Patent Publication Number: US-2018051443-A1

Title: Electric rotating device

Description:
TECHNICAL FIELD 
     The present invention relates to an electric rotating device configured such that a plurality of coils wind around a stator core arranged around a rotor. 
     BACKGROUND ART 
     One example of a conventional electric apparatus having a power generator function will be explained in reference to  FIG. 5  (see PTL 1, for example). An electric apparatus  1  is provided at a hybrid excavator. As shown in  FIG. 5 , the hybrid excavator includes: a hydraulic pump  2 ; an electric motor  4  configured to drive the hydraulic pump  2 ; a hydraulic circuit (not shown) including an actuator portion driven by operating oil ejected from the hydraulic pump  2 ; and a cooling passage  3  into which drain oil (operating oil) of the hydraulic pump  2  flows. The drain oil of the hydraulic pump  2  flows into the cooling passage  3  to cool the electric motor  4 . Thus, the electric motor  4  can be cooled with higher cooling efficiency than an air-cooling method. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Laid-Open Patent Application Publication No. 2010-53596 
     SUMMARY OF INVENTION 
     Technical Problem 
     Each of electric motors such as the electric motor  4  included in the electric apparatus  1  shown in  FIG. 5  is configured such that: when the electric motor operates, a coil winding around a stator core generates heat; and the generated heat is discharged through the stator core and a casing to an outside. An electric insulating sheet is interposed between the coil and the stator core. Regarding the electric insulating sheet, electrical insulation performance and heat transfer performance tend to conflict with each other. Therefore, if the electrical insulation property of the electric insulating sheet is improved, heat transfer is disturbed by the electric insulating sheet. On this account, the heat generated by the coil is hardly discharged to the outside of the casing. Thus, in the case of reducing the size of the electric motor or improving the performance of the electric motor, how to cool the coil is important. 
     The present invention was made to solve the above problems, and an object of the present invention is to provide an electric rotating device capable of improving cooling performance of coils. 
     Solution to Problem 
     An electric rotating device of the present invention includes: a casing including an internal space; a rotor accommodated in the internal space of the casing and supported by the casing so as to be rotatable; a stator core accommodated in the internal space of the casing and provided at the casing so as to be located around the rotor with an interval; a plurality of coils provided so as to be spaced apart from one another in a circumferential direction and winding around the stator core; and a cooling liquid enclosed in the inner space of the casing such that a part of the rotor and respective parts of the coils are immersed in the cooling liquid. 
     According to the electric rotating device of the present invention, when the rotor rotates, the cooling liquid in the casing is stirred by centrifugal force to be moved toward the stator core. With this, a large number of coils provided at the stator core can contact the cooling liquid, so that the heat can be removed from the coils by the cooling liquid. The heat removed by the cooling liquid is indirectly transferred to the casing through the stator core or directly transferred to the casing and can be discharged to an outside of the casing through the casing. To be specific, the heat of the coils can be discharged through the cooling liquid, the stator core, and the casing to the outside of the casing. Thus, the cooling performance of the coils can be improved. With this, for example, when an electric insulating layer is provided between the coil and the stator, the coil can be cooled while securing performance of the electric insulating layer. 
     In the present invention, it is preferable that the electric rotating device be such a vertical type that a rotating shaft of the rotor is arranged substantially in parallel with a vertical direction. 
     According to the above configuration, by the centrifugal force generated by the rotation of the rotor, the cooling liquid is moved toward the stator core over the entire periphery of the rotor, and a liquid surface of the cooling liquid forms a mortar shape. With this, all of the coils can be immersed in the cooling liquid, and the coils can be entirely immersed in the cooling liquid. Therefore, all the coils can be entirely and efficiently cooled. 
