JPH06107015A - Driving force distributor for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To prevent deterioration of durability for a friction engaging means which controls a driving force distribution rate to front wheels and rear wheels without deteriorating power performance and running performance in a four- wheel drive vehicle. CONSTITUTION:It is detected whether any different diameter tire above the predetermined reference is mounted or not (S602), and a fastening force calculated on the basis of the difference between the rotational frequency of front wheels and that of rear wheels is corrected so that an actual yaw rate matches a target yaw rate, so that a friction engaging means is controlled, if only it is not detected that any different diameter tire is mounted, (S603-S605). When it is detected that a different diameter tire is mounted, the modification of the fastening force on the basis of the difference between the target yaw rate and the actual yaw rate is forbidden, and the friction engaging means is controlled on the basis of the fastening force calculated on the basis of the difference between the front wheels rotational frequency and the rear wheels rotational frequency (S606).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving force distribution device for a four-wheel drive vehicle which controls the fastening force of friction engagement means to control the driving force distribution to the front and rear wheels.

[0002]

2. Description of the Related Art Driving force and lateral force generated in a vehicle tire are
Although it depends on the road surface friction coefficient and the driving force applied to the tires, four-wheel drive vehicles basically use four tires for the driving force output from the engine. And excellent running stability. If the front wheels or the rear wheels have a relatively excessive driving force and slippage occurs on those wheels, the driving force distribution ratio to the front and rear wheels should be increased in order to achieve better power performance and running stability. Is changed to reduce the driving force of the wheel in which slip occurs, and all four wheels generate sufficient driving force.

By the way, the lateral force generated on the tire decreases with an increase in the driving force of the tire. Therefore, if the driving force applied to the rear wheels is too large, the lateral force generated on the rear wheels during turning becomes small and the oversteer tendency ( On the contrary, if the driving force applied to the front wheels is too large, the lateral force of the front wheels at the time of turning becomes small, and therefore the understeer tendency (drift-out tendency) is exhibited. Further, when tire slip is large, the friction circle of the tire becomes small, and the amount of driving force and lateral force generated is reduced. As described above, the distribution of the driving force to the front and rear wheels in the four-wheel drive vehicle influences not only the power performance and the running stability but also the steer characteristic, and therefore, JP-A-3-
In the apparatus disclosed in Japanese Patent No. 31030, the fastening force of the friction engagement means that changes the driving force distribution ratio to the front and rear wheels is controlled based on the slip state of the wheels and the yawing state of the vehicle.

According to the apparatus described in the above publication, the first clutch engagement force is obtained based on the difference between the front and rear wheel rotation speeds, and
The second clutch engaging force is calculated so that the yawing momentum matches the target value, the second clutch engaging force is added to the first clutch engaging force, and the clutch engaging force is controlled based on the added value. For example, in a four-wheel drive vehicle in which a part of the driving force applied from the engine to the rear wheels is distributed to the front wheels, the rear wheels slip when turning and the lateral force of the rear wheels is lost. When the steering tendency occurs, the second clutch engaging force based on the yawing momentum is added to the first clutch engaging force based on the front and rear wheel rotation speed difference, and the clutch engaging force is controlled based on the added value. Therefore, the driving force distribution ratio to the front wheels is increased, the slip of the rear wheels is suppressed, and the oversteering tendency is corrected.

[0005]

By the way, when tires of different diameters are mounted on the front wheels and the rear wheels, such as when different kinds of tires are mounted, a friction coefficient for controlling the driving force distribution ratio to the front and rear wheels. A large relative rotation occurs in the coupling means, and when a large fastening force is applied to the friction engagement means at this time, heat is generated in the friction engagement means. In such cases,
In the above conventional device, in addition to the first clutch engaging force based on the front-rear wheel rotational speed difference, when the steer characteristic tends to oversteer, the second based on the yawing momentum.
The clutch engagement force is also applied to the friction engagement means, and the engagement force becomes large as a whole. Further, such a large engagement force is applied to the friction engagement means for a long time during turning, so that the friction engagement means is generated. There is a problem that the amount of heat generation increases and the durability of the friction engagement means deteriorates.

The present invention has been made in view of the above circumstances, and is a friction member for controlling a driving force distribution ratio to front and rear wheels without deteriorating the power performance and traveling stability of a four-wheel drive vehicle. The purpose is to prevent deterioration of the durability of the composite means.

