JPH0853058A - Antiskid control of four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To correctly carry out the antiskid control by carrying out control so that the average of the slip rate of a rear wheel becomes smaller than that of a front wheel, during the antiskid control. CONSTITUTION:When the number of revolution of a pump 41 on the front wheel 15, 18 side is increased larger than that of a pump 42 on the rear wheel 16, 17 side, a hydraulic pressure is generated to operate an actuator, and a multidisc clutch 43 is press-attached to increase the restraining force of the front wheels 15 and 18 and the rear wheels 16 and 17, and the approximation to the four-wheel drive mode is performed. In the reverse case, the restraining force for the front wheels 15 and 18 and the rear wheels 16 and 17 is weakened, and the approximation to the two-wheel drive mode is performed. During the antiskid control, the transition from the four-wheel drive mode to the two-wheel drive mode is controlled so that the average value of the slip rate between the rear wheels 16 and 17 and the front wheels 15 and 18 is obtained, and the slip rate of the rear wheels 16 and 17 becomes smaller than that of the front wheels 15 and 18. Accordingly, the transition to the two-wheel drive mode can be facilitated, and the correct antiskid control can be carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-skid control method for a four-wheel drive vehicle in which the restraining force between the front wheels and the rear wheels is variable.

[0002]

2. Description of the Related Art Conventionally, when the front wheel rotation speed becomes larger than the rear wheel rotation speed, the restraining force between the front wheel and the rear wheel becomes stronger and the four-wheel drive mode is approached. Conversely, the front wheel rotation speed becomes the rear wheel rotation speed. When it becomes smaller, the restraining force of the front wheels and the rear wheels is weakened, and control for approaching the two-wheel drive mode, that is, variable four-wheel drive control is performed. By this control, the vehicle approaches the four-wheel drive mode during forward acceleration and the two-wheel drive mode during constant forward speed or deceleration.

[0003]

Conventionally, during the anti-skid control, since the front wheel and the rear wheel are independently brake-controlled, the front wheel rotational speed and the rear wheel rotational speed fluctuate. As a result, the four-wheel drive mode may be approached during anti-skid control. Therefore, when the four-wheel drive mode tendency is large, the estimated vehicle body speed obtained from the wheel speed may deviate from the actual vehicle body speed.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to more accurately perform antiskid control in four-wheel drive in which the restraining force between the front wheels and the rear wheels is changed.

[0005]

The present invention is a four-wheel drive in which the front wheel and rear wheel restraining force is greater when the front wheel rotational speed is greater than the rear wheel rotational speed, and vice versa. In the anti-skid control method of a vehicle, if the front and rear wheels have a large restraining force during anti-skid control, the threshold value for shifting the rear wheel to the decompression mode is made shallow, and the rear wheel brake fluid pressure reduction signal is output. Anti-skid control method for a four-wheel drive vehicle, or when the restraining force between the front wheels and the rear wheels is large during the anti-skid control, by increasing the pressure reduction pulse of the rear wheels, An anti-skid control method for a four-wheel drive vehicle characterized by increasing the number of revolutions and controlling the restraining force between the front wheels and the rear wheels to weaken, or the brake fluid pressure of the rear wheels during the anti-skid control. Delay the pressure increase timing of Is used to suppress the decrease in the number of rotations of the rear wheels and to control the restraining force between the front wheels and the rear wheels in a direction of weakening the restraining force of the front wheels and the rear wheels. By controlling the brake fluid pressure increase pulse of the rear wheels, the decrease in the rotational speed of the rear wheels is suppressed, and the restraining force between the front wheels and the rear wheels is controlled to be weakened. It is in the anti-skid control method of the vehicle.

[0006]

EXAMPLES Examples will be described below with reference to the drawings.

