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You are an expert at summarizing long articles. Proceed to summarize the following text: 
[0001]    BACKGROUND OF INVENTION 
         [0002]    1. Field of the Invention 
         [0003]    This invention is directed to a release mechanism for a mandrel of a jarring device commonly referred to as a jar. Jars are used in the well drilling industry to free downhole tools that may become lodged in a well. An upward or downward force can be supplied to a tubular string which includes the affected tool in order to break free the tool from the well bore. 
         [0004]    2. Description of Related Art 
         [0005]    Typically, a release mechanism in the form of an annular collet is provided which normally prevents axial movement of the mandrel. The mandrel is spring biased to move with significant force in an upward or downward direction. If a sufficient force is placed on the mandrel, the collet will release. 
         [0006]    U.S. Pat. No. 5,022,473 discloses a release assembly which comprises a plurality of angular segments 62 and 162 that engage in slots 86 and 88, and 186 and 188 respectively. It has been found that this arrangement can result in the segments 62 and 162 becoming out of alignment which could result in the failure of the release mechanism. As disclosed in the patent, the jar requires two sets of release lugs to withstand the anticipated tensile load. In this design the two lug assemblies must be spaced further apart than the total travel of the jar to prevent the lower lug from inadvertently engaging the groove of the upper lug assembly. If a third lug assembly were necessary it would have to be spaced a distance greater than the jar stroke from the lower set. This would significantly increase the total length of the jar and also the cost. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention solves the above noted problem by providing a plurality of angular lug segments each of which has two or more projections that engage corresponding grooves in the mandrel. 
         [0008]    In order to avoid misalignment or a jarring situation, the projections having either a differing width or are spaced at different distances. The grooves on the mandrel have a complimentary configuration as will be explained below. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0009]      FIG. 1  is a cross-sectional view of a first embodiment of the release lugs as shown in a neutral position. 
           [0010]      FIG. 2  is a cross-sectional view of the first embodiment of the release lugs just prior to release of the mandrel. 
           [0011]      FIG. 3  is a cross-sectional view of the release lugs of  FIG. 1  in a release position with the mandrel initially moving. 
           [0012]      FIG. 4  is a cross-sectional view of the mandrel in a completely released position. 
           [0013]      FIG. 5  is a perspective view of a release lug according to a first embodiment of the invention. 
           [0014]      FIG. 6  is a perspective view of a plurality of release lugs forming a release mechanism according to a first embodiment of the invention. 
           [0015]      FIG. 7  is a cross-sectional view of a second embodiment of the release lugs shown in a neutral position. 
           [0016]      FIG. 8  is a cross-sectional view of the release lugs of the second embodiment in a fully released mode. 
           [0017]      FIG. 9  is a segmented cross-sectional view of an entire jar including the release lugs of  FIG. 7 . 
           [0018]      FIG. 10  is a cross-sectional view taken along line  10 - 10  of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  illustrates a release mechanism including a plurality of release lugs  17  surrounding mandrel  21  of the jar such as that shown in  FIG. 9 . 
         [0020]    The jar includes a central housing  11 , a Belleville spring stack  12 , a restrictor orifice  14  and one or more check valves  13 , an annular sleeve  15  surrounding mandrel  21  and an annular trigger sleeve  16  having an inwardly projecting lip  33 . Annular trigger sleeve  16  is spring biased against a shoulder  9  provided in housing  11  by a spring  19  at lip  33 . A lubricant fitting housing  151  is threadedly coupled to the downhole portion of housing  11 . 
         [0021]    As shown in  FIG. 5 , each release lug  17  includes a plurality of projections  18  of varying width on its interior surface. Projections  18  in this embodiment are evenly spaced from each other. The exterior surface of the release lug includes a plurality of grooves  37  which are adapted to receive projections  36  of the trigger sleeve  16  as shown in  FIG. 4 . A plurality of smaller grooves  41 ,  42 ,  43  and  44  are also provided on the exterior surface of release lugs  17  and are adapted to hold garter springs  38  as shown in  FIG. 6 . A plurality of the release lugs are used to form a release mechanism as shown in  FIG. 6  having spaces  43  between the release lugs. Although six release lugs are shown any number of segments for example, 2 thru 12 may be used. 
