Patent Publication Number: US-6662603-B2

Title: Tubular latch

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Serial No. 60/325,698, entitled Mortise Lock, filed on Sep. 28, 2001 and is a Continuation-In-Part application of U.S. application Ser. No. 10/219,140 filed Aug. 15, 2002, entitled Mortise Latch. 
     BACKGROUND OF THE INVENTION 
     Tubular latches are the most common latching devices used for residential and commercial doors today. They are available in two “backsets,” 2¾ inches and 2⅜ inches. Backset is the distance from the face of the latch to the center of the latch hub/spindle. Tube latches also typically have two spring strengths, one spring strength for levers and one spring strength for knobs. The lever latch has a relatively strong spring for several reasons. First, the spring is strong to support the weight of the levers which are cantilevered from the center of the latch hub. Second, the spring is strong to resist the added torque created by the lever. The knob latch has a relatively weaker spring since the weight of its knobs is evenly distributed around the latch hub. Additionally, the knob is smaller and therefore a user applies less torque to the latch hub when rotating the knob. 
     Tubular latches also come in an assortment of variations. Typically, manufacturers use one of two finishes for the latch bolt, satin brass and satin nickel. A tubular latch may also be available in either a “passage” type or a “privacy” type. A passage latch is used on doors where no privacy is required such as closets, pantries, laundry rooms, and the like. A privacy latch is used where privacy is required, such as bathrooms, bedrooms, and the like. The privacy feature is integral to the latch body. A pushbutton operates perpendicular to the face of the door to engage the privacy feature and prevent the latch from allowing the door to open. Pushing the pushbutton towards the latch activates the privacy feature and rotating the knob or lever about the latch hub cancels the privacy feature and allows the latch to be unlatched. 
     Tube latches are required to fit a specific door preparation. The maximum diameter of the latch body is typically one inch. The face plate is typically one inch by two inches. The backset is either 2⅜ inches or 2¾ inches. Privacy latches are typically used on doors predrilled with a 2⅛ inch hole through the door faces. 
     In the past, lock dealers were required to inventory specific latches for each combination of backset, spring strength, finish, and privacy or passage type. This resulted in the dealer having to inventory numerous individual latches. The present invention allows one latch to be used for knob strength, lever strength, and backset (2⅜ inch or 2¾ inch). A privacy adapter may be added for the privacy feature. Therefore, a dealer will only have to inventory one latch for each finish, e.g., a satin brass latch and a satin nickel latch, and one privacy adaptor. 
     A conventional tubular latch as shown in FIG. 1 includes a latch L resiliently held in a housing S fixed in a tubular hole formed in a door R and operatively retracted for opening the door by biasing a door handle H (direction R 1 ) whereby a cam C as rotated (in direction R 2 ) by the handle H will pull a driving plate D secured with the latch L to retract the latch L in rearward direction R 3  for opening the door. 
     For biasing the handle H for opening the door, a rotating angle A (such as 70 degrees) provides a stroke L 2  for retracting the latch L in direction R 3  for opening the door. This is equal to an arc length of the rotated cam C of the handle H and the retraction of the latch L is directly actuated by rotating the cam C and handle H. 
     U.S. Pat. No. 5,020,836 discloses a tubular latch that includes a biasing lever pivotally mounted on the housing of the latch. Here, the novel feature of this invention is the addition of a biasing lever and related structure which allows for a smaller degree of handle rotation to fully open the latch bolt. This patent is fully incorporated by reference. 
     BRIEF SUMMARY OF THE INVENTION 
     A tubular latch is provided which includes a latch case, a latch bolt, a hub having a cam, a slider member, a latch spring adjuster plate, and a slider member spring. The latch bolt is axially movable within the latch case from an extended position to a retracted position. The hub is rotatably mounted within the latch case and receives a door handle shaft. The hub is rotatable from a first position wherein the latch bolt is in the extended position to a second position wherein the latch bolt is in the retracted position. The cam is integral to an outer surface of the hub and has one or two driving surfaces. Rotational movement of the hub causes the driving surface to rotate with the hub. The slider member is movable from a first axial position in the latch case wherein the slider member is in an extended position to a second axial position in the latch case wherein the slider member is in a retracted position. The slider member is moveable by rotational movement of the hub causing the driving surface of the cam to drive the slider member from the extended position to the retracted position. The latch spring adjuster plate is moveable axially within the latch case and is adjustable and securable to a desired axial position within the latch case. Finally, a slider member spring is included for biasing the slider member away from the latch spring adjuster plate, whereby changing of the desired axial position of the latch spring adjuster plate changes an initial compression amount of the slider member spring. 
     One or more adjuster plate screws may be used for securing the latch spring adjuster plate to the desired position within the case. The adjuster plate screws may includes a screw head accessible from the outside of the casing. The screw head is preferably adjacent to the latch bolt. A latch bolt shaft connected between the latch bolt and the slider member may be included that is adjustable in length. Here, the latch bolt shaft may include a front latch bolt portion and a rear slider member portion where the front latch bolt portion and the rear slider member portion are adapted to be secured to one another by a spring clip. Finally, the latch bolt shaft may be a one-piece integral unit where the shaft has a plurality of grooves. One of the grooves may be for being received in a slider member keyhole slot to allow for effective adjustability of length of the latch bolt. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     The invention will be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: 
     FIG. 1 cutaway, front elevational view of a prior art tubular latch. 
