Patent Publication Number: US-2010120569-A1

Title: Driving apparatus for hybrid vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the U.S. National Phase of PCT/JP2008/062677 filed Jul. 14, 2008, which claims priority from Japanese Patent Application No. 2007-186857 filed Jul. 18, 2007, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     The present invention relates to a driving apparatus installed in a hybrid vehicle that uses an engine and a motor as drive sources. 
     In a driving apparatus for a hybrid vehicle that uses an engine (an internal combustion engine) and a motor as drive sources, power from two systems must be transmitted to a drive shaft connected to a drive wheel via a differential device, and various constructions have been proposed as a power train constitution used for this purpose. One of these constructions, for example, is a vehicle driving apparatus in which a generator, a power splitting planetary gear mechanism, a motor speed reducing planetary gear mechanism, and a motor are disposed coaxially with an input shaft (an output shaft of an engine) in this order from the engine side (Japanese Patent Application Publication No. 2006-298314). In this vehicle driving apparatus, power from the engine and power from the motor with the torque being amplified by the motor speed reducing planetary gear mechanism are synthesized by a counter gear portion so that the resulting synthesized torque can be transmitted to a drive shaft via a differential device. 
     SUMMARY 
     However, in the vehicle driving apparatus described above, the overall physical constitution of the driving apparatus is large, leading to an increase in cost. The reason for this is that since the generator, the power splitting planetary gear mechanism, the motor speed reducing planetary gear mechanism, and the motor are disposed coaxially, an axial dimension of the driving apparatus increases in length, and therefore a bearing of the motor is disposed in a space on the inner periphery of the motor (an inner side of a coil) in order to reduce the axial length of the driving apparatus. In other words, the bearing is disposed inside the motor. As a result, the size of the motor in a radial direction increases, leading to an increase in the overall physical constitution of the driving apparatus. 
     Further, the motor speed reducing planetary gear mechanism is used to transmit the power of the motor to the counter gear portion by amplifying the torque. In other words, a planetary gear mechanism is used to reduce rotation of the motor. As a result, the cost of the driving apparatus increases. Moreover, there is a limit to the magnitude of a reduction ratio of the planetary gear mechanism that can be set relative to its size, and therefore high performance is required of the motor, leading to increases in the physical constitution and cost of the motor. As a result, the overall physical constitution of the driving apparatus increases, leading to an increase in the cost. 
     The present invention has been designed to solve the problems described above, and it is an object of the present invention to provide a driving apparatus for a hybrid vehicle in which the overall size and cost of the driving apparatus can be reduced. 
     A driving apparatus for a hybrid vehicle according to the present invention, which has been designed to solve the problems described above, includes: an input shaft linked to an engine; a generator; a motor; a differential gear device including a first gear element linked to a rotary shaft of the generator, a second gear element linked to the input shaft, and a third gear element that transmits power to a drive shaft; and a counter gear that is linked to the third gear element of the differential gear device and drive-linked to the motor. In the driving apparatus, the generator, the differential gear device, and the counter gear are disposed coaxially with the input shaft, the motor is disposed on a different axis parallel to the input shaft on an opposite side of the generator, the differential gear device, and the counter gear to an engine-linked side of the input shaft in an axial direction, motor bearings for rotatably supporting a rotary shaft of the motor are disposed on an outer side of the motor, the motor is disposed to overlap at least one of first axis constitutional components disposed coaxially with the input shaft in a radial direction, and a differential gear device side bearing of the motor bearings, which is positioned on the differential gear device side, is disposed to overlap at least one of the first axis constitutional components in the axial direction. 
     Note that the first axis constitutional components include, in addition to the generator, the differential gear device, the counter gear, and the input shaft, all constitutional components of the driving apparatus (an oil pump, bearings, and so on, for example) disposed coaxially with the input shaft (on a first axis) and components required to disposed these components (cases of the components, fixing members of the components such as bolts and nuts, and so on, for example). 
     In this driving apparatus for a hybrid vehicle, the motor is disposed on a different axis parallel to the input shaft on the opposite side of the generator, differential gear device, and counter gear to the engine-linked side of the input shaft in the axial direction, and therefore the rotation of the motor can be reduced using a spur gear or a helical gear instead of a planetary gear mechanism. In other words, the rotation of the motor can be reduced using the counter gear for transmitting power to the drive shaft (i.e. by transmitting the rotation of the motor to the counter gear via a smaller gear than the counter gear). In so doing, a larger reduction ratio than that of a planetary gear mechanism can be used, and therefore high performance is no longer required of the motor. Accordingly, the size and cost of the motor can be reduced. Furthermore, since a planetary gear mechanism is not required to reduce the rotation of the motor, the size of the driving apparatus in the axial direction can be reduced, thereby reducing the cost. 
