Claims:1. A sub-assembly (8) for a rock drilling unit (4) wherein the sub-assembly (8) is configured to transmit torque and axial forces between a rotating head (5) and a drilling tool (7);
and wherein the sub-assembly (8) comprises:
a first coupling element (13) at a first end of the sub-assembly (8) for coupling the sub-assembly (8) to the rotating head (5);
a second coupling element (14) at an opposite second end of the sub-assembly (8) for coupling the sub-assembly (8) to the drilling tool (7);
an axial floating arrangement (15) for providing an allowed limited axial relative movement between the first coupling element (13) and the second coupling element (14), and comprising several axial drive pins (16) for transmit-ting the torque;
at least one axial fluid passageway (17) passing centrally through the axial floating arrangement (15);
an axial dampening arrangement comprising at least one first end cushion element (18) and at least one second end cushion element (19) for damp-ening axial shocks at extreme axial positions of the axial floating arrangement (15); and
a torsional dampening arrangement for absorbing torsional shocks;
characterized in that
the mentioned drive pins (16) comprise first ends (16a) mounted im-movably and second ends (16b) mounted with clearances (20), whereby the drive pins (16) are configured to be bent in relation to their first ends (16a) under tor-sional shocks and the drive pins (16) serve as torsional dampening elements of the mentioned torsional dampening arrangement.

2. The sub-assembly as claimed in claim 1, characterized in that
the drive pins (16) serve as metallic spring elements.

3. The sub-assembly as claimed in claim 1 or 2, characterized in that
the drive pins (16) are made of spring steel.

4. The sub-assembly as claimed in any one of the preceding claims 1 - 3, characterized in that
the torque is configured to be transmitted between the drive pins (16) and the second coupling element (14) directly by means of their contact surfaces.

5. The sub-assembly as claimed in any one of the preceding claims 1 - 4, characterized in that
number of the drive pins (16) is 8 – 12 and they are spaced evenly around the central fluid passageway (17).

6. The sub-assembly as claimed in any one of the claims 1 - 5, characterized in that
the second end portions (16b) of the drive pins (16) are provided with cushion rings (32) surrounding the drive pins (16) for assisting the dampening.

7. The sub-assembly as claimed in any one of the preceding claims 1 - 6, characterized in that
the axial dampening arrangement comprises a ring-shaped top pad (18) and a ring-shaped bottom pad (19); and
the top and bottom pads (18, 19) are made of resilient cushion mate-rial.

8. The sub-assembly as claimed in any one of the preceding claims 1 - 7, characterized in that
the first coupling element (13) comprises a first cover element (21) provided with a protruding adapter pin (22) and a second cover element (23) at an axial distance from the first cover element (21);
a housing element (24) with cylinder-like configuration is arranged between the first cover element (21) and the second cover element (23) for providing a floating space (25) for the axial floating arrangement (15);
the second coupling element (14) comprises an adapter housing (26) for receiving a coupling end of the drilling tool and protruding into an opposite direction relative to the adapter pin (22), and the second coupling element (14) further comprises a stem (27) which is arranged inside the housing element (24) and is able to slide axially inside the floating space (25);
the first cover element (21) is provided with several first blind open-ings (28) for receiving the first ends (16a) of the drive pins (16), and the second cover element (23) is provided several second blind openings (29) for receiving the second ends (16b) of the drive pins (16), whereby the drive pins (16) are mounted between the first and second blind openings (28, 29);
the stem (27) comprises several through openings (30) at the drive pins (16) whereby the drive pins (16) penetrate axially through the stem (27);
a ring-shaped top pad (18), which is provided with a central opening for the fluid passageway (17) and several radial openings for the drive pins (16), is located inside the floating space (25) at a side of the first coupling end (13);
a ring-shaped bottom pad (19), provided with a central opening for the stem (27) of the second coupling end (14) and several radial openings for the drive pins (16), is located inside the floating space (25) at a side of the second coupling end (14);
the axial fluid passageway (17) being a sleeve-like element a first end of which is mounted immovably to the first connecting element (13) and a sec-ond end portion being connected slidingly to the second connecting element (14);
and wherein the mentioned first blind openings (28) of the first cover element (21) and the first ends (16a) of the drive pins (16) have tight fit connec-tions, whereas the second blind openings (29) of the second cover element (23) and the second ends (16b) of the drive pins (16) have clearance fit connections.