<A> Outline of ABS control (FIGS. 1 and 2) The brake pedal 11 is used for anti-skid (ABS) control.
When the wheel is depressed, the hydraulic pressure generated from the master cylinder 12 is transferred to each wheel 15 via the ABS hydraulic unit 2.
The wheel brakes 14 to 18 are applied to brake the wheels. When the brake is applied strongly and the wheels slip, the electronic control unit 3 is based on the signal from the wheel speed sensor 51.
As a result, each wheel 15 to 1 is passed through the ABS hydraulic unit 2.
The anti-skid control is performed for 8. The electronic control unit 3 includes a dedicated hardware device, an input device 31,
The configuration of a general computer device such as the processing device 32 and the output device 33 can be adopted.

<B> Schematic configuration of hydraulic system (FIG. 3) The hydraulic system shows an example of X piping, and the two independent first hydraulic circuits 21 and 21 are provided via the master cylinder 12. It has two hydraulic circuits 22. The main reservoir 13 is a reservoir of brake fluid supplied to the master cylinder.
The first hydraulic circuit 21 is connected to the wheel brakes 14 of the right front wheel 18 and the left rear wheel 17 via the input valve 23, and is connected to the auxiliary reservoir 27 via the output valve 24. Similarly, the second hydraulic circuit 22 connects the right rear wheel 1 via the input valve 23.
6 and the wheel brake 14 of the left front wheel 15, and is connected to the auxiliary reservoir 27 via the output valve 24.

Anti-skid control brake pump 25
Are driven by the motor 26. The electronic control unit 3
Upon receiving the signal from the wheel speed sensor 51, the slip ratio of the wheel is obtained from the wheel speed and the estimated vehicle body speed. When this exceeds a predetermined threshold value, the anti-skid control is started, and the first and second hydraulic circuits 21, In order to increase the hydraulic pressure of 22, the motor 26 is operated to operate the pump 25, and the opening and closing of the input valve 23 and the output valve 24 are controlled so that the brake fluid in the auxiliary reservoir 27 is removed from the first and second hydraulic circuits 21. , 22 to adjust the brake fluid pressure of the wheel brakes 14.

<C> Example of operating state of anti-skid device (FIG. 4) In FIG. 4, the horizontal axis represents the passage of time after the start of braking, and FIG. 4 (a) shows the estimated vehicle speed, wheel speed, and slip. Shows the threshold. FIG. 4B shows the wheel acceleration. 4C shows the operating state of the input valve, FIG. 4D shows the operating state of the output valve, and FIG. 4E shows the braking torque.

When the wheel is decelerated by the start of braking and reaches the deceleration threshold value, it is determined that the wheel is approaching the lock, the input valve is closed, the pressure increase is prohibited, and the braking torque is maintained substantially constant. (Around time t1).

At this time, since the braking torque is excessive due to the operation delay of the hydraulic control system and the like, the wheel speed continues to further decrease and reaches the further deceleration threshold value or the slip threshold value. If it exceeds, it is determined that the risk of wheel locking has occurred, the output valve is opened, and the braking torque is reduced (near time t2).

In this case, the output valve is closed at the time when the set pressure reducing pulse ends or when the wheel indicates acceleration, the pressure reducing is prohibited, and the braking torque is maintained substantially constant (around time t3).

As the braking torque decreases, the acceleration of the wheels gradually increases. As a result, when the wheel returns to the slip threshold or less and exceeds the set acceleration, it is determined that the wheels are recovering, and the output valve The braking torque is maintained substantially constant with the door closed (near time t4).

When the wheel acceleration is stable and continues for a certain period of time, the braking torque is increased stepwise while opening the input valve instantaneously (around time t5).

As the braking torque increases, the wheels begin to decelerate again, and when the deceleration threshold is reached, it is determined that the wheels are approaching the lock, the input valve is closed, and the pressure increase is prohibited. The braking torque is kept substantially constant (near time t6). After that, the above cycle is repeated until the vehicle stops.