[0007]

The present invention, as shown in FIG. 1, shows the structure of the friction engagement means 1 provided in the power transmission path and the friction engagement based on the difference between the front and rear wheel rotation speeds. Fastening force calculation means 2 for calculating the fastening force of the means 1, and fastening for correcting the fastening force calculated so that the actual yaw rate matches the target yaw rate based on the difference between the set target yaw rate and the actual yaw rate of the vehicle. A driving force distribution device for a four-wheel drive vehicle, comprising: force correction means 3; and controlling the friction engagement means 1 based on the corrected fastening force to control driving force distribution to the front and rear wheels. A different diameter tire detection means 4 for detecting whether a different diameter tire exceeding a predetermined standard is mounted on the rear wheel, and when the different diameter tire detection means 4 detects that a different diameter tire is mounted. In the fastening force correction means 3 By providing a correction prohibiting means 5 prohibits correction based on the difference between the target yaw rate and the actual yaw rate that is intended to achieve the above object.

[0008]

According to the present invention, as long as the different-diameter tire detecting means 4 does not detect that a different-diameter tire that exceeds a predetermined reference is mounted, the front-rear wheel is determined by the fastening force calculating means 2 as in the above-mentioned conventional apparatus. The engagement force calculated based on the rotational speed difference is corrected by the engagement force correction means 3 so that the actual yaw rate matches the target yaw rate, and the frictional engagement means 1 is controlled based on the corrected engagement force.

However, in the present invention, when the different-diameter tire detecting means 4 detects that a different-diameter tire exceeding a predetermined standard is mounted, the correction inhibiting means 5 is used.
Therefore, the correction based on the difference between the target yaw rate and the actual yaw rate by the fastening force correction means 3 is prohibited, and the frictional engagement means based on the uncorrected fastening force, that is, the fastening force calculated by the fastening force calculation means 2. Control 1 Therefore, in this case, the frictional engagement means 1 is given a fastening force based on the front-rear wheel rotation speed difference, but is prevented from being given a fastening force increased by the correction.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic diagram showing an embodiment of a four-wheel drive vehicle to which the present invention is applied. Reference numeral 10 is an engine, 20 is an automatic transmission, 30 is a planetary gear type center differential device, and 40 is a rear propeller. Shaft, 50 is a chain,
Reference numeral 60 is a front propeller shaft, 70 is a front differential, 80 is a front drive shaft, and 90 is a center differential clutch (a friction engagement means for changing the driving force distribution ratio to the front and rear wheels).

The engine 10 is installed vertically at the front of the vehicle, and the power from the engine 10 is provided with a fluid type torque converter 21 and a speed change unit 22, and has four forward gears and one reverse gear.
The power transmitted to the automatic transmission 20 having a well-known configuration for automatically changing the gear position of the gear, and the power that has passed through the automatic transmission 20 is
It is transmitted to the center differential device 30 via the output shaft 24.

The center differential device 30 includes a sun gear 31, a planetary pinion 32 that meshes with the sun gear 31, a carrier 33 that rotatably supports the planetary pinion 32 around the sun gear 31, and a ring gear 34 that meshes with the planetary pinion 32. With output shaft 2
The power transmitted to 4 is input from the carrier 33 of the center differential device 30, and part of the power is transmitted to the rear propeller shaft 40 via the ring gear 31.
A part is transmitted to the chain 50 via the sun gear 31. And the rear propeller shaft 4
The power transmitted to the 0 side is transmitted to the left and right rear wheels via a rear differential and a rear drive shaft (not shown) which are power transmission paths thereafter, and the power transmitted to the chain 50 side is transmitted to the front propeller shaft 60. , Front differential 70, front drive shaft 8
It is transmitted to the left and right front wheels (not shown) via 0.

The center differential clutch 90 has a wet multi-plate clutch and connects the carrier 33 of the center differential device 30 and the sun gear 31 in a torque transmitting relationship, and applies a fastening force to the center differential clutch 90. That is, by applying the engagement hydraulic pressure, the differential of the center differential device 30 is limited, and the driving force distribution ratio to the front and rear wheels can be changed according to the magnitude of the engagement hydraulic pressure. .

