JP2851386B2 - Torque distribution control device for four-wheel drive vehicle - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a torque distribution control device for a four-wheel drive vehicle.

(Prior Art) In a four-wheel drive vehicle that drives four wheels in front, rear, left and right by an engine output, the torque distribution of each wheel is not always set to the same state, but is variably controlled to the optimum distribution according to the driving state. Such a torque distribution control device is generally known.

For example, Japanese Patent Application Laid-Open No. 1-247223 discloses that the turning motion of a vehicle is divided into a time when entering a straight running to a turning travel, a time during a steady turning, and a time when exiting from a turning running to a straight running. There is disclosed a proposal to perform torque distribution control in accordance with the turning state of a vehicle based on the steering angle and the steering angle change rate of the vehicle. In other words, this proposal reduces the torque distribution to the front wheels by absorbing the driving force of the front wheels by the brakes in order to increase the turning performance of the vehicle when turning and entering, while reducing the driving force of the rear wheels to increase straightness when turning and exiting. To reduce the torque distribution to the rear wheels and to make the load on the tires of the front and rear wheels uniform.

(Problems to be Solved by the Invention) By the way, on a high μ road surface having a high friction coefficient of the road surface (hereinafter referred to as μ as necessary), the vehicle behaves substantially corresponding to the change of the steering angle and the vehicle speed. However, since the tire slip ratio is large on a low μ road surface, the movement of the vehicle is delayed with respect to a change in the steering angle and a change in the vehicle speed. For example, the lateral acceleration remains even after the end of steering.

On the other hand, in the case of the above-described conventional technique, the control at the time of escape ends when the steering angle becomes zero or near the same.
However, even at that time, on a low μ road surface, a relatively large lateral acceleration remains in the vehicle, and the rear wheels increase in side slip due to an increase in the driving torque accompanying the end of the escape control, and the running stability of the vehicle is increased. Is impaired. That is, quick convergence from turning to straight running cannot be obtained.

In addition, for example, when the next turning steering is performed immediately after the end of the escape steering, such as traveling on an S-shaped curve, the torque distribution control at the time of turning approach is performed, so that a side slip occurs on the rear wheels. Nevertheless, the driving torque is further increased, and the skidding is further increased.

Therefore, the present invention suppresses the above-mentioned side slip of the rear wheel at the time of exit from turning on a low μ road surface, thereby enabling stable turning traveling.

(Means for Solving the Problems) In order to solve such a problem, the present invention corrects the determination of the turning state in accordance with the actual state of the vehicle, thereby controlling the torque distribution control at the time of turning escape. It is intended to improve the stability of the cornering by allowing the vehicle to continue until the end.

That is, a torque distribution control device for that purpose is shown in FIG.

In the figure, reference numeral 1 denotes a four-wheel drive vehicle, and an engine 2
The output of the engine 2 is transmitted to the left and right front wheels 6, 7 and the left and right rear wheels 8, 9 via a center differential 3, a front differential 4, and a rear differential 5, respectively.

Numeral 10 is a torque distribution changing means for adjusting the amount of transmission of the engine output to the four wheels 6 to 9 and changing the torque distribution to the four wheels 6 to 9. The transmission amount is adjusted by controlling the brake devices 11 to 14 provided. Reference numeral 16 denotes a torque distribution control unit that controls the torque distribution change unit 10.

And a steering state detecting means 17 for detecting a steering state of the vehicle, and a means for detecting a lateral acceleration or a side slip angle generated in the vehicle for controlling the torque distribution changing means 10.
And turning state determining means for determining an escape state in which the vehicle escapes from turning to straight running based on the steering state of the vehicle.
And an escape determination maintaining means for maintaining the determination of the escape state until the lateral acceleration or the side slip angle becomes a predetermined value or less when the escape state is determined by the turning state determination means. .

Then, the torque distribution control means 16 receives the outputs of the turning state determination means 19 and the escape determination maintenance means 20,
When the escape state is determined, the orc distribution ratio of the front and rear wheels is set to be larger for the front wheels than when it is not determined, and the torque distribution is changed based on the set torque distribution ratio. The means 10 is controlled.

