Patent Publication Number: US-2010116518-A1

Title: Coupling arrangement for coupling rock drill shank

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a coupling arrangement for coupling a drill shank of a rock drill unrotatably but axially movably with respect to a rotation bushing locating around the drill shank while the shank is mounted in place in the rock drill and rotating the drill shank, in which arrangement the rotation bushing comprises, in relation to the direction of rotation, at least one power transmission surface substantially in the direction of the rotation axis, transverse to the direction of rotation and facing the direction of rotation, and correspondingly, the drill shank comprises an equal number of power reception surfaces substantially in the same direction and facing from the power trans-mission surfaces to the direction of rotation, whereby the rotation torque is transferred during rotation from the rotation bushing through the power trans-mission and power reception surfaces to the drill shank. 
     In rock drilling apparatuses a drill rod is rotated during drilling with a separate rotation motor, which in most cases is a hydraulic motor. The rotation motor rotates a separate coupling piece, typically a rotation bushing. The rotation bushing, in turn, rotates a drill shank, to which a drill rod is coupled with a standard threaded joint and in which percussion pulses required in drilling are induced with a percussion piston of the rock drill or a like mechanism. 
     Typically, the coupling between the rotation bushing and the drill shank is implemented by using axial grooving in the rotation bushing, and correspondingly, in the drill shank, whereby they engage unrotatably but axially movably with one another. In that case the lateral surfaces of the grooves act as transmission and reception surfaces of the rotation torque. 
     A problem with the current solutions is that the lateral surfaces of the grooves rub against one another during drilling, while the rotation torque of the rotation motor presses the surfaces against one another. This results in heating and deteriorating of the surfaces. The larger the rotation torque to be transmitted, the axial movement between the drill shank and the rotation bushing as well as the percussion frequency of the drill, the higher the friction force acting between the surfaces. 
     Various solutions have been proposed to solve this problem. One method employs oblique grooving, whereby as a result of a translational movement produced by an impact, the surfaces disengage and the movement takes place without friction between the surfaces. On the other hand, in this solution a movement produced by a reflection pulse causes a reversed phenomenon, whereby a reflected compression wave causes a percussion-like load spike on the contact surfaces. Consequently, as both friction and load spike affect the surfaces, the contact surfaces may get damaged mechanically. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The object of the present invention is to provide a coupling arrangement by which current problems may be considerably reduced. 
     The arrangement of the invention is characterized in that the arrangement includes power transmission members between each power transmission surface and a corresponding power reception surface, which power transmission members, as the drill shank moves in relation to the rotation bushing in the longitudinal direction thereof, rotate along the power trans-mission surface and correspondingly along the power reception surface, and through which the rotation torque is transferred from the power transmission surface to the power reception surface. 
     The basic idea of the invention is that between the power transmission and power reception surfaces of the rotation bushing and the drill shank there are mounted transmission members serving as bearings, which rotate along the surfaces, as the drill shank and the rotation bushing move longitudinally with respect to one another. The basic idea of an embodiment of the invention is that in the rotation bushing and in the drill shank there are provided a plurality of mutually aligned grooves and that in the grooves there are placed balls that act as transmission members and, on one hand, transmit the rotation torque from the rotation bushing to the drill shank, and, on the other hand, allow the axial movement between them substantially without sliding friction. 
     The invention has an advantage that when rolling transmission members, such as balls, are used between the rotation bushing and the drill shank, there are no mutually abrasive surfaces in the rotation bushing and the drill shank. Further, a sufficient number of rolling transmission members in each groove are capable of transmitting a required rotation torque without excessive surface pressure, whereby mechanical damage will not occur. Still further, as the drill shank moves in its longitudinal direction with respect to the rotation bushing, the transmission members roll against the counterpart surfaces of the rotation bushing and the drill shank, whereby at its most advantageous all friction is substantially just rotation friction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described in greater detail in connection with the attached drawings, in which 
         FIG. 1  is a schematic view of a conventional rock drill, 
         FIG. 2  is a schematic view of a front end of the rock drill partly cut open and provided with a coupling arrangement of the invention, 
         FIGS. 3   a  to  3   c  are schematic views of a front end of the rock drill and some details of the solution, cut along line A-A of  FIG. 2 , 
         FIGS. 4   a  and  4   b  show some other embodiments of the invention cut open, 
         FIGS. 5   a  and  5   b  show still some other embodiments of the invention, and 
         FIG. 6  is a schematic view of yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION 
     In  FIGS. 1 to 6 , like reference numerals refer to like parts, except when the embodiment in some respects differs from the others. Thus, like parts have not been separately provided with reference numerals in all figures, unless essential for the sake of clarity. 