As a device for controlling the engagement hydraulic pressure of the center differential clutch 90, a hydraulic control device 100 mainly composed of a linear solenoid valve, and a four-wheel drive electronic control device (4WD) for controlling a linear solenoid valve. -E
The electronic control unit 110 is provided with a steering angle sensor 111, a wheel speed sensor 112 provided for each wheel, a yaw rate sensor 113, a throttle opening sensor 114, and other sensors, and a neutral switch 11.
5, signals from respective switches such as the idle switch 116 are input. Then, the electronic control unit 110
The linear solenoid valve is controlled on the basis of these input parameters, whereby the center differential clutch 90
The engagement hydraulic pressure of is controlled.

Next, in the electronic control unit 110,
The control specifically executed will be described based on FIGS. 3 to 15. FIG. 3 is a flowchart showing an overall outline of control, and this control flow is executed, for example, every 8 ms.

First, in step S100, various signals are taken in to obtain the steering angle δ, the rotational speed of each wheel, the throttle opening θ, etc., and the front wheel rotational speed N _F and the rear wheel rotational speed N _{R are} calculated.
Is calculated as the average rotation speed of each of the left and right wheels, and the vehicle speed V is estimated based on the rotation speed of each wheel.

In the following step S200, the front wheel rotation speed N
_{Based on F} , the rear wheel rotation speed N _R, and the different diameter ratio K _IK , which will be described later, the front and rear wheel rotation speed difference ΔN _FR as a parameter representing the slip state of the wheel is ΔN _FR = | K _IK × N _F −N _R | It is calculated by the formula. Here, the different diameter ratio K _IK is a ratio of the diameters of the front wheels and the rear wheels, and is obtained as a ratio (N _R / N _F ) of the front wheel rotational speed N _F and the rear wheel rotational speed N _R, and therefore, By multiplying and correcting the front wheel rotational speed N _F with the different diameter ratio K _IK , the front and rear wheel rotational speed difference is removed from the front and rear wheel rotational speed difference ΔN _FR , except for the front and rear wheel rotational speed difference caused by the tire diameter difference between the front wheel and the rear wheel. ΔN _FR is set to accurately correspond to the slip state of the wheel.

Next, in step S300, the different diameter ratio K _IK is calculated, and based on the different diameter ratio K _IK , the different diameter degrees of the tires mounted on the front wheels and the rear wheels are judged, and the different diameter difference flag A is calculated. , Different diameter difference flag B is set or reset. The determination of the different diameter is based on the idea that the control content of the engagement hydraulic pressure of the center differential clutch 90 should be changed according to the different diameter.

Steps S400 to S700
Then, the control oil pressure of the center differential clutch 90 is calculated based on the above-mentioned various parameters. First, step S40
In the start control at 0, the control oil pressure is calculated based on the throttle opening θ in the low vehicle speed range, and the control oil pressure is corrected based on the steering angle δ. As a result, the starting acceleration and climbing performance in the low vehicle speed range are obtained, and the tight corner braking phenomenon is prevented. In the starting slip control in step S500, the slip of the wheels is determined based on the front-rear wheel rotation speed difference ΔN _FR in the low vehicle speed range, and if the slip is determined, the center differential clutch 90 is directly connected to the control hydraulic pressure. Set the control hydraulic pressure. This prevents wheel slippage in the low vehicle speed range.

Step S600 is a step relating to the present invention. In the turning control in step S600, the control oil pressure is calculated based on the front / rear wheel rotation speed difference ΔN _FR , and the control oil pressure is used for the steering angle δ and the vehicle speed V. Based on the deviation Δγ between the target yaw rate γ _* obtained from the above and the actual yaw rate γ detected by the yaw rate sensor 113, the actual yaw rate γ is corrected so as to match the target yaw rate γ _* .
As a result, the control hydraulic pressure is increased when the vehicle is in the oversteer tendency, and conversely, the control hydraulic pressure is reduced when the vehicle is in the understeer tendency, and the steer characteristic is corrected.

Further, in the control at the time of tip-in in step S700, when the throttle opening θ is equal to or less than the predetermined opening, the control oil pressure for directly connecting the center differential clutch 90 is set as the control oil pressure, thereby driving the engine. , The rattling shock of the drive system due to the switching of the driven parts is reduced.

Next, in step S800, the maximum control hydraulic pressure of the control hydraulic pressures obtained in steps S400 to S700 is determined as the control hydraulic pressure to be adopted, and in the inhibit control in the following step S900, the different diameter difference flag B is set. If the different diameter difference flag B is set, the control oil pressure is replaced with "0". Then, in step S1000, a signal for controlling the linear solenoid valve is output based on the finally determined control oil pressure.

