Abstract:
An apparatus is provided for guide bars used in cutting operations, and more particularly to prolonging the life of the nose sprocket and/or reducing the tendency of guide bar separation in the nose sprocket region, by reconfiguring the nose sprocket outer race and/or the cutting chain drive tang.

Description:
RELATED APPLICATION  
       [0001]     The present application is a continuation application of utility application Ser. No. 10/626,250 filed on Jul. 23, 2003, entitled “LOW FIT NOSE SPROCKET AND CUTTING CHAIN,” and claims priority to said utility application. The specification of said application is also hereby fully incorporated by reference in its entirety, except for those sections, if any, that are inconsistent with this specification 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to guide bars used in cutting operations, and more particularly to reducing the tendency of side wall separation in the nose sprocket region of the guide bar by reconfiguring the nose sprocket components and/or cutting chain drive links to improving the nose sprocket&#39;s resistance to side wall separation, and/or prolong the life of the nose sprocket.  
       BACKGROUND OF INVENTION  
       [0003]     Cutting chain guide bars are used in a variety of cutting operations. These operations include but are not limited to wood cutting by chain saws and tree harvesters, and aggregate cutting saws. Typically, one end of the guide bar is operably interconnected to a drive mechanism. The other end typically has a nose sprocket that allows the cutting chain to traverse the end of the guide bar. Nose sprockets are well known in the art and commonly consist of an outer race that has a number of teeth disposed about the periphery. The outer race has an inner bore that is sized to encompass an inner race. The inner bore is sized such that roller bearings can be trapped between the outer race and inner race, thereby enabling the outer race to rotate around the inner race. The nose sprocket is positioned between the guide bar side walls and secured between the side walls, usually by placing several rivets from one side wall to the other such that the rivets pass through the inner race.  
         [0004]     Sprocket nose guide bars, and particularly of the type referred to as “laminate guide bars,” are susceptible to increased separation of the side walls at the nose end of the bar (sometimes referred to as “splitting of the side walls”). For example, during a cutting operation where the cutting chain is traversing the nose sprocket, the resistive forces of the material being cut tends to urge side deflection of the cutting chain relative to the nose of the bar. This side deflection can translate into a splitting force that urges increased opening or separation of the side walls, particularly at the nose end of the guide bar. This separation may provide an escape route for the bearings and ultimately render the guide bar inoperable. Thus there is a need to reduce the occurrence of side wall separation of the bar at the nose end of the chain saw guide bar.  
         [0005]     In evaluating the causes of the undesirable side wall separation tendency, it has been found that by increasing the inner race diameter, one can move the rivets that secure the side walls together and hold the inner race in place closer to the outer periphery of the guide bar nose. Moving the rivets closer to the nose periphery provides greater resistance to the separation forces encountered by the side walls and ultimately reduces the tendency of the nose sprocket to fail.  
         [0006]     Because the outer dimension of the outer race is substantially fixed, given the size of the guide bar and application, increasing the inner race diameter necessarily requires reducing the web width of the outer race, where the web width is the distance between the edge of the inner bore to the bottom of a gullet. Such a reduction potentially weakens the outer race and causes the sprocket teeth to be more susceptible to splitting due to the prying forces applied by the drive tangs of the cutting chain as they traverse the nose sprocket of the guide bar.  
         [0007]     Thus there is an need to design a nose sprocket or cutting chain drive tang such that the rivets can be positioned closer to the periphery of the guide bar nose to prevent side wall separation, without weakening the outer race such that it becomes more susceptible to splitting.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0008]     The present invention helps solve the problem of side wall separation of the nose end of guide bars and can prolong the life of the nose sprocket. Whereas the problem concerns the location of the rivets, which location is dictated by the diameter of the inner race, it was reasoned that a strengthening of the outer race would permit a reduction in the web width and thus permit a larger inner race diameter to be used. The larger diameter enables the outward movement of the holding rivets, thus providing better resistance to side wall separation.  
