JP5458901B2 - Driving force distribution control device for four-wheel drive vehicle - Google Patents

Description

  The present invention relates to a driving force distribution control device applied to a four-wheel drive vehicle.

  As a conventional driving force distribution control device for a four-wheel drive vehicle, a center differential device that distributes the driving force of a driving source to the driving shafts of the front and rear wheels while allowing the differential to be distributed, and the differential of the center differential device is limited. (For example, refer to Patent Document 1).

  In the driving force distribution control device described in Patent Document 1, for example, the difference in rotational speed between the front and rear wheels becomes large, such as when starting on a road surface with different front and rear friction coefficients, or when accelerating a four-wheel drive vehicle with rear wheel bias. In such a case, the clutch engaging force is strengthened to limit the differential between the front and rear wheels.

Japanese Patent Application Laid-Open No. 11-1129

  However, if the engagement force of the clutch is simply increased according to the difference in rotational speed between the front and rear wheels, the running stability may be impaired depending on the running state of the vehicle. For example, when a four-wheel drive vehicle that strengthens the clutch engagement force according to the rotational speed difference between the front and rear wheels is in an oversteer state (a state in which the vehicle body changes its direction beyond the steering amount) during turning. The present inventors have confirmed that it may take time to eliminate the oversteer state.

  Therefore, an object of the present invention is to provide a driving force distribution control device for a four-wheel drive vehicle capable of suppressing an oversteer state during turning.

In order to achieve the above object, a driving force distribution control device for a four-wheel drive vehicle according to the present invention is configured such that a driving force of a driving source of a vehicle is transmitted between a driving shaft on a front wheel side and a driving shaft on a rear wheel side. a differential mechanism which allows a differential distribution, the differential between the drive shaft, a clutch for limiting the tightening force generated in response to a supplied current, the current for controlling the engagement force of said clutch A control unit that generates a command value, and the control unit detects a difference in rotational speed difference between the front and rear wheels from a current command value that increases as the throttle opening increases when the vehicle enters an oversteer state . A subtraction current command value obtained by subtracting a current command value that increases in accordance with the increase is generated, and the engagement force of the clutch is controlled based on the subtraction current command value .

  According to this configuration, the differential restriction between the front wheel and the rear wheel in the oversteer state is suppressed, and the braking force due to the differential restriction is prevented from acting on the front wheel side.

Further, the control unit, when the vehicle becomes the over-steering state and deceleration state, may be so as to reduce the engagement force of the clutch.

  According to this configuration, it is possible to more appropriately prevent the braking force due to the differential restriction from acting on the front wheel side.

  According to the present invention, it is possible to suppress an oversteer state during turning of a four-wheel drive vehicle.

FIG. 1 is a schematic diagram showing a four-wheel drive vehicle equipped with a driving force distribution control device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a configuration of a differential device of the driving force distribution control device according to the embodiment of the present invention. FIG. 3 is a block diagram showing a configuration of a control unit of the driving force distribution control apparatus according to the embodiment of the present invention. 4A and 4B show torque maps stored in the storage unit 12 of the control unit of the driving force distribution control apparatus according to the embodiment of the present invention. FIG. 4A shows a feedforward torque map, and FIG. 4B shows a feedback torque map. (C) shows an oversteer control torque map. FIG. 5 is a schematic view showing a situation when a four-wheel drive vehicle equipped with the driving force distribution control device according to the embodiment of the present invention is turning in an oversteer state. FIG. 6 is a flowchart showing an operation procedure of the control unit of the driving force distribution control apparatus according to the embodiment of the present invention.

[Embodiment]
FIG. 1 shows a configuration example of a four-wheel drive vehicle equipped with a driving force distribution control device according to the present invention. The four-wheel drive vehicle 101 receives an engine 102 as a drive source, a transmission 103 that shifts the rotation of the output shaft of the engine 102, and a driving force output from the transmission 103 via an input shaft 104. A driving force distribution control device 1 that outputs to a front drive shaft 105 as a drive shaft and a propeller shaft 109 as a drive shaft on the rear wheel side.

  The driving force output to the front drive shaft 105 is transmitted to the pair of front axle shafts 107a and 107b via the front differential 106, and a pair of front wheels 108a and 108b coupled to the pair of front axle shafts 107a and 107b, respectively. Drive.

