JP2002274355A - Anti-skid control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the increase of the tendency of a wheel to lock when braking lightly by the smallest braking in an anti-skid control device. SOLUTION: A means for forming a decompression threshold in a control unit of the anti-skid control device normally uses a basic decompression threshold λ1 as a control start threshold of a driven wheel. But when decompression control by anti-skid control to a driving wheel is executed, decompression by the anti-skid control to the driven wheel is not executed, and a road surface frictional state determining means determines that it is in a low frictional state, a relative relationship between the control start threshold and a wheel speed is corrected in the direction allowing easy control intervention.

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 device for performing so-called anti-skid control for controlling brake fluid pressure in order to prevent wheels from locking during braking.

[0002]

2. Description of the Related Art In general, an anti-skid control device includes a pressure increasing control for increasing a braking fluid pressure, a pressure decreasing control for decreasing a braking fluid pressure, and a braking fluid in accordance with a relative relationship between a vehicle speed and a wheel speed (a so-called slip ratio). It is configured to execute a holding control for keeping the pressure constant and a gentle pressure increasing control for gradually increasing the brake fluid pressure. Also, in the conventional anti-skid control device,
In determining the vehicle speed, it is general to calculate the approximate wheel speed of the four wheels, for example, by approximating the maximum speed as a pseudo vehicle speed VI. Also, based on the vehicle speed VI, the vehicle speed is lower than the vehicle speed VI. That is, a configuration is known in which a control start threshold value λ1 corresponding to a wheel speed having a predetermined slip ratio is obtained, and when the wheel speed Vw falls below the control start threshold value λ1, anti-skid control is started.

[0003]

When a braking operation is performed while the vehicle is traveling in a low friction state such as an icy road (hereinafter, the friction coefficient is referred to as μ), the driver does not lock the wheels. They tend to step on the brake pedal slowly and slowly. However, when such a light braking operation is performed, the conventional anti-skid control device mounted on the two-wheel drive vehicle may have the following problems.

That is, when the braking is performed lightly, the master cylinder pressure is relatively low, and the pressure of the wheel cylinder does not increase much. Therefore, as shown in the time chart of FIG. The tendency of deceleration is greater due to engine braking, etc. compared to the driven wheels (the front wheel is used as the drive wheel in the figure), or the front wheel has a larger effective wheel brake diameter than the rear wheel, that is, the braking force distribution is more Is large, the front wheel tends to decelerate more than the rear wheel, and the wheel speed VwF of the front wheel falls below the pressure reduction threshold λ1, and the pressure reduction by the anti-skid control is performed on the front wheel. The wheel speed VwR is smaller than the control start threshold value λ1,
There is a possibility that a phenomenon in which the anti-skid control is not performed on the rear wheels may occur. Such a state in which the rear wheels are braked at the slip ratio just before the control start threshold value λ1 is referred to as “barely braking” in this specification. Such a phenomenon is particularly likely to occur in a front-wheel drive vehicle in which the rear wheel load tends to be low.

When the vehicle is traveling on a low μ road as described above, "slightly braking" is performed, and the wheel speed Vw of the front wheels is reduced by "slightly braking" and engine braking is performed to execute anti-skid control. As described above, the actual vehicle speed Vcar, which is the actual vehicle speed, is reduced when the anti-skid control is not performed but the actual vehicle speed Vcar is lower than the actual vehicle speed Vwcar due to “slightly braking” as described above.
Is reduced by a slight slip, and is formed by the rear wheel speed VwR which is higher than the front wheel speed (this is referred to as the "downward movement" of the pseudo vehicle speed VI). As a result, the pseudo vehicle speed VI calculated based on the rear wheel speed VwR is calculated to be lower than the actual vehicle speed Vcar, and the control start threshold calculated based on the pseudo vehicle speed VI is further calculated. λ1 is also calculated to be lower than the optimum value corresponding to the actual vehicle speed Vcar. For this reason, it is difficult for the wheel speed of the rear wheel to fall below the control start threshold value λ1, and there is a possibility that the locking tendency of the rear wheel becomes strong.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In an anti-skid control device, even if light braking by "slightly braking" is performed, it is possible to suppress the tendency of the rear wheels to lock. It is an object.

