Vehicle powertrain unit

Abstract

Vehicle drive unit (1) comprising: a plurality of actuators (2) generating torques, a plurality of drive shafts (3, 310a) to which the torques generated by the actuators (2) are applied, an axle (4) transmitting force to a wheel (6) of a vehicle, and a reduction mechanism (5, 501, 601) reducing a rotational speed between the drive shaft (3, 310a) and the axle (4), wherein the torques applied to the drive shafts (3, 310a) are transmitted to the axle (4) while being multiplied to generate at least one of a driving force and a braking force of the vehicle, wherein the reduction mechanism (5, 501, 601) comprises: a planetary gear unit (7) having a sun gear (10), a ring gear (11) and a carrier (12), an external gear (14) being mounted in an outer circumferential section of the gear ring (11) is formed, at least one outer gear set (9),which comprises the following: a first planet gear (21) that is meshed with the external gear (14), a second planet gear (22) that is arranged on the same axis of rotation as the first planet gear (21) and rotates integrally with the first planet gear (21), and at least one planet gear shaft (23, 31, 91) that rotates integrally with the first planet gear (21) and the second planet gear (22), a center gear (18) that is arranged on the same axis of rotation as the sun gear (10) and rotates integrally with the sun gear (10), a pilot gear (19) that is arranged between the center gear (18) and the second planet gear (22) and is meshed with both the center gear (18) and the second planet gear (22), at least one sun gear shaft (15) that rotates integrally with the center gear (18) and the sun gear (10), a carrier shaft (16) that rotates integrally with the carrier (12) rotates and is designed as the axis (4), and at least a countershaft (20, 41),which rotates integrally with the countershaft (19), wherein the drive shafts (3) comprise at least one of: the at least one sun gear shaft (15), the at least one planet gear shaft (23, 31, 91) or the at least one countershaft (20, 41), wherein the vehicle drive unit (1) comprises: several outer gear sets (9) or several countershafts (20, 40), wherein the actuators (2) comprise several drive actuators (51, 52, 71, 81, 82) which generate drive torques, and the drive torques generated by the drive actuators (51, 52, 71, 81, 82) are each applied to the drive shaft (3).

Description

BACKGROUNDField of the InventionEmbodiments of the present invention relate to the field of a vehicle drive unit for generating a driving force and a braking force.Background Art DiscussionA wheel motor is located in an inner peripheral portion of a wheel frame of a vehicle, and directly drives wheels by outputting a driving torque to generate a driving force of the vehicle. The wheel motor described in JP 2007-153 266 A has been miniaturized using general components. According to the teachings of JP 2007-153 266 A, an outer rotor of a traction motor and a brake disc are integrated.JP 2008-275 112 A describes a high-speed reduction combined planetary gear mechanism including a first planetary gear mechanism and a second planetary gear mechanism. The first planetary gear mechanism includes a first sun gear, a first ring gear, and a first carrier. Similarly, the second planetary gear mechanism includes a second sun gear, a second ring gear, and a second carrier. In the combined planetary gear mechanism, the first sun gear and the second sun gear are coupled on the same rotation axis, the first ring gear and the second ring gear are integrated, and the second carrier is fixed to a fixed frame. The second sun gear and the first sun gear serve as an input shaft, and the first carrier serves as an output shaft.According to the teachings of JP 2008-275 112 A, by arranging the plurality of planetary gears held by the second carrier whose rotation has been stopped in a non-axis symmetrical manner, flexibility in selecting the number of teeth increases by a multiple of the number of planetary gears (Np) (i.e., by Np times). By increasing the flexibility in selecting the number of teeth by Np times, it becomes possible to obtain a high reduction ratio of Np times of a conventional configuration.The wheel motor of the type described in JP2007-153 266A can drive the wheels directly and without an intermediate differential gear or intermediate drive shaft as in a conventional vehicle. Therefore, the flexibility of the vehicle body design is higher, and the comfort or the transport capacity of the vehicle can be improved even more compared to a conventional vehicle. Moreover, since the left and right drive wheels can be independently controlled, the steering stability or the turning behavior of the vehicle can be improved.On the other hand, in the vehicle in which the wheel motor is installed, the unsprung masses of the vehicle increase, and the traveling quality of the vehicle or the traction characteristics of the tires decrease. Therefore, the wheel motor must be as small and light as possible. Moreover, it is desirable that a motor drive unit or brake unit installed in the vehicle is also downsized and made lighter.A vehicle drive unit such as a wheel motor or a motor drive unit or a brake unit can be downsized and made lighter by being combined with the reduction mechanism described in JP 2008-275 112 A. For example, in a motor drive unit, a drive torque output by a motor can be multiplied by combining the motor and the reduction mechanism. As a result, the motor drive unit can be miniaturized using a miniaturized motor.As described above, the compound planetary gear mechanism described in JP 2008-275 112 A can realize a larger reduction ratio than a single planetary gear mechanism. Moreover, the reduction ratio can be increased by increasing the number of planetary gears. However, the compound planetary gear mechanism according to the teachings of JP 2008-275 112 A is configured by coupling two sets of the planetary gear mechanism via a common ring gear. Therefore, the number of planetary gears is limited by the number of teeth or the inner diameter of the ring gear, which is an internal gear. For this reason, a limit is also set to increase the reduction ratio.That is, there is still air in further downsizing and weight reduction of a vehicle drive unit such as a motor drive unit or brake unit by use of a reduction mechanism configured to increase a reduction ratio.A vehicle drive unit having a plurality of actuators which generate torques, and a plurality of drive shafts to which the torques generated by the actuators are applied, is known from DE 197 09 579 A1. Here, an axle transmits power to a wheel of a vehicle, and a reduction mechanism reduces a rotation speed between the drive shafts and the axle. At this time, the torques applied to the drive shafts are transmitted to the axle while being multiplied to generate a driving force of the vehicle. The reduction mechanism includes a planetary gear unit having a sun gear, a ring gear, and a carrier. Regarding the prior art, reference is also made to U.S. Pat. No. 1,604,112 A, DE 10 2014 203 999 A1, US 2013 / 0 324 347 A1, DE 11 2015 001 522 T5 and DE 44 34 237 A1.SUMMARYAspects of embodiments of the present invention are based on the technical problems set forth above, and it is therefore an object of embodiments of the present invention to provide a vehicle drive unit that has been downsized and made lighter by combining an actuator such as a drive motor or a brake device and a reduction mechanism. This object is achieved with the features of the independent claims, advantageous refinements being the subject matter of the dependent claims.According to the vehicle drive unit of the present invention, a torque generated by an actuator, such as a driving torque or a braking torque, is multiplied by a reduction mechanism to be transmitted to an axle. The reduction mechanism in the vehicle drive unit includes an external gear formed in an outer peripheral section of a ring gear of a planetary gear unit. Moreover, by a first planetary gear meshed with the external gear, the torque between the ring gear and a center gear is transmitted via a second planetary gear that rotates integrally with the first planetary gear and a counter gear meshed with the second planetary gear. The center gear is coupled to a sun gear of the planetary gear unit via a sun gear shaft and rotates integrally with the sun gear. Thus, when the torque is applied to the sun gear shaft, a counter shaft or a planetary gear shaft, the torque is transmitted from the center gear, the counter gear or the second planetary gear to the ring gear via the planetary gear shaft and the first planetary gear. At this moment, the first planetary gear rotates in the same rotational direction as the center gear and the sun gear. As a result, the ring gear rotates in a reverse rotational direction of the sun gear and a carrier. Therefore, a reduction ratio can be increased as the ring gear reversely rotates, compared with a planetary gear unit where, for example, the rotation of a ring gear is stopped to perform reduction between a sun gear and a carrier. Therefore, the reduction mechanism in the vehicle drive unit of the present invention makes it possible to more significantly increase the reduction ratio between the sun gear and the carrier, as compared with a conventional reduction device, without suffering a remarkable increase in size. That is, the reduction mechanism in the vehicle drive unit of the present invention has a high reduction function that makes it possible to obtain a significantly higher reduction ratio than in the related art.Moreover, in the reduction mechanism in the vehicle drive unit of the present invention, since the power transmission between the planetary gear unit and a drive shaft is through the external gear located in the outer circumferential section of the ring gear, restrictions due to the number of planetary gears or the number of teeth of the planetary gears of the planetary gear unit can be more significantly alleviated than the configuration described in, for example, JP 2008-275 112 A where the power transmission is through the internal teeth of a ring gear; or such restrictions have no effect at all. As a result, the flexibility in adjusting the reduction ratio can be significantly increased, and a larger reduction ratio can be obtained. Therefore, the vehicle drive unit of the present invention enables the torque generated by the actuator to be transmitted to the axle with significant multiplication by the reduction mechanism having the high reduction function. Therefore, the actuator can be sufficiently miniaturized to a degree that an output torque is significantly multiplied. As a result, significant downsizing and weight reduction of the vehicle drive unit can be achieved.Moreover, thanks to the vehicle drive unit of the present invention, a drive torque generated by a drive actuator such as an electric motor can be transmitted to the axle significantly multiplied by the reduction mechanism. Therefore, the drive actuator can be miniaturized to such a degree that output drive torque is multiplied, and a light, compact drive unit can be configured.Moreover, according to the vehicle drive unit of the present invention, at least two drive shafts are provided, and drive actuators are respectively disposed on these drive