Background of the invention

[0001] The invention relates to a pressure medium-operated percussion device of a rock breaking device for providing impact pulses to a rock breaking tool. The percussion device comprises a percussion piston, on the working pressure surfaces of which a pressure medium is directed to act, whereby the percussion piston moves back and forth in the impact and return directions. The work cycle of the percussion piston is controlled by a control valve that has positions for directing the pressure medium to act on the working pressure surfaces of the percussion piston and away from them. The operation of the control valve is controlled using a pressure pulse generated as the percussion piston moves according to its work cycle.

[0002] Further, the invention relates to a method for controlling the work cycle of a percussion piston of a hydraulic percussion device.

[0003] The field of the invention is described in more detail in the preambles of the independent claims of the application.

[0004] Percussion devices intended to break rock have a percussion piston that moves back and forth and hits a tool or intermediate piece on the forward side of the percussion piston. Hydraulic percussion devices typically have a control valve that directs pressure medium flows to the working pressure surfaces of the percussion piston and away from them, thus controlling the reciprocating movement or work cycle of the percussion piston. The position of the control valve is altered in relation to the position of the percussion piston by directing the pressure medium along pressure medium channels to the working pressure surfaces of the valve. Flanges on the percussion piston displace the pressure medium flow required to move the valve. It has been found that in controlling the control valve a large quantity of pressure medium is momentarily required and that leakage flows over the percussion piston flanges are high. Owing to these facts, the efficiency of conventional percussion devices is insufficient.

Brief description of the invention

[0005] It is an object of the present invention to provide a novel percussion device of a rock breaking device and a method for controlling its work cycle. [0006] The percussion device of the invention is characterized in that when seen in a radial direction of the percussion piston, the impulse space is defined by the percussion piston and the frame; and the first pressure connection comprises at least one impulse channel provided in the frame.

[0007] The method of the invention is characterized by by generating a pressure pulse in an annular impulse space defined in a radial direction by the percussion piston and the frame and transmitting the pressure pulse from the impulse space in an impulse channel provided in the frame to the control valve, which is located at a distance from the impulse space.

[0008] The idea is to control the work cycle of the percussion piston by a pressure-controlled control valve whose position is changed in at least one extreme position thereof by delivering a pressure pulse to a pressure surface of the valve, thus providing the valve with an initial impulse to a change movement. The pressure pulse is generated in an impulse space from which the percussion piston closes the pressure connection during its movement, whereby a closed pressure space is formed. The impulse space is an annular space defined, when seen in the radial direction of the percussion piston, by the percussion piston and the frame of the percussion device. The frame is provided with at least one impulse channel through which the pressure pulse is transmitted to the valve.

[0009] An advantage of the present solution is that it permits a simple and strong structure for detecting the position of the percussion piston. The generated pressure pulse is used to initiate a change in the position of the control valve. It is no longer necessary to control large pressure fluid volumes by means of percussion piston flanges to move the control valve. Moreover, since it is possible to reduce leakage flows, efficiency can be improved. Edge or skirt leakage of a percussion piston is a significant single leakage in conventional percussion devices. The disclosed solution allows sufficiently long sealing surfaces to be formed and leakages to be reduced.

[0010] According to an embodiment, the control valve is located separate from the impulse space.

[0011] According to an embodiment, at least in the impact direction of the percussion piston there is provided an impulse space, a pressure pulse formed in which is used to detect the position of the percussion piston in the impact direction. The pressure pulse generated in the impulse space in the impact direction provides the control valve with an initial impulse towards a position that will cause a percussion piston movement to the return direction.

[0012] According to an embodiment, the position of the percussion piston is detected in both travel directions, that is, in the impact and return directions, by means of pressure pulses generated in the impulse spaces. In that case the percussion device comprises a first impulse space in the impact direction of the percussion piston and a second impulse space in the return direction of the percussion piston. The pressure pulses generated in the impulse spaces deliver an initial impulse to the control valve in both extreme positions thereof.

[0013] According to an embodiment, the percussion piston comprises one impulse flange with impulse edges to the impact direction and the return direction.

[0014] According to an embodiment, the percussion piston comprises two impulse flanges arranged at an axial distance from each other. The first impulse flange has an impact-direction impulse edge and the second impulse flange a return-direction impulse edge.

[0015] According to an embodiment, the control valve is a sleevelike piece around the percussion piston. In addition, the sleeve-like control valve is placed at an axial distance from the impulse spaces in the percussion device.

[0016] According to an embodiment, the control valve is a slide valve comprising a mechanical pressure-controlled control slide. The control slide of the slide valve is located separate from the percussion piston and the impulse space.

[0017] According to an embodiment, the percussion piston comprises two impulse flanges arranged at an axial distance from each other. The impulse flanges have diameters that are different is size, which means that the displacement volumes of the impulse flanges are different in the impact direction and the return direction. This embodiment allows the magnitude of the pressure pulse to be acted on in different travel directions of the percussion piston.

[0018] According to an embodiment, a first impulse flange on the impact-direction side has a smaller diameter than a second impulse flange on the return-direction side. In that case a lower velocity of the percussion piston in the return direction is compensated for by a greater pressure surface com- pared with the impact direction, in which the velocity is higher. This embodiment allows an impulse pulse with a substantially equal magnitude in both the impact and the return direction to be generated. This is significant when the pressure pulse is used for generating a force for acting on the position of the control slide of the control valve. There are also other ways for compensating for the difference in velocity between the impact direction and the return direction of the percussion piston than the impulse flanges and corresponding surfaces.