FIG. 4 is a flow chart showing the tire diameter difference correction processing in step S300 of FIG. 3, and this control flow is performed in order to reduce the load on the electronic control unit 110 in the control cycle of every 8 ms. Is executed every 512 ms, for example, every 512 ms.

First, in step S301, it is determined whether or not the center differential clutch 90 is engaged, and whether or not the vehicle is in a traveling state in which a front-rear wheel rotational speed difference does not occur. In other words, control pressure P of the center differential clutch 90 is less than the reference value P _IK, the vehicle speed V is less than the reference value V _IK1 or more and a reference value V _IK2, the absolute value of the yaw rate gamma | gamma | reference value gamma _The vehicle is in a straight running state below _IK , and the throttle opening θ is a reference value θ set for each gear.
It is determined whether or not all the conditions that the wheels under _i are in a traveling state in which no slip occurs and that the neutral switch 115 is off are satisfied. The reason why the vehicle speed V is limited to the predetermined range is to avoid the influence of relatively large noise of the wheel speed in the low vehicle speed range and the high speed vehicle range.

If all the above conditions are satisfied, the ratio of the diameters of the front wheels and the rear wheels, that is, the different diameter ratio K _IK is calculated in step S302. This different diameter ratio K _IK
Is the ratio of the front wheel speed N _F and the rear wheel speed N _R (N _R / N
_F ) is required.

Next, in steps S303 to S306, upper and lower limit guards for removing noise are applied to the different diameter ratio K _IK . That is, in step S303, if the different diameter ratio K _IK is determined whether the lower limit value K _IK1 below is determined lower limit K _IK1 below, step S30
In 4, the lower limit value K _IK1 adopted as the value of the different diameter ratio K _IK, In step S305, the different diameter ratio K _IK is determined whether the upper limit value K _IK2 above, determines the upper limit value K _IK2 more If so, in step S306, the upper limit value K
_IK2 is adopted as the value of the different diameter ratio K _IK .

In a succeeding step S307, in order to judge the magnitude of the diameter deviation between the front wheels and the rear wheels, that is, the magnitude of the deviation in the rotational speeds of the front and rear wheels, the diameter difference K _IK and the diameter difference between the front and rear wheels are determined. Absolute value ΔK _IK of the difference from “1” which is the value when there is no value is obtained. This absolute value (hereinafter referred to as the different diameter width) ΔK _IK is different from the tire diameter when tires of different diameters such as different tires are attached to the front wheels and the rear wheels, or when a chain is attached to either one of them. When there is a difference, the value becomes larger, and when the tire diameter difference becomes larger, the value becomes larger.

In the following step S308, the different diameter width ΔK _IK
Is greater than or equal to the predetermined reference value ΔK _IK1 , and the reference value Δ
If it is determined to be K _IK1 or more, it is determined that different-diameter tires that exceed a predetermined standard are mounted on the front wheels and the rear wheels, and the different-diameter difference flag A is set in step S309,
On the contrary, if it is determined that it is smaller than the reference value ΔK _IK1 , the different diameter difference flag A is reset in step S310. Further, in the following step S311, the different diameter width Δ
If it is determined that K _IK is greater than or equal to a larger reference value ΔK _IK2 , and if it is determined to be greater than or equal to the reference value ΔK _IK2 , it is determined that front and rear wheels have different diameter tires that exceed control limits. , Step S312, different diameter difference flag B
On the contrary, when it is determined that the difference is smaller than the reference value ΔK _IK2 , the different diameter difference flag B is reset in step S313. The different diameter difference flag A and the different diameter difference flag B are used as flags for changing the control content of the engagement hydraulic pressure of the center differential clutch 90 described later.

FIG. 5 is a flow chart showing the processing of the starting control in step S400 of FIG. 3, and is a control flow executed to obtain the starting acceleration and the climbing performance in the low vehicle speed range.