         [0009]     Analysis of the load distribution as applied to the outer race, determined that the sprocket tooth design could be improved with a variety of changes to the sprocket configuration, which would strengthen the outer race. These changes may include: (a) providing a relief at the upper portion of the teeth, which causes the moment arm of the affected tooth edge applied force vector to lower toward the bottom of the tooth (lowers the moment arm of that force); (b) providing the bottom curved gullet with a more shallow curve (greater radius of curvature), as a shallow versus a steeper curve (smaller radius of curvature) has greater resistance to splitting; and (c) providing a inverted or inwardly relieved portion on the upper edge portions of the cutting chain drive link tang. With the improvements described, a similar nose sprocket strength is retained with a lesser outer race web width, which allows for a greater diameter for the inner race without changing the outside dimension of the outer race. This in turn allows outward movement of the rivets and a lessening of the likelihood of side wall separation.  
         [0010]     The present invention also may help prolong the life of the nose sprocket, regardless of the side wall separation concern. The changes identified above separately or together can strengthen the outer race by having the teeth better resist splitting as the forces will be applied to the lower stronger portion of the tooth.  
         [0011]     These and other variations as well as the invention itself will become more readily apparent upon reference to the following detailed description that follows. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0012]      FIG. 1  is a side cross sectional view of a nose sprocket in accordance with one embodiment of the present invention;  
         [0013]      FIG. 2  is an enlarged side cross sectional view of a portion of the nose sprocket of  FIG. 1 ;  
         [0014]      FIG. 3  is an enlarged side cross sectional view of a portion of an outer race in accordance with a second embodiment of the present invention;  
         [0015]      FIG. 4  is an enlarged side cross sectional view of a portion of an outer race in accordance with a third embodiment of the present invention;  
         [0016]      FIG. 5  is a side cross sectional view of a nose sprocket and cutting chain in accordance with a fourth embodiment of the present invention;  
         [0017]      FIG. 6  is an enlarged side cross sectional view of a drive link tang of the cutting chain shown in  FIG. 4 ; and  
         [0018]      FIG. 7  is an enlarged side cross sectional view of a portion of an outer race in accordance with a fifth embodiment of the present invention. 
     
    
     DESCRIPTION  
       [0019]     In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.  
         [0020]      FIG. 1  is a side cross sectional view of a guide bar in accordance with the present invention. Guide bar  10  has opposable side walls  12 , 14 . Core  16  may be disposed within side walls  12 , 14 . A groove  18  is formed between side walls  12 , 14  with core  16  acting as the floor of groove  18 . Guide bar  10  has a rear end (not shown) that is adapted for operational engagement with a machine, including but not limited to a chain saw tree harvester and/or an aggregate cutting saw. Guide bar  10 -also has a nose end  22 , opposite the rear end.  
         [0021]     Disposed within the nose end  22  is a nose sprocket  24 . Nose sprocket  24  may include an inner race  26 , an outer race  28  and a plurality of bearings  30 . Inner race  26  has a predetermined diameter  32 , which may be dependent on factors such as guide bar size. Inner race  26  is fixed between side walls  12 , 14  such that inner race  26  does not move during operation. In the illustrated embodiment, inner race  26  is fixed between side walls  12 , 14  by a plurality of rivets  34 . Rivets  34  also may help to secure side walls  12 , 14  in a fixed relation to each other and therefore may help to resist separation of side walls  12 , 14  at the nose end  22 . In other embodiments, the inner race  26  may be fixed between side walls  12 , 14  by other means, including but not limited to welds, screws, metal fusion, high-strength adhesives and the like.  
         [0022]     Outer race  28  has an inner bore  36 , which has a bore diameter  38 . Bore diameter  38  is greater than inner race diameter  32 . This allows the outer race  28  to be rotatably disposed about the periphery of inner race  26 . Bearings  30  are disposed between the peripheral edge of inner race  26  and the inner bore  36  of outer race  28 , and enable the outer race  28  to rotate around fixed inner race  26 .  
