JP2897260B2 - Brake pressure control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake pressure control device such as an anti-skid control device or a traction control device. It relates to a device for controlling pressure.

[Conventional technology]

A conventional anti-skid control system is disclosed in JP-B-59-2050.
As disclosed in Japanese Patent Publication No. 8 (2006), a wheel speed and a wheel acceleration are obtained, a plurality of levels of the reference speed or the reference acceleration are obtained by calculation, and a control mode of the actuator is set by comparing each reference level with the wheel speed and the wheel acceleration. And then controlled the brake pressure.

[Problems to be solved by the invention]

However, in the above-described conventional apparatus, the control gradient of the brake pressure is not continuous with respect to the continuous events of the wheel speed and the wheel acceleration, and the brake is excessively released or over-applied. The vehicle feel is likely to deteriorate, and there is still room for improvement in braking efficiency.

The present invention has been made in view of the above points, and has as its object to set a control gradient of a brake pressure almost continuously in accordance with a slip state of a vehicle to improve vehicle feeling and braking efficiency.

[Means for solving the problem]

For this reason, as shown in FIG. 1, the present invention provides a plurality of wheel speed sensors for detecting the rotation speed of a wheel, and a first calculation for calculating a wheel speed and a wheel acceleration based on a detection signal of the wheel speed sensor. Means, an estimated vehicle speed is calculated from the wheel speeds, a second calculating device for calculating an estimated vehicle deceleration from the estimated vehicle speeds, and a reference speed calculating device for calculating a target reference speed from the estimated vehicle speeds. Deviation calculating means for calculating a first deviation between the wheel speed and the reference speed, and a second deviation between the wheel acceleration and the estimated vehicle deceleration; and arbitrarily weighting the first deviation and the second deviation. And a pressure gradient calculating means for calculating a continuous control gradient for decreasing and increasing the brake pressure from the slip state quantity. A drive time setting means for setting a driving time ratio of the actuator based on the calculated pressure gradient drives the actuator based on the driving time ratio,
Control means for controlling a brake fluid pressure applied to a wheel cylinder of the wheel.

[Action]

According to the present invention, the wheel speed V _W, wheel acceleration G _W, from the reference velocity V _S of the estimated vehicle deceleration G _B and the target, computes the slip state quantity W of the wheel based on the following equation.

W = K _a (V _W −V _S ) + K _b (G _W −G _B ) The slip state quantity W is a continuous quantity with a positive or negative sign, and a positive value indicates a demand on the pressure increasing side, and a negative value indicates a demand on the pressure reducing side, The larger the absolute value is, the larger the required value for increasing the pressure gradient is. A continuous pressure gradient of decreasing and increasing the brake pressure is calculated according to the slip state amount.

Based on the calculated pressure gradient, a drive time ratio of the actuator, for example, a time ratio of depressurization, holding, and pressure increase of the actuator is set, and the brake pressure gradient is controlled almost continuously according to the wheel slip state. In this way, the brake pressure is finely controlled, and the vehicle feeling and the braking efficiency are improved.

FIG. 2 shows the configuration of one embodiment of the present invention. This embodiment is an example in which the present invention is applied to a front engine / rear drive four-wheeled vehicle.

Electromagnetic pickup type or magnetoresistive element (MRE) type wheel speed sensors 5, 6, 7, 8 are arranged on the right front wheel 1, the left front wheel 2, the right rear wheel 3 and the left rear wheel 4, respectively. The pulse signal is output in accordance with the rotation of No. 4.

Further, hydraulic brake devices (wheel cylinders) 11 to 14 are provided on the wheels 1 to 4, respectively, and the hydraulic pressure from the master cylinder 16 is applied to the hydraulic brake devices 11 through actuators 21 to 24 and hydraulic lines. Sent to ~ 14. The depression state of the brake pedal 15 is detected by the stop switch 25, and an ON signal is output during braking, and an OFF signal is output during non-braking.