First, in step S401, it is determined whether or not a condition for executing the start control is satisfied, that is, whether or not the vehicle speed is in a low vehicle speed range, based on whether or not the vehicle speed V is equal to or lower than a reference value V _ST. to decide. If an affirmative decision is made,
In step S402, the control oil pressure P _ST is set to a large value according to the magnitude of the throttle opening θ shown in FIG. 6, and the absolute value | δ | of the steering angle δ shown in FIG.
Of the correction coefficient K (| δ
|) And P _ST = K (| δ |) × P (θ). The larger the throttle opening θ, the more easily the wheels slip, which deteriorates the starting acceleration and the climbing performance. Therefore, the larger the throttle opening θ, the larger the control hydraulic pressure P _ST . Further, when the control oil pressure P _ST is set to a large value, a tight corner braking phenomenon occurs at the time of turning, and therefore the correction oil pressure increases as the absolute value | δ | of the steering angle δ increases due to the correction coefficient K (| δ |). P
_ST is corrected to a small value. On the other hand, step S401
If a negative determination is made, the control oil pressure P _ST is set to “0” in step S403.

According to this control flow, in the low vehicle speed range, the engagement hydraulic pressure of the center differential clutch 90 is increased, the differential limiting force of the center differential device 30 is increased, and the driving force distribution ratio to the front wheels is increased. Since the vehicle speed is increased, it is possible to obtain the starting acceleration and the climbing performance in the low vehicle speed range. Further, during turning in the low vehicle speed range, the engagement hydraulic pressure of the center differential clutch 90 is lowered, and the differential limiting force of the center differential device 30 is reduced. Therefore, the tight corner braking phenomenon can also be effectively prevented.

In the above control flow, the control oil pressure P _ST
Is the control oil pressure P _ST calculated in step S402.
Or it becomes immediately changed is that the "0" set in step S403, in order to prevent the abrupt change of the driving force distribution rate for the front and rear wheels, the control pressure P _ST, the control is calculated pressure P _ST or It may be gradually increased or decreased toward "0".

By the way, at the time of turning at a large steering angle in the low vehicle speed range, the control hydraulic pressure P _ST is set to a small value in order to prevent the tight corner braking phenomenon, and therefore,
The wheels may slip when the driving force load is excessive when traveling on a low friction coefficient road. Therefore, in the present embodiment, the slip control at the start is executed to prevent the slip of the wheels in this case. FIG. 8 is a flow chart showing the processing of starting slip control in step S500 of FIG.

First, in step S501, it is determined whether or not a condition for executing the start-time slip control is satisfied. When this control is not executed, that is, when the control flag is reset in the step described later, the vehicle speed V is equal to or lower than the reference value V _SS and the front and rear wheel rotation speed difference ΔN _FR is equal to or higher than the reference value ΔN _FRSS. If the condition is satisfied, the control flag is set in step S502, and in step S503, the center differential clutch 90 is directly connected to the control oil pressure P _SS. Control oil pressure P
Set the _RID (θ). The control oil pressure P _RID (θ) is calculated based on the throttle opening θ because the oil pressure required to directly connect the center differential clutch 90 differs depending on the magnitude of the driving force. Then, in the control routine after this control is executed, in step S501,
Whether or not the vehicle speed V satisfies the reference value V _SS or less and the throttle opening θ satisfies the reference value θ _SS or more is determined, and this control is performed until the vehicle speed V exceeds the reference value V _SS or the accelerator is released. Then, the throttle opening θ is continued until it becomes smaller than the reference value θ _SS . On the other hand, if a negative determination is made in step S501, the control flag is reset in step S504, and the subsequent step S50.
In 5, the control oil pressure P _SS is set to “0”.

According to this control flow, when slip occurs on the wheels in the low vehicle speed range, the center differential clutch 9
0 is directly connected, the differential of the center differential device 30 is limited, and the driving force distribution ratio to the front wheels is increased. Therefore, slipping of the wheels can be effectively prevented.

In the control flow, if it is determined that the conditions for executing the slip control at start are not satisfied, the control oil pressure P _SS is immediately reduced to "0". In order to prevent a sudden change in the driving force distribution ratio to the front and rear wheels, it may be gradually reduced to "0".

Next, the turning control processing in step S600 of FIG. 3 according to the present invention will be described with reference to FIGS. 9 to 12. FIG. 9 is a flowchart showing the processing of turning control.

[0038] First, in step S601, whether or not a condition for executing the turning-state control are satisfied, that is, whether the vehicle speed V is the reference value V _TUN1 or more and the reference value V _TUN2 below. This execution condition is for avoiding the influence of noise having a relatively large wheel speed in the low vehicle speed range and the high vehicle speed range as described above. If an affirmative determination is made, it is determined in step S602 whether or not the different diameter difference flag A is set. If the different diameter difference flag A is reset, steps S603 through S605 are performed. On the other hand, if the different diameter difference flag A is set, the process proceeds to step S606.