         [0023]     Outer race  28  also has a plurality of teeth  40  disposed about its outer periphery. A gullet  42  is formed between adjacent teeth  40 . Each tooth  40  has a leading edge  44  and a trailing edge  46 . Cutting chain  60  may include a plurality of links or elements, such as cutting link  66  and drive link  62 . Drive link  62  may have a tang  64  which is adapted to engage the portion of the outer race  28  formed by the leading edge  44  of a tooth  40 , the gullet  42  and the trailing edge  46  of an adjacent tooth  40 . Tooth  40  also has a lower portion  50  and a relieved upper portion  48 . By providing a relief at the upper portion  48  of tooth  40 , tang  64  is urged to engage the lower portion  50  of tooth  40 . Such engagement helps ensure that the radial forces applied by drive link  62  and tang  64  caused during operation will be distributed to the lower portion  50  of outer race  28 . This may result in an increased resistance to the splitting tendency of the outer race  28  caused by the prying forces applied to the teeth  40  as the cutting chain  60  traverses the nose end  22  of guide bar  10 . Accordingly, this strengthening may prolong the life of the nose sprocket.  
         [0024]     Strengthening outer race  28  not only can prolong the life of the nose sprocket  24 , but may also enable web width  52  (width of material required between the inner bore  36  and the bottom of gullet  42 ) to be decreased without sacrificing operational strength. By decreasing the web width  52 , the diameter of the inner race  32  can be correspondingly increased, thereby subsequently enabling positioning the rivets closer to the outer periphery of the nose end  22  of guide bar  10 . This may increase the resistance of nose end  22  to side wall separation caused by the sideward deflection encountered by the cutting chain during cutting operations, without sacrificing operational life of the outer race  28 .  
         [0025]      FIG. 2  is an enlarged cross sectional view of the nose sprocket  24  shown in  FIG. 1 . Teeth  40  are shaped such that the upper portion  48  is slightly relieved when compared to the lower portion  50 , both on the leading edge  44  and trailing edge  46 . The relieved upper portion  48  of leading edge  44  and trailing edge  46  encourages the contact of tang  64  with the lower portion  50  of leading edge  44  and trailing edge  46  during operation. Tang  64  may also contact gullet  42 , which also increases the strength of outer race  26 . By urging contact of the tang  64  to the lower portions  50  and gullet  42 , the operational forces will be directed to the stronger area of the outer race  28 , which in turn may increase resistance of outer race  28  to splitting due to the prying forces typically caused by the drive tang  64  contact with the upper portions  48  of the leading edge  44  and trailing edge  46 .  
         [0026]      FIG. 3  is an enlarged side cross sectional view a portion of an outer race  70  in accordance with a second embodiment of the present invention. Center line  72  bisects gullet  74  formed between tooth  76  and adjacent tooth  78 . The lower portion  80  of leading edge  82  of tooth  76  has a predetermined pitch, which forms a first angle  84  with respect to centerline  72 . The upper portion  81  may have a different pitch, which forms a second angle  86  with respect to center line  72 . Having second angle  86  being greater that first angle  84  may provide the necessary relief and urge the contact of the tang (not shown) toward the lower portion  80 , thereby increasing the strength of outer race  70 .  
         [0027]      FIG. 4  illustrates an enlarged cross sectional view of an outer race in accordance with a third embodiment of the present invention. Center line  90  bisects gullet  92 , which is formed between tooth  94  and adjacent tooth  96 . Teeth  94 ,  96  have a lower portion  98  and a relieved upper portion  100 . The pitch of the lower portion  98  has an angle  102  with respect to centerline  90 . The pitch of the relieved upper portion  100  has approximately the pitch of the lower portion  98 . The relief of the relieved upper portion  100  is formed by offsetting the relieved upper portion  100 . Accordingly, the tang (not shown) may be urged to engage the lower portion  98  of tooth  94  and possibly the gullet  92 .  
         [0028]     It can be appreciated by one skilled in the art that the relief of the upper portion of the tooth need only be such that the tang is encouraged to contact the lower portion of the tooth at the leading and trailing edges in order to shift the operational forces lower on the tooth and gullet where the ability to resist the prying or splitting forces is increased. Again, this increases the strength of the outer race such that the nose sprocket life can be prolonged or the web width can be decreased to allow for an increase in the inner race diameter so that the rivets can be positioned closer to the nose end periphery to resist side wall separation.  