Normally, when the brake pedal 15 is depressed, a hydraulic pressure is generated in the master cylinder 16 and the wheels 1 to 4 can be braked. However, as a hydraulic source for slip control, the reservoirs 19 and 20 are driven by electric motors. Hydraulic pumps 17, 18 for sucking brake fluid and generating hydraulic pressure are also provided. An electronic control circuit (ECU) 30 controls these actuators 21 to 24 so that the hydraulic brake devices 11 to
Adjust the brake hydraulic pressure of 14 and adjust the braking force for each wheel. That is, each of the actuators 21 to 24 has a pressure increasing position,
An electromagnetic three-position valve having a pressure reducing position and a holding position. For example, in the case of the actuator 21, the brake hydraulic pressure is increased at the position A, the brake hydraulic pressure is held at the position B, and the brake hydraulic pressure is released to the reservoir 19 at the position C, and the pressure is reduced. I do. In addition, this 3
The position valve is in the pressure increasing mode when not energized, and is in the holding or pressure reducing mode depending on the current level when energized.

The ECU 30 is supplied with power when the ignition switch is turned on, receives signals from the speed sensors 5 to 8 and the stop switch 25, performs arithmetic processing for anti-skid control, and controls the actuators 21 to 24. Generate a signal.

The ECU 30 is of a microcomputer type and has a CPU, RO
M, RAM and I / O circuits are provided, and the signals of the wheel speed sensors 5 to 8 are input, and the signals are processed to
~ 24 drive signals are output.

 Next, the operation of the ECU 30 will be described.

When the ignition key is turned on, the ECU 30 executes a main routine shown in FIG. First, in step 100, an initialization process is performed. Here, the initialization process is a process of clearing various variables and counter contents of the RAM and resetting flags and the like.
Steps to be repeatedly executed after the initialization process
110 shifts to the following process, first, processing for calculating the estimated vehicle speed V _B (step 110). The estimated vehicle speed V _B is
Wheel speed V of each wheel calculated in step 200
_{W **} (In the following description, "**" indicates the right front wheel 1.
As "FR" for the front left wheel 2 as "FL", and as "RR" for the right rear wheel 3
In the case of the left rear wheel 4, "RL" is a suffix which is displayed respectively) and the maximum value is selected, and the maximum wheel speed and the previous estimated vehicle speed obtained by the previous estimated vehicle speed calculation process are selected. , a practical upper limit value of the vehicle acceleration can take the vehicle traveling state, the vehicle deceleration of the upper and lower speed limit in consideration of the upper limit of the (negative acceleration), the intermediate value between the estimated vehicle body speed V _B. When the estimated vehicle body speed V _B is braking, it changes as shown by the example Figure 10 (a).

Next, in step 110, the current estimated vehicle speed V _{B (n)} calculated in step 110 (hereinafter, the subscript n indicates the current calculated value, and n-1 indicates the previously calculated value), estimated vehicle velocity V _{B (n-1),} from the time interval ΔT and the predetermined LSB adjustment constants K _C of this calculated time from the last calculated time, calculates an estimated vehicle body deceleration G _B in equation (1).

_{G B = K C (V B} (n) -V B (n-1) / ΔT ...... (1) the estimated vehicle deceleration G _B changes as shown by Figure 10 (b).

Next, in step 130, the reference speed V _S as the wheel speed target, made from the estimated vehicle body speed V _B obtained in the previous step 110 by the arithmetic expression such as the following equation.

Reference speed V _S = K · V _B −ΔV Here, K and ΔT are predetermined constants, for example, K = 0.9
5, ΔV = 2 km / h. The reference speed V _S changes as shown by the dashed line in FIG. 10 (a).

Next, at step 140, a system abnormality check is performed. In this process, the data corresponding to the operating state of the system element in the normal operation of the system stored in the ROM in advance and the data representing the operating state of the system element captured in this processing are compared and examined, and a system error is detected. When it is determined that there is no abnormality, the abnormality flag indicating the system abnormality state is set. On the other hand, when it is determined that there is no abnormality, the abnormality flag is reset.

Next, at step 150, it is determined whether or not the system is abnormal by referring to the abnormality flag. If the abnormality flag is not set, i.e., if the system is operating normally, the process proceeds to the estimated vehicle body speed V _B processing step 110. On the other hand, if it is determined that the abnormality flag is set,
That is, if a system abnormality has occurred or an abnormal operation is being performed, step 160 and step 170 are sequentially performed, and then the process proceeds to step 110.

Step 160 is a step for notifying the driver that an abnormality has occurred in the system so that it can be confirmed that the anti-skid control is not effective.
If it is determined in 140 that there is an abnormality in the system, an indicator lamp (not shown) is turned on.

