JP3034302B2 - Anti-skid brake system for vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an anti-skid brake device for a vehicle that performs anti-skid control by controlling brake fluid pressure of wheels at the time of braking.

(Prior Art) Conventionally, as described in Japanese Patent Publication No. 61-226, for example, in order to prevent the wheels from being locked due to excessive brake fluid pressure during braking and impairing braking performance, etc. An anti-skid brake device is known which controls a brake fluid pressure of a wheel so that a slip rate of the wheel is set to a target slip rate separately set (usually a slip rate at which a maximum friction coefficient between the wheel and the road surface is obtained). .

Generally, the anti-skid brake device as described above is
A brake mechanism for generating a brake fluid pressure according to the depression force of a brake pedal, guiding the brake fluid pressure to brake means provided on each wheel to operate the brake means, and a brake fluid guided to the brake means for each wheel. Anti-skid control means for controlling the pressure by opening and closing a valve or the like.

By the way, a booster is used as necessary for the brake mechanism.
A hydraulic booster as described in JP-A 63-63 is known.

As a brake mechanism using such a hydraulic booster, the hydraulic booster generates an assist hydraulic pressure that is increased according to the pedaling force, and the assist hydraulic pressure is directly applied to the rear wheels as a brake hydraulic pressure, and the assist hydraulic pressure is increased. A configuration has been considered in which a brake fluid pressure generated by a master cylinder or the like is applied to the front wheels via a brake. With this configuration, compared to a case where the brake hydraulic pressure generated by the master cylinder or the like is applied to the front and rear wheels via the assist hydraulic pressure generated by the hydraulic booster,
The depression stroke of the brake pedal can be shortened, and the brake feeling is improved.

On the other hand, the behavior of the wheels differs according to the road surface friction coefficient (road surface μ). Therefore, in order to perform high-precision anti-skid control, the road surface μ is detected and based on the detected road surface μ, that is, while referring to the road surface μ, Control is needed.

However, it is generally difficult to know the road surface μ before or at the start of the anti-skid control. Usually, the anti-skid control is started assuming a general road surface μ, that is, medium to high μ.

(Problems to be Solved by the Invention) However, when the anti-skid control is started assuming the medium to high μ as described above, for example, when the vehicle tends to lock on a low μ road like an ice-burn-like road surface, Appropriate control cannot be performed at the beginning of the control, and a delay occurs in avoiding the locked state.

Therefore, in the anti-skid brake device, it is possible to detect that the road surface μ is low at the start of the control, especially when the road is a low μ road, and to start the anti-skid control in consideration of the low μ road. desired.

The object of the present invention, in view of the above circumstances, in the case of a low μ road,
An object of the present invention is to provide an anti-skid brake device that detects that the road surface μ is low at the start of control and starts anti-skid control in consideration of a low μ road.

(Means for Solving the Problems) In order to achieve the above object, an anti-skid brake device according to the present invention provides an assist hydraulic pressure generated in a hydraulic booster as a direct brake hydraulic pressure to act on a rear wheel, An anti-skid brake device for a vehicle, comprising: a brake mechanism for applying a brake hydraulic pressure generated via hydraulic pressure to front wheels; and anti-skid control means for controlling wheel slip by controlling the brake hydraulic pressure. The anti-skid control means calculates an estimated vehicle speed based on the maximum wheel speed of the vehicle or a wheel speed near the start of braking based on a deceleration corresponding to a road surface friction coefficient, and calculates the estimated vehicle speed and the wheel speed. The slip ratio of the wheel is obtained based on the deviation, and the brake fluid pressure is controlled in accordance with the slip ratio. Road surface friction coefficient determining means for determining that the road surface friction coefficient is low when the anti-skid control is entered before the front wheel is provided, and the rear wheel is positioned ahead of the front wheel based on the output of the road surface friction coefficient determining means. In this method, the brake fluid pressure is controlled by lowering the road surface friction coefficient for obtaining the estimated vehicle body speed for a predetermined time from when the anti-skid control is started.

(Operation) In a brake mechanism in which the assist hydraulic pressure generated in the hydraulic booster is directly applied to the rear wheels as brake hydraulic pressure and the brake hydraulic pressure generated through the assist hydraulic pressure is applied to the front wheels, first, a hydraulic mechanism is used. An assist fluid pressure, which is a brake fluid pressure for the rear wheels, is generated in the booster, and subsequently a brake fluid pressure for the front wheels is generated through the generated assist fluid pressure. In the region where the pressure is extremely low, first, the brake fluid pressure on the rear wheel first rises, then the brake fluid pressure on the front wheel rises with a delay, and when the brake fluid pressure rises to some extent thereafter, the difference between the two increases. It is almost negligible.

