Patent Publication Number: US-2016248302-A1

Title: Drive unit, method for removing inverter, and method for installing inverter

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2015-032038 filed with the Japan Patent Office on Feb. 20, 2015, the entire content of which is hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a drive unit, a method for removing an inverter, and a method for installing an inverter. 
     2. Description of the Related Art 
     JP-A-2011-182480 discloses an integrated power conversion apparatus and rotating electrical machine. 
     SUMMARY 
     A drive unit includes: an electric motor; a circuit case that houses an inverter therein and is installed on the electric motor; a first cooling flow passage that is provided, in contact with the inverter, in the circuit case and lets a cooling liquid flow therethrough; a second cooling flow passage that is provided in the electric motor and lets the cooling liquid flow therethrough in communication with the first cooling flow passage; and an open end that is provided on at least one end side of the first cooling flow passage so as to be capable of being opened to the outside of the flow passage for the cooling liquid when the circuit case is installed on the electric motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a transport machine; 
         FIG. 2  is a perspective view of a drive unit; 
         FIG. 3  is a perspective view of the drive unit seen from a direction different from that in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the drive unit taken along line IV-IV in  FIG. 2 ; 
         FIG. 5  is a cross-sectional view of the drive unit taken along line V-V in  FIG. 2 ; 
         FIG. 6  is a perspective view illustrating the state in which a circuit case is separated from an electric motor; 
         FIG. 7  is a perspective view of the drive unit seen from a direction different from that in  FIG. 6 ; 
         FIG. 8  is a perspective view of the drive unit without illustration of the circuit case in  FIG. 2 ; 
         FIG. 9  is a perspective view of the drive unit without illustration of the circuit case in  FIG. 3 ; 
         FIG. 10  is a perspective view of an internal structure of a circuit case body; 
         FIG. 11  is a cross-sectional view of the drive unit taken along line XI-XI in  FIG. 4 ; 
         FIG. 12  is a cross-sectional view of the drive unit taken along line XII-XII in  FIG. 4 ; 
         FIG. 13  is a diagram illustrating an inverter removal procedure; 
         FIG. 14  is a diagram illustrating the inverter removal procedure; 
         FIG. 15  is a diagram illustrating the inverter removal procedure; 
         FIG. 16  is a diagram illustrating the inverter removal procedure; and 
         FIG. 17  is a diagram illustrating the inverter removal procedure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     A drive unit according to one embodiment of the present disclosure includes: an electric motor; a circuit case that houses an inverter therein and is installed on the electric motor; a first cooling flow passage that is provided, in contact with the inverter, in the circuit case and lets a cooling liquid flow therethrough; a second cooling flow passage that is provided in the electric motor and lets the cooling liquid flow therethrough in communication with the first cooling flow passage; and an open end that is provided on at least one end side of the first cooling flow passage so as to be capable of being opened to the outside of the flow passage for the cooling liquid when the circuit case is installed on the electric motor. 
     A method for removing an inverter according to one embodiment of the present disclosure, includes: (A) in a drive unit including an electric motor fixed to a transport machine and a circuit case that houses an inverter and is installed on the electric motor from above, discharging a cooling liquid from a cooling flow passage provided, in contact with the inverter, in the circuit case; (B) after the discharging (A) of the cooling liquid, removing an electric system in the inverter; and (C) after the removing (B) of the electric system, removing the circuit case from the electric motor. 
     A method for installing an inverter according to one embodiment of the present disclosure, includes: (a) installing a circuit case housing an inverter to an electric motor fixed to a transport machine; (b) after the installing (a) of the circuit case, connecting an electric system to the inverter; and (c) after the connecting (b) of the electric system, passing a cooling liquid through a cooling flow passage provided, in contact with the inverter, in the circuit case. 
     According to an embodiment of the present disclosure, the inverter can be easily replaced. 
     Embodiment of the present disclosure will be described below in detail with reference to the drawings. In the following description, identical elements or elements having identical functions will be given identical reference signs, and duplicated descriptions thereof will be omitted. 
     [Drive Unit] 
     As illustrated in  FIG. 1 , a drive unit  1  is mounted as a power source in a transport machine  9  such as an automobile or a railway vehicle. In the following description, the term “upper and lower sides” refers to the upper and lower sides of the drive unit  1  mounted in a transport machine  9 . As illustrated in  FIGS. 2 to 4 , the drive unit  1  includes an electric motor  2  and an inverter unit  3 . 
     (Electric Motor) 
     The electric motor  2  is a synchronous-type or an induction-type three-phase AC motor, for example. The electric motor  2  has a rotor  11 , a stator  12 , a rotation detector  13 , and a motor case  20 . The rotor  11  includes a shaft  14  and a field magnet (not illustrated) such as a permanent magnet. The stator  12  surrounds the rotor  11  (see  FIG. 5 ). The stator  12  includes an armature winding, for example, and generates a rotating magnetic field with supply of three-phase AC power. The rotation detector  13  is a resolver, for example, and detects the rotation angle of the rotor  11 . 