Step 170 is a step of performing fail-safe processing when the system is abnormal. In this step 170, control for cutting off the energization of the pressure increasing, holding, and pressure reducing electromagnetic solenoids in each of the four actuators 21 to 24 is performed. Processing for outputting a signal is performed.

4 and 5 are flowcharts showing a timer interrupt routine that is started at a predetermined cycle during the execution of the main routine process described above. In this interrupt routine, processing for four wheels is performed for FR wheels → FL wheels →
The processing is executed in the order of the RR wheel and the RL wheel in order, and when the processing for the four wheels is completed, the processing exits the timer interrupt routine.

First, in step 200, processing for calculating the wheel speed _{VW **} is executed. In this wheel speed calculation step 200, a predetermined calculation formula is calculated based on the difference between the count value of the vehicle speed pulse at the time of the current process execution and the count value of the vehicle speed pulse at the time of the previous process execution, and the time interval. In addition to the calculation, a filtering process, that is, a process of averaging the wheel speeds obtained by a plurality of continuous calculations is performed as necessary.

Next, in step 210, processing for calculating the wheel acceleration GW _** is executed. This wheel acceleration calculation step 210
Then, a predetermined calculation formula is calculated based on the difference between the wheel speed calculated in step 200, the difference between the wheel speeds of the same wheel calculated last time, and the calculation time interval. Similar processing is also performed to make pulsating components of wheel speed and wheel acceleration.

Next, in step 220, a first deviation between the reference speed V _S and the wheel velocity V _{W **} calculated in Step 130 (V W _**
−V _S ). This first deviation has a positive or negative value,
When the wheel speed is higher than the reference speed, the wheel speed becomes a positive value, and when the wheel speed is lower, the wheel speed becomes a negative value. During braking, the wheel speed changes as shown in FIG. 10 (c).

Next, in step 230, the calculated estimated vehicle body deceleration at a wheel acceleration G _{W **} and step 120 calculated in step 210 and the second deviation amount between the (negative acceleration) G _B (G W _** -
G _B ). This second deviation amount is a positive value when the wheel acceleration is positive and negative and the wheel acceleration is larger than the estimated vehicle body deceleration (negative acceleration), and becomes a negative value when the wheel acceleration is smaller than the estimated vehicle body deceleration. At the time of switching, it changes as shown in FIG. 10 (d).

Next, in step 240, step 220 and step 230
In the first deviation amount obtained _{(V W **} -V _S) and the second deviation amount _{(G W **} -G _B), multiplied by (3) respectively weighting coefficient K _A, K _B as shown by the formula Then, the wheel slip state quantity W _** is calculated.

_{W ** = K A (V W} ** -V S) + K B (G W ** -G B) ......... (3) The coefficient K _B conversion for converting the status quantity of the wheel speed It also has the meaning of a coefficient, for example, a coefficient equivalent to 2 km / h at 1G. The wheel slip state quantity W _** thus obtained also has positive and negative values, and is a continuous state quantity indicating the tendency of the wheels to slip. That is, as the slip state quantity W _** is negative and larger, the slip coefficient of the wheel is larger, the pressure reduction gradient of the brake pressure of the corresponding wheel is increased, and the slip value can be used as a required value for quickly releasing the brake pressure. it can. Also, as the slip state amount W _** is positive and the value is larger, the wheels are more likely to recover, and the pressure increase gradient of the brake oil pressure can be increased and used as a required value for increasing the brake oil pressure again. When the value of the slip state quantity W _** is small and is near 0, the wheel speed and the wheel acceleration are also near the target slip and around the vehicle body deceleration, and the brake oil pressure may be used as a required value for substantially maintaining the brake oil pressure. it can. This slip state quantity W _** is the tenth
It changes as shown in FIG.

Next, in step 250, it is determined whether the anti-skid control is being performed or the control has not been started. The determination is made based on whether the control flag F _STA described in the following steps is 1 or 0. First, the case where the control has not been started will be described. When it is determined in step 250 that the control is not being performed (F _STA =
0) When the determination is made, the process proceeds to step 260, and it is determined whether the control start determination condition is satisfied. For example, stop switch
26 is turned on, and it is determined whether or not the wheel slip state amount of the previous step 240 is equal to or less than a negative predetermined value.
If the control start condition is satisfied at 0, step 271
To set the control-in-progress determination flag _FSTA to 1, and then jump to step 300 in FIG. If the control start condition is not satisfied, the process jumps to step 400 in FIG.

