JPH058713A - Slip control device for vehicle - Google Patents

Abstract

PURPOSE:To appropriately set a threshold and improve control accuracy by lessening the threshold of a slip ratio, for decompression-controlling brake pressure, according to the lowering of a body speed, and also setting the lowering ratio high or low according to a brake pressure control cycle. CONSTITUTION:A body speed is calculated with a means 30 based on a wheel speed detected with means 26-29, and also a wheel slip ratio is computed with a means 31 based on the wheel and body speeds in a control unit UTR. When the slip ratio calculated at the time of braking is lowered to a given threshold or less, a means 38, for adjusting brake pressure so as to decompress the brake pressure, is controlled with a means 37. In this constitution, the threshold of various slip ratios, lowering respectively at lowering ratios different in high and low according to lowering of the body speed, is memorized in a means 35. The control cycle of the brake pressure is discriminated with a means 36, and moreover the thresholds of the various slip ratios are read with a means 34 according to a discriminated control cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slip control device for a vehicle, which controls an increase or decrease of a brake pressure based on a slip rate of a wheel speed to suppress an excessive braking force during braking.

[0002]

2. Description of the Related Art Conventionally, anti-skid brake control has been known for the purpose of preventing wheel lock or skid state during braking.

In this anti-skid brake control, the wheel speed during braking and the vehicle body speed are detected, the slip ratio of the wheel is calculated from the detected wheel speed and the vehicle speed, and the brake pressure is calculated based on this slip ratio. The increase / decrease control is performed. That is, when the slip ratio after increasing the brake pressure falls below a preset threshold value, the brake pressure is reduced, and the braking force is reduced to restore the wheel speed. Further, when the slip ratio after the brake pressure is reduced returns to a preset threshold value or more, the brake pressure increase control is performed again, the braking force is increased, and the wheel speed is reduced. By repeating the increase / decrease control of the brake pressure, the vehicle body speed is reduced according to a predetermined gradient while avoiding the locked state or skid state of the wheels.

By the way, the slip ratio of the wheel is calculated as a ratio (%) of the wheel speed to the vehicle speed,
When the difference between the vehicle speed and the wheel speed, that is, when the slip amount of the wheels is the same, the slip rate increases as the vehicle speed decreases. Therefore, when the threshold value of the slip ratio is set to a constant value regardless of the vehicle body speed, as the vehicle body speed decreases, the slip ratio decreases to a lower threshold value with a smaller amount of slip of the wheels. The brake pressure reduction timing is earlier. Especially when the threshold of the slip ratio is set high,
In the low speed range, when the wheel speed is slightly decreased, the threshold value of the slip ratio is decreased to control the brake pressure so that so-called hunting easily occurs.

In order to solve this problem, conventionally, in setting the threshold value of the slip ratio, for example, Japanese Patent Publication No. 62-4205.
It is known that a relatively small value is set when the wheel speed is high, and a relatively large value is set when the wheel speed is low as shown in Japanese Patent Laid-Open No.

[0006]

In the anti-skid brake control described above, in the pressure reduction control of the brake pressure in the first cycle immediately after the start of braking, the friction coefficient of the road surface cannot be known. The speed is restored and the locked state of the wheels is released quickly, while the second
In the brake pressure reduction control after the second cycle, it is desirable to estimate the friction coefficient of the road surface and perform the brake pressure reduction control based on the estimation result.

In the conventional anti-skid brake control,
Since a constant slip ratio threshold value is set according to the vehicle body speed regardless of the control cycle, for example, when the rate of decrease of the threshold value with respect to the vehicle body speed is made relatively large, the brake pressure reduction control in the first cycle in the low speed range is performed. Is delayed, and it becomes difficult to reduce the brake pressure early to recover the wheel speed. On the other hand, when the rate of decrease of the threshold value with respect to the vehicle body speed is made relatively small, the above problem is solved, but in the low speed range, the brake pressure depressurization timing becomes early even after the second cycle, and hunting easily occurs.