(Operation) In the torque distribution control device, basically, the turning state determining unit 19 determines the escape state based on the detection result of the steering state detecting unit 17, and the turning state is determined based on the determination result. Corresponding four-wheel torque distribution control is performed. Thus, when the turning state determining means 19 determines the escape state, the subsequent determination of the turning state changes depending on the lateral acceleration or the side slip angle occurring in the vehicle.

That is, when the escape state is determined by the turning state determination means 19, the escape determination maintaining means 20 maintains the determination of the escape state until the lateral acceleration or the sideslip angle becomes a predetermined value or less.

Therefore, as in the case of a high μ road surface, when the movement of the vehicle does not significantly delay with respect to the change in the steering angle or the change in the vehicle speed, and the lateral acceleration or the side slip angle becomes equal to or less than a predetermined value, substantially equal to the end of the turning steering, the vehicle escapes. The determination of the state and the escape control based on the state end in a form substantially corresponding to the steering state.

On the other hand, on a low μ road surface, a relatively large lateral acceleration or a side slip angle remains even after the turning steering is completed. The side slip angle is maintained until it becomes equal to or less than the predetermined value, and the torque distribution control at the time of escape is continuously performed. Further, even when the next turning steering is performed immediately after the turning steering ends, the control at the time of escape is continued.

(Effects of the Invention) Therefore, according to the present invention, the determination of the escape state is maintained until the lateral acceleration or the side slip angle generated in the vehicle is detected and the magnitude thereof becomes equal to or smaller than a predetermined value. As a result, the determination of the state matches the actual state of the vehicle, and when escaping from turning, torque distribution control that emphasizes running stability that suppresses rear skid of the rear wheels is continued until after turning steering is completed. It is possible to enhance the convergence from turning to straight running, and to improve the running stability of the vehicle when entering from straight running to turning and exiting from turning continue alternately. it can.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

<Description of Overall Configuration> FIG. 2 shows the overall configuration of the embodiment (the same reference numerals are used for components corresponding to those shown in FIG. 1).

First, the output of the engine 2 is input via a transmission 31 to a transfer 3 having a center differential for equally transmitting the engine output to the front wheel side and the rear wheel side. The front differential 4 is connected to a front wheel output shaft 32 of the transfer 2, and left and right front wheels 6 and 7 are connected to the front differential 4 via a front wheel drive shaft 33. Similarly, rear differential 5
Is connected to a rear wheel output shaft 34 of the transfer 3, and the rear left and right rear wheels 8 and 9 are connected to the rear differential 5 by a rear wheel drive shaft 35.
Are connected via

Brake controller 10 as torque distribution changing means
Are the brake devices 11 to 14 disposed on the four wheels 6 to 9 respectively.
And a brake pressure control valve for separately controlling the brake pressure supplied to the motor and its actuator. The opening of the throttle valve 36 of the engine 2 is adjusted by a throttle motor 37.

Reference numeral 15 denotes an engine controller as engine output changing means, which receives an accelerator signal from an accelerator sensor 38 that detects an accelerator operation amount of the driver, outputs an operation control signal to the throttle motor 37, and outputs an operation control signal to the throttle motor 37. While the opening of the throttle valve 36 is adjusted to correspond to the accelerator operation amount, the engine output torque required for changing the torque distribution is obtained by receiving a control signal from the torque distribution controller 16 as torque distribution control means. This is to change the engine output.

The torque distribution controller 16 uses the accelerator sensor 38
In addition to the above signals, various signals for measuring the amount of movement or the amount of operation for performing the torque distribution control to the four wheels 6 to 9 are input, and control signals are output to the brake controller 10 and the engine controller 15. The output sources of the various signals are as follows.

A steering angle sensor 40 for detecting a steering angle of a wheel A lateral acceleration sensor 41 for detecting a lateral acceleration generated in a vehicle A wheel speed sensor 44 for detecting a rotation speed of each wheel 6 to 9 A rotation speed sensor 45 for detecting an engine rotation speed 45 A vehicle speed Sensor 46 Gear position sensor 47 for detecting the gear position (gear position) of transmission 25 Boost pressure sensor for detecting the boost pressure of engine 2
48 The yaw rate sensor 49 for detecting the yaw rate of the vehicle 49. That is, the torque distribution controller 16 determines the torque distribution ratio between the front wheels 6, 7 and the rear wheels 8, 9 according to the turning state of the vehicle. R1) and left wheel 6,
A distribution ratio setting means for setting a torque distribution ratio R2 between the right wheels 8 and the right wheels 7, 9 (hereinafter referred to as a left / right distribution ratio as required) for determining a turning state for setting the distribution ratio. Means. In this case, the steering angle sensor 40 constitutes a steering state detecting means for determining the turning state, and the lateral acceleration sensor 41 is used for maintaining the determination of the escape state. The yaw rate sensor 49 is used to maintain the determination of the escape state, and is used together with other sensors to set the distribution ratios R1 and R2.