Next, it is determined in step 250 that the control is already being performed (F _STA =
The case where 1) has been performed will be described.
To determine whether the control end condition is satisfied. For example, the vehicle body estimated speed V _B 0 km / h, and the or it is determined that the vehicle has stopped, or step switch 26 determines whether or not the OFF. If the control end condition is satisfied in step 290, the process jumps to step 291 to reset the control-in-progress determination flag _FSTA to 0, and then jumps to step 400. If the control termination condition is not satisfied, the process jumps to step 300, where control is continued.

Next, the flowchart of FIG. 5 will be described.
Steps 300 to 391 show processing during anti-skid control, and steps 400 to 420 show processing before control or at the end of control.

First, the processing during control will be described. Step 300
Then, the slip state quantity W _** obtained earlier is used as the hydraulic pressure gradient ratio.
Convert to WP _{G **} (0 ± 100%). In this process, the gradient on the pressure increasing side is set to 0 to create a subsequent hydraulic gradient.
+ 100%, and the gradient on the decompression side corresponds to 0-100%,
In order to set the hydraulic gradient by the time combination of holding and increasing pressure and holding and reducing pressure, respectively, the wheel slip state amount W _** is converted into a hydraulic gradient ratio WPG _** in a relationship as shown in FIG. It is processing for.

Next, in step 310, a hydraulic pressure gradient correction amount MP _{G **} for correcting the hydraulic pressure gradient by the continuous time in the pressure increasing mode and the continuous time in the pressure reducing mode is calculated. As shown in FIGS. 7 and 8, this processing is performed for the continuous time T _UP in the pressure increasing side (0 to + 100% in the hydraulic pressure gradient) mode and in the pressure decreasing side (0 to -100% in the hydraulic pressure gradient) mode. _Rapid changes in road surface conditions (low μ
In this case, the hydraulic pressure gradient correction amount for quickly adapting the brake hydraulic pressure to a high-μ road and a high-μ road to a low-μ road is considered. That is, when the pressure increase mode is continuous and there is no tendency of the wheels to slip (pressure reduction output) even if the pressure is increased for a long time, the correction amount is gradually increased according to the increase of the time T _UP as shown in FIG. increasing the MP _G, thereby increasing the pressure increase gradient, etc. when Noriutsuri from low μ road to the high μ road,
Increase brake hydraulic pressure quickly. Further, the correction amount MP _G shown in FIG. 8, immediately after the reduced pressure trend began, the road surface friction coefficient - considers just beyond the mu peak slip rate (μ-S) characteristic, once slightly larger vacuum If the recovery of the wheels is slow even after the brake oil pressure is released continuously after the output of the pressure reduction mode time (for example, a transition from a high μ road to a low μ road), the pressure reduction gradient is increased.

Next, at step 320, the hydraulic pressure gradient ratio WP _{G **} obtained at steps 300 and 310 and the hydraulic pressure gradient correction amount MP _{G **} are added to obtain a final hydraulic pressure gradient P _{G **} as shown in equation (4). Calculate.

P _{G **} = WP _{G **} + MP _{G **} (4) This hydraulic gradient P _{G **} is limited as a value between -100 and 0 + 100%.
_The pressure increasing mode (0% ≦ P _G)
≤ + 100%) and pressure reduction mode (-100% ≤ P _G <0%).
The hydraulic pressure gradient is controlled by the drive time ratio in the pressure reduction or holding mode. The hydraulic gradient P _G changes as shown in FIG. 10 (f).

In step 330, the pressure increase mode (P _** ≧≧) is determined by the sign of the final hydraulic pressure gradient P _** calculated in step 320.
0) and a pressure reduction mode (PG _** <0). Here, first, when it is determined that the pressure reducing mode (PG _** <0), the process of the pressure reducing mode is executed in step 340 and thereafter, and when it is determined that the pressure increasing mode (PG _** ≧ 0). In step 370 and thereafter, processing in the pressure increase mode is executed.

First, processing in the decompression mode from step 340 will be described. Decompression gradient PG _** (-100% ≤PG _** <0%)
From the value of, the drive time ratio of the decompression and holding position of the brake oil pressure of the actuator is calculated from a map set in the ROM of the microcomputer in advance or PG _**.
From the value of.

