A latch lock system for a door that is mountable in a doorframe, the latch lock system including a main housing including a spindle and lever, a bolt having a nose part that is attractable to a magnet, the bolt being slidable in the main housing between extended and retracted positions, a spring biasing the bolt to its retracted position, a secondary housing including a strike plate in the doorframe, a magnet mounted in the secondary housing, the magnet having a magnetic force greater than the spring force which will pull the bolt to its extended position when the door is in its closed position and the bolt is aligned with the magnet.

RELATED CASE 
       [0001]    This application claims priority under 35 USC Sections 119 and/or 120 of Provisional Patent Application Ser. No. 61/791, 998 filed Mar. 15, 2013, owned by the present applicant, the contents of which are incorporated herein by reference, 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention is in the field of door lock assemblies and particularly the interaction of a moving bolt of the lock assembly and a cooperating strike plate in a doorframe. 
       BACKGROUND AND PRIOR ART 
       [0003]    Door latch assemblies are well known in the prior art including both spring-biased bolts and deadbolts which engage a strike plate in a door frame. A characteristic of spring-biased moving bolts is that the bolt is always resiliently biased to its extended or open position whether the door is open or closed, with the distal part of the bolt inserted into the aperture of a strike plate. When a door closes and the bolt head initially engages the exposed edge of a strike plate, the bolt will momentarily be pushed inwardly against the spring force, and with further pivoting of the door which may be less than one inch, the bolt then moves outward by said spring force into the strike plate aperture and door latching is complete. This is an almost universal arrangement for automatic latching to occur whenever a door is pivoted to its closed position, so that there is no requirement for a user to manually latch a closed door to keep it from reopening. This is in contrast to a deadbolt which may be driven manually, or by key operation via a lock cylinder or other independent actuation. 
         [0004]    An inherent characteristic of a spring-biased bolt is that after it is momentarily pushed into its retracted position against the spring force, which occurs as the bolt engages an edge of the strike plate, this bolt then springs outward or distally into the aperture of the strike plate, until such motion is blocked (a) by a stop element engaging the proximal or other portion of the bolt, or (b) by a stop element located in the door frame or located inwardly of the strike plate. Regardless of the exact mechanism in the latch assembly that stops the outward motion of the moving bolt, this stopping invariably causes a significant amount of sound in all manner of locks from doors in rooms, automobile doors and frames, luggage locks, etc. In many cases the sound is annoying or distracting and sometimes detrimental as described below. 
         [0005]    In patient rooms in hospitals this clicking or clacking door-closing noise is a particular and potentially serious problem. Typically in hospitals, nurses must enter patients' rooms frequently and at all hours of the day and night, where the door latch clacking would repeatedly awaken other patients in the room not being treated by that particular visit of the nurse. Furthermore, door latch clacking in one room would create disturbing noise to patients in adjacent rooms. 
         [0006]    Typical prior art patents and applications which disclose and/or pertain to door latches and door levers include the following publications which are incorporated here with by reference: applicants co-pending application Ser. Nos. 12/590,135 and 12/856,811 and 29/416,689 and other U.S. Pat. Nos. 6,351,976; 4,236,396; 1,463,341; 6,742,820; 5,529,354; 5,947,535; 5,658,026; 4,502,720; and published applications 2010/0072762 and 2006/0071484. 
         [0007]    The above-described door latch noise situations have been in existence for decades if not hundreds of years, operating with the same fundamental noise issue every time the door is closed. The present invention addresses this situation and provides a new structure that substantially overcomes the noise problem described above. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0008]    A first object of the present invention is to provide a door latch structure which will allow a latch to automatically engage and lock with a strike plate with a relatively quiet operation. 
         [0009]    A further object is to provide a door latch structure where the bolt is maintained in a retracted state while the doors open, and when the door is closed a magnet or other element draws the bolt to its latch state extending through the aperture in the strike plate in the doorframe. 
         [0010]    An additional object is to provide a door latch structure as described above where the magnetic force attracting the bolt is adjustable by varying the axial position of the magnet in the strike plate assembly. 
         [0011]    A still additional object is to provide a door latch structure as described above which includes a sound damping element situated either in the strike plate subassembly or in the latch assembly in the door, which either slows the movement of the bolt so that it does not impact against a stop element, or by other means deadens the sound of the bolt reaching its stop position. 
         [0012]    Another object is to provide a door latch structure is described above with a shoulder or other radially extending element from the bolt's proximal area that engages a stop or retarding element fixedly positioned in the latch assembly. 
         [0013]    A further object is to control or vary the speed and/or force of the moving bolt by coupling a hydraulic piston to the bolt stem, or by placing a cushion or other brake element in the path of the bolt, or by engaging the bolt or bolt stem, or creating some other friction feature. 
         [0014]    Another object is to vary the magnet force by choosing a material with more or less magnetic force or by choosing a bolt head material that has more or less response to a magnetic field. 
         [0015]    The objects are further set forth as embodiments listed below. 
         [0000]    1. A latch lock system for a door that is mountable in a door frame, said door when pivoted to a closed position has a side edge aligned with said door frame, said latch lock system, comprising:
 
a. a main housing mountable in a door and including a spindle and lever,
 
b. a bolt having a body part and at one end a nose part that is attractable to a magnet, said bolt being slidable in said main housing between:
 
         [0016]    i. an extended position where said nose part extends transversely to be external of the side edge of the door, and 
         [0017]    ii. a retracted position where said nose part is inward of said side edge of said door, 
         [0000]    c. a spring mounted in said main housing and biasing said bolt to said retracted position with a spring retraction force Fs,
 
d. a secondary housing including a strike plate mountable in said door frame generally adjacent said main housing in said door, and
 
e. a magnet mounted in said secondary housing to be generally aligned with said nose part of said bolt in said main housing in said door, said magnet having a magnetic force Fm which is greater than said spring force Fs and which will pull said bolt to its extended position when said door is in its closed position and said bolt is aligned with said magnet,
 
f. said spindle being coupled to said bolt's body part, said spindle being movable between:
 
