Patent Publication Number: US-2005115379-A1

Title: Saw chain for a power chain saw

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a saw chain for the guide bar of a power chain saw, comprising pivotably interconnected chain links, including drive links, cutting links, and connecting links, wherein each drive link is pivotably connected with several lateral connecting links and a lateral cutting link such that in the longitudinal direction of the chain, successive cutting links are alternatingly disposed on the right and the left longitudinal sides of the chain, and the cutting link is provided with a cutting tooth and a depth limiter that leads the cutting tooth in the direction of travel of the chain, whereby the drive link that is adjacent to the depth limiter is provided with a support protuberance that in the longitudinal direction of the chain extends in the region of the depth limiter of the cutting link, and a support surface of the support protuberance, at least when the saw chain travels about the end of the guide bar, cooperates in a supporting manner with the top surface of the depth limiter in the groove cut into a work piece.  
      A saw chain of this type is known from U.S. Pat. No. 3,180,378. Each second drive link has a support protuberance that extends rearwardly in the direction of travel of the chain approximately from the center of the drive link, and in this manner extends the depth limiter of the cutting link toward the front in the direction of travel of the chain. As a result, the kick-back tendency of the power chain saw can be lowered, especially during contact with the end of the bar.  
      GB 2 109 455 A discloses a chain saw where each second cutting link carries a support protuberance, that, when the saw chain is extended, ends below the top surface of the depth limiter of the cutting link. During travel or reversal about the end of the guide bar, the support protuberance pivots toward the front in the direction of travel of the chain and increases the effective support surface, as a result of which the kick-back tendency is lower during contact with the bar end.  
      It is an object of the invention to provide a saw chain for a power chain saw that has an only low kick-back tendency at a high cutting power. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:  
       FIG. 1  shows an isometric partial view of one exemplary embodiment of a saw chain that is traveling on a guide bar;  
       FIG. 2  shows an isometric view of an extended portion of the saw chain of  FIG. 1 ;  
       FIG. 3  is a side view of the saw chain of  FIG. 2 ;  
       FIG. 4  is a side view of a drive link of the saw chain; and  
       FIG. 5  is an isometric view of the drive link of  FIG. 4 . 
    
    
     SUMMARY OF THE INVENTION  
      The spacing of the support protuberance to the cutting tooth, measured in the longitudinal direction of the chain, when the saw chain is straight or extended, is less than the spacing of the depth limiter to the cutting tooth, so that when the chain is extended, the support protuberance is effective in the region between the depth limiter and the cutting tooth and ensures a reliable support.  
      During the travel or reversal over the end of the guide bar, due to the kinematics the spacing of the support protuberance to the cutting tooth changes to a reversal spacing that is greater than the spacing of the depth limiter to the cutting tooth. During the reversal at the end of the guide bar, the support protuberance is thus pivoted forwardly out of the region of the depth limiter in the direction of travel of the chain, as a result of which on the one hand the support surface is enlarged in the longitudinal direction of the chain, and on the other hand an effective support also results transverse to the direction of travel of the chain.  
      Pursuant to an advantageous further development of the invention, the support protuberance essentially extends in a portion of the drive link that is connected via a rivet pin with the portion of the cutting link that is provided with the depth limiter.  
      The drive link has an approximately perpendicular central plane that is disposed parallel to the center axes of the rivet openings and is provided centrally between the center axes. This central plane divides the drive link into a leading and a trailing half, whereby the support protuberance is disposed in the trailing half over its entire length that is effective in the longitudinal direction of the chain. As a result, the effectiveness of the support protuberance is increased during the travel about the end of the guide bar.  
      Pursuant to a particular structural embodiment, the end face of the support protuberance that faces the cutting tooth is oriented essentially parallel to the central plane of the drive link, whereby as a supplement thereto, the support surface of the support protuberance is disposed at a right angle to the central plane of the drive link, and hence at a right angle to the end face. By means of a transition of combined, changing radii, the support surface merges into an upper main body plane of the central or drive link. The particular structural configuration of the contour of the drive link ensures an advantageous manufacture as well as assembly to form the chain composite.  
      Further specific features of the present application will be described in detail subsequently.  
     Description of Specific Embodiments  
      The saw chain  1  illustrated in  FIG. 1  runs on a guide bar  2 , which is secured to a non-illustrated power chain saw. For the guidance of the saw chain  1 , a guide groove or channel  3  is provided in the outer periphery of the guide bar  2 . Drive links  6  of the saw chain  1  are centrally guided in the guide channel  3  in the direction of travel  4  of the chain.  