When the different diameter difference flag A is reset, first, in step S603, the coefficient K _1V is calculated. This coefficient K _1V is the vehicle speed V, the wheel base L,
From stability factor K _h , K _1V = V / {L (1
+ K _h × V ² )}, and then in step S604, the target yaw rate γ _* and the yaw rate sensor 1 calculated by multiplying the coefficient K _1V by the steering angle δ.
The deviation Δγ from the actual yaw rate γ detected in 13 is Δγ = γ
It is calculated by the formula (γ _* −γ). Then, step S
In 605, the control pressure P _TUN the control oil pressure P _1V obtained by the front and rear wheel rotational speed difference .DELTA.N _FR shown in FIG. 10 (ΔN _FR)
And P _TUN = K (Δγ) × P _1V (Δ) based on the correction coefficient K (Δγ) obtained from the deviation Δγ shown in FIG.
N _FR ).

On the other hand, when the different diameter difference flag A is set, the control oil pressure P _TUN is determined in step S606.
The control oil pressure P _2V (ΔN _FR ) determined by the front and rear wheel rotation speed difference ΔN _FR shown in FIG. 12 is set.

When it is determined in step S601 that the conditions for executing the turning control are not satisfied, the process proceeds to step S607, and in step S607,
The control oil pressure P _TUN is set to “0”.

According to this control flow, the different diameter difference flag A
Is reset, the engagement hydraulic pressure of the center differential clutch 90 is increased according to the slip of the wheels, the differential limiting force of the center differential device 30 is increased, and the driving force distribution ratio to the front wheels is increased. Although it is increased, during turning, when there is an oversteer tendency, the engagement hydraulic pressure of the center differential clutch 90 is further increased, the drive force distribution ratio to the front wheels is further increased, and conversely, when there is an understeer tendency, The engagement hydraulic pressure of the differential clutch 90 is lowered, and the driving force distribution ratio to the rear wheels is increased. Therefore, running stability can be obtained, and the steer characteristic can be made to match the desired steer characteristic.

By the way, when tires having different diameters exceeding the predetermined standard are mounted on the front wheels and the rear wheels, a relatively large relative rotation occurs in the center differential clutch 90. When a large engagement hydraulic pressure is applied to the differential clutch 90 for a long time, the amount of heat generated in the center differential clutch 90 increases and the durability of the center differential clutch 90 deteriorates.

Therefore, in the above control flow, the control oil pressure P
The calculation of _TUN is different when the different diameter difference flag A is reset and when the different diameter difference flag A is set. That is, when the different diameter difference flag A is set, the correction of the control oil pressure based on the deviation between the target yaw rate and the actual yaw rate is prohibited, and the engagement oil pressure of the center differential clutch 90 is increased by this correction. from prevented, also control oil pressure itself based on the front and rear wheel rotational speed difference .DELTA.N _FR, control pressure P _1V illustrated in FIG. 10 used in the case of different diameter difference flag a is reset (.DELTA.N _FR),
When the control oil pressure in the low front / rear wheel rotational speed difference range shown in FIG. 12 is changed to the control oil pressure P _2V (ΔN _FR ) and the wheel slip is relatively small, the center differential clutch 90 is engaged with the oil pressure. Is being given. Therefore, according to the control flow, it is possible to prevent the durability of the center differential clutch 90 from being deteriorated without deteriorating the running stability.

The control oil pressure P _TUN may be gradually increased or decreased toward the set control oil pressure P _TUN in order to prevent a sudden change in the driving force distribution ratio to the front and rear wheels. The target yaw rate γ _* may be corrected according to the lateral acceleration or the road surface friction coefficient.

FIG. 13 is a flow chart showing the control processing at the time of chip-in in step S700 of FIG. 3, in order to reduce the rattling shock of the drive system due to the switching between driving and driving of the engine. 9 is a control flow executed to directly connect the differential clutch 90.

First, in step S701, it is determined whether or not the condition for executing the control at the time of chip-in is satisfied, that is, the vehicle speed V is not less than the reference value V _{GA1 and not} more than the reference value V _GA2 , and the steering angle δ. The absolute value | δ | of is less than or equal to the reference value δ _GA , and it is determined whether or not all the conditions that the different diameter difference flag A is reset are satisfied. Here, the condition that the vehicle speed V is within the above-mentioned predetermined range is that if the vehicle speed V is too high, direct connection of the center differential clutch 90 will cause an adverse effect. This is because if it is too low, it becomes the engine drive range and the meaning of this control becomes meaningless. In addition, the steering angle δ
The reason for this is that the tight corner braking phenomenon occurs when the center differential clutch 90 is directly connected when the steering angle δ is large.

