JP2018070047A - Power distribution device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suitably distribute a torque to each wheel according to an application degree of traction onto each wheel.SOLUTION: A power distribution device 11, which is equipped with control means 16 which distributes torques from a front wheel drive motor 4 and a rear wheel drive motor 8 of a vehicle 1 to a front wheel 2 and a rear wheel 3, comprises: running state determination means 12 which determines a running state of the vehicle 1; and road surface determination means 17 which determines a state of a road surface on which the vehicle 1 runs. When it is determined by the running state determination means 12 that the vehicle is in an acceleration state or a steady running state in the case that it is determined by the road surface determination means 17 that the road surface is a downhill having a prescribed slope or more, the control means 16 further reduces a difference in torque distribution to the front wheel 2 and the rear wheel 3 compared with the case that the road surface is an uphill or a flat road.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a power distribution device that distributes torque from a drive source of a vehicle to drive wheels and subordinate wheels.

Conventionally, when a vehicle accelerates or decelerates or travels on an inclined road surface (uphill / downhill), the traction applied to each wheel of the vehicle changes, and the behavior does not depend on the road surface condition. In order to prevent it from becoming stable, power distribution devices have been developed. The power distribution device improves the running performance and stability of the vehicle by distributing the torque generated by the drive source to the front wheels and the rear wheels.
As a power distribution device that distributes torque generated by a drive source, Patent Document 1 controls torque distribution to drive wheels and subordinate wheels from the value of torque distributed to subordinate wheels calculated based on the road surface condition. A torque distribution device is disclosed.

Japanese Patent Laid-Open No. 9-048254

  By the way, when the vehicle is traveling on a steep downhill in which the vehicle is inclined forward so that a load is applied to the front wheels, the load does not move as much as when traveling on a flat road. For this reason, when traveling on a steep downhill, the degree of traction applied to the front wheels and the rear wheels is different, and there is a problem that torque distribution to the front wheels and the rear wheels becomes insufficient.

  Accordingly, an object of the present invention is to propose a power distribution device capable of appropriately distributing torque to each wheel in accordance with the degree of traction applied to each wheel.

  The present invention relates to a power distribution device including a control unit that distributes torque from a drive source of a vehicle to drive wheels and subordinate wheels, a travel state determination unit that determines a travel state of the vehicle, and a road surface state on which the vehicle travels Road surface determining means for determining whether the road surface is determined to be in an accelerated state or a steady traveling state by the traveling state determining means when the road surface determining means determines that the road surface is a downhill having a predetermined slope or more. When the road surface is uphill or flat, the difference in torque distribution between the driving wheel and the dependent wheel is made smaller.

  In the present invention, when the road surface is a downhill of a predetermined slope or more and the vehicle is in an accelerating state or a steady running state, the difference in torque distribution between the driving wheel and the dependent wheel is smaller than when the road surface is an uphill or a flat road. Therefore, the torque can be appropriately distributed to the drive wheel and the subordinate wheel according to the degree of traction applied to each wheel of the vehicle traveling on the downhill.

FIG. 1 is a system configuration diagram of a drive system of a vehicle. (Example) FIG. 2 is a system configuration diagram of the power distribution device. (Example) FIG. 3 is a flowchart of road surface condition determination. (Example) FIG. 4 is a flowchart for determining torque distribution on a downhill. (Example) FIG. 5A is a diagram showing torque distribution during acceleration on a downhill, FIG. 5B is a diagram showing torque distribution during deceleration on a downhill, and FIG. 5C is steady running on a downhill. It is a figure which shows the torque distribution at the time. (Example) FIG. 6 is a flowchart for determining torque distribution on an uphill. (Example) 7A is a diagram showing torque distribution during acceleration on an uphill, FIG. 7B is a diagram showing torque distribution during deceleration on an uphill, and FIG. 7C is a steady running on an uphill. It is a figure which shows the torque distribution at the time. (Example) FIG. 8 is a flowchart for determining torque distribution on a flat road. (Example) 9A is a diagram showing torque distribution during acceleration on a flat road, FIG. 9B is a diagram showing torque distribution during deceleration on a flat road, and FIG. 9C is steady running on a flat road. It is a figure which shows the torque distribution at the time. (Example)

  The object of the present invention is to make it possible to appropriately distribute torque to each wheel in accordance with the degree of traction applied to each wheel. When the vehicle is in a running state, it is realized by reducing the difference in torque distribution between the drive wheels and the dependent wheels as compared with the case where the road surface is uphill or flat.

