Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1999-03-18
2000-08-08
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031151, 3031154, 3031134, 3031132, B60T 842
Patent
active
060990872
DESCRIPTION:
BRIEF SUMMARY
This invention relates to hydraulic braking systems for vehicles of the kind in which braking is provided under the control of electronic means by assessing a driver's braking demand electronically and by the use of an electrically controlled actuator, a brake pressure is applied to a wheel brake in proportion to the driver's demand.
In such a system it is preferable that a conventional supply of hydrostatic braking pressure is available to be switched into a brake line to actuate the brake if or when the electronic means fail or malfunction.
In one known hydraulic braking system, disclosed in DE-A1-3 424 912, braking is provided under the control of electronic means by assessing a driver's braking demand electronically and by the use of a first and second electrically controlled actuator associated with a respective first and second wheel brake. In the event of failure, brake pedal force can be "pushed-through" from the master cylinder to the wheel brakes. The pressure across the two brakes cannot, however, be balanced and is dependent upon the individual pressures applied by each actuator.
We are also aware of WO-A-94/25322 in which braking is provided by the use of an electrically controlled pressure source, wherein the braking system comprises a pedal operated master cylinder which is connected to a first brake through a single electrically controlled pressure source, and an isolator valve which permits fluid connection between the first front wheel brake and a second front wheel brake. In the event of failure, the isolator (or cutoff) valve is opened to allow pressure from the master cylinder to be applied to both wheel brakes. The master cylinder requires the provision of a separate brake line independent of the pressure source to provide the connection to the brakes.
According to our invention we provide an hydraulic braking system for vehicles in which braking is provided under the control of electronic means by assessing a driver's braking demand electronically and by the use of at least a first and a second electrically controlled actuator, said braking system comprising a pedal-operated hydrostatic master cylinder connected to a first front wheel brake for a first wheel through said first electrically controlled actuator and said second electrically controlled actuator is connected to a second brake for a different wheel, characterised by further comprising an isolator valve which permits fluid communication between said first front wheel brake and said second front wheel brake, and in that both first and second actuators comprise a piston working in a bore to pressurise fluid in a pressure space in advance of the bore, and in addition the first electrically controlled actuator only incorporates a normally open isolator valve which is closed during normal brake operation but which is otherwise open to define a first flow path through the first actuator and to the brake upon failure of the electronic means, and by said isolator valve being open in the event of failure of the electronic means to define a second flow path through which fluid from the first flow path can pass to apply the second front wheel brake independently of the operation of the second actuator and by flow through the pressure space in the second actuator.
Normally, when the electronic control means is operational the isolator valve is open so that the two front wheel brakes are mutually applied by both a first and second electrically controlled actuator. This establishes a balanced operating pressure across the axle of the vehicle despite any small inconsistencies in pressure supplied from either of the two electrically driven actuators.
Preferably, the first actuator incorporates a second normally open isolator valve which is closed during normal brake operation to isolate the brakes from the master cylinder. Upon failure of the electrical/electronic control, the second isolator valve is adapted to be open or remain open if electrical activation has not taken place, to allow communication between the driver applied master cyl
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Heibel Helmut
Mortimer Ivan
Kramer Devon
Lucas Industries Public Limited Company
Oberleitner Robert J.
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