  The driving force output to the propeller shaft 109 is transmitted to the pair of rear axle shafts 111a and 111b via the rear differential 110, and drives the pair of rear wheels 112a and 112b connected to the pair of rear axle shafts 111a and 111b, respectively. To do.

  The driving force distribution control device 1 includes a control unit 10, a differential mechanism 1A, and a clutch mechanism 2. The differential mechanism 1A and the clutch mechanism 2 constitute a differential device 1B.

  The control unit 10 determines the wheel speed of each wheel from the wheel speed sensor 10a for the right front wheel 108a, the wheel speed sensor 10b for the left front wheel 108b, the wheel speed sensor 10c for the right rear wheel 112a, and the wheel speed sensor 10d for the left rear wheel 112b. Receive information. Further, the control unit 10 receives information on the yaw rate when the four-wheel drive vehicle 101 is traveling from the yaw rate sensor 10e, receives information on the steering angle from the steering angle sensor 10f, and indicates the output of the engine 102 from the throttle opening sensor 10g. Receives information on throttle opening. The control unit 10 controls the clutch mechanism 2 based on these pieces of information.

  The differential mechanism 1 </ b> A includes a cage 3 coupled to rotate integrally with the input shaft 104, a plurality of planetary gears 4 held in a holding hole formed in the cage 3, and an inner peripheral side of the cage 3 The sun gear 5 that meshes with the planetary gear 4 and the internal gear 6 that meshes with the planetary gear 4 on the outer peripheral side of the cage 3. A cylindrical member 50 is connected to the inner periphery of the sun gear 5 so as to rotate integrally, and a gear 105a provided on the front drive shaft 105 meshes with a gear 50a provided on the outer periphery of the cylindrical member 50, so that the front drive shaft is engaged. 105 is connected. The internal gear 6 is connected so as to rotate integrally with the propeller shaft 109.

(Configuration of differential device 1B)
FIG. 2 is a cross-sectional view illustrating a configuration example of the differential device 1B. The differential device 1 </ b> B includes a differential mechanism 1 </ b> A and a clutch mechanism 2, and the differential mechanism 1 </ b> A and the clutch mechanism 2 are accommodated in a differential case 7. In the differential mechanism 1A, a cage 3, a sun gear 5 and an internal gear 6 are arranged coaxially and relatively rotatable.

(Configuration of differential mechanism 1A)
The cage 3 is provided at the outer periphery of the connecting portion 31 formed with a spline fitting portion 31a for connecting the input shaft 104 in a relatively non-rotatable manner at the center, and rotates the plurality of planetary gears 4 in rotation. A holding portion 32 in which a plurality of holding holes 32a for holding is formed is integrally formed.

In the planetary gear 4, a large diameter portion 41 and a small diameter portion 42 having different pitch circle diameters D ₁ and D ₂ (D ₁ > D ₂ ) are integrally formed in the axial direction. The revolution outer peripheral side of the large diameter portion 41 and the revolution inner peripheral side of the small diameter portion 42 are supported by the support surface 32 b and the support surface 32 c of the holding portion 32 of the cage 3.

  The sun gear 5 is a cylindrical member in which a gear portion 5b that meshes with the gear portion 41a of the large-diameter portion 41 of the planetary gear 4 is formed on the outer peripheral surface, and a spline fitting portion 5c is formed on the inner peripheral surface. The aforementioned cylindrical member 50 (shown in FIG. 1) is fitted to the spline fitting portion 5c so as not to be relatively rotatable.

  The internal gear 6 is provided at the outer periphery of the connecting portion 61 formed with a spline fitting portion 61a for connecting the propeller shaft 109 in a relatively non-rotatable manner at the center, and a clutch described later on the outer peripheral surface thereof. A clutch coupling portion 62 formed with a spline fitting portion 62a into which the inner clutch plate 21 of the mechanism 2 is fitted, and a gear portion 42a of the small-diameter portion 42 of the planetary gear 4 provided on the outer peripheral side of the clutch coupling portion 62; A gear meshing portion 63 formed with a meshing gear portion 63a is integrally formed.

