Patent Publication Number: US-11655827-B2

Title: Pump device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. § 371 U.S. National Stage Entry application claiming priority to PCT Patent Application No. PCT/JP2019/036338 filed Sep. 17, 2019, which claims priority to Japanese Patent Application No. 2018-178686 filed Sep. 25, 2018, each of which is hereby incorporated herein by reference in its entirety for all purposes. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     The present disclosure relates generally to pump devices, and more particularly, to pump devices for pumping gas. 
     Japanese Unexamined Patent Publication No. 2012-17712 discloses a conventional pump device for pumping gas. The pump device comprises a motor portion with a rotor rotatably disposed in a rotor chamber. The pump device also includes a pump portion with an impeller rotatably disposed in a pump chamber and coupled to the rotor. 
     BRIEF SUMMARY 
     An object to be solved by the present disclosure is to provide a pump device configured to suppress grease loss from the bearing with a simple and inexpensive configuration. 
     Another object to be solved by the present disclosure is to provide a pump device configured to improve the drainage property of the pump chamber, thereby reducing the likelihood of impeller malfunction due to freezing. 
     The above-mentioned objects can be achieved by embodiments described herein. 
     A first embodiment of the present disclosure is a pump device for pumping a gas. The pump device comprises a motor portion including a rotor rotatably disposed in a rotor chamber and a pump portion including an impeller rotatably disposed in a pump chamber and coupled to the rotor. A bearing rotatably supports a rotor shaft of the rotor and is injected with a grease. The bearing is provided in a partition wall separating the rotor chamber from the pump chamber. At least two breathing passages that interconnect the rotor chamber and the pump chamber are formed in the partition wall. 
     According to the first embodiment, a circulation flow passage flows from the pump chamber to the rotor chamber and back to the pump chamber, and is formed by at least two breathing passages provided in the partition wall separating the rotor chamber from the pump chamber. Since gas flows preferentially through the circulation flow passage that bypasses the bearing, grease loss from the bearing may be suppressed. Also, unlike the pump device according to Japanese Unexamined Patent Publication No. 2012-17712, since a suction device is not required, grease loss from the bearing may be suppressed with a simple and inexpensive configuration. 
     A second embodiment of the present disclosure is a pump device for pumping a gas. The pump device comprises a motor portion including a rotor rotatably disposed in a rotor chamber, and a pump portion including an impeller rotatably disposed in a pump chamber and coupled to the rotor. A discharge port of the pump chamber is positioned on a lower side of the pump chamber in a vehicle mounted state. The bottom surface of the downstream end of the discharge port is positioned lower than the bottom surface of the upstream end of the discharge port. 
     According to the second embodiment, a liquid in the pump chamber is configured to be discharged from the discharge port by naturally flowing downwardly. Therefore, the drainage performance of the pump chamber is improved. Additionally, the likelihood of malfunction of the impeller due to freezing may be suppressed. 
     According embodiments of pump devices of the present disclosure, grease loss from the bearing can be suppressed with a simple and inexpensive configuration. 
     According to embodiments of pump devices of the present disclosure, the drainage performance of the pump chamber may be improved and a malfunction of the impeller due to freezing can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a front view of a centrifugal pump according to a first embodiment. 
         FIG.  2    is a cross-sectional view of the centrifugal pump of  FIG.  1    taken along line II-II in  FIG.  1   , wherein the centrifugal pump includes a second casing. 
         FIG.  3    is an enlarged partial view of the cross-section of the centrifugal pump in  FIG.  2    showing a main part of the centrifugal pump. 
         FIG.  4    is a partial cross-sectional, front view of the centrifugal pump of  FIG.  1    showing the second casing. 
         FIG.  5    is a cross-sectional view of the second casing of  FIG.  4    taken along line V-V in  FIG.  4   . 
         FIG.  6    is an enlarged, partial cross-sectional view showing a main part of a centrifugal pump according to a second embodiment. 
         FIG.  7    is an enlarged, partial cross-sectional view showing a main part of a centrifugal pump according to a third embodiment. 
         FIG.  8    is an enlarged, partial cross-sectional view showing a main part of a centrifugal pump according to a fourth embodiment. 
         FIG.  9    is a partial, cross-sectional front view of a second casing according to a fifth embodiment. 
         FIG.  10    is a cross-sectional view of a main part of a centrifugal pump according to a sixth embodiment. 
