Patent Publication Number: US-2016248313-A1

Title: Electric Water Pump

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese Patent applications serial No. 2015-30146, filed on Feb. 19, 2015, the respective contents of which are hereby incorporated by reference into this application. 
     FIELD OF THE INVENTION 
     The present invention relates to an electric water pump. More particularly, the present invention is concerned with an electric water pump having a pump unit and motor unit connected to each other by a magnetic coupling. 
     BACKGROUND OF THE INVENTION 
     In recent years, the necessity of energy saving has come to be emphasized in the field of industrial equipment, home electric appliances, or automotive parts. At present, a half or more of an amount of electric power used within the nation is consumed for driving of rotary electric machines. 70% or more of the use of electric power is occupied by the use for electrical operation, or especially, the use for systems employing an impeller, such as, motor-driven pumps and ventilation fans. As for the use for power generation, the use of electric power is attributable to utilization of a system employing an impeller such as a water-wheel generator. A typical motor-driven pump has a motor unit and pump unit coupled to each other by a shaft, and has a motor used as a driving source. In this case, a shaft coupling and other coupling parts are arranged in an axial direction. This poses a problem in that the dimension in the axial direction gets longer. In an attempt to shorten the dimension in the axial direction, a motor-integrated pump having the shaft of the motor directly coupled to an impeller has been put on the market. However, since the pump unit is filled with water or any other liquid, a pump chamber in which the impeller rotates has to be sealed for fear the liquid may leak out. Even in the motor-integrated pump, the sealing is achieved in a space between the pump chamber and motor. As a structure of achieving the sealing for fear the liquid may leak out, a structure of disposing an O ring formed with a rubber member or an oil seal is adopted. A structure of achieving the sealing via a rotating piece such as a shaft has a drawback that regular maintenance is needed. 
     Patent literature 1 (Japanese Patent Application Laid-Open No. 6-280779) discloses a liquid pump system that has a rotator incorporated in it, and that includes a pump body which feeds a liquid from the inside by means of the rotation of the rotator, and a motor which is disposed outside the pump body and transmits the rotation of a rotor to the rotator using a magnetic coupling. Herein, the rotor includes a first magnet that is a driving magnet which forms the magnetic coupling and that serves as a rotor magnet of the motor. The rotator includes a second magnet that is a driven magnet which forms the magnetic coupling and that is driven to rotate due to a magnetic field induced by the first magnet. 
     In a pump system having a structure like the one disclosed in the patent literature 1, a driving magnet that forms a magnetic coupling is also used as a motor magnet that is presumably included in an axial motor structure. A transmission torque cannot therefore be increased. For adapting the disclosed structure to a pump system that is intended to exert a large torque, a motor unit has to be large in size. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a highly reliable and compact electric water pump. 
     The present invention adopts a structure of an electric water pump having a motor unit which includes an axial gap motor and driving magnets, and a pump unit which includes passive magnets that are magnetically coupled to the driving magnets in a radial direction. 
     According to an aspect of the present invention, a highly reliable and compact electric water pump can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional diagram of an electric water pump  100 ; 
         FIG. 2  is an exploded perspective diagram of a pivotal part of the electronic water pump  100 ; 
         FIG. 3  is a sectional diagram of a motor unit  200 ; 
         FIG. 4  is an exploded perspective diagram of a pivotal part of the motor unit  200 ; 
         FIG. 5A  is a perspective diagram of an output-side rotor  230 ; 
         FIG. 5B  is a perspective diagram of the output-side rotor  230 ; 
         FIG. 6  is a sectional diagram of a partition  10 ; 
         FIGS. 7A-7D  are a perspective diagram showing a structure of an iron core of an axial gap motor; 
         FIG. 8  is a sectional schematic diagram of an output-side rotor  230  of another embodiment; and 
         FIG. 9  is a sectional schematic diagram of the output-side rotor  230  of still another embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, embodiments of the present invention will be described below. 
     First Embodiment 
     A first embodiment will be described below in conjunction with  FIG. 1  to  FIG. 6 . 
       FIG. 1  is an exploded perspective diagram of major parts of an electric water pump  100  in accordance with the present embodiment. The electric water pump  100  broadly includes a motor unit  200  and pump unit  300 . The motor unit  200  and pump unit  300  are separated from each other with a partition  10  between them.  FIG. 2  is a sectional diagram of the electric water pump  100 . The motor unit  200  and pump unit  300  are stored in a housing  20 . 
