Patent ID: 7419015

Claim:
A rock drilling machine comprising at least: a frame; a percussion element for generating stress pulses; a shank arranged at the front of the percussion element in the percussion direction, the shank comprising a percussion surface for receiving said stress pulses; and an axial bearing comprising at least: a first piston and a second piston; between the pistons, an axial first contact surface and an axial second contact surface, said first and second axial contact surfaces being perpendicular to a longitudinal axis of the drilling machine, the contact surfaces being located in the same pressure space; at least one pressure duct for leading pressure fluid from a pressure source to the axial bearing; pressure surfaces in the pistons, on which surfaces the pressure fluid is arranged to act for axial movement of the pistons; and in which the pistons are arranged in the axial bearing to push the shank along a different travel length towards the percussion direction; the force of said pistons, by the action of the pressure fluid towards the percussion direction, being dimensioned such that the percussion surface is adjustable during drilling at the desired axial point for receiving the stress pulses, wherein the same pressure fluid fed to the axial bearing is arranged to act on said piston contact surfaces and pressure surfaces.