<Description of Brake Controller 10> In FIG. 3, reference numeral 59 denotes a first hydraulic line for the brake device 11 of the front wheel 6, and reference numeral 60 denotes a second hydraulic line for the brake device 12 of the right front wheel 7, each of which is a brake. First and second brake pressure control valves 61 and 62 for controlling the supply of pressure are provided. The two braking pressure control valves 61 and 62 are configured such that the cylinders 61a and 61a are controlled by pistons 61b and 62b to control the volume of the chambers 61c and 62c and the control chambers 61d and 62
It is divided into d. The variable volume chambers 61c and 62c apply the braking pressure generated by the master cylinder 58 to the brake devices 11 and 12 described above.
Is to be supplied to

The pistons 61b, 61b are biased by the springs 61e, 62e in the direction in which the volumes of the variable volume chambers 61c, 62c increase, and the biasing force of the springs 61e, 62e is controlled by the control pressure introduced into the control chambers 61d, 62d. The variable displacement chambers 61c, 62c are moved in the direction of contraction, and are provided with check valves 61f, 62f that close the braking pressure inlets of the variable volume chambers 61c, 62c by the movement in the contraction direction. Therefore, the control rooms 61d and 62d
The control pressure is introduced to the piston 61b and the piston 61b
e, 62e, the master cylinder 58 and the variable volume chambers 61c, 62c are shut off, and these chambers 6
The braking pressure generated in 1c and 62c is supplied to each of the brake devices 11 and 12.

On the other hand, in order to operate each of the braking pressure control valves 61 and 62, first and second actuators 63 and 64 each including a pressure increasing solenoid valve 63a, 64a and a pressure reducing solenoid valve 63b, 64b are provided. Have been. The pressure increasing solenoid valves 63a and 64a
Are disposed on control pressure supply lines 69, 70 leading to the control chambers 61d, 62d of the braking pressure control valves 61, 62 via a relief valve 66, and the pressure reducing solenoid valves 63b, 64b are disposed in the control chambers 61d, 62d. Are arranged on the drain lines 67 and 68 led from. These solenoid valves 63a, 63b, 64a, 64b are controlled to open and close by a signal from the torque distribution controller 16, and when the pressure-increasing electrode valves 63a, 64a are opened and the pressure-decreasing solenoid valves 63b, 64b are shut off. When the control pressure is introduced into the control chambers 61d, 62d of the braking pressure controls 61, 62, the pressure-increasing electromagnetic valves 63a, 64a are shut off and the pressure-reducing electromagnetic valves 63b, 64b are opened, the control pressure from the control chambers 61d, 62d is released. The control pressure is discharged.

The brake devices 13 and 14 for the left and right rear wheels 8 and 9 are not shown, but have the same structure as the brake devices 11 and 12 for the front wheels 6 and 7 described above. Independent braking pressure can be applied to the brake devices 11 to 14.

Next, the torque distribution controller 16 will be described.

<Overall Process Flow> The overall process flow starts at a predetermined measurement timing after the start, and the sensors 38, 40, 41, 44 to 4 shown in FIG.
According to the signal from 9, accelerator opening, steering angle, lateral acceleration,
Each wheel speed, engine speed, vehicle speed, gear position, boost pressure, and the actual yaw rate of the vehicle are measured, and a front-rear distribution ratio R1 and a left-right distribution ratio R2 are set according to a turning state, and a brake controller 10 and an engine controller 15 are set. Is performed.

In the present embodiment, the front-rear distribution ratio R1 is 0 for front-rear uniform distribution, and a drive torque of 0 (rear wheel) for the front wheels 6 and 7 at +0.5.
The driving torque is the maximum at 8, 9), and the opposite relationship is set at -0.5. The left / right distribution ratio R2 is set so that 0 is a right / left uniform distribution, and a driving torque of 0 (the driving torque of the right wheels 7, 9 is maximum) at +0.5 and a reverse relationship at −0.5. ing.

