Patent Publication Number: US-2022221071-A1

Title: Air valve and fuel cell system using air valve

Description:
TECHNICAL FIELD 
     This application claims priority to Japanese Patent Application No. 2019-078708 filed on Apr. 17, 2019, the contents of which are hereby incorporated by reference into the present application. The present specification relates to an air valve and a fuel cell system using an air valve. 
     BACKGROUND ART 
     In a fuel cell system, an oxygen source (air gas) and a hydrogen source (hydrogen gas) are supplied to a fuel cell stack to generate electricity. Gas that was not used in the electricity generation is discharged to the outside of the fuel cell system as air off-gas and hydrogen off-gas. Japanese Patent Application Publication No. 2018-137150 (termed Patent Document 1 hereinafter) discloses a configuration of an air system (passage for supplying air gas to a fuel cell stack) in a fuel cell system. In the fuel cell system of Patent Document 1, air gas (outside air) is supplied to a fuel cell stack by using a compressor. A valve (an inlet sealing valve) is arranged on an air supply passage that connects the compressor to the fuel cell stack, and a flow rate of the air gas to be supplied to the fuel cell stack is thereby adjusted. Another valve (an outlet integrated valve) is arranged on an air discharge passage for discharging air off-gas, and a flow rate of the air off-gas is thereby adjusted. Further, the air supply passage is connected to the air discharge passage via a bypass passage, and a valve (a bypass valve) is arranged on the bypass passage. In Patent Document 1, the air gas is supplied from the air supply passage to the air discharge passage through the bypass passage to adjust the pressure in the air supply passage (adjust the difference between the pressure frontward of the inlet sealing valve and the pressure rearward of the inlet sealing valve). 
     SUMMARY OF INVENTION 
     As disclosed in Patent Document 1, connecting the bypass passage to the air supply passage enables the air gas in the air supply passage to be supplied not only to the fuel cell stack but also to a member other than the fuel cell stack. However, supplying the air gas in the air supply passage to multiple sites (the fuel cell stack and the member other than the fuel cell stack) requires a valve to be arranged on the bypass passage and also requires an actuator (a motor, etc.) that actuates the valve. This increases the number of components in the fuel cell system and also increases the size of the fuel cell system. The present specification provides a valve (an air valve) that can achieve a compact fuel cell system. 
     A first technique disclosed in the present specification is an air valve that is arranged in an air system of a fuel cell stack and is configured to control a flow of air gas to be supplied to the fuel cell stack. The air valve may comprise a supply valve configured to open and close an air supply passage through which the air gas to be supplied to the fuel cell stack from outside flows; a switching valve configured to switch between a state in which the air gas supplied from the outside flows through the air supply passage and a state in which the air gas supplied from the outside flows through a bypass passage that branches from the air supply passage and bypasses a member arranged downstream of the air valve; and a link mechanism connected to the supply valve and the switching valve and configured to actuate the supply valve and the switching valve. The link mechanism may comprise an arm portion fixed at the supply valve and a cam plate fixed at the switching valve, wherein the cam plate includes a guide portion with which the arm portion is to contact. In this air valve, the guide portion may comprise a first region that is a region where the arm portion moves for an opening-closing movement of the supply valve; and a second region that is independent from the first region and is a region where the arm portion moves for an opening-closing movement of the switching valve. 
     A second technique disclosed in the present specification is the air valve according to the first technique, wherein a third region may be arranged between the first region and the second region and the third region is a region where neither of the opening-closing movement of the supply valve nor the opening-closing movement of the switching valve is performed. 
     A third technique disclosed in the present specification is the air valve according to the first or second technique, wherein the cam plate may be fixed to a cam gear connected to a motor. The cam gear may be biased in a direction in which the cam gear rotates when the supply valve is opened, such that the arm portion is in contact with the first region while the supply valve is closed. 
     A fourth technique disclosed in the present specification is the air valve according to any one of the first to third techniques, wherein the second region may comprise a contact portion that has an arc shape of which distance from a rotation center of the cam plate is constant. The arm portion may move in contact with the contact portion while the switching valve is actuated. 
     A fifth technique disclosed in the present specification is the air valve according to any one of the first to fourth techniques, wherein the cam plate may comprise a fitting portion configured to fit with the arm portion when the supply valve is closed. The fitting portion may be a groove recessed in a radially inward direction of the cam plate. 
     A sixth technique disclosed in the present specification is the air valve according to any one of the first to fifth techniques, wherein the first region may comprise a straight portion configured to contact the arm portion while the supply valve is closed. The straight portion may be maintained in a contact state with the arm portion for a predetermined period from an opening start of the supply valve. 
     A seventh technique disclosed in the present specification is the air valve according to any one of the first to fifth techniques, wherein a length of the second region may be longer than a length of the first region. 
     An eighth technique disclosed in the present specification is a fuel cell system comprising the air valve according to any one of the first to seventh techniques. In the fuel cell system, a humidifier may be arranged between the air valve and the fuel cell stack, and the bypass passage may be connected to the air supply passage and bypass the humidifier. Further, the switching valve may contact an inner wall of the air supply passage to block the air supply passage between the supply valve and the humidifier when the supply valve is closed. 
     A ninth technique disclosed in the present specification is the fuel cell system according to the eighth technique, wherein the air valve may comprise a tubular first flow section connected to the air supply passage at a position upstream of the supply valve; and an air flow section, wherein one end thereof is connected to the air supply passage at a position downstream of the supply valve, another end thereof is connected to the bypass passage, and an intermediate portion thereof is connected to the first flow section. Further, a downstream end of the supply valve may be located closer to the one end of the air flow section than an upstream end of the supply valve when the supply valve is fully open. 
