Patent ID: 7234548

Claim:
A hydraulic rotary percussive hammer drill comprising a body containing a reciprocating percussion piston sliding under the effect of a main hydraulic supply circuit, this main circuit also being intended to cause the sliding of a roughly annular abutment piston housed in a cavity of the body, and having, on the one hand, a front face intended to position a shank a predetermined distance away from the percussion piston and, on the other hand, a rear face facing a rear wall of the cavity, wherein: an external hydraulic supply circuit is able, when the main circuit is shut down, to introduce fluid under pressure between the rear face of the abutment piston and the rear wall of the cavity so as to maintain a space between these items; and the external circuit opens into the rear end of the cavity and in that a sliding annular sleeve is placed around a rear part of the abutment piston and is able, on the one hand, to prevent the introduction of the fluid delivered by the external circuit when a pressure in a rear chamber is above or equal to a predetermined value and, on the other hand, to allow this fluid to be introduced when the pressure in the rear chamber is below the determined value.