[0007]

To achieve the above object, the present invention provides a wheel speed detecting means for detecting a wheel speed, and a pseudo vehicle speed calculating means for calculating a pseudo vehicle speed based on the wheel speed. Control start threshold value forming means for forming a control start threshold value based on the pseudo vehicle body speed; and a braking force for a wheel for preventing locking of the wheel based on the wheel speed and the control start threshold value. Anti-skid control means for controlling the friction of the traveling road surface is determined to be a low friction state, the anti-skid control means, the anti-skid control means, If the state determination means determines that the friction is low, and one of the front and rear wheels performs anti-skid control, and the other does not perform anti-skid control. And a means, characterized in that the wheels do not run an anti-skid control is to correct the relative relationship of the anti-skid control execution easy direction to the wheel speed and the control start threshold value.

[0008] The invention described in claim 2 is the first invention.
The anti-skid control device described in (1) is characterized in that the invention is applied to at least one of a front wheel drive vehicle that drives only the front wheels and a vehicle in which the front wheels are larger in the front wheels than the rear wheels.

[0009] The invention described in claim 3 is the first invention.
Or the anti-skid control device according to 2, further comprising a brake fluid pressure adjusting means for performing pressure reduction control of a brake fluid pressure in order to prevent wheel lock based on the wheel speed and the control start threshold value, The determining means includes: a first road surface friction state determination for determining a low friction state when the vehicle body deceleration is smaller than a predetermined low friction state determination threshold; and a predetermined low friction time by anti-skid control. The second to determine the low friction state when the state determination time is exceeded
And / or determining at least one of the road surface friction states.

[0010] The invention described in claim 4 is the invention according to claim 3.
3. The anti-skid control device according to claim 1, wherein the vehicle body deceleration is determined based on a change rate of the pseudo vehicle speed calculated by the pseudo vehicle speed calculating means.

[0011]

According to the present invention, when the driver is traveling on a low μ road such as an icy road, “brake braking” is performed, and anti-skid control is performed on one of the front and rear wheels. However, if a state occurs in which the anti-skid control is not performed on the other side, the control start threshold value forming means corrects the relative relationship between the control start threshold value and the wheel speed in a direction in which the anti-skid control is easily started. Therefore, the wheel speed is more likely to fall below the control start threshold value, so that it is determined that there is a tendency to lock, and anti-skid control is executed. As a result, the wheel speeds of the wheels for which the anti-skid control is not performed match the actual vehicle speed Vcar, and the pseudo vehicle speed obtained based on the wheel speeds is eliminated. The effect of being able to solve the problem that the locking tendency of the wheel that is not executed becomes strong can be solved.

According to the second aspect of the present invention, the front wheel is a driving wheel and the rear wheel is a driven wheel, or the braking force distribution of the front wheel is set to be larger than that of the rear wheel. In the case of the rear wheel, the wheel load is low in the former case, and the braking force distribution is low in the latter case, so the anti-skid control is not performed for the rear wheel. The speed is lower than the actual vehicle speed, and as a result, a “fall” of the pseudo vehicle speed and the control start threshold value is likely to occur. Therefore, as described above, the present invention that corrects the relative relationship between the control start threshold value and the wheel speed in the direction in which the anti-skid control is easily started for the wheel on which the anti-skid control is not started becomes more effective.

According to the third or fourth aspect of the present invention, the road surface friction state determining means includes a first road surface friction state determination based on the vehicle deceleration and a second road surface friction determination based on the decompression time. Since at least one of the state determination and the state determination is performed, a means for detecting an acceleration such as an acceleration sensor is not required for the low μ determination, and the road surface friction state determination can be performed at low cost. By performing both of these two determinations, the low μ road determination can be performed more reliably. Claim 4
In the invention described in the above, in the first road surface friction state determination,
Since the vehicle body deceleration is obtained from the change rate of the pseudo vehicle speed calculated by the pseudo vehicle speed calculation means, it is possible to determine without using a means for detecting acceleration such as an acceleration sensor, and the road surface friction state is inexpensive. A decision can be made.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment) An anti-skid control device according to this embodiment corresponds to the invention described in all claims, and the configuration will be described first. FIG. 2 is a hydraulic circuit diagram showing a main part of a brake device to which the anti-skid control device according to the embodiment of the present invention is applied. In the figure, reference numeral 1 denotes a master cylinder. The master cylinder 1 is configured to generate a hydraulic pressure when a driver operates a brake pedal (not shown).