9. The sub-assembly as claimed in claim 8, characterized in that
the second blind openings (29) of the second cover element (23) are provided with cushion space portions (34) provided with cushion rings (32) made of resilient material.

10. The sub-assembly as claimed in claim 7 or 9, character-ized in that
the mentioned resilient material is polyurethane.

11. The sub-assembly as claimed in any one of the preceding claims 1 - 10, characterized in that
magnitude of the mentioned clearances (20) is 1 – 3 mm.

12. A rock drilling rig (1) for drilling drill holes (10) to a rock sur-face,
wherein the rock drilling rig (1) comprises:
a movable carrier (2);
at least one drilling mast (3);
a drilling unit (4) comprising a feed device (6) for moving the drilling unit (4) on the drilling mast (3) in a drilling direction (A) and return direction (B), and a rotating head (5) for rotating (R) a drilling tool (7) around its longitu-dinal axis;
a sub-assembly (8) coupled between the rotating head (5) and the drilling tool (7) for transmitting axial forces and torque between the rotating head (5) and the drilling tool (7), and wherein the sub-assembly (8) is configured to allow axial floating between the rotating head (5) and the drilling tool (7) and to absorb axial and torsional shocks;
characterized in that
the sub-assembly (8) is as claimed in any one of the preceding claims 1 – 11.

13. A method of absorbing vibrations in rotary drilling,
wherein the method comprises:
rotating (R) a drilling tool (7) around its longitudinal axis by means of a rotating device (5);
providing a sub-assembly (8) between the rotating device (5) and the drilling tool (7) for allowing axial floating movement between the rotating de-vice (5) and the drilling tool (7) and for transmitting axial forces and torque;
transmitting the torque by means of several axial drive pins (16) of the sub-assembly (8);
absorbing axial shocks by means of an axial dampening arrangement of the sub-assembly (8) comprising axial cushion elements (18, 19); and
absorbing torsional shocks by means of a torsional dampening ar-rangement of the sub-assembly (8);
characterized by
implementing the drive pins (16) as elements of the torsional damp-ening arrangement;
providing the drive pins (16) cantilever type configuration by mount-ing their first ends (16a) immovably and allowing their opposite second ends (16b) to move in transverse direction when torsional shocks are subjected to the sub-assembly (8);
and allowing the drive pins (16) to bend (33) when subjected to the torsional shocks and absorbing torsional vibrations by material properties of the drive pins (16).

14. The method as claimed in claim 13, characterized by
providing the mountings of the second ends (16b) of the drive pins with clearances (20).

15. The method as claimed in claim 13 or 14, characterized by
providing the mountings of the second end portions (16b) of the drive pins (16) with dedicated dampening rings (32);
and supporting the second ends (16a) of drive pins (16) having loose mountings with the dampening rings (32) and absorbing vibrations caused by the movements of the free second ends (16b).
, Description:[048] Figure 1 shows a rock drilling rig 1 intended for surface drilling. The rock drilling rig 1 comprises a movable carrier 2 and at least one drilling mast 3 con-nected to the carrier 2. The mast 3 is provided with a drilling unit 4 provided with a rotating head 5 supported on the mast 3 and being movable in a drilling direc-tion A and return direction B by means of a feed device 6. The rotating head 5 is connected to a drilling tool 7 by means of a sub-assembly 8. The drilling tool 7 is shown in a simplified manner for clarity reasons. The drilling tool 7 may com-prise one or more tubular elongated elements and a drill bit 9 at its distal end. The rotating head 5 rotates R the drilling tool 7 around its longitudinal axis and the drilling tool 7 is simultaneously fed towards a rock surface being drilled. This is known as rotary drilling method. Drilling cuttings are flushed by feeding flush-ing fluid from a flushing system Fs via the drilling tool 7 to a drill hole 10 being drilled so that the drilling cuttings are flushed away from the drill hole 10. The drilling unit 4 may be hydraulic whereby it may be connected to a hydraulic sys-tem Hs.

[049] Figure 2 discloses another solution which differs from the one shown in Figure 1 in that there is an impact device 11 mounted between a drill bit 9 and a drilling tool 7. The disclosed solution is intended for a down-the-hole drilling method, known also as DTH-drilling. Also, in this case a sub-assembly 8 is need-ed between a rotating head 5 and the drilling tool 7. A drilling unit 4 can be mounted movably on a feed beam 12, or in a similar manner as is shown in Fig-ure 1.