Embodiments of the present invention will be described below with reference to the drawings. 1 to 9 show an embodiment of the present invention.
As shown in FIG. 1, the vehicle 1 includes left and right front wheels 2 and left and right rear wheels 3. The vehicle 1 is equipped with a front wheel drive motor 4 as a drive source. The front wheel drive motor 4 is driven by the power of the battery 5 and generates torque for driving the front wheel 2. The torque generated by the front wheel drive motor 4 is output to the left and right front wheels 2 via the front wheel side drive axle 7 by the front wheel side differential 6.
Further, the vehicle 1 is equipped with a rear wheel drive motor 8 as a drive source. The rear wheel drive motor 8 is driven by the electric power of the battery 5 and generates torque for driving the rear wheel 3. Torque generated by the rear wheel drive motor 8 is output to the left and right rear wheels 3 by the rear wheel side differential 9 through the rear wheel side drive axle 10.
The front wheel drive motor 4 and the rear wheel drive motor 8 function as an electric motor that generates torque that causes the vehicle 1 to travel. Further, the front wheel drive motor 4 and the rear wheel drive motor 8 function as generators that are driven by power from the front wheels 2 and the rear wheels 3 to generate regenerative power, respectively. The regenerated power is supplied to the battery 5 and charged.
The vehicle 1 travels by driving the front wheels 2 with the torque of the front wheel drive motor 4 and driving the rear wheels 3 with the torque of the rear wheel drive motor 8. Thus, the vehicle 1 is a four-wheel drive vehicle in which the front wheels 2 driven by the front wheel drive motor 4 are drive wheels and the rear wheels 3 driven by the rear wheel drive motor 8 are subordinate wheels.

The torque transmitted from the front wheel drive motor 4 of the vehicle 1 to the front wheel 2 and the torque transmitted from the rear wheel drive motor 8 to the rear wheel 3 are torque-distributed by the power distribution device 11.
As shown in FIG. 2, the power distribution device 11 includes travel state determination means 12 that determines the travel state of the vehicle 1. An accelerator sensor 13, a brake sensor 14, and a vehicle attitude sensor 15 are connected to the traveling state determination unit 12. The vehicle attitude sensor 15 includes an acceleration sensor that detects, for example, gravity, vibration, and movement acting on the object and obtains information such as the inclination and movement of the object.
The traveling state determination unit 12 determines whether the vehicle 1 is in an acceleration state or a deceleration state based on the accelerator pedal depression amount detected by the accelerator sensor 13 and the brake pedal depression amount detected by the brake sensor 14. The traveling state determination unit 12 determines whether the vehicle posture with respect to the road surface detected by the vehicle posture sensor 15 is forward or backward, and determines whether the vehicle load is applied to the front wheel 2 or the rear wheel 3 more.
The traveling state determination means 12 determines whether the traveling state of the vehicle 1 is an acceleration state, a deceleration state, or a steady traveling state based on the accelerator pedal depression amount, the brake pedal depression amount, and the vehicle posture. The traveling state determination unit 12 outputs the determination result to the control unit 16.
The power distribution device 11 includes road surface determination means 17 that determines the state of the road surface on which the vehicle 1 travels. A vehicle attitude sensor 15 is connected to the road surface determination means 17. Based on the vehicle attitude relative to the road surface detected by the vehicle attitude sensor 15, the road surface judging means 17 determines whether the road surface on which the vehicle 1 travels is downhill (downhill road), uphill (uphill road), or flat road. Determine. Furthermore, the road surface determination means 17 determines whether it is a downhill beyond a predetermined gradient, when the road surface state is a downhill. The road surface determination unit 17 outputs the determination result to the control unit 16.

