Abstract:
A latch mechanism for a manhole cover in which a rotatable operator member has a threaded portion engaged with a threaded bore in a cam pin which rides in a pair of cam slots in a latching member to cause the latching member to be extended or retracted upon rotation of the operator member in either direction. The threads disengage when the latch member reaches a fully retracted position so that the operating member can freely spin thereafter in the same direction, while the threads reengage when the operator member is rotated in the opposite direction to begin movement of the latch member out of the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/527,776 filed on Aug. 26, 2011. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention concerns latch mechanisms and more particular lock or latch mechanisms particularly adapted for use in securing manhole covers in place, as described in U.S. Pat. Nos. 7,484,908 and 7,891,904 issued to the present inventor, both incorporated by reference herein. 
         [0003]    The mechanisms described therein use an operating member comprised of a threaded bolt. 
         [0004]    As described in those patents, it is advantageous that the bolt not be allowed to be separated from the mechanism where it could be lost or be dropped into the manhole vault. Also, removal of the bolt by someone tampering with the cover should be prevented. 
         [0005]    While a mechanism for reducing the frequency of separating the bolt is described in U.S. Pat. No. 7,891,904, that mechanism does not positively prevent removal of the bolt from the latch mechanism. 
         [0006]    Accordingly, it is an object of the present invention to provide a latching mechanism in which a threaded operator member such as a special bolt is positively retained within the latching mechanism so as to preclude removal of the member. 
     
    
     
       DESCRIPTION OF THE DRAWING VIEWS 
         [0007]      FIG. 1  is a fragmentary sectional view of a manhole cover installation having a latch mechanism according to the present invention installed thereon. 
           [0008]      FIG. 2  is an exploded pictorial view of the components of the latching mechanism according to the present invention shown in  FIG. 1 . 
           [0009]      FIG. 2A  is an enlarged pictorial view of the flanged nut and spring shown in  FIG. 2 . 
           [0010]      FIG. 3  is an enlarged pictorial rotated view of a cam pin and a mating segment of a threaded operator member included in the latching mechanism shown in  FIGS. 1 and 2 . 
           [0011]      FIG. 4  is a view in partial section of the latching mechanism shown in  FIGS. 1 and 2  in the retracted unlatched condition. 
           [0012]      FIG. 4A  is an enlarged fragmentary front view of a lower portion of a main threaded portion of the operator member. 
           [0013]      FIG. 5  is a view in partial section of the latching mechanism as shown in  FIG. 4  but in the latched extended condition. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
         [0015]    Referring to  FIG. 1 , a portion of a manhole cover  10  is shown, seated over a manhole vault  12 . As described in U.S. Pat. No. 7,891,904, the manhole cover  10  normally rests on a radially inward extending rim  14  projecting in a liner  16  forming the vault  12 . 
         [0016]    In an explosion, the manhole cover  10  is designed to rise up but only to a limited extent to create a space to controllably vent gases generated by the explosion. A latch mechanism  18  is mounted between a pair of downwardly extending, spaced apart ribs  20  fixed to the underside of the cover  10 . A latch member  22  normally projects out radially from a latch housing  24  to engage the underside of the rim  14  to limit upward travel of the manhole cover  10 , with other fixed stop features also provided around the perimeter of the manhole cover to keep the manhole cover  10  from tipping as it rises to insure that the manhole cover  10  does not fly free. As described in the above referenced patents, the latching mechanism  18  can be allowed to pivot down when an explosion generates a force sufficient to fracture a shear pin (not shown) in order to allow a greater upward movement of the manhole cover  10 . 
         [0017]    The present invention comprises an improvement of the latch mechanism  18 . 
         [0018]    The components are shown in  FIG. 2  and include the latch housing  24  which slidably receives a cylindrical body portion  26  of the latch member  22 , with a sleeve bearing  28  sized to be slidable fit with the cylindrical portion  26  and also itself slidable into a bore  30  in the housing  24 . 
         [0019]    The latch member  22  has an engagement portion  32  at its projecting end (at the left in the Drawings), formed with a flat having a series of ribs  34  on its upper surface for engagement with the undersurface of rim  14 . 
         [0020]    A threaded elongated operator member here comprised of a bolt  36  has a body portion  37  slidable into a bore  38  extending vertically into the top of the housing  24 . A left hand threaded flanged nut  40 , compressed wave spring  42  received in a counter bore  45  in the nut flange  43 , and washer  44  are received on the threaded bottom stem  46  of the operator member  36 , the washer  44  engaging a flange  39  surrounding a bore  38  at the bottom thereof formed in the housing  24  to retain the operator member  36  in the bore  38 . The spring  42  keeps the washer  44  abutting flange  39 . 
         [0021]    A slight clearance space  41  exists between the washer  44  and the flange  43  on the flanged nut  40  which allows the member  36  to move slightly as described below 
         [0022]    A lengthwise extending vertical slot  48  in the center of the latch member  22  receives the operator member  36 , which passes completely through the slot  48 , with the stem portion  46  received in a counterbore  45  extending into the bottom of housing  24 , the flanged nut  40 , spring  42 , and washer  44  placed on the stem  46  and received in the counterbore  45 . 
         [0023]    A pair of aligned camming slots  50  are formed in the cylindrical portion  26  of the member  22 , each extending from one side of the latching member  22  into the center slot  48  which each receive a respective end of a cam pin  52  which has a central threaded cross bore  54  through which the operator bolt  36  passes with a threaded interengagment between a central threaded section  60  of the operator member  22 . 
         [0024]    The operator member  36  has a flanged head  56  for engagement with a wrenching tool to be rotated, the head  54  optionally being of a special shape for security purposes, as described in the above referenced patents. 
