Patent Publication Number: US-2022216765-A1

Title: Drive unit for electric vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-001629 filed on Jan. 7, 2021, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     This present disclosure relates to a drive unit for an electric vehicle. 
     2. Description of Related Art 
     In the electric vehicle disclosed in Japanese Unexamined Patent Application Publication No. 2010-252584, as a drive source for the vehicle, an originally mounted internal combustion engine is removed and a motor is installed instead of the internal combustion engine. 
     SUMMARY 
     As in JP 2010-252584 A, where a motor is used in substitution for an internal combustion engine, a motor used in another vehicle may be reused. Here, among hybrid vehicles using an internal combustion engine and a motor as drive sources, there are those of a type in which an output shaft of an internal combustion engine is connected to an output shaft of a motor via a clutch. Then, in a motor in this type of hybrid vehicle, a clutch is provided as an assembly integral with the motor. Where such motor is reused in an electric vehicle, the clutch is mounted in the electric vehicle together with the motor. However, when the motor and the clutch are mounted in the electric vehicle, the clutch, which has a function that transmits torque of the motor to an internal combustion engine in the hybrid vehicle, is an unused component that does not function in any way when mounted in the electric vehicle because the internal combustion engine has been disconnected. 
     A drive unit for an electric vehicle for solving the above problem includes: a motor including a tubular rotor, a stator located radially outward of the rotor as viewed from a center axis of the rotor, and an output shaft that rotates integrally with the rotor and that transmits a drive force of the rotor to a drive wheel; a connecting shaft capable of rotating coaxially with the output shaft; a hydraulic clutch interposed between the rotor and the connecting shaft, the hydraulic clutch switching between transmission and non-transmission of torque between the rotor and the connecting shaft; and an auxiliary including an input shaft, the auxiliary being driven by rotation of the input shaft. The input shaft is mechanically linked with the connecting shaft such that torque from the rotor can be input to the input shaft. 
     In the above configuration, the motor is connected to the auxiliary via the clutch and the connecting shaft. Therefore, the auxiliary is driven by motive power of the motor. In this way, the above configuration enables using the clutch integrated with the motor, as a component that transmits motive power of the motor to the auxiliary. Therefore, it is possible to effectively use reused components without any waste. 
     The drive unit for an electric vehicle may include: a hydraulic pump that supplies a hydraulic fluid to the hydraulic clutch; and a control device that controls hydraulic pressure of the hydraulic fluid supplied from the hydraulic pump to the hydraulic clutch. 
     With the above configuration, it is possible to make the hydraulic clutch operate via the control device irrespective operation of the motor to switch between transmission and non-transmission of torque. Accordingly, it is possible to freely drive or stop the auxiliary as necessary. 
     The drive unit for an electric vehicle may include, where a first direction is a direction in which the connecting shaft is located as viewed from the motor, of directions along the center axis of the rotor, a case that receives the motor, the connecting shaft and the hydraulic clutch, and an attachment that is located in the first direction as viewed from the motor, and that is attached to the case. The attachment may include a plurality of bolt holes. The auxiliary may be connected to the attachment via a bolt inserted in a bolt hole selected from the plurality of bolt holes. 
     As in the above configuration, use of the attachment enables disposing any of auxiliaries at a proper position without changing a structure for attachment of the auxiliary, the structure being inside the case, for the auxiliary. In other words, the case can be used in common. Also, the attachment includes the plurality of bolt holes. Therefore, any of auxiliaries can be disposed at a proper position without changing the attachment for the auxiliary, by selecting bolt holes at suitable positions from among the plurality of the bolt holes according to a shape and dimensions of the auxiliary to be attached to the attachment. In other words, the attachment can be used in common. 
     In the drive unit for an electric vehicle, the auxiliary may be located in the first direction as viewed from the attachment and be located outside the case, the connecting shaft may extend through the attachment, the input shaft may be disposed in parallel with the connecting shaft, and an endless power transmission component located outside the case and looped around the input shaft and the connecting shaft may be provided. 
     Where the linking structure using the endless power transmission component is used as in the above configuration, as long as the input shaft is disposed in parallel with the connecting shaft, the input shaft and the connecting shaft can be linked in such a manner as to be capable of rotating integrally. In other words, it is possible to freely change the disposition of the auxiliary as long as the condition that the input shaft is disposed in parallel with the connecting shaft is met. Therefore, the degree of flexibility in disposition of the auxiliary is enhanced. Also, since the auxiliary is located outside the case, work of detaching and attaching the auxiliary can easily be performed. Therefore, it does not take much trouble to, for example, replace the auxiliary or change the disposition of the auxiliary. 
     In the drive unit for an electric vehicle, the attachment may include a through-hole through which the connecting shaft extends; and a bearing that rotatably supports the connecting shaft is located inside the through-hole. In this configuration, there is no need to separately provide a structure that supports the bearing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG. 1  is a schematic configuration diagram of an electric vehicle; 
         FIG. 2  is a schematic diagram illustrating manners of connections in a drive mechanism in a case; 
         FIG. 3  is an enlarged view of region  3  in  FIG. 2 ; and 
         FIG. 4  is a plan view of an attachment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     An embodiment of an electric vehicle to which a drive unit for an electric vehicle is applied will be described with reference to the drawings. 
     Schematic Configuration of Electric Vehicle 
     As illustrated in  FIG. 1 , an electric vehicle  100  includes a motor compartment  102 , a dash panel  106  and a vehicle cabin  104 . The motor compartment  102  is a space defined in a part on the front side of the electric vehicle  100 . The dash panel  106  is a wall portion that defines a rear end of the motor compartment  102 . The vehicle cabin  104  is a space defined on the opposite side of the dash panel  106  from the motor compartment  102 . The vehicle cabin  104  provides a riding space for occupants. 
