Patent Publication Number: US-7896100-B2

Title: Valve device for a percussion device and a percussion device for a rock drilling machine

Description:
FIELD OF THE INVENTION 
     The invention concerns a valve device for a percussion device for a rock drilling machine according to the preamble of claim  1  and a percussion device for a rock drilling machine including such a valve device. 
     BACKGROUND OF THE INVENTION 
     From U.S. Pat. No. 5,372,196 is previously known a percussion device, which includes a percussion piston, which is reciprocatingly movable in a machine housing. The reciprocating movement of the percussion piston is controlled by a valve device, wherein the valve element is movable to and fro in the machine housing. At its rear end, the machine housing has a space which is supplied with pressure fluid and thus drives the percussion piston in the forward direction. 
     A second chamber that can be pressurized is arranged for back-driving of the percussion piston. The movement of the valve device and thereby the percussion piston is controlled as a response to the position of a valve portion on the percussion piston in the housing, through periodically pressurizing a first pressure surface of the valve body. On a second, permanently pressurized pressure surface, a force is acting, which is less than the force acting on the valve body when pressurizing, because of the different areas of the pressure surfaces. 
     The known percussion device works well and aims at reaching percussive frequencies in the magnitude of 150 Hz. Recently set desires for higher working rate and better economy during rock drilling have however resulted in the desire for yet higher percussive frequencies and valve devices with shorter response time. 
     AIM AND MOST IMPORTANT FEATURES OF THE INVENTION 
     At the background of these desires it is an aim of the present invention to provide a development of a percussion device of the kind initially mentioned that has the possibility of faster valve movements and thereby percussion devices with higher percussive frequency. 
     This aim is obtained through a valve device as stated initially through the features in patent claim  1 . 
     The corresponding is obtained in a percussion device of the kind initially stated through the features of the characterizing portion of claim  9 . 
     By providing at least two signal conduit portions, which co-operate with a corresponding number of valve control edges, faster signal fluid pressure transmission is allowed and thereby possibility of increased valve switch speed and thereby increased percussive frequency. This can be achieved with respect to slender percussion pistons, which are constructed for optimizing the percussive effect, since the open area for signal pressure transmission is multiplied and at least doubled through the invention given the same percussion piston diameter. 
     Through the invention it is achieved that a signal fluid pressure can be reached much faster in the signal conduit at the moment when the respective valve control edges open the respective port. Even if the flow that builds up the pressure is small, it has surprisingly proven to have great importance to be able to multiply the opening of the signal conduit in such a way as is allowed through the invention. 
     Corresponding advantages are achieved in a percussion device for a rock drilling machine according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be described in more detail based on embodiments and with reference to the annexed drawings, wherein: 
         FIG. 1  diagrammatically shows a percussion device according to the invention with the percussion piston in a first position, 
         FIG. 2  shows a detail of the percussion device of  FIG. 1  in larger scale in a first position, and 
         FIG. 3  shows a detail of a percussion device of  FIG. 1  in larger scale in a second position. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     The percussion device  1  shown in  FIG. 1  includes inside a machine housing  2  a reciprocating percussion piston  3 , which with a rear pressure surface  6  is subjected to the pressure of a pressurized fluid which is present in a first chamber  5  in a forward driving direction of the percussion piston  3  for acceleration before performing an impact against a tool (not shown). In this figure P stands for pressure, R for return and D for drainage. 
     At a distance from the first chamber, the percussion piston  3  is surrounded by a driving piston  7 , which with a driving surface including a first driving area  9  and a second driving area  10  is actuated by the pressure of a pressurized fluid in a second chamber  8  for back-driving the percussion piston  3  after a completed impact. This aspect of the percussion device in  FIGS. 1 and 2  is however not an object of the present invention and is therefore not described more closely here. 
     The first chamber  5  can be permanently pressurized, whereas the second chamber  8  can be periodically pressurized over the main valve  4 ′ of the percussion device in a manner that is per se previously known, wherein the valve element of the main valve  4 ′ is controlled by the position of the percussion piston  3 , which over a valve portion V on the percussion piston actuates the valve element  4 ′ of the main valve for pressurizing and evacuating, respectively, of the second chamber  8 . 