[0019] According to an embodiment, around the percussion piston there is provided a sleeve-like control valve which is arranged to move in an axial direction between a first control position and a second control position. On the outer rim of the sleeve-like control valve there are control pressure surfaces acting in the impact direction and in the return direction, the pressure of the pressure medium acting on which is arranged to determine the position of the control valve. The impulse spaces are also at an axial distance from the control valve. Further still, the impulse spaces are closer to the impact surface at the forward end of the percussion piston than the control valve. A possible alternative embodiment is one in which the structure is otherwise similar but the axial order of the control components is the opposite, the control valve being positioned closer to the impact surface than the impulse spaces.

[0020] According to an embodiment the impulse channels are drillings formed to the frame of the percussion device, through which the impulse spaces are connected to the pressure surfaces of the control valve.

[0021] According to an embodiment, there is provided a holding circuit in association with the control valve, the holding circuit being arranged to direct pressure medium to the control pressure surfaces of the control slide and to hold the control slide in place in a first end position and in a second end position. A pressure pulse directed from the impulse spaces along the impulse channels causes a momentary force to the control slide, the force triggering the control slide to move towards the opposite end position. In other words, the pressure pulse provides a momentary force effect on the control slide and pushes it in movement. When the initial impulse has been given, the forces generated by the holding circuit finish the movement of the control slide to the end position, where the control slide remains waiting for the next pressure pulse and the subsequent movement to the opposite end position. The control valve provided with the holding circuit may comprise a sleeve-like control slide around the percussion piston or the control valve may be a slide valve positioned separate from the percussion piston.

[0022] According to an embodiment, the holding pressure is activated by the control valve through its movement of change. In other words, the holding pressure and holding force caused by it are not activated directly by the force of the percussion piston.

[0023] According to an embodiment, the control valve is provided with at least one pressure surface the pressures of the pressure medium acting on which may be adjusted. This adjustment allows the velocity of the control valve to be acted on in the travel direction controlling the return direction of the percussion piston. The pressure adjustment and the resulting adjustment of the velocity may be used to act on the stroke length of the percussion piston, and thereby also on the impact frequency of the percussion device.

[0024] According to an embodiment, the percussion device comprises one or more start-up valves or start-up circuits that enable to force a control valve of a percussion device in a stopped position to its predetermined extreme position for starting a new work cycle of the percussion device. The percussion piston can also be moved by means of a start-up valve to a predetermined position for start-up. After the start-up the percussion device operates until supply of pressure medium thereto is discontinued.

[0025] According to an embodiment, the frame of the percussion device comprises a frame part detachably attached to the frame. Further still, at least one impulse space is formed such that it is defined by the percussion piston and the frame part. The frame part may be a kind of a replaceable cartridge, for example, or a similar structure.

Brief description of the figures

[0026] Some embodiments will be explained in more detail in the attached drawings, in which

Figure 1 is a schematic side view of a rock drilling rig, in which the percussion devices of the present application may be utilized;

Figure 2 is a schematic side view of a rock drilling unit, in which the percussion devices of the present application may be utilized;

Figure 3 is a schematic side view of an excavator equipped with a breaking hammer, in which the percussion devices of the present application may be utilized; Figure 4 shows in a simplified manner steps and features related to the control of a percussion device;

Figure 5a is a schematic cross-sectional view of an embodiment of a percussion device in which a work cycle is controlled by a sleeve-like control valve;

Figure 5b shows an enlarged part of the control valve of Figure 5a;

Figure 6 is a schematic cross-sectional view of an embodiment of a percussion device in which a work cycle is controlled by an alternative sleevelike control valve;

Figure 7 is a schematic cross-sectional view of an embodiment of a percussion device in which the percussion piston is provided with two impulse flanges and a work cycle is controlled by a sleeve-like control valve;

Figure 8 is a schematic cross-sectional view of a percussion device in which the control valve is a slide valve positioned separate from the percussion piston;

Figure 9 is a schematic cross-sectional view of a percussion device comprising a start-up valve;

Figure 10 is a schematic cross-sectional view of a percussion device the frame of which is without narrow counter flanges;

Figure 1 1 is a schematic cross-sectional view of a percussion device, in which the percussion piston is equipped with a plural number of flanges of different sizes for providing pressure connections from impulse spaces;

Figure 12 is a schematic cross-sectional view of a percussion device, in which the impact-direction impulse space is between the percussion piston and the frame and the return-direction impulse space is between the percussion piston and the control valve;

Figures 13 and 14 are schematic cross-sectional views of parts of percussion devices in which the percussion piston closes a pressure channel from the impulse space, whereby a closed pressure space is formed and a pressure pulse generated;

Figures 15 and 16 are schematic views of a principle for dimensioning the pressure surfaces of a control valve;

Figure 17 is a schematic cross-sectional view of an embodiment of a different percussion device, in which a control unit applies pressure data to control an electric pilot control valve, which in turn controls a control valve located around a percussion valve; and Figure 18 is a schematic cross-sectional view of an embodiment of a second different percussion device, in which a control unit applies pressure data to control an electric control valve, which directs pressure medium directly to a working pressure space of the percussion piston.

