VEHICLE DRIVE DEVICE

A vehicle drive device comprises: an electric motor as a drive force source for running, the vehicle drive device further comprising one end portion of an output rotating member of the electric motor being coupled to first drive wheels via a first power connecting/disconnecting device selectively interrupting power transmission, the other end portion of the output rotating member being coupled to second drive wheels through a second power connecting/disconnecting device selectively interrupting power transmission at a shift ratio different from a shift ratio between the one end portion and the first drive wheels, and the first power connecting/disconnecting device and the second power connecting/disconnecting device being alternatively put into a power transmittable state of transmitting power so as to shift gears between the first drive wheels or the second drive wheels and the electric motor.

MODE FOR CARRYING OUT THE INVENTION

First Example

FIG. 1is a schematic for explaining a vehicle drive device10to which the present invention is applied. The vehicle drive device10is preferably used in an electric vehicle8(hereinafter referred to as a vehicle8) running with power of an electric motor MG

As depicted inFIG. 1, the vehicle drive device10has a transaxle case12(hereinafter referred to as a “case12”) as a non-rotating member attached to a vehicle body by bolts etc., and includes the electric motor MG; a first reduction gear14, a second reduction gear16, a first clutch C1, and a second clutch C2in the case12that is a housing of the vehicle drive device10. The vehicle drive device10also includes a first differential gear device18(first differential gear18) and a second differential gear device20(second differential gear20) outside the case12. For example, the electric motor MG is disposed between front wheels22and rear wheels24such that an axial direction of the electric motor MG matches a longitudinal direction of the vehicle8. When the power of the electric motor MG is transmitted to the front wheels22that are first drive wheels in the vehicle8, the first clutch C1is engaged and the second clutch C2is released. As a result, the power of the electric motor MG is transmitted from an output rotating member26of the electric motor MG, or specifically, one end portion26aof the output rotating member26, sequentially through the first clutch C1, the first reduction gear14, the first differential gear device18, and a pair of first drive axles28(first drive shafts28) respectively coupling the first differential gear device18and a pair of the front wheels22, to the pair of the front wheels22. Conversely, when the power of the electric motor MG is transmitted to the rear wheels24that are second drive wheels, the first clutch C1is released and the second clutch C2is engaged. As a result, the power of the electric motor MG is transmitted from the output rotating member26of the electric motor MG; or specifically, another end portion26bof the output rotating member26, sequentially through the second clutch C2, the second reduction gear16, the second differential gear device20, and a pair of second drive axles30(second drive shafts30) respectively coupling the second differential gear device20and a pair of the rear wheels24, to the pair of the rear wheels24. Therefore, a power transmission path from the one end portion26aof the output rotating member26of the electric motor MG to the front wheels22has the one end portion26a, the first clutch C1, the first reduction gear14, the first differential gear device18, the first drive axles28, and the front wheels22sequentially coupled in series. On the other hand, a power transmission path from the other end portion26bof the output rotating member26to the rear wheels24has the other end portion26b, the second clutch C2, the second reduction gear16, the second differential gear device20, the second drive axles30, and the rear wheels24sequentially coupled in series. The first reduction gear14, the first clutch C1, the electric motor MG; the second clutch C2, and the second reduction gear16are arranged in series on a rotation axis of the electric motor MG The front wheels22and the rear wheels24have the same wheel diameter.

The electric motor MG is disposed on a center portion of the vehicle8and is a so-called motor generator having a motor function of outputting the power for vehicle running to at least one of the front wheels22and the rear wheels24and an electric generation function. Therefore, the electric motor MG acts as a drive force source for running. Specifically, the electric motor MG includes an electric motor stator32fixed to the inside of the case12, an electric motor rotor34rotating inside the electric motor stator32, and the output rotating member26rotating integrally with the electric motor rotor34and acting as an electric motor output shaft. The electric motor MG is electrically connected via an inverter36to an electric storage device38, and the electric motor MG and the electric storage device38are configured such that electric power can mutually be given and received. The electric storage device38is, for example, a battery (secondary battery) such as a lead storage battery or an electric energy source such as a capacitor.

