Patent Publication Number: US-2021194309-A1

Title: Rotary electric machine, stator thereof and manufacturing method of rotary electric machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Patent Application No. PCT/JP2019/027830 filed on Jul. 15, 2019, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2018-171801 filed in Japan filed on Sep. 13, 2018, the entire disclosure of the above application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure in this specification relates to a rotary electric machine, a stator thereof, and a manufacturing method of the rotary electric machine. 
     BACKGROUND 
     A rotary electric machine may have at least one electrical conductive member to provide at least one electrical connection. It is required to keep electrical insulation of the conductive member. In the above aspects, or in other aspects not mentioned, there is a need for further improvements in a rotary electric machine, a stator thereof, and a manufacturing method of the rotary electric machine. 
     SUMMARY 
     A disclosed stator of a rotary electric machine, comprised: a stator core which provides a plurality of slots; and a stator coil mounted on a stator core, wherein the stator coil includes: a coil end positioned at an end of the stator core; a bus bar made of a conductive member electrically connected to a coil terminal included in the coil end; a holder which is a container made of an insulating member for accommodating the bus bar, is arranged in an axial direction of the stator core, and has an opening facing the stator core. 
     According to the stator of the rotating electric machine disclosed, the holder is positioned so that the opening faces the stator core. As a result, the wall surface of the holder is positioned on the outside of the stator core. This improves insulation performance. 
     The rotary electric machine disclosed herein includes the stator of the rotary electric machine, a rotor magnetically coupled to the stator, and a housing that accommodates the stator and the rotor and faces the wall surface of the holder. 
     A disclosed manufacturing method of a rotary electric machine comprises: mounting a stator coil on a stator core providing a plurality of slots; positioning the coil end at an end of the stator core; assembling a bus bar unit by mounting a bus bar made of a conductive member from an opening of a holder made of an insulating member; positioning the bus bar unit so that the opening faces an axial end of the stator core; electrically connecting the coil terminal included in the coil end and the bus bar; and positioning a housing in a radial direction outside and/or an axial direction outside of a wall of the holder. 
     According to the manufacturing method of the rotary electric machine disclosed herein, the housing is positioned on an outside in the radial direction and/or an outside in the axial direction of the wall of the holder. This improves insulation performance. 
     The disclosed aspects in this specification adopt different technical solutions from each other in order to achieve their respective objectives. Reference numerals in parentheses described in claims and this section exemplarily show corresponding relationships with parts of embodiments to be described later and are not intended to limit technical scopes. The objects, features, and advantages disclosed in this specification will become apparent by referring to following detailed descriptions and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure is further described with reference to the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of a rotary electric machine according to a first embodiment; 
         FIG. 2  is a circuit diagram of a stator coil; 
         FIG. 3  is a perspective view of a stator; 
         FIG. 4  is a perspective view of a bus bar unit; 
         FIG. 5  is a perspective view of a plurality of bus bars; 
         FIG. 6  is a plan view of the bus bar unit; 
         FIG. 7  is a plan view of the plurality of bus bars; 
         FIG. 8  is a plan view of one bus bar; 
         FIG. 9  is a perspective view of the bus bar unit; 
         FIG. 10  is a cross-sectional view on a line X-X of  FIG. 6 ; 
         FIG. 11  is a cross-sectional view on a line XI-XI of  FIG. 6 ; 
         FIG. 12  is a cross-sectional view on a line XII-XII of  FIG. 6 ; 
         FIG. 13  is a perspective view of a neutral point bus bar; 
         FIG. 14  is a perspective view of a neutral point bus bar; 
         FIG. 15  is a circuit diagram of a stator coil of a second embodiment; 
         FIG. 16  is a perspective view of a stator; 
         FIG. 17  is a perspective view of a bus bar unit; 
         FIG. 18  is a perspective view of a plurality of bus bars; 
         FIG. 19  is a plan view of the bus bar unit; 
         FIG. 20  is a plan view of the plurality of bus bars; 
         FIG. 21  is a plan view of one bus bar; 
         FIG. 22  is a cross-sectional view of a bus bar unit of a third embodiment; 
         FIG. 23  is a cross-sectional view of a bus bar unit of a fourth embodiment; 
         FIG. 24  is a cross-sectional view of a bus bar unit of a fifth embodiment; 
         FIG. 25  is a cross-sectional view of a bus bar unit of a sixth embodiment; 
       and 
         FIG. 26  is a circuit diagram of a stator coil of a seventh embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Patent Literature 1: JP2017-153261A, Patent Literature 2: JP2000-166150A, and Patent Literature 3: JP2018-125924A disclose a stator of a rotary electric machine. The contents of literatures are incorporated by reference as explanation of technical elements in this specification. 
     These stators have a variety of coil ends. In particular, Patent Literature 1 discloses a holder accommodating a plurality of bus bars. The plurality of bus bars provide connecting members at a coil end. The plurality of bus bars are fixed to the holder by an adhesive resin. In the above-mentioned configuration, bubbles may be generated in the adhesive resin. In addition, the bubbles can become pinholes. Bubbles and pinholes may impair insulation performance. From another view point, the adhesive resin may be more easily damaged than the holder. 
     It is an object disclosed to provide a rotary electric machine, a stator thereof, and a manufacturing method of the rotary electric machine which have improved insulation performance. It is another object disclosed to provide a rotary electric machine, a stator thereof, and a manufacturing method of the rotary electric machine which have improved insulation performance for a plurality of bus bars. It is yet another object disclosed to provide a rotary electric machine, a stator thereof, and a manufacturing method of the rotary electric machine which have improved insulation performance between a housing and a bus bar. 
     Hereinafter, a plurality of embodiments are described with reference to the drawings. In some embodiments, functionally and/or structurally corresponding and/or associated parts may be given the same reference numerals, or reference numerals with different digit placed on equal to or higher than a hundred place. For corresponding parts and/or associated parts, it is possible to make reference to the description of other embodiments. 
     First Embodiment 
     In  FIG. 1 , the rotary electric machine  1  is a motor generator. The rotary electric machine  1  is operatively connected to the internal combustion engine  2  (ENG). The internal combustion engine  2  provides power for various devices. In this specification, the devices may include a vehicle, an air conditioner, a pumping device, or the like. Furthermore, the term vehicle includes a car, a ship, an aircraft, a simulation device, and an amusement device. 
