JPH0948333A - Braking force control device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the occurrence of a wheel lock, secure the high stability of a vehicle even on a road surface having a low friction coefficient, accelerate the ABS control cycle, and shorten the braking distance by employing the ABS control for the distribution control of the braking force proportional to the dynamic load of each wheel. SOLUTION: When a control unit 7 outputs the power value corresponding to the distributed braking force of each wheel, a solenoid valve 8 feeds the air pressure proportional to the current value to an air booster 10. The oil pressure proportional to the air pressure is fed to a wheel cylinder 11, and braking force is generated on each wheel. The control unit 7 determines the distributed braking force in response to the total braking force based on the brake action quantity detected by a pedal stroke sensor 1 and the dynamic load of each wheel based on the detected values of a longitudinal acceleration sensor 6 and lateral acceleration sensors 4, 5. The slip ratio of each wheel is calculated based on the revolving speed of each wheel detected by a tire rotation sensor 3 and the estimated vehicle body speed during braking, and the distributed braking force is controlled in response to it.

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 for a vehicle.

[0002]

2. Description of the Related Art In order to ensure good braking characteristics of a vehicle,
The total braking force required for the vehicle is calculated, the longitudinal load and the lateral acceleration are added to correct the shared load ratio of each wheel, and the total braking force is distributed as a braking force to each wheel according to the shared load ratio. Something is known (JP-A-6-1611)
No. 7).

[0003]

However, in this conventional example, on a road surface having a high coefficient of friction, wheel locking does not occur, and the ability of each wheel can be maximized while maintaining a stable vehicle posture. On a road surface having a low coefficient of friction such as a snow road, there is no function to prevent the wheel lock, so there is a possibility that the stability of the vehicle may be impaired during sudden braking.

The present invention aims to solve such problems.

[0005]

In the present invention, as shown in FIG. 8, a brake actuator a for individually generating a braking force for each wheel, a means b for detecting a static load on each wheel,
A means c for detecting longitudinal acceleration and lateral acceleration of the vehicle body,
Means d for calculating the dynamic load of each wheel from these detected values
A means e for detecting the amount of brake operation, a means f for obtaining the total braking force required for braking the vehicle from the amount of brake operation, and a means f for calculating the total braking force and the distribution ratio according to the dynamic load of each wheel for each wheel. The means g for calculating the distributed braking force, the means h for detecting the rotational speed of each wheel, the means i for calculating the vehicle body speed from the average rotational speed of the wheels, and the vehicle body speed during braking from this vehicle body speed and the longitudinal acceleration. Means j for estimating, means k for calculating the slip ratio for each wheel from the rotational speed of each wheel and the estimated vehicle speed, and zero for the command value of the distributed braking force when the slip ratio is greater than the target value for each wheel. When the slip ratio is smaller than the target value, a means m for outputting a command value corresponding to the distributed braking force to the brake actuator, respectively.

[0006]

According to the present invention, the total braking force required for braking the vehicle is obtained from the brake operation amount, and when the dynamic load of each wheel is calculated, the distributed braking force of each wheel and the dynamic braking force are calculated. It is determined from the distribution rate according to the dynamic load. During braking, the slip ratio of each wheel is monitored, and when the slip ratio is smaller than the target value, the command value corresponding to the distributed braking force of each wheel is output, and when the slip ratio exceeds the target value, the command value of the distributed braking force. Becomes zero. In other words, since the distributed braking force acting on each wheel is turned on and off at the timing obtained by the ABS (antilock brake system), the occurrence of wheel lock is avoided, and even on a road surface with a low friction coefficient,
It is possible to ensure high stability of the vehicle.

[0007]

FIG. 1 is a block diagram of a brake braking force control system showing an embodiment of the present invention, and FIG. 2 is a block diagram of a control system showing one wheel. , ABS (Anti-lock brake system)
It is configured to control. Each wheel is provided with a wheel cylinder 11 that receives hydraulic pressure to generate a braking force, and these cylinders 11 are connected to the air booster 10 by hydraulic lines. The air booster 10 supplies a hydraulic pressure proportional to the input air pressure to the wheel cylinder 11, and is connected to the air reservoir 20 via a solenoid valve 8 for piping. Then, when the control unit 7 described later outputs a current value corresponding to the distributed braking force of each wheel, the solenoid valve 8 supplies an air pressure proportional to the current value to the air booster 10.