     Advantageous Effects of Invention 
     According to the first technique, it is possible to control both the flow rate of fluid flowing in the air supply passage and the flow rate of fluid flossing in the bypass passage with the single air valve. That is, the number of actuators can be reduced as compared to a configuration in which valves (valve bodies and actuators that actuate the valves) are arranged separately on the air supply passage and the bypass passage. Thus, the number of components in the fuel cell system can be reduced and downsizing of the fuel cell system can be achieved. As long as one end of the bypass passage is connected to the air supply passage (the bypass passage branches from the air supply passage), another end thereof may be connected to any appropriate position. For example, in a case where a device etc. is connected to the air supply passage between the air valve and the fuel cell stack, the other end of the bypass passage may be connected to a position downstream of the device etc. (connected to the air supply passage between the device etc. and the fuel cell stack). That is, the bypass passage may bypass the device etc. arranged on the air supply passage between the air valve and the fuel cell stack. Alternatively, the other end of the bypass passage may be connected to a position downstream of the fuel cell stack (air discharge passage). That is, the bypass passage may bypass the fuel cell stack. 
     According to the second technique, it is ensured that the supply valve and the switching valve are prevented from being actuated simultaneously. As a result, an amount of the air gas to travel to the fuel cell stack through the air supply passage and an amount of the air gas to flow through the bypass passage can be adjusted after an amount of the air gas introduced to the air supply passage from the outside has stabilized. 
     According to the third technique, it is ensured that the arm portion is in contact with the cam plate while the supply valve is closed. In other words, according to the third technique, there is no gap (no play) between the arm portion and the cam plate and the opening degree of the valve (the supply valve, the switching valve) can be detected accurately. The cam gear may be biased in the rotational direction (in the direction in which the cam gear rotates when the supply valve is opened) by a biasing member such as a coil spring etc. or by using the output of the motor. That is, the motor may apply torque in the rotational direction of the cam gear while the supply valve is closed. 
     According to the fourth technique, the structure of the air valve (the cam plate) can be simplified. As described, according to the teachings disclosed in the present specification, the supply valve and the switching valve are actuated at different timings (they are not actuated simultaneously). Thus, while the supply valve is not actuated (while the arm portion is moving in the second region), the air valve simply needs to maintain the posture of the arm portion. With the second region that has the arc shape of which distance from the rotation center of the cam plate is constant, the arm portion moves in the second region without changing its posture. Since the posture of the arm portion does not change, a structure for maintaining the engagement of the arm portion with the cam plate while the arm portion moves in the second region can be omitted, and thus the structure of the cam plate can be simplified. 
     According to the fifth technique, it is possible to prevent the arm portion from straying from the cam plate (prevent the arm portion from disengaging from the cam plate) when the arm portion moves to an end of the first region (the position where the supply valve closes). Further, since the fitting portion (fitting groove) is a groove recessed in the radially inward direction of the cam plate, the size of the cam plate can be reduced as compared to a configuration in which the fitting portion is arranged in the circumferential direction of the cam plate. 
     According to the sixth technique, it is possible to reduce the change in the force applied to the arm portion from the cam plate (torque for actuating the supply valve) in the early stage of the opening of the supply valve (for a predetermined period from the opening start). 
     According to the seventh technique, it is possible to control with high precision the flow rate of the air gas flowing through the air supply passage and the flow rate of the air gas flowing through the bypass passage (ratio of the flow rates). 
     According to the eighth technique, it is possible to curtail the adhesion of the moisture (condensation water) generated by the humidifier to the supply valve while the supply valve is closed (while the fuel cell system is not in operation). It is possible to curtail the corrosion of the valve body, valve seat, sealing material, etc., and further to curtail the freezing of the valve body. Curtailing freezing of the valve body (fixing of the valve body with the valve seat) reduces torque for actuating the valve body and reduces a power consumption when the supply valve is opened. 
     According to the ninth technique, it is possible to make the coefficient of discharge when the air gas flows through the air supply passage larger than the coefficient of discharge when the air gas flows through the bypass passage. The air supply passage causes a larger pressure drop (passage resistance) than the bypass passage since the humidifier is arranged on the air supply passage. By making the coefficient of discharge of the air supply passage larger than the coefficient of discharge of the bypass passage, it is possible to reduce a difference between the flow rates of air gas flowing through the passages (the air supply passage, the bypass passage) when the opening degree of the switching valve is equal for the passages. That is, according to the ninth technique, it is possible to compensate the pressure drop in the air supply passage due to the humidifier being arranged thereon. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a schematic diagram of a fuel cell system; 
         FIG. 2  illustrates an internal structure of an air supply valve; 
         FIG. 3  illustrates a schematic diagram of a link mechanism configured to actuate valve bodies; 
         FIG. 4  illustrates explanatory diagrams for operations of the air supply valve; 
         FIG. 5  illustrates passage switching timings for an air supply passage and a bypass passage; 
         FIG. 6  illustrates a schematic diagram of a fuel cell system according to a variant; 
         FIG. 7  illustrates an internal structure of an air supply valve according to the variant; 
         FIG. 8  illustrates a schematic diagram of a link mechanism according to the variant; 
         FIG. 9  illustrates an enlarged view of the area enclosed by a broken line IX in  FIG. 8 ; and 
         FIG. 10  illustrates a cross-sectional view along a line X-X in  FIG. 10 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (Fuel Cell System) 
     Referring to  FIG. 1 , a fuel cell system  100  will be described. The fuel cell system  100  comprises a fuel cell stack  20 , a hydrogen system  10  that supplies hydrogen gas to the fuel cell stack  20 , an air system  30  that supplies air gas (outside air) to the fuel cell stack  20 , and a controller  25 . In the fuel cell system  100 , electricity is generated by using hydrogen gas supplied through the hydrogen system  10  and oxygen gas (air gas) supplied through the air system  30 . The hydrogen system  10  comprises a hydrogen gas supply device  2 , a hydrogen supply passage  4 , and a hydrogen discharge passage  8 . The hydrogen gas supply device  2  comprises a hydrogen tank, a regulator, an injector, etc. The hydrogen gas supply device  2  is controlled by the controller  25 . The hydrogen gas supply device  2  supplies hydrogen gas to the fuel cell stack  20  through the hydrogen supply passage  4  based on a control signal of the controller  25 . Hydrogen gas discharged from the fuel cell stack  20  (hydrogen off-gas) is discharged to the outside of the fuel cell system  100  through the hydrogen discharge passage  8 . Although details will be described later, the hydrogen discharge passage  8  is connected to a diluter  42 . The hydrogen off-gas is discharged to the outside of the fuel cell system  100  after having been diluted in the diluter  42 . 