<Turning state control> This control basically determines the front-rear distribution ratio R1 based on the sideslip angle of the rear wheels 8, 9, while determining the left-right distribution ratio R2 so as to obtain a target yaw rate. It is. Then, the distribution ratios R1 and R2 are corrected according to the turning state of the vehicle.

More specifically, the control is executed according to the flow shown in FIG. 4, and the turning state determination flag F is used for this control. First, the meaning of the flag F will be described below.

F = 0: Straight running state F = 1: Entering state from straight running to turning running F = 2: Steady turning running state F = 3: Escape state from turning running to straight running In the control, first, the turning state is determined (step S21). If the vehicle is in the turning state (step S22), the front-rear distribution ratio R1 based on the sideslip angle of the rear wheels 8, 9 is determined, and the left-right distribution based on the yaw rate The ratio R2 is determined sequentially (steps S23, S24). Then, in the case of the entering state and the exiting state of the turning traveling, the correction control of the front-rear distribution ratio R1 is performed based on the steering angle and the steering angle change rate (step
S25-S28).

-Judgment of turning state (step S21)-The flow of this judgment control is shown in FIG. That is, basically, the turning state of the vehicle is determined from the steering angle and the steering angle change rate obtained by the steering angle sensor 40, and this determination result is corrected by the lateral acceleration by the lateral acceleration sensor 41 and the yaw rate by the yaw rate sensor 49. Will do.
This correction uses the second flag CF, and its meaning is as follows.

CF = 0... State where correction is not required for vehicle behavior change CF = 1... State where correction is required for vehicle behavior change This will be specifically described below.

First, when the vehicle speed is lower than the set value (at an extremely low speed), since the side slip of the vehicle is not a problem, F = 0 and CF = 0 regardless of the steering angle and its change rate (step S31, S3
2). Then, in step S33, the previous determination is F =
3 (escape state), and if not, a turning state determination I is made according to the map shown in FIG. 6 (step S3).
Four). That is, the contents of the determination are as follows.

Steering angle is less than θ1 and steering angle change rate is less than 1; F = 0 (straight running state), CF = CF (no change to CF setting) Steering angle is θ1 or more and steering angle change rate is positive (steering angle increasing direction) ) And the steering angle change rate is 1 or more; F = 1 (entering state), CF = CF The steering angle is θ1 or more and the steering angle change rate is 2 to 3; F = 2 (steady turning state), CF = CF The steering angle is θ1 or more and the steering angle change rate is 3 to 4; (3>
4) F = 3 (Escape state), CF = CF Steering angle change rate is 4 or less; F = 3, CF = 1 Next, when it is determined that F = 3 (Escape state) in step S33, see FIG. The turning state determination II is performed according to the map shown (step S35). In other words, here, even when the steering is completed at the time of escape (even if the steering angle becomes zero or close to it), it is necessary to correct the vehicle behavior change until the lateral acceleration becomes less than or equal to the predetermined value | G1 | (Escape state), and the CF is set. Specifically, it is as follows.

The steering angle is equal to or more than + θ2 (from the left steering angle to a predetermined value θ2 of the right steering angle) and the lateral acceleration is equal to or more than + G1 (the rightward acceleration is near zero), or the steering angle is equal to or less than -θ2 (from the right steering angle to the left steering angle). And the lateral acceleration is -G1 or less (to the extent that the leftward acceleration is close to zero); CF = 1, the steering angle is + θ2 to -θ2, and the lateral acceleration is + G1 to G1; CF =
0 Other areas; CF = CF Next, when F = 0 (straight running state), disturbance determination is performed according to the map shown in FIG. 8 (steps S36 and S37).
That is, the yaw rate is -Y1 to + Y1 and the lateral acceleration is -G1.
CF = 0 is set only when the value is + G1, and CF = 1 is set as a state in which a disturbance is occurring (a state in which a change in the behavior of the vehicle requires correction).

As a result of the above determinations, when CF = 1 is set, the turning state determination flag is forcibly set to F = 3 (escape state) and the setting of CF = 3 is continued until CF = 0, CF
At the time when = 0, the turning state determination I is performed (steps S38 and S39).

