JP3118984B2 - Driving force distribution device for four-wheel drive vehicles - Google Patents

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 for controlling the distribution of driving force to front and rear wheels by controlling the fastening force of frictional engagement means.

[0002]

2. Description of the Related Art Driving force and lateral force generated in a vehicle tire are
Although it depends on the coefficient of road friction and the driving force applied to the tires, the four-wheel drive vehicle basically uses four tires to handle the driving force output from the engine. And excellent running stability. If the driving force of the front wheel or the rear wheel becomes relatively excessive and the wheel slips, the driving force distribution ratio to the front and rear wheels is increased in order to exhibit better power performance and running stability. The driving force of the slipping wheel is reduced by changing the driving force so that all four wheels generate sufficient driving force.

[0003] Incidentally, the lateral force generated in the tire decreases with an increase in the driving force of the tire. Therefore, if the driving force applied to the rear wheel is too large, the lateral force generated in the rear wheel at the time of turning becomes small, and the oversteer tendency ( On the other hand, 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, so that the vehicle tends to understeer (drift-out tendency). Further, when the slip of the tire is large, the friction circle of the tire becomes small, and the amount of generation of the driving force and the lateral force decreases. Thus, the distribution of the driving force to the front and rear wheels in a four-wheel drive vehicle affects not only the power performance and running stability but also the steering characteristics.
In the apparatus described in Japanese Patent No. 31030, the fastening force of the friction engagement means for changing the distribution ratio of the driving force 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 front and rear wheel rotational speed difference,
The second clutch engagement force is determined so that the yawing momentum coincides with the target value, the second clutch engagement force is added to the first clutch engagement force, and the clutch engagement force is controlled based on the added value. For example, in a four-wheel drive vehicle in which a part of the driving force given to the rear wheels from the engine is distributed to the front wheels, the rear wheels slip when turning and the lateral force of the rear wheels is lost. When the vehicle tends to steer, the second clutch engagement force based on the yawing momentum is added to the first clutch engagement force based on the front and rear wheel rotational speed difference, and the clutch engagement force is controlled based on the added value. Therefore, the ratio of the distribution of the driving force to the front wheels is increased, the slip of the rear wheels is suppressed, and the oversteering tendency is corrected.

[0005]

When tires of different diameters are mounted on the front wheel and the rear wheel, for example, when different types of tires are mounted, the frictional member for controlling the distribution ratio of the driving force to the front and rear wheels is controlled. A large relative rotation occurs in the joining means. At this time, when a large fastening force is applied to the friction engagement means, heat is generated in the friction engagement means. In such a case,
In the above-described conventional apparatus, in addition to the first clutch engagement force based on the front-rear wheel rotational speed difference, the second clutch based on the yawing momentum when the steering characteristic is oversteering.
The clutch engagement force is also applied to the friction engagement means, and the overall engagement force is increased, and since such a large engagement force is applied for a long time during turning, the friction engagement means is generated. There has been a problem that the amount of heat generated increases and the durability of the friction engagement means deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to a friction system for controlling a driving force distribution ratio to front and rear wheels without deteriorating the power performance and running stability of a four-wheel drive vehicle. It is intended to prevent deterioration of the durability of the combining means.

[0007]

