Latch Mechanism For Manhole Cover with Captured Operator

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.

1 . A latch mechanism including a housing with a cavity formed therein in which a latch member is received, said latch member movable lengthwise in said cavity to be extended or retracted to a position a latching end portion thereof protruding from said housing; an operator member received into an opening in said housing and through a lengthwise extending central slot formed in said latch member; said latch member having a pair of aligned angled cam slots formed therein, extending in the same general direction of said extending and retracting motion of said latch member, each cam slot lying on either side of said central slot receiving said operator member; a cam pin having a pair of ends each end slidably received in a respective cam slot; said cam pin having a threaded bore formed intermediate said pair of ends, said operator member passing through said threaded bore and having an external thread engageable with threads of said cam pin threaded bore upon rotation of said operator member in either direction, said operator member restrained against axial movement in said housing so that as said operator member is rotated in either direction said cam pin is moved up or down and in turn acts on the side sides of said cam slots to move said latch member in either an extending or retracting direction of said end portion. 
     
     
         2 . The latch mechanism according to  claim 1  wherein said lengthwise slot limits the extent of movement of said latching member by abutting either side of said operator member in said respective extended and retracted position of said latching member. 
     
     
         3 . The latch mechanism according to  claim 1  wherein said threaded portion of said operator member terminates as said latching member reaches a fully retracted position so that the threads on said portion and said threaded bore of said cam pin are disengaged and no further camming action drive occurs. 
     
     
         4 . The latch mechanism according to  claim 3  wherein said operator member is axially restrained by flanged elements fixed on either end thereof and engaging said housing to limit axial movement in said housing to a slight clearance. 
     
     
         5 . The latch mechanism according to  claim 4  wherein one flanged element has a resiliently compressed element interposed between said flange and said element to allow limited axial movement and which also urges said threaded portion of said operator member towards said threaded bore, causing said reengagement of said threads of threaded portion of said operator member and said threaded bore in said cam pin upon rotating said operator member in a direction extending said latch member and maintaining full retraction of said latch member with said threads disengaged. 
     
     
         6 . The latch mechanism according to  claim 3  wherein the last thread of said threaded portion of said operator member is machined squared to an axis of rotation of said operator member to be tapered in width and blended into said operator member. 
     
     
         7 . The latch mechanism according to  claim 1  further combined with a manhole cover, attached to the underside thereof at the outer perimeter so that said latching member when extended engages a feature on fixed structure surrounding said manhole cover when said manhole cover is installed on a manhole vault.