[0027] In the figures, some embodiments are shown in a simplified manner for the sake of clarity. An attempt has been made to indicate like parts with like reference numerals in the figures.

Detailed description of some embodiments

[0028] Figure 1 shows a rock drilling rig 1 that comprises a movable carrier 2 which is provided with one or more drilling booms 3. The drilling boom 3 is provided with a rock drilling unit 4 that comprises a feed beam 5, a rock drilling machine 6 arranged on the feed beam 5 and a feed device 7, with which the rock drilling machine 6 may be moved on the feed beam 5 in the impact direction A and return direction B. The rock drilling unit 4 may be used to drill boreholes for excavating rock, or it may be used to drill boreholes for reinforcements to be set into the rock, for example.

[0029] Figure 2 shows a rock drilling unit 4 that comprises a rock drilling machine 6, to the drill shank 8 of which a drilling tool 9 is attached with a drill bit 10 at its outermost end. The rock drilling machine 6 comprises a percussion device 1 1 to provide impact pulses to the drill shank 8 that, in turn, transmits the impact pulses through the drilling tool 9 to the rock 12 being drilled. At the same time, the rock drilling machine 6 is fed by means of the feed device 7 toward the rock, whereby buttons on the drill bit 10 break the rock and a borehole 13 is formed. Typically, the rock drilling machine 6 also comprises a rotating device 14 for rotating the drill shank 8 and the attached drilling tool 9 around its longitudinal axis. The rock drilling machine 6 comprises a frame 15 that may be fastened to a carriage 16 arranged to be supported by the feed beam 5. The frame 15 of the rock drilling machine may have a space, into which the percussion device 1 1 and the related components are arranged.

[0030] Figure 3 shows an excavator 17 with a moveable carrier 2 and a boom 3 equipped with a breaking hammer 18. The breaking hammer 18 may be used to break boulders, rock, earth's crust and the like. The breaking hammer 18 comprises a frame 19, inside which a percussion device 1 1 is arranged to provide impact pulses to a tool 20 that under the influence of the impact pulses penetrates the material 12 to be broken and breaks it. [0031] The percussion devices, their various embodiments and feature combinations shown in the following Figures 4 to 18 may be used as percussion devices in rock drilling machines and breaking hammers of the type described above.

[0032] Figure 4 illustrates the steps related to the operation of a percussion device. The percussion device is started up by directing hydraulic pressure to it from a pump or a similar pressure source along pressure medium channels. The percussion device may be equipped with one or more startup valves that forcibly control a control valve to a predefined position for the start-up of the percussion device. Also the percussion piston may be moved to a predefined position for start-up. The pressure acting on the working pressure surfaces of the percussion piston of the percussion device makes the percussion piston perform a reciprocating movement according to its work cycle. The control valve directs the supply of pressure fluid to the pressure surfaces so that the motion of the percussion piston changes between the impact direction and return direction. An impulse edge of the percussion piston closes the pressure connection from the impulse space around the piston, which causes a sudden pressure increase, that is, a pressure pulse, in the closing impulse space. This pressure pulse provides an initial impulse for the alternating movement of the control valve, i.e. the pressure pulse allows the control valve to be made to change from one extreme position to the other. The percussion device continues its operation for as long as pressure fluid pressure is directed thereto.

[0033] Figures 5a and 5b show an embodiment of the percussion device 1 1 . The basic mechanical structure of the percussion device 1 1 may be cartridge-type. This type of impact cartridge 24 may be arranged as a single, ready assembled unit into a space provided in the frame of a rock drilling machine or a breaking hammer. The term percussion device 1 1 as used in this application refers not only to the impact cartridge 24 shown in the figures but also, however, to a conventional structure consisting of a plural number of separate components and assembled into a percussion device space provided in a rock breaking apparatus.

[0034] The frame 25 of the percussion device 1 1 may be a substantially tubular elongated piece. The impact-direction A end of the frame 25 may be provided with a first end sleeve 26 that may comprise one or more bearings 27 and one or more seals 28. Correspondingly, the return-direction B end of the frame 25 may be provided with a second end sleeve 29 that may also comprise a bearing 30 and seals 31 . End sleeves 26 and 29 such as these are easy and quick to install and to replace, when necessary. The sections between the seals 28, 31 and the bearings 27, 30 may be connected to drain channels 32 to conduct possible leakage flows into a tank.

[0035] The percussion device 1 1 comprises an elongated percussion piston 33 with an impact surface 70 at its impact-direction A end to hit a shank or directly a tool, when the percussion piston 33 moves back and forth according to its work cycle. The percussion piston 33 comprises sections 33a to 33d of different diameters, whereby the percussion piston 33 has working pressure surfaces 34a and 34b to which pressure fluid pressure may be directed to act on so that the percussion piston 33 moves in a desired travel direction. The first working pressure surface 34a is in a first working pressure space 35, known as a front space, to which a continuous pressure fluid pressure is directed from a pressure channel 36, whereby a force acts on the percussion piston 33 during the entire work cycle and endeavours to move it into the return direction B. The second working pressure surface 34b is in a second working pressure space 37, known as a back space, that is connected to a pressure channel 38 to provide the impact movement A of the percussion piston 33 and to a tank channel 39 to provide the return movement B. The pressure fluid flow to and from the working pressure space 37 is controlled by a control valve 40, which is an elongated sleeve-like piece arranged around the percussion piston 33 into a space formed in the frame 25. When the control valve 40 moves in the impact direction A to its left-side extreme, or, control position, it closes the pressure channel 38 and, at the same time, opens the tank channel 39. Correspondingly, when the control valve 40 moves in the return direction B from its left-side control position to its right-side extreme, or, control position, it closes the tank channel 39 and opens the pressure channel 38. The second working pressure surface 34b is dimensioned to have a clearly larger surface area than the first working pressure surface 34a, whereby the movements of the percussion piston 33 can be controlled by simply altering the pressure of the pressure fluid acting in the second working pressure space 37. The position change of the control valve 40 takes place in relation to the position of the percussion piston 33. The following discusses in more detail how to control the work cycle of the percussion piston 33, that is, the movement from the percussion point to the rear turning point and back, by means of the control valve 40.