The invention according to claim 1 is
A frictional engagement means 1 is provided in a power transmission path for distributing power to the front and rear wheels, and by controlling a fastening force of the frictional engagement means 1 based on a diameter difference between the front and rear wheels, In a driving force distribution device for a four-wheel drive vehicle capable of controlling the distribution of driving force to a vehicle, a diameter difference determining means 2 for determining whether or not the diameter difference between the front and rear wheels is equal to or greater than a first predetermined value. ,
When the diameter difference determining means 2 determines that the diameter difference between the front and rear wheels is equal to or more than a first predetermined value, the engagement force of the friction engagement means 1 is determined as a throttle opening and a steering angle at a predetermined vehicle speed or less. Or a second value calculated to determine that one of the front and rear wheels is slipping at a predetermined vehicle speed or less and to bring the front and rear wheels into a directly connected state. or the actual yaw rate of the vehicle, the third value is calculated as the target yaw rate coincide, which is set in advance or, in the case where the acceleration request for the vehicle has run out, before Symbol friction engagement means
It calculated so that to increase Tokoro value increments below the value to be directly connected the fourth value, or, better to release the frictional engagement means
And a fastening force selecting means 3 for selecting a maximum value of a fifth value in which a force overcoming the force urging in the direction is set to zero . According to a second aspect of the present invention, in addition to the configuration of the first aspect, the diameter difference determining means 2 determines that a diameter difference between the front and rear wheels is equal to or greater than a second predetermined value larger than the first predetermined value. Function to determine whether
The fastening force selection means 3 includes a function of setting the fastening force of the friction engagement means 1 to zero when it is determined that the diameter difference between the front and rear wheels is equal to or greater than the second predetermined value. It is characterized by having.

[0008]

According to the first aspect of the present invention, a tight corner braking phenomenon at the time of turning of the vehicle, a slip of the front wheel or the rear wheel at low vehicle speed or at the time of uphill, a steering characteristic and a steering stability at the time of turning of the vehicle. Judgment of various kinetic performances, such as reduction of rattling shock, in which the distribution of driving force suddenly changes while the vehicle is running, and the difference in diameter between the front and rear wheels affects these kinetic performances Only when it is determined that the frictional engagement means has the first value calculated from the first value or the
The largest of the fifth values is selected.

According to the second aspect of the present invention, the same effect as that of the first aspect can be obtained, and a decrease in the exercise performance due to a difference in diameter between the front and rear wheels can be suppressed by controlling the distribution of the driving force to the front and rear wheels. If it is possible, any one of the first to fifth values is selected as the fastening force of the friction engagement means, and if it is impossible to suppress the driving force distribution control to the front and rear wheels, , The fastening force of the friction engagement means is set to zero.

[0010]

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

The engine 10 is installed vertically at the front of the vehicle. Power from the engine 10 is provided with a fluid torque converter 21 and a transmission unit 22.
The power transmitted to the automatic transmission 20 having a well-known configuration that automatically switches the gears of the gears is transmitted through the automatic transmission 20,
The power 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 meshed with the sun gear 31, a carrier 33 rotatably supporting the planetary pinion 32 around the sun gear 31, and a ring gear 34 meshed with the planetary pinion 32. Output shaft 2
4 is input from the carrier 33 of the center differential device 30 and partially
34 to the rear propeller shaft 40,
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 right and left 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
0 to the left and right front wheels (not shown).

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 including a linear solenoid valve, and a four-wheel drive electronic control device (4WD) for controlling the linear solenoid valve -E
The electronic control unit 110 includes 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;
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 based on these input parameters, whereby the center differential clutch 90 is controlled.
Is controlled.

Next, in the electronic control unit 110,
The control that is specifically executed will be described with reference to FIGS. FIG. 3 is a flowchart showing the overall outline of the control. This control flow is executed, for example, every 8 ms.

First, in step S100, various signals are fetched to obtain the steering angle δ, the rotation speed of each wheel, the throttle opening θ, and the like. The front wheel rotation speed N _F and the rear wheel rotation speed N _R
Is obtained 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 speed N
_{Based on F} , the rear wheel rotation speed N _R, and a different diameter ratio K _IK , which will be described later, a front-rear wheel rotation speed difference ΔN _FR as a parameter representing a slip state of the wheel is calculated as ΔN _FR = | K _IK × N _F −N _R | It is calculated by the following equation. Here, different diameter ratio K _IK is the ratio of the diameter of the front wheel and the rear wheel, is determined as a ratio between the front wheel rotation number N _F and the rear wheel rotational speed _{N R (N R / N F} ), therefore, the front wheel rotational speed N _F by multiplying corrected by different diameter ratio K _IK, except the front and rear wheel rotation speed difference caused by the tire diameter difference from the front and rear wheel rotational speed difference .DELTA.N _FR between the front wheels and the rear wheels, front and rear wheel rotation speed difference ΔN _FR is precisely adapted to the wheel slip state.

