Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-06-09
2001-01-30
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S117100
Reexamination Certificate
active
06179393
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The invention is based on a directional control valve which is suitable for the load-independent control of the direction and speed of a hydraulic load.
A directional control valve is disclosed by German Offenlegungsschrift 23 42 498. It has a control slide which is axially displaceable in a slide bore in a valve housing and, in a neutral position, shuts off two load chambers on the slide bore from a feed chamber and, in two operating positions on either side of the neutral position, selectively connects one of the two load chambers to a feed chamber and connects the respectively other load chamber to a return chamber. In each of two accommodation chambers, which are located opposite each other and are made in the control slide from the opposite ends thereof, there is arranged a brake piston, which opens a flow path between a load chamber and a return chamber in each case only to such an extent that the hydraulic load can no longer lead the amount of fluid flowing toward it, that is to say that no lack of filling is produced in the flow line between said hydraulic load and the other load chamber. For this purpose, the brake piston is acted on by a spring with the effect of reducing the opening cross section of the flow path, and is acted on by the pressure in the other load chamber with the effect of enlarging the opening cross section. For the application of pressure, the control slide has a longitudinal slide bore, which can be connected via a transverse bore to the other load chamber and which opens into a pressure chamber between the bottom of an accommodation chamber and the brake piston located in this accommodation chamber. The longitudinal bore runs eccentrically in the control slide. In order to apply pressure to the other brake piston, there is a further longitudinal slide bore running eccentrically in the control slide, and a further transverse bore.
In the directional control valve disclosed by German Offenlegungsschrift 23 42 498, two feed chambers run around the slide bore at a distance from each other. The control slide has two annular grooves which are spaced apart axially from each other and of which each is respectively used to connect one of the two feed chambers to a load chamber. In the piston collar between the two annular grooves, the control slide has two further, narrower annular grooves which are separated from each other by a narrow web. One longitudinal slide bore is connected to the one narrow annular groove by a first transverse bore, and the other longitudinal slide bore is connected to the other narrow annular groove by a second transverse bore. A load indicator channel, which in the neutral position of the control slide is covered by the narrow web between the two narrow annular grooves, opens into the slide bore. Depending on the direction in which the control slide is moved from the neutral position, the load indicator channel is opened toward one or the other annular groove, and hence the load pressure prevailing in the respective load chamber is indicated in the load indicator channel.
While the directional control valve according to German Offenlegungsschrift 23 42 498 has two feed chambers, and a load indicator channel opens into the slide bore between these two feed chambers, the brochure 9129 8557-02 (GB) from Voac Hydraulics AB discloses a directional control valve, designated K170LS, in which, in a slide bore, a return chamber, a load chamber, a single feed chamber, another load chamber and a further return chamber follow one another, and a load indicator channel opens into the slide bore laterally at a point, that is to say, as viewed from a load chamber, on the other side of the adjacent return chamber. Using such an arrangement, it is possible for the directional control valve to be shorter in the axial direction of the control slide than that from German Offenlegungsschrift 23 42 498. In the directional control valve according to the above-mentioned brochure, a longitudinal bore which is closed on both sides runs centrally through the control slide, and three transverse bores or transverse bore stars lead from said longitudinal bore to the outside of the control slide. In the neutral position of the control slide, a first transverse bore star is located at a short distance from a load chamber, between the latter and the feed chamber. The second transverse bore star is located at a short distance from the other load chamber, between the latter and the feed chamber. Finally, a third transverse bore opens into an annular groove on the outside of the control slide and, in the neutral position of the control slide, is located symmetrically in relation to the mouth of the load indicator channel and, in every position of the control slide, connects the longitudinal slide bore to the load indicator channel.
SUMMARY OF THE INVENTION
The invention is based on the object of further developing a directional control valve of the precharacterizing clause of claim
1
, that is to say a directional control valve having brake pistons in the control slide, in such a way that it is of more simple construction and is cheaper to produce.
According to the invention, this object is achieved in the case of such a directional control valve having the features of the precharacterizing clause of claim
1
by the fact that a single longitudinal slide bore extends from the one pressure chamber in one brake piston to the other pressure chamber in the other brake piston, and by the fact that if the control slide is displaced from the neutral position, the longitudinal slide bore can be connected either to one load chamber or to the other load chamber, depending on the direction of displacement. As a result of the presence of only one longitudinal slide bore, which leads to both pressure chambers in both brake pistons, the control slide is simplified and its production is made cheaper. The invention is based on the surprising finding that the control of a hydraulic load is not influenced if, in addition to the brake piston which controls the opening cross section of the flow path between the one load chamber and a return chamber and is acted on by the pressure in the other load chamber, the other brake piston is also subjected to the pressure in the other load chamber. Although the other brake piston is lifted from the bottom of the accommodation bore, the other return chamber remains closed by the control slide in relation to the other load chamber.
In a directional control valve according to the invention, too, at one point to the side of all the working chambers, the load indicator channel is open toward the slide bore, with the effect of producing a short axial design. In order to make such an arrangement of the load indicator channel possible, one brake piston is provided with a longitudinal load indicator bore which is open with respect to the pressure chamber in front of one end of this brake piston and is closed with respect to the spring chamber in front of the other end of this brake piston, and via which the longitudinal slide bore is connected to the opening of the load indicator channel into the slide bore.
The connection between the longitudinal load indicator bore in one brake piston and the load indicator channel is expediently produced via a transverse bore in the brake piston and via a transverse bore in [lacuna] sleeve surrounding the brake piston and belonging to the control slide.
An axial and/or a peripheral offset between the two transverse bores is advantageously compensated for by an annular groove which is located between the brake piston and the sleeve of the control slide, preferably on the outside of the brake piston.
If two brake pistons are accommodated in the control slide, it is usual for these two brake pistons to be formed in the same way or at least very similarly, with the effect of a low diversity of parts. Each brake piston has an annular groove which is located in the flow path between the load chamber and the return chamber and on each side of which there is a piston collar
Farber Martin A.
Kramer Devon
Mannesmann Rexroth AG
Oberleitner Robert J.
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