| 摘要 |
An electrohydraulic, pilot-controlled directional control valve (10) having a spool (27) with variable overlap is proposed which in the normal regulating operation works with zero overlap of its control edges (35 to 38) and for a safety function in an emergency safely shuts off an inflow chamber (16) by positive overlap of the allocated control edges (36, 37) and relieves two motor chambers (17, 18) to the return. The spool (27), lying in a position-control circuit (13), consists of two parts (28, 29), the outer piston-like sections (31, 34) of which can be acted upon at the end face by a control pressure. Their inner piston-like sections (32, 33) abut coaxially in the inflow chamber (16), have one pressure face (55, 56) each, and together carry a sleeve (52) which seals off a parting line (41) with a hollow space (43) which is relieved to the tank (26) and in which a second stop (48) lies which limits the stroke distance when the spool parts (28, 29) are spread apart. If the pilot control (12) fails, the pressure in the inflow chamber (16) presses both spool parts (28, 29) apart by the stroke distance as a result of the control chambers (22, 23) now relieved of the control pressure, so that the inflow chamber (16) is now safely shut off by control edges (36, 37) with positive overlap and the motor chambers (17, 18) are relieved. <IMAGE>
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