Fluid-pressure and analogous brake systems – Speed-controlled – Wheel speed sensor and braking pressure sensor
Patent
1996-06-20
1998-09-15
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Wheel speed sensor and braking pressure sensor
303DIG11, 3031151, 3031191, 303DIG4, 3031135, B60T 826, B60T 834, B60T 842
Patent
active
058069399
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to vehicle broken and more particularly, related to a hydraulic brake system with electronic anti-lock control, including a pedal-operated multi-circuit braking pressure generator, electrically operable hydraulic valves which are inserted in pressure fluid conduits, and low-pressure accumulators which take up the pressure fluid that is withdrawn from the wheel brakes in the periods of braking pressure reduction and return the pressure fluid to the braking pressure generator after brake release.
BACKGROUND OF THE INVENTION
A brake system of this type is disclosed in German published patent application No. 31 09 372. In this prior art brake system, a hydraulic pump for the return delivery of the pressure fluid withdrawn from the wheel brakes in the periods of braking pressure reduction is eliminated to reduce manufacturing costs. Instead, the pressure fluid withdrawn by way of outlet valves is received in a low-pressure accumulator. After brake release, the pressure fluid flows back into the brake circuits. There are two brake circuits with a diagonal brake circuit arrangement. Each brake circuit has a common inlet and outlet valve assembly and, in addition, another electrically commutatable inlet valve which is inserted in the pressure fluid conduit leading to the rear-wheel brake. The inlet valve is shiftable to its closed condition in response to the anti-lock control, on the one hand, and load-responsively, on the other hand.
The control quality in this known system is rather poor. When any one of the four vehicle wheels starts to lock, both valves leading to the rear wheels are switched to close simultaneously. The objective is that at least one rear wheel remains stable. As soon as a second wheel shows a locking tendency, the braking pressure in one of the two circuits is decreased and subsequently kept constant in addition to continuously shutting off the rear wheels. Assuming that road conditions remain constant, this switched condition will not be changed until the termination of the braking operation. For safety reasons, the hydraulic pressure in only one of the two diagonal brake circuits is reduced at the same time. This type of control is rather primitive because it temporarily admits locking of the wheels or the application of too low braking forces to the wheels.
An object of the present invention is to provide a brake system with anti-lock control which, equally, does not require a hydraulic energy source and whose function, nevertheless, is not inferior to the function of a "complete" ABS in the majority of situations, above all in critical situations. The objective is that driving stability is maintained and fail-safety of the braking function is not limited.
It has been found that this object can be achieved by the present invention which involves the provision of two hydraulically isolated brake circuits in a diagonal brake circuit arrangement and one low-pressure accumulator per brake circuit which has two separate inlets for the connection of the rear wheel and the front wheel and is designed so that the pressure fluid flow from the front-wheel brake is shut off when a predetermined filling ratio or residual volume in the accumulator is reached.
The present invention is based on the recognition that, principally, the duration of a braking operation with anti-lock control is limited to a short time period and that the condition actually critical with respect to driving dynamics is present only at the commencement of braking. The driving condition becomes less critical with the growing duration of braking and at a reduced speed of the vehicle. When braking during cornering, the translational force required decreases as the driving speed is reduced. Steering maneuvers should be possible above all shortly after braking with anti-lock control is initiated to avoid an obstacle early.
Also, in the majority of cases, conditions change shortly after the commencement of a controlled braking operation so that a maximum deceleration is not necessary
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English Translation of International Preliminary Examination Report for Application PCT/EP94/03300.
Search Report of the German Patent Office for Application No. P4334838.6.
Buschmann Gunther
Feigel Hans-Jorg
Butler Douglas C.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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