-Slip angle control (step S23)-The front-rear distribution ratio R1 based on the slip angle is determined by the steering angle sensor 40,
Using the vehicle speed sensor 46 and the yaw rate sensor 49, the sideslip angle γ of the rear wheels 8, 9 due to the influence of the yaw motion of the vehicle is obtained based on the following equation, and is performed according to the characteristic map shown in FIG.

γ = Yaw.r · l _r / V Yaw.r; measured yaw rate l _r ; distance of rear wheel from center of gravity of vehicle V; vehicle speed In this case, when side slip angle γ = 0, front-rear distribution ratio R1 = 0 and side slip The front-rear distribution ratio R1 is determined to increase in the minus direction as the angle γ increases in the plus and minus directions. In this case, the yaw rate Yaw.
r indicates that the right turn is in the plus direction, and the above-mentioned γ is plus or minus, which corresponds to the right turn and left turn of the vehicle.

−Yaw rate correction− In determining the left / right distribution ratio R2 based on the yaw rate,
Calculate the target yaw rate Y.cal corresponding to the high μ road surface from the minimum wheel speed v, the steering angle θ, and the wheelbase l, and calculate the target yaw rate Y.cal from the difference from the actually measured yaw rate Yaw.r. The feedback control of R2 is performed.

In this case, the target yaw rate Y.cal is calculated by the following equation.

Y.cal = v / (1 + Av ² ) · θ / l A is a factor for obtaining vehicle behavior characteristics on a high μ road surface, and is obtained from the characteristic map shown in FIG.

Then, ΔY = Y.cal−Yaw.r is obtained, a drive torque difference between the left and right wheels corresponding to the deviation ΔY is obtained, and then a ratio of the drive torque difference to the driver required torque is obtained, and this is calculated as a left / right distribution ratio R2. It is assumed that. Specifically, it is as follows.

R2 = k ・ ΔY / Tr k is a constant for obtaining a driving torque difference between the left and right wheels corresponding to the deviation ΔY, and Tr is a driver required torque. this
Tr detects an accelerator opening and an engine speed (RPM) by an accelerator sensor 38 and a speed sensor 45, calculates an engine driving torque from a map shown in FIG. 11 based on the accelerator opening and a gear position sensor 47. From the gear ratio detected from the above.

-Correction of R1 based on turning state determination result- In the state of entry into turning (F = 1), the characteristic diagram of correction coefficients a and b and the calculation formula of R1 (R1 = a +
As described in (b + R1), correction is performed such that R1 increases as the steering angle increases and as the steering angle change rate increases.

On the other hand, in the state of escape from turning (F = 3), the characteristic diagram of the correction coefficients a and b and the calculation formula of R1 (R1 = a
As described in (+ b + R1), the correction is made so that R1 decreases as the steering angle increases and the steering angle change rate increases.

<Engine, brake control> The front-rear distribution ratio R1 set by the above-mentioned turning state response control
Then, the necessary torque Ts for executing the torque distribution control by the left / right distribution ratio R2 is calculated according to the following equation.

Ts = 4 × (| R1 | +0.5) × (| R2 | +0.5) × Tr Then, while controlling the engine controller 15 so as to obtain the required torque Ts, based on the distribution ratios R1 and R2. Braking torque TBFR (for right front wheel), TBFL (for left front wheel), TBRR (for right rear wheel) and TBRL applied to each wheel 6-9
(For the left rear wheel) is calculated in accordance with the following equation, and the brake controller 10 is controlled so that these braking torques can be obtained.

TBFR = Ts-4 (0.5-R1) x (0.5 + R2) x Ts TBFL = Ts-4 (0.5-R1) x (0.5-R2) x Ts TBRR = Ts-4 (0.5 + R1) x (0.5 + R2) x Ts TBRL = Teng-4 (0.5 + R1) x (0.5-R2) x Ts <Effects of the embodiment> From straight running at a speed higher than the set vehicle speed, enter into turning, steady turning, and escape to straight running. Will be described.