Further, in the conventional anti-skid brake control, since the rate of decrease of the threshold value of the slip ratio with respect to the vehicle speed is constant regardless of the friction coefficient of the road surface, the brake pressure reduction control suitable for the friction coefficient of the road surface is performed. Is difficult to do.

The present invention has been made in view of the above problems, and is suitable by making the threshold value for the first cycle different from the threshold value for the second cycle and thereafter and setting the threshold value in consideration of the friction coefficient of the road surface. An object of the present invention is to provide a slip control device for a vehicle, which can perform various anti-skid brake controls.

[0010]

The invention according to claim 1 is
Wheel speed detecting means for detecting the rotational speed of the wheel, brake pressure adjusting means for adjusting the brake pressure, vehicle speed calculating means for calculating the vehicle speed of the vehicle based on the detected wheel speed, and the detected wheel Slip ratio calculating means for calculating the slip ratio of the wheel from the speed and the calculated vehicle speed, and the slip ratio calculated during braking is compared with a predetermined threshold value, and when the slip ratio falls below the threshold value, the brake pressure is reduced. In a slip control device for a vehicle, which comprises a control means for controlling the brake pressure adjusting means so as to reduce the pressure, a first slip ratio threshold value is set so as to decrease in accordance with the decrease in the vehicle speed. Storage means for storing a map and a second map in which the slip ratio threshold value is preset so that the rate of decrease of the slip ratio threshold value with respect to the vehicle speed is larger than that of the first map; When the control cycle is determined to be the first cycle, a cycle determination means for determining the control cycle of the pressure is read from the threshold value of the slip ratio according to the vehicle speed from the first map, and the control cycle is the second cycle. When it is judged that the eyes are on and after, the threshold value reading means for reading the threshold value of the slip ratio according to the vehicle speed from the second map is provided.

According to a second aspect of the present invention, the wheel speed detecting means for detecting the rotational speed of the wheel, the brake pressure adjusting means for adjusting the brake pressure, and the vehicle body speed of the vehicle based on the detected wheel speed. A vehicle body speed calculating means, a slip rate calculating means for calculating a wheel slip rate from the detected wheel speed and the calculated vehicle speed, and a slip rate calculated during braking is compared with a predetermined threshold value, When the slip ratio falls below a threshold value, in a vehicle slip control device comprising a control means for controlling the brake pressure adjusting means so as to reduce the brake pressure, in accordance with a detection signal of the wheel speed detecting means. Acceleration / deceleration calculating means for calculating acceleration and deceleration of wheel speeds, road surface state estimating means for estimating a friction coefficient of a road surface from the calculated accelerations and decelerations of wheel speeds, and for reducing the vehicle speed. Storage means for storing a threshold value of the slip ratio using the vehicle body speed and the road surface friction coefficient as parameters so that the decrease rate with respect to the vehicle speed increases with the increase of the road surface friction coefficient. A threshold value reading means for reading the threshold value of the slip ratio from the storage means based on the road surface friction coefficient estimated by the road surface state estimating means and the vehicle body speed calculated by the vehicle body speed calculating means. .

[0012]

According to the invention of claim 1, the slip ratio of the wheel is calculated from the wheel speed and the vehicle speed calculated based on the wheel speed, and when the slip ratio of the wheel falls below a predetermined threshold value. The brake pressure reduction control is performed.

The threshold value of the slip ratio is stored in advance in the first and second maps so as to decrease in accordance with the decrease in the vehicle speed, and the decrease rate of the threshold value with respect to the vehicle speed in the first map is
It is set smaller than that of the second map.

Then, when the anti-skid brake control is in the first cycle, a threshold value according to the vehicle speed is set from the first map, and in the second and subsequent cycles, the second threshold is set.
A threshold value is set according to the vehicle speed from the map. That is, when the vehicle body speed is in the low speed range, the threshold value of the slip ratio in the second cycle and thereafter becomes smaller than the threshold value of the slip ratio in the first cycle, and the brake pressure after boosting / holding in the second cycle and thereafter is reduced. The depressurization timing of is later than that in the first cycle. As a result, in the first cycle, the wheels are unlocked early and the second
From the cycle onward, the wheels can be braked while preventing hunting.