shafts. Therefore, a drive unit can be configured that includes at least two drive actuators. In the vehicle drive unit configured in this manner, each of the drive actuators may be used as a main system, and the other of the drive actuators may be used as a backup system. Therefore, a compact drive unit of excellent reliability can be configured.Moreover, according to the vehicle drive unit of the present invention, a plurality of the drive actuators whose characteristics are different can be used. For example, a motor suitable for medium and low speeds and a motor suitable for high power and high speeds may be used as the drive actuators. Therefore, a driving force that is matched to the traveling circumstances can be efficiently generated. Therefore, a compact drive unit of excellent reliability and good energy efficiency can be configured.Moreover, according to the vehicle drive unit of the present invention, at least two drive shafts may be provided, and a drive actuator that generates a drive torque and a brake actuator that generates a brake torque may be respectively disposed on these drive shafts. Therefore, not only a braking force but also a driving force can be generated in the vehicle drive unit. Therefore, a compact drive unit having a braking function can be configured.Moreover, according to the vehicle drive unit of the present invention, at least four drive shafts may be provided, and a plurality of drive actuators and a plurality of brake actuators may be respectively disposed on these at least four drive shafts. Each of the drive actuators and each of the brake actuators may be used as a main system, and the other of the drive actuators and the other of the brake actuators may be used as a backup system. Therefore, a compact drive unit of excellent reliability and having a braking function can be configured.Moreover, according to the vehicle drive unit of the present invention, in the case of arranging at least two brake actuators, an ordinary brake actuator and a parking brake actuator may be used. Therefore, a compact drive unit of excellent reliability and having a usual braking function and a parking brake function can be configured.Moreover, according to the vehicle drive unit of the present invention, in the case of arranging at least two drive actuators and at least two brake actuators, a plurality of drive actuators whose characteristics are different may be provided, an ordinary brake actuator and a parking brake actuator. Therefore, a compact drive unit of excellent reliability and having a usual braking function and a parking braking function and, moreover, having good energy efficiency can be configured.Moreover, according to the vehicle drive unit of the present invention, the above-described type of drive unit or a drive unit having a braking function may be disposed on an inner side of a wheel frame of a wheel. That is, a so-called wheel motor may be configured. Therefore, significant downsizing and weight reduction of the wheel motor can be achieved. As a result, the unsprung masses of a vehicle in which the wheel motor is installed can be significantly reduced, and the ride comfort of the vehicle or the traction characteristics of tires can be improved.Moreover, according to the vehicle drive unit of the present invention, the actuator may be disposed between the reduction mechanism and the wheel frame. That is, the actuator may be disposed on a side on which the axle extends toward the wheel frame in a rotation axis direction of the axle. Therefore, the actuator and the drive shaft to which a torque is applied from the actuator are not disposed on a rear side opposite to the wheel frame of the reduction mechanism. As a result, the rear side of the reduction mechanism can be easily disposed in a vehicle body, for example, via a suspension mechanism. Therefore, a compact wheel motor having excellent installation characteristics can be configured.Moreover, according to the vehicle drive unit of the present invention, the drive unit having a braking function is installed in the vehicle as a pair of a left unit that transmits torque to a left wheel and a right unit that transmits torque to a right wheel. Therefore, a so-called on-board compact drive unit can be configured. Moreover, at least one of the driving force and the braking force generated in the left and right wheels may be independently controlled. Therefore, for example, a vehicle that enables torque vectoring can be configured.Moreover, according to the vehicle drive unit of the present invention, a clutch coupling the left unit sun gear shaft and the right unit sun gear shaft is provided. Therefore, the associated left and right sun gear shafts can be coupled by engaging the clutch, and differential rotation between the left and right wheels can be limited. Therefore, a compact on-board drive unit having a differential limiting function can be configured.Moreover, according to the vehicle drive unit of the present invention, in each of the left unit and the right unit, the actuator is disposed between the reduction mechanism and the wheel. That is, the actuator is located on the side where the axle extends toward the wheel in the rotational axis direction of the axle. Therefore, the actuator and the drive shaft to which the torque of the actuator is applied are not disposed on the rear side opposite to the wheel of the reduction mechanism. As a result, in the case where the left unit and the right unit are arranged such that their respective associated rear sides face each other, the size in the rotation axis direction of the axis can be reduced. Therefore, a compact on-board drive unit can be configured, the construction of which has been made smaller particularly in a vehicle width direction.Moreover, according to the vehicle drive unit of the present invention, a braking torque generated by a brake actuator such as an electromagnetic brake or a regenerative brake motor can be transmitted to the axle significantly multiplied by the reduction mechanism. Therefore, the brake actuator can be miniaturized to such a degree that the output brake torque is multiplied, and a light-weight, compact brake unit can be configured.Moreover, according to the vehicle drive unit of the present invention, at least two drive shafts may be provided, and the brake actuators may be respectively disposed on these drive shafts. Each of the brake actuators may be used as a main system and the other of the brake actuators may be used as a backup system. Therefore, a compact brake unit of excellent reliability can be configured.Moreover, according to the vehicle drive unit of the present invention, in the case of arranging at least two brake actuators, there may be an ordinary brake actuator and a parking brake actuator. Therefore, a compact brake unit of excellent reliability and having a usual brake function and a parking brake function can be configured.Moreover, according to the vehicle drive unit of the present invention, the brake actuator may be disposed between the reduction mechanism and the wheel. More specifically, the brake actuator may be disposed on the side where the axle extends toward the wheel in the rotational axis direction of the axle. Therefore, the brake actuator and the drive shaft to which the braking torque from the brake actuator is applied are not disposed on the rear side opposite to the wheel of the reduction mechanism. As a result, a compact in-wheel brake unit having excellent installation characteristics or a compact in-vehicle brake unit whose construction has been made smaller in the vehicle width direction in particular can be configured.Moreover, according to the vehicle drive unit of the present invention, the brake actuator may be configured of a service brake mechanism and a parking brake mechanism. Therefore, a brake unit can be configured that additionally includes a parking brake function that holds the braking force to keep the vehicle continuously at a standstill during parking. Moreover, according to the vehicle drive unit of the present invention, the parking brake mechanism may also be configured of a brake motor, a spindle mechanism, and a brake motor-oriented reduction mechanism. The spindle mechanism is activated by an output torque of the brake motor. The brake motor-oriented reduction mechanism is configured by a geared reduction mechanism using a planetary gear unit and reducing a rotational speed between an output shaft (rotor shaft) of the brake motor and a drive shaft (spindle) of the spindle mechanism. That is, the brake motor-oriented reduction mechanism transmits the output torque of the brake motor to the spindle mechanism while multiplying. Therefore, the brake motor can be miniaturized to such a degree that the output torque is multiplied. As a result, downsizing and weight reduction of the parking brake mechanism and thus of the brake actuator can be achieved. Therefore, a compact brake unit having an ordinary brake function and a parking brake function can be configured.BRIEF DESCRIPTION OF THE DRAWINGSFeatures, aspects and advantages of exemplary embodiments of the present invention will be better understood with reference to the following description and the accompanying drawings, which are not intended to limit the invention in any way. FIG. 1 is a schematic illustration showing a first embodiment of a vehicle drive unit, FIG. 2 is a cross-sectional view showing a configuration of a reduction mechanism in the vehicle drive unit of the present invention, FIG. 3 is a nomographic diagram for explaining a reduction function of the reduction mechanism in the vehicle drive unit of the present invention, FIG. 4 is a schematic illustration showing a second embodiment of the vehicle drive unit, FIG. 5 is a schematic illustration showing a third embodiment of the vehicle drive unit, FIG. 6 is a schematic illustration showing a fourth embodiment of the vehicle drive unit, FIG. 7 is a schematic illustration showing a fifth embodiment of the vehicle drive unit, FIG. 8 is a schematic illustration showing a sixth embodiment of the vehicle drive unit, FIG. 9 is a schematic illustration showing a seventh embodiment of the vehicle drive unit, FIG. 10 is a schematic illustration showing an eighth embodiment of the vehicle drive unit, FIG. 11 is a cross-sectional view showing a specific configuration of the vehicle drive unit shown in FIG. 10 , FIG. 12 is a schematic illustration showing a ninth embodiment in which the vehicle drive unit is used to configure a wheel motor, FIG. 13 is a schematic illustration showing a tenth embodiment in which the vehicle drive unit is used to configure an on-board drive unit, FIG. 14 is a cross-sectional view showing a specific configuration of the on-board drive unit shown in FIG. 13 , FIG. 15 is a cross-sectional view for explaining a configuration of a brake actuator in the vehicle drive unit of the present invention, FIG. 16 is a view showing an example of a brake motor-oriented reduction mechanism installed in the brake actuator shown in FIG. 15 , FIG. 17 is a cross-sectional view showing an eleventh embodiment in which the vehicle drive unit is used to configure an on-board drive unit; and FIG. 18 is a cross-sectional view showing a twelfth embodiment in which the vehicle drive unit is used to configure an on-board drive unit.