Abstract:
A pump includes a pump part provided with an impeller having a plurality of blades for sucking and discharging a liquid; a pump case accommodating the pump part; a rotor installed to the impeller to rotate the impeller; a motor part accommodating a stator disposed around an outer periphery of the rotor to drive the rotor and a driving circuit for controlling the stator; a partition member for isolating the motor part from the pump part to protect the motor part therefrom. The pump further includes a reservoir space disposed in the impeller; an extra passage provided between the rotor and the partition member and connected to the reservoir space to introduce the liquid thereto from the blades; and one or more reflux passages, formed at the impeller, for flowing the liquid in the reservoir space back to the blades.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a pump driven by a motor to suck and discharge a liquid, and a liquid supply apparatus having same. 
     BACKGROUND OF THE INVENTION 
     Generally, a pump includes a motor part having a stator generating a magnetic field and a controller controlling the stator; a pump part having an impeller driven by the magnetic field generated by the stator to suck and discharge a liquid such as water; and a partition member isolating the motor part from the pump part. 
     The pump part increases the pressure of the sucked liquid to discharge same by the impeller. In case of a centrifugal pump, the impeller has a plurality of blades fixed thereto, the whole body of each blade being curved backward with respect to a rotational direction to reduce loads applied thereto. 
     Since, however, the pressure in the centrifugal pump is increased by a centrifugal force, the rotational speed needs to be increased in order to discharge the liquid with a higher pressure by using a small pump. For this reason, when a gas-laden liquid is sucked, there occurs a problem that the liquid and the gas are separated by the strong centrifugal force applied thereto, and the gas having a smaller specific gravity than the liquid stagnates around a central part of the impeller, thereby decreasing the performance of the pump. 
     To solve the problem, a pump having a guide member projecting from a pump case towards the impeller has been proposed (see, for example, Japanese Patent Laid-open Application No. 2001-234894). 
     By employing such a pump case, the gas bubbles ladened in the liquid are disaggregated by the portion of the guide member disposed at a central part of the impeller and discharged through a discharge port, thereby preventing the gas from stagnating in the impeller. 
     However, if a pumping rate is small and the gas is admixed into the liquid, the flow of the liquid becomes less. In such a case, it is difficult to guide the disaggregated gas bubbles to the discharge port disposed at an outer periphery of the impeller, even with the scheme disclosed in the Patent Application supra. 
     If a central part of a portion of the liquid discharged by the impeller is fed back into the impeller through a reflux passage for example, it may be possible to discharge the gas stagnant at the central part of the impeller. However, in an exterior rotor structure in which a stator is installed inside the rotor as in the Patent Application supra, it is not possible to feed a sufficient amount of liquid back into the central part of the impeller, so that it is difficult to discharge the gas continuously introduced by being laden in the liquid. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a pump and a liquid supply apparatus capable of preventing a gas from stagnating in an impeller to thereby effectively discharge the gas and provide a high lift (high pressure pump output) and low flow rate pump output. 
     In accordance with an embodiment of the present invention, there is provided a pump including a pump part provided with an impeller having a plurality of blades for sucking and discharging a liquid; a pump case accommodating the pump part; a rotor installed to the impeller to rotate the impeller; a motor part accommodating a stator disposed around an outer periphery of the rotor to drive the rotor and a driving circuit for controlling the stator; a partition member for isolating the motor part from the pump part to protect the motor part therefrom. The pump further comprises a reservoir space disposed in the impeller; an extra passage provided between the rotor and the partition member and connected to the reservoir space to introduce the liquid thereto from the blades; and one or more reflux passages, formed at the impeller, for flowing the liquid in the reservoir space back to the blades. 
     With the pump structure described above, even when the flow rate is small, the liquid fed through the extra passage and stored in the reservoir space can be introduced into the central part of the impeller in a pump chamber with a sufficient flow rate via the reflux passage. As a result, it is possible to efficiently discharge the gas stagnating in the central part of the impeller. 
     Therefore, in accordance with the present invention, it is possible to provide a pump capable of effectively discharging the gas stagnating in an impeller and providing a high lift and low flow rate pump output. 
     In addition, it is possible that the reflux passages are disposed adjacent to a bearing provided at the central part of the impeller. 
     With such a structure, a pressure difference between the reservoir space and the central part of the impeller can be maximized and the liquid stored in the reservoir space can be discharged via the reflux passage into the central part of the impeller where the gas stagnates to disaggregate the gas bubbles. 
     It is also preferable that the reflux passages are formed at the central part of the impeller at identical angular intervals. 
     With such a structure, balance of the impeller may be maintained to suppress vibrations of the pump. 
     In addition, a passage may be preferably formed outside the extra passage at an inner sidewall of the pump case on a substantially same plane as a liquid flow direction of the impeller. 
