Abstract:
A percussive device including, inside a machine housing ( 3 ), a reciprocally moveable percussive piston ( 2 ), the movement of which being controllable through a control valve ( 5 ), which is arranged to alternatively connect a chamber to a pressure source and to low pressure in dependence of a signal describing the axial position of the percussive piston, wherein valve means ( 16 ) are arranged to allow adjustment of in which axial position of the percussive piston said signal is transmitted, through respectively opening and blocking of connection between one or a plural of said control channels ( 10,11,12,13 ) and the control valve. The invention also concerns a rock drilling machine and a method.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention concerns a percussion device according to the preamble of claim  1 . The invention also concerns a rock drilling machine including such a percussion device. 
       BACKGROUND OF THE INVENTION 
       [0002]    EP-0 080 446 (Atlas Copco AB) discloses a rock drilling machine, wherein the feeding force is transmitted from the housing to the drill string or the drill string adapter over a damper. The damper yields from the reflected compressive shock waves and the yield is detected and used to control a control pin which adjust the stroke length for the percussive piston such that the reflective shock wave energy is minimized. 
         [0003]    In particular, the control pin is an adjustment means which adjusts in what axial position of the percussive piston a pressure signal is transmitted to a to-and-fro moveable valve body, wherein means are arranged in order to control the control pin as a response to the pressure signal such that the operation of the percussion device is modified for reduction of reflected shock wave. In an alternative embodiment the control pin is controlled after analysis of a drilling parameter in connection to the drill string. 
         [0004]    The known drilling machine functions well but is gives limited possibilities to easily control the axial turning-positions of the percussive piston. 
       THE AIM AND MOST IMPORTANT FEATURE OF THE INVENTION 
       [0005]    It is an aim of the present invention to provide a percussive device of the kind indicated above, which is an improvement of the known percussive device. In particular it is an aim of the invention to provide a percussion device with simpler and more secure adjustment possibilities as concerns the movement of a percussive piston. 
         [0006]    This aims are obtained according to the invention through the features of the characterizing portion of claim  1 . 
         [0007]    Hereby is achieved that a distinct adjustment of the stroke length of the percussive piston is possible in a secure manner. This is a great advantages, since the possibility is provided to simply control the stroke length by emitting simple, uncomplicated on (and possible off) signals to the valve elements in order to vary percussive energy emitted from the percussion device as a response to the requirements that exists in the particular operating situations. This as a contrast to the back ground art, wherein a valve body is moved between several different axial positions for the respective opening of several axially separated control channels. 
         [0008]    If it is desired to change the striking position of a percussion device, the setting channel (control channel) for high pressure can be moved reward, i.e. in the direction away from the drill shank, which results in longer strike length and more power in each strike. Given the same pressure it takes longer time to accelerate the piston when the strike length is longer, which results in drilling with a lower frequency. 
         [0009]    Generally it can be said to be a desire to vary the percussive energy of the percussion device according to the variations of the hardness of the rock. In particular it is desired to control the percussion device in this respect after the requirements that exist in an actual portion of a rock. Through the invention, the percussion device can be controlled with simple means in the direction of optimizing drilling and reduction of shock wave reflexes, which the drilling process does not benefit from. 
         [0010]    In general for a drilling process there are indications to the extent that drilling with a new drill bit is preformed with too high percussive energy. This because with a new drill bit, only a smaller portion of the actuation units of the drill bit will come into actual engagement with the rock. After a certain wear of the drill bit, however, the percussive energy will gradually automatically be adjusted to a somewhat worn shape of the engagement portions of the drill bit, whereby the efficiency of the drilling process will increase. With continued wear of the drill bit, the efficiency will, however, drop again because of less good adaption of the percussive energy to the actual appearance of the drill bit. 
         [0011]    The invention makes it possible to take account of this phenomenon and that a percussive energy is controlled in order to be better adapted to the state of wear of the drill bit. These gives the possibility to achieve increased drilling rate with the same percussive effect, reduced strain in the drill steel, less reflexes from the rock, which in turn can result in that a smaller damping unit will be necessary. Through the invention, a drilling machine can be easily adapted to varied drill bit wear, rock strength and drill bit size. The drilling machine can hereby be set in advance for certain of the parameters which are known or be controlled during drilling after need and sensed parameters. 
