JP2000095079A - Anti-skid control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust slipping of a wheel occurring during braking, by starting an anti-skid control, considering that a slipping degree is excessively large when wheel acceleration from which a deceleration component is removed exceeds a given threshold. SOLUTION: When a wheel approaches to a lock tendency and it becomes anti-skid control starting timing, wheel acceleration rapidly drops. At this time, the wheel acceleration dVWBF** from which a deceleration component is removed exceeds a given set value. Thus, judgment of the anti-skid control starting timing (pressure reducing timing) is accurately performed. Since such rapid dropping of the wheel acceleration occurs regardless of level of road surface frictional coefficient when a vehicle is run and braked on a general actual road surface, the anti-skid control starting can accurately be started either on the road surface with high μ and low μ, and pressure reducing control can be performed at the accurate pressure reducing timing.

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 adjusting a wheel slip that occurs during braking of a vehicle.

[0002]

2. Description of the Related Art Conventionally, an anti-skid control device obtains a wheel acceleration (deceleration) or a wheel acceleration after a low-pass filter (hereinafter referred to as a wheel acceleration or the like) for each wheel, and calculates a wheel cylinder based on the wheel acceleration or the like. By controlling the increase / decrease of the brake fluid pressure (hereinafter referred to as W / C pressure), the slip state of the vehicle is maintained to be appropriate, and the tendency to lock the wheels is avoided.

[0003] Specifically, the anti-skid control device includes:
When the wheel acceleration or the like is larger than a predetermined threshold value and the wheels tend to lock, the brake fluid in each wheel cylinder is released to the reservoir to reduce the brake fluid pressure (hereinafter referred to as W / C pressure). The control is performed by maintaining the W / C pressure when the locking tendency is released by the pressure reduction, and increasing or decreasing the control of increasing the W / C pressure at a predetermined timing when the locking tendency is released. ing.

On the other hand, the anti-skid control start timing (and pressure reduction timing) depends on the friction coefficient of the road surface on which the vehicle travels, that is, on a high μ road surface having relatively high road friction and a low μ road surface having relatively low road friction. Therefore, the anti-skid control start timing is adjusted by changing the set value according to the type of road surface.

[0005]

However, when the level of the friction coefficient of the road surface is erroneously determined, for example, when the threshold value is set lower than that of the low μ road surface by determining that the road surface is a high μ road surface. On the other hand, as shown in FIG. 5 (b), if the road surface is low μ, the reduction of the W / C pressure must be started at the required timing, so that the slip state of the vehicle becomes appropriate. It cannot be maintained.

[0006] The present invention has been made in view of the above points,
An object of the present invention is to provide an anti-skid control device in which anti-skid control is started and controlled accurately regardless of the level of the friction coefficient of a road surface.

[0007]

In order to solve the above problems, the present invention employs the following technical means. According to the first aspect of the present invention, a wheel deceleration component in a low frequency range is removed from a wheel acceleration (dVW **) detected based on a wheel speed, and a wheel acceleration (dVWBF) from which the deceleration component has been removed. When **) exceeds a predetermined threshold value, it is determined that the slip state is excessive and anti-skid control is started.

The wheel acceleration (dVWBF **) from which such a deceleration component has been removed changes its value when there is a sharp drop in wheel deceleration, regardless of whether the road surface is high μ or low μ. Therefore, when the wheel acceleration (dVWBF **) from which the deceleration component has been removed exceeds a predetermined threshold,
By starting the anti-skid control and starting the depressurization during the anti-skid control, the anti-skid control can be performed accurately regardless of the high μ road surface or the low μ road surface.

Specifically, as described in claim 2, a band-pass filter for removing a low-frequency band and a high-frequency band of wheel acceleration (dVW **);
The deceleration component of the wheel acceleration can be removed by a high-pass filter that passes a high-frequency band of the wheel acceleration (dVW **). Also, as shown in claim 4,
A deceleration component of the wheel acceleration (dVW **) is extracted by a low-pass filter that passes a low frequency band of the wheel acceleration (dVW **), and the extracted deceleration component is subtracted from the wheel acceleration (dVW **). By doing so, it is possible to remove the deceleration component.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 1 is a schematic diagram illustrating a configuration of an anti-skid control device to which the present invention is applied. As shown in FIG. 1, a front right wheel 1, a front left wheel 2, a rear right wheel 3, and a rear left wheel 4
Are respectively provided with wheel speed sensors 5 to 8 of an electromagnetic pickup type or an electric resistance element (MRE) type, and generate a pulse signal according to the rotation of each wheel 1 to 4.