     The rotary electric machine  1  is electrically connected to the control device  3  (CNT). The control device  3  includes an inverter circuit. The rotary electric machine  1  is driven by the internal combustion engine  2  and outputs electric power, when functioning as a generator. The control device  3  functions as a rectifier circuit that rectifies the electric power output from the rotary electric machine  1  when the rotary electric machine  1  is used as a generator. The rotary electric machine  1  may assist a rotation of the internal combustion engine  2  when functioning as an electric motor. The control device  3  supplies multiphase AC power to the rotary electric machine  1  when the rotary electric machine  1  is used as an electric motor. In this embodiment, the multiphase AC power is three-phase power. 
     The control device  3  is an electronic control unit. The control device  3  provides a control system. The control system has at least one arithmetic processing unit (CPU) and at least one memory device (MMR) as a storage medium for storing programs and data. The control system is provided by a microcomputer comprising a computer readable storage medium. The storage medium is a non-transitional tangible storage medium that non-temporarily stores a computer readable program. The storage medium may be provided as a semiconductor memory, a magnetic disk, or the like. The control system may be provided by one computer or a group of computer resources linked via a data communication device. Means and/or functions provided by the control system can be provided by software recorded in a substantive memory device and a computer that can execute the software, software only, hardware only, or some combination of them. For example, the control system can be provided by a logic called if-then-else type, or a neural network tuned by machine learning. Alternatively, for example, if the control system is provided by an electronic circuit that is hardware, the control system may be provided by a digital circuit or an analog circuit that includes a large number of logic circuits. 
     The rotary electric machine  1  has a rotor  4  and a stator  10 . The rotor  4  is rotatable around an axis AX. The stator  10  is a cylindrical shape having the axis AX. In the following description, terms of an axial direction, a radial direction, and a circumferential direction are defined based on the axis AX. The rotor  4  and the stator  10  are accommodated in a housing  6 . The housing  6  fixes the stator  10  and supports the rotor  4  in a rotatable manner. The housing  6  may provide components for the internal combustion engine  2 . For example, the housing  6  may provide a part of a crankcase or a part of a transmission case. The housing  6  has a first housing  7  with a bottomed cylindrical shape and a second housing  8  with a bottomed cylindrical shape. The rotor  4  and the stator  10  are housed between a first housing  7  and a second housing  8 . 
     The rotor  4  is magnetically coupled with the stator  10 . The rotor  4  is supported by a shaft  5  so as to be rotatable with respect to the housing  6 . The shaft  5  provides a rotational shaft. The rotational shaft is connected to the internal combustion engine  2 . The rotor  4  is disposed in a radial direction inside of the stator  10 . The rotor  4  has a plurality of magnetic poles arranged along the circumferential direction. The plurality of magnetic poles are formed by a plurality of permanent magnets embedded in the rotor  4 . The rotor  4  can be provided by various structures. The rotor  4  has, for example, 8 magnetic poles, i.e., N pole: 4 pieces and S pole: 4 pieces. 
     The rotary electric machine  1  has a power terminal member  9 . The rotary electric machine  1  has a plurality of power terminal members  9 . The power terminal member  9  is a terminal for electrically connecting the rotary electric machine  1  and the control device  3 . The power terminal member  9  is used as an output terminal member when outputting electric power, and as an input terminal member when receiving electric power. The power terminal member  9  can also be called an external connection terminal member of the rotary electric machine  1 . 
     The stator  10  has a stator core  11 . The stator core  11  is a cylindrical shape. The stator core  11  is an annular shape. The stator core  11  has a plurality of steel plates laminated along the axial direction. The stator core  11  has a plurality of slots arranged in the circumferential direction. The plurality of slots are arranged at an equal pitch with respect to the circumferential direction. The plurality of slots may be arranged at several different pitches. The plurality of slots extend in the axial direction so as to penetrate the plurality of steel plates. Further, the plurality of slots extend in the radial direction. A typical stator core  11  has an annular back core. The stator core  11  has a plurality of teeth extending out in the radial direction inside from the back core. The plurality of teeth form a plurality of slots between them. For example, the stator core  11  has 48 slots. 
     The stator  10  has a stator coil  12 . The stator coil  12  is attached to the stator core  11 . The stator coil  12  has straight portions  13  and coil ends  14  and  15 . The straight portion  13  extends straight. The straight portion  13  is housed in the slot. The coil ends  14  and  15  are positioned at ends of the stator core  11 . The coil ends  14  and  15  protrude from the stator core  11  in the axial direction. The coil ends  14  and  15  are bundles of a plurality of conductors included in the stator coil  12 . At the coil ends  14  and  15 , one conductor connects one straight portion  13  positioned in one slot to one straight portion  13  positioned in another different slot. 
     The coil ends  14  and  15  may be provided by continuous turn portions of the conductor. The coil ends  14  and  15  may be provided by joint portions joining different conductors. These examples are disclosed in Patent Literature 2: JP2000-166150A or Patent Literature 3: JP2018-125924A. 
     The stator coil  12  has coil terminals  16 . The coil terminals  16  are leader wires extending from the coil end  14 . The stator coil  12  includes a plurality of coil terminals  16 . The coil terminals  16  provide both ends of a plurality of coils as multiphase windings. In this embodiment, since the three-phase winding is provided, at least six coil terminals  16  are provided. Further, in this embodiment, one phase is provided by the parallel connection of (n) coils. Therefore, the stator coil  12  has a (6×n) coil terminals  16 . In this embodiment, one phase is provided by the parallel connection of four coils. Therefore, the stator coil  12  includes 24 coil terminals  16 . 
     One coil can be provided by a continuous wire or by joining multiple segments. In this embodiment, a single coil is provided by a plurality of joined segments. Note that the plurality of segments can be joined by various joining methods. As a joining method, for example, TIG welding, electric resistance welding, solder joining, or the like can be used. In addition, one coil is a coil that can be regarded as one phase. One coil may include a plurality of coil elements having different electrical angles. For example, one coil can include a plurality of coil elements having electrical angles that differ by several degrees. 
