JPH04135956A - Vehicle anti-skid brake - Google Patents

Abstract

PURPOSE:To stop a vehicle at a short brake distance when a detected steering angle is more than a predetermined value, by changing a control threshold value that vehicle wheel brake efficiency may become higher when a detected vehicle speed is high and lower when it is low. CONSTITUTION:An anti-skid brake is equipped with a control means 3 which conducts the increase/decrease control of vehicle wheel brake pressure by mans of a brake pressure adjusting means 2 according to a predetermined control threshold value on the basis of a vehicle wheel speed detected by means of a vehicle wheel speed detecting means 1, and a control threshold value changing means 5 which changes a control threshold value on the basis of a vehicle speed and a steering angle. The means 5, when a steering angle is more than a predetermined value, changes a threshold value that vehicle wheel brake efficiency may become higher when a vehicle speed is high, and lower when the vehicle speed is low. Thus, both brakability at the time of high speed travel and turning travelability at the time of low speed travel can be satisfied.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an anti-skid brake device for a vehicle.

(Prior Art) Anti-skid brake devices basically reduce wheel speed or deceleration to a predetermined deceleration (control threshold), or reduce wheel speed or target slip rate (control threshold). By controlling the increase or decrease of the braking pressure applied to the wheels (hereinafter simply referred to as ABS control as needed), it is possible to prevent the wheels from locking or skidding during braking, thereby improving directional stability. This allows the vehicle to stop within a short braking distance without losing its performance.

There are various proposals for controlling the braking pressure. For example, Japanese Patent Laid-Open No. 62-253560 proposes achieving both braking effectiveness and maneuverability by changing the target slip ratio according to the rotation angle of the steering wheel. There is a disclosure of technology that aims to achieve this. In other words, when the rotation angle of the steering wheel is large, the braking pressure is controlled with the goal of a low slip ratio in order to improve maneuverability, and when the rotation angle of the steering wheel is small, the braking pressure is controlled with the goal of a high slip ratio. This control increases the braking effect.

(Problem to be solved by the invention) By the way, when braking is applied to the wheels while driving at high speed, it is desirable to be able to stop the vehicle quickly with the shortest possible braking distance. When activated, this device itself takes into consideration the fact that the vehicle turns during braking, and controls the braking pressure to be increased or decreased to obtain a predetermined side drag force (reaction force from the road surface). , the vehicle is not necessarily provided with the highest possible braking effect.

On the other hand, when braking is applied to the wheels while driving at low speeds, turning is sometimes required to avoid obstacles in front, but the anti-skid brake device described above aims to achieve both braking performance and turning performance. Therefore, it is not possible to necessarily satisfy the required turning performance.

(Means for Solving the Problems) In order to solve such problems, the present invention makes it possible to change the threshold value of braking pressure control according to the vehicle speed.

That is, specific means for this purpose include wheel speed detection means for detecting the rotational speed of the wheels, braking pressure adjustment means for adjusting the braking pressure of the wheels, and a predetermined wheel speed detection means based on the wheel speed detected by the wheel speed detection means. A vehicle speed detection means for detecting vehicle speed; and a control means for controlling the braking pressure adjusting means to increase or decrease the braking pressure according to a control threshold of the vehicle; The vehicle is characterized by comprising a control threshold changing means for changing the control threshold so that the braking efficiency of the wheels is high when the vehicle speed is high, and the braking efficiency of the wheels is low when the vehicle speed is low. It is.

In this case, the control threshold value may be changed when the steering angle is equal to or greater than a predetermined value.

(Function) The anti-skid brake device described above is equipped with a means for changing the threshold value for braking pressure control according to the vehicle speed, so when the vehicle speed is high, the control threshold value is set to lock the wheels more than usual. By changing the pressure so that it is applied, that is, increasing the braking efficiency of the wheels, it is possible to stop the vehicle in a shorter braking distance than usual.

In this case, the wheels tend to lock up, making it impossible to secure a sufficient lateral force necessary for cornering. However, it is generally difficult to turn the vehicle while applying the brakes from a high-speed driving state, and it is also generally not useful for avoiding obstacles, for example. Therefore, even if the turning performance is somewhat sacrificed, sufficient braking force is obtained to stop the vehicle as quickly as possible.

