Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1998-11-19
2001-12-11
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S119100, C303S163000, C303S169000, C303S113100
Reexamination Certificate
active
06328390
ABSTRACT:
This application claims priority under 35 U.S.C. Sec. 119 to No.
9-337908
filed in Japan on Nov. 21, 1997, the entire content of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brake control system for a vehicle, which is adapted to increase the braking force applied to wheels automatically, if necessary, when a brake pedal is depressed.
2. Description of the Related Arts
According to a known brake-assist control system, in the case where a vehicle driver depressed a brake pedal rapidly or deeply when driving the vehicle, the braking force applied to each wheel is increased so as to assist the driver to apply the braking force to the wheel. The conventional brake-assist control system is usually adapted to control a boosting power of a vacuum booster. For example, a Japanese Patent Laid-open Publication No.8-230634 discloses a system for performing a brake-assist control by means of a hydraulic pressure pump for use in an anti-skid control system. In that publication, a method and apparatus for controlling the anti-lock control system or a traction control system are proposed to save the power of the vacuum booster fully or partially. Also, in that publication, a dual hydraulic pressure circuit system is employed between a master cylinder and wheel brake cylinders, and a return pump is disposed in a passage in each hydraulic pressure circuit, while other structure is not clear, due to its insufficient description.
According to the brake system which divides the hydraulic pressure circuit between the master cylinder and the wheel brake cylinder into two hydraulic pressure circuits, and disposes the pressure pump in each circuit to be used as an auxiliary pressure source, the hydraulic braking pressure in each circuit is varied, because the characteristic of one of the pumps is different from that of the other pump. Therefore, especially in the diagonal hydraulic pressure circuit (X-circuit), the braking forces applied to the left and right wheels are different from each other, so that the stability of the vehicle might be deteriorated. In order to solve this problem, an input valve and an output valve as disclosed in that publication may be controlled with respect to each wheel. However, those valves are to be controlled so as to reduce the variation of the auxiliary pressure in addition to the control of the input valves and output valves used in the anti-lock control, so that noise caused in controlling the operation of those valves shall not be neglected.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a brake control system which is arranged to divide a hydraulic pressure circuit between a master cylinder and wheel brake cylinders into two hydraulic pressure circuits, and dispose a hydraulic pressure pump in each hydraulic pressure circuit, and which is adapted to increase the braking force automatically, if necessary, by controlling as small number of valves as possible, so as to equalize the hydraulic braking pressure fed from the hydraulic pressure pump into each hydraulic pressure circuit, when a brake pedal is depressed.
In accomplishing the above and other objects, a brake control system for a vehicle includes wheel brake cylinders operatively mounted on front and rear wheels of the vehicle, respectively, a master cylinder for pressurizing brake fluid to supply braking pressure to the wheel brake cylinders in response to depression of a brake pedal, a pair of main passages for communicating the master cylinder with the wheel brake cylinders to provide a dual hydraulic pressure circuit system. A pair of first valve devices are provided for opening or closing the main passages, respectively. A pair of pressure pumps are disposed between the first valve devices and the wheel brake cylinders in the main passages, respectively. The pressure pump is adapted to introduce from an inlet thereof the brake fluid and pressurize the brake fluid to supply the hydraulic braking pressure to the wheel brake cylinders. A pair of auxiliary passages are provided for communicating each inlet of the pump with the master cylinder. A pair of second valve devices are provided for opening or closing the auxiliary passages, respectively. Wheel speed sensors are provided for detecting wheel speeds of the wheels, and a slip rate calculation device is provided for calculating slip rates of the wheels on the basis of the wheel speeds detected by the wheel speed sensors. And, a controller is adapted to control at least one of the first valve device and the second valve device to equalize the slip rates of a pair of wheels, with the wheel brake cylinders operatively mounted thereon and disposed in different hydraulic pressure circuits, and placed at the left side and right side of the vehicle, respectively, when a difference between the slip rates of the wheels placed at the left side and right side of the vehicle exceeds a predetermined value.
The controller may be adapted to calculate a deceleration difference between a desired vehicle deceleration and an estimated vehicle deceleration calculated on the basis of the wheel speeds detected by the wheel speed sensors, and set a first duty of the first valve device and a second duty of the second valve device in accordance with the deceleration difference. Accordingly, by controlling the second duty of the second valve device, with the first valve device placed in its closed position, or controlling the first duty of the first valve device, with the second valve device placed in its closed position, the hydraulic braking pressure in the wheel brake cylinder of each of the wheels is controlled equalize the slip rates of the wheels. The present system is especially effective to the front left and right wheels in the diagonal hydraulic pressure circuit system.
The brake control system may further include a modulator which is disposed between the master cylinder and the wheel brake cylinders in each of the hydraulic pressure circuits for modulating the hydraulic braking pressure in each of the wheel brake cylinders in accordance with a pressure mode selected from at least a pressure increasing mode and a pressure decreasing mode. Each inlet of the pressure pump is connected with a passage between the modulator and the first valve device in each hydraulic pressure circuit.
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Fukami Masanobu
Itoh Takayuki
Tozu Kenji
Yokoyama Satoshi
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Oberleitner Robert J.
Williams Thomas J.
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