     The stator coil  12  has a bus bar unit  20 . The bus bar unit  20  electrically connects the stator coil  12  so as to form a multiphase connection. The bus bar unit  20  connects a plurality of coil terminals  16  to provide a star connection or a delta connection. In this embodiment, the bus bar unit  20  provides the star connection. The bus bar unit  20  includes a plurality of bus bars  30 . The plurality of bus bars  30  are made of conductive members. The bus bar unit  20  has end bus bars that provide three input or output terminals, i.e., power terminals in the star connection. The bus bar unit  20  has a neutral point bus bar that provides a neutral point in the star connection. 
     The bus bar unit  20  has a holder  21 . The holder  21  is made of an insulating material. The holder  21  has an arc shape. The holder  21  may be a polyhedron. The holder  21  may be annular. The holder  21  is arranged along the coil end  14 . The holder  21  is arranged outer side than the coil end  14  in the axial direction. In addition, at least a portion of the holder  21  is arranged outer side than the coil end  14  in the radial direction. The holder  21  faces a corner of the outside in the radial direction of the coil end  14 . The holder  21  is a container for accommodating the bus bar  30  in an inside. 
     In  FIG. 1 , a plurality of bus bars  30  are exemplified as one bus bar  30 . In  FIG. 1 , the inside of the holder  21  is schematically shown. The plurality of bus bars  30  provide a plurality of dispersive terminal members  31 . The dispersive terminal members  31  are also called coil connection terminals. The dispersive terminal members  31  extend from the holder  21 . The dispersive terminal member  31  has a shape that can be called a J-shape or a U-shape. The dispersive terminal member  31  extends toward the coil end  14  in the axial direction from the holder  21 , then extends outward in the radial direction, and further extends in the axial direction along the radial direction outside of the holder  21 . The plurality of dispersive terminal members  31  are electrically connected to the plurality of coil terminals  16 . The plurality of dispersive terminals  31  are electrically connected to the plurality of coil terminals  16  in the radial direction outside of the holder  21 . The coil terminals  16  and the dispersive terminal members  31  are electrically connected at joint portions  17 . The joint portion  17  can be provided by various joining methods. As a joining method, for example, TIG welding, electric resistance welding, solder joining, or the like can be used. 
     The plurality of bus bars  30  provide a plurality of collective terminal members  31 . The collective terminal member  32  is also called a power connection terminal member. The plurality of collective terminal members  32  are electrically connected to the plurality of power terminal members  9 . The collective terminal member  32  extend from the holder  21 . The collective terminal member  32  has a shape that can be called a J-shape or a U-shape. The collective terminal member  32  extends towards the coil end  14  in the axial direction from the holder  21 , then extends outward in the radial direction, and further extends in the axial direction along the radial direction outside of the holder  21 . The plurality of collective terminal members  32  are electrically connected to the plurality of power terminal members  9  in the radial direction outside of the holder  21 . The collective terminal member  32  and the power terminal member  9  are electrically connected at the joint portion  18 . The joint portion  18  can be provided by various joining methods. As a joining method, for example, TIG welding, electric resistance welding, solder joining, or the like can be used. 
       FIG. 2  shows a multi-phase connection of the stator coil  12 . The stator coil  12  employs the star connection as a multi-phase connection. The stator coil  12  has a U phase, a V phase, and a W phase. The stator coil  12  has a plurality of U-phase coils  12   u  that provide U-phase. The stator coil  12  has a plurality of V-phase coils  12   v  that provide V-phase. The stator coil  12  has a plurality of W-phase coils  12   w  that provide W-phase. In this embodiment, the stator coil  12  has four U-phase coils  12   u , four V-phase coils  12   v , and four W-phase coils  12   w.    
     The plurality of bus bars  30  have a U-phase bus bar  30   u  that provides a U-phase power terminal. The U-phase bus bar  30   u  has four dispersive terminal members  31 . The U-phase bus bar  30   u  is connected to each of the four U-phase coils  12   u  at the four joint portions  17   u . The U-phase bus bar  30   u  is connected to the power terminal member  9  at the joint portion  18   u . Therefore, the U-phase bus bar  30   u  provides a so-called crossover wire that connects four U-phase coils  12   u  to the power terminal. 
     The plurality of bus bars  30  have a V-phase bus bar  30   v  that provides a V-phase power terminal. The V-phase bus bar  30   v  has four dispersive terminal members  31 . The V-phase bus bar  30   v  is connected to each of the four V-phase coils  12   v  at the four joint portions  17   v . The V-phase bus bar  30   u  is connected to the power terminal member  9  at the joint portion  18   v . Therefore, the V-phase bus bar  30   v  provides a so-called crossover wire that connects four V-phase coils  12   v  to the power end. 
     The plurality of bus bars  30  have a W-phase bus bar  30   w  that provides a W-phase power terminal. The W-phase bus bar  30   w  has four dispersive terminal members  31 . The W-phase bus bar  30   w  is connected to each of the four W-phase coils  12   w  at the four joint portions  17   w . The W-phase bus bar  30   u  is connected to the power terminal member  9  at the joint portion  18   w . Therefore, the W-phase bus bar  30   w  provides a so-called crossover wire that connects four W-phase coils  12   w  to the power end. 
     The plurality of bus bars  30  have a plurality of neutral point bus bars  41 . The two neutral point bus bars  41   a  and  41   b  provide two star connections. One neutral point bus bar  41   a  has six terminal members. Two neutral point bus bars  41   a  and  41   b  provide twelve terminal members. The neutral point bus bar  41   a  is joined to the coil terminals for the neutral point at two joint portions  19   u , two joint portions  19   v , and two joint portions  19   w . The neutral point bus bar  41   b  is connected to the coil terminals for the neutral point at two joint portions  19   u , two joint portions  19   v , and the two joint portions  19   w.    
       FIG. 3  shows an appearance of one end of the stator  10 . The stator core  11  has one end surface  11   a  and the other end surface  11   b . The coil end  14  extends in the axial direction from one end surface  11   a . The coil end  14  extends in the axial direction from the other one end surface  11   b . The bus bar unit  20  is positioned in the axial direction of the coil end  14 . The bus bar unit  20  is positioned in a predetermined angle range including the angle range in which the power terminal members  9  is positioned. The holder  21  is positioned away from the coil end  14  with respect to the axial direction. 
     In the drawings, 12 joint portions  17  are shown. One joint portion  17  electrically connects one coil terminal  16  and one dispersive terminal member  31 . The coil terminal  16  is L-shaped. The coil terminals  16  are drawn out from the radial direction outside surface of the coil end  14 . The coil terminals  16  extend towards the axial direction outside from the coil end  14 . The dispersive terminal member  31  extends towards the radial direction outside from the holder  21  and then extends in the axial direction outside at the radial direction outer end. The coil terminals  16  and the dispersive terminal members  31  both form the joint portion  17  at end portions extending along the axial direction. 