         FIG.  11    is a cross-sectional view of a main part of a centrifugal pump according to a seventh embodiment. 
         FIG.  12    is a cross-sectional view of a main part of a centrifugal pump according to an eighth embodiment. 
         FIG.  13    is a cross-sectional view of a main part of a centrifugal pump according to a ninth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In Japanese Unexamined Patent Publication No. 2012-17712, a bearing comprising a ball bearing, which rotatably supports the rotor shaft, is provided in a partition wall separating the rotor chamber from the pump chamber. Lubricating grease is supplied into the bearing. A communication hole in the partition wall interconnects the rotor chamber and the pump chamber. A flow of gas from the pump chamber to the inside of the rotor chamber via the communication hole is generated by the operation of a suction device that reduces pressure inside of the rotor chamber. This allows for the suppression of grease loss. Inclusion of the suction device increases costs, however, if the suction device is omitted, a circulation flow passage from the pump chamber to the rotor chamber and back to the pump chamber is formed by a communication gap between the bearing members and the communication hole in the partition wall. The circulation flow passage may enhance the likelihood of grease loss when gas passes through the bearing. 
     In Japanese Unexamined Patent Publication No. 2012-17712, it is not assumed that the pump device is mounted on a vehicle. Therefore, when the pump device is mounted on the vehicle, liquid, such as water generated due to dew condensation or the like, may remain in the pump chamber. This may cause the impeller to malfunction, for instance due to freezing. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. 
     In a first embodiment, for example, a centrifugal pump used as a purge pump mounted on a vehicle such as an automobile will now be described. The purge pump can increase the flow rate of a purge gas flowing from a canister to an intake passage of an internal combustion engine (an engine).  FIG.  1    is a front view showing the centrifugal pump.  FIG.  2    is a cross-sectional view taken along line II-II in  FIG.  1   .  FIG.  3    is a cross-sectional view showing a main part of the centrifugal pump. The directions in the figures show the vertical direction, right-left direction, and front-rear direction of the centrifugal pump. The vertical direction corresponds to the top-and-bottom direction based on the direction of gravity when the centrifugal pump is mounted to a vehicle (i.e., in a vehicle mounted state). The left-right direction and the front-rear direction do not limit the arrangement direction of the centrifugal pump. The centrifugal pump may also be referred to as a “pump device” in the present disclosure. 
     As shown in  FIG.  2   , a centrifugal pump  10  includes a pump portion  12  and a motor portion  14  coupled end-to-end in the axial direction (the front-back direction). A casing  16  of the centrifugal pump  10  includes a first casing  18 , a second casing  20 , and a third casing  22 , which are coupled end-to-end in the axial direction to form the casing  16 . 
     The first casing  18  and the second casing  20  may be fastened together by, for example, a plurality of screws. The second casing  20  and the third casing  22  may be fastened together by, for example, a plurality of screws. An O-ring (not shown) for sealing between the first casing  18  and the second casing  20  may be interposed therebetween. An O-ring (not shown) for sealing between the second casing  20  and the third casing  22  may be interposed therebetween. The first to third casings  18 ,  20 ,  22  may be made of, for example, resin. 
     The motor portion  14  can be a brushless motor including a stator  30  and a rotor  32 . A motor casing defining a rotor chamber  34  has a hollow cylindrical shape and y is formed by the second casing  20  and the third casing  22 . The third casing  22  includes a cylindrical wall part  36 , a cylindrical extension part  37 , and a rear end wall part  38 . The cylindrical wall part  36  has a cylindrical shape and extends in the front-rear direction. The cylindrical extension part  37  extends backward from an inner periphery of the rear end of the cylindrical wall part  36 . The rear wall part  38  closes the rear end opening of the cylindrical extension part  37 . A stepped recessed  39  is formed on the inner periphery of the front-end of the cylindrical wall part  36 . A retainer  40 , which has a cylindrical shape and is made of metal, is positioned inside the extension cylinder part  37 . 
     The stator  30  is embedded in the cylindrical wall part  36  by insert molding. The stator  30  may be completely covered with the resin the forms the cylinder wall part  36 . The stator  30  may be provided with, for example, a stator core and a stator coil, and may be formed in an annular shape. 