-At the time of entry into turning traveling-Turning state determination I is performed using the map shown in Fig. 6, and when the steering angle is θ1 or more and the steering angle change rate is plus 2 or more, or when the steering angle change rate is 1 or more, It is determined that F = 1 (entering state). If there is no disturbance determination in the straight running before this entry state, CF = 0, and therefore, there is no forced exit state setting in step S39.

The front-rear distribution ratio R1 is determined by the slip angle control so that the rear wheels 8,
The torque distribution to the rear wheels 8, 9 is set to be smaller as the sideslip angle γ of the vehicle 9 increases, but since the approaching state is determined, the steering angle is determined by the correction control in step S26 in FIG. And the correction coefficient as the steering angle change rate increases
By increasing a and b, R1 is set to be larger in the plus direction than zero, that is, the torque distribution to the front wheels 6, 7 is set to be smaller. Therefore, the driving force of the front wheels 6, 7 is absorbed by the brake, and the torque distribution to the front wheels 6, 7 is reduced, and the turning performance of the vehicle is improved.

On the other hand, the left / right distribution ratio R
Since the characteristic on the road surface is set by the feedback control so as to obtain the target yaw rate, a large yaw rate can be obtained even on a low μ road surface, and the turning performance can be improved.

-Steady Turning Travel-According to the turning state determination I, when the steering angle is equal to or more than θ1 and the steering angle change rate is 2 to 3, F = 2 (steady turning state) is determined. In this case, since the previous approach state is CF = 0,
This CF determination is continued as it is, and does not become F = 3.

Since F = 2 as described above, the front-rear distribution ratio
There is no correction control based on the steering angle of R1 or the like. However, on a low μ road surface, the side slip angle γ of the rear wheels 8, 9 increases as the vehicle continues to turn, and accordingly the front-rear distribution ratio R1 by the slip angle control increases in the negative direction. Therefore, the rear wheel
Since the torque distribution to the rear wheels 8 and 9 is reduced, an increase in the sideslip of the rear wheels 8 and 9 on a low μ road surface is suppressed.

-At the time of escape from turning traveling-According to the turning state determination I, when the steering angle is θ1 or more and the steering angle change rate is 3 to 4, F = 3 (escape state) and CF = CF are determined, When the rate of change is 4 or less, F = 3, CF = 1
Is determined, turning state determination II is performed using the map shown in FIG.

Usually, when the steering angle is large (+) at the beginning of the escape, the lateral acceleration is large (-), so that CF = 1 is set. Also in the case of a left turn, the steering angle is increased to (-) and the lateral acceleration is increased to (+), so that CF = 1 is set. Therefore, the setting of F = 3 is performed again (step S39).

In this case, the front-rear distribution ratio R1 increases in the negative direction due to the slip angle control and the escape correction control step S28 (both a and b are negative) in FIG. Therefore, the torque distribution of the rear wheels 8, 9 is greatly reduced, so that the rear wheels 8, 9
Side skidding is suppressed.

Thus, once F = 3 is set, the turning state determination I and the disturbance determination are not performed, and only the turning state determination II is performed. Then, if the escape traveling state is continued as it is, the steering angle eventually becomes zero or a reverse value (for example, from plus to minus), but even in this case, if the lateral acceleration does not fall below the predetermined value G1, In the turning state judgment II, CF = 1 is maintained, so F = 3 (escape state)
Is maintained as it is.

Therefore, even after the end of turning steering, the front-rear distribution ratio R1 increases in the negative direction and the torque distribution of the rear wheels 8, 9 is suppressed to a small value by the correction control step S28 at the time of escape in FIG. The sideslip of wheels 8 and 9 is suppressed, and the vehicle smoothly converges to straight running.

Then, when the lateral acceleration becomes equal to or less than the predetermined value G1, CF = 0 is set by the turning state determination II, so that the determination in step S38 becomes No, and the turning state determination I
Move to

Before or after the steering angle becomes zero,
Even when the steering angle change rate is close to zero, that is, when the vehicle turns into a steady turning state, or when the steering angle increases again and enters the approaching state, unless the lateral acceleration becomes equal to or less than the predetermined value G1, CF = 1 is set. Therefore, the determination of the escape state is maintained, and it is possible to avoid a situation in which the torque distribution to the rear wheels 8, 9 is increased despite the occurrence of skidding.