     Further, the motor bearings are disposed on the outside of the motor, and therefore the size of the motor in the radial direction can be reduced. Furthermore, the motor is disposed so as to overlap at least one of the first axis constitutional components in the radial direction, and therefore the motor shaft can be brought closer to the first axis. As a result, increases in the size of the driving apparatus in the radial direction when the motor is disposed on a different axis from the input shaft can be minimized. 
     Moreover, the differential gear device side bearing of the motor bearings, which is positioned on the differential gear device side, is disposed to overlap the first axis constitutional components in the axial direction, and therefore, even when the motor bearings are disposed on the outside of the motor, the axial length of the driving apparatus is not affected. In other words, the axial size of the driving apparatus can be sufficiently reduced by eliminating the need for a planetary gear mechanism to reduce the rotation of the motor. 
     Hence, with the driving apparatus for a hybrid vehicle according to the present invention, the size and cost of the motor can be reduced, and the rotation of the motor can be reduced using the counter gear instead of a planetary gear mechanism. Therefore, the overall size and cost of the driving apparatus can be reduced. 
     In the driving apparatus for a hybrid vehicle according to the present invention, the generator, the differential gear device, and the counter gear are preferably disposed coaxially with the input shaft in this order from the engine-linked side of the input shaft, and an output shaft of the motor preferably overlaps the generator in the radial direction. 
     With this constitution, the motor and counter gear can be disposed close to each other, and the output shaft of the motor can be prevented from overlapping the generator, which has a large radial dimension, in the axial direction. As a result, the length of the output shaft of the motor can be shortened, thereby reducing the cost and further reducing the radial size of the driving apparatus. 
     In the driving apparatus for a hybrid vehicle according to the present invention, one of the first axis constitutional components that overlaps the motor bearings in the axial direction is preferably an oil pump. 
     By overlapping the oil pump, which has a small radial dimension, with the motor bearings in the axial direction in this manner, the radial size of the driving apparatus can further be reduced. 
     In the driving apparatus for a hybrid vehicle according to the present invention, the generator, the differential gear device, the counter gear, and the oil pump are preferably disposed coaxially with the input shaft in this order from the engine-linked side of the input shaft. 
     With this constitution, the motor and counter gear can be disposed close to each other, and the motor bearings can be overlapped with the oil pump, which has a small radial dimension, in the axial direction. As a result, the length of the output shaft of the motor can be shortened, thereby reducing the cost and further reducing the radial size of the driving apparatus. 
     In the driving apparatus for a hybrid vehicle according to the present invention, the oil pump is preferably disposed on a terminal end portion of the input shaft and driven by a rotation of the input shaft. 
     By disposing the oil pump on the terminal end portion of the input shaft in this manner such that the oil pump is driven directly by the input shaft, the need for a new mechanism to drive the oil pump is eliminated, and therefore the axial length of the first axis can be shortened, thereby reducing the cost. As a result, the axial size and cost of the driving apparatus can further be reduced. 
     In the driving apparatus for a hybrid vehicle according to the present invention, the drive shaft is preferably disposed parallel to the input shaft, an output gear of the motor preferably meshes with the counter gear, the counter gear is preferably disposed parallel to the input shaft so as to mesh with a counter driven gear of a counter shaft that transmits power to the drive shaft, and a final drive pinion gear of the counter shaft preferably meshes with a final ring gear of a differential device that transmits power to the drive shaft. 
     Hence, the single counter gear can serve as a speed reducing mechanism of the motor and a gear for transmitting power from the input shaft to the drive shaft, and therefore the need to provide a separate speed reducing mechanism for reducing the rotation of the motor is eliminated. Accordingly, a dedicated space for disposing a speed reducing mechanism is not required, and therefore the axial size of the driving apparatus can be reduced. 
     In the driving apparatus for a hybrid vehicle according to the present invention, an oil pump gear chamber that accommodates an oil pump gear mechanism provided in the oil pump is preferably formed integrally with a motor case that accommodates and supports the motor. 
     Further, the oil pump gear chamber is preferably provided in a first extension portion extending such that the motor case partially surrounds the oil pump gear mechanism. 
     By forming the gear chamber that accommodates the oil pump gear mechanism in the motor case in this manner, the motor case and a casing of the oil pump can be formed integrally. As a result, the oil pump and the motor can be disposed close to each other in the axial direction. Hence, the axial length of the driving apparatus can be shortened even further, thereby further reducing the overall size of the driving apparatus. 
     Moreover, since the motor case and the casing of the oil pump are formed integrally, the number of components is reduced, thereby reducing the number of assembly processing steps correspondingly. As a result, the cost of the driving apparatus can be further reduced. 
     In the driving apparatus for a hybrid vehicle according to the present invention, an oil pump cover that closes an opening in the oil pump gear chamber is preferably fixed to the motor case by a snap ring. 