[050] Figures 3 and 4 disclose a sub-assembly 8 comprising a first coupling ele-ment 13 at a first end for coupling the sub-assembly 8 to the rotating head, and a second coupling element 14 at an opposite second end for coupling the sub-assembly 8 to the drilling tool. The sub-assembly is also provided with an axial floating arrangement 15 for providing an allowed limited axial relative move-ment between the first coupling element 13 and the second coupling element 14. The axial floating arrangement comprises several axial drive pins 16 for trans-mitting torque between the coupling elements 13, 14. There is an axial fluid pas-sageway 17 passing centrally through the axial floating arrangement 15. The sub-assembly 8 comprises an axial dampening arrangement comprising at least one first end cushion element 18 and at least one second end cushion element 19 for dampening axial shocks at extreme axial positions of the axial floating arrange-ment 15.

[051] The mentioned drive pins 16 comprise first ends 16a mounted immovably and second ends 16b mounted with clearances 20, which are shown better in Fig-ure 5. The drive pins 16 are configured to be bent in relation to their first ends 16a under torsional shocks. The drive pins 16 serve as torsional dampening ele-ments.

[052] The first coupling element 13 comprises a first cover element 21 provided with a protruding adapter pin 22 and a second cover element 23 at an axial dis-tance from the first cover element 21. A cylinder shaped housing element 24 is arranged between the first cover element 21 and the second cover 23 element for providing a floating space 25 for the axial floating arrangement 15.

[053] The second coupling element 14 comprises an adapter housing 26 for re-ceiving a coupling end of the drilling tool. The adapter housing 26 protrudes into an opposite direction relative to the adapter pin 22. Further, the second coupling element 14 comprises a stem 27 which is arranged inside the housing element 24 and can slide axially inside the floating space 25.

[054] The first cover element 21 is provided with several first blind openings 28 for receiving the first ends 16a of the drive pins 16. The second cover element 23 is provided several second blind openings 29 for receiving the second ends 16b of the drive pins 16. Thereby, the drive pins 16 are mounted between the first and second blind openings 28, 29. The stem 27 comprises several through openings 30 through which the drive pins 16 penetrate axially.

[055] The ring-shaped top pad 18 is provided with a central opening for the fluid passageway 17 and several radial openings for the drive pins 16, and it is located inside the floating space 25 at a side of the first coupling end 13. The ring-shaped bottom pad 19 is provided with a central opening for the stem part 27 of the sec-ond coupling end 14 and has several radial openings for the drive pins 16. The bottom pad 19 is located inside the floating space 25 at a side of the second cou-pling end 14. The axial fluid passageway 17 is a substantially sleeve-like element a first end of which is mounted immovably to the first connecting element 13 and a second end portion is connected slidingly to the second connecting element 14. The stem 27 can slide axially in relation to the tubular fluid passageway 17 and its sealings 31.

[056] The mentioned first blind openings 28 of the first cover element 21 and the first ends 16a of the drive pins 16 have tight fit connections, whereas the second blind openings 29 of the second cover element 23 and the second ends 16b of the drive pins 16 have clearance fit connections. Further, the second end portions 16b are provided with cushion rings 32 surrounding the drive pins 16 and are thereby configured to assist the dampening.

[057] Figure 5 discloses the above mentioned clearance 20 and the cushion ring 32 in an enlarged view. The second blind openings 29 of the second cover ele-ment 23 are provided with cushion space portions 34 for receiving the cushion rings 32.

[058] Figure 6 shows in a simplified manner bending 33 of disclosed cantilever supported drive pin 16. When the first cover 22 moves in left direction, the drive pin 16 follows that movement. Movement of the stem 27 is resisted since it is connected to the drilling tool. When sudden high forces occur i.e., the torque shocks exist, then the drive pin 16 bends 33 in a manner typical for a cantilever support, which is fixed at it one end. The cantilever support arrangement requires that the second end 16b of the drive pin 16 can move laterally and this is possible because of the clearance 20. In Figure 6 there is no separate dampening ring at second end portion 16b of the drive pin 16, but it is possible to implement such dampening ring or any other resilient dampening element, dampening mass, or material therein if needed.

[059] Figure 7 shows some components of a sub-assembly 8. The structure of the sub-assembly 8 is in accordance with the Figures 3 and 4.
The drawings and the related description are only intended to illus-trate the idea of the invention. In its details, the invention may vary within the scope of the claims.