According to the second aspect of the present invention, the threshold value of the slip ratio decreases as the vehicle speed decreases, and the decrease ratio with respect to the vehicle speed increases as the road friction coefficient increases. Is stored in advance as a map using the vehicle speed and the friction coefficient of the road surface as parameters.

The threshold value of the slip ratio after the second cycle is read from the map based on the estimated road surface friction coefficient and the vehicle speed. If the vehicle speed is low,
The larger the friction coefficient of the road surface, the smaller the value is set, and the slip ratio of the wheel is less likely to fall below the threshold value, and the decompression timing of the brake pressure is delayed. As a result, as the vehicle speed decreases on the high μ road, the vehicle body is stopped by locking the wheels.

[0017]

FIG. 2 shows a vehicle equipped with a slip control device according to the present invention. This vehicle is provided with left and right front wheels 1 and 2 that are driven wheels and left and right rear wheels 3 and 4 that are driving wheels. The driving force of an engine 5 is an automatic transmission 6, a propeller shaft 7, a differential 8 and left and right. Axles 9, 10
It is configured to be transmitted to the rear wheels 3 and 4 via.

Each of the wheels 1 to 4 has a brake device 11 to 14 which comprises disks 11a to 14a which rotate integrally with the wheels and a caliper 11 which receives the supply of braking pressure and controls the rotation of the disks 11a to 14a. Is provided, and these brake devices 11 to 14 are drive-controlled by a brake control system 15 described later.

The brake control system 15 has a booster 17 for increasing the stepping force of the brake pedal 16 and a master cylinder 18 for generating a brake hydraulic pressure according to the stepping force increased by the booster 17. The front wheel braking pressure supply line 19 guided from the master cylinder 18 is branched into two paths, and the front wheel branch braking pressure lines 19a and 19b are connected to the brake devices 11 and 12 of the left and right front wheels 1 and 2. The brake 11 of the left front wheel 1 is connected to the calipers 11a and 12a, respectively.
A first valve unit 20 including an electromagnetic on-off valve 20a and an electromagnetic relief valve 20b is arranged in one of the front wheel branch braking pressure lines 19a leading to the right front wheel 2 and a braking device 12 for the right front wheel 2. A second valve unit 21 including an electromagnetic on-off valve 21 and an electromagnetic relief valve 21b is also installed on the other front wheel branch braking pressure line 19b leading to the same as the first valve unit 20. There is.

On the other hand, in the rear wheel braking pressure supply line 22 guided from the master cylinder 18, an electromagnetic on-off valve 23a is provided as with the first and second valve units 20 and 21.
And a third valve unit 23, which is also composed of an electromagnetic relief valve 23b, is installed, and the rear wheel braking pressure supply line 22 includes the third valve unit 2
The branch braking pressure lines 22a, 22b for the rear wheels are branched into two paths on the downstream side of 3, and are connected to the calipers 13b, 14b of the brake devices 13, 14 on the left and right rear wheels 2, 3, respectively.

Incidentally, the relief valves 20b, 21b, 2
The brake oil discharged from 3b is returned to the reservoir tank 18a of the master cylinder 18 via a drain line (not shown).

The first to third valve units are independently driven and controlled by the control unit UTR, and the first and second valve units 20 and 21 are controlled.
The braking force of the braking device 11 for the left front wheel 1 and the braking device 12 for the right front wheel 2 is variably controlled by the operation of the control valve, and the braking devices 13, 14 of the left and right rear wheels 3, 4 are controlled by the operation of the third valve unit 23. The power is variably controlled.