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)Preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. Referring now to FIG. 1, there is shown a first embodiment of the vehicle drive unit according to the present invention. As shown in FIG. 1, a vehicle drive unit 1 includes an actuator 2, a drive shaft 3, an axle 4, and a reduction mechanism 5.The actuator 2 includes drive actuators 51, 51 such as an electric motor, and brake actuators 61, 62 such as a brake device or a regenerative motor (i.e., a generator). That is, the actuator 2 generates torque such as driving torque for driving a vehicle or braking torque for braking the vehicle. By using, as the actuator 2, the drive actuator 51 (or 52) that generates a driving torque, this vehicle drive unit 1 shown in FIG. 1 serves as a drive unit of the vehicle. Further, by using, as the actuator 2, the brake actuator 61 (or 62) that generates a braking torque, the vehicle drive unit 1 serves as a brake unit of the vehicle.The input shaft 3 is coupled to a sun gear shaft 15, a counter shaft 20 or a planetary gear shaft 23, which will be discussed later. In other words, the sun gear shaft 15, the counter shaft 20, or the planetary gear shaft 23 serves as the input shaft 3.A later-discussed carrier shaft 16 is coupled to the axle 4. In other words, the support shaft 16 serves as the axle 4, and power is transmitted from the axle 4 to a wheel 6 of the vehicle.The reduction mechanism 5 includes a planetary gear unit 7, a counter gear set 8, and an outer gear set 9. the reduction mechanism 5 reduces a rotational speed between the input shaft 3 and the axle 4 and transmits the torque of the input shaft 3 to the axle 4.The planetary gear unit 7, which is of a single pinion type, has: a sun gear 10, a ring gear 11 and a carrier 12 as rotational elements that differentially rotate with respect to each other, and a plurality of planet gears 13 supported by the carrier 12 and interposed between the sun gear 10 and the ring gear 11. In an outer circumferential section of the ring gear 11, an external gear 14, which will be discussed later, is formed, which is meshed with a first planetary gear 21, which will be discussed later, of the external gear set 9.The planetary gear unit 7 is supported in a housing 17 of the reduction mechanism 5 through the sun gear shaft 15 and the carrier shaft 16. The sun gear shaft 15 of the sun gear 10 rotates integrally with a later-discussed center gear 18, and the carrier shaft 16 of the carrier 12 rotates integrally with the carrier 12, The sun gear shaft 15 and the carrier shaft 16 are arranged in a manner that allows them to rotate relative to each other on the same rotation axis.In the vehicle drive unit 1 shown in FIG. 1, the input shaft 3 is coupled to the sun gear shaft 15. That is, the sun gear shaft 15 serves as the input shaft 3 in this vehicle drive unit 1. That is, the carrier shaft 16 serves as the axle 4 in this vehicle drive unit 1.Note that it is also possible to use a double planetary gear planetary gear unit in the vehicle drive unit 1 instead of the single planetary gear planetary gear unit 7.The counter gear set 8 includes the center gear 18 and at least one counter gear 19. in the vehicle drive unit 1 shown in FIG. 1, the counter gear set 8 includes the center gear 18 and two counter gears 19. the center gear 18 is mounted on the sun gear shaft 15 of the sun gear 10, and the counter gear 19 is mounted on the counter shaft 20 in an integrally rotatable manner. The counter gear 19 is located between the center gear 18 and a second planetary gear 22 of the outer gear set 9 and is meshed with both the center gear 18 and the second planetary gear 22.The outer gear set 9 includes the first planetary gear 21, the second planetary gear 22, and the planetary gear shaft 23. the first planetary gear 21 is a gear having a smaller diameter than the external gear 14 and is meshed with the external gear 14. The second planetary gear 22 also has a smaller diameter than the external gear 14 and is meshed with the counter gear 19. The reduction mechanism 5 in the embodiments of the present invention includes at least one set of the above-described type of outer gear sets 9, and the vehicle drive unit 1 shown in FIG. 1 includes two sets of the outer gear sets 9.FIG. 2 shows a specific configuration of the reduction mechanism 5 shown in FIG. 1. As described above, the reduction mechanism 5 includes the planetary gear unit 7, the counter gearset 8, and the outer gearset 9.The input shaft 3 and the sun gear shaft 15 are supported in a rotatable manner in the housing 17 by a bearing 24 installed in the housing 17. The axle 4 and the support shaft 16 are supported in a rotatable manner in the housing 17 by a bearing 25 installed in the housing 17. In an end section on an inner side of the housing 17 of the support shaft 16, a bearing 26 is installed. The sun gear shaft 15 and the carrier shaft 16 are coupled in a manner that allows them to rotate relative to each other by means of this bearing 26. In this way, the drive shaft 3 and the axle 4 are arranged on the same rotational axis CL 1.The planetary gear unit 7 is disposed in parallel with the counter gearset 8 on the inside of the housing 17. The sun gear 10 is mounted on the sun gear shaft 15, and the sun gear 10 and the sun gear shaft 15 are supported in a rotatable manner in the housing 17 by the bearing 24. The carrier 12 is integrally formed with the carrier shaft 16, and the carrier 12 and the carrier shaft 16 are supported in a rotatable manner in the housing 17 by the bearing 25. The external gear 14 is formed in the outer circumferential section of the ring gear 11, and the external gear 14 is meshed with the first planetary gear 21 of the external gear set 9.The center gear 18 is mounted on the sun gear shaft 15 so as to rotate integrally with the sun gear shaft 15, and the counter gear 19 is mounted on the counter shaft 20 so as to rotate integrally with the counter shaft 20. The counter shaft 20 is arranged parallel to the sun gear shaft 15 and is supported in a rotatable manner in the housing 17 by a bearing 27 and a bearing 28 installed in the housing 17.The outer gear set 9 is located on an outer circumferential side of the planetary gear unit 7 and the counter gear set 8, and the first planetary gear 21 is mounted on the planetary gear shaft 23 so as to rotate integrally with the planetary gear shaft 23 and so as to be meshed with the external gear 14. Similarly, the second planetary gear 22 is mounted on the planetary gear shaft 23 so as to rotate integrally with the planetary gear shaft 23 and so as to be meshed with the counter gear 19. In other words, the first planetary gear 21 and the second planetary gear 22 are arranged on the same rotation axis CL 2 as shown in FIG. 2 The planetary gear shaft 23 is arranged parallel to the sun gear shaft 15 and is supported in a rotatable manner in the housing 17 by a bearing 29 and a bearing 30 installed in the housing 17. Therefore, the first planetary gear 21, the second planetary gear 22, and the planetary gear shaft 23 of the outer gear set 9 all rotate as a single body, and the torque is transmitted between the external gear 14 and the center gear 18 and the counter gear 19.In order to transmit the torque between the external gear 14 and the center gear 18, the reduction mechanism 5 includes at least one set of the external gear sets 9. It should be noted that the same number of counter gears 19 as the existing number of outer gear sets 9 are arranged. For example, assuming that four sets of the outer gear sets 9 are arranged in the peripheral edge of the ring gear 11, four counter gears 19 are arranged to engage four second planetary gears 22, respectively.In the reduction mechanism 5 shown in FIGS. 1 and 2, the torque applied to the center gear 18 can be transmitted to the external gear 14 to rotate the ring gear 11. Since the sun gear shaft 15 and the input shaft 3 integrally rotate, the torque applied to the input shaft 3 is directly transmitted to the sun gear 10 of the sun gear shaft 15. In this situation, the torque is transmitted between the center gear 18 and the external gear 14 via the counter gear set 8 and the external gear set 9. Due to the torque transmitted to the external gear 14, the ring gear 11 is caused to rotate in a reverse rotational direction to the rotational directions of the center gear 18 and the sun gear 10. As a result, a rotational speed of the carrier 12 with respect to a rotational speed of the sun gear 10 is significantly reduced by the differential action of the planetary gear unit 7. In other words, a reduction ratio between the input shaft 3 and the axle 4 can be increased.The nomographic diagram of FIG. 3 shows rotational speeds of each of the rotation elements in the planetary gear unit 7 in the case that the sun gear 10 rotates due to a torque applied to the input shaft 3 and the sun gear shaft 15. As mentioned above, the planetary gear unit 7 shown in FIGS. 1 and 2 is a single pinion planetary gear unit, the sun gear shaft 15 serves as the input shaft 3, and the carrier shaft 16 serves as the axle 4 (i.e., an output shaft). Therefore, the sun gear (S) 10 serves as an input element (IN), and the carrier (C) 12 serves as an output element (OUT).As shown by the broken line in FIG. 3, in a conventional reduction device, a rotation speed of the output member is reduced with respect to a rotation speed of the input member by using the sun gear (S) as the input member (IN) and the carrier (C) as the output member (OUT), and fixing the ring gear (R). In contrast, in the reduction mechanism 5 according to the embodiment in which the sun gear (S) 10 is used as the input member and the carrier (C) 12 is used as the output member, the ring gear (R) 11 rotates in a reverse rotation direction to the rotation directions of the sun gear 10 and the carrier 12, That is, when the sun gear 10 is rotated in a forward direction by the torque of the input shaft 3, the ring gear 11 is rotated in a reverse direction by the torque transmitted from the center gear 18 of the counter gear set 8 to the external gear 14 via the outer gear set 9. As a result of the ring gear 11 rotating in the reverse direction with respect to the rotational direction of the sun gear 10, the rotational speed of the carrier 12 is significantly reduced with respect to the rotational speed of the sun gear 10. Thus, in the reduction mechanism 5 of the present embodiment shown by the solid line in FIG. 3, the reduction ratio between the input member and the output member is larger than the reduction ratio between the input member and the output member in the conventional reduction device shown by the broken line in FIG. 3.Moreover, since the ring gear 11 is rotated in the reverse direction by the torque applied to the external gear 14, flexibility in setting a gear ratio increases more than in a configuration where power transmission is performed by internal teeth of the ring gear as in the aforementioned compound planetary gear mechanism described in JP-A 2008-275112. As a result, the reduction ratio between the input shaft 3 and the axle 4 can be significantly increased.In a single pinion planetary gear unit in which the sun gear is used as the input member, the carrier is used as the output member, and the ring gear is fixed, the reduction ratio γ is expressed as: where Zs is the number of teeth of the