The master cylinder 1 includes a brake pipe 2
And is connected to the wheel cylinder 3 via. In the middle of the brake pipe 2, the upstream (master cylinder 1 side) and downstream (wheel cylinder 3
Side), a pressure reduction state in which the brake fluid of the wheel cylinder 3 is released to the drain circuit 4, and a holding state in which the brake pipe 2 is shut off to maintain the brake fluid pressure of the wheel cylinder 3. Control valve 5 is provided. That is, the hydraulic pressure of the wheel cylinder 2 can be arbitrarily controlled based on the switching of the control valve 5. The control valve 5 may be constituted by two solenoid valves, a pressure-intensifying valve for switching the brake pipe 2 between a communicating state and a shut-off state, and a pressure-reducing valve for switching the drain circuit 4 between a communicating state and a shut-off state.

The drain circuit 4 is provided with a reservoir 6 capable of storing brake fluid. A recirculation circuit 8 is provided for connecting the reservoir 6 to a position upstream of the control valve 5 of the brake pipe 2, and the recirculation circuit 8 supplies the brake fluid stored in the reservoir 6 to the brake pipe 2. Is provided with a pump 7 for reflux.

In FIG. 2 described above, the configuration of the range surrounded by the dashed line is combined as one brake unit 11. Although FIG. 2 illustrates the configuration for one wheel, the overall configuration is as shown in FIG. 1, and the brake unit 11 includes four wheels FR (right front wheel), FL (left front wheel), and RR (right The brake unit 1 is configured to be able to control brake fluid pressures of wheel cylinders 3 (not shown in FIG. 1) of RL (rear left wheel) and RL (left rear wheel), respectively.
Reference numeral 1 corresponds to a brake fluid pressure adjusting means in the claims. Incidentally, the anti-skid control device according to the embodiment is applied to a front-wheel drive vehicle that drives a front wheel and drives a rear wheel.

The operation of the control valve 5 and the pump 7 of the brake unit 11 is controlled by a control unit 12. The control unit 12 corresponds to the anti-skid control means in the claims.
As input means, there are provided wheel speed sensors 13, 13, 13, 13 for detecting rotation speeds of the wheels FR, FL, RR, RL. The wheel speed sensor 13 has a well-known configuration in which the pulse of the output signal changes according to the rotation speed of the wheel. Further, a longitudinal acceleration switch and a longitudinal acceleration sensor may be provided as necessary. The longitudinal acceleration switch has a structure in which the output is switched between Lo and Hi when the longitudinal acceleration is equal to or more than a predetermined value and less than a predetermined value.

Next, the anti-skid control of this embodiment will be described. FIG. 3 shows the overall flow of the anti-skid control for controlling the brake fluid pressure for each wheel in order to prevent the wheels from locking during braking, and the part that executes this control corresponds to the anti-skid control means.

This brake control is performed at a cycle of 10 msec.
A sensor frequency is obtained from the number of sensor pulses and the cycle of each wheel speed sensor 13 generated every time, and a wheel speed Vw and a wheel acceleration △ Vw are calculated. In the following description or drawings, FR, F
When the symbols L, RR and RL are given, they indicate the wheel speed or wheel acceleration of the wheel.
When x is added, the symbols FR, FL, RR, RL
, That is, any one of the wheels. Further, when pointing to one or both of the front wheels, it is simply displayed as F, and when pointing to either or both of the rear wheels, it is simply displayed as R. In step S2, based on the wheel speed Vw, for example, the maximum one of the four wheel speeds is calculated as the pseudo vehicle speed VI. In step S3, the vehicle body deceleration VI is determined based on the change rate of the pseudo vehicle body speed VI.
Calculate K. An example of a method of obtaining the vehicle body deceleration VIK will be briefly described. For example, 1.3 g or 1.4 g, which is the deceleration at the time of high-μ road braking, is set as an initial value, and the anti-skid control is performed. This value is used in the first cycle, and thereafter, the wheel speed V0 at the start of braking is used.
And the wheel speed VP at the time when the wheel speed Vw returns to the pseudo vehicle body speed VI or when the wheel speed Vw departs from the pseudo vehicle body speed VI after the return is calculated by dividing by the time required for this change. In step S4, a calculation is performed to find a pressure reduction threshold value λ1, which is a threshold value for determining the start of anti-skid control.
The details will be described later.

