is a reciprocating compressor, and includes a compression section  16  including a cylinder  5  and a piston  7 , and a drive mechanism for driving the piston  7 . The drive mechanism includes a crankcase  6 , a crankshaft  8 , a drive section not shown, a cross guide  10 , a crosshead  12 , and a connecting rod  14 . 
     In the crankcase  6 , the crankshaft  8  is provided rotatably around a horizontal axis. The drive section not shown is connected to the crankshaft  8 , and transmits power to the crankshaft  8  to rotate the crankshaft  8 . 
     The cross guide  10  is a tubular member continuously provided to the crankcase  6 . In the cross guide  10 , the crosshead  12  is housed reciprocatably in an axial direction of the cross guide  10 . The connecting rod  14  connects the crankshaft  8  and the crosshead  12 , and converts the rotary motion of the crankshaft  8  into a linear reciprocating motion for transmission to the crosshead  12 . 
     The compression section  16  is constituted by a multistage compression mechanism, and includes a first compression section  61  for performing first-stage compression of hydrogen gas, and a second compression section  62  for performing second-stage compression of hydrogen gas. The cylinder  5  has a first cylinder section  63  included in the first compression section  61  and a second cylinder section  66  included in the second compression section  62 . The piston  7  has a first piston  64  included in the first compression section  61  and a second piston  67  included in the second compression section  62 . 
     The first cylinder section  63  is formed in a tubular shape. One end of the first cylinder section  63  is coupled to an axial end of the cross guide  10 . 
     The interior space of the first cylinder section  63  functions as a first cylinder chamber  63   a . In the first cylinder chamber  63   a , the first piston  64  is reciprocatably housed. The first piston  64  is connected to the crosshead  12  by the piston rod  24 . Thus, the first piston  64  moves with the crosshead  12  in an integrated manner. 
     The second cylinder section  66  is formed integrally with the first cylinder section  63 . The second cylinder section  66  is formed with a bottomed hole that communicates with the first cylinder chamber  63   a  and extends in an axial direction of the second cylinder section  66 . An axial end of the hole is closed by an end wall  66   c  of the second cylinder section  66 . The hole functions as a second cylinder chamber  66   a . The second cylinder chamber  66   a  reciprocatably houses the second piston  67 . 
     The first cylinder chamber  63   a  and the second cylinder chamber  66   a  are spaces both in circular cross-sectional shapes. The second cylinder chamber  66   a  is smaller in diameter than the first cylinder chamber  63   a , and is formed coaxially with the first cylinder chamber  63   a . In the first cylinder chamber  63   a , a space between the first piston  64  and a partition wall  25  on the piston rod  24  side functions as a first compression chamber  63   b  for compressing hydrogen gas. 
     The second piston  67  is connected to an end of the first piston  64  opposite to an end to which the piston rod  24  is connected, and extends from the first piston  64  to the side opposite to the piston rod  24 . The first piston  64  and the second piston  67  are formed both in cylindrical shapes. The second piston  67  is smaller in diameter than the first piston  64 . 
     In the second cylinder chamber  66   a , a space between the second piston  67  and the end wall  66   c  of the second cylinder section  66  functions as a second compression chamber  66   b  in which hydrogen gas compressed in the first compression chamber  63   b  is further compressed. That is, a compression chamber  16   a  of the compression section  16  includes the first compression chamber  63   b  and the second compression chamber  66   b.    
       FIG. 2  is a cross-sectional view of the compression apparatus taken in the position of arrows II-II in  FIG. 1 . The first cylinder section  63  includes a first inlet valve chamber  69   a , a first inlet side communication passage  70   a , a first inlet passage  71 , a first delivery valve chamber  69   b , a first delivery side communication passage  70   b , and a first delivery passage  72 . 
     The first inlet valve chamber  69   a  and the first delivery valve chamber  69   b  are located on the opposite sides of the first compression chamber  63   b . The first inlet valve chamber  69   a  and the first delivery valve chamber  69   b  individually extend in a direction perpendicular to the moving direction of the first and second pistons  64  and  67  in a horizontal plane. 