On the other hand, when the vehicle speed is low, the control threshold value is changed in a direction in which the braking efficiency of the wheels becomes lower than that under normal control, that is, in a direction in which the locking becomes shallower. The turning performance of the vehicle can be improved by utilizing the state of the vehicle running at low speed.

If the control threshold value is changed in accordance with the vehicle speed when the steering angle is equal to or greater than a predetermined value, steering while applying braking from a high-speed driving state can be performed, for example, when there is an obstacle ahead. Therefore, it can be considered that the situation requires a quick stop, and in such a case, the vehicle can be stopped quickly with a short braking distance. On the other hand, steering while applying braking from a low-speed running state can be seen as a situation where cornering is required, and cornering performance in such a case can be ensured.

(Effects of the Invention) Therefore, according to the present invention, in the anti-skid brake system of a vehicle, the control threshold is changed so that the braking efficiency becomes high when driving at high speed, and the control threshold is changed so that the braking efficiency becomes low when driving at low speed. By making this change, it is possible to achieve both braking performance at high speeds and cornering performance at low speeds.

Further, in the case where the control threshold value is changed when the steering angle is equal to or greater than a predetermined value, the control threshold value can be changed by grasping the situation in which the vehicle is placed.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall structure of the embodiment.

That is, the anti-skid brake system for a vehicle includes a control means 3 for controlling the braking pressure of the wheels to be increased or decreased by the braking pressure adjusting means 2 according to a predetermined control threshold value based on the wheel speed detected by the wheel speed detecting means; The control threshold changing means 5 changes the control threshold based on the angle. Then, when the steering angle is greater than or equal to a predetermined value, the control threshold value changing means 5 changes the threshold value so that when the vehicle speed is high, the dynamic efficiency of the wheels is increased by 1jJ, and when the vehicle speed is low, the braking efficiency of the wheels is increased. The control threshold value is changed so that the value becomes lower.

More specifically, as shown in FIG. 2, the vehicle according to this embodiment has left and right front wheels.

12 is the driven wheel, left and right rear wheels 13.14 are the driving wheels,
The output torque of the engine] 5 is transmitted from the automatic transmission 16 to the propeller shaft] 7, the differential gear] 8, and the left and right drive shafts 19.
20 to the left and right rear wheels]3]4.

Each of the wheels 11 to 14 has discs 2 a to 24 a that rotate integrally with these wheels, and a caliper 2 that brakes the rotation of the discs 21 a to 24 a by receiving braking pressure.
Brake devices 21 to 24 are provided in which brake devices 1b to 24b are biased.

The brake control system for operating the brake devices 21 to 24 includes a brake pedal 26 operated by the driver.
a booster 27 that increases the stepping force of the booster 2;
A master cylinder 28 generates braking pressure in response to the force increased by 7. master cylinder 28
The two front wheel brake pressure supply lines extended from are the left front wheel brake pressure supply line 29a and the right front wheel brake pressure supply line 2.
9b, and are connected to calipers 21a and 22b of brake device 2122, respectively. The braking pressure supply line 29a for the left front wheel is provided with a first valve unit 30 consisting of an electromagnetic on-off valve 30a and an electromagnetic relief valve 30b, and the braking pressure supply line 29b for the right front wheel is provided with an electromagnetic on-off valve 30a and a solenoid relief valve 30b. A second valve unit 31 consisting of a valve 31a and an electromagnetic relief valve 31b is provided.

A rear wheel braking pressure supply line 32 extending from the master cylinder 28 is provided with a third valve unit 33 consisting of an electromagnetic on-off valve 33a and an electromagnetic relief valve 33b. And this rear wheel braking pressure supply line 3
2 is a braking pressure supply line 32a for the left rear wheel and a braking pressure supply line 3 for the right rear wheel on the downstream side of the third valve unit 33.
2b, and are connected to calipers 23a and 24b of brake devices 23 and 24, respectively.