sun gear and Zr is the number of inner teeth of the ring gear. Note that the reduction ratio γ in this case is the ratio of the rotational speed NIN of the input member with respect to the rotational speed NOUT of the output member (that is, γ=NIN / NOUT). In the planetary gear unit of this kind, the reduction ratio γ that can be achieved in a self-contained manner is about 4 to 10. For example, if we assume that an outer diameter of the planetary gear unit in the combined planetary gear mechanism described in JP-A 2008-275112 is 300 mm, a reduction ratio γ of about 100 at the maximum can be obtained. In contrast, in the reduction mechanism 5 in the embodiments of the present invention, there is a high degree of flexibility in setting the gear ratio without being limited by the number of inner teeth or the inner diameter of the ring gear 11 as described above. Therefore, a reduction ratio γ of about 10000 can be obtained theoretically.That is, the vehicle drive unit 1 in the embodiments of the present invention includes the reduction mechanism 5 that enables setting of a reduction ratio considerably larger than in a conventional configuration. In the reduction mechanism 5, a set of the planetary gear unit 7 and a set of the counter gear set 8 are arranged in parallel as a parallel gear pair. Therefore, the reduction ratio of the reduction mechanism can be significantly increased, for example, as compared with a reduction device having a conventional combined planetary gear mechanism of the type described in JP-A 2008-275112 or a reduction device having a two-stage transmission train, in the case of comparable sizes. In other words, the reduction mechanism 5 can be miniaturized.Moreover, in the vehicle drive unit 1, the torque generated by the actuator 2 can be transmitted to the axle 4 significantly multiplied by the reduction mechanism 5. Therefore, the actuator 2 can be miniaturized. As a result, the vehicle drive unit 1 can be significantly downsized and made lighter compared with a conventional drive unit or brake unit.More specifically, in the case of using the drive actuator 51 (or 52) as the actuator 2 in the vehicle drive unit 1 shown in FIG. 1, a drive torque generated by the drive actuator 51 (or 52) can be transmitted to the axle 4 significantly multiplied by the reduction mechanism 5. Therefore, the drive actuator 51 (or 52) can be significantly downsized. In contrast, in the case of using the brake actuator 61 (or 62) as the actuator 2, a brake torque generated by the brake actuator 61 (or 62) can also be transmitted to the axle 4 significantly multiplied by the reduction mechanism 5. Therefore, the brake actuator 61 (or 62) can be significantly downsized.In the vehicle drive unit 1 shown in FIGS. 1 and 2, the torque generated by the actuator 2 is applied to the input shaft 3 (that is, the sun gear shaft 15). Instead, it is also possible that torques generated by a plurality of the actuators 2 are applied to a plurality of the drive shafts 3 in the vehicle drive unit 1, respectively. Note that in other examples of the vehicle drive unit 1 described below, elements common to the aforementioned vehicle drive unit 1 shown in FIGS. 1 and 2 are assigned like reference numerals.The vehicle drive unit 1 shown in FIG. 4 includes a plurality of the outer gear sets 9 including a plurality of the first planetary gears 21, a plurality of the second planetary gears 22, and a plurality of the planetary gear shafts 23. In the vehicle drive unit 1 shown in FIG. 4, two sets of the outer gear sets 9 are shown, but three or more sets of the outer gear sets 9 may be provided. The first planetary gear 21 and the second planetary gear 22 are respectively mounted on each of the planetary gear shafts 23. In addition, a plurality of the drive shafts 3 are arranged. The drive shafts 3 are respectively coupled to end sections on one side (the left side in FIG. 4 ) of the planetary gear shafts 23. In other words, end sections on one side of the planetary gear shafts 23 extend outside the housing 17, and protruding portions form the drive shafts 3. In the example shown in FIG. 4, the two planetary gear shafts 23 serve as the drive shafts 3, respectively. this vehicle drive unit 1 shown in FIG. 4 further includes two of the actuators 2, and output shafts (not illustrated) of each of the actuators 2 are coupled to the drive shafts 3, respectively.The vehicle drive unit 1 shown in FIG. 5 comprises a plurality of the countershaft gear sets 8, which each comprise the countershaft gear 19 and a plurality of countershafts 41. In the vehicle drive unit 1 shown in FIG. 5, two of the counter gears 19 and two of the counter shafts 41 are shown. However, two or more of the counter gears 19 and two or more of the counter shafts 41 may be provided. The counter gears 19 are respectively mounted on each of the counter shafts 41. In addition, a plurality of the drive shafts 3 are arranged. The input shafts 3 are respectively coupled to end sections on one side (the left side in FIG. 5 ) of the counter shafts 41. In other words, end sections on one side of the countershafts 41 extend outside the housing 17, and those protruding portions serve as the drive shafts 3. In the example shown in FIG. 5, the two countershafts 41 serve as the drive shafts 3, respectively. The vehicle drive unit 1 shown in FIG. 5 further includes two of the actuators 2, and output shafts (not illustrated) of each of the actuators 2 are coupled to the drive shafts 3, respectively.As described above, in the vehicle drive units 1 shown in FIGS. 4 and 5, a plurality of the drive shafts 3 are arranged, and the actuators 2 are respectively coupled to each of the drive shafts 3 to apply a torque thereto. Therefore, a transmission system of the torque generated by one of the actuators 2 can be used as a main system, and a transmission system of the torque generated by the other of the actuators 2 can be used as a sub-system. Therefore, the reliability of the vehicle drive unit 1 can be improved.In the vehicle drive unit 1 shown in FIG. 6, a plurality of the drive shafts 3 are arranged, and the drive actuator 51 and the drive actuator 52 are respectively coupled to each of the drive shafts 3. A permanent magnet synchronous motor or an induction motor may be used as the drive actuator 51 and the drive actuator 52, for example.That is, in the vehicle drive unit 1 shown in FIG. 6, at least a single pair of the drive actuator 51 and the drive actuator 52 are arranged. Therefore, a transmission system of the drive torque generated by the drive actuator 51 can be used as a main system, and a transmission system of the drive torque generated by the drive actuator 52 can be used as a sub-system. For the above reasons, the reliability of the vehicle drive unit 1 can be improved.Motors having different power output characteristics may be used as the drive actuator 51 and the drive actuator 52, respectively. For example, a synchronous motor suitable for medium and low vehicle speeds may be used as the drive actuator 51, and an induction motor suitable for high vehicle speeds may be used as the drive actuator 52. In this case, by changing the engine used according to a vehicle speed or a fetched driving force amount, the driving force can be efficiently generated according to the running conditions. Therefore, the energy efficiency of the driving unit can be improved.In the vehicle drive unit 1 shown in FIG. 7, a plurality of the drive shafts 3 are arranged, and the brake actuator 61 and the brake actuator 62 are respectively coupled to each of the drive shafts 3. For example, an electromagnetic brake that brakes a rotation element due to a magnetic attractive force generated by the flow of an electric current, an electric brake that generates a friction braking force using a spindle mechanism driven by an electric motor, and a regenerative brake that brakes a rotation element using a resistive force generated when electricity is generated by a motor may be used as the brake actuator 61 and the brake actuator 62.That is, in the vehicle drive unit 1 shown in FIG. 7, at least a single pair of the brake actuator 61 and the brake actuator 62 is arranged. Therefore, a transmission system of the brake torque generated by the brake actuator 61 may be used as a main system, and a transmission system of the brake torque generated by the brake actuator 62 may be used as a sub-system. Therefore, the reliability of the brake unit can be improved.Brake mechanisms having various functions or applications may be used as the brake actuator 61 and the brake actuator 62, respectively. For example, if we assume that an electromagnetic brake that generates a braking torque due to the flow of an electric current or a regenerative brake is used as the brake actuator 61, the brake actuator 61 may be used as a service brake actuator. On the other hand, if we assume that an electric brake operating with a spindle mechanism is used as the brake actuator 62, the brake actuator 62 may be used as a parking brake actuator. In this case, the brake actuator 62 generates a brake torque due to the flow of an electric current and maintains the brake torque in a state when the flow of the electric current has been stopped.In the vehicle drive unit 1 shown in FIG. 8, a plurality of the drive shafts 3 are arranged, and a drive actuator 71 and a brake actuator 72 are respectively coupled to each of the drive shafts 3.In the vehicle drive unit 1 shown in FIG. 8, at least two of the drive shafts 3 are arranged, and the drive actuator 71 and the brake actuator 72 are respectively coupled to each of the drive shafts 3. Therefore, a driving force and a braking force can be generated by the vehicle drive unit 1.In the vehicle drive unit 1 shown in FIG. 9, at least four of the drive shafts 3 are arranged, and drive actuators 81, 82 that generate drive torques and brake actuators 83, 84 that generate brake torques are respectively coupled to each of the drive shafts 3.In this vehicle drive unit 1 shown in FIG. 9, two of the planetary gear shafts 23, two of the counter shafts 41, and four of the drive shafts 3 are arranged. The input shafts 3 are respectively coupled to each of the planetary gear shafts 23, and the drive actuator 81 and the drive actuator 82 are respectively coupled to the input shafts 3. Moreover, the input shafts 3 are respectively coupled to the counter shafts 41, and the brake actuator 83 and the brake actuator 84 are respectively coupled to the input shafts 3. Instead, it is also possible that the drive actuator 81 is coupled to one of the input shafts 3 coupled to the planetary gear shafts 23, and that the brake actuator 83 is coupled to the other of the input shafts 3 coupled to the planetary gear shafts 23. Moreover, it is possible that the drive actuator 82 is coupled to one of the input shafts 3 which are coupled to the countershafts 41 and that the brake actuator 84 is coupled to the other of the input shafts 3 which are coupled to the countershafts 41. It is also possible that the vehicle drive unit 1 shown in FIG. 9 is equipped with four of the planetary gear shafts 23, and that the drive shafts 3 are respectively coupled to each of the planetary gear shafts 23. In this case, the drive actuators 81, 82 and the brake actuators 83, 84 are respectively coupled to each of the drive shafts 3. Alternatively, it is also possible