By the way, as described above, when tires having different diameters exceeding the predetermined reference are mounted on the front wheels and the rear wheels, the center differential clutch 90 undergoes a relatively large relative rotation, and the center differential clutch 90 is opened. When directly connected, internal circulation torque accumulates, power performance deteriorates, and in some cases, center differential clutch 90 slips and durability of center differential clutch 90 deteriorates. The present control is executed over a relatively long period of time as compared with the control at the time of starting control and the control at the time of starting slip control which are completed in a short time, and the above-mentioned problem becomes remarkable. Therefore, the fact that the different diameter difference flag A is reset is introduced as the execution condition of this control.

When it is determined in step S701 that all of the above conditions are satisfied, it is determined in subsequent step S702 whether the idle switch 118 is on. When it is determined that the idle switch 118 is on, in step S703,
The control oil pressure P _GA is gradually increased by a predetermined value ΔP _GA1 , and in steps S704 and S705, the control oil pressure P _GA is guarded by the control oil pressure P _RID (θ) that directly connects the center differential clutch 90. Also, step S
When it is determined in 701 that the execution condition of the control at the time of chip-in is not satisfied, or step S702
When it is determined that the idle switch 118 is off in step S706, the control hydraulic pressure P is set in step S706.
_GA is gradually decreased by a predetermined value ΔP _GA2 , and step S70
In step 4 and step S705, the control oil pressure P _GA is guarded with "0".

According to this control flow, when the throttle is fully closed, the engagement hydraulic pressure of the center differential clutch 90 is gradually increased, the center differential clutch 90 is directly connected, and the throttle is fully closed. Even if it is opened from the top, the engagement hydraulic pressure is gradually lowered, so that the engagement hydraulic pressure remains high for a predetermined time thereafter, and therefore, a sudden change in the driving force distribution ratio to the front and rear wheels is prevented. However, rattling shock of the drive system due to switching between driving and driving the engine can be reduced. Further, when tires having different diameters that exceed a predetermined standard are mounted on the front wheels and the rear wheels, this control is prohibited, so that deterioration of power performance can be prevented and durability of the center differential clutch 90 is deteriorated. Can also be prevented.

FIG. 14 is a flow chart showing the processing for determining the control oil pressure in step S800 of FIG. 3, and the control flow for deciding which control oil pressure is to be adopted among the control oil pressures obtained in the above respective controls. Is.

First, steps S801 to S
At 804, the control oil pressure P _* is set as the initial oil pressure. The center differential clutch 90 is acted on by the spring force of the return spring that biases the clutch in the releasing direction. Therefore, unless the spring force of the return spring is applied to the clutch, no clutch engagement force is generated. . For this reason, control delay occurs in the clutch engagement force, and in this embodiment, the control oil pressure P _* is set as the initial oil pressure, and the center differential clutch 90 has an oil pressure that is within the spring force of the return spring in advance. Is given to eliminate the control delay.

By the way, when the control hydraulic pressure P _* set as described above is always applied to the center differential clutch 90 as the initial hydraulic pressure, when the initial hydraulic pressure is larger than the spring force of the return spring, the clutch engaging force is always generated. At this time, when tires having different diameters that exceed a predetermined reference are mounted on the front wheels and the rear wheels, and when the vehicle is traveling at a high vehicle speed, the center differential clutch 90 is relatively engaged. A large relative rotation occurs, which deteriorates the durability of the center differential clutch 90. Therefore, step S
In step 801, it is determined whether or not the different diameter difference flag A is set, and in step S802, it is determined whether or not the vehicle speed is high based on whether or not the vehicle speed V is equal to or higher than the reference value V _* . If a negative determination is made in both of these steps, the control oil pressure P is determined in step S803.
_* To set the control oil pressure P _FREE sufficient to overcome the spring force of the return spring, in any of the steps, if a positive determination is made, at step S804, the control hydraulic pressure P _* is set to "0" . Then, in step S805, it is determined that the control oil pressure P is the maximum control oil pressure among the control oil pressures P _ST , P _SS , P _TUN , P _GA , and P _* obtained in the above-mentioned respective controls.

