Abstract:
A vehicle drive device that has a stator and a rotor disposed on the inside of the vehicle wheel and drives the wheel, wherein the whole stator can be intensively cooled without causing an increase in production costs. The vehicle drive device comprises: the stator that has a stator core ( 20 ) and a hollow stator coil ( 30 ), is arranged on the inside of the rotating vehicle wheel ( 10 ), and electrically generates magnetic force; the rotor that has permanent magnets ( 11 ) connected to the wheel ( 10 ), and applies rotational force to the wheel ( 10 ) using the magnetic force of the stator; a cooling medium that flows through the hollow section of the stator coil ( 20 ); and a first radiator unit ( 50 ) that releases heat from the cooling medium.

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle driving apparatus for driving an automobile wheel. 
     BACKGROUND ART 
     Conventionally, some proposals have been made about an in-wheel motor provided with an electric motor in an automobile wheel, and a cooling structure for such an in-wheel motor. For example, Patent Literature (hereinafter, referred to as PTL) 1 proposes a configuration in which oil is put in a casing surrounding a stator coil of an in-wheel motor to cool the stator coil. 
     As a technique relevant to the invention of the present application, PTL 2 discloses a configuration for cooling an electromagnetic coil by causing fluid to flow through a hollow portion of the electromagnetism coil. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     
         