         [0022]    In the rest position shown in  FIG. 1 , surfaces  35  of the release lugs are in contact with the interior surface of trigger sleeve  16  and projections  18  are located within grooves  32  provided on the outer surface of mandrel  21 . As an upward force is applied to mandrel  21  which would be from the left as shown in  FIG. 1 , mandrel  21  and release lugs  17  will travel to the left, thereby compressing Belleville spring stack  12 . As the surfaces  35  align with grooves  31  of the trigger sleeve  16 , the beveled surfaces of the projections and grooves of the trigger sleeve, release lugs and mandrel grooves will allow the surfaces to be forced outwardly into grooves  31  resulting in projections  18  disengaging from grooves  32  in the mandrel. The mandrel then is free to move in an upward direction or to the left as shown in  FIG. 4 . The overall operation of a hydraulic jar is well known and explained in U.S. Pat. Nos. 6,290,004 and 7,510,008, the entire contents of which are expressly incorporate herein by reference thereto. 
         [0023]    In order to reload the jar, a downward force is placed on the mandrel which will move the mandrel downward. The garter springs  38  will cause the release lugs to return to their original position with the projections  18  in grooves  32 . 
         [0024]    Spring  19  which is now compressed will move trigger sleeve  16  back to the neutral position shown in  FIG. 1 . In the embodiment of  FIGS. 7 and 8 , the release lugs  57  have been changed to include a plurality of projections  58  that are non-uniformly spaced apart from each other rather than having varying widths. The grooves  59  in the mandrel are also spaced apart accordingly to receive projections  59  in the neutral position as shown in  FIG. 7 . The outer surfaces of the release lugs are formed in the same fashion as the lugs shown in  FIG. 5  so that in the released position of  FIG. 8 , surfaces  35  of the release lug are located within grooves  31  of the trigger sleeve  16 . 
         [0025]      FIG. 9  illustrates an embodiment of a complete jarring tool that incorporates the release lugs of the embodiment shown in  FIGS. 7 and 8 . The jar includes a connector  100  for connecting the jar to a tubular string, upper housing members  102  and  103 , lubricating fitting  104 , central housing  11 , a lower lubricating fitting  151 , lower housing member  152  and lower connector  141 . The jar also includes a Bellville spring stack  12 . The housing members are threadably connected to each other at  130 ,  131 ,  132 ,  133 ,  134  and  135 . The mandrel of the jar includes an upper portion  160  which is threadedly connected to connector  100 , a central portion  21  and a lower portion  153 . The mandrel portions are connected together by threads at  136  and  158 . Suitable seals are provided at  121 ,  122 ,  123 ,  124 ,  125 ,  126 ,  129  and  139 . A floating piston  127  surrounds the lower portion of mandrel  153 . A lubricating material is introduced into the housing through fittings  140  and  141 . The upper portion of the mandrel  160  includes an annular raised portion  138  which acts as a hammer against an anvil shoulder  137  on housing upper end member  102 . As shown in  FIG. 10 , upper housing member  103  may comprise a hexagon surface  171  which received a hexagon outer surface  172  on the mandrel portion  160 . 
         [0026]    The jarring tool of  FIG. 9  may incorporate the release lugs shown in the embodiments of  FIG. 5  or that of the embodiment of  FIGS. 7 and 8 . 
         [0027]    Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.

Summary:
A release mechanism for a jarring tool is formed by a plurality of segmented release lugs. Each lug includes a plurality of axial spaced projections on an inner surface and a plurality of grooves on an outer surface. The projections have either different widths or are separated by varying distances and releaseably engage corresponding grooves in a mandrel located within a housing of the tool. The release lugs are positioned between a trigger sleeve and the mandrel.