     The second casing  20  generally has an annular plate shape. The second casing  20  includes a boss part  42  having a hollow cylindrical shape and being concentrically formed in the center part of the rear surface of the second casing  20 . As shown in  FIG.  3   , a shaft hole  43  extends axially through the boss part  42 . The boss part  42  is fit into the front-end part of the cylindrical wall part  36  of the third casing  22  with a predetermined gap therebetween. 
     An annular projection  46  extends circumferentially about the boss part  42  at a predetermined radial distance therefrom and is concentrically disposed on the rear surface of the second casing  20 . The annular projection  46  may have a square cross section. The annular projection  46  is into the front end opening of the stepped recessed part  39  of the third casing  22 . 
     As shown in  FIG.  2   , the rotor  32  is rotatably disposed in the rotor chamber  34 . The rotor  32  includes a rotor shaft  48  and permanent magnets  50 . The rotor shaft  48  may be made of, for example, a metal, and may be composed of a solid shaft. The permanent magnets  50  are positioned at a center of the rotor shaft  48  in the axial direction and define a plurality of circumferentially arranged magnetic poles. A front-end part of the rotor shaft  48  is rotatably supported within the boss part  42  of the second casing  20  by a bearing  52 . 
     As shown in  FIG.  3   , the bearing  52  is a ball bearing including an outer ring  53 , an inner ring  54 , and balls  55  positioned between rings  53 ,  54 . In this embodiment, the inner ring  54  is press-fitted into the rotor shaft  48  from the front, and the outer ring  53  is press-fitted into the boss part  42  in the second casing  20  from the rear. A front-end part of the rotor shaft  48  defines an end part on an output side and is inserted into a center part of the boss part  42  of the second casing  20 . 
     As shown in  FIG.  2   , the rear end of the rotor shaft  48  is rotatably supported within the retainer  40  of the third casing  22  by an auxiliary bearing  57 . The auxiliary bearing  57  is a ball bearing and includes an outer ring, an inner ring, and balls disposed between the outer ring and the inner ring. The inner ring is fixed to the rotor shaft  48  and the outer ring is clearance-fitted in the retainer  40 . A detent mechanism for stopping rotation of the outer ring may be provided between the third casing  22  and the outer ring of the auxiliary bearing  57 . 
     A control circuit (not shown) for controlling power supply to the stator  30  may be provided on the rear side of the third casing  22 . An external connector connected to an external power source may be connected to a connector part (not shown) formed in the third casing  22 . The motor portion  14  may be driven by electric power supplied from an external power source. 
     As shown in  FIG.  2   , the pump portion  12  includes an impeller  62  is coupled to and rotated by the motor portion  14 . The portions of the pump casing that form a pump chamber  64  include the first casing  18  and the second casing  20 . The pump chamber  64  has a hollow cylindrical shape that is short in the axial direction. An intake port  66 , which has a hollow cylindrical shape and projects forward, is formed in the central part of the first casing  18 . An intake opening  67 , which provides fluid communication between the inside and the outside of the pump chamber  64 , is formed inside the intake port  66 . 
     The first casing  18  has a short cylindrical shape that opens the rear surface. An annular flow passage groove  69  is disposed along the outer periphery of the pump chamber  64  and is concentrically formed at the rear surface of the front wall of the first casing  18  (the surface on the pump chamber  64  side). The flow passage groove  69  has a substantially semicircular cross-sectional shape.  FIG.  4    is a front view showing the second casing  20 .  FIG.  5    is a cross-sectional view taken along line V-V in  FIG.  4   . 
     As shown in  FIG.  4   , an annular wall  72  is concentrically formed on the front side of the second casing  20 . As shown in  FIG.  5   , the annular wall  72  has a square crosssectional shape. As shown in  FIG.  2   , the outer peripheral part of the annular wall  72  is fit into the inner peripheral part of the first casing  18 . The second casing  20  may also be referred to as the “partition wall” in the present disclosure. 
     As shown in  FIG.  1   , a discharge port  74  having a hollow cylindrical shape is formed at the lower end of the first casing  18 . The discharge port  74  projects outward from the outer periphery of the first casing  18  in a tangential direction, that is, outward in a clockwise direction when viewed from the front. A discharge opening  75  is provided inside the discharge port  74 . As shown in  FIG.  2   , the discharge opening  75  extends in the tangential direction of the flow passage groove  69 . The upstream end of the discharge opening  75  is in fluid communication with the lower end of the pump chamber  64 . A bottom surface of the upstream end  75   a  of the discharge opening  75  is connected to a lower end of an outer periphery of the pump chamber  64 . 