     According to the above configuration, the cooling liquid moved toward the stator core by the centrifugal force flows upward along an inner surface of the casing and then flows downward along the mortar-shaped liquid surface toward the rotor. After the cooling liquid reaches the vicinity of the rotor, the cooling liquid is again moved toward the inner surface of the casing by the centrifugal force. As above, the cooling liquid can be circulated in the internal space of the casing. By circulating the cooling liquid, the cooling liquid in the casing can be prevented from locally becoming high in temperature. Thus, the electric rotating device can be efficiently cooled. 
     In the present invention, it is preferable that an amount of the cooling liquid enclosed in the internal space of the casing be set such that: an amount of heat discharged from the casing per unit time is larger than an amount of heat transferred from the coils to the cooling liquid per unit time; and the amount of heat transferred per unit time becomes a maximum value or a value close to the maximum value. 
     According to the above configuration, the amount of cooling liquid enclosed in the internal space of the casing is set such that the amount of heat discharged from the casing per unit time becomes larger than the amount of heat transferred from the coils to the cooling liquid per unit time. With this, an entire amount of heat generated by the coils can be discharged through the cooling liquid and the casing to the outside. Thus, the heat can be prevented from being accumulated in the internal space of the casing, and the coils can be efficiently cooled. Further, the amount of cooling liquid is set such that the amount of heat discharged from the casing per unit time becomes the maximum value or a value close to the maximum value. With this, an ability of the cooling liquid that removes heat from the coils can be maximally extracted. Thus, a significant cooling effect of the coils can be obtained. 
     The electric rotating device according to the present invention may be an electric motor, a power generator, or an electric motor having a power generator function. 
     This electric rotating device can be applied as an electric motor, a power generator, or an electric motor having a power generator function. 
     The electric rotating device according to the present invention may be a turning electric motor of a construction machine. 
     Since the turning electric motor of the construction machine repeatedly starts up and stops many times and generates a large amount of heat, the electric rotating device according to the present invention is effective for preventing overheat. 
     Advantageous Effects of Invention 
     The present invention can improve the cooling performance of the coils. 
     The above object, other objects, features, and advantages of the present invention will be made clear by the following detailed explanation of preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal sectional view showing a principle of an electric rotating device according to one embodiment of the present invention. 
         FIG. 2  is a longitudinal sectional view showing a circulation passage of a cooling liquid enclosed in a casing of the electric rotating device shown in  FIG. 1 . 
         FIG. 3  is a diagram showing a relation among the amount of enclosed cooling liquid shown in  FIG. 1 , the amount of heat transferred to the cooling liquid, and the amount of heat discharged from the casing. 
         FIG. 4  is a side view showing a construction machine at which the electric rotating device shown in  FIG. 1  is provided. 
         FIG. 5  is a circuit diagram showing an electric motor provided at a conventional hybrid excavator and having a power generator function. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one embodiment of an electric rotating device according to the present invention will be explained in reference to  FIGS. 1 to 4 . An electric rotating device  11  can be applied as an electric motor, a power generator, or an electric motor having a power generator function. The electric rotating device  11  can be used in various machines and apparatuses such as construction machines. The present embodiment will explain an example in which the electric rotating device  11  is applied as a turning vertical electric motor of a construction machine  12  shown in  FIG. 4 . As one example of the construction machine  12 ,  FIG. 4  shows a hydraulic excavator. However, the construction machine  12  may be a crane or the like. The construction machine  12  may or may not be a hybrid type using oil pressure and electricity. 
     The hydraulic excavator (construction machine)  12  shown in  FIG. 4  includes: a base carrier  13 ; a revolving super structure  14  mounted on the base carrier  13  so as to be turnable; and an excavating work machine  15  attached to the revolving super structure  14  and configured to perform excavating work and the like. The electric rotating device  11  is mounted on the revolving super structure  14  and driven by electricity stored in a power storage device (not shown). The revolving super structure  14  is turned by driving force of the electric rotating device  11 . Further, the revolving super structure  14  is turned by driving force of a hydraulic motor (not shown). 