Therefore, when the wheels lock at the beginning of braking, that is, when the brake fluid pressure is extremely low, the rear wheels lock before the front wheels.

By the way, in a general brake mechanism, the distribution of the brake fluid pressure is set so that the front wheels are locked before the rear wheels, so when the brake mechanism having the above configuration is adopted, only when the brake fluid pressure is extremely low, The rear wheel locks first. Locking when the brake fluid pressure is extremely low means that the road surface is an ice-burn-like ultra-low μ road.

Therefore, when the rear wheels are locked first as described above, it is determined that the road surface μ is low, and control is performed based on the information that the road surface μ is low, so that a highly accurate Skid control becomes possible.

Since the anti-skid control based on the information on the low μ road is performed for a predetermined time, the anti-skid control on the low μ road is performed based on the information on the low μ road from the beginning of the control during the predetermined time during the predetermined time. Can control,
Quick lock avoidance control becomes possible.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, A is an automobile provided with the anti-skid brake device according to the present embodiment. In car A, left and right front wheels 1FL and 1FR are driven wheels, and left and right rear wheels 1RL and 1RR.
Are drive wheels. That is, after the generated torque of the engine 2 mounted on the front of the vehicle body passes through the automatic transmission 3, the propeller shaft 4, and the differential gear 5, the left driving shaft
The power is transmitted to the rear left wheel 1RL via 6L, while being transmitted to the rear right wheel 1RR via the right drive shaft 6R.

Configuration of Automatic Transmission The automatic transmission 3 includes a torque converter 11 and a multi-stage transmission gear mechanism 12. The shift is performed by changing the combination of the excitation and the demagnetization of the plurality of solenoids 13a incorporated in the hydraulic circuit of the transmission gear mechanism 12. Further, the torque converter 11 has a hydraulically operated lock-up clutch 11A. By switching between excitation and demagnetization of a solenoid 13b incorporated in a hydraulic circuit of the clutch, engagement and engagement of the lock-up clutch 11A are performed. Release is performed.

The solenoids 13a and 13b are controlled by a control unit UAT for an automatic transmission. This control unit UAT
As is known, the shift characteristic and the lock-up characteristic are stored in advance, and the shift control and the lock-up control are performed based on these characteristics. For this control, the control unit UA
T is a throttle opening signal from a throttle opening sensor 61 for detecting the opening of a throttle valve 43 connected to an accelerator pedal 42 provided in the intake passage 41, and a vehicle speed signal from a vehicle speed sensor 62 for detecting the vehicle speed. (In the embodiment, a rotation speed signal of the propeller shaft 4).

Brake fluid pressure adjusting mechanism configuration Each wheel 1FR to 1RR is provided with a brake 21FR to 21RR. Brake fluid pressure is supplied to calipers (brake cylinders) 22FR to 22RR of the brakes 21FR to 21RR via pipes 23FR to 23RR.

The structure for supplying the brake fluid pressure to each of the brakes 21FR to 21RR is as follows.

First, when the brake pedal 25 is depressed, an assist hydraulic pressure is generated by boosting the depressing force to the hydraulic booster 26, which is a booster. Subsequently, the brake hydraulic pressure is transmitted to the tandem type master cylinder 27 via the assist hydraulic pressure. Is generated.

The assist hydraulic pressure generated in the hydraulic booth 26 is directly applied to the brake pipe 23 for the rear wheel as brake hydraulic pressure.
R, 23RL and 23RR are transmitted to the left and right rear wheel brakes 21RL and 21RR, respectively. The brake fluid pressure generated in the master cylinder 27 is supplied to the right front wheel brake pipe 23FR through the right front wheel brake pipe 23FR connected to the first discharge port 27a.
Brake for the left front wheel is transmitted to the 21FR and is connected to the second outlet 27b through the brake pipe 23FR for the front left wheel.
It is transmitted to 21FL.

The hydraulic booster 26 is supplied with hydraulic fluid pressure from a pump 29 via a pipe 28, and excess hydraulic fluid is returned to a reservoir tank 31 via a return pipe 30.