      The saw chain  1  comprises individual, pivotably interconnected chain links, which are embodied as lateral connecting links  5 , central drive links  6 ,  6   a , and lateral cutting links  7 .  
      As shown in FIGS.  2  to  5 , the drive link  6  comprises a main body  16  that, in the longitudinal direction  8  of the chain ( FIG. 2 ), is provided with two rivet openings  17  and  18  that are spaced apart by a distance z. The main body  16  has an upper main body plane  19  that is disposed approximately parallel to a connecting plane  20  ( FIGS. 3, 5 ) that is determined by the center axes  21  and  22 . Formed on that side of the main body  16  that is opposite the main body plane  19  is a drive extension  15  that extends into the guide channel  3  of the guide bar  2 . Facing toward the front in a direction of travel  4  of the chain, the drive extension  15  has a lubricant opening  14  into which a drive nose  13  conveys lubricant that the drive nose  13  receives from the base of the guide channel  3  of the guide bar  2 . In a manner not illustrated in greater detail, the lubricant that is received is conveyed to the rivet opening  17  via a lubricant channel  12  that is formed in the side surface of the drive link  6 .  
      Each drive link  6  is pivotably connected via rivet pins  29  with several lateral connecting links  5  and a cutting link  7  ( FIGS. 2, 3 ).  
      The drive link  6  has an approximately perpendicular central plane  10  that extends parallel to the center axes  21  and  22  of the pivot openings  17  and  18 . The central plane  10  furthermore symmetrically divides the connecting plane  20  that is defined between the center axes  21  and  22 .  
      By means of the central plane  10 , which is perpendicular to the main body plane  19 , the drive link is divided into a leading half  9  and a trailing half  11 . The half  11 , which trails in the direction of travel of the chain, is provided with a support projection or protuberance  30  that extends beyond the main body plane  19  by a prescribed height H. The drive link having the support protuberance  30 , and shown in  FIGS. 4 and 5 , is arranged in the composite chain connection in such a way that the leading half  9  of the drive link  6  is connected with two connecting links  5  ( FIGS. 2, 3 ), while the trailing half  11  on the one longitudinal side  24  of the chain is connected with a connecting link  5  and on the other longitudinal side of the chain is connected with a cutting link  7 . In this connection, the support protuberance  30  is arranged in such a way that it is disposed in the region of a depth limiter  26  that is provided on the cutting link  7  and leads a cutting tooth  25 . Disposed between two drive links  6  having a support protuberance  30  is a drive link  6   a  having a planar main body plane  19 , so that in the longitudinal direction  8  of the chain, drive links  6  having support protuberances  30  alternate with drive links  6   a  having no support protuberance. In this connection, the position of the cutting links  7  relative to the longitudinal sides  23  and  24  of the chain are provided in such a way that in the longitudinal direction  8  of the chain, successive cutting links  7  are alternatingly disposed on the right and the left longitudinal sides  23 ,  24 . The cutting links  7  disposed on a given longitudinal side  23  or  24  of the chain are respectively separated from one another, in the longitudinal direction  8  of the chain, by three connecting links  5 .  
      The support protuberance  30  of a central drive link  6  extends, in the longitudinal direction  8  of the chain, in the region of the depth limiter  26  of the cutting link  7 , whereby a support surface  31  of the support protuberance  30 —and also the top surface  27  of the depth limiter  26 —face the base of a cutting groove in a work piece. In this connection, the support surface  31  and the top surface  27  cooperate in a supporting manner, at least in the reversal region of the tip or end of the guide bar  2 , to lower a kick-back action. As shown in  FIG. 1 , in the reversal region of the end  28  of the guide bar  2 , the top surface  27  and the support surface  31  are disposed at approximately the same height, or the support surface  31  is preferably disposed below the top surface  27 .  
