Patent ID: 7000387

Claim:
A hydraulic spool valve having a spool-valve piston, which is arranged in a housing bore in a manner allowing it to be displaced longitudinally and which is assigned, on each end side, a respective compression spring which counteracts a displacement of the spool-valve piston towards this compression spring, while the two compression springs together, owing to their pre-stress, effect a neutral central position of the spool-valve piston, which position encompasses one region and in which the through flow of hydraulic fluid through the spool-valve is blocked, having two inlet bores and an outlet bore arranged between them, for hydraulic fluid, the inlet bores and the outlet bore all leading into the housing bore and a difference in pressure of the hydraulic fluid situated in the two inlet bores causing the spool-valve piston to be displaced, with the consequence that, in the extended end position of the spool-valve piston, the outlet bore is connected to that inlet bore in which the lower pressure of the hydraulic fluid prevails, characterized in that for each compression spring an expansion path, starting from the pre-stressed state and limited by a stop, is provided in such a manner that the spool-valve piston, when displaced on both sides out of its neutral central position into an intermediate position defined by the stop, is acted upon by the two compression springs, but, after the stop has come into effect and the intermediate position has been exceeded in the direction of the extended end position, is only acted upon by the one compression spring, which in each case counteracts the displacement of the said spool-valve piston, and in that even as the spool-valve piston approaches the intermediate position from the neutral central position a connection between the outlet bore and the inlet bore of lower pressure is produced, the flow cross section of this connection being smaller than when the spool-valve piston has exceeded the intermediate position.