that the vehicle drive unit 1 shown in FIG. 9 is equipped with four of the countershafts 41 and that the drive shafts 3 are each coupled to each of the countershafts 41. In this case, the drive actuators 81, 82 and the brake actuators 83, 84 are respectively coupled to each of the drive shafts 3.In this way, the vehicle drive unit 1 shown in FIG. 9 includes at least a single pair of the drive actuators 81, 82 and at least a single pair of the brake actuators 83, 84. in the vehicle drive unit 1 shown in FIG. 9, each of the drive actuators 81 (or 82) and each of the brake actuators 83 (or 84) may be used as a main system, and the other of the drive actuators 82 (or 81) and the other of the brake actuators 84 (or 83) may be used as a sub-system. Therefore, the vehicle drive unit 1 shown in FIG. 9 has a braking function and makes it possible to improve reliability.Moreover, a low-rotation motor may be used as the drive actuator 81, and a high-rotation motor may be used as the drive actuator 82. In addition, one of the brake actuators 83, 84 may be used as a service brake actuator and the other of the brake actuators 83, 84 may be used as a parking brake actuator. Therefore, the reliability of the vehicle drive unit 1 can be further improved, and the energy efficiency can be improved.In the vehicle drive unit 1 in the embodiments of the present invention, the actuator 2 may be disposed on a wheel 6 side of the reduction mechanism 5 in a direction of the rotation axis CL 1 of the axle 4.The vehicle drive unit 1 shown in FIGS. 10 and 11 includes a plurality of the outer gear sets 9. more specifically, it includes a plurality of the first planetary gears 21, a plurality of the second planetary gears 22, and a plurality of planetary gear shafts 91. in FIGS. 10 and 11, two sets of the outer gear sets 9 are shown, but three or more sets of the outer gear sets 9 may be provided. The first planetary gear 21 and the second planetary gear 22 are respectively mounted on each of the planetary gear shafts 91. Moreover, a plurality of the drive shafts 3 are arranged, and the drive shafts 3 are respectively coupled to end sections on one side (the right side in FIGS. 10 and 11 ) of the plurality of planetary gear shafts 91. In other words, the end sections on one side of the planetary gear shafts 91 extending outside the housing 17 serve as the drive shafts 3.In the vehicle drive unit 1 shown in FIGS. 10 and 11, output shafts (not illustrated) of the actuators 2 are respectively coupled to each of the drive shafts 3, and torques of each of the actuators 2 are applied to the drive shafts 3. It is possible that at least one of the aforementioned drive actuators 51, 51 or brake actuators 61, 62 is used as the actuators 2, for example.That is, in the vehicle drive unit 1 shown in FIGS. 10 and 11, the drive shafts 3 and the axle 4 extend in the same direction. Such a vehicle drive unit 1 can be easily installed inside a wheel frame of the vehicle as a wheel motor. Alternatively, it is also possible that two of the drive units have their associated rear sides on an opposite side to the actuators 2 facing each other to form an on-board drive unit. In order that the vehicle drive unit 1 shown in FIG. 11 can be used as a wheel motor, a flange 93 of the axle 4 is fixed to the wheel 6 by bolts 92. Moreover, the vehicle drive unit 1 is fixed to a vehicle body by bolts 94. An example of this vehicle drive unit 1 shown in FIG. 11 used to form a wheel motor is shown in FIG. 12.A wheel motor 100 shown in FIG. 12 includes the vehicle drive unit 1 and the wheel 6 shown in FIGS. 10 and 11. In the vehicle drive unit 1 used in the wheel motor 100, the drive actuator 51 (or 52) is used as at least one of the actuators 2 as a main drive source of the vehicle.As shown in the above-mentioned FIG. 11, a tip 16 aof the support shaft 16 extends toward an outer side (the right side in FIGS. 11 and 12 ) of the housing 17, and the axle 4 is coupled to this tip 16 a. As mentioned above, the flange 93 for fixing the wheel 6 to the axle 4 is formed in an end section 4a of the axle 4. The flange 93 is formed further outward in a width direction than the actuator 2 in the direction of the rotation axis CL 1 of the axle 4.The wheel 6 includes a tire 101 having ground contact with a road surface and a wheel frame 102 provided with the tire 101. The vehicle drive unit 1 is located in an inner peripheral edge of this wheel frame 102. That is, the actuators 2, the drive shafts 3, the axle 4, and the reduction mechanism 5 are disposed in the inner circumferential edge of the wheel frame 102. The wheel frame 102 is fixed to the flange 93 of the axle 4 by the bolts 92. The actuators 2 are coupled to the housing 17 between the reduction mechanism 5 and the wheel frame 102 in the direction of the rotation axis CL 1.In the wheel motor 100, the housing 17 is coupled to a suspension mechanism 103 of the vehicle by the bolts 94.Using the vehicle drive unit 1 shown in FIGS. 10 and 11 as the wheel motor 100, the wheel motor 100 can be significantly downsized and made lighter. As a result, the unsprung masses of the vehicle can be significantly reduced, and a driving quality of the vehicle or the traction characteristics of the tires can be improved.Moreover, in the wheel motor 100, the actuators 2 are disposed between the reduction mechanism 5 and the wheel frame 102. Therefore, the actuators 2 and the drive shafts 3 are not disposed on a rear side facing the suspension mechanism 103 of the reduction mechanism 5. As a result, the rear side of the reduction mechanism 5 can be easily coupled to the vehicle body through the suspension mechanism 103.In the wheel motor 100 shown in FIG. 12, a single drive actuator 51 (or 52) and a single brake actuator 61 (or 62) are arranged as the actuators 2. However, in the wheel motor 100, the number of actuators 2 may be changed as needed. For example, the wheel motor 100 may be provided with only one drive actuator 51 (or 52), or may be provided with two or more drive actuators 51 (or 52). Alternatively, the wheel motor 100 may be provided with at least one drive actuator 51 (or 52) and two or more brake actuators 61 (or 62).Moreover, the wheel motor 100 shown in FIG. 12 need only be provided with at least one brake actuator 61 (or 62) without being provided with a drive actuator. In this case, the wheel motor 100 serves as a brake unit.FIGS. 13 and 14 show an example of two sets of the vehicle drive unit 1 used to constitute an on-board two-motor drive unit 200. More specifically, the on-board two-motor drive unit 200 is formed by combining a left-side unit 202 and a right-side unit 204. The left unit 202 includes: the axle 4 that transmits power to a left wheel 201 (or 6), the actuators 2, the drive shafts 3, and the reduction mechanism 5.The left unit 202 and the right unit 204 both have the same configuration as the above-mentioned vehicle drive unit 1 of any one of the foregoing examples. In the on-board two-motor drive unit 200 shown in FIGS. 13 and 14, the aforementioned vehicle drive unit 1 shown in FIG. 10 is used as the left unit 202 and the right unit 204.The left unit 202 and the right unit 204 are both equipped with a plurality of the drive shafts 3, and the actuators 2 are respectively coupled to the one of the drive shafts 3. In the example shown in FIGS. 13 and 14, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are used as the actuators 2.The left unit 202 and the right unit 204 are arranged such that their respective mating rear sides 17 aface each other. Therefore, the axis 4 of the left unit 202 and the axis 4 of the right unit 204 are arranged on the same axis, and each extends outward in a vehicle width direction.In the on-board two-motor drive unit 200, a clutch 205 is located between the left unit 202 and the right unit 204. The left unit 202 has a left clutch section 206 formed in a tip on an inner side in the vehicle width direction of the sun gear shaft 15, and the right unit 204 has a right clutch section 207 formed in a tip on an inner side in the vehicle width direction of the sun gear shaft 15. The left clutch section 206 of the left unit 202 and the right clutch section 207 of the right unit 204 are selectively coupled by the clutch 205.More specifically, the clutch 205 serves as a differential limiting mechanism that limits differential rotation between the left wheel 201 and the right wheel 203 by frictionally engaging the sun gear shaft 15 of the left unit 202 with the sun gear shaft 15 of the right unit 204. In the example shown in FIG. 14, an electromagnetic clutch is used as the clutch 205. The clutch 205 generates a frictional engagement force due to an elastic force of a compression coil spring in a state where no electric current is conducted, and generates, by flowing an electric current, a magnetic attraction force to reduce the frictional engagement force. For example, when no electric current flows in the clutch 205, the clutch 205 is engaged by a biasing force due to the compression coil spring, and differential rotation between the left wheel 201 and the right wheel 203 is limited. In contrast, when electric current flows in the clutch 205, the clutch 205 is disengaged, and the left wheel 201 and the right wheel 203 may differentially rotate.Using the vehicle drive unit 1 in the embodiments of the present invention to form the on-board two-motor drive unit 200, the on-board two-motor drive unit 200 can be significantly downsized and made lighter. Therefore, the vehicle can be made lighter and, moreover, the energy efficiency can be improved. In addition, the on-board two-motor drive unit 200 can be easily mounted in a vehicle, and the vehicle interior can be enlarged. Moreover, in the on-board two-motor drive unit 200, the driving force and the braking force generated in the left wheel 201 and the right wheel 203 can be independently controlled. Therefore, torque vectoring is enabled in a vehicle in which the onboard two-motor drive unit 200 is mounted.Moreover, the actuators 2 are arranged between the reduction mechanism 5 and the wheel 6 in both the left unit 202 and the right unit 204. In other words, the actuators 2 and the drive shafts 3 to which a torque is applied from the actuators 2 are not disposed on the rear surface 17 aof the reduction mechanism 5. Therefore, a width of the on-board two-motor drive unit 200 can be reduced.In the on-board two-motor drive unit 200, a drive actuator 51 (or 52) and a brake actuator 61 (or 62) are arranged as the actuators 2. However, in the on-board two-motor drive unit 200, the number of actuators 2 may be changed as needed. For example, the on-board two-motor drive unit 200 may be provided with only one drive actuator 51 (or 52), or may be provided with two or more drive actuators 51 (or 52). Alternatively, the on-board two-motor drive unit 200 may be provided with at least one drive actuator 51 (or 52) and two or more brake actuators 61 (or 62).Moreover, the left unit 202 and the right unit 204 need only be provided with at least one brake actuator 61 (or 62) without being provided with a drive actuator. In this case, the on-board two-motor drive unit 200 serves as a brake unit.FIG. 15 shows an example of a specific configuration of the brake actuator 61 ( 62, 72, 83, or 84) in the embodiments of the present invention. The brake actuator 61 ( 62, 72, 83, or 84) shown in