JPH06263021A - Braking force control device - Google Patents

Abstract

PURPOSE:To provide a braking force control device by which responsiveness of increasing and decreasing pressure adjusting control of a wheel cylinder(W/C) can be improved easily and effectively even in an ABS actuator or the like causing a response delay. CONSTITUTION:A controller of a device calculates (130) an increasing and decreasing pressure commanding value DELTAP of W/C, and outputs a driving signal I (150) of an actuator to regulate an increasing and decreasing pressure quantity of the W/C. The driving signal I corrects the increasing and decreasing pressure commanding value P so as to become [k(DELTAP+tau.(d/dt)DELTAP)], and at that time, a time constant (p) is applied (135 and 140) after being changed so as to become a large value in the vicinity of zero of W/C pressure P. The increasing and decreasing pressure commanding value is corrected (a response delay of an actuator approximate to first order lag is canceled) by a first order lead element (DELTAP+tau.(d/dt)DELTAP), and the time constant (tau) of the first order lead element is changed, and a delay in the vicinity of zero of the W/C pressure is also compensated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a braking force control device, and more particularly to a braking force control device suitable for use in the case of having an actuator system for continuously controlling a wheel cylinder pressure by an input command signal.

[0002]

2. Description of the Related Art As a braking force control device, for example, a control device using a proportional control valve as described in JP-A-4-87867 is known. According to this, the wheel cylinder pressure can be continuously controlled by an electric command, and anti-skid (ABS) control and traction control (TCS) can be applied.

[0003]

The control of the wheel cylinder pressure as described above is useful in the above aspects, but there is room for improvement in view of the following points. . For example, in the case of controlling the ABS, at this time, mainly based on the information on the wheel rotation speed, the pressure reduction amount of the wheel cylinder pressure of the control target wheel that is likely to be locked is calculated and used as a command value to the actuator. To do. here,
The actuator generally has a response delay, and even if a pressure reduction command is issued due to the delay, the required amount of pressure reduction is not immediately performed. If the pressure is not quickly reduced by a sufficient amount, it is difficult to secure the responsiveness of the braking force control by adjusting the wheel cylinder hydraulic pressure, and if the responsiveness can be improved, the control can be improved. If we try to improve the responsiveness by manufacturing an actuator with high response delay as much as possible and mounting it, there is a tendency to be disadvantageous in terms of cost, weight, etc. Depending on the measures, ignoring
It is difficult to avoid the burden of increasing the weight. A desirable remedy is to be as low cost and simple as possible, and to effectively increase the responsiveness of the braking force control even with the existing proportional control method.

Therefore, the object of the present invention is to improve the drive system of the actuator for controlling the braking force applied to the wheels, and to improve the response of the wheel cylinder pressure adjustment control as described above even if there is a response delay. Can be eliminated,
It is an object of the present invention to provide a braking force control device capable of easily realizing more effective braking force control of this kind.

[0005]

According to the present invention, the following braking force control device is provided (FIG. 1). A device for controlling the braking force of a wheel, which is input with a pressure increasing / decreasing command value calculating unit for calculating a pressure increasing / decreasing command value of a wheel cylinder of a wheel to be controlled based on a vehicle state detecting unit such as a wheel rotation speed. An actuator that adjusts the amount of pressure increase / decrease of the wheel cylinder based on the drive signal, a wheel cylinder pressure detection unit that detects the hydraulic pressure of the wheel cylinder, and the drive signal is ΔP + τ · (d / dt) ΔP, where τ is The time constant, ΔP is a command value for increasing / decreasing the wheel cylinder, and (d / dt) ΔP is a correction means for correcting the command value for increasing / decreasing pressure so as to correspond to the rate of change of ΔP. an increasing / decreasing command value correcting means including a time constant changing means for changing τ based on a detection signal of the wheel cylinder pressure detecting means so that τ takes a large value near zero of the wheel cylinder pressure. A braking force control device characterized by being provided.