     The air system  30  comprises a compressor  32 , an air supply passage  34 , an air discharge passage  40 , an FC bypass passage  36 , an air supply valve  50 , and an air discharge valve  38 . The FC bypass passage  36  is an example of bypass passage, and the air supply valve  50  is an example of air valve. The compressor  32  pumps the outside air to the air supply passage  34  as air gas. An air cleaner (not illustrated) is arranged upstream of the compressor  32 . Thus, clean air gas is supplied to the air supply passage  34 . The air supply passage  34  connects the compressor  32  with the fuel cell stack  20 . The air supply valve  50  is arranged on the air supply passage  34 . Specifically, the air supply passage  34  comprises an upstream air supply passage  34   a  that connects the compressor  32  with the air supply valve  50  and a downstream air supply passage  34   b  that connects the air supply valve  50  with the fuel cell stack  20 . When the compressor  32  is actuated and the air supply valve  50  communicates the upstream air supply passage  34   a  with the downstream air supply passage  34   b,  the outside air is supplied to the fuel cell stack  20  as air gas. Details of the air supply valve  50  will be described later. 
     The air discharge passage  40  is connected to the fuel cell stack  20  and discharges air off-gas from the fuel cell stack  20 . The air discharge passage  40  is connected to the diluter  42 . In the diluter  42 , the hydrogen off-gas supplied through the hydrogen discharge passage  8  is diluted by the air off-gas supplied through the air discharge passage  40 . The diluted gas is discharged to the outside of the fuel cell system  100  through a discharge pipe  44 . The air discharge valve  38  is arranged on the air discharge passage  40 . The air discharge valve  38  is a butterfly valve and is controlled by the controller  25 . By adjusting the opening degree of the air discharge valve  38 , an amount of the air off-gas to be supplied to the diluter  42  is adjusted and thus the concentration of the hydrogen off-gas is adjusted. 
     The FC bypass passage  36  connects the air supply passage  34  with the air discharge passage  40 . Specifically, one end of the FC bypass passage  36  is connected to the air supply valve  50  and another end thereof is connected to the air discharge passage  40  at a position downstream of the air discharge valve  38 . When the air supply valve  50  connects the air supply passage  34  (the upstream air supply passage  34   a ) to the FC bypass passage  36 , the air gas in the air supply passage  34  is supplied to the air discharge passage  40 . The FC bypass passage  36  is a passage that bypasses the fuel cell stack  20  and connects the air supply passage  34  with the air discharge passage  40 . 
     (Air Supply Valve) 
     Referring to  FIGS. 2 and 3 , the air supply valve  50  will be described.  FIG. 2  illustrates an internal structure of the air supply valve  50  (air flow section  52 ).  FIG. 3  illustrates a valve actuator  70  that actuates valve bodies  60 ,  64  in the air flow section  52 . The valve actuator  70  is an example of link mechanism. As illustrated in  FIGS. 2 and 3 , the air supply valve  50  comprises the air flow section  52  through which the air gas supplied from the compressor  32  flows, the valve bodies  60 ,  64  that change flow passages in the air flow section  52 , and the valve actuator  70  that actuates the valve bodies  60 ,  64 . The valve actuator  70  is arranged outside the air flow section  52 . First, the structure in the air flow section  52  will be described. 
     As illustrated in  FIG. 2 , the air flow section  52  comprises a tubular first flow section  52   a  connected to the upstream air supply passage  34   a  and a tubular second flow section  52   b.  One end of the second flow section  52   b  is connected to the downstream air supply passage  34   b  and another end thereof is connected to the FC bypass passage  36 . A flange  53   a  is formed at one end of the first flow section  52   a  and is connected to the upstream air supply passage  34   a.  Another end of the first flow section  52   a  is connected to an axially intermediate portion of the second flow section  52   b,  more specifically an axially central portion of the second flow section  52   b.  The first flow section  52   a  and the second flow section  52   b  are in communication with each other, and their cross-sectional shape (flow passage shape) is substantially a T-shape. 
     The first valve body  60  is arranged at the other end side of the first flow section  52   a.  The first valve body  60  is an example of supply valve. The first valve body  60  is connected to a first shaft  62  and rotates with rotation of the first shaft  62 . The first valve body  60  can control the flow rate of the air gas to be supplied from the first flow section  52   a  to the second flow section  52   b.  That is, by rotating the first valve body  60 , the flow rate of the air gas flowing through a first flow passage  54  in the first flow section  52   a  (flow rate of the air gas to be supplied to the second flow section  52   b ) can be varied. The first valve body  60  can be considered as a valve that varies the total flow rate of the air gas to be supplied to the downstream air supply passage  34   b  and the FC bypass passage  36 , which will be described later. 
     A flange  53   b  is formed at the one end of the second flow section  52   b  and is connected to the downstream air supply passage  34   b.  A flange  53   c  is formed at the other end of the second flow section  52   b  and is connected to the FC bypass passage  36 . The second valve body  64  is arranged at the central portion of the second flow section  52   b.  The second valve body  64  is an example of switching valve. The second valve body  64  is connected to a second shaft  66  and rotates with rotation of the second shaft  66 . The second valve body  64  can control the flow direction of the air gas supplied to the second flow section  52   b  from the first flow section  52   a.  The air supply valve  50  can be considered as comprising both a supply valve (the first valve body  60 ) and a switching valve (the second valve body  64 ). 
