Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1995-12-06
1997-11-04
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031162, 3031192, 303900, 303DIG2, B60T 844
Patent
active
056831501
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic brake system with slip control.
BACKGROUND OF THE INVENTION
The discontinuous pressure fluid control in slip-controlled brake systems using digitally controllable inlet and outlet valves causes undesirable noise emission due to the pulse-like pressure variation.
Therefore, various provisions for reducing the noise level during the ABS/TCS control phases have been proposed. Among others, international patent application PCT/EP 00 266 is referred to. This application discloses the arrangement of pressure pulsation dampers in the main pressure lines proximate the braking pressure generator or in the shunt line of the electromagnetic inlet and outlet valves. The used pressure pulsation dampers are vibration-damping elastomeric energy accumulator elements which, due to their defined volume expansion, flow length and throttling properties, prevent the transmission of sound emissions, which result from valve switching frequencies, to the mass-loaded and, consequently, vibrating brake system.
A relatively soft pedal feel and the increase of the pedal travel are undesirable effects of the volume absorption of pressure fluid during the braking operation which is additionally caused by the above-described pressure pulsation dampers. FR-A-2680742 discloses the arrangement of each one electromagnetically controllable restrictor in the main brake line between the inlet and outlet valve and the wheel brake. Thus, the restrictor will adopt its operating position reducing the fluid flow to the wheel brake in response to a control signal issued by a controlling and regulating electronic unit. When the restrictor maintains its above-mentioned operating position both in the phase of braking pressure increase and braking pressure reduction during anti-lock control operations, rapid pressure reduction in the wheel brakes is prevented by the restrictor effect. In lack of a sufficient re-acceleration ability of the wheel on surfaces having a low coefficient of friction, undesirable wheel lock can occur. A comparable circuit configuration is disclosed in EP-A-0 247 264.
DE-A-34 27 802 discloses a hydraulic brake system having an invariable restrictor in a return line connected to the suction side of the pump. The pressure fluid propagating from the braking pressure generator through a main pressure line to the wheel brakes flows through the invariable restrictor exclusively in the pressure reduction phase of a braking pressure control operation when the combination valve (comprising inlet valve and outlet valve) adopts the outlet valve position in which there is a pressure fluid connection between the wheel brakes and the return line leading to the suction side of the pump.
U.S. Pat. No. 4,957,330 discloses a hydraulic brake system with slip control having a control piston in a housing which includes both a pressure port of the master cylinder and a pressure port of the wheel brake for achieving the controllable restrictor function, so that the control piston, as a function of the pressure difference on both end surfaces of the control piston, varies the flow cross-section of the main pressure line which extends through the housing of the control piston. In any case, a restrictor function is ensured upon termination of the pressure maintenance phase of an anti-lock braking operation because the pressure difference on the control piston will then reach its maximum. The pressure modulation valve of the wheel brake is arranged separately of the controllable restrictor valve in the main pressure line.
Therefore, it is an object of the present invention to maintain a possibly unmodified simple basic structure of the nowadays customary brake systems and to provide a solution of effectively reducing the noise that is due to the valve operating positions, and the transmission of noise.
Thus, the present invention is based on the idea of reducing the pressure pulses of different intensity, caused by the switching frequencies of the valves, as a function of the pressure differ
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Burgdorf Jochen
Dinkel Dieter
Volz Peter
Butler Douglas C.
ITT Automotive Europe GmbH
Lewis J. Gordon
Twomey Thomas N.
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