     As shown in  FIG.  1   , the discharge opening  75  is disposed on the lower side, in the vertical direction, in the state where the centrifugal pump  10  is mounted on a vehicle. A bottom surface of the downstream end  75   b  of the discharge opening  75  is located at a position lower than the bottom surface of the upstream end  75   a  of the discharge opening  75 . The bottom surface of the discharge opening  75  may be inclined obliquely downward from the bottom surface of the upstream end  75   a  toward the bottom surface of the downstream end  75   b.    
     As shown in  FIG.  2   , the impeller  62  is rotatably housed in the pump chamber  64 . The impeller  62  includes a substrate part  77 , a cylindrical shaft part  79 , and a plurality of blade parts (not shown). The substrate part  77  has a disc-shape. The cylindrical shaft section  79  has a hollow cylindrical shape, and is formed concentrically on the rear surface of the substrate part  77 . The blade parts may be formed at predetermined circumferential intervals and may radiate from the center section of the front surface of the substrate part  77 . The substrate part  77  is positioned within the annular wall  72  of the second casing  20 . As shown in  FIG.  3   , the cylindrical shaft part  79  is rotatably disposed in the shaft hole  43  of the second casing  20 . 
     A front end of the rotor shaft  48  is fit into the cylindrical shaft part  79  of the impeller  62 . Accordingly, the impeller  62  rotates integrally with the rotor  32 . A slight gap may be set between the opposed surfaces of the substrate part  77  of the impeller  62  and the second casing  20 . 
     The motor portion  14  may be driven by electric power supplied from an external power source. Then, the impeller  62  rotates together with the rotor  32 , so that the purge gas can be taken in through the intake opening  67  and sent to the pump chamber  64 . The purge gas may be pressurized by the rotation of the impeller  62 , and then discharged from the discharge opening  75 . In this way, purge gas may be pumped by the centrifugal pump  10 . 
     As shown in  FIGS.  3  to  5   , two linear communication holes  81  provide fluid communication between the rotor chamber  34  and the pump chamber  64  formed in the second casing  20 . Each communication hole  81  has a front end opening  81   a , which opens in the vicinity of the shaft hole  43  on the front surface of the second casing  20  on the pump chamber  64  side, and a rear end opening  81   b  opposite to the front end opening  81   a.    
     As shown in  FIG.  4   , the front end opening  81   a  and the rear end opening  81   b  of each communication hole  81  are arranged so as to be aligned along the radial direction of the second casing  20 . The two communication holes  81  may be arranged at a position higher than the rotor shaft  48  (e.g., in the vertical direction). That is, the front end opening  81   a  of both communication holes  81  may be arranged at a position higher than a center axis of the rotor shaft  48  (e.g., in the vertical direction). Both communication holes  81  may be angularly spaced apart from each other by about 90° about the axis  20 L of the second casing  20 . Thus, the front end opening  81   a  of both communication holes  81  may be arranged at a position adjacent to each other. The communication hole  81  may also be referred to as a “breathing passage” in the present disclosure. In addition, the phrase “positioned adjacent to each other” in the present disclosure refers to, for example, a position where the shortest distance between the front-end openings  81   a  of the adjacent communication holes  81  is equal to or less than the diameter of the shaft hole  43 . 
     According to the first embodiment, the circulation flow passage, which flows from the pump chamber  64  to the rotor chamber  34  and back to the pump chamber  64 , is formed by both communication holes  81  in the second casing  20  partitioning the rotor chamber  34  and the pump chamber  64 . That is, one of the communication holes  81  may serve as a flow passage from the pump chamber  64  to the rotor chamber  34 , and the other communication hole  81  may serve as a flow passage from the rotor chamber  34  to the pump chamber  64 . Therefore, since the gas flows preferentially through the circulation flow passage that bypasses the bearing  52 , grease loss from the bearing  52  may be suppressed. Also, unlike the pump device according to Japanese Unexamined Patent Publication No. 2012-17712, since the suction device is not required, grease loss from the bearing  52  may be suppressed with a relatively simple and inexpensive configuration. 
     The front-end openings  81   a  of both communication holes  81  are arranged at positions adjacent to each other. Therefore, the pressure difference between both communication holes  81  may be reduced, thereby offering the potential to further suppress the grease loss from the bearing  52 . 
