JPH06144171A - Braking force control device - Google Patents

Abstract

(57) [Abstract] [Purpose] Appropriate braking force according to the road surface condition is applied to the rear wheel side to ensure vehicle stability in the road condition where the road surface μ is not uniform and to ensure that the road surface μ is uniform. Achieves both improved braking performance under road conditions. [Structure] The actuator 22 includes a three-position solenoid valve of ON / OFF control type capable of controlling pressure reduction, pressure retention, and pressure increase, and the master cylinder hydraulic pressure Pm corresponding to the depression force of the brake pedal 18
Is supplied from the master cylinder 20, and the rear wheel braking fluid pressure is supplied in response to the braking fluid pressure control signal S from the control unit 21.
PR and front wheel braking hydraulic pressures PFL and PFR are individually controlled. The control unit 21 controls the rear wheel rotation speed VR, the left front wheel rotation speed VFL, the right front wheel rotation speed VFR, the steering angle θ, the braking signal B, and the like based on the input road wheel condition such that the road surface condition has a large road surface μ difference. The braking force is adjusted by controlling the rear wheel brake hydraulic pressure so that the braking force is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle braking force control device capable of variably controlling braking hydraulic pressures (brake hydraulic pressures) of left and right rear wheels.

[0002]

2. Description of the Related Art As a conventional example of a braking force control device for controlling a rear wheel brake hydraulic pressure, there is one disclosed in Japanese Patent Laid-Open No. 4-133846. In this conventional example, in order to prevent early rear wheel lock during braking of the vehicle, the increase in the rear wheel brake hydraulic pressure is limited. At that time, since the split point (critical fluid pressure point) for starting the restriction of the rear wheel brake fluid pressure is not fixed but is set by variable control,
The braking force on the rear wheel side is smaller than that on the front wheel side, and stability during braking is secured.

[0003]

However, when the braking force control of the above-mentioned conventional example is performed, the braking force on the rear wheel side is larger than that on the front wheel side in a road surface situation where the road surface μ such as the left and right split μ road surface is not uniform. The smaller the size, the more stable the vehicle is on the rear wheel side, but in the road surface condition where the road surface μ is uniform, the braking force on the rear wheel side can be increased even though the braking force can be increased. However, there is a problem that sufficient braking performance cannot be obtained.

According to the present invention, by applying an appropriate braking force according to the road surface condition to the rear wheel side, the vehicle stability is ensured in the road surface condition in which the road surface μ is not uniform and the road surface in which the road surface μ is uniform. The purpose is to achieve compatibility with improvement of braking performance in a situation.

[0005]

To this end, the braking force control apparatus of the present invention comprises a braking fluid pressure control means for variably controlling at least the braking fluid pressure of the rear wheels. Based on the road surface μ detecting means for detecting the road surface μ of each of the left and right wheels and the detection information of the road surface μ detecting means, the braking force of the rear wheel is reduced as the road surface situation in which the road surface μ difference between the left and right wheels is large. And a braking hydraulic pressure control signal adjusting means for instructing the hydraulic pressure control signal to the hydraulic pressure control means.

[0006]

According to the present invention, when the hydraulic pressure control means variably controls the braking hydraulic pressure of at least the rear wheels, the braking hydraulic pressure control signal adjusting means adjusts the rear road surface condition such that the road surface μ difference between the left and right wheels is large. Since a braking hydraulic pressure control signal is output to the hydraulic pressure control means so that the braking force on the wheel side becomes smaller than that on the front wheel side, stability of the vehicle is ensured in a road surface condition where the road surface μ is uneven, such as a left and right split road surface. Is sufficiently ensured, and in a road surface condition in which the road surface μ is uniform, the braking force on the rear wheel side can be increased as much as possible to realize a desired braking performance.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a system diagram showing a configuration of a first embodiment of a braking force control device of the present invention. In the figure, 10 and 11 are left and right front wheels, and 12 and 13 are left and right rear wheels, respectively. This braking force control device is configured so that the left and right front wheels 10 and 11 are individually anti-skid controlled, and the left and right rear wheels 12 and 13 are commonly anti-skid controlled. The left and right front wheels 10 and 11 are rotated by a steering wheel 14. The vehicle is steered to steer the vehicle, and the left and right rear wheels 12, 13 are driven by the engine via the propeller shaft 16 and the differential gear 17 to drive the vehicle.