      The support protuberance  30  essentially extends in a portion  11  of the drive link  6  that is connected via a rivet pin  29  with the portion  37  of the cutting link  7  that is provided with the depth limiter  26  ( FIG. 2 ). The dimension of the support protuberance  30  measured in the longitudinal direction  8  of the chain is such that when the saw chain  1  is straight or extended, the spacing a of the support protuberance  30  to the cutting tooth  25 , measured in the longitudinal direction  8  of the chain, is less than the spacing b that the depth limiter  26  has to the cutting tooth  25 . The kinematic dimensions are selected such that as the saw chain  1  travels around the end  28  of the guide bar  2 , the spacing a of the support protuberance  30  to the cutting tooth  25  increases in such a way to a reversal spacing A that as the saw chain  1  travels around the end  28  of the guide bar  2 , the reversal spacing A is greater than the spacing b of the depth limiter  26  to the cutting tooth  25 . In so doing, when the saw chain  1  is extended, the space between the cutting tooth  25  and the leading depth limiter  26  is partially delimited by the support protuberance  30 . When the saw chain  1  is extended, the support surface  31  is disposed approximately at the level of the top surface  27  of the depth limiter  26 , or slightly below the top surface  27  of the depth limiter  26 , as can be seen from the side view in  FIG. 3 .  
      During the travel or reversal about the end  28  of the guide bar  2 , due to the kinematics, a relative movement occurs between the depth limiter  26  and the support protuberance, as a result of which the support protuberance  30  and the support surface  31  are pivoted out of the space between the depth limiter  26  and the cutting tooth  25 . At the same time, during the travel about the end  28  of the guide bar  2 , the support surface  31  drops relative to the top surface  27 , so that in the region of the end  28  the support surface  21  comes to rest below the top surface  27  or approximately at the same height as the top surface  27 . A support of the saw chain  1  in the cutting base is effective over a width that essentially corresponds to the width S ( FIG. 2 ) of the cutting tooth  25 . As a consequence of this large support surface, which extends not only transverse to the longitudinal direction  8  of the chain but also in the longitudinal direction  8  of the chain, the kick-back tendency during contact with the bar end  28  can be kept low.  
      In the illustrated embodiment, the support protuberance  30  has such a height H that it corresponds approximately to the height T ( FIG. 3 ) of the depth limiter  26  of the cutting link  7 . The support surface  31  and the top surface  27  are then disposed at the same height. In this connection, the support protuberance  30  has an end face  33  that faces the cutting tooth  25  and that is disposed essentially parallel to the central plane  10  of the drive link  6 . The support surface  31  of the support protuberance  30  is preferably disposed at a right angle  32  to the end face  33 , and hence also at an approximately right angle to the central plane  10  of the drive link  6 .  
      The support surface  31  of the support protuberance  30  extends over a length, in the longitudinal direction  8  of the chain, that—when viewed in plan—extends from a region after the center axis  21  of the trailing rivet opening  17  up to into a region ahead of the center axis  21  of the rivet opening  17 . In the illustrated exemplary embodiment, the end face  33  is disposed by a distance x after the center axis  21  in the longitudinal direction  8  of the chain, i.e., the center axis  21  leads the end face  33  in the direction of travel  4  of the chain by the distance x. The leading edge  34  of the support surface  31  is disposed—as viewed in plan upon the support surface  31 —by a distance y to the center axis  21  of the trailing rivet opening  17 , i.e., the leading edge  31  is disposed ahead of the center axis  21  of the trailing rivet opening  17  in the direction of travel  4  of the chain by a distance y.  
      The support surface  31  merges into the main body plane  19  via a transition  35  of changing radii R c , R b . In this connection, first adjoining the edge  34  is a convex, smaller radius R c , which then extends in a concave, many times greater radius R b  that merges tangentially into the main body plane  19 . The transition  35  preferably continues in a portion  36  that is disposed below the main body plane  19  and begins approximately on a level with the center axis  22  of the leading rivet opening  18 . The ending portion  36  is convexly rounded with a radius R a , whereby the radius R a  is preferably less than the radius R b . The radius R a  merges into a tangent  38  that is disposed at an angle  39  of approximately 10° to 50°, in particular approximately 30°, to the main body plane  19 . The tangent  38  merges via a small radius into a front end face  40  that is disposed parallel to the central plane  10 , that faces toward the front in the direction of travel  4  of the chain, and that is disposed at a right angle  45  to the working or support surface  31 . Adjoining the leading end face  40  is the boundary edge  41  of the drive extension  15 . The boundary edge  41  is disposed at an angle  42  of about 50° to the central plane  10 .  
      The trailing boundary edge  43  is disposed at an angle  34  to the central plane  10 , whereby the angles  42  and  44  are preferably the same.  
      The specification incorporates by reference the disclosure of German priority document 103 56 636.8 filed Dec. 1, 2003.  
      The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.