     In the first inlet valve chamber  69   a , a first inlet valve  74   a  is housed and fixed by a first inlet valve fixing flange  75   a . The first inlet side communication passage  70   a  is a passage for connecting the first compression chamber  63   b  and the first inlet valve chamber  69   a . In the first delivery valve chamber  69   b , a first delivery valve  74   b  is housed and fixed by a first delivery valve fixing flange  75   b . The first delivery side communication passage  70   b  is a passage for connecting the first compression chamber  63   b  and the first delivery valve chamber  69   b.    
     The first inlet passage  71  is disposed on the upper side of the first inlet valve chamber  69   a , and extends downward from the upper surface of the first cylinder section  63  to be connected to the first inlet valve chamber  69   a . To the upper end of the first inlet passage  71 , a supply pipe  76  is connected to supply hydrogen gas from a supply source not shown therethrough. 
     The first delivery passage  72  extends from the first delivery valve chamber  69   b  to the lower surface of the first cylinder section  63 . The first delivery passage  72  has a first delivery passage opening  72   a  opening in the lower surface of the first cylinder section  63 . 
       FIG. 3  is a cross-sectional view of the compression apparatus taken in the position of arrows III-III in  FIG. 1 . The lower surface of the second cylinder section  66  and the lower surface of the first cylinder section  63  are formed flush in a planar shape. That is, in the compressor  2 , an area opposite to the gas cooler  4  is formed by a flat surface. 
     The second cylinder section  66  includes a second inlet valve chamber  78   a , a second inlet side communication passage  79   a , a second inlet passage  80 , a second delivery valve chamber  78   b , a second delivery side communication passage  79   b , and a second delivery passage  81 . 
     The second inlet valve chamber  78   a  and the second delivery valve chamber  78   b  are located on the opposite sides of the second compression chamber  66   b . The second inlet valve chamber  78   a  and the second delivery valve chamber  78   b  individually extend in a direction perpendicular to the moving direction in a horizontal plane. In the second inlet valve chamber  78   a , a second inlet valve  83   a  is housed and fixed by a second inlet valve fixing flange  84   a . The second inlet side communication passage  79   a  is a passage for connecting the second compression chamber  66   b  and the second inlet valve chamber  78   a . In the second delivery valve chamber  78   b , a second delivery valve  83   b  is housed and fixed by a second delivery valve fixing flange  84   b . The second delivery side communication passage  79   b  is a passage for connecting the second compression chamber  66   b  and the second delivery valve chamber  78   b.    
     The second inlet passage  80  is disposed on the lower side of the second inlet valve chamber  78   a , and extends upward from the lower surface of the second cylinder section  66  to be connected to the second inlet valve chamber  78   a . The second inlet passage  80  has a second inlet passage opening  80   a  opening in the lower surface of the second cylinder section  66 . 
     The second delivery passage  81  is disposed on the upper side of the second delivery valve chamber  78   b , and extends downward from the upper surface of the second cylinder section  66 . To the upper end of the second delivery passage  81 , a communicating pipe  85  is connected. 
     The gas cooler  4  is a heat exchanger for cooling hydrogen gas compressed in the compressor  2  by water as a cooling fluid, and includes a main body  38 , a supply header  42  (see  FIG. 3 ), and a recovery header  44  (see  FIG. 3 ). 
     The main body  38  is a laminated body in which gas plates  46  and water plates  48  are stacked in layers between a pair of end plates  50  and  50 . In this embodiment, a partition plate  88  is interposed in a middle position of the main body  38 . The main body  38  is divided into two parts by the partition plate  88 . 
     Specifically, the main body  38  includes a first cooling section  86  that is a heat exchanger for cooling hydrogen gas after first-stage compression, and a second cooling section  87  that is a heat exchanger for cooling hydrogen gas after second-stage compression. The interior of the main body  38  is partitioned into the first cooling section  86  and the second cooling section  87  by the partition plate  88 . 
     The first cooling section  86  is disposed on the compressor  2  side with respect to the partition plate  88 , and the second cooling section  87  is disposed opposite to the compressor  2  with respect to the partition plate  88 . 
     The first cooling section  86  and the second cooling section  87  each include the gas plates  46  and the water plates  48 . The gas plates  46  and the water plates  48  are disposed alternately. 