     The electric water pump  100  of the present embodiment is characterized by such points that an axial gap motor is included in the motor unit  200  and that a radial magnetic coupling in which the partition  10  intervenes is adopted to transfer power between the motor unit  200  and pump unit  300 . The structure will be described below. 
       FIG. 3  is an enlarged sectional diagram of the motor unit  200  shown in  FIG. 2 . The motor unit  200  includes a motor stator  240 , motor rotors  230  and  231 , and a motor-side shaft  220 . The motor unit  200  included in the present embodiment includes an axial gap motor that has the motor stator  240  and motor rotors  230  and  231  arranged in an axial direction with predetermined gaps among them. 
     The axial gap motor includes plural motor stator iron cores  241  in the circumferential direction of the motor-side shaft  220 . A motor stator coil  242  is wound about the periphery of each of the motor stator iron cores  241 , whereby the motor stator  240  is formed. The motor stator  240  is disposed substantially in the center in the axial direction of the motor-side shaft  220 . 
     An output-side rotor  230  and anti-output-side rotor  235  are arranged on both sides of the motor stator  240  in the axial direction. The output-side rotor  230  is disposed on the left side in  FIG. 3 , and the anti-output-side rotor  235  is disposed on the right side in  FIG. 3 . Gaps among the stator  240  and the rotors  230  and  235  which constitute the motor unit  200  are designed to have an appropriate dimensional relationship for the purpose of exerting maximum efficiency. 
       FIG. 4  is an exploded perspective diagram showing the output-side rotor  230 , anti-output-side rotor  23   5 , and motor stator  240  out of the parts constituting the motor unit  200 . 
     The anti-output-side rotor  235  has anti-output-side rotor magnets  236  retained on one of surfaces of a substantially disk-like anti-output-side rotor yoke  238  with an anti-output-side rotor heel piece  237  between them. In the present embodiment, the plural anti-output-side rotor magnets  236  are disposed while being separated in the circumferential direction. An anti-output-side magnet positioning member  239  is interposed between adjoining ones of the plural anti-output-side rotor magnets  236 . A shaft insertion hole  225  into which the motor-side shaft  220  is inserted and fitted is formed in the center of the anti-output-side rotor yoke  238 . 
     The motor stator  240  has, as mentioned above, the plural motor stator iron cores  241  each of which has the motor stator coil  242  wound about it. In the present embodiment, nine pairs of the motor stator iron core  241  and motor stator coil  242  are disposed in the circumferential direction of the motor-side shaft  220 . A motor-side bearing retainer  222  is formed in the center of the motor stator  240 . A motor-side bearing  221  is fitted into the motor-side bearing retainer  222 . 
     The output-side rotor  230  has substantially the same structure as the anti-output-side rotor  235 . The output-side rotor  230  has output-side rotor magnets  231  retained on one of surfaces of a substantially disk-like output-side rotor yoke  233  with an output-side rotor heel piece  232  between them. An output-side magnet positioning member  234  is interposed between adjoining ones of the plural output-side rotor magnets  231  that are separated in the circumferential direction. The output-side rotor yoke  233  retains the output-side rotor magnets  231  on the surface of the output-side rotor yoke on which the motor stator  240  is disposed. Further, the output-side rotor yoke  233  has a cylindrical yoke, which looks like the one shown in  FIG. 5A  and  FIG. 5B , formed on the surface opposite to the surface on which the motor stator  240  is disposed. 
     Referring to  FIG. 5A  and  FIG. 5B , the structure of the output-side rotor  230  included in the electric water pump of the present embodiment will be described below.  FIG. 5A  is a perspective diagram showing the output-side rotor  230  seen on the side of the pump unit  300 .  FIG. 5B  is a perspective diagram showing the output-side rotor  230  seen on the side of the motor stator  240 . 
     The output-side rotor yoke  233  included in the present embodiment is formed to have a bottomed cylindrical shape with a part, the back of which retains the output-side rotor magnets  231 , as a bottom. Specifically, the output-side rotor yoke  233  includes an output-side rotor yoke bottom  233   a  and output-side rotor yoke cylinder  233   b.  The output-side rotor yoke cylinder  233   b  is formed on a side opposite to a side, on which the output-side rotor magnets  231  are formed, with the output-side rotor yoke bottom  233   a  between them. The output-side rotor yoke bottom  233   a  and output-side rotor yoke cylinder  233   b  are formed to have substantially the same outer diameter. In the present embodiment, the output-side rotor yoke bottom  233   a  and output-side rotor yoke cylinder  233   b  are made of a material such as iron, aluminum, or stainless steel to be integrated into one body. 