         [0025]    To extend the engagement portion of the latch member  22 , the operator member  36  is rotated in a direction so that the threaded engagement pulls the cam pin  52  upward which thus engages the upper wall  58  of each of the slots  50 , camming the latch member  22  to the left and causing the engagement portion  32  out of the housing  24 , as viewed in  FIG. 4 . 
         [0026]    Rotation of the operator member  36  in the other direction reverses the motion of the latch member  22 , in a direction so as to retract the engagement portion  32  of the latch member until the catch member  22  reaches and abuts the ends of the slots  50 . 
         [0027]    The threads of threaded section  60  on the operator member  36  and the threads of the threaded bore  54  of the cam pin  52  pass out of engagement as the operator member  36  moves down slightly allowed by the clearance space  41  and the lowest thread in section  60  pass out of engagement from each other. 
         [0028]    Continued rotation of the operator member  36  in the same direction thus has no effect on the position of the cam pin  52 , and the operator member  36  merely spins freely with the contacting threads sliding past each other. 
         [0029]    The section  62  of the operator member beyond the threaded section  60  is machined to a diameter sized to be able to be slidably received in the threaded bore  54  of the cam pin  52 . 
         [0030]    The lowest thread  64  on threads section  60  is machined to be square to the axis of rotation, and thus abut the flat face  66  machined on the cam pin  52  ( FIG. 3 ) flattens the uppermost thread in the bore  54 . The last thread  64  thus tapers down and its end blends into the diameter of section  62  ( FIG. 4A ). 
         [0031]    The spring  42  acting between washer  44  and flanged nut  40  urges the last thread  64  of the threaded portion  60  against the uppermost thread in the bore  54 , but rotation in the retraction direction has no effect as the first thread in bore  54  and partial thread  64  merely slide over and past each other. There will be a slight clicking sound and motion as the partial thread  64  rides past the flattened first thread in the bore  54 . 
         [0032]    The compressed wave spring  42  continues to urge these threads together so that the latch member  32  is held fully retracted. 
         [0033]    When the operator member  22  is rotated in the opposite direction, the thread  64  immediately engages the threads in threaded bore  54  and extending motion of the latch member  22  begins. Thus, cross threading is prevented and proper reengagement is insured. 
         [0034]    Seals  68 ,  70 ,  72  may be provided to prevent moisture from entering the mechanism  18 . 
         [0035]    Seal  72  is held in recess  71  to the rear of flange  43  on the flanged nut  40 . 
         [0036]    The seal  68  normally engages the cylindrical body  26  in service as the latch member  22  is then extended. 
       Operation 
       [0037]    With the end of the latch member  22  positioned against latch housing wall  18  of latch housing  3 , clockwise rotation of operating member  36  causes the thread  60  on operating member  36  to engage threaded bore  54  in cam pin  52 . Continued clockwise rotation of operator member  36  advances operator member thread  60  into the threaded bore  54  of cam pin  52  which in turn draws the cam pin  52  upward. This action develops a camming force exerted by the cam pin  52  against upper wall of each of the cam slots  50  formed in the latch member  22 . The length of central slot  48  limits the horizontal travel of the latch member in moving from a fully retracted to a fully extended position. 
         [0038]    As a result, the latch member  22  is moved to extend out of latch housing  24 . 
         [0039]    Further clockwise rotation of operating member  36  continues until cam pin  52  reaches the end of the cam slots  50  and operating member  22  reaches the end of slot  48 . Operating member  22  is torqued to specification, the latch member end  32  now fully extended and locked in that position. 
         [0040]    To retract the end  32  of latch member  22  back into the latch housing  24 , operating member  36  is rotated counterclockwise. 
         [0041]    The upper face of the left hand threaded flanged nut  40  is mounted to the threaded end of the operating member stem  46  and is moved towards thrust washer  44  disposed against flange  39  at the bottom of the latch housing  24 . Counterclockwise rotation of operating member  36  compresses wave spring  42  against flanged nut  40  and forces cam pin  52  against the lower side of each of the cam slots  50 . 
         [0042]    As the cam pin  52  continues to be moved down against the lower sides of slots  50 , the latch member  22  is retracted by the camming action of the cam pin  52 . The latch member end  32  is fully retracted when the threaded section  60  contacts the right hand end of the slot  48 . 
         [0043]    When the latch member  22  is fully retracted, operator member  36  will spin freely, since the threads  60  are then totally disengaged from the threads in the threaded bore  54  as described above. 
         [0044]    Compressed wave spring  42  urges the bottommost thread  64  of threads  60  against the flattened uppermost thread in thread bore  54  of the cam pin  52 . If the operator member  36  continues to be turned counterclockwise, compressed wave spring  20  forces cam pin  52  to the end of slot  48  and fully retracts the latch member end  32  into latch housing  24 . Continued counterclockwise rotation of operator member  36  causes a ratcheting sound as the lowest thread rotates past the uppermost thread in bore  54 . This assures proper reengagement of the threads  60  and the thread in threaded bore  54  when operating member  36  is again rotated clockwise. 
         [0045]    Operator member  22  can freely rotate in the counterclockwise direction due to the clearance  41  so that operator member head  56  will be raised up and lowered slightly with respect to the latch housing top surface as the operator member  36  is continued to be rotated. 
         [0046]    Accordingly, the operator member  36  remains completely enclosed and captured in the latch mechanism  18  at all times, including when the latch mechanism  18  is being operated and cannot be removed from the housing  24  without a complete removal and disassembly of the latch mechanism  18 . No torque specification is needed when retracting the latch member  22 .