Patent ID: 8151900

Claim:
Percussion apparatus driven by a pressurized incompressible fluid, comprising: a body inside which are arranged two coaxial bores: one bore serving as a slidable mounting of a tool, and another bore that is stepped, comprising different successive cross sections, forming a piston cylinder for a striking piston having a stepped configuration, the striking piston moving in a reciprocating manner inside the piston cylinder and coming, during each cycle, to strike the tool, the stepped configuration of the striking piston delimiting with the piston cylinder at least one top chamber and a bottom chamber supplied sequentially with an incompressible fluid under high pressure, under action of a directional flow valve, a network of channels leading into the piston cylinder, of which some of the channels, based on their function, are connected through the directional flow valve to at least one of a high-pressure network and a low-pressure network, depending on an operating cycle of the striking piston, a control device that varies a stroke of the striking piston between a long stroke and a short stroke, the control device being connected on one hand to the directional flow valve and on another hand to at least one channel leading into the piston cylinder of the striking piston to be placed in fluid communication with the bottom chamber during upward movement of the striking piston, and a braking chamber placed in a zone of the piston cylinder situated on a side of the tool, that is closed by a shoulder of the striking piston when the striking piston moves past a theoretical striking position, wherein the control device comprises a control device cylinder, into which at least a first channel and a second channel lead, the first channel also leading into the piston cylinder of the striking piston and the second channel being connected to the directional flow valve, a spool being mounted in the control device cylinder, a first face of the spool being situated in a first chamber permanently subjected to a determined pressure, and a second face of the spool being situated in a second chamber connected to the braking chamber by a third channel opening in the braking chamber.