     As shown in  FIG. 1 , the electric rotating device  11  is, for example, a turning vertical three-phase electric motor, and a rotating speed of the electric rotating device  11  is controlled by an inverter. The electric rotating device  11  includes a rotor  16 , a stator  17 , a casing  18 , and a cooling liquid  19 . 
     The rotor  16  includes a rotating shaft  16   a . A columnar rotor main body  16   b  is provided at the rotating shaft  16   a . Both end portions of the rotating shaft  16   a  are supported by the casing  18  through bearings (not shown) such that the rotating shaft  16   a  is rotatable. The rotating shaft  16   a  of the rotor  16  is arranged substantially in parallel with a vertical direction. Thus, the electric rotating device  11  is used as a vertical electric motor. The stator  17  is arranged around the rotor  16  with an interval therebetween. 
     The stator  17  is a so-called stator and includes: a stator core  21  formed by stacking thin steel plates; and a plurality of coils  22 . The stator core  21  includes a yoke portion  21   a  and a plurality of teeth portions  21   b . The yoke portion  21   a  is formed in a substantially cylindrical shape. The plurality of teeth portions  21   b  are integrally provided on an inner peripheral surface of the yoke portion  21   a . Each of the teeth portions  21   b  projects from the inner peripheral surface of the yoke portion  21   a  in a radially inward direction and is formed to be long in an upward/downward direction. The teeth portions  21   b  are arranged on the inner peripheral surface of the yoke portion  21   a  at regular intervals in a circumferential direction. The coils  22  wind around the respective teeth portions  21   b  through electric insulating sheets  23  having an electrical insulation property. The coils  22  are arranged at regular intervals in the circumferential direction. 
     The stator  17  configured as above is provided so as to be fixed to an inner peripheral surface of the casing  18 . The inner peripheral surface of the casing  18  is formed to be cylindrical around the rotating shaft  16   a  of the rotor  16 . The stator  17  is arranged on the inner peripheral surface of the casing  18  such that an outer peripheral surface of the stator core  21  is provided along the inner peripheral surface of the casing  18 . As above, the rotor  16  and the stator  17  are accommodated in an inner space  18   a  of the casing  18 . In addition, a predetermined amount of cooling liquid  19  is enclosed in the inner space  18   a  of the casing  18 . 
     The cooling liquid  19  is a heat medium that removes heat generated by the coils  22  that are main heat sources and transfers the heat to the stator core  21  and the casing  18 . The cooling liquid  19  transfers the heat of the coils  22  indirectly or directly to the casing  18  and discharges the heat to an outside through the casing  18 . The cooling liquid  19  is enclosed in the inner space  18   a  of the casing  18 . A part of the rotor  16  and a part of the stator  17  (more specifically, a lower end portion of the rotor  16  and lower end portions of the coils  22 ) are immersed in the cooling liquid  19 . Used as the cooling liquid  19  is insulating oil having electrical insulation performance to prevent electric conduction among various components. It is preferable that the electrical insulation performance of the insulating oil be stable for a long period of time. Further, it is preferable the cooling liquid  19  be low in viscosity in an operating temperature range of the electric rotating device  11 . With this, bubbles formed in the cooling liquid  19  easily rise to a liquid surface  19   a , and the formation of the bubbles in the liquid can be suppressed. Further, the bubbles risen to the liquid surface  19   a  can be easily extinguished. With this, a decrease in cooling ability by the bubbles can be suppressed. The cooling liquid  19  may obtain a deforming property by adding an antifoaming agent to the insulating oil. As with the above, the decrease in cooling ability by the bubbles can be suppressed by the cooling liquid  19  to which the antifoaming agent is added. 