The control unit UTR is supplied with a detection signal of the brake switch 25 for detecting whether or not the brake pedal 16 is stepped on and detection signals of wheel speed sensors 26-29 for detecting the rotation speeds of the respective wheels. The control unit UTR generates a control signal for anti-skid brake control based on these detection signals, and outputs the control signal to the first to third valve units 2
0, 21, 23 to output the braking control to the left and right front wheels 1 and 2 and the rear wheels 3 and 4 for slipping, respectively.
Perform in parallel for each valve unit.

FIG. 1 is a diagram showing a block configuration in the control unit UTR.

In the figure, reference numeral 30 is a vehicle speed calculating means for calculating the vehicle speed during braking. Since the vehicle body speed cannot be accurately detected when the wheels 1 to 4 are slipping, the vehicle body speed calculating means 30 calculates the vehicle body speed based on the wheel speed Vw obtained from the detection signals of the wheel speed sensors 26 to 29. Calculate Vr. Reference numeral 31 is a slip ratio calculating means for calculating the slip ratios of the wheels 1 to 4, and calculates the slip ratio S from the wheel speed Vw and the pseudo vehicle body speed vr by the following equation.

Slip rate (S1) = (wheel speed Vw / pseudo vehicle body Vr) × 100 [%] Further, 32 is an acceleration / deceleration calculating means for calculating the acceleration and deceleration of the wheel speed Vw. The acceleration / deceleration calculation means 32
The result of dividing the difference between the previous value and the current value of the wheel speed Vw by the sampling cycle Δt (for example, 7 ms) is converted into gravity acceleration to calculate the acceleration AW and the deceleration DW of the wheel speed Vw. Reference numeral 33 is a road surface state estimating means for estimating the friction coefficient of the road surface. The road surface state estimating means 33 estimates the friction coefficient of the road surface from the acceleration AW of the wheel speed Vw and the deceleration DW according to the flowchart shown in FIG.

That is, when the control operation for estimating the friction coefficient is started, first, after reading various data, according to the flag Fabs indicating that the anti-skid brake control is being performed, it is determined whether or not the anti-skid brake control is currently being performed. It is determined (# 10, # 11). If the result of this determination is NO, and it is confirmed that the anti-skid brake control is not currently being performed, if the friction coefficient value MU is high μ
"3" indicating the road is set (# 12).

On the other hand, if it is confirmed in step # 11 that the anti-skid brake control is currently being performed, in steps # 13, # 14 and # 16,
Based on the deceleration DW or the acceleration AW of the wheel speed Vw at the time of the previous control, the road surface condition is high μ road, medium μ road, and low μ road.
The road is classified into roads, and the friction coefficient value MU corresponding to each road surface state is set.

That is, it is determined whether or not the deceleration DW is smaller than a preset reference deceleration "-20G", and the acceleration AW is a preset first reference acceleration "10G" and a second reference. It is determined whether the acceleration is greater than "20G". Then, as a result of the above determination, when it is confirmed that the deceleration DW is equal to or less than the reference deceleration "-20G", "1" indicating the low μ road is set to the friction coefficient value MU (# 15). , Acceleration AW is reference acceleration “20
If it is confirmed that the friction coefficient value MU is larger than "G", "3" indicating the high μ road is set to the friction coefficient value MU (# 17),
When it is confirmed that the acceleration AW is within the range of “10 to 20 G”, “2” indicating the medium μ road is set to the friction coefficient value MU (# 18).

Returning to FIG. 1, reference numeral 34 is a threshold value reading means for reading the threshold value of the slip ratio and the threshold value of the deceleration from the map stored in the threshold value storage means described later. Threshold reading means 34
Reads the threshold value of the slip ratio and the threshold value of deceleration to the control means 37, which will be described later, based on the determination result from the control cycle determination means 36, which will be described later, the estimation result from the road surface state estimating means 33, and the pseudo vehicle speed Vr. Reference numeral 35 stores a map of wheel speed deceleration threshold values for determining the start timing of anti-skid brake control, which will be described later, and a slip ratio threshold map for determining the start timing of brake pressure reduction control. It is a threshold storage means.

