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

Abstract

A 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 cooperation with a braking recess (11) in the cylinder (4) for the establishment of a braking chamber in advanced positions of the impact piston, wherein a throttle slit (17) is arranged to be established between the land portion (12) and the braking recess (11). 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). The invention also concerns a method and a hydraulic rock drilling machine.

Claims

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.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will now be described in greater detail by way of embodiments and with reference to the annexed drawings, wherein:

(2) FIG. 1 shows a part section of a hydraulic rock drilling machine equipped with a percussion device according to the invention in a sectional view,

(3) FIGS. 2 and 3 show a detail of the sectional view in FIG. 1 in a large scale with an impact piston in different positions, and

(4) FIG. 4 shows diagrammatically a detail of another embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

(5) Like and similar elements have in some cases been given same reference signs.

(6) FIG. 1 shows in a sectional view a hydraulic rock drilling machine 1 including a housing 2, wherein an impact distance 3 is moveable to and fro inside the cylinder 4. The impact piston 3 acts against a shank adapter 5 and is guided by a piston guiding device 6, which is part of a piston guiding unit 7. The rock drilling machine 1 as usual also includes i.a. a damping device and a rotation device etc., which are, however, not subject of the present invention and are therefore not further described here.

(7) In FIG. 2 is shown the arrangement around the piston guiding device 6 in respect of the present invention in greater detail. The piston guiding device 6 is thus in this embodiment part of said piston guiding unit 7, which suitably is comprised of a integral component which besides the piston guiding device 6 includes a number of other elements such as a braking recess 11. The braking recess 11 is comprised of a ring-shaped room which has a circular cylindrical outer envelope surface and is open in a direction opposite to an impact direction R of the impact piston 3.

(8) The braking recess 11 is arranged to co-operate with a land portion 12 being shaped as a radial extension of the impact piston 3 in advanced position of the impact piston 3 for establishment of a braking chamber.

(9) The piston guiding unit 7 further includes an equalizing chamber 13, which is arranged between the braking recess 11 and the piston guiding device 6 and which communicates with a permanently pressurized drive chamber 15 arranged for return strokes of the impact piston 3. A pressure channel 14 is provided for ensuring a supply of hydraulic medium from the drive chamber 15 to the equalizing chamber 13.

(10) As seen in the impact direction R in front of the piston guiding device 6, there is a draining chamber 9, also being received by the piston guiding unit 7, for draining hydraulic medium/pressure medium escaping passed the piston guiding device 6. In front of the draining chamber 9, as seen in said impact direction R, is further positioned a sealing device 8, which in this embodiment includes two axially separated piston seals. Other configurations of the sealing device can exist.

(11) In FIGS. 1 and 2 is shown the approximate position of the impact piston during normal drilling operation of the rock drilling machine when, because of a prevailing desired impact position of the impact piston, the land portion 12 does not enter into the braking recess 11.

(12) In FIG. 3 is shown the region of the piston guiding device 6 with the land portion 12 in an advanced position 27 (clarified with dot-interrupted line), wherein a throttle slit 17 is established between wall portions of the land portion 12 and the braking recess 11.

(13) Such advanced positions occur during idle strikes of the percussion device and can also occur during drilling when the drill bit meets a cavity or weak rock, and for example when the rock drilling machine is used for scaling purposes. The shank adapter has then been able to advance forward in the impact direction from its normal position during normal drilling operation.

(14) When the land portion 12 of the impact piston enters into the braking recess 11 and the braking chamber is established, a high pressure is formed aiming to decelerate the impact piston. This high pressure leads to the escape of hydraulic medium from the braking recess on the one hand through the throttle slit 17, on the other hand through a throttle slit 16 formed between the impact piston 3 and an inwardly directed ring surface between the braking recess and the adjacent equalizing chamber 13.

(15) With an interrupted line at 28 is in FIG. 3 illustrated the position of the land portion 12 in the most advanced position of the impact piston which is limited purely mechanically in that the shank adapter has reached a position with contact against a stop in the housing of the rock drilling machine.

(16) Through the pressure medium supplied equalizing chamber 13, potential pressure peaks emanating from the entry of the land portion into the braking recess are effectively reduced, pressure peaks that would otherwise be harmful for the sealing device. Further is achieved, through supplying hydraulic medium through the pressure channel 14, that cavitation effects on the piston guiding device are effectively reduced during return strokes of the impact piston.

(17) As an alternative to being comprised of an integral component, the piston guiding unit can be comprised of plural, for example two, three or more parts which together are insertable into the cylinder. Each one of these parts can exhibit one or more of the different elements: the piston guiding device 6, the braking recess 11, the draining chamber 9, the sealing device 8 and the equalizing chamber 13.

(18) In FIG. 4 is illustrated a second embodiment of the invention, wherein no equalizing chamber is arranged, but instead the pressure channel 14, which in this case communicates with the separate high pressure generator 29, debouches in a forward region of the braking recess 11 itself. This region is in front of a position where the land portion 12 is in its most advanced position of the impact piston according to the above. This position is indicated with an interrupted line at 28. The equalized and in particular cavitation suppressing action of the inventive device occurs through the continuously provided support of hydraulic medium in this region of the braking recess 11.

(19) In the variant in FIG. 4, the land portion 12 has been provided with a land flange 18, which is possible but not necessary to use in a device according to the invention.

(20) 19 indicate a one way valve, which is positioned in the pressure channel 14 in order to prevent a back-flow of hydraulic medium during the instantaneous pressure increase occurring when the land portion 12 with high speed enters into the braking recess 11.

(21) The invention can be modified within the scope of the following claims.

(22) It is possible to provide hydraulic medium in different ways to the pressure channel, wherein the variant illustrated in FIG. 2 with continuous communication between the equalizing chamber and the drive chamber is a simple and effective solution on which can be realized without particularly complicated measures. It is, however, also realizable, within the scope of the invention, with different pressure medium sources to provide a regulating device arranged to regulate pressure and/or flow in the pressure channel such that such a pressure and flow, respectively, only exists when the braking chamber is expected to be established, as for example during idle strikes, scaling etc.

(23) The cylinder of the rock drilling machine can be constructed otherwise and the braking chamber can be received directly in the housing instead of, as is shown in FIGS. 1-3, be arranged in a separate component.