[0036] The outer rim of the percussion piston 33 has an impulse flange 41 and the frame 25 has a first counter-flange 42 and a second counter- flange 43. The counter flanges 42 and 43 are at an axial distance from one another. The percussion piston 33 and the frame 25 define an annular impact- direction first impulse space 44 and, correspondingly, return-direction second impulse space 45 in a radial direction. On a portion between the impulse spaces 44, 45 there is provided an interspace 46 connected to a pressure line 47. The purpose of the impulse flange 41 , counter-flanges 42, 43 and impulse spaces 44, 45 is to generate, as the percussion piston approaches its extreme position, a pressure pulse that is used to alter the position of the control valve 40 and, consequently, to change the travel direction of the percussion piston 33.

[0037] The impulse flange 41 comprises axial surfaces K1 and K2 that define the impulse spaces 44, 45 in the axial direction when the percussion piston 33 moves toward the impulse space. In Figure 5a, the surface K1 decreases the volume of the impulse space 44, when the piston 33 moves in the impact direction A. The impulse flange 41 has an impact-direction impulse edge S1 and a return-direction impulse edge S2. When the impulse edge S1 arrives at the counter-flange 42, it closes the pressure connection Y1 from the impulse space 44, after which no more pressure medium can flow from the impulse space 44 to the interspace 46. The impulse space 44 then becomes a closed pressure space, and a pressure pulse is generated. Similarly, during the return movement B, the second impulse edge S2 in the percussion piston 33 arrives at the second counter-flange 43 and closes a pressure connection Y2, as a result of which the second impulse space 45 becomes a closed pressure space, and a pressure pulse is generated.

[0038] The pressure pulse is transmitted from the first impulse space 44 on a first impulse channel 59 to a first control pressure surface 52 of the control valve 40. Correspondingly, the pressure pulse is transmitted from the second impulse space 45 on a second impulse channel 58 to a second control pressure surface 51 of the control valve 40. In other words, the impulse channels 58, 59 allow the pressure pulse to be conveyed to act directly on the control pressure surfaces 51 , 52 of the control valve 40. The pressure fluid flow in the impulse channels 58, 59 is extremely low because the channels only convey the pressure pulse and the initial impulse required to change the position of the control valve 40 and not the entire fluid volume required by the control valve 40 movement. The impulse channels 58, 59 may be drillings or similar channels made to the frame 25.

[0039] In Figure 5a the control valve 40 has moved to its extreme position in the return direction B, where it is kept by the forces acting on its control pressure surfaces until it receives an initial impulse by a pressure pulse delivered from the first impulse channel 59 to change its position into the impact direction A. As the pressure pulse disturbs the position of balance of the control valve in the extreme position, forces acting on its other control pressure surfaces may complete the change in position of the control valve. In its extreme positions, the control valve 40 is subjected to holding forces ensuring that the valve is continuously synchronized to the movements of the percussion piston.

[0040] Figure 5b shows an enlarged part of the control valve 40 of Figure 5a. The control pressure surface 51 is subjected to a pressure of a pressure line P because it is connected to the pressure line P through the impulse channel 58, impulse space 45 and interspace 46. When the control valve 40 is in its right-side extreme position, the working pressure channel 38 is open and the tank channel 39 closed. Further, a tank channel 60 and a first holding channel 61 associated with the holding circuit of the control valve 40 are closed. A second holding channel 62 is open, its pressure acting on the holding surfaces 63 of the holding circuit and pushing the valve to the right. Hence the holding surface 63 acting to move the valve 40 to the right is subject to a pressure, whereas the holding surface 64 acting to move it to the left is free of pressure. In that case, the valve 40 remains in this position for as long as its position is disturbed by a pressure pulse delivered from the second impulse channel 59 acting on the control pressure surface 52. The valve 40 thus receives a sudden impact of force and moves slightly to the left, causing the pressure of the holding channel 61 to be directed to the holding surfaces 64 of the holding circuit. This force may complete the movement of the valve 40 to its left-side extreme position. As the valve 40 moves to the left, the control pressure surfaces 63 are connected to the tank channel 60. When the valve 40 is in its left-side extreme position, the pressure channel 38 is closed. The tank channel 39 is open, thus allowing pressure fluid to flow from the working pressure space 37 into the tank through a clearance 65 between the percussion piston 33 and the control valve 40. The percussion piston 33 begins its movement to the return direction B and when it approaches again its extreme position, a pressure pulse is generated in the second impulse space 45 and transmitted through the impulse channel 58 to the control pressure surface 51 of the valve. The pressure thus makes the valve move towards the return direction B, and the holding surface 64 is connected to the tank channel 39. At the same time, connection from the tank channel 60 to the control pressure surfaces closes and the connection to the holding channel 62 opens. The pressure fluid acting in the holding channel 62 moves the valve 40 to its right-side extreme position.