The map of the threshold value of the wheel speed deceleration is such that the wheels 1 to
4 is obtained in advance by experiments or the like as a value that causes a lock, and in the present embodiment, for example, (high μ road threshold, medium μ road threshold, low μ road threshold) = (− 3.0 G, −2. 0G,
-1.5G).

The map of the threshold value of the slip ratio is
It is composed of two types of maps, a first map applied to the brake pressure reduction control in the first cycle and a second map applied to the brake pressure reduction control in the second and subsequent cycles. As shown in FIG. 4, the threshold value of the slip ratio is set to decrease in accordance with the decrease in the vehicle body speed, and the decrease rate of the threshold value with respect to the vehicle body speed in the first map is set smaller than that in the second map. . Further, the second map has a plurality of threshold values for the vehicle body speed with the friction coefficient of the road surface as a parameter as shown in FIG. 5, and the reduction rate of the threshold value with respect to the vehicle body speed means that the friction coefficient of the road surface decreases. It is getting smaller accordingly.

The threshold value of the slip ratio of the first map is such that the frictional condition of the road surface cannot be estimated in the first cycle immediately after the start of the anti-skid brake control.
Road friction coefficient is not set as a parameter.
However, as the threshold value of the slip ratio in the first cycle,
A threshold considering the low μ road has been experimentally obtained in advance,
The rate of decrease of the threshold with respect to the vehicle speed is substantially the same as or lower than the rate of decrease of the threshold on the low μ road of the second map. It should be noted that the threshold value on the low μ road of the second map may be used as the first map.

Returning to FIG. 1, reference numeral 36 is a control cycle discriminating means for discriminating whether or not the anti-skid brake control is for the first cycle. This determination result is input to the threshold value reading means 34, and the threshold value reading means 34 reads the map of the threshold value of the first or second slip ratio from the threshold value storage means 35 based on the determination result.

Further, 37 is a control means for controlling the increase / decrease of the brake pressure. The control means 37 uses the brake pedal 6
When the wheel is depressed and the deceleration of the wheel immediately after the start of braking is compared with the threshold value of the deceleration read by the threshold value reading means 34, and when the deceleration of the wheel falls below the threshold value, the brake pressure after pressure increase is held. A control signal is generated. Further, the wheel slip ratio after increasing and maintaining the brake pressure and the threshold value reading means 3
The threshold value of the slip ratio read in 4 is compared, and when the slip ratio of the wheel falls below the threshold value, a control signal for reducing the brake pressure is generated.

The control signal is supplied to the brake pressure calculating means 38.
The brake pressure calculating means 38 receives these control signals to generate a braking pressure control signal, and the braking pressure control signal is supplied to the first to third valve units 20, 21, 23.
Output to each.

The first to third valve units 20, 2
1, 23 are opening / closing valves 20a, 2 based on the braking pressure control signal.
1a, 23a and the relief valves 20b, 21b, 23b are opened / closed by duty control, respectively, whereby the braking force corresponding to the slip state is applied to the front wheels 1, 2 and the rear wheels 3, 3.
4 to generate.

When the anti-skid brake control is not performed, the first to third valve units 20,
The braking pressure control signal is not output to 21, 23, and the on-off valves 20a, 21a, 23a are kept open, while the relief valves 20b, 21b, 23b are kept closed. As a result, the brake pressure generated in the master cylinder 18 according to the depression force of the brake pedal 16 is supplied to the brake devices 11 to 14 of the left and right front wheels 1 and 2 and the rear wheels 3 and 4 via the braking pressure supply lines 19 and 22. The braking pressure corresponding to the depression force of the brake pedal 16 is directly applied to the wheels 1 to 4.

Next, the brake pressure control operation of the slip control device according to the present invention will be described with reference to FIG. The increase / decrease control of the brake pressure is performed for each valve unit of the first to third valve units, but here, the first valve unit will be described as an example.