The output rotating member26of the electric motor MG projects toward the both axial sides of the electric motor MG and the power of the electric motor MG is output from the one end portion26aand the other end portion26bof the output rotating member26. In short, the electric motor MG outputs the power of the electric motor MG to the both axial sides of the electric motor MG. The one end portion26aof the output rotating member26of the electric motor MG acts as a first electric motor output shaft26aoutputting the power of the electric motor MG to the first reduction gear14, and the other end portion26bof the output rotating member26acts as a second electric motor output shaft26boutputting the power of the electric motor MG to the second reduction gear16. Therefore, the first electric motor output shaft26aand the second electric motor output shaft26bintegrally rotate around the rotation axis of the electric motor MG

The first reduction gear14includes a first reduction gear input shaft40coupled via the first clutch C1to the one end portion26aof the output rotating member26, and a first reduction gear output shaft42coupled to the first differential gear device18. The first reduction gear14includes, for example, a gear device or a belt power transmission device, and changes a rotation speed at a constant first shift ratio γ1 (=rotation speed of the first reduction gear input shaft40/rotation speed of the first reduction gear output shaft42) for power transmission between the first reduction gear input shaft40and the first reduction gear output shaft42. The shift ratio is also referred to as a reduction ratio or a gear ratio.

The second reduction gear16includes a second reduction gear input shaft44coupled via the second clutch C2to the other end portion26bof the output rotating member26, and a second reduction gear output shaft46coupled to the second differential gear device20. The second reduction gear16has the same structure as the first reduction gear14, includes, for example, a gear device or a belt power transmission device, and changes a rotation speed at a constant second shift ratio γ2 (=rotation speed of the second reduction gear input shaft44/rotation speed of the second reduction gear output shaft46) for power transmission between the second reduction gear input shaft44and the second reduction gear output shaft46. The second shift ratio γ2 of the second reduction gear16is a shift ratio different from the first shift ratio γ1 of the first reduction gear14. Although the magnitude relation between the both shift ratios γ1 and γ2 is not particularly limited, the first shift ratio γ1 is set to a value greater than the second shift ratio γ2 in this example.

The first clutch C1and the second clutch C2are wet multi-plate type hydraulic friction engagement devices in which a plurality of friction plates overlapped with each other is pressed by a hydraulic actuator, and are engaged, released, and slipped by hydraulic control. The first clutch C1and the second clutch C2are in a power transmission state of transmitting power when engaged and are in a power transmission interruption state of interrupting power transmission when released. When slipped, the clutches C1and C2can adjust a transmittable torque capacity and allow a rotation speed difference between the input/output members. Because of such a configuration, the first clutch C1interposed between the one end portion26aof the output rotating member26of the electric motor MG and the first reduction gear14acts as a first power connecting/disconnecting device selectively interrupting the power transmission between the one end portion26aand the first reduction gear14. In other words, the first reduction gear14is coupled to the one end portion26aof the output rotating member26in a power connectable/disconnectable manner. The second clutch C2interposed between the other end portion26bof the output rotating member26and the second reduction gear16acts as a second power connecting/disconnecting device selectively interrupting the power transmission between the other end portion26band the second reduction gear16. In other words, the second reduction gear16is coupled to the other end portion26bof the output rotating member26in a power connectable/disconnectable manner.

The first differential gear device18and the second differential gear device20are differential gear devices generally used in a vehicle and transmitting power while allowing a mutual rotation difference of a pair of drive wheels. A shift ratio γdf1 of the first differential gear device18(=rotation speed of the first reduction gear output shaft42/rotation speed of the first drive axles28) is preliminarily set to the same value as a shift ratio γdf2 of the second differential gear device20(=rotation speed of the second reduction gear output shaft46/rotation speed of the second drive axles30).

In the vehicle drive device10configured as described above, the first reduction gear14, the second reduction gear16, the first clutch C1, and the second clutch C2act as a two-speed gear shifting device50alternatively switching the first shift ratio γ1 and the second shift ratio γ2 as a whole. For example, if the first clutch C1is engaged and the second clutch C2is released, a shift ratio of the gear shifting device50is switched to the first shift ratio γ1 and, conversely, if the first clutch C1is released and the second clutch C2is engaged, the shift ratio of the gear shifting device50is switched to the second shift ratio γ2. In short, in the vehicle drive device10, the front wheels (first drive wheels)22and the rear wheels (second drive wheels)24are alternatively coupled to the output rotating member26of the electric motor MG by the first clutch C1and the second clutch C2for shifting gears between the front wheels22or the rear wheels24and the electric motor MG In other words, a shift ratio is switched between the front wheels22or the rear wheels24to which the power of the electric motor MG is transmitted and the electric motor MG.

