VALVE CYLINDER, IMPACT DEVICE AND METHOD

Abstract

A hydraulic system, rock drilling rig, and method for limiting output performance of a hydraulic drilling actuator temporarily under execution of a safety function feature of a hydraulic system is provided. The output performance is limited by limiting produced hydraulic fluid flow in a hydraulic circuit of the hydraulic drilling actuator, whereby a restricted magnitude of the fluid flow is produced at a hydraulic pump. This way a restricted operation mode is enabled and is controlled by a control unit.

Claims

1. A valve cylinder for a hydraulic impact device of a rock breaking apparatus, the valve cylinder comprising: an elongated piece having a central axis, a front end and a rear end; a central opening extending from the front end to the rear end, and through which central opening a percussion piston is mountable, at least two pressure spaces limited by radial surfaces of the central opening and being located at an axial distance from each other; and a plurality of axial pressure fluid channels connecting the at least two pressure spaces, wherein one of the at least two pressure spaces is a control pressure space located at the rear end of the valve cylinder and is configured to receive a sleeve-like control valve, wherein the control pressure space is provided with an inner radial groove including a bottom surface defining a radial extension of the inner radial groove in relation to the central opening adjacent the inner radial groove, and wherein the axial pressure fluid channels pass the inner radial groove without fluid connection with the inner radial groove, the inner radial groove having minimum radial dimensions at portions of the axial fluid channels and maximum radial dimension at intermediate sections located between the axial fluid channels, whereby a size of the inner radial groove is increased when compared to a simple groove with a circular bottom surface corresponding to the minimum radial dimensions at the portions of the axial fluid channels.

2. The valve cylinder as claimed in claim 1, wherein the bottom surface of the radial groove includes several curved surfaces.

3. (canceled)

4. (canceled)

5. (canceled)

6. The valve cylinder as claimed in claim 1, wherein the plurality of axial fluid channels is comprises three channels.

7. The valve cylinder as claimed in claim 1, wherein the inner radial groove is made by a milling technique.

8. The valve cylinder as claimed in claim 1, wherein the inner radial groove is located at a front end portion of the control pressure space.

9. The valve cylinder as claimed in claim 1, wherein the bottom surface of the inner radial groove is provided with at least one transverse fluid channel providing a fluid connection between the inner radial groove and an outer surface of the valve cylinder.

10. The valve cylinder as claimed claim 1, wherein the axial fluid channels are spaced around the central opening whereby a cross-section of the valve cylinder includes fluid channel sections and intermediate sections located between the fluid channel sections, the bottom surface of the inner radial groove is being provided with several transverse fluid channels at each intermediate section and wherein a thickness of a wall of the valve cylinder at the groove is smaller at the intermediate sections compared to the fluid channel sections.

11. An impact device of a rock breaking apparatus the impact device comprising: a body provided with a central space; a percussion cartridge arranged axially inside a rear portion of the central space and including a valve cylinder according to claim 1; a percussion piston passing through the percussion cartridge and being movable in an impact direction towards a front end of the impact device and in a reverse direction towards a rear end of the impact device; a working pressure space provided with hydraulic pressure fluid for moving the percussion piston in the reverse direction; a control pressure space at a rear end of the valve cylinder and being provided with a sleeve-like control valve for controlling hydraulic pressure affecting at the control pressure space and to thereby controlling a reciprocating movement of the percussion piston, wherein the valve cylinder is provided with a pilot pressure space for providing pressure pulses in response to movement of the percussion piston in the impact direction and, wherein the valve cylinder is provided with several a plurality of axial fluid channels arranged for connecting the pilot pressure space and the control pressure space.

