Patent Publication Number: US-11378094-B2

Title: Centrifugal compressor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/JP2018/024688, filed on Jun. 28, 2018, which claims priority based on Japanese Patent Application No. 2017-126760, filed on Jun. 28, 2017, the entire contents of which are incorporated by reference herein. 
    
    
     BACKGROUND ART 
     Technical Field 
     The present disclosure relates to a centrifugal compressor in which an auxiliary flow passage communicating to a main flow passage is formed. 
     Related Art 
     In some cases, a centrifugal compressor has an auxiliary flow passage communicating to a main flow passage. A compressor impeller is arranged in the main flow passage. On an upstream side of the compressor impeller in the main flow passage, a flow passage width is reduced by a narrowing portion. The main flow passage and the auxiliary flow passage communicate to each other through an upstream communication portion and a downstream communication portion. An on-off valve is arranged in the auxiliary flow passage. In a range of a small flow rate, the on-off valve is closed. When the flow rate becomes larger, the on-off valve is opened and a flow-passage sectional area is increased. 
     In the centrifugal compressor described in Patent Literature 1, a spherical flow passage is formed in an auxiliary flow passage. An inner peripheral surface and an outer peripheral surface of the spherical flow passage are concentric spherical surfaces. A plurality of valve bodies of on-off valves are arrayed in a rotation direction of a compressor impeller. The valve bodies each have an arc shape conforming to the inner peripheral surface and the outer peripheral surface of the spherical flow passage. The valve bodies are supported so as to be rotatable by rotation shafts. A plurality of rotation shafts are provided in a radial pattern. Axial centers of the rotation shafts pass through curvature centers of the inner peripheral surface and the outer peripheral surface of the spherical flow passage. Through rotation of the rotation shafts, the plurality of valve bodies are arrayed substantially in flush with one another, thereby closing the valve. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent No. 5824821 
       
    
     SUMMARY 
     Technical Problem 
     However, as described in Patent Literature 1, an opening/closing mechanism configured to open and close the auxiliary flow passage is complicated. Therefore, there has been a demand for development of a technology for simplifying the structure thereof. 
     The present disclosure has an object to provide a centrifugal compressor capable of simplifying structure. 
     Solution to Problem 
     In order to solve the above-mentioned problem, according to one embodiment of the present disclosure, there is provided a centrifugal compressor, including: an impeller; a main flow passage which receives the impeller and extends in a rotation axis direction of the impeller; an auxiliary flow passage which includes an upstream communication portion communicating to the main flow passage and a downstream communication portion communicating to the main flow passage at closer to the impeller than the upstream communication portion, and extends in a rotation direction of the impeller; a plurality of opening/closing portions which each have an opening portion and are arranged in the auxiliary flow passage; and a drive unit configured to move at least one of the plurality of opening/closing portions in the rotation direction. 
     The centrifugal compressor may further include a narrowing portion projecting toward an inner side in a radial direction of the impeller with respect to the upstream communication portion and the downstream communication portion. 
     The centrifugal compressor may further include an impeller-side flow passage portion which is provided in the auxiliary flow passage, includes the downstream communication portion, and extends toward an inner side in a radial direction of the impeller as approaching the impeller, wherein the plurality of opening/closing portions are arranged closer to the upstream communication portion than the impeller-side flow passage portion. 
     The plurality of opening/closing portions may include a first opening/closing portion and a second opening/closing portion located closer to the downstream communication portion than the first opening/closing portion, and the first opening/closing portion may include a pair of first guide portions whose separation distance decreases as approaching the downstream communication portion away from the upstream communication portion. 
     The plurality of opening/closing portions may include a first opening/closing portion and a second opening/closing portion located closer to the downstream communication portion than the first opening/closing portion, and the second opening/closing portion may include a pair of second guide portions whose separation distance increases as approaching the downstream communication portion away from the upstream communication portion. 
     A plan-view shape of the opening portion at least may have a length in the rotation direction on a radially inner side shorter than that on a radially outer side or may have both end portions in the rotation direction in a curved shape. 
     Effects of Disclosure 
     According to the present disclosure, the centrifugal compressor is capable of simplifying structure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic sectional view of a turbocharger. 
         FIG. 2  is an extraction view of the broken-line portion of  FIG. 1 . 