When the pitch circle diameter of the sun gear 5 is D ₃ and the pitch circle diameter of the internal gear 6 is D ₄ , the input to the sun gear 5 and the internal gear 6 is input from the input shaft 104 when the clutch mechanism 2 is not operating. The generated driving force is distributed at a ratio of D ₃ / D ₁ (sun gear 5): D ₄ / D ₂ (internal gear 6). In the present embodiment, each pitch circle diameter is set so that D ₃ / D ₁ <D ₄ / D ₂ , that is, the driving force distributed to the internal gear 6 is larger than the driving force distributed to the sun gear 5. Has been. As a result, the four-wheel drive vehicle 101 has a rear-wheel-biased driving force distribution configuration in which a larger driving force is transmitted to the rear wheels 112a and 112b than the front wheels 108a and 108b.

  The differential case 7 includes a bottomed cylindrical first housing 71 and a second housing 72 coupled to rotate integrally with the first housing 71 so as to cover the opening of the first housing 71. It is rotatably supported by the vehicle body (not shown) of the driving vehicle 101.

  The first housing 71 includes a bottom portion 711 and a cylindrical portion 712 formed integrally with the bottom portion, and the bottom portion 711 is coupled so as to rotate integrally with the sun gear 5. An annular washer 76 is disposed between the bottom 711 and the planetary gear 4. Further, a spline fitting portion 712a to which an outer clutch plate 22 of the clutch mechanism 2 described later is fitted is formed on a portion of the inner peripheral surface of the cylindrical portion 712 facing the spline fitting portion 62a of the internal gear 6. Yes.

  The second housing 72 is configured by integrally coupling a first element 721, a second element 722, and a third element 723. The first element 721 is made of a magnetic material such as carbon steel, and is screwed and coupled to the opening 721 a of the cylindrical portion 712 of the first housing 71. The second element 722 is a ring-shaped member made of a nonmagnetic material such as stainless steel, and is joined to the inner peripheral surface of the first element 721 by welding. The third element 723 is made of a magnetic material such as carbon steel, and is coupled to the inner peripheral surface of the second element 722 by welding. A bearing 73 is disposed between the inner peripheral surface of the third element 723 and the outer peripheral surface of the connecting portion 61 of the internal gear 6, and the axial end surface of the third element 723 and the axial end surface of the connecting portion 61 of the internal gear 6. A bearing 74 is disposed between the two.

  On the opposite side of the second housing 72 from the differential mechanism 1 </ b> A, an annular accommodation space 72 a that opens in the same direction as the first housing 71 is formed.

(Configuration of clutch mechanism 2)
The clutch mechanism 2 is axially movable to the inner clutch plate 21 that is axially movable and relatively non-rotatable to the spline fitting portion 62a of the internal gear 6, and the spline fitting portion 712a of the first housing 71. It has the clutch 20 which consists of the outer clutch plate 22 fitted so that relative rotation was impossible, and the press mechanism 200 which presses the clutch 20. FIG.

  The pressing mechanism 200 includes an armature 23 fitted to the spline fitting portion 712a of the first housing 71 so as to be axially movable and relatively non-rotatable, the electromagnetic coil 24 housed in the housing space 72a of the second housing 72, A yoke 25 that holds the electromagnetic coil 24 is included.

  The yoke 25 is supported by a bearing 75 disposed between the outer periphery of the third element 723 of the second housing 72. Between the outer peripheral surface of the yoke 25 and the inner peripheral surface of the first element 721 of the second housing 72 and between the inner peripheral surface of the yoke 25 and the outer peripheral surface of the third element 723 of the second housing 72 Air gaps are formed at intervals of.

  A current is supplied to the electromagnetic coil 24 from the control unit 10 through wiring not shown. When the electromagnetic coil 24 is energized, the yoke 25, the first element 721 of the second housing 72, the inner clutch plate 21, the outer clutch plate 22, the armature 23, and the third element 723 of the second housing 72 are used as magnetic paths. A magnetic field is generated, and the armature 23 is drawn toward the second housing 72 side. Then, the inner clutch plate 21 and the outer clutch plate 22 are pressed, and the fastening force of the clutch 20 is generated. The fastening force of the clutch 20 is a differential limiting force that limits the differential between the sun gear 5 and the internal gear 6, and thus the front drive shaft 105 and the propeller shaft 109.

(Configuration of control unit 10)
FIG. 3 is a block diagram illustrating a configuration of the control unit 10. The control unit 10 receives signals from a processing execution unit 11 configured by a CPU (Central Processing Unit) and the like, a storage unit 12 configured by a storage element such as a ROM and a RAM, and various sensors 10a to 10g. An input circuit 13 and an output circuit 14 for supplying current to the electromagnetic coil 24 are provided.