         Japanese Patent Application Laid-Open No. 2005-086894
 
PTL 2
 
         Japanese Patent Application Laid-Open No. HEI 10-022068 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     When the configuration for immersing the stator coil in oil to cool the stator coil is employed in order to cool the in-wheel motor, the circumference of the stator coil needs to be covered with a sealed casing. When the configuration for covering a portion including a rotational element with the sealed casing is employed, the casing is required to have high rigidity and machining accuracy, which causes a problem of an increase in the manufacturing cost of the in-wheel motor. 
     The technique for cooling the electromagnetic coil disclosed in PTL 2 focuses on cooling of only the electromagnetic coil and differs from a configuration involving the necessity of cooling both a stator coil and a stator core like an in-wheel motor. In an in-wheel motor, a stator core generates a large amount of heat because of a strong oscillating magnetic field, and therefore a stator coil needs to be cooled significantly. 
     It is an object of the present invention to enable a whole stator to be cooled a significantly without increasing the manufacturing cost in a vehicle driving apparatus which is provided with a stator and a rotor inside an automobile wheel to drive the wheel. 
     Solution to Problem 
     A vehicle driving apparatus according to an aspect of the present invention includes: a stator that includes a stator core and a hollow stator coil, that is placed inside an automobile wheel, and that electrically generates a magnetic force; a rotor that includes a permanent magnet connected to the wheel and that applies a rotational force to the wheel by the magnetic force of the stator; a cooling medium that flows through a hollow portion of the stator coil; and a first radiator section that radiates heat of the cooling medium. 
     A vehicle driving apparatus according to an aspect of the present invention employs a configuration in which a side of the stator coil that is in contact with the stator core has a linear shape in a lateral cross section of wiring of the stator coil. 
     Advantageous Effects of Invention 
     According to the present invention, the stator can be cooled significantly without increasing the manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configuration diagram illustrating a vehicle driving apparatus according to Embodiment 1 of the present invention; 
         FIG. 2  is a perspective view illustrating the supporting structure of a wheel and a stator of the vehicle driving apparatus according to Embodiment 1 of the present invention; 
         FIG. 3  is a partially cutaway perspective view illustrating the structure of a stator coil of the vehicle driving apparatus according to Embodiment 1 of the present invention; 
         FIG. 4  is a partially cutaway perspective view illustrating the structure of a stator coil of a vehicle driving apparatus according to Embodiment 2 of the present invention; 
         FIG. 5  is a partially cutaway perspective view illustrating the structure of a stator coil of a vehicle driving apparatus according to Embodiment 3 of the present invention; and 
         FIG. 6  is a configuration diagram illustrating an additional configuration in a vehicle driving apparatus according to Embodiment 4 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. 
     (Embodiment 1) 
       FIG. 1  is a configuration diagram illustrating a vehicle driving apparatus according to Embodiment 1 of the present invention, and  FIG. 2  is a perspective view illustrating the supporting structure of a wheel and a stator of the vehicle driving apparatus. 
     As illustrated in  FIG. 1 , the vehicle driving apparatus according to Embodiment 1 mainly includes wheel  10 , permanent magnet  11 , stator core  20 , stator coil  30 A, pipe member  30  continuously connected to stator coil  30 A, motor driving apparatus  40 , and radiator  50 . 
     In these elements, permanent magnet  11 , stator core  20 , and stator coil  30 A constitute an electromagnetic motor (referred to as in-wheel motor). Wheel  10  and permanent magnet  11  constitute the rotor of the electromagnetic motor, and stator core  20  and stator coil  30 A constitute the stator of the electromagnetic motor. 
     Wheel  10  is, for example, a wheel of an electric vehicle, and a tire is attached to the outer periphery of the wheel while a space for placing stator core  20  is provided on the inner circumference side. As illustrated in  FIG. 2 , wheel  10  is rotatably supported by axle  18  via frame  13  and ring bearing  15 . Axle  18  is unrotatably fixed to the vehicle body. 
     Permanent magnet  11  is fixed to the inner peripheral surface of wheel  10  and is placed so that an S pole and an N pole appear at each predetermined angle. 
     Stator core  20  is formed of a magnetic substance. Stator core  20  has a plurality of magnetic pole portions  21  each having an end surface that faces permanent magnet  11  and that emits a magnetic flux. Stator core  20  has a body portion around which stator coil  30 A is wound. Stator coil  30 A is tightly wound around stator core  20 , which in turn, ensures high thermal conductivity between stator core  20  and stator coil  30 A. As illustrated in  FIG. 2 , stator core  20  is unrotatably held by unrotatable axle  18  with a small gap provided between the end surface of magnetic pole portion  21  and permanent magnet  11 . 
       FIG. 3  is a partially cutaway perspective view illustrating the structure of stator coil  30 A.  FIG. 3  represents a state where the wiring of stator coil  30 A is cut in the longitudinal direction and a direction orthogonal to the longitudinal direction. 
     Stator coil  30 A is a coil generating a magnetic field in stator core  20  due to a current flowing through stator coil  30 A. As illustrated in  FIG. 3 , the wiring of stator coil  30 A is a tubular shape having hollow portion  33  in its inside, and a cooling medium flows through hollow portion  33  to cool the stator. The cooling medium is, for example, cooling oil. 
     The wiring of stator coil  30 A is larger in thickness than wiring of a simple lead wire and cannot therefore be wound around stator core  20  many times. However, a large current flowing through stator coil  30 A can generate a necessary quantity of magnetic flux in the stator. 
     As illustrated in  FIG. 3 , the wiring of stator coil  30 A mainly includes insulation coating  31  formed of a material such as resin covering the outer periphery, metallic pipe  32  for carrying electricity, and hollow portion  33  which is the hollow portion of metallic pipe  32 . Metallic conduit  32  is formed of a material having high heat conductivity, such as copper. Insulation coating  31  is an insulator formed of a material having high heat conductivity. 
     Pipe member  30  has the same configuration as the wiring of stator coil  30 A. Pipe member  30  functions as wiring for electrically connecting motor driving apparatus  40  to stator coil  30 A and as piping for connecting stator coil  30 A to radiator  50  to feed a cooling medium. As illustrated in  FIG. 2 , pipe member  30  passes up to the inside of wheel  10  through via hollow portion of axle  18 . 
     Motor driving apparatus  40  causes a current to flow through stator coil  30 A on the basis of a driving operation and drives the rotation of wheel  10 . Electrodes  41   a  and  41   b  of motor driving apparatus  40  are electrically connected to metallic pipe  32  of pipe member  30  by lead wires. These lead wires penetrate insulation coating  31  of pipe member  30  and are connected to internal metallic pipe  32 . 
     In  FIG. 1 , two lines are connected from motor driving apparatus  40  to stator coil  30 A. However, in using the electromagnetic motor as a multiphase motor, a plurality of stator coils  30 A may be wound around stator core  20 , and three or more lines may be connected from motor driving apparatus  40  to three or more pipe members  30  connected to stator coils  30 A. Stator core  20  may be configured to have three or more magnetic pole portions  21 . Motor driving apparatus  40  can then control currents flowing through the plurality of stator coils  30 A to thereby drive the multiphase motor. 