As the detection means necessary for control, a load sensor 2 for detecting the load on each wheel, a longitudinal acceleration sensor 6 for detecting the longitudinal acceleration of the vehicle, and lateral accelerations on the front and rear axes are respectively detected. There are provided lateral acceleration sensors 4, 5, a pedal stroke sensor 1 for detecting a pedal operation amount of a foot brake, and a tire rotation sensor 3 for detecting a rotation speed of each wheel. For fail-safe, a brake air pressure sensor 9 that detects the air pressure downstream of the solenoid valve 8 in the brake pipe as the braking force generated by the wheel cylinder 11 is added.

The control unit 7, which constitutes a control system together with these detecting means, has an input processing circuit 12 for various sensor signals and a dynamic load calculation for obtaining a dynamic load of each wheel from each wheel load and longitudinal acceleration and lateral acceleration. Circuit 13,
An estimated vehicle speed calculation circuit 14 for calculating an estimated vehicle speed during braking from the average rotational speed of the front wheels (non-driving wheels) and the longitudinal acceleration;
For each wheel, a slip ratio calculation circuit 15 for calculating the slip ratio from the wheel speed and the estimated vehicle speed, a brake air pressure calculation circuit 16 and a brake air pressure output circuit 17 are provided.

The brake air pressure calculation circuit 14 stores a data map as shown in FIG. 3, sums the detected loads of the wheels as the vehicle weight, and calculates the brake air pressure Pb as the required vehicle braking force from the vehicle weight and the brake operation amount. The data map is searched to calculate the brake air pressure Pbi of each wheel (the distributed braking force of the wheel number i) that distributes the brake air pressure Pb according to the dynamic load of each wheel. Further, a target value (for example, 0.2) of the slip ratio of each wheel is set, the calculated value of the slip ratio is compared with the target value for each wheel, and when the slip ratio is larger than the target value, zero is set as the brake air pressure,
When the slip ratio is smaller than the target value, Pbi is commanded as the brake air pressure. The brake air pressure output circuit calculates a current value corresponding to the command value of the brake air pressure, outputs the current value to the solenoid valve 8 as a brake actuator, and the wheel cylinder 11 via the air booster 10.
(Brake means) is activated.

FIGS. 3 and 4 are flow charts for explaining the control contents of the control unit 7, which are started by turning on the engine key, perform a predetermined initialization in step 1, and then repeatedly perform subsequent slips in a predetermined cycle. To do. In step 2, the brake stroke amount Ba from the pedal stroke sensor 1, the wheel speeds Vw1 to Vw4 from the tire rotation sensors 3, and the longitudinal acceleration G from the longitudinal acceleration sensor.
The lateral accelerations Gyf and Gyr are read from the lateral acceleration sensor. Then, in step 3, the wheel speed Vw1
When Vw4 is zero and the longitudinal acceleration Gx is zero, it is determined that the vehicle is stopped, and in step 4, the detection values Ws1 to Ws4 of the load sensors of the wheels are stored.

In step 3, the wheel speeds Vw1 to Vw
4 or at least one of the longitudinal acceleration Gx is not zero, the brake operation amount Ba is set to the set value θ in step 5.
In comparison with (the pedal angle at which the brake actually starts to take into consideration the mechanical play of the brake pedal), when Ba <θ, it is determined that the vehicle is in a running state, and in step 6, zero is commanded as the brake air pressure. In step 7, the average wheel speed (Vw1 + Vw2) / 2 of the front wheels is stored as the vehicle speed.

When Ba ≦ θ, it is determined that the vehicle is in a braking state, and the process proceeds from step 5 to step 8 where the static load Ws1 of each wheel is
~ Stored value of Ws4 and longitudinal acceleration Gx and lateral acceleration Gy
The dynamic loads W1 to W4 of each wheel are calculated from the detected values of f and Gyr, and in step 9, the static loads Ws1 to Ws4 of each wheel are calculated.
The stored value of Wvh is summed up and the total value W
By searching the map data from vh and the brake operation amount Ba, the required total braking force is the brake air pressure P.
Find b. Then, in step 10, the distribution ratio based on the dynamic loads W1 to W4 of each wheel is calculated, and in step 11, the distribution braking force of each wheel is determined from each distribution ratio and the total braking force Pb to obtain these braking forces. Calculate the brake air pressure Pbi to the air booster required for.

