Electrically controllable valve

Disclosed is an electrically controllable valve accommodating in its valve housing (4) a second valve member (6) that is operable by the first valve member (2) in order to be able to variably adjust a second valve opening cross-section (A2) that is arranged in series to the first valve opening cross-section (A1), and a third valve opening cross-section (A3) that is releasable by means of the first valve member (2) is positioned in series arrangement to the first valve opening cross-section (A1) in order to limit the hydraulic pressure to a mechanically preset value.

BACKGROUND OF THE INVENTION

The present invention relates to an electrically controllable valve, in particular for use in a shock absorber, including an actuator and a first valve member operable by the actuator and cooperating with a valve seat (control edge) in the valve housing in order to variably adjust a first valve opening cross-section.

DE 44 27 905 A1 discloses an electrically controllable valve, including an actuator, a first valve member operable by the actuator and cooperating with a valve seat (control edge) in the valve housing in order to be able to variably adjust a first valve opening cross-section.

An object of the invention is to configure a valve of the indicated type with least possible effort in such a fashion that a pressure controlling and pressure limiting function is achieved by using simple, functionally reliable means.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved for a solenoid valve of the type at issue by an electrically operable valve, including an actuator, a first valve member operable by the actuator and cooperating with a valve seat (control edge) in the valve housing in order to variably adjust a first valve opening cross-section. A second valve member (6) operable by the first valve member (2) is arranged in the valve housing (4) in order to variably adjust a second valve opening cross-section (A2) that is arranged in series to the first valve opening cross-section (A1), and a third valve opening cross-section (A3) that is releasable by means of the first valve member (2) is positioned in series arrangement to the first valve opening cross-section (A1) for limiting the hydraulic pressure to a mechanically preset value.

Further features, advantages, and possible applications of the invention can be seen in the subsequent description of an embodiment for a valve in different operating positions.

DETAILED DESCRIPTION OF THE DRAWINGS

Initially, the principal design of the valve shall be described exemplarily for all illustrations by way ofFIG. 1.

FIG. 1shows a longitudinal cross-sectional view of an electrically operable valve, which is preferably used for controlling a shock absorber in a motor vehicle. The valve comprises an electric actuator1, a first valve member2that is directly operable by the actuator1and cooperates with a control edge3in the valve housing4. The cooperation of the first valve member2with the control edge3using the actuator1achieves a variably adjustable first valve opening cross-section A1, through which a controlled fluid flow (so-called primary flow) propagates in the direction of the valve outlet channel16that is disposed in the area of the valve member2.

Besides, a second valve opening cross-section A2is arranged in front of the first valve opening cross-section A1between the conically expanded inside portion of the valve housing4and an annular-disc-shaped second valve member6, which is to be actuated by the actuator1by way of a tappet-shaped extension7that is fitted at the first valve member2and the outside diameter of which corresponds to the outside diameter of the first valve member2. The variable second valve opening cross-section A2is thus positioned upstream of the first valve opening cross-section A1in series connection with the first valve opening cross-section A1, and both valve opening cross-sections A1, A2can be opened and closed reciprocally proportional to each other by means of the first valve member2.

Further, a third valve cross-section A3, which is normally closed by the end face of the extension7, is provided in the second valve member6. For closing the second valve opening cross-section A2, the second valve member6is configured as an annular-disc-shaped seat valve member, which is movable into abutment on a housing step14(conical step of the valve housing4). A valve inlet channel17opens into the valve housing4upstream of the second valve member6.

The first valve member2in the area of the first valve opening cross-section A1is preferably designed as valve piston guided in the valve housing4, which, in the electrically de-energized condition of the actuator1, is always lifted from the control edge3by means of a resetting spring5that acts on the second valve member6so that the first valve opening cross-section A1is opened at least in part. In addition, this provides a hydraulic connection between the valve outlet channel and valve inlet channel16,17through the aperture8at the second valve member6.

The resetting spring5is arranged between the second valve member6and the valve housing4so that, in the non-energized condition of the actuator1, the second valve member6is always in sealing abutment on the housing step14(conical step of the valve housing4), and exclusively the aperture8of the second valve member6is released, which aperture is designed as a circumferential notch in the embodiment at issue, so that, in the non-energized condition of the actuator1, an insignificant passage exists in the area of the third valve opening cross-section A3in order to safeguard the hydraulic connection between the valve inlet and outlet channels17,16, which connection is dependent on the cross-section of the aperture8.

Further, a compression spring9is interposed between the first valve member2and a spring stop11arranged between the actuator1and the valve member2, said spring counteracting only weakly the hydraulic pressure in the valve inlet channel17and the resetting spring5. To accommodate and guide the compression spring9and the disc-shaped spring stop11, the first valve member2includes an actuating pin10on its end face remote from the extension7. Under the permanent effect of the compression spring9, the spring stop11either is supported on the inside wall of the valve housing4or on a stop shoulder of a thrust member12connected to the actuating pin10. The thrust member12is sealed within the valve housing4and, in a preferred embodiment, projects with its end face remote from the spring stop11into the electromagnetic actuator1, which is composed of an armature13that actuates the thrust member12.