The braking system for the vehicle is constructed as follows. That is, the stepping force of the brake pedal 18 is increased by the booster 19 and then supplied to the master cylinder 20,
The master cylinder hydraulic pressure Pm corresponding to the depression force of the brake pedal 18 is supplied from the master cylinder 20 to the actuator 22. The actuator 22 constitutes an anti-skid device together with the control unit 21, and when the anti-skid operation is under control by the control unit 21, which will be described later, one of the master cylinder hydraulic pressures Pm is applied to the rear wheel 12,
While supplying pressure as a common rear wheel braking hydraulic pressure (break hydraulic pressure) PR to the wheel cylinders 23 and 24 while adjusting the pressure so that 13 does not lock, the other of the master cylinder hydraulic pressure Pm is applied to the front wheels 10 and 11.
The front wheel braking fluid pressure (break fluid pressure) PF is applied to each wheel cylinder 25 and 26 while individually adjusting the pressure so that the
Supplied as L and PFR. A well-known proportioning valve (P valve) 27 is provided in the supply system of the rear wheel braking hydraulic pressure PR.
Shall be inserted.

The actuator 22 is provided with a solenoid valve for hydraulic pressure control corresponding to each supply system, and with these solenoid valves, the brake hydraulic pressures PR, PFL, PFR are individually supplied according to the braking hydraulic pressure control signal S from the control unit 21. Control to adjust the wheel cylinder pressure. As each solenoid valve, an ON / OFF control type three-position solenoid valve that can control decompression, pressure holding (holding), and pressure increase for known actuator control (ABS control) is used. Is reduced, the corresponding hydraulic pressure is maintained at the pressure maintaining position, and the corresponding hydraulic pressure is increased toward the master cylinder hydraulic pressure Pm which is the original pressure at the pressure increasing position.

The control unit 21 includes rear left and right wheels 1
Rotation speed V of the propeller shaft 16 which is the average rotation speed of 2 and 13
Rotation speed signal from rear wheel rotation sensor 28 that detects R, rotation speed signal from left front wheel rotation sensor 29 that detects rotation speed VFL of left front wheel 10, and right front wheel rotation that detects rotation speed VFR of right front wheel 11. A signal from the steering angle sensor 15 that detects the steering angle (steering angle) θ of the steering wheel (handle) 14 and a signal B from the brake switch 31 that indicates the presence or absence of braking while inputting the rotation speed signal from the sensor 30. And so on.

The control unit 21 includes a microcomputer, and when performing anti-skid control, the input signals VR, VFL, VFR, θ, and
Based on B, the rear wheel brake fluid pressure control is performed so that the braking force of the rear wheels is reduced as the difference between the road surfaces μ of the left and right wheels calculated from the road surface μ of the left and right wheels is increased. Adjustment.

FIG. 2 is a flow chart illustrating an antiskid control program executed by the microcomputer in the control unit 21 in the first embodiment. That is, in the control program of FIG. 2 that is repeatedly executed at predetermined intervals, first, step 100
Then, the wheel rotation speeds VR, VFL, VFR, the steering angle θ, and the brake actuation signal B are read from the above sensors, and in the next step 101, the actuation state of the brake is judged by the presence or absence of the brake actuation signal B. If it is determined in this step 101 that the vehicle is not being braked (when the brake switch 31 is OFF), it is out of the scope of the rear wheel brake hydraulic pressure control of the present embodiment, so that the control to be described later is performed in the next step 102. Flag used; FLAG1 and FLAG2 are reset (FL
AG1 = 0, FLAG2 = 0) and then control step
Continue to 103. On the other hand, if it is determined that the vehicle is braking, step 102 is skipped and the control immediately proceeds to step 103. Therefore, the states of FLAG1 and FLAG2 when the previous braking was performed are held.

