WO2014080279A1

WO2014080279A1 - Power transmission apparatus for vehicle

Info

Publication number: WO2014080279A1
Application number: PCT/IB2013/002829
Authority: WO
Inventors: Yoshiro OBAYASHI; Masayuki Arai
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2012-11-22
Filing date: 2013-11-18
Publication date: 2014-05-30
Also published as: JP2014104766A

Abstract

An ADD mechanism (7) and a motor generator (8) are provided between a front differential device (41) and a right front wheel (4R) in a rear wheel drive-based four-wheel-drive vehicle. In a two- wheel drive mode, the ADD mechanism (7) is released to stop rotation of a ring gear (43) fixed to the front differential device (41) in order to avoid co-rotation. In a four-wheel drive mode, the ADD mechanism (7) is engaged such that a drive force of the right front wheel (4R) is increased during a left turn by causing the motor generator (8) to output a torque in a normal rotation direction, and a drive force of a left front wheel (4L) is increased during a right turn by causing the motor generator (8) to output a torque in a reverse rotation direction.

Description

POWER TRANSMISSION APPARATUS FOR VEHICLE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates to a power transmission apparatus for a vehicle. More particularly, the invention relates to improvement of a power transmission apparatus capable of switching among states of torque transmission to a wheel.

2. Description of Related Art

[0002] As disclosed in, for example, Japanese Patent Application Publication No. 2004-9954 (JP 2004-9954 A) and Japanese Patent Application Publication No.

2010- 125896 (JP 2010-125896 A), there are conventional vehicles capable of switching between a two-wheel drive state and a four-wheel drive state. Vehicles of this type can be switched between a four-wheel drive state (hereinafter, also referred to as a four-wheel drive mode) in which power from a power source is respectively transmitted to main drive wheels and driven wheels and a two-wheel drive state (hereinafter, also referred to as a two-wheel drive mode) in which power from the power source is only transferred to the main drive wheels.

[0003] In addition, Japanese Patent Application Publication No. 2008-89075 (JP 2008-89075 A) discloses a configuration in which a hollow shaft is attached to a differential case of a differential device on a driven wheel side and an electric motor is coupled to the hollow shaft via a one-way clutch. Furthermore, by interposing a clutch between a planetary gear mechanism coupled to one of the driven wheels and the electric motor and placing the clutch in an engaged state, the configuration enables power of the electric motor to be transmitted to the one driven wheel via the planetary gear mechanism. Moreover, by switching between a state of causing the electric motor to generate a torque in a normal rotating direction and a state of causing the electric motor to generate a torque in a reverse rotating direction, switching can be performed between a state in which a right-side driven wheel is accelerated and a state in which a left-side driven wheel is accelerated.

SUMMARY OF THE INVENTION

[0004] The power transmission apparatus disclosed in JP 2008-89075 A is configured to be incapable of cutting off power transmission between a ring gear that is integrally provided on a differential case and the driven wheels. As a result, the ring gear or a propeller shaft rotates (co-rotates) with a rotation of the driven wheels in a two- wheel drive state and dragging loss may increase and fuel consumption rate may decline.

[0005] In addition, a technique which achieves with a simple configuration both a mechanism enabling power distribution control (so-called torque vectoring control) which is aimed to improve turning performance of the vehicle by setting drive forces of left and right wheels so as to differ from one another and a mechanism that switches between a two-wheel drive state and a four-wheel drive state has not yet been proposed.

[0006] The invention provides a power transmission apparatus for a vehicle, the power transmission apparatus being capable of avoiding co-rotation of the ring gear with a rotation of a wheel and improving vehicle travel performance by performing power distribution control on left and right wheels.

[0007] A first aspect of the invention relates to a power transmission apparatus for a vehicle. The power transmission apparatus includes a ring gear, a differential device, a transmission engaging/disengaging mechanism, and a motor. The ring gear configured to transmit power from a power source. The differential device is connected to the ring gear. The power transmission apparatus is configured to transmit power from a side gear of the differential device to at least one wheel of a pair of wheels. The transmission engaging/disengaging mechanism is provided on a first power transmission path between the side gear and the other wheel of the pair of wheels. The transmission

engaging/disengaging mechanism is configured to switch between a power transmitted state and a power non-transmitted state between the side gear and the other wheel. The motor is provided on a second power transmission path between the side gear and the one wheel or on the first power transmission path between the side gear and the other wheel.

[0008] In the power transmission apparatus, the motor may be configured to be switched in accordance with a vehicle travel state between a state in which the motor generates a torque in a rotating direction that causes the vehicle to advance and a state in which the motor generates a torque in a rotating direction that is opposite to the rotating direction, when the transmission engaging/disengaging mechanism is in the power transmitted state.

[0009] According to this matter specifying the invention, when the transmission engaging/disengaging mechanism (a power transmission engaging/disengaging

mechanism) is set to the power non-transmitted state, power transmission between the side gear of the differential device and the one wheel is cut off (power becomes

non-transmitted). Therefore, even when left and right wheels are rotating with travel of the vehicle, the ring gear does not rotate in a state in which power from the power source is not transmitted to the ring gear. In other words, since co-rotation of the ring gear with the rotations of the wheels can be avoided, dragging loss due to the co-rotation can be prevented from occurring and energy efficiency can be improved. For example, when an internal combustion engine is used as the power source, an improvement in fuel consumption rate can be achieved.

[0010] On the other hand, when the transmission engaging/disengaging mechanism is set to the power transmitted state, power transmission between the side gear of the differential device and the one wheel can be performed. In this case, by applying a torque from the motor to a power transmission path, a vehicle travel state with high travel performance can be realized. For example, when causing the motor to generate a torque in a vehicle advancing direction and applying the torque to a power transmission path, a torque on a wheel connected to a power transmission path on a side where the motor is arranged increases and a drive force of the wheel can be increased. Conversely, causing the motor to generate a torque in a vehicle backing direction (a braking torque) and applying the torque to a power transmission path, the torque on the wheel connected to the power transmission path on a side where the motor is arranged decreases while a torque that is transmitted to an opposite-side power transmission path via the differential device increases. As a result, a torque on a. wheel connected to the opposite-side power transmission path increases and a drive force of the wheel can be increased.

[0011] As described above, with this solution, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration.

[0012] The power transmission apparatus may be configured to cause the motor to generate electric power by transmitting a rotative force of the wheel to the motor via the first power transmission path to drive the motor when the vehicle decelerates and when the transmission engaging/disengaging mechanism is in the power transmitted state.

[0013] Accordingly, a braking force during vehicle deceleration travel can be converted into electric energy and used to charge a power storage device and the like, and an improvement in energy efficiency can be achieved.

[0014] Specific examples of arrangement positions of the transmission engaging/disengaging mechanism and the motor include the following.

[0015] In the power transmission apparatus, the transmission

engaging/disengaging mechanism and the motor may be provided on the first power transmission path.

[0016] A more specific configuration in this case involves providing the motor closer to one of the wheels than the transmission engaging/disengaging mechanism on the power transmission path between the side gear of the differential device and the wheel. In other words, in the power transmission apparatus, the motor may be provided closer to the other wheel than the transmission engaging/disengaging mechanism on the first power transmission path.

[0017] Alternatively, a configuration may be adopted in which the motor is provided closer to the side gear than the transmission engaging/disengaging mechanism on the power transmission path between the side gear of the differential device and the one wheel. In other words, in the power transmission apparatus, the motor may be provided closer to the side gear than the transmission engaging/disengaging mechanism on the first power transmission path.

[0018] In addition, other arrangement positions of the transmission

engaging/disengaging mechanism and the motor include a configuration in which the transmission engaging/disengaging mechanism is provided on the power transmission path between the side gear of the differential device and the one wheel and the motor is provided on the power transmission path between the side gear of the differential device and the other wheel. In other words, in the power transmission apparatus, the

transmission engaging/disengaging mechanism may be provided on the first power transmission path and the motor may be provided on the second power transmission path.

[0019] In particular, in the case of a configuration in which the motor is provided closer to the side gear than the transmission engaging/disengaging mechanism, a state in which co-rotation of the motor with a rotation of a wheel is avoided can be realized in the power non-transmitted state of the transmission engaging/disengaging mechanism. Even in this case, an improvement in energy efficiency can be achieved.

[0020] In addition, with a configuration in which the transmission

engaging/disengaging mechanism is provided on the power transmission path between the side gear of the differential device and the one wheel and the motor is provided on the power transmission path between the side gear of the differential device and the other wheel, the differential device can be arranged at an approximately central position in a width direction of the vehicle and the degree of freedom in arrangement positions of the transmission engaging/disengaging mechanism and the motor can be increased.

[0021] Specific examples of control of the motor when switching the transmission engaging/disengaging mechanism from the power non-transmitted state to the power transmitted state include performing torque control of the motor so that a rotation speed on the power transmission path closer to the side gear than the transmission

engaging/disengaging mechanism and a rotation speed on the power transmission path closer to the wheel than the transmission engaging/disengaging mechanism are

synchronized with each other. In other words, the power transmission apparatus may be configured to, when the transmission engaging/disengaging mechanism is switched from the power non-transmitted state to the power transmitted state, control the torque of the motor so as to synchronize the rotation speed on the first power transmission path closer to the side gear than the transmission engaging/disengaging mechanism and the rotation speed on the first power transmission path closer to the wheel than the transmission engaging/disengaging mechanism with each other.

[0022] Accordingly, an operation for switching the transmission

engaging/disengaging mechanism from the power non-transmitted state to the power transmitted state can be performed in a smooth manner and reliability of the switching operation can be increased. In addition, since a special synchronizing mechanism need not be provided, the complexity of the configuration does not increase.

[0023] The transmission engaging/disengaging mechanism can also be configured as follows. Specifically, the transmission engaging/disengaging mechanism includes a first power transmission engaging/disengaging mechanism portion (a first mechanism) and a second power transmission engaging/disengaging mechanism portion (a second mechanism). The first power transmission engaging/disengaging mechanism portion is configured to switch between the power transmitted state and the power non-transmitted state between the side gear of the differential device and the one wheel. In addition, the second power transmission engaging/disengaging mechanism portion is configured to switch between a released state in which the side gear of the differential device and a differential case are relatively rotatable and an engaged state in which the side gear of the differential device and the differential case are relatively nonrotatable. In other words, in the power transmission apparatus, the transmission engaging/disengaging mechanism may include a first mechanism which switches between the power transmitted state and the power non-transmitted state between the side gear and the other wheel and a second mechanism which switches between a released state in which the side gear and a case of the differential device are relatively rotatable and an engaged state in which the side gear and the case of the differential device are relatively nonrotatable. [0024] In this case, the transmission engaging/disengaging mechanism is configured to respectively couple the side gear of the differential device, the differential case, and the one wheel to one another to be relatively nonrotatable by establishing the power transmitted state between the side gear of the differential device and the one wheel using the first power transmission engaging/disengaging mechanism portion and placing the side gear of the differential device and the differential case in the engaged state in which the side gear and the differential case are relatively nonrotatable using the second power transmission engaging/disengaging mechanism portion. In other words, in the power transmission apparatus, the transmission engaging/disengaging mechanism may be configured to couple the side gear, the case, and the other wheel to one another to be relatively nonrotatable by establishing the power transmitted state between the side gear and the other wheel using the first mechanism and placing the side gear and the case in the engaged state using the second mechanism.

[0025] According to these configurations, by establishing the power

non-transmitted state between the side gear of the differential device and the one wheel using the first power transmission engaging/disengaging mechanism portion and making the side gear of the differential device and the differential case relatively rotatable using the second power transmission engaging/disengaging mechanism portion, co-rotation of the ring gear with rotations of the wheels can be avoided, dragging loss due to the co-rotation can be prevented from occurring, and energy efficiency can be improved.

[0026] In addition, by establishing the power non-transmitted state between the side gear of the differential device and the one wheel using the first power transmission engaging/disengaging mechanism portion and making the side gear of the differential device and the differential case relatively nonrotatable using the second power

transmission engaging/disengaging mechanism portion, a state is entered in which power transmitted from the power source to the ring gear is only transmitted to the one wheel via the side gear (one wheel-locked mode). In this configuration, by providing a motor on the power transmission path of the other wheel, respective drive forces of the left and right wheels can be adjusted by different drive sources (power sources such as an internal combustion engine and a motor) and control of drive forces of the respective wheels can be performed at high accuracy.

[0027] In addition, in a case where the power transmitted state is established between the side gear of the differential device and the one wheel using the first power transmission engaging/disengaging mechanism portion and the side gear of the differential device and the differential case are made relatively rotatable using the second power transmission engaging/disengaging mechanism portion, a torque from the motor is applied to the power transmission path and a vehicle travel state with high travel performance can be realized. In other words, as described earlier, when causing the motor to generate a torque in a vehicle advancing direction and applying the torque to a power transmission path, a torque on a wheel connected to a power transmission path on a side where the motor is arranged increases and a drive force of the wheel can be increased. Conversely, causing the motor to generate a torque in a vehicle backing direction (a braking torque) and applying the torque to a power transmission path, a torque on a wheel connected to a power transmission path on a side where the motor is arranged decreases while a torque that is transmitted to an opposite-side power transmission path via the differential device increases. As a result, a torque on a wheel connected to the opposite-side power transmission path increases and a drive force of the wheel can be increased (a torque vectoring mode).