The brake pipes 23FL and 23FR pass through the brake pipes 23FL and 23FR, respectively, and the left and right front wheel brakes 21FL and 21FR.
Pressure adjusting means 30F for adjusting the brake fluid pressure supplied to the
L, 30FR are provided, and both brake pipes 23R are provided on the brake pipe 23R, which is a common part of the brake pipes 23RL, 23RR.
Hydraulic pressure adjusting means 30R for commonly adjusting brake hydraulic pressure supplied to left and right rear wheel brakes 21RL, 21RR through L, 23RR
Are arranged.

Each of the above-mentioned fluid pressure adjusting means 30FL, 30FR, 30R is disposed on a solenoid on-off valve 31FL, 31FR, 31R, and a relief pipe 32FL, 32FR, 32R connected to the downstream side of the valve 31FL, 31FR, 31R, respectively. And the electromagnetic on-off valves 33FL, 33FR, and 33R.

Each of the above-mentioned hydraulic pressure adjusting means 30FL, 30FR, 30R is controlled by a control unit UAB which is an anti-skid control means. That is, when the anti-skid control is not performed, the valves 33FL, 33FR, and 33R are closed as illustrated, and the valves 31FL and 33FL are closed.
When the brake pedal 25 is depressed, the brake fluid pressure is supplied to the brakes 21FR, 21FL, 21RL, 21RR via the hydraulic booster 26 and the master cylinder 27.

As will be described later, when the slip ratio of each wheel 1FL, 1FR, 1RL, 1RR with respect to the road surface is increased and the anti-skid control is performed, the duty is controlled by the duty control of each valve 31FL, 33FL, 31FR, 33FR, 31R, 33R. The hydraulic pressure is increased, reduced, and maintained. More specifically, each valve 31FL, 33FL, 31
When FR, 33FR, 31R, 33R is closed, the brake fluid pressure is maintained, and when the valves 31FL, 31FR, 31R are opened, and when the valves 33FL, 33FR, 33R are closed, the pressure is increased, and the valves 31FL, 31FR, The pressure is reduced when the valve 31R is closed and the valves 33FL, 33FR, 33R are open.

As shown in FIG. 3, the hydraulic booster 26 includes a hydraulic chamber 80. The hydraulic chamber 80 has an inflow port 80a through which the hydraulic fluid delivered from the pipe 28 by the pump 29 flows. An outflow port 80b is formed to allow the assist hydraulic pressure to flow out to the pipe 23R as brake hydraulic pressure, and a brake pedal rod 25a that moves in the direction of arrow A is inserted by the brake pedal 25, and a cylindrical pressing rod is inserted into the rod 25a. The body 82 is slidably fitted in the direction of arrow A.
Further, an opening / closing body 84 having a communication hole 84a is disposed in the inflow port 80a, and both ends of a lever 86 are rotatable with respect to the opening / closing body 84 and the rod 25a, respectively, and at least one end is in a vertical direction in the drawing. The lever 86 is connected to be slightly displaceable, and the lever 86 is rotatably supported at the intermediate point 86a by the protruding portion 82a of the pressing body 82, and the intermediate point 86a forms the rotation fulcrum of the lever 86. The master cylinder 27 has the same structure as a conventionally known tandem-type master cylinder, and includes first and second pistons 27c and 27d inside.

In the hydraulic booster 26 and the master cylinder 27 configured as described above, first, when the brake pedal 25 is depressed, the rod 25a moves to the left in the drawing, and accordingly, the lever 86 rotates counterclockwise about the fulcrum 86a. The opening / closing member 84 moves to the right side in the drawing, and the communication hole 84 is set in the inflow port 80a.
The hydraulic pressure is supplied from the pipe 28 into the hydraulic pressure chamber 80, and the hydraulic pressure pushes the pressing body 82 to the left in the drawing, whereby the fulcrum 86a of the lever 86 is pulled to the left in the drawing. The opening / closing body 84 is also moved to the left side in the figure,
Thereby, the inflow port 80a is closed.

In the hydraulic booster 26, an assist hydraulic pressure boosted in accordance with the depression stroke (depression force) of the brake pedal 25 is generated in the hydraulic pressure chamber 80 while repeating the above-described operation. The brake fluid directly acts on the rear wheels 1RL, 1RR from the outflow port 80b via the pipe 23R, that is, acts on the brakes 21RL, 21RR of the rear wheels.

Further, in the master cylinder 27, a brake hydraulic pressure is generated by a brake pedal depression force transmitted through the brake pedal rod 25a and a pressing force by the assist hydraulic pressure transmitted through the pressing body 82, The brake fluid pressure acts on the left and right front wheels 1FL and 1FR via the pipes 23FL and 23FR as described above, that is, acts on the front wheel brakes 21FL and 21FR.