If desired or required, the first valve member2may of course be configured as a seat valve rather than as a slide valve. When the valve member2is designed as a plunger piston guided in the valve housing4, a pressure distributor groove15is preferably disposed at the outside periphery of the plunger piston, through which the fluid propagates for pressure balance into the space of the valve housing4in which the compression spring9is disposed. Sealing of this space in the direction of the actuator takes place in the simplest case by way of the metallically sealing thrust member12, which is inevitably acted upon by fluid pressure as well.

Subsequently, the different valve positions and the associated pressure variations shall now be indicated exemplarily by way ofFIGS. 1 to 4.

FIG. 1shows the valve with the features on which the invention is based in a first pressure control position, in which the exciting current corresponds to the maximum electric actuating current of the valve coil fitted to the valve housing4, with the result that the adjusted fluid flow can penetrate the valve in one direction under high fluid pressure. Due to the maximum exciting current imax, the armature13displaces the assembly comprising the thrust member12, the spring stop11, the compression spring9, the first and second valve pistons2,6, and the extension7in opposition to the resetting spring5to the left, with the result that the second valve piston6moves away from the housing step14, while the first valve piston2approaches the control edge3for pressure control.

FIG. 1ashows the pressure control characteristic curve for the pressure control function illustrated inFIG. 1. To this end, the pressure rise p is plotted on the ordinate of the diagram inFIG. 1a, while the volume flow Q is plotted along the abscissa, indicating that due to the high exciting current imax, the desired high volume flow Q of the fluid is characterized by a steep pressure rise p of the hydraulic pressure.

Different fromFIG. 1,FIG. 2shows the valve in a control position, in which the exciting current corresponds to the minimum electric actuating current of the valve coil12. Caused by the minimum exciting current imin, the armature13displaces the assembly composed of the thrust member12, the spring stop11, the compression spring9, the first and second valve piston2, and the extension7only insignificantly to the left in opposition to the effect of the resetting spring5, with the result that the second valve piston6moves only insignificantly away from the housing step14, while for pressure control the first valve piston2approaches the control edge3by the amount of travel covered by the second valve piston6. Hence, the pressure control characteristic curve illustrated in the diagram according toFIG. 2ais accomplished in this pressure control position, and a flat pressure rise with increasing volume flow Q can be taken from said curve.

FIG. 3shows the valve in a first fail-safe position in which the valve is not actuated or actuatable electrically (exciting current I=0) and in which the second valve opening cross-section A1is quasi closed except for the leakage through the aperture8. In this arrangement, the armature13remains in its position remote from the thrust member12, with the result that the second valve member6bears against the housing step14that forms the valve seat, due to the effect of the resetting spring5. As the first valve member2is supported on the front face of the second valve member6remote from the resetting spring5, the first valve member2automatically moves way from the control edge3by the dimension, which corresponds to the closure travel of the second valve member6. Consequently, an insignificant fluid flow propagates exclusively through the aperture8to the open first valve opening cross-section A1, from which results the course of characteristic curve that is characteristic of the aperture effect.

Based on the illustration ofFIG. 3,FIG. 4shows the valve in a so-called second fail-safe position, which differs from the first fail-safe position shown inFIG. 3in that the hydraulic inlet pressure that acts on the end face of the extension7lifts the extension7from its seat surface on the second valve member6, whereby the third valve opening cross-section A3between the extension7and the second valve member6is released, through which a secondary fluid flow is conducted to the first valve opening cross-section A1and from there to the valve outlet channel16in parallel to the primary fluid flow that enters via the aperture8in a throttled fashion. Compressed by the compression spring9, the thrust member12is positioned shortly in front of the armature13in this valve position. The force F1of the compression spring9is thus rated smaller than the hydraulic force that results from the hydraulic pressure p and the end face A0at the thrust member12. Compression spring9has a lower rate of spring rigidity compared to the resetting spring5.

Corresponding to the diagram according toFIG. 4a, a pressure limiting function develops, which is basically set due to the constructive layout of the first valve piston2and the compression spring9and in which the secondary fluid flow of the second valve piston6passes through the latter's open third valve opening cross-section A3in parallel to the primary flow through the aperture8. Due to the hydraulic displacement of the extension7in the direction of the housing step14, the fluid propagates through the second valve opening cross-section A2in a throttled fashion to the first, un-throttled valve opening cross-section A1, with the valve outlet channel16being connected thereafter.

The two valve members2,6are suitably configured in such a way that the flow forces that develop in the passage are balanced to a great extent.

LIST OF REFERENCE NUMERALS