JP3199484B2 - Anti-lock brake device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-lock brake device for a vehicle, and more particularly to an anti-lock brake device adapted to be able to cope with braking when the vehicle is running at high speed on a normal road .

[0002]

2. Description of the Related Art Conventionally, in an anti-lock brake device for preventing locking of wheels during sudden braking of a vehicle such as an automobile, a pseudo vehicle speed is obtained based on a detected wheel speed. The target wheel speed which is a predetermined ratio is set. Then, when the detected wheel speed falls below the target wheel speed, pressure reduction control is started to start reducing the brake fluid pressure of the wheel cylinder (see, for example, Japanese Patent Application Laid-Open No. 60-261767).

[0003]

However, in such a conventional antilock brake device, the ratio of the target wheel speed to the pseudo vehicle speed at which the pressure reduction control is started is constant regardless of the magnitude of the vehicle speed. In other words, since the slip ratio is set to be always constant, in the braking operation over the entire region of the traveling speed of the vehicle,
There has been a problem that a stable behavior of the vehicle may not always be obtained. For example, if the slip ratio is set to be constant so as to be suitable for braking at a relatively low speed, the wheel slip amount increases during high-speed braking of the vehicle, so that the stability of the vehicle is impaired.

The reason for this is that the friction coefficient μ (referred to as road surface μ) between the tire and the road surface decreases as the vehicle speed increases, so that the brake hydraulic pressure (the lock hydraulic pressure and the lock hydraulic pressure) that matches the peak value of the road surface μ In other words, if the brake fluid pressure exceeds this, the wheels tend to lock).
When the lock hydraulic pressure decreases, the amount of overshoot of the brake hydraulic pressure with respect to the lock hydraulic pressure increases, and the slip amount of the wheel increases. This will be described with reference to the characteristic diagram of FIG. 5. _PW is a brake fluid pressure applied to the wheel cylinder, and braking is started at a, and the brake fluid pressure is increased. V is the pseudo vehicle speed, _VW is the wheel speed, V _S1 is the target wheel speed, and S _r1 is the target slip ratio of the wheel speed to the pseudo vehicle speed. Here, the solid line indicates a case where the target slip ratio S _r1 is set to be constant even at high speed, similarly to at low speed.

[0005] Thus, although the wheel speed V _W with the increase of the brake fluid pressure P _W is lowered, the target wheel speed V _S1 to start the pressure reduction is set to the pseudo vehicle speed remains constant ratio At high speed, the target wheel speed V _S1 is large. Therefore, even if the brake fluid pressure P _W exceeds the lock fluid pressure P _L , pressure increase is continued, and an overshoot A of the brake fluid pressure is generated between b and c. Then, when the wheel speed V _W reaches the target wheel speed V _S1 , the pressure reduction control is started.
Due to the influence of the overshoot A described above, the wheel slip amount C increases.

On the other hand, a recovery of the wheel speed V _W is expected due to the pressure reduction control. However, the recovery is delayed due to the influence of the large wheel slip amount C and the wheel inertia, and the excessive pressure reduction B of the brake fluid pressure P _W is performed. The excessive pressure reduction causes the shortage of the braking force to continue for a long time (d to e).

SUMMARY OF THE INVENTION An object of the present invention is to provide an anti-lock brake device which solves the conventional problems and can obtain a stable behavior of the vehicle with respect to braking in the entire traveling speed range of the vehicle on a normal road surface. It is in.

[0008]

In order to achieve the above object, the present invention provides a wheel speed detecting means for detecting a wheel speed of a wheel, and a pseudo vehicle body speed based on the wheel speed detected by the wheel speed detecting means. and the pseudo vehicle body speed calculating means for obtaining the corresponding pseudo vehicle body speed in a predetermined ratio, in anti-lock brake system comprising a vacuum threshold value setting means for setting a vacuum threshold value for starting the pressure reduction of the brake fluid pressure of the wheel cylinder, the And before the decompression threshold in normal road running
It causes different predetermined ratio corresponding to the serial pseudo vehicle speed for each specific speed region of the pseudo vehicle speed, the decompression
In the anti-lock brake device in which the threshold is set to be smaller at low speed than at high speed, the pressure-reducing threshold is
Furthermore, at the time of medium speed, a predetermined
Is set to be smaller than the decompression threshold value at the time of low speed set by the ratio .