[0006]

In the present invention, when controlling the wheel braking force,
Where the pressure increase / decrease command value calculating means calculates the pressure increase / decrease command value of the wheel cylinder of the wheel based on the vehicle state such as the wheel rotation speed, and the actuator for adjusting the pressure increase / decrease amount of the wheel cylinder is driven based on the input drive signal, In that case, the drive signal is ΔP + τ · (d / dt) ΔP, where τ is the time constant, ΔP is the wheel cylinder pressure increase / decrease command value, and (d / dt) ΔP is the value corresponding to the rate of change of ΔP. Further, the pressure increasing / decreasing command value correcting means corrects the pressure increasing / decreasing command value, and at that time, the time constant τ is near zero of the wheel cylinder pressure based on the detection signal of the wheel cylinder pressure detecting means by the time constant varying means. Then, it is applied to the correction as it is changed to take a large value.

Therefore, the control can be made to output a command in consideration of the response of the actuator in advance, and for example, for the response delay of the actuator which is close to the first-order delay, the pressure increase / decrease command value is corrected by, for example, a first-order advance element. It is possible to control so that the delay can be canceled, and the time constant can be changed by changing the time constant of the primary advance element to a large value near zero of the wheel cylinder pressure so that the wheel cylinder pressure becomes zero. It also makes it possible to compensate for delays in the vicinity.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 shows an embodiment of the present invention. Here, the configuration of one wheel side of each wheel of the vehicle is shown including a proportional control valve, but it is assumed that the other wheel side has the same components. In the figure, reference numeral 1 is a brake pedal, 2 is a master cylinder (M / C), 3 is a disc brake device arranged for each wheel, and 4 is provided on the disc brake device 3 individually. The wheel cylinder pressures P _i (i = 1 to 4 (where the subscript i is, for example, 1 is the left front wheel side, 2 is the right front wheel side, 3 is the left rear wheel side, and 4 is the right rear wheel side). The wheel cylinders (W / C) to which the side means) are added. The disc brake device 3 has a pad and a rotor, and when the wheel cylinder piston makes a stroke, they come into contact with each other, and a brake force (braking force) is applied to the wheels.

For each of the front, rear, left and right wheels, the brake hydraulic pressure system can be provided with an electronic hydraulic control valve 5 as shown, a brake pressure combiner 12, and the like. In the system according to the present invention, improvement in responsiveness can be easily realized by improving the actuator driving method.
As the brake hydraulic system, the one disclosed in the above publication can be basically applied.

The outline thereof will be described below. The master cylinder 2 generates a master cylinder pressure P _M during braking according to the operating force applied to the brake pedal 1. The electronic hydraulic control valve 5 has a master cylinder pressure chamber 50 to which the master cylinder pressure P _M is supplied from the master cylinder pressure port 5e.
The pressure generated by the master cylinder pressure P _M is used on the pressure increasing side, and the force generated by the proportional solenoid 52 is used by the spool 51.
It is a control valve used on the pressure reducing side of. On the left side of the spool 51, the port 510 on the input port 5a side is opened and the port 511 on the drain port 5d side is closed. Proportional solenoid 5
The spool position is adjusted by the operation of the solenoid plunger 61 in accordance with the input signal to the control signal 2, and the spool 51 moves to the right by the right movement of the plunger 61. Input port 5a, port 5
10, the oil passage 9 of the control oil pressure P _C obtained through the output port 5c reaches the wheel cylinder pressure oil passage 11 via the brake pressure synthesizer 12, and the wheel cylinder 4
It is used for adjusting the amount of pressure increase / decrease. The control of the control valve 5 can be performed for each channel by the command current I (I _i ) from the controller 13 to the proportional solenoid 52 based on the amount of pressure increase / decrease for the corresponding wheel cylinder 4.

The control device is connected to an input port 5a of the electronic hydraulic control valve 5 via an accumulator pressure oil passage 6, and has an oil pump 7a, a check valve 7b and an accumulator 7a.
an external hydraulic pressure source 7 constituted by c, and provided in a branch oil passage 6a of the accumulator pressure oil passage 6;
An electromagnetic switching valve 8 that causes the traction control (TCS) pressure P _{T based} on the accumulator pressure P _s to act on the pressure increasing side of the spool 51 via the TCS port 5 b of the electronic hydraulic control valve 5 by opening the valve. Have.

The brake pressure synthesizer 12 has a control hydraulic oil passage 9 from the electronic hydraulic control valve 5 and a master cylinder pressure oil passage 1.
0 is connected. The brake pressure combiner 12 connects the master cylinder pressure oil passage 10 and the wheel cylinder pressure oil passage 11 when the control oil pressure P _C is not generated.
Port 12c through 7, allowed direct by 12a, in the event of a control oil pressure P _C, under the switching of the valve 17, controlled by the difference in pressure receiving area of the stepped plunger 121 in the right line of the step plunger 121 hydraulic P _C from the high pressure The wheel cylinder pressure is P (P _i ).