Further, wheel cylinders 11 to 14 are disposed on the wheels 1 to 4, respectively. The brake fluid pressure from the master cylinder 16 is applied to two-position valves (pressure increase control valves) 21 to 24 as valve means. It is sent to each wheel cylinder 11 to 14 via each hydraulic line. The master cylinder 16
Generates brake fluid pressure by depressing the brake pedal 27, and the depressed state of the brake pedal 27 is detected by a stop switch 29.

The wheel cylinders 11 and 14 are connected to a reservoir 37 via two-position valves (pressure reduction control valves) 31 and 34, and the wheel cylinders 11 and 14 are connected via two-position valves (pressure reduction control valves) 32 and 33. Connected to the reservoir 39. In addition, each two-position valve 21-24 and 31-3
Reference numeral 4 denotes an electromagnetic two-position valve having a communication position and a blocking position.

Further, upstream and downstream of the two-position valves 21 to 24,
The check valves 41a to 44a allow the wheel cylinders 11 to
Bypass pipes 41 to 44 are provided for flowing only the pressure oil from 14 to the master cylinder 16. further,
The reservoirs 37, 39 and the master cylinder 16 are connected by hydraulic lines via check valves 47, 49, and only the flow of pressure oil from the reservoirs 37, 39 to the master cylinder 16 is permitted.

The detection signals of the wheel speed sensors 5 to 8 and the stop switch 29 are inputted to an electronic control circuit (hereinafter referred to as ECU) 50. The ECU 50 includes a CPU, R
A well-known microcomputer having an OM, a RAM, and an I / O.
, And 31-34. This control signal is composed of a pressure increase output, a hold output, and a pressure decrease output generated for each of the wheels 1 to 4. Here, the operation of the two-position valves 21 to 24 and 31 to 34 corresponding to each output will be described by taking the right front wheel 1 as an example.

To generate a pressure-increasing output at the right front wheel 1 means to generate a control signal so that the two-position valve 21 is set to the communicating position and the two-position valve 31 is set to the shut-off position. Thereby, the brake fluid pressure generated by the master cylinder 16 is supplied to the wheel cylinder 11 as it is. To generate the holding output at the right front wheel 1 means to generate a control signal so that the two-position valves 21 and 31 are both set to the shut-off position. As a result, the brake fluid pressure of the wheel cylinder 11 is maintained. If the brake pedal 27 is released during the continuation of the holding output, the pressure oil flows through the bypass pipe 41 and the brake fluid pressure of the wheel cylinder 11 is reduced.

To generate a reduced pressure output on the right front wheel 1 means to generate a control signal so that the two-position valve 21 is set to the shut-off position and the two-position valve 31 is set to the communication position. Thereby, the pressure oil of the wheel cylinder 11 flows into the reservoir 37, and the brake fluid pressure is reduced. The ECU 50
Performs the same output for the other wheels 2-4. Next, details of the processing executed by the ECU 50 will be described with reference to the flowcharts of FIGS. When the ignition switch is turned on, the ECU 50 executes a main routine shown in FIG. Note that the ECU 50 executes this main routine for each of the wheels 1 to 4 in a time-sharing manner.

When the process is started, first, in step 1000,
Executes initialization processing. By this initialization process,
Perform initialization processing such as memory clear, flag reset, etc.
In the following step 2000, a predetermined time T is set in order to execute the transition arithmetic processing every predetermined time Ta (for example, 5 ms).
a to determine whether a predetermined time Ta has elapsed.
Wait for elapse.