When both the first clutch C1and the second clutch C2are released, the vehicle drive device10enters a neutral state in which the power of the electric motor MG is transmitted to none of the front wheels22and the rear wheels24. Conversely, when both the first clutch C1and the second clutch C2are engaged, the front wheels22and the rear wheels24are locked due to friction with a running road surface even if the electric motor MG is not energized and is in an idly rotatable state. Therefore, the vehicle drive device10can produce a hill hold function preventing the vehicle8from moving backward on a climbing road, for example. Given that the hill hold function is produced by the engagement of the first clutch C1and the second clutch C2, the first clutch C1and the second clutch C2are preferably of a normally close type engaged when no oil pressure is applied.

The vehicle drive device10of this example has the following effects (A1) and (A2). (A1) According to this example, as depicted inFIG. 1, the one end portion26aof the output rotating member26of the electric motor MG is coupled via the first clutch (first power connecting/disconnecting device) C1to the front wheels (first drive wheels)22. On the other hand, the other end portion26bof the output rotating member26is coupled via the second clutch (second power connecting/disconnecting device) C2to the rear wheels (second drive wheels)24. Since the second shift ratio γ2 of the second reduction gear16is different from the first shift ratio γ1 of the first reduction gear14, the shift ratio between the other end portion26band the rear wheels24is different from the shift ratio between the one end portion26aand the front wheels22. When the first clutch C1and the second clutch C2are alternatively engaged, i.e., the power transmission state is alternatively achieved, in the vehicle drive device10, gears are shifted between the front wheels22or the rear wheels24and the electric motor MG Therefore, with regard to the gear shifting device50that is the power transmission mechanism transmitting the power of the electric motor MG to the front wheels22or the rear wheels24, or specifically, the power transmission mechanism made up of the first reduction gear14, the second reduction gear16, the first clutch C1, and the second clutch C2, enlargement is prevented from occurring on the side of the one end portion26aof the output rotating member26of the electric motor MG in a biased manner and, therefore, design restriction on a mounting position of the electric motor MG in the vehicle8can be reduced as compared to the case of disposing a stepped transmission only on the side of the one end portion26aof the output rotating member26, for example. In other words, a degree of freedom of design related to the mounting position of the electric motor MG is increased. A rotation speed of the electric motor MG can be changed at shift ratios different from each other for running the vehicle8.

(A2) According to this example, by coupling only the one end portion26aof the output rotating member26of the electric motor MG through the first clutch C1to the front wheels22or by coupling only the other end portion26bof the output rotating member26of the electric motor MG through the second clutch C2to the rear wheels24, the front wheels22and the rear wheels24can alternatively be driven. Therefore, for example, if a drive wheel slips in either the front wheels22or the rear wheels24, the drive wheels associated with the power transmission are switched such that the power of the electric motor MG is transmitted to the other drive wheels so as to cause the other drive wheels to generate a drive force. By switching the drive wheels associated with the power transmission in this way, the running performance of the vehicle8can be improved, for example, on a running road on which wheels easily slip, as compared to a two-wheel drive vehicle only either the front wheels22or the rear wheels24are driven.

Other examples of the present invention will be described. In the following description of the examples, the portions mutually common to the examples are denoted by the same reference numerals and will not be described.

Second Example

In the description of this example (second example), the points common with the first example will not be described and the points different from the first example will mainly be described.FIG. 2is a schematic for explaining a vehicle drive device110included in an electric vehicle108(hereinafter referred to as a vehicle108) of this example. As can be seen from comparison betweenFIGS. 1 and 2, the vehicle drive device110of this example is different from the vehicle drive device10of the first example in that the first reduction gear14of the first example is replaced with a transmission112. The vehicle drive device110is the same as the vehicle drive device10of the first example except the replacement.

