JP2736745B2 - Anti-skid control method for four-wheel drive vehicle - Google Patents

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 that makes the restraining force between front and rear wheels 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 of the front wheel and the rear wheel becomes stronger and approaches the four-wheel drive mode, and conversely, the front wheel rotation speed decreases to the rear wheel rotation speed. On the other hand, when it becomes smaller, the restraining force between 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. With this control, the vehicle approaches the four-wheel drive mode during forward acceleration, and approaches the two-wheel drive mode during forward constant speed or deceleration.

[0003]

Conventionally, during anti-skid control, the front wheel and the rear wheel are independently brake-controlled, so that the front wheel speed and the rear wheel speed vary. As a result, the vehicle may approach the four-wheel drive mode during the anti-skid control. Therefore, when the tendency of the four-wheel drive mode 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 anti-skid control in four-wheel drive in which the front and rear wheel restraining forces are changed.

[0005]

SUMMARY OF THE INVENTION The present invention provides a four-wheel drive system in which the front wheel and the rear wheel have a larger restraining force when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel than when the rotation speed of the rear wheel is higher than the reverse speed. In the anti-skid control method for a vehicle, during anti-skid control, the average of the slip rates of the rear wheels is made smaller than the average of the slip rates of the front wheels to increase the rotational speed of the rear wheels.
An anti-skid control method for a four-wheel drive vehicle, characterized by controlling the binding force between the wheels and the rear wheels to be weakened , or
In the anti-skid control method for a four-wheel drive vehicle in which the front wheel and the rear wheel have a larger restraining force when the rotation speed of the front wheel is larger than the rotation speed of the rear wheel, By making it easier to output the pressure reduction signal of the brake fluid pressure of the wheels, the rotation speed of the rear wheels is increased,
An anti-skid control method for a four-wheel drive vehicle, characterized by controlling in a direction to weaken the restraining force , or when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel, than when the reverse is true. In an anti-skid control method for a four-wheel-drive vehicle having a large front wheel and rear wheel restraining force, the number of rotations of the rear wheel is increased by increasing the pressure reduction pulse of the rear wheel during the anti-skid control to increase the rotation speed of the rear wheel. Anti-skid control method for a four-wheel drive vehicle, characterized in that control is performed in the direction in which the restraining force of the vehicle is reduced, or when the rotational speed of the front wheel is higher than the rotational speed of the rear wheel, and vice versa. In the anti-skid control method for a four-wheel drive vehicle in which the front and rear wheels have a greater restraining force than the front wheel and the rear wheel, during the anti-skid control, the timing of increasing the brake fluid pressure of the rear wheel is delayed to reduce the rotational speed of the rear wheel. With the front wheels Anti-skid control method for a four-wheel drive vehicle, characterized in that control is performed in a direction to reduce the restraining force of the wheels, or when the rotation speed of the front wheels is larger than the rotation speed of the rear wheels, and vice versa. An anti-skid control method for a four-wheel drive vehicle in which the front and rear wheels have a greater restraining force than
During anti-skid control, by reducing the pressure increase pulse of the brake fluid pressure of the rear wheel, the reduction of the rotation speed of the rear wheel is suppressed and the control is performed in the direction to weaken the restraining force of the front and rear wheels. The anti-skid control method for a four-wheel drive vehicle.

[0006]

Embodiments will be described below with reference to the drawings.

<A> Outline of ABS Control (FIGS. 1 and 2) Anti-skid (ABS) control is performed by the brake pedal 11.
Is depressed, the hydraulic pressure generated from the master cylinder 12 is transmitted through the ABS hydraulic unit 2 to each wheel 15.
The wheel brakes 14 to 18 are applied, and the wheels are braked. When the brake is strongly applied and the wheel slips, the electronic control unit 3 is controlled based on a signal from the wheel speed sensor 51.
, Each wheel 15-1 through the ABS hydraulic unit 2
8, anti-skid control is performed. Note that the electronic control unit 3 is 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 an X pipe, and two independent first hydraulic circuits 21 and 21 are connected via a master cylinder 12. It has a two hydraulic circuit 22. The main reservoir 13 is a reservoir for the 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 an input valve 23, and connected to an auxiliary reservoir 27 via an output valve 24. Similarly, the second hydraulic circuit 22 is connected to 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 an auxiliary reservoir 27 via an output valve 24.

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

<C> Example of operating state of anti-skid device (FIG. 4) In FIG. 4, the abscissa indicates the time elapsed after the start of braking, and FIG. 4 (a) shows the estimated vehicle speed, wheel speed and slip. Indicates a threshold. FIG. 4B shows the wheel acceleration. 4C shows the operation state of the input valve, FIG. 4D shows the operation 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, pressure increase is prohibited, and the braking torque is maintained substantially constant. (Near time t1).

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

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

As the braking torque decreases, the wheel acceleration gradually increases. As a result, when the wheel speed returns to the slip threshold value or less and when the wheel speed exceeds the set acceleration value, it is determined that the wheel is recovering. The braking torque is maintained substantially constant while being closed (around time t4).

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

As the braking torque increases, the wheels start 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 (around time t6). Thereafter, the above cycle is repeated until the vehicle stops.