If the answer is Yes in step 2000, the process proceeds to step 3000, where the wheel speed sensors 5
The wheel speed VW ** of each of the wheels 1 to 4 is calculated based on the rotation speed signals from. Here, “**” indicates each wheel 1
4 is a generic term for the symbols FR, RL, RR, and FL, that is, “VW **” is VWFR, VWRL, VWRR,
VWFL, which indicates wheel speeds for the right front wheel 1, the left rear wheel 2, the right rear wheel 3, and the left front wheel 4, respectively.

In the following step 4000, step 30
By differentiating the wheel speed VW ** obtained in 00, the wheel acceleration dVW ** of each of the wheels 1 to 4 is calculated.
Then, in step 5000, the wheel acceleration dVW ** of each of the wheels 1-4 obtained in step 4000 is subjected to band-pass filter processing. For example, band-pass filtering is performed using a hand-pass filter that passes a band of 3 to 30 Hz. As a result, the wheel acceleration dVWBF ** excluding the vehicle body deceleration component is obtained, and only the case where the wheel acceleration dVW ** drops sharply in the deceleration direction is extracted.

Next, in step 6000, step 3
The vehicle speed (estimated vehicle speed) is calculated on the basis of the maximum speed VWmax among the wheel speeds VW ** of the wheels 1-4 obtained at 000. This processing is performed by, for example, the maximum speed VWma of the wheel speeds VWFR to VWRL of the wheels 1 to 4.
x is within a range from an acceleration limit value Vα obtained by adding a predetermined value to the vehicle speed VB (n-1) obtained last time to a deceleration limit value Vβ obtained by subtracting a predetermined value from the vehicle speed VB (n-1). It is determined whether the maximum speed VWmax is equal to V from the acceleration limit value Vα.
If it is within the range up to β, the maximum speed VWmax is set as it is as the vehicle speed VB. If the maximum speed VWmax exceeds the acceleration limit value Vα, the acceleration limit value Vα is set to the vehicle speed VB.
B, the maximum speed VWmax deceleration speed limit value Vβ
Is executed, the deceleration limit speed Vβ is set as the vehicle speed VB.

In the following step 7000, each of wheels 1 to 4 is determined based on the determined vehicle speed VB and wheel speed VW **.
Is calculated. Thereafter, in step 8000, the slip ratio S of each of the wheels 1-4 is set.
W ** and wheel acceleration dVWBF ** excluding deceleration component
The calculation of the control mode is performed for each of the wheels 1 to 4 based on.
The details of this process will be described with reference to the flowchart of the four-wheel control mode calculation shown in FIG.

Next, the details of step 8000 in FIG. 2 will be described with reference to the flowchart shown in FIG. This routine is a two-position valve 21 to 2 for each wheel 1-4.
4 and 31 to 34, and is executed four times in total for the FR wheel 1, the FL wheel 2, the RR wheel 3, and the RL wheel 4. The setting of this control mode includes pressure increase output, pressure decrease output,
This is performed in order to determine a control condition of how long the held output is to be performed and in what state. The details of each control mode will be described later.

First, at step 210, it is determined whether or not the stop switch 29 is ON, that is, whether or not the vehicle is being braked. Until the stop switch 29 is turned on, the routine proceeds to step 220, in which the control flag of the wheel is reset, and the control mode of the two-position valves 21 to 24 and 31 to 34 of the wheel is set to the pressure increasing mode. To end the processing. Here, the pressure increase mode is a mode in which the above-described pressure increase output is continuously generated. That is, the brake fluid pressure generated by the master cylinder 16 in the normal brake during vehicle braking is directly applied to the wheel cylinders 11 to 1.
4 is supplied.

On the other hand, when the stop switch 29 is turned on, the routine proceeds to step 240, where it is determined whether or not the control flag is set. In other words, immediately after the stop switch 29 is turned on, the control flag is in the reset state.
50, the slip ratio S of the wheel being determined
It is determined whether W ** is larger than the target slip ratio KS0 (for example, 20%).

If No in step 250,
Proceeding to step 220, the control-in-progress flag is reset, the control mode of the relevant wheel is set to the pressure increase mode, and the process ends. If Yes in step 250, the process proceeds to step 255, where the wheel acceleration dVWBF ** from which the deceleration component obtained by the band-pass filter processing has been removed is a predetermined set value (threshold), for example, -0.5G It is determined whether or not: As described above, the start of the anti-skid control (that is, the timing of starting the pressure reduction of the W / C pressure) is determined based on the wheel acceleration dVWBF ** from which the deceleration component has been removed. can do.