The transmission112included in the vehicle drive device110is disposed between the one end portion26aof the output rotating member26of the electric motor MG and the front wheels22, or specifically, disposed between the first clutch C1and the first differential gear device18. The transmission112includes a transmission input shaft114coupled via the first clutch C1to the one end portion26aof the output rotating member26, and a transmission output shaft116coupled to the first differential gear device18, can change a shift ratio between the transmission input shaft114and the transmission output shaft116(=rotation speed of the transmission input shaft114/rotation speed of the transmission output shaft116), and performs power transmission at the selected shift ratio. Specifically, although the transmission112may be a manual transmission, the transmission112is a stepped automatic transmission automatically making a shift in this example. In other words, the transmission112is an automatic transmission mechanism in which any of predefined multiple shift stages (shift ratios) is alternatively established, and includes a plurality of planetary gear devices and pluralities of hydraulically actuated clutches and brakes for performing the shift. Specifically, the transmission112is a two-speed automatic transmission. Therefore, the transmission112has a first-speed shift stage on the lower vehicle speed side and a second-speed shift stage on the higher vehicle speed side alternatively established, and a shift ratio of the transmission112is larger on the first-speed shift stage than the second-speed shift stage. The shift ratio of the transmission112corresponding to the first-speed shift stage is set in advance to the same shift ratio as the second shift ratio γ2 of the second reduction gear16. Therefore, when the transmission112is shifted to the first-speed shift stage, the shift ratio between the one end portion26aof the output rotating member26of the electric motor MG and the front wheels22is set to the same shift ratio as the shift ratio between the other end portion26bof the output rotating member26and the rear wheels24.

The vehicle drive device110of this example has the following effect in addition to the effects (A1) and (A2) of the first example described above. According to this example, the transmission112capable of changing a shift ratio is disposed between the one end portion26aof the output rotating member26of the electric motor MG and the front wheels.22. By shifting the transmission112, the shift ratio between the one end portion26aof the output rotating member26and the front wheels22is set to the same shift ratio as the shift ratio between the other end portion26bof the output rotating member26and the rear wheels24. Therefore, after the transmission112is shifted such that the shift ratio between the one end portion26aof the output rotating member26and the front wheels22is set to the same shift ratio as the shift ratio between the other end portion26bof the output rotating member26and the rear wheels24, the vehicle108can be put into a four-wheel drive state by coupling the one end portion26aof the output rotating member26to the front wheels22through the engagement of the first clutch C1and coupling the other end portion26bof the output rotating member26to the rear wheels24through the engagement of the second clutch C2.

Third Example

In the description of this example (third example), the points common with the first example will not be described and the points different from the first example will mainly be described.FIG. 3is a schematic for explaining a vehicle drive device210included in an electric vehicle208(hereinafter referred to as a vehicle208) of this example. As can be seen from comparison betweenFIGS. 1 and 3, the vehicle drive device210of this example is different from the vehicle drive device10of the first example in that the first reduction gear14is replaced with a first reduction gear214, the second reduction gear16is replaced with a second reduction gear216, and a third clutch C3, a fourth clutch C4, a fifth clutch C5, and a third reduction gear218are added. The vehicle drive device210is the same as the vehicle drive device10of the first example except the replacement.

As depicted inFIG. 3, the vehicle drive device210includes the electric motor MG, the first to fifth clutches C1to C5, the first reduction gear214, the second reduction gear216, the third reduction gear218, the first differential gear device18, and the second differential gear device20. The first clutch C1, the electric motor MG, and the second clutch C2in the vehicle drive device210are arranged in series on a first axis RC1that is the rotation axis of the electric motor MG. The third clutch C3, the third reduction gear218, the fifth clutch C5, and the fourth clutch C4are arranged in series on a second axis RC2parallel to the first axis RC1. The first reduction gear214is disposed across the first axis RC1and the second axis RC2and, therefore, the first reduction gear214includes a first reduction gear input shaft220having the first axis RC1as the rotation axis and a first reduction gear output shaft222having the second axis RC2as the rotation axis.

The second reduction gear216is also disposed across the first axis RC1and the second axis RC2and therefore includes a second reduction gear input shaft224having the first axis RC1as the rotation axis and a second reduction gear output shaft226having the second axis RC2as the rotation axis.