Next, in step S300, the different diameter ratio K _IK is calculated, and the different diameters of the tires mounted on the front and rear wheels are determined based on the different diameter ratio K _IK. , Sets or resets the different diameter difference flag B. The determination of the different diameter is made 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 various parameters and the like. First, step S40
In the starting control at 0, the control oil pressure is calculated based on the throttle opening θ and the control oil pressure is corrected based on the steering angle δ in a low vehicle speed range. As a result, start acceleration and climbing performance in a low vehicle speed range are obtained, and the tight corner braking phenomenon is prevented. In the starting slip control in step S500, wheel slip is determined based on the front and rear wheel rotational speed difference ΔN _FR in a low vehicle speed range, and if slip is determined, the center differential clutch 90 is directly connected to the control hydraulic pressure. Is set. This prevents the wheels from slipping in a low vehicle speed range.

Step S600 is a step related to the present invention. In the turning control in step S600, a control oil pressure is calculated based on the front-rear wheel rotational speed difference ΔN _FR , and the control oil pressure is changed to the steering angle δ and the vehicle speed V. The actual yaw rate γ is corrected 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 so as to match the target yaw rate γ _* .
As a result, the control oil pressure is increased when there is a tendency to oversteer, and conversely, the control oil pressure is decreased when there is a tendency to understeer, thereby correcting the steering characteristics.

In the tip-in control 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. In addition, the rattling shock of the driving system due to the switching of the driven is reduced.

Next, in step S800, it is determined that the maximum control oil pressure among the control oil pressures obtained in steps S400 to S700 is adopted as the control oil pressure. In the subsequent inhibit control in step S900, the different diameter difference flag B is set. If the different diameter difference flag B is set based on this, 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 obtained control oil pressure.

FIG. 4 is a flow chart showing the processing for correcting the tire diameter difference in step S300 of FIG. 3 described above. This control flow is performed to reduce the load on the electronic control unit 110 in the control cycle of every 8 ms. Is executed every predetermined control cycle, 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 running state in which there is no difference between the front and rear wheel rotational speeds. 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 traveling substantially straight below _IK , and the throttle opening θ is the reference value θ set for each gear.
It is determined whether or not all the conditions are satisfied that the vehicle is in a running state in which slip does not occur on wheels below _i , and that neutral switch 115 is off. 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 a low vehicle speed region or a high speed vehicle region.

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

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 K
_IK2 is adopted as the value of the different diameter ratio K _IK .

In the following step S307, in order to determine the magnitude of the deviation in the diameter between the front and rear wheels, that is, the magnitude of the deviation in the rotational speed of the front and rear wheels, the diameter difference between the different diameter ratio K _IK and the front and rear wheels is determined. The absolute value ΔK _IK of the difference from “1”, which is the value in the case where there is no, is determined. This absolute value (hereinafter, referred to as a different diameter width) ΔK _IK is determined by a tire diameter such as when tires having different diameters such as different kinds of tires are mounted on a front wheel and a rear wheel, or when a chain is mounted on one of them. When there is a difference, the difference becomes larger, and as the tire diameter difference becomes larger, the difference becomes larger.

In the following step S308, the different diameter width ΔK _IK
Is greater than or equal to a predetermined reference value ΔK _IK1 and the reference value Δ
If it is determined that K _IK1 or more, it is determined that different diameter tires exceeding a predetermined standard are mounted on the front wheel and the rear wheel, and the different diameter difference flag A is set in step S309,
Conversely, if it is determined that the difference is smaller than the reference value ΔK _IK1 , the different diameter difference flag A is reset in step S310. In the subsequent step S311, the different diameter width Δ
K _IK is determined whether more or larger reference value [Delta] K _IK2 above, if it is determined that the reference value [Delta] K _IK2 above, as different-diameter tire beyond the limits of control between the front and rear wheels are mounted In step S312, the different diameter difference flag B
On the other hand, if 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 flowchart showing the starting control process in step S400 in FIG. 3, and is a control flow executed to obtain starting acceleration and hill-climbing performance in a low vehicle speed range.