         [0012]    In a preferred embodiment of the invention, the control is possible as a response to a parameter describing the drilling process, such as for example drilling rate or pressure in a damping chamber or as a result of shock wave amplitude, measured through shock wave measurements. 
         [0013]    Further advantages are obtained through further aspects of the invention, which will be apparent from the following description of an embodiment. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0014]    The invention will now be described in greater detail by way of embodiments and with reference to the annexed drawings, wherein: 
           [0015]      FIG. 1  shows grammatically, in an axial section, a part of a drilling machine including a percussion device according to the invention, 
           [0016]      FIG. 2  shows diagrammatically, in an axial section, a valve means according to the invention in a percussion device, 
           [0017]      FIG. 3   a - d  shows in sections the valve means in  FIG. 2  in different positions, 
           [0018]      FIG. 4   a - d  shows in sections another valve means according to the invention in different settings, and 
           [0019]      FIG. 5  illustrates a block diagram over a method wherein the invention is employed. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0020]      FIG. 1  shows a part of a rock drilling machine  1  including a percussion device with a percussion piston  2 . A valve for switching pressure medium for driving the percussive piston is indicated with  5 . Further is included a central positioning unit  6  and a rotation unit, a damping unit etc. which are not shown on  FIG. 1 . The percussive piston  2  is reciprocally moveable inside the machine housing  3 . 
         [0021]    In the machine housing  3  there are, in the area of a percussive piston land  8 , a number of control channels  10 - 13  which are arranged to co-operate, with their channel openings, with a first edge  14  of the percussive piston land  8 . An interrupted line indicates at  14 ′ a position of the first edge  14  when the percussive piston has retracted after a strike so that the opening to the control channel  10  is uncovered. 
         [0022]    A chamber  4  that can be pressurized receives in a per se known manner a drive face on the percussive piston in the form of drive flank of a percussive piston land. 
         [0023]    For chosen communication between the different control channels and a signal conduit  15 , which leads to the valve  5  for switching the movement direction of the percussion device, there is arranged a valve means  16 , the function of which is explained below. 
         [0024]    The percussive piston  2  is actuated by high fluid pressure in the chamber  4  towards a striking position in order to initiate a strike in the direction to the right, as seen in the Figure, in a per se known manner, against a drill shank. In the return chamber  9 , which receives a flank of a percussive piston land having a surface being smaller than the surface of the flank in the chamber  4 , there prevails during operation, in a manner known per se, during the return drive of the percussive piston, the high pressure. 
         [0025]    When the drive chamber  4 , by switching of the valve  5  is drained to tank, thereby occurs a return drive of the percussive piston  2  such that it after a while has been moved in the direction to the left, as seen in  FIG. 1 , into a position where the control edge  14  is in the shown position  14 ′, as an example. Hereby the higher pressure in the chamber  9  will be transmitted to the signal conduit  15 , over one of the control channels  10 - 13 , which is chosen, for switching the valve  5  to the left, as seen in the Figure, in order to transmit high pressure to the chamber  4  and thereby initiation of a new strike. 
         [0026]      FIG. 2  shows the valve means  16  according to a first embodiment, wherein two concentric valve elements control how the control channels  10 - 14  communicate with the signal conduit  15 . 
         [0027]    The valve means  16  includes a first valve element  17  and, arranged concentrically inside this, a second valve element  18 . Both valve elements have cylindrical general configuration and are moveable axially as desired. A valve housing  19  which receives the valve elements, exhibits at its right flank end a constant pressure chamber  20 , inside which prevails a pressure P d , permanently acting on both valve elements, which thus from this pressure are pressed to the left as seen in  FIG. 2 . 
         [0028]    The first valve element  17  has on its opposite, left, side a first control chamber  21 , which at choice is fed with a first pressure P 1  which is of such a magnitude that the pressurizing of the first control chamber  21  displaces the first valve element from the shown position to a position to the right against the action of the pressure P d . A second control chamber  22  is arranged, at choice, to be pressurized by a second pressure P 2 , which is able to press the second valve element  18  to the right against the action of the pressure P d . In this embodiment this means resting against an inward shoulder  23  on the first valve element  17 . Other solutions with completely independent first and second valve elements are within the scope of the invention. 