In the first reduction gear214, the first reduction gear input shaft220is coupled via the first clutch C1to the one end portion26aof the output rotating member26of the electric motor MG The first reduction gear output shaft222has one end coupled via the third clutch C3to the first differential gear device18and the other end relatively non-rotatably coupled to a third reduction gear input shaft228of the third reduction gear218. The first reduction gear214is the same as the first reduction gear14of the first example except the first reduction gear input shaft220having the first axis RC1as the rotation axis and the first reduction gear output shaft222having the second axis RC2as the rotation axis. Therefore, the shift ratio of the first reduction gear214(=rotation speed of the first reduction gear input shaft220/rotation speed of the first reduction gear output shaft222) is the first shift ratio γ1 same as the first reduction gear14of the first example. For confirmation, the one end and the other end of the first reduction gear output shaft222integrally rotate around the second axis RC2.

In the second reduction gear216, the second reduction gear input shaft224is coupled via the second clutch C2to the other end portion26bof the output rotating member26of the electric motor MG The second reduction gear output shaft226has one end coupled via the fourth clutch C4to the second differential gear device20and the other end coupled via the fifth clutch C5to a third reduction gear output shaft230of the third reduction gear218. The second reduction gear216is the same as the second reduction gear16of the first example except the second reduction gear input shaft224having the first axis RC1as the rotation axis and the second reduction gear output shaft226having the second axis RC2as the rotation axis. Therefore, the shift ratio of the second reduction gear216(=rotation speed of the second reduction gear input shaft224/rotation speed of the second reduction gear output shaft226) is the second shift ratio γ2 same as the second reduction gear16of the first example. For confirmation, the one end and the other end of the second reduction gear output shaft226integrally rotate around the second axis RC2.

The third reduction gear218has the same structure as the first reduction gear14or the second reduction gear16of the first example and changes a rotation speed at a constant third shift ratio γ3 (=rotation speed of the third reduction gear input shaft228/rotation speed of the third reduction gear output shaft230) for power transmission between the third reduction gear input shaft228and the third reduction gear output shaft230. The third shift ratio γ3 is a shift ratio different from both the first shift ratio γ1 of the first reduction gear214and the second shift ratio γ2 of the second reduction gear216. In this example, when the vehicle208runs with the power of the electric motor MG; the power may be transmitted from the third reduction gear input shaft228to the third reduction gear output shaft230or, inversely, the power may be transmitted from the third reduction gear output shaft230to the third reduction gear input shaft228.

The third clutch C3, the fourth clutch C4, and the fifth clutch C5are the same wet multi-plate type hydraulic friction engagement devices as the first clutch C1and the second clutch C2described in the first example and are engaged, released, and slipped by hydraulic control. The third clutch C3interposed between the first reduction gear214and the front wheels22as depicted inFIG. 3acts as a third power connecting/disconnecting device selectively interrupting the power transmission between the first reduction gear214and the front wheels22. In other words, the first reduction gear214is coupled to the front wheels22in a power connectable/disconnectable manner. The fourth clutch C4interposed between the second reduction gear216and the rear wheels24acts as a fourth power connecting/disconnecting device selectively interrupting the power transmission between the second reduction gear216and the rear wheels24. In other words, the second reduction gear216is coupled to the rear wheels24in a power connectable/disconnectable manner. The fifth clutch C5interposed between the second reduction gear216and the third reduction gear218acts as a fifth power connecting/disconnecting device selectively interrupting the power transmission between the second reduction gear216and the third reduction gear218. In other words, the second reduction gear216and the third reduction gear218are coupled to each other in a power connectable/disconnectable manner.

Describing the power transmission path of the vehicle drive device210configured in this way, the one end portion26aof the output rotating member26of the electric motor MG is coupled to the front wheels22sequentially through the first clutch C1, the first reduction gear214, the third clutch C3, the first differential gear device18, and the first drive axles28in series. On the other hand, the other end portion26bof the output rotating member26of the electric motor MG is coupled to the rear wheels24sequentially through the second clutch C2, the second reduction gear216, the fourth clutch C4, the second differential gear device20, and the second drive axles30in series. The front wheel22side of the first reduction gear214, i.e., the first reduction gear output shaft222, and the rear wheel24side of the second reduction gear216, i.e., the second reduction gear output shaft226, are coupled to each other through the fifth clutch C5and the third reduction gear218in series.