<D> ABS control in four-wheel drive (FIG. 5)
-Fig. 7) In a four-wheel drive vehicle in which the front wheel and the rear wheel have larger restraining force when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel, the front wheel rotation speed and the rear wheel rotation speed are higher. Two pumps that rotate in synchronization with the number of pumps are provided, and a pump on the front wheel side (front pump) is used by utilizing the difference in the amount of circulating oil between discharge and suction between these pumps.
When the rotation speed of the rear wheel 41 becomes higher than the rotation speed of the rear-wheel-side pump (rear pump) 42, the actuator generates an oil pressure to actuate the multi-plate clutch 43 to increase the restraining force between the front wheel and the rear wheel. Move closer to wheel drive mode. Conversely, when the rotation speed of the front wheel side pump (front pump) 41 becomes smaller than the rotation speed of the rear wheel side pump (rear pump) 42,
The hydraulic pressure decreases, the multi-plate clutch 43 is loosened, the binding force between the front wheel and the rear wheel is weakened, and the vehicle approaches the two-wheel drive mode. As described above, the tendency of the four-wheel drive mode and the tendency of the two-wheel drive mode are switched according to the magnitude of the front wheel rotation speed and the rear wheel rotation speed (see, for example, Japanese Patent Application Laid-Open No. 3-224830). Further, there is a vehicle in which a one-way clutch is provided between a front wheel and a rear wheel (for example, see Japanese Utility Model Laid-Open No. 59-188731).

As the estimated vehicle speed under control, basically, if the maximum wheel speed of the four wheel speeds is selected, an estimated vehicle speed close to the actual vehicle speed can be calculated. However, when all four wheels are locked, the principle cannot be used, and the estimated vehicle speed that decelerates at a predetermined inclination is used.

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

When the anti-skid control is performed on a low-μ road surface where the road surface is slippery, the brake control is performed independently on the front wheels and the rear wheels. Is limited by the multi-plate clutch 43, so that the wheel speeds of the front and rear wheels are synchronized. As a result, the above-mentioned principle cannot be used, and as shown in FIG. 7, since the estimated vehicle speed is decelerated at a predetermined inclination, the estimated vehicle speed is different from the actual vehicle speed. Therefore, during anti-skid control, control is performed to approach the two-wheel drive mode.

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

<A> Transition to Two-Wheel Drive Mode by Pressure Reduction Mode (FIGS. 8 and 4) As the rear wheel speed is higher than the front wheel speed, the restraining force between the front and rear wheels is weakened, and the two-wheel drive mode is used. As we move into trends,
The shift from the four-wheel drive mode tendency to the two-wheel drive mode tendency during the anti-skid control can be performed by increasing the rear wheel rotation speed by making the rear wheel depressurization mode earlier. For this purpose, it is only necessary to make it easier to output a pressure reduction signal for the rear wheels. Therefore, the average of the slip ratio of the rear wheel and the front wheel is obtained, and control is performed so that the slip ratio of the rear wheel is smaller than that of the front wheel as shown in FIG. Alternatively, for example, in FIG. 4, the slip threshold or the deceleration threshold is lowered. Alternatively, the apparent rear wheel speed is reduced by reducing a predetermined value to the rear wheel speed.

<B> Flow for shifting to the two-wheel drive mode in the depressurization mode (FIG. 9) It is determined whether or not the brake control is under anti-skid (ABS) control. It is determined whether the mode tendency is strong. This determination method determines the average wheel speed of the left and right front wheels and the average wheel speed of the left and right rear wheels,
The magnitude relationship between these wheel speeds is examined. 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 tendency of the four-wheel drive mode is strong. If the four-wheel drive mode does not tend to be strong and 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, processing for shifting to the tendency of the two-wheel drive mode, for example, subtracting a predetermined value β 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 the two-wheel drive mode by increasing the pressure reduction pulse (FIGS. 10 and 4) When the restraining force of the front wheel and the rear wheel is large, the tendency of the two-wheel drive mode is promptly increased by increasing the pressure reduction amount. Can be transferred to. For this purpose, for example, as shown in the flow of FIG. 10, the presence or absence of the decompression mode is checked, and in the case of the decompression mode, the process of calculating the decompression pulse time is performed, and then the average wheel speed of the front wheels becomes equal to the average wheel speed of the rear wheels. It is determined whether the value is greater than the value obtained by adding the offset value α. If it is larger, it is determined that the tendency of the four-wheel drive mode is strong, and the process of increasing the pressure reduction pulse time is performed to recover the rear wheel slip tendency earlier. To increase the pressure reduction signal of the rear wheel, for example, in FIG.
The decompression pulse time output at the decompression timing (t2) is increased to delay the decompression stop timing (t3).