     The motor case  20  houses the rotor  11  and the stator  12 , and is fixed in the transport machine  9 . The motor case  20  has a cylindrical body  21  and end walls  22 A and  22 B closing both ends of the cylindrical body  21 . The motor case  20  houses the rotor  11  and the stator  12  inside the cylindrical body  21 . The shaft  14  of the rotor  11  is rotatably held by the end walls  22 A and  22 B. The stator  12  is fixed to the inner periphery surface of the cylindrical body  21 . The shaft  14  has one end (hereinafter, referred to as “output end”)  14   a  penetrating through the end wall  22 A and extending to the outside of the motor case  20 . 
     In the following description, the direction along the shaft  14  will be called “longitudinal direction of the electric motor  2 .” The direction orthogonal to the vertical direction and the longitudinal direction will be called “width direction of the electric motor  2 .” The term “upper and lower sides” refers to the upper and lower sides in the vertical direction. The simple expression “lateral direction” includes “all directions crossing the vertical direction.” Note that the ±Z direction indicated in the figures shows an up-and-down direction (vertical direction). The ±X direction shows the direction along the shaft  14 , that is, the longitudinal direction of the electric motor  2 . The ±Y direction shows the width direction of the electric motor  2 . 
     The cylindrical body  21  has therein an annular cavity  21   a  surrounding the stator  12  (see  FIG. 5 ). The cylindrical body  21  has drain hole  21   d  in the lower part (see  FIG. 4 ). The drain hole  21   d  communicates with the cavity  21   a  and opens to the outside. The drain hole  21   d  is filled by a screwed drain plug  24 , for example. 
     As illustrated in  FIG. 5 , the cylindrical body  21  has side holes  21   b  and  21   c  formed in the side portions. The side holes  21   b  and  21   c  communicate with the cavity  21   a  and open to the outside. The side holes  21   b  and  21   c  are opposite to each other on the periphery of the cylindrical body  21 . The side hole  21   b , the cavity  21   a , and the side hole  21   c  are included in a series of flow passage R 2 . 
     As illustrated in  FIGS. 2 and 3 , joint pipes  23 A and  23 B are provided at periphery edges of the side holes  21   b  and  21   c , respectively. The joint pipes  23 A and  23 B protrude outward from the outer periphery surface of the cylindrical body  21 . The joint pipes  23 A and  23 B bend in the middle toward the cylindrical body  21 . The tips of the joint pipes  23 A and  23 B open in the direction along the outer periphery surface of the cylindrical body  21 . That is, the drive unit  1  further includes the pair of joint pipes  23 A and  23 B connected to respective both ends of the flow passage R 1 . 
     As illustrated in  FIG. 6 , a connecting portion  31  and columns  36 A and  36 B are provided on the upper part of the cylindrical body  21 . The connecting portion  31  is positioned on the upper part of the cylindrical body  21  at the side distant from the output terminal  14   a . The columns  36 A and  36 B are positioned on the upper part of the cylindrical body  21  at the side near the output terminal  14   a.    
     The connecting portion  31  has a power supply terminal  32 , a signal connector  34 , and a peripheral wall  35 . The power supply terminal  32  and the signal connector  34  are aligned along the width direction of the electric motor  2 . The power supply terminal  32  has input terminals  33 U,  33 V, and  33 W corresponding to three-phase AC power. The input terminals  33 U,  33 V, and  33 W are connected to the winding of the stator  12  and aligned along the width direction of the electric motor  2 . The signal connector  34  is connected to the rotation detector  13  (see  FIG. 4 ). The peripheral wall  35  protrudes upward from the outer periphery surface of the cylindrical body  21  and surrounds the power supply terminal  32  and the signal connector  34 . The peripheral wall  35  has upwardly opened positioning holes  35   a  and  35   b  in the upper surface. 
     The columns  36 A and  36 B are aligned along the width direction of the electric motor  2  and protrude upward. 
     The peripheral wall  35  and the columns  36 A and  36 B support a circuit case  50  (described later) of the inverter unit  3  in conjunction with each other. The positioning holes  35   a  and  35   b  serve as attachment portions for positioning the circuit case  50 . That is, the drive unit  1  further includes the positioning holes  35   a  and  35   b  as an example of the first attachment portion provided in the upper part of the electric motor  2 . 
     The foregoing configuration of the electric motor  2  is a mere example and the configuration of the electric motor  2  is not limited to this. For example, the field magnet may be provided at the stator  12  side and the armature winding at the rotor  11  side. 
     (Inverter Unit) 
     As illustrated in  FIGS. 4, 8, and 9 , the inverter unit  3  has an inverter  40  and the circuit case  50 . The inverter  40  has a circuit board  41 , a smoothing capacitor  42 , a heat sink  43 , output terminals  44 U,  44 V, and  44 W, relay conductors  45 P and  45 N, a signal cable  46 , and input terminals  48 P and  48 N. 
     The circuit board  41  includes a switching circuit for power conversion and a control circuit for controlling the switching circuit. The switching circuit and the control circuit may be mounted on the same substrate or may be mounted on separate substrates. The circuit board  41  converts DC power into three-phase AC power at a desired frequency and supplies the three-phase AC power to the electric motor  2 . The smoothing capacitor  42  smooths out an input voltage from a DC power source. The heat sink  43  is stacked on the circuit board  41  and absorbs heat generated by the switching elements and others on the circuit board  41  to discharge the same to the outside. 