In the next step 350, a signal is output to any one of the actuators 21 to 24 in order to control the brake hydraulic pressure of the corresponding wheel according to the drive time ratio of the pressure reduction and the hold obtained in step 340, and the actuator 11 Drive ~ 14 to control brake hydraulic pressure.

In step 360, a counter T _{DW **} for monitoring the continuous time of the pressure reduction mode is counted up for correction of the hydraulic pressure gradient described in step 310, and in step 361, the pressure increase mode continuous time monitoring counter T _UP Clear _** . Then, the process jumps to step 430 to determine whether or not the calculation of all the wheels is completed.

Next, when it is determined in step 330 that the value of the hydraulic pressure gradient PG _** is positive, processing in the pressure increasing mode from step 370 will be described. In the same manner as in the depressurization mode, in step 370, the drive time ratio of the pressure increase and the holding valve is calculated from the value of the pressure increase gradient PG _** (0% ≤PG _** ≤100%) by a map or calculation. Ask. Next, at step 380, the actuators 21 to 24 of the corresponding wheels are
A signal is output to any of the above to control the brake hydraulic pressure. In step 390, the counter T _{UP **} for monitoring the continuous time in the pressure increasing mode is counted up for the hydraulic pressure gradient correction in step 310, and in step 391, the pressure reducing mode continuous time monitoring counter is cleared. Then, it is determined in step 430 whether all the wheels have been completed. If not, the process returns to step 200 in FIG. 4 to perform the processing of the next wheel, and a series of similar processing is performed thereafter.

FIG. 9 has been described in steps 340 and 350 and steps 370 and 380. Depending on the value of the hydraulic gradient P _G, actuator pressure increase, hold, by changing the time ratio of the reduced pressure, shows a time chart for controlling the hydraulic gradient.

If the hydraulic pressure gradient P _G is a value between 0 to + 100%, and FIG. 9 waveform (1) of (a) ~ (6) pressure increasing as indicated by the retention of the driving time ratio, the brake hydraulic pressure P It is increased at the gradient shown by the characteristic lines (1) to (6) in FIG. 9 (b).

Also, if the hydraulic pressure gradient P _G is a value between 0 to -5 100%
Assuming that the drive time ratio between the pressure reduction and the holding as shown by the waveforms (7) to (11) in FIG. 9A, the brake hydraulic pressure P is shown in FIG. 9B.
In the characteristic lines (7) to (11).

In this manner, the drive time ratio of the hydraulic control mode (pressure increase, pressure reduction, or holding) of the actuator can be continuously changed in accordance with the slip state of the wheel and the continuous time of the hydraulic pressure gradient.

However, in the hydraulic brake devices 11 to 14, the brake oil pressure P changes, for example, as shown by a solid line in FIG. 10 (g). In FIG. 10 (g), the change in the brake oil pressure according to the prior art is indicated by a broken line. However, in the present invention, the brake pressure is excessively reduced (excessive pressure reduction) or excessively applied (excessive reduction) as indicated by A and B in FIG. There is no excessive pressure increase, and the brake oil pressure fluctuation is reduced as a whole, and the braking efficiency and the vehicle feeling during braking are improved.

Lastly, if the control is not being performed or if it is determined that the control has been completed, the hydraulic pressure gradient correction amount MP _{G **} and the pressure increase mode continuous time monitoring counter T _{UP *} are determined in steps 400 and 410 by the processing of step 400 and subsequent steps _{. *} , Clears the decompression mode continuous time monitoring counter T _{DW **} , outputs a pressure increase signal to the actuator in step 420, and the normal master cylinder 16 communicates with the wheel cylinders 11 to 14 to perform normal brake operation. Return to the state.

In the above-described embodiment, an example of a system in which the hydraulic pressure adjusting function of the actuator has a pressure increasing, holding, and pressure reducing mode has been described. However, other hydraulic modes, for example, an actuator having only a pressure increasing and a pressure reducing may be used. Can continuously control the hydraulic pressure gradient by changing the duty ratio of pressure increase and pressure reduction. In addition, even with actuators such as gradual increase, rapid increase, gradual decrease, and sudden decrease, the pressure increase side can change the hydraulic pressure gradient by a combination of gradual increase, rapid increase, or gradual decrease. Alternatively, the hydraulic gradient can be continuously controlled by a combination of gradual increase. Further, the with linear pressure regulating valve that can be controlled continuously hydraulic gradient actuator, the hydraulic pressure gradient P _G obtained may be controlled by directly applied.