     The discharge opening  75  of the pump chamber  64  is disposed on the lower side (in the vertical direction) of the pump chamber  64  in the vehicle mounted state. The bottom surface of the downstream end  75   b  of the discharge opening  75  is disposed at a position lower than the bottom surface of the upstream end  75   a  of the discharge opening  75 . Therefore, the liquid in the pump chamber  64  may be discharged from the discharge opening  75  by naturally flowing downward. As a result, the liquid discharge property of the pump chamber  64  may be improved, thereby suppressing the malfunction of the impeller  62  due to freezing. 
     The front end openings  81   a  of both communication holes  81  are disposed at a position higher than the rotor shaft  48 . Therefore, liquid such as water generated by dew condensation or the like in the pump chamber  64  may be prevented from entering the rotor chamber  34  via the communication hole  81 . As a result, deterioration of the durability of the motor portion  14  may be improved. 
     Since a second embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  6    is a cross-sectional view showing a main part of a centrifugal pump according to the second embodiment. As shown in  FIG.  6   , in the second embodiment, the distance R 1  from the central axis  20 L of the second casing  20  to the center of the front end opening  81   a  of the communication hole  81  on one side (upper side in  FIG.  6   ) of the axis  20 L and the distance R 2  from the central axis  20 L of the second casing  20  to the center of the front end opening  81   a  of the other communication hole  81  may be set as different distances. That is, the distances R 1  and R 2  may be set to R 1  is greater than R 2 . 
     Since a third embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  7    is a cross-sectional view showing a main part of a centrifugal pump according to the third embodiment. As shown in  FIG.  7   , in the third embodiment, a front end opening  82   a  of a communication hole  82  on one side (upper side in  FIG.  7   ) is opened to the shaft hole  43  of the second casing  20 . The front end opening  82   a  is positioned on the shaft hole  43  located at the front side of the bearing  52  (the pump chamber  64  side). According to the third embodiment, a breathing passage  85  is formed by: the communication hole  82  on one side, and a gap between the shaft hole  43  in the second casing  20  and the cylindrical shaft part  79  of the impeller  62 . 
     According to the third embodiment, the breathing passage  85  communicates with a portion of the pump chamber  64  on the lowest pressure side of the pump chamber  64 . Further, the front end opening  81   a  of the communication hole  81  is also opened to the shaft hole  43  of the second casing  20  at the front side of the bearing  52 . 
     Since a fourth embodiment is a modification of the third embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  8    is a cross-sectional view showing a main part of a centrifugal pump according to the fourth embodiment. As shown in  FIG.  8   , in the fourth embodiment, a communication groove  87  extends linearly from the front end opening  82   a  of the communication hole  82  toward the pump chamber  64  and is formed on the inner periphery of the shaft hole  43  of the second casing  20 . According to the fourth embodiment, a breathing passage  89  is formed by: the communication hole  82  on one side, a gap between the shaft hole  43  of the second casing  20  and the cylindrical shaft part  79  of the impeller  62 , and the communication groove  87 . 
     When the opening areas of the communication hole  81  and the communication groove  87  are set to be the same or substantially the same, the system is effective at suppressing grease loss from the bearing  52 . In another embodiment, the communication hole  81  may have the same configuration as the breathing passage  89 . 
     Since a fifth embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  9    is a front view showing a second casing according to the fifth embodiment. As shown in  FIG.  9   , in the fifth embodiment, both communication holes  81  are located at a position lower than the rotor shaft  48 . According to the fifth embodiment, any liquid that is about to accumulate in either of communication holes  81  may be discharged by naturally flowing down. 
     Since a sixth embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  10    is a cross-sectional view showing a main part of a centrifugal pump according to the sixth embodiment. As shown in  FIG.  10   , a guide recess  92  is formed at the lower end of the annular wall  72  of the second casing  20 . The guide recess  92  has a guide surface  93 , which is inclined obliquely downward from the rear side to the front side. A passage area at the rear surface of the impeller  62  at the lower end of the pump chamber  64  is enlarged by the guide recess  92 . The guide surface  93  of the guide recess  92  may guide the liquid at the rear surface of the impeller  62  toward the discharge opening  75 . 
     According to the sixth embodiment, the surface tension of the liquid accumulated on the rear surface side of the impeller  62  at the lower end of the pump chamber  64  may be reduced due to the guide recess  92 . Accordingly, the liquid may quickly and naturally flow down toward the discharge opening  75 . As a result, the drainage performance of the pump chamber  64  may be further improved. 