     The output terminals  44 U,  44 V, and  44 W extend from the circuit board  41  and output the three-phase AC power generated by the circuit board  41 . The output terminals  44 U,  44 V, and  44 W are connected to the input terminals  33 U,  33 V, and  33 W, respectively. The relay conductors  45 P and  45 N connect the circuit board  41  with the smoothing capacitor  42  to guide DC power to the circuit board  41 . The signal cable  46  extends from the circuit board  41 . The signal cable  46  transmits an output signal from the rotation detector  13  to the control circuit on the circuit board  41 . A signal connector  47  is provided at the tip of the signal cable  46 . The signal connector  47  is connected to the signal connector  34 . The input terminals  48 P and  48 N jut from the smoothing capacitor  42 . A terminal  91 P of a power cable  90 P and a terminal  91 N of a power cable  90 N are connected to the input terminals  48 P and  48 N, respectively. 
     As illustrated in  FIGS. 2 to 4 , the circuit case  50  houses the inverter  40  and is installed on the electric motor  2  from above. The circuit case  50  has a case body  51  and a top plate  60 . 
     The case body  51  has an upwardly opened peripheral wall  53  and a bottom portion  52  closing the bottom of the case body  51 . The bottom portion  52  and the peripheral wall  53  are rectangular-shaped in planar view. However, the bottom portion  52  and the peripheral wall  53  may not be necessarily so shaped. Positioning protrusions  54 A and  54 B are provided on the lower surface of the bottom portion  52  (see  FIGS. 6 and 7 ). 
     The positioning protrusions  54 A and  54 B are attached to (e.g. fit into or inserted into) the positioning holes  35   a  and  35   b  in the upper part of the electric motor  2  from above, respectively. That is, the drive unit  1  further includes the positioning protrusions  54 A and  54 B as an example of a second attachment portion that is provided on the lower part of the circuit case  50  and attached to the first attachment portion from above. The attachment of the positioning protrusions  54 A and  54 B to the positioning holes  35   a  and  35   b  allows the circuit case  50  to be easily positioned relative to the electric motor  2 . At that time, a pair of parallel surfaces constituting the outer periphery surface of the peripheral wall  53  aligns with the longitudinal direction of the electric motor  2 . The other pair of parallel surfaces constituting the outer periphery surface of the peripheral wall  53  aligns with the width direction of the electric motor  2 . 
     An installation margin  58  jutting to the lateral direction (for example, the width direction of the electric motor  2 ) is formed at the lower part of the circuit case  50 . When the positioning protrusions  54 A and  54 B are attached to the positioning holes  35   a  and  35   b , the installation margin  58  is positioned on the peripheral wall  35  and the columns  36 A and  36 B. The installation margin  58  is fastened by bolts B 1  from above to the peripheral wall  35  and the columns  36 A and  36 B. That is, the drive unit  1  further includes the bolts B 1  as an example of a member for fastening the circuit case  50  to the electric motor  2  from above. 
     Grip handles  55 A and  55 B are provided at the outside of the case body  51 . The handles  55 A and  55 B jut outward from the pair of parallel surfaces along the width direction of the electric motor  2  on the outer periphery surface of the peripheral wall  53 , for example. The handles  55 A and  55 B can be used for carrying the case body  51  at the time of installation onto or removal from the electric motor  2 . 
     In the case body  51 , a protuberance  56  is formed on the upper surface of the bottom portion  52  (see  FIG. 10 ). The protuberance  56  extends along the width direction of the electric motor  2 . Both ends of the protuberance  56  are connected to the inner surface of the peripheral wall  53 . Accordingly, the inside of the case body  51  is divided into an area A 1  at the side near the output terminal  14   a  and an area A 2  at the side distant from the output terminal  14   a.    
     The protuberance  56  has a groove  56   a  in the upper surface along the width direction of the electric motor  2 . The peripheral wall  53  has side holes  53   a  and  53   b  (see  FIG. 11 ). The side holes  53   a  and  53   b  are connected to the both ends of the groove  56   a  and opened to the lateral direction of the peripheral wall  53  (for example, the width direction of the electric motor  2 ). The side holes  53   a  and  53   b  are opened to the pair of parallel surfaces along the longitudinal direction of the electric motor  2  on the outer periphery surface of the peripheral wall  53 . The side holes  53   a  and  53   b  are positioned under the groove  56   a . The opening directions of the side holes  53   a  and  53   b  are opposite to each other. 
     A joint pipe  57 A protruding from the peripheral wall  53  to the lateral direction (for example, the width direction of the electric motor  2 ) is provided at the periphery edge of the side hole  53   a . In addition, a joint pipe  57 B protruding from the peripheral wall  53  to the lateral direction (for example, the width direction of the electric motor  2 ) is provided at the periphery edge of the side hole  53   b . That is, the drive unit  1  further includes the pair of joint pipes  57 A and  57 B that protrudes from the circuit case  50  to the lateral direction (for example, the width direction of the electric motor  2 ) and is connected to the both ends of the flow passage R 1 . The pair of joint pipes  57 A and  57 B is bent to the lateral direction (for example, the longitudinal direction of the electric motor  2 ). Accordingly, open ends D 1  (see  FIGS. 3 and 13 ) of the joint pipes  57 A and  57 B are close to the peripheral wall  53 . Further, the opening directions of the joint pipes  57 A and  57 B align with the outer periphery surface of the peripheral wall  53 . 