<D> ABS control in four-wheel drive (see FIG. 5)
(Fig. 7) The front wheel rotation speed and the rear wheel rotation speed are greater in the four-wheel drive vehicle in which the front wheel and the rear wheel have a greater binding force when the front wheel rotation speed is higher than the rear wheel rotation speed, and vice versa. Two pumps that rotate in synchronism with the number are installed, and the pump on the front wheel side (front pump) is used by utilizing the difference in the amount of circulating oil for discharge and suction between these pumps.
When the rotation speed of 41 becomes higher than the rotation speed of the pump (rear pump) 42 on the rear wheel side, hydraulic pressure is generated to operate the actuator, and the multi-plate clutch 43 is pressed to increase the restraining force between the front wheel and the rear wheel. Move closer to wheel drive mode. On the contrary, when the rotation speed of the front wheel side pump (front pump) 41 becomes lower than the rotation speed of the rear wheel side pump (rear pump) 42,
The hydraulic pressure is reduced, the multi-plate clutch 43 is loosened, the restraining force between the front wheels and the rear wheels is weakened, and the two-wheel drive mode is approached. In this way, the tendency of the four-wheel drive mode and the tendency of the two-wheel drive mode are switched depending on the magnitude of the front wheel rotation speed and the rear wheel rotation speed (see, for example, Japanese Patent Laid-Open No. 3-224830). Also, there is one in which a one-way clutch is provided between the front wheel and the rear wheel (see, for example, Japanese Utility Model Laid-Open No. 59-188731).

As the estimated vehicle body speed during control, basically, if the highest wheel speed among the four wheel speeds is selected, the estimated vehicle body speed close to the actual vehicle body speed can be calculated. However, when going to lock all four wheels, the principle cannot be used, and the estimated vehicle speed for deceleration at a predetermined inclination is used.

When the tendency of the two-wheel drive mode is large,
As shown in FIG. 6, since either of the wheels is close to the actual vehicle speed, the estimated vehicle speed close to the actual vehicle speed can be calculated.

When the tendency of the four-wheel drive mode is large, especially when the anti-skid control is performed on a low μ road surface where the road surface is slippery, the front wheel and the rear wheel are independently brake-controlled, but the front wheel shaft and the rear wheel shaft are controlled. Is differentially limited by the multi-plate clutch 43, so that the wheel speeds of the four front wheels and the rear wheels are synchronized. As a result, the above principle cannot be used, and as shown in FIG. 7, the estimated vehicle body speed decelerating at a predetermined inclination is used, and therefore the estimated vehicle body speed and the actual vehicle body speed are separated from each other. Therefore, during the anti-skid control, control is performed so as to approach the two-wheel drive mode.

The following is an example of shifting or holding to the two-wheel drive mode tendency during anti-skid control.

<a> Transition to two-wheel drive mode by depressurization mode (FIGS. 8 and 4) As the rear wheel rotation speed is larger than the front wheel rotation speed, the restraining force between the front wheel and the rear wheel becomes weaker, and the two-wheel drive mode is set. As the trend shifts
The transition from the four-wheel drive mode tendency to the two-wheel drive mode tendency during the anti-skid control can be performed by speeding up the rear wheel depressurization mode and increasing the rear wheel rotation speed. For that purpose, the pressure reduction signal of the rear wheels may be easily output. Therefore, the average of the slip ratios of the rear wheels and the front wheels is calculated, and the slip ratio of the rear wheels is controlled to be smaller than that of the front wheels as shown in FIG. Alternatively, for example, in FIG. 4, the slip threshold value or the deceleration threshold value is lowered. Alternatively, the apparent rear wheel rotational speed is reduced by subtracting a predetermined value from the rear wheel rotational speed.