     When the second valve body  64  is in the state indicated with the solid line in  FIG. 2 , the air gas supplied from the first flow section  52   a  to the second flow section  52   b  flows through a second flow passage  56  and the downstream air supply passage  34   b  and is then supplied to the fuel cell stack  20 . When the second valve body  64  is in the state indicated with the broken line in  FIG. 2 , the air gas supplied from the first flow section  52   a  to the second flow section  52   b  flows through a third flow passage  58  and the FC bypass passage  36  and is then supplied to the air discharge passage  40  (also see  FIG. 1 ). When the second valve body  64  is controlled such that it takes a middle position between the solid line and the broken line, the air gas can be supplied to both the fuel cell stack  20  and the air discharge passage  40 . The second valve body  64  can be considered as a valve that varies a percentage of air gas to be directly supplied to the fuel cell stack  20  out of the air gas supplied from the compressor  32  to the air supply valve  50 . 
     (Valve Actuator) 
     As shown in  FIG. 3 , the valve actuator  70  is arranged outside the air flow section  52 . In  FIG. 3 , the internal structure of the air flow section  52  (the valve bodies  60 ,  64 , the flow passages  54 ,  56 ,  58 ) is indicated with broken lines. The valve actuator  70  is housed in the same housing (not shown) in which the air flow section  52  is housed. The valve actuator  70  comprises a motor gear  72  fixed on an output shaft of a motor (not illustrated), a first gear  74 , a second gear  76 , a cam (cam plate)  78 , a first arm  82 , and a second arm  84 . The second gear  76  is an example of cam gear. The first gear  74  is a dual gear, in which a large-diameter gear  74   a  is engaged with the motor gear  72  and a small-diameter gear  74   b  is engaged with the second gear  76 . The second gear  76  is fixed to the cam  78 . The number of teeth of the large-diameter gear  74   a  is greater than the number of teeth of the motor gear  72 , and the number of teeth of the second gear  76  is greater than the number of teeth of the small-diameter gear  74   b.  Thus, output torque of the motor can be increased (rotational speed of the motor can be reduced) by the motor gear  72 , the first gear  74 , and the second gear  76 . The use of the gears  74 ,  76  allows the motor to actuate (rotate) the cam  78  even when the motor is of small size (low torque). 
     The cam  78  includes a cam groove  78   a,  and a roller  80  is arranged in the cam groove  78   a.  The roller  80  is movable along the cam groove  78   a  and is rotatably supported on the first arm  82 . The roller  80  and the first arm  82  are an example of arm portion. The first arm  82  is fixed on the first shaft  62  and rotates in response to the movement (rotation) of the cam  78 . When the first arm  82  rotates, the first shaft  62  rotates and the first valve body  60  rotates. The first arm  82  rotates in response to the rotation of the cam  78  until the cam  78  rotates by a predetermined angle, whereas it does not rotate, even when the cam  78  rotates, after the rotation angle of the cam  78  has exceeded the predetermined angle. Specifically, the first arm  82  rotates in response to the rotation of the cam  78  until the first valve body  60  rotates so that it shifts from a state in which the first valve body  60  closes the first flow passage  54  to a state in which the first valve body  60  opens (fully opens) the first flow passage  54 , whereas the first arm  82  does not rotate, even when the cam  78  rotates, after the first valve body  60  has shifted to the state in which it opens the first flow passage  54 . That is, the first valve body  60  does not rotate after the rotation angle of the cam  78  has exceeded the predetermined angle. The cam  78  comprises a second arm actuating portion  78   b  for actuating the second arm  84 , which will be described later. 
     The second arm  84  is fixed on the second shaft  66 . The rotation axis of the second arm  84  (the second shaft  66 ) is the same as the rotation axis of the second gear  76 . However, the second arm  84  is not fixed to the second gear  76  (nor the cam  78  fixed to the second gear  76 ). The second arm  84  therefore does not integrally rotate with the second gear  76  nor the cam  78 . However, the second arm  84  rotates with the rotation of the cam  78  after the rotation angle of the cam  78  has exceeded the predetermined angle. When the second arm  84  rotates, the second shaft  66  rotates and the second valve body  64  rotates. The valve actuator  70  actuates the first arm  82  and the second arm  84  with a single motor, without using separate motors for actuating the first arm  82  and the second arm  84 . 
     The second arm  84  comprises a contact portion  84   a  configured to contact the second arm actuating potion  78   b.  When the second gear  76  (the cam  78 ) rotates by the predetermined angle and the second arm actuating portion  78   b  contacts the contact portion  84   a,  the second arm  84  rotates with the rotation of the second gear  76  (the cam  78 ). Specifically, as illustrated in  FIG. 3 , when the first valve body  60  closes the first flow passage  54 , the second arm actuating portion  78   b  is offset from the contact portion  84   a  by an angle α 1  with respect to the second shaft  66  (the rotation axis of the second gear  76 ). Thus, the second arm  84  (the second valve body  64 ) does not rotate until the second gear  76  (the cam  78 ) rotates by the angle α 1 , whereas it starts rotating once the rotation angle of the second gear  76  exceeds the angle α 1 . The second arm  84  is biased with a spring (not illustrated) such that the second valve body  64  is in the state illustrated in  FIG. 3  (in the state in which the second valve body  64  fully opens the second flow passage  56 ). Therefore, while the second arm actuating portion  78   b  is not in contact with the contact portion  84   a,  the second flow passage  56  is fully open. Hereinafter, operation of the air supply valve  50  (how the first valve body  60  and the second valve body  64  move when the valve actuator  70  is in operation) will be described in detail. 
     (Operation of Air Supply Valve) 
     Referring to  FIG. 4 , an operation  90  of the air supply valve  50  will be described. In  FIG. 4 , the gears  72 ,  74  in  FIG. 3  are not illustrated. A state (A) illustrates a state in which the air supply valve  50  is closed. That is, in the state (A), the first valve body  60  closes the first flow passage  54 , the air gas does not flow through the second flow passage  56  nor the third flow passage  58 , and the air gas is not supplied to the downstream air supply passage  34   b  nor the FC bypass passage  36  (the fuel cell stack  20  nor the air discharge passage  40 ). 