         FIG. 3A  is a sectional view taken along the line IIIa-IIIa of  FIG. 2 . 
         FIG. 3B  is a sectional view taken along the line IIIb-IIIb of  FIG. 2 . 
         FIG. 3C  is a view for illustrating a state in which, in the cross section of  FIG. 3B , a first opening/closing portion takes a position different from that of  FIG. 3B . 
         FIG. 4A  is a sectional view taken at the same position as  FIG. 3A  (sectional view taken along the line IIIa-IIIa of  FIG. 2 ). 
         FIG. 4B  is a sectional view taken at the same position as  FIG. 3A  (sectional view taken along the line IIIa-IIIa of  FIG. 2 ). 
         FIG. 5A  is a sectional view taken at the same position as  FIG. 2 . 
         FIG. 5B  is a sectional view taken along the line Vb-Vb of  FIG. 5A . 
         FIG. 6A  is a sectional view taken at a position corresponding to  FIG. 3A  in a first modification example. 
         FIG. 6B  is a sectional view taken at a position corresponding to  FIG. 3B  in the first modification example. 
         FIG. 6C  is a sectional view taken at a position corresponding to  FIG. 3A  in a second modification example. 
         FIG. 6D  is a sectional view taken at a position corresponding to  FIG. 3B  in the second modification example. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Now, with reference to the attached drawings, one embodiment of the present disclosure is described in detail. The dimensions, materials, and other specific numerical values represented in the embodiment are merely examples used for facilitating the understanding of the present disclosure, and do not limit the present disclosure otherwise particularly noted. Elements having substantially the same functions and configurations herein and in the drawings are denoted by the same reference symbols to omit redundant description thereof. Further, illustration of elements with no direct relationship to the present disclosure is omitted. 
       FIG. 1  is a schematic sectional view of a turbocharger C. In the following description, the direction indicated by the arrow L illustrated in  FIG. 1  corresponds to a left side of the turbocharger C, and the direction indicated by the arrow R illustrated in  FIG. 1  corresponds to a right side of the turbocharger C. A part of the turbocharger C on a compressor impeller  9  (impeller) side, described later, functions as a centrifugal compressor. In the following, description is made of the turbocharger C as one example of applications of the centrifugal compressor. However, the application of the centrifugal compressor is not limited to the turbocharger C. The centrifugal compressor may be incorporated into a device other than the turbocharger C, or may be solely provided. 
     As illustrated in  FIG. 1 , the turbocharger C includes a turbocharger main body  1 . The turbocharger main body  1  includes a bearing housing  2 . A turbine housing  4  is coupled to the left side of the bearing housing  2  with a fastening bolt  3 . A compressor housing  100  is coupled to the right side of the bearing housing  2  with a fastening bolt  5 . 
     The bearing housing  2  has a bearing hole  2   a . The bearing hole  2   a  passes through the turbocharger C in a right-and-left direction. Bearings  6  are provided in the bearing hole  2   a . In  FIG. 1 , full-floating bearings are illustrated as one example of the bearings  6 . However, the bearings  6  may be other radial bearings such as semi-floating bearings or rolling bearings. The bearings  6  are configured to support the shaft  7  so that the shaft  7  is freely rotatable. A turbine impeller  8  is provided at a left end portion of the shaft  7 . The turbine impeller  8  is accommodated in the turbine housing  4  so as to be freely rotatable. A compressor impeller  9  is provided at a right end portion of the shaft  7 . The compressor impeller  9  is accommodated in the compressor housing  100  so as to be freely rotatable. 
     The compressor housing  100  has a main flow passage  101 . The main flow passage  101  is opened on the right side of the turbocharger C. The main flow passage  101  extends in a rotation axis direction of the compressor impeller  9  (hereinafter simply referred to as “rotation axis direction”). The main flow passage  101  is connected to an air cleaner (not shown). The compressor impeller  9  is arranged in the main flow passage  101 . 
     As described above, under a state in which the bearing housing  2  and the compressor housing  100  are coupled to each other with the fastening bolt  5 , a diffuser flow passage  10  is formed. The diffuser flow passage  10  is formed by opposed surfaces of the bearing housing  2  and the compressor housing  100 . The diffuser flow passage  10  increases air in pressure. The diffuser flow passage  10  is annularly formed so as to extend from an inner side toward an outer side in a radial direction of the shaft  7 . The diffuser flow passage  10  communicates to the main flow passage  101  on the radially inner side. 