<B> Transition flow to the two-wheel drive mode in the pressure reduction mode (FIG. 9) It is determined whether or not the brake control is in the anti-skid (ABS) control, and if the ABS control is in operation, the four-wheel drive is performed. It is determined whether the mode tendency is strong. This determination method obtains the average wheel speed of the left and right front wheels and the average wheel speed of the left and right rear wheels,
Examine the relationship between these wheel speeds. For example, when the average wheel speed of the front wheels is larger than the value obtained by adding the offset value α to the average wheel speed of the rear wheels, it is determined that the four-wheel drive mode tendency is strong. If the tendency of the four-wheel drive mode is not strong and it is close to the two-wheel drive mode, normal ABS control processing is performed. If the tendency of the four-wheel drive mode is strong, a transition process to the tendency of the two-wheel drive mode, for example, a predetermined value β is subtracted from the rear wheel speed obtained from the wheel speed sensor 51 to create an apparent wheel speed, Based on this, ABS control is performed.

<C> Transition to two-wheel drive mode by increasing decompression pulse (FIGS. 10 and 4) When the restraining force of the front and rear wheels is large, the two-wheel drive mode tends to be increased earlier by increasing the decompression amount. Can be moved to. Therefore, for example, as in the flow of FIG. 10, the presence or absence of the decompression mode is checked, and in the decompression mode, the decompression pulse time is calculated, and then the average wheel speed of the front wheels becomes the average wheel speed of the rear wheels. It is determined whether the value is larger than the value obtained by adding the offset value α. If it is large, it is determined that the tendency of the four-wheel drive mode is strong, and the pressure reducing pulse time increasing process is performed to recover the slip tendency of the rear wheels earlier. To increase the rear wheel decompression signal, for example, in FIG.
The pressure reduction pulse time output at the pressure reduction timing (t2) is increased to delay the pressure reduction stop timing (t3).

<D> Holding the two-wheel drive mode by delaying the pressure increase timing (FIGS. 11 and 4) The larger the rear wheel rotation speed, the greater the tendency of the two-wheel drive mode. It is good to keep a tendency to suppress the braking of. Therefore, for example, FIG.
As in the flow of No. 1, the presence or absence of the pressure boosting mode is checked, and in the pressure boosting mode, the pressure boosting pulse time calculation process is performed.
The average wheel speed of the front wheels is offset from the average wheel speed of the rear wheels by an offset value α
It is determined whether the value is larger than the value obtained by adding. If it is large, it is determined that the tendency of the four-wheel drive mode is strong, and further,
It is determined whether or not the delay time has expired. If it has not been completed, the pressure-increasing pulse is delayed to suppress the decrease in the rear wheel rotation speed and maintain the two-wheel drive mode tendency. To delay the pressure increase timing, for example, in FIG. 4, the pressure increase pulse is not immediately output at the pressure increase timing (t5), but the pressure increase pulse is output after a predetermined time has elapsed.

<E> Holding the two-wheel drive mode by decreasing the pressure boosting pulse (FIGS. 12 and 4) As a method for keeping the brake braking of the rear wheels in a tendency to be suppressed during the anti-skid control, for example, the flow of FIG. As described above, the presence or absence of the pressure increasing mode is checked, and in the case of the pressure increasing mode, the pressure increasing pulse time is calculated, and then the average wheel speed of the front wheels is a value obtained by adding the offset value α to the average wheel speed of the rear wheels. Determine if it is greater than. If it is large, it is determined that the tendency of the four-wheel drive mode is strong, and the pressure-increasing pulse is reduced to suppress the reduction of the rear wheel rotation speed and maintain the tendency of the two-wheel drive mode. Also, the width of the pressure boosting pulse can be reduced to maintain the two-wheel drive mode tendency. In order to reduce the pressure increase signal of the rear wheel, for example, in FIG. 4, the time of the pressure increase pulse output at the pressure increase timing (t5) is shortened.

[0027]

The present invention has the following effects. <B> During anti-skid control, the two-wheel drive mode tendency should be maintained as much as possible, and the estimated vehicle speed obtained from wheel speed measurement should be adjusted to the actual vehicle speed so that anti-skid control can be performed more accurately. To <B> During the anti-skid control, the shift to the two-wheel drive mode tendency is facilitated, and the anti-skid control can be performed more accurately. <C> By delaying the timing of increasing the brake fluid pressure of the rear wheels, it is possible to suppress the decrease in the rear wheel rotation speed, maintain the two-wheel drive mode tendency, and perform the antiskid control more accurately. <D> An increase in the brake fluid pressure of the rear wheels is suppressed, a decrease in the rear wheel rotation speed is suppressed, and the tendency of the two-wheel drive mode is maintained to enable more accurate anti-skid control.