In other words, the one end portion26aof the output rotating member26of the electric motor MG is coupled to the front wheels22sequentially through the first clutch C1, the first reduction gear214, and the third clutch C3in series, and is coupled to the rear wheels24sequentially through the first clutch C1, the first reduction gear214, the third reduction gear218, the fifth clutch C5, and the fourth clutch C4in series. The other end portion26bof the output rotating member26of the electric motor MG is coupled to the rear wheels24sequentially through the second clutch C2, the second reduction gear216, and the fourth clutch C4in series, and is coupled to the front wheels22sequentially through the second clutch C2, the second reduction gear216, the fifth clutch C5, the third reduction gear218, and the third clutch C3in series. Therefore, the fifth clutch C5selectively interrupts the power transmission from the first clutch C1to the rear wheels24in the power transmission path from the one end portion26aof the output rotating member26to the rear wheels24and selectively interrupts the power transmission from the second clutch C2to the front wheels22in the power transmission path from the other end portion26bof the output rotating member26to the front wheels22.

FIG. 4is an engagement table for explaining a relationship between alternatively established shift stages and engagement states of the first to fifth clutches C1to C5in a gear shifting device232made up of the first to fifth clutches C1to C5, the first reduction gear214, the second reduction gear216, and the third reduction gear218. As depicted inFIG. 4, the gear shifting device232acts as a four-speed transmission. Specifically, a first shift stage G1is established by engaging the first clutch C1, the fourth clutch C4, and the fifth clutch C5and releasing the second clutch C2and the third clutch C3; a second shift stage G2is established by engaging the first clutch C1and the third clutch C3and releasing the second clutch C2, the fourth clutch C4, and the fifth clutch C5; a third shift stage G3is established by engaging the second clutch C2and the fourth clutch C4and releasing the first clutch C1, the third clutch C3, and the fifth clutch C5; and a fourth shift stage G4is established by engaging the second clutch C2, the third clutch C3, and the fifth clutch C5and releasing the first clutch C1and the fourth clutch C4. At the first shift stage G1, the power of the electric motor MG is transmitted to the rear wheels24and the shift ratio of the gear shifting device232in this case is the product of the first shift ratio γ1 and the third shift ratio γ3. At the second shift stage G2, the power of the electric motor MG is transmitted to the front wheels22and a shift ratio of the gear shifting device232in this case is the first shift ratio γ1. At the third shift stage G3, the power of the electric motor. MG is transmitted to the rear wheels24and the shift ratio of the gear shifting device232in this case is the second shift ratio γ2. At the fourth shift stage G4, the power of the electric motor MG is transmitted to the front wheels22and the shift ratio of the gear shifting device232in this case is the product of the second shift ratio γ2 and the inverse of the third shift ratio γ3. The numbers of the first to fourth shift stages G1to G4are given for convenience and the first to fourth shift stages G1to G4are not arranged in order of magnitude of the shift ratio.

When the second shift stage G2is established, the fourth clutch C4is engaged and the fifth clutch C5is slipped so that the power of the electric motor MG is transmitted not only to the front wheels22but also to the rear wheels24. Therefore, the vehicle208is put into the four-wheel drive state. In this case, the slipped clutch may be changed such that the fourth clutch C4is slipped while the fifth clutch C5is engaged. If the third shift stage G3is established, the third clutch C3is engaged and the fifth clutch C5is slipped so that the power of the electric motor MG is transmitted not only to the rear wheels24but also to the front wheels22. Therefore, the vehicle208is put into the four-wheel drive state. In this case, the slipped clutch may be changed such that the third clutch C3is slipped while the fifth clutch C5is engaged. The fifth clutch C5is engaged or slipped to put the vehicle208into the four-wheel drive state and therefore may be referred to as a four-wheel drive power connecting/disconnecting device.