     A state (B) illustrates a state in which the second gear  76  (the cam  78 ) has rotated by the angle Δ 1  (see  FIG. 3 ), the roller  80  has moved within the cam groove  78   a,  and the first valve body  60  has rotated so that the first flow passage  54  is fully open. In the state (B), the second arm actuating portion  78   b  is in contact with the contact portion  84   a.  Therefore, when the second gear  76  further rotates, the second arm  84  rotates and the second valve body  64  rotates. In other words, during the transition from the state (A) to the state (B), the second flow passage  56  is open and the third flow passage  58  is closed since the second valve body  64  does not rotate. Thus, during the transition from the state (A) to the state (B), the air gas is supplied only to the downstream air supply passage  34   b  and is not supplied to the FC bypass passage  36 . That is, during the transition from the state (A) to the state (B), the air gas supplied to the air supply valve  50  from the compressor  32  is supplied only to the fuel cell stack  20 . 
     A state (C) illustrates a state in which the second arm  84  (the second valve body  64 ) has rotated with the second gear  76  (the cam  78 ) so that the second flow passage  56  is closed and the third flow passage  58  is fully open. In the state (C), the air gas is supplied only to the FC bypass passage  36  and is not supplied to the downstream air supply passage  34   b.  That is, in the state (C), the air gas supplied to the air supply valve  50  from the compressor  32  is supplied only to the air discharge passage  40 . During the transition from the state (B) to the state (C), the first valve body  60  does not rotate and the first flow passage  54  remains fully opened. Therefore, during the transition from the state (B) to the state (C), the flow rate of the air gas flowing through the first flow passage  54  (the total flow rate of the air gas flowing through the second flow passage  56  and the third flow passage  58 ) does not change, whereas the ratio of the flow rate of the air gas supplied to the fuel cell stack  20  and the flow rate of the air gas supplied to the air discharge passage  40  changes. 
     In the air supply valve  50 , the state of the air supply valve  50  transitions from the state (A), through the state (B), to the state (C) in this order with the rotation of the single motor. Thus, in the air supply valve  50 , the use of only one motor allows switching among the following states for the downstream air supply passage  34   b  and the FC bypass passage  36 : the state in which the downstream air supply passage  34   b  and the FC bypass passage  36  are both closed (the state (A)); the state in which only the downstream air supply passage  34   b  is open and the FC bypass passage  36  is closed (from the state (A) to the state (B)); the state in which the downstream air supply passage  34   b  and the FC bypass passage  36  are both open and the ratio of the air gas flowing through the both passages  34   b,    36  changes (from the state (B) to the state (C)); and the state in which only the FC bypass passage  36  is open and the downstream air supply passage  34   b  is closed (the state (C)). 
     As described, during the transition from the state (B) to the state (C), the roller  80  moves within the cam groove  78   a  as the second gear  76  (the cam  78 ) rotates, whereas the first arm  82  does not rotate. This occurs because the distance from the rotation axis of the second gear  76  (the cam  78 ) to the roller  80  does not change during the transition from the state (B) to the state (C) (because the cam groove  78   a  in which the roller  80  moves is on an arc of the rotation axis of the second gear  76 ). To the contrary, during the transition from the state (A) to the state (B), the first arm  82  rotates as the roller  80  moves. This occurs because the distance from the rotation axis of the second gear  76  (the cam  78 ) to the roller  80  (the position of the cam groove  78   a  in which the roller  80  moves) gradually increases during the transition from the state (A) to the state (B). That is, in the valve actuator  70 , the cam groove  78   a  is formed to cause the roller  80  to move away from the rotation axis of the second gear  76  until the second gear  76  (the cam  78 ) rotates by the angle α 1  and also to cause the roller  80  to be positioned at a constant distance from the rotation axis of the second gear  76  after the second gear  76  (the cam  78 ) has rotated by the angle α 1 . 
     The timings when the first valve body  60  and the second valve body  64  are actuated can be adjusted by changing the shape of the cam groove  78   a.  For example, it is possible to prohibit the second valve body  64  from moving for a predetermined period (for a period in which the second gear  76  rotates by a predetermined rotation angle) after the first valve body  60  has fully opened. Alternatively, an adjustment can be made such that the second valve body  64  starts moving before the first valve body  60  fully opens (while the opening degree of the first valve body  60  is increasing). The timings when the first valve body  60  and the second valve body  64  are actuated can be adjusted also by changing the angle α 1  between the second arm actuating portion  78   b  and the contact portion  84   a,  without changing the shape of the cam groove  78   a.  That is, the timings when the first valve body  60  and the second valve body  64  are actuated can be adjusted in an easier manner than changing the shape of the cam groove  78   a.  Hereinafter, as a variant of the valve actuator  70 , how the timings when the first valve body  60  and the second valve body  64  are actuated are adjusted by changing the angle α 1  between the second arm actuating portion  78   b  and the contact portion  84   a  to an angle α. 
     (Variant) 
     A variant  92  of  FIG. 5  illustrates relationships between rotation angles θ of the second gear  76  and flow rates of air gas supplied to the downstream air supply passage  34   b  and the FC bypass passage  36  (flow rates of air gas flowing through the second flow passage  56  and the third flow passage  58 ). Lines  94  indicate flow rates of air gas flowing through the second flow passage  56  (flow rates of air gas to be supplied to the fuel cell stack  20 ), and lines  96  indicate flow rates of air gas flowing through the third flow passage  58  (flow rates of air gas to be supplied to the air discharge passage  40 ) (also see  FIGS. 1, 2 ). 
