Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-02-22
2001-05-22
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S113100, C303S116200, C303S003000, C303S015000
Reexamination Certificate
active
06234588
ABSTRACT:
CROSS REFERENCE TO THE RELATED APPLICATION
The present application is based upon and claims the benefit of priority of the prior Japanese patent application No. Hei 10-38679 filed on Feb. 20, 1998, the content of which is incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a brake system so called “brake by wire system” in which the state of a braking operation by a driver is converted to an electric signal for inducing a wheel braking force.
2. Description of Related Art
The brake by wire system is well known. In this system, an electric signal representing the state of brake pedal operation by a driver, i.e., the amount of brake pedal stroke or brake pedal depression pressure, is generated. A wheel braking force can be induced based on the electric signal. The conventional brake by wire system employs, as examples for inducing a wheel braking force, a method of directly pressing a brake pad against a brake disk separately in each wheel by using ultrasonic motors or a method of producing a wheel cylinder pressure by using a two-position valve and a pump, as disclosed in Japanese patent Laid-open publication No. Hei 9-188242, under the title of “brake fluid pressure control apparatus”.
SUMMARY OF THE INVENTION
It is an object of the present invention, in a hydraulic type brake system for generating wheel cylinder pressure by using brake fluid, to provide a brake by wire type system that is simple in its construction but has a better characteristic and features on the control for producing braking force. To achieve this object, a linear differential pressure control valve and a pump are provided for generating and controlling a wheel cylinder pressure. Thus, a completely or partly shut-off control and a flow through control for the brake fluid in the hydraulic conduit in accordance with a commanded current can be flexibly and accurately accomplished. As a result, an adequate control responsive to the braking requirement by a driver can be easily realized.
It is an another object of the invention to provide a brake by wire type system in which the detected brake fluid pressure difference between a pair of the left and right wheel cylinders for a vehicle can be easily compensated by means of mechanical or electronic adjustment. To achieve this object, in addition to first and second linear differential pressure control valves respectively disposed in each of the two conduits branched out from the brake fluid conduit communicating to a reservoir, a third linear differential pressure control valve is provided at the brake fluid conduit between the reservoir and the branched out portion of the conduit. While the first and second linear differential pressure control valves control each pressure of the left and right wheel cylinder, independently, the third linear differential pressure control valve controls commonly both pressures of the left and right wheel cylinders. To prevent from imposing unnecessary yawing moment to a vehicle, it is inevitable to keep the braking force difference between the left and right wheels at a normal braking operation at the minimum. The third linear differential pressure control valve serves to keep the difference between a pair of wheel cylinder pressures to a level less than the predetermined amount to be required for the prevention of the unnecessary yawing moment of the vehicle.
It is a further object of the invention to provide a fail safe hybrid construction incorporating not only a brake by wire function but also a mechanical brake function directly responsive to the brake pedal operation by a driver. According to the above described invention, even if a malfunction takes place in the brake by wire function, the mechanical brake function for the front wheels or the front and rear wheels will serve. Furthermore, to facilitate the hybrid function, a servo function directly responsive to driver's brake pedal depression is provided under the help of the pump driven by a signal separately generated at the time of the brake pedal depression, even if an electronically control unit for the brake by wire function does not work. For this purpose, the brake system of this invention has a brake fluid conduit extending from a portion between a two-position valve and the third linear differential pressure control valve to a servo room of a master cylinder.
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Denso Corporation
Kramer Devon
Oberleitner Robert J.
Pillsbury & Winthrop LLP
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