     Radiator  50  performs heat exchange between the ambient air and the cooling medium flowing through stator coil  30 A and radiates heat of the cooling medium. Radiator  50  and pipe member  30  are connected to each other with electric insulation so that no current flows between the two. Radiator  50  is provided with a pump to circulate the cooling medium between stator coil  30 A and radiator  50 . Alternatively, the pump may be provided in the exterior of radiator  50 . 
     In the vehicle driving apparatus according to Embodiment 1, motor driving apparatus  40  causes a current to flow through stator coil  30 A according to a driving operation. This current generates a magnetic flux in stator coil  30 A and stator core  20 , and exerts electromagnetic force on permanent magnet  11  and wheel  10 . Wheel  10  then rotates because of this electromagnetic force. Wheel  10  rotates while being supported via bearing  15  by unrotatable axle  18 . 
     In the vehicle driving apparatus according to Embodiment 1, the cooling medium cooled in radiator  50  flows inside stator coil  30 A through pipe member  30 . Therefore, although stator core  20  and stator coil  30 A generate heat accompanied with driving of the motor, stator coil  30 A is directly cooled by the cooling medium. Furthermore, since stator coil  30 A contacts stator core  20  with high heat conductivity, stator core  20  is significantly cooled by stator coil  30 A. 
     (Embodiment 2) 
       FIG. 4  is a partially cutaway perspective view illustrating the structure of a stator coil of the vehicle driving apparatus according to Embodiment 2 of the present invention. 
     In the vehicle driving apparatus according to Embodiment 2, pipe member  30  included in stator coil  30 A has one surface  35  having a flat shape. Flat surface  35  is wound around stator core  20  so as to be in contact with stator core  20 . In other words, the side in contact with stator core  20  (surface  35 ) has a linear shape in a lateral cross section of pipe member  30  (cross section orthogonal to the longitudinal direction). 
     This configuration can increase the contact density between stator core  20  and stator coil  30 A, thus enabling higher thermal conductivity between stator core  20  and stator coil  30 A. 
     Furthermore, in pipe member  30  included in stator coil  30 A according to Embodiment 2, inner peripheral surface  36  on the side of stator core  20  of hollow portion  33  is formed in a flat shape. In other words, hollow portion  33  in a lateral cross section of pipe member  30  on the side of stator core  20  is formed in a linear shape and has a larger width on the side of stator coil  30 A than on the opposite side of stator coil  30 A. 
     This configuration can cause the cooling medium flowing through hollow portion  33  to have a higher flow rate on the side near stator core  20  and can cool stator core  20  more intensively. 
     Therefore, the vehicle driving apparatus according to Embodiment 2 can cool stator core  20  more significantly and can cool the whole stator more equally. 
     (Embodiment 3) 
       FIG. 5  is a partially cutaway perspective view illustrating the structure of a stator coil of a vehicle driving apparatus according to Embodiment 3 of the present invention. 
     In the vehicle driving apparatus according to Embodiment 3, pipe member  30  included in stator coil  30 B has one surface  35  having a flat shape similarly to Embodiment 2. Furthermore, in Embodiment 3, hollow portion  33  of pipe member  30  included in stator coil  30 B is formed in a rectangular shape in a cross section and is placed eccentrically toward stator core  20 . 
     This configuration can cause the cooling medium flowing through hollow portion  33  to absorb more heat on the side near stator core  20  and can therefore cool stator core  20  more intensively. 
     Therefore, the vehicle driving apparatus according to Embodiment 3 can cool stator core  20  more significantly and can cool the whole stator more equally. 
     (Embodiment 4) 
       FIG. 6  is a configuration diagram illustrating an additional configuration in a vehicle driving apparatus according to Embodiment 4 of the present invention. In  FIG. 6 , pipe member  30 , stator coil  30 A, motor driving apparatus  40 , and radiator  50  in  FIG. 1  are omitted to mainly illustrate the additional configuration of Embodiment 4. 
     The vehicle driving apparatus according to Embodiment 4 includes pipe member  30 , stator coil  30 A, motor driving apparatus  40 , and radiator (the first radiator)  50  similarly to Embodiment 1. Furthermore, the vehicle driving apparatus according to Embodiment 4 includes pipe member  60  and second radiator  70  as illustrated in  FIG. 6 . 
     Pipe member  60  allows a cooling medium (for example, cooling oil) to flow through its inside and is partially embedded in the inside of stator core  20 . Pipe member  60  contacts stator core  20  with high thermal conductivity. Alternatively, pipe member  60  may be connected to a through-hole provided in a path having many ranges inside stator core  20 . 
     Second radiator  70  performs heat exchange between the cooling media flowing through pipe member  60  and the ambient air and radiates heat of the cooling medium. Second radiator  70  is provided with a pump to circulate the cooling medium between pipe member  60  and second radiator  70 . Alternatively, the pump may be provided in the exterior of second radiator  70 . 
     According to the vehicle driving apparatus of Embodiment 4, in addition to cooling of stator core  20  by stator coil  30 A, direct cooling of stator core  20  by pipe member  60  can be performed to suppress generation of heat of stator core  20  more. Accordingly, the whole stator is cooled more equally. 
     Each embodiment of the present invention has been described thus far. 
     In the description of each embodiment, the wiring of stator coil  30 A has the same configuration as pipe member  30  extending to the exterior of the stator. However, the structures of the two elements may be different so that the portion of stator coil  30 A has high thermal conductivity while the portion of pipe member  30  extending to the exterior of the stator has low thermal conductivity. 
     The material of insulation coating  31  of stator coil  30 A and/or the material of metallic pipe  32  may be different between a side in contact with stator core  20  and the opposite side of stator core  20 . More specifically, the material on the side in contact with stator core  20  may have high thermal conductivity, and the material on the opposite side of stator core  20  may have low thermal conductivity. 
     In each embodiment, the tubular axle is employed, and pipe member  30  passes through the inside of the tubular axle and is introduced into stator core  20 . However, it is possible to employ a configuration in which the axle is provided with a through-hole, and this through-hole and stator coil  20  are connected together and thus introduce the cooling medium. In this case, a lead wire can be provided in the axle, and the motor driving apparatus can cause a current to flow in stator coil  20  through this lead wire. 
     The disclosure of Japanese Patent Application No. 2011-225863, filed on Oct. 13, 2011, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a driving apparatus of an electric vehicle, for example. 
     REFERENCE SIGNS LIST 
     
         
           10  Wheel 
           11  Permanent magnet 
           20  Stator core 
           21  Magnetic pole portion 
           30  Pipe member 
           30 A Stator coil 
           31  Insulation coating 
           32  Metallic pipe 
           33  Hollow portion 
           40  Motor driving apparatus 
           50  First radiator 
           60  Pipe member 
           70  Second radiator