Sub-assembly, rock drilling rig, and method of absorbing vibrations in drilling

A sub-assembly for a rock drilling unit, wherein the sub-assembly is configured to transmit torque and axial forces between a rotating head and a drilling tool, the sub-assembly comprising:

• a first coupling element located at a first end of the sub-assembly for coupling the sub-assembly to the rotating head, wherein the first coupling element includes a first cover element provided with a protruding adapter pin and a second cover element located at an axial distance from the first cover element, wherein a housing element having a cylinder-like configuration is arranged between the first cover element and the second cover element for providing a floating space for the axial floating arrangement, and;
• a second coupling element located at an opposite, second end of the sub-assembly for coupling the sub-assembly to the drilling tool;
• an axial floating arrangement for providing an allowed limited axial relative movement between the first coupling element and the second coupling element, the axial floating arrangement including a plurality of axial drive pins for transmitting the torque;
• at least one axial fluid passageway passing centrally through the axial floating arrangement;
• an axial dampening arrangement having at least one first end cushion element and at least one second end cushion element for dampening axial shocks at extreme axial positions of the axial floating arrangement;
• and
• a torsional dampening arrangement for absorbing torsional shocks, wherein the plurality of axial drive pins include first ends mounted immovably and second ends mounted with clearances, whereby the plurality of axial drive pins are configured to be bent in relation to the first ends under torsional shocks and the plurality of axial drive pins serve as torsional dampening elements of the torsional dampening arrangement, wherein the first cover element is provided with a plurality of first blind openings arranged for receiving the first ends of the plurality of axial drive pins, and the second cover element is provided with a plurality of second blind openings arranged for receiving the second ends of the plurality of axial drive pins, whereby the plurality of axial drive pins are mounted between the first and second blind openings, the first blind openings of the first cover element and the first ends of the plurality of axial drive pins having tight fit connections, whereas the second blind openings of the second cover element and the second ends of the plurality of axial drive pins have clearance fit connections.