     The stator  10  has six collective terminal members  32 . A group of collective terminal members  32 , i.e., two collective terminal members  32  adjacent to each other in a short distance with respect to the circumferential direction provide substantially one collective terminal member  32  of one bus bar. The three groups of collective terminal members  32  provide the power terminals for the U-phase, the V-phase, and the W-phase. In other words, the bus bar unit  20  has 3 groups and 6 collective terminal members  32 . 
     The bus bar unit  20  has a neutral point bus bar  41 . The neutral point bus bar includes a plurality of neutral point bus bars  41   a  ( 41   b ). The neutral point bus bar  41   a  ( 41   b ) is independent of the holder  21 . The neutral point bus bar  41   a  ( 41   b ) is arranged along the coil end  14  in the radial direction outside of the coil end  14 . The neutral point bus bar  41   a  and the neutral point bus bar  41   b  are arranged in the radial direction outside of the coil end  14  so as not to overlap each other. 
       FIG. 4  shows the bus bar unit  20 . The illustrated bus bar unit  20  includes a holder  21  and a plurality of bus bars  30  housed in the holder  21 . The illustrated bus bar unit  20  does not include the neutral point bus bar  41   a  ( 41   b ). The illustrated bus bar unit  20  provides so-called crossover wires that connect the plurality of coils to the power terminal. 
       FIG. 5  shows a plurality of bus bars  30 . The plurality of bus bars  30  have three bus bars  35 ,  36 , and  37 . The three bus bars  35 ,  36 , and  37  each provide a U-phase bus bar  30   u , a V-phase bus bar  30   v , and a W-phase bus bar  30   w . The three bus bars  35 ,  36 , and  37  are electrically isolated from each other. The three bus bars  35 ,  36 , and  37  are arranged in multiple layers with respect to the radial direction. The bus bar  35  is arranged in a radial direction most inside. The bus bar  35  is also called an inner layer bus bar  35 . The bus bar  37  is arranged in a radial direction most outside. The bus bar  37  is also called an outer layer bus bar  37 . The bus bar  36  is arranged between the inner layer bus bar  35  and the outer layer bus bar  37 . The bus bar  36  is also called a middle layer bus bar  36 . 
     Each of the plurality of bus bars  30  has a main member  38  extending along the circumferential direction. The main member  38  has an arc shape. The main member  38  may be a polyhedron. The main member  38  has a height H 38  with respect to the axial direction. The main member  38  extends in a ribbon shape along the circumferential direction. 
     The bus bar  35  has two partial bus bars  35   a  and  35   b  that are independent with respect to the circumferential direction. The partial bus bar  35   a  has an arc shape of 90 degrees or less. The partial bus bar  35   a  has two dispersive terminal members  31 . The partial bus bar  35   a  has one collective terminal member  32 . The partial bus bar  35   b  has an arc shape of 90 degrees or less. The partial bus bar  35   b  has two dispersive terminal members  31 . The partial bus bar  35   b  has one collective terminal member  32 . Both the partial bus bar  35   a  and the partial bus bar  35   b  are arranged in the inner layer. The partial bus bar  35   a  and the partial bus bar  35   b  provide a bus bar  35  that occupies an angle range of 90 degrees or more. 
     The bus bar  36  has two partial bus bars  36   a  and  36   b  that are independent with respect to the circumferential direction. The partial bus bar  36   a  has an arc shape of 120 degrees or less. The partial bus bar  36   a  has two dispersive terminal members  31 . The partial bus bar  36   b  has one collective terminal member  32 . The partial bus bar  36   b  has an arc shape of 120 degrees or less. The partial bus bar  36   a  has two dispersive terminal members  31 . The partial bus bar  36   b  has one collective terminal member  32 . Both the partial bus bar  36   a  and the partial bus bar  36   b  are arranged in the middle layer. The partial bus bar  36   a  and the partial bus bar  36   b  are arranged continuously in the circumferential direction to provide the bus bar  36  that occupies an angle range of 120 degrees or more. 
     The bus bar  37  has two partial bus bars  37   a  and  37   b  which are independent with respect to the circumferential direction. The partial bus bar  37   a  has an arc shape of 90 degrees or less. The partial bus bar  37   a  has two dispersive terminal members  31 . The partial bus bar  37   a  has one collective terminal member  32 . The partial bus bar  37   b  has an arc shape of 90 degrees or less. The partial bus bar  37   b  has two dispersive terminal members  31 . The partial bus bar  37   b  has one collective terminal member  32 . Both the partial bus bar  37   a  and the partial bus bar  37   b  are arranged in the outer layer. The partial bus bar  37   a  and the partial bus bar  37   b  provide a bus bar  37  that occupies an angle range of 90 degrees or more. 
     In this embodiment, the plurality of partial bus bars provide one bus bar. As a result, the size of the partial bus bar can be reduced. The plurality of partial bus bars facilitate the manufacturing process. Further, one bus bar includes a plurality of collective terminal members  32 . As a result, it is possible to avoid current concentration. 
       FIG. 6  shows the bus bar unit  20 .  FIG. 6  shows a plane view viewed from the arrow VI of  FIG. 3 . All terminal members  31  and  32  extend towards in the radial direction outside of the holder  21 . 
       FIG. 7  shows the plurality of bus bars  30 . The plurality of collective terminal members  32  are centrally arranged. The centralized arrangement of the plurality of collective terminal members  32  enables efficient connection work with the plurality of power terminal members  9 . On the other hand, the plurality of dispersive terminal members  31  are arranged in a dispersive manner along the coil end  14 . The dispersive arrangement of the plurality of dispersive terminal members  31  suppresses confusions of the coil terminals  16  at the coil end  14 . Distances between the plurality of dispersive terminal members  31  are associated with the pitch of the plurality of slots or multiples of the pitch.  FIG. 8  shows one bus bar  37 . One bus bar is divided into two pieces at a center position where the collective terminal members  32  and  32  should be disposed. The two partial bus bars  37   a  and  37   b  have a symmetrical shape. 