[0028] Furthermore, in a case where the power transmitted state is established between the side gear of the differential device and the one wheel using the first power transmission engaging/disengaging mechanism portion and the side gear of the differential device and the differential case are made relatively nonrotatable using the second power transmission engaging/disengaging mechanism portion, by respectively coupling the side gear of the differential device, the differential case, and the one wheel to one another so as to be relatively nonrotatable, a state is entered in which a difference in rotation does not arise between the left and right wheels. Therefore, high traveling performance of the vehicle can be produced (a differential lock mode). Moreover, in this case, by causing the motor to generate a torque in a forward rotating direction, assistance of a forward drive force can be provided to the left and right wheels. As a result, even higher traveling performance can be produced.

[0029] Examples of configurations in a case where the respective solutions described above are applied to a vehicle that can be switched between a two-wheel drive state and a four-wheel drive state include the following. Specifically, a power switching mechanism is provided which is capable of switching between an engaged state in which power from the power source is transmitted to driven wheels, and a released state in which the power is not transmitted to the driven wheels. In addition, in a two-wheel drive state in which the power from the power source is only transmitted to main drive wheels, the power transmission engaging/disengaging mechanism enters the power non-transmitted state and the power switching mechanism enters the released state, and in a four-wheel drive state in which the power from the power source is transmitted to both the main drive wheels and the driven wheels, the power transmission engaging/disengaging mechanism enters the power transmitted state and the power switching mechanism enters the engaged state. In other words, in the power transmission apparatus, the vehicle may include a switching mechanism that switches between an engaged state in which power from the power source is transmitted to driven wheels, and a released state in which the power from the power source is not transmitted to the driven wheels. The transmission

engaging/disengaging mechanism may be configured to be in the power non-transmitted state in the two-wheel drive state in which the power from the power source is only transmitted to the main drive wheels. The switching mechanism may be configured to be in the released state in the two-wheel drive state. The transmission engaging/disengaging mechanism may be configured to be in the power transmitted state in the four-wheel drive state in which the power from the power source is transmitted to both the main drive wheels and the driven wheels. The switching mechanism may be configured to be in the engaged state in the four-wheel drive state.

[0030] According to this configuration, both a mechanism that enables power distribution control aimed to improve travel performance of the vehicle by setting drive forces of left and right wheels so as to differ from one another and a mechanism that switches between a two-wheel drive state and a four-wheel drive state can be realized.

[0031] In the invention, co-rotation of the ring gear with a rotation of a wheel can be avoided and an improvement of vehicle travel performance due to power distribution control performed on left and right wheels can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a schematic configuration diagram showing a four-wheel-drive vehicle according to a first embodiment;

FIG. 2 is a block diagram showing a schematic configuration of a control system of a four-wheel-drive vehicle;

FIGS. 3 A to 3E-are schematic configuration diagrams showing a front wheel-side power transmission system of a four-wheel-drive vehicle according to the first embodiment, wherein FIG. 3A is a diagram showing a state of the power transmission system in a fuel economy priority mode, FIG. 3B is a diagram showing a state of the power transmission system in a four-wheel drive mode during straight travel, FIG. 3C is a diagram showing a state of the power transmission system in a torque vectoring mode during a left turn, FIG. 3D is a diagram showing a state of the power transmission system in a torque vectoring mode during a right turn, and FIG. 3E is a diagram showing a state of the power

transmission system in a torque vectoring mode during regenerative deceleration;

FIG. 4 is a flow chart showing a procedure of travel mode switching control according to the first embodiment;

FIG. 5 is a diagram showing a motor target torque map used in a torque vectoring mode;

FIG. 6 is a schematic configuration diagram showing a front wheel-side power transmission system of a four-wheel-drive vehicle according to a first modification; FIG. 7 is a schematic configuration diagram showing a front wheel-side power transmission system of a four-wheel-drive vehicle according to a second modification;

FIG. 8 is a schematic configuration diagram showing a four-wheel-drive vehicle according to a third modification;

FIG. 9 is a schematic configuration diagram showing a four-wheel-drive vehicle according to a second embodiment;

FIGS. 10A to 10D are a schematic configuration diagrams showing a front wheel-side power transmission system of a four-wheel-drive vehicle according to the second embodiment, wherein FIG. 1 OA is a diagram showing a state of the power transmission system in an ADD mode, FIG. 10B is a diagram showing a state of the power transmission system in a one wheel-locked mode, FIG. 1 OC is a diagram showing a state of the power transmission system in a differential lock mode, and FIG. 10D is a diagram showing a state of the power transmission system in a torque vectoring mode;

FIG. 1 1 is a flow chart showing a procedure of travel mode switching control according to the second embodiment; and

FIG. 12 is a schematic configuration diagram showing a four-wheel-drive vehicle according to a modification of the second embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0033] Hereinafter, embodiments of this invention will be described with reference to the drawings.

[0034] (First embodiment)

First, a first embodiment will be described. In the first embodiment, a case will be described in which this invention is applied to a four-wheel-drive vehicle based on an FR (front engine, rear drive) system with a longitudinally mounted engine. Specifically, a case will be described in which the invention is applied to a rear wheel drive-based four-wheel-drive vehicle having a two-wheel drive mode in which power from an engine is only transmitted to rear wheels (main drive wheels) and a four-wheel drive mode in which the power from the engine is transmitted to both front wheels (driven wheels) and the rear wheels.

[0035] FIG. 1 is a schematic configuration diagram of a four-wheel-drive vehicle according to the first embodiment.

[0036] As shown in FIG. 1 , the four-wheel-drive vehicle includes an engine (a power source; an internal combustion engine) 1 which generates power for vehicle travel, a transmission (a transmission mechanism) 2 which changes a rotation speed of an output shaft (a crankshaft) of the engine 1 , and a transfer (a power distribution mechanism) 3 which distributes rotative power output from the transmission 2 to a front propeller shaft 40 on a side of front wheels 4L and 4R and to a rear propeller shaft 50 on a side of rear wheels 5L and 5R. Hereinafter, a power transmission system including the engine 1 , the transmission 2, the transfer 3, and the respective propeller shafts 40 and 50 will be described.

[0037] — Engine— The engine 1 is a conventional power apparatus which burns fuel and outputs power such as a gasoline engine or a diesel engine. For example, the engine 1 is configured to be controlled a throttle opening amount (a control amount of an intake air amount) of a throttle valve (not shown) provided in an intake passage, a fuel injection amount, an ignition timing, and the like. The control amounts are controlled by an electronic control unit (ECU) 100 (refer to FIG. 2) to be described later.

[0038] — Transmissio — The transmission 2 is arranged on a rear side of the engine 1 via a torque converter (not shown). The transmission 2 is, for example, a stepped (planetary gear-type) automatic transmission which sets gear stages (gear steps) using frictional engagement elements such as a plurality of clutches and a brake and a planetary gear device. The frictional engagement elements are hydraulic frictional engagement elements such as a multi-step clutch or a brake whose engagement is controlled by a hydraulic actuator. In addition, the clutches and the brake are configured so that engaged/released states are switched and excessive hydraulic pressure in the engaged/released states is controlled by excitation/non-excitation of a linear solenoid valve of a hydraulic pressure control device (not shown) and by current control. A configuration is adopted in which, by controlling hydraulic pressure that is applied to the frictional engagement elements in this manner, engagement and release of the respective factional engagement elements are controlled and, consequently, a predetermined shift step (for example, a predetermined shift step among six forward shift steps, or a reverse step) is established. In this manner, the transmission 2 changes a torque and a rotation speed by performing a shifting operation with respect to rotative power input from the engine 1 and outputs the changed torque and rotation speed to the transfer 3. Moreover, the transmission 2 may alternatively be a continuously variable transmission (CVT) (e.g., belt-type continuously variable transmission) which adjusts speed ratios in a stepless manner.

[0039] — Transfer— The transfer 3 is arranged on a rear side of the transmission 2 and includes a drive sprocket 31 , a driven sprocket 32, a chain 33 wound between the drive sprocket 31 and the driven sprocket 32, and the like. The drive sprocket 31 is attached to the rear propeller shaft 50 so as to be integrally rotatable. The driven sprocket 32 can be coupled to the front propeller shaft 40 via a disconnect mechanism (a power switching mechanism) 6 to be described later. Due to the chain 33 wound around the respective sprockets 31 and 32, at the transfer 3, a part of the power from the engine 1 is transmitted to the rear propeller shaft 50 and another part of the power is transmitted to the driven sprocket 32 via the drive sprocket 31 and the chain 33.

[0040] — Front propeller shaft and Front differential device— The front propeller shaft 40 extends forward from the transfer 3. The front propeller shaft 40 is coupled to left and right front drive shafts (a front drive shaft may be considered to be a shaft that constitutes a "power transmission path" according to the invention) 42L and 42R via a front differential device 41 that is a differential mechanism. The left and right front wheels 4L and 4R are coupled to the left and right front drive shafts 42L and 42R.

[0041] Specifically, a ring gear 43 is provided on a differential case (case) 41a of the front differential device 41 so as to be integrally rotatable. The ring gear 43 meshes with a drive pinion gear 44 that is integrally provided at a front end of the front propeller shaft 40. [0042] In addition, the front differential device 41 is configured to include a pair of pinion gears 41b provided inside the differential case 41a and a pair of side gears 41c which meshes with the pinion gears 41b. The respective pinion gears 41b are rotatably supported by a pinion gear shaft 45 that is arranged in a direction perpendicular to an axial direction of the front drive shafts 42L and 42R inside the differential case 41a. In other words, the respective pinion gears 41b revolve around the axis of the front drive shafts 42L and 42R together with the differential case 41a and are rotatable around an axis of the pinion gear shaft 45. When power transmitted via the transfer 3 and the front propeller shaft 40 is input to the differential case 41a via the ring gear 43, the differential case 41a rotates while the pinion gears 41b in the differential case 41a revolve around the axis of the front drive shafts 42L and 42R while causing the side gears 41 c to rotate. As a result, power is transmitted to the front drive shafts 42L and 42R. In addition, when a difference in rotations arises between the left and right front wheels 4L and 4R (the left and right front drive shafts 42L and 42R) during turning of the vehicle and the like, the left and right side gears 41c relatively rotate with a rotation of the pinion gears 41b around the axis of the pinion gear shaft 45 and absorb the difference in rotations between the left and right front drive shafts 42L and 42R.

[0043] — Rear propeller shaft and Rear differential device— The rear propeller shaft 50 extends backward from the transfer 3. The rear propeller shaft 50 is coupled to left and right rear drive shafts 52L and 52R via a rear differential device 51 that is a differential mechanism. The left and right rear wheels 5L and 5R are coupled to the left and right rear drive shafts 52L and 52R.

[0044] Specifically, a ring gear 53 is provided on a differential case (a case) 51a of the rear differential device 51 so as to be integrally rotatable. The ring gear 53 meshes with a drive pinion gear 54 that is integrally provided at a rear end of the rear propeller shaft 50.

[0045] Since the rear differential device 51 shares the same configuration as the front differential device 41 described earlier, a description of the configuration of the rear differential device 51 will be omitted. [0046] — Disconnect mechanism— A disconnect mechanism 6 is provided between the transfer 3 and the front propeller shaft 40. The disconnect mechanism 6 is configured to switch between a transmitted state in which torque transmission (power transmission) is performed between the transfer 3 and the front propeller shaft 40 and a non-transmitted state (a cutoff state) in which torque transmission is not performed.

[0047] Specifically, the disconnect mechanism 6 includes a transfer-side engaging plate 61 coupled to the driven sprocket 32 of the transfer 3 so as to be integrally rotatable, a propeller shaft-side engaging plate 62 attached to a rear end of the front propeller shaft 40 so as to be integrally rotatable, a disconnect sleeve 63 which switches between engagement and disengagement of the transfer-side engaging plate 61 and the propeller shaft-side engaging plate 62, and the like.

[0048] The transfer-side engaging plate 61 and the propeller shaft-side engaging plate 62 have a same diameter and splines are respectively formed on outer circumferential surfaces thereof. Meanwhile, a spline capable of engaging the splines formed on the respective outer circumferential surfaces of the transfer-side engaging plate 61 and the propeller shaft-side engaging plate 62 is formed on an inner circumferential surface of the disconnect sleeve 63. The disconnect sleeve 63 is configured to be slidingly moved in a direction of the axis of the front propeller shaft 40 by a disconnect actuator 64.

Accordingly, the disconnect sleeve 63 is capable of slidingly moving between a position at which the disconnect sleeve 63 only engages the propeller shaft-side engaging plate 62 (or the transfer-side engaging plate 61) (a position shown in FIG. 1) and a position at which the disconnect sleeve 63 engages both the propeller shaft-side engaging plate 62 and the transfer-side engaging plate 61 (a position shown in FIG. 3B). When the disconnect sleeve 63 is at the position where the disconnect sleeve 63 only engages one of the engaging plates (for example, the propeller shaft-side engaging plate 62), a torque is not transmitted from the transfer 3 to the front propeller shaft 40 (a non-transmitted state; a released state of the disconnect mechanism 6). Conversely, when the disconnect sleeve 63 is at the position where the disconnect sleeve 63 engages both the propeller shaft-side engaging plate 62 and the transfer-side engaging plate 61 , a torque can be transmitted from the transfer 3 to the front propeller shaft 40 (an engaged state of the disconnect mechanism 6). Moreover, examples of the disconnect actuator 64 include an electric actuator that uses an electric motor as a drive source, a hydraulic actuator, and the like.