When the brake pedal 16 is depressed at time To, the brake pressure generated in the master cylinder 18 gradually increases, and this braking force causes the wheel speed Vw1 of the left front wheel 1 to increase.
Decreases. The deceleration DW1 of the wheel speed Vw1 is calculated by the acceleration / deceleration calculating means 32 and the threshold reading means 34.
Is compared with the deceleration threshold value -3G on the high μ road read in step S3. When the deceleration DW1 of the wheel speed Vw1 falls below the threshold value -3G, the phase shifts from phase 0, which is the non-control state of the antiskid brake control, to phase 2, and the antiskid brake control is started.

The anti-skid brake control is started from the phase 2 in which the brake pressure after the pressure increase is held, and thereafter,
The first cycle ends after the phase 3 for reducing the brake pressure after pressure increase / holding and the phase 4 for holding the brake pressure after pressure reduction. Subsequently, the second cycle is started from the phase 1 to increase the brake pressure again from the time Td, and thereafter, the second cycle is completed after passing through the phases 2 to 4, the same as the second cycle from the time Te. The brake pressure increase / decrease control is repeated for several cycles.

As described above, in the first cycle of the anti-skid brake control, the high μ is set as the threshold value of the wheel deceleration.
The road threshold is read out. This is because the friction coefficient of the road surface cannot be estimated in the first cycle. Therefore, if the threshold value (-1.5 G) on the low μ road is used, even if the deceleration of the wheel is slightly decreased, the value is equal to or less than the threshold value. This is to prevent the anti-skid control from being lowered and starting the anti-skid control unnecessarily.

Subsequently, during the phase 2, the slip ratio S1 is calculated by the slip ratio calculating means 31 from the wheel speed Vw1 and the slip ratio corresponding to the vehicle speed read from the first map by the threshold value reading means 34. It is compared with a threshold. For example, when the threshold value 90% at the time of high speed is set as the threshold value of the slip ratio, when the slip ratio S1 decreases to 90% or less at the time Tb, the phase 2 shifts to the phase 3,
The brake pressure reduction control is started. The relief valve 20b of the first valve unit 20 is turned on / off according to a predetermined duty ratio, whereby the brake pressure is reduced with a predetermined gradient, the braking force is gradually reduced, and the rotational force of the left front wheel 1 is restored.

Subsequently, at time Tc, the wheel speed Vw of the left front wheel 1
When the deceleration DW1 of 1 and the acceleration AW1 each become 0, the phase shifts from phase 3 to phase 4, the brake pressure is maintained at the level after deceleration, and during this phase 4, the wheel speed Vw1 increases again.

Then, the wheel speed Vw1 recovered at time Td
When the slip ratio S1 of 6 exceeds the threshold 90% of the slip ratio again, the phase shifts from phase 4 to phase 1 and the antiskid brake control of the second cycle is started.

Immediately after the transition to the phase 1 of the second cycle, the opening / closing valve 20b of the first valve unit 20 remains at 100 for the initial rapid pressure increase time Tp2 set based on the duration of the phase 5 in the first cycle. The opening and closing is performed at a duty ratio of%, the brake pressure is increased steeply, and then the on-off valve 20b is opened and closed at a predetermined duty ratio, and the brake pressure is increased at a gentler gradient than the above gradient.

On the other hand, in the second and subsequent cycles, the road surface state estimating means 33 causes the wheel speed Vw1 in the previous cycle.
From the deceleration DW1 and acceleration AW1 of the road surface friction coefficient μ
Is estimated, and the threshold values of deceleration and slip ratio are set based on the friction coefficient μ of the road surface and the vehicle body speed Vr. That is, as the deceleration threshold value, a threshold value corresponding to the friction coefficient of the road surface is read from the map stored in the threshold value storage means 35,
As the threshold value of the slip ratio, a predetermined threshold value is read from the second map stored in the threshold value storage means 35 using the friction coefficient of the road surface and the vehicle body speed as parameters.