The electronic hydraulic control valve 5 includes a first plunger 5 between the master cylinder pressure chamber 50 and the spool 51.
3, the second plunger 54, the pedestal 55, and the third plunger 54 are arranged, and the valve case 60 and the first plunger 5 are arranged.
The first spring 57 is inserted between the valve case 6 and
A second spring 58 is interposed between 0 and the second plunger 54. The first spring 57 is set to a higher setting force than the second spring 58, and a third spring 59 that pushes the spool 51 rightward in the drawing is inserted on the proportional solenoid 52 side of the spool 51.

In the brake pressure synthesizer 12, a control hydraulic chamber 122 communicating with the input port 12abc is formed on the large diameter side of the step plunger 121, and a wheel cylinder pressure communicating with the output port 12b is formed on the small diameter side of the step plunger 121. A chamber 123 is formed in which the master cylinder pressure port 1
2c is provided. The stepped plunger 121 is the return spring 1
24 is urged to the left in the figure.

During normal braking, the force generated by the master cylinder pressure P _M generated by the brake operation acts on the spool 51 of the electronic hydraulic control valve 5 on the pressure increasing side, and the proportional solenoid 5
The force of the second plunger 61 acts on the spool 51 on the pressure reducing operation side. In the control valve 5, the accumulator pressure P _s from the external hydraulic power source 7 is used as a base pressure to increase the pressure in proportion to the master cylinder pressure P _M , and the smaller the force of the plunger 61 is, the higher the control pressure P is. _C is output. The control oil pressure P _C is supplied to the brake pressure combiner 12, and the wheel cylinder pressure P is made higher than the control oil pressure P _C due to the difference in pressure receiving area of the step plunger 121, and is supplied to the wheel cylinder 4. That is, a boosting function for increasing the master cylinder pressure P _M is obtained, and the force by the plunger 61 of the proportional solenoid 52 of the control valve 5 is externally controlled to obtain the wheel cylinder pressure P with an arbitrary boosting characteristic. The function is demonstrated.

When a wheel lock is likely to occur at the time of sudden braking or low μ road braking, the boosting characteristic obtained by the proportional solenoid plunger control of the control valve 5 is set to a characteristic slightly lower than the maximum boosting characteristic. In other words, by externally controlling the force of the plunger 61 of the proportional solenoid 52 in accordance with the slip condition of the wheel, the wheel cylinder pressure P can be increased, held, or reduced, and the antiskid ( ABS) control is performed.

When the drive wheel slip occurs due to the sudden depression of the accelerator pedal, etc., the traction control pressure P _{T is applied} to the pressure increasing side of the spool 51 of the hydraulic control valve 5 by opening the electromagnetic switching valve 8. Spool 51
Operates in the direction of increasing pressure, and the control oil pressure P _C reduces the amount of force by the plunger 61 of the proportional solenoid 52 of the control valve 5 from the maximum pressure determined by the external pressure applied by opening the electromagnetic switching valve 8. The pressure can be arbitrarily controlled according to the external control of the plunger 61 of the proportional solenoid 52, and the pressure increase / decrease amount of the wheel cylinder 4 can be adjusted.
TCS control by this is performed. As described above, the structure and operation of the electronic hydraulic control valve 5 and the like in the brake hydraulic system may be basically the same as those described in the above-mentioned publication.

The controller 13 for driving and controlling the proportional solenoid 52 of the electrohydraulic control valve 5 and the solenoid 81 of the electromagnetic switching valve 8 has wheel rotation speeds (wheel speeds) ω _{1 to} ω ₄ of each wheel.
A signal from a wheel speed sensor 15 arranged to detect
A signal from the master cylinder pressure sensor 16 and a signal from the longitudinal acceleration sensor 14 are respectively input, and further, in the present example, the wheel cylinder pressures P _{1 to} P ₄ are arranged to be detected. The signal from the sensor 20 is input.

