Percussion device for a hydraulic rock drilling machine, method of operation of a percussion device and hydraulic rock drilling machine including a percussion device

1. Percussion device for a hydraulic rock drilling machine ( 1 ) including, inside a cylinder ( 4 ), a to and fro moveable impact piston ( 3 ), which is provided with a land portion ( 12 ) for co-operation with a braking recess ( 11 ) in the cylinder ( 4 ) for the establishment of a braking chamber in advanced positions of the impact piston relative to a normal impact position, as seen in an impact direction (R) of the percussion device, wherein a throttle slit ( 17 ) is established between wall portions of the land portion ( 12 ) and the braking recess ( 11 ), and wherein the percussion device includes a piston guiding device ( 6 ) which is positioned in front of the braking recess ( 11 ) as seen in the impact direction (R),

wherein:

a pressure channel ( 14 ), being connected to a pressure medium source, is arranged to debouch in the cylinder ( 4 ) between the piston guiding device ( 6 ) and a position of the land portion ( 12 ) in a most advanced position of the impact piston ( 3 ).

2. Percussion device according to claim 1 ,

wherein the pressure channel ( 14 ) is arranged to debouch in an equalizing chamber ( 13 ) being arranged between the braking recess ( 11 ) and the piston guiding device ( 6 ).

3. Percussion device according to claim 2 ,

wherein the equalizing chamber ( 13 ) is ring-shaped.

4. Percussion device according to claim 3 ,

wherein a slit throttling ( 16 ) acting against the impact piston ( 3 ) is formed between the braking recess ( 11 ) and the equalizing chamber ( 13 ).

5. Percussion device according to claim 2 ,

wherein a slit throttling ( 16 ) acting against the impact piston ( 3 ) is formed between the braking recess ( 11 ) and the equalizing chamber ( 13 ).

6. Percussion device according to claim 2 ,

wherein the braking recess ( 11 ), the piston guiding device ( 6 ) and the equalizing chamber ( 13 ) are arranged in a piston guiding unit ( 7 ) which is insertable into a housing of the rock drilling machine ( 1 ).

7. Percussion device according to claim 1 ,

wherein the pressure channel ( 14 ) is arranged to debouch in a region of the braking recess ( 11 ) being positioned most closely to the piston guiding device ( 6 ).

8. Percussion device according to claim 7 ,

wherein in the pressure channel ( 14 ) there is arranged a one way valve ( 19 ) which is open in a direction of a mouth in the braking recess ( 11 ).

9. Percussion device according to claim 1 , wherein

said pressure medium source is any one from the group: a drive chamber ( 15 ) in the percussion device, a supply channel for percussion pressure, a separate high pressure generator ( 29 ).

10. Percussion device according to claim 1 , wherein

a regulating device is arranged to regulate pressure and/or flow in the pressure channel.

11. Percussion device according to claim 1 , wherein

the land portion ( 12 ) co-operating with the braking recess ( 11 ) includes a radially extending land flange ( 18 ).

12. Hydraulic rock drilling machine including a percussion device according to claim 1 .

13. Method for operation of a percussion device for a hydraulic rock drilling machine ( 1 ) including, driving an impact piston ( 3 ) to and fro inside a cylinder ( 4 ), wherein a land portion ( 12 ) on the impact piston ( 3 ) co-operates with a braking recess ( 11 ) in the cylinder in advanced positions of the impact piston ( 3 ) relative to a normal impact position, as seen in an impact direction (R) of the percussion device, wherein a throttle slit ( 17 ) is established between wall portions of the land portion ( 12 ) and the braking recess ( 11 ), and wherein the impact piston is guided by a piston guiding device ( 6 ) which is positioned in front of the braking recess ( 11 ) as seen in the impact direction (R),

wherein:

hydraulic medium from a pressure medium source is supplied in the cylinder ( 4 ) between the piston guiding device ( 6 ) and a position of the land portion ( 12 ) in a most advanced position of the impact piston ( 3 ).

14. Method according to claim 13 ,

wherein the pressure medium is supplied to an equalizing chamber ( 13 ) being arranged between the braking recess ( 11 ) and the piston guiding device ( 6 ).

15. Method according to claim 14 ,

wherein the pressure medium is supplied to a ring-shaped equalizing chamber ( 13 ).

16. Method according to claim 15 ,

wherein in active state with the land portion ( 12 ) entering the braking recess ( 11 ), hydraulic fluid escaping from the braking recess ( 11 ) is throttled in a slit throttling ( 16 ) being formed between the braking recess ( 11 ) and the equalizing chamber ( 13 ).

17. Method according to claim 14 ,

wherein in active state with the land portion ( 12 ) entering the braking recess ( 11 ), hydraulic fluid escaping from the braking recess ( 11 ) is throttled in a silt throttling ( 16 ) being formed between the braking recess ( 11 ) and the equalizing chamber ( 13 ).

18. Method according to claim 13 ,

wherein the pressure medium is supplied in a region of the braking recess ( 11 ) being positioned most closely to the piston guiding device ( 6 ).

19. Method according to claim 13 , wherein

said hydraulic medium is supplied from any one from the group: a drive chamber ( 15 ) in the percussion device, a supply channel for percussion pressure, a separate high pressure generator ( 29 ).

20. Method according to claim 13 , wherein

pressure and/or flow in the pressure channel ( 14 ) is regulated.