In step S5, it is determined whether or not the wheel speed Vw is lower than the pressure reduction threshold value λ1. If the wheel speed Vw is lower than the pressure reduction threshold value λ1, the process proceeds to step S7, in which the anti-skid control is being executed. The flag ASxx is set to = 1, and in the subsequent step S8, the anti-skid timer AS is set to 150 (which indicates 1.5 sec), and further, the process proceeds to step S9.
The depressurization control for switching the control valve 5 to the depressurized state is executed, and the process further proceeds to step S10 to increment the depressurization time counter DECTxx for each wheel. That is, the pressure reduction time counter DECTxx counts the time during which the pressure reduction control is performed in step S9.

If NO is determined in step S5 (if Vw ≧ λ1), the process proceeds to step S6, where it is determined whether or not the wheel acceleration ΔVw is less than a preset holding threshold. If the wheel speed is greater than the threshold value, it is determined that the wheel speed has returned to step S11 and pressure increase control (switching of the control valve 5 to the pressure increase state) is performed.
Proceeding to step S12, the decompression time counter DECTx
Clear x to 0. On the other hand, if the wheel acceleration ΔVw is smaller than the holding threshold in step 6, the process proceeds to step S13.
To hold control (switch control valve 5 to hold state)
I do.

When any one of steps S10, S12 and S13 is completed, the process proceeds to step S14 to determine whether or not 10 ms has elapsed. If 10 ms has elapsed, the process proceeds to step S15 to reset the anti-skid timer AS. It decrements (subtracts by 1), and further proceeds to step S16 to determine whether or not the anti-skid timer AS has become 0. When AS = 0, that is, when the anti-skid control ends, the process proceeds to step S17, where the control flag is set. After clearing ASxx, the process returns to step S1. If AS ≠ 0 in step S16, the process directly returns to step S1. That is, the control-in-progress flag ASxx
Is reset to 0 until the first pressure reduction control of the anti-skid control is performed. After that, when the first pressure reduction control is executed, the control-in-progress flag ASxx = 1 is set, and the anti-skid timer is set. While the AS is counted down from 150 and the anti-skid timer AS is counted down to 0, the control-in-progress flag A
Sxx is kept at 1, anti-skid timer AS is set to 0
Then, the in-control flag ASxx = 0 is reset to end the anti-skid control.

Next, an example of the pressure reduction threshold value calculation process in step S4 in FIG. 3 will be described with reference to the flowchart in FIG. Further, as this description, the calculation processing of the pressure reduction threshold value of the rear wheel which is the driven wheel, which is a feature of the present invention, will be described. First, in step 501, it is determined whether or not the front wheel control flag ASF is set to 1, that is, whether anti-skid control has been started for at least one of the front wheels (accurately, whether or not pressure reduction has been performed). Judge, A
If SF = 1 and the anti-skid control has been started, the process proceeds to step 502. If ASF ≠ 1 and the anti-skid control has not been started, the process proceeds to step 510, where Basic decompression threshold λ1
(RR) is calculated using the formula of λ1 = VI × 0.95-8 km / h. In this equation, 8 km / h is
It corresponds to x1 in the claims.

Next, in step 502, it is determined whether or not the count value of the decompression time counter DECTxx has exceeded a preset low friction state determination time of 100 msec. If DECTxx> 100 msec, step 5 is performed.
03, the low μ flag LμF indicating that the vehicle is traveling on the low μ road is set to = 1, and the low μ judgment timer L
Set μT to 60. That is, this step 50
2 performs the second road surface friction state determination in the claims, and determines that the vehicle is traveling on a low μ road when the pressure reduction time exceeds a preset low friction state determination time. , Low μ flag LμF = 1.

In the following step 504, the low μ judgment timer LμT is decremented (counted down by 1).
Is determined to be 0 or less, and if LμT ≦ 0, in a succeeding step 506, the low μ flag Lμ flag F is set to =
Reset to zero.