That is, in this embodiment, the first channel adjusts the braking pressure of the brake device 21 of the left front wheel 1 by the operation of the first valve unit 30, and the second valve unit 3
1, the second channel adjusts the braking pressure of the brake device 22 of the right front wheel 12, and the third valve unit 33 adjusts the braking pressure of the brake devices 23, 24 of the left and right rear wheels 13, 14 by the operation of the third valve unit 33. and a third channel, and each of these channels is controlled independently of each other. The first to third valve units 30, 3], 33 constitute the braking pressure adjusting means 3.

The control unit 34 that controls the first to third channels receives a brake signal from a brake sensor 35 that detects whether or not the brake pedal 26 is being depressed and the speed at which the brake pedal 26 is depressed, and a brake signal from each of the wheels 11 to 14. Wheel speed signals from wheel speed sensors 37 to 40 as wheel speed detection means 1 for detecting the rotational speed of the vehicle, a vehicle speed signal from the vehicle speed sensor 41, and a steering angle signal from the steering angle sensor 42 are input, and the ABS Control is performed in parallel for each of the five channels.

That is, the control unit 34 controls each wheel 1
Based on the wheel speeds 1 to 14, the valve units 30, 31, and 33 control each wheel 11 to
It is equipped with a control means 3 for increasing and decreasing the braking pressure of 14, and a control threshold value changing means 5, and the on-off valves 30a, 31a, 33a and the relief valve 30b of each of the first to third valve units 30, 31°33. 31b and 33b are controlled to open and close by duty control. The brake oil discharged from the relief valves 30b, 31b, and 33b is as follows. It is returned to the reservoir tank 28a of the master cylinder 28 by a dosing line (not shown).

The control unit 34 will be specifically explained below.

The control means 3 includes a pseudo vehicle speed setting section and a control threshold setting section, and determines whether phase 0 (ABS non-control state) or phase I (
Braking pressure reduction during ABS control g), phase ■
(maintenance state after pressure reduction), phase ■ (sudden pressure state after pressure reduction and maintenance), and phase ■ (slow pressure increase state after sudden pressure increase), and set the braking pressure control signal corresponding to each phase to the first ~3rd valve unit) 30, 31, and 33.

The pseudo vehicle speed Vr is set as a convenient vehicle speed based on the wheel speed, since the vehicle speed cannot be accurately detected when the wheels 11 to 14 are slipping, and the four wheels 11= The highest wheel speed among the 14 wheel speeds is set as the pseudo vehicle speed Vr, while the amount of speed change is varied from 1, 2G・Δt at a high friction coefficient to 0.3G・Δt at a low friction coefficient depending on the friction coefficient of the road surface. It is set between , and is corrected as follows. Note that Δt is the sampling period of the control unit 34 (for example, 7 as).

Vr”-Vr-(1,2G ・Δt~0.3G-Δ
t) The control threshold is set independently for each channel, and in this example, the control threshold is used to determine the transition from Phase 0 (when ABS is not controlled) to Phase I (decompression). first wheel deceleration threshold G1 of phase I
A second wheel deceleration threshold G2 for determining the transition from phase ■ to phase ■ (holding), a first slip rate threshold SL for determining transition from phase ■ to phase ■ (sudden pressure), and phase ■
There is a wheel acceleration threshold value G3 for determining the transition from phase 2 to phase 2 (slow pressure increase), and a second slip rate inter-value S2 for determining the transition from phase 2 to phase 1. The above control threshold is
It is appropriately set according to the pseudo vehicle speed Vr and the friction coefficient of the road surface.

Regarding the wheel speed of the rear wheels 13 and 14, the smaller of the two wheel speeds is selected as the rear wheel speed. Further, the slip rate is calculated according to the following formula.

Slip ratio - (1 - Wheel speed ÷ Pseudo vehicle speed) x 100 In this case, as shown in Figure 3, the setting of the above control threshold in normal ABS control is to avoid excessively increasing the lateral drag coefficient μL of the wheels against the road surface. It is set so that the coefficient of friction μ between the road surface and the wheels can be increased without decreasing it, that is, so that characteristics in the range of Ss can be obtained. In other words, a high friction coefficient μ means high braking efficiency, and a high lateral drag coefficient μ only means good stability or steering performance when cornering.
As shown in FIG. 3, it is difficult to achieve both braking efficiency and cornering performance, and in the normal ABS control, the control threshold is set so as to achieve both of these as much as possible.

