JP3328324B2 - Anti-skid brake system for all-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 an anti-skid brake device for an all-wheel drive vehicle.

[0002]

2. Description of the Related Art Recently, as is well known by the name of an ABS device, an anti-skid brake device for preventing wheels from locking during braking has been mounted on many vehicles. At the time of the ABS control, that is, the braking force control, there are at least two types of control modes, that is, the control of the braking force decrease and the control of the braking force increase.

[0003] Whether or not the wheels are locked can usually be determined by a slip value (lock value) obtained from the pseudo vehicle body speed theoretically obtained and the actual wheel speed.
Therefore, it can be determined whether or not to start the braking force control by determining whether or not the slip value has exceeded a predetermined threshold value. In this case, the larger the pseudo vehicle speed is set to a larger value, the stronger the tendency of the wheels to be locked, and the control mode is such that the braking force is reduced.

[0004] On the other hand, when the driving wheel generates an acceleration spin that is excessively rotated with respect to the road surface, traction control for preventing the acceleration spin by applying a braking force to the driving wheel is often performed. ing. The number of vehicles that perform both the traction control and the ABS control tends to increase. In this case, it has been proposed that the traction control is prohibited during the ABS control so that the two controls do not interfere with each other (Japanese Patent Laid-Open No. 1-171616).
No. 0).

As described above, how to accurately estimate the pseudo vehicle speed is extremely important in performing the ABS control with high accuracy. If the following wheels are present, the pseudo vehicle speed can be estimated fairly accurately without being affected by acceleration or the like. On the other hand, in an all-wheel drive vehicle in which all wheels are drive wheels, such as a four-wheel drive vehicle, since there is no driven wheel, a drive wheel speed detection that detects each drive wheel speed independently is provided. Generally, the maximum driving wheel speed among the detected driving wheel speeds is set as the pseudo vehicle speed (see Japanese Utility Model Laid-Open No. 63-46276).

[0006]

By the way, in the case of an all-wheel drive vehicle traveling on a quite slippery road surface such as a snowy road,
The driving wheel speed temporarily decreases greatly due to the shift down of the transmission during acceleration (the torque applied to the driving wheels decreases due to the absorption of the inertia of the driving system), and thereafter the driving wheel speed increases. Things may happen. In this case, when the drive wheel speed temporarily decreases significantly, the lock of the drive wheel occurs, and the ABS control is started.

[0007] As described above, when the ABS control is started due to a temporary decrease in the drive wheel speed, the ABS control is generally in a state in which the control is not terminated for a predetermined time in preparation for the next relock. On the other hand, since the pseudo vehicle body speed is set to be large by the increase in the drive wheel speed after the temporary decrease in the drive wheel speed, even when the drive wheel speed is increasing, the drive wheels tend to lock. Is more likely to be determined.

Therefore, even if the brake pedal is depressed immediately after the ABS control is started due to a temporary decrease in the driving wheel speed, the ABS control is in a control mode of reducing the braking force. This causes a problem that a sufficient braking force cannot be secured at the beginning of braking.

The present invention has been made in view of the above-described circumstances. Even when a brake operation is performed immediately after the driving wheel speed temporarily decreases, such as during a downshift, the brake operation is performed. An object of the present invention is to provide an anti-skid brake device for an all-wheel drive vehicle capable of securing a sufficient braking force with a good response in response to a key operation.

[0010]

Means for Solving the Problems In order to achieve the above object, the present invention has the following configuration. That is, in an all-wheel drive vehicle in which all wheels are drive wheels, drive wheel speed detection means for independently detecting the drive wheel speed of each drive wheel, and each drive detected by the drive wheel speed detection means A pseudo vehicle speed setting means for setting a maximum driving wheel speed among the wheel speeds as a pseudo vehicle speed, and a slip value indicating a lock tendency of each driving wheel based on the pseudo vehicle speed setting device and the driving wheel speed detecting device. Means for determining when the wheel deceleration is equal to or more than a predetermined value or the slip value is equal to or more than a predetermined value even when the brake pedal is not operated, and the control is continued for a predetermined time. Braking force control means for outputting a control signal for performing braking force control on the drive wheels so as to prevent locking of the drive wheels based on the slip value determined by the slip value determination means; Work During the control by the braking force control means during the first predetermined time during which acceleration is generated in the drive wheel, the time during which the deceleration occurs in the drive wheel, which is measured immediately after the first predetermined time, or Changing means for changing the control by the braking force control means so as to suppress a decrease in braking force when the slip value is larger by a predetermined amount than a second predetermined time which is a time during which the slip value is more likely to be locked than a predetermined slip value; Is provided.