Further, in step 507, it is determined whether or not the control flag ASR for the rear wheels is set to = 1. If ASR = 1, the process proceeds to step 510.
If SR ≠ 1, the process proceeds to step 508 to determine whether or not the low μ flag LμF is set to 1. If the low μ flag LμF = 1, the process proceeds to step 511 to set the low μ flag as a low pressure reduction threshold. μ road surface decompression threshold λμ (RR)
The calculation is performed using an equation of μ = VI × 0.95-4 km / h. In step 508, the low μ flag LμF
If = 1 has not been set, step 509
To determine whether or not the vehicle body deceleration VIK is less than the preset low friction state determination value of 0.3 g.
If IK ≧ 0.3 g, proceed to step 510,
If K <0.3 g, the process proceeds to step 511. That is, the determination in step 509 corresponds to the first road surface friction state determination in the claims, and has a function of supplementing the determination on the low μ road that could not be determined by the second road surface friction state determination. .

That is, in the present embodiment, when the anti-skid control is performed on the front wheels and the anti-skid control is not performed on the rear wheels, step 5
In step 08, it is determined whether or not a low μ road determination has been made based on the pressure reduction time. If the low μ road determination has been made, in step 511, the low μ road surface pressure reduction threshold λμ is set. Ask. If it is determined in step 508 that the low μ road has not been determined, the process proceeds to step 509 to perform low μ road determination based on the vehicle body deceleration VIK. If the low μ road determination has been performed, step 511 is performed. To determine the low μ road surface pressure reduction threshold λμ road.

Next, the operation of the embodiment will be described with reference to the time chart of FIG. FIG. 5 shows an example of a case where braking is performed on a low μ road. In other words, when the driver gradually brakes on a low μ road, the front wheel, which is the driving wheel, may be actuated by the engine brake, and the front wheel may have a larger effective diameter of the wheel brake than the rear wheel. However, while a braking force greater than that of the rear wheel is generated, the braking force of the rear wheel, which is a driven wheel, may be smaller than that of the front wheel. In FIG. 5, the difference in braking force between the front and rear wheels causes the wheel speed V of the front wheels.
wF is lower than the pressure reduction threshold value λ1, and the pressure reduction by the anti-skid control is started, while the wheel speed Vw of the rear wheel is
R is the vehicle speed Vcar without falling below the pressure reduction threshold λ1.
Shows a state that is gradually decreasing. In this case, when the wheel speed VwF of the front wheels falls below the pressure reduction threshold value λ1 and the anti-skid control is started, steps S5 → S
Based on the flow of 7 → S8 → S9 → S10, the anti-skid flag ASFR or ASFL of the front wheels is set to = 1 as shown, and the decompression time timer DECTxx is added while the decompression control is being executed. . On the other hand, for the rear wheels, the anti-skid flag ASRR or ASRL is maintained at 0 without decompression. And, as described above, the wheel speed VwR of the rear wheel is reduced to the pressure reduction threshold λ1.
, The pseudo vehicle speed VI formed based on the highest value of the wheel speed Vw also gradually decreases with respect to the actual vehicle speed Vcar as shown in the figure.

In the first control cycle in which the anti-skid control is started, 1.3 g of the body deceleration VIK is used beforehand. After that, the wheel speed VwR of the rear wheel is changed to the pseudo body speed. When the vehicle returns to VI or separates after returning, the vehicle body deceleration VIK is calculated from the difference between the pseudo vehicle speed at or near that time and the pseudo vehicle speed at the start of control and the time required for the change. You. In the illustrated example, the calculated vehicle deceleration VIK
Is smaller than 0.3 g.

Therefore, in the running state and the control state as in the example shown in this figure, in the control for calculating the pressure reduction threshold, before the time t1 when the pressure reduction of the front wheels is executed, the steps of the flowchart of FIG. Based on the flow of 501 → 510, a basic pressure reduction threshold λ1 is calculated. Thereafter, when the pressure reduction of the front wheels is started, in the flowchart of FIG. 4, steps 501 → 502 → 504 → 505 →
Based on the flow of 506 → 507 → 508 → 509 → 510, the basic pressure reduction threshold λ1 is calculated as the pressure reduction threshold.