First, in step S401, it is determined whether or not a condition for executing start-time control is satisfied, that is, whether or not the vehicle is in a low vehicle speed range, based on whether or not the vehicle speed V is equal to or less than a reference value _VST. to decide. If a positive 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.
Correction coefficient K (| δ
) And P _ST = K (| δ |) × P (θ). The larger the throttle opening θ, the more likely the wheels are to slip, thereby deteriorating the starting acceleration and climbing performance. Therefore, the larger the throttle opening θ, the larger the control oil pressure _PST . If the control oil pressure _PST is set to a large value, a tight corner braking phenomenon occurs during turning, so that the control oil pressure becomes larger as the absolute value | δ | P
_ST is corrected to a small value. On the other hand, step S401
In, when a negative determination is made, at step S403, it is set to "0" to control pressure P _ST.

According to this control flow, in a 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 reduced. As a result, start acceleration and climbing performance in a low vehicle speed range can be obtained. Further, when turning in a low vehicle speed range, the engagement hydraulic pressure of the center differential clutch 90 is reduced, 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 hydraulic pressure P _ST
Is the control oil pressure P _ST calculated in step S402.
Alternatively, the control hydraulic pressure _PST is immediately changed to "0" set in step S403. However, in order to prevent a sudden change in the driving force distribution ratio to the front and rear wheels, the control hydraulic pressure _PST is set to the calculated control hydraulic pressure _PST or You may make it increase and decrease gradually toward "0".

When turning at a large steering angle in a low vehicle speed range, the control oil pressure _PST is set to a small value in order to prevent a tight corner braking phenomenon.
When driving on an road with a low coefficient of friction with excessive driving force, wheels may slip. Therefore, in the present embodiment, the slip at the time of starting is executed to prevent the wheel from slipping in this case. FIG. 8 is a flowchart showing the slip control process at start in step S500 in FIG.

First, in step S501, it is determined whether or not a condition for executing the start-time slip control is satisfied. If this control is not being executed, that is, when the control flag is reset in step which will be described later, the vehicle speed V is the reference value V _SS below and the front and rear wheel rotational speed difference .DELTA.N _FR is the reference value .DELTA.N _FRSS more determining whether to satisfy the condition, if this condition is met, at step S502, it sets the control flag in the subsequent step S503, the center differential clutch 90 directly connected to the control oil pressure P _SS Control oil pressure P
Set _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 the execution of this control, in step S501,
It is determined whether or not the vehicle speed V is equal to or less than the reference value V _SS and the throttle opening θ satisfies the condition of being equal to or more than the reference value θ _SS , and this control is performed until the vehicle speed V exceeds the reference value V _SS or the accelerator is released. And 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 process proceeds to step S50.
In 5, it is set to "0" to the control hydraulic pressure P _SS.

According to this control flow, when a slip occurs in 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, the slip of the wheel can be effectively prevented.

In the above 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 between the front and rear wheels, the driving force distribution ratio may be gradually reduced to “0”.

Next, the turning control process in step S600 of FIG. 3 according to the present invention will be described with reference to FIGS. FIG. 9 is a flowchart showing a process 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 to avoid the influence of the relatively large noise of the wheel speed in the low vehicle speed range or 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 has been set. If the different diameter difference flag A has been reset, the processing proceeds to steps S603 to S605. The process proceeds to the process. On the other hand, when the different diameter difference flag A is set, the process proceeds to the process of step S606.