The controller 13 is composed of a microcomputer, and its arithmetic processing circuit executes processing in accordance with a braking force control program based on predetermined input information input from the sensors, and outputs a drive control signal via an output circuit. Is output. At the time of braking, as described above, the ABS control for preventing the wheel lock is executed as described above, and the TCS control is also performed by the brake force applied to the wheel to suppress the slip of the driving wheel at the time of starting or sudden acceleration. Done.

For example, in the case of ABS control, based on the information of the wheel rotation speed, the pressure reduction amount of the wheel cylinder pressure of the wheel that is likely to be locked is calculated, and the control is performed with the calculated pressure reduction amount as a command value. In the case of the method, by controlling the braking force by the skid cycle so that the slip amount of each wheel falls within a predetermined range for each wheel, the pressure is reduced when it is likely to lock, and the pressure is increased when the wheel rotation speed is restored. The pressure can be adjusted and controlled so that maximum braking efficiency is achieved for each wheel, and wheel locking is avoided.

When controlling the wheel braking force by adjusting the pressure increasing / decreasing amount of each wheel cylinder in this way, the controller 13 calculates the pressure increasing / decreasing command value of each wheel cylinder based on the vehicle state such as the wheel rotation speed. Based on this, a drive signal for the corresponding electro-hydraulic control valve 5 for adjusting the wheel cylinder pressure increase / decrease corresponding thereto is obtained. In this case, the controller 13 considers the response of the control system including the control valve 5 in advance. Then, the process of correcting the pressure increase / decrease command value is also executed. Furthermore, the time constant applied in the correction process is
When the corresponding wheel cylinder pressure P is near zero, a time constant changing process is executed to change the time constant to a large time constant. The memory circuit of the controller 13 stores a time constant-wheel cylinder pressure table (see FIG. 4) for changing the time constant, together with a control program including the above-described pressure increase / decrease command value correction processing.

FIG. 3 shows a micro controller in the controller 13.
The above-mentioned pressure increase / decrease command value correction processing executed by the computer.
Shows an example of a control program including processing
It is a flowchart. This program is at regular intervals
To be executed. First, in step 100, the wheel speed sensor is
Based on the output of the wheel and cylinder pressure sensors
Wheel speed ω_i(I = 1 to 4) and wheel cylinder pressure P
_i(I = 1 to 4) and are read. Next step 1
At 10, the vehicle speed is estimated. Here, the wheel speed ω
₁~ Ω _FourFrom the fluctuation of the vehicle speed ω₀Estimation of
For such an estimation method, known anti-skid (A
The same as the method for calculating the vehicle speed used in BS) control.
It may be like.

The next step 120 is a process of calculating the deviation ε between the vehicle speed value ω ₀ obtained above and the wheel speed value read above, and the deviation ε _i (ε ₁ ~) of the wheel speed for each wheel.
ε ₄ )

[Equation 1] ε _i = ω ₀ −ω _i --- 1 is calculated. In the following step 130, the pressure increase / decrease command value ΔP _i (i =
1 to 4)

[Equation 2] ΔP _i = Kε _i + L (d / dt) ε _i --- 2 The ABS that controls the wheel rotation speed based on the pressure increase / decrease command value is different from the ABS that uses a three-position switching solenoid valve, for example, but the ABS that uses a proportional control valve is a so-called PD (proportional + differential control) type ABS. It is feedback control. Here, K and L in the above equation 2 are the feedback gains thereof.

When the pressure increasing / decreasing command value ΔP _i of each wheel cylinder is calculated in this way, a command to output the pressure increasing / decreasing amount of each wheel cylinder to be adjusted by the electronic hydraulic control valve based on the calculated value, specifically, Specifically, in this example, the pressure-converted current value supplied to the proportional solenoid is calculated, but in this case, from the following viewpoint, the pressure increase / decrease command value Δ
P _{i is} corrected, and the drive signal I _i (step 150) is determined and output based on the corrected pressure increase / decrease command value.

That is, basically, the command is output in consideration of the response of the actuator of the system in advance. In this case, considering that it is difficult to accurately represent the response with an equation, it is assumed that the response is approximated by a first-order delay. When the actuator delay is approximated to the first-order delay, the first-order advance element is used to correct the pressure increase / decrease command value. When correcting the pressure increase / decrease command value, regarding the time constant applied to the correction, in particular, when the wheel cylinder pressure is near zero, the responsiveness is poor because the wheel cylinder piston moves. Keep it large.

