Patent Publication Number: US-2005123415-A1

Title: Fluid machine

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a fluid machine that draws fluid into a pump chamber by rotation of a rotor and discharges the fluid out of the pump chamber through an outlet.  
      In a conventional fuel cell system that generates electric power using hydrogen gas and oxidizing gas as reactive gas, water is produced during generation of electric power. To discharge the generated water from the fuel cell, the hydrogen gas and the oxidizing gas are supplied to the fuel cell by an amount greater than a consumption amount required to generate electric power. Therefore, the hydrogen gas discharged from the fuel cell (so called hydrogen off-gas) includes unreacted hydrogen gas. Discharging the unreacted hydrogen gas deteriorates fuel economy of the fuel cell system. Therefore, the hydrogen off-gas is circulated and returned to the fuel cell to improve the fuel economy of the fuel cell system.  
      A fluid machine is used in the fuel cell system as means for forcibly circulating the hydrogen off-gas (see Japanese Laid-Open Patent Publication No. 2003-151592). That is, the fuel cell system of the above publication draws the hydrogen off-gas discharged from the fuel cell to the fluid machine via a condenser, which separates gas from liquid. The machine draws the hydrogen off-gas into a pump chamber and mixes the drawn hydrogen off-gas with new hydrogen gas supplied from a hydrogen tank. The hydrogen off-gas that is mixed with the new hydrogen gas is supplied to an anode of the fuel cell again. The ambient air, which serves as the oxidizing gas, is supplied to a cathode of the fuel cell via another fluid machine.  
      The fluid machine having such a function has been proposed in, for example, Japanese Laid-Open Patent Publication No. 2002-54587. The fluid machine of this Publication is an air pump that supplies air (oxidizing gas) to a fuel cell. The pump includes a motor housing and a pump housing, which are integrally attached to each other. The motor housing defines a motor chamber, which accommodates a motor. The pump housing defines a pump chamber, which accommodates a rotor, which rotates in accordance with rotation of the motor. The motor chamber and the pump chamber are separated by a bottom wall (dividing wall) of the motor housing through which a rotary shaft of the motor extends. A sealing material is provided at a portion of the bottom wall where the rotary shaft is inserted.  
      As described above, a fluid machine (hydrogen pump) for drawing hydrogen gas (hydrogen off-gas) and supplying it to the fuel cell is provided in the fuel cell system besides the fluid machine (air pump) for drawing air and supplying it to the fuel cell. In this case, the fluid machine (hydrogen pump) has substantially the same structure as the fluid machine (air pump) disclosed in Japanese Patent Publication No. 2002-54587 except that the fluid to be drawn and supplied is not air but hydrogen off-gas.  
      However, drawing and supplying hydrogen off-gas with the fluid machine disclosed in Japanese Patent Publication No. 2002-54587 arises the following problems. That is, since the hydrogen off-gas has characteristics to penetrate through metal, the hydrogen off-gas often penetrates through the bottom wall (dividing wall) of the motor housing, which separates the pump chamber from the motor chamber, and enters the motor chamber. Although a sealing material is provided at a portion of the bottom wall of the motor housing where the rotary shaft of the motor is inserted through, a slight gap exists to permit the rotary shaft to rotate. Therefore hydrogen off-gas moves from the pump chamber to the motor chamber through the slight gap.  
      In general, air is sealed in the motor chamber during assembly. Therefore, the oxygen contained in the air in the motor chamber and the hydrogen in the hydrogen off-gas that entered the motor chamber might react and generate water in the motor chamber. If water is generated as described above, members (such as a motor) in the motor chamber might be corroded. As a result, the performance of the fluid machine might deteriorate.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an objective of the present invention to provide a fluid machine that prevents water from being generated in a motor chamber even if fluid that contains hydrogen leaks from a pump chamber to the motor chamber, and prevents the performance of the fluid machine from deteriorating.  