When the different diameter difference flag A has been reset, first, in step S603, a coefficient _K1V is calculated. The coefficient K _1V is _calculated based on the vehicle speed V, the wheel base L,
From the stability factor K _h , K _1V = V / ｛L (1
+ K _h × V ² )｝. 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 are calculated.
The deviation Δγ from the actual yaw rate γ detected in step 13 is Δγ = γ
(Γ _* −γ). Then, step S
At 605, the control oil pressure P _TUN is changed to the control oil pressure P _1V (ΔN _FR ) obtained from the front and rear wheel rotational speed difference ΔN _FR shown in FIG.
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, in step S606, the control oil pressure P _TUN
Is set to the control oil pressure P _2V (ΔN _FR ) obtained from the front and rear wheel rotational speed difference ΔN _FR shown in FIG.

If it is determined in step S601 that the execution condition of the turning control is not satisfied, the process proceeds to step S607, and in step S607,
Set the control oil pressure P _TUN 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 in accordance with 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 reduced. However, when the vehicle tends to oversteer at the time of turning, the engagement hydraulic pressure of the center differential clutch 90 is further increased, and the driving force distribution ratio to the front wheels is further increased. The engagement hydraulic pressure of the differential clutch 90 is reduced, and the driving force distribution ratio to the rear wheels is increased. Therefore, running stability can be obtained, and the steering characteristics can be matched with desired steering characteristics.

When tires having different diameters exceeding a predetermined standard are mounted on the front wheel and the rear wheel, a relatively large relative rotation occurs in the center differential clutch 90. When a large engagement oil 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 hydraulic pressure P
The calculation of _TUN is different between the case where the different diameter difference flag A is reset and the case where 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. The control oil pressure itself based on the front and rear wheel rotation speed difference ΔN _FR is also determined from the control oil pressure P _1V (ΔN _FR ) shown in FIG. 10 used when the different diameter difference flag A is reset.
When the control oil pressure in the low front and rear wheel rotational speed difference region shown in FIG. 12 is changed to “0” and the control oil pressure P _2V (ΔN _FR ), and the slip of the wheel is relatively small, the engagement oil pressure is applied to the center differential clutch 90. Is prevented from being given. Therefore, according to the above control flow, it is possible to prevent the durability of the center differential clutch 90 from deteriorating without deteriorating 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 between the front and rear wheels. Further, 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 described above. In order to reduce the rattling shock of the driving system due to the switching between the driving and the driven of the engine, the center is reduced. This is a control flow that is executed to connect the differential clutch 90 directly.

[0047] First, in step S701, the whether conditions for performing time tip-control are satisfied, i.e., the vehicle speed V is less than the reference value V _GA1 or more and a reference value V _GA2, steering angle δ [delta] | | absolute value that is less than the reference value [delta] _GA, determines whether to satisfy all the conditions of that the different diameter difference flag a is reset. Here, the condition that the vehicle speed V is within the above-mentioned predetermined range is because, if the vehicle speed V is too high, an adverse effect is caused by directly connecting the center differential clutch 90, and the vehicle speed V If it is too low, it becomes an engine drive region and the meaning of this control is lost. Also, the steering angle δ
The reason is that if the center differential clutch 90 is directly connected when the steering angle δ is large, a tight corner braking phenomenon occurs.

As described above, when tires having different diameters exceeding a predetermined reference are mounted on the front wheel and the rear wheel, relatively large relative rotation occurs in the center differential clutch 90, and the center differential clutch 90 is disengaged. If it is directly connected, the internal circulating torque accumulates and the power performance deteriorates. In some cases, the center differential clutch 90 slips and the durability of the center differential clutch 90 deteriorates. This control is executed for a relatively long time with respect to the control that is completed in a short time of the start control and the start slip control, and the above-described problem becomes remarkable . In its This, conditions that you different diameter difference flag A is reset as the execution condition of the control
It has put Ri taken in the matter.