From this point of view, in the following processing, the response of the present system, which is mainly a proportional control valve, is approximated by a first-order lag, so that in the present program example, the lag can be compensated by using a first-order advance element. Thus, the processing for correcting the pressure increase / decrease command value and changing τ according to the wheel cylinder pressure P _i with the time constant τ is added.

To this end, first, in step 135 following the step 130 for calculating the pressure increase / decrease command value for each wheel cylinder, every time this step 135 is executed, the step 140 for correcting the next pressure increase / decrease command is executed. The time constant τ _i (i = 1 to 4) used for this is determined according to the wheel cylinder pressure P _i . FIG. 4 shows an example of a time constant τ-wheel cylinder pressure P table applicable to such processing. The time constant τ _i has a large value in a low region near the wheel cylinder pressure P _i , and the wheel cylinder As the pressure P _i becomes higher, the value becomes smaller,
It is set as τ _i data depending on the wheel cylinder pressure P _i with the characteristic of the tendency as shown in the figure. By introducing this variable characteristic, when the wheel cylinder pressure is near zero, the piston strokes while the pad and the rotor are in contact with each other, which is useful for improving the point where the response is particularly poor. Using the above table of characteristics,
As a result, the time constant τ _i corresponding to the value of the wheel cylinder pressure P _i at that time read in step 100 is searched and obtained, and the process of determining the value of τ _i to be applied to the correction formula described later is executed.

Then, in step 135, the time constant τ _i is determined based on the characteristic of increasing the time constant near the wheel cylinder pressure of zero, and then in step 140, the entire system is approximated with a first-order lag to correct and increase or decrease the pressure. Calculate the command value. That is, the correction of the pressure increase / decrease command value ΔP _i according to the equation 2 obtained in step 130 is performed according to the following equation to obtain the corrected value ΔP _i (A) (i = 1 to 4).

ΔP _i (A) = ΔP _i + τ _i · (d / dt) ΔP _i --- 3 where (d / dt) ΔP _i represents the rate of change of ΔP _i . By the steps 135 and 140, the pressure increase / decrease command value Δ
As P _i is corrected, in the correction process,
When the detected wheel cylinder pressure P _i is near 0, the time constant τ _i is applied to the equation 3 as a large value, and the corrected pressure increase / decrease command value ΔP _i (A) is calculated.

After calculating the corrected pressure increase / decrease command value by the above equation 3, the drive signal I _i (in step 150) is executed based on the corrected pressure increase / decrease command value ΔP _i (A) every time this step is executed. i = 1 to 4)

(4) I _i = κ · ΔP _i (A) --- 4 where κ is calculated from the current / pressure conversion constant,
Determine and output.

As described above, in this program example,
If the pressure increase / decrease command value ΔP of the corresponding wheel cylinder is calculated based on the wheel rotation speed ω _i (steps 100 to 13)
0), the current value I input to the proportional solenoid 52 for adjusting the amount of increase / decrease of the wheel cylinder 4 of FIG. 2 by the electronic hydraulic control valve 5 is the corrected increase / decrease command value ΔP.
It is calculated based on (A) (steps 135, 1
40, 150), the force exerted by the solenoid plunger 61 acting on the spool 51 of the control valve 5 described above can be externally controlled as a force corresponding to the drive signal I of Expression 4, whereby the wheel cylinder pressure P is adjusted and controlled. To be done. In this case, in the present embodiment, the drive signal I is κ
・ ΔP (A), that is, κ (ΔP + τ ・ (d / dt) ΔP)
The pressure increase / decrease command value ΔP can be corrected so that
Even if there is a response delay, the calculated pressure increase / decrease command value ΔP is corrected by the primary advance element, and as a result, the primary advance element (ΔP + τ ·
It is possible to easily improve the response delay by improving the control process that cancels the delay by using (d / dt) ΔP).

Therefore, according to this control, in the ABS control, for example, when the pressure reduction amount of the wheel cylinder pressure of the control target wheel which is likely to be locked is calculated and used as a command value to the actuator, the response delay of the actuator is delayed. It is possible to avoid the situation that a sufficient amount of pressure is not immediately reduced even when a pressure reduction command is issued with, and even if an existing actuator that continuously controls the wheel cylinder pressure by an electric signal is used, Can be realized by improving the actuator drive system, and only the arithmetic processing on the control program is added (step 140). Even in the case of 4 channels, the cost and weight of introducing an actuator with high capacity for each channel can be improved. There is no problem of increase, and it suffices to incorporate the correction processing of each wheel cylinder pressure increase / decrease command value ΔP _i , Control responsiveness can be enhanced easily and at low cost.