[0011] The changing means may advance the control end timing of the braking force control means. Further, the changing means sets the pseudo vehicle speed for determining the slip value to a pseudo vehicle speed lower than the pseudo vehicle speed set by the pseudo vehicle speed setting device based on a predetermined pseudo acceleration. It can be.

[0012]

The fact that the first predetermined time is longer than the second predetermined time by a predetermined amount strongly indicates that the driving wheel speed is increasing, and that the ABS control is unnecessary or the necessity thereof is weak. In such a case, the degree of reduction in the braking force due to the ABS control is reduced. Therefore, even if the brake operation is performed immediately after the start of the ABS control due to the decrease in the drive wheel speed, the state immediately shifts to the state in which the decrease in the braking force is suppressed as described above.
Sufficient braking force is secured from the beginning of the braking operation.

[0013] By adopting the configuration as described in claim 2, it is preferable in that the control for lowering the braking force is forcibly terminated and a sufficient braking force is ensured.

According to the third aspect of the present invention, the pseudo vehicle speed is changed to a value smaller than the pseudo vehicle speed obtained in accordance with the actual increase in the driving wheel speed, and the next relocking is performed. In addition, sufficient braking force can be secured at the initial stage of the brake operation.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings. Description of FIG. 1 1FR is right front wheel, 1FL is left front wheel, 1RR is right rear wheel, 1FR
RL is the left rear wheel. Reference numeral 2 denotes an engine. The generated torque of the engine 2 is transmitted to a center differential 5 via a clutch 3 and a transmission 4. The generated torque of the engine 2 transmitted to the center differential 5 is transmitted to the right and left rear wheels 1RR and 1RL via the right and left drive shafts 8R or 8L after passing through the propeller shaft 6 and the differential device 7. At the same time, the engine 2 transmitted to the center differential 5
Is transmitted to the left and right front wheels 1FR and 1FL via the right and left drive shafts 11R or 11L after passing through the propeller shaft 9 and the differential device 10. As described above, the automobile is a four-wheel drive vehicle in which all four wheels 1FR to 1RL are all drive wheels.

Each of the wheels 1FR to 1RL is provided with a brake device 12FR to 12RL. In the embodiment, each of the brake devices 12FR to 12RL is a disk brake including a disk that rotates integrally with a wheel and a caliper having a built-in wheel cylinder.

Numeral 13 denotes a brake fluid pressure adjusting device, which is connected to a pipe 14, 15, 16 or 1
7, brake devices 12FR to 12RL for each wheel
And are connected independently. The brake fluid pressure from a master cylinder (not shown) is supplied to the fluid pressure adjusting device 13. In the ABS control, the fluid pressure supplied to the pipes 14 to 17 is independently controlled. In addition, three states of a braking force decrease (fluid pressure decrease), a braking force increase (hydraulic pressure increase), and a braking force holding (hydraulic pressure holding) are switched. Of course, when the ABS control is not performed, the hydraulic pressure adjusting device 13 supplies the brake hydraulic pressure from the master cylinder to each of the brake devices 12FR to 12RL as it is. In addition,
Since the fluid pressure adjusting device 13 itself that performs such an operation is well known, further description is omitted.

U is a control unit constructed by using a microcomputer. The control unit U receives signals from at least the sensors S1 to S4.
The control unit U outputs a predetermined control signal to the hydraulic pressure adjusting device 13. Each of the sensors S1 to S4 is a wheel speed sensor that independently detects the driving wheel speed of each of the driving wheels 1FR to 1RL.