[0049] — ADD mechanism— An automatic differential disconnect (ADD) mechanism (a power transmission engaging/disengaging mechanism) 7 is provided on the right-side front drive shaft 42R among the left and right front drive shafts 42L and 42R. The ADD mechanism 7 is configured to switch between a power transmitted state in which torque transmission (power transmission) is performed between the front differential device 41 and the right front wheel 4R and a power non-transmitted state (a cutoff state) in which torque transmission is not performed.

[0050] Specifically, the right-side front drive shaft 42R is divided into a differential-side front drive shaft 42Ra that is positioned on a side of the front differential device 41 and a wheel-side front drive shaft 42Rb that is positioned on a side of the right front wheel 4R. The ADD mechanism 7 includes a differential-side engaging plate 71 attached to an outside end of the differential-side front drive shaft 42Ra in the vehicle width direction, a front wheel-side engaging plate 72 attached to an inside end of the. wheel-side front drive shaft 42Rb in the vehicle width direction, an ADD sleeve 73 which switches between engagement and disengagement of the differential-side engaging plate 71 and the front wheel-side engaging plate 72, and the like.

[0051] The differential-side engaging plate 71 and the front wheel-side engaging plate 72 have a same diameter and splines are respectively formed on outer circumferential surfaces thereof. Meanwhile, a spline capable of engaging the splines formed on the respective outer circumferential surfaces of the differential-side engaging plate 71 and the front wheel-side engaging plate 72 is formed on an inner circumferential surface of the ADD sleeve 73. The ADD sleeve 73 is configured to be slidingly moved in a direction of the axis of the front drive shaft 42R by an ADD actuator 74. Accordingly, the ADD sleeve 73 is capable of slidingly moving between a position at which the ADD sleeve 73 only engages the front wheel-side engaging plate 72 (or the differential-side engaging plate 71 ) (a position shown in FIG. 1) and a position at which the ADD sleeve 73 engages both the front wheel-side engaging plate 72 and the differential-side engaging plate 71 (a position shown in FIG. 3B). When the ADD sleeve 73 is at the position where the ADD sleeve 73 only engages one of the engaging plates (for example, the front wheel-side engaging plate 72), a torque is not transmitted from the front differential device 41 to the right front wheel 4R (a non-transmitted state; a released state of the ADD mechanism 7). Conversely, when the ADD sleeve 73 is at the position where the ADD sleeve 73 engages both the front wheel-side engaging plate 72 and the differential-side engaging plate 71 , a state is entered in which a torque can be transmitted from the front differential device 41 to the right front wheel 4R (an engaged state of the ADD mechanism 7). Moreover, examples of the ADD actuator 74 include an electric actuator that uses an electric motor as a drive source, a hydraulic actuator, and the like.

[0052] — Motor generator— A motor generator (a motor) 8 is arranged on the wheel-side front drive shaft 42Rb. The motor generator 8 is an alternating-current (AC) synchronous generator including a rotor 81 and a stator 82. The rotor 81 is made of a permanent magnet and. is integrally rotatable with the wheel-side front drive shaft 42Rb. The stator 82 is wound by a three-phase winding. The motor generator 8 functions both as a motor (an electric motor) and as a generator.

[0053] In addition, the motor generator 8 is connected to a battery (a power storage device) B via an inverter 200 (refer to FIG. 2). The inverter 200 is controlled by the ECU 100 and regeneration or power running (assistance) of the motor generator 8 is set by controlling the inverter 200. In this case, regenerative power is charged into the battery B via the inverter 200. In addition, drive power for the motor generator 8 is supplied from the battery B via the inverter 200.

[0054] — ECU— he ECU 100 is an electronic control device which executes operation control of the engine 1 , control of the disconnect actuator 64 and the ADD actuator 74, torque control of the motor generator 8, and the like and includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), a backup RAM, and the like. [0055] The ROM stores various control programs, maps which are referenced when the various control programs are executed, and the like. The CPU executes arithmetic processing based on the various control programs and the maps stored in the ROM. The RAM is a memory that temporarily stores the result of computations by the CPU, data input from the respective sensors, and the like. The backup RAM is a ' non- volatile memory that stores data and the like which must be stored when, for example, the engine 1 is shut down.

[0056] As shown in FIG. 2, connected to the ECU 100 are: a crank position sensor 91 which transmits a pulse signal each time the crankshaft of the engine 1 makes a rotation of a predetermined angle; a throttle opening amount sensor 92 which detects an opening amount of a throttle valve arranged in an intake passage of the engine 1 ; an accelerator depression amount sensor 93 which detects an accelerator depression amount Acc that is an accelerator pedal depression amount; a brake pedal sensor 94 which detects a pedal force applied to a brake pedal (brake pedal force); a two wheel drive/four wheel drive (2 WD/4 WD) changeover switch 95 which is arranged in a vicinity of a driver's seat and which is operated by a driver; a left front wheel rotation speed sensor 96L which detects a rotation speed of the left front wheel 4L; a right front wheel rotation speed sensor 96R which detects a rotation speed of the right front wheel 4R; a left rear wheel rotation speed sensor 97L which detects a rotation speed of the left rear wheel 5L; a right rear wheel rotation speed sensor 97R which detects a rotation speed of the right rear wheel 5R; a steering angle sensor 98 which detects a steering angle that is an amount by which a steering wheel (not shown) is steered (an amount of steering by the driver); a disconnect sleeve position detection sensor 99A which detects a sliding movement position of the disconnect sleeve 63; an ADD sleeve position detection sensor 99B which detects a sliding movement position of the ADD sleeve 73; and the like. Further connected to the ECU 100 are a water temperature sensor which detects engine cooling water temperature, an airflow meter which detects an intake air amount, a shift position sensor which detects a shift lever position of the transmission 2, and the like. Signals from the respective sensors are input to the ECU 100. [0057] Based on output signals of the various sensors, the ECU 100 executes various controls of the engine 1 including throttle opening amount control (intake air amount control), fuel injection amount control, and ignition timing control of the engine 1. In addition, the ECU 100 executes engagement/release control of the disconnect mechanism 6 which controls a sliding movement position of the disconnect sleeve 63 using the disconnect actuator 64 and engagement/release control of the ADD mechanism 7 which controls a sliding movement position of the ADD sleeve 73 using the ADD actuator 74 to switch between a two- wheel drive state and a four-wheel drive state. Furthermore, the ECU 100 performs output torque control of the motor generator 8.

[0058] Specifically, when the disconnect mechanism 6 is released by the disconnect actuator 64 and the ADD mechanism 7 is released by the ADD actuator 74, a drive state of the vehicle is a two-wheel drive state (refer to the states shown in FIGS. 1 and 3A). On the other hand, when the disconnect mechanism 6 is engaged by the disconnect actuator 64 and the ADD mechanism 7 is engaged by the ADD actuator 74, the drive state of the vehicle is a four-wheel drive state (refer to the state shown in FIG. 3B).

[0059] In the two-wheel drive state, the transfer 3 and the front propeller shaft 40 are cut off from each other by the disconnect mechanism 6 and therefore a torque is not transmitted between the transfer 3 and the front propeller shaft 40. In other words, a power transmission path is established which transmits a torque input from the

transmission 2 to the transfer 3 only to the rear propeller shaft 50. Accordingly, in the two-wheel drive state, a torque is only transmitted to the rear wheels 5L and 5R and a torque is not transmitted to the front wheels 4L and 4R. In addition, since the ADD mechanism 7 is released in the two-wheel drive state, a state is entered in which the front differential device 41 (more specifically, the side gear 41 c of the front differential device 41) and the right front wheel 4R are cut off from each other (the power non-transmitted state) and the respective front wheels 4L and 4R are capable of rotation without requiring rotations of the differential case 41 a and the ring gear 43 of the front differential device 41. As described above, in the two- wheel drive state, rotations of the front propeller shaft 40 and the ring gear 43 stop due to being released by the disconnect mechanism 6 and the ADD mechanism 7, and dragging loss due to the rotations of the front propeller shaft 40 and the ring gear 43 no longer occurs.

[0060] Meanwhile, in the four-wheel drive state, the transfer 3 and the front propeller shaft 40 are coupled to each other by the disconnect mechanism 6 and a torque is transmitted between the transfer 3 and the front propeller shaft 40. In other words, a power transmission path is established which transmits a torque input from the

transmission 2 to the transfer 3 to both the front propeller shaft 40 and the rear propeller shaft 50. In addition, since the ADD mechanism 7 is engaged in the four-wheel drive state, a torque is transmitted between the front differential device 41 (more specifically, the side gear 41 c of the front differential device 41 ) and the right front wheel 4R (the power transmitted state). Accordingly, in the four-wheel drive state, torque is respectively transmitted to the front wheels 4L and 4R and the rear wheels 5L and 5R.

[0061] Furthermore, in the four-wheel drive state, when causing the motor generator 8 to generate a torque in a normal rotating direction (a vehicle advancing direction), a torque in a forward rotating direction of the right-side front drive shaft 42R increases and a drive force of the right front wheel 4R increases. On the other hand, when causing the motor generator 8 to generate a torque in a reverse rotating direction (a vehicle backing direction), the torque acts as a braking force with respect to the forward rotating direction of the right-side front drive shaft 42R and the drive force of the right front wheel 4R decreases. Accordingly, a drive force of the left front wheel 4L increases (a detailed description will be given later).

[0062] — Vehicle travel modes— Next, travel modes of the vehicle configured as shown above will be described.

[0063] A four-wheel-drive vehicle according to the first embodiment is

configured to be switchable between travel in a fuel economy priority mode in which a two-wheel drive state is entered and travel in a four-wheel drive mode in accordance with a sliding movement position of the disconnect sleeve 63 of the disconnect mechanism 6 and a sliding movement position of the ADD sleeve 73 of the ADD mechanism 7. In addition, the four-wheel drive mode is configured to be further switched to four travel modes. Specifically, the four-wheel drive mode can be switched to a four-wheel drive mode during straight travel, a torque vectoring mode during a left turn, a torque vectoring mode during a right turn, and a torque vectoring mode during regenerative deceleration. A detailed description will be given below.

[0064] <Fuel economy priority mode>

First, the fuel economy priority mode will be described.

[0065] FIG. 3A is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the fuel economy priority mode. As shown in FIG. 3A, in the fuel economy priority mode, the disconnect sleeve 63 is moved to a position at which the disconnect sleeve 63 only engages the propeller shaft-side engaging plate 62 and the disconnect mechanism 6 is released. In addition, the ADD sleeve 73 is moved to a position at which the ADD sleeve 73 only engages the front wheel-side engaging plate 72, and the ADD mechanism 7 is also released. Accordingly, a torque is not transmitted from the transfer 3 to the front propeller shaft 40 and a torque is similarly not transmitted between the front differential device 41 and the right front wheel 4R or, in other words, the left and right front wheels 4L and 4R are cut off.

[0066] Therefore, the drive state of the vehicle in the fuel economy priority mode is the two- wheel drive state and a power transmission path is established which transmits a torque input from the transmission 2 to the transfer 3 only to the rear propeller shaft 50. In the two-wheel drive state, a torque is only transmitted to the rear wheels 5L and 5R and a torque is not transmitted to the front wheels 4L and 4R.

[0067] In addition, in the fuel economy priority mode, since the disconnect mechanism 6 and the ADD mechanism 7 are both released, rotations of the front propeller shaft 40 and the ring gear 43 are stopped as described above. Since dragging loss due to the rotations of the front propeller shaft 40 and the ring gear 43 no longer occurs, an improvement in fuel consumption rate can be achieved.

[0068] <Four-wheel drive mode during straight travel>

Next, the four-wheel drive mode during straight travel will be described. [0069] FIG. 3B is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the four-wheel drive mode during straight travel. As shown in FIG. 3B, in the four-wheel drive mode during straight travel, the disconnect sleeve 63 is moved to a position at which the disconnect sleeve 63 engages both the propeller shaft-side engaging plate 62 and the transfer-side engaging plate 61 and the disconnect mechanism 6 is engaged. In addition, the ADD sleeve 73 is moved to a position at which the ADD sleeve 73 engages both the front wheel-side engaging plate 72 and the differential-side engaging plate 71 and the ADD mechanism 7 is also engaged. Accordingly, a state is entered in which a part of the torque transmitted to the transfer 3 is transmitted to the front propeller shaft 40 and approximately equally distributed to the left and right front wheels 4L and 4R from the front differential device 41.

[0070] As described above, in the four-wheel drive mode, a power transmission path is established which transmits a torque input from the transmission 2 to the transfer 3 to both. the front propeller shaft 40 and the rear propeller shaft 50 and a torque is transmitted to both the front wheels 4L and 4R and the rear wheels 5L and 5R.

[0071] In addition, in the four-wheel drive mode during straight travel, energization of the motor generator 8 is basically stopped and a torque is not generated by ■ the motor generator 8. Moreover, since the rotor 81 of the motor generator 8 integrally rotates with the right-side front drive shaft 42R, a difference in inertial forces arises between the left and right front drive shafts 42L and 42R due to the presence of the rotor 81. Therefore, when a difference in drive forces of the left and right front wheels 4L and 4R arises due to the difference in inertial forces, torque control of the motor generator 8 may be performed so as to eliminate the difference in drive forces. For example, during startup in the four-wheel drive mode, a torque in the normal rotating direction may be generated by the motor generator 8 in order to favorably secure startup performance so that a difference in drive forces of the left and right front wheels 4L and 4R does not arise.