  The process execution unit 11 functions as the basic control unit 111 and the oversteer control unit 112 by operating according to the program 120 stored in the storage unit 12. In addition to the program 120, the storage unit 12 stores a feedforward torque map 121, a feedback torque map 122, and an oversteer control torque map 123.

  FIG. 4 shows an example of a torque map stored in the storage unit 12, where (a) shows a feedforward torque map 121, (b) shows a feedback torque map 122, and (c) shows an oversteer control torque map 123. Show.

(Basic control)
The feed forward torque map 121 shows the relationship between the throttle opening and the first current command value. As shown in FIG. 4A, the feedforward torque map 121 shows the characteristics of the first current command value that increases with an increase in the throttle opening and gradually decreases.

  The feedback torque map 122 shows the relationship between the differential rotation speed that is the difference between the average rotation speed of the front wheels 108a and 108b and the average rotation speed of the rear wheels 112a and 112b and the second current command value. As shown in FIG. 4B, the feedback torque map 122 shows the characteristic of the second current command value that is substantially proportional to the differential rotation speed.

  The basic control unit 111 controls the fastening force of the clutch 20 with reference to the feedforward torque map 121 and the feedback torque map 122. More specifically, the current command value is obtained by adding the first current command value obtained by referring to the feedforward torque map 121 and the second current command value obtained by referring to the feedback torque map 122, and A command signal is sent to the output circuit 14 so that the current of the current command value is supplied to the electromagnetic coil 24.

  As a result, when the driver performs an operation to increase the throttle opening for acceleration, the first current command value increases and the energization current of the electromagnetic coil 24 increases. Then, the fastening force of the clutch 20 increases and the differential limiting force increases. As a result, the driving force transmitted to the front wheels 108a and 108b and the rear wheels 112a and 112b is made uniform, and the occurrence of slip is suppressed.

  For example, when slip occurs in the front wheels 108a and 108b or the rear wheels 112a and 112b and the differential rotational speed increases, the second current command value increases and the energization current of the electromagnetic coil 24 increases. Then, the fastening force of the clutch 20 increases and the differential limiting force increases. As a result, the slip converges.

(Vehicle behavior in oversteer condition)
FIG. 5 shows a situation when the four-wheel drive vehicle 101 is turning on the left curve in an oversteer state. Such an oversteer state can occur, for example, when the driver depresses the accelerator excessively and the rear wheels 112a and 112b drift out. In such a case, the driver usually performs a counter steer operation for operating the steering in a direction (right direction) opposite to the turning direction (left direction).

  In such a state, the rear wheels 112a and 112b are inclined with respect to the vehicle traveling direction (indicated by the arrow A), while the front wheels 108a and 108b are directed in the direction along the vehicle traveling direction. Therefore, the rotational speed of the front wheels 108a and 108b becomes faster than the rotational speed of the rear wheels 112a and 112b, and the differential rotational speed increases.

  If the four-wheel drive vehicle 101 includes the basic control unit 111 and does not include the oversteer control unit 112, the second command current increases due to an increase in the differential rotational speed and is supplied to the electromagnetic coil 24. The differential limiting force by the clutch 20 increases due to the increase in current. This differential limiting force acts so that the rotational speeds of the front wheels 108a and 108b are equal to the rotational speed of the rear wheels 112a and 112b, so that the braking force is applied to the front wheels 108a and 108b due to the increase of the differential limiting force. An acceleration force acts on the wheels 112a and 112b. Then, a counterclockwise yaw moment indicated by an arrow B is generated in the four-wheel drive vehicle 101, and a stronger oversteer state is established.

  However, since the control unit 10 of the four-wheel drive vehicle 101 according to the present embodiment includes the oversteer control means 112 described below, it is possible to avoid the situation described above.

(Oversteer control)
The oversteer control is a control executed by the oversteer control means 112 when the four-wheel drive vehicle 101 is in an oversteer state during turning. The oversteer control means 112 performs control to reduce the current supplied to the electromagnetic coil 24 with reference to the oversteer control torque map 123 when the oversteer state is reached.

  The oversteer control torque map 123 shows the relationship between the differential rotational speed that is the difference between the average rotational speed of the front wheels 108a and 108b and the average rotational speed of the rear wheels 112a and 112b and the third current command value. As shown in FIG. 4C, the oversteer control torque map 123 shows the characteristic of the third current command value that gradually increases as the differential rotational speed increases.