FIG. 15 is a flow chart showing the process of the inhibit control in step S900 of FIG. 3 above. Whether the engagement hydraulic pressure of the center differential clutch 90 is controlled by the finally determined control hydraulic pressure P or not. It is a control flow to judge.

First, in step S901, it is determined whether or not the different diameter difference flag B is set. If tires with excessively different diameters are installed on the front and rear wheels,
Excessive relative rotation occurs in the center differential clutch 90, and the durability of the center differential clutch 90 deteriorates. Further, when the center differential clutch 90 is directly connected, the internal circulation torque is accumulated and the power performance is deteriorated, and in some cases, the center differential clutch 90 is connected.
There is a problem that slippage occurs and the durability of the center differential clutch 90 deteriorates. Therefore, the different diameter difference flag B
If is set, the process proceeds to step S902, and the control oil pressure P finally obtained in step S902 is set to "0".

In this embodiment, the drive force distribution to the front and rear wheels is controlled by the center differential clutch.
The present invention is not limited to this, and can be applied to, for example, a configuration that switches between the two-wheel drive state and the four-wheel drive state and controls the driving force distribution to the front and rear wheels. Further, in the present embodiment, the clutch engagement force based on the front and rear wheel rotation speed difference is configured to be multiplied and corrected by the correction coefficient based on the deviation between the target yaw rate and the actual yaw rate, but the present invention is not limited to this. The present invention can also be applied to a configuration in which the clutch engagement force based on the front and rear wheel rotation speed difference is added and corrected by a correction coefficient based on the deviation between the target yaw rate and the actual yaw rate.

[0057]

As described above, according to the present invention,
When it is detected that a tire with a different diameter that exceeds a predetermined standard is detected, the correction based on the difference between the target yaw rate and the actual yaw rate is prohibited, and the friction coefficient is calculated based on the engagement force calculated from the difference between the front and rear wheel rotation speeds. Since the engagement means is controlled, the frictional engagement means is given a certain amount of fastening force, and it is prevented that a large fastening force is given while preventing deterioration of power performance and traveling stability. It is possible to prevent deterioration of durability of the friction engagement means.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a four-wheel drive vehicle to which the present invention has been applied.

FIG. 3 is a flowchart showing an overall outline of control in this embodiment.

FIG. 4 is a flowchart showing a tire different diameter correction process.

FIG. 5 is a flowchart showing a process of starting control.

FIG. 6 is a diagram showing a control hydraulic pressure based on a throttle opening.

FIG. 7 is a diagram showing a correction coefficient based on an absolute value of a steering angle.

FIG. 8 is a flowchart showing a process of starting slip control.

FIG. 9 is a flowchart showing processing of control during turning.

FIG. 10 is a diagram showing a control hydraulic pressure based on a front / rear wheel rotation speed difference.

FIG. 11 is a diagram showing a correction coefficient based on a deviation between a target yaw rate and an actual yaw rate.

FIG. 12 is a diagram showing a control hydraulic pressure based on a front / rear wheel rotation speed difference.

FIG. 13 is a flowchart showing processing of control at the time of chip-in.

FIG. 14 is a flowchart showing a process of determining control oil pressure.

FIG. 15 is a flowchart showing processing of inhibit control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Friction engaging means 2 Engaging force calculating means 3 Engaging force correcting means 4 Different diameter tire detecting means 5 Correction inhibiting means

Claims (1)

[Claims] 1. A friction engagement means provided in a power transmission path, an engagement force calculation means for calculating an engagement force of the friction engagement means on the basis of a front-rear wheel rotational speed difference, and a set target yaw rate. A fastening force correction unit that corrects the fastening force calculated so that the actual yaw rate matches the target yaw rate based on the difference from the actual yaw rate of the vehicle, and the frictional engagement unit is based on the corrected fastening force. In a drive force distribution device for a four-wheel drive vehicle that controls and controls the drive force distribution to the front and rear wheels, a different diameter that detects whether the front wheels and the rear wheels have different diameter tires that exceed a predetermined reference The tire detection means and, when the different-diameter tire detection means detects that a different-diameter tire is mounted, a correction prohibition hand that prohibits the correction based on the difference between the target yaw rate and the actual yaw rate by the fastening force correction means. A drive force distribution device for a four-wheel drive vehicle, which is provided with a step.