       FIG. 9  shows a back surface of the bus bar unit  20 . The holder  21  has an opening  22 . The holder  21  can also be called an arc-shaped container around the axis AX. The opening  22  is open towards the axial direction. The opening  22  is wide open to be able to receive the plurality of bus bars  30  along the axial direction. The plurality of bus bars  35 ,  36 , and  37  partially overlap each other with respect to the radial direction. Moreover, the plurality of bus bars  35 ,  36 , and  37  are arranged so as to be offset from each other with respect to the circumferential direction. Therefore, the angle range in which the holder  21  extends in the circumferential direction is wider than the angle range of any one of the plurality of bus bars  35 ,  36 , and  37 . Further, the holder  21  has a non-arrangement angle range in which no bus bar is accommodated at both ends as an arc shape. The non-arrangement angle range is formed on the inside at one end of the arc. The non-arrangement angle range is formed on the outside at the other one end of the arc. The plurality of terminal members  31  and  32  extend in the radial direction outside from each of the inner layer, the middle layer, and the outer layer. The plurality of terminal members  31  and  32  are arranged radially with respect to the axis AX. 
     Returning to  FIG. 3 , the holder  21  is a container made of an insulating member and houses the bus bar  30 . The holder  21  is arranged in the axial direction of the stator core  11 . The opening  22  is open toward the stator core  11 . The opening  22  faces the stator core  11 . The bus bar unit  20  is positioned so that the opening  22  faces the one end surface  11   a  of the stator core  11 . The bus bar unit  20  is positioned in the axial direction outside of the coil end  14 . As a result, the bus bar unit  20  is positioned so that the opening  22  faces the coil end  14 . The bus bar unit  20  is positioned on the axial direction outside of the coil end  14  so that the holder  21  is turned down. 
       FIG. 10  shows an end face of a cut surface portion in an X-X line of  FIG. 6 . The holder  21  has a plurality of partition walls  26  for defining an inner layer, a middle layer, and an outer layer in the inside. The holder  21  has an opening  22 . The holder  21  has a bottom wall  23 , an outer wall  24  in the radial direction outside, and an inner wall  25  in the radial direction inside. The outer wall  24  provides an outer surface  24   a  in the radial direction outside. The inner wall  25  provides an inner surface  25   a  in the radial direction inside. Further, the holder  21  has one or more partition walls  26 . The partition wall  26  divides the inside of the holder  21  into a plurality of layers, i.e., grooves with respect to the radial direction. The illustrated embodiment has two partition walls  26   a  and  26   b . The outer wall  24  and the inner wall  25  have heights H 24  and H 25 . The height H 24  and the height H 25  are equal (H 24 =H 25 ). The partition walls  26   a  and  26   b  have a height H 26 . The height H 26  is lower than the height H 24  or the height H 25  (H 26 &lt;H 24 , H 26 &lt;H 25 ). Thicknesses of the partition walls  26   a  and  26   b  in the radial direction are thicker than thicknesses of the outer wall  24  and the inner wall  25  in the radial direction. This difference in thickness satisfies the electrical insulation performance. The partition wall  26  is a wall that is continuous along the circumferential direction. However, the partition wall  26  may be provided by a plurality of walls intermittently provided along the circumferential direction. Further, the partition wall  26  may have one or more openings that penetrate in the radial direction. The partition wall  26  may be also called a rib. 
     The outer wall  24 , the inner wall  25 , and the plurality of partition walls  26   a  and  26   b  form a plurality of slit-shaped bus bar chambers. The illustrated embodiment forms three bus bar chambers. Each of the bus bars  35 ,  36 , and  37  is inserted in each bus bar chamber. Also in this embodiment, the plurality of partition walls  26   a  and  26   b  provide a long creep distance among the plurality of bus bars  35 ,  36 , and  37  arranged in a multiple layered manner in the radial direction. Therefore, the plurality of partition walls  26   a  and  26   b  suppress creep discharge. 
     The bus bars  35 ,  36 , and  37  may be press-fitted into the bus bar chamber. Further, a gap may be positively formed between the holder  21  and the bus bars  35 ,  36 , and  37 . Further, contact portions and gaps may be alternately formed between the holder  21  and the bus bars  35 ,  36 , and  37 . The gap allows the presence of a resin member described later. 
     The holder  21  has an insulating resin member  27  applied to the opening  22 . The resin member  27  is applied from the opening  22 . The resin member  27  is applied to the inside of the holder  21 . The resin member  27  adheres the inner surface of the holder  21  to the surfaces of the bus bars  35 ,  36 , and  37 . The resin member  27  is filled in the inside of the holder  21 . The resin member  27  covers the main member  38  of the bus bars  35 ,  36 , and  37 . 
     The resin member  27  is a potting resin. The resin member  27  is dropped from the opening  22  and cured in the holder  21 . The surface  27   a  of the resin member  27  is in contact with the side surfaces of the plurality of walls  24 ,  25 , and  26  at a boundary line  27   b . The surface  27   a  is curved in a concave shape. A height of the resin member  27  is lower than the heights of the plurality of walls  24 ,  25 , and  26 . The resin member  27  has a surface  27   a  lower than apexes of the plurality of walls  24 ,  25 , and  26 . 
     Focusing on the bus bar  35 , the holder  21  has the partition wall  26   b  positioned in the radial direction inside and the inner wall  25  positioned in the radial direction outside. The bus bar  35  is housed in a groove surrounded by the bottom wall  23 , the partition wall  26   b , and the inner wall  25 . The resin member  27  covers the bus bar  35 . 
     Focusing on the bus bar  36 , the holder  21  has the partition wall  26   a  positioned in the radial direction inside and the partition wall  26   b  positioned in the radial direction outside. The bus bar  36  is housed in a groove surrounded by the bottom wall  23 , the partition wall  26   a , and the partition wall  26   b . The resin member  27  covers the bus bar  36 . 
     Focusing on the bus bar  37 , the holder  21  has the partition wall  26   a  positioned in the radial direction inside and the outer wall  24  positioned in the radial direction outside. The bus bar  37  is housed in a groove surrounded by the bottom wall  23 , the outer wall  24  and the partition wall  26   a . The resin member  27  covers the bus bar  37 . 
     Further, the holder  21  has an inner wall  25  positioned in the radial direction most inside and an outer wall  24  positioned in the radial direction most outside. The resin member  27  has a surface  27   a  lower than apexes of the inner wall  25  and the outer wall  24 . As a result, the resin member  27  is separately arranged in each of the plurality of grooves provided by the holder  21 . 