FIG. 15 includes: a service brake mechanism 301 that is operated during normal braking; and a parking brake mechanism 302 that is operated during parking or stopping to maintain a braking force. A multi-disc electromagnetic brake that is activated to stop a predetermined rotational member by flowing an electric current is used as the service brake mechanism 301. The service brake mechanism 301 includes a friction plate 303, a pressure plate 304, a spool 305, and an output shaft 306.The friction plate 303 includes: a plurality of rotation plates 303 aof which at least a part is formed by a magnetic body; and a plurality of fixed plates 303 bof which at least a part is formed by a magnetic body. In the example shown in FIG. 15, the friction plate 303 includes three rotation plates 303 aand three fixed plates 303 b. The rotation plates 303 aare fixed to the output shaft 306 so as to rotate integrally with the output shaft 306. The fixed plates 303 bare installed in a housing 307 of the brake actuator 61 ( 62, 72, 83, or 84) so as to be able to move in an axial direction of the output shaft 306 but not to be able to rotate in a rotational direction of the output shaft 306. These rotation plates 303 aand fixed plates 303 bare alternately arranged in a direction of the rotation axis CL 2.The pressure plate 304 is formed as an annular magnetic body. The pressing plate 304 is installed in the housing 307 so as to be able to move in the direction of the rotation axis CL 2 but not to rotate in the rotation direction of the output shaft 306.The coil 305 is fixed to the housing 307 and generates a magnetic attractive force by applying a certain voltage thereto. The magnetic attractive force generated by the coil 305 acts on the friction plate 303 and the pressure plate 304, and causes the pressure plate 304 to be pulled toward a friction plate 303 side. Therefore, due to the flow of an electric current in the coil 305, the friction plate 303 is pressed by the pressure plate 304, the rotation plates 303 aand fixed plates 303 bof the friction plate 303 frictionally engage, and a braking torque is generated.For example, as shown in the aforementioned FIG. 11, the output shaft 306 is coupled to the input shaft 3 and the planetary gear shaft 91 of the reduction mechanism 5, and rotates integrally with these input shaft 3 and planetary gear shaft 91. moreover, as described above, the rotation plates 303 aare attached to the output shaft 306 so as to rotate integrally with the output shaft 306. Therefore, the braking torque generated by frictional engagement of the rotation plates 303 aand the fixed plates 303 bis transmitted through the output shaft 306 to the output shaft 306 of the reduction mechanism 5.Therefore, in this service brake mechanism 301, the magnetic attractive force generated by the flow of an electric current in the coil 305 causes the pressure plate 304 to be pulled to the friction plate 303 side and the friction plate 303 to be pressed by the pressure plate 304. As a result, the rotation plates 303 aand the fixed plates 303 bengage with each other. In other words, the service brake mechanism 301 generates the braking torque by flowing an electric current in the coil 305.The parking brake mechanism 302 is configured to be able to generate a braking torque when being activated by the flow of an electric current, and to be able to maintain the braking torque in a state where the flow of the electric current has been stopped. More specifically, the parking brake mechanism 302 includes a brake motor 308, a spindle mechanism 308, and a brake motor-oriented reduction mechanism 310.The brake motor 308 is an electric motor that generates driving torque when activated by the flow of an electric current. The brake motor 308 includes: a stator 308 a, a rotor 308 b, and a rotor shaft 308 cthat rotates integrally with the rotor 308 b. The stator 308a is fixed to the housing 307 in a non-rotatable manner. The rotor shaft 308c constitutes an output shaft of this brake motor 308 and rotates integrally with a later-discussed input shaft 310a of the brake motor-oriented reduction mechanism 310.The spindle mechanism 309 converts a rotational motion into a linear motion and presses the pressure plate 304 against the friction plate 303 side (the left side in FIG. 15 ) in the direction of the rotation axis CL 2, thereby generating an axial force to cause a frictional engagement between the rotation plates 303 aand the fixed plates 303 b. In addition, the spindle mechanism 309 is configured so that even if the electric current has stopped flowing while the axial force is generated, it is possible to maintain a state in which the rotation plates 303 aand the fixed plates 303 bare frictionally engaged to brake the output shaft 306. The spindle mechanism 309 is configured of a pressing member 309 aand a spindle member 309 b.The pressing member 309a is constituted by a disc-shaped non-magnetic body. A receiving spindle section 309 cof the spindle is formed in a central portion of the pressing member 309 aso as to penetrate the pressing member 309 ain a disc thickness direction of the pressing member 309 a(a left-right direction in FIG. 15 ). The pressing member 309 ais installed in the housing 307 so as to be able to move in the direction of the rotation axis CL 2 but not to rotate in the rotation direction of the output shaft 306. The pressing member 309 ais disposed adjacent to the pressing plate 304 in the direction of the rotation axis CL 2. The pressing member 309 ahas a contact surface 309 dcontacting the pressing plate 304 and causing an axial force (a pressing force) in the direction of the rotation axis CL 2 to act on the pressing plate 304.The spindle member 309 bis a rotation shaft of the spindle mechanism 309, and has a slide-in spindle section 309 eformed in an outer periphery of the spindle member 309 b. The spindle member 309b rotates integrally with an output shaft 310b of the brake motor-oriented reduction mechanism 310 to be discussed later.The male spindle section 309e of the spindle member 309b is screwed into the female spindle section 309c of the pressing member 309a. The receiving spindle section 309 cand the inserting spindle section 309 eof the spindle mechanism 309 are formed by, for example, a ball screw or a trapezoidal thread or a square thread spindle.The spindle mechanism 309 generates an axial force in a forward movement direction by rotating the spindle member 309 bin a forward direction, thereby bringing the pressing member 309 atoward the pressing plate 304 in the direction of the rotation axis CL 2. Moreover, by rotating the spindle member 309 bin a reverse direction, the spindle mechanism 309 generates an axial force in a backward movement direction that removes the pressing member 309 afrom the pressing plate 304 in the direction of the rotation axis CL 2.The brake motor-oriented reduction mechanism 310 has the input shaft 310 aand the output shaft 310 b, and reduces the rotation speed of the output shaft 310 bwith respect to the rotation speed of the input shaft 310 a. In other words, the brake motor-oriented reduction mechanism 310 transmits the torque applied to the input shaft 310 ato the output shaft 310 b, while multiplying. The rotor shaft 308 cof the brake motor 308 is coupled to the drive shaft 310 a. That is, the drive shaft 3 10a rotates integrally with the rotor shaft 308c. The spindle member 309 bof the spindle mechanism 309 is coupled to the output shaft 310 b. That is, the output shaft 310 brotates integrally with the spindle member 309 b.That is, in this parking brake mechanism 302, an output torque of the brake motor 308 is multiplied by the brake motor-oriented reduction mechanism 310 to be transmitted to the spindle mechanism 309. Therefore, the brake motor 308 can be miniaturized and the parking brake mechanism 302 can be miniaturized and made lighter. In addition, the brake actuator 61 (62, 72, 83 or 84) can be significantly downsized and made lighter.The parking brake mechanism 302 applies torque in a forward rotational direction to the spindle member 309 bof the spindle mechanism 309. Consequently, the rotation plates 303 aand the fixed plates 303 bare frictionally engaged with each other to apply a braking torque to the output shaft 306. The braking torque of the parking brake mechanism 302 applied to the output shaft 306 can be reduced by applying a torque in a reverse rotational direction to the spindle member 309 b.In the spindle mechanism 309 of the parking brake mechanism 302, a reversing efficiency for rotating the spindle member 309 bin the rearward direction by retracting the pressing member 309 ais set to a lower value than a forward efficiency for moving the pressing member 309 ain the forward direction by rotating the spindle member 309 bin the forward direction. Therefore, the output shaft 306 can be continuously stopped by pushing the pushing member 309 aand the pushing plate 304 in the forward direction by the spindle mechanism 309. For this reason, after stopping the output shaft 306 by operating the spindle mechanism 309 by the brake motor 308, the output shaft 306 can be continuously stopped by the parking brake mechanism 302 even when the supply of power to the service brake mechanism 301 and the brake motor 308 is stopped.The brake motor-oriented reduction mechanism 310 in the above-mentioned parking brake mechanism 302 may be constituted by, for example, a gear mechanism 401 similar to the above-mentioned reduction mechanism 5, as shown in FIG. 16. This transmission mechanism 401 shown in FIG. 16 includes the planetary gear unit 7, the counter gearset 8, and the outer gearset 9. Therefore, the transmission mechanism 401 and the reduction mechanism 5 have basically the same configuration even if they have different sizes. In FIG. 16, elements common to the aforementioned reduction mechanism 5 shown in FIGS. 1 and 2 are assigned the same reference numerals.In the transmission mechanism 401 shown in FIG. 16, the sun gear shaft 15 serves as the input shaft 310 aof the brake motor-oriented reduction mechanism 310, and the carrier shaft 16 serves as the output shaft 310 bof the brake motor-oriented reduction mechanism 310. The rotor shaft 308 cof the brake motor 308 is coupled to the input shaft 310 a, and the spindle member 309 bof the spindle mechanism 309 is coupled to the output shaft 310 b. Therefore, the brake motor-oriented reduction mechanism 310 constituted by the gear mechanism 401 can transmit the output torque of the brake motor 308 to the spindle mechanism 309 while multiplying.As mentioned above, the brake motor-oriented reduction mechanism 310 configured using this gear mechanism 401 also enables setting of a considerably larger reduction ratio as compared with a conventional configuration. Therefore, this brake motor-oriented reduction mechanism 310 enables the output torque of the brake motor 308 to be transmitted to the spindle mechanism 309 significantly multiplied. As a result, the brake motor 308 can be significantly downsized. Consequently, the brake actuator 61 ( 62, 72, 83, or 84) can be significantly downsized and made lighter.FIGS. 17 and 18 show another example of an on-board two-motor drive unit configured using the vehicle drive unit 1 in the embodiments of the present invention. Note that, in FIGS. 17 and 18, elements common to those in the above-discussed