In step 103, it is determined whether the wheel acceleration dVFL / dt of the left front wheel 10 calculated from the wheel rotation speed VFL is less than a predetermined value (threshold value) α, and a low μ that satisfies dVFL / dt <α.
If NO, set FALG1 in step 104 (FL
AG1 = 1). On the other hand, in the case of high μ such that dVFL / dt ≧ α, step 104 is skipped and control is immediately stepped.
Since the processing proceeds to step 105, the state of FLAG1 when the previous time is low μ is held. Similarly, in the next step 105, the wheel acceleration dVFR of the right front wheel 11 calculated from the wheel rotation speed VFR.
/ Dt is judged to be less than a predetermined value (threshold value) α, and dVFR
In case of low μ such that / dt <α, in step 106 FALG2
Is set (FLAG2 = 1). On the other hand, dVFR / dt ≧ α
In case of high μ, the control immediately proceeds to step 107 by skipping step 106, so that the state of FLAG2 when the previous time is low μ is held. In steps 103 to 106, the control unit 21 functions as road surface μ detecting means.

In step 107, FLAG1 and FL
It is determined whether or not the states of AG2 match, and if they do not match, the pressure reduction threshold correction amount Δλr is set to a predetermined value β in step 108 (Δλr = β). As a result, in the next step 110, the pressure reduction threshold value λr is corrected by adding the pressure reduction threshold value correction amount Δλr to change the pressure reduction threshold value λr (λr = λr + Δλr). On the other hand, step 10 above
If the states of FLAG1 and FLAG2 match in step 7, the pressure reduction threshold λr is set to 0 in the next step 109 (Δλr = 0), and the pressure reduction threshold λr calculated in the next step 110 is reached. Remains unchanged and retains its previous state. In the above steps 107 to 110, the control unit 21 functions as a braking fluid pressure control signal adjusting means.

In the next step 111, the above step 110 is performed.
The braking force is adjusted by controlling the wheel cylinder hydraulic pressure PR of the rear wheels by the normal ABS control using the depressurizing threshold value obtained in step 1. In this step 111, the control unit 21 and the actuator 22 control the braking hydraulic pressure. Functions as a means. As the ABS control, for example, the pressure increasing / decreasing control illustrated in FIG. 3 is used. In the pressure increasing / decreasing control, which of the pressure reducing zone, the pressure holding (holding) zone, and the pressure increasing zone corresponds to, Whether the rear wheel slip amount Sr exceeds the pressure reduction threshold value λr and whether the rear wheel acceleration is
Judgment is made based on whether or not dVR / dt exceeds the threshold value αr, and the wheel cylinder hydraulic pressure control (pressure increase, pressure retention, pressure reduction) in the corresponding zone is performed.

The operation of the above control will be described with reference to the timing chart of FIG. FIG. 4 shows the wheel rotation speeds (wheel speeds) VFL and VFR of the left and right front wheels 10 and 11 (in the illustrated example, the right front wheel speed VFR is shown by a solid line and the left front wheel speed VFL is shown by a dotted line), and the brake switch 31 is turned on / off. OFF state, wheel acceleration dVFL / dt of the left front wheel 10 and wheel acceleration dVFR / dt of the right front wheel 11 (in the illustrated example, the wheel acceleration speed of the right front wheel is shown by a solid line, and the wheel acceleration of the left front wheel is shown by a dotted line), FLAG1 and FLAG2, which represent the road surface condition (road surface μ) of the left and right front wheels, and the decompression threshold correction amount Δλr are respectively represented in time series.