     As illustrated in  FIG. 2 , the electric vehicle  100  includes a case  10 , an attachment  20 , a drive mechanism  18  and drive wheels  108 . As illustrated in  FIG. 1 , the case  10  is located inside the motor compartment  102 . The case  10  is made of, for example, an aluminum alloy. As illustrated in  FIG. 2 , the case  10  includes a case body  12 . Furthermore, the case body  12  includes a first case body  12 A and a second case body  12 B. The first case body  12 A has a tubular shape overall. The second case body  12 B has a bottomed tubular shape overall. The first case body  12 A and the second case body  12 B are integrally coupled with one opening of the first case body  12 A and an opening of the second case body  12 B butted against each other. The attachment  20  occludes an opening, on the side opposite to the opening to which the second case body  12 B is coupled, of the first case body  12 A. As a result, a component resulting from integration of the case body  12  and the attachment  20  has a columnar shape with a space defined inside, overall. In the below, when the above two parts forming the case body  12  are individually described, the two parts are respectively referred to as the first case body  12 A and the second case body  12 B in the description, and when the two parts are collectively described, the two parts are collectively referred to as the case body  12 . 
     The drive mechanism  18  is mainly located inside the case body  12 . The drive mechanism  18  includes a connecting shaft  72 , a hydraulic clutch  60 , a motor generator  50 , a torque converter  82  and a transmission mechanism  86 . In a direction along a center axis of the case body  12 , the above components are basically arranged in the order mentioned above from the attachment  20  toward a bottom part of the second case body  12 B. The hydraulic clutch  60  and the motor generator  50  alone are located at respective positions that are identical to each other in a direction along the center axis of the case body  12 . A part of the connecting shaft  72 , the hydraulic clutch  60  and the motor generator  50  are located inside the first case body  12 A. The connecting shaft  72  extends through the attachment  20  and is partly located outside the case body  12 . The torque converter  82  and a major part of the transmission mechanism  86  are located inside the second case body  12 B. The transmission mechanism  86  extends through the bottom part of the second case body  12 B and is partly located outside the case body  12 . 
     Schematic manners of connections of the components of the drive mechanism  18  and basic functions of the components are as follows. The connecting shaft  72  is connected to an output shaft (hereinafter, referred to as a motor output shaft)  52  of the motor generator  50  via the hydraulic clutch  60 . The hydraulic clutch  60  switches between transmission and non-transmission of torque between the connecting shaft  72  and the motor output shaft  52 . The motor generator  50  is an electric power generator motor and serves as a drive source of the electric vehicle  100 . The motor output shaft  52  is connected to an input shaft of the torque converter  82 . The torque converter  82  is a fluid coupling. The torque converter  82  switches between transmission and non-transmission of torque between the input shaft and an output shaft of the torque converter  82 . The torque converter  82  includes a lock-up clutch  84 . The lock-up clutch  84  switches between mechanical connection and disconnection between the input shaft and the output shaft of the torque converter  82 . The output shaft of the torque converter  82  is connected to an input shaft of the transmission mechanism  86 . The transmission mechanism  86  changes a gear ratio, which is a difference in rotation speed between the input shaft and an output shaft, in multiple stages. The transmission mechanism  86  outputs torque according to the gear ratio. The output shaft of the transmission mechanism  86  extends to the outside of the case body  12  through the case body  12 . The output shaft of the transmission mechanism  86  is connected to the drive wheels  108  via a differential gear. The differential gear allows occurrence of a difference in rotation speed between the left and right drive wheels  108 . In  FIG. 2 , illustration of the differential gear is omitted. 
     The electric vehicle  100  includes an inverter  90  and a battery  92 . The battery  92  is electrically connected to the motor generator  50  via the inverter  90 . The battery  92  supplies electric power to the motor generator  50  and stores electric power supplied from the motor generator  50 . As illustrated in  FIG. 1 , the battery  92  is located under a floor of the vehicle cabin  104 . The inverter  90  performs DC-AC conversion between the battery  92  and the motor generator  50 . The inverter  90  is located inside the motor compartment  102 . 
     Detailed Structure of Vicinity of Motor Generator 
     In the drive mechanism  18 , the motor generator  50 , the hydraulic clutch  60  and the connecting shaft  72  are integrally included in an assembly. In the below, structures of mutual connection of these components will be described. 
     As illustrated in  FIG. 3 , the hydraulic clutch  60  includes a hub  62 , a drum  66 , a plurality of first friction plates  63 , a plurality of second friction plates  64 , an end plate  65 , a moving mechanism  67  and a lid body  61 . The hub  62  has a bottomed tubular shape overall. The connecting shaft  72  having a rod-like shape extends through a bottomed part of the hub  62 . A center axis of the hub  62  and a center axis of the connecting shaft  72  are coincident with each other. The hub  62  and the connecting shaft  72  rotate integrally. Inside the hub  62 , a distal end of the connecting shaft  72  does not reach an opening of the hub  62 . 
     The plurality of first friction plates  63  are located on an outer circumferential surface of the hub  62 . The plurality of first friction plates  63  are arranged in a direction along the center axis of the hub  62 . The first friction plates  63  each have an annular shape. The first friction plates  63  each project radially from the outer circumferential surface of the hub  62 . The first friction plates  63  are movable in directions along the center axis of the hub  62  relative to the hub  62 . 
     The drum  66  is located on the radially outer side relative to the hub  62  overall as viewed from the center axis of the hub  62 . The drum  66  has a bottomed tubular shape overall. The drum  66  has an inner diameter that is larger than an outer diameter of the hub  62 . The drum  66  receives the hub  62 . An opening of the drum  66  faces in a direction opposite to a direction in which the opening of the hub  62  faces. A center axis of the drum  66  and the center axis of the hub  62  are coincident with each other. The motor output shaft  52  having a rod-like shape extends through a bottomed part of the drum  66 . The center axis of the drum  66  and a center axis of the motor output shaft  52  are coincident with each other. The drum  66  and the motor output shaft  52  rotate integrally. In other words, the motor output shaft  52  is capable of rotating coaxially with the connecting shaft  72 . The motor output shaft  52  extends up to the inside of the hub  62  and faces the connecting shaft  72 . In other words, the motor output shaft  52  and the connecting shaft  72  are adjacent to each other in a direction along the center axes of the motor output shaft  52  and the connecting shaft  72 . In the below, of directions along the center axes of the connecting shaft  72  and the motor output shaft  52 , a direction in which the connecting shaft  72  is located as viewed from the motor output shaft  52  is referred to as “first direction” and a direction in which the motor output shaft  52  is located as viewed from the connecting shaft  72  is referred to as “second direction”. 