[0041] The holding circuit of the control valve 40 thus comprises at least the holding channels 61 and 62 and the holding surfaces 63 and 64. The holding circuit holds the valve 40 in its extreme positions and, on the other hand, completes the movement of the valve 40 after the valve has first been given an initial impulse to move away from its extreme position. The impulse means are only associated with the generating of the initial impulse.

[0042] Figure 5b further shows a replacement pressure channel 66 that allows pressure fluid to be conveyed to the impulse space at the moment when the percussion piston changes its direction of travel and the pressure in the pressure space decreases. The replacement pressure channel allows the slowing down of the percussion piston movement and cavitation in the impulse space to be avoided. Also other embodiments disclosed in this application may be provided with replacement pressure channels.

[0043] A further point to be made is that the pressure channels 38, 62, 66 and 61 may be under normal impact pressure of the percussion device 1 1 .

[0044] One of the advantages of the embodiment of Figures 5a and 5b is that only minor amounts of the pressure fluid used in controlling the control valve end up into the tank. This improves the efficiency of the percussion device.

[0045] Figure 6 shows an alternative structure of the fully hydrau- lically controlled percussion device 1 1 of Figures 5a and 5b. The control valve 40 is in its right-side extreme position, where its control pressure surface 51 is subject to a pressure from the channel 67 and, further, a pressure of the pressure line P through the impulse channel 58, impulse space 45 and interspace 46. When a pressure pulse formed in the first impulse space 44 is transmitted along the impulse channel 59 to the second control pressure surface 52, the valve 40 receives an impulse to move to the left. Since the surface area the second control pressure surface 52 is dimensioned to be clearly larger than the first control pressure surface 51 , the valve 40 moves further to the left. The pressure of the pressure channel 67 acts on the second control pressure surface 52 and moves the valve to its extreme position on the left. The pressure acting from the pressure channel 67 on the control pressure surface 52 keeps the valve in this position until its position is again disturbed by delivering a new pressure pulse from the second impulse space 45. The pressure pulse acts on the first control pressure surface 51 and makes the valve 40 move to the right. At that moment the impact-direction A end surface 68 of the valve is subjected to the pressure of the pressure channel 38, and together with the force acting from the pressure channel 67 on the control pressure surface 51 the pressure completes the movement of the valve 40 into the extreme position shown in the figure. The dimensioning of the pressure surfaces for the holding action of the control valve may be performed according to the principles disclosed later in connection with Figures 15 and 16.

[0046] The percussion device 1 1 of Figure 7 comprises the control valve 40, whose basic structure and operation correspond to those disclosed in Figures 5a and 5b. Hence the valve 40 has e.g. a holding circuit and the related channels and pressure surfaces. The construction shown in Figure 7 differs from that shown in the previous figures at least in that the frame 25 is in two parts and comprises a first frame part 25a and a second frame part 25b with a contact surface 69 in between. A further difference in the embodiment of Figure 7 is that the percussion piston 33 has two impulse flanges 41 a and 41 b at an axial distance from one another. The diameter D1 of the impact-direction impulse flange 41 a is smaller than the diameter D2 of the return-direction impulse flange 41 b. The velocity of the percussion piston 33 in the impact direction A is clearly greater than the velocity in the return direction B. The return- direction impulse flange 41 b may be dimensioned to be greater than the impact-direction impulse flange 41 a in a manner that enables to compensate for the difference in pressure pulse size caused by the velocity differences. The size of the pressure pulse is proportional to the velocity of the percussion piston and to the surface area of the impulse flange displacing pressure fluid. If pressure pulses generated in different directions are not compensated for by displacement surface areas of different sizes, the size differences between pressure pulses may be taken into account in the dimensioning of the control pressure surfaces of the control valve 40. Suitable dimensioning of clearances may also take care of the compensation.

[0047] In the embodiment of Figure 7 the first counter flange 42 is in the first frame part 25a and the second counter flange 43 in the second frame part 25b. This structure allows the axial distance between the counter flanges 42, 43 to be changed and thereby the moment to be acted on when the position of the percussion piston 33 is detected and a change in the position of the control valve 40 is triggered. The contact surface 69 between the frame parts 25a, 25b may be provided with spacer plates, for example, or the frame parts may be interconnected by a threaded joint that allows them to be steplessly turned in relation to and away from one another. By acting on the distance between the counter flanges 42, 43, it is possible to influence the stroke length of the percussion piston 33 and thereby also on the stroke frequency and stroke velocity.

[0048] Both impulses flanges 41 a, 41 b of Figure 7 are provided with an impulse edge S1 , S2 and a surface K1 , K2. Hence the principle of generating a pressure pulse is similar to that described earlier on.