     With such a structure, the gas laden in the liquid accelerated together with the liquid by the impeller can be in a laminar flow. Therefore, the flow direction of the gas can remain unchanged up to the inner sidewall of the pump case, so that the gas can be prevented from getting into the extra passage. 
     It is also preferable that the extra passage is disposed at an angle of 90° or greater with respect to the liquid flow direction of the impeller. 
     With such a structure, the laminar flow direction of the gas accelerated with the liquid in the impeller is not changed much, even when the flow rate in the extra passage is increased. Therefore, it is possible to prevent the gas getting into the extra passage. 
     Further, a front shroud may be preferably disposed at an upper surface of the blades facing the pump case to cover the blades. 
     With such a structure, it is possible to prevent leakage of the gas-ladened liquid guided into the impeller and can be effectively discharged. 
     Further more, the impeller may have a slide bearing rotating by using the liquid sucked into the pump part as a lubricant. 
     As a result, the liquid serving as the lubricant between the shaft and the bearing decreases a friction therebetween. Thus, it is possible to suppress wearing of the bearing, thereby increasing a life span of the bearing. 
     In addition, when the pump is installed in a liquid supply apparatus such as a cooling or the like apparatus, it is possible to improve the performance of the liquid supply apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become apparent from the following description of embodiments given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a cooling apparatus for an electronic part in accordance with an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of a pump in accordance with the embodiment of the present invention; and 
         FIG. 3  is an enlarged cross sectional view of an inlet opening of an extra passage of the pump in accordance with the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a specific embodiment in accordance with the present invention will be described with reference to the accompanying drawings. 
     As shown in  FIG. 1 , a heat generating component  1  is mounted on a substrate  2 , and a heat sink  3  is disposed thereon to perform heat exchange with the heat generating component  1  by using a coolant to cool same. 
     In addition, a heat radiator  4  for removing heat from the coolant, a reservoir tank  5  for storing the coolant, and a small pump  6  for circulating the coolant are disposed. Further, a pipe  7  is provided to connect the heat sink  3 , the heat radiator  4 , the reservoir tank  5 , and the pump  6 . The components  3  to  7  constitute a cooling apparatus. 
     The coolant in the reservoir tank  5  is pumped by the pump  6  to be sent to the heat sink  3  through the pipe  7 . Heat of the heat generating component  1  is transferred to the coolant so that the temperature of the coolant increases. The coolant then is sent to the heat radiator  4 . As a result, the coolant is cooled in the heat radiator  4  and then returned to the reservoir tank  5 . As described above, such a cooling system cools the heat generating component  1  by circulating the coolant using the pump  6 . 
     As shown in  FIG. 2 , the pump  6  includes a pump case  11 , a partition member  16 , a pump part  20 , and a motor part  21 , which is isolated from the pump case  11  and the pump part  20  by the partition member  16 . The pump part  20  is disposed in a space sealed by the partition member  16  and the pump case  11  having a suction port  12  and a discharge port  13 . The pump part  20  includes an closed type impeller  14  having a rear shroud  14   b , on which a plurality of blades  14   a  for pressurizing the fluid are disposed from the center of rotation to the outer periphery thereof in a radial direction and a front shroud  14   c  connected to the blades  14   a . The pump part  20  further includes a rotor magnet (rotor)  15  integrally formed with the impeller  14 ; a shaft  17  fixed to the pump case  11  and the partition member  16  at its both ends; a bearing  18  fixed to the impeller  14  to rotatably support the shaft  17  and formed of a resin having abrasion resistance and low friction such as PPS (polyphenylene sulfide) resin containing carbon; and a thrust bearing  19  fixed to the pump case  11 . 
     A stator  21   a  constituting the motor part  21  is fixed to an annular recess part  25  of the partition member  16 . A driving circuit  21   b  for driving the stator  21   a  is fixed to the stator  21   a.    
     In addition, the blades  14   a  of the impeller  14  are fixed to the rear shroud  14   b  to be curved backward with respect to a rotational direction in order to reduce loads of the blades, and a plurality of reflux passages  22  in communication with a rear surface of the impeller  14  are opened around the bearing  18  disposed at equal angular intervals at the central part of the impeller  14 . The reflux passages  22  preferably have a diameter of about 0.5 mm to 1.0 mm. If the diameter is too small, the liquid is not supplied into the central part of the impeller  14 . If the diameter is too large, the liquid supply into the central part of the impeller  14  is increased, but pressure drop also increases to lower the entire lift of the pump. 
     At the back side of the impeller  14 , there is provided a reservoir space  23  formed of a substantially entire cavity enclosed by an inner periphery of the rotor magnet  15 . The liquid is sucked into the reservoir space  23  via an extra passage  24  formed between the rotor magnet  15  disposed at the outer periphery of the impeller  14  and the partition member  16 , and the extra passage  24  is connected to the reservoir space  23  through a lower part of the rotor magnet  15 . The extra passage  24  has a structure that an inlet opening thereof is narrowest. 