     Further, a compressor scroll flow passage  11  is provided to the compressor housing  100 . The compressor scroll flow passage  11  has an annular shape. The compressor scroll flow passage  11  is positioned, for example, on the radially outer side of the shaft  7  with respect to the diffuser flow passage  10 . The compressor scroll flow passage  11  communicates to a suction port of an engine (not shown). The compressor scroll flow passage  11  communicates also with the diffuser flow passage  10 . Rotation of the compressor impeller  9  causes air to be taken into the compressor housing  100  from the main flow passage  101 . The air having been taken is accelerated by an action of a centrifugal force in a course of flowing through between blades of the compressor impeller  9 . The air having been accelerated is increased in pressure in the diffuser flow passage  10  and the compressor scroll flow passage  11 . The air having been increased in pressure is introduced to the suction port of an engine. 
     The turbine housing  4  has a discharge port  12 . The discharge port  12  is opened on the left side of the turbocharger C. The discharge port  12  is connected to an exhaust gas purification device (not shown). Moreover, a flow passage  13  and a turbine scroll flow passage  14  are provided in the turbine housing  4 . The turbine scroll flow passage  14  has an annular shape. The turbine scroll flow passage  14  is located, for example, on an outer side with respect to the flow passage  13  in a radial direction of the turbine impeller  8 . The turbine scroll flow passage  14  communicates to a gas inflow port (not shown). Exhaust gas to be discharged from a discharge manifold (not shown) of the engine is introduced to the gas inflow port. The gas inflow port communicates also to the flow passage  13 . The exhaust gas having been introduced from the gas inflow port to the turbine scroll flow passage  14  is introduced to the discharge port  12  through the flow passage  13  and between blades of the turbine impeller  8 . The exhaust gas having been introduced to the discharge port  12  causes the turbine impeller  8  to rotate in a course of flow. 
     In addition, the rotation force of the turbine impeller  8  is transmitted to the compressor impeller  9  via the shaft  7 . As described above, the air is increased in pressure by the rotation force of the compressor impeller  9  and is introduced to the suction port of the engine. 
       FIG. 2  is an extraction view of the broken-line portion of  FIG. 1 . As illustrated in  FIG. 2 , the compressor housing  100  has the main flow passage  101  and an auxiliary flow passage  102 . The main flow passage  101  includes a radially contracted portion  101   a , an upstream parallel portion  101   b , a radially expanded portion  101   c , and a downstream parallel portion  101   d . The radially contracted portion  101   a  is reduced in inner diameter toward the compressor impeller  9  side. The radially contracted portion  101   a  is opened at an end surface of a cylindrical portion  100   a  of the compressor housing  100 . The upstream parallel portion  101   b  is parallel to the rotation axis direction. The upstream parallel portion  101   b  is continuous from the radially contracted portion  101   a  toward the compressor impeller  9  side. The radially expanded portion  101   c  is increased in inner diameter toward the compressor impeller  9  side. The radially expanded portion  101   c  is continuous from the upstream parallel portion  101   b  toward the compressor impeller  9  side. The downstream parallel portion  101   d  is parallel to the rotation axis direction. The downstream parallel portion  101   d  is continuous from the radially expanded portion  101   c  toward the compressor impeller  9  side. The radially contracted portion  101   a , the upstream parallel portion  101   b , and the radially expanded portion  101   c  are located on an upstream side with respect to blades  9   a  of the compressor impeller  9 . The blades  9   a  of the compressor impeller  9  are arranged on an inner peripheral side of the downstream parallel portion  101   d.    
     The main flow passage  101  has a narrowing portion  101   e  formed of the radially contracted portion  101   a , the upstream parallel portion  101   b , and the radially expanded portion  101   c . The narrowing portion  101   e  projects toward an inner side in the radial direction of the compressor impeller  9  with respect to the inner peripheral surface of the downstream parallel portion  101   d . The narrowing portion  101   e  projects, for example, toward the inner side in the radial direction of the compressor impeller  9  with respect to an upstream communication portion  103  and a downstream communication portion  104 , which are described later. The narrowing portion  101   e  is located, for example, between the upstream communication portion  103  and the downstream communication portion  104  in the rotation axis direction. The narrowing portion  101   e  is opposed to the compressor impeller  9  in the rotation axis direction. A part of the main flow passage  101  having the narrowing portion  101   e  is reduced in flow passage sectional area by the narrowing portion  101   e . The main flow passage  101  may have at least the narrowing portion  101   e . For example, the radially contracted portion  101   a  and the radially expanded portion  101   c  may be continuous with each other without the upstream parallel portion  101   b , and the narrowing portion  101   e  may be formed at a connection portion therebetween. 