     The bottom portion  52  has an opening  52   a  at a portion corresponding to an area A 2 . The opening  52   a  is positioned in correspondence with the connecting portion  31 . The peripheral wall  53  has openings  53   c  and  53   d  in either one of a pair of wall portions along the longitudinal direction of the electric motor  2 . The openings  53   c  and  53   d  are opened to an area A 1  within the case body  51 . The openings  53   c  and  53   d  accept the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N, respectively. That is, the drive unit  1  further includes the openings  53   c  and  53   d  as an example of openings (third openings) that are formed in the side portions of the circuit case  50  and accept the terminals  91 P and  91 N 
     As illustrated in  FIGS. 4 and 11 , the circuit board  41  is attached to the top of the protuberance  56  via the heat sink  43 . The circuit board  41  and the heat sink  43  are fastened to the protuberance  56  from above by fastening members (not illustrated) such as bolts. In this state, the side holes  53   a  and  53   b  and the groove  56   a  are included in the flow passage R 1  in contact with the heat sink  43  of the inverter  40  (see  FIG. 11 ). 
     As illustrated in  FIG. 2 , the joint pipe  57 A is connected to a supply source of a cooling liquid via a liquid supply hose  4 . Accordingly, the cooling liquid passes through the flow passage R 1 . That is, the drive unit  1  further includes the flow passage R 1  as an example of a first cooling flow passage that is provided, in contact with the inverter  40 , in the circuit case  50  and lets the cooling liquid through. The cooling liquid is water, for example. The supply source of the cooling liquid is a radiator of the transport machine  9 , for example. 
     As illustrated in  FIGS. 4 and 11 , the groove  56   a  serves as a heat absorber that extends in the direction crossing the vertical direction and contacts the inverter  40 . The side hole  53   a  serves as a liquid supplier that guides the cooling liquid from the side portion of the circuit case  50  to the heat absorber. The side hole  53   b  serves as a liquid discharger that guides the cooling liquid from the heat absorber to the side portion of the circuit case  50 . 
     As illustrated in  FIG. 3 , the joint pipe  57 B is connected to the joint pipe  23 B via a relay hose  5 . Accordingly, the flow passage R 1  and the flow passage R 2  communicate with each other. As a result, the cooling liquid discharged from the flow passage R 1  further passes through the flow passage R 2 . That is, the drive unit  1  further includes the flow passage R 2  as an example of a second cooling flow passage that is provided in the electric motor  2  and communicates with the first cooling flow passage to let the cooling liquid through. 
     As illustrated in  FIG. 2 , the joint pipe  23 A provided at the side opposite to the joint pipe  23 B is connected to the supply source of the cooling liquid via a circulation hose  6 . Accordingly, the cooling liquid circulates between the flow passages R 1  and R 2  and the supply source. 
     According to such piping, even in the state in which the circuit case  50  is installed on the electric motor  2 , the ends of the joint pipes  57 A and  57 B can be opened by detaching the hoses  4  and  5  (see  FIGS. 12 and 13 ). The joint pipes  57 A and  57 B protrude from the case body  51  to the lateral direction (for example, the width direction of the electric motor  2 ), and bend to the lateral direction (for example, the longitudinal direction of the electric motor  2 ). Accordingly, the opening direction of the joint pipes  57 A and  57 B are not oriented upward or downward in the vertical direction. Therefore, the both ends of the flow passage R 1  are opened to the lateral direction of the circuit case  50  (for example, the longitudinal direction of the electric motor  2 ). 
     The connecting portion between the joint pipe  57 A and the hose  4  and the connecting portion between the joint pipe  57 B and the hose  5  serve such that, when the circuit case  50  is installed on the electric motor  2 , the ends of the flow passage R 1  (for example, the open ends D 1  of the joint pipes  57 A and  57 B) are opened to the outside of the flow passage for cooling liquid. The ends of the flow passage R 1  can be opened to the outside of the flow passage for cooling liquid by detaching the hoses  4  and  5  from the joint pipes  57 A and  57 B. Opening the ends of the flow passage R 1  to the outside of the flow passage for cooling liquid includes bringing the ends of the flow passage R 1  into the state in which the cooling liquid is discharged from the ends to the outside of the flow passage for cooling liquid, for example. 
     The open ends D 1  of the joint pipes  57 A and  57 B (see  FIG. 13 ) can be opened to the outside of the flow passage for cooling liquid when the circuit case  50  is installed on the electric motor  2 . The open ends D 1  of the joint pipes  57 A and  57 B can be opened to the outside of the flow passage for cooling liquid by detaching the hoses  4  and  5  from the joint pipes  57 A and  57 B, for example. That is, the drive unit  1  further includes the open end D 1  that is provided at least at one end of the flow passage R 1  in such a manner as to be capable of being opened to the outside of the flow passage for cooling liquid when the circuit case  50  is installed on the electric motor  2 . Opening the open end D 1  to the outside of the flow passage for cooling liquid includes bringing the open end D 1  into the state in which the cooling liquid is discharged from the open end D 1  to the outside of the flow passage for cooling liquid, for example. 