     Hereinafter, operation of the pump and the cooling apparatus having same in accordance with the embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . 
     When an electric power is applied from an external power supply (not shown), currents flow through coils of the stator  21   a  controlled by the driving circuit  21   b  provided in the pump  6  to thereby generate a rotational magnetic field. When the rotational magnetic field is applied to the rotor magnet  15 , physical force is applied to the rotor magnet  15 . Since the rotor magnet  15  is integrally formed with the impeller  14 , a rotational torque is applied to the impeller  14 , thereby causing the impeller  14  to rotate to drive the pump  6 . 
     When the pump  6  is driven, rotation of the impeller  14  makes the central part of the impeller  14  brought into a negative pressure, and the coolant in a reservoir tank  5  is sucked into the central part of the impeller  14  together with gas bubbles via the suction port  12 . 
     The sucked coolant is guided along the blades  14   a  toward the outer periphery thereof by a centrifugal force of the impeller  14  while being pressurized. In addition, the gas bubbles having a specific gravity smaller than the coolant are collected at the central part of rotation by the centrifugal force, and the amount of liquid thereat reduces, which causes the gas bubbles to aggregate to become a larger gas mass. In accordance with the embodiment of the present invention, however, the coolant pressurized in the reservoir space  23  is discharged via the reflux passages  22  to the central part of the impeller  14  having the negative pressure. Therefore, the gas bubbles  27  at the central part of the impeller  14  are disaggregated and the coolant flow rate thereat is also increased, thereby allowing the gas bubbles  27  to be guided to the outer periphery of the impeller  14  with the coolant. 
     A volute passage  26  is formed at an inner sidewall of the pump case  11  on a substantially same plane as a coolant flow direction of the rear shroud  14   b  of the impeller  14 . The volute passage  26  is formed to have a gently curved plane around the outer periphery of the impeller  14  and the width thereof (i.e. a distance between the outer periphery of the impeller  14  and that of the volute passage  26 ) gradually increases towards the discharge port  13 . The coolant flows at the outer periphery of the impeller  14  in a laminar fashion along a substantially normal direction to the rotation direction thereof, and the opening of the extra passage  24  is formed to have an angle of Θ (90° or more) with respect to the coolant flow direction. Therefore, the coolant containing the gas bubbles  27  can be guided to the volute passage  26  while preventing the gas bubbles  27  from getting into the extra passage  24 . Further, since the volute passage  26  is formed outside the extra passage  24  at the inner sidewall of the pump case  11  on the same plane as the fluid flow direction, the gas bubbles  27  are guided to the outside of the extra passage  24  and prevented from being introduced into the extra passage  24 . 
     The extra passage  24  preferably has an opening width of about 0.2 mm to 0.7 mm. If the inlet opening width is too small, it would be difficult to supply the coolant into the reservoir space  23 , and if the opening width is too large, the gas bubbles  27  may be readily introduced thereinto. In addition, in order to reduce pressure loss, the other portion than the opening (e.g., a portion between a lower part of the rotor magnet  15  and the partition member  16 ) of the extra passage  24  has a larger width. The coolant guided to the volute passage  26  is guided to the discharge port  13  in the pressurized state and discharges the gas bubbles  27 . 
     When the pump  6  is driven to discharge the high pressure coolant from the discharge port  13 , the coolant in the reservoir tank  5  is sent to the heat sink  3  through the pipe  7  and heated after being heat-exchanged with the heat generating component  1 . The heated coolant is then sent to the heat radiator  4  and cooled after passing therethrough. The cooled coolant is returned to the reservoir tank  5 . 
     As described above, the cooling system of the embodiment is capable of cooling the heat generating component  1  by circulating the coolant using the pump  6 . The passage in the heat sink  3  has a high flow resistance in order to increase heat absorption performance. 
     In accordance with the embodiment, even when the flow rate is low, the liquid stored in the reservoir space  23  through the extra passage  24  is introduced into the impeller  14  through the reflux passages  22 . Therefore, it is possible to obtain a sufficient inner flow rate in the pump chamber to thereby efficiently discharge the gas  27  to be otherwise stagnant in the central part of the impeller  14 . 
     In addition, since the coolant is sucked through the central part of the impeller, it is possible to decrease a friction between the bearing  18  and the shaft  17  by the lubrication of the liquid therebetween, thereby lengthening the life span of the pump and providing a high lift pump output. 
     The pump structure in accordance with the embodiment of the present invention can be applied to various pumps used in a fuel cell apparatus or a cooling apparatus. 
     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from and scope of the invention as defined in the following claims.