       FIG. 1  is a schematic view of a rock drill  1 . It includes a rotation motor  2  that is coupled in a manner known per se to rotate a drill shank  3  through a separate, not visible, rotation bushing. A drill rod and a drill bit are coupled to the drill shank  3  in a manner known per se using threads (not shown). 
       FIG. 2  shows a front end of the rock drill cut open in the longitudinal direction thereof. It comprises a body  1   a , onto which other parts are mounted. It shows how a toothed wheel  4  on the axis of the rotation motor  2  is engaged through a transmission gear  5  to rotate a rotation bushing  6  that rotates on schematically shown bearings  1   b . The rotation bushing  6 , in turn, is located around the drill shank  3 . A percussion piston  7  known per se, of which only the end is seen here, strikes on the head of the drill shank  3  when the rock drill is running and makes the drill shank  3  and the drill rod connected thereto, known per se and not shown here, move towards the rock to be drilled, i.e. to the left in the situation shown in  FIG. 2 . 
     In the solution of  FIG. 2 , the outer diameter of the drill shank  3  is slightly smaller than the inner diameter of the rotation bushing  6 , and consequently they are not in direct contact with one another. Instead, in the drill shank  3  and in the rotation bushing  6  there are provided grooves  3   a  and  6   a  such that they are radially aligned. In accordance with an embodiment, there are three grooves, whereby they are symmetrically spaced at 120-degree intervals on the outer surface of the drill shank, and correspondingly, on the inner surface of the rotation bushing  6 . The grooves  3   a ,  6   a  are further provided with balls serving as transmission members  8  and being substantially equal in size with the grooves, and they keep the drill shank  3  and the rotation bushing  5  substantially aligned in the radial direction. The number of balls may be selected in accordance with the rotation torque to be transmitted and the diameter of the drill rod/drill bit. 
     As shown in  FIG. 2 , at one end of the grooves of the rotation bushing and in a corresponding manner of the drill shank there are shoulders  3   b  and  6   b , respectively, which prevent the balls from falling off. Thus, the shoulder  6   b  of the rotation bushing  6  is located towards the rear end of the rock drill, i.e. towards the end on the side of the percussion piston  7 , and the shoulder  3   b  of the drill shank is located towards the front end of the rock drill  1 . 
       FIGS. 3   a  and  3   b  show schematically the front end and a detail of the solution cut along line A-A of  FIG. 2 . This shows how the rotation bushing  6  and the drill shank  3  comprise grooves  3   a ,  6   a , respectively, that are mutually aligned in the circumferential direction and preferably symmetrically round the circumference. In the embodiment of  FIGS. 3   a  and  3   b  the number of grooves  3   a ,  6   a  is three each. In this solution no surfaces are in contact with each other between the drill shank  3  and the rotation bushing  6 , but they are only interconnected by means of the balls serving as transmission members  8  in the grooves and all forces are transmitted via the balls from the rotation bushing  6  to the drill shank  3  and vice versa. In cross section circular-arch-shaped parts  6   c  of semi-circular grooves  6   a  act as power transmission surfaces of the rotation bushing in normal direction of rotation, i.e. during drilling, and correspondingly, in cross section circular-arch-shaped parts  6   d  of grooves  6   a  act in the opposite direction of rotation, used for instance for unscrewing threads. Correspondingly, in cross section circular-arch-shaped parts  3   c  and  3   d  of semi-circular grooves  3   a  of the drill shank grooves  3   a  act as power reception surfaces. 
       FIG. 3   c  shows schematically an alternative detail of the solution of  FIG. 3   b , cut open along line A-A as shown in  FIG. 2 . In this case the shape of the grooves  6   a  provided in the rotation bushing  6  is such that its cross-sectional arch exceeds 180 degrees. The grooves  6   a  and the balls  8  are dimensioned such that the width W of the opening in the groove  6   a  facing the drill shank  3  is smaller than the diameter D of the balls serving as transmission members  8 . As a result, the balls are not able to fall off the grooves  6   a  during mounting. Correspondingly, instead of rotation bushing  6 , grooves of this kind may also be provided in the drill shank  3 . 
       FIGS. 4   a  and  4   b  show schematically some other embodiments of the invention, in the same way as in  FIG. 3  in partial cross section at line A-A. 