     The auxiliary flow passage  102  is formed in the cylindrical portion  100   a  of the compressor housing  100 . The auxiliary flow passage  102  is formed on a radially outer side of the main flow passage  101 . The auxiliary flow passage  102  extends in a rotation direction of the compressor impeller  9  (hereinafter simply referred to as “rotation direction” and corresponding to a circumferential direction of the shaft  7  and a circumferential direction of a separation wall portion  105  described later). The auxiliary flow passage  102  includes a parallel portion  102   a  and an impeller-side flow passage portion  102   b . An inner wall surface of the parallel portion  102   a  extends in the rotation axis direction. 
     The impeller-side flow passage portion  102   b  extends, for example, toward the radially inner side as approaching the compressor impeller  9 . A sectional shape of the impeller-side flow passage portion  102   b  parallel to the rotation axis of the compressor impeller  9  (hereinafter simply referred to as “rotation axis”) is curved. A curvature center of the impeller-side flow passage portion  102   b  is located on the radially inner side (lower right side in  FIG. 2 ) with respect to the impeller-side flow passage portion  102   b . However, the curvature center of the impeller-side flow passage portion  102   b  may be located on the radially outer side (upper left side in  FIG. 2 ) with respect to the impeller-side flow passage portion  102   b . Moreover, a sectional shape of the impeller-side flow passage portion  102   b  parallel to the rotation axis may be a straight-line shape. 
     The auxiliary flow passage  102  communicates to the main flow passage  101  through the upstream communication portion  103  and the downstream communication portion  104 . The upstream communication portion  103  and the downstream communication portion  104  are opening portions which are open to the main flow passage  101 . The upstream communication portion  103  is opened to the radially contracted portion  101   a . The downstream communication portion  104  is opened to the radially expanded portion  101   c . The downstream communication portion  104  is opened on the upstream side with respect to the compressor impeller  9  in the main flow passage  101 . The downstream communication portion  104  is located on the compressor impeller  9  side with respect to the upstream communication portion  103 . The upstream communication portion  103  is provided at the parallel portion  102   a . The downstream communication portion  104  is provided at the impeller-side flow passage portion  102   b.    
     The separation wall portion  105  is provided to the compressor housing  100 . The separation wall portion  105  is provided inside the cylindrical portion  100   a . The separation wall portion  105  is located between the auxiliary flow passage  102  and the main flow passage  101  in the radial direction. The separation wall portion  105  partitions the main flow passage  101  and the auxiliary flow passage  102 . The separation wall portion  105  has, for example, an annular shape. However, the shape of the separation wall portion  105  is not limited to the annular shape, and a part of the separation wall portion  105  in the circumferential direction may be cut out. An inner periphery of the separation wall portion  105  faces the radially contracted portion  101   a , the upstream parallel portion  101   b , and the radially expanded portion  101   c  of the main flow passage  101 . An outer periphery of the separation wall portion  105  faces the parallel portion  102   a  and the impeller-side flow passage portion  102   b  of the auxiliary flow passage  102 . In other words, an inner peripheral surface of the separation wall portion  105  forms a part of the main flow passage  101 . An outer peripheral surface of the separation wall portion  105  forms a part of the auxiliary flow passage  102 . 
       FIG. 3A  is a sectional view taken along the line IIIa-IIIa of  FIG. 2 .  FIG. 3B  is a sectional view taken along the line IIIb-IIIb of  FIG. 2 .  FIG. 3C  is a view for illustrating a state in which, in the cross section of  FIG. 3B , a first opening/closing portion  106  takes a position different from that of  FIG. 3B . As illustrated in  FIG. 2 ,  FIG. 3A ,  FIG. 3B , and  FIG. 3C , a first opening/closing portion  106  and a second opening/closing portion  107  are provided at the parallel portion  102   a  of the auxiliary flow passage  102 . The first opening/closing portion  106  and the second opening/closing portion  107  are located at the parallel portion  102   a  on an impeller-side flow passage portion  102   b  side (compressor impeller  9  side) with respect to the center of the parallel portion  102   a  in the rotation axis direction. However, one or both of the first opening/closing portion  106  and the second opening/closing portion  107  may be provided at the impeller-side flow passage portion  102   b.    