As for the brake fluid pressure, the dimensions and the like of the pressing body 82 are appropriately set so that the brake fluid pressure acting on the rear wheels and the brake fluid pressure acting on the front wheels become the same pressure.
However, as described above, the brake fluid pressure for the rear wheels immediately rises in response to the depression of the brake pedal 25 because the assist fluid pressure generated by the hydraulic booster 26 is directly used, but the brake fluid pressure for the front wheels is increased. Is generated using the above-mentioned assist hydraulic pressure, the initial state of the brake hydraulic pressure, that is, in an extremely low pressure region where the brake hydraulic pressure is, for example, about 10 atm, is as shown in FIG. In addition, it rises later than the brake fluid pressure for the rear wheels.

A brake mechanism is constituted by the brake pedal 25, the hydraulic booster 26, the master cylinder 27, the brake pipes 23FL to 23RR, and the brakes 21FL to 21RR.

Configuration of Control Unit Signals from wheel speed sensors 64 to 67 for detecting wheel speeds are input to a control unit UAB, which is an anti-skid control unit that controls the hydraulic pressure adjusting units 30FL, 30FR, 30R.

The control unit UAB has an input interface for receiving signals from the above sensors, a CPU, a ROM, and a RAM.
And a drive circuit for driving the valves 31FL, 33FL, 31FR, 33FR, 31R, 33R.The ROM has a control program and various maps required for anti-skid control. The RAM is provided with various memories necessary for executing the control.

Next, the contents of the anti-skid control by the control unit UAB will be described with reference to FIG.

FIG. 2 is a diagram showing an example of changes in the wheel speed and brake fluid pressure of the wheels subjected to the anti-skid control.

As shown in the drawing, and began braking depress the brake pedal at the time point t ₁ now. Then, it is assumed that the brake fluid pressure is increased by depressing the pedal, and accordingly, the wheel speed starts to decrease, and the vehicle tends to lock. Then, the control unit UAB determines that tendency to lock the change of the wheel speed of the wheel, immediately starts the vacuum it is determined that the vacuum phase is t ₂ time. The determination of the locking tendency is appropriately made, for example, when the wheel deceleration becomes equal to or more than a predetermined value or when the slip ratio becomes larger than a predetermined threshold.

The slip rate may be any value as long as it is a numerical value indicating the degree of slip of the wheel. The deceleration according to the friction coefficient μ of the road surface, for example, 1.2 g (high μ) from the maximum wheel speed of the four wheel speeds or the vehicle speed near the start of braking (wheel speed) as the estimated vehicle speed. ) To 0.3 g (low μ).

Then, the pressure was reduced the brake fluid pressure, when the increase in the slip ratio has stopped, i.e. the wheel deceleration is determined to hold phase at t ₃ when becomes zero hold the brake fluid pressure, wheel speed by the retention increased to increase the brake fluid pressure slip ratio is determined at or wheel acceleration decreases to the threshold value is a pressure increase phase at t ₄ when equal to or greater than a predetermined value (first predetermined amount surge pressure then slow pressure increase ), and the same way or wheel deceleration slip rate exceeds the threshold value or less under reduced pressure at time t _5, which becomes a predetermined value or more, and held at t ₆ the increase of the slip ratio is stopped, the slip When the rate drops to the threshold value or the wheel acceleration exceeds a specified value
boosts at t _7, such vacuum holding the control to converge the slip rate to the target slip rate while repeating the pressure increase of the cycle.

Road Surface μ Determination In the anti-skid control, when the rear wheel enters the anti-skid control before the front wheel, it is determined that the road surface friction coefficient (road surface μ) is low, and information indicating that the road surface μ is low is obtained. The control unit UAB is configured to control the brake fluid pressure on the basis of the control.

As described above, the anti-skid control is started when it is determined that the wheel speed has decreased and the vehicle tends to lock. Therefore, the fact that the rear wheels have entered the anti-skid control before the front wheels means that the rear wheels have a tendency to lock before the front wheels.

However, as described above, in the brake mechanism in which the assist hydraulic pressure generated in the hydraulic booster is directly applied to the rear wheels as the brake hydraulic pressure and the brake hydraulic pressure generated through the assist hydraulic pressure is applied to the front wheels, When the brake fluid pressure rises, that is, in a region where the brake fluid pressure is extremely low, the brake fluid pressure on the rear wheel first increases first, and then the brake fluid pressure on the front wheel increases with a delay.