     As shown in  FIG. 4 , each gas plate  46  is a rectangular plate formed from stainless steel. Each gas plate  46  has an inflow passage through hole  46   d  and a discharge passage through hole  46   e . Further, a plurality of gas channel grooves  46   a , a distribution section groove  46   b , and a recovery section groove  46   c  are formed in one surface of each gas plate  46 . The distribution section groove  46   b  is connected to the inflow passage through hole  46   d , and the recovery section groove  46   c  is connected to the discharge passage through hole  46   e . When the gas plates  46  and the water plates  48  are stacked on each other, gas flow channels  54  are formed by the gas channel grooves  46   a  and the water plates  48 . 
     As shown in  FIG. 5 , like the gas plates  46 , each water plate  48  is a rectangular plate formed from stainless steel. Each water plate  48  has an inflow passage through hole  48   b  and a discharge passage through hole  48   c . A plurality of water channel grooves  48   a  is formed in one plate surface of each water plate  48 . When the water plates  48  and the gas plates  46  are stacked on each other, cooling water flow channels  57  are formed by the water channel grooves  48   a  and the gas plates  46 . 
     The end plates  50  are each a rectangular plate formed from stainless steel. The end plate  50  on the first cooling section  86  side is diffusion bonded to the lower surface of the cylinder  5  (the first cylinder section  63  and the second cylinder section  66 ) of the compressor  2 , and is in close contact with the lower surface. Specifically, being kept in close contact with each other, the cylinder  5  and the end plate  50  are pressurized under a temperature condition lower than or equal to the melting points of their base materials to an extent that it causes minimum plastic deformation, and bonded utilizing the diffusion of atoms occurring between the bonded surfaces. The upper surface of the end plate  50  is a flat surface and constitutes an area opposite to the cylinder  5  of the compressor  2 . 
     An inflow passage through hole  50   b  and a discharge passage through hole  50   d  are formed in the end plate  50  (see  FIGS. 2 and 3 ). Hydrogen gas discharged from the compressor  2  and introduced into the gas cooler  4  passes through the inflow passage through hole  50   b . Hydrogen gas discharged from the gas cooler  4  passes through the discharge passage through hole  50   d.    
     The gas plates  46  in the first cooling section  86  are disposed opposite in orientation to those in the second cooling section  87 , and also the end plates  50   a  and the water plates  48  are disposed opposite in orientation likewise. That is, the positional relationship between the distribution section grooves  46   b  and the recovery section grooves  46   c  of the gas plates  46  in the first cooling section  86  is opposite to that in the second cooling section  87 , and also the positional relationship between the inflow passage through holes  46   d  and the discharge passage through holes  46   e  in the first cooling section  86  is opposite to that in the second cooling section  87 . For the end plates  50   a  and the water plates  48 , the positional relationship between the inflow passage through holes  48   b  and  50   b  and the discharge passage through holes  48   c  and  50   d  in the first cooling section  86  is opposite to that in the second cooling section  87 . 
     Adjacent plates of the gas plates  46 , the water plates  48 , the end plates  50 , and the partition plate  88  are bonded to each other by diffusion bonding. 
     In the first cooling section  86 , the inflow passage through holes  46   d ,  48   b , and  50   b  of the respective plates communicate with each other, thereby forming a first gas inflow passage  52   a  extending in the plate stacking direction. An opening  52   c  on the inflow side of the first gas inflow passage  52   a  communicates with the first delivery passage opening  72   a  of the first delivery passage  72 . Thus, hydrogen gas compressed in the first compression section  61  and flowing through the first delivery side communication passage  70   b  and the first delivery passage  72  flows into the first gas inflow passage  52   a . The hydrogen gas flowing through the first gas inflow passage  52   a  is introduced into the gas flow channels  54  in the first cooling section  86 . Accordingly, hydrogen gas is allowed to flow from the compressor  2  into the gas cooler  4  without flowing through any pipe. 