[0009]

According to the present invention, the pressure reduction threshold value for starting the pressure reduction of the brake fluid pressure of the wheel cylinder is determined with respect to the pseudo vehicle speed.
The predetermined ratio is set differently for each specific speed region of the vehicle. Therefore, it is possible to control the slip amount of the wheel to be appropriate in accordance with the vehicle speed, and it is possible to always obtain a stable vehicle behavior with respect to braking in the entire traveling speed range of the vehicle on the normal road surface traveling.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In FIG. 1, wheel speed sensors 12 and 16 for generating wheel speed pulses in accordance with the rotation of a right front wheel 10 and a left front wheel 14, which are steering wheels, respectively, right rear wheels 20 and a left rear wheel, which are driving wheels. Wheel speed sensors 24 and 26 for generating wheel speed pulses in accordance with the rotation of the motor 22 are provided, and these sensors are connected to a control unit (hereinafter referred to as an ECU) 40 including a microcomputer. Also, as shown in FIG.
A wheel cylinder 50 disposed on each wheel,
A main fluid passage 54 communicates with a master cylinder 52 that generates brake fluid pressure when a driver depresses a brake pedal, and switches the brake fluid pressure of each wheel cylinder 50 in the middle of the main fluid passage 54. Actuator units 60 are interposed.

The actuator unit 60 has a switching control valve 62 for switching between increasing and decreasing the hydraulic pressure of the wheel cylinder 50, a reservoir 64 for storing the brake fluid when the wheel cylinder 50 is depressurized, and a reservoir 64. A pump 66 for returning the stored brake fluid to the main fluid passage 54.

The operation of this embodiment having the above configuration will be described below.

In the ECU 40, as shown in the control flowchart of FIG. 3, first, after initialization, in step S1, each of the wheel speed sensors 12, 16, 24,
26, the right front wheel 10, the left front wheel 14, the right rear wheel 2
The wheel speeds of 0 and the left rear wheel 22 are calculated, and the pseudo vehicle speed is calculated based on the maximum value.

Next, the process proceeds to step S2, where the calculation of the wheel acceleration / deceleration and the calculation of the wheel slip ratio are performed. Then, the process proceeds to step S3, in which a pressure reduction threshold value for starting the reduction of the brake fluid pressure of the wheel cylinder is obtained by a table lookup based on the above-described pseudo vehicle body speed. In this embodiment, the pressure reduction threshold is given as a speed value that gives a predetermined slip ratio to the pseudo vehicle speed, as illustrated in FIG. That is, when the vehicle speed is around 10 km / h, the decompression threshold is 8.5 km / h, and the slip ratio at this time is 8 km / h.
5%, the vehicle speed is 11 km / h around 50 km / h, the slip ratio is 22%, and the slip ratio is 17 km around 70 km / h.
%, Around 10 km / h, 10% and around 200 km / h, 8.5%. It is preferable to set the slip ratio to gradually decrease as the vehicle speed increases. However, according to the tuning with the actual vehicle, as shown by the solid line in FIG.
In the range of 70 km / h, a better result is obtained when the slip ratio is temporarily reduced instead of the linear characteristic (for example, the slip ratio is 9% at around 110 km / h and around 140 km / h). In FIG. 4, a two-dot chain line shows a case where the slip ratio is constant at 10%.

In step S3, when the pseudo vehicle speed is, for example, 70 km / h, 12 km / h is selected as the pressure reduction threshold, and the target wheel slip ratio at this time is determined as 17%.

Further, in step S4, step S
The wheel slip ratio obtained in step 2 and the target wheel slip ratio based on the pressure reduction threshold obtained in step S3 are compared. Here, when the wheel slip ratio is larger than the target value, the process proceeds to step S6, and brake hydraulic pressure reduction control is performed.
That is, the ECU 40 sends the actuator unit 60
A switching signal is sent to the switching control valve 62, and the master cylinder 52 and each wheel cylinder 50 are shut off, and each wheel cylinder 50 and the reservoir 64 are communicated.