Based on the determination results input from the traveling state determination unit 12 and the road surface determination unit 17, the control unit 16 transmits the torque of the front wheel drive motor 4 transmitted to the front wheels 2 and the rear wheel drive motor 8 transmitted to the rear wheels 3. Torque is determined, and torque distribution between the front wheels 2 and the rear wheels 3 is determined.
The control means 16 drives the front wheel drive motor 4 and the rear wheel drive motor 8, respectively, so as to generate torque with the determined torque distribution. The torque generated by the front wheel drive motor 4 and the torque generated by the rear wheel drive motor 8 are output to the front wheel 2 and the rear wheel 3, respectively, and drive the front wheel 2 and the rear wheel 3 respectively with the determined torque distribution torque.
In the torque distribution, when the road surface determination unit 17 determines that the road surface is a downhill with a predetermined slope or more, the control unit 16 determines that the traveling state determination unit 12 determines that the vehicle is in an acceleration state or a steady traveling state. The torque transmitted to the front wheel 2 and the rear wheel 3 are transmitted rather than the difference ΔT1 between the torque distribution of the torque transmitted to the front wheel 2 and the torque transmitted to the rear wheel 3 when the road surface is an uphill or flat road. The difference ΔT2 in the torque distribution of the torques to be distributed is reduced (ΔT1> ΔT2).
In addition, when the road surface determination unit 17 determines that the road surface is a downhill, the control unit 16 outputs to the front wheel 2 that is a drive wheel when the traveling state determination unit 12 determines that the vehicle is in an acceleration state. The torque Tr output to the rear wheel 3 which is a dependent wheel is more largely distributed than the torque Tf (Tf <Tr).
Further, based on the determination results input from the traveling state determination unit 12 and the road surface determination unit 17, the control unit 16 is driven by the regenerative torque of the front wheel drive motor 4 that is driven by the power from the front wheels 2 to generate regenerative power and the rear wheels 3. The regenerative torque of the rear wheel drive motor 8 that is driven by the power of the regenerative power to generate regenerative power is determined, and the regenerative torque distribution of the front wheel drive motor 4 and the rear wheel drive motor 8 is determined.
The control means 16 drives the front wheel drive motor 4 and the rear wheel drive motor 8 with power from the front wheels 2 and the rear wheels 3, respectively, so as to generate regenerative power with the regenerative torque of the determined regenerative torque distribution. The power regenerated by the front wheel drive motor 4 and the power regenerated by the rear wheel drive motor 8 are supplied to the battery and charged.

Next, torque distribution by the power distribution device 11 will be described with reference to the flowcharts of FIGS.
As shown in FIG. 3, when the road surface state determination program starts, the power distribution device 11 determines the road surface state in which the vehicle 1 travels by the road surface determination unit 17 (100), and from the determination result of the road surface determination unit 17. It is determined whether the road surface is a downhill (200).
When the determination (200) of the downhill is YES, the power distribution device 11 determines the torque distribution during the downhill by the control means 16 (300), and returns to the determination of the road surface state (100). The power distribution device 11 determines whether the road surface is an uphill from the determination result of the road surface determination means 17 when the determination (200) of the downhill is NO (400).
When the judgment (400) of the uphill is YES, the power distribution device 11 determines the torque distribution during the uphill by the control means 16 (500), and returns to the judgment of the road surface condition (100). The power distribution device 11 determines that the road surface is a flat road from the determination result of the road surface determination unit 17 when the determination (400) of the uphill is NO, and the control unit 16 determines torque distribution on the flat road ( 600), the process returns to road surface condition determination (100).

As shown in FIG. 4, in the downhill torque distribution determination (300), when the program starts, the power distribution device 11 determines the traveling state of the vehicle 1 by the traveling state determination means 12 (301), and the traveling state It is determined from the determination result of the determination means 12 whether the vehicle 1 is in an acceleration state (302). The traveling state determination means 12 determines that the vehicle 1 is accelerating (acceleration state) when the accelerator pedal depression amount is larger than before, the brake pedal depression amount is “0”, and the vehicle posture is tilted backward from the immediately preceding state. .
When the determination of the acceleration state (302) is YES, the power distribution device 11 has the traction of the rear wheel 3 larger than the traction of the front wheel 2 as shown in FIG. The torque Tr output to the rear wheel 3 is set to be larger than the output torque Tf (Tf <Tr) (303), and it is determined from the determination result of the road surface determination means 17 whether the road surface is a downhill with a predetermined slope or more. (304).
When the determination (304) of the downhill above the predetermined gradient is YES, the power distribution device 11 calculates the difference ΔT2 between the torque distribution of the torque output to the front wheels 2 and the torque output to the rear wheels 3 by the control means 16. It is set to be smaller (ΔT1> ΔT2) than the difference ΔT1 in the torque distribution between the torque output to the front wheels 2 and the torque output to the rear wheels 3 when the vehicle is on an uphill or flat road and is in an acceleration state ( 305), the process returns to the determination of the running state (301).
The power distribution device 11 returns to the determination (301) of the traveling state when the determination (304) of the downhill above the predetermined gradient is NO.
Note that the torque distribution difference ΔT2 between the front wheel 2 and the rear wheel 3 in the case of a downhill is set smaller (ΔT1> ΔT2) than the torque distribution difference ΔT1 in the case of an uphill or flat road. (305) is, for example, (front wheel torque) :( rear wheel torque) = 20: 80 (ΔT1 = 60) on a flat road, but (down front wheel torque) :( rear) Wheel torque) = 40: 60 (ΔT2 = 20).