     Since a seventh embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  11    is a cross-sectional view showing a main part of a centrifugal pump according to the seventh embodiment. As shown in  FIG.  11   , a guide recess  95  is formed on the inner periphery of the lower end of the annular wall  72  of the second casing  20 . A rear surface  96  of the guide recess  95  is formed along the same plane as the front surface of the second casing  20 . The passage area at the rear side of the impeller  62  at the lower end of the pump chamber  64  is enlarged by the guide recess  95 . A lower surface  97  of the guide recess  95  is horizontally oriented. The lower surface  97  of the guide recess  95  may guide the liquid at the rear surface of the impeller  62  toward the discharge opening  75 . 
     According to the seventh embodiment, the surface tension of the liquid accumulated at the rear surface of the impeller  62  at the lower end of the pump chamber  64  may be reduced due to the guide recess  95 . Accordingly, the liquid may quickly and naturally flow down toward the discharge opening  75 . As a result, the drainage performance of the pump chamber  64  may be further improved. 
     Since an eighth embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  12    is a cross-sectional view showing a main part of a centrifugal pump according to the eighth embodiment. As shown in  FIG.  12   , a guide groove  100  extends through the annular wall  72  of the second casing  20  in the vertical direction at the lower end of the annular wall  72 . The passage area at the rear surface of the impeller  62  at the lower end of the pump chamber  64  is enlarged by the guide groove  100 . A liquid reservoir  102 , which has a recessed shape, is formed at the lower end of the outer peripheral surface of the pump chamber  64  of the first casing  18 . The liquid reservoir  102  is positioned at a lower end of the pump chamber  64 . The liquid reservoir  102  has a bottom lower than the bottom surface of the upstream end  75   a  of the discharge opening  75 . 
     According to the eighth embodiment, the surface tension of the liquid accumulated at the rear surface of the impeller  62  at the lower end of the pump chamber  64  may be reduced due to the guide groove  100 . Accordingly, the liquid may quickly and naturally flow down. Further, the liquid flowing down from the rear surface of the impeller  62  at the lower end of the pump chamber may be discharged to the discharge opening  75  or may accumulate in the liquid reservoir  102 . 
     Since a ninth embodiment is a modification of the first embodiment, the modified parts will be described, and the substantially duplicate description will be omitted.  FIG.  13    is a cross-sectional view showing a main part of a centrifugal pump according to the ninth embodiment. As shown in  FIG.  13   , in the ninth embodiment, a horizontal member  104 , which lays horizontally in the circumferential direction, is formed at the front upper corner of the guide groove  100 . A partition  106  is provided between the horizontal member  104  and the second casing  20 , so as to partition the space between the horizontal member  104  and the second casing  20  into a plurality of spaces in the circumferential direction. 
     According to the ninth embodiment, the guide groove  100  is provided with the horizontal member  104  and the partition  106 . Accordingly, a pressure drop from the pump chamber  64  to the liquid reservoir  102  may be suppressed. In other embodiments, the partitions  106  may be omitted. 
     The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the present disclosure. For example, the pump device of the present disclosure may be applied to a pump device used for pumping a gas other than a purge gas such as air. The present disclosure may also be applied to a pump device other than a centrifugal pump. Further, the brushless motor of the motor portion  14  may be replaced with a bushed motor. The number of breathing passages may be increased to three or more. The shape and/or arrangement of the breathing passages may be modified as appropriate. 
     In the present disclosure, various aspects and embodiments are disclosed. A first aspect is a pump device for pumping a gas. The pump device comprises a motor portion in which a rotor is provided in a rotor chamber in a rotatable manner, and a pump portion in which an impeller coupled to the rotor is provided in a pump chamber in a rotatable manner. A bearing, which rotatably supports a rotor shaft of the rotor and is injected with a grease, is provided in a partition wall separating the rotor chamber from the pump chamber. At least two breathing passages that interconnect the rotor chamber and the pump chamber are formed in the partition wall. 
     According to the first aspect, a circulation flow passage, which flows from the pump chamber to the rotor chamber and back to the pump chamber, is formed by the at least two breathing passages provided in the partition wall separating the rotor chamber from the pump chamber. Therefore, since a gas preferentially flows through the circulation flow passage that bypasses the bearing, grease loss from the bearing may be suppressed. Also, unlike the pump device according to Patent Document 1, since a suction device is not required, grease loss from the bearing may be suppressed with a simple and inexpensive configuration. 