     Motor-side magnets  250  that are magnetized to have plural poles are retained on the internal circumference of the output-side rotor yoke cylinder  233   b.  The motor-side magnets  250  are formed like arcs along the internal circumference of the output-side rotor yoke cylinder  233   b.  In the present embodiment, a total of eight motor-side magnets  250  are arranged in the circumferential direction so that adjoining magnets have reverse poles. Herein, when seen from the pump unit  300  along the motor-side shaft  220 , the motor-side magnets  250   a,    250   b,    250   c,    250   d,    250   e,    250   f,    250   g,  and  250   h  are counterclockwise arranged in that order. 
     The output-side rotor magnets  231  may be, as shown in  FIG. 5B , formed with donut-like ring magnets. In this case, the output-side rotor magnets  231  can have plural magnetic poles alternated in a circumferential direction. The ring magnets can concurrently take on the plural polarities as an integrated body during magnetization. Thus, the output-side rotor magnets  231  that are highly precise and cause a little error can be obtained. At this time, since the direction of magnetization for the output-side rotor magnets  231  is orthogonal to the direction of magnetization for the motor-side magnets  250 , adverse effects on the magnets  231  and magnets  250  respectively due to magnetization are limited. In addition, since the necessity of the magnet positioning members like the ones shown in  FIG. 4  is obviated, the number of parts can be decreased. 
     The present embodiment has eight magnetic poles. However, as long as the number of magnetic poles refers to an integral multiple of a pair of poles (north and south), any number of magnetic poles will do. The electric water pump of the present embodiment makes it possible to independently design the number of poles of rotor magnets included in an axial gap motor, and the number of poles of driving magnets and passive magnets which form a magnetic coupling between the motor unit and pump unit. 
     Referring back to  FIG. 2 , the relationship between the motor unit  200  and pump unit  300  will be described below. As mentioned above, the motor unit  200  and pump unit  300  are disposed in the housing  20  with the partition  10  between them. The partition  10  is non-conductive and preferably made of a nonmagnetic material. However, if the partition  10  is made of a resin material such as plastic, a desired strength cannot be ensured depending on the thickness of the partition  10 . Therefore, the partition may be formed with a nonmagnetic metal such as stainless steel. 
       FIG. 6  is a partially sectional diagram of the partition  10  shown in  FIG. 2 . In  FIG. 6 , the locations of the motor-side magnets  250  and pump-side magnets  350  which will be described later are also hatched. 
     The partition  10  includes a bottomed cylindrical part  13  that is formed along the internal surface of the output-side rotor yoke  233  formed to have a bottomed cylindrical shape. The pump unit  300  is disposed in a space formed with the bottomed cylindrical part  13  of the partition  10 . 
     The partition  10  further includes a pump-side shaft  320  that extends from the center of the bottom of the bottomed cylindrical part  13  in a direction parallel to the axial direction of the motor-side shaft  220 . The pump-side shaft  320  is disposed coaxially with the motor-side axis  220 . 
     The partition  10  further includes a bottomed annular part  12  that opens in a direction, in which the motor unit  200  is disposed, outside the bottomed cylindrical part  13  in the radial direction. In a space formed with the bottomed annular part  12  of the partition  10 , the output-side rotor yoke cylinder  233   b  and output-side rotor magnets  231  are disposed. 
     As shown in  FIG. 2 , a pump-side rotor  330  is disposed in the bottomed cylindrical part  13 . The pump-side rotor  330  is retained by a pump-side bearing  321  located in the center of the pump-side rotor  330  so that the pump-side rotor  330  can be rotated about the pump-side shaft  320 . The pump-side magnets  350  are arranged on the periphery of the pump-side rotor  330  in the radial direction of the pump-side rotor  330 . The pump-side magnets  350  are provided with the same number of poles as the number of poles of the motor-side magnets  250 . In the present embodiment, eight pump-side magnets  350  are included (see  FIG. 1 ). 
     Accordingly, the motor-side magnets  250  and pump-side magnets  350  are magnetically coupled to each other, and a torque is transmitted in a contactless manner with the partition  10  between the motor-side magnets  250  and pump-side magnets  350 . Since the permanent magnets are opposed to the other permanent magnets in a radial direction, a gap magnetic flux can be increased. Therefore, a larger torque can be transmitted by means of a magnetic coupling. Although the structure including gaps derived from the presence of the partition  10  is adopted, a torque generated by the motor unit  200  can be transmitted over one plane. In addition, the outer diameter of a contactless torque transmission plane can be decreased if necessary. 