     In the first cooling section  86 , the discharge passage through holes  46   e ,  48   c , and  50   d  communicate with each other, thereby forming a first gas discharge passage  53   a  extending in the plate stacking direction. An opening  53   c  on the discharge side of the first gas discharge passage  53   a  communicates with the second inlet passage opening  80   a  of the second inlet passage  80 . Thus, hydrogen gas cooled by cooling water in the first cooling section  86  passes through the opening  53   c  of the first gas discharge passage  53   a . The hydrogen gas is discharged to the second compression section  62 . 
     In the second cooling section  87 , the inflow passage through holes  46   d ,  48   b , and  50   b  of the respective plates communicate with each other, thereby forming a second gas inflow passage  52   b  extending in the plate stacking direction. The second gas inflow passage  52   b  guides hydrogen gas compressed in the second compression section  62  and introduced into the second cooling section  87  through the communicating pipe  85  into the gas flow channels  54  in the second cooling section  87 . 
     In the second cooling section  87 , the discharge passage through holes  46   e ,  48   c , and  50   d  communicate with each other, thereby forming a second gas discharge passage  53   b  extending in the plate stacking direction. The second gas discharge passage  53   b  discharges hydrogen gas cooled by cooling water in the second cooling section  87  to a discharge pipe  89 . 
     As shown in  FIG. 3 , to one side of the right and left sides of the main body  38 , the supply header  42  to which a cooling water supply pipe  58  is connected is attached, and to the other side, the recovery header  44  to which a cooling water recovery pipe  59  is connected is attached. In the gas cooler  4 , cooling water flows from the cooling water supply pipe  58  through the supply header  42 , the cooling water channels  57  (see  FIG. 5 ), and the recovery header  44  to the cooling water recovery pipe  59 . 
     When the compression apparatus is driven, hydrogen gas is taken in from the first inlet passage  71  into the first compression chamber  63   b  via the first inlet valve  74   a  (see  FIG. 2 ). In the first compression chamber  63   b , the hydrogen gas is compressed by the first piston  64  and discharged from the first cylinder section  63  through the first delivery side communication passage  70   b  and the first delivery passage  72 . The hydrogen gas flows into the first cooling section  86  of the gas cooler  4  through the first delivery passage opening  72   a . That is, the first delivery side communication passage  70   b  and the first delivery passage  72  function as a circulation passage  77  for guiding hydrogen gas compressed in the cylinder  5  to the heat exchanger. 
     In the first cooling section  86 , the hydrogen gas flows from the first gas inflow passage  52   a  into the gas flow channels  54  ( FIG. 4 ), and is cooled by exchanging heat with cooling water flowing through the cooling water flow channels  57  ( FIG. 5 ). The cooled hydrogen gas is discharged from the first cooling section  86  to the second compression chamber  66   b  via the first gas discharge passage  53   a . In the second compression chamber  66   b , the hydrogen gas is further compressed by the second piston  67 . 
     The hydrogen gas compressed in the second compression chamber  66   b  is discharged through the second delivery passage  81  to the communicating pipe  85 . The hydrogen gas discharged to the communicating pipe  85  flows into the second gas inflow passage  52   b  of the second cooling section  87 . After cooled in the second cooling section  87 , the hydrogen gas flows into the second gas discharge passage  53   b  and is discharged to the discharge pipe  89 . 
     In the compression apparatus according to this embodiment, since the gas cooler  4  is directly fixed to the compressor  2 , piping between the compressor  2  and the gas cooler  4  can be omitted. As a result, space for piping installation becomes unnecessary, and thus the compression apparatus can be reduced in size. Further, the number of pipes can be reduced, which also contributes to a reduction in the number of components. Moreover, since the gas cooler  4  and the cylinder  5  are in close contact by diffusion bonding, without the provision of a sealing member for sealing against hydrogen gas, the possibility of gas leakage can be reduced when a high-pressure gas discharged from the compressor  2  flows through the circulation passage. 
     In this embodiment, one surface of the cylinder  5  facing the gas cooler  4  (or the first cooling section  86 ) and one surface of the gas cooler  4  (or the first cooling section  86 ) facing the cylinder  5  contact each other on the entire surfaces. These surfaces facing each other are diffusion bonded. This allows the surfaces to be bonded to be pressurized evenly during diffusion bonding. Thus, the possibility of gas leakage can be reduced more securely. 
     In this embodiment, since the gas cooler  4  consists of the plurality of plates  46  and  48  stacked in layers, good efficiency of cooling hydrogen gas by cooling water can be achieved. Further, the gas cooler  4  can be easily mounted to the compressor  2 . 
     In this embodiment, in the gas cooler  4 , since the adjacent plates  46  and  48  are diffusion bonded to each other, the possibility of leakage of hydrogen gas or cooling water from between the plates  46  and  48  can be reduced. 
     It should be considered that the embodiment disclosed now is illustrative in all respects and is not limiting. The scope of the present invention is indicated not by the description of the above-described embodiment but by the scope of claims, and also includes all modifications within a meaning and scope equivalent to the scope of claims. 
     For example, as the gas cooler  4 , other various plate-type heat exchangers such as plate-fin type heat exchangers may be used. A plate-fin heat exchanger is different from a microchannel heat exchanger in the manner in which a groove shape is machined and the manner in which stacked layers are bonded to each other, but has a structure functionally similar to that of the microchannel heat exchanger. A tube-type heat exchanger may also be used as the heat exchanger. 
     In the above-described embodiment, the compressor  2  is configured to include the compression section  16  composed of the plurality of compression sections  61  and  62 , which is not limiting. Alternatively, as shown in  FIG. 6 , for example, the compressor  2  may be configured to include a single-stage compression-type compression section  16 , or may include a compression section with three or more stages (not shown). In a compression apparatus including the single compression section  16  as shown in  FIG. 6 , the interior of a cylinder  5  is divided into two spaces by a piston  7 . The space opposite to a piston rod  24  functions as a compression chamber  16   a . A delivery passage  18  communicating with the compression chamber  16   a  is provided at the cylinder  5 . An opening  18   a  of the delivery passage  18  is formed in the lower surface of the cylinder  5 . The delivery passage  18  communicates with gas flow channels  54  of a gas cooler  4 . The gas cooler  4  is not configured to be divided into a first cooling section  86  and a second cooling section  87 , and thus a partition plate  88  is not provided. Thus, hydrogen gas introduced from the delivery passage  18  into the gas flow channels  54  is cooled by cooling water in the gas flow channels  54 , and then discharged from a discharge pipe  89  of the gas cooler  4 . 
     Further, application may be made to a compression apparatus in which a cross guide  10  and a cylinder  5  are coupled in a vertical direction so that the moving direction of a piston  7  is a vertical direction, and a gas cooler  4  is mounted to a side of the cylinder  5 . 
     The gas flow channels  54  may alternatively be formed in a meandering shape on the plate surface of each gas plate  46 . The cooling water flow channels  57  may alternatively be formed in a meandering shape on the plate surface of the each water plate  48 . This configuration can increase the surface areas of the gas flow channels  54  and the cooling water flow channels  57 , allowing for more effective cooling of hydrogen gas. The compression apparatus in the above-described embodiments may be used for a gas lighter than air such as helium gas or natural gas other than hydrogen gas, and may be used for compression of a gas such as carbon dioxide. 
     In the above-described embodiments, the upper surface of the gas cooler  4  and the lower surface of the cylinder  5  of the compressor  2  are individually formed flat, and are configured to be solid-phase bonded over the entire surfaces. However, this is not limiting. For example, as shown in  FIG. 7 , the lower surface of a cylinder  5  may be configured such that it partially has an area that is not flat, and at a recessed area  5   a , the lower surface of the cylinder  5  is not in close contact with the upper surface of a gas cooler  4 . That is, the cylinder  5  may be configured such that an area in which a first delivery passage  72  opens and an area in which a gas inflow passage  52   a  opens in the gas cooler  4  are not diffusion bonded. However, also in this case, an area surrounding an opening  72   a  of the first delivery passage  72  needs to be diffusion bonded to the gas cooler  4  at the lower surface of the cylinder  5 . 
     The above-described embodiments have a structure in which the gas cooler  4  and the cylinder  5  are diffusion bonded, which is not limiting. For bonding between the gas cooler  4  and the cylinder  5 , another solid-phase bonding such as explosive welding may be used.