     By fixing the oil pump cover to the motor case by a snap ring in this manner, a bolt is not used to fix the oil pump cover, in contrast to a conventional driving apparatus, and therefore, since a bolt head does not exist, the need to secure space for disposing the bolt head is eliminated. As a result, the oil pump and the gear mechanism (the differential gear device and the counter gear) of the driving apparatus can be disposed close to each other in the axial direction. Hence, the axial length of the driving apparatus can be shortened even further, thereby further reducing the overall size of the driving apparatus. 
     In the driving apparatus for a hybrid vehicle according to the present invention, a bearing holding portion for holding a counter gear bearing that rotatably supports the counter gear is preferably formed integrally with the motor case that accommodates and supports the motor. 
     By forming the bearing holding portion for holding the counter gear bearing on the motor case in this manner, the motor case and bearing holding portion can be formed integrally. As a result, the counter gear and motor can be disposed close to each other in the axial direction. Hence, the axial length of the driving apparatus can be shortened even further, thereby further reducing the overall size of the driving apparatus. 
     Moreover, since the motor case and the bearing holding portion are formed integrally, the number of components is reduced, thereby reducing the number of assembly processing steps correspondingly. As a result, the cost of the driving apparatus can further be reduced. 
     Further, the bearing holding portion is preferably provided in a second extension portion formed to further extend from the first extension portion, which extends such that the motor case partially surrounds the oil pump gear mechanism provided in the oil pump, so as to surround a boss portion of the counter gear. 
     By providing the bearing holding portion in the second extension portion that further extends from the first extension portion in this manner, the oil pump and counter gear can be disposed even closer to each other in the axial direction. As a result, the motor, the oil pump, and the gear mechanism (the differential gear device and the counter gear) can be disposed closer to each other in the axial direction. Hence, the axial length of the driving apparatus can be shortened even further, thereby further reducing the overall size of the driving apparatus. 
     In the driving apparatus for a hybrid vehicle according to the present invention, in a vehicle installed state, the motor is preferably disposed such that the rotary shaft of the motor is positioned between the input shaft and the drive shaft in a vehicle front-rear direction and above the input shaft. 
     By disposing the motor in this manner, an empty space between the input shaft and the drive shaft can be used, and therefore the size of the driving apparatus can be reduced while preventing reduction in the minimum ground clearance of the vehicle. 
     With the driving apparatus for a hybrid vehicle according to the present invention, as described above, the overall size and cost of the driving apparatus can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a skeleton diagram of a driving apparatus according to an embodiment. 
         FIG. 2  is a schematic sectional view showing the constitution of the driving apparatus according to the embodiment. 
         FIG. 3  is an enlarged sectional view of the vicinity of an oil pump. 
         FIG. 4  is a diagram showing arrangement relationships among various components provided in the driving apparatus according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A most preferred embodiment of a driving apparatus for a hybrid vehicle according to the present invention will be described in detail below with reference to the drawings. The present embodiment relates to a transverse driving apparatus installed in a front engine/front drive (FF) vehicle. The driving apparatus according to the present embodiment will now be described with reference to  FIGS. 1 to 4 .  FIG. 1  is a skeleton diagram of the driving apparatus according to the present embodiment.  FIG. 2  is a schematic sectional view showing the constitution of the driving apparatus according to the present embodiment.  FIG. 3  is an enlarged sectional view of the vicinity of an oil pump.  FIG. 4  is a diagram showing arrangement relationships among various components provided in the driving apparatus according to the present embodiment. 
     As shown in  FIG. 1 , the driving apparatus according to the present embodiment includes an input shaft  11  into which power from an engine (not shown) is input, a motor/generator MG 1 , a motor/generator MG 2 , a differential gear device  20  to which the motor/generator MG 1 , the motor/generator MG 2 , and the input shaft  11  are connected, an oil pump  30  connected to the input shaft  11 , and a differential device  40  connected to the differential gear device  20 . Thus, power from the engine and power from the motor/generator MG 2  can be transmitted to a drive shaft  12  connected to a drive wheel via the differential gear device  20  and the differential device  40 . 
     The input shaft  11  is disposed coaxially (on a first axis) with a crankshaft (not shown) of the engine such that the power from the engine (not shown) is transmitted to the input shaft  11  via a damper mechanism (not shown). The motor/generator MG 1  is disposed coaxially with the input shaft  11 , in other words, on the first axis. The motor/generator MG 1  functions as a motor driven by a power supply (a motoring function) and as a generator that converts mechanical energy into electrical energy (a regenerating function). The motor/generator MG 1  operates mainly as a generator, but is also used as a starter of the engine. An alternating current synchronous motor/generator, for example, may be used as the motor/generator MG 1 . A storage device such as a battery or a capacitor and a well-known fuel cell, for example, may be used as a power supply device for supplying power to the motor/generator MG 1 . Note that the motor/generator MG 1  according to the present embodiment corresponds to a “generator” of the present invention. 