The vehicle drive device210of this example has the following effect in addition to the effects (A1) and (A2) of the first example described above. According to this example, the one end portion26aof the output rotating member26of the electric motor MG is coupled to the front wheels (first drive wheels)22sequentially through the first clutch C1, the first reduction gear214, and the third clutch C3in series, and is coupled to the rear wheels (second drive wheels)24sequentially through the first clutch C1, the first reduction gear214, the third reduction gear218, the fifth clutch C5, and the fourth clutch C4in series. The fifth clutch C5selectively interrupts the power transmission from the first clutch C1to the rear wheels24in the power transmission path from the one end portion26aof the output rotating member26to the rear wheels24. Therefore, if the fourth clutch C4is engaged in a running state of transmitting the power of the electric motor MG from the one end portion26aof the output rotating member26to the front wheels22, the power of the electric motor MG can selectively be transmitted by the fifth clutch C5to the rear wheels24as well, thereby putting the vehicle208into the four-wheel drive state.

According to this example, the other end portion26bof the output rotating member26of the electric motor MG is coupled to the rear wheels24sequentially through the second clutch C2, the second reduction gear216, and the fourth clutch C4in series, and is coupled to the front wheels22sequentially through the second clutch C2, the second reduction gear216, the fifth clutch C5, the third reduction gear218, and the third clutch C3in series. The fifth clutch C5selectively interrupts the power transmission from the second clutch C2to the front wheels22in the power transmission path from the other end portion26bof the output rotating member26to the front wheels22. Therefore, if the third clutch C3is engaged in a running state of transmitting the power of the electric motor MG from the other end portion26bof the output rotating member26to the rear wheels24, the power of the electric motor MG can selectively be transmitted by the fifth clutch C5to the front wheels22as well, thereby putting the vehicle208into the four-wheel drive state. In other words, if the vehicle208is put into the four-wheel drive state by the fifth clutch C5, a gear change can be made between the electric motor MG and the front/rear wheels22,24by the first clutch C1and the second clutch C2.

According to this example, the one end portion26aof the output rotating member26of the electric motor MG is coupled to the front wheels22sequentially through the first clutch C1, the first reduction gear214, and the third clutch C3while the one end portion26bof the output rotating member26is coupled to the rear wheels24sequentially through the second clutch C2, the second reduction gear216, and the fourth clutch C4. The first reduction gear output shaft222acting as a rotating member on the front wheel22side of the first reduction gear214and the second reduction gear output shaft226acting as a rotating member on the rear wheel24side of the second reduction gear216are coupled to each other through the fifth clutch C5and the third reduction gear218in series. Therefore, the vehicle drive device210can alternatively establish the first shift stage G1with the one end portion26aof the output rotating member26coupled through the first reduction gear214and the third reduction gear218in series to the rear wheels24, the second shift stage G2with the one end portion26aof the output rotating member26coupled through the first reduction gear214to the front wheels22, the third shift stage G3with the other end portion26bof the output rotating member26coupled through the second reduction gear216to the rear wheels24, and the fourth shift stage G4with the other end portion26bof the output rotating member26coupled through the second reduction gear216and the third reduction gear218in series to the front wheels22, gear changes can be made in a total of four speeds. When the second shift stage G2or the third shift stage G3is established, the fifth clutch C5can be slipped to transmit power so as to put the vehicle208into the four-wheel drive state.

Although the examples of the present invention has been described in detail with reference to the drawings, these are merely an embodiment and the present invention can be implemented in variously modified and improved forms based on the knowledge of those skilled in the art.

For example, although the clutches C1to C5are wet multi-plate type hydraulic friction engagement devices in the first to third examples, the clutches C1to C5are not particularly limited in terms of the operational type given that the clutches are power connecting/disconnecting devices capable of connecting/disconnecting power transmission, and may be dry clutches or may be magnetic-powder-type, electromagnetic-type, and mechanical-type engagement devices such as powder (magnetic powder) clutches, electromagnetic clutches, and meshing type dog clutches.

Although the front wheels22correspond to the first drive wheels of the present invention and the rear wheels24correspond to the second drive wheels of the present invention in the first to third examples, conversely, the front wheels22may correspond to the second drive wheels of the present invention and the rear wheels24may correspond to the first drive wheels of the present invention.