     The first opening/closing portion  106  includes a main body portion  106   a  formed of an annular plate member. The first opening/closing portion  106  is not limited to the annular shape, and, for example, a part thereof in the circumferential direction may be cut out. The first opening/closing portion  106  is not limited to the plate member, and may have a cylindrical shape having a thickness in the rotation axis direction. A through hole  106   a   1  is formed at a center of the main body portion  106   a  of the first opening/closing portion  106 . The main body portion  106   a  of the first opening/closing portion  106  is freely rotatably supported by the separation wall portion  105  inserted through the through hole  106   a   1 . 
     The main body portion  106   a  of the first opening/closing portion  106  has first opening holes  106   b  (opening portions). The first opening holes  106   b  each pass through the main body portion  106   a  in the rotation axis direction. A plurality of first opening holes  106   b  are formed apart from each other in the circumferential direction. Here, description is made of a case in which the number of the first opening holes  106   b  is, for example, four. However, the number of first opening holes  106   b  may be one, two, three, or five or more. Further, when the number of the first opening holes  106   b  and the number of second opening holes  107   a  described later are each set to an odd number, an effect of resonance suppression is expected. In a plan-view shape of the first opening hole  106   b  (shape as viewed from the rotation axis direction or sectional shape perpendicular to the rotation axis direction), a length of the first opening hole  106   b  in the rotation direction on the inner side in the radial direction (radially inner side) is shorter than that on the outer side in the radial direction (radially outer side). 
     In the first opening hole  106   b , an inner wall surface on the radially inner side and an inner wall surface on the radially outer side each have an arc shape. Curvature centers of the arcs are located at a center of the main body portion  106   a  (on the rotation axis or on the axial center of the shaft  7 ). In the first opening hole  106   b , the inner wall surface on the radially inner side and the inner wall surface on the radially outer side are connected to each other by inner wall surfaces extending in the radial direction. 
     The second opening/closing portion  107  is an annular rib which is formed integrally with an inner wall surface on the radially outer side and an inner wall surface on the radially inner side (outer peripheral surface of the separation wall portion  105 ) at the parallel portion  102   a  of the auxiliary flow passage  102 . The separation wall portion  105  is held by the second opening/closing portion  107  in the compressor housing  100 . However, the separation wall portion  105  may be formed separately from the compressor housing  100  and mounted to the compressor housing  100 . 
     The second opening/closing portion  107  is not limited to the annular shape, and, for example, a part thereof in the circumferential direction may be cut out. The second opening/closing portion  107  has a thickness in the rotation axis direction larger than that of the first opening/closing portion  106 . However, the second opening/closing portion  107  may have a thickness equal to that of the first opening/closing portion  106 , or may be thinner than the first opening/closing portion  106 . 
     The second opening/closing portion  107  has second opening holes  107   a  (opening portions). The second opening holes  107   a  each pass through the second opening/closing portion  107  in the rotation axis direction. A plurality of (the same number as the first opening holes  106   b ) second opening holes  107   a  are formed apart from each other in the circumferential direction. A plan-view shape of each second opening hole  107   a  is substantially the same as that of the first opening hole  106   b . However, as long as the auxiliary flow passage  102  can be opened and closed as described later, the plan-view shapes of the first opening/closing portion  106  and the second opening/closing portion  107  may be different from each other. 
     As illustrated in  FIG. 3B  and  FIG. 3C , a projection portion  106   c  is formed on the outer peripheral surface of the first opening/closing portion  106 . The cylindrical portion  100   a  of the compressor housing  100  has a through hole  100   b  passing therethrough in the radial direction. The through hole  100   b  extends longer in the circumferential direction than the first opening hole  106   b  and the second opening hole  107   a . The projection portion  106   c  is located inside the through hole  100   b . The projection portion  106   c  may be formed integrally with the first opening/closing portion  106 . After the first opening/closing portion  106  is mounted to the compressor housing  100 , the projection portion  106   c  may be mounted to the first opening/closing portion  106 . 