[0072] <Torque vectoring mode during left turn>

Next, a torque vectoring mode during a left turn will be described. [0073] FIG. 3C is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the torque vectoring mode during a left turn. As shown in FIG. 3C, in the torque vectoring mode during a left turn, both the disconnect mechanism 6 and the ADD mechanism 7 are engaged in a similar manner to the four-wheel drive mode during straight travel.

[0074] In addition, torque control of the motor generator 8 is performed in order to generate a torque in the normal rotating direction (the vehicle advancing direction) and, accordingly, a drive force in the forward rotating direction at the right front wheel 4R is increased. In other words, power from the engine 1 transmitted to the front differential device 41 via the front propeller shaft 40 is transmitted to the left front wheel 4L via the left-side front drive shaft 42L. On the other hand, power from the engine 1 transmitted to the front differential device 41 via the front propeller shaft 40 is transmitted to the right front wheel 4R via the right-side front drive shaft 42R and, at the same time, the torque generated by the motor generator 8 is also transmitted to the right front wheel 4R via the right-side front, drive shaft 42R. In other words, due to the torque transmitted to the right front wheel 4R exceeding the torque transmitted to the left front wheel 4L, the drive force of the right front wheel 4R relatively increases and turning ability during a left turn of the vehicle is enhanced.

[0075] <Torque vectoring mode during right turn>

Next, a torque vectoring mode during a right turn will be described.

[0076] FIG. 3D is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the torque vectoring mode during a right turn. As shown in FIG. 3D. in the torque vectoring mode during a right turn, both the disconnect mechanism 6 and the ADD mechanism 7 are engaged in a similar manner to the four-wheel drive mode during straight travel and the torque vectoring mode during a left turn.

[0077] In addition, torque control of the motor generator 8 is performed in order to generate a torque (a braking torque) in the reverse rotating direction (the vehicle backing direction) and, accordingly, a drive force in the forward rotating direction at the right front wheel 4R is reduced. In other words, power from the engine 1 transmitted to the front differential device 41 via the front propeller shaft 40 is transmitted to the left front wheel 4L via the left-side front drive shaft 42L. On the other hand, power from the engine 1 transmitted to the front differential device 41 via the front propeller shaft 40 is transmitted to the right front wheel 4R via the right-side front drive shaft 42R and, at the same time, the torque (a braking torque) generated by the motor generator 8 is also transmitted to the right front wheel 4R. As the torque transmitted to the right front wheel 4R decreases in this manner, the torque transmitted to the left front wheel 4L increases. In other words, a reaction force of the braking torque is transmitted from the right-side front drive shaft 42R to the front differential device 41, the left and right side gears 41c relatively rotate with the rotation of the pinion gears 41 b around the pinion gear shaft 45 (a rotation speed of the left-side side gear 41c increases relative to a rotation speed of the right-side side gear 41c), and the torque transmitted to the left-side front drive shaft 42L is increased. Accordingly, due to the torque transmitted to the left front wheel 4L exceeding the torque transmitted to the right front wheel 4R, the drive force of the left front wheel 4L relatively increases and turning ability during a right turn of the vehicle is enhanced.

[0078] <Torque vectoring mode during regenerative deceleration>

Next, a torque vectoring mode during regenerative deceleration will be described.

[0079] FIG. 3E is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the torque vectoring mode during regenerative deceleration. As shown in FIG. 3E, in the torque vectoring mode during regenerative deceleration, both the disconnect mechanism 6 and the ADD mechanism 7 are engaged in a similar manner to the four-wheel drive mode and the respective torque vectoring modes.

[0080] In addition, by controlling the inverter 200, the motor generator 8 is placed in a driven state by a rotative force of the right-side front drive shaft 42R (a rotative force of the right front wheel 4R due to a frictional force between the road surface and the right front wheel 4R during travel). Accordingly, power generation is performed by the motor generator 8. The power regenerated by the motor generator 8 is charged to the battery B via the inverter 200.

[0081] — Travel mode switching control— Next, travel mode switching control will be described. The travel mode switching control is for selecting any of the vehicle travel modes described earlier in accordance with a vehicle travel state and the like.

[0082] FIG. 4 is a flow chart showing a procedure of the travel mode switching control. The flow chart shown in FIG. 4 is executed every few milliseconds during travel of the vehicle (when a vehicle speed calculated based on output signals of the respective wheel rotation speed sensors 96L, 96R, 97L, and 97R is equal to or greater than a predetermined vehicle speed (for example, 5 km/h)).

[0083] First, in step ST1 , output values of the respective sensors are read. For example, information that is read include the accelerator depression amount Acc detected by the accelerator depression amount sensor 93, information on a brake pedal force detected by the brake pedal sensor 94, information on respective wheel rotation speeds detected by the respective wheel rotation speed sensors 96L, 96R, 97L, and 97R, and .·- information on a steering angle of the steering wheel detected by the steering angle sensor 98. In addition, a signal (a 2WD/4WD changeover signal) from the 2 WD/4 WD changeover switch 95 that is operated by the driver is also read.

[0084] Subsequently, the procedure proceeds to step ST2 and a determination is made on whether or not four-wheel drive travel conditions are satisfied. Examples of the four-wheel drive travel conditions include a case where four-wheel drive travel has been selected by the driver using the 2WD/4WD changeover switch 95. In addition, a determination that four-wheel drive travel conditions are satisfied is also made when a mutual deviation among the respective wheel rotation speeds detected by the respective wheel rotation speed sensors 96L, 96R, 97L, and 97R is equal to or greater than a predetermined value (when a mutual deviation among the respective wheel rotation speeds is equal to or greater than a predetermined value due to traveling on a rough road, traveling on a low μ road, and the like). [0085] When the four-wheel drive travel conditions are not satisfied and a determination of NO is made in step ST2, the procedure proceeds to step ST3 and travel in the fuel economy priority mode is performed. In other words, as shown in FIG. 3A, both the disconnect mechanism 6 and the ADD mechanism 7 are released and the output torque from the motor generator 8 is controlled to "0". Moreover, in this case, by controlling the disconnect actuator 64 while detecting the sliding movement position of the disconnect sleeve 63 by the disconnect sleeve position detection sensor 99A and controlling the ADD actuator 74 while detecting the sliding movement position of the ADD sleeve 73 by the ADD sleeve position detection sensor 99B, both the disconnect mechanism 6 and the ADD mechanism 7 are released.

[0086] On the other hand, when the four-wheel drive travel conditions are satisfied and a determination of YES is made in step ST2, the procedure proceeds to step ST4 and a transition is made to a travel state in the four-wheel drive mode. In other words, the disconnect mechanism 6 and the ADD mechanism 7 are both engaged. Even in this case, by controlling the disconnect actuator 64 while detecting the sliding movement position of the disconnect sleeve 63 by the disconnect sleeve position detection sensor 99A and controlling the ADD actuator 74 while detecting the sliding movement position of the ADD sleeve 73 by the ADD sleeve position detection sensor 99B, both the disconnect mechanism 6 and the ADD mechanism 7 are engaged.

[0087] Subsequently, in step ST5, a determination is made on whether or not the vehicle is currently decelerating. Specifically, the vehicle is determined to be

decelerating when the accelerator depression amount Acc detected by the accelerator depression amount sensor 93 is equal to or smaller than a predetermined depression amount or when the brake pedal force detected by the brake pedal sensor 94 is equal to or greater than a predetermined value. Thresholds of the accelerator depression amount Acc and the brake pedal force used to determine that the vehicle is decelerating are

appropriately set.

[0088] When the vehicle is not decelerating and a determination of NO is made in step ST5, the procedure proceeds to step ST6 and a determination is made on whether or not the steering angle of the steering wheel that is detected by the steering angle sensor 98 is approximately "0" or, in other words, whether or not the driver intends to travel straight.

[0089] When the steering angle of the steering wheel is approximately "0" and the driver intends to travel straight, a determination of YES is made in step ST6 and the procedure proceeds to step ST7. In step ST7, a determination is made on whether or not a difference has arisen between the rotation speed of the left front wheel 4L that is detected by the left front wheel rotation speed sensor 96L and the rotation speed of the right front wheel 4R that is detected by the right front wheel rotation speed sensor 96R. In other words, a determination is made on whether or not a difference in rotation speeds has arisen due to a difference in surface resistances at the left front wheel 4L and the right front wheel 4R and stable straight travel cannot be performed even though the steering angle of the steering wheel is approximately "0". Moreover, causes of the difference in rotation speeds between the left and right front wheels 4L and 4R include a difference in inertial forces of the left and right front drive shafts 42L and 42R due to the presence of the motor generator 8.

[0090] When a difference has not arisen between the rotation speed of the left front wheel 4L and the rotation speed of the right front wheel 4R or when the difference is smaller than the predetermined value and a determination of NO is made in step ST7, a return is made as-is without performing output torque control of the motor generator 8. In other words, travel in the four-wheel drive mode (the four-wheel drive mode during straight travel described with reference to FIG. 3B) is performed without performing torque control of the motor generator 8.

[0091] On the other hand, when a difference has arisen between the rotation speed of the left front wheel 4L and the rotation speed of the right front wheel 4R and a determination of YES is made in step ST7, the procedure proceeds to step ST8 and output torque control of the motor generator 8 is performed. Specifically, the output torque of the motor generator 8 is controlled so that a torque (an assistive torque) is applied to the wheel 4R (or 4L) having a lower rotation speed. [0092] Specifically, when the rotation speed of the right front wheel 4R is lower than the rotation speed of the left front wheel 4L, torque control of the motor generator 8 is performed in order to generate a torque in the normal rotating direction (the vehicle advancing direction) and, accordingly, a drive force of the right front wheel 4R in the forward rotating direction is increased. On the other hand, when the rotation speed of the left front wheel 4L is lower than the rotation speed of the right front wheel 4R, torque control of the motor generator 8 is performed in order to generate a torque in the reverse rotating direction (the vehicle backing direction) and, accordingly, a torque transmitted to the left front wheel 4L is increased with the reduction of a torque transmitted to the right front wheel 4R and a drive force of the left front wheel 4L in the forward rotating direction is increased.

[0093] At this point, the greater the difference between the rotation speed of the left front wheel 4L and the rotation speed of the right front wheel 4R, the greater the torque output from the motor generator 8 in order to equalize the drive forces of the respective wheels 4L and 4R and enhance straight travel performance of the vehicle.

[0094] On the other hand, when the steering angle of the steering wheel is not approximately "0" and the driver intends to make a turn (a left turn or a right turn), a determination of NO is made in step ST6 and the procedure proceeds to step ST9.

[0095] In step ST9, a determination is made on whether or not the steering angle of the steering wheel that is detected by the steering angle sensor 98 is on a left turn side.

[0096] When the steering angle of the steering wheel is on the left turn side and a determination of YES is made in step ST9, the procedure proceeds to step ST 10 and a transition is made to the torque vectoring mode during a left turn (FIG. 3C). In other words, torque control of the motor generator 8 is performed in order to generate a torque (a positive torque) in the normal rotating direction (the vehicle advancing direction) and, accordingly, a drive force in the forward rotating direction at the right front wheel 4R is increased. As a result, turning ability of a left turn of the vehicle is enhanced.

[0097] In this torque control of the motor generator 8, a torque in the normal rotating direction is controlled according to a motor target torque map shown in FIG. 5. The motor target torque map extracts a motor target torque using an accelerator depression amount and a steering angle as parameters, and is created in advance by an experiment, a simulation, or the like and stored in the ROM of the ECU 100. As shown in FIG. 5, the greater the accelerator depression amount and the greater the steering angle, a greater value is set as the motor target torque. Since it is estimated that the greater the accelerator depression amount and the greater the steering angle, the higher the travel performance (turning performance) that is required by the driver, the motor target torque is set to a greater value in order to enhance the turning ability of the vehicle.

[0098] On the other hand, when the steering angle of the steering wheel is on the right turn side and a determination of NO is made in step ST9, the procedure proceeds to step ST1 1 and a transition is made to the torque vectoring mode during a right turn (FIG. 3D). In other words, torque control of the motor generator 8 is performed in order to generate a torque (a braking torque) in the reverse rotating direction (the vehicle backing direction) and, accordingly, a drive force in the forward rotating direction at the left front wheel 4L is increased. As a result, turning ability of a right turn of the vehicle is enhanced.

[0099] In this torque control of the motor generator 8, the greater the accelerator depression amount and the greater the steering angle, a greater value is set as the braking torque.

[0100] In addition, when the vehicle is decelerating and a determination of YES is made in step ST5, the procedure proceeds to step S12 and a transition is made to the torque vectoring mode during regenerative deceleration (FIG. 3E). In other words, by controlling the inverter 200, the motor generator 8 is placed in a driven state by the rotative force of the right-side front drive shaft 42R to cause the motor generator 8 to perform power generation. The power regenerated by the motor generator 8 is charged to the battery B via the inverter 200.

[0101] As described above, in the first embodiment, in the fuel economy priority mode, by releasing both the disconnect mechanism 6 and the ADD mechanism 7, rotations of the front propeller shaft 40 and the ring gear 43 can be stopped. As a result, dragging loss due to the rotations of the front propeller shaft 40 and the ring gear 43 can be eliminated and an improvement in fuel consumption rate can be achieved. In addition, in the torque vectoring modes during respective turns, high turning performance can be realized by the torque control of the motor generator 8. Furthermore, in the torque vectoring mode during regenerative deceleration, a braking force during vehicle deceleration can be converted into electric energy to be used to charge the battery B and an improvement in energy efficiency can be achieved. As described above, in the first embodiment, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration.