If it is determined in step S701 that all the above conditions are satisfied, it is determined in next step S702 whether or not the idle switch 118 is on. Then, when it is determined that the idle switch 118 is on, in step S703,
Control pressure P _GA was increased predetermined value [Delta] P _GA1 increments gradually, step S704 and, at step S705, the guard at the control oil pressure P _RID (theta) to the control oil pressure P _GA directly connected to the center differential clutch 90. Step S
In 701, when it is determined that the execution condition of the chip-in-time control is not satisfied, or in step S702
In step S706, when it is determined that the idle switch 118 is off, the control oil pressure P
_GA is gradually decreased by a predetermined value ΔP _GA2 , and step S70
4, and, in step S705, the guard at the control oil pressure P _GA "0".

According to this control flow, when the throttle is fully closed, the engagement oil pressure of the center differential clutch 90 is gradually increased, the center differential clutch 90 is directly engaged, and the throttle is fully closed. Even if it is opened, the engagement oil pressure is gradually reduced, so that the engagement oil pressure is maintained high within a predetermined time thereafter, thereby preventing a sudden change in the driving force distribution ratio to the front and rear wheels. However, rattling shock of the drive system due to switching between driving and driven of the engine can be reduced. Further, when tires having different diameters exceeding a predetermined standard are mounted on the front wheel and the rear wheel, this control is prohibited, so that deterioration of power performance can be prevented, and deterioration of durability of the center differential clutch 90 can be prevented. Can also be prevented.

FIG. 14 is a flowchart showing the process of determining the control oil pressure in step S800 of FIG. 3. The control flow for determining which control oil pressure to use from among the control oil pressures obtained in each of the above-described controls. It is.

First, steps S801 to S801
At 804, a control oil pressure P _* is set as an initial oil pressure. The spring force of the return spring that urges the clutch in the release direction acts on the center differential clutch 90. Therefore, unless the spring force of the return spring acts on the clutch, no clutch engagement force is generated. . For this reason, a control delay occurs in the clutch engagement force. In this embodiment, the control oil pressure P _* is set as the initial oil pressure, and the hydraulic pressure of the center differential clutch 90 is limited to the spring force of the return spring in advance. , The control delay is eliminated.

If the control oil pressure P _* set as described above is always applied to the center differential clutch 90 as the initial oil pressure, the clutch engagement force is always generated when the initial oil pressure is too large than the spring force of the return spring. At this time, when tires having different diameters exceeding a predetermined reference are mounted on the front wheel and the rear wheel, or when running at a high vehicle speed, the center differential clutch 90 is relatively Large relative rotation occurs, and therefore, the durability of the center differential clutch 90 deteriorates. Therefore, step S
At 801, it is determined whether or not the different diameter difference flag A is set. At step S 802, 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 each of these steps, the control hydraulic pressure P is determined in step S803.
_{In *} , the control oil pressure P _FREE that is only within the spring force of the return spring is set, and if an affirmative determination is made in any of the steps, the control oil pressure P _* is set to “0” in step S804. . Then, in step S805, it is determined that the control oil pressure P adopts the maximum control oil pressure among the control oil pressures P _ST , P _SS , P _TUN , P _GA , and P _* obtained in the above control.

FIG. 15 is a flowchart showing the inhibit control process in step S900 of FIG. 3, and it is determined whether or not the engagement oil pressure of the center differential clutch 90 is controlled by the finally obtained control oil pressure P. It is a control flow to determine.

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 mounted on the front and rear wheels,
There is a problem that excessive relative rotation occurs in the center differential clutch 90 and durability of the center differential clutch 90 deteriorates. Further, when the center differential clutch 90 is directly connected, the internal circulating torque is accumulated and the power performance deteriorates.
, And the durability of the center differential clutch 90 deteriorates. Therefore, the different diameter difference flag B
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 driving 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 a two-wheel drive state and a four-wheel drive state and controls the distribution of driving force to front and rear wheels. In the present embodiment, the clutch engagement force based on the front-rear wheel rotation speed difference is multiplied and corrected by a 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 a deviation between the target yaw rate and the actual yaw rate.