     The lid body  61  closes the opening of the drum  66 . The lid body  61  extends through the connecting shaft  72 . The plurality of second friction plates  64  are located on an inner circumferential surface of the drum  66 . The plurality of second friction plates  64  are arranged in a direction along the center axis of the drum  66 . The second friction plates  64  each have an annular shape. The second friction plates  64  project radially from the inner circumferential surface of the drum  66 . The second friction plates  64  are disposed such that the first friction plates  63  and the second friction plates  64  are alternately disposed. The second friction plates  64  face the adjacent first friction plates  63 , respectively. The second friction plates  64  are movable relative to the drum  66  in directions along the center axis of the drum  66 . In the below, a group of friction plates formed by the plurality of first friction plates  63  and the plurality of second friction plates  64  is referred to as “plate group”. 
     The end plate  65  is located on the inner circumferential surface of the drum  66 . The end plate  65  has an annular shape. The end plate  65  projects radially from the inner circumferential surface of the drum  66 . The end plate  65  is located in the first direction relative to the plate group. The end plate  65  faces a friction plate located at an end in the first direction of the plate group. The end plate  65  is immovable relative to the drum  66  in the directions along the center axis of the drum  66 . 
     The moving mechanism  67  includes a fixed plate  68 , a piston  69 , a plurality of springs  67 A, and a fluid chamber  67 B. The fixed plate  68  is located inside the drum  66 . The fixed plate  68  has an annular shape. The fixed plate  68  is attached to the motor output shaft  52  via a hole in a center of the fixed plate  68 . In other words, the fixed plate  68  projects radially from the motor output shaft  52 . The fixed plate  68  is immovable relative to the motor output shaft  52  in the directions along the center axis of the motor output shaft  52 . 
     The piston  69  is located between the fixed plate  68  and the bottom part of the drum  66  inside the drum  66 . The piston  69  includes a piston body  69 A and a contact portion  69 B. The piston body  69 A has an annular shape. The piston body  69 A is attached to the motor output shaft  52  via a hole in the center of the piston body  69 A. In other words, the piston body  69 A projects radially from the motor output shaft  52 . The piston body  69 A is immovable relative to the motor output shaft  52  in the directions along the center axis of the motor output shaft  52 . 
     The contact portion  69 B projects in the first direction from the piston body  69 A. The contact portion  69 B is located at a part on the outer circumferential side of the piston body  69 A. The contact portion  69 B continuously extends over an entire circumference of the piston body  69 A. A projecting end of the contact portion  69 B faces a friction plate located at an end in the second direction of the plate group. 
     The plurality of springs  67 A are attached to the piston body  69 A and the fixed plate  68 . The plurality of springs  67 A are circumferentially arranged at equal intervals. The plurality of springs  67 A bias the piston  69  in the second direction, which is a direction away from the plate group. 
     The fluid chamber  67 B is a space defined between the piston body  69 A and the bottom part of the drum  66 . In other words, the fluid chamber  67 B is located on the opposite side of the piston  69  from the plurality of springs  67 A and in the second direction relative to the piston  69 . The fluid chamber  67 B is supplied with a hydraulic fluid from a later-described hydraulic pressure adjustment mechanism  120 . According to a relationship in magnitude between hydraulic pressure in the fluid chamber  67 B and a biasing force of the plurality of springs  67 A, the piston  69  moves close to or away from the plate group and the end plate  65 . As a result, an operating state of the hydraulic clutch  60  changes. 
     In other words, where the hydraulic pressure in the fluid chamber  67 B is larger than the biasing force of the plurality of springs  67 A, the piston  69  moves close to the plate group and the end plate  65 . In this case, the piston  69  sandwiches the plate group jointly with the end plate  65 . As a result, the first friction plates  63  and the second friction plates  64  adjacent to one another come into contact with one another. In other words, the hydraulic clutch  60  is engaged. In this case, torque is transmitted between the hub  62  and the drum  66 . On the other hand, where the hydraulic pressure in the fluid chamber  67 B is smaller than the biasing force of the plurality of springs  67 A, the piston  69  moves away from the plate group and the end plate  65 . In this case, the piston  69  releases the plate group jointly with the end plate  65 . As a result, the first friction plates  63  and the second friction plates  64  are disposed at respective positions that are spaced from one another. In other words, the hydraulic clutch  60  is disengaged. In this case, no torque is transmitted between the hub  62  and the drum  66 . 
     The hydraulic clutch  60  described above is incorporated inside the motor generator  50 . The motor generator  50  includes a rotor  53  and a stator  54  in addition to the above-described motor output shaft  52 . 
     The rotor  53  is located radially outward of the drum  66  as viewed from the center axis of the drum  66 . The rotor  53  has a tubular shape. The rotor  53  has an inner diameter that is substantially the same as an outer diameter of the drum  66 . The rotor  53  surrounds the drum  66 . An inner circumferential surface of the rotor  53  is fixed to the drum  66 . The rotor  53  is connected to the motor output shaft  52  via the drum  66 . The rotor  53  rotates integrally with the motor output shaft  52 . 
     The stator  54  includes a stator body  55 , a plurality of teeth  56  and a coil  57 . The stator body  55  is located radially outward of the rotor  53  as viewed from a center axis of the rotor  53 . The stator body  55  has a tubular shape. The stator body  55  has an inner diameter that is larger than an outer diameter of the rotor  53 . The stator body  55  surrounds the rotor  53 . A center axis of the stator body  55  is coincident with the center axis of the rotor  53 . 
     The plurality of teeth  56  project from an inner circumferential surface of the stator body  55 . The plurality of teeth  56  are circumferentially arranged at equal intervals. There is space between projecting ends of the plurality of teeth  56  and an outer circumferential surface of the rotor  53 . In  FIG. 3 , illustration of the space is omitted. The coil  57  is wound on the plurality of teeth  56 . The coil  57  is partially located outward of opposite end surfaces of the stator body  55 . 