     The open ends D 1  are provided at the ends of the joint pipes  57 A and  57 B. The open ends D 1  open the flow passage R 1  to the lateral direction of the circuit case  50  (for example, the longitudinal direction of the electric motor  2 ). Opening the flow passage R 1  by the open ends D 1  includes bringing the open ends D 1  into the state in which the cooling liquid is discharged from the open ends D 1  to the outside of the flow passage R 1 , for example. This state of the open ends D 1  is realized by detaching the hoses  4  and  5  from the joint pipes  57 A and  57 B, for example. The phrase “the outside of the flow passage for cooling liquid” means the outside of the flow passage when the hoses  4  and  5  are connected to the joint pipes  57 A and  57 B, respectively. 
     As illustrated in  FIG. 9 , the output terminals  44 U,  44 V, and  44 W extending from the circuit board  41  are arranged on the input terminals  33 U,  33 V, and  33 W via the opening  52   a , respectively. The output terminals  44 U,  44 V, and  44 W are fastened by bolts B 2  from above to the input terminals  33 U,  33 V, and  33 W respectively. That is, the drive unit  1  further includes the bolts B 2  as an example of members fastening the output terminals  44 U,  44 V, and  44 W of the inverter  40  from above to the input terminals  33 U,  33 V, and  33 W of the electric motor  2 . 
     The signal connector  47  of the signal cable  46  extending from the circuit board  41  is connected to the signal connector  34  via the opening  52   a  (see  FIGS. 8 and 16 ). 
     As illustrated in  FIGS. 4 and 8 , the smoothing capacitor  42  is housed in the area A 1  of the case body  51 . The smoothing capacitor  42  is arranged such that the input terminals  48 P and  48 N jut to the side opposite to the protuberance  56 . The input terminals  48 P and  48 N jut from the smoothing capacitor  42  in different lengths. In the longitudinal direction of the electric motor  2 , the positions of the tips of the input terminals  48 P and  48 N correspond to the positions of the openings  53   c  and  53   d  (see  FIG. 10 ), for example. 
     The terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N are introduced into the area A 1  from the openings  53   c  and  53   d , respectively (see  FIG. 12 ). The terminals  91 P and  91 N introduced into the area A 1  are arranged on the input terminals  48 P and  48 N, respectively. The terminals  91 P and  91 N are fastened by bolts B 3  from above to the input terminals  48 P and  48 N, respectively. That is, the drive unit  1  further includes the bolts B 3  as an example of members fastening the terminals  91 P and  91 N from above to the input terminals  48 P and  48 N. 
     As illustrated in  FIG. 8 , sealing members  92 P and  92 N are provided at the outer peripheries of the power cables  90 P and  90 N, respectively. The sealing members  92 P and  92 N are in contact with the outer surface of the peripheral wall  53  to seal the gap between the opening  53   c  and the power cable  90 P and the gap between the opening  53   d  and the power cable  90 N (also see  FIG. 10 ). The sealing members  92 P and  92 N are fastened to the peripheral wall  53  by fastening members (not illustrated) such as bolts, for example, from the lateral direction (for example, the width direction of the electric motor  2 ). 
     As illustrated in  FIGS. 2 to 4 and 14 , the top plate  60  is arranged on the case body  51  and closes the upper part of the peripheral wall  53 . The top plate  60  is fastened by bolts B 4  to the peripheral wall  53  from above. The top plate  60  has openings  60   a  and  60   b . The opening  60   a  is positioned above the connecting portions between the terminals  91 P and  91 N and the input terminals  48 P and  48 N. The opening  60   b  is positioned above the connecting portions between the output terminals  44 U,  44 V, and  44 W and the input terminals  33 U,  33 V, and  33 W. That is, the drive unit  1  further includes the opening  60   a  as an example of a first opening that is provided in the upper part of the circuit case  50  and opens the input terminals  48 P and  48 N of the inverter  40 . The drive unit  1  further includes the opening  60   b  as an example of a second opening that is provided in the upper part of the circuit case  50  and opens the output terminals  44 U,  44 V, and  44 W. 
     Covers  61 A and  61 B are arranged on the top plate  60  to cover the openings  60   a  and  60   b , respectively. The covers  61 A and  61 B are fastened by bolts B 5  to the top plate  60  from above. That is, the drive unit  1  further includes the covers  61 A and  61 B that cover the openings  60   a  and  60   b , respectively. The drive unit  1  further includes the bolts B 5  as an example of members fastening the covers  61 A and  61 B to the circuit case  50  from above. 
     [Method for Replacing the Inverter] 
     Subsequently, the procedure for replacing the inverter unit  3  will be described. In general, the inverter is shorter in lifetime than an electric motor. Accordingly, it is assumed that there is the need for the drive unit  1  that the inverter unit  3  can be replaced while the electric motor  2  is mounted in the transport machine  9  to be driven. The procedure described above is a procedure for replacing the inverter unit  3  without having to remove the electric motor  2  from the transport machine  9  in accordance with this need. 
     (Procedure for Removing the Inverter) 
     First, as illustrated in  FIG. 13 , the hoses  4  and  5  are detached from the joint pipes  57 A and  57 B to discharge the cooling liquid from the end of the joint pipe  57 B. That is, the cooling liquid is discharged from the flow passage R 1  as the first cooling flow passage. At that time, the discharge of the cooling liquid can be facilitated by pressurization from the joint pipe  57 A side or suction from the joint pipe  57 B side. The cooling liquid may be discharged from the end of the joint pipe  57 A. In this case, the discharge of the cooling liquid can be facilitated by pressurization from the joint pipe  57 B side or suction from the joint pipe  57 A side. 