     Next, the movement of the cooling liquid  19  in the electric rotating device  11  will be explained in reference to  FIG. 2 . As described above, the electric rotating device  11  is a turning vertical three-phase electric motor. By the rotation of the rotor  16 , the cooling liquid  19  in the casing  18  rotates in the same direction around the rotor  16 , and centrifugal force is applied to the cooling liquid  19 . With this, the cooling liquid  19  is moved toward the stator  17 , and the liquid surface  19   a  of the cooling liquid  19  is formed in a mortar shape. With this, the coils  22  are entirely immersed in the cooling liquid  19 , that is, in the present embodiment, the entire coils  22  from lower end portions thereof to upper end portions thereof are immersed in the cooling liquid  19 , so that the heat of the entire coils  22  can be transferred from the entire coils  22  to the cooling liquid  19 . Therefore, the entire coils  22  can be effectively cooled. 
     Further, the cooling liquid  19  circulates in the inner space  18   a  of the casing  18  by the rotation of the rotor  16 . To be specific, the cooling liquid  19  flows in the vicinity of the rotor  16  to be moved from the rotor  16  toward the stator  17  and further flows upward along the coils  22  through spaces each between the yoke portion  21   a  of the stator core  21  and the teeth portion  21   b . In addition, the cooling liquid  19  flows upward and also gets into gaps of the stator core  21  to reach the inner peripheral surface of the casing  18  through the gaps. With this, a contact area of the cooling liquid  19  with the inner peripheral surface of the casing  18  increases. When the cooling liquid  19  reaches the liquid surface  19   a , it flows downward along the liquid surface  19   a  toward the rotor  16 . When the cooling liquid  19  reaches the rotor  16 , the cooling liquid  19  is again moved toward the stator  17  by the rotor  16 . As above, the cooling liquid  19  circulating in the inner space  18   a  removes the heat from the coils  22 , transfers the heat directly to the casing  18  or indirectly to the casing  18  through the stator core  21 , and discharges the heat to the outside through the casing  18 . With this, even when the electric insulating sheet  23  is interposed between the coil  22  and the stator core  21 , the heat of the coil  22  can be discharged through the cooling liquid  19  and the casing  18  to the outside, so that the coils  22  can be efficiently cooled. Further, by circulating the cooling liquid  19 , the cooling liquid  19  can also remove heat from the rotor  16  and the stator core  21  and discharge the heat through the casing  18  to the outside. As above, the heat can be removed from the components  16 ,  21 , and  22  and discharged through the casing  18  to the outside. Thus, the entire electric rotating device  11  can be efficiently cooled. Further, by circulating the cooling liquid  19 , the cooling liquid  19  in the inner space  18   a  can be prevented from locally becoming high in temperature. Thus, the electric rotating device can be efficiently cooled. 
     According to the electric rotating device  11  configured as above, it is unnecessary to provide pipes and passages of the cooling liquid  19  close to heat generating portions. Thus, the electric rotating device  11  that is low in cost and small in size can be produced. Further, since the cooling liquid  19  is enclosed in the inner space  18   a  of the casing  18 , the cooling liquid  19  is not heated from an outside of the electric rotating device  11 . Therefore, the electric rotating device  11  can realize a stable cooling characteristic. 
     According to the electric rotating device  11  configured as above, the amount of heat transferred from the coils  22  to the cooling liquid  19  per unit time and the amount of heat discharged from the casing  18  to the outside per unit time change in accordance with the amount of cooling liquid  19  enclosed in the inner space  18   a . Referring to  FIG. 3 , the following will explain a relation among an amount V (m 3 ) of cooling liquid  19  in the electric rotating device  11 , an amount Q (W) of heat transferred from the coils  22  to the cooling liquid  19  per unit time, and an amount R (W) of heat discharged from the casing  18  to the outside per unit time. 