     A drive unit  108  is provided on an outer peripheral surface of the cylindrical portion  100   a  on a through hole  100   b  side. The drive unit  108  includes an actuator formed of, for example, a motor and a solenoid. A distal end of the projection portion  106   c  is mounted to the drive unit  108 . The drive unit  108  is configured to move the projection portion  106   c  in the rotation direction. That is, the drive unit  108  moves the first opening/closing portion  106  in the rotation direction. As long as the first opening/closing portion  106  can be moved in the rotation direction, any mechanism or structure may be adopted to the drive unit  108 . The first opening/closing portion  106  slides in the rotation direction on the outer peripheral surface of the separation wall portion  105 . The first opening/closing portion  106  moves between a closing position illustrated in  FIG. 3B  and an opening position illustrated in  FIG. 3C . 
       FIG. 4A  and  FIG. 4B  are each a sectional view taken at the same position as  FIG. 3A  (sectional view taken along the line IIIa-IIIa of  FIG. 2 ).  FIG. 4A  is an illustration of a state in which the first opening/closing portion  106  takes the closing position.  FIG. 4B  is an illustration of a state in which the first opening/closing portion  106  takes the opening position. In  FIG. 4A , the first opening/closing portion  106  which can be seen through the second opening holes  107   a  of the second opening/closing portion  107  is illustrated with cross hatching. In  FIG. 4A , the first opening holes  106   b  of the first opening/closing portion  106  are indicated by broken lines. In  FIG. 4A  and  FIG. 4B , the projection portion  106   c  of the first opening/closing portion  106  is illustrated with solid black. 
     As illustrated in  FIG. 4A , when the first opening/closing portion  106  takes the closing position, the second opening holes  107   a  of the second opening/closing portion  107  are closed by the main body portion  106   a  of the first opening/closing portion  106 ; the first opening holes  106   b  of the first opening/closing portion  106  are closed by the second opening/closing portion  107 . In such a manner, the auxiliary flow passage  102  is closed. As illustrated in  FIG. 4B , when the first opening/closing portion  106  takes the opening position, the first opening holes  106   b  are aligned with (overlap) the second opening holes  107   a . In such a manner, the auxiliary flow passage  102  is opened. 
     In a range with a small flow rate, the drive unit  108  moves the first opening/closing portion  106  to the closing position. The entire amount of air flows through the main flow passage  101 . When the flow rate increases, the drive unit  108  moves the first opening/closing portion  106  to the opening position. The air flows through both the main flow passage  101  and the auxiliary flow passage  102 . That is, the flow-passage sectional area increases. Through the increase in flow-passage sectional area, the reduction in operation range on the large flow rate side due to provision of the narrowing portion  101   e  can be suppressed. By that amount, a degree of reduction in flow-passage sectional area of the main flow passage  101  by the narrowing portion  101   e  can be increased, thereby increasing the operation range on the small flow rate side. The compression efficiency on the small flow rate side is improved. Through the use of the first opening/closing portion  106  and the second opening/closing portion  107 , the opening/closing structure for the auxiliary flow passage  102  can be simplified. 
     Here, a length of the first opening hole  106   b  in the rotation direction may be substantially equal to a length of a wall portion in the rotation direction between adjacent first opening holes  106   b . A length of the second opening hole  107   a  in the rotation direction may be substantially equal to a length of a wall portion in the rotation direction between adjacent second opening holes  107   a . In this case, the auxiliary flow passage  102  can be completely closed, thereby securing a large flow passage sectional area given when the auxiliary flow passage  102  is opened. However, the length of the first opening hole  106   b  in the rotation direction may be longer than or shorter than the length of the wall portion in the rotation direction between adjacent first opening holes  106   b . The length of the second opening hole  107   a  in the rotation direction may be longer than or shorter than the length of the wall portion in the rotation direction between adjacent second opening holes  107   a.    
       FIG. 5A  is a sectional view taken at the same position as  FIG. 2 . However, the first opening/closing portion  106  takes the closing position in  FIG. 2 , whereas the first opening/closing portion  106  takes the opening position in  FIG. 5A .  FIG. 5B  is a sectional view taken along the line Vb-Vb of  FIG. 5A . As illustrated in  FIG. 5A  and  FIG. 5B , a fin  109  is mounted to the first opening/closing portion  106 . A fin main body  109   a  of the fin  109  has an annular shape. The fin  109  is mounted to an end surface of the first opening/closing portion  106  on an upstream communication portion  103  side. Here, when the fin  109  is arranged, as described later, a flow of air is adjusted on upstream by an upstream guide portion  109   d  of the fin  109 . Accordingly, air can easily flow into the first opening holes  106   b  of the first opening/closing portion  106 . 