       FIG. 4  shows an embodiment in which cylindrical rollers are used as rolling transmission members  8  instead of round balls. In this embodiment the grooves  3   a  and  6   a  are substantially rectangular and the rolling transmission members  8 , i.e. cylindrical rollers, are mounted axially transversely to the rotation axis of the drill shank  3 , and correspondingly, the rotation bushing  6 . Thus, the round surface of the rollers rolls along the sides of the grooves  3   a  and  6   a  that act as power transmission and power reception surfaces transmitting rotation torque from the rotation bushing to the drill shank. Naturally in this embodiment the end surfaces of the rollers may slide to some extent against the bottom of either one of the grooves, but because no considerable forces are transmitted in that direction, i.e. in the radial direction, no considerable sliding friction will occur, and consequently no substantial wear will appear either. 
       FIG. 4   b  shows yet another embodiment of the invention, in which rollers having curved surfaces are used as rolling transmission members  8 , and correspondingly, surfaces of substantially their shape. In this case, rolling takes place along curved surfaces, and no considerable sliding and consequently sliding friction occurs. 
       FIGS. 5   a  and  5   b  are schematic front views of other embodiments of the invention in the same way in cross section as in  FIG. 3 . In these embodiments the outer diameter of the drill shank  3  is larger than the inner diameter of the rotation bushing  6 . Thus, both the drill shank  3  and the rotation bushing  6  comprise grooves  3   a  and  6   a , which are so large in size that parts between the grooves of the drill shank and correspondingly of the rotation bushing, i.e. ridges  3   e  and  6   e , fit in the grooves of one another. 
       FIG. 5   a  shows a solution in which the grooves  3   a  and  6   a  of the drill shank  3  and the rotation bushing  6  are dimensioned such that there will be space for transmission members  8   a  and  8   b  between the transmission surfaces thereof. In this embodiment there are transmission members in six spaces such that the transmission surface on either side of the transmission members  8   a  and  8   b  is substantially equal in height with the transmission member  8   a  or  8   b . In this embodiment the power transmission from the rotation bushing to the drill shank takes place during drilling, and correspondingly, when rotation takes place in the opposite direction, with three transmission member sets  8   a  and  8   b , whereby one transmission member set may comprise one or more transmission members between the same power transmission and power reception surfaces. Thus, the transmission members  8   a  transmit the rotation torque during drilling as rotation takes place in the direction of arrow B. Correspondingly, the transmission members  8   b  transmit the rotation torque as the drill rod is rotated backwardly, for instance, when it is dismounted. 
       FIG. 5   b  shows yet another embodiment of the invention. It comprises transmission members  8  in the direction of rotation only on one side between the drill shank and the rotation bushing, whereby they transmit the rotation torque to the drill shank  3  during normal drilling, i.e. as rotation takes place in the direction of arrow B. As the drill rod is dismounted, rotation takes place in the opposite direction, of course. As a whole, this is relatively insignificant as compared with the rotation associated with normal drilling, and therefore rotation in the opposite direction may employ the solution of  FIG. 5   b , in which the transmission of the rotation torque takes place in the dismounting stage from the rotation bushing to the drill shank by means of conventional sliding surfaces  3   f  and  6   f  known per se. 
       FIG. 6  shows yet another embodiment of the invention, the front end of the rock drill cut open in the longitudinal direction as in  FIG. 2 . This embodiment corresponds  FIG. 2  in all other respects, but it shows a second shoulder  3   g  also at the end of the drill shank  3  on the side of the percussion piston  7 , whereby the rotation bushing does not necessarily require a shoulder  6   b . Alternatively, the shoulders may be in the rotation bushing  6  only. Further, it shows springs  9  that are placed on both sides of the balls acting as transmission members  8 , between the balls and the shoulders  3   b  and  6   b  of the drill shank  3  and the rotation bushing  6 , respectively. Mounted in this manner they push the transmission members  8  towards the centre of the space between the shoulders  3   b  and  6   b . In a situation where only the drill shank or the rotation bushing  6  includes shoulders, the springs are naturally placed only between the shoulders of the drill shank  3  and the rotation bushing, respectively, and the transmission members  8 . 
     The invention is described in the above specification and the drawings only by way of example, and it is not in any way restricted thereto. If desired, the number of grooves may vary and there may be one or more grooves. Because of symmetry and a tight contact surface, however, it is advantageous to have two or three pairs of power transmission and power reception surfaces with transmission members rolling therebetween. When there are used transmission members of cylindrical or some other shape that have a clearly defined, shape-related rotation axis, the grooves and the surfaces may be oblique in the circumferential direction with respect to the radial direction of the drill shank and the rotation bushing such that the axes of the transmission members are obliquely set. The details of the various embodiments set forth may be modified and used in connection with other embodiments within the scope of the inventive idea.