When the determination of the acceleration state (302) is NO, the power distribution device 11 determines whether the vehicle 1 is in a deceleration state from the determination result of the traveling state determination means 12 (306). The traveling state determination means 12 determines that the vehicle 1 is decelerating (decelerated state) when the accelerator pedal depression amount is “0”, the brake pedal depression amount is larger than before, and the vehicle posture is tilted forward from the immediately preceding state. .
When the determination of the deceleration state (306) is YES, the power distribution device 11 determines that the traction of the front wheel 2 is larger than the traction of the rear wheel 3 as shown in FIG. The regenerative torque Rf of the front wheel drive motor 4 driven by the power of the rear wheel is set larger than the regenerative torque Rr of the rear wheel drive motor 8 driven by the power from the rear wheel 3 (Rf> Rr) (307), and the running state Return to the determination (301). The power distribution device 11 can efficiently obtain regenerative energy and increase the deceleration amount of the vehicle 1 by increasing the regeneration amount of the front wheel 2 that requires more traction during deceleration.
When the determination (306) of the deceleration state is NO, the power distribution device 11 determines that the vehicle 1 is in a steady traveling state from the determination result of the traveling state determination unit 12. When the accelerator pedal depression amount is equal to that immediately before, the brake pedal depression amount is “0”, and the vehicle posture is equal to the immediately preceding state, the traveling state determination unit 12 determines that the vehicle 1 is traveling at a constant speed (steady traveling state). judge.
When the power distribution device 11 determines that the vehicle 1 is in a steady running state, the traction of the front wheels 2 is larger than the traction of the rear wheels 3 as shown in FIG. The torque distribution (Tf: Tr) between the torque Tf output to the front wheel 2 and the torque Tr output to the rear wheel 3 is set (308), and the road surface is a downhill having a predetermined slope or more from the determination result of the road surface determination means 17. (309).
The power distribution device 11 determines that the torque Tf output to the front wheel 2 and the torque output to the rear wheel 3 by the control means 16 in the same manner as (305) when the determination (309) of the downhill above the predetermined gradient is YES. The difference in torque distribution ΔT2 between Tr is the difference in torque distribution between the torque Tf output to the front wheels 2 and the torque Tr output to the rear wheels 3 when the vehicle is in an uphill or flat road and is in a steady running state. It is set to be smaller than ΔT1 (ΔT1> ΔT2) (310), and the process returns to the traveling state determination (301).
The power distribution apparatus 11 returns to the determination (301) of a driving state, when determination (309) more than a predetermined gradient is NO.

As shown in FIG. 6, in the uphill torque distribution determination (500), when the program starts, the power distribution device 11 determines the traveling state of the vehicle 1 by the traveling state determination means 12 (501), and the traveling state It is determined from the determination result of the determination means 12 whether the vehicle 1 is in an accelerated state (502). The traveling state determination means 12 determines that the vehicle 1 is accelerating (acceleration state) when the accelerator pedal depression amount is larger than before, the brake pedal depression amount is “0”, and the vehicle posture is tilted backward from the immediately preceding state. .
When the acceleration state determination (502) is YES, the power distribution device 11 has the traction of the rear wheel 3 larger than the traction of the front wheel 2 as shown in FIG. The torque Tr output to the rear wheel 3 is set to be larger than the output torque Tf (Tf <Tr) (503), and the process returns to the determination of the running state (501). In the acceleration state, the torque Tr output to the rear wheel 3 is increased, so that the front wheel 2 with low traction is prevented from idling and the energy loss of the front wheel 2 due to idling is reduced.