  When the oversteer control unit 112 determines that the four-wheel drive vehicle 101 is in the oversteer state based on the information received from the various sensors 10a to 10g, the oversteer control unit 112 refers to the oversteer control torque map 123 to determine the third current command value. The signal of the current command value obtained by subtracting the third current command value from the first current command value calculated by the basic control means 111 is sent to the output circuit 14. Thereby, the differential limiting force in the oversteer state is reduced as compared with the case where only the basic control means 111 is provided.

  In addition, the phenomenon that the oversteer state is promoted as described above is conspicuous at the time of deceleration with the throttle closed, for example. Therefore, the oversteer state is determined from the first current command value in the oversteer state and the deceleration state. You may make it perform the process which subtracts a 3rd electric current command value and makes it a electric current command value. Next, an example of the operation of the control unit 10 when processing is performed in this manner will be described.

(Operation of control unit 10)
FIG. 6 is a flowchart showing an operation procedure of the control unit 10. The control unit 10 repeatedly performs the process shown in this flowchart at a predetermined control cycle.

  The basic control means 111 calculates the first current command value by referring to the feedforward torque map 121 based on the throttle opening information received by the throttle opening sensor 10g (S10).

  Next, the basic control means 111 calculates a second current command value by referring to the feedback torque map 122 based on the wheel speed information of each wheel received from the wheel speed sensors 10a to 10d (S11).

  Next, the oversteer control means 112 determines whether or not the four-wheel drive vehicle 101 is in an oversteer state (S12). This determination can be made, for example, based on whether or not the average rotational speed of the front wheels 108a and 108b is higher than the average rotational speed of the rear wheels 112a and 112b. Further, this determination may be performed based on the yaw rate information received from the yaw rate sensor 10e or the steering angle information received from the steering angle sensor 10f.

  If it is determined in step S12 that the vehicle is in the oversteer state, the oversteer control unit 112 determines whether or not the four-wheel drive vehicle 101 is decelerating (S13). This determination may be made based on a time change of the wheel speed information of each wheel received from the wheel speed sensors 10a to 10d, and whether the throttle opening degree received from the throttle opening sensor 10g is equal to or less than a predetermined threshold value. It may be determined depending on whether or not.

  If it is determined in step S13 that the vehicle is decelerating, the oversteer control means 112 refers to the oversteer control torque map 123 based on the differential rotational speed between the front wheels 108a and 108b and the rear wheels 112a and 112b. Then, the third current command value is calculated (S14).

  Next, the oversteer control means 112 calculates a current command value by subtracting the third current command value calculated in step S14 from the first current command value calculated in step S10 (S15), and outputs the current command value. The data is sent to the circuit 14 (S16). In addition, when the result of this subtraction becomes a negative value, the current command value is set to zero.

  On the other hand, if it is determined in step S12 that the vehicle is not in the oversteer state, or if it is determined in step S13 that the vehicle is not decelerating, the first current command value calculated in step S10 and the second current command calculated in step S11 are used. The current command value is calculated by adding the values (S17), and the current command value is sent to the output circuit 14 (S18).

  Then, the output circuit 14 supplies a current corresponding to the current command value to the electromagnetic coil 24. Thus, the process of the control unit 10 in one control cycle is completed.

(Effect of this embodiment)
According to the present embodiment described above, when the vehicle is in the oversteer state and the deceleration state, the differential limiting force does not increase as the differential rotation speed increases, and the oversteer state during turning is suppressed. can do.

[Other embodiments]
As mentioned above, although the drive force distribution control apparatus of this invention was demonstrated based on said embodiment, this invention is not limited to said embodiment, In various aspects in the range which does not deviate from the summary. For example, the following modifications are possible.

(1) In the above embodiment, the current command value is obtained by subtracting the third current command value from the first current command value in the oversteer state and the deceleration state. In some cases, the current command value sent to the output circuit 14 may be zero without calculating the third current command value.

(2) In the above embodiment, the current command value is obtained by subtracting the third current command value from the first current command value when the vehicle is in the oversteer state and the deceleration state, but the deceleration state is not determined. In the oversteer state, the current command value may be obtained by subtracting the third current command value from the first current command value.