12. A method of preventing cavitation in a hydraulic impact device of a rock breaking apparatus, the method comprising: increasing a volume of a hydraulic space between an inner surface of a control pressure space of the impact device and an outer surface of a sleeve-like control valve mounted reciprocatively inside the control pressure space; providing the inner surface of the control pressure space with a groove at a cross-section where are a plurality of transverse fluid channels arranged for feeding hydraulic pressure fluid to and from the control pressure space; and increasing the volume of the hydraulic space by shaping a bottom of the groove to expand towards an outer surface of the impact device at the transverse fluid channels, whereby a shape of a bottom line of the groove deviates from a circle.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0036] Some embodiments are described in more detail in the accompanying drawings, in which

[0037] FIG. 1 is a schematic side view of a rock drilling unit provided with a hydraulic rock drilling machine,

[0038] FIG. 2 is a schematic side view of an excavator provided with a hydraulic breaking hammer,

[0039] FIG. 3 is a schematic and cross-sectional side view of a rock drilling machine comprising a hydraulic impact device,

[0040] FIG. 4 is a schematic and cross-sectional side view of a valve cylinder, and

[0041] FIG. 5 is a schematic view of the valve cylinder of FIG. 4 cut at a cross-section E-E and showing bottom shape of a groove.

[0042] For the sake of clarity, the figures show some embodiments of the disclosed solution in a simplified manner. In the figures, like reference numerals identify like elements.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

[0043] FIG. 1 shows a rock drilling unit 1 intended for drilling holes to a rock surface. The rock drilling unit 1 is typically mounted to a drilling boom 2 of a rock drilling rig. The drilling unit 1 is provided with a feed beam 3 and a rock drilling machine 4 supported on it. A drilling tool 5 is connectable to the drilling machine 4. The rock drilling machine 4 may comprise a shank adaptor 6 at a front end of the rock drilling machine 4 for connecting the tool 5. At an opposite end of the tool 5 is a drill bit 7. The rock drilling machine 4 comprises an impact device 8 for providing the drilling tool 5 with impact pulses for breaking the rock, and a rotating device 9 for rotating R the drilling tool 5 around its longitudinal axis. The rock drilling machine 4 further comprises a basic body 10 for mounting the impact device 8, the rotating device 9, and possible other devices and elements needed. The rock drilling machine 4 may be moved on the feed beam 3 by means of a feed device 11 in a drilling or feed direction A and in a return direction B. The rock drilling machine 4 is hydraulically operable whereby the impact device 8 and the rotating device 9 are connected to a hydraulic system HS. Further, the impact device 8 may be in accordance with the solution disclosed in this document and may thereby comprise the disclosed valve cylinder.

[0044] FIG. 2 discloses a hydraulic breaking hammer 12 mounted to a boom 13 of an excavator 14 and connected to a hydraulic system HS of the excavator 14. The breaking hammer 12 comprises a hydraulic impact device 8 for generating impact pulses to a breaking tool 15 connectable to the breaking hammer 1. The breaking tool 15 can move in an impact direction A and a return direction B during the rock breaking. The impact device 8 may be in accordance with the solution disclosed in this document and may thereby comprise the disclosed valve cylinder.

[0045] FIG. 3 discloses a rock drilling machine 4 comprising a body 10, an impact device 8, a rotating device 9, a flushing housing 16, an open space 17 for receiving a shank adaptor, and a gear housing 18. The flushing housing 16 and gear housing 18 are located at a front end Fe of the body 10, whereas the impact device 8 is located at a rear end Re. The shank adapter can be mounted to the open space 17 and its rear end can be connected to rotating elements at the gear housing 18 so that the shank adapter and a drilling tool connectable to the shank adapter can be rotated by means of the rotating device 9. Flushing fluid can be fed via the flushing housing 16 to an axial flushing channel of the shank adapter and further to the drilling tool.

[0046] The impact device 8 comprises a percussion piston 19 which is arranged to move in a reciprocating manner in the impact direction A and return direction B. At a front end of the percussion piston 19 is an impact surface 20 which is configured to strike the shank adapter. The impact device 8 comprises a percussion cartridge 21 which is arranged axially inside a rear portion Re2 of a central space 22 of the body 10. The percussion cartridge 21 comprises a valve cylinder 23 through which the percussion piston 19 passes. The impact device 8 comprises a working pressure space 24 provided with hydraulic pressure fluid for moving the percussion piston 19 in the reverse direction B. There is a control pressure space 25 at a rear end Re2 of the valve cylinder 23. The control pressure space 25 is provided with a sleeve-like control valve 26 for controlling hydraulic pressure affecting at the control pressure space 25 and to thereby control reciprocating movement of the percussion piston 19. The pressure in the control valve space 25 moves the percussion piston 19 in the impact direction because working pressure areas of the percussion piston in the impact direction A are greater therein compared to working pressure areas or the percussion piston at the working pressure space 24 and affecting in the return direction B. In the working pressure space 24 there may prevail continuous high pressure during the operation, whereas in the control pressure space 25 magnitude of the pressure can be changed by means of the control valve 26 for making the percussion piston 19 to execute the reciprocating movement. Further, the valve cylinder 23 is provided with a pilot pressure space 27 for providing pressure pulses in response to movement of the percussion piston 19 in the impact direction A. The valve cylinder 23 is further provided with several axial fluid channels 28 for connecting the pilot pressure space 27 and the control pressure space 25. The pressure pulses generated in the pilot pressure space 27 affect on control surfaces of the control valve 26 and make it to change its control position.