     Attachment 
     The motor generator  50  is connected to the case body  12  via the attachment  20 . As described above, the attachment  20  is a component that occludes an opening of the first case body  12 A. In the below, first, a configuration of the attachment  20  will be described, and then, a structure of attachment of the motor generator  50  via the attachment  20  will be described. 
     The attachment  20  includes an attachment body  21 , a projection portion  30 , a plurality of bolt holes  39  and a plurality of attaching portions  38 . The attachment  20  is made of, for example, an aluminum alloy. 
     The attachment body  21  has a round plate-like shape. The attachment body  21  includes a through-hole  23  that opens in each of opposite surfaces of the attachment body  21 . An inner surface of the through-hole  23  includes a body small diameter portion  25 , and a body large diameter portion  27  that is larger in diameter than the body small diameter portion  25 . The body small diameter portion  25  and the body large diameter portion  27  are adjacent to each other. In other words, the inner surface of the through-hole  23  has a stepped shape. Center axes of the body small diameter portion  25  and the body large diameter portion  27  are coincident with each other. The diameter of the body small diameter portion  25  is larger than a diameter of the connecting shaft  72 . The diameter of the body large diameter portion  27  is substantially equal to an outer diameter of a later-described bearing  78 . The body large diameter portion  27  and a body step surface  26 , which is a step surface between the body small diameter portion  25  and the body large diameter portion  27 , configure a bearing supporting portion  24 . 
     The projection portion  30  projects from the attachment body  21 . More specifically, the projection portion  30  projects from a surface in which the body large diameter portion  27  opens, of the opposite surfaces of the attachment body  21 . The projection portion  30  has a tubular shape. A center axis of the projection portion  30  is coincident with a center axis of the through-hole  23 . An inner circumferential surface of the projection portion  30  includes a projection small diameter portion  35  and a projection large diameter portion  37  that is larger in diameter than the projection small diameter portion  35 . The projection small diameter portion  35  and the projection large diameter portion  37  are coincident with each other. In other words, an inner circumferential surface of the projection portion  30  has a stepped shape. Center axes of the projection small diameter portion  35  and the projection large diameter portion  37  are coincident with each other. The projection large diameter portion  37  is located closer to a distal end of the projection portion  30  than the projection small diameter portion  35  is. The diameter of the projection small diameter portion  35  is substantially equal to the inner diameter of the stator body  55 . The diameter of the projection large diameter portion  37  is substantially equal to an outer diameter of the stator body  55 . The projection large diameter portion  37  and a projection step surface  36 , which is a step surface between the projection small diameter portion  35  and the projection large diameter portion  37 , configure a stator supporting portion  34 . 
     The plurality of bolt holes  39  extend through the attachment body  21 . As illustrated in  FIG. 4 , some of the plurality of bolt holes  39  are located in a part closer to an outer circumference of the attachment body  21 . These bolt holes  39  are circumferentially arranged at equal intervals. Also, some of the plurality of bolt holes  39  are located in a part closer to an inner circumference of the attachment body  21 . These bolt holes  39  are circumferentially arranged at equal intervals. In  FIG. 4 , in order to illustrate the bolt holes  39  in a recognizable manner, the bolt holes  39  are enlarged and exaggerated. Also, in  FIG. 4 , not all of the plurality of bolt holes  39  are illustrated: some of the plurality of bolt holes  39  are skipped. 
     The plurality of attaching portions  38  project from an outer circumferential surface of the projection portion  30 . The plurality of attaching portions  38  are circumferentially arranged at equal intervals. Each attaching portion  38  has a rectangular plate-like shape. Each attaching portion  38  includes an attaching hole extending through the attaching portion  38 . In  FIG. 4 , in order to illustrate the attaching portions  38  in a recognizable manner, the attaching portions  38  are enlarged and exaggerated. Also, in  FIG. 3 , only one of the plurality of attaching portions  38  is illustrated. 
     As illustrated in  FIG. 3 , the case  10  includes a plurality of case attaching portions  13  as structure portions for attaching the attachment  20 . The plurality of case attaching portions  13  are located at an end portion of the first case body  12 A in a direction along the center axis of the case body  12 . The case attaching portions  13  project from an outer circumferential surface of the first case body  12 A. The plurality of case attaching portions  13  are circumferentially arranged at equal intervals. Each case attaching portion  13  has a rectangular plate-like shape. Each case attaching portion  13  includes an attaching hole extending through the case attaching portion  13 . In  FIG. 3 , only one of the plurality of case attaching portions  13  is illustrated. 
     Structure for Attachment of Motor Generator 
     The motor generator  50  is attached to the attachment  20  configured as described above. The electric vehicle  100  includes a bearing  78  for attaching the connecting shaft  72  to the attachment  20  together with the motor generator  50 . 
     In a state in which attachment  20  is attached to the motor generator  50 , the attachment body  21  faces the motor generator  50  in a direction along the center axes of the motor output shaft  52  and the connecting shaft  72 . The attachment body  21  is located in the first direction relative to the motor generator  50 . The center axis of the through-hole  23  of the attachment body  21  is coincident with the center axes of the motor output shaft  52  and the connecting shaft  72 . The projection portion  30  projects toward the motor generator  50 . In the words, of the projection small diameter portion  35  and the projection large diameter portion  37 , the projection large diameter portion  37  is located closer to the motor generator  50  relative to the projection small diameter portion  35 . Likewise, of the body small diameter portion  25  and the body large diameter portion  27  of the through-hole  23 , the body large diameter portion  27  is located closer to the motor generator  50  relative to the body small diameter portion  25 . 
     In the disposition of the attachment  20  as above, a part, closer to the attachment  20 , of the stator  54 , that is, a part on the first direction side of stator  54  is fitted in the stator supporting portion  34  configured by the projection portion  30  of the attachment  20 . The stator supporting portion  34  supports the stator  54 . In other words, the projection large diameter portion  37  supports an outer circumferential surface of the stator body  55 . Also, the projection step surface  36  supports an end surface of the stator body  55 . 