         [0029]      FIG. 5  is a side cross sectional view of a guide bar nose sprocket and cutting chain in accordance with a fourth embodiment of the present invention. Guide bar  110  is similar to that described with regard to  FIG. 1 . Nose sprocket  124  is disposed within the nose end  122  of guide bar  110 . Nose sprocket  124  includes inner race  126 , an outer race  128  and a plurality of bearings  130 . The outer race  128  has a bore diameter  138  that is greater than inner race diameter  132 , such that outer race  128  is rotatably disposed about the periphery of inner race  126 . Outer race  128  also has a plurality of conventional teeth  140  disposed about the perimeter. The teeth  140  have a substantially uniform leading edge  144  and trailing edge  146 , such that there is no discernible relief. Gullet  142  is formed by adjacent teeth  140  and is adapted to receive a tang  164  of a cutting chain  160 .  
         [0030]     To encourage application of the radial forces toward the lower portion  150  of the leading edge  144  and trailing edge  146 , drive tang  164  may have inverted or inwardly relieved portions  158  formed therein.  FIG. 6  is an enlarged cross sectional view of drive link  162  with tang  164  having inwardly relieved portions  158 . Inwardly relieved portion  158  may be formed in the upper portion of tang leading edge  154  and upper portion of tang trailing edge  156 . In other embodiments, relieved portions  158  can be more or less in set, tapered, or in other formations such that the lower portion of tang  164  is urged to contact the lower portion  150  of teeth  140 .  
         [0031]     Referring back to  FIG. 5 , the inwardly relieved portions  158  of tang  162  may cause the operational forces to be directed to lower portion  150  of teeth  140 , which in turn may result in outer race  128  being more resistant to splitting and ultimately prolong the life of the nose sprocket. Also, web width  152  of outer race  128  may also be decreased without sacrificing the resulting strength. Reducing the web width  152  can then allow the inner race diameter  132  to be increased, which in turn allows positioning of rivets  134  closer to the periphery of nose end  122 . Positioning rivets  132  closer to the outer periphery of nose end  122  may thus increase the resistance of the nose end  122  to the side wall separation tendencies encountered when in operation.  
         [0032]      FIG. 7  is an enlarged cross sectional view of an outer race in accordance with a fifth embodiment of the present invention. Outer race  228  includes an inner bore  236  and a plurality of teeth  240  disposed about the periphery. Each tooth  240  has an abbreviated leading edge  244  and an abbreviated trailing edge  246 . Abbreviated leading edge  244  of one tooth and the abbreviated trailing edge  246  of an adjacent tooth form gullet  242 . Abbreviated edges  244  and  246  have a substantially uniform pitch from an area close to the tooth tip  234 , to the gullet termination point  258 . Gullet  242  then has radius of curvature  256 . Because leading and trailing edges  244 ,  246  are abbreviated, the radius of curvature  256  is larger than a conventional radius of curvature  259  that would be caused if the pitch of the leading and trailing edges continued in a substantially flat manner until the transition into the gullet (shown by broken lines and being substantially v-shaped). Though still somewhat v-shaped, the abbreviated leading and trailing edges  244 ,  246  result in a gullet having a more flat bottom that is more bowl-shaped, thereby having an increased diameter at the bottom of the gullet.  
         [0033]     By increasing the radius of curvature and forming a more shallow bowl-shaped gullet, the radial forces will be urged toward the lower portion of the tooth and thereby allow the outer race to better resist the splitting forces, which in turn may prolong the life of the nose sprocket and/or enable decreasing the web width. Again, decreasing the web width allows the inner race diameter (not shown) to be increased. Increasing the inner race diameter will increase the resistance to side wall separation at the nose end of the guide bar because the rivets or other fixing means are positioned closer to the periphery of the nose sprocket.  
         [0034]     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.