<D> Holding the two-wheel drive mode by delaying the pressure increase timing (FIGS. 11 and 4) As the rear wheel rotation speed increases, the two-wheel drive mode tendency increases. It is better to keep a tendency to suppress brake braking. Therefore, for example, FIG.
As in the flow of 1, the presence or absence of the pressure increase mode is checked, and in the case of the pressure increase mode, the pressure increase pulse time is calculated.
The average wheel speed of the front wheel is offset from the average wheel speed of the rear wheel by the offset value α.
It is determined whether the value is larger than the value obtained by adding. If it is larger, it is determined that the tendency of the four-wheel drive mode is strong.
It is determined whether or not the delay time has expired. If not completed, the pressure-increasing pulse is delayed to suppress a decrease in the rear wheel rotation speed, and the two-wheel drive mode tendency is maintained. In order to delay the pressure increase timing, for example, in FIG. 4, the pressure increase pulse is not output immediately at the pressure increase timing (t5), but is output after a predetermined time elapses.

<E> Holding the two-wheel drive mode by reducing the pressure-increasing pulse (FIGS. 12 and 4) During the anti-skid control, as a method for maintaining the tendency to suppress the rear-wheel brake braking, for example, a method shown in FIG. As described above, the presence or absence of the pressure increase mode is checked, and in the case of the pressure increase mode, the pressure increase pulse time is calculated, and then the average wheel speed of the front wheels is 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 larger, it is determined that the tendency of the four-wheel drive mode is strong, and a process of decreasing the pressure increase pulse is performed to suppress a decrease in the rear wheel rotation speed, and the tendency of the two-wheel drive mode is maintained. Also, the width of the pressure increase pulse can be reduced to maintain the tendency of the two-wheel drive mode. 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 to be reduced.

[0027]

The present invention has the following effects. <A> During anti-skid control, the two-wheel drive mode tendency is maintained as much as possible, so that the estimated vehicle speed obtained from the measurement of the wheel speed is matched with 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> The timing of increasing the brake fluid pressure of the rear wheels is delayed to suppress a decrease in the number of revolutions of the rear wheels, maintain the tendency of the two-wheel drive mode, and perform more accurate anti-skid control. <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 anti-skid control can be performed more accurately while maintaining the tendency in the two-wheel drive mode.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an ABS control.

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

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

FIG. 4 is a time chart of ABS control.

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

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

FIG. 7 is an explanatory diagram of actual vehicle speed and wheel speed in a 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 shifting to a two-wheel drive mode in a decompression mode.

FIG. 10 is a flowchart of a transition to a two-wheel drive mode by increasing the pressure-reducing pulse.

FIG. 11 is a flowchart for shifting to a two-wheel drive mode due to a delay in pressure increase timing.

FIG. 12 is a flowchart for shifting to a two-wheel drive mode by reducing the pressure increase pulse.

[Explanation of symbols]

 2 ... ABS hydraulic unit 3 ... Electronic control device 41 Front pump 42 Rear pump 43 Multi-plate clutch

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hiroshi Oshiro 8000 Nakase, Hamakita City, Shizuoka Prefecture Inside Nisshinbo Spinning Machinery Co., Ltd. (56) References JP-A-2-26673 (JP, A) JP-A-62-160952 (JP, A) JP-A-4-169335 (JP, A) JP-A-63-143466 (JP, U)

Claims (5)

(57) [Claims] An anti-skid control method for a four-wheel drive vehicle in which the front wheel and the rear wheel have a larger restraining force when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel, and vice versa. During skid control, the average of the rear wheel slip ratio is set to be smaller than the average of the front wheel
To increase the number of revolutions and reduce the binding force between the front and rear wheels
And controlling the direction, four-wheel drive anti-skid control method of the vehicle. 2. An anti-skid control method for a four-wheel drive vehicle in which a front wheel and a rear wheel have a larger restraining force when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel, and vice versa. During skid control, it is possible to increase the number of rotations of the rear wheels by making it easier to output a pressure reduction signal for the brake fluid pressure of the rear wheels.
An anti-skid control method for a four-wheel drive vehicle, wherein the control is performed in a direction in which the binding force between the front wheel and the rear wheel is reduced . 3. An anti-skid control method for a four-wheel drive vehicle in which the front wheel and the rear wheel have a larger restraining force when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel, and vice versa. During skid control, by increasing the pressure reduction pulse of the rear wheel, the rotation speed of the rear wheel is increased, and the restraining force between the front wheel and the rear wheel is controlled to be weakened. Skid control method. 4. An anti-skid control method for a four-wheel drive vehicle in which the front wheels and the rear wheels have a larger restraining force when the rotation speed of the front wheels is higher than the rotation speed of the rear wheels, and vice versa. During skid control, by delaying the pressure increase of the brake fluid pressure of the rear wheel, the reduction of the rotation speed of the rear wheel is suppressed, and the control is performed in a direction to reduce the restraining force of the front wheel and the rear wheel. An anti-skid control method for a four-wheel drive vehicle. 5. An anti-skid control method for a four-wheel drive vehicle in which the front wheel and the rear wheel have a greater restraining force when the rotation speed of the front wheel is higher than the rotation speed of the rear wheel, and vice versa. During skid control, by decreasing the pressure increase pulse of the brake fluid pressure of the rear wheel, the decrease in the rotational speed of the rear wheel is suppressed, and the control is performed in a direction to reduce the binding force between the front wheel and the rear wheel. An anti-skid control method for a four-wheel drive vehicle.