[0047] The control pressure space 25 is provided with an inner radial groove 29 at a front end portion Fe2 of the control pressure space 25. Bottom of the radial groove 29 is provided with one or more transverse fluid channels 30 providing fluid connection between the groove 29 and a pressure port 31. The purpose of the radial groove 29 is to provide an enlarged space at the transverse fluid channels 30 and to thereby prevent hydraulic cavitation when the control valve 26 executes control measures.

[0048] The impact device 8 disclosed in FIG. 3 may be utilized also in a rock breaking hammer. Then there is no rotating device, gearing housing, flushing housing and the shank adapter. The percussion piston may be arranged to strike to an impact surface of a breaking tool.

[0049] FIG. 4 discloses a valve cylinder 23 of a percussion cartridge. The valve cylinder 23 is an elongated piece with a central axis Ca and comprises a central opening 32 extending from a front end Fe2 of the elongated valve cylinder 23 to its rear end Re2. A percussion piston is mountable through the central opening 32. There are two pressure spaces 25, 27 limited by radial surfaces of the central opening 32 and being located at an axial distance from each other. Several axial pressure fluid channels 28 connect the mentioned pressure spaces 25, 27. A control pressure space 25 is located at the rear end portion Re2 of the valve cylinder 23 and is configured to receive a sleeve-like control valve. The control pressure space 25 is provided with an inner radial groove 29 comprising a bottom surface 33 defining radial extension of the groove 29 in relation to the central opening 32 adjacent the groove 29. The mentioned axial pressure fluid channels 28 pass the radial groove 29 without being in fluid connection with the groove 29. Further, cross-sectional shape of the bottom of the mentioned radial groove 29 is rotationally non-symmetrical and comprises surfaces at several different distances from the central axis. However, this cannot be seen in the cross section in FIG. 4 but is shown in FIG. 5. The groove 29 is in fluid connection to an outer surface of the valve cylinder 23 by means of one or more transverse fluid channels 30.

[0050] FIG. 5 discloses the shape of the bottom surface 33 the groove 29. As can be seen, the bottom surface 33 comprises several curved surfaces with different radiuses R1, R2 and R3. The axial fluid channels 28 are evenly spaced around the central opening 32 in the cross-section at the radial groove 29 whereby there are intermediate sections 34 between the axial fluid channels 28. The groove 29 has its minimum radial dimensions at portions 35 of the axial fluid channels 28 and maximum radial dimensions at the intermediate sections 34. The radial dimensions of the groove 29 at the intermediate sections decrease continuously from the middle towards sections 35 with the axial fluid channels 28, whereby the shapes of the bottoms 33 are curved at the intermediate sections 34. Number of the axial fluid channels 28 may be three and the shapes of bottoms 33 of the grooves 29 at the intermediate sections 34 may be circular arches. Because of the shape of the bottom 33 of the groove 29, a thickness of a wall Wt1 of the valve cylinder 23 at the groove 29 is greater at the fluid channel sections 35 compared to thickness of a wall Wt2 at the intermediate sections 34.

[0051] The disclosed enlarged volumes of the grooves and the shapes of the bottoms of the grooves may also be implemented in solutions where there is only one axial fluid channel, and further when there are several axial fluid channels which are not evenly space around the open space of the valve cylinder.

[0052] The drawings and the related description are only intended to illustrate the idea of the invention. In its details, the invention may vary within the scope of the claims.