drawings are given the same reference numerals.An on-board two-motor drive unit 500 shown in FIG. 17 is constituted by two sets of an on-board vehicle drive unit 1. More specifically, the on-board two-motor drive unit 500 is formed by combining a left-side unit 502 and a right-side unit 503. The left unit 502 includes: the axle 4 that transmits power to a left wheel (not illustrated), the actuators 2, the drive shafts 3, and a reduction mechanism 501. On the other hand, the right unit 503 includes: the axle 4 that transmits power to a right wheel (not illustrated), the actuators 2, the drive shafts 3, and the reduction mechanism 501.The reduction mechanism 501 has basically the same configuration as the aforementioned reduction mechanism 5 shown in FIGS. 13 and 14. however, the reduction mechanism 501 shown in FIG. 17 includes only a single set of the outer gear set 9. Even if only a single set of the outer gear set 9 is arranged as in this example shown in FIG. 17, the ring gear 11 is supported in a rotatable manner by the planetary gear 13 engaging the inner teeth of the ring gear 11.The left unit 502 and the right unit 503 both include a plurality of the drive shafts 3, and a plurality of the actuators 2 are respectively coupled to each of the drive shafts 3. In the example shown in FIG. 17, the input shafts 3 are respectively coupled to the counter shaft 20 and the planetary gear shaft 91. That is, the counter shaft 20 and the planetary gear shaft 91 serve as the input shafts 3. In addition, in the example shown in FIG. 17, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are arranged as the actuators 2. Note that the brake actuator 61 (or 62) may include the service brake mechanism 301 and the parking brake mechanism 302 as in the aforementioned example shown in FIG. 15.The left unit 502 and the right unit 503 are arranged such that respective mating rear sides 17 aface each other. Therefore, the axis 4 of the left unit 502 and the axis 4 of the right unit 503 are arranged on the same axis, and each extends outward in the vehicle width direction.The left unit 202 and the right unit 204 in the aforementioned on-board two-motor drive unit 200 shown in FIGS. 13 and 14 both have a plurality of the actuators 2 disposed on the outside of the vehicle. That is, the plurality of actuators 2 are disposed on an opposite side to the back surface 17 ain the direction of the rotation axis CL 1. Therefore, the plurality of actuators 2 are each disposed on an outer circumferential side in the radial direction of the axis 4 along the axis 4. In the aforementioned example shown in FIG. 14, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are respectively disposed on the outer circumferential side in the radial direction of the axis 4 along the axis 4. In contrast, it is also possible that the on-board two-motor drive unit in the embodiments of the present invention includes the plurality of actuators 2 arranged on an inner side of the vehicle. That is, the plurality of actuators 2 may be disposed on the rear side 17 aof the housing 17 in the direction of the rotation axis CL 1. Alternatively, it is possible that certain of the plurality of actuators 2 are disposed on the rear surface 17 aof the housing 17 in the direction of the rotation axis CL 1.In the on-board two-motor drive unit 500 shown in FIG. 17, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are disposed on the rear side 17 a(the right side in FIG. 17 ) in the left unit 502. An output shaft 51 a(or 52 a) of the drive actuator 51 (or 52) is coupled to the input shaft 3 which rotates integrally with the counter shaft 20. An output shaft 61 a(or 62 a) of the brake actuator 61 (or 62) is coupled to the input shaft 3 which rotates integrally with the planetary gear shaft 91. Similarly, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are disposed on the rear side 17 a(the left side in FIG. 17 ) in the right unit 503. The output shaft 51 a(or 52 a) of the drive actuator 51 (or 52) is coupled to the input shaft 3 which rotates integrally with the counter shaft 20. The output shaft 61 a(or 62 a) of the brake actuator 61 (or 62) is coupled to the input shaft 3 that rotates integrally with the planetary gear shaft 91.In the example shown in FIG. 17, the output shaft 51 a(or 52 a) of the drive actuator 51 (or 52) has a clutch section 51 b(or 52 b) extending in an opposite direction to an extending direction of the output shaft 51 a(or 52 a). Moreover, the clutch section 51 b(or 52 b) of the drive actuator 51 (or 52) in the left unit 502 and the clutch section 51 b(or 52 b) of the drive actuator 51 (or 52) in the right unit 503 are coupled by the clutch 205. The clutch 205 has a similar configuration to the aforementioned clutch 205 shown in FIGS. 13 and 14, and functions in a similar manner to the clutch 205 shown in FIGS. 13 and 14. Therefore, in the example shown in FIG. 17, the clutch 205 is located between the left unit 502 and the right unit 503 in the vehicle width direction, and is configured to selectively couple the above-mentioned clutch section 51 b(or 52 b) in the left unit 502 and the clutch section 51 b(or 52 b) in the right unit 503.Thus, in the on-board two-motor drive unit 500 shown in FIG. 17, the plurality of actuators 2 are arranged inward in a width direction of the vehicle. That is, the plurality of actuators 2 are disposed on the rear surface 17 ain the direction opposite to the extending direction of the axis 4 without extending across the axis 4. As a result, a size in the radial direction of the axle 4 can be reduced as compared with the case where the plurality of actuators 2 are arranged to sandwich the axle 4. Therefore, a configuration in a height direction and the front-rear direction of the on-board two-motor drive unit 500 can be downsized.An on-board two-motor drive unit 600 shown in FIG. 18 is constituted by two sets of the on-board vehicle drive unit 1. More specifically, the on-board two-motor drive unit 600 is formed by combining a left-side unit 602 and a right-side unit 603. The left unit 602 includes: the axle 4 that transmits power to a left wheel (not illustrated), the actuators 2, the drive shafts 3, and a reduction mechanism 601. On the other hand, the right unit 603 includes: the axle 4 that transmits power to a right wheel (not illustrated), the actuators 2, the drive shafts 3, and the reduction mechanism 601.The reduction mechanism 601 has basically the same configuration as the aforementioned reduction mechanism 501 shown in FIG. 17. The reduction mechanism 601 shown in Fig. 18 is also provided with a single set of the outer gear set 9. Note that the reduction mechanism 601 may include two or more sets of the outer gear sets 9. The ring gear 11 is supported in a rotatable manner by the planetary gear 13 engaging the inner teeth of the ring gear 11.The left unit 602 and the right unit 603 both include a plurality of the drive shafts 3, and the actuators 2 are respectively coupled to each of the drive shafts 3. In the example shown in FIG. 18, the input shafts 3 are respectively coupled to the sun gear shaft 15 and the planetary gear shaft 91. That is, the sun gear shaft 15 and the planetary gear shaft 91 serve as the input shafts 3. In addition, in this example shown in FIG. 18, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are arranged as the actuators 2. Note that the brake actuator 61 (or 62) may include the service brake mechanism 301 and the parking brake mechanism 302 as in the aforementioned example shown in FIG. 15.The left unit 602 and the right unit 603 are arranged such that respective mating rear sides 17 aface each other. Therefore, the axis 4 of the left unit 602 and the axis 4 of the right unit 603 are arranged on the same axis, and each extends outward in the vehicle width direction.As mentioned above, in the on-board two-motor drive unit in the embodiments of the present invention, it is possible that certain ones of the plurality of actuators 2 are disposed on the rear side 17 aof the housing 17 in the direction of the rotation axis CL 1.In the on-board two-motor drive unit 600 shown in FIG. 18, the drive actuator 51 (or 52) is located on the rear side 17 aof the housing 17 in the direction of the rotation axis CL 1. On the other hand, the brake actuator 61 (or 62) is located on an extension side of the axle 4 in the direction of the rotation axis CL 1. More specifically, the drive actuator 51 (or 52) is located on the rear side 17 a(the right side in FIG. 18 ) in the left unit 602. On the other hand, the brake actuator 61 (or 62) is located on a side opposite to the rear side 17 a(the left side in FIG. 18 ) in the left unit 602. The output shaft 51 a(or 52 a) of the drive actuator 51 (or 52) is coupled to the input shaft 3 which rotates integrally with the sun gear shaft 15. The output shaft 61 a(or 62 a) of the brake actuator 61 (or 62) is coupled to the input shaft 3 that rotates integrally with the planetary gear shaft 91. Similarly, the drive actuator 51 (or 52) is located on the rear side 17 a(the left side in FIG. 18 ) in the right unit 603. On the other hand, the brake actuator 61 (or 62) is located on a side opposite to the rear side 17 a(the right side in FIG. 18 ) in the right unit 603. The output shaft 51 a(or 52 a) of the drive actuator 51 (or 52) is coupled to the input shaft 3 which rotates integrally with the sun gear shaft 15. The output shaft 61 a(or 62 a) of the brake actuator 61 (or 62) is coupled to the input shaft 3 that rotates integrally with the planetary gear shaft 91.Also in the example shown in FIG. 18, the output shaft 51 a(or 52 a) of the drive actuator 51 (or 52) has the clutch section 51 b(or 52 b). Moreover, the clutch section 51 b(or 52 b) of the drive actuator 51 (or 52) in the left unit 602 and the clutch section 51 b(or 52 b) of the drive actuator 51 (or 52) in the right unit 603 are coupled by the clutch 205. Therefore, in this example shown in FIG. 18, the clutch 205 is located between the left unit 602 and the right unit 603 in the vehicle width direction, and is configured to selectively couple the above-mentioned clutch section 51 b(or 52 b) in the left unit 602 and the clutch section 51 b(or 52 b) in the right unit 603.That is, in the on-board two-motor drive unit 600 shown in FIG. 18, certain of the plurality of actuators 2 are disposed inward in the width direction of the vehicle. That is, the plurality of actuators 2 are arranged to be divided between the inner side and the outer side in the width direction of the vehicle without extending across the axle 4. Therefore, the size in the radial direction of the axis 4 can be reduced as compared with the case where the plurality of actuators 2 are arranged along the axis 4. Moreover, by partitioning the plurality of actuators 2 between the inner side and the outer side in the width direction of the vehicle, the plurality of actuators 2 can be arranged to overlap each other in the radial direction of the axle 4. For example, in the example shown in FIG. 18, the drive actuator 51 (or 52) and the brake actuator 61 (or 62) are arranged to overlap each other in the radial direction of the axis 4. As a result, a decrease in the radial direction of the axis 4 can be achieved. Therefore, the configuration in the height direction and the front-rear direction of the on-board two-motor drive unit 600 can be made smaller.