Although the transmission112is a two-speed automatic transmission in the second example, the transmission112may be an automatic transmission with three or more speeds.

Although the shift ratio corresponding to the first-speed shift stage of the transmission112is the same as the second shift ratio γ2 of the second reduction gear16in the second example, the shift ratio corresponding to the second-speed shift stage instead of the fist-speed shift stage may be the same as the second shift ratio γ2 of the second reduction gear16.

Although the transmission112is a stepped transmission in the second example, the transmission112may be a continuously variable transmission (CVT) capable of continuously varying the shift ratio. If the transmission112is a continuously variable transmission, the second shift ratio γ2 of the second reduction gear16is preferably included in a shift ratio variation range.

Although the vehicle drive device110of the second example has the transmission112disposed between the one end portion26aof the output rotating member26of the electric motor MG and the front wheels22, the second reduction gear16may further be replaced with a transmission capable of varying a shift ratio. If two transmissions are disposed in this way, the shift stages of the respective transmissions are preferably set in advance such that the shift ratios become the same as each other at any shift stages selected by the respective transmissions.

Although the first reduction gear14and the first differential gear device18are devices separated from each other in the first example, the first reduction gear14and the first differential gear device18may make up one device having the respective functions together. Although the second reduction gear16and the second differential gear device20are devices separated from each other, the second reduction gear16and the second differential gear device20may make up one device having the respective functions together. The same applies to the second example and the transmission112and the first differential gear device18may make up one device having the respective functions together.

Although the fifth clutch C5is interposed between the second reduction gear216and the third reduction gear218inFIG. 3of the third example, the fifth clutch C5may not be interposed at this position and may be interposed between the first reduction gear214and the third reduction gear218.

Although the vehicle drive device210includes the third clutch C3, the fourth clutch C4, and the third reduction gear218in the third example, the vehicle drive device210may be configured without the third clutch C3, the fourth clutch C4, and the third reduction gear218as depicted inFIG. 5. In a vehicle drive device310without the third clutch C3, the fourth clutch C4, and the third reduction gear218depicted inFIG. 5, the one end portion26aof the output rotating member26of the electric motor MG is coupled via the first clutch C1to the front wheels22in the power transmission path and is coupled to the rear wheels24through the first clutch C1and the fifth clutch C5in series at the same shift ratio as the shift ratio between the one end portion26aand the front wheels22. The other end portion26bof the output rotating member26of the electric motor MG is coupled via the second clutch C2to the rear wheels24and is coupled to the front wheels22through the second clutch C2and the fifth clutch C5in series at the same shift ratio as the shift ratio between the other end portion26band the rear wheels24. In the vehicle drive device310ofFIG. 5, either the first clutch C1or the second clutch C2is engaged and the other is released so that the power of the electric motor MG is transmitted to at least either the front wheels22or the rear wheels24. The vehicle drive device310is shifted by switching the engaged clutch between the first clutch C1and the second clutch C2. While only either the first clutch C1or the second clutch C2is engaged, the engagement of the fifth clutch C5results in the four-wheel drive state, in which the power of the electric motor MG is transmitted to both the front wheels22and the rear wheels24, and the release of the fifth clutch C5results in a two-wheel drive state, in which the power of the electric motor MG is transmitted to only either the front wheels22or the rear wheels24.

Although each of the first reduction gears14,214, the second reduction gears16,216, and the third reduction gear218reduces and transmits the rotation speed of the input shaft to the output shaft in the first to third examples, conversely, the gears may increase and transmit the rotation speed of the input shaft to the output shaft. One of the first shift ratio γ1, the second shift ratio γ2, and the third shift ratio γ3 may be one.

Although each of the electric motor MG the first clutch C1, and the second clutch C2is a mechanically independent constituent element of the vehicle drive device10,110, or210in the first to third examples, the constituent elements may not mechanically be independent of each other and, for example, the electric motor MG the first clutch C1, and the second clutch C2may make up one device including those functions.

NOMENCLATURE OF ELEMENTS

10,110,210: vehicle drive device

14,214: first reduction gear

16,216: second reduction gear

26: output rotating member

26a: one end portion of the output rotating member26

26b: other end portion of the output rotating member26

218: third reduction gear

MG: electric motor