     A length of the fin  109  in the rotation axis direction is, for example, longer than that of the first opening/closing portion  106  and the second opening/closing portion  107 . However, the length of the fin  109  in the rotation axis direction may be equal to that of one of the first opening/closing portion  106  and the second opening/closing portion  107 , or may be shorter than that of the first opening/closing portion  106  or the second opening/closing portion  107 . 
     A plan-view shape of the fin  109  is substantially the same as that of, for example, the first opening/closing portion  106 . However, the plan-view shapes of the fin  109  and the first opening/closing portion  106  may be different from each other. The fin main body  109   a  has, at a center thereof, a through hole through which the separation wall portion  105  is inserted. The fin  109  rotates integrally with the first opening/closing portion  106 . The fin  109  may be formed integrally with the first opening/closing portion  106 . 
     The fin  109  has introduction holes  109   b . The introduction holes  109   b  pass through the fin main body  109   a  in the rotation axis direction. A plurality of (the same number as the first opening holes  106   b ) introduction holes  109   b  are formed apart from each other in the circumferential direction. The introduction hole  109   b  is continuous with the first opening hole  106   b  toward the upstream communication portion  103  side (side away from the compressor impeller  9 ). 
     The introduction hole  109   b  includes a parallel portion  109   c  and an upstream guide portion  109   d . An inner wall surface of the parallel portion  109   c  extends in the rotation axis direction. The parallel portion  109   c  is continuous with the first opening hole  106   b  toward the upstream communication portion  103  side (side away from the compressor impeller  9 ). The upstream guide portion  109   d  is continuous with the parallel portion  109   c  toward the upstream communication portion  103  side (side away from the compressor impeller  9 ). 
     As illustrated in  FIG. 5A , a pair of guide surfaces  109   e  (first guide portions) are inner wall surfaces of the upstream guide portion  109   d  which are opposed to each other in the radial direction. The pair of guide surfaces  109   e  are inclined with respect to the rotation axis direction. The pair of guide surfaces  109   e  are reduced in separation distance therebetween in the radial direction as extending from the upstream communication portion  103  side toward a downstream communication portion  104  side. The guide surface  109   e  on the radially outer side extends toward the radially inner side as extending toward the compressor impeller  9 . The guide surface  109   e  on the radially inner side extends toward the radially outer side as extending toward the compressor impeller  9 . 
     As illustrated in  FIG. 5B , a pair of guide surfaces  109   f  (first guide portions) are inner wall surfaces of the upstream guide portion  109   d  which are opposed to each other in the rotation direction. The pair of guide surfaces  109   f  are inclined with respect to the rotation axis direction. The pair of guide surfaces  109   f  are reduced in separation distance therebetween in the rotation direction as extending from the upstream communication portion  103  side toward the downstream communication portion  104  side. 
     The guide surfaces  109   e  and  109   f  of the upstream guide portion  109   d  allow air to easily flow into the parallel portion  109   c . The parallel portion  109   c  adjusts a flow of air. The air is allowed to easily flow into the first opening hole  106   b  of the first opening/closing portion  106 , thereby reducing pressure loss. However, any one of the parallel portion  109   c  and the upstream guide portion  109   d  may be omitted. Only one of the guide surfaces  109   e  and  109   f  may be provided to the upstream guide portion  109   d.    
     As illustrated in  FIG. 5A , the second opening hole  107   a  includes a pair of guide surfaces  107   b  (second guide portions). The pair of guide surfaces  107   b  are inner wall surfaces of the second opening hole  107   a  which are opposed to each other in the radial direction. The pair of guide surfaces  107   b  are inclined with respect to the rotation axis direction. The pair of guide surfaces  107   b  are increased in separation distance therebetween in the radial direction as extending from the upstream communication portion  103  side toward the downstream communication portion  104  side. The guide surface  107   b  on the radially outer side extends toward the radially outer side as extending toward the compressor impeller  9 . The guide surface  107   b  on the radially inner side extends toward the radially inner side as extending toward the compressor impeller  9 . 