     The example (a) shows a case in which the angle α between the second arm actuating portion  78   b  and the contact portion  84   a  is smaller than the angle α 1 , the example (b) shows a case in which the angle α is equal to the angle α 1  (i.e., the valve actuator  70 ), and the example (c) shows a case in which the angle α is larger than the angle α 1 . An angle θ 0  is an angle at which the first valve body  60  closes the first flow passage  54  (corresponding to the state (A) in  FIG. 4 ). An angle θ 1  is an angle at which the opening degree of the first valve body  60  is its maximum and the total flow rate of the air gas flowing through the second flow passage  56  and the third flow passage  58  is its maximum (corresponding to the state (B) in  FIG. 4 ). An angle θ 2  is an angle at which the second valve body  64  closes the second flow passage  56  and opens only the third flow passage  58  (corresponding to the state (C) in  FIG. 4 ). 
     In the example (a), when the second gear  76  rotates by the angle α 1  from its initial state (from the angle θ 0 ), the opening degree of the first valve body  60  reaches the maximum and the flow rate of the air gas flowing through the second flow passage  56  (the line  94 ) reaches the maximum. Between the angle θ 0  and the angle θ 1 , the flow rate of the air gas flowing through the second flow passage  56  increases as the opening degree of the first valve body  60  increases. In the example (a), the second arm actuating portion  78   b  does not contact the contact portion  84   a  even though the second gear  76  rotates by the angle θ 1  (see the state (B) in  FIG. 4  for comparison). Therefore, even though the rotation angle of the second gear  76  has reached the angle θ 1 , the second valve body  64  does not start rotating and the flow rate of the air gas flowing through the third flow passage  58  is “zero”. The second valve body  64  starts rotating after the rotation angle of the second gear  76  reaches the angle α. Between the angle α and the angle θ 2 , the flow rate of the air gas flowing through the second flow passage  56  decreases and the flow rate of the air gas flowing through the third flow passage  58  (the line  96 ) increases. Then, when the rotation angle of the second gear  76  reaches the angle θ 2 , the air gas flows through only the third flow passage  58 . 
     In the example (a), the switching between the second flow passage  56  and the third flow passage  58  is performed after the flow rate of the air gas introduced to the air supply valve  50  (the flow rate in the first flow passage  54 ) has been stabilized. Thus, the example (a) facilitates controlling the ratio of the flow rate of the air gas to be supplied to the downstream air supply passage  34   b  and the flow rate of the air gas to be supplied to the FC bypass passage  36 . Further, it is possible to supply the maximum amount of air gas to the fuel cell stack  20  without controlling the rotation angle of the second gear  76  with high precision, because the period in which the air gas flows through only the second flow passage  56  can be prolonged. 
     The example (b) corresponds to the valve actuator  70 . When the rotation angle of the second gear  76  reaches the angle α (the angle α 1 ), the opening degree of the first valve body  60  reaches the maximum and the second valve body  64  starts rotating. Thus, when the flow rate of the air gas flowing through the second flow passage  56  (the line  94 ) reaches the maximum, the switching between the second flow passage  56  and the third flow passage  58  starts. That is, immediately after the flow rate of the air gas flowing through the first flow passage  54  has reached the maximum, the control over the ratio of the flow rate of the air gas to be supplied to the downstream air supply passage  34   b  and the flow rate of the air gas to be supplied to the FC bypass passage  36  (the line  96 ) starts. The example (b) is highly responsive to the flow passage switching (adjustment in the air gas amount to be supplied to the downstream air supply passage  34   b  and the air gas amount to be supplied to the FC bypass passage  36 ) in response to the rotation of the second gar  76  (drive of the motor). 
     In the example (c), when the rotation angle of the second gear  76  reaches the angle α, the second valve body  64  starts rotating before the opening degree of the first valve body  60  reaches the maximum (before the rotation angle of the second gear  76  reaches the angle α 1 ). During a period from when the rotation angle of the second gear  76  has reached the angle α to when it reaches the angle α 1 , the flow rate of the air gas flowing through the second flow passage  56  (the line  94 ) remains constant, whereas the flow rate of the air gas flowing through the third flow passage  58  (the line  96 ) increases. After the angle α 1 , the flow rate of the air gas flowing through the second flow passage  56  decreases, whereas the flow rate of the air gas flowing through the third flow passage  58  increases. The example (c) is useful when the flow rate of the air gas to be supplied to the downstream air supply passage  34   b  (the fuel cell stack  20 ) needs to be limited. 
     As described, in the fuel cell system  100 , the flange  53   b  is connected to the downstream air supply passage  34   b,  and the flange  53   c  is connected to the FC bypass passage  36 . However, the flange  53   b  may be connected to the FC bypass passage  36 , and the flange  53   c  may be connected to the downstream air supply passage  34   b.  In this case, when the motor starts, the state of the fuel cell system  100  transitions in the following order: a state in which both the downstream air supply passage  34   b  and the FC bypass passage  36  are closed; a state in which only the FC bypass passage  36  is open and the downstream air supply passage  34   b  is closed; a state in which both the downstream air supply passage  34   b  and the FC bypass passage  36  are open; and a state in which only the downstream air supply passage  34   b  is open and the FC bypass passage  36  is closed. 
     (Variant of Fuel Cell System) 
     Referring to  FIG. 6 , a fuel cell system  200  will be described. The fuel cell system  200  is a variant of the fuel cell system  100 . Thus, elements of the fuel cell system  200  that are substantially the same as the elements of the fuel cell system  100  are indicated with the same reference signs as those of the fuel cell system  100  or indicated with reference signs of which last two digits are the same as those of the fuel cell system  100 , and description for them may be omitted. In the fuel cell system  200 , a humidifier  37  is arranged in an air system  30 . Further, an air supply valve  150  is arranged on an air supply passage  34 , an air discharge valve  38  is arranged on an air discharge passage  40 , and a bypass valve  39  is arranged on an FC bypass passage  36 . 
     The humidifier  37  is arranged on the air supply passage  34  and the air discharge passage  40 . Specifically, the humidifier  37  is connected to the air supply passage  34  at a position between the air supply valve  150  and a fuel cell stack  20  and is connected to the air discharge passage  40  at a position between the fuel cell stack  20  and the air discharge valve  38 . The humidifier  37  adjusts humidity (moisture content) of air to be supplied to the fuel cell stack  20  and humidity of air off-gas to be supplied to a diluter  42 . 
