Fluid-pressure and analogous brake systems – Speed-controlled – Braking pressure demand or braking force desire
Reexamination Certificate
1999-01-21
2001-02-20
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Braking pressure demand or braking force desire
C303S113400, C303S176000, C303S167000
Reexamination Certificate
active
06189986
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a braking force control apparatus, and more particularly to a braking force control apparatus which generates a braking force larger than that generated during a normal control, when a braking operation that satisfies a predetermined execution condition is performed.
DESCRIPTION OF THE RELATED ART
As disclosed in Japanese Laid-Open Patent Application No. 4-121260, there is known a braking force control apparatus which generates an increased braking force larger than a braking force during a normal control, when it is detected that an emergency braking operation is performed on an automotive vehicle. The conventional apparatus of the above publication is provided with a brake booster which generates a boosted pressure in response to a braking operation force Fp on a brake pedal of the vehicle, or the boosted pressure being equal to the braking operation force Fp multiplied by a given magnification factor. The boosted pressure is delivered from the brake booster to a master cylinder. The master cylinder generates a master cylinder pressure Pmc in response to the boosted pressure delivered from the brake booster, and the master cylinder pressure Pmc is proportional to the braking operation force Fp.
Further, the conventional apparatus of the above publication is provided with a high-pressure source having a pump which generates a brake-assist pressure. The high-pressure source generates a brake-assist pressure in accordance with a drive signal supplied by a control circuit. When a speed of the braking operation of the brake pedal exceeds a given speed, it is determined that an emergency braking operation is performed by a vehicle operator, and the control circuit supplies a drive signal to the high-pressure source, the drive signal requesting a maximum brake-assist pressure to be generated by the high-pressure source. Both the brake-assist pressure generated by the high-pressure source and the master cylinder pressure Pmc generated by the master cylinder are supplied to a switching valve, and the switching valve delivers a larger one of the brake-assist pressure and the master cylinder Pmc to wheel cylinders of the vehicle.
In the conventional apparatus of the above publication, when the speed of the braking operation is below the given speed, the master cylinder pressure Pmc, which is proportional to the braking operation force Fp, is supplied to the wheel cylinders. Hereinafter, the control that is performed to generate the braking force by the braking operation under such a condition will be called a normal control. On the other hand, when the speed of the braking operation is above the given speed, the brake-assist pressure, which is generated by the high-pressure source, is supplied to the wheel cylinders. Hereinafter, the control that is performed to generate an increased braking force larger than the braking force generated during the normal control, under such a condition, will be called a brake-assist control.
In the conventional apparatus of the above publication, when the braking operation of the brake pedal is performed at a normal speed, the braking force is controlled to the magnitude that is proportional to the braking operation force Fp, and, when the emergency braking operation of the brake pedal is performed, the braking force is quickly increased to be larger than the braking force during the normal control.
In the conventional apparatus of the above publication, the braking force acting on the vehicle after the brake-assist control is started is speedily increased to a maximum braking force at the time of a maximum braking operation force acting on the brake pedal. Generally, a deceleration that the vehicle occupant senses in response to the maximum braking operation force acting on the brake pedal when the vehicle is running at a high speed is smaller than that when the vehicle is running at a low speed. If the brake-assist control is performed for both during the high-speed running and during the low-speed running in the same manner, the ride comfort as a result of the execution of the brake-assist control during the low-speed running is likely to become degraded.
In the conventional apparatus of the above publication, when a braking operation that satisfies a predetermined execution condition is performed, the brake-assist control is always performed in the same manner regardless of whether the vehicle speed is high or low. Therefore, when the brake-assist control is performed during the low-speed running, the conventional apparatus can speedily increase the braking force that acts on the vehicle after the brake-assist control is started. However, the conventional apparatus produces an unnecessarily large deceleration after the brake-assist control is started in such a case, and the ride comfort will be degraded.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide an improved braking force control apparatus in which the above-described problems are eliminated.
Another, more specific object of the present invention is to provide a braking force control apparatus which changes a rate of increase of a braking force accompanied by a start of a brake-assist control, in accordance with a vehicle speed, preventing an unnecessarily large deceleration from being produced by the brake-assist control during a low-speed running of the vehicle.
In order to achieve the above-mentioned objects, one aspect of the present invention is to provide a braking force control apparatus which includes a means for performing a normal control to generate a braking force on a vehicle in accordance with a braking operation force, and a means for performing a brake-assist control to generate an increased braking force larger than the braking force generated during the normal control, characterized in that the apparatus comprises a braking force increasing characteristic change means for changing a rate of increase of the braking force accompanied by a start of the brake-assist control, in accordance with a vehicle speed.
According to the above-described braking force control apparatus of the present invention, when a predetermined braking operation is performed, the execution of the normal control is stopped and the execution of brake-assist control is started. After the start of the execution of the brake-assist control, the braking force on the vehicle is increased. The vehicle occupant senses a large deceleration if the braking force on the vehicle is too quickly increased. The sensed deceleration of the vehicle occupant depends upon the vehicle speed. The lower the vehicle speed, the larger the sensed deceleration. As the braking force control apparatus of the present invention is provided with the braking force increasing characteristic change means, it is possible to change the rate of increase of the braking force produced after the start of the brake-assist control, in accordance with the vehicle speed. Hence, the braking force control apparatus of the present invention is effective in achieving the functions of the brake-assist control in an appropriate manner for all the ranges of the vehicle speed without degrading the ride comfort of the vehicle occupant.
In a preferred embodiment of the present invention, the braking force control apparatus may be constructed such that the braking force increasing characteristic change means decreases the rate of increase of the braking force in accordance with a decrease in the vehicle speed.
According to the above-described braking force control apparatus of the present invention, the rate of increase of the braking force produced after the start of the brake-assist control will decrease as the vehicle speed becomes lower. Hence, it is possible to prevent an unnecessarily large deceleration from being produced after the start of the brake-assist control during a low-speed running of the vehicle.
In another preferred embodiment of the present invention, the braking force control apparatus may be constructed such that the braking force increasing
Hashimoto Yoshiyuki
Shimizu Satoshi
Kramer Devon
Oberleitner Robert J.
Toyota Jidosha & Kabushiki Kaisha
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