[0102] In addition, according to the first embodiment, when switching from the two-wheel drive mode to the four-wheel drive mode (including the respective torque vectoring modes) or, in other words, when a transition is made from a state in which the ADD sleeve 73 of the ADD mechanism 7 only engages the .front wheel-side engaging plate 72 to a state in which the ADD sleeve 73 engages both the front wheel -side engaging plate 72 and the differential-side engaging plate 71 , the output torque of the motor generator 8 can be controlled in order to approximately match the rotation speed of the wheel-side front drive shaft 42Rb to the rotation speed of the differential-side front drive shaft 42Ra. In other words, the ADD sleeve 73 can be slidingly moved in a state in which the rotation speed of the front wheel-side engaging plate 72 that is provided on the wheel-side front drive shaft 42Rb so as to be integrally rotatable and the rotation speed of the

differential-side engaging plate 71 that is provided on the differential-side front drive shaft 42Ra so as to be integrally rotatable are synchronized with one another. As a result, the engagement of the ADD sleeve 73 to the differential-side engaging plate 71 can be performed in a smooth manner and reliability of the engagement operation can be increased. In addition, since a special synchronizing mechanism need not be provided, the complexity of the configuration does not increase.

[0103] (First modification) Next, a first modification will be described. The first modification differs from the first embodiment in arrangement positions of the ADD mechanism 7 and the motor generator 8. Since other configurations and operations are similar to those of the first embodiment, only the arrangement positions of the ADD mechanism 7 and the motor generator 8 will be described below.

[0104] FIG. 6 is a schematic configuration diagram showing a power

transmission system on the side of the front wheels 4L and 4R in a four-wheel-drive vehicle according to the first modification. As shown in FIG. 6, in the four-wheel-drive vehicle according to the first modification, the arrangement positions of the ADD mechanism 7 and the motor generator 8 are switched with respect to the arrangement positions in the first embodiment. Specifically, the motor generator 8 is arranged on the side of the front differential device 41 and the ADD mechanism 7 is arranged on the side of the right front wheel 4R. In other words, the motor generator 8 is arranged closer to the side gear 41c than the ADD mechanism 7. Consequently, the motor generator 8 is provided on the differential-side front drive shaft 42Ra.

[0105] In the first modification, a similar effect to that of the first embodiment can be produced. In other words, by switching among respective travel modes, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration.

[0106] In addition, according to the configuration of the first modification, in the fuel economy priority mode, since the motor generator 8 and the right front wheel 4R are cut off from each other, a state can be realized in which co-rotation of the motor generator 8 with a rotation of the right front wheel 4R is avoided.

[0107] (Second modification)

Next, a second modification will be described. The second modification differs from the first embodiment in the arrangement position of the motor generator 8. Since other configurations and operations are similar to those of the first embodiment, only the arrangement position of the motor generator 8 will be described below. [0108] FIG. 7 is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in a four-wheel-drive vehicle according to the second modification. As shown in FIG. 7, in the

four-wheel-drive vehicle according to the second modification, the motor generator 8 is arranged on the left-side front drive shaft 42L.

[0109] Therefore, in the torque vectoring mode during a right turn, torque control of the motor generator 8 is performed in order to generate a torque in the normal rotating direction (the vehicle advancing direction) and, accordingly, the drive force in the forward rotating direction at the left front wheel 4L is increased to enhance turning ability of a right turn of the vehicle.

[0110] On the other hand, in the torque vectoring mode during a left turn, torque control of the motor generator 8 is performed in order to generate a torque in the reverse rotating direction (the vehicle backing direction) and, accordingly, the drive force in the forward rotating direction at the right front wheel 4R is increased to enhance turning ability of a left turn of the vehicle.

[0111] Even in the second modification, a similar effect to that of the first embodiment can be produced. In other words, by switching among respective travel modes, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration.

[0112] In addition, according to the configuration of the second modification, the front differential device 41 can be arranged at an approximately central position in the vehicle width direction, and a degree of freedom of the arrangement positions of the .ADD mechanism 7 and the motor generator 8 can be increased compared to the first embodiment and the first modification.

[0113] Moreover, arrangement positions of the ADD mechanism 7 and the motor generator 8 are not limited to those in the first embodiment and the respective

modifications. For example, both the ADD mechanism 7 and the motor generator 8 may be provided on the left-side front drive shaft 42L. In this case, a configuration in which the ADD mechanism 7 is arranged on the side of the front differential device 41 and the motor generator 8 is arranged on the side of the left front wheel 4L and a configuration in ' which the ADD mechanism 7 is arranged on the side of the left front wheel 4L and the motor generator 8 is arranged on the side of the front differential device 41 may be adopted. Furthermore, a configuration in which the ADD mechanism 7 is arranged on the left-side front drive shaft 42L and the motor generator 8 is arranged on the right-side front drive shaft 42R may also be adopted.

[0114] (Third modification)

Next, a third modification will be described. In the third modification, a case will be described in which the invention is applied to a stand-by four-wheel-drive vehicle based on an FF (front engine, front drive) system with a horizontally mounted engine. In other words, a case will be described in which the invention is applied to a front wheel drive-based four-wheel-drive vehicle with a two-wheel drive mode in which power from an engine is only transmitted to front wheels (main drive wheels) and a four-wheel drive mode in which the power from the engine is transmitted to both the front wheels and rear wheels (driven wheels).

[0115] FIG. 8 is a schematic configuration diagram of a four-wheel-drive vehicle according to the third modification.

[0116] As shown in FIG. 8, the four-wheel-drive vehicle according to the third modification includes an engine 1 , a transmission 2, a front differential device 41 , a transfer 3, a propeller shaft 50, an electronic control coupling (a power switching mechanism) 9, a rear differential device 51 , and the like.

[0117] Hereinafter, the engine 1 , the transmission 2, the front differential device 41, the transfer 3, the propeller shaft 50, the electronic control coupling 9, the rear differential device 51, and the like will be described.

[0118] — Engine— The engine 1 is a conventional power apparatus which is constituted by a gasoline engine, a diesel engine, or the like and which burns fuel and outputs power in a similar manner to that of the first embodiment. [0119] — Transmission and front differential device— The transmission 2 is arranged on a lateral side of the engine 1 via a torque converter (not shown). The transmission 2 is, for example, a stepped (planetary gear-type) automatic transmission which sets gear steps using frictional engagement elements such as a plurality of clutches and a brake and a planetary gear device. Moreover, the transmission 2 may alternatively be a belt-type CVT or the like which adjusts speed ratios in a stepless manner.

[0120] An output gear (not shown) is coupled to an output shaft of the transmission 2 so as to be integrally rotatable. The output gear meshes with a ring gear 43 of the front differential device 41 and power transmitted to the output shaft of the transmission 2 is transmitted to left and right front wheels 4L and 4R via the front differential device 41 and front drive shafts 42L and 42R.

[0121] — Transfer— The transfer 3 includes a drive gear 34 coupled to the front differential device 41 so as to be integrally rotatable and a driven gear 35 that meshes with the drive gear 34, and changes a torque transmitting direction from a vehicle width direction to rearward of the vehicle. The propeller shaft 50 is coupled to the driven gear 35 so as to be integrally rotatable. The propeller shaft 50 has a first propeller shaft 50A on a front side of the electronic control coupling 9 and a second propeller shaft 50B on a rear side of the electronic control coupling 9, and is coupled to left and right rear wheels 5L and 5R via the electronic control coupling 9, the rear differential device,51 , and rear drive shafts (a rear drive shaft may be considered to be a shaft that constitutes a "power transmission path" according to the invention) 52L and 52R. In addition, a torque transmitted from the front differential device 41 to the transfer 3 is transmitted to the propeller shaft 50 and the electronic control coupling 9, and when the electronic control coupling 9 is in an engaged state (a coupling torque transmitted state; hereinafter, sometimes also referred to as a fastened state), the torque is transmitted (distributed) to the left and right rear wheels 5L and 5R via the rear differential device 51 and the rear drive shafts 52L and 52R.

[0122] — Rear differential device— A ring gear 53 is provided on a differential case 5 la of the rear differential device 51 so as to be integrally rotatable. The ring gear 53 meshes with a drive pinion gear 54 that is integrally provided at a rear end of the second propeller shaft 50B.

[0123] In addition, the rear differential device 51 includes a pair of pinion gears 51b provided inside the differential case 51 a and a pair of side gears 51c which mesh with the pinion gears 51b. The respective pinion gears 51 b are rotatably supported by a pinion gear shaft 55 that is arranged in a direction perpendicular to an axial direction of the rear drive shafts 52L and 52R inside the differential case 51a. In other words, the respective pinion gears 51 b revolve around the axis of the rear drive shafts 52L and 52R together with the differential case 51a and are rotatable around an axis of the pinion gear shaft 55.

When power transmitted via the transfer 3 and the propeller shafts 50A and 50B is input to the differential case 51 a via the ring gear 53, the differential case 51 a rotates and the pinion gears 51b in the differential case 51a cause the side gears 51c to rotate while revolving around the axis of the rear drive shafts 52L and 52R. As a result, power is transmitted to the rear drive shafts 52L and 52R. In addition, when a difference in rotations arises between the left and right rear wheels 5L and 5R (the left and right rear drive shafts 52L and 52R) during turning of the vehicle and the like, the left and right side gears 51c relatively rotate with a rotation of the pinion gears 51b around the axis of the pinion gear shaft 55 and absorb the difference in rotations between the left and right rear drive shafts 52L and 52R.

[0124] — Electronic control coupling— The electronic control coupling 9 is, for example, a pilot clutch type coupling and includes a main clutch constituted by a multi-plate friction clutch, a pilot clutch (an electromagnetic multi-plate clutch), a cam mechanism, an electromagnet, and the like. The electronic control coupling 9 is configured such that the pilot clutch is engaged by an electromagnetic force of the electromagnet and the engagement force is transmitted to the main clutch by the cam mechanism to cause an engagement of the main clutch (for a specific configuration, for example, refer to Japanese Patent Application Publication No. 2010-254135 (JP

2010-254135 A)). [0125] The electronic control coupling 9 is also configured to control a torque capacity or, in other words, a coupling torque Tc by controlling an excitation current Ie that is supplied to the electromagnet, and a drive torque distribution ratio to the rear wheels 5L and 5R with respect to a total drive torque can be adjusted in a stepless manner within a range of, for example, 0% to 50%. The excitation current Ie to the electromagnet of the electronic control coupling 9 is controlled by the ECU 100. Moreover, the configurations of the ECU 100 and sensors connected to the ECU 100 are similar to those in the first embodiment.

[0126] For example, when the excitation current Ie to the electronic control coupling 9 is "0", the main clutch is placed in a disengaged (released) state and a transmission rate of the transmission torque Tc is "0%". Therefore, a travel state equivalent to a front wheel drive state (a two-wheel drive state due to front wheel drive) is realized. On the other hand, when the excitation current Ie to the electronic control coupling 9 is increased, the transmission torque Tc increases. When the excitation current Ie reaches maximum, the transmission rate of the transmission torque Tc is "100% (the drive torque distribution ratio is 50%)" or, in other words, a drive torque distribution to the rear wheels 5L and 5R becomes maximum and a travel state equivalent to a direct connection four wheel drive state is realized. In this manner, a drive torque distribution among front and rear wheels can be variably controlled in accordance with the excitation current Ie to the electronic control coupling 9.

[0127] Moreover, one of the basic controls of the electronic control coupling 9 by the ECU 100 involves, for example, supplying the excitation current Ie and generating the transmission torque Tc when skidding occurs at the front wheels 4L and 4R during travel in a two-wheel drive state in which the excitation current Ie to the electromagnet of the electronic control coupling 9 is "0". Accordingly, the vehicle makes a transition from the two-wheel drive state to the four-wheel drive state and travel stability is secured. In addition, in this case, the greater the amount of skidding of the front wheels 4L and 4R, the higher the value of the excitation current Ie in order to set a higher transmission torque Tc. Moreover, a determination regarding whether or not skidding of the front wheels 4L and 4R has occurred is made by comparing respective wheel rotation speeds detected by the respective wheel rotation speed sensors 96L, 96R, 97L, and 97R (refer to FIG.2). In addition, even when the driver selects a 4WD travel mode using the 2WD/4WD

changeover switch 95 arranged in a vehicle cabin, the excitation current Ie is supplied to generate the transmission torque Tc. Accordingly, the vehicle makes a transition from the two- wheel drive state to the four-wheel drive state.

[0128] In the third modification, the electronic control coupling 9 performs the same function as the disconnect mechanism 6 in the first embodiment. In other words, the electronic control coupling 9 switches between a transmitted state in which torque transmission (power transmission) is performed between the transfer 3 and the second propeller shaft 50B and a non-transmitted state (a cutoff state) in which torque

transmission is not performed.

[0129] — ADD mechanism— An ADD mechanism 7 is provided on the left-side rear drive shaft 52L among the left and right rear drive shafts 52L and 52R. The ADD mechanism 7 is configured to switch between a transmitted state in which torque transmission (power transmission) is performed between the rear differential device 51 and the left rear wheel 5L and a non-transmitted state (a cutoff state) in which torque

transmission is not performed.