Description of FIG . 2 The contents of the ABS control by the control unit U will be described with reference to FIG. In this ABS control, phase 0, phase 1, phase 2, phase 3, phase 5
Is used, and the meaning is as follows. Phase 0: means that non-ABS control is being performed. Phase 1: means pressure increase (braking force increase). Phase 2: Holding after non-ABS control or after pressure increase (braking force holding). Phase 3: Means pressure reduction (braking force reduction). Phase 5: means holding after decompression. The slip value indicating the tendency to lock the wheels is determined, for example, by the following equation. The estimation of the pseudo vehicle speed will be described later. Of course, the smaller the slip value, the stronger the tendency to lock the drive wheels, indicating that the braking force is reduced (the brake fluid pressure is reduced) by the ABS control. "Slip value = (wheel speed / pseudo vehicle speed) x 100%"

Assuming the above, ABS control is not performed until time t1, and the wheel speed, that is, the drive wheel speed is gradually decreased from the pseudo vehicle speed as the brake fluid pressure increases. To go. Due to the decrease in the drive wheel speed, at time t1, that is, at the time A, the deceleration of the drive wheel speed increases to a predetermined value as the ABS control start condition.

The ABS control is started from the point A, which is performed by first maintaining the brake hydraulic pressure. During this holding, the drive wheel speed also decreases, and when the slip value decreases to a predetermined threshold value as shown at point B, pressure reduction is performed. Due to this decompression, the degree of decrease in the drive wheel speed becomes weaker, and at time C, the deceleration approaches zero. At the point C at which the deceleration becomes close to 0, the holding is performed, whereby the drive wheel speed gradually increases, and at the point D, the slip value returns to the predetermined threshold value. From this point D,
The pressure is increased, but the pressure is increased rapidly in the initial stage and then gradually increased.

Due to the pressure increase, the deceleration of the drive wheel speed again increases at the point E to the predetermined value set as the ABS control start condition. Thus, after the brake fluid pressure is maintained, if the slip value decreases to a predetermined threshold value at the point F, the pressure is reduced. Then, the brake hydraulic pressure is maintained from the time point G corresponding to the time point C.

The above is an outline of the ABS control. One cycle of control is a period from the end of the phase 5 (start of pressure increase) to be maintained after the pressure reduction to the end of the next phase 5. However, this one cycle is a failure only when the ABS control starts.
The period from the start of holding phase 2 to the end of phase 5 (because the ABS control is started from phase 2). The threshold value when the phase is changed is changed in accordance with the road surface μ (coefficient of friction), and specific examples of the threshold value in accordance with the road surface μ are shown in the following table.

[0024]

[Table 1]

The illustration 3 in FIG. 3, flow showing a control example of the present invention - are bets, - Cha
In the following description, P indicates a step. First, at P1, it is determined whether the ABS control is currently being performed. If the determination in P1 is NO, in P6, the maximum driving wheel speed among the four driving wheel speeds is set as the pseudo vehicle speed Vref.

If the determination in P1 is YES, in P2, the deceleration time TD indicating that the drive wheel is decelerating is counted. Next, in P3, it is determined whether or not the drive wheel has shifted to an acceleration state indicating acceleration. If the determination in P3 is NO, the process returns to P2, and the deceleration time is counted up in this way.

If the determination in P3 is YES, in P4, it is determined whether the acceleration time is equal to or greater than a value obtained by adding a predetermined amount α (> 0) to the deceleration time TD up to the point in time when P3 becomes YES. Is determined. If the determination in P4 is NO, the process returns to P6. Also, if the determination in P4 is YES,
In P5, the ABS control is forcibly terminated.

Description of FIG . 4 FIG . 4 schematically shows the control contents of FIG. In FIG. 4, downshifting is performed at time t11 for acceleration, and the driving wheel speed, particularly a part of the driving wheel speed, sharply decreases. Thus, the ABS control is started from the time t11. Until the time point t12, the driving wheels show the deceleration, and the time period from the time t11 to the time t12 is the deceleration time TD.

After time t12, the drive wheels show acceleration, and at time t13, the acceleration time becomes TD + α.
When the ABS control is started at the time t11, the ABS control is normally continued for a predetermined set time, and the time when the set time has elapsed from the time t11 is the time t14.