[0057]

As described above, according to the first aspect of the present invention, the tight corner braking phenomenon at the time of turning of the vehicle, the slip of the front wheel or the rear wheel at low vehicle speed or at the time of climbing a hill, the turning of the vehicle. Comprehensively evaluate various types of motion performance such as steering characteristics and steering stability at the time, and reduction of rattling shock (that is, rapid speed change) where the distribution of driving force changes rapidly while the vehicle is running. Then, only when it is determined that the diameter difference between the front and rear wheels affects these kinetic performances, the first value to be calculated corresponding to various kinetic performances as the fastening force of the frictional engagement means. The largest of the fifth values is selected. Therefore,
By controlling the fastening force of the frictional engagement means, it is possible to suppress such a decrease in the kinetic performance, and it is possible to prevent the power performance and running stability inherently possessed by the four-wheel drive vehicle from being impaired. According to the second aspect of the present invention, in addition to the same effects as those of the first aspect, it is possible to suppress a decrease in exercise performance due to a difference in diameter between the front and rear wheels by controlling the distribution of driving force to the front and rear wheels. If any of the first to fifth values is selected as the fastening force of the friction engagement means, and it is impossible to suppress the driving force distribution control to the front and rear wheels, The fastening force of the friction engagement means is set to zero. That is, the fastening force of the friction engagement means can be controlled according to the degree of the difference in diameter between the front and rear wheels, and the ability to adapt to changes in the situation is improved.

[Brief description of the 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 is applied.

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

FIG. 4 is a flowchart illustrating a process of correcting a tire different diameter;

FIG. 5 is a flowchart illustrating a start-time control process;

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

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

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

FIG. 9 is a flowchart illustrating a process of turning control;

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

FIG. 11 is a diagram illustrating 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 oil pressure based on a front-rear wheel rotation speed difference.

FIG. 13 is a flowchart illustrating a process of controlling at the time of chip-in;

FIG. 14 is a flowchart illustrating a process of determining a control hydraulic pressure.

FIG. 15 is a flowchart illustrating a process of an inhibit control.

[Explanation of symbols]

1 friction engagement means 2 diameter differences determined hand stage 3 fastening force selecting means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-37424 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B60K 17/348

Claims (2)

(57) [Claims] 1. A frictional engagement means is provided in a power transmission path for distributing power to front and rear wheels, and by controlling a fastening force of the frictional engagement means based on a diameter difference between the front and rear wheels, In the driving force distribution device for a four-wheel drive vehicle capable of controlling the distribution of driving force to the front and rear wheels, a diameter difference determination for determining whether a diameter difference between the front and rear wheels is equal to or greater than a first predetermined value. Means for determining whether the diameter difference between the front and rear wheels is equal to or greater than a first predetermined value by the diameter difference determining means. Or a second value calculated to determine that one of the front and rear wheels is slipping at a predetermined vehicle speed or less and to bring the front and rear wheels into a directly connected state. Value or the actual yaw rate of the vehicle Third value and a target yaw rate that has been set has been calculated to match, or, in the case where the acceleration request for the vehicle has run out, Tokoro value increments below the value of the previous SL frictional engagement means directly
Fourth value calculated for so that to increase, or, said friction
Zero force to overcome the force urging in the direction to release the engagement means
And a fastening force selecting means for selecting a maximum value among the fifth values set in ( 4). 2. The diameter difference judging means includes a function of judging whether or not the diameter difference between the front and rear wheels is equal to or greater than a second predetermined value larger than the first predetermined value. The fastening force selection means includes a function of setting the fastening force of the friction engagement means to zero when it is determined that the diameter difference between the front and rear wheels is equal to or greater than the second predetermined value. four-wheel drive vehicle driving force distribution apparatus according to claim 1 you <br/> characterized.