     A plurality of bolts B 1  extend through the stator body  55 . The bolts B 1  extend through the entirety of the stator body  55  in a direction along the center axis of the stator body  55 . More specifically, each bolt B 1  is inserted through the stator body  55  from the second direction side, which is opposite to the projection step surface  36 , toward the first direction side. Each bolt B 1  reaches a thick part of the projection portion  30 . The bolts B 1  fix the attachment  20  and the motor generator  50  to each other in an integrated manner. In  FIG. 3 , only one of the plurality of bolts B 1  is illustrated. 
     Also, in the above-described disposition of the attachment  20 , the connecting shaft  72  extends through the through-hole  23 . Then, the bearing  78  is interposed between the inner surface of the through-hole  23  and the connecting shaft  72 . The bearing  78  rotatably supports the connecting shaft  72 . Although illustration is omitted in  FIG. 3 , the bearing  78  has a publicly known structure in which a plurality of balls are interposed between an annular outer ring and an annular inner ring. The bearing  78  has a circular ring-like shape overall. The bearing  78  is fitted in the bearing supporting portion  24  configured by the through-hole  23  of the attachment  20 . The bearing supporting portion  24  supports the bearing  78 . In other words, the body large diameter portion  27  supports an outer circumferential surface of the bearing  78 . Also, the body step surface  26  supports an end surface of the outer ring of the bearing  78 . 
     The attachment  20  to which the motor generator  50  is attached is attached to the case body  12  via the plurality of case attaching portions  13 . More specifically, in a state in which the attachment  20  is attached to the case body  12 , the plurality of attaching portions  38  of the attachment  20  face the plurality of case attaching portions  13 . Bolts B 2  extend through the respective attaching holes of the attaching portions  38  and the case attaching portions  13  facing each other. The bolts B 2  fix the attaching portion  38  and the case attaching portion  13  to each other in an integrated manner. 
     Auxiliary 
     The electric vehicle  100  includes a compressor  40 . The compressor  40  is an auxiliary that feeds compressed air to an air-conditioning unit of the electric vehicle  100 . The compressor  40  includes a compressor case  42 , a compressor body  44  and an input shaft  46 . 
     The compressor case  42  includes a case body  42 A and a plurality of compressor attaching portions  42 B. The case body  42 A has a columnar shape in which space is defined inside, overall. The plurality of compressor attaching portions  42 B are located at an end portion of the case body  42 A in a direction along a center axis of the case body  42 A. The compressor attaching portions  42 B project from an outer circumferential surface of the case body  42 A. The plurality of compressor attaching portions  42 B are circumferentially arranged at equal intervals. Each compressor attaching portion  42 B has a rectangular plate-like shape. 
     The compressor body  44  is located inside the case body  42 A. The compressor body  44  includes a mechanism that feeds compressed air. The input shaft  46  is connected to the compressor body  44 . The input shaft  46  extends in a direction along the center axis of the case body  42 A. The input shaft  46  is rotatably supported by the compressor body  44 . Upon the input shaft  46  being rotated, the compressor body  44  is driven. The input shaft  46  extends through an end surface of the case body  42 A at an end portion of the case body  42 A, the end portion being opposite to the end portion at which the compressor attaching portions  42 B are located. In other words, a part of the input shaft  46  is located outside the case body  42 A. 
     Like the motor generator  50 , the compressor  40  is attached to the case  10  via the attachment  20 . The compressor  40  is located in the first direction relative to the attachment  20 . In other words, the compressor  40  is located outside the case  10 . In a state in which the compressor  40  is attached to the attachment  20 , one end surface of the case body  42 A of the compressor  40 , on the side on which the compressor attaching portions  42 B are located, faces the attachment body  21 . The plurality of compressor attaching portions  42 B face some of the plurality of bolt holes  39  of the attachment  20 . Bolts B 3  extend through the respective compressor attaching portions  42 B. The bolts B 3  reach the insides of the bolt holes  39 . The bolts B 3  fix the compressor attaching portions  42 B and the attachment  20  to each other in an integrated manner. In a state in which the compressor  40  is attached to the attachment  20 , the input shaft  46  is parallel to the connecting shaft  72 . 
     The electric vehicle  100  includes an endless belt  75 . The belt  75  is looped around the connecting shaft  72  and the input shaft  46  of the compressor  40 . The belt  75  transmits rotation of the connecting shaft  72  to the input shaft  46 . 
     Hydraulic Pressure Adjustment Mechanism 
     The electric vehicle  100  includes a hydraulic pressure adjustment mechanism  120  and a control device  130 . The hydraulic pressure adjustment mechanism  120  includes a fluid pan  122 , a hydraulic pressure circuit  124  and a hydraulic pump  126 . 
     The fluid pan  122  stores the hydraulic fluid. The hydraulic pump  126  is an electrical pump to be driven by a dedicated electric motor that is different from the motor generator  50 . The hydraulic pump  126  supplies the hydraulic fluid stored in the fluid pan  122  to the hydraulic pressure circuit  124 . The hydraulic pressure circuit  124  is connected to the fluid chamber  67 B of the hydraulic clutch  60 . The hydraulic pressure circuit  124  includes a solenoid valve  124 A. The hydraulic pressure supplied to the fluid chamber  67 B is adjusted according to opening or closing of the solenoid valve  124 A. 
     The control device  130  can be configured as one or more processors that perform various types of processing according to a computer program (software). The control device  130  may be configured as one or more dedicated hardware circuits, such as application-specific integrated circuits (ASICs), that perform at least some of various types processing or a circuitry including a combination of such dedicated hardware circuits. The one or more processors each include a CPU and memories such as a RAM and a ROM. The memories store program codes or commands configured to make the CPU perform processing. The memories, that is, computer-readable mediums may be any available mediums that can be accessed by a general-purpose or dedicated computer. The CPU controls the hydraulic pressure adjustment mechanism  120  including the hydraulic pump  126  and the solenoid valve  124 A, by executing a program stored on the ROM. By controlling the hydraulic pressure adjustment mechanism  120 , the CPU controls hydraulic pressure of the hydraulic fluid to be supplied to the fluid chamber  67 B of the hydraulic clutch  60 . 