     The driving magnets that are magnetically coupled to the passive magnets are disposed without a joint member on the side of the driving shaft of the motor unit. Therefore, a highly reliable pump system can be constructed. 
     Similarly to the pump-side rotor  330 , an impeller  310  is disposed to be able to rotate about the pump-side shaft  320 . The impeller  310  is fixed to a screw, which is located at the distal end of the pump-side shaft  320 , in a thrust direction using an impeller fastening washer and impeller fastening nut which are not shown. 
     In the present embodiment, the outer diameter of the pump-side magnets  350  is smaller than the outer diameter of the impeller  310  (see  FIG. 1 ). Accordingly, a fluid such as water, oil, or air that flows through the impeller  310  flows smoothly. This exerts an effect of preventing breakdown of the impeller  310 , which is derived from turbulence, or reducing noise. 
     The magnetic coupling between the pump unit and motor unit is attained with a radial structure. This prevents such an incident that the motor-side magnets  250  that are driving magnets and the partition  10  come into contact with each other because of a change in the internal pressure of the pump unit. Eventually, reliability improves. 
       FIG. 7A  to  FIG. 7D  show examples of other structures of the motor stator iron cores  241  of the motor unit  200 .  FIG. 7A  shows an iron core that is structured by layering electromagnetic steel sheets or foils, which are made of such a material as iron-based amorphous, FINEMET, or nanocrystal, in a circumferential direction.  FIG. 7B  shows an example in which a dust core or an iron core formed by compressively molding powder of ferrite is utilized.  FIG. 7C  shows an example in which an iron core that is structured by layering electromagnetic steel sheets or foils, which are made of such a material as iron-based amorphous, FINEMET, or nanocrystal, in the circumferential direction has rectangular sections.  FIG. 7D  shows an iron core formed by appending directionality to an iron core made of a soft magnetic material as shown in any of  FIGS. 7A to 7C . In an axial gap motor, since a magnetic flux flows in an axial direction, anisotropy is provided in the direction of the magnetic flux. 
     In the electric water pump of the present embodiment, a special magnetic material can be adopted as the iron cores of the axial gap motor. Therefore, the motor unit can be designed to be quite efficient. 
     Second Embodiment 
       FIG. 8  is a sectional diagram of an output-side rotor  230  of an electric water pump in accordance with a second embodiment. 
     In the first embodiment, the outer diameter Dm of the output-side rotor yoke bottom  233   a  and the outer diameter Dc of the output-side rotor yoke cylinder  233   b  are substantially identical to each other. In the present embodiment, an output-side rotor yoke  233  is formed so that the outer diameter Dc of an output-side rotor yoke cylinder  233   b  is smaller than the outer diameter Dm of an output-side rotor yoke bottom  233   a.    
     As long as an axial length remains unchanged, the magnitude of a transmission torque provided by a magnetic coupling can be determined with the number of magnetic poles involved in the magnetic coupling and the outer diameter of the magnetic coupling. Therefore, when the structure of the present embodiment is adopted, a magnetic coupling-integrated electric water pump characteristic of a little inertia can be provided. 
     Third Embodiment 
       FIG. 9  is a sectional diagram of an output-side rotor  230  of an electric water pump in accordance with a third embodiment. 
     In the first embodiment, the output-side rotor yoke bottom  233   a  that retains the output-side rotor magnets  231  in an axial direction and the output-side rotor yoke cylinder  233   b  that retains the motor-side magnets  250  in a radial direction are integrated into one member ( 233 ). In an output-side rotor yoke included in the present embodiment, an output-side rotor yoke bottom  233   a  that retains output-side rotor magnets  231  in the axial direction, and an output-side rotor yoke cylinder  233   b  that retains motor-side magnets  250  in the radial direction are formed as different members. For example, in the present embodiment, the output-side rotor yoke bottom  233   a  is made of iron, while the output-side rotor yoke cylinder  233   b  is made of aluminum. In this case, the inertia of a rotator can be reduced. 
     The aforesaid electric water pumps of the embodiments can be applied to a wide range of usages in which a compact and highly efficient pump system is needed. For example, the electric water pumps can be applied to general rotator systems including an industrial pump, compressor, industrial fan, water-wheel generation system for small water power usages, onboard electric water pump, onboard electric oil pump, pump for home electric appliances, and ventilator for home electric appliances, and to driving or power generation systems that employ an impeller.