; [0130] Specifically, the left-side rear drive shaft 52L is divided into a

differential-side rear drive shaft 52La that is positioned on a side of the rear differential device 51 and a wheel-side rear drive shaft 52Lb that is positioned on a side of the left rear wheel 5L. The ADD mechanism 7 includes a differential-side engaging plate 75 attached to an outside end of the differential-side rear drive shaft 52La in the vehicle width direction, a rear wheel-side engaging plate 76 attached to an inside end of the wheel-side rear drive shaft 52Lb in the vehicle width direction, an ADD sleeve 77 which switches between engagement and disengagement of the differential-side engaging plate 75 and the rear wheel-side engaging plate 76, and the like.

[0131] The differential-side engaging plate 75 and the rear wheel-side engaging plate 76 have a same diameter and splines are respectively formed on outer circumferential surfaces thereof. Meanwhile, a spline capable of engaging the splines formed on the respective outer circumferential surfaces of the differential-side engaging plate 75 and the rear wheel-side engaging plate 76 is formed on an inner circumferential surface of the ADD sleeve 77. The ADD sleeve 77 is configured to be slidingly moved in a direction of the axis of the rear drive shaft 52L by an ADD actuator 74. Accordingly, the ADD sleeve 77 is capable of slidingly moving between a position at which the ADD sleeve 77 only engages the rear wheel-side engaging plate 76 (or the differential-side engaging plate 75) (a position shown in FIG. 8) and a position at which the ADD sleeve 77 engages both the rear wheel-side engaging plate 76 and the differential-side engaging plate 75. When the ADD sleeve 77 is at the position where the ADD sleeve 77 only engages one of the engaging plates (for example, the rear wheel-side engaging plate 76), a state is entered in which a torque is not transmitted from the rear differential device 51 to the left rear wheel 5L (a non-transmitted state; a released state of the ADD mechanism 7). Conversely, when the ADD sleeve 77 is at the position where the ADD sleeve 77 engages both the rear wheel-side engaging plate 76 and the differential-side engaging plate 75, a state is entered in which a torque can be transmitted from the rear differential device 51 to the left rear wheel 5L (an engaged state of the ADD mechanism 7).

[0132] — Motor generator— A motor generator 8 is arranged on the wheel-side rear drive shaft 52Lb. The motor generator 8 is an AC synchronous generator including a rotor 81 which is made of a permanent magnet and which is integrally rotatable with the wheel-side rear drive shaft 52Lb and a stator 82 wound by a three-phase winding, and the motor generator 8 functions both as a motor (an electric motor) and as a generator.

[0133] In addition, the motor generator 8 is connected to a battery B via an inverter 200 (refer to FIG. 2). The inverter 200 is controlled by the ECU 100 and regeneration or power running (assistance) of the motor generator 8 is set by controlling the inverter 200. In this case, regenerative power is charged into the battery B via the inverter 200. In addition, drive power for the motor generator 8 is supplied from the battery B via the inverter 200. [0134] Even in the third modification, travel can be performed in various travel modes in a similar manner to the first embodiment. Specifically, switching can be performed between travel in a fuel economy priority mode in which a two-wheel drive state is entered and travel in a four-wheel drive mode in accordance with a transmission torque Tc of the electronic control coupling 9 and a sliding movement position of the ADD sleeve 77 of the ADD mechanism 7. In addition, the four-wheel drive mode is configured to be further switched to the four travel modes described earlier.

[0135] <Fuel economy priority mode>

In the fuel economy priority mode, the electronic control coupling 9 is released (the transmission torque Tc is set to "0"). In addition, the ADD sleeve 77 is moved to a position at which the ADD sleeve 77 only engages the rear wheel-side engaging plate 76 and the ADD mechanism 7 is also released. Accordingly, a state is entered in which a torque is not transmitted from the transfer 3 to the second propeller shaft 50B and a torque is similarly not transmitted between the rear differential device 51 and the left rear wheel 5L or, in other words, a state is entered in which the left and right rear wheels 5L and 5R are cut off.

[0136] Therefore, in the fuel economy priority mode, drive state of the vehicle is the two-wheel drive state and a power transmission path is established which transmits a torque output from the transmission 2 only to the front drive shafts 42L and 42R. In the two-wheel drive state, a torque is only transmitted to the front wheels 4L and 4R and a torque is not transmitted to the rear wheels 5L and 5R.

[0137] In addition, in the fuel economy priority mode, since the electronic control coupling 9 and the ADD mechanism 7 are both released, rotations of the second propeller shaft 50B and the ring gear 53 are stopped. Since dragging loss due to the rotations of the second propeller shaft 50B and the ring gear 53 no longer occurs, an improvement in fuel consumption rate can be achieved.

[0138] <Four-wheel drive mode during straight travel>

In a four-wheel drive mode during straight travel, the electronic control coupling 9 is fastened. In addition, the ADD sleeve 77 is moved to a position at which the ADD sleeve 77 engages both the rear wheel-side engaging plate 76 and the differential-side engaging plate 75 and the ADD mechanism 7 is also engaged. Accordingly, a part of the torque transmitted to the transfer 3 is transmitted to the second propeller shaft 50B and

approximately equally distributed to the left and right rear wheels 5L and 5R from the rear differential device 51.

[0139] In such a four-wheel drive mode, a torque is transmitted between the transfer 3 and the second propeller shaft 50B. Accordingly, in the four-wheel drive mode, a power transmission path is established which transmits a torque input from the

transmission 2 to the transfer 3 to both the front drive shafts 42L and 42R and the rear drive shafts 52L and 52R, and a torque is transmitted to both the front wheels 4L and 4R and the rear wheels 5L and 5R.

[0140] In addition, in the four-wheel drive mode during straight travel,

energization of the motor generator 8 is basically stopped and a torque is not generated by the motor generator 8. Moreover, since the rotor 81 of the motor generator 8 integrally rotates with the left-side rear drive shaft 52L, a difference in inertial forces arises between the left and right rear drive shafts 52L and 52R due to the presence of the rotor 81.

Therefore, when a difference in drive forces of the left and right rear wheels 5L and 5R arises due to the difference in inertial forces, torque control of the motor generator 8 may be performed so as to eliminate the difference in drive forces. For example, during startup in the four-wheel drive mode, a torque in the normal rotating direction may be generated by the motor generator 8 in order to favorably secure startup performance so that a difference in drive forces of the left and right rear wheels 5L and 5R does not arise.

[0141] <Torque vectoring mode during right turn>

In a torque vectoring mode during a right turn, the electronic control coupling 9 is fastened and the ADD mechanism 7 is engaged in a similar manner to the four-wheel drive mode during straight travel.

[0142] In addition, torque control of the motor generator 8 is performed in order to generate a torque in the normal rotating direction (the vehicle advancing direction) and, accordingly, a drive force in the forward rotating direction at the left rear wheel 5L is increased. In other words, power from the engine 1 transmitted to the rear differential device 51 via the propeller shaft 50 is transmitted to the right rear wheel 5R via the right-side rear drive shaft 52R. On the other hand, power from the engine 1 transmitted to the rear differential device 51 via the propeller shaft 50 is transmitted to the left rear wheel 5L via the left-side rear drive shaft 52L and, at the same time, the torque generated by the motor generator 8 is also transmitted to the left rear wheel 5L. In other words, due to the torque transmitted to the left rear wheel 5L exceeding the torque transmitted to the right rear wheel 5R, the drive force of the left rear wheel 5L relatively increases and turning ability during a right turn of the vehicle is enhanced.

[0143] <Torque vectoring mode during left turn>

In a torque vectoring mode during a left turn, the electronic control coupling 9 is fastened and the ADD mechanism 7 is engaged in a similar manner to the four-wheel drive mode during straight travel and the torque vectoring mode during a right turn.

[0144] In addition, torque control of the motor generator 8 is performed in order to generate a torque (a braking torque) in the reverse rotating direction (the vehicle backing direction) and, accordingly, a drive force in the forward rotating direction at the left rear wheel 5L is reduced. In other words, power from the engine 1 transmitted to the rear differential device 51 via the propeller shaft 50 is transmitted to the right rear wheel 5R via the right-side rear drive shaft 52R. On the other hand, power from the engine 1 transmitted to the rear differential device 51 via the propeller shaft 50 is transmitted to the left rear wheel 5L via the left-side rear drive shaft 52L and, at the same time, the torque (a braking torque) generated by the motor generator 8 is also transmitted to the left rear wheel 5L. As the torque transmitted to the left rear wheel 5L decreases in this manner, the torque transmitted to the right rear wheel 5R increases. In other words, a reaction force of the braking torque is transmitted from the left-side rear drive shaft 52L to the rear differential device 51 , the left and right side gears 51c relatively rotate with the rotation of the pinion gears 51b around the pinion gear shaft 55, and the torque transmitted to the right-side rear drive shaft 52R is increased. Accordingly, due to the torque transmitted to the right rear wheel 5R exceeding the torque transmitted to the left rear wheel 5L, the drive force of the right rear wheel 5R relatively increases and turning ability during a left turn of the vehicle is enhanced.

[0145] <Torque vectoring mode during regenerative deceleration>

In a torque vectoring mode during regenerative deceleration, the electronic control coupling 9 is fastened and the ADD mechanism 7 is engaged in a similar manner to the four-wheel drive mode during straight travel and the respective torque vectoring modes.

[0146] In addition, by controlling the inverter 200, the motor generator 8 is placed in a driven state by a rotative force of the left-side rear drive shaft 52L (a rotative force of the left rear wheel 5L due to a frictional force between the road surface and the left rear wheel 5L during travel). Accordingly, power generation is performed by the motor generator 8. The power regenerated by the motor generator 8 is charged to the battery B via the inverter 200.

[0147] Since travel mode switching control in the third modification is performed in a similar manner to that of the first embodiment (the travel mode switching control described with reference to the flow chart shown in FIG. 4), a description thereof will be omitted.

[0148] Even with the third modification, a similar effect to that of the first embodiment can be produced. In other words, by switching among respective travel modes, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration.

[0149] (Second embodiment)

Next, a second embodiment will be described. In the second embodiment, a case will be described in which this invention is applied to a stand-by four-wheel-drive vehicle based on an FR system with a vertically mounted engine. In addition, the second embodiment differs from the first embodiment in the configuration of the ADD mechanism (power transmission engaging/disengaging mechanism) 7. Therefore, only the configuration of the ADD mechanism 7, respective vehicle travel modes, and travel mode switching control will be described below. [0150] FIG. 9 is a schematic configuration diagram of a four-wheel-drive vehicle according to the second embodiment.

[0151] As shown in FIG. 9, the four-wheel-drive vehicle according to the second embodiment also includes an engine (a power source) 1 which generates power for vehicle travel, a transmission 2 which changes a rotation speed of an output shaft of the engine 1 , and a transfer (a power distribution mechanism) 3 which distributes rotative power output from the transmission 2 to a front propeller shaft 40 on a side of front wheels 4L and 4R and to a rear propeller shaft 50 on a side of rear wheels 5L and 5R. Since configurations of these components are similar to those of the first embodiment, a description of the configurations will be omitted. In addition, since configurations of the respective differential devices 41 and 51 and the disconnect mechanism (the power switching mechanism) 6 are also similar to those of the first embodiment, a description of the configurations will be omitted. In FIG. 9, components similar to the components of the four-wheel-drive vehicle according to the first embodiment are denoted by the same reference numerals.

[0152] — ADD mechanism— Next, the ADD mechanism 7 that is a characteristic part of the second embodiment will be described. The ADD mechanism 7 is provided on the right-side front drive shaft 42R among the left and right front drive shafts 42L and 42R. The ADD mechanism 7 is configured to switch between a power transmitted state in which torque transmission (power transmission) is performed between the front differential device 41 and the right front wheel 4R and a power non-transmitted state (a cutoff state) in which torque transmission is not performed. Moreover, in FIG. 9, similar components and components having similar functions to those of the ADD mechanism 7 according to the first embodiment are denoted by the same reference numerals.

[0153] Hereinafter, the configuration of the ADD mechanism 7 will be described in detail.

[0154] The right-side front drive shaft 42R is divided into a differential-side front drive shaft 42Ra that is positioned on a side of the front differential device 41 and a wheel-side front drive shaft 42Rb that is positioned on a side of the right front wheel 4R. The ADD mechanism 7 includes a differential case-side engaging plate 79 attached to the differential case 41a on a side of the right front wheel 4R so as to be integrally rotatable, a differential-side engaging plate 71 attached to an outside end of the differential-side front drive shaft 42Ra in the vehicle width direction, a front wheel-side engaging plate 72 attached to an inside end of the wheel-side front drive shaft 42Rb in the vehicle width direction, an ADD sleeve 73 which switches engagement states of the differential case-side engaging plate 79, the differential-side engaging plate 71, and the front wheel-side engaging plate 72, and the like. The respective engaging plates 79, 71 , and 72 are arranged in an order of the differential case-side engaging plate 79, the differential-side engaging plate 71 and the front wheel-side engaging plate 72 from the front differential device 41 toward the right front wheel 4R.