Claims

A vehicle drive unit (1) comprising: a plurality of actuators (2) that generate torques; a plurality of drive shafts (3, 310a) to which the torques generated by the actuators (2) are applied; an axle (4) that transmits power to a wheel (6) of a vehicle; and a reduction mechanism (5, 501, 601) that reduces a rotational speed between the drive shaft (3, 310a) and the axle (4), wherein the torques applied to the drive shafts (3, 310a) are transmitted to the axle (4) while being multiplied to generate at least one of a drive force and a braking force of the vehicle, wherein the reduction mechanism (5, 501, 601) comprises: a planetary gear unit (7) having a sun gear (10), a ring gear (11), and a carrier (12), an external gear (14) formed in an outer circumferential section of the ring gear (11), at least one external gear set (9) including a first planetary gear (21) that is meshed with the external gear (14), a second planetary gear (22) that is disposed on the same rotation axis as the first planetary gear (21) and rotates integrally with the first planetary gear (21), and at least one planetary gear shaft (23, 31, 91) that rotates integrally with the first planetary gear (21) and the second planetary gear (22), a center gear (18) that is disposed on the same rotation axis as the sun gear (10) and rotates integrally with the sun gear (10), a counter gear (19) that is disposed between the center gear (18) and the second planetary gear (22) and is meshed with both the center gear (18) and the second planetary gear (22), at least one sun gear shaft (15) that rotates integrally with the center gear (18) and the sun gear (10), a carrier shaft (16) that rotates integrally with the carrier (12) and that is configured as the axle (4), and at least one counter shaft (20, 41) that rotates integrally with the counter gear (19), wherein the drive shafts (3) include at least one of: the at least one sun gear shaft (15), the at least one planetary gear shaft (23, 31, 91), or the at least one counter shaft (20, 41), wherein the vehicle drive unit (1) includes: a plurality of external gear sets (9) or a plurality of counter shafts (20, 40), wherein the actuators (2) include a plurality of drive actuators (51, 52, 71, 81, 82) that generate drive torques, and the drive torques generated by the drive actuators (51, 52, 71, 81, 82) are respectively applied to the drive shaft (3).The vehicle drive unit (1) according to claim 1, wherein the actuators (2) include a plurality of the drive actuators (51, 52, 71, 81, 82) whose characteristics differ, and the driving torques generated by the plurality of drive actuators (51, 52, 71, 81, 82) whose characteristics differ are applied to the drive shafts (3), respectively.A vehicle drive unit (1) comprising: a plurality of actuators (2) that generate torques; a plurality of drive shafts (3, 310a) to which the torques generated by the actuators (2) are applied; an axle (4) that transmits power to a wheel (6) of a vehicle; and a reduction mechanism (5, 501, 601) that reduces a rotational speed between the drive shaft (3, 310a) and the axle (4), wherein the torques applied to the drive shafts (3, 310a) are transmitted to the axle (4) while being multiplied to generate at least one of a drive force and a braking force of the vehicle, wherein the reduction mechanism (5, 501, 601) comprises: a planetary gear unit (7) having a sun gear (10), a ring gear (11), and a carrier (12), an external gear (14) formed in an outer circumferential section of the ring gear (11), at least one external gear set (9) including a first planetary gear (21) that is meshed with the external gear (14), a second planetary gear (22) that is disposed on the same rotation axis as the first planetary gear (21) and rotates integrally with the first planetary gear (21), and at least one planetary gear shaft (23, 31, 91) that rotates integrally with the first planetary gear (21) and the second planetary gear (22), a center gear (18) that is disposed on the same rotation axis as the sun gear (10) and rotates integrally with the sun gear (10), a counter gear (19) that is disposed between the center gear (18) and the second planetary gear (22) and is meshed with both the center gear (18) and the second planetary gear (22), at least one sun gear shaft (15) that rotates integrally with the center gear (18) and the sun gear (10), a carrier shaft (16) that rotates integrally with the carrier (12) and that is configured as the axle (4), and at least one countershaft (20, 41) that rotates integrally with the countershaft gear (19), the drive shafts (3) including at least one of: the at least one sun gear shaft (15), the at least one planetary gear shaft (23, 31, 91), or the at least one countershaft (20, 41), the vehicle drive unit (1) including: a plurality of external gear sets (9) or a plurality of countershafts (20, 41), the actuators (2) including at least one drive actuator (51, 52, 71, 81, 82) that generates a drive torque, and at least one brake actuator (61, 62, 72, 83, 84) that generates a brake torque, and the driving torque and the braking torque are applied to the driving shafts (3), respectively.The vehicle drive unit (1) according to claim 3, comprising a plurality of drive actuators (51, 52, 71, 81, 82) and a plurality of brake actuators (61, 62, 72, 83, 84), wherein the drive torques generated by the drive actuators (51, 52, 71, 81, 82) and the brake torques generated by the brake actuators (61, 62, 72, 83, 84) are applied to the drive shafts (3), respectively.The vehicle drive unit (1) according to claim 4, wherein the brake actuators (61, 62, 72, 83, 84) include a usual brake actuator (61, 72, 83, 84) that is activated by flowing an electric current to generate the brake torque and a parking brake actuator (62) that is activated by flowing an electric current to generate the brake torque and that is capable of maintaining the brake torque when the flow of the electric current has been stopped, and the brake torque generated by the usual brake actuator (61, 72, 83, 84) and the brake torque generated by the parking brake actuator (62) are applied to the drive shafts (3), respectively.The vehicle drive unit (1) according to claim 5, comprising a plurality of drive actuators (51, 52, 71, 81, 82) whose characteristics differ, wherein the driving torques generated by the drive actuators (51, 52, 71, 81, 82) whose characteristics differ, the braking torque generated by the ordinary brake actuator (61, 72, 83, 84), and the braking torque generated by the parking brake actuator (62) are applied to the drive shafts (3), respectively.The vehicle drive unit (1) according to any one of claims 1 to 6, wherein the wheel (6) comprises a tire (101) having ground contact with a road surface and a wheel frame (102) equipped with the tire (101), and the actuators (2), the drive shafts (3), the axle (4) and the reduction mechanism (5, 501, 601) are disposed in an inner circumferential portion of the wheel frame (102), and the wheel frame (102) is coupled to the axle (4).The vehicle drive unit (1) according to claim 7, wherein the drive shafts (3) include the plurality of planetary gear shafts (23, 31, 91) or the plurality of counter shafts (20, 41), and the actuators (2) are located between the reduction mechanism (5) and the wheel frame (102) in a direction of the rotation axis (CL1) of the axle (4).The vehicle drive unit (1) according to any one of claims 1 to 6, wherein the wheel (6) is a left wheel (201) and a right wheel (203) disposed on both sides in a vehicle width direction, the vehicle drive unit (1) comprises: a left side unit (202, 502, 602) having an axle (4) transmitting power to the left wheel (201), actuators (2), drive shafts (3) and a reduction mechanism (5, 501, 601); and a right side unit (204, 503, 603) having an axle (4) transmitting power to the right wheel (203), actuators (2), drive shafts (3) and a reduction mechanism (5, 501, 601), and the left unit (202, 502, 602) and the right unit (204, 503, 603) are disposed to face each other, wherein extending directions of their respective axes (4) are made opposite to each other in the vehicle width direction.The vehicle drive unit (1) according to claim 9, wherein the left unit (202) includes a left clutch section (206) in which the sun gear shaft (15) extends in a direction away from the left wheel (201) in the vehicle width direction, the right unit (204) includes a right clutch section (207) in which the sun gear shaft (15) extends in the direction away from the right wheel (203) in the vehicle width direction, and the vehicle drive unit (1) further includes a clutch (205) that selectively couples the left clutch section (206) and the right clutch section (207).The vehicle drive unit (1) according to claim 9 or 10, comprising a plurality of outer gear sets (9) or a plurality of counter shafts (20, 40), wherein the drive shafts (3) include the plurality of planetary gear shafts (91) or the plurality of counter shafts (20), actuators (2) are located in the left unit (202) between the reduction mechanism (5) and the left wheel (201) in the vehicle width direction, and actuators (2) are located in the right unit (204) between the reduction mechanism (5) and the right wheel (203) in the vehicle width direction.The vehicle drive unit (1) according to claim 1, wherein the actuators (2) include at least one brake actuator (61, 62, 72, 83, 84) that generates a brake torque, and the brake torque is applied to the drive shafts (3).The vehicle drive unit (1) according to claim 12, comprising a plurality of external gear sets (9) or a plurality of counter shafts (20, 40), wherein the drive shafts (3) comprise the plurality of planetary gear shafts (91) or the plurality of counter shafts (20), and the actuators (2) are located between the reduction mechanism (5) and the wheel (6) in a direction of the rotation axis (CL1) of the axle (4).The vehicle drive unit (1) according to claim 13, comprising a plurality of brake actuators (61, 62, 72, 83, 84), wherein the braking torques generated by the plurality of brake actuators (61, 62, 72, 83, 84) are applied to the drive shafts (3), respectively.The vehicle drive unit (1) according to claim 14, wherein the plurality of brake actuators (61, 62, 72, 83, 84) include a usual brake actuator (61) that is activated by flowing an electric current to generate the brake torque and a parking brake actuator (62) that is activated by flowing an electric current to generate the brake torque and that is capable of maintaining the brake torque when the flow of the electric current has been stopped, and the brake torque generated by the usual brake actuator (61) and the brake torque generated by the parking brake actuator (62) are applied to the drive shafts (3), respectively.The vehicle drive unit (1) according to claim 14 or 15, wherein the drive shafts (3) include the plurality of planetary gear shafts (23, 31, 91) or the plurality of counter shafts (20, 41), and the actuators (2) are located between the reduction mechanism (5) and the gear (6) in a direction of the rotation axis (CL1) of the axle (4).

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