     In the present embodiment, a drive unit for an electric vehicle includes the motor generator  50 , the hydraulic clutch  60 , the connecting shaft  72 , the compressor  40 , the belt  75 , the bearing  78 , the attachment  20 , the case  10 , the hydraulic pressure adjustment mechanism  120  and the control device  130 . 
     Method of Attachment of Motor Generator and Compressor 
     A method of attachment of the motor generator  50  and the compressor  40  to the case  10  will be described. 
     The motor generator  50  is a reused motor generator originally mounted in another vehicle. The other vehicle is a hybrid vehicle with an internal combustion engine and a motor generator as drive sources. As hybrid vehicles, there are hybrid vehicles of a type including an internal combustion engine and a single motor generator. In this type of hybrid vehicle, a crankshaft, which is an output shaft of an internal combustion engine, is sometimes connected to an output shaft of a motor generator via a clutch. The motor generator in this case incorporates the clutch inside a rotor. The motor generator mounted in the electric vehicle  100  is a motor generator of this type. The connecting shaft  72  connected to the hydraulic clutch  60  is one originally used for connection of the crankshaft of the internal combustion engine. In other words, the clutch is a clutch originally interposed between the output shaft of the motor generator and the crankshaft, the clutch functioning to switch between transmission and non-transmission of torque between the output shaft of the motor generator and the crankshaft. 
     For attachment of the motor generator  50  and the compressor  40  to the case  10 , various necessary components such as the motor generator  50 , the compressor  40 , the attachment  20  and the case  10  are separately provided in advance. As described above, the motor generator  50  is a reused article from another hybrid vehicle and includes the hydraulic clutch  60  and the connecting shaft  72  in an integrated manner. Also, the case  10  is divided in the first case body  12 A and the second case body  12 B. The torque converter  82  and the transmission mechanism  86  are housed in the second case body  12 B. The first case body  12 A and the second case body  12 B are not case bodies newly designed for the reused motor generator  50  but case bodies according to a common standard, the case bodies being available for other electric vehicles. Likewise, the attachment  20  is an attachment according to a common standard, the attachment being available for other electric vehicles, and is designed to have dimensions conforming to the case  10 . 
     Attachment work is performed as follows. First, the motor generator  50  is attached to the attachment  20  that is not yet attached to the case body  12 . More specifically, the bearing  78  with the connecting shaft  72  inserted is placed in the bearing supporting portion  24  of the attachment  20 . Also, the stator  54  of the motor generator  50  is placed in the stator supporting portion  34  of the attachment  20 . Then, in this state, the stator  54  is fixed to the attachment  20  via the bolts B 1 . 
     Next, the attachment  20  is attached to the case body  12 . In other words, the attaching portions  38  of the attachment  20  and the case attaching portions  13  are aligned and fixed to each other via the bolts B 2 . Subsequently, the first case body  12 A and the second case body  12 B are joined together after various adjustment works being performed. An example of the adjustment works is work for connecting the motor output shaft  52  and the input shaft of the torque converter  82 . Also, another example of the adjustment works is work for connecting the hydraulic pressure circuit  124  to the fluid chamber  67 B of the hydraulic clutch  60 . 
     Next, the compressor  40  is attached to the attachment  20 . In other words, bolt holes  39  of the attachment  20  and the compressor attaching portions  42 B are aligned and fixed to each other via the bolts B 3 . At this time, from among the plurality of bolt holes  39  provided in the attachment  20 , bolt holes  39  located at positions suitable for attachment of the compressor  40  to the attachment  20  are used. The bolt holes  39  to be used can be selected according to a shape and dimensions of the compressor case  42 . Also, the bolt holes  39  to be used can be selected in consideration of a position at which the compressor case  42  should be disposed in view of disposition of other components inside the motor compartment  102 . 
     When the compressor  40  is attached to the attachment  20 , the belt  75  is looped around the input shaft  46  of the compressor  40  and the connecting shaft  72  in advance in a non-tensed manner. Then, the belt  75  is tensed when attachment of the compressor  40  is completed. 
     Through the above process, the motor generator  50  and the compressor  40  can be attached to the case  10  via the attachment  20 . 
     Operation of Embodiment 
     The control device  130  adjusts the hydraulic pressure in the fluid chamber  67 B of the hydraulic clutch  60  through control of the hydraulic pressure adjustment mechanism  120 . In response to the adjustment, an operating state of the hydraulic clutch  60  changes. In other words, upon an increase in hydraulic pressure in the fluid chamber  67 B of the hydraulic clutch  60 , the hydraulic clutch  60  is engaged. In this case, torque is transmitted from the rotor  53  of the motor generator  50  to the connecting shaft  72 . The torque transmitted to the connecting shaft  72  is input to the input shaft  46  of the compressor  40  via the belt  75 . Upon the input shaft  46  rotating in response to the torque, the compressor body  44  is driven. On the other hand, upon a decrease in hydraulic pressure in the fluid chamber  67 B of the hydraulic clutch  60 , the hydraulic clutch  60  is disengaged. In this case, no torque is transmitted from the rotor  53  of the motor generator  50  to the connecting shaft  72 . In this case, operation of the belt  75  and the input shaft  46  of the compressor  40  stops. Then, the compressor body  44  enters a stop state. 
     Effects of Embodiment 
     (1) Where a motor generator used in another vehicle is reused, the hydraulic clutch  60  and the connecting shaft  72  integrated with the motor generator  50  in an assembly are also reused. In the present embodiment, the motor generator  50  is connected to the compressor  40  via the hydraulic clutch  60  and the connecting shaft  72 . Therefore, as described in the Operation of Embodiment section above, it is possible to drive the compressor  40  by transmitting motive power of the motor generator  50  to the compressor  40 . In this way, in the present embodiment, the hydraulic clutch  60  and the connecting shaft  72  can be used as components that transmit motive power of the motor generator  50  to the compressor  40 . In other words, it is possible to effectively use reused components without any waste. 