[0155] The respective engaging plates 79, 71 , and 72 have a same diameter and splines are respectively formed on outer circumferential surfaces thereof. Meanwhile, a spline capable of engaging the splines formed on the respective outer circumferential surfaces of the engaging plates 79, 71 , and 72 is formed on an inner circumferential surface of the ADD sleeve 73. The ADD sleeve 73 is configured to be slidingly moved in a direction of the axis of the front drive shaft 42R by an ADD actuator 74. Accordingly, the ADD sleeve 73 is capable of slidingly moving among a position at which the ADD sleeve 73 only engages the differential case-side engaging plate 79 (or the front wheel-side engaging plate 72) (a position depicted by a solid line or an imaginary line in FIGS. 9 and 10A; hereinafter, referred to as a "first slide position"), a position at which the ADD sleeve 73 engages the differential case-side engaging plate 79 and the differential-side engaging plate .71 but does not engage the front wheel-side engaging plate 72 (a position shown in FIG. 10B; hereinafter, referred to as a "second slide position"), a position at which the ADD sleeve 73 engages all of the engaging plates 79, 71 , and 72 (a position shown in FIG. 10C; hereinafter, referred to as a "third slide position"), and a position at which the ADD sleeve 73 engages the differential-side engaging plate 71 and the front wheel-side engaging plate 72 but does not engage the differential case-side engaging plate 79 (a position shown in FIG. 10D; hereinafter, referred to as a "fourth slide position"). [0156] When the ADD sleeve 73 is at the first slide position, the respective engaging plates 79, 71, and 72 are not engaged with one another and the side gear 41c and the differential case 41a of the front differential device 41 and the wheel-side front drive shaft 42Rb are capable of free relative rotation.

(0157] When the ADD sleeve 73 is at the second slide position, the side gear 41c and the differential case 41a of the front differential device 1 become integrally rotatable and the wheel-side front drive shaft 42Rb becomes capable of free relative rotation with respect to the side gear 41c and the differential case 41a of the front differential device 41.

[0158] When the ADD sleeve 73 is at the third slide position, the side gear 41c and the differential case 41a of the front differential device 41 and the wheel-side front drive shaft 42Rb become integrally rotatable.

[0159] When the ADD sleeve 73 is at the fourth slide position, the side gear 41c of the front differential device 41 and the wheel-side front drive shaft 42Rb become integrally rotatable and the differential case 41a becomes capable of free relative rotation with respect to the side gear 41c of the front differential device 41 and the wheel-side front drive shaft 42Rb.

[0160] The differential-side engaging plate 71, the front wheel-side engaging plate 72, and the ADD sleeve 73 may be considered to be a first power transmission engaging/disengaging mechanism portion (a first mechanism) (a mechanism portion which switches between a power transmitted state and a power non-transmitted state between a side gear of a differential device and one of the wheels) according to this invention. In addition, the differential case-side engaging plate 79, the differential-side engaging plate 71 , and the ADD sleeve 73 may be considered to be a second power transmission engaging/disengaging mechanism portion (a second mechanism) (a mechanism portion which switches between a released state in which a side gear and a differential case of a differential device are capable of relative rotation and an engaged state in which the side gear and the differential case of the differential device are incapable of relative rotation) according to this invention. [0161] — Motor generator— A motor generator (a motor) 8 is arranged on the wheel-side front drive shaft 42Rb. Since the configuration of the motor generator 8 is similar to that of the first embodiment, a description thereof will be omitted.

[0162] — Vehicle travel modes— Next, travel modes (vehicle travel modes) of the four-wheel-drive vehicle configured as shown above will be described.

[0163] A four-wheel-drive vehicle according to the second embodiment is configured to be switchable between travel in an ADD mode (corresponds to the fuel economy priority mode according to the first embodiment) in which a two- wheel drive state is entered and travel in a four-wheel drive mode in accordance with a sliding movement position of the disconnect sleeve 63 of the disconnect mechanism 6 and a sliding movement position of the ADD sleeve 73 of the ADD mechanism 7. In addition, the four-wheel drive mode is configured to be further switched to three travel modes. Specifically, the four-wheel drive mode can be switched to a one wheel-locked mode, a differential lock mode, and a torque vectoring mode. A detailed description will be given below.

[0164] <ADD mode>

First, the ADD mode will be described.

[0165] FIG. 1 OA is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the ADD mode. As shown in FIG. 10A, in the ADD mode, the disconnect sleeve 63 is moved to a position at which the disconnect sleeve 63 only engages the propeller shaft-side engaging plate 62 and the disconnect mechanism 6 is released. In addition, the ADD sleeve 73 is moved to the first slide position and the respective engaging plates 79, 71 , and 72 are not engaged with one another. In other words, the side gear 41 c and the differential case 41 a of the front differential device 41 and the wheel-side front drive shaft 42Rb become capable of free relative rotation.

[0166] Accordingly, a torque is not transmitted from the transfer 3 to the front propeller shaft 40 and a torque is similarly not transmitted between the front differential device 41 and the right front wheel 4R or, in other words, the left and right front wheels 4L and 4R are cut off.

[0167] Therefore, in the ADD mode, the drive state of the vehicle is the two-wheel drive state and a power transmission path is established which transmits a torque input from the transmission 2 to the transfer 3 only to the rear propeller shaft 50. In the two-wheel drive state, a torque is only transmitted to the rear wheels 5L and 5R and a torque is not transmitted to the front wheels 4L and 4R.

[0168] In addition, in the ADD mode, since the disconnect mechanism 6 and the ADD mechanism 7 are both released, rotations of the front propeller shaft 40 and the ring gear 43 are stopped. Since dragging loss due to the rotations of the front propeller shaft 40 and the ring gear 43 no longer occurs, an improvement in fuel consumption rate can be achieved.

[0169] One wheel-locked mode>

Next, the one wheel-locked mode will be described.

[0170] FIG. 10B is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the one wheel-locked mode. As shown in FIG. 10B, in the one wheel-locked mode, the disconnect sleeve 63 is moved to a position at which the disconnect sleeve 63 engages both the propeller shaft-side engaging plate 62 and the transfer-side engaging plate 61 and the disconnect mechanism 6 is engaged.

[0171] In addition, the ADD sleeve 73 is moved to the second slide position and engages the differential case-side engaging plate 79 and the differential-side engaging plate 71 but does not engage the front wheel-side engaging plate 72. In other words, the side gear 41c and the differential case 41a of the front differential device 41 become integrally rotatable and the wheel-side front drive shaft 42Rb becomes capable of free relative rotation with respect to the side gear 41c and the differential case 41a of the front differential device 41.

[0172] As a result, power from the engine 1 transmitted to the front differential device 41 via the front propeller shaft 40 is transmitted to the left front wheel 4L via the left-side front drive shaft 42L. Conversely, a drive force of the right front wheel 4R is adjusted by control of an output torque of the motor generator 8. In other words, respective drive forces of the left front wheel 4L and the right front wheel 4R can be adjusted by different drive sources. When the drive force of one of the front wheels 4L (or 4R) becomes deficient, equal drive forces of the left and right front wheels 4L and 4R can be obtained by controlling the respective drive sources.

[0173] differential lock mode>

Next, the differential lock mode will be described.

[0174] FIG. IOC is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the differential lock mode. In the differential lock mode, the disconnect mechanism 6 is engaged in a similar manner to the one wheel-locked mode.

[0175] In addition, as shown in FIG. IOC, the ADD sleeve 73 is moved to the. third slide position and the ADD sleeve 73 engages all engaging plates 79, 71, and 72. In other words, the side gear 41 c and the differential case 41a of the front differential device 41 and the wheel-side front drive shaft 42Rb become integrally rotatable.

[0176] As a result, a difference in rotations does not arise between the left and right front wheels 4L and 4R and traveling performance of the vehicle can be enhanced. In addition, in the differential lock mode, the left and right front wheels 4L and 4R can be provided with assistance of a' forward drive force by causing the motor generator 8 to generate a torque in the forward rotating direction.

[0177] <Torque vectoring mode>

Next, the torque vectoring mode will be described.

[0178] FIG. 10D is a schematic configuration diagram showing a power transmission system on the side of the front wheels 4L and 4R in the torque vectoring mode. In the torque vectoring mode, the disconnect mechanism 6 is engaged in a similar manner to the one wheel-locked mode and the differential lock mode.

[0179] In addition, as shown in FIG. 10D, the ADD sleeve 73 is moved to the fourth slide position and engages the differential-side engaging plate 71 and the front wheel-side engaging plate 72 but does not engage the differential case-side engaging plate 79. In other words, the side gear 41 c of the front differential device 41 and the wheel-side front drive shaft 42Rb become integrally rotatable and the differential case 41a becomes capable of free relative rotation with respect to the side gear 41c of the front differential device 41 and the wheel-side front drive shaft 42Rb.

[0180] In the torque vectoring mode, a power transmitted state similar to that of the torque vectoring modes according to the first embodiment is obtained. Specifically, a torque vectoring mode during a left turn in which torque control of the motor generator 8 is performed in order to generate a torque in a normal rotating direction (a vehicle advancing direction) and a drive force in the forward rotating direction at the right front wheel 4R is increased, a torque vectoring mode during a right turn in which torque control of the motor generator 8 is performed in order to generate a torque (a braking torque) in a reverse rotating direction (a vehicle backing direction) and the drive force in the forward rotating direction at the right front wheel 4R is reduced in order to increase a drive force in the forward rotating direction at the left front wheel 4L, and a torque vectoring mode during regenerative deceleration in which the motor generator 8 is placed in a driven state by controlling the inverter 200 using a rotative force of the right-side front drive shaft 42R in order to cause the motor generator 8 to generate power are to be selected in accordance with a vehicle travel state (a steering angle, an accelerator depression amount, and the like).

[0181] — Travel mode switching control— Next, travel mode switching control according to the second embodiment will be described. The travel mode switching control is for selecting any of the travel modes described earlier in accordance with a vehicle travel state and the like.

[0182] FIG. 1 1 is a flow chart showing a procedure of the travel mode switching control. The flow chart shown in FIG. 1 1 is executed every few milliseconds during travel of the vehicle. [0183] First, in step STl, output values of the respective sensors are read. The operation of step STl is performed in a similar manner to the operation of step STl shown in the flow chart in FIG. 4 according to the first embodiment.

[0184] Subsequently, the procedure proceeds to step ST2 and a determination is made on whether or not four-wheel drive travel conditions are satisfied. The operation of step ST2 is also performed in a similar manner to the operation of step ST2 shown in the flow chart in FIG. 4 according to the first embodiment.

[0185] When the four-wheel drive travel conditions are not satisfied and a determination of NO is made in step ST2, the procedure proceeds to step ST21 and a transition is made to a travel state in the ADD mode. In other words, by releasing the disconnect mechanism 6 and moving the ADD sleeve 73 to the first slide position, the side gear 41c and the differential case 41a of the front differential device 41 and the wheel-side front drive shaft 42Rb become capable of free relative rotation and the drive state of the vehicle is a two-wheel drive state.

[0186] On the other hand, when the four-wheel drive travel conditions are satisfied and a determination of YES is made in step ST2, the procedure proceeds to step ST22 and a determination is made on whether or not the steering angle of the steering wheel that is detected by the steering angle sensor 98 is approximately "0" or, in other words, whether or not the driver intends to travel straight.

[0187] When the steering angle of the steering wheel is approximately "0" and the driver intends to travel straight, a determination of YES is made in step ST22 and the procedure proceeds to step ST23. In step ST23, a determination is made on whether or not a difference has arisen between the rotation speed of the left front wheel 4L that is detected by the left front wheel rotation speed sensor 96L and the rotation speed of the right front wheel 4R that is detected by the right front wheel rotation speed sensor 96R. In other words, a determination is made on whether or not a difference in rotation speeds has arisen due to a difference in surface resistances at the left front wheel 4L and the right front wheel 4R and stable straight travel cannot be performed even though the steering angle of the steering wheel is approximately "0". Moreover, causes of the difference in rotation speeds between the left and right front wheels 4L and 4R include a difference in inertial forces of the left and right front drive shafts 42L and 42R due to the presence of the motor generator 8.

[0188] When a difference has not arisen between the rotation speed of the left front wheel 4L and the rotation speed of the right front wheel 4R or the difference is smaller than the predetermined value and a determination of NO is made in step ST23, a transition is made to a travel state in the torque vectoring mode. In the torque vectoring mode in this case, since the driver intends to travel straight and a difference has not arisen between the rotation speed of the left front wheel 4L and the rotation speed of the right front wheel 4R, the vehicle travels in a normal four-wheel drive mode without performing output torque control of the motor generator 8.

[0189] On the other hand, when a difference has arisen between the rotation speed of the left front wheel 4L and the rotation speed of the right front wheel 4R and a determination of YES is made in step ST23, the procedure proceeds to step ST24 to determine whether or not the difference in rotations between the front wheels 4L and 4R is less than a predetermined amount a. The predetermined amount a is set in advance based on an experiment, a simulation, or the like.

[0190] When a difference in rotations has arisen between the front wheels 4L and 4R but the difference in rotations is less than the predetermined amount a, a determination of YES is made in step ST24 and a transition is made to step ST25. In step ST25, a transition is made to a travel state in the one wheel-locked mode. In other words, the disconnect mechanism 6 is engaged, the ADD sleeve 73 is moved to the second slide position, the side gear 41c and the differential case 41a of the front differential device 41 become integrally rotatable, and the wheel-side front drive shaft 42Rb becomes capable of free relative rotation with ^"respect to the side gear 41c and the differential case 41a of the front differential device 41. Accordingly, a state is entered in which the drive force of the left front wheel 4L is controlled by a torque from the engine 1 and the drive force of the right front wheel 4R is controlled by an output torque of the motor generator 8·. As a result, the difference in rotations between the front wheels 4L and 4R can be eliminated. [0191] On the other hand, when the difference in rotations between the front wheels 4L and 4R is equal to or greater than the predetermined amount a, a determination of NO is made in step ST24 and a transition is made to step ST30. In step ST30, a transition is made to a travel state in the differential lock mode. In other words, by engaging the disconnect mechanism 6 and moving the ADD sleeve 73 to the third slide position, the side gear 41c and the differential case 41a of the front differential device 41 and the wheel-side front drive shaft 42Rb become integrally rotatable. As a result, a state is entered in which a difference in rotations does not arise between the left and right front wheels 4L and 4R and traveling performance of the vehicle can be enhanced. In addition, in the differential lock mode, assistance of a forward drive force can be provided by causing the motor generator 8 to generate a torque in the forward rotating direction.