When the determination of the acceleration state (502) is NO, the power distribution device 11 determines whether the vehicle 1 is in a deceleration state from the determination result of the traveling state determination means 12 (504). The traveling state determination means 12 determines that the vehicle is decelerating (decelerated state) when the accelerator pedal depression amount is “0”, the brake pedal depression amount is larger than before, and the vehicle posture is tilted forward from the immediately preceding state.
When the determination of the deceleration state (504) is YES, the power distributor 11 determines that the traction of the front wheel 2 is larger than the traction of the rear wheel 3 as shown in FIG. The regenerative torque Rf of the front wheel drive motor 4 driven by the power of the rear wheel is set larger than the regenerative torque Rr of the rear wheel drive motor 8 driven by the power from the rear wheel 3 (Rf> Rr) (505), and the running state Return to the determination (501). The power distribution device 11 can efficiently obtain regenerative energy and increase the deceleration amount of the vehicle 1 by increasing the regeneration amount of the front wheel 2 that requires more traction during deceleration.
When the determination of the deceleration state (504) is NO, the power distribution device 11 determines that the vehicle 1 is in the steady traveling state from the determination result of the traveling state determination unit 12. When the accelerator pedal depression amount is equal to that immediately before, the brake pedal depression amount is “0”, and the vehicle posture is equal to the immediately preceding state, the traveling state determination unit 12 determines that the vehicle 1 is traveling at a constant speed (steady traveling state). judge.
When the power distribution device 11 determines that the vehicle 1 is in the steady running state, the traction of the rear wheel 3 is larger than the traction of the front wheel 2 as shown in FIG. The torque Tr output to the rear wheel 3 is set to be larger than the torque Tf (Tf <Tr) (506), and the process returns to the determination of the running state (501). In the setting of torque distribution in the steady running state (506), the torque output to the front wheel 2 where the traction slips small is reduced, and the torque output to the rear wheel 3 where the traction does not slip greatly increases.

As shown in FIG. 8, in the torque distribution determination (600) on the flat road, when the program starts, the power distribution device 11 determines the traveling state of the vehicle 1 by the traveling state determination means 12 (601), and the traveling state It is determined from the determination result of the determination means 12 whether the vehicle 1 is in an accelerated state (602). The traveling state determination means 12 determines that the vehicle is accelerating (acceleration state) when the accelerator pedal depression amount is larger than before, the brake pedal depression amount is “0”, and the vehicle posture is tilted backward from the immediately preceding state.
When the determination of the acceleration state (602) is YES, the power distribution device 11 has the traction of the rear wheel 3 larger than the traction of the front wheel 2 as shown in FIG. The torque Tr output to the rear wheel 3 is set to be larger than the output torque Tf (Tf <Tr) (603), and the process returns to the determination of the running state (601). In the acceleration state, the torque Tr output to the rear wheel 3 is increased, so that the front wheel 2 with low traction is prevented from idling and the energy loss of the front wheel 2 due to idling is reduced.

When the determination of the acceleration state (602) is NO, the power distribution device 11 determines whether the vehicle 1 is in a deceleration state from the determination result of the traveling state determination means 12 (604). The traveling state determination means 12 determines that the vehicle 1 is decelerating (decelerated state) when the accelerator pedal depression amount is “0”, the brake pedal depression amount is larger than before, and the vehicle posture is tilted forward from the immediately preceding state. .
When the determination of the deceleration state (604) is YES, the power distribution device 11 has the traction of the front wheel 2 larger than the traction of the rear wheel 3 as shown in FIG. The regenerative torque Rf of the front wheel drive motor 4 driven by the power of the rear wheel is set larger than the regenerative torque Rr of the rear wheel drive motor 8 driven by the power from the rear wheel 3 (Rf> Rr) (605), and the running state Return to the determination (601). The power distribution device 11 can efficiently obtain regenerative energy and increase the deceleration amount of the vehicle 1 by increasing the regeneration amount of the front wheel 2 that requires more traction during deceleration.
When the determination of the deceleration state (604) is NO, the power distribution device 11 determines that the vehicle 1 is in a steady traveling state from the determination result of the traveling state determination unit 12. When the accelerator pedal depression amount is equal to that immediately before, the brake pedal depression amount is “0”, and the vehicle posture is equal to the immediately preceding state, the traveling state determination unit 12 determines that the vehicle 1 is traveling at a constant speed (steady traveling state). judge.
When the power distribution device 11 determines that the vehicle 1 is in the steady running state, the control means 16 outputs the torque Tf output to the front wheel 2 and the rear wheel 3 in accordance with the road surface traction, as shown in FIG. Torque distribution (Tf: Tr) with the torque Tr to be performed is set (606), and the process returns to the determination of the running state (601). In the torque distribution setting (606) in the steady running state, the torque of the wheel that slips is reduced, and the torque of the wheel that does not slip is increased.