     Alternatively, instead of detaching the hose  5  from the joint pipe  57 B, the hose  4  may be detached from the joint pipe  57 A and the drain plug  24  be detached from the drain hole  21   d  of the motor case  20  to discharge the cooling liquid from the drain hole  21   d . That is, out of the both ends of the flow passage R 1 , the end opposite to the end connected to the flow passage R 2  may be opened to discharge the cooling liquid from the flow passage R 1  through the drain hole  21   d  of the flow passage R 2 . After that, the hose  5  may be detached from the joint pipe  57 B to further discharge the cooling liquid left in the flow passage R 1  from either of the ends of the joint pipes  57 A and  57 B. 
     Alternatively, instead of detaching the hoses  4  and  5  from the joint pipes  57 A and  57 B, the drain plug  24  may be detached from the drain hole  21   d  to discharge the cooling liquid from the drain hole  21   d . Further, after that, the hoses  4  and  5  may be detached from the joint pipes  57 A and  57 B, respectively, to discharge the cooling liquid left in the flow passage R 1  from either of the ends of the joint pipes  57 A and  57 B. 
     As described above, the groove  56   a  aligns with the width direction of the electric motor  2 . The side holes  53   a  and  53   b  are opened in the lateral direction of the circuit case  50  (for example, the width direction of the electric motor  2 ). Accordingly, in any of the discharge methods, the cooling liquid is discharged from the flow passage R 1  along the direction crossing the vertical direction. 
     Next, as illustrated in  FIG. 14 , the bolts B 5  fastening the covers  61 A and  61 B to the top plate  60  are removed upward, and the covers  61 A and  61 B are removed from the top plate  60 . Accordingly, the openings  60   a  and  60   b  are opened. 
     Next, the electric system formed by the inverter  40  is removed. Specifically, as illustrated in  FIG. 15 , the bolts B 3  fastening the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N to the input terminals  48 P and  48 N are removed upward, and the terminals  91 P and  91 N are extracted from the circuit board  41 . Accordingly, the terminals  91 P and  91 N are removed from the input terminals  48 P and  48 N. After that, as illustrated in  FIG. 16 , the bolts B 2  fastening the output terminals  44 U,  44 V, and  44 W to the input terminals  33 U,  33 V, and  33 W are removed upward. Accordingly, the output terminals  44 U,  44 V, and  44 W are removed from the input terminals  33 U,  33 V, and  33 W. Further, the signal connector  47  is removed upward from the signal connector  34 . 
     Next, as illustrated in  FIG. 17 , the bolts B 1  fastening the circuit case  50  to the electric motor  2  are removed upward to detach the circuit case  50  from the electric motor  2 . At that time, the handles  55 A and  55 B may be gripped to carry the circuit case  50 . 
     (Procedure for Installing the Inverter) 
     The inverter unit  3  is installed by following the procedure for removal in reverse. First, the inverter unit  3  is placed on the electric motor  2  fixed to the transport machine  9  (see  FIG. 17 ). At that time, the positioning protrusions  54 A and  54 B are attached to the positioning holes  35   a  and  35   b . Accordingly, the inverter unit  3  is correctly positioned. After that, the circuit case  50  is fastened by the bolt B 1  to the electric motor  2  from above. 
     Next, the electric system in the inverter  40  is connected. Specifically, the signal connector  47  is first connected to the signal connector  34  from above. Then, the output terminals  44 U,  44 V, and  44 W are fastened by the bolts B 2  from above to the input terminals  33 U,  33 V, and  33 W. Accordingly, the output terminals  44 U,  44 V, and  44 W are connected to the input terminals  33 U,  33 V, and  33 W (see  FIG. 16 ). After that, the terminals  91 P and  91 N are inserted into the area A 1  through the openings  53   c  and  53   d . The terminals  91 P and  91 N are fastened by the bolts B 3  from above to the input terminals  48 P and  48 N. Accordingly, the terminals  91 P and  91 N are connected to the input terminals  48 P and  48 N (see  FIG. 15 ). 
     Next, the covers  61 A and  61 B are arranged to cover the openings  60   a  and  60   b , respectively. Then, the covers  61 A and  61 B are fastened by the bolts B 5  to the top plate  60  from above (see  FIG. 14 ). 
     Next, the hose  5  is connected to the joint pipe  57 B, and the hose  4  is connected to the joint pipe  57 A (see  FIG. 13 ). After that, the cooling liquid is passed through the flow passages R 1  and R 2 . As described above, the groove  56   a  aligns with the width direction of the electric motor  2 , and the side holes  53   a  and  53   b  are opened in the lateral direction of the circuit case  50  (for example, the width direction of the electric motor  2 ). Accordingly, the cooling liquid is passed through the flow passage R 1  in the direction crossing the vertical direction. Accordingly, the replacement of the inverter unit  3  is completed. 