     The holder  21  is made of resin. The holder is a resin molded product molded by injection molding. The resin member  27  is made of a soft resin that is softer than the resin forming the holder  21 . The resin member  27  is also an adhesive resin member that adheres the bus bar  30  and the holder  21 . The resin member  27  embeds the bus bar  30  in the inside the opening  22  of the holder  21 . The resin member  27  is a thermosetting resin. 
     Returning to  FIG. 3 , the resin member  27  faces one end surface  11   a  of the stator core  11 . The resin member  27  faces the coil end  14 . 
       FIG. 11  shows an end face of a cut surface portion in the X-X line of  FIG. 6 . A cut surface of one dispersive terminal member  31  is shown. The dispersive terminal member  31  has a first portion  31   a . The first portion  31   a  extends from the main member  38  along the axial direction. The first portion  31   a  protrudes from the opening  22 . The dispersive terminal member  31  has a second portion  31   b . The second portion  31   b  extends in the radial direction outside from the end of the first portion  31   a  along the radial direction. The second portion  31   b  projects in the radial direction outside from the holder  21 . The dispersive terminal member  31  has a third portion  31   c . The third portion  31   c  extends from a distal end of the second portion  31   b  along the axial direction so as to overlap with the radial direction outside of the holder  21 . The third portion  31   c  reaches a position overlapping with the holder  21  with respect to the radial direction. The third portion  31   c  faces the outer surface  24   a  of the holder  21 . At the position of  FIG. 11 , the outer layer bus bar  37  does not exist. The plurality of bus bars  35 ,  36 , and  37  partially overlap each other with respect to the radial direction. Moreover, the plurality of bus bars  35 ,  36 , and  37  are arranged so as to be offset from each other with respect to the circumferential direction. 
       FIG. 12  shows an end surface of a cut surface portion in a XII-XII of  FIG. 6 . A cut surface of one collective terminal member  32  is shown. The collective terminal member  32  has a first portion  32   a . The first portion  32   a  extends from the main member  38  along the axial direction. The first portion  32   a  protrudes from the opening  22 . The collective terminal member  32  has a second portion  32   b . The second portion  32   b  extends towards the radial direction outside from the end of the first portion  32   a  along the radial direction. The second portion  32   b  projects in the radial direction outside from the holder  21 . The collective terminal member  32  has a third portion  32   c . The third portion  32   c  extends from a distal end of the second portion  32   b  along the axial direction so as to overlap the radial direction outside of the holder  21 . The third portion  32   c  reaches a position overlapping with the holder  21  with respect to the radial direction. The third portion  32   c  faces the outer surface  24   a  of the holder  21 . 
       FIG. 11  and  FIG. 12  show the plurality of terminal members  31  and  32  included in one bus bar  36 . The plurality of terminal members  31  and  32  extend from the opening  22  of the holder  21 . These terminal members  31  and  32  extend from the surface of the resin member  27 . The bus bar  30  has a main member  38  extending in the circumferential direction. The holder  21  has a groove deeper than the height H 38  of the main member  38 . The opening  22  is also the opening of the groove. 
       FIG. 13  shows one of the neutral point bus bars  41 .  FIG. 14  shows the bus bar  44  of the neutral point bus bars  41 . The neutral point bus bar  41  is intended to be mounted on the side surface of the coil end  14 . The neutral point bus bar  41  has an arc shape. The neutral point bus bar  41  has a main body portion  42  covered with an insulating member. The main body portion  42  extends along the circumferential direction. The main body portion  42  accommodates a bus bar  44  made of a conductive material. The neutral point bus bar  41  has a plurality of terminal members  43  extending in the axial direction. In the illustrated example, the neutral point bus bar  41  has six terminal members  43 . The terminal member  43  is joined to the coil terminal  16  for neutral point connection. In this embodiment, since the two neutral point bus bars  41  are used, a total of 12 terminal members are provided. 
     A manufacturing method of the rotary electric machine  1  is described. The method for manufacturing the rotary electric machine  1  includes a step of assembling the rotor  4 , a step of assembling the stator  10 , and a step of accommodating the rotor  4  and the stator  10  in the housing  6 . The rotor assembling step and the stator assembling step may be in a reverse order. The assembling step of the stator  10  includes a step of manufacturing the stator core  11  that provides a plurality of slots, a step of mounting the stator coil  12  on the stator core  11 , and a step of positioning the coil end  14  at an end of the stator core  11 . The step of positioning the coil end  14  includes a step of arranging the plurality of coil terminals  16  at predetermined positions by pulling out the plurality of coil terminals  16  from the coil end  14 . 
     The assembling step of the stator  10  includes a step of assembling the bus bar unit  20 . The bus bar unit assembling step includes a step of molding the holder  21  by injection molding of an insulating resin. At this step, the holder  21  having the opening  22  is formed. A plurality of partition walls  26   a  and  26   b  are formed in the inside the holder  21  so as to form a plurality of grooves. The bus bar unit assembling step includes a step of mounting the bus bar  30  made of a conductive member from the opening  22  of the holder  21  made of an insulating member. 
     The bus bar unit assembling step includes a step of applying the insulating resin member  27  from the opening  22 . This step is a step in which the resin member  27  is dropped from the opening  22  by potting and cured. At this step, the holder  21  is positioned with the opening  22  facing upward in a direction of gravity. The resin member  27  is dropped from above into the opening  22 . The resin member  27  forms a concave surface  27   a  due to shrinkage during the curing or surface tension. The resin member  27  is applied so as to embed the plurality of bus bars  30 . 
     The bus bar unit assembling steps may be performed independently. The bus bar unit assembling step may be performed before the other steps. The bus bar unit assembling step may include a step of coating an adhesive to the inside of the holder  21  and a step of mounting the bus bar  30  after that. In the bus bar unit assembling step, the resin member  27  may be applied after that. The assembling step of the stator  10  includes a step of positioning the bus bar unit  20  so that the opening  22  faces the one end surface  11   a  in the axial direction of the stator core  11 . At this time, the bus bar unit  20  is inverted from the posture at the step of applying the resin member  27 . In a typical method of manufacturing a stator, the stator  10  is positioned so that the coil end  14  is on top, and the bus bar unit  20  is placed on the coil end  14 . At this time, the bus bar unit  20  is positioned so that the opening  22  faces downward. This step is also a step in which the resin member  27  is positioned so as to face one end surface  11   a  of the stator core  11 . From another point of view, this step is also a step of positioning the bus bar unit  20  so that the opening  22  faces the coil end  14 . Further, in other words, this step is also a step in which the bus bar unit  20  is positioned so that the resin member  27  faces the coil end  14 . As a result, the bottom wall  23  of the holder  21  is positioned in the axial direction outside of the stator  10 . 