[0192] In step ST22, when it is determined that the steering angle of the steering wheel is not approximately "0" and the driver intends to make a turn (a left turn or a right turn), a determination of NO is made and the procedure proceeds to step ST26.

[0193] In step ST26, a determination is made on whether or not the steering angle of the steering wheel that is detected by the steering angle sensor 98 is on a left turn-side.

[0194] When the steering angle of the steering wheel is on the left turn side and a determination of YES is made in step ST26, the procedure proceeds to step ST27 and a transition is made to the torque vectoring mode during a left turn. In other words, torque control of the motor generator 8 is performed in order to generate a torque (a positive torque) in the normal rotating direction (the vehicle advancing direction) and, accordingly, a drive force in the forward rotating direction at the right front wheel 4R is increased. As a result, turning ability of a left turn of the vehicle is enhanced.

[0195] In this torque control of the motor generator 8, a torque in the normal rotating direction is controlled according to a motor target torque map shown in FIG. 5 in a similar manner to the first embodiment.

[0196] On the other hand, when the steering angle of the steering wheel is on the right turn side and a determination of NO is made in step ST26, the procedure proceeds to step ST28 and a transition is made to the torque vectoring mode during a right turn. In other words, torque control of the motor generator 8 is performed in order to generate a torque (a braking torque) in the reverse rotating direction (the vehicle backing direction) and, accordingly, a drive force in the forward rotating direction at the left front wheel 4L is increased. As a result, turning ability of a right turn of the vehicle is enhanced.

[0197] In this torque control of the motor generator 8, the greater the accelerator depression amount and the greater the steering angle, a greater value is set as the braking torque.

[0198] In addition, during the torque vectoring mode in step ST29 or the differential lock mode in step ST30, a determination is made in step ST31 regarding whether or not the vehicle is currently decelerating. This determination is performed in a similar manner to the operation of step ST5 shown in the flow chart in FIG. 4 according to the first embodiment.

[0199] When the vehicle is not decelerating and a determination of NO is made in step ST31 , the present travel mode is continued.

[0200] On the other hand, when the vehicle is decelerating and a determination of

YES is made in step ST31 , the procedure proceeds to step ST32 and a transition is made to the torque vectoring mode during regenerative deceleration. In other words, by controlling the inverter 200, the motor generator 8 is placed in a driven state by the rotative force of the right-side front drive shaft 42R to cause the motor generator 8 to perform power generation. The power regenerated by the motor generator 8 is charged to the battery B via the inverter 200.

[0201] Even with the second embodiment, a similar effect to that of the first embodiment can be produced. Specifically, by switching among respective travel modes, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration. In other words, a vehicle travel state in which drive forces of the left and right front wheels 4L and 4R are independently controlled, a vehicle travel state capable of producing high traveling performance, and a vehicle travel state capable of producing high turning performance can be realized. [0202] (Modification)

Next, a modification of the second embodiment will be described. In this

modification, a ease will be described in which the configuration of the second

embodiment is applied to a stand-by four-wheel-drive vehicle based on an FF system with a horizontally mounted engine.

[0203] FIG. 12 is a schematic configuration diagram of a four-wheel-drive vehicle according to this modification. In FIG. 12, similar components and components having similar functions to those of the third modification are denoted by the same reference numerals and a description thereof will be omitted.

[0204] In this modification, an electronic control coupling 9 is provided between the front differential device 41 and the second propeller shaft 50B in a similar manner to the third modification. In addition, an ADD mechanism 7 is provided on the left-side rear drive shaft 52L. The ADD mechanism 7 is configured approximately the same as that according to the second embodiment.

[0205] Specifically, the ADD mechanism 7 includes a differential case-side engaging plate 79 provided on the differential case 5 la on a side of the left rear wheel 5L so as to be integrally rotatable, a differential-side engaging plate 71 attached to an outside end of the differential-side rear drive shaft 52La in the vehicle width direction, a rear wheel-side engaging plate 72 attached to an inside end of the wheel-side rear drive shaft 52Lb in the vehicle width direction, an ADD sleeve 73 which switches engagement states of the differential case-side engaging plate 79, the differential-side engaging plate 71 and the rear wheel-side engaging plate 72, and the like. The respective engaging plates 79, 71 , and 72 are arranged in an order of the differential case-side engaging plate 79, the differential-side engaging plate 71 and the rear wheel-side engaging plate 72 from the rear differential device 51 toward the left rear wheel 5L.

[0206] In addition, due to the slide position of the ADD sleeve 73 being switched among the "first slide position" to the "fourth slide position" by the ADD actuator 74, switching among the ADD mode, the one wheel-locked mode, the differential lock mode, and the torque vectoring mode can be performed. [0207] In the ADD mode, the ADD sleeve 73 is moved to the first slide position and the side gear 51c and the differential case 51a of the rear differential device 51 and the wheel-side rear drive shaft 52Lb are capable of free relative rotation.

[0208] Accordingly, the drive state of the vehicle becomes a two-wheel drive state, and since dragging loss due to rotations of the second propeller shaft 50B and the ring gear 53 is eliminated, an improvement in fuel consumption rate can be achieved.

[0209] In the one wheel-locked mode, the ADD sleeve 73 is moved to the second slide position, the side gear 51c and the differential case 51a of the rear differential device 51 become integrally rotatable, and the wheel-side rear drive shaft 52Lb becomes capable of free relative rotation with respect to the side gear 51c and the differential case 5 la of the rear differential device 51.

[0210] Accordingly, respective drive forces of the left rear wheel 5L and the right rear wheel 5R can be adjusted by different drive sources (the engine 1 and the motor generator 8) . When the drive force of one of the rear wheels 5L (or 5R) becomes deficient, equal drive forces of the left and right, rear wheels 5L and 5R can be obtained by controlling the drive source of the deficient drive force.

[0211] In the differential lock mode, the ADD sleeve 73 is moved to the third slide position and the side gear 51c and the differential case 51 a of the rear differential device 51 and the wheel-side rear drive shaft 52Lb become integrally rotatable.

[0212] As a result, a difference in rotations does not arise between the left and right rear wheels 5L and 5R and traveling performance of the vehicle can be enhanced. In addition, in the differential lock mode, the left and right rear wheels 5L and 5R can be provided with assistance of a forward drive force by causing the motor generator 8 to generate a torque in the forward rotating direction.

[0213] In the torque vectoring mode, the ADD sleeve 73 is moved to the fourth slide position, the side gear 5 lc of the rear differential device 51 and the wheel-side rear drive shaft 52Lb become integrally rotatable, and the differential case 51a becomes capable of free relative rotation with respect to the side gear 51c of the rear differential device 51 and the wheel-side rear drive shaft 52Lb. [0214] Accordingly, a torque vectoring mode during a right turn in which torque control of the motor generator 8 is performed in order to generate a torque in a normal rotating direction (a vehicle advancing direction) and a drive force in the forward rotating direction at the left rear wheel 5L is increased, a torque vectoring mode during a left turn in which torque control of the motor generator 8 is performed in order to generate a torque (a braking torque) in a reverse rotating direction (a vehicle backing direction) and the drive force in the forward rotating direction at the left rear wheel 5L is reduced in order to increase a drive force in the forward rotating direction at the right rear wheel 5R, and a torque vectoring mode during regenerative deceleration in which the motor generator 8 is placed in a driven state by controlling the inverter 200 using a rotative force of the left-side rear drive shaft 52L in order to cause the motor generator 8 to generate power are to be selected.

[0215] Even with this modification, a similar effect to that of the first and second embodiments can be produced. Specifically, by switching among respective travel modes, switching between a vehicle travel state in which an improvement in energy efficiency can be made and a vehicle travel state with high travel performance can be achieved with a relatively simple configuration.

[0216] —Other embodiments-—

In the respective embodiments and the respective modifications presented above, cases where this invention is applied to conventional vehicles (vehicles that are only mounted with an engine as a power source) have been described. However, the invention is not limited to such vehicles. For example, the invention can also be applied to hybrid vehicles (vehicles that are mounted with an engine arid an electric motor as power sources that output power to a propeller shaft) and electric vehicles (vehicles that are only mounted with an electric motor as a power source).

[0217] In addition, in the respective embodiments and the respective

modifications presented above, cases where this invention is applied to a driven wheel-side power transmission system in a power transmission apparatus in which power from a power source is distributed to main drive wheels and driven wheels have been described. However, the invention is not limited thereto and can also be applied to a driven

wheel-side power transmission system which is independent of a main drive wheel-side power transmission system and which is driven by power from a dedicated power source. For example, the invention can be applied to a rear wheel-side power transmission system of a power transmission apparatus disclosed in Japanese Patent Application Publication No. 2012-217281 (JP 2012-217281 A).

[0218] Furthermore, while a motor is constituted by the motor generator 8 and generates power during deceleration of a vehicle in the respective embodiments and the respective modifications presented above, configurations adopting an electric motor that does not generate power are also encompassed in the technical ideas of this invention.

[0219] This invention is applicable to a power transmission system of a four-wheel-drive vehicle capable of torque vectoring control.

Claims

CLAIMS:

1. A power transmission apparatus for a vehicle, comprising:

a ring gear configured to transmit power from a power source,

a differential device connected to the ring gear, the power transmission apparatus being configured to transmit power from a side gear of the differential device to at least one wheel of a pair of wheels,

a transmission engaging/disengaging mechanism provided on a first power transmission path between the side gear and the other wheel of the pair of wheels, the transmission engaging/disengaging mechanism being configured to switch between a power transmitted state and a power non-transmitted state between the side gear and the other wheel, and

a motor provided on a second power transmission path between the side gear and the one wheel or on the first power transmission path between the side gear and the other wheel.

2. The power transmission apparatus according to claim 1 , wherein

the motor is configured to be switched in accordance with a vehicle travel state between a state in which the motor generates a torque in a rotating direction that causes the vehicle to advance and a state in which the motor generates a torque in a rotating direction that is opposite to the rotating direction, when the transmission engaging/disengaging mechanism is in the power transmitted state.

3. The power transmission apparatus according to claim 1 or 2, wherein

the power transmission apparatus is configured to cause the motor to generate electric power by transmitting a rotative force of the wheel to the motor via the first power transmission path to drive the motor when the vehicle decelerates and when the transmission engaging/disengaging mechanism is in the power transmitted state.

4. The power transmission apparatus according to any one of claims 1 to 3, wherein the transmission engaging/disengaging mechanism and the motor are provided on the first power transmission path.

5. The power transmission apparatus according to claim 4, wherein

the motor is provided closer to the other wheel than the transmission

engaging/disengaging mechanism on the first power transmission path.

6. The power transmission apparatus according to claim 4, wherein

the motor is provided closer to the side gear than the transmission

engaging/disengaging mechanism on the first power transmission path.

7. The power transmission apparatus according to any one of claims 1 to 3, wherein

the transmission engaging/disengaging mechanism is provided on the first power transmission path, and

the motor is provided on the second power transmission path.

8. The power transmission apparatus according to any one of claims 1 to 7, wherein

the power transmission apparatus is configured to, when the transmission

engaging/disengaging mechanism is switched from the power non-transmitted state to the power transmitted state, control the torque of the motor so as to synchronize the rotation speed on the first power transmission path closer to the side gear than the transmission engaging/disengaging mechanism and the rotation speed on the first power transmission path closer to the wheel than the transmission engaging/disengaging mechanism with each other.

9. The power transmission apparatus according to any one of claims 1 to 8, wherein

the transmission engaging/disengaging mechanism includes a first mechanism that switches between the power transmitted state and the power non-transmitted state between the side gear and the other wheel, and a second mechanism that switches between a released state in which the side gear and a case of the differential device are relatively rotatable and an engaged state in which the side gear and the case of the differential device are relatively nonrotatable.

10. The power transmission apparatus according to claim 9, wherein

the transmission engaging/disengaging mechanism is configured to couple the side gear, the case, and the other wheel to one another to be relatively nonrotatable by establishing the power transmitted state between the side gear and the other wheel using the first mechanism and placing the side gear and the case in the engaged state using the second mechanism.

1 1 . The power transmission apparatus according to any one of claims 1 to 10, wherein the vehicle includes a switching mechanism that switches between an engaged state in which power from the power source is transmitted to driven wheels, and a released state in which the power from the power source is not transmitted to the driven wheels,

the transmission engaging/disengaging mechanism is configured to be in the power non-transmitted state in a two-wheel drive state in which the power from the power source is only transmitted to main drive wheels,

the switching mechanism is configured to be in the released state in the two-wheel drive state,

the transmission engaging/disengaging mechanism is configured to be in the power transmitted state in a four-wheel drive state in which the power from the power source is transmitted to both the main drive wheels and the driven wheels, and

the switching mechanism is configured to be in the engaged state in the four-wheel drive state.