     A humidifier bypass passage  35  is connected to the air supply passage  34  (downstream air supply passage  34   b ). The humidifier bypass passage  35  is an example of bypass passage. The humidifier bypass passage  35  bypasses the diluter  42 , and is connected to the air supply passage  34  (the downstream air supply passage  34   b ) at a position upstream of the diluter  42  and at a position downstream thereof. More specifically, in the fuel cell system  200 , one end (upstream end) of the humidifier bypass passage  35  is connected to the air supply valve  150  (an example of air valve). When the air supply valve  150  communicates the air supply passage  34  (the downstream air supply passage  34   b ) with the humidifier bypass passage  35 , air gas supplied to the air supply passage  34  is supplied to the fuel cell stack  20  without flowing through the humidifier  37 . On the other hand, when the air supply valve  150  communicates with the downstream air supply passage  34   b,  air gas supplied to the air supply passage  34  is supplied to the fuel cell stack  20  through the humidifier  37 . 
     (Variant of Air Supply Valve) 
     Referring to  FIGS. 7 to 10 , the air supply valve  150  will be described. The air supply valve  150  is a variant of the air supply valve  50 . Thus, elements of the air supply valve  150  that are substantially the same as the elements of the air supply valve  50  are indicated with the same reference signs as those of the air supply valve  50  or indicated with reference signs of which last two digits are the same as those of the air supply valve  50 , and description for them may be omitted. In the fuel cell system  200 , the air supply valve  50  may be used instead of the air supply valve  150 . In this case, the flange  53   b  may be connected to the downstream air supply passage  34   b  and the flange  53   c  may be connected to the humidifier bypass passage  35 . Alternatively, the flange  53   b  may be connected to the humidifier bypass passage  35  and the flange  53   c  may be connected to the downstream air supply passage  34   b.    
       FIG. 7  illustrates the internal structure of the air supply valve  150 . In the air supply valve  150 , a flange  53   b  is connected to the humidifier bypass passage  35  and a flange  53   c  is connected to the downstream air supply passage  34   b  (see  FIG. 2  for comparison). In  FIG. 7 , a state in which the air supply valve  150  is closed (air gas is not supplied to the fuel cell stack  20 ) is indicated with solid lines, and a state in which a first valve body  60  has rotated (the air supply valve  150  is open) and a state in which a second valve body  64  has rotated (passage through which air gas flows has been switched) are indicated with broken lines. 
     As illustrated in  FIG. 7 , in the state in which the air supply valve  150  is closed (the first valve body  60  is closed), the second valve body  64  is in contact with an inner wall of a second flow section  52   b  to block the air supply passage  34  (the downstream air supply passage  34   b ) between the first valve body  60  and the humidifier  37 . The air supply valve  150  therefore prevents adhesion of moisture generated in the humidifier  37  to the first valve body  60  when the fuel cell system  200  is not in operation. 
     In the air supply valve  150 , when the first valve body  60  is fully open (in the state indicated by the broken lines), a downstream end of the first valve body  60  is located closer to the flange  53   b  (side connected to the downstream air supply passage  34   b ) than an upstream end thereof. This makes a coefficient of discharge when the air gas flows through the downstream air supply passage  34   b  (when the second valve body  64  is in the solid line state) larger than a coefficient of discharge when the air gas flows through the humidifier bypass passage  35  (when the second valve body  64  is in the broken line state). The air gas experiences a pressure drop by flowing through the humidifier  37 . The above configuration can reduce the difference between the fluid pressure when the air gas flows through the downstream air supply passage  34   b  and the fluid pressure when the air gas flows through the humidifier bypass passage  35 , and thus improves diversion control while the second valve body  64  is actuated. 
       FIG. 8  illustrates a valve actuator  170  configured to actuate the valve bodies  60 ,  64 . The valve actuator  170  is an example of link mechanism. In the valve actuator  170 , a second gear  176  is engaged with a small-diameter gear  74   b  of a first gear  74 . The second gear  176  is fixed to a cam  178  (an example of cam plate). A magnet  65  is arranged on a surface of the second gear  176 . The magnet  65  faces a rotation angle detection sensor (not illustrated). The rotation angle detection sensor detects the rotation angle of the second gear  176 . Further, a support member  182  that supports an arm portion  181  is fixed on a first shaft  62 . A roller  80  is rotatably supported at an end of the arm portion  181 . 
     The cam  178  comprises a fitting portion  179  in which the roller  80  is fitted when the air supply valve  150  is closed and a guide portion  180  along which the roller  80  moves while contacting it when the air supply valve  150  is open (when the first valve body  60  or the second valve body  64  are actuated). The fitting portion  179  is a groove formed by a part of the periphery of the cam  178  being recessed in a radially inward direction of the cam  178 . The fitting portion  179  prevents the roller  80  from straying away from the cam  178  when the air supply valve  150  is closed (when the first valve body  60  is closed). The second gear  176  is biased in the direction indicated with an arrow  55  (in a direction that brings the air supply valve  150  to open) while the air supply valve  150  is closed. Thus, the roller  80  is maintained in a contact state with a wall surface of the fitting portion  179 . A contact portion is arranged on a back surface of the second gear  176 , although this is not illustrated. The contact portion is fixed on a second shaft  66  and contacts the second gear  176  (the cam  178 ) when the second gear  176  (the cam  178 ) rotates by a predetermined rotation angle. 
     Basic operation of the valve actuator  170  is substantially the same as that of the valve actuator  70 . That is, when the second gear  176  (the cam  178 ) rotates, the first shaft  62  rotates and the first valve body  60  is actuated while the roller  80  is moving in a first region  191  where the distance from the rotation axis of the second gear  176  to the roller  80  gradually increases. Further, the first shaft  62  does not rotate and the first valve body  60  is not actuated while the roller  80  is moving in a second region  192  where the distance from the rotation axis of the second gear  176  is constant. While the roller  80  is moving in the second region  192 , the second shaft  66  rotates and the second valve body  64  is actuated. In the valve actuator  170 , a third region  193  is arranged between the first region  191  and the second region  192 . The third region  193  is not involved with the actuation of first valve body  60  nor the actuation of the second valve body  64 . The third region  193  can be formed by adjusting the position of the above-described contact portion fixed on the second shaft  66 . 