     The motor/generator MG 1  includes a stator  50  fixed to a transaxle case  80 , to be described below, and a rotatable rotor  51 . The stator  50  includes a stator core  52  and a coil  53  wound around the stator core  52 . The rotor  51  and the stator core  52  are respectively formed by stacking a plurality of magnetic steel sheets of a predetermined thickness in a thickness direction. Note that the plurality of magnetic steel sheets are stacked in an axial direction of the input shaft  11 . A rotor shaft  13  is disposed in the center of the rotor  51  such that the rotor  51  and the rotor shaft  13  are linked. As a result, the rotor  51  and the rotor shaft  13  rotate integrally. The rotor shaft  13  is a hollow shaft, and the input shaft  11  is disposed inside the rotor shaft  13 . The input shaft  11  and rotor shaft  13  are constituted to be rotatable relative to each other. Bearings  54 ,  55  supporting the rotor shaft  13  are disposed in an inner space of the rotor  51 . Note that the rotor shaft  13  according to the present embodiment corresponds to a “rotary shaft of the generator” of the present invention. 
     The differential gear device  20  is disposed coaxially with the motor/generator MG 1 , i.e. coaxially with the input shaft  11 . In other words, the differential gear device  20  is also provided on the first axis. The differential gear device  20  is disposed adjacent to the motor/generator MG 1  in the axial direction of the input shaft  11 . The differential gear device  20  is constituted by a so-called single pinion planetary gear set. More specifically, the differential gear device  20  includes a sun gear  21 , a ring gear  22  disposed coaxially with the sun gear  21 , and a planetary carrier  24  supporting a planetary pinion gear  23  that meshes with the sun gear  21  and ring gear  22 . The sun gear  21  is linked to the rotor shaft  13 , and the planetary carrier  24  is linked to the input shaft  11 . Further, a counter gear  25  is linked to the ring gear  22 . The counter gear  25  and the differential gear device  20  together constitute a gear mechanism  29 . Note that the sun gear  21  according to the present embodiment corresponds to a “first gear element” of the present invention, the planetary carrier  24  corresponds to a “second gear element” of the present invention, and the ring gear  22  corresponds to a “third gear element” of the present invention. 
     Further, the oil pump  30  is disposed adjacent to the differential gear device  20  coaxially with the motor/generator MG 1  and the differential gear device  20  (i.e. on the first axis). The oil pump  30  is a known gear pump which generates oil pressure by driving an oil pump gear mechanism (a drive gear, a driven gear, and a crescent) provided in a casing. The oil pressure generated by the oil pump  30  is used to lubricate the various parts of the driving apparatus (in particular, lubrication in the differential gear device  20 ) and to perform clutch operations. The oil pump  30  is connected to the input shaft  11 , and the oil pump gear mechanism is activated to generate oil pressure by a rotary power transmitted from the input shaft  11 . By disposing the oil pump  30  in the immediate vicinity of the differential gear device  20  in this manner, an oil passage constitution for supplying oil from the oil pump  30  to the differential gear device  20  is made extremely simple and short. Note that the oil pump  30  will be described in detail below. 
     Hence, in the driving apparatus according to the present embodiment, the motor/generator MG 1 , the differential gear device  20 , the counter gear  25 , and the oil pump  30  are disposed coaxially with the input shaft  11  in sequence from the engine side. In other words, the input shaft  11 , motor/generator MG 1 , differential gear device  20 , counter gear  25 , and oil pump  30  are provided on the first axis. 
     Meanwhile, the motor/generator MG 2  is disposed on a different axis (a second axis) parallel to the input shaft  11 . The motor/generator MG 2  is disposed on the opposite side of the gear mechanism  29  to the motor/generator MG 1  in the axial direction. Furthermore, the motor/generator MG 2  is disposed so as to overlap at least one of the first axis constitutional components in the radial direction. Note that the first axis constitutional components include not only the motor/generator MG 1 , differential gear device  20 , counter gear  25 , input shaft  11 , and oil pump  30 , but also components (bearings and the like) disposed on the first axis to form the driving apparatus and components required to dispose these components (cases of the various components, fixing members such as nuts, and so on). In the present embodiment, the first axis constitutional components that overlap the motor/generator MG 2  in the radial direction are the motor/generator MG 1 , the differential gear device  20 , the counter gear  25 , the input shaft  11 , the oil pump  30  (including the casing), a bearing  26  of the counter gear  25 , a fixing member for the bearing  26 , and so on. By arranging the motor/generator MG 2  in this manner, the second axis can be brought close to the first axis, and therefore increases in the size of the driving apparatus in the radial direction occurring when the motor/generator MG 2  is disposed on the second axis are minimized. 