[0049] Figure 8 shows a percussion device 1 1 with impulse means 41 , S1 , S2, K1 , K2, 44, 45 similar to those in the preceding figures for generating pressure pulses on the basis of the position of the percussion piston 33. A difference in the embodiment of Figure 8 is that the control valve is a slide valve 77 positioned physically separate from the percussion piston 33. The slide valve 77 may comprise a separate frame 78 or it may be formed to the frame of the percussion device. The slide valve 77 comprises a mechanical control slide 79 that may be an elongate sleeve-like piece, as disclosed in the figure, or, alternatively, it may be a rod-like control means. The control slide 79 has control positions, in which it directs pressure fluid from the pressure channel 80 along the channel 57 into the working pressure space 37 and, correspondingly, away from it into the tank channel 81 . On the outer rim of the control slide 79 there are provided control pressure surfaces 51 , 52, on which a pressure pulse from the impulse spaces 44, 45 is conveyed to act through the impulse channels 58, 59. Associated with the control slide there is also a holding circuit comprising holding channels 61 , 62 and pressure surfaces 63, 64. The operating principle of the slide valve 77 corresponds to that disclosed with reference to Figure 5b. [0050] The basic construction and operation of the percussion device 1 1 shown in Figure 9 correspond to what is shown in Figure 6. However, the embodiment of Figure 9 differs from the one shown in Figure 6 in that it comprises a start-up valve 82, which in Figure 6 is shown in a situation where no pressure fluid is fed to the percussion device 1 1 from the pressure channel 83. In that case the start-up valve 82 is not under the influence of the control pressure, but the valve 82 has been moved to the left at a position b by a spring 84. When the percussion device 1 1 is started again, pressure fluid is supplied into the pressure channel 83, the start-up valve 82 directing the fluid to the control pressure surface 85 of the control valve 40, which makes the valve 40 move to the impact direction A. This starts the operation of the percussion device 1 1 and the percussion piston 33 begins its reciprocating movement according to its work cycle, guided by the control valve 40. The start-up valve 82 assumes its normal operating position a when pressure in the pressure channel 83 has risen and acted on the start-up valve 82 through the control channel 86. The purpose of the start-up valve 82 is to ensure that the control valve 40 moves by forced control to a position in which the percussion piston 33 moves toward the return direction B. Upon start-up, a channel P _s is connected to the pressure channel 83 and after start-up to the tank T.

[0051] The control channel 86 of the start-up valve 82 may be provided with a throttle 87 that allows the pressure level in which the start-up valve 82 moves to the operating position a to be acted on. The throttle 87 may be adjustable or provided with a fixed setting.

[0052] The control valve 40 may be provided with a start-up surface area for forcibly controlling the valve to the front position when the percussion device is started up. This surface area may also be used for adjusting stroke length. After the start-up of the percussion device and when pressure in the pressure space comprising the start-up surface area is then increased, the backward velocity of the control valve may be slowed down. As a result, stroke length increases and stroke frequency decreases.

[0053] The following Figures 10 to 14 aim at demonstrating that a pressure pulse may be generated in different ways although the basic principle remains the same.

[0054] The basic idea and construction in the embodiment of Figure 10 is similar to those of the previous embodiments. A difference, however, is that the counter flanges 42' and 43' are not narrow flanges in the axial direc- tion. When the impulse flange 41 penetrates the impact-direction A impulse space 44 or the return-direction B impulse space 45, a pressure pulse is generated that triggers a change in the position of the control valve 40. The closure of the impulse space opens when the control valve 40 changes its position.

[0055] Figure 1 1 shows a percussion device 1 1 provided with a start-up valve 82, the percussion piston 33 of the device comprising a plural number of different flanges 33a to 33h, and an impulse flange 41 . In that case the impulse flange 41 does not comprise impulse edges S1 , S2 but these are located in the flanges 33d and 33e. The impulse edges S1 and S2 close the pressure connections Y1 and Y2 to the channels 71 and 72 at the extreme positions of the percussion piston 33, whereby closed impulse spaces 44, 45 are formed. The pressure pulses are transmitted along the impulse channels 58, 59 to the control valve 40, which may correspond to the one shown in Figure 6. It is also possible to use the slide valve 77 shown in Figure 8.

[0056] Figure 12 shows a percussion device 1 1 with an annular impulse space 44 in the impact direction A between the frame 25 and the percussion piston 33. The percussion piston has a first impulse flange 41 a with an impulse edge S1 that closes the impulse space 44. The impulse means in the return direction B are different. The second impulse space 45 is formed into the annular space between the percussion piston 33 and the sleeve-like control valve 40. The inner rim of the control valve 40 has a counter-flange 43 and the back part of the percussion piston 33 has, at the location of the valve 40, a second impulse flange 41 b with an impulse edge S2 and a frontal surface K2. A pressure pulse generated in the second impulse space 45 acts directly on the pressure surface 76 on the back surface of the control valve 40. Between the part 29 and the pressure surface 76 there is a gap, which is not shown in the figure. Thus, Figure 12 shows a combination of two different impulse generation principles. The pressure surfaces of the control valve 40 are dimensioned in such a manner that holding forces act on the valve in the extreme positions thereof in accordance with the principles shown in Figures 15 and 16, for instance.

[0057] Figure 13 shows in a highly simplified manner two alternative manners for generating a pressure pulse. In the first alternative the impulse flange 41 in the percussion piston 33 is provided with an impulse edge S1 a that closes a pressure connection Y1 a in the frame 25. A closed impulse space 44 is then formed as well as a pressure pulse that is transmitted along the impulse channel 59 to the control valve. In the second alternative there is a pressure connection Y1 b provided in the percussion piston 33. In that case the impulse edge S1 b is at the opening of the channel or drilling that forms the pressure connection Y1 b.