The deceleration and acceleration of the wheels are obtained by dividing the difference between the previous value and the current value of the wheel speed by the sampling period Δt, and converting the result into gravitational acceleration.

When detecting the friction coefficient of the road surface, when ABS control is not performed, the road surface is uniformly determined to be a high-friction road surface, and after ABS control is entered, the friction coefficient of the road surface is detected based on wheel deceleration and wheel acceleration. It is.

That is, when the wheel deceleration is large and the wheel acceleration is small, the road surface is determined to be low friction, when the wheel deceleration is small and the wheel acceleration is large, the road surface is determined to be high friction, and in other cases, the road surface is determined to be medium friction.

Therefore, the control means 3 normally performs control to increase or decrease the braking pressure as shown in FIG.

(2) That is, when the brake pedal 26 is depressed while the vehicle is running at a constant speed, the braking pressure generated by the master cylinder 28 increases, and the wheel speed decreases accordingly.

■ When the wheel deceleration becomes larger than the first wheel deceleration threshold G1, the system shifts to ABS control and selects Phase I;
The braking pressure is reduced according to a predetermined pressure reduction pattern.

(2) When the wheel deceleration becomes smaller than the second wheel deceleration threshold G2, phase (2) is selected and the braking pressure is maintained in a reduced pressure state.

■ When the slip rate decreases as the reduced pressure is maintained and exceeds the first slip rate threshold Sl, phase ■ is selected.
A sudden increase in braking pressure takes place.

(2) When the wheel acceleration decreases due to the sudden pressure increase and becomes equal to or less than the wheel acceleration threshold value 03, phase (2) is selected and the braking pressure is gradually increased.

(2) When the slip rate exceeds the second slip rate threshold S2 due to the above-mentioned gradual pressure increase, Phase I is selected.

As described above, the braking pressure is controlled to increase/decrease independently of each other for each of the first to third channels, thereby preventing each wheel from locking or skitting, without losing directional stability. This will allow the vehicle to stop within a short braking distance.

Next, the control threshold value changing means 5 will be explained.

The control threshold changing means 5 changes the control threshold according to the vehicle speed obtained by the vehicle speed sensor 41 and the steering angle obtained by the steering angle sensor 42, and when the steering angle θH is greater than or equal to a predetermined value θHo. , when the vehicle speed V is equal to or higher than the predetermined value v, the control threshold value is set such that the braking efficiency of the wheels increases (
When the vehicle speed V is less than a predetermined value v, the control threshold value is changed to a direction in which the braking efficiency of the wheels is lowered (shallower lock). Further, if the steering angle θH is less than the predetermined value θHo, normal ABS control is performed without changing the control threshold.

In this case, a steering angle of θHo or more is, for example, the steering angle when the steering wheel is operated when there is an obstacle in front of the vehicle, and a vehicle speed of 2 or more means, for example, that the vehicle is originally turning. This refers to a vehicle speed that is extremely fast. The control threshold value is changed so that the slip rate threshold value is increased and the slope of the pseudo vehicle speed Vr becomes larger on the negative side.

Specifically, when information is obtained that the steering angle θH is greater than or equal to a predetermined value of 680 and the vehicle speed V is greater than or equal to the predetermined value V, the steering speed shifts from phase 0 (when ABS is not controlled) to phase I (depressurization). First wheel deceleration threshold Gl for determination and phase I
Deceleration threshold G for determining transition from to phase ■ (holding)
2 is a first slip rate threshold S2 for determining the transition from phase ■ (maintaining reduced pressure) to phase ■ (sudden pressure), and a second slip rate for determining transition from phase ■ to phase I. The threshold value S2 is high, that is, the pseudo vehicle speed V
Also, the wheel acceleration threshold G3 for determining the transition from phase ■ to phase ■ (slow pressure increase) is set so that the depth increases as seen from r.
A predetermined correction is made to each threshold value so as to lower the threshold value.