     (2) In the present embodiment, as components for switching the operating state of the hydraulic clutch  60 , the hydraulic pressure adjustment mechanism  120  dedicated to the hydraulic clutch  60  and the control device  130  that controls the hydraulic pressure adjustment mechanism  120 , which are not linked with operation of the motor generator  50 , are provided. Therefore, it is possible to switch the operating state of the hydraulic clutch  60  irrespective of operation of the motor generator  50 . Accordingly, it is possible to freely drive or stop the compressor  40  as necessary. 
     (3) There are a plurality of models of compressors. Then, the compressors differ in shape and dimensions depending on the models. If a compressor that is different in shape and dimensions is used, it is necessary to change a structure to which the compressor is to be attached, according to the shape and the dimensions of the compressor. In other words, depending on the model of the compressor  40  mounted in the electric vehicle  100 , the electric vehicle  100  is required to include an attachment structure conformable to the mounted compressor  40 . 
     In order to meet the requirement, it is conceivable to change the structure of the case  10  according to the shape and dimensions of the compressor  40 . However, the case  10  occupies quite a large capacity in the motor compartment  102  and has considerably large dimensions. Therefore, a mold for manufacturing the case  10  also has considerably large dimensions. Where the mold has large dimensions, considerable costs are required to modify a shape of the mold or prepare a new mold. Accordingly, a design change of the case  10  cause a considerable increase in cost. Also, there is a restriction on space for receiving the case  10  in the motor compartment  102 . From these points, for the case  10 , there is a need to use a common case. 
     Therefore, in the present embodiment, the compressor  40  is attached to the case  10  using the attachment  20 . The attachment  20  includes the plurality of bolt holes  39  as a structure for attachment of the compressor  40 . Using bolt holes  39  at suitable positions from among the plurality of bolt holes  39  according to the shape and dimensions of the compressor  40  enables properly attaching the compressor  40  to the attachment  20  irrespective of the shape and dimensions of the compressor  40 . The present embodiment enables properly attaching a compressor  40  to a case  10  having a shape determined in advance, irrespective of the shape and dimensions of the compressor  40 . 
     Also, a position to which the compressor  40  is to be attached may be restricted in view of disposition of other components inside the motor compartment  102 . Even in such case, bolt holes  39  at suitable positions from among the plurality of bolt holes  39  are used to allow the compressor  40  to be disposed at a proper position according to a layout inside the motor compartment  102 , enabling attaching the compressor  40  to a case  10  having a shape determined in advance. 
     (4) In the present embodiment, the connecting shaft  72  and the input shaft  46  of the compressor  40  are linked using the belt  75 . Where the connecting shaft  72  and the input shaft  46  are linked using the belt  75 , as long as the connecting shaft  72  and the input shaft  46  are disposed in parallel with each other, even if a distance between the connecting shaft  72  and the input shaft  46  changes, the connecting shaft  72  and the input shaft  46  can be linked by adjusting a length of the belt  75 . In other words, the configuration of the present embodiment using the belt  75  allows change in position of the compressor  40  under the condition that the connecting shaft  72  and the input shaft  46  are parallel to each other. Therefore, it is possible to dispose the compressor  40  at a necessary position according to the shape and dimensions of the compressor  40  or a requirement for a position for attachment of the compressor  40  due to the layout inside the motor compartment  102  such as those described in (3) above. 
     (5) In the present embodiment, the compressor  40  is disposed outside the case  10 . Therefore, even where a necessity for changing the position for attachment of the compressor  40  arises, work of detaching and attaching the compressor  40  can easily be performed. Therefore, even where a necessity for replacing the compressor  40  with a compressor of a different model or changing disposition of the compressor  40  according to the layout inside the motor compartment  102  arises, work for such replacement or change does not take much trouble. 
     (6) In the present embodiment, the bearing  78  is supported by the attachment  20 . More specifically, an outer circumferential surface of the bearing  78  is supported by the body large diameter portion  27 , and an end surface of the bearing  78  is supported by the body step surface  26 . Use of such stepped shape enables the bearing  78  to be stably supported. Also, in the present embodiment, the stator  54  of the motor generator  50  is supported by the attachment  20 . More specifically, the outer circumferential surface of the stator body  55  is supported by the projection large diameter portion  37  and an end surface of the stator body  55  is supported by the projection step surface  36 . Use of such stepped shape enables the stator  54  to be also stably supported. As above, the connecting shaft  72  and the hydraulic clutch  60  are integrated with the motor generator  50 . As a result of the bearing  78  supporting the connecting shaft  72 , and the stator  54  being both stably supported, the entire motor generator  50  can stably be supported. 
     As described above, the mold for manufacturing the case  10  is a considerably large-scaled mold. Even if fine structures such as the stepped shapes above are provided at particular positions for supporting the bearing  78  and the stator  54  in such mold, it is difficult to determine the positions accurately. On the other hand, the attachment  20  used in the present embodiment has dimensions enough to connect the motor generator  50  and a wall surface of the case  10 . In other words, the dimensions of the attachment  20  are considerably small in comparison with the case  10 . A mold for manufacturing such the attachment  20  can be designed with high accuracy even if fine shapes such as the stepped shapes are designed at a particular position. Therefore, in the present embodiment in which supporting structures are provided in the attachment  20 , accuracy of positions at which the supporting structures are provided is enhanced. Therefore, it is possible to more stably support the motor generator  50 . 
     Alterations 
     The present embodiment can be altered as follows. Any combination of the present embodiment and the below alterations is possible as long as such combination causes no technical contradiction. 
     The procedure for attaching the motor generator  50  and the compressor  40  to the case  10  is not limited to the above example in the embodiment. For example, after the motor generator  50  is attached to the attachment  20 , the compressor  40  may be attached to the attachment  20  before attachment of the attachment  20  to the case  10 . The attachment  20  may be attached to the case  10  afterward. 
     The connecting shaft  72  may be divided in, for example, two parts at an intermediate position in a direction along the center axis of the connecting shaft  72 . In other words, the connecting shaft  72  may be configured by combining a plurality of components. 