[Brief description of drawings]

FIG. 1 is a schematic diagram of ABS control.

FIG. 2 is a block diagram of an electronic control unit.

FIG. 3 is a block diagram of an ABS hydraulic unit.

FIG. 4 is a time chart diagram of ABS control.

FIG. 5 is an explanatory diagram of control of four-wheel drive.

FIG. 6 is an explanatory diagram of actual vehicle body speed and wheel speed in a two-wheel drive mode.

FIG. 7 is an explanatory diagram of actual vehicle speed and wheel speed in four-wheel drive mode.

FIG. 8 is an explanatory diagram for shifting to a two-wheel drive mode.

FIG. 9 is a flow chart of transition to the two-wheel drive mode in the pressure reduction mode.

FIG. 10 is a flow chart showing a transition to a two-wheel drive mode due to an increase in decompression pulse.

FIG. 11 is a flow chart of transition to a two-wheel drive mode due to a delay in pressure increase timing.

FIG. 12 is a flow chart of transition to a two-wheel drive mode due to a decrease in pressure boosting pulse.

[Explanation of symbols] 2 ... ABS hydraulic unit 3 ... Electronic control unit 41 ... Front pump 42 ... Rear pump 43 ... Multi-plate clutch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Oshiro Nakase 8000, Hamakita City, Shizuoka Prefecture Nisshinbo Co., Ltd. Hamakita Seiki Co., Ltd. (72) Inventor Hiroaki Kosugi 8000 Nakase, Hamakita City, Shizuoka Prefecture Nisshinbo Co., Ltd.

Claims (5)

[Claims] 1. An anti-skid control method for a four-wheel drive vehicle in which the front wheel and rear wheel restraining force is greater when the front wheel rotational speed is greater than the rear wheel rotational speed, and vice versa. An anti-skid control method for a four-wheel drive vehicle, characterized in that the average of the slip ratios of the rear wheels is controlled to be smaller than the average of the slip ratios of the front wheels during skid control. 2. An anti-skid control method for a four-wheel drive vehicle in which the front wheel and rear wheel restraining force is greater when the number of revolutions of the front wheels is greater than that of the rear wheels and vice versa. An anti-skid control method for a four-wheel drive vehicle, characterized in that a signal for reducing the brake fluid pressure of the rear wheels is easily output during skid control. 3. An anti-skid control method for a four-wheel drive vehicle in which the front wheel and rear wheel restraining force is greater when the front wheel rotational speed is higher than the rear wheel rotational speed, and vice versa. During skid control, the pressure reduction pulse of the rear wheels is increased to increase the number of rotations of the rear wheels, and the restraining force between the front wheels and the rear wheels is weakened. Skid control method. 4. An anti-skid control method for a four-wheel drive vehicle in which the front wheel and rear wheel restraining force is greater when the front wheel rotational speed is greater than the rear wheel rotational speed, and vice versa. During skid control, by delaying the timing of increasing the brake fluid pressure on the rear wheels, the decrease in the rotational speed of the rear wheels is suppressed, and the control force is controlled to weaken the restraining force between the front wheels and the rear wheels. , 4 wheel drive anti-skid control method. 5. An anti-skid control method for a four-wheel drive vehicle, wherein the front wheel and rear wheel restraining force is greater when the front wheel rotational speed is greater than the rear wheel rotational speed, and vice versa. During skid control, the brake fluid pressure increase pulse for the rear wheels is reduced to suppress the reduction in the rotational speed of the rear wheels and control is performed in a direction that weakens the restraining force between the front wheels and the rear wheels. , 4 wheel drive anti-skid control method.