Thus, when the road surface is a downhill with a predetermined slope or more and the vehicle 1 is in an acceleration state or a steady running state, the power distribution device 11 has the torque of the front wheels 2 and the rear wheels 3 in the case of an uphill or flat road. Since the torque distribution difference ΔT2 between the front wheels 2 and the rear wheels 3 is made smaller than the distribution difference ΔT1 (ΔT1> ΔT2), depending on the degree of traction applied to each wheel of the vehicle 1 traveling on the downhill, Torque can be appropriately distributed to 2 and the rear wheel 3.
For this reason, the power distribution device 11 can prevent the behavior from becoming unstable depending on the state of the road surface, and can improve the running performance and stability of the vehicle 1.
Further, when the road surface is a downhill and the vehicle 1 is in an acceleration state, the power distribution device 11 increases the torque Tr output to the rear wheel 3 more than the torque Tf output to the front wheel 2 (Tf <Tr). Therefore, it is possible to prevent idling of the front wheel 2 with small traction, to reduce the energy loss of the front wheel 2 due to idling, and to improve the running performance and stability of the vehicle 1.
Further, the power distribution device 11 can efficiently obtain regenerative energy and increase the deceleration amount of the vehicle 1 by increasing the regeneration amount of the front wheel 2 that requires more traction during deceleration.
In the above-described embodiment, the accelerator sensor 13, the brake sensor 14, and the vehicle attitude sensor 15 are provided. However, by using the accelerator sensor, the brake sensor, and the vehicle attitude sensor that are already mounted on the conventional vehicle 1, the components There is no point increase. Further, in the vehicle 1 in which the skid prevention device (ESP: Electronic Stability Program) is already mounted, the sensor of the skid prevention device can be used as a vehicle attitude sensor.
In the above embodiment, one front wheel drive motor 4 for driving the left and right front wheels 2 and one front wheel drive motor 8 for driving the left and right rear wheels 3 are provided. Even in a vehicle provided with a drive motor (such as an in-wheel motor), torque distribution in an acceleration state, a deceleration state, and a steady running state can be performed as in the present invention.
Further, in a vehicle in which drive motors (such as in-wheel motors) are provided on the left and right front wheels and the left and right rear wheels, the vehicle cornering state is determined by the detection signals of the accelerator sensor, the brake sensor, and the vehicle attitude sensor as in the present invention. The cornering performance can be improved by determining and performing a larger torque distribution on the outer wheel that is loaded than the inner wheel that is not loaded.

  The power distribution device according to the present invention is capable of appropriately distributing torque to each wheel according to the degree of traction applied to each wheel. The present invention can be applied to a vehicle equipped with a motor to drive drive wheels and dependent wheels.

DESCRIPTION OF SYMBOLS 1 Vehicle 2 Front wheel 3 Rear wheel 4 Front wheel drive motor 5 Battery 6 Front wheel side differential device 7 Front wheel side drive axle 8 Rear wheel drive motor 9 Rear wheel side differential device 10 Rear wheel side drive axle 11 Power distribution device 12 Running state determination Means 13 Accelerator sensor 14 Brake sensor 15 Vehicle attitude sensor 16 Control means 17 Road surface judgment means

Claims (2)

  In a power distribution device including a control unit that distributes torque from a driving source of a vehicle to driving wheels and subordinate wheels, a traveling state determining unit that determines a traveling state of the vehicle and a state of a road surface on which the vehicle travels are determined. Road surface determining means, and when the road surface determining means determines that the road surface is a downhill of a predetermined slope or more, the control means is in an acceleration state or a steady driving state by the traveling state determining means. When judged, the power distribution device is characterized in that the difference in torque distribution between the drive wheel and the dependent wheel is made smaller than when the road surface is an uphill or flat road.   When the road surface determining means determines that the road surface is a downhill when the road surface determining means determines that the road surface is in an accelerating state, the control means determines that the dependent wheel is more than the torque of the driving wheel. The power distribution device according to claim 1, wherein torque is largely distributed.

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