If the wheel slip ratio is smaller than the target value in step S4, the process proceeds to step S5,
Here, it is determined whether or not the wheel acceleration / deceleration obtained in step S2 is higher than a predetermined holding level. If it is larger than the predetermined holding level, the hydraulic pressure of the wheel cylinder 50 is likely to be insufficient, and the routine proceeds to step S7, where the brake hydraulic pressure increase control is performed. In this case, the switching control valve 62 of the actuator unit 60 is driven so that the master cylinder 52 and each wheel cylinder 50 are in communication.

Conversely, if the wheel acceleration / deceleration is smaller than the predetermined holding level in step S5, step S8
The brake fluid pressure holding control is performed. In this case, the switching control valve 62 is driven to a position where the wheel cylinder 50 cuts off the communication with the master cylinder 52 and the reservoir 64, respectively.

After the control in any of steps S6, S7 or S8 is performed, the process proceeds to step S9, where the time is adjusted for 5 ms, and the process returns to step S1. In other words, the above-described control routine is executed every 5 ms.

The state of the above-mentioned control will be further described with reference to a characteristic diagram shown in FIG. 5 in comparison with a conventional example.

In this embodiment, the target wheel speed V _S2 at high speed and the target slip ratio S _r2 are set as the pressure reduction threshold for starting the deceleration control as shown by the broken line in FIG. Set smaller than at low speed. In this example, the pressure reduction is started at b 'and the brake fluid pressure does not overshoot with respect to the lock fluid pressure P _L , and the recovery time of the wheel speed is shortened as compared with the conventional art. It can be understood that the control cycle is short and the control is performed extremely smoothly. Therefore, it is possible to prevent the unstable behavior of the vehicle due to the increase in the slip amount and the shortage of the braking force due to the excessive pressure reduction from occurring for a long time.

[0023]

As is apparent from the above description, according to the present invention, the predetermined ratio of the pressure reduction threshold for starting the reduction of the brake fluid pressure to the pseudo vehicle speed is different for each specific speed range of the vehicle. Is set. Therefore, it is possible to control the slip amount of the wheel to be appropriate according to the vehicle speed, and it is possible to always obtain stable vehicle behavior with respect to braking in the entire traveling speed range of the vehicle.

1. Since the excessive deceleration of the wheels does not occur, the recovery time of the wheel speed due to the decrease in the brake fluid pressure is reduced, and the braking force shortage period can be prevented from continuing for a long time.

2. Since the peak value of the friction coefficient μ between the wheel and the road surface is determined depending on the vehicle body speed and the wheel slip amount, by setting the wheel slip amount according to the vehicle body speed, the friction coefficient between the wheel and the road surface is always determined. It can be kept near the peak value.

3. A stable braking force can be obtained in the entire traveling speed range of the wheels during normal road traveling .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a system outline of an antilock brake device according to the present invention.

FIG. 2 is a configuration diagram illustrating a brake hydraulic circuit according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating an example of a control procedure according to the embodiment.

FIG. 4 is a diagram showing a relationship between a pseudo vehicle speed and a pressure reduction threshold.

FIG. 5 is a diagram showing control characteristics.

[Explanation of symbols]

 10, 14, 20, 22 Wheels 12, 16, 24, 26 Wheel speed sensor 40 Control unit 50 Wheel cylinder 62 Switching control valve

Claims (2)

(57) [Claims] 1. A wheel speed detecting means for detecting a wheel speed of a wheel; a pseudo vehicle speed calculating means for obtaining a pseudo vehicle speed based on the wheel speed detected by the wheel speed detecting device; corresponds with a ratio, a anti-lock braking system which includes a vacuum threshold value setting means for setting a vacuum threshold value for starting the pressure reduction of the brake fluid pressure of the wheel cylinder, the previous vacuum threshold value in normal road travel
It causes different predetermined ratio corresponding to the serial pseudo vehicle speed for each specific speed region of the pseudo vehicle speed, the decompression
In an anti-lock brake device in which a threshold is set to be smaller at low speed than at high speed, the pressure-reducing threshold is
Furthermore, at the time of medium speed, a predetermined
The anti-lock brake device is set to be smaller than the pressure reduction threshold value at the time of low speed, which is set at the ratio of: 2. The anti-lock brake device according to claim 1, wherein the medium speed is at least a speed within a range of 70 km / h to 170 km / h.