     [Advantageous Effects of this Embodiment] 
     As described above, the drive unit  1  includes the electric motor  2 , the circuit case  50  that houses the inverter  40  and is installed on the electric motor  2 , the flow passage R 1  that is provided, in contact with the inverter  40 , in the circuit case  50  and lets the cooling liquid through, the flow passage R 2  that is provided in the electric motor  2  and lets the cooling liquid through in communication with the flow passage R 1 , and the open end D 1  that is provided on at least one end side of the flow passage R 1  so as to be capable of being opened to the outside of the flow passage for cooling liquid when the circuit case  50  is installed on the electric motor  2   
     According to this configuration, when the circuit case  50  is installed on the electric motor  2 , the liquid can be drained from the flow passage R 1 . Accordingly, the electric system can be removed when the cooling liquid is drained from the flow passage R 1 . Therefore, the inverter  40  can be easily replaced. 
     The circuit case  50  may be installed on the electric motor  2  from above. In addition, the open ends D 1  may open the flow passage R 1  in the lateral direction of the circuit case  50  (for example, the longitudinal direction of the electric motor  2 ). In this case, the liquid can be drained from the flow passage R 1  in the direction crossing the alignment direction of the circuit case  50  and the electric motor  2 . Accordingly, it is possible to suppress liquid dripping into the connecting portion between the circuit case  50  and the electric motor  2  in a more reliable manner. Therefore, the inverter  40  can be replaced more easily. 
     The flow passage R 1  may have the heat absorber (groove  56   a ) that extends in the direction crossing the vertical direction in contact with the inverter  40 , the liquid supplier (side hole  53   a ) that guides the cooling liquid from the side portion of the circuit case  50  to the heat absorber, and the liquid discharger (side hole  53   b ) that guides the cooling liquid from the heat absorber to the side portion of the circuit case  50 . The liquid supplier and the liquid discharger may be positioned under the heat absorber. In this case, the cooling liquid can be discharged more easily prior to the removal of the electric system. Therefore, the inverter  40  can be replaced more easily. 
     The drive unit  1  may further include the pair of joint pipes  57 A and  57 B that protrude from the circuit case  50  in the lateral direction (for example, the width direction of the electric motor  2 ) and connect to the both ends of the flow passage R 1 . The open end D 1  may be provided at one end of at least one of the pair of joint pipes  57 A and  57 B. In this case, by providing the open ends D 1  at the ends of the joint pipes  57 A and  57 B protruding in the lateral direction, it is possible to suppress more reliably liquid dripping into the connecting portion between the circuit case  50  and the electric motor  2 . Therefore, the inverter  40  can be replaced more easily. 
     The pair of joint pipes  57 A and  57 B may be bent in the lateral direction (for example, the longitudinal direction of the electric motor  2 ). In this case, the hose arrangement can be shifted toward the circuit case  50  and the electric motor  2 . As a result, it is possible to achieve space saving. In addition, it is possible to suppress liquid dripping into the connecting portion between the inverter  40  and the electric motor  2  more reliably as compared to the case where the joint pipes  57 A and  57 B are bent immediately below. Therefore, the inverter  40  can be replaced more easily. 
     The drive unit  1  may further include the members (bolts B 1 ) that fasten the circuit case  50  to the electric motor  2  from above, the first opening (opening  60   a ) that is provided in the upper part of the circuit case  50  and opens the input terminals  48 P and  48 N of the inverter  40 , the members (bolts B 3 ) that fasten the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N to the input terminals  48 P and  48 N of the inverter  40  from above, the first cover (cover  61 A) that covers the first opening, the second opening (opening  60   b ) that is provided in the upper part of the circuit case  50  and opens the output terminals  44 U,  44 V, and  44 W of the inverter  40 , the members (bolts B 2 ) that fasten the output terminals  44 U,  44 V, and  44 W of the inverter  40  to the input terminals  33 U,  33 V, and  33 W of the electric motor  2  from above, and the second cover (cover  61 B) that covers the second opening. 
     In this case, the direction of discharging the cooling liquid crosses the direction of removing the electric system and the mechanical system. Accordingly, it is possible to suppress more reliably liquid dripping into the connecting portion in the electric system and the connecting portion in the mechanical system. In addition, by covering with a cover the opening for opening upward the connecting portion in the electric system, it is possible to suppress more reliably liquid dripping into the connecting portion in the electric system. Therefore, the inverter  40  can be replaced more easily. 
     The drive unit  1  may further include the third openings (openings  53   c  and  53   d ) that are provided in the side portions of the circuit case  50  and accepts the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N. In this case, by passing the power cables  90 P and  90 N through the third openings, it is possible to seal the opening  60   a  with the cover  61 A in a more secure manner. Accordingly, it is possible to suppress more reliably liquid dripping into the connecting portion in the electric system. Therefore, the inverter  40  can be replaced more easily. 
     The drive unit  1  may further include the first attachment portion (positioning holes  35   a  and  35   b ) that is provided in the upper part of the electric motor  2  and the second attachment portion (positioning protrusions  54 A and  54 B) that is provided on the lower part of the circuit case  50  and attached into the first attachment portion from above. In this case, even when the electric motor  2  is mounted in the transport machine  9  to be driven, the electric motor  2  and the circuit case  50  can be easily positioned. Therefore, the inverter  40  can be replaced more easily. 
     The drive unit  1  may further include the grip handles  55 A and  55 B provided at the outside of the circuit case  50 . In this case, the circuit case  50  can be easily removed and re-arranged. Therefore, the inverter  40  can be replaced more easily. 