By the way, the brake mechanism in the present embodiment is basically set so that the front wheel locks earlier than the rear wheel, similarly to a general brake mechanism. Therefore, the situation where the rear wheel locks first is determined by the above-mentioned brake mechanism. Due to the construction, it occurs only in the region where the brake fluid pressure on the rear wheel side rises first, that is, only when the brake fluid pressure is extremely low. Locking when the brake fluid pressure is extremely low means that the road surface is an ice-burn-like low μ road. Therefore, when the rear wheel is locked first as described above, it is determined that the road surface μ is low.

The information that the road surface μ determined as described above is low is immediately reflected in the anti-skid control.For example, as described above, the deceleration for obtaining the estimated vehicle speed is a value corresponding to the low μ, for example, 0.3 g Or the amount of increase or decrease of the brake fluid pressure is appropriately changed.

Note that the determination of the road surface μ is performed by the road surface μ determination means including the control unit UAB.

By determining that the road surface μ is low when the rear wheel locks first as described above, it is possible to reliably detect that the road is a low μ road, and that the detection is performed at the start of locking, that is, anti-skid control. Low μ because it is done at the start
In the case of a road, anti-skid control can be performed based on the information that the road is a low μ road from the beginning of the control, and control for avoiding lock can be performed quickly.

FIG. 5 is a flowchart showing an example of the procedure for determining the road surface μ.

In this example, first, each wheel speed is input in S1, and it is determined whether or not the anti-skid control is being performed in S2, and if it is under control, it is determined in S3 whether or not the rear wheel has first entered the anti-skid control. ,
If the rear wheels have entered anti-skid control first, it is determined that the road surface μ is low, and the road surface μ is set to be low for a predetermined time from the start of the anti-skid control in S4, and the predetermined time depends on the low road surface μ. Control.

(Effect of the Invention) As described above, the anti-skid brake device according to the present invention causes the assist hydraulic pressure generated in the hydraulic booster to act directly on the rear wheel as the brake hydraulic pressure and generates the assist hydraulic pressure via the assist hydraulic pressure. A brake mechanism that uses the brake fluid pressure applied to the front wheels is adopted, and an estimated vehicle speed is obtained from the maximum wheel speed of the vehicle or a wheel speed near the start of braking based on a deceleration according to a road surface friction coefficient. The slip rate of the wheel is obtained based on the deviation between the wheel speed and the wheel speed, the brake fluid pressure is controlled according to the slip rate, and it is determined that the road surface μ is low when the rear wheel is locked first. Since the road surface friction coefficient for obtaining the estimated vehicle body speed for a predetermined time is reduced, the anti-skid control corresponding to the low μ road can be performed during the predetermined time, and the rapid Lock avoidance control can be performed.

[Brief description of the drawings]

1 is an overall configuration diagram showing an embodiment of a vehicle anti-skid brake device according to the present invention, FIG. 2 is a diagram showing a basic example of anti-skid control, and FIG. 3 is a partially cutaway view showing a hydraulic booster. FIG. 4 is a diagram showing the rise of brake fluid pressure, and FIG. 5 is a flowchart showing an example of road surface μ determination. 1FL, 1FR, 1RL, 1RR ... wheel UAB ... anti-skid control means UAB ... road surface μ judgment means

Claims (1)

(57) [Claims] 1. A brake mechanism for causing an assist hydraulic pressure generated in a hydraulic booster to directly act on a rear wheel as a brake hydraulic pressure and for applying a brake hydraulic pressure generated via the assist hydraulic pressure to a front wheel, and the brake An anti-skid brake device for a vehicle, comprising: anti-skid control means for controlling wheel slip by controlling a hydraulic pressure, wherein the anti-skid control means includes a maximum wheel speed of the vehicle or a value near the start of braking. An estimated vehicle speed is obtained from the wheel speed based on the deceleration corresponding to the road surface friction coefficient, a wheel slip ratio is obtained based on a deviation between the estimated vehicle speed and the wheel speed, and the brake fluid pressure is determined according to the slip ratio. Road friction coefficient is determined to be low when the rear wheels enter the anti-skid control before the front wheels. A coefficient determining means for determining the estimated vehicle body speed for a predetermined time from when the rear wheel enters the anti-skid control before the front wheel based on an output of the road friction coefficient determining means, and lowering the road surface friction coefficient. An anti-skid brake device for a vehicle, which controls the brake fluid pressure.