Thereafter, in the illustrated example, at time t2, the front wheel depressurization time timer DECTxx is set to 100 msec.
At this point, steps 502 → 5
Proceeding to 03, the low μ flag LμF = 1 is set.
By maintaining the low μ flag LμF in a state of being set to = 1 during the counting of 60, that is, for 600 msec, the pressure reduction threshold is reduced to the low μ road pressure reduction threshold λμ and the basic pressure reduction threshold λ1. For a short period of time, frequent switching is prevented to maintain control stability.
Then, when the low μ flag LμF is set, the flow proceeds to steps 507 → 508 → 511, and the low μ road surface pressure reduction threshold λμ is calculated as the pressure reduction threshold. Therefore,
At this time t2, the pressure reduction threshold changes to a shallow value as shown. Next, at the time t3, the wheel speed VwR of the rear wheel returns to the pseudo vehicle speed VI, so that the vehicle body deceleration VIK can be calculated (in the example shown, the vehicle deceleration VIK is equal to 0.1 V).
3g). The cycle RR is a flag that is set to = 1 when the control cycle of the rear wheel ends one cycle. Therefore, at time t4, the wheel speed VwR of the rear wheel falls below the low μ road surface pressure-reducing threshold value λμ, and the anti-skid control is also performed on the rear wheel. Incidentally, in the illustrated example, if the pressure reduction threshold remains at the basic pressure reduction threshold λ1, the wheel speed VwR of the rear wheel does not fall below the pressure reduction threshold, and the anti-skid control is not started. in this way,
The start of the anti-skid control for the rear wheels also eliminates the slip of the rear wheel speed VwR and returns to the actual vehicle speed Vcar.

When the anti-skid control is started for the rear wheels, the flow proceeds from step 507 to step 510 in the flowchart of FIG. 4, and the basic pressure reduction threshold λ1 is calculated as the pressure reduction threshold. . However, since the rear wheel speed VwR returns to the actual vehicle speed Vcar by executing the anti-skid control, the basic pressure-reducing threshold λ1 does not decrease deeply.
Thereafter, anti-skid control is appropriately performed on the rear wheels.

The front wheel decompression time timer DECTxx
Before counting 100 msec, the rear wheel speed V
wR returns to the pseudo vehicle speed VI, and the vehicle deceleration VIK is calculated. If this value is smaller than 0.3 g as shown in the figure, in the flowchart of FIG. → The flow of 511
At that time, the low μ road surface pressure reduction threshold λμ is calculated as the pressure reduction threshold, and also in this case, the anti-skid control is performed on the rear wheels at this time.

As described above, in the present embodiment, "slightly braking" is performed on a low μ road, and anti-skid control is performed on the front wheels, but anti-skid control is performed on the rear wheels. When the pseudo vehicle body speed VI and the basic pressure reduction threshold λ1 “fall below” the appropriate values in a state where the control is not executed, a configuration is used in which a low μ road surface pressure reduction threshold λμ shallower than the basic pressure reduction threshold λ1 as the control start threshold. Therefore, it is possible to prevent the pseudo wheel speed VI and the basic pressure reduction threshold λ1 from returning to the appropriate values by executing the pressure reduction by the anti-skid control also on the rear wheels, thereby preventing the tendency of the rear wheels to lock. Is obtained. Further, in the present embodiment, when executing this determination, the low μ road determination is performed by the decompression time timer DECTxx.
In addition, since the vehicle body deceleration VIK obtained by the calculation is used, there is no need to provide an expensive sensor such as a longitudinal acceleration sensor or a longitudinal acceleration switch, and an effect that the entire apparatus can be configured at low cost can be obtained. In addition, if it is determined that the road is a low μ road by either of the two determinations of the decompression time timer DECTxx and the vehicle body deceleration VIK obtained by the calculation, it is determined that the road is a low μ road, and it can be reliably determined. The effect is obtained. In particular, the low μ road judgment by the decompression time timer DECTxx is
This is effective for determining the low μ road in the first control cycle in which the vehicle body deceleration VIK is not created.

Although the embodiment has been described with reference to the drawings, the present invention is not limited to this embodiment. For example, in the embodiment, the low μ road determination is made based on the decompression time and the vehicle deceleration. However, the low μ road determination may be made using only one of them, or the longitudinal acceleration sensor may be used. Alternatively, the determination may be made based on the deceleration obtained by the longitudinal acceleration switch. Also, when making a low μ road determination based on the decompression time,
In the embodiment, the road is determined to be a low μ road at 100 msec, but may be an arbitrary value according to vehicle characteristics. That is,
Within this depressurization time, the hydraulic pressure of the brake is substantially zero.
If it is set to an arbitrary value such as Mpcm ² , the road surface friction state corresponding to the decompression time is low μ such as a snow compaction or an icy road.
The road can be determined. Furthermore, low μ due to vehicle deceleration
In the case of performing road judgment, in the embodiment, a low μ
Although the road is determined, it may be an arbitrary value that matches the vehicle characteristics.