     Similarly to the motor/generator MG 1 , the motor/generator MG 2  functions as a motor driven by a power supply (a motoring function) and as a generator that converts mechanical energy into electrical energy (a regenerating function). The motor/generator MG 2  operates mainly as a motor. An alternating current synchronous motor/generator, for example, may be used as the motor/generator MG 2 . A storage device such as a battery or a capacitor, a known fuel cell, for example, may be used as a power supply device. Note that the motor/generator MG 2  according to the present embodiment corresponds to a “motor” of the present invention. 
     The motor/generator MG 2  includes a stator  60  fixed to the transaxle case  80  to be described below, and a rotatable rotor  61 . The stator  60  includes a stator core  62  and a coil  63  wound around the stator core  62 . The rotor  61  and the stator core  62  are respectively formed by stacking a plurality of magnetic steel sheets of a predetermined thickness in a thickness direction. Note that the plurality of magnetic steel sheets are stacked in the axial direction. A rotor shaft  14  is disposed in the center of the rotor  61  such that the rotor  61  and the rotor shaft  14  are linked. The rotor shaft  14  is supported by bearings  64 ,  65 . An output gear  66  is attached to an end portion of the rotor shaft  14 . Thus, the rotor  61 , the rotor shaft  14 , and the output gear  66  rotate integrally. The output gear  66  meshes with the counter gear  25 . Note that the rotor shaft  14  according to the present embodiment corresponds to a “rotary shaft of the motor” of the present invention, the bearings  64 ,  65  correspond to “motor bearings” of the present invention, and the bearing  64  corresponds to a “differential gear device side bearing” of the present invention. 
     The bearings  64 ,  65  supporting the rotor shaft  14  are disposed in a space on the outside of the rotor  61 . As a result, the radial size of the motor/generator MG 2  is reduced. The bearing  64  is disposed to overlap at least one of the first axis constitutional components in the axial direction. In the present embodiment, the bearing  64  is disposed to overlap the oil pump  30  in the axial direction. 
     Further, the rotor shaft  14  overlaps the motor/generator MG 1  in the radial direction. The motor/generator MG 1 , the differential gear device  20 , and the counter gear  25  are disposed on the first axis in order from the engine side, and therefore the motor/generator MG 2  can be disposed close to the counter gear  25  and the rotor shaft  14  can be prevented from overlapping the motor/generator MG 1 , which has a large radial dimension, in the axial direction. As a result, the length of the rotor shaft  14  can be shortened, leading to cost reduction and reduction in the radial size of the driving apparatus. 
     By disposing the motor/generator MG 2  on a different axis (the second axis) parallel to the input shaft  11  on the opposite side of the gear mechanism  29  to the motor/generator MG 1  in this manner, rotation of the motor/generator MG 2  can be reduced by the counter gear  25  and the output gear  66  without the use of a planetary gear. Therefore, a greater reduction ratio than that of a planetary gear can be set such that the motor/generator MG 2  no longer requires high performance. As a result, the size and cost of the motor/generator MG 2  is reduced. Further, the bearings  64 ,  65  of the motor/generator MG 2  are disposed on the outside of the motor/generator MG 2 , and therefore the radial size of the motor/generator MG 2  is further reduced. Moreover, a planetary gear is not used to reduce the rotation of the motor/generator MG 2 , and therefore the axial size and cost of the driving apparatus are reduced. Furthermore, the bearing  64  is disposed so as to overlap at least one of the first axis constitutional components in the axial direction, and therefore the axial length of the driving apparatus is not affected even when the bearings  64 ,  65  of the motor/generator MG 2  are disposed on the outside of the motor/generator MG 2 . 
     Further, a counter shaft  15  is disposed on a different axis (a third axis) parallel to the input shaft  11 . The counter shaft  15  is formed with a counter driven gear  70  and a final drive pinion gear  71 . The counter driven gear  70  meshes with the counter gear  25 , and the final drive pinion gear  71  meshes with a final ring gear  44  of the differential device  40 . 
     Here, the counter gear  25  also meshes with the output gear  66  of the motor/generator MG 2 , as described above. In other words, the counter gear  25  meshes with both the output gear  66  and the counter driven gear  70 . Hence, the counter gear  25  acts as both a reduction mechanism for the motor/generator MG 2  and a gear mechanism for transmitting power from the input shaft  11  to the drive shaft  12 . 
     The differential device  40  includes a plurality of pinion gears  42 , a side gear  43  that meshes with the plurality of pinion gears  42 , and the final ring gear  44  coupled to the plurality of pinion gears  42 . The drive shaft  12  connected to the drive wheel is linked to the side gear  43  of the differential device  40 . 