If we explain the change in the control threshold value with reference to FIG. 3, this change will result in a slip ratio Sμ that provides the highest friction coefficient μ (maximum braking efficiency) or higher even if it sacrifices the lateral drag coefficient μL. This is done with the goal of increasing the slip rate (longer or deeper).

In addition, when the steering angle θH is greater than or equal to the predetermined value θHo, the vehicle speed V is equal to or greater than the predetermined value V.
When information is obtained that the slip ratio is less than the threshold value, the slip ratio threshold value is changed to a lower value and the slope of the pseudo vehicle speed Vr is reduced.

Specifically, the first slip rate threshold S1, the second slip rate threshold S2, the deceleration threshold G1, and the acceleration threshold G2 are corrected and changed in a manner opposite to the previous case. For example, the control threshold value is changed with the aim of achieving a slip ratio near SμL that allows a high lateral drag coefficient μL to be obtained even if the friction coefficient μ is sacrificed.

FIG. 5 is a flowchart showing the change control of the control threshold value,
A brake signal, each wheel speed signal, a vehicle speed signal, and a steering angle signal are input, and the steering angle θH is a predetermined value θH.

For sharpening that is larger than this, check the vehicle speed and set it to this vehicle speed V or a predetermined value V.
In this case, change the control threshold to deepen the lock and
BS control is performed (steps 81 to S4), and when the vehicle speed V is less than a predetermined value V, the control threshold is changed to a shallow lock value and AB control is also performed (step S5). On the other hand, the steering angle θ
When H is less than the predetermined value 080, normal ABS control is performed without changing the control threshold (step S6).

Therefore, for example, if there is a sudden jump from the side of the road to the front of the vehicle while driving at high speed, and the driver turns the steering wheel to the right or left without strongly pressing the brake pedal, the lock will be deeper than usual. By performing ABS control, the braking efficiency of the wheels is increased, and the vehicle can be stopped in a short braking distance. On the other hand, when driving at low speed and turning while stepping on the brake, ABS control with a shallower lock than usual is performed to obtain an appropriate amount of lateral drag on the wheels necessary for turning. It is possible to improve turning stability and steering performance.

Also, when the steering wheel is turned, normal ABS control is performed, and when it is not, in other words, when braking while driving straight, it is possible to consider deepening the lock. If the control threshold value is changed according to the vehicle speed as shown in FIG.

Further, in the above embodiment, when the steering angle θH is less than the predetermined value 080, normal ABS control is performed, or ABS control with deep locking may be performed.

Further, in a situation where the snow is compressed and solidified on a snowy road, ABS control may be performed to deepen the lock to improve braking efficiency.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention. Fig. 1 is a configuration diagram of a control system of the embodiment, Fig. 2 is an overall configuration diagram of an anti-skid brake device, and Fig. 3 is a slip ratio, thick friction coefficient, and lateral drag coefficient. FIG. 4 is a time chart of normal ABS control, and FIG. 5 is a flow chart showing control threshold change control. 1... Wheel speed detection means 2... Braking pressure adjustment means 3... Control means 5... Control threshold value changing means 41... Vehicle speed Sensor 42...The steering angle sensor exerts a force

Claims (2)

[Claims] (1) wheel speed detection means for detecting the rotational speed of the wheels; braking pressure adjustment means for adjusting the braking pressure of the wheels; and the braking pressure being set according to a predetermined control threshold based on the wheel speed detected by the wheel speed detection means. an anti-skid brake device for a vehicle, comprising: a control means for controlling the braking pressure adjusting means to increase or decrease the braking pressure; An anti-skid brake device for a vehicle, characterized in that the anti-skid brake device for a vehicle is provided with a control threshold value changing means for changing the control threshold value so that the braking efficiency of the wheels becomes high when the vehicle speed is low, and the braking efficiency of the wheels becomes low when the vehicle speed is low. (2) A steering angle detecting means for detecting a steering angle is provided, and the control threshold changing means changes the control threshold when the steering angle detected by the steering angle detecting means is equal to or greater than a predetermined value. The anti-skid brake device for a vehicle according to (1).