Fluid handling – Processes
Patent
1997-01-27
1998-11-17
Lee, Kevin
Fluid handling
Processes
25112902, 3031192, F16K 3106, B60T 836
Patent
active
058363343
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on an electromagnetically actuated valve, especially for slip-controlled hydraulic brake systems in motor vehicles. The invention also relates to a method for switching such a valve.
Such a valve is known from German Patent Disclosure DE 39 34 771 Cl. It has a control piston, forming a stop for the magnet armature, disposed in the valve dome; the piston is guided longitudinally displaceably on a tappet that originates at the valve body and penetrates the magnet armature. With its bottom remote from the armature, the control piston defines the control chamber, which communicates with the pressure fluid inlet of the known valve through a pressure fluid conduit that penetrates the tang and the control piston coaxially. While the magnet armature is pressure-equalized on both face ends, pressure fed into the control chamber is capable of displacing the control piston axially toward a stop. As a result, the stroke of the magnet armature is reduced by a predetermined amount, and the consequence is throttling of the flow cross section.
This mode of operation of the known valve is usable in slip-controlled hydraulic brake systems, in which the pressure fluid inlet communicates with the master cylinder and the pressure fluid outlet communicates with one wheel brake cylinder. For instance if in brake slip control the valve is switched into its closing position by excitation of the magnet coil, and on reduction of the pressure in the wheel brake cylinder a pressure drop of sufficient height is created between the pressure fluid inlet and the pressure fluid outlet, this causes the above-described displacement of the control piston, with the result that when the valve opens the aforementioned throttling of the flow cross section becomes operative as long as the pressure difference exists between the inlet and the outlet. Because of the reduced pressure gradient when a pressure buildup of brake slip control follows a pressure reduction, the reduction in the flow cross section has an advantageous effect on the quality of control and on the noise produced by the brake system. In normal braking without the danger of wheel locking, conversely, the full flow cross section of the valve is available, which favors a desired short response time of the brake system upon brake actuation.
However, the permanent setting of the throttle flow cross section in the known valve is a disadvantage, because it subjects the flow quantity to fluctuations dependent on the differential pressure. Moreover, the flow quantity is quite substantially dependent on the absolute magnitude of the flow cross section; that is, the stop needs to have a very close tolerance. Moreover, the valve is relatively expensive, because of the required control piston.
ADVANTAGES OF THE INVENTION
The valve according to the invention has the advantage over the prior art that the flow cross section of the seat valve adjusts automatically to largely constant flow quantities that are less than in full opening, as a function of the forces acting on the armature, but without magnetic force, given a sufficiently large pressure drop between the inlet and outlet side of the valve. The engineering expense for achieving this mode of operation of the valve of the invention as a flow regulating valve is extraordinarily slight, because the generation of pressure head in the partial valve chamber is effected by a stroke-dependent deflection of the flow of pressure fluid in the geometrically relatively simply shaped seat valve region. Since only the valve tappet determines the mode of operation, the functional reliability of the valve is very high.
Advantageous further features of and improvements to the valves possible by means of the provisions recited hereinafter.
Suitable features for the seat valve region can be achieved at low production expense.
The further feature of the invention is advantageous because as a result, in a simple way, a separation in terms of pressure of the two armature face ends is created, for creating force exerted on th
REFERENCES:
patent: 5167442 (1992-12-01), Alaze et al.
patent: 5295656 (1994-03-01), Campbell et al.
patent: 5605386 (1997-02-01), Ziegler et al.
patent: 5649748 (1997-07-01), Oehler et al.
Hohl Guenther
Huebner Hans-Peter
Maisch Wolfgang
Mittwollen Norbert
Oehler Martin
Greigg Edwin E.
Greigg Ronald E.
Lee Kevin
Robert & Bosch GmbH
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