     As shown in  FIG. 2 , the respective constitutional components of the driving apparatus, disposed as described above, are accommodated in and fixed to the hollow transaxle case  80 . The transaxle case  80  is attached to an outer wall of the engine. The transaxle case  80  includes an engine side housing  81 , an extension housing  82 , and an end cover  83 . The engine side housing  81 , extension housing  82 , and end cover  83  are formed by molding a metallic material such as aluminum. 
     The engine side housing  81 , the extension housing  82 , and the end cover  83  are disposed in the transaxle case  80  in order from the engine side. The outer wall of the engine and the engine side housing  81  are fixed to each other such that an open end  84  on one end of the engine side housing  81  contacts the outer wall of the engine. Further, the engine side housing  81  and the extension housing  82  are fixed to each other such that an open end  85  on the other end of the engine side housing  81  contacts an open end  86  on one end of the extension housing  82 . The end cover  83  is attached so as to close an open end  87  on the other end of the extension housing  82 , whereby the end cover  83  and the extension housing  82  are fixed to each other. 
     The motor/generator MG 1  is accommodated in and supported by the engine side housing  81 , while the motor/generator MG 2  is accommodated in and supported by the extension housing  82 . In other words, the engine side housing  81  also serves as a case for the motor/generator MG 1 , while the extension housing  82  also serves as a case for the motor/generator MG 2 . Note that the extension housing  82  according to the present embodiment corresponds to a “motor case” of the present invention. Hence, the driving apparatus according to the present embodiment is constituted as a so-called transaxle in which the differential gear device  20  and the differential device  40  are incorporated collectively into the transaxle case  80 . 
     Next, the arrangement and constitution of various components provided in the vicinity of the oil pump  30  will be described in detail with reference to  FIG. 3 . As shown in  FIG. 3 , the oil pump  30  includes an oil pump gear mechanism  31  disposed in an oil pump gear chamber  32 , and an oil pump cover  33  that closes an opening of the oil pump gear chamber  32 . The oil pump gear chamber  32  is formed on the inside of a first extension portion  82   a  formed by extending a part of the extension housing  82  in the axial direction toward the gear mechanism  29 . Thus, the oil pump gear chamber  32  opens toward the gear mechanism  29 . The oil pump cover  33  closing the opening of the oil pump gear chamber  32  is fixed to the extension housing  82  at a radial end portion by a tapered snap ring  34 . Hence, a casing of the oil pump  30  is constituted by the first extension portion  82   a  and the oil pump cover  33 . 
     By constituting the oil pump  30  in this manner, the motor/generator MG 2  and the oil pump  30  can be disposed close to each other in the axial direction. Further, the oil pump cover  33  is fixed by the tapered snap ring  34 , and therefore a bolt is not used to fix the oil pump cover, in contrast to a conventional driving apparatus. As a result, there is no need to secure space to dispose a bolt head, and therefore the oil pump  30  and the gear mechanism  29  can be disposed even closer to each other in the axial direction. Moreover, the oil pump gear chamber  32  is formed integrally with the extension housing  82 , and therefore the number of components is reduced. 
     Here, the first extension portion  82   a  extends to the vicinity of a ring gear shaft  16  and an end portion of a boss portion  17  of the counter gear  25  so as to surround the periphery of the oil pump gear mechanism  31 . The input shaft  11  penetrates the oil pump cover  33  such that a terminal end portion of the input shaft  11  is positioned within the oil pump gear chamber  32 . The oil pump gear mechanism  31  is attached to the terminal end portion of the input shaft  11 . Hence, in the oil pump  30 , the rotation of the input shaft  11  is transmitted to the oil pump gear mechanism  31  such that oil in the oil pump gear chamber  32  can be pumped. Note that the oil pumped by the oil pump  30  is supplied to the differential gear device  20  and other constitutional components of the driving apparatus via an oil passage or the like formed in the input shaft  11 . 
     Hence, the oil pump  30  is disposed on the terminal end portion of the input shaft  11  and driven by the rotation of the input shaft  11 . Therefore, the need for a new mechanism to drive the oil pump  30  can be eliminated, thereby reducing the axial length of the first axis and therefore reducing the cost correspondingly. As a result, the axial size and cost of the driving apparatus can be further reduced. 
     Further, the oil pump  30  is disposed to overlap the motor/generator MG 2  in the radial direction and to overlap the bearing  64  of the motor/generator MG 2  in the axial direction. Hence, the axial length of the driving apparatus is not affected even when the bearings  64 ,  65  of the motor/generator MG 2  are disposed on the outside of the motor/generator MG 2 . 