      To achieve the above-mentioned objective, the present invention provides a fluid machine. The machine includes a motor and a motor housing. The motor housing defines a motor chamber for accommodating the motor. The motor chamber is filled with inert gas. A rotor rotates in accordance with rotation of the motor. A pump housing defines a pump chamber for accommodating the rotor. A dividing wall is located between the pump housing and the motor housing. The pump housing and the motor housing are attached to each other via the dividing wall.  
      Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
       FIG. 1  is a plan cross-sectional view illustrating a hydrogen pump according to one embodiment of the present invention; and  
       FIG. 2  is a partially enlarged view of  FIG. 1  explaining the state where hydrogen off-gas enters the motor chamber of the pump shown in  FIG. 1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      One embodiment of the present invention will now be described with reference to  FIGS. 1 and 2 .  
       FIG. 1  shows a hydrogen pump  10 , which is one type of fluid machine used in a fuel cell system. That is, the fluid machine in this embodiment is a fluid pump for fluid including hydrogen. The hydrogen pump  10  of this embodiment is formed by a motor portion M and a pump portion P. The motor portion M includes a substantially cup-shaped motor housing  11 , which has a closed first end (left end in  FIG. 1 ) and an open second end (right end in  FIG. 1 ), and a partition (dividing member)  12 , which is coupled to the motor housing  11  to close the opening. The inner surface of the motor housing  11  and the inner surface of the partition  12  define a motor chamber  13 . The motor chamber  13  is filled with inert gas (such as nitrogen) G.  
      The pump portion P includes a substantially oval cup-shaped pump housing  14 , which has an open first end (left end in  FIG. 1 ) and a bearing block (dividing member)  16 , which is coupled to the pump housing  14  with bolts  15  to close the opening. The inner surface of the pump housing  14  and the inner surface of the bearing block  16  define a pump chamber  17 . In this embodiment, the partition  12  and the bearing block  16  form a dividing wall. The motor housing  11  is open toward the dividing wall and the pump housing  14  is open toward the dividing wall. The dividing wall closes the motor housing  11  and the pump housing  14 .  
      A substantially oval cup-shaped gear housing  18  is secured to a second end (right end in  FIG. 1 ) of the pump housing  14  of the pump portion P with bolts (not shown). The gear housing  18  is smaller than the pump housing  14 . The outer surface of the second end of the pump housing  14  and the inner surface of the gear housing  18  define a gear chamber  19 . The outer surface of the partition  12  and the outer surface of the bearing block  16  are secured to each other with bolts (not shown) so that the motor portion M is integrated with the pump portion P. An O-ring  20  is arranged between the motor housing  11  and the partition  12 , the pump housing  14  and the bearing block  16 , the pump housing  14  and the gear housing  18 , and the partition  12  and the bearing block  16  as a sealing member to keep the interior sealed from the outside.  
      A bearing  22  is located at a bottom portion  21  of the motor housing  11 . The bearing  22  is coaxial with the motor housing  11  and faces the interior of the motor chamber  13 . The bearing  22  rotatably supports a first end (left end in  FIG. 1 ) of a drive shaft (rotary shaft)  23 . A second end of the drive shaft  23  extends to the interior of the gear chamber  19  through a through hole  12   a  formed in the partition  12 , a through hole  16   a  formed in the bearing block  16 , and a through hole  24   a  formed in a bottom portion  24  of the pump housing  14 .  
      The second end of the drive shaft  23  is rotatably supported by a bearing  25  located at the bottom portion  24  of the pump housing  14 , and the middle portion of the drive shaft  23  is rotatably supported by a bearing  26  provided in the bearing block  16 . A motor rotor  27  is secured to the drive shaft  23  in the motor chamber  13 . A motor stator  28  is secured to the motor housing  11  such that the motor stator  28  is located on the outer circumferential side of the motor rotor  27 . The motor rotor  27  and the motor stator  28  form an electric motor  29 .  