Then, in step 12, the vehicle speed (Vw1 +
The vehicle speed Va during braking is estimated from the stored value of Vw2) / 2 immediately before the braking and the detected value of the longitudinal acceleration Gx, and in step 13, the estimated vehicle speed Va and the detected values of the wheel speeds Vw1 to Vw4 of each wheel are estimated. Calculate the slip ratio λi. Then, in step 14, the slip ratio λi is set to the target value λ ₀ for each wheel,
If the slip ratio λi is smaller than the target value λ ₀ , the calculated value Pbi is calculated as the brake air pressure in step 15.
When the slip ratio λi is larger than the target value λ ₀ , zero is output as the brake air pressure in step 16.

After that, when the estimated vehicle speed Va becomes zero or less in step 17, the brake operation amount Ba is calculated in step 18.
Is compared with the set value θ. If it is larger than the set value θ, the calculated value Pbi is output as the brake air pressure in step 19, and if it is less than the set value θ, zero is output as the brake air pressure in step 20.

With such a configuration, distributed braking force according to the dynamic load of each wheel is obtained, the slip ratio of each wheel is monitored during braking, and when the slip ratio is smaller than the target value, the distribution of each wheel is distributed. A command value corresponding to the braking force is output, and when the slip ratio exceeds the target value, the command value of the distributed braking force becomes zero. In other words, since the distributed braking force acting on each wheel is turned on and off at the timing obtained by the ABS (anti-lock braking system), the occurrence of wheel lock is avoided, and the high stability of the vehicle is maintained even on the road surface with a low friction coefficient. Can be secured.

By the way, if the conventional ABS control is adopted in a vehicle in which wheel load varies greatly, the brake air pressure is constant regardless of the wheel load, and therefore the wheel with a light load has a large slip ratio as shown in FIG. The slip rate tends to be higher than the slip rate, the wheel speed recovery is delayed when the brake is released, and the control cycle of pressurization and depressurization of the brake air pressure becomes long, but the ABS control of each wheel is distributed as in this embodiment. When the braking force is used, the slip ratios of the wheels are averaged as shown in FIG. 7 and the wheel speed with a light load is quickly returned when the brake is released, so that the braking distance can be shortened.

The vehicle weight Wvh and the brake operation amount B
Although the required brake air pressure Pb is obtained from the data map search process from a, the brake corresponding to the change in the vehicle weight Wvh is determined by determining the reference value and the correction coefficient of the brake characteristic without depending on the data map search process. The air pressure Pb may be calculated. Also, this control system is
It is not limited to OH type brakes, but can be widely applied to full air type and hydraulic type brakes.

[0019]

In summary, according to the present invention, since the ABS control is adopted for the distribution control of the braking force proportional to the dynamic load of each wheel, the occurrence of wheel lock is avoided and even on the road surface having a low friction coefficient. , High stability of the vehicle can be secured. In addition, the control cycle of pressurization and depressurization of the ABS control is accelerated, and the braking distance can be shortened.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram of a control system.

FIG. 3 is a brake air pressure characteristic diagram of a data map.

FIG. 4 is a flowchart illustrating control contents of a control unit.

FIG. 5 is a flowchart illustrating control contents of a control unit.

FIG. 6 is a characteristic diagram of a slip ratio in conventional ABS control.

FIG. 7 is a characteristic diagram of a slip ratio in this embodiment.

FIG. 8 is a configuration diagram of the present invention.

[Explanation of symbols]

 1 pedal stroke sensor 2 wheel load sensor 3 tire rotation sensor 4 front axle lateral acceleration sensor 5 rear axle lateral acceleration sensor 6 longitudinal acceleration sensor 7 control unit 8 solenoid valve 9 brake air pressure sensor 10 air booster 11 wheel cylinder

Claims (1)

[Claims] 1. A brake actuator for individually generating a braking force for each wheel, a means for detecting a static load on each wheel, a means for detecting longitudinal acceleration and lateral acceleration of a vehicle body, and each wheel based on these detected values. The means for calculating the dynamic load, the means for detecting the amount of brake operation, the means for obtaining the total braking force required for braking the vehicle from the amount of brake operation, the total braking force and the dynamic load for each wheel A means for calculating the distributed braking force of each wheel from the distribution ratio, a means for detecting the rotation speed of each wheel, a means for calculating the vehicle body speed from the average rotation speed of the wheels, and a means for calculating the vehicle body speed from the vehicle body speed and the longitudinal acceleration. A means for estimating the vehicle body speed, a means for calculating the slip rate for each wheel from the rotational speed of each wheel and the estimated vehicle body speed, and zero for the command value of the distributed braking force when the slip rate is greater than the target value for each wheel. To A braking force control device for a vehicle, comprising: means for outputting a command value corresponding to the distributed braking force to the brake actuator when the slip ratio is smaller than the target value.