In turning state judgment I, the steering angle change rate is small, F = 3, CF = CF
In the turning state determination II, if the lateral acceleration is set to be small and CF = CF, then CF = 0 in the approaching state or the steady turning state before that, and consequently CF = 0 Become. Accordingly, the determination in step S38 becomes No, and the determination of the turning state determination I can be obtained. Therefore, once the exit state is determined and the vehicle again enters the entry state, a determination of F = 1 is obtained, and the front-rear distribution ratio R1 is reduced from zero by the correction control in step S26 in FIG. , That is, the torque distribution to the front wheels 6, 7 is reduced, and the turning performance of the vehicle can be improved.

In turning state judgment I, the steering angle change rate is large, F = 3, CF = 1
In this case, although the behavior of the vehicle changes drastically, the lateral acceleration decreases for some reason, and even if CF = CF is set in the turning state determination II, the result is CF. = 1
Therefore, the determination of F = 3 (escape state) is forcibly obtained in step S39, and the turning state determination I can be prevented from being performed. In other words, even if the driver performs corrective steering when the behavior of the vehicle changes drastically and the vehicle temporarily enters the approaching state or the steady turning state, the determination of the escape state is maintained and the torque distribution to the rear wheels 8, 9 is reduced. Thus, a change in the behavior of the vehicle can be quickly contained.

The above can be better understood with reference to FIG. That is, FIG. 12 compares the present embodiment with a conventional example in which the turning state is determined only by a change in the steering angle. As shown in the figure, in the case of the conventional example, the determination of the escape state ends when the steering angle becomes zero, whereas in the case of the embodiment, the determination of the escape state is extended and the conventional approach state is determined. It extends to the judgment part.

Further, in the case of the above embodiment, in the straight running state, the disturbance is determined based on the map shown in FIG. 8, so that when the vehicle fluctuates due to a large crosswind during the straight running,
By setting CF = 1, it is possible to forcibly determine F = 3, that is, the escape state, and reduce the torque distribution to the rear wheels 8 and 9 to quickly accommodate the change in the behavior of the vehicle.

[Brief description of the drawings]

1 is an overall configuration diagram of the present invention, FIGS. 2 and 3 show an embodiment of the present invention, FIG. 2 is an overall configuration diagram, FIG. 3 is a circuit diagram showing torque distribution changing means, and FIG. FIG. 5 is a flowchart of turning state determination, FIG. 6 is a map of turning state determination I, FIG. 7 is a map of turning state determination II, and FIG. 8 is a map of disturbance determination. Fig. 9, Fig. 9 is a map diagram of the front-rear torque distribution ratio setting according to the slip angle, Fig. 10 is a characteristic diagram showing the relationship between the wheel speed and the factor A, and Fig. 11 shows the relationship between the driver's required torque and the accelerator opening. FIG. 12 is a graph showing a comparison between the embodiment and the conventional example regarding the turning state determination. DESCRIPTION OF SYMBOLS 1 ... 4 wheel drive vehicle 2 ... Engine 3 ... Center differential 4 ... Front differential 5 ... Rear differential 6-9 ... Wheels 10 ... Torque distribution changing means 11-14 ... Brake device 16 ... Torque Distribution control means 17 ... Steering state detecting means 18 ... Means for detecting lateral acceleration or sideslip angle 19 ... Turning state determining means 20 ... Escape determination maintaining means

Claims (1)

(57) [Claims] In a four-wheel drive vehicle in which four front, rear, left and right wheels of the vehicle are driven by engine output, the amount of engine output transmitted to the four wheels is controlled to change the distribution of drive torque to the four wheels. Means for changing the torque distribution; means for detecting the steering state of the vehicle; means for detecting the lateral acceleration or the side slip angle generated in the vehicle; and escape from the turning traveling to the straight traveling based on the steering state of the vehicle. Turning state determining means for determining the state, and when the escape state is determined by the turning state determining means,
An escape determination maintaining means for maintaining the determination of the escape state until the lateral acceleration or the side slip angle becomes a predetermined value or less, and an escape state is determined by receiving outputs from the turning state determination means and the escape determination maintenance means. In this case, the torque distribution ratio of the front and rear wheels is set to be larger than that of the front wheel compared to when it is not determined, and the torque distribution changing means is controlled based on the set torque distribution ratio. Means for controlling the torque distribution of a four-wheel drive vehicle.