If the answer is Yes, the program proceeds to step 260, in which a control flag is set, and the program proceeds to step 270. If No, the process proceeds to step 220. next,
In step 270, it is determined whether or not the slip ratio SW ** of the wheel is larger than a predetermined slip ratio KS1. The predetermined slip rate KS1 is equal to the target slip rate K
Smaller than S0. For example, if KS1 = 20%, K
S1 is set to be 15%.

If Yes in step 270, the process proceeds to step 280, where it is determined whether the wheel acceleration dVWBBF ** from which the deceleration component of the wheel has been removed is smaller than 0G, that is, the wheel rapidly drops in the deceleration direction. Is determined. Ye at step 280
If it is s, the process proceeds to step 290, and the two-position valves 21 to 24
Then, the pressure reduction mode is set as the control mode of 31 to 34, and the processing is ended. If No in step 280, the process proceeds to step 300, where the two-position valves 21 to 24 and 3
The holding mode is set as the control mode of 1 to 34, and the process ends.

Here, the decompression mode is a mode in which the above-mentioned decompression output is continuously generated for a certain period of time, or a holding output and a decompression output are alternately and repeatedly generated (for example, by switching every 15 ms). The hold mode is a mode in which the above-described hold output is continuously generated. That is, when the wheel acceleration dVWBF ** from which the deceleration component is removed is 0 G or less and the wheels tend to lock, the brake fluid pressure of the wheel cylinders 11 to 14 is reduced by the pressure reduction mode, and the deceleration component is removed. Wheel acceleration dVWBF **
Is greater than 0 G and the locking tendency is gradually being eliminated, the brake fluid pressure is held in the holding mode.

In the decompression mode, the control mode setting determines the change cycle of the decompression output and the holding output. On the other hand, if No in step 270, step 31
The process proceeds to 0, and it is determined whether the control mode of the pulse pressure increasing mode has been executed a predetermined number of times. Here, the pulse pressure increasing mode means that the pressure of the wheel cylinder of the brake device is changed in the change cycle by alternately changing the pressure increase output and the holding output to the two-position valves 21 to 24 and 31 to 34 in a predetermined cycle. This is a mode in which the pressure is gradually increased in accordance with a corresponding pressure increase pattern. In this control mode setting, a change cycle and the like are determined, and the pressure increase and decrease are provided.

If Yes in step 310, the wheel lock tendency is completely suppressed, and the wheels will not slip even if the hydraulic control is terminated.
Proceeding to step 220, the control-in-progress flag is reset,
The control mode of the two-position valves 21 to 24 and 31 to 34 is set to the pressure increasing mode, and the process is terminated. That is, it returns to the normal brake. If No in step 310, the process proceeds to step 320, in which the control of the pulse increasing mode is kept set, and the process ends.

After the respective control modes are determined by the above-described processing, thereafter, in steps 710 to 740 of the timer interrupt routine shown in FIG.
2 corresponding to each of FL wheel 2, RR wheel 3 and RL wheel 4
A solenoid drive output corresponding to the determined control mode is executed for the position valve drive solenoid. Next, a time chart when the anti-skid control based on the above processing is performed is shown in FIG. For reference, FIG. 5B shows a time chart when anti-skid control is performed based on the wheel acceleration as in the related art. In the time chart according to the conventional processing of FIG. 5B, the set value of the wheel acceleration which is a condition for starting the anti-skid control is high μ even though the road surface on which the vehicle is traveling is a low μ road surface. This shows a case where the setting is for road surface.

First, when the occupant depresses the brake pedal 27, the wheel speed decreases as shown in FIGS. 5 (a) and 5 (b). At this time, the wheel acceleration dVWBF * from which the deceleration component used in the processing of the present embodiment has been removed
* Indicates 0G as shown in FIG. 5A, and the wheel acceleration dVW used in the conventional processing in which the deceleration component is not removed is as shown in FIG. 5B. Is decreasing.

