Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1996-03-25
1997-09-23
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
303900, B60T 836, B60T 850, F16K 3106, G05D 1620
Patent
active
056696752
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to an electromagnetically actuated valve, particularly for slip-controlled hydraulic brake systems in motor vehicles.
A valve of this kind is disclosed by DE 39 34 771 C1, FIG. 3. It has a control piston which is arranged in the valve dome, forms a stop for the magnet armature and is guided in longitudinally displaceable fashion on a stud which emanates from the valve body and passes through the magnet armature. With its end remote from the armature, the control piston delimits a control chamber which is connected to the pressure-medium inlet of the known valve by a pressure-medium passage which passes coaxially through the stud and the control piston. While the magnet armature is pressure-balanced at both ends, pressure fed into the control chamber can displace the control piston axially against a stop. The stroke of the magnet armature is thereby reduced by a predetermined amount, resulting in a restriction of the flow cross section.
This action of the known valve can be used in slip-controlled hydraulic brake systems, in which the pressure-medium inlet is connected to the brake master cylinder and the pressure-medium outlet is connected to a wheel brake cylinder. If, for example, during a brake-slip control operation, the valve is switched to its closed position by excitation of the solenoid and, during reduction of the pressure in the wheel brake cylinder, a sufficient pressure drop is generated between the pressure-medium inlet and the pressure-medium outlet, this brings about the above-described displacement of the control piston with the consequence that, when the valve is opened, the abovementioned restriction of the cross section of flow comes into effect and this persists for as long as the pressure difference between the inlet and the outlet exists. Because of the reduced pressure gradient during the pressure build-up which follows a pressure reduction in a brake-slip control operation, the reduction in the cross section of flow has an advantageous effect on the quality of control and noise characteristics of the brake system. During a normal braking operation without the risk of lock-up, on the other hand, the full cross section of flow of the valve is available, favoring a short response time of the brake system upon brake actuation, which is desirable.
However, in the case of the known valve, the fixed setting of the restricted cross section of flow is disadvantageous because, as a result, the flow rate is subject to fluctuations dependent on the differential pressure. In addition, the flow rate is considerably dependent on the absolute size of the cross section of flow, i.e. the stop must be very narrowly toleranced. Due to the requirement for a control piston, the valve is furthermore relatively expensive.
ADVANTAGES OF THE INVENTION
In contrast, the valve according to the invention has the advantage that, given a sufficiently large pressure drop between the inlet and the outlet side of the valve, the cross section of flow of the first seat valve with the second seat valve closed adjusts automatically as a function of the forces acting on the armature, but without a magnetic force, to largely constant flow rates lower than when the first seat valve is fully open. The outlay on construction to achieve this action of the valve according to the invention as a flow control valve is extremely low.
Advantageous further developments and improvements of the valve specified herein are possible by means of the measures presented hereinafter.
It is particularly advantageous as regards costs and functional reliability to construct the second seat valve with just one component interacting with the valve seat, the elasticity of this component being exploited to maintain the closed position over a certain stroke range of the magnet armature.
The guidance of the pressure-medium jet into the space bounded by the baffle element furthermore proves advantageous because the back pressure generated in this way increases the pressure drop acting on the magnet armature.
BRIEF
REFERENCES:
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patent: 5167442 (1992-12-01), Alaze et al.
patent: 5203617 (1993-04-01), Wilde
patent: 5218996 (1993-06-01), Schmitt-Matzon
patent: 5335984 (1994-08-01), Alaze et al.
patent: 5370450 (1994-12-01), Volz et al.
patent: 5402824 (1995-04-01), Hosoya et al.
patent: 5423602 (1995-06-01), Takahashi et al.
patent: 5425575 (1995-06-01), Schmidt et al.
Herderich Hans-Jurgen
Herzog Kurt
Heugle Bernhard
Hohl Gunther
Mueller Klaus
Butler Douglas C.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
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