     The assembling step of the stator  10  includes a step of electrically connecting the plurality of coil terminals  16  included in the coil end  14  and the plurality of terminal members  31  and  32 . The plurality of terminal members  31  and  32  and the plurality of coil terminals  16  are positioned in the radial direction outside of the holder  21 . Further, one of the terminal members  31  and  32  and one of the coil terminals  16  to be electrically joined are positioned at the same angular position in the circumferential direction. Therefore, a plurality of joining operations can be easily performed. At this time, the bus bar unit  20  is positioned so as to be separated from the coil end  14 , and in that state, the plurality of coil terminals  16  and the plurality of terminal members  31  and  32  are joined. As a result, the bus bar unit  20  is supported by the plurality of coil terminals  16  and the plurality of terminal members  31  and  32 . Further, this step includes joining the coil terminals  16  for the neutral point and the neutral point bus bars  41   a  and  41   b.    
     The step of accommodating the rotor  4  and the stator  10  in the housing  6  includes a step of positioning the housing  8  on the radial direction outer side and/or the axial direction outer side of the bottom wall  23  of the holder  21 . 
     According to the embodiment described above, a rotary electric machine having improved insulation performance, a stator thereof, and a method for manufacturing the rotary electric machine are provided. Since the opening  22  faces one end surface  11   a , the exposure of the bus bar  30  housed in the holder  21  is suppressed. Therefore, lowering of the insulation performance in the assembling step or the maintenance step is suppressed. 
     Further, the holder  21  is positioned in the outside by the resin member  27  facing the one end surface  11   a . As a result, the resin member  27  is protected at the assembling step or the maintenance step. Since the holder  21  having relatively few defects in the insulating member faces the outside, the insulating performance is improved. On the other hand, since the resin member  27 , which is relatively prone to defects, is positioned to face the stator core  11 , deterioration of insulation performance due to defects is suppressed. Defects include, for example, air bubbles, pinholes, foreign matter and the like. When the resin member  27  is a potting resin or a soft resin, the protective effect is remarkable. As a result, deterioration of insulation performance is suppressed. 
     According to this embodiment, the bus bar  30  can be protected from cooling medium, i.e., fluid for the stator  10 . The cooling medium reaches the surface of the opening  22  or the resin member  27 . At the same time, the cooling medium brings foreign matter. In this embodiment, the holder  21  is arranged so that the opening  22  or the resin member  27  faces one end surface  11   a . Therefore, a strong flow of the cooling medium does not reach the opening  22 . Further, direct arrival and arrival of foreign matter to the opening  22  are suppressed. As a result, deterioration of insulation performance is suppressed. In particular, when a liquid such as water or oil is used as the cooling medium, the effect of suppressing the arrival of foreign matter and the effect of protecting the resin member  27  are remarkable. 
     Second Embodiment 
     This embodiment is a modification based on the preceding embodiment. In the above embodiment, four phase coils are connected as one phase. Alternatively, one phase may include one or more phase coils. For example, two, three, five, six and the like are possible. In this embodiment, two phase coils are connected. 
     In  FIG. 15 , one phase is provided by a parallel connection of two phase coils.  FIG. 16  shows the stator  10 .  FIG. 17  shows the bus bar unit  20 .  FIG. 18  shows a plurality of bus bars  30 .  FIG. 19  shows the bus bar unit  20 .  FIG. 20  shows a plurality of bus bars  30 .  FIG. 21  shows one bus bar. In this embodiment, a bus bar unit  20  which is half of the above embodiment is used. There is only one neutral point bus bar  41 . In this embodiment, the plurality of bus bars  235 ,  236 , and  237  are provided by the partial bus bars  35   a ,  36   a , and  37   a  of the above embodiment. 
     Third Embodiment 
     This embodiment is a modification based on the preceding embodiment. In the above embodiment, the resin member  27  is separately arranged in each of the plurality of grooves. Alternatively, the resin member  27  may be continuously arranged across the plurality of grooves. 
       FIG. 22  shows an end face of the bus bar unit  20 . The resin member  27  is continuously arranged over a plurality of grooves. The surface  327   a  extends beyond the partition walls  26   a  and  26   b  and is continuous over adjacent grooves. In this embodiment, a boundary line  327   b  is positioned on the side surface of the outer wall  24  and the side surface of the inner wall  25 . 
     Fourth Embodiment 
     This embodiment is a modification based on the preceding embodiment. In the above embodiment, the resin member  27  is only a potting resin. Alternatively, the resin member  27  may contain a plurality of resin materials. 
       FIG. 23  shows an end face of the bus bar unit  20 . The assembling step of the bus bar unit  20  includes a step of applying the adhesive  427  to the inner surface of the holder  21  before mounting the bus bar  30 . The assembling step of the bus bar unit  20  includes a step of arranging the bus bar  30  in the holder  21 , a step of adhering the bus bar  30  with the adhesive  427 , and a step of applying the resin member  27  thereafter. A portion of the adhesive  427  is extruded between the holder  21  and the bus bar  30 . The adhesive  427  provides an adhesive resin member. Therefore, the bus bar  30  is covered with both the adhesive  427  and the resin member  27 . 
     Fifth Embodiment 
     This embodiment is a modification based on the preceding embodiment. In the above embodiment, the bus bar unit  20  accommodates a plurality of bus bars  35 ,  36 ,  37  for crossover wires. Alternatively, the bus bar unit  20  may accommodate the neutral point bus bar  41 . 
       FIG. 24  shows the bus bar unit  20 . The holder  21  has a partition wall  526   c  in addition to the above embodiment. A groove for accommodating the neutral point bus bar  41  is defined between the partition wall  526   c  and the inner wall  25 . The neutral point bus bar  41  is housed between the partition wall  526   c  and the inner wall  25 . 