[0058] The solution of Figure 14 does not show an impulse flange at all, but the impulse space 44 is defined in the axial direction by the frontal surface K1 of the percussion piston portion 33c. The impulse edge S1 is in the percussion piston portion 33b. A pressure pulse is generated when the percussion piston 33 moves to left in the figure so that the impulse edge S1 passes the pressure connection Y1 . Thus pressure medium can no longer move along the channel from the impulse space 44 to the pressure space 75.

[0059] The principles illustrated in Figures 13 and 14 may be applied both in the impact direction A and the return direction B.

[0060] Figures 15 and 16 illustrate in more detail the principles of dimensioning the working pressure surfaces of the control valves 40 of Figures 6, 9, 1 1 and 12. As can be seen in the figures, the surface areas A1 and A2 of the control pressure surfaces 51 and 52 in the control valve 40 differ in size. Likewise, the surface areas A3, A4 and A5 of the control pressure surfaces 68, 85 and 91 at the ends of the control valve 40 may be dimensioned to differ in size.

[0061] The embodiment of Figures 15 and 16 is associated with a solution in which a momentarily closed pressure space forms during the impact and return directions of the percussion piston, the pressure pulse thus generated being used for controlling the position of the control valve.

[0062] The operating principle of the control valve 40 shown in Figures 15 and 16 differs from the operation of the valve shown in Figures 5a and 5b, for example, because the valve does not have separate pressure surfaces for generating holding forces but employs the control surfaces 51 and 52 as well as the pressure surfaces 68, 85 and 91 provided at the ends of the valve and dimensioned in the manner to be disclosed below. In the back working space 37 of the percussion piston, the pressure varies during the work cycle, and this pressure variation is utilized in generating holding forces F _pi to.

[0063] In Figure 15 the control valve 40 is in a position in which the back working space 37 is connected to the tank pressure because the percussion piston is in a return-direction B movement. The control pressure surfaces 51 and 52 are subjected to an impact pressure. The surface area A2 of the control pressure surface 52 has been dimensioned larger in size than the surface area A1 of the control pressure surface 51. In that case the control valve 40 is subjected to the holding force F _pi to, which holds the control valve 40 in the position shown in Figure 15.

[0064] The size of the holding force F _pi to acting on the control valve 40 can be calculated as follows:

F _pit0 =P-(A ₂ -A _l )-T-(A ₃ -A ₄ -A ₅ )=P-AA _l -T-(AA ₂ -A ₅ ), wherein ΔΑι represents the difference between the control pressure surfaces 51 and 52 and ΔΑ ₂ the difference between the surface areas A3 and A4 of the pressure surfaces 68 and 91 at the ends of the control valve 40.

[0065] Figure 16 shows the position of the control valve 40 when the percussion piston has moved in the return direction B so close to the changing position that the return-direction side impulse surface of the percussion piston penetrates the impulse space 45 and causes a momentary pressure pulse. The pressure pulse is transmitted on the impulse channel 58 to the control pressure surface 51 of the control valve 40, the control valve 40 thus receiving an initial stimulus to change its position, i.e. the pressure pulse triggers the valve to move. When the control valve 40 is in the position according to Figure 16, the back working space 37 is connected to the pressure channel P, as a result of which the control valve 40 is subjected to the holding force Fpito, whose size may be calculated as follows:

F _pit0 =-P-(A ₂ -A _l )+P-(A ₃ -A,)-T-A ₅ = P ^■ (AA ₂ - AA,) - T ^■ A ₅

[0066] To ensure that the directions of the holding forces F _pi to are always correct, the surface areas may be determined as follows:

T

>-( ^AA 2 - ^A s)'

wherein ΔΑι represents the difference between the control pressure surfaces 51 and 52

T wherein ΔΑ ₂ represents the difference between the pressure surface areas at the back working space 37 at the ends of the control valve 40. [0067] An advantage of the embodiment of Figures 15 and 16 is, among other things, that the structure of the control valve can be made very simple. In addition, leakages caused by the control valve may be insignificant.

[0068] Figures 17 and 18 of this application illustrate further percussion devices that differ from those presented above and from the solutions defined in the independent claims. The idea is that at least one impulse space is provided with a pressure sensor for detecting a pressure pulse generated in the impulse space. Pressure data is transmitted from the sensor to a control unit, which applies the pressure data to control a control valve. The control valve may direct a pressure medium flow directly to at least one working pressure surface of a percussion piston and away from there. Alternatively, the control unit applies the pressure data to control at least one pilot control valve that controls a main control valve. The main control valve comprises a control slide that allows the pressure medium flow to be directed to and from one or more working pressure surfaces of the percussion piston. The control unit may be provided with a control strategy and its control parameters may be changed, which allows the percussion device to be controlled in a versatile manner.

[0069] In Figure 17 the percussion device 1 1 is pre-controlled by means of an electrically controlled valve 21 . The valve 21 is controlled by one or more control units 22 receiving measurement data from sensors 23a and 23b. The control unit 22 may be provided with a control strategy which it follows to control the operation of the percussion device, taking the measurement data into account. The term 'sensors' may also refer to other means producing measurement data, such as measurement devices, measuring means and detectors.