Now, after time t11, for example, t12 and t1
If the normal ABS control is performed until the above-mentioned set time t14 when the brake pedal is depressed between step 3 and step 3, the sufficient braking force is actually applied to the drive wheels.
This is at least after elapse of t14 which is the ABS control end set time.

On the other hand, in the present invention, the ABS control is forcibly terminated when the drive wheel shows acceleration and the acceleration time reaches TD + α at time t13. Therefore, the braking force on the drive wheels becomes sufficiently large immediately after the passage of t13 (see the broken line in FIG. 4). That is, t13 and t1
4, sufficient braking force will be secured faster.

Although the embodiment has been described above, the present invention is not limited to this and includes, for example, the following case. First, at the time point t13 when the process of P5 in FIG. 3 is performed, the setting of the pseudo vehicle body speed can be changed in a direction to suppress the reduction of the braking force. For example, after time t13,
A predetermined pseudo acceleration, for example, 0.6G (G is a gravitational acceleration,
0.6G is equivalent to acceleration per second). The pseudo vehicle speed can be changed so as to be updated every control cycle every minute. The pseudo vehicle speed set in this way is indicated by a chain line in FIG. Indicated by This pseudo acceleration may be set to be equal to or less than the theoretical maximum acceleration of the vehicle body, taking into account the grip force of the drive wheels, and by doing so, the pseudo vehicle speed is smaller than the maximum drive wheel speed, that is, The slip value is determined to have a weak locking tendency, and is changed to a direction in which the braking force is increased.

At P2 in FIG. 3, instead of the deceleration time,
The slip value may be set to a time at which the locking tendency becomes stronger than a predetermined threshold value.

After passing through P5, AB
The ABS control may be prohibited for a predetermined time from the processing of P5 so that the S control is not started.

The control shown in FIG. 3 may be performed only when a downshift is detected, or may be performed only during a predetermined time after the downshift is detected.

[Brief description of the drawings]

FIG. 1 is an overall system diagram showing one embodiment of the present invention.

FIG. 2 is a time chart showing an example of ABS control.

FIG. 3 is a flowchart showing a control example of the present invention.

FIG. 4 is a time chart schematically showing the control example of FIG. 3;

[Explanation of symbols]

 1FR to 1FL: drive wheel 12FR to 12FL: brake device 13: hydraulic pressure control device 14 to 17: brake pipe S1 to S4: sensor (drive wheel speed) U: control unit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B60T 8/58

Claims (3)

(57) [Claims] 1. In an all-wheel drive vehicle in which all wheels are drive wheels, drive wheel speed detection means for independently detecting drive wheel speeds of each drive wheel; Pseudo vehicle body speed setting means for setting the maximum driving wheel speed among the driving wheel speeds as the pseudo vehicle body speed; anda locking tendency of each driving wheel based on the pseudo vehicle body speed setting means and the driving wheel speed detecting means. A slip value determining means for determining a slip value to be indicated, and when the wheel deceleration becomes a predetermined value or more or the slip value becomes a predetermined value or more even when the brake pedal is not operated, the control is started and the control is continued for a predetermined time. The driving wheel is set so as to prevent the locking of the driving wheel based on the slip value determined by the slip value determining means .
A braking force control unit that outputs a control signal for performing the braking force control, and a first predetermined time during which acceleration is generated in the driving wheels during control by the braking force control unit when the brake is not operating.
The first predetermined time is measured by immediately after the deceleration of the drive wheel or the second predetermined time in which the slip value is more likely to lock than the predetermined slip value. Changing means for changing the control by the braking force control means so as to suppress a decrease in the braking force. An anti-skid brake device for an all-wheel drive vehicle, comprising: 2. An anti-skid for an all-wheel drive vehicle according to claim 1, wherein said changing means hastens the control end time of said braking force control means.
Brake device . 3. The method of claim 1, wherein the changing means, prior to in preference to the pseudo vehicle speed setting means
By setting the pseudo vehicle speed for determining the slip value based on a predetermined pseudo acceleration, the pseudo vehicle speed setting means can be used.
Set the pseudo vehicle speed lower than the pseudo vehicle speed set by
Anti-skid brake for all-wheel drive vehicles
Rake device .