     Further, a second extension portion  82   b  is formed in the extension housing  82  as a continuation of the first extension portion  82   a.  The second extension portion  82   b  extends to a point immediately before a wheel surface  25   a  of the counter gear  25  so as to surround the boss portion  17  of the counter gear  25 . The bearing  26  that supports the counter gear  25  is held by an inner peripheral surface  82   c  of the second extension portion  82   b.  Note that the bearing  26  is constituted by a bearing that restricts movement in both the axial direction and the radial direction, such as an angular contact bearing. With this constitution, the oil pump  30  and the counter gear  25  can be disposed close to each other in the axial direction. Further, a holding portion of the bearing  26  is formed integrally with the extension housing  82 , and therefore the number of components is reduced. Note that the inner peripheral surface  82   c  according to the present embodiment corresponds to a “bearing holding portion” of the present invention. 
     Arrangement relationships between the various components provided in the driving apparatus according to the present embodiment will now be described with reference to  FIG. 4 . In  FIG. 4 , a side on which the input shaft  11  is disposed serves as a vehicle front side, and a side on which the drive shaft  12  is disposed serves as a vehicle rear side. As shown in  FIG. 4 , the rotor shaft  14  of the motor/generator MG 2  is disposed to the rear of the input shaft  11 , the counter shaft  15  is disposed to the rear of the rotor shaft  14 , and the drive shaft  12  is disposed to the rear of the counter shaft  15 . Further, the rotor shaft  14  is disposed above the input shaft  11 , while the counter shaft  15  and the drive shaft  12  are disposed below the input shaft  11 . Note that the counter shaft  15  is disposed below the drive shaft  12 . In other words, the rotor shaft  14  is disposed so as to be positioned between the input shaft  11  and the drive shaft  12  and above the input shaft  11 . With this shaft arrangement, the motor/generator MG 2  provided on a different axis from the input shaft  11  can be disposed in an empty space existing between the input shaft  11  and the drive shaft  12 , and therefore the radial size of the driving apparatus can be reduced. Moreover, reduction in a minimum ground clearance of the vehicle can be prevented. 
     The driving apparatus constituted as described above is controlled by an electronic control device that controls the entire vehicle. More specifically, a signal from an ignition switch, a signal from an engine speed sensor, a signal from a brake switch, a signal from a vehicle speed sensor, a signal from an accelerator opening sensor, a signal from a shift position sensor, a signal from a resolver that detects the respective rotation speeds of the motor/generators MG 1 , MG 2 , and so on are input into the electronic control device. On the basis of these signals, the electronic control device calculates required torque to be transmitted to the drive shaft  12 . On the basis of the calculation result, signals for controlling an intake air amount, a fuel injection amount, and an ignition timing of the engine, signals for controlling outputs of the motor/generators MG 1 , MG 2 , and so on are output from the electronic control device to the respective portions, whereby an overall operation of the driving apparatus is controlled. 
     More specifically, when power (torque) output from the engine is to be transmitted to the drive shaft  12 , the torque of the engine is transmitted to the planetary carrier  24  via the input shaft  11 . The torque transmitted to the planetary carrier  24  is then transmitted to the drive shaft  12  via the ring gear  22 , the counter gear  25 , the counter driven gear  70 , the counter shaft  15 , the final drive pinion gear  71 , and the differential device  40 , whereby a driving force is generated. 
     When the torque of the engine is transmitted to the planetary carrier  24  at this time, the motor/generator MG 1  functions as a generator such that power generated by the motor/generator MG 1  is charged to the storage device (not shown). 
     On the other hand, when the motor/generator MG 2  is driven as a motor such that the power thereof is transmitted to the drive shaft  12 , the power (torque) of the motor/generator MG 2  is transmitted to the output gear  66  via the rotor shaft  14 , and the rotation of the output gear  66  is reduced and then transmitted to the counter gear  25 . This reduced rotation is then synthesized with the torque of the engine by the counter gear  25 , and the resulting synthesized torque is transmitted to the drive shaft  12  via the counter driven gear  70 , the counter shaft  15 , the final drive pinion gear  71 , and the differential device  40  to generate a driving force. 
     Hence, in the driving apparatus according to the present embodiment, the motor/generator MG 2  is disposed on a different axis parallel to the input shaft  11  on the opposite side of the gear mechanism  29  to the motor/generator MG 1  in the axial direction, and therefore the rotation of the motor/generator MG 2  can be reduced by the counter gear  25  and the output gear  66  without using a planetary gear. As a result, the reduction ratio can be made larger than that of a planetary gear, and therefore high performance is no longer required of the motor/generator MG 2 . Accordingly, the size and cost of the motor/generator MG 2  can be reduced. Further, the bearings  64 ,  65  of the motor/generator MG 2  are disposed on the outside of the motor/generator MG 2 , and therefore the radial size of the motor/generator MG 2  can also be reduced. Thus, increases in the radial size of the driving apparatus occurring when the motor/generator MG 2  is provided on a different axis from the input shaft  11  can be minimized. Moreover, a planetary gear is not used to reduce the rotation of the motor/generator MG 2 , and therefore the axial size and cost of the driving apparatus can be reduced. 