Thereafter, when the vehicle approaches the wheel locking tendency and the anti-skid control start timing comes, the wheel acceleration drops sharply. At this time, the wheel acceleration dVWBF ** obtained by removing the deceleration component used in the processing of the present embodiment is:
Exceeds the set value. Therefore, the determination of the anti-skid control start timing (pressure reduction timing) is accurately performed. Since such a sharp drop in wheel acceleration occurs on a general actual road surface when braking and irrespective of the level of the road surface friction coefficient, anti-skid control is performed on both high μ and low μ road surfaces. Can be accurately started, and the pressure reduction control can be performed at an accurate pressure reduction timing.

On the other hand, although the wheel acceleration dVW used in the conventional processing is reduced, the wheel acceleration does not exceed the set value because the set value for the high μ road surface has been set, and the anti-skid Control does not start correctly. Thus, the wheel acceleration dVWBF ** from which the deceleration component has been removed
Is used as a parameter for judging decompression timing,
The decompression timing can be accurately determined regardless of the road surface or the low μ road surface.

In the present embodiment, the start timing of the anti-skid control has mainly been described. However, the start of the pressure reduction control described above means only the start of the pressure reduction control performed when the anti-skid control is started. Instead of meaning
This means that each pressure reduction control is started during the anti-skid control, and in both cases, it is possible to accurately start the pressure reduction control.

(Other Embodiments) In the above-described embodiment, the wheel deceleration component in the low frequency band is removed by the band-pass filter processing. The same effect as in the embodiment can be obtained. Furthermore, the difference obtained by subtracting the wheel acceleration dVWLF ** after the low-pass filter processing from the wheel acceleration dVW ** before the filter processing is obtained by removing the wheel deceleration component in the low frequency range from the wheel acceleration dVW **. Therefore, even if the pressure reduction timing is determined using this difference, the same effect as in the above embodiment can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an anti-skid control device according to the present invention.

FIG. 2 is a flowchart showing a main routine of the anti-skid control device shown in FIG.

FIG. 3 is a flowchart of a control mode calculation process in FIG.

FIG. 4 is a flowchart of a solenoid driving process by a timer interrupt process.

FIG. 5A is a time chart when a process according to an embodiment of the present invention is executed, and FIG. 5B is a time chart when a conventional process is executed.

[Explanation of symbols]

1 ... right front wheel, 2 ... left front wheel, 3 ... right rear wheel, 4 ... left rear wheel, 5
-8: Wheel speed sensor, 11-14: Wheel cylinder,
21 to 24, 31 to 34 ... two-position valve, 27 ... brake pedal, 29 ... stop switch, 50 ... ECU.

Claims (4)

[Claims] 1. Wheel speed (VW **) of wheels (1-4)
Wheel speed detecting means (5-8) for detecting a slip state of the vehicle based on the wheel speed (VW **), and an anti-skid when the detected slip state becomes excessive. An anti-skid control device that starts the control and controls the brake fluid pressure applied to the wheels (1 to 4) to increase or decrease the brake fluid pressure, wherein a wheel acceleration detected based on the wheel speed ( dVW
**), a wheel deceleration component in a low frequency range is removed, and when the wheel acceleration (dVWBF **) from which the deceleration component is removed exceeds a predetermined threshold value, it is determined that the slip state is excessive. An anti-skid control device for starting pressure reduction control. 2. A band-pass filter for removing a low-frequency band and a high-frequency band of the wheel acceleration (dVW **), wherein the band-pass filter removes the deceleration component. The anti-skid control device according to claim 1, wherein: 3. A high-pass filter that passes a high-frequency band of the wheel acceleration (dVW **), wherein the high-pass filter removes the deceleration component. 3. The anti-skid control device according to claim 1. 4. A low-pass filter that passes a low-frequency band of the wheel acceleration (dVW **), and a deceleration component of the wheel acceleration (dVW **) is extracted by the low-pass filter. The anti-skid control device according to claim 1, wherein the deceleration component is removed by subtracting a deceleration component from the wheel acceleration (dVW **).