In the operation example of FIG. 4, the wheel speeds VFL and VFR are maintained at the predetermined value V ₀ before the instant t1, and after the instant t1 when the brake switch 31 turns from ON to OFF, one of the front wheels (the left front wheel 11 In (), the wheel speed sharply decreases, and (actually, it is a deceleration because the wheel speed is in the decreasing direction) falls below the threshold value α after the instant t2. With this,
After the instant t2, FLAG1 is set, but the wheel acceleration dVFR / dt of the right front wheel 11 has not fallen below the threshold value α, so FLAG2 remains reset. Therefore, until the instant t3 when the wheel acceleration dVFR / dt of the right front wheel 11 falls below the threshold value α, FLAG1 and FLAG2
Therefore, it is determined that the road surface condition is a left-right split road surface having a large road surface μ difference between the left and right wheels by executing step 107 in FIG.
By executing step 8, the decompression threshold correction amount Δ
λr rises to a predetermined value β. With the increase of Δλr, the decompression threshold value λr calculated in step 110 is λr = λr ₀ + β, where λr ₀ is the normal time.

As a result, while the road surface is on the left and right split road surface, the rear wheel brake hydraulic pressure control for reducing the braking force of the rear wheels is performed in the ABS control executed based on the pressure reduction threshold value λr. As a result, the stability of the vehicle can be secured as desired.

On the other hand, in the control of FIG. 2, the moment when the wheel accelerations of the left and right front wheels both fall below the threshold value α.
After t3, it is determined that the road surface condition is not the left / right split road surface by executing step 107, and thus step 109 is executed and the decompression threshold value λr is returned to the normal value λr = λr _0. When the road surface condition is such that the road surface μ is uniform, the braking force on the rear wheel side can be made suitable for the road surface condition, and sufficient braking performance can be obtained.

FIG. 5 is a flow chart exemplifying a main part of an anti-skid control program executed by the microcomputer in the control unit 21 in the second embodiment. The second embodiment is suitable for cases where the brake fluid pressure increase / decrease control is not performed on all wheels (during slow braking, etc.), and an electric proportioning valve is used.
I am using 27. Therefore, in the entire system diagram (not shown), the control unit 21 inputs a control signal to the electric proportioning valve 27.

This electric proportioning valve 27
Has a characteristic as shown in FIG. 6, and in the range until the master cylinder pressure Pm reaches a predetermined value P ₀ corresponding to the split point SP, the master cylinder pressure Pm becomes 1: 1 as the master cylinder pressure Pm increases. The rear-wheel braking hydraulic pressure (brake hydraulic pressure) PR supplied to the rear-wheel wheel cylinders increases in a corresponding relationship, but the master cylinder pressure Pm increases in a range exceeding a predetermined value P ₀ corresponding to the split point SP. The ratio (gain) of the increase in the rear wheel braking hydraulic pressure PR corresponding to is decreased.
In addition, the characteristic of FIG. 6 is that the split point SP is changed to appropriately combine the portion where the increase rate of the rear wheel braking hydraulic pressure PR is large and the portion where the increase rate of the rear wheel braking hydraulic pressure PR is small to adjust the rear wheel braking hydraulic pressure PR to the desired characteristic. Can be applied (for details, see Japanese Patent Laid-Open No.
-133846).

In the control program of FIG. 5 which is repeatedly executed at predetermined intervals, first in step 120, the wheel rotation speeds VFL and VFR are read from the left and right front wheel rotation sensors 29 and 30, and in the next step 121, VFL and VFR are read. More left and right front wheel acceleration (actually deceleration) dVFL / dt and dV
Calculate FR / dt, and in the next step 122, change the acceleration deviation (actually deceleration deviation) ΔdVF / dt between the left and right front wheels by ΔdV
F / dt = | dVFR / dt-dVFL / dt |

In the next step 123, the split point SP is obtained by referring to the map of FIG. 7 by ΔdVF / dt. The map of FIG. 7 represents the ΔdVF / dt-SP characteristic curve, and when ΔdVF / dt changes, SP also changes accordingly. Then, in the next step 124, the control unit 21 outputs a control signal to the electric proportioning valve 27 so that the split point SP obtained as described above is reached.