         [0029]    In  FIG. 3   a  to  3   d  the function of the valve in  FIG. 2  is explained in greater detail. 
         [0030]    The valve means  16  is in  FIG. 3   a  shown in a position when the “uppermost” situated control channel  13  alone is in connection with the signal conduit  15 , which it is permanently through a permanent communication. The other control channels  10 - 12  are blocked. 
         [0031]    It shall here be emphasised that the term open in this connection means that channel portions of a connection between the control channel and the respective control channels is open for the possibility of fluid transmission. It is, however, not excluded that a control channel having a channel portion open can be included in a connection which is blocked as seen totally along its extension by the effect of a second valve element blocking a second channel portion. 
         [0032]    In  FIG. 3   a  the first valve element  17  is shown in its first position, wherein first portions F 1  of connections between a first subset  10  and  12 , of the control channels and the control valve  5  are blocked by this first valve element  17 . No (or a lower) control pressure prevails in each one of the control chambers  21  and  22 . The second valve element  18  is shown in its first position, wherein a second portion F 2  of a connection between a second subset  10  (/ 11 ) of the control channels and the control valve  5  is blocked. 
         [0033]    In the embodiment in  FIG. 3   a , the first valve element is constructed such that a portion F 3  of connection between the control valve and a control channel  11  from the second subset is open. The position of the second valve, however, blocks according to the above the further connection with a control valve  5 . Hereby only the control channel  13  is in connection with the control valve  5 , whereas the second control channels  10 ,  11  and  12  are blocked along their connections. 
         [0034]    The control channels  10 - 13  are axially separated with the same spacing, and the distance between the channel portions  24  and  25  in the first valve element (approximately) corresponds to the distance 2×L, wherein, in this embodiment, L is the distance between centres of two adjacent control channels. It should be noted that a differently constructed embodiment can be designed with a variation of distance between the different openings in order to achieve a desired characteristic of the percussion device. 
         [0035]    Reference numerals  24 ′ and  25 ′ concern surrounding turned out grooves in the cylindrical outer wall of the first valve element in per se known manner for valve bodies of similar kind. The turned out groove  25 ′ has an axial extension which (about) corresponds to L for reasons that will appear below. 
         [0036]    The second valve element  18  exhibits two piston portions  27  and  28  sealing against an inner cylindrical space in the first element  17 , and the intermediate, turned out groove  26 , has a width exceeding 2×L. It should be observed that channelling from the control channels can be arranged such that mutual distances between openings in the valve means  17  deviate from distance between the openings in the percussive piston cylinder. 
         [0037]    In  FIG. 3   b  prevails a control pressure P 1  in the control chamber  21  but no (or a lower) control pressure in the control chamber  22 . The first valve element  17  is switched to a second position, wherein the channel portions  24  and  25  are in open connection with the control channels  10  and  12  respectively. The control channel  11  is, however, locked and the turned out groove  25 ′ transmits fluid connection through open connection with each one of the control channels  12  and  13 . The portions F 1  are open. 
         [0038]    The second valve element  18  is still in its first position and blocks through its piston portion  27  the channel portion  24 . The second portion F 2  is blocked. In the shown position, both control channels  12  and  13 , but not the control channels  10  and  11  have fluid connection with the signal conduit  15 . 
         [0039]    In  FIG. 3   c  there prevails no (or a lower) control pressure inside the control chamber  21 , but the control pressure P 2  prevails in the control chamber  22 . The first valve element  17  is in the first position, the same as in  FIG. 3   a , whereas the second valve element  18  is in a second position, with its axial end, positioned towards the not shown drill shank, lying against the inwardly directed shoulder  23  in the first valve element. Said second portion F 2  is open. A channel  26  being formed by a turned out cavity in the second valve element  18  and the inner surface of the first valve element  17  together with the upper parts of the channel portions  24  and  25  constitutes an open connection over said second portion F 2 . The result of this is at the control channel  11  over the channel portion  24 , the turned out cavity  26  and the channel portion  25  has fluid connection with the control channel  13  and thereby with the signal conduit  15 . The control channel  10  is blocked along its extension. 
         [0040]    In  FIG. 3   d  the control pressure P 1  prevails in the control chamber  21  and the control pressure P 2  in the control chamber  22 . The first valve element  17  is in its second position, the same as in  FIG. 3   b , whereas the second valve element  18  is also in its second position lying against the inward directed shoulder  23 . The result of this is that the control channel  10  has fluid connection with the control channel  13  and thereby with the signal conduit  15  over the channel portions  24  and  25  and the turned out cavities  26  and  25 ′. The portions F 1  and F 2  are open. The turned out cavity  26  in the second valve element  18  and the inner surface of the first valve element  17  together with the upper parts of the valve portions  24  and  25  constitute, as is indicated above, an open connection. 
         [0041]      FIGS. 4   a - 4   d  show an alternative embodiment of the present invention, wherein in a valve means  16 ′, three valve bodies  30 - 32  acting against respective valve seats are arranged to control opening and blocking respectively of one control channel each. Also in this embodiment only two control pressures are needed for its actuation. 
         [0042]    With a first control pressure P 1  in the control chambers  30 ′ and  32 ′, both valve elements  30  and  32  are in their first positions, wherein the connection portion F 1  (through the valve element  30 ) is blocked and thereby the connection between control channels  10  and  12  as well as the control valve. Through a second control pressure P 2  in the control chamber  31 ′, the valve element  31  in its first position, whereby the connection portion F 2  between the respective control channels and the control valve is blocked and thereby the control channel  11  (and also the control channel  10 ), which is shown in  FIG. 4   a.    
         [0043]    By switching control pressure such that in the control chamber  30 ′ a lower pressure P 0  prevails, it is provided an open connection with control channel  10  as well as  12 . The connection portion F 1  is open, but because the second control pressure P 2  prevails in the control chamber  31 , the connection portion F 2  is blocked and thereby the connection between the control valve and the control channel  11  (and also the control channel  10 ), which is shown in  FIG. 4   b.    
         [0044]    Because the first control pressure P 1  prevails in the control chambers  30 ′ and  32 ′, the control chamber  10  as well as  12  are blocked, and by a lower pressure P 0  prevailing in the control chamber  31 ′, it is provided an open connection with the control channel  11  which is shown in  FIG. 4   c . The connection portion F 2  is open. 
         [0045]    Since in all control chambers  30 ′,  31 ′ and  32 ′ the lower pressure P 0  prevails, the connection portions F 1  and F 2  are open. Further, a connection portion F 4  between the upper part of the control channel  10  and the portion F 2  is open. Thus is provided an open connection with all control channels  10 - 12 , which is shown in  FIG. 4   d.    
         [0046]    Other different valve embodiments can come into question for achieving the desired function. 
         [0047]    Altogether, the longest strike length of the percussive piston is achieved if all control channels  10 ,  11  and  12  are blocked such that only the control channel  13  communicates with the signal conduit  15 , whereby the valve  5  is switched at a late stage of the return movement of the percussive piston. Shortest strike length is achieved if the control channel  10  communicates with the signal conduit  15 , whereby the valve  5  is switched at an early stage of the return movement of the percussive piston. 
         [0048]    In  FIG. 5  is indicated a method sequence for obtaining a strike in a percussive device, wherein: 
         [0049]    Position  40  indicates start of the sequence. 
         [0050]    Position  41  indicates generating a strike in a percussive device. 
         [0051]    Position  42  indicates obtaining a parameter signal concerning a parameter describing the drilling process such as a pressure in a damping chamber. 
         [0052]    Position  43  indicates analysing the signal obtained in position  42  and generating a signal for switching the valve element in correspondence thereto for modifying the strike length of the percussive piston. 
         [0053]    Position  44  indicates generating a strike in the percussive device with the modified stroke length. 
         [0054]    Position  45  indicates the end of the sequence. 
         [0055]    The invention can be modified further within the scope of the following claims. The percussion device can work according to the different principles besides what is shown on  FIG. 1 , with permanently applied pressure in the striking direction of the percussive piston and alternating pressurizing for the return stroke or vice versa. 
         [0056]    The invention can be applied for controlling the upper turning position of the percussive piston as well as its lower turning position. It can also be applied in applications without rotational unit and damper, for example on so called breakers.