      A driven shaft  30 , which is parallel to the drive shaft  23 , is located in the pump chamber  17  of the pump portion P. The ends of the driven shaft  30  are rotatably supported by a bearing  31  provided in the bottom portion  24  of the pump housing  14  and a bearing  32  provided in the bearing block  16 . A two-blade drive rotor  33  and a two-blade driven rotor  34  are secured to the drive shaft  23  and the driven shaft  30  in the pump chamber  17 , respectively. A second end (right end) of the driven shaft  30  extends to the interior of the gear chamber  19  through the bottom portion  24  of the pump housing  14  in the same manner as the second end (right end) of the drive shaft  23 . A drive gear  35  secured to the second end of the drive shaft  23  and a driven gear  36  secured to the second end of the driven shaft  30  engage with each other in the gear chamber  19 .  
      A seal ring (sealing material)  37  is located in the bearing block  16  next to the bearing  26  on the side facing the drive rotor  33  to seal the gap between the drive shaft  23  and the bearing block  16 . The seal ring  37  is located between the inner surface of the through hole  16   a  and the drive shaft  23 . In the same manner, a seal ring (sealing material)  37  is located in the bearing block  16  next to the bearing  32  on the side facing the driven rotor  34  to seal the gap between the driven shaft  30  and the bearing block  16 . In this embodiment, a seal ring  37  is also located in the bottom portion  24  of the pump housing  14  next to the bearing  25  on the side facing the drive rotor  33  to seal the gap between the drive shaft  23  and the pump housing  14 . In the same manner, a seal ring (sealing material)  37  is located in the bottom portion  24  of the pump housing  14  next to the bearing  31  on the side facing the driven rotor  34  to seal the gap between the driven shaft  30  and the pump housing  14 .  
      The hydrogen pump  10  is placed such that an imaginary plane that includes the axes of the drive shaft  23  and the driven shaft  30  is horizontal. An inlet (not shown) is formed in the ceiling of the pump housing  14  of the pump portion P to draw hydrogen off-gas discharged from the fuel cell, which is not shown, into the pump chamber  17 . An outlet  38  is formed in the bottom portion of the pump chamber  17  to discharge the hydrogen off-gas drawn by the rotation of the rotors  33 ,  34  from the pump chamber  17 . Therefore, the hydrogen off-gas drawn into the pump chamber  17  from the inlet is discharged through the outlet  38  and supplied to the fuel cell again. As described above, the hydrogen pump  10  repeats drawing and supplying operation in which hydrogen off-gas is drawn into the pump chamber  17  and then discharged.  
      The operation of the hydrogen pump (fluid machine)  10  constituted as described above will now be described. The operation performed when hydrogen off-gas in the pump chamber  17  enters the motor chamber  13  will mainly be discussed below.  
      In a case where the hydrogen pump  10  repeats the drawing and supplying operation of hydrogen off-gas as described above, part of the hydrogen off-gas drawn into the pump chamber  17  from the inlet might enter the motor chamber  13  via the through hole  16   a  of the bearing block  16  and the through hole  12   a  of the partition  12  as shown in  FIG. 2 . That is, although the seal ring  37  is located in the through hole  16   a  of the bearing block  16 , a slight gap is formed between the seal ring  37  and the drive shaft  23  to permit the drive shaft  23  to rotate.  
      A gap is also formed between the through hole  12   a  of the partition  12  and the circumferential surface of the drive shaft  23  to permit the drive shaft  23  to rotate. Therefore, the hydrogen off-gas drawn into the pump chamber  17  might enter the motor chamber  13  through the gaps. Since the hydrogen gas (hydrogen off-gas) has the characteristics to penetrate through metal, the hydrogen off-gas might penetrate through the bearing block  16  and the partition  12 , which are made of metal material (for example, aluminum alloy), and enter the motor chamber  13 .  
      However, in this embodiment, since the motor chamber  13  is filled with inert gas (nitrogen) G, that is, there is no residual air (oxidizing gas), the hydrogen off-gas that entered the motor chamber  13  does not generate water by a reaction with the air (oxidizing gas). Therefore, even if hydrogen off-gas enters the motor chamber  13 , water is not generated by a reaction with air (oxidizing gas). Therefore, members such as electric motor  29  in the motor chamber  13  are prevented from corroding. As a result, the performance of the hydrogen pump  10  is prevented from deteriorating.  