In the second embodiment, based on the characteristic diagram of FIG. 6, as the acceleration deviation ΔdVF / dt of the left and right front wheels becomes larger, in other words, the left / right split road surface becomes larger as the road surface μ difference between the left and right wheels becomes larger, the split point becomes larger. Since SP approaches 0 and the braking fluid pressure control gain decreases to reduce the braking force, the stability of the vehicle is ensured. Also,
The smaller the acceleration deviation ΔdVF / dt of the left and right front wheels, in other words, the smaller the uniform μ road surface μ difference between the left and right wheels,
Since the split point SP is increased and the braking fluid pressure control gain is increased to enhance the braking force, the braking force on the rear wheel side can be increased as much as possible to realize a desired braking performance. Further, the braking hydraulic pressure control of the second embodiment is AB
The effect can be exhibited regardless of whether the S control is activated or not.

In each of the above embodiments, whether or not the road surface is a split μ road surface is determined by a flag showing the state of wheel acceleration of the left and right front wheels; a mismatch between FLAG1 and FLAG2, and an acceleration deviation between the left and right front wheels. Instead, the wheel rotational speed difference between the left and right front wheels may be used. Further, in each of the above-described embodiments, the reduction of the brake fluid pressure of the rear wheel is continued until the brake is turned off. However, it corresponds to the first front wheel pressure reduction during the predetermined period immediately after the start of the braking (for example, during the ABS operation). Only during the period). Furthermore, in each of the above-described embodiments, the three-channel ABS control for controlling the rear wheels in common is applied, but it may be applied to the four-channel ABS system.

[0026]

As described above, according to the braking force control apparatus of the present invention, when the hydraulic pressure control means variably controls the braking hydraulic pressure of at least the rear wheels, the braking hydraulic pressure control signal adjusting means controls the left and right wheels. Since a braking fluid pressure control signal is issued to the hydraulic pressure control means so that the braking force on the rear wheel side becomes smaller than that on the front wheel side when the road surface μ difference is larger, the appropriate braking force according to the road surface condition is applied. This is provided on the wheel side, so that sufficient vehicle stability is ensured in road conditions where the road surface μ is uneven, such as on the left and right split road surfaces. The desired braking performance can be realized by increasing the braking force of No. 1 as much as possible.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration of a first embodiment of a braking force control device of the present invention.

FIG. 2 is a flow chart illustrating an anti-skid control program executed by a microcomputer in the control unit 21 in the first embodiment.

FIG. 3 is implemented in the anti-skid control of the same example,
It is a figure which illustrates the control pattern of pressure increase / decrease control of wheel cylinder hydraulic pressure.

FIG. 4 is a timing chart for explaining the operation of the same example.

FIG. 5 is a flowchart illustrating a main part of an antiskid control program executed by a microcomputer in the control unit 21 in the second embodiment.

FIG. 6 shows an electric proportioning valve of the same example,
It is a characteristic view showing a master cylinder pressure-rear wheel braking hydraulic pressure characteristic in relation to a split point.

FIG. 7 is a diagram showing a left-right front wheel acceleration deviation-split point characteristic curve of the same example.

[Explanation of symbols]

10, 11 Front wheels 12, 13 Rear wheels 14 Steering wheel 15 Steering angle sensor 18 Brake pedal 20 Master cylinder 21 Control unit (road surface μ detection means, braking fluid pressure control signal adjustment means) 22 Actuator 23 to 26 Wheel cylinder 27 Proportioning valve (Brake hydraulic pressure control means) 28 Rear wheel rotation sensor 29 Left front wheel rotation sensor 30 Right front wheel rotation sensor 31 Brake switch

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

Claims (1)

[Claims] 1. A braking force control device comprising a braking fluid pressure control means for variably controlling a braking fluid pressure of at least rear wheels, a road surface μ detecting means for detecting a road surface μ of each of left and right wheels, and the road surface μ. Based on the detection information of the detection means, a braking fluid pressure control signal for instructing the hydraulic pressure control means to reduce the braking force of the rear wheels as the road surface condition in which the road surface μ difference between the left and right wheels is large is increased. A braking force control device comprising a control signal adjusting means.