     A change in the amount Q of heat transferred from the coils  22  per unit time with respect to the amount V (m 3 ) of cooling liquid  19  enclosed in the casing  18  forms a parabola in which the amount Q of heat transferred becomes a maximum heat transfer amount Q MAX  when the amount V of cooling liquid  19  is a predetermined liquid amount V 1 . In each of a case where the amount of cooling liquid  19  is larger than the predetermined liquid amount V 1  and a case where the amount of cooling liquid  19  is smaller than the predetermined liquid amount V 1 , the amount Q of heat transferred from the coils  22  to the cooling liquid  19  per unit time becomes smaller than the maximum heat transfer amount Q MAX . A reason why the change in the amount Q of heat transferred from the coils  22  to the cooling liquid  19  per unit time with respect to the amount V of cooling liquid  19  forms the parabola, and the amount Q of heat transferred becomes smaller when the amount V of cooling liquid  19  is smaller than the liquid amount V 1  is because an area of surfaces of the coils  22  which surfaces contact the cooling liquid  19  becomes small. Another reason is because when the amount V of cooling liquid  19  is larger than the liquid amount V 1 , the amount of heat transferred from the coils  22  to the cooling liquid  19  becomes small by heat generated by stirring the cooling liquid  19 . 
     The amount R of heat discharged per unit time is an amount of heat generated in the casing  18  and discharged through the casing  18  to the outside per unit time, and examples of the heat generated in the casing  18  include: heat generated at the coils  22  and the like by current flowing through the coils  22  by the operation of the electric rotating device  11 ; and heat generated by stirring the cooling liquid  19  by the rotor  16 . The contact area of the rotor  16  with the cooling liquid  19  increases as the amount V of cooling liquid  19  increases. Therefore, the amount R of heat discharged per unit time increases in proportion to the amount V of cooling liquid  19  in the casing  18 . 
     Regarding the amount Q of heat transferred per unit time and the amount R of heat discharged per unit time which amounts have the above characteristics, when the amount V of cooling liquid  19  is small (i.e., less than a liquid amount V 2 ), the amount Q of heat transferred per unit time exceeds the amount R of heat discharged per unit time. In this case, the amount of heat dischargeable to the outside of the casing  19  becomes small with respect to the heat generated by the coils  22 . This may cause a case where the coils  22  overheat, and it becomes difficult to continue the operation. Therefore, in the electric rotating device  11 , it is preferable that the amount V of cooling liquid  19  be set, that is, the amount V of cooling liquid  19  be set to be not less than the liquid amount V 2  such that the amount Q of heat transferred per unit time becomes smaller than the amount R of heat discharged per unit time. Further, in the electric rotating device  11 , to remove a larger amount of heat from the coils  22 , the amount of cooling liquid  19  is set, that is, the amount V of cooling liquid  19  is set in a setting range of not less than a liquid amount V 3  and not more than a liquid amount V 4  such that the amount Q of heat transferred per unit time becomes the maximum heat transfer amount Q MAX  or a value close to the maximum heat transfer amount Q MAX  (i.e., a value in a range around the maximum heat transfer amount Q MAX ). It should be noted that each of the liquid amounts V 3  and V 4  is larger than the liquid amount V 2 . 
     As above, the amount V of cooling liquid  19  in the casing  18  is set to such an amount that the amount Q of heat transferred per unit time becomes smaller than the amount R of heat discharged per unit time. With this, the coils  22  can be efficiently cooled. Further, the electric rotating device  11  configured as above can be adopted as a turning electric motor of the construction machine  12  such as an electric excavator. The turning electric motor repeatedly starts up and stops many times and generates a large amount of heat. However, by adopting the electric rotating device  11 , the cooling can be effectively performed, and the overheating can be prevented. 
     In the embodiment, the electric rotating device  11  is applied as the electric motor. Instead of this, the electric rotating device  11  may be applied as a power generator or an electric motor having a power generator function. 
     From the foregoing explanation, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Therefore, the foregoing explanation should be interpreted only as an example and is provided for the purpose of teaching the best mode for carrying out the present invention to one skilled in the art. The structures and/or functional details may be substantially modified within the scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               11  electric rotating device 
               12  construction machine 
               13  base carrier 
               14  revolving super structure 
               15  excavating work machine 
               16  rotor 
               16   a  rotating shaft 
               16   b  rotor main body 
               17  stator 
               18  casing 
               18   a  internal space 
               19  cooling liquid 
               21  stator core 
               22  coil