Fluid handling – Self-proportioning or correlating systems – Supply and exhaust type
Patent
1998-08-28
2000-08-08
Ryznic, John E.
Fluid handling
Self-proportioning or correlating systems
Supply and exhaust type
251 38, 91445, 91468, G05D 700, F16K 3112, F15B 1108
Patent
active
060986476
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulically controllable load-holding brake valve for double-acting consumers as generically defined by the preamble to claim 1.
This valve is known from Swiss Patent CH 54 30 28. The load-holding brake valve has as its pilot valve a ball seat valve which requires very sensitive control by the opening piston in order to enable a constant increase in flow from the very onset and to avoid an abrupt opening action.
It is therefore the object of the invention to embody a load-holding brake valve of the type referred to above in such a way that very sensitive pressure relief of the main piston is effected without an abrupt rise in volumetric flow. If a progressive opening action of the valve is to be attained, the reduction in the load volume flow must be effected very uniformly and steadily.
The term "progressive opening action" is understood here to mean that the opening is essentially proportional to the control pressure, but in any case there is a defined dependency, free of bumping and jarring, between the opening cross section and the control pressure (in other words, the first and second derivations of the function "opening of the valve via the control pressure" are finite and steady for every variation in the control pressure).
This object is attained by a load-holding brake valve as defined by the characteristics of claim 1.
The pilot piston, adjacent to its sealing face, has a piston shank (pilot tappet), which is guided with slight play in the seat bore. The piston shank has a succession of a plurality of cross-sectional regions over the course of its length. The maximal cross section follows and corresponds to the seat cross section. It has essentially only a very slight play relative to the seat bore (pilot conduit). The region of maximal cross section is very short and can tend toward zero.
This is followed by the throttling region. By means of it, the valve tappet forms a throttle restriction in the seat bore (pilot conduit), the throttling action of which restriction becomes steadily--and preferably progressively--less upon displacement of the tappet and/or the resultant emergence from the pilot conduit. At a point in the throttling region, preferably already shortly after the pilot piston lifts away from its seat, the throttling action is so great that it is substantially greater than the throttle action of the compensation throttle. From then on, the throttling action relative to the pilot conduit drops, with an increasing opening travel of the opening piston and displacement of the pilot tappet, in such a way that the function of the throttling action is steady over the displacement length of the pilot tappet. The throttling action preferably initially drops only slightly and then ever more markedly with an increasing displacement path; the length and cross section of the tappet are accordingly adapted in such a way that the tappet and the pilot conduit of the main piston, at the onset of opening of the pilot piston, forms a very small throttling gap, whose throttling action is substantially greater than that of the compensation throttle, and then until the minimal cross section is reached forms a steadily larger throttling gap, whose throttling action decreases steadily and preferably more and more with the length of motion of the pilot tappet and the opening piston, so that the closing forces acting on the main piston drop. This is attained by the special embodiment of the throttle bore in terms of its length and cross section. In particular, two designs of the cross section are possible:
In the first embodiment, the cross section begins at the maximal cross section and then drops steadily over its length until reaching the minimal cross section. The decreasing throttling action is attained in that the throttling gap of the pilot tappet relative to the pilot conduit wall increases steadily, beginning at the throttling gap of the maximal cross section.
In the second embodiment, the cross section again begins at the maximal cross section; it then decreases over a
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Haussler Hubert
Hristov Ivan
Staiger Hans
Zurcher Josef
Beringer-Hydraulik AG
Ryznic John E.
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