When the deceleration DW1 of the left front wheel 1 falls below the threshold value of the deceleration as in the first cycle, the phase 1 shifts to the phase 2 and the brake pressure holding control after the pressure increase is performed. When the slip ratio S1 falls below the threshold value of the set slip ratio, the phase shifts from phase 2 to phase 3 and the brake pressure reduction control after pressure increase / hold is performed.

As described above, in the anti-skid brake control, the threshold value of the slip ratio is decreased in accordance with the decrease in the vehicle body speed. Therefore, the slip amount of the wheel (the vehicle speed And the wheel speed), the slip ratio of the wheel decreases below the threshold value, and the start timing of the pressure reduction control after increasing / holding the brake pressure is not advanced in accordance with the decrease in the vehicle body speed. As a result, hunting can be prevented in the low speed region of the vehicle speed.

Further, two types of slip rate threshold maps having different reduction rates with respect to the vehicle speed are provided, and in the first cycle of the anti-skid brake control, the slip rate threshold values are set from the first reduction rate lower map. After the second cycle, the slip rate threshold is set from the second map having a large decrease rate. Therefore, when the vehicle body speed is low, the first cycle is the second cycle. The slip ratio of the wheel falls below the threshold faster than the eyes and below,
The brake pressure after boosting / holding can be quickly reduced. As a result, the wheel speed after braking can be quickly recovered in the first cycle immediately after the start of the anti-skid brake control, in which the friction coefficient of the road surface cannot be estimated. Especially, in the case of a low μ road, the wheels are locked in the first cycle. Even in such a case, there is an advantage that the locked state can be quickly released to recover the wheel speed.

From the second cycle onward, as the friction coefficient of the road surface becomes higher, the rate of decrease of the slip ratio threshold value with respect to the vehicle speed is increased. The timing of reducing the brake pressure after the pressure increase / hold is delayed, the wheels can be locked to stop the vehicle body, and hunting of the brake pressure increase / decrease control can be prevented.

By the way, when the wheels are locked on the low μ road, it is difficult to quickly restore the wheel speed because the road surface reaction force is small even if the brake pressure is reduced, and the vehicle body becomes unstable due to the wheel slip. . In the above-described embodiment, the threshold value of the slip ratio after the second cycle is set to be small according to the decrease in the vehicle speed even on the low μ road, but in order to solve the above-mentioned problem, as shown in FIG. On low μ roads,
The threshold value may be increased according to the decrease in vehicle speed. In this way, on low μ roads, the timing for reducing the brake pressure after boosting / holding is accelerated, slippage due to wheel locking is prevented, and directional stability can be maintained until the vehicle body stops. .

Although the threshold value of the slip ratio is continuously changed with respect to the vehicle body speed in the above embodiment, the vehicle body speed is divided into regions, and the threshold value is changed stepwise in each divided region. May be.

[0054]

As described above, according to the present invention, the threshold value of the slip ratio for the brake pressure reduction control is reduced according to the decrease of the vehicle speed, and the decrease ratio of the threshold value of the slip ratio with respect to the vehicle speed is reduced. Since the second and subsequent cycles are made larger than those in the first cycle, the decompression timing for decompressing the brake pressure after boosting / holding in the first cycle is earlier than the decompression timing in the second and subsequent cycles. Become. As a result, in the first cycle where the friction coefficient of the road surface is not known, the wheels are unlocked quickly, and the second cycle is quickly entered to enable suitable anti-skid brake control.

In the brake pressure reduction control after the second cycle, the threshold value of the slip ratio is decreased in accordance with the decrease in the vehicle speed, and the decrease rate of the threshold value of the slip ratio with respect to the vehicle speed is increased by the friction coefficient of the road surface. Therefore, on a road surface with a large friction coefficient, the lower the speed range, the later the brake pressure decompression start timing will be delayed, and the wheels can be locked to stop the vehicle body quickly and prevent hunting. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a block configuration of a slip control device according to the present invention.