     As illustrated in  FIG. 5B , a pair of guide surfaces  107   c  (second guide portions) are inner wall surfaces of the second opening hole  107   a  which are opposed to each other in the rotation direction. The pair of guide surfaces  107   c  are inclined with respect to the rotation axis direction. The pair of guide surfaces  107   c  are increased in separation distance therebetween in the rotation direction as extending from the upstream communication portion  103  side toward the downstream communication portion  104  side. 
     The guide surfaces  107   b  and  107   c  of the second opening hole  107   a  allow air to easily flow out from the second opening hole  107   a , thereby reducing pressure loss. However, the guide surfaces  107   b  and  107   c  are not essentially required, and the second opening hole  107   a  may extend in parallel with the rotation axis direction. 
     The fin  109  may be provided on the compressor impeller  9  side (downstream communication portion  104  side) with respect to the second opening/closing portion  107 . In this case, the fin  109  is arranged in a state of being reversed in orientation in the rotation axis direction. The fin  109  may be omitted, and the guide surfaces  109   e  and  109   f  of the fin  109  may be provided to the first opening/closing portion  106 . 
       FIG. 6A  is a sectional view taken at a position corresponding to  FIG. 3A  in a first modification example.  FIG. 6B  is a sectional view taken at a position corresponding to  FIG. 3B  in the first modification example.  FIG. 6C  is a sectional view taken at a position corresponding to  FIG. 3A  in a second modification example.  FIG. 6D  is a sectional view taken at a position corresponding to  FIG. 3B  in the second modification example. 
     As illustrated in  FIG. 6A , in the first modification example, in a plan-view shape of each of second opening holes  207   a  (opening portions), both end portions  217   a  in the rotation direction each have a curved shape. Curvature centers of the both end portions  217   a  are located on an inner side of the second opening hole  207   a . As illustrated in  FIG. 6B , in a plan-view shape of each of first opening holes  206   b  (opening portions), both end portions  216   b  in the rotation direction each have a curved shape. Curvature centers of the both end portions  216   b  are located on an inner side of the first opening hole  206   b . The first opening holes  206   b  and the second opening holes  207   a  each have, for example, an arc shape which is concentric with the through hole  106   a   1  formed in the main body portion  106   a  of the first opening/closing portion  106 . That is, the first opening holes  206   b  and the second opening holes  207   a  each have, for example, an arc shape with a curvature center located at a center of the main body portion  106   a  (on the rotation axis or on the axial center of the shaft  7 ). 
     As illustrated in  FIG. 6C , in the second modification example, a plan-view shape of each of second opening holes  307   a  (opening portions) is circular. As illustrated in  FIG. 6D , a plan-view shape of each of first opening holes  306   b  (opening portions) is circular. 
     The one embodiment of the present disclosure has been described above with reference to the attached drawings, but, needless to say, the present disclosure is not limited to the embodiment. It is apparent that those skilled in the art may arrive at various alternations and modifications within the scope of claims, and those examples are construed as naturally falling within the technical scope of the present disclosure. 
     For example, in the embodiment and modification examples described above, description is made of the case in which the first opening/closing portion  106  and the second opening/closing portion  107  are provided as a plurality of opening/closing portions. However, three or more opening/closing portions may be provided. When the opening portions of the opening/closing portions are arranged so as not to align when viewed from the rotation axis direction, the auxiliary flow passage  102  is substantially closed. When the opening portions of the opening/closing portions are arranged so as to align, the auxiliary flow passage  102  is opened. 
     Moreover, in the embodiment and modification examples described above, description is made of the case in which only the first opening/closing portion  106  operates. However, the second opening/closing portion  107  may be formed separately from the compressor housing  100  and operate. 
     Moreover, in the embodiment and modification examples described above, description is made of the case in which the first opening/closing portion  106  and the second opening/closing portion  107  are arranged on the upstream communication portion  103  side with respect to the impeller-side flow passage portion  102   b . In this case, the pressure loss is reduced as compared to a case in which the first opening/closing portion  106  and the second opening/closing portion  107  are provided to the impeller-side flow passage portion  102   b.    
     INDUSTRIAL APPLICABILITY 
     The present disclosure can be used for a centrifugal compressor having an auxiliary flow passage communicating to a main flow passage.