      The inert gas (nitrogen) G in the motor chamber  13  is prevented from leaking into the pump chamber  17  by the seal ring  37  located in the through hole  16   a  of the bearing block  16 . The O-rings  20 , which function as the sealing members, prevent the inert gas (nitrogen) G from leaking outside from the contact portion between the motor housing  11  and the partition  12  and the contact portion between the partition  12  and the bearing block  16  passing through the through hole  12   a  of the partition  12 . The O-rings  20  further prevent water from entering the motor chamber  13  from the contact portion between the motor housing  11  and the partition  12  and the contact portion between the partition  12  and the bearing block  16 .  
      The preferred embodiment has the following advantages.  
      (1) Even if hydrogen off-gas enters the motor chamber  13  from the pump chamber  17 , the motor chamber  13  is filled with inert gas (nitrogen) G, that is, there is no air (oxidizing gas). Therefore, water is not generated in the motor chamber  13  by a reaction between hydrogen and air. Accordingly, the members such as the electric motor  29  in the motor chamber  13  are prevented from being corroded by water, and the performance of the hydrogen pump  10  is reliably prevented from deteriorating.  
      (2) Since the diffusion velocity of nitrogen that fills the motor chamber  13  as the inert gas G is slower (about ⅓) than that of the air, the nitrogen does not leak from the motor chamber  13  easily. Therefore, the performance of the hydrogen pump  10  is maintained for a long period.  
      (3) The sealing material, which is the seal ring  37  in this embodiment, is located in the through hole  16   a  of the bearing block  16  through which the drive shaft  23  extends. Therefore, the seal ring  37  reliably prevents inert gas G in the motor chamber  13  from leaking into the pump chamber  17  through where (through hole  16   a ) the drive shaft  23  extends in the bearing block  16 .  
      (4) The sealing member, which is the O-ring  20  in this embodiment, is located at the contact portion between the motor housing  11  and the partition  12 . Therefore, the inert gas G in the motor chamber  13  is reliably prevented from leaking outside from the contact portion between the motor housing  11  and the partition  12 . The O-ring  20  also prevents water from entering the motor chamber  13  via the contact portion from the outside.  
      (5) The sealing member, which is the O-ring  20  in this embodiment, is located at the contact portion between the partition  12  and the bearing block  16 . Therefore, the inert gas G in the motor chamber  13  is reliably prevented from leaking outside from the contact portion between the partition  12  and the bearing block  16 . The O-ring  20  also prevents water from entering the motor chamber  13  via the contact portion from the outside.  
      The invention may be embodied in the following forms.  
      In the preferred embodiment, the dividing wall is formed by the partition (dividing member)  12 , which closes the opening of the motor housing  11 , and the bearing block (dividing member)  16 , which closes the opening of the pump housing  14 . However, the dividing wall may be formed by only the bearing block  16 . In this case, the bearing block  16  closes the opening of the motor housing  11  and the opening of the pump housing  14 .  
      In the preferred embodiment, the O-ring  20  is used as the sealing member located at the contact portion between the motor housing  11  and the partition  12 . However, the sealing member other than the O-ring  20  may be used as long as the sealing member prevents inert gas G from leaking outside via the contact portion and water from entering via the contact portion.  
      In the preferred embodiment, the sealing material, which is the seal ring  37 , is located in the through hole  16   a  of the bearing block  16 . However, the seal ring  37  may be located in the through hole  12   a  of the partition  12 .  
      In the preferred embodiment, the motor chamber  13  is filled with the inert gas G, which is nitrogen. However, any inert gas other than nitrogen (for example, argon, helium, neon, xenon, and krypton) may be used as long as the inert gas does not react with hydrogen and generate water. The motor chamber  13  may be filled with mixed gas (for example, nitrogen and neon) that is the mixture of several types of inert gases G.  
      In the preferred embodiment, the present invention is embodied in the hydrogen pump  10 , which circulates hydrogen gas (hydrogen off-gas) in the fuel cell system. However, the present invention may be embodied in any fluid machine (hydrogen pump) other than that used in the fuel cell system as long as the fluid machine draws and supplies fluid that includes hydrogen.  
      The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.