FIG. 2 is a diagram showing a configuration of a vehicle including a slip control device according to the present invention.

FIG. 3 is a flowchart for estimating a friction coefficient of a road surface.

FIG. 4 is a diagram showing a threshold value of a slip ratio with respect to a vehicle speed.

FIG. 5 is a diagram showing a threshold value of a slip ratio with respect to a vehicle body speed with a friction coefficient of a road surface as a parameter.

FIG. 6 is a diagram for explaining the operation of anti-skid brake control by the slip control device according to the present invention.

FIG. 7 is a diagram showing a second embodiment of the threshold value of the slip ratio with respect to the vehicle body speed with the friction coefficient of the road surface as a parameter.

[Explanation of symbols]

1, 2 front wheels 3,4 rear wheels 11-14 Brake device 15 Brake control system 16 brake pedal 17 Booster 18 Master cylinder 19,22 Braking pressure supply line 20,21,23 valve unit 26-29 Wheel speed sensor 30 Vehicle speed calculation means 31 slip ratio calculating means 32 Acceleration / deceleration calculation means 33 Road surface condition estimating means 34 Threshold reading means 35 threshold storage means 36 Control cycle determination means 37 Control means 38 Brake pressure calculation means UTR control unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Makoto Kawamura             3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda             Within the corporation

Claims (2)

[Claims] 1. Wheel speed detecting means for detecting a wheel rotation speed, brake pressure adjusting means for adjusting a brake pressure, and vehicle speed calculating means for calculating a vehicle speed of the vehicle based on the detected wheel speed. The slip ratio calculating means for calculating the slip ratio of the wheel from the detected wheel speed and the calculated vehicle speed, and the slip ratio calculated during braking are compared with a predetermined threshold value, and when the slip ratio falls below the threshold value, In a vehicle slip control device including a control unit that controls the brake pressure adjusting unit to reduce the brake pressure,
A first map in which the threshold value of the slip ratio is preset so as to decrease in accordance with the decrease in the vehicle body speed, and a slip ratio threshold value such that the rate of decrease of the slip ratio threshold value with respect to the vehicle body speed becomes larger than that of the first map. Is stored in advance, a storage means storing therein a second map set in advance, a cycle determining means for determining a control cycle of the brake pressure, and when the control cycle is determined to be the first cycle, from the first map And a threshold value reading means for reading the threshold value of the slip ratio according to the vehicle speed from the second map when the threshold value of the slip ratio according to the vehicle speed is read and the control cycle is determined to be the second cycle or later. A vehicle slip control device characterized by the above. 2. A wheel speed detecting means for detecting a rotation speed of a wheel, a brake pressure adjusting means for adjusting a brake pressure, and a vehicle speed calculating means for calculating a vehicle speed of the vehicle based on the detected wheel speed. The slip ratio calculating means for calculating the slip ratio of the wheel from the detected wheel speed and the calculated vehicle speed, and the slip ratio calculated during braking are compared with a predetermined threshold value, and when the slip ratio falls below the threshold value, In a vehicle slip control device including a control unit that controls the brake pressure adjusting unit to reduce the brake pressure,
Acceleration / deceleration calculating means for calculating acceleration and deceleration of the wheel speed according to the detection signal of the wheel speed detecting means, and road surface state estimating means for estimating a friction coefficient of the road surface from the calculated acceleration and deceleration of the wheel speed. The threshold value of the slip ratio using the vehicle body speed and the road surface friction coefficient as parameters is set such that the vehicle body speed decreases with the decrease of the vehicle body speed, and the decrease rate with respect to the vehicle body speed increases with the increase of the road surface friction coefficient. Preliminarily stored storage means, threshold value reading means for reading the slip ratio threshold value from the storage means based on the road surface friction coefficient estimated by the road surface state estimation means and the vehicle body speed calculated by the vehicle body speed calculation means. A slip control device for a vehicle, comprising: