Abstract:
The invention relates to an impact mechanism comprising a housing ( 32 ) with at least two stroke adjustment channels ( 18, 19, 20 ); an adjustment arrangement ( 31 ) with at least two adjustment pin channels ( 35, 36, 37, 135, 136, 137 ) arranged to interact in a manner that can be selected with the stroke adjustment channels ( 18, 19, 20 ); and a hammer piston ( 1 ) that performs reciprocating motion in the housing ( 32 ) in order to impact repetitively onto an anvil ( 2 ), which hammer piston ( 1 ) has a stroke length that can be selected with the aid of adjustment pin channels ( 35, 36, 37, 135, 136, 137 ) and the stroke adjustment channels ( 18, 19, 20 ). According to the invention, the adjustment arrangement ( 31 ) comprises an elastic element ( 48 ) arranged to maintain the adjustment arrangement ( 31 ) in place for the stroke length that has been selected; and an operating means ( 34 ) arranged to select adjustment pin channel ( 35, 36, 37, 135, 136, 137 ) and thus the stroke length of the hammer piston ( 1 ).

Description:
TECHNICAL AREA 
       [0001]    The present invention concerns an impact mechanism according to the introduction of claim  1 . 
       THE PRIOR ART 
       [0002]    In rock drills and other hydraulic impact mechanisms, a hammer piston performs reciprocating motion in a cylindrical housing and makes repetitive impacts onto a shank adapter or other type of anvil. The length of stroke is the distance that the hammer piston travels between the positions at which the hammer piston changes its direction of motion. The stroke length can be controlled with the aid of a stroke adjustment arrangement, such as in the form of a stroke adjustment pin, in such a manner that the adjustment of the adjustment arrangement selects between different channels or combinations of channels, which influences, for example, the position at which the hammer piston is to change its direction of motion at the rear position. The energy and frequency of the impacts are in this way influenced. 
         [0003]    Several different variants of stroke adjustment arrangements are available. U.S. Pat. No. 4,413,687 reveals a drill in which the operator must first withdraw a spring-loaded locking pin from a recess in the adjustment pin. The operator must subsequently continue to apply a force onto the locking pin in order to hold the locking pin away from the adjustment pin, while the adjustment pin is axially displaced. The locking pin can subsequently be placed into another recess in the adjustment pin. The disadvantage is that two hands are required to change the stroke length. Since the spring-load locking pin is externally located, it will be influenced by rough handling and there is a risk that its lifetime will be short. 
         [0004]    U.S. Pat. No. 3,780,621 reveals a drill in which a locking screw must be removed from a pin in order to change the stroke length. The pin can subsequently be axially displaced and the locking screw is used to lock the pin in its new position. The disadvantage is that tools are required to change the stroke length. 
         [0005]    An adjustment pin for the changing of stroke length is shown on Page 56 of the Atlas Copco manual, fourth edition, published by Ljungföretagen AB, Örebro, Sweden in 1982. The adjustment pin has three channels along the axis for the selection of stroke length, which channels can be selected by loosening a nut, turning the pin, and then retightening the nut. The disadvantage is that tools are required to change the stroke length. 
         [0006]    Various variants of more or less automatic adjustment of stroke length are revealed in, for example, EP 0 080 446, EP 0 112 810, WO 2007/097677 and WO 2008/033075. These work well, but are also complicated and consequently expensive. 
       DESCRIPTION OF THE INVENTION 
       [0007]    The purpose of the present invention is to solve the problems of adjusting the stroke length using prior art technology. This purpose is achieved according to the invention through the distinctive features in claim  1 . 
         [0008]    The advantages are that the stroke length can be changed manually, with one hand, in a rapid, simple and cheap manner, without the need of tools or complicated constructions. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0009]    The invention will be explained in more detail with the aid of a preferred embodiment and with reference to the attached drawings, of which: 
           [0010]      FIGS. 1   a - d  show an overview of how an impact mechanism works and how change of the stroke length can be carried out. 
           [0011]      FIGS. 2   a - c  and  3   a - c  show a first embodiment in cross-sections, overview and side views. 
           [0012]      FIGS. 4   a - c  show an overview and side views of a second embodiment. 
           [0013]      FIGS. 5   a - c  and  6   a - c  show a third embodiment in cross-sections, overview and side view. 
           [0014]      FIGS. 7   a - c  and  8   a - c  show a fourth embodiment in cross-sections, overview and side view. 
       
    
    
     PREFERRED EMBODIMENT 
       [0015]      FIGS. 1   a - d  show schematically a prior art hydraulic down-the-hole impact drill with an impact mechanism of the alternating pressure type, arranged in a housing. The impact mechanism comprises a hammer piston  1  that moves forwards and backwards and impacts upon a shank adapter  2  or similar. The shank adapter  2  then transfers the impact energy through a drill string (not shown in the drawings) and a drill bit (not shown in the drawings) to the rock. 
         [0016]    The forward end  3  of the hammer piston is here denoted as the end that makes impact with the shank adapter  2 , while the rear end  4  of the hammer piston is the end that is directed away from the shank adapter  2 . The hammer piston  1  in this example comprises a forward piston boom  5  with a forward driving area  6 , and a rear piston boom  7  with a rear driving area  8 . The forward and backward motion is controlled with the aid of a valve piston  9  and a number of channels. An intake accumulator  25  and a return accumulator  24  even out peaks of pressure during the process. 
         [0017]    The valve piston  9  is in its first position in  FIG. 1   a . A forward signal channel  10  is open to high pressure  11 , through the valve piston  9 , to the rear driving area  8  of the hammer piston. A backwards signal channel  14  is open from the forward driving area  6  of the hammer piston, through the valve piston  9 , to low pressure  23 . 
         [0018]    This gives a pressure of the rear driving area  8  of the hammer piston, but not on the forward driving area  6  of the hammer piston, which causes the hammer piston  1  tomove forwards towards the shank adapter  2 . The rear piston boom  7  blocks a passage to a first adjustment channel  12 , which later will cause a reversal of the motion of the piston. 
         [0019]    The hammer piston  1  continues its motion forwards in  FIG. 1   b . When the hammer piston  1  approaches the shank. adapter  2 , the rear piston boom  7  no longer blocks passage to the first adjustment channel  12 . This causes the first adjustment area  13  of the valve piston to be placed under pressure, which causes the valve piston  9  to move to its second position. 
         [0020]    The valve piston  9  has moved to its second position in  FIG. 1   c . In this way, the backwards signal channel  14  is instead open to high-pressure  11 , through the valve piston  9 , to the forward driving area  6  of the hammer piston. The passage from high pressure  11  to the forward signal channel  10  is closed, such that the rear driving area  8  of the hammer piston is no longer under pressure, and is instead connected to low pressure  23  through the valve piston  9 . This change in pressure changes the direction of motion of the hammer piston  1 , such that the hammer piston  1  is instead forced backwards. 
         [0021]    The hammer piston  1  is moving backwards in  FIG. 1   d . An adjustment arrangement in the form of an adjustment pin  15  makes it possible to set the length of the stroke. The adjustment pin  15  in this example has a first adjustment pin channel (notshown), a second adjustment pin channel  16  and a third adjustment pin (not shown). A fundamental stroke adjustment channel  17 , a first stroke adjustment channel  18 , a second stroke adjustment, channel  19  and a third stroke adjustment channel  20  are present in the housing. The fundamental stroke adjustment channel  17  is connected through a second adjustment channel  21  to the second adjustment area  22  of the valve piston. 
         [0022]    If the adjustment pin  15  is placed into a first position, the first adjustment pin channel will connect the fundamental stroke adjustment channel  17  with the first stroke adjustment channel  18 . If the adjustment pin  15  is placed into a second position, the second adjustment pin channel  16  will connect the fundamental stroke adjustment channel  17  with the second stroke adjustment channel  19 . If the adjustment pin  15  is placed into a third position, the third adjustment pin channel will connect the fundamental stroke adjustment channel  17  with the third stroke adjustment channel  20 . 
         [0023]    The adjustment pin  15  is shown in  FIG. 1   d  in its second position. When the hammer piston  1  during its backwards motion opens the first stroke adjustment channel  18  to pressure  11 , nothing will happen, since the first stroke adjustment channel  18  in this position is not connected to the fundamental stroke adjustment channel  17 . 
         [0024]    When the hammer piston  1  has moved a small distance further backwards, however, the second stroke adjustment channel  19  is opened to pressure. The second adjustment pin channel  16  connects the second stroke adjustment channel  19  with the fundamental stroke adjustment channel  17 , and thereby with the second adjustment channel  21  and the second adjustment area  22  of the valve piston. This causes the second adjustment area  22  of the valve piston to be placed under pressure, which causes the valve piston  9  to move to its first position. The passage to the backwards signal channel  14  is closed, such that the forward driving area  6  of the hammer piston is no longer placed under pressure. The hammer piston  1  is in this way forced to change direction and move forwards again, and the stroke cycle begins again according to  FIG. 1   a.    
         [0025]    If the adjustment pin  16  had instead been placed into its first position, the second adjustment area  22  of the valve piston would have been placed under pressure already when the hammer piston  1  passed the first stroke adjustment channel  18 . The hammer piston  1  would therefore have changed direction earlier. In a corresponding manner, if the adjustment pin  16  had been placed into its third position, the second adjustment area  22  would not have been placed under pressure until the hammer piston  1  had passed the third stroke adjustment channel  20 . The hammer piston  1  would therefore have changed direction later. The stroke length of the hammer piston  1  can in this way be selected, and in association with this, impacts of different energy and frequency can be obtained. 
         [0026]    The adjustment pin  15  in  FIGS. 1   a - d  can be adjusted as stated in the Atlas Copco manual above, through the adjustment pin  15  having several adjustment pin channels that can be selected by means of rotation through first unscrewing a nut, then rotating the adjustment pin to another position, and then rescrewing the nut. Another alternative is to remove the adjustment pin  15  by unscrewing and to exchange it for another type with another adjustment pin channel. Both alternatives require a tool and are therefore difficult to carry out. 
         [0027]    A solution according to the invention is shown in the following drawings, which solution can be used in, for example, an impact mechanism of the alternating pressure type described above, or similar, instead of the adjustment pin  15  shown in the drawings. The invention can be used also in impact mechanism of the constant pressure type and in other conceivable impact mechanisms in which it is necessary to adjust the stroke length. It is not relevant whether the hammer piston impacts onto a shank adapter, as described above, or directly onto the drill bit or drill string, or alternatively onto a chisel or similar. All of these can be regarded as variants of an anvil onto which to make impacts. 
         [0028]    An adjustment arrangement in the form of an adjustment pin  31  or similar, mounted in a housing  32  in an impact mechanism is shown in  FIGS. 2   a - c  and  3   a - c .  FIG. 3   a  shows only the adjustment pin  31 .  FIG. 3   c  shows only the housing  32 , seen from the side.  FIGS. 2   a - c  and  FIG. 3   b  show the housing  32  with the adjustment pin  31  mounted. 
         [0029]    The adjustment pin has an inner end  33  and an outer end  34 . The adjustment pin  31  has a first groove  35 , a second groove  36  and a third groove  37 . It is preferable that these grooves be longitudinal grooves milled along the axis  38  of the adjustment pin, and that they be separated from each other. The grooves  35 ,  36 ,  37  have the function of the adjustment pin channels described above, and they can, as has been described above, be used to connect a fundamental stroke adjustment channel  17  in the housing with a first stroke adjustment channel  18 , a second stroke adjustment channel  19  or a third stroke adjustment channel  20 , respectively. It is thus possible to select an adjustment pin channel and in this way to select a stroke adjustment channel by means of rotation. 
         [0030]    These adjustment pin channels  35 ,  36 ,  37  and stroke adjustment channels  18 ,  19 ,  20  may be designed in different manners: the number of channels and their appearance is not relevant, as long as a similar function is carried out. In particular, the number of channels may be two or four, just as advantageously as three. 
         [0031]    There is preferably an attachment arrangement  43  on the adjustment pin  31  in the form of a peg  43  or similar, which here has the shape of an egg but may have another appearance. The peg  43  fits into an attachment arrangement  44 ,  45 ,  46  in the housing in the form of three indentations  44 ,  45 ,  46 . By selecting the indentation  44 ,  45 ,  46  with which the peg is brought into contact, also the amount by which the adjustment pin  31  is to be rotated is selected, and thus also which of the adjustment pin channels  35 ,  36 ,  37  and by extension which of the stroke adjustment channels  18 ,  19 ,  20  is to be selected. In this way the stroke length is selected: compare this with the description above. 
         [0032]    In order to obtain higher strength, the adjustment pin  31  may have two or three pegs  43   a ,  43   b ,  43   c  circularly arranged around the adjustment pin  31 , such that they can make contact with more than one indentation  44 ,  45 ,  46  at the same time, see the example shown in  FIGS. 4   a - c.    
         [0033]    Alternatively, and in contrast, the peg or pegs may be arranged in the housing  32 , while the indentations are arranged in the adjustment pin  31 . Also other attachment arrangements may be conceived without changing the function. 
         [0034]    The adjustment pin  31  may be mounted in the housing with the aid of, for example, a nut  49  with a hole  50 , through which the outer end  34  of the adjustment pin can pass. 
         [0035]    A flange or similar  47  is present on the adjustment pin  31 , as is also an elastic element in the form of a spring  48  or similar that in its tensioned condition makes contact at one  51  of its ends with the flange  47  and at the other  52  of its ends with the nut  49  or with another part of the housing  32 . The nut  49  or other parts attached to the housing  32  in this context are to be considered to be a part of the housing  32 . 
         [0036]    Through the adjustment pin  31  being placed under axial spring-load in this manner, the peg  43  is held in place in the selected indentation  44 ,  45 ,  46 , which ensures that the adjustment pin channels  35 ,  36 ,  37  are held in place and function as intended. 
         [0037]    A further alternative is that the flange  47  itself be designed as three pegs that are sufficiently broad for the spring  48  to be able to make contact also with them. 
         [0038]    In order to change the adjustment pin channel  35 ,  36 ,  37  and thus also the stroke length, the operator pulls the outer end  34  of the adjustment pin or another corresponding operating means  34  and thus compresses the spring  48 . The operator pulls until the peg  43  becomes released from the indentation  44 ,  45 ,  46 . It is now possible to rotate the adjustment pin  31 , and it is possible to fit it into another indentation  44 ,  45 ,  46 . When the operator releases the outer end  34  of the adjustment pin, the spring force will cause the adjustment pin to regain its position, while the peg  43  is held fast in a new indentation  44 ,  45 ,  46 . 
         [0039]    The outer end  34  of the adjustment pin may be provided with a pin  53  or similar in order to either facilitate grip on the adjustment pin  31  or indicate which of the three positions the adjustment pin  31  has been set against markings  55 ,  56 ,  57  on the housing, or both facilitate grip on the adjustment pin  31  and indicate which of the three positions the adjustment pin  31  has been set against markings  55 ,  56 ,  57  on the housing. 
         [0040]    An embodiment is shown in  FIGS. 5   a - c  and  6   a - b  in which the spring  48  is arranged such that the outermost end  34  is depressed instead of being withdrawn during change of the adjustment pin channel  35 ,  36 ,  37 , whereby the spring  48  is compressed in order to release the peg  43  from the indentation  44 . 
         [0041]      FIG. 6   b  shows in cross-section also how the adjustment pin channels  35 ,  36 ,  37  are separated from each other. 
         [0042]    Also other variants of elastic elements  48  can be envisioned such as, for example, elements that are pulled apart rather than being compressed. This is the case for all embodiments. 
         [0043]      FIGS. 7   a - c  and  8   a - b  show a further embodiment. It is necessary in the embodiments previously described that the impact mechanism is not in operation in order to be able to adjust the stroke length. The adjustment pin channels  35 ,  36 ,  37  in these cases included grooves or similar that were separated from each other. 
         [0044]    In contrast,  FIGS. 7   a - c  and  8   a - b  show three adjustment pin channels  135 ,  136 ,  137  that transition into each other. This ensures that, independently of how the adjustment pin  31  has been rotated, a connection will always be formed between the fundamental stroke adjustment channel  17  and one of the stroke adjustment channels  18 ,  19 ,  20 , and this in turn ensures that the impact mechanism can function, independently of how the adjustment pin  31  has been rotated. 
         [0045]    The attachment arrangements  43  and  44  are loosened in  FIGS. 7   a - c  and  8   a - b  from each other through the outer end  34  being pulled out. In order for a connection between the fundamental stroke adjustment channel  17  and one of the stroke adjustment channels  18 ,  19   20  to be maintained also when the outer end  34  is pulled out, the adjustment pin channels  135 ,  136 ,  137  in the embodiment shown in  FIGS. 7   a - c  and  8   a - b  are longer than in the previously shown embodiments. 
         [0046]    The corresponding is, of course, true if the embodiment shown in  FIGS. 5   a - c  and  6   a - b  is designed in a corresponding manner with adjustment pin channels that transition into each other, whereby the extension of the adjustment pin channels, naturally, must be made in the other direction, in order to make possible change of stroke length through the outer end  34  being depressed instead. 
         [0047]    The invention is, of course, not limited to the example described above: it can be modified within the framework of the attached claims.