     The auxiliary connected to the motor generator  50  is not limited to the compressor  40 . The auxiliary only needs to be one driven according to rotation of an input shaft. For example, as the auxiliary, a pump for power steering may be employed. A driver&#39;s force of operating a steering wheel is assisted according to hydraulic pressure generated by driving the pump. 
     A plurality of auxiliaries may be attached to the case  10 . Use of the plurality of bolt holes  39  in the attachment  20  enables attachment of a plurality of auxiliaries to the attachment  20 . In this case, a belt  75  is provided for each auxiliary and positions of the belts  75  are shifted from each other in a direction along the center axis of the connecting shaft  72 . It is only necessary that the belts  75  be looped around respective input shafts of the auxiliaries and the connecting shaft  72  in such state. Accordingly, rotation of the connecting shaft  72  can be transmitted to the input shafts of the respective auxiliaries. 
     The auxiliary may be disposed inside the case  10 . Provision of space for disposition of the auxiliary between the attachment  20  and the motor generator  50  enables attachment of the auxiliary to the attachment  20  inside the case  10 . In order to provide space for disposition of the auxiliary between the attachment  20  and the motor generator  50 , it is only necessary that a position for providing the stator supporting portion  34  be adjusted. 
     An endless power transmission component linking the input shaft of the auxiliary and the connecting shaft  72  are not limited to the belt  75 . For example, as the endless power transmission component, a chain may be employed. In this case, it is only necessary to fix a sprocket to the input shaft of the auxiliary and the connecting shaft  72 . 
     A configuration that links the input shaft of the auxiliary and the connecting shaft  72  is not limited to a configuration using the endless power transmission component. For example, the input shaft of the auxiliary and the connecting shaft  72  may be disposed coaxially and be mechanically linked via, for example, a gear mechanism. 
     Disposition of the plurality of bolt holes  39  is not limited to the example in the embodiment. For example, the plurality of bolt holes  39  may be arranged irregularly. In order to enable an auxiliary to be attached at any of various positions in the attachment  20 , it is preferable that bolt holes  39  be provided at various positions in the attachment  20 . 
     Depending on the model of the motor generator  50  to be reused, dimensions of the motor generator  50  may differ. In this case, for example, it is necessary to change the diameter of the projection large diameter portion  37  included in the stator supporting portion  34 , according to the model of the motor generator  50 . For such case, for example, a plurality of types of attachments  20  that are different from one another in diameter of the projection large diameter portion  37  may be provided in advance and a proper one may be selected from the plurality of types of attachments  20 . 
     The configuration of the stator supporting portion  34  is not limited to the example in the above embodiment. For example, the stepped shape at the inner circumferential surface of the projection portion  30  may be eliminated and an inner diameter of the projection portion  30  may be made constant over an entire length of the projection portion  30 . Then, the stator supporting portion  34  may be configured by the inner circumferential surface of the projection portion alone. In this case, for example, the stator body  55  being pressed onto the inner circumferential surface of the projection portion  30  enables stably supporting the stator  54 . 
     It is not essential to provide a structure that supports the stator  54  at the attachment  20 . For example, if it is possible to support the stator  54  using an existing structure in the case  10 , there is no need to support the stator  54  via the attachment  20 . 
     The configuration of the bearing supporting portion  24  is not limited to the example in the above embodiment. Like the aforementioned alteration of the stator supporting portion  34 , for example, the stepped shape at the inner surface of the through-hole  23  may be eliminated and a diameter of the through-hole  23  may be made constant over an entire length of the through-hole  23 . 
     Like the alteration of the structure that supports the stator  54 , it is not essential to provide a structure that supports the bearing  78  at the attachment  20 . The structure for attaching the auxiliary to the attachment  20  is not limited to the structure using the bolt holes  39 . For example, as the structure for attaching the auxiliary to the attachment  20 , a recess or a projection may be provided in the attachment. Then, the auxiliary may be fitted to or pressed into the recess or the projection. 
     The auxiliary may be attached to the case  10  without using the attachment  20 . If the auxiliary can be attached to the case  10  using an existing structure in the case  10 , there is no need to use the attachment  20 . 
     If the attachment  20  is not used to attach the auxiliary, the motor generator  50  and the bearing  78  to the case  10 , the attachment  20  may be eliminated. 
     A mechanism that adjusts the hydraulic pressure in the fluid chamber  67 B of the hydraulic clutch  60  is not limited to the example in the above embodiment. For example, the hydraulic pressure in the fluid chamber  67 B of the hydraulic clutch  60  may be adjusted using motive power of the motor generator  50 . In this case, the operating state of the hydraulic clutch  60  switches in coordination with operations of the motor generator  50  such as rotation and stoppage of the rotor  53 . Where an auxiliary requiring a driving state to be switched in coordination with operation of the motor generator  50  is connected, it is possible to drive the auxiliary at a proper timing even if the above method is employed for the mechanism that adjusts the hydraulic pressure in the fluid chamber  67 B. 
     The material of the case  10  is not limited to the example in the above embodiment. For the material of the case  10 , a material that is proper for receiving the components of the drive mechanism  18  only needs to be employed. In consideration of weight of the components of the drive mechanism  18 , it is preferable that the material be a material having adequate stiffness. Also, in consideration of the components of the drive mechanism  18  generating heat, it is preferable that the material be excellent in heat dissipation performance. 
     The material of the attachment  20  is not limited to the example in the above embodiment. For the material of the attachment  20 , a material that is proper for attaching the motor generator  50  to the case body  12  only needs to be employed. Like the alteration relating to the material of the case  10 , a proper material that is suitable in the perspective of, for example, stiffness and heat dissipation performance only needs to be employed. Also, the material of the attachment  20  may be the same as or different from the material of the case  10 . The attachment  20  is a part of a heat transmission passage from the motor generator  50  to the case  10 . From such perspective, it is preferable that the material of the attachment  20  be a material having a thermal conduction efficiency that is equal to or exceeds a thermal conduction efficiency of the case  10 .