     The procedure for removing the inverter unit  3  in the drive unit  1  includes: (A) discharging the cooling liquid from the flow passage R 1  when the electric motor  2  is fixed to the transport machine  9 ; (B) after the discharging (A) of the cooling liquid, removing the electric system in the inverter  40 ; and (C) after the removing (B) of the electric system, removing the circuit case  50  from the electric motor  2 . 
     According to this procedure, it is possible to remove the electric system when the cooling liquid is drained from the flow passage R 1 . In addition, it is possible to remove the mechanical system when the electric system is removed. Therefore, even when the electric motor  2  is mounted in the transport machine  9 , the inverter  40  can be easily replaced. 
     During the removing (B) of the electric system, after the removal of the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N from the input terminals  48 P and  48 N of the inverter  40 , the output terminals  44 U,  44 V, and  44 W of the inverter  40  may be removed from the input terminals of the electric motor  2 . In this case, when the power supply is shut off, the output terminals  44 U,  44 V, and  44 W of the inverter  40  can be removed from the input terminals  33 U,  33 V, and  33 W of the electric motor  2 . Therefore, the inverter  40  can be replaced more easily. 
     During the discharging (A) of the cooling liquid, the cooling liquid may be discharged from the flow passage R 1  in the direction crossing the vertical direction. During the removing (B) of the electric system, the members (bolts B 3 ) fastening the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N to the input terminals  48 P and  48 N of the inverter  40  and the members (bolts B 3 ) fastening the output terminals  44 U,  44 V, and  44 W of the inverter  40  to the input terminals  33 U,  33 V, and  33 W of the electric motor  2  may be removed upward. During the removing (C) of the circuit case  50 , the members (bolts B 1 ) fastening the circuit case  50  to the electric motor  2  may be removed upward. In this case, the direction of discharging the cooling liquid crosses the direction of removing the electric system and the mechanical system. Accordingly, it is possible to suppress more reliably liquid dripping into the connecting portion in the electric system and the connecting portion in the mechanical system. Therefore, the inverter  40  can be replaced more easily. 
     During the discharging (A) of the cooling liquid, the cooling liquid may be discharged from the flow passage R 1  by at least either of pressurization and suction. In this case, the cooling liquid can be discharged more reliably prior to the removal of the electric system. Accordingly, it is possible to suppress more reliably liquid dripping into the connecting portion in the electric system. Therefore, the inverter  40  can be replaced more easily. 
     The procedure for attaching the inverter unit  3  to the electric motor  2  includes: (a) attaching the circuit case  50  to the electric motor  2  fixed to the transport machine  9 ; (b) after the attaching (a) of the circuit case  50 , connecting the electric system to the inverter  40 ; (c) after the connecting (b) of the electric system, passing the cooling liquid through the flow passage R 1 . 
     According to this procedure, the electric system can be connected when the circuit case  50  is definitely positioned relative to the electric motor  2  by the connection of the mechanical system. By connecting the electric system prior to the passage of the cooling liquid, the electric system can be connected in the absence of the cooling liquid. Accordingly, the inverter  40  can be easily replaced even when the electric motor  2  is mounted in the transport machine  9 . 
     During the connecting (b) of the electric system, after the connection of the output terminals  44 U,  44 V, and  44 W of the inverter  40  to the input terminals  33 U,  33 V, and  33 W of the electric motor  2 , the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N may be connected to the input terminals  48 P and  48 N of the inverter  40 . In this case, when the power supply is shut off, the output terminals  44 U,  44 V, and  44 W of the inverter  40  can be connected to the input terminals  33 U,  33 V, and  33 W of the electric motor  2 . Therefore, the inverter  40  can be replaced more easily. 
     During the attaching (a) of the circuit case  50 , the circuit case  50  may be fastened to the electric motor  2  from above. During the connecting (b) of the electric system, the output terminals  44 U,  44 V, and  44 W of the inverter  40  may be fastened from above to the input terminals  33 U,  33 V, and  33 W of the electric motor  2 . Further, during the connecting (b) of the electric system, the terminal  91 P of the power cable  90 P and the terminal  91 N of the power cable  90 N may be fastened from above to the input terminals  48 P and  48 N of the inverter  40 . During the passing (c) of the cooling liquid, the cooling liquid may be passed through the flow passage R 1  along the direction crossing the vertical direction. In this case, the direction of passing the cooling liquid crosses the direction of connecting the electric system and the mechanical system. Accordingly, it is possible to suppress more reliably liquid dripping into the connecting portion in the electric system and the connecting portion in the mechanical system. Therefore, the inverter  40  can be replaced more easily. 
     The embodiment has been described so far. The technique of the present disclosure is not limited to the foregoing embodiment. The technique of the present disclosure can be modified in various manners without deviating from the gist of the present disclosure. The first attachment portion and the second attachment portion are not limited to the foregoing ones (the positioning protrusions  54 A and  54 B and the positioning holes  35   a  and  35   b ). For example, the positioning holes may be provided on the circuit case  50  side, and the positioning protrusions to be attached to the positioning holes may be provided on the electric motor  2  side. The various fastening members are not limited to the bolts described above as examples. The various fastening members may be press-fit pins, for example. 
     The foregoing detailed description has been presented for the purposes of illustration and description. Many modifications and variations are possible in light of the above teaching. It is not intended to be exhaustive or to limit the subject matter described herein to the precise form disclosed. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims appended hereto.