     FIG. 2 is a cutaway, front elevational view of a tubular latch (excluding a latch carrier) in accordance with one preferred embodiment of the present invention. 
     FIG. 3 is a front view of a latch spring adjuster plate for use with the tubular latch of FIG.  2 . 
     FIG. 4 is a front elevation view of latch carrier for securing the tubular latch of FIG. 2 in a door. 
     FIG. 5 is a side elevation view of the latch carrier of FIG.  4 . 
     FIG. 6 is a side elevation view of an adjustable latch bolt and shaft for use with the tubular latch of FIG.  2 . 
     FIG. 7 is a partial isometric view of a slider member for use with the adjustable latch bolt and shaft of FIG.  6 . 
     FIG. 8 is a side elevation view of an alternate embodiment of a latch bolt and shaft (with spring clip) for use with the tubular latch of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like part numbers refer to like elements throughout the several views, there is shown in FIG. 2 a tubular latch  10  in accordance with one preferred embodiment of the present invention. The tubular latch  10  includes a latch case  12 , a latch bolt  14 , a hub  16 , a slider member  22 , and a slider member spring  26 . As described above with respect to a prior art tubular latch, rotation of the hub  16  (by a handle or knob) causes a cam  18  to rotate. The cam  18  has a pair of driving surfaces  20 , one of which bears against one of surfaces  21  on the slider member  22  which causes the slider member  22  to move axially (to the right in the drawing) against the slider member spring  26 . When the slider member  22  moves axially to the right, it draws the latch bolt  24  to its retracted position. When the hub  16  is freed to rotate back to its home position (i.e., the handle is let go), the spring  26  causes the latch bolt to extend back out to its fully extended position. The latch bolt  14  may extend and retract independently of the rest of the tubular latch mechanism via spring  34 . Other elements of a tubular latch not described here are well known elements in the prior art, for example, as shown in FIG.  1 . 
     The tubular latch  10  is secured in the latch carrier  42  as shown in FIGS. 4 and 5. Latch notches  44  are aligned with latch carrier notches  46  and are secured with a spring clip (not shown) thereby securely mating the tubular latch  10  with its latch carrier in a door (see FIG. 1 for an example of door installation). 
     Two novel features of a preferred embodiment of the tubular latch  10  will now be described in detail. The first is an adjustable spring tension feature to allow for use of either a knob or a lever, and the second is an adjustable latch bolt shaft length to allow the tubular latch  10  to be installed in doors requiring a backset of, for example, either 2¾ inches or 2⅜ inches. 
     The adjustable spring tension feature is as follows. In prior art tubular latch designs, a latch spring plate P bears directly on the cam C of the latch. See FIG.  1 . As can be seen in FIGS. 2 and 4, the preferred design of the present invention uses three elements: a latch spring adjuster plate  24 , a pair of adjuster plate screws  28  and a pair of counterbored through holes  48 . The latch spring adjuster plate  24  has a pair of threaded holes for accepting the threaded adjuster plate screws  28 . The latch spring adjuster plate  24  travels axially within the slider member  22  (and latch case  12 ) and may be continuously adjusted by turning the adjuster plate screws  28  (via screw heads  30  that are accessible on the latch carrier  42 ) thereby shortening or lengthening the distance between the latch bolt  14  and the latch spring adjuster plate  24 . The spring  26  remains captured between the latch spring adjuster plate  24  and an end of the slider member  22 . By shortening or lengthening this distance, the static length of the spring  26  is increased or decreased thereby increasing or decreasing the amount of force required at the hub  16  to move the latch bolt  14  to its retracted position. Either knobs or levers can thereby be accommodated. 
     The second novel feature is an adjustable latch bolt shaft length to allow the tubular latch  10  to be installed in doors requiring a backset of, for example, either 2¾ inches or 2⅜ inches. This can be accomplished in several ways, for example, as shown in FIGS. 6-8. As can be seen in FIGS. 6 and 7, the length of the latch bolt shaft  32 C can be adjusted by including grooves  38  that are adapted to fit into keyhole slot  40  of the slider member. As shown here, there are two grooves  38 . One of these grooves  38  may be set to properly size the latch bolt for a 2¾ inch backset while the second of these grooves may be set to properly size the latch bolt for a 2⅜ inch backset. It is understood that many other similar means may be used, for example, using C-clips in a round through hole that fit into the grooves  38  rather than the using the keyhole slot  40  as shown here. As can be seen in FIG. 8, another device for adjusting the length of the latch bolt shaft is shown. Here, the latch bolt shaft has two portions  32   a  and  32   b  these fit together by mating knurling and then are rigidly secured to one another by a spring clip  36 . 
     While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.