     The valve device V,  4 ′,  4 ″ includes a to and fro movable valve body  20 , the movement of which is controlled as a response to the position of the valve portion V by periodically pressurizing a signal chamber  21  influencing the movement of the valve element, over signal conduit means  22 . Said signal conduit means  22  has at least two signal conduit portions  23 ,  24  which are arranged for essentially simultaneous pressurizing through co-operation with a correspondingly number of valve control edges  25 ,  26  on the valve portion of the percussion piston. 
       27  indicates pressure conduit means, which are branched in two pressure conduit portions  28  and  29  axially in front of and behind the signal conduit portions. In the first position of the percussion piston shown in  FIG. 1  (which is more clear in detail in  FIG. 2 ) said signal conduit means  22 ,  23 ,  24  are blocked from fluid contact with said pressure conduit means  27 ,  28 ,  29 . Instead said signal conduit means are in fluid contact with evacuation conduit means  30 ,  31 ,  32 . 
     Hereby the valve body will be driven to the right, as seen in the figure, through the permanent pressurizing of the chamber  33 . In particular the signal chamber  1  receives a first piston portion of the valve element, which has a greater surface subjected to pressure than a second piston portion, which is received in the chamber  33  intended for constant pressurizing. This way it is achieved that the same pressure in both chambers  21  and  33  results in displacement of the valve element  20  to the left as seen in the figure. 
     The driving chamber  8  will be evacuated (and blocked from contact with the working pressure P for the percussion device), through the position of the valve body  20  (in  FIG. 1 ), whereby the pressure in the first chamber  5  will drive the percussion piston in the direction of an impact. 
     In  FIG. 2  is shown in more detail that the edges  34  and  35 , respectively, of a respective valve chamber  36 ,  38  in the valve housing portion are arranged to co-operate with valve control edges  25 ,  26  being present on the percussion piston, which in the shown position have closed the fluid contact between the pressure conduit portions  28  and  29  and the respective signal conduit portion  23 ,  24 . Control edges  42  and  43  on control guiding flanges on the percussion piston have in this position instead opened in respect of edges of control chamber  38  and  39  for fluid contact between signal conduit portions  23  and  24  and the respective evacuation conduit portions  31  and  32 . 
       FIG. 3  shows the percussion device  1  with the percussion piston  3  in a second position just after a performed impact against a tool (not shown). In the shown position in  FIG. 3  of the machine, according to this embodiment, further kinetic energy can be regained when an increased fluid pressure in a cushioning chamber  12 , after entering therein of the cushioning piston  7 , is transmitted to a pressure source over a regain channel  15  and auxiliary valve  4 ″ (see  FIG. 1 ). This aspect is however not part of the present invention and will not be described more here. 
     In  FIG. 3  is further shown that the edges  34  and  35  of a respective valve chamber  36 ,  38  in the valve housing portion are arranged to co-operate with respective control edges  25 ,  26  on the percussion piston in such a way that, in the shown position, it is opened for fluid contact between the pressure conduit portions  28  and  29  and the respective signal conduit portion  23 ,  24 . Hereby the signal chamber  21  ( FIG. 1 ) is pressurized and the valve element  20  is driven to the left for pressurizing the driving chamber  8  and is obtained back-driving of the percussion piston  3  to the right as seen in the figure. The control edges  42  and  43  of guiding flanges on the percussion piston have passed co-operating edges of chambers in the valve housing portion, whereby fluid communication between the signal conduit portions and the respective evacuation conduit portions  31  and  32  are blocked. 
     The invention can be modified within the scope of the following claims. The percussion piston can be constructed otherwise, with differently designed means so as to constitute the valve portion. The positioning of control chambers belonging to the signal, pressure and evacuation conduit portions can be different, for example positioned axially in another order. The guiding flanges on the percussion piston can also be designed correspondingly otherwise. The valve  4 ′ can have another construction and as an example have spring-return or alternating pressurizing on both sides. 
     The invention makes it possible, through the increase of signal transmission speed, to provide percussion devices with slender percussion pistons that are well designed for their percussive action and yet effective means for fast valve movements and higher percussive frequencies with relatively simple and cost effective means. 
     It is not necessary for the invention that the kinetic energy of the driving piston is regained in the manner that is indicated above in  FIG. 1 . 
     The embodiment with an extra driving piston  7  is to regard as one of several possible arrangements. The invention finds its application also in respect of conventional percussion devices.