     Further, in the above embodiment, the resin member  27  provides a concave surface  27   a . Alternatively, the resin member  27  may have a variety of surfaces. 
     In  FIG. 24 , the resin member  27  has a surface  527   a  inclined with respect to the bottom wall  23 . The inclination of the surface  527   a  depends on a posture of the holder  21  at a time of curing. The surface  527   a  is linear. 
     Sixth Embodiment 
     This embodiment is a modification based on the preceding embodiment. In the above embodiment, the bus bar unit  20  has a resin member  27 . Alternatively, the bus bar unit  20  may not include the resin member  27 . 
       FIG. 25  shows an end face of the bus bar unit  20 . The bus bar unit  20  accommodates a plurality of bus bars  35 ,  36 , and  37  in a plurality of grooves. The bus bar unit  20  has a cavity  628 . Also in this embodiment, the plurality of partition walls  26   a  and  26   b  provide a long creep distance among the plurality of bus bars  35 ,  36 , and  37  arranged in multiple layers in the radial direction. Therefore, the plurality of partition walls  26   a  and  26   b  suppress creep discharge. 
     Seventh Embodiment 
     This embodiment is a modification based on the preceding embodiment. In the above embodiment, two neutral point bus bars  41   a  and  41   b  are used. Alternatively, one neutral point bus bar may be used. 
     In  FIG. 26 , the stator coil  12  has one neutral point bus bar  741 . The neutral point bus bar  741  connects 12 phase coils. 
     Further, the plurality of phase coils forming one phase may be dispersed in one phase. The four phase coils  712   u ,  712   v , and  712   w  include two groups of phase coils having different electric angles. The two groups of phase coils have dispersed electrical angles in a range of several degrees to several tens of degrees. 
     Other Embodiments 
     The disclosure in this specification, the drawings, and the like is not limited to the illustrated embodiments. The disclosure encompasses the illustrated embodiments and variations thereof by those skilled in the art. For example, the present disclosure is not limited to the combinations of components and/or elements shown in the embodiments. The present disclosure may be implemented in various combinations. The present disclosure may have additional portions which may be added to the embodiments. The present disclosure encompasses omission of the components and/or elements of the embodiments. The present disclosure encompasses the replacement or combination of components and/or elements between one embodiment and another. The disclosed technical scope is not limited to the description of the embodiment. Several technical scopes disclosed are indicated by descriptions in the claims and should be understood to include all modifications within the meaning and scope equivalent to the descriptions in the claims. 
     The disclosure in the specification, drawings and the like is not limited by the description of the claims. The disclosures in the specification, the drawings, and the like encompass the technical ideas described in the claims, and further extend to a wider variety of technical ideas than those in the claims. Therefore, various technical ideas can be extracted from the disclosure of the specification, the drawings and the like without being limited to the description of the claims. 
     In the above embodiments, the rotary electric machine  1  provides an electric motor. Alternatively, the rotary electric machine  1  may provide an electric motor. In this case, the stator coil  12  is also called a field winding. Alternatively, the rotary electric machine  1  may provide a generator. In this case, the stator coil  12  is also called an armature winding. 
     In the above embodiment, the stator coil  12  has coil ends  14  and  15  at both ends of the stator core  11 . The coil end  14  is arranged so as to face the opening  22 . The coil end  14  can be provided in various forms. In one form, the stator coil  12  may be formed by winding a plurality of continuous conductors. In this case, the coil end  14  is provided by a group of bend portions of continuous wires. In one other form, the stator coil  12  may be provided by a plurality of segment conductors. In this case, the coil end  14  is provided by turn portions of the segment conductors or joint portions joining a plurality of segment conductors. The segment conductor is U-shaped or I-shaped. The shape of such a coil end is disclosed in, for example, Patent Literature 2: JP2000-166150A. JP2000-166150A is incorporated by reference in its entirety in this application. The plurality of segment conductors may be connected by a plurality of connecting conductors arranged at the coil end  14 . The shape of such a coil end is disclosed in, for example, Patent Literature 3: JP2018-125924A. JP2018-125924A is incorporated by reference in its entirety in this application. 
     In the above embodiment, the holder  21  is made of resin. Alternatively, the holder  21  may be made of an insulating member such as ceramic. 
     In the above embodiment, the holder  21  is arranged outer side than the coil end  14  in the axial direction. Alternatively or additionally, the holder  21  may be arranged outer side than the coil end  14  in the radial direction. In the above embodiment, the holder  21  faces the corner on the radial direction outside of the coil end  14 . Alternatively, the holder  21  may be arranged only in the axial direction of the coil end  14 . 
     In the above embodiment, one phase is provided by a plurality of phase coils connected in parallel. Alternatively, a series connection may be included in one phase. For example, one phase may be provided by connecting two phase coils connected in parallel and two phase coils connected in parallel in series. 
     In the above embodiment, the plurality of terminal members  31  and  32  in the bus bar unit  20  have a shape that can be called a J-shape or a U-shape. Alternatively, the plurality of terminal members  31  and  32  can be provided in various shapes such as an I-shape and an L-shape. For example, the plurality of terminal members  31  and  32  may be provided by only the first portions  31   a  and  32   a  in  FIG. 11  and  FIG. 12 . Further, the plurality of terminal members  31  and  32  may be provided by the first portions  31   a  and  32   a  and the second portions  31   b  and  32   b  in  FIG. 11  and  FIG. 12 . 
     In the above embodiment, the bus bar unit  20  is supported by a plurality of coil terminals  16 . Alternatively, the bus bar unit  20  may be connected to the stator core  11  or the coil end  14 . The holder  21  may have, for example, a plurality of legs for contacting the stator core  11  or the coil end  14 . The plurality of legs may be formed by projecting a part of the walls  24 ,  25 , and  26  in the axial direction. The plurality of legs may be fixed to the stator core  11  or the coil end  14  by a fixing mechanism such as adhesion, snap fit, or screwing. 
     In the above embodiment, the coil terminals  16  and the bus bar unit  20  are illustrated so as to be exposed. Alternatively, the coil terminals  16  and/or the bus bar unit  20  may have a powder coating layer applied to them. The powder coating layer can be provided, for example, so as to cover the coil terminals  16 , the joints  17  and  18  and the terminal members  31  and  32 . The powder coating layer may cover the entire coil end  14 . The powder coating layer may cover the bus bar unit  20 .