Patent ID: 7290622

Claim:
An impact device for generating a stress pulse in a tool, the impact device comprising: a frame to which the tool is connectible; a transmission member disposed between the frame and the tool, the transmission member including: a transmission piston defining a first pressure surface; and a tool-side end being in contact with the tool either directly or indirectly at least part of the time during the generation of the stress pulse; a stress element generating a force between the frame and the transmission member such that the force tends to push the transmission member towards the tool; a first hydraulic fluid space disposed on a tool-side relative to the transmission member and partially defined by the first pressure surface; and a hydraulic control system for leading pressurized hydraulic fluid into said first hydraulic fluid space and for enabling sudden flow of the hydraulic fluid out of said first hydraulic fluid space such that said force between the frame and the transmission member causes, either directly or indirectly via the transmission member and when the transmission member is in contact with the tool, a force compressing the tool in its longitudinal direction and, due to the effect thereof, a stress pulse in the tool in its axial direction, the hydraulic control system including: a hydraulic fluid channel for feeding pressurized hydraulic fluid into the impact device; a discharge channel for leading the hydraulic fluid out of the impact device; and a rotatingly installed control valve having a first set of control openings for leading the hydraulic fluid intermittently from the first hydraulic fluid space to the discharge channel, and the first set of control openings substantially simultaneously open a connection between the first hydraulic fluid space and the hydraulic fluid discharge channel, wherein the control valve includes: a second set of control openings for intermittently leading the hydraulic fluid from the hydraulic fluid channel to the first hydraulic fluid space; and several parallel control channels which simultaneously open a connection between the hydraulic fluid channel and the first hydraulic fluid space in such a way that the connection from the hydraulic fluid channel to the first hydraulic fluid space and, correspondingly, from the first hydraulic fluid space to the discharge channel open alternatively.