In the embodiment, an example in which the present invention is applied to a front wheel drive vehicle has been described. This front wheel drive vehicle is more likely to cause problems due to marginal braking, and the effect of applying the present invention is remarkably obtained. However, it can be applied to a rear wheel drive vehicle. Although not described in the embodiment, the pressure reduction threshold of the front wheel may be obtained by a known means. To give an example, the calculation is performed based on the equation shown in step 510 of the embodiment. Further, when it is determined that the road is a low μ road based on the vehicle body deceleration VIK or the detected deceleration, the value may be changed to a value shallower than a normal pressure reduction threshold, as in the process of step 511. In addition, 8 km / h and 4 km / h used in these equations are not limited to these, and an optimal value according to the vehicle type is appropriately used. Further, in the embodiment, the example in which the control start threshold value is increased and the correction is performed in the direction in which the control intervention is easy has been described. However, the wheel speed may be corrected so as to decrease, and as a result, the control intervention may be performed. Any method may be used as long as the relative relationship between the control start threshold value and the wheel speed is corrected in a direction that is easy to perform.

[Brief description of the drawings]

FIG. 1 is an overall view of an anti-skid control device according to an embodiment.

FIG. 2 is a hydraulic circuit diagram showing a main part of the embodiment.

FIG. 3 is a flowchart showing a flow of anti-skid control in the embodiment.

FIG. 4 is a flowchart illustrating a flow of a pressure reduction threshold calculation according to the embodiment;

FIG. 5 is a time chart showing an operation example of the embodiment.

FIG. 6 is a time chart showing an operation example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Master cylinder 2 Brake piping 3 Wheel cylinder 4 Drain circuit 5 Switching valve 6 Reservoir 7 Pump 8 Recirculation circuit 11 Brake unit 12 Control unit 13 Wheel speed sensor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuya Wada Nissan Motor Co., Ltd., Nissan Motor Co., Ltd. (72) Inventor Toru Kojima 2 Takaracho, Kanagawa Ward, Yokohama City, Kanagawa Prefecture F Terms (Reference) 3D046 BB23 BB28 FF04 HH23 HH26 HH36 HH46 JJ02 JJ06

Claims (4)

[Claims] 1. A wheel speed detecting means for detecting a wheel speed; a pseudo vehicle speed calculating means for calculating a pseudo vehicle speed based on the wheel speed; and a control start threshold value based on the pseudo vehicle speed. An anti-skid control device comprising: a control start threshold value forming unit; and an anti-skid control unit that controls a braking force of a wheel based on the wheel speed and the control start threshold value so as to prevent locking of the wheel. Road surface friction state determination means for determining whether the friction state of the running road surface is a low friction state, the anti-skid control means determines that the road surface friction state determination means is in a low friction state, and one of the front and rear wheels If the anti-skid control is executed for the other wheel and the other is not executing the anti-skid control, the wheel that is not executing the anti-skid control Anti-skid control device, characterized in that the easily perform the de control direction to correct the relative relationship of the wheel speed and the control start threshold value. 2. The anti-wheel drive system according to claim 1, wherein the braking force distribution of the front and rear wheels is applied to at least one of a front wheel drive vehicle that drives only the front wheels and a vehicle in which the front wheels are larger than the rear wheels. Skid control device. 3. A brake fluid pressure adjusting means for performing pressure reduction control of a brake fluid pressure to prevent locking of wheels based on a wheel speed and a control start threshold value. The first road surface friction state determination for determining the low friction state when the speed is smaller than the preset low friction state determination threshold, and the pressure reduction time by the anti-skid control exceeds the predetermined low friction state determination time. 3. The anti-skid control device according to claim 1, wherein at least one of a second road surface friction state determination that is determined as a low friction state is performed. 4. 4. The anti-skid control device according to claim 3, wherein the vehicle body deceleration is determined based on a change rate of the pseudo vehicle speed calculated by the pseudo vehicle speed calculating means. Skid control device.