     The oil pump  30 , which is one of the first axis constitutional components, is disposed to overlap the motor/generator MG 2  in the radial direction and overlap the bearing  64  disposed on the outside of the motor/generator MG 2  in the axial direction. Therefore, the axial length of the driving apparatus is not affected even when the bearings  64 ,  65  of the motor/generator MG 2  are disposed on the outside of the motor/generator MG 2 , and as a result, the axial size of the driving apparatus can be sufficiently reduced as described above. 
     Further, by making the rotor shaft  14  of the motor/generator MG 2  overlap the motor/generator MG 1  in the radial direction, the motor/generator MG 2  can be disposed close to the counter gear  25 , and the rotor shaft  14  is prevented from overlapping the motor/generator MG 1  in the axial direction. Therefore, the length of the rotor shaft  14  can be shortened, thereby reducing the cost, and the radial size of the driving apparatus can be reduced. 
     Further, the oil pump  30  is disposed on the terminal end portion of the input shaft  11  so as to be driven directly by the rotation of the input shaft  11 , and therefore a new mechanism for driving the oil pump  30  becomes unnecessary, thereby reducing the axial length of the first axis and the cost correspondingly. Hence, the axial size of the driving apparatus can further be reduced, thereby further reducing the cost. Furthermore, the oil pump  30  is disposed in the immediate vicinity of the differential gear device  20 , and therefore the constitution of an oil passage for supplying oil from the oil pump  30  to the differential gear device  20  can be made extremely simple and short. As a result, the number of processing steps required to provide the oil passage in the driving apparatus can be reduced, which contributes to cost reduction of the driving apparatus. 
     Further, a part of the extension housing  82  that accommodates and supports the motor/generator MG 2  extends toward the gear mechanism  29  to form the first extension portion  82   a  and the second extension portion  82   b  forming a continuation of the first extension portion  82   a.  The gear chamber  32  of the oil pump  30  is provided on the inside of the first extension portion  82   a,  and the bearing  26  of the counter gear  25  is held by the inner peripheral surface  82   c  of the second extension portion  82   b.  As a result, the motor/generator MG 2  and oil pump  30  can be brought closer together in the axial direction, and the oil pump  30  and counter gear  25  can be brought closer together in the axial direction. Moreover, the oil pump gear chamber  32  and the holding portion of the bearing  26  can be formed integrally in the extension housing  82 , and therefore the number of components can be reduced. Accordingly, the axial size of the driving apparatus can be reduced even further, thereby further reducing the cost of the driving apparatus. 
     Furthermore, the oil pump cover  33  that closes the opening in the gear chamber  32  of the oil pump  30  is fixed to the extension housing  82  by the tapered snap ring  34 , and therefore, in contrast to a conventional driving apparatus, there is no need to secure space to dispose a bolt head of a bolt for fixing the oil pump cover. Hence, the oil pump  30  and the gear mechanism  29  can be disposed close to each other in the axial direction, which contributes to reduction in the size of the driving apparatus. 
     According to the driving apparatus of the present embodiment, as described in detail above, the motor/generator MG 1 , differential gear device  20 , counter gear  25 , and oil pump  30  are disposed coaxially with the input shaft  11  in this order from the engine side, while the motor/generator MG 2  is disposed on a different axis parallel to the input shaft  11  on the opposite side of the gear mechanism  29  to the motor/generator MG 1  in the axial direction and the bearings  64 ,  65  of the motor/generator MG 2  are disposed on the outside of the motor/generator MG 2 . Further, the oil pump  30 , which is one of the first axis constitutional components, is disposed to overlap the motor/generator MG 2  in the radial direction and overlap the bearing  64  of the motor/generator MG 2  that is positioned on the gear mechanism  29  side in the axial direction. Therefore, the size and cost of the motor/generator MG 2  can be reduced, the rotation of the motor/generator MG 2  can be reduced without using a planetary gear, and the number of processing steps required to provide the oil passage can be reduced. Accordingly, the overall size of the driving apparatus can be reduced, and the cost of the driving apparatus can also be reduced. 
     Note that the embodiment described above is merely an example which does not limit the present invention in any way, and various amendments and modifications may be applied within a scope of the present invention without departing from the spirit of the present invention. For example, in the above embodiment, an example in which the present invention is applied to a transverse driving apparatus installed in a front engine/front drive (FF) vehicle has been described, but the present invention may also be applied to a transverse driving apparatus installed in a rear engine/rear drive (RR) vehicle. 
     Further, in the above embodiment, the gear that meshes with the output gear  66  of the motor/generator MG 2  and the gear that transmits power to the drive shaft  12  are shared (i.e. a single counter gear is used), but the respective gears may be provided separately (i.e. two counter gears may be provided).