Further, in this control, the pressure increase / decrease command value is corrected by the primary advance element (the actuator response delay approximated to the primary delay is canceled), and the time constant τ _i of the primary advance element is changed to the wheel cylinder pressure P _i. Can be appropriately changed according to the above (step 135). As a result, when the pressure of the wheel cylinder 4 is near zero, the piston strokes while the pad and rotor are in contact with each other, so that the response is particularly poor, and at the same time, ΔP _i + τ _i ·
The time constant τ _i of (d / dt) ΔP _i can be changed by the detected wheel cylinder pressure P _i so as to be large near zero of the wheel cylinder pressure. As described above, in the present control, by further changing the time constant τ _i of the first-order advance element, it is possible to compensate the delay when the wheel cylinder pressure P _i is near zero, which is also effective in this respect. can do.

The present invention is not limited to the above embodiment. For example, the actuator is not limited to the configuration shown in FIG. 2 and can be applied to other configurations. Although the control by both the ABS and the TCS is shown, the control may be performed only by the ABS, for example. Further, the braking force control may be performed by a 3-channel method instead of the 4-channel method. Further, the present invention can also be applied to braking force control in which vehicle behavior control is performed by applying a braking force difference to the left and right wheels. In that case, for example, two wheels on the left and right of the front wheel or two wheels on the left and right of the rear wheel are used as control target wheels. May be carried out. Furthermore, the present invention has means for calculating the pressure increase / decrease command value of the wheel cylinder of the control target wheel based on the vehicle state such as the wheel rotation speed, and an actuator for adjusting the pressure increase / decrease amount of the wheel cylinder based on the drive signal. If the response delay of the actuator is to be improved by the drive system, it can be widely applied regardless of the degree of the response delay.
The effect can be obtained.

[0034]

According to the present invention, when the wheel cylinder braking force is controlled by calculating the wheel cylinder pressure increase / decrease command value and adjusting the wheel cylinder pressure increase / decrease amount by driving the actuator, the responsiveness of the actuator is improved. Not only can the wheel cylinder pressure increase / decrease command value be corrected so that the drive signal takes into consideration, but the time constant can also be appropriately changed and controlled according to the wheel cylinder pressure. Can improve the response of the wheel cylinder pressure adjustment control easily, and by changing the time constant, the delay in the vicinity of zero wheel cylinder pressure can be compensated, and the response of the control can be improved more effectively. it can.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a braking force control device of the present invention.

FIG. 2 is a system diagram of a braking force control device according to an embodiment of the present invention.

FIG. 3 is a flowchart of an example of a control program executed by a controller.

FIG. 4 is a diagram showing an example of time constant characteristic data applicable to the program.

[Explanation of symbols]

 1 Brake Pedal 2 Master Cylinder 3 Disc Brake Device 4 Wheel Cylinder 5 Electronic Hydraulic Control Valve 7 External Hydraulic Source 8 Electromagnetic Switching Valve 12 Brake Pressure Synthesizer 13 Controller 15 Wheel Speed Sensor 17 Shutoff Valve 20 Wheel Cylinder Pressure Sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoki Maruko 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. A device for controlling a braking force of a wheel, which calculates an increase / decrease command value for calculating an increase / decrease command value of a wheel cylinder of a wheel to be controlled based on a vehicle state detecting means such as a wheel rotation speed. Means, an actuator for adjusting the amount of pressure increase / decrease of the wheel cylinder based on an input drive signal, a wheel cylinder pressure detection means for detecting the hydraulic pressure of the wheel cylinder, and the drive signal is ΔP + τ · (d / dt) ΔP where τ is a time constant, ΔP is a wheel cylinder pressure increase / decrease command value, and (d / dt) ΔP is correction means for correcting the pressure increase / decrease command value so as to correspond to the rate of change of ΔP. An increase / decrease command including time constant changing means for changing the time constant τ based on the detection signal of the wheel cylinder pressure detecting means so that the time constant τ takes a large value near zero of the wheel cylinder pressure. Braking force control apparatus characterized by comprising comprises a correction means.