Hydraulically operated hammer drill

Abstract

A hydraulically operated hammer drill includes a housing in which a striking piston is displaceably disposed for alternating movement. The striking piston is driven in striking and return directions by a first operating pressure. A rotatable, tool receiving device is connected to the housing for receiving an insertion end of a drilling tool and permitting displacement of the insertion end in the longitudinal direction when charged by the striking piston. A rotation drive mechanism, driven by a second operating pressure, is mounted for rotatably driving the tool receiving device during longitudinal displacement of the insertion end. A control unit is disposed along a pressure conduit supplying the first operating pressure for alternatingly switching the direction of movement of the striking piston by controlling application of the driving medium to control faces of the striking piston. A first control member is responsive to the second operating pressure for reducing the first operating pressure when the second operating pressure exceeds a first limit value. A second control member varies the magnitude of the expulsion pressure when a second limit value is exceeded, the second limit value being a function of the magnitude of either the first or second operating pressure.