(3) Although the case where the driving force distribution control device 1 has the planetary gear type differential mechanism 1A has been described in the above embodiment, the present invention is not limited thereto, and for example, a gear shaft is attached to a pair of pinion gears supported by a differential case. The driving force distribution control device may be configured using a bevel gear type differential mechanism having a pair of side gears that are engaged at right angles.

(4) In the above-described embodiment, the case where the driving force distribution control device 1 has the differential mechanism 1A having a rear-wheel-biased driving force distribution configuration has been described. The driving force distribution control device may be configured using an unbalanced differential mechanism.

(5) Although the case where the clutch 20 of the driving force distribution control device 1 is pressed by the magnetic force of the electromagnetic coil 24 has been described in the above embodiment, the present invention is not limited thereto, and the clutch may be pressed by, for example, hydraulic pressure. In this case, the control unit controls the engagement force of the clutch by adjusting the hydraulic pressure.

(6) The drive source is not limited to the engine 102, and for example, an electric motor may be used. Or it is good also as a drive source combining an internal combustion engine like an engine and an electric motor.

DESCRIPTION OF SYMBOLS 1 ... Driving force distribution control apparatus, 1A ... Differential mechanism, 1B ... Differential apparatus, 2 ... Clutch mechanism, 3 ... Cage, 4 ... Planetary gear, 5 ... Sun gear, 5b ... Gear part, 5c ... Spline fitting , 6 ... internal gear, 7 ... differential case, 10 ... control unit, 10a, 10b, 10c, 10d ... wheel speed sensor, 10d ... wheel speed sensor, 10e ... yaw rate sensor, 10f ... steering angle sensor, 10g ... throttle opening Sensor, 11 ... Processing execution unit, 12 ... Storage unit, 13 ... Input circuit, 14 ... Output circuit, 20 ... Clutch, 21 ... Inner clutch plate, 22 ... Outer clutch plate, 23 ... Armature, 24 ... Electromagnetic coil, 25 ... Yoke 31 ... connecting portion 31a ... spline fitting portion 32 ... holding portion 32a ... holding hole 32b ... support surface 32c ... support surface 41 ... large diameter portion 41a ... gear portion 4 ... small diameter part, 42a ... gear part, 50 ... cylindrical member, 50a ... gear, 61 ... connecting part, 61a ... spline fitting part, 62 ... clutch connecting part, 62a ... spline fitting part, 63 ... gear meshing part, 63a DESCRIPTION OF SYMBOLS ... Gear part, 71 ... 1st housing, 72 ... 2nd housing, 72a ... Accommodating space, 73 ... Bearing, 74 ... Bearing, 75 ... Bearing, 76 ... Washer, 101 ... Four-wheel drive vehicle, 102 ... Engine, 103 ... Transmission, 104 ... Input shaft, 105 ... Front drive shaft, 105a ... Gear, 106 ... Front differential, 107a, 107b ... Front axle shaft, 108a ... Right front wheel, 108b ... Left front wheel, 109 ... Propeller shaft, 110 ... Rear differential, 111 ... Basic control means, 111a, 111b ... Rear axle shaft, 1 2 ... Oversteer control means, 112a ... Right rear wheel, 112b ... Left rear wheel, 120 ... Program, 121 ... Feed forward torque map, 122 ... Feedback torque map, 123 ... Oversteer control torque map, 200 ... Pressing mechanism, 711 ... bottom, 712 ... cylindrical portion, 712a ... spline fitting portion, 721 ... first element, 721a ... opening, 722 ... second element, 723 ... third _element, D _1, D _2, D 3, _{D 4} ... Pitch circle diameter

Claims (2)

A differential mechanism for allowing and distributing the driving force of the driving source of the vehicle to the driving shaft on the front wheel side and the driving shaft on the rear wheel side while allowing the differential between these driving shafts;
A clutch for limiting a differential between the drive shafts by a fastening force generated according to a supplied current ;
And a control unit for generating a current command value for controlling the engagement force of the clutch,
The control unit subtracts a current command value that increases as the rotational speed difference between the front and rear wheels increases from a current command value that increases as the throttle opening increases when the vehicle enters an oversteer state. and generated a subtraction current command value, based on this subtraction current command value of a four-wheel drive vehicle which controls the engagement force of the clutch driving force distribution control apparatus. Wherein, when the vehicle becomes the over-steering state and the deceleration state, the driving force distribution control device for a four-wheel drive vehicle according to claim 1 for reducing the engagement force of the clutch.

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