     Referring to  FIG. 9 , the first region  191 , the second region  192 , and the third region  193  will be described. The first region  191  is a region from an inner surface of the fitting portion  179  (a surface thereof that is closer to the rotation axis of the cam  178  (the second gear  176 )) to a site where the distance from the rotation center of the cam  178  becomes constant. In the first region  191 , its curvature is not constant and the distance from the rotation center of the cam  178  varies. The second region  192  is independent (separated) from the first region  191  and has an arc shape of which distance from the rotation center of the cam  178  is constant. That is, the second region  192  has a constant curvature. The third region  193  has an arc shape of which distance from the rotation center of the cam  178  is constant, and the length of the third region  193  can be adjusted to adjust the timing when the second valve body  64  starts moving with the rotation of the second gear  176  as described. As clearly illustrated in  FIGS. 8 and 9 , the length of the second region  192  is longer than the length of the first region  191 . 
     The first region  191  includes a straight portion  191   a  and a curve portion  191   b.  The curve portion  191   b  is arranged between the straight portion  191   a  and the third region  193 . While the valve actuator  70  is closed, the arm portion  181  (the roller  80 ) is in contact with the straight portion  191   a.  When the valve actuator  70  is started, the arm portion  181  (the roller  80 ) first moves along the straight portion  191   a  while maintaining the contact with the first region  191 . This stabilizes a force applied to the arm portion  181  (the roller  80 ) in an early stage after the valve actuator  70  is started (within a predetermined period from the start of the valve actuator  70 ). That is, torque for actuating the first valve body  60  is stabilized. For example, if the entire first region  191  is curved, it is required to control the machining accuracy (reduce dimensional variation) for the cam  178  with high precision in order to stabilize the force applied to the arm portion  181  in the early stage after the valve actuator  70  is started. The first region  191  including the straight portion  191   a  facilitates the machining of the first region  191  and easily stabilizes the drive torque for the first valve body  60 . 
       FIG. 10  illustrates a cross sectional view of the second gear  176 . As described, the second gear  176  is biased in the direction of the arrow  55  while the air supply valve  150  is closed (also see  FIG. 8 ). A coil spring  196  is arranged at the back surface of the second gear  176 . One end of the coil spring  196  is fixed to a protruding portion  177  on the back surface of the second gear  176 , and another end thereof is fixed to a protruding portion  194  of a housing  190  of the air supply valve  150 . The second gear  176  is biased by the coil spring  196  in the direction of the arrow  55 . Positioning the coil spring  196  between the second gear  176  and the housing  190  prevents the second gear  176  from moving in a direction of the rotation axis. The distance between the magnet  65  and the rotation angle detection sensor (not illustrated) is thereby stabilized and the rotation angle of the second gear  176  can be detected accurately. 
     OTHER EMBODIMENTS 
     The embodiments above describe an example in which one end of the bypass passage is connected to the air supply passage and another end thereof is connected to the air discharge passage and an example in which one end of the bypass passage is connected to the air supply passage at a position upstream of the humidifier and another end thereof is connected to the air supply passage at a position downstream of the humidifier. However, the bypass passage (the other end thereof) may not necessarily be connected as described in the embodiments. What is important in the teachings disclosed herein is that a single air valve (air supply valve) performs the switching among a state in which the air supply passage and the bypass passage are both closed, a state in which the air supply passage is open and the bypass passage is closed, and a state in which the air supply passage is closed and the bypass passage is open. 
     Other important points in the teachings disclosed herein are that the supply valve configured to open and close the air supply passage and the switching valve configured to switch the air supply passage and the bypass passage are actuated by the arm portion fixed at the supply valve and the link mechanism comprising the cam plate fixed at the switching valve, and that the link mechanism comprises the guide portion including the first region where the arm portion moves for the opening-closing movement of the supply valve and the second region where the arm portion moves for the opening-closing movement of the switching valve, wherein the second region is independent from the first region. Thus, the first region and the second region may be adjacent to each other, for example. That is, it is not always necessary to arrange the third region where neither of the opening-closing movement of the supply valve nor the opening-closing movement of the switching valve is performed, between the first region and the second region. Without the third region, the size of the cam plate can be reduced. 
     Other than a coil spring, a biasing member such as a leaf spring, a rubber block, etc. may be used to bias the cam gear (second gear) in the direction in which the cam gear rotates when the supply valve is opened. Alternatively, the biasing member may be omitted and the cam gear may be biased by the motor applying torque in the direction in which the cam gear rotates when the supply valve is opened to the cam gear while the supply valve is closed. Alternatively, the biasing member may be omitted and shape(s) of the cam plate and/or the arm portion may be changed to prevent a positional change of the cam plate and the roller (arm portion) while the air supply valve is closed. 
     The configuration of the cam plate is not limited to those described in the embodiments. For example, the fitting portion configured to fit with the roller (arm potion) when the supply valve is closed, the straight portion of the first region, etc. may be omitted as appropriate. The length of the first region may be longer than the length of the second region to make the actuation speed of the supply valve slower than that of the switching valve. 
     While specific examples of the present disclosure have been described above in detail, these examples are merely illustrative and place no limitation on the scope of the patent claims. The techniques described in the patent claims also encompasses various changes and modifications to the specific examples described above. The technical elements explained in the present specification or drawings provide technical utility either independently or through various combinations. The present disclosure is not limited to the combinations described at the time the claims are filed. Further, the purpose of the examples illustrated by the present specification or drawings is to satisfy multiple objectives simultaneously, and satisfying any one of those objectives gives technical utility to the present disclosure.