Fluid-pressure and analogous brake systems – Multiple systems – Fluid pressure and electric
Reexamination Certificate
1999-12-03
2001-06-19
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Multiple systems
Fluid pressure and electric
Reexamination Certificate
active
06247762
ABSTRACT:
This application claims priority under 35 U.S.C. Sec. 119 to No. 10-361898 filed in Japan on Dec. 4, 1998, 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 braking system for applying braking force to wheels of a vehicle, and more particularly to the braking system having a pressure generator for generating a hydraulic braking pressure to wheel brake cylinders in response to operation of a brake pedal, and a stroke simulator for providing a dummy braking load to the brake pedal.
2. Description of the Related Arts
With respect to a vehicle braking system, an apparatus called “brake by wire” has been noted recently. The brake by wire apparatus is provided with a pressure generator for generating a hydraulic braking pressure independent of a conventional master cylinder, and adapted to control a braking pressure control valve device in response to operation of the brake pedal to supply the hydraulic braking pressure from the pressure generator to the wheel brake cylinders, and supply the hydraulic braking pressure output from the master cylinder to a stroke simulator, as shown in Japanese Patent Laid-open Publication No. 2-49943, for example. The publication discloses a braking apparatus having a servo pressure generating device, wherein a device associated with the master cylinder for providing a brake feeling, which corresponds to the stroke simulator, is connected to a brake passage, which is opened or closed by an electromagnetic valve device. The valve device is turned on when a servo braking system is normal, and turned off when it is failed. The braking apparatus has a pressure control valve with a plurality of positions to be selected.
According to the braking apparatus as disclosed in that publication, if the pressure control valve or the like is failed, for example, it is necessary for a vehicle driver to apply a relatively large force to the brake pedal to obtain a sufficient braking force. In order to solve this problem, it can be proposed to provide a conventional booster such as a hydraulic booster or vacuum booster. In this case, however, if either one of those boosters is installed in that braking apparatus, the hydraulic braking pressure applied to the stroke simulator will be large even in the normal state. In order to overcome this problem, therefore, it is necessary to install a spring with a large spring constant in the stroke simulator. As a result, the stroke simulator is made large in size, and high in cost.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a vehicle braking system which applies a hydraulic braking pressure generated by a pressure generator to a wheel brake cylinder, through a pressure control valve device controlled in response to operation of a brake pedal, and which includes a stroke simulator for allowing the brake pedal to advance in response to the amount of operation of the brake pedal, wherein a sufficient braking force can be obtained with an ordinary depressing force applied to the brake pedal, even if the pressure generator, pressure control valve device and the like are abnormal, and wherein it can be made small in size and low in cost.
In accomplish the above and other objects, a vehicle braking system is provided with a pressure generator for generating a hydraulic braking pressure, a wheel brake cylinder which is operatively mounted on each wheel of the vehicle for applying a braking force to the wheel with the hydraulic braking pressure supplied by the pressure generator, a pressure control valve device which is disposed in a passage for communicating the pressure generator with the wheel brake cylinder, and which controls the hydraulic braking pressure supplied to the wheel brake cylinder, and an electronic controller for controlling the pressure control valve device at least in response to an amount of operation of a brake pedal. A master cylinder is provided for communicating with the wheel brake cylinder and supplying the hydraulic braking pressure into the wheel brake cylinder in response to operation of the brake pedal, when at least one of the pressure generator, the pressure control valve device and the electronic controller is abnormal. A stroke simulator is connected to the master cylinder for allowing the brake pedal to advance in response to the amount of operation of the brake pedal. And, a servo device is provided for assisting the master cylinder to operate when at least one of the pressure generator, the pressure control valve device and the electronic controller is abnormal.
Preferably, the servo device is a hydraulic servo device for supplying the hydraulic braking pressure into the master cylinder in response to operation of the brake pedal. This braking system may further include a valve device which prohibits the operation of the hydraulic servo device when all of the pressure generator, the pressure control valve device and the electronic controller are normal, and which allows the operation of the hydraulic servo device when at least one of the pressure generator, the pressure control valve device and the electronic controller is abnormal.
The servo device may be a vacuum servo device for assisting the master cylinder to operate in response to operation of the brake pedal, with negative pressure used for activating the vacuum servo device as a power source. This braking system may further include a valve device which prohibits the operation of the vacuum servo device when all of the pressure generator, the pressure control valve device and the electronic controller are normal, and which allows the operation of the vacuum servo device when at least one of the pressure generator, the pressure control valve device and the electronic controller is abnormal.
REFERENCES:
patent: 5567021 (1996-10-01), Gaillard
patent: 5951116 (1999-09-01), Nagasaka
patent: 6027182 (2000-02-01), Nagasaka
patent: 6058705 (2000-05-01), Schunck
patent: 2-99061 (1990-08-01), None
patent: 2-49943 (1990-10-01), None
Hamada Toshiaki
Inden Masahiro
Kusano Akihito
Toda Hiroshi
Aisin Seiki Kabushiki Kaisha
Bartz C. T.
Burns Doane , Swecker, Mathis LLP
Schwartz Christopher P.
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