Also, the case where the present invention is applied to an anti-skid control device has been described.However, a traction control device that aims to improve the stability on slippery road surfaces and the acceleration performance by suppressing the acceleration slip of the drive wheels by the brake hydraulic pressure. It is applicable, and the wheel acceleration side slip state is similarly obtained from the slip amount of the wheel speed on the wheel acceleration side and the wheel acceleration, and the hydraulic gradient of the hydraulic actuator can be continuously controlled according to this amount.

In addition to the hydraulic control, in the traction control, the concept of continuous wheel slip state monitoring can be used to operate the throttle opening, fuel injection amount, ignition timing, etc. The operation amount can be changed smoothly.

Further, the slip amount of the wheel was obtained from the combined value of the wheel slip amount and the wheel acceleration amount for compensating the delay, but it is also conceivable that the gradient of the hydraulic pressure may be varied only by the wheel slip amount. The acceleration term may be considered as the correction amount for.

〔The invention's effect〕

As can be seen from the above description, the present invention extends not only in the case of the return of the brake pressure but also in the entire brake control, how to apply the brake pressure to the state where the braking force is most applied to the slip state at that time. It is made in consideration of how to do it. As described above, according to the present invention, the gradient of the brake pressure is set almost continuously according to the slip state of the vehicle, and an excellent effect of improving the vehicle feeling and the braking efficiency can be obtained.

[Brief description of the drawings]

1 is a block diagram showing the present invention, FIG. 2 is a schematic diagram showing one embodiment of the present invention, FIGS. 3 to 5 are flowcharts for explaining the operation, and FIGS. 6 to 10 are the explanation of the operation. FIG. 1-4 ... wheels, 5-8 ... wheel speed sensors, 21-24 ...
Actuator, 30 ... Electronic control circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60T 8/66

Claims (5)

(57) [Claims] 1. A plurality of wheel speed sensors for detecting a rotational speed of a wheel; first calculating means for calculating a wheel speed and a wheel acceleration based on a detection signal of the wheel speed sensor; Second calculating means for calculating a speed and further calculating an estimated vehicle body deceleration from the estimated vehicle speed; reference speed calculating means for calculating a target reference speed from the estimated vehicle speed; A deviation amount calculating means for calculating a first deviation amount and a second deviation amount between the wheel acceleration and the estimated vehicle body deceleration; arbitrarily weighting each of the first deviation amount and the second deviation amount to obtain a sum to obtain a slip state Means for calculating a slip state amount as an amount, pressure gradient calculating means for calculating a continuous control gradient of pressure reduction and pressure increase of the brake pressure from the slip state amount, and a pressure gradient based on the calculated pressure gradient. Drive time setting means for setting a drive time ratio of the actuator, and control means for driving the actuator based on the drive time ratio and controlling a brake fluid pressure applied to a wheel cylinder of the wheel. Brake pressure control device. 2. The control device according to claim 1, wherein the driving time ratio is set in a plurality of driving time ratios determined in advance so as to have a plurality of gradients in both the pressure increasing direction and the pressure decreasing direction of the wheel cylinder pressure. The brake pressure control device according to claim 2, wherein the brake pressure control device is selected from the following. 3. The pressure gradient calculating means calculates a slip state quantity from the slip state quantity calculated by the slip state quantity calculating means.
The drive time ratio is set so as to increase the pressure gradient of the pressure reduction of the brake pressure as the distance in one direction indicating the locked state of the wheel is increased, and the lock state of the wheel is restored from the target slip state amount by the slip state amount. 2. The brake pressure control device according to claim 1, wherein the drive time ratio is set so as to increase the pressure gradient of the increase in brake pressure as the vehicle moves in the other direction indicating the state. 4. The apparatus according to claim 1, wherein said pressure gradient calculating means includes a correcting means for correcting the control gradient so as to increase according to a length of continuous time of the wheel cylinder pressure increasing mode. 2. The brake pressure control device according to claim 1. 5. The pressure gradient calculating device according to claim 1, wherein said pressure gradient calculating device includes a correcting device for correcting the wheel cylinder pressure so as to increase the pressure reducing gradient according to the length of continuous time in the pressure reducing mode. The brake pressure control device according to the paragraph.