[0070] In the situation shown in Figure 17, the percussion piston 33 has moved in the impact direction A so that the impulse flange 41 has moved from the interspace 46 to the first counter-flange 42. In that case the impulse edge S1 closes the pressure connection Y1 to the first impulse space 44, whereby a pressure pulse detectable by the pressure sensor 23a is generated. On the basis of the measurement data of the pressure sensor 23a the control unit 22 detects that the percussion piston 33 has reached its predetermined position in the impact direction A and thus it may issue a control command along a control line 48 to the electric pilot control valve 21 to change the position thereof so that the valve moves to the left from the position shown in Fig- ure 17. The change in the position of the pilot control valve 21 changes the position of the control valve 40 and, further, the travel direction of the percussion piston 33.

[0071] When the percussion piston 33 moves in the return direction B toward its extreme position, the impulse edge S2 closes the pressure connection Y2, whereby a closed pressure space is formed and a pressure pulse generated. The pressure pulse generated in the second impulse space 45 is detected by the second pressures sensor 23b, thus allowing the movement of the percussion piston 33 in the impact direction B to the predetermined position to be detected. On the basis of the measurement data and the control strategy provided, the control unit 22 issues a control command along the control line 49 to the electric pilot control valve 21 , which changes its position to correspond to the situation shown in Figure 17.

[0072] The control valve 40 of Figure 17 comprises, on the outer rim thereof, a flange 50, a first control pressure surface 51 and a second control pressure surface 52. The pressure acting on the control pressure surfaces 51 , 52 may be changed by connecting the control pressure surfaces either to the pressure line P or the tank line T, in which case the control valve moves either to the impact direction A or the return direction B. In the situation of Figure 17, the pilot control valve 21 is in the position a, in which the first control pressure surface 51 is connected to the pressure line P and the second control pressure surface 52 to the tank line T, the control valve 40 having moved to the return direction B. When a pressure pulse is detected in the first impulse space 44, the control unit 22 moves the pilot control valve 21 to the left to the position b in the figure, whereby the second control pressure surface 52 is connected through the pressure channel 53 to the pressure line P and the first control pressure surface 51 is connected through the pressure channel 54 to the tank line T. As a result, a force acts on the control valve 40 and moves it to the left from the position shown in the figure, whereby the working pressure channel 38 closes and the tank channel 39 opens. This decreases the pressure acting on the second working pressure surface 34b and the percussion piston 33 changes its direction of travel towards the return direction B. When a pressure pulse from the second impulse space 45 is detected, the control valve 40 is moved back to its position shown in Figure 17 by the control applied by the control valve 22 and the pilot control valve 21 . [0073] The percussion device 1 1 shown in Figure 18 differs from the one in Figure 17 in that it does not have any sleeve-like control valve. Instead, the control unit 22 has been configured to control an electric control valve 56, which has been configured, in turn, to control pressure fluid flows directly to and from the second working pressure space 37 along the channel 57. In the situation of Figure 18 the control valve 56 is in a position where it directs pressure fluid from the pressure line P into the working pressure space 37, whereby the percussion piston 33 thus moving towards the impact direction A. When the impulse flange 41 sets at the first counter flange 42, a pressure pulse is generated and detected, on the basis of which the control unit 22 issues a control command to change the position of the control valve 56. The control valve 56 thus moves to the left in the figure, opening the connection from the working pressure space 37 to the tank T. As a result, the percussion piston 33 changes its direction of travel.

[0074] To facilitate understanding the figures of this patent application indicate all channels connected to the tank with the letter T. The channels in the pressure line are marked with the letter P.

[0075] For practical reasons, the embodiments of the all figures have not been described in detail and completely with reference to every figure, but the structures and operating principles shown in different figures may also be used to understand the embodiments in other figures.

[0076] Unlike in the embodiments disclosed in the figures of this application, the front space 35 may also be a space with a varying pressure. In that case the control valve 40, 77 is configured to also control pressure fluid supply to and from this space.

[0077] Further, in contrast to the figures of this application, the return-direction end of the percussion piston 33 may move in a pressure space, such as a pressure space of a pressure accumulator, in which case the return movement of the percussion piston charges pressure energy into the pressure accumulator which can then be used during the next stroke movement.

[0078] The figures of this application show the structure of the percussion device 1 1 and the pressure medium channels leading thereto as a cartridge-type structure. This type of impact cartridge may be arranged in place into a space provided in the frame of a rock drilling machine or a breaking hammer. Alternatively, the structure may be a conventional construction. [0079] In many of the figures, reference marking H indicates a long edge or a skirt that is made possible by the construction of the invention. Thanks to such a long sealing surface, leakages between the control valve 33 and frame 25 may be insignificant. The efficiency of the percussion device 1 1 is then good.

[0080] In this application the term "trigger" is used to describe a situation where a pressure pulse provides the initial stimulus for or initiates a change in the position of the control valve. In other words, the pressure pulse triggers a chain of events as a result of which the control valve moves to a position that causes the direction of travel of the percussion piston to change.

[0081] A pressure pulse is a sudden, impulse-like pressure having a higher pressure than the basic pressure and a short duration. However, this type of pressure pulse may provide a change in the prevailing state, even if some other pressure and pressure surfaces were used in performing the change.

[0082] In some cases, the features disclosed in this patent application may be used as such, irrespective of other features. On the other hand, when necessary, features disclosed in this application may be combined in order to provide various combinations.

[0083] The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.