     A second aspect is a pump device according to the first aspect, wherein openings at the pump chamber side of the at least two breathing passages may be arranged adjacent to each other. 
     According to the second aspect, a pressure difference between the at least two breathing passages may be reduced, thereby further suppressing the loss of grease from the bearing. 
     A third aspect is a pump device according to the first or second aspect, wherein the opening on the pump chamber side of at least one of the breathing passages may be open to a shaft hole. The rotor shaft penetrates the shaft hole and the shaft hole is positioned at the pump chamber side of the bearing. 
     According to the third aspect, at least one breathing passage may communicate with a position on a lowest pressure side of the pump chamber. 
     A fourth aspect is a pump device according to any one of the first to third aspects, wherein a discharge opening of the pump chamber may be arranged on a lower side of the pump chamber in a vertical direction of the pump chamber, the vertical direction corresponding to the pump device in a vehicle mounted state. The bottom surface of the downstream end of the discharge opening may be arranged at a position lower than the bottom surface of the upstream end of the discharge opening. 
     According to the fourth aspect, liquid in the pump chamber may be discharged from the discharge opening by naturally flowing down. As a result, the drainage property of the pump chamber may be improved, and the malfunction of the impeller due to freezing may be suppressed. 
     A fifth aspect is a pump device according to the fourth aspect, wherein the opening on the pump chamber side of the at least two breathing passages may be located at a position higher than the rotor shaft. 
     According to the fifth aspect, liquid in the pump chamber may be prevented from entering the rotor chamber via the breathing passages. Therefore, a decrease in durability of the motor portion may be improved. 
     A sixth aspect is a pump device for pumping gas, which may include a motor portion in which a rotor is provided in a rotor chamber in a rotatable manner, and a pump portion in which an impeller coupled to the rotor is provided in a pump chamber in a rotatable manner. A discharge port of the pump chamber is arranged on a lower side of the pump chamber in a vertical direction of the pump chamber, the vertical direction corresponding to the pump device being in a vehicle mounted state. The bottom surface of a downstream end of the discharge port is arranged at a position lower than the bottom surface of an upstream end of the discharge port. 
     According to the sixth aspect, a liquid in the pump chamber may be capable of being discharged from the discharge port by naturally flowing down. Therefore, drainage performance of the pump chamber can be improved, and malfunction of the impeller due to freezing may be suppressed. 
     A seventh aspect is a pump device according to the sixth aspect, wherein a guide recess, which guides a liquid at the rear surface of the impeller toward the discharge opening while enlarging a passage area at the rear surface of the impeller, may be formed at the lower end of the pump chamber. 
     According to the seventh aspect, the surface tension of the liquid accumulated at the rear surface side of the impeller at the lower end of the pump chamber may be reduced due to the guide recess. Accordingly, the liquid may quickly and naturally flow down toward the discharge port. As a result, the drainage performance of the pump chamber may be further improved. 
     An eighth aspect is a pump device according to the sixth aspect, wherein a liquid reservoir, which has a bottom lower than a bottom surface on the intake opening side of the discharge opening, may be formed at the lower end of the pump chamber. 
     According to the eighth aspect, the liquid flowing down at the rear surface side of the impeller at the lower end of the pump chamber may be discharged toward the discharge opening and/or may accumulate in the liquid reservoir. 
     While the embodiments of the disclosure have been described with reference to specific configurations, it will be apparent to those skilled in the art that many alternatives, modifications, and variations may be made without departing from the scope of the present disclosure. Accordingly, embodiments of the present disclosure are intended to embrace all such alternatives, modifications, and variations that may fall within the spirit and scope of the appended claims. Embodiments of the present disclosure should not be limited to the representative configurations, but may be modified, for example, as described below. 
     The various examples described above in detail with reference to the attached drawings are intended to be representative of the present disclosure, and are thus non-limiting embodiments. The detailed description is intended to teach a person of skill in the art to make, use, and/or practice various aspects of the present teachings, and thus does not limit the scope of the disclosure in any manner. Furthermore, each of the additional features and teachings disclosed above may be applied and/or used separately or with other features and teachings in any combination thereof, to provide an improved pump device, and/or methods of making and using the same.