         [0018]    i. a release position where it allows said bolt to freely move between the bolt's retracted and extended positions, as said bolt is drawn by said spring force Fs and magnetic force Fm respectively, and 
         [0019]    ii. and engage position where said spindle drives said bolt to the bolt's retracted position, thus overcoming said magnetic force Fm pulling said bolt toward its extended position. 
         [0000]    2. The latch lock system according to Claim  1 , where said secondary housing defines a recess opening with a front claim through which said bolt extends in its extended position, said magnet being positionable in said secondary housing at different distances from said front plane to vary the magnetic force Fm applicable to said nose part of said bolt.
 
3. The latch lock system according to Claim, where said spring in said main housing is adjustable to vary its spring force Fs biasing said bolt toward its retracted position
 
4. The latch lock system according to Claim  1 , further comprising a second magnet in said nose part of said bolt to enhance magnetic attraction between said bolt and said magnet in said secondary housing.
 
5. The latch lock system according to Claim  4 , where said second magnet is axially positionable at different distances relative to said side edge of said door to vary the bolt's attractability to said magnet in said secondary housing in said door frame.
 
6. The latch lock system according to Claim  1 , comprising: (a) a keylock cylinder in said main housing spaced apart from said spindle, and (b) a pivotable link having (i) a proximal part drivable by said keylock cylinder, and (ii) a distal part engageable to said bolt's body part to restrain said bolt in its extended position, notwithstanding any force applied by said spindle to move said bolt to its retracted position.
 
7. The latch lock system according to Claim  1 , further comprising a shock absorbing element engaged to said bolt in said main housing to reduce shock and noise of said bolt when moved to its extended position.
 
8. The latch lock system according to Claim  7 , wherein said shock absorbing element is a spring mounted in said main housing and engaging said bolt.
 
9. The latch lock system according to Claim  7 , where said shock absorbing element is a hydraulic cylinder and piston combination.
 
10. The latch lock system according to Claim  1 , further comprising a shock absorbing element in said secondary housing engaged by said bolt nose part to reduce shock and noise of said bolt, when said bolt is moved to its extended position.
 
11. The latch lock system according to Claim  10 , wherein said secondary housing comprises a strike plate with a recess into which said bolt nose part extends in its extended position, and said shock absorbing element is a resilient liner on the surface of said recess in said secondary housing.
 
12. The latch lock system according to Claim  1 , wherein said secondary housing comprises a strike plate with a recess into which said bolt nose part extends in its extended position, said bolt nose part converges to a smaller cross-section at its distal part, and said recess is defined by walls that converge inwardly to conform to the shape of said bolt's nose part.
 
13. The latch lock system according to Claim  1 , further comprising (a) an additional secondary housing mountable in an upper part of said door frame, (b) an additional main housing and additional bolt mountable in an upper part of said door adjacent said additional secondary housing, and (c) a link coupled to said spindle to drive said bolt and additional bolt simultaneously to their respective retracted positions.
 
         [0020]    These and other objects will be evident from the drawings and descriptions herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a fragmentary exploded perspective view of a door with its latch bolt approaching the strike plate in a doorframe, 
           [0022]      FIG. 2  is a front elevation view in section of the new latch assembly, 
           [0023]      FIG. 3  is a fragmentary plan view in section of the latch assembly taken along line  3 - 3  in  FIG. 2 , 
           [0024]      FIGS. 4A ,  4 B and  4 C are sectional views taken along line  4 - 4  in  FIG. 1  showing details of the magnet associated with the strike plate, 
           [0025]      FIG. 4D  is an elevation view of the strike plate, 
           [0026]      FIG. 4E  is a sectional view taken along line  4 E- 4 E in  FIG. 4D , 
           [0027]      FIG. 4F  is a sectional view taken along line  4 F- 4 F in  FIG. 4D   
           [0028]      FIG. 5  is a fragmentary front elevation view of the door and frame of  FIG. 1  shown in closed state, 
           [0029]      FIG. 6  is a fragmentary plan view in section taken along line  6 - 6  in  FIG. 5 , 
           [0030]      FIG. 6A  is an and elevation view of the bolt, 
           [0031]      FIG. 6B  is a sectional view taken along line  6 B- 6 B in  FIG. 6A  and 
           [0032]      FIGS. 7 and 8  are schematic elevation views of the latch bolt mechanism coupled to the key lock cylinder. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0033]      FIG. 1  illustrates the environment of the present invention which is a door latch assembly  10  situated in a door  12  that is pivotally mounted in a door frame where the door latch assembly's sliding bolt  16  can engage a strike plate  18  situated in door frame  20 . Door  12  is shown in a partially open state with its bolt  16  situated to move along dashed line  23  into aperture  19  of strike plate  18  when door  12  completes pivoting to its closed position. Also shown in  FIG. 1  is door lever  24  mounted pivotally on door  12  to cooperate with the latch assembly  10  for a person to manually pivot lever  24  to retract bolt  16  from its extended position in a strike plate when the door is closed. 
         [0034]      FIG. 2  illustrates the new latch assembly  10 , shown for illustrative purpose, with its front plate removed. As seen, bolt  16  is situated in a retracted position so that its distal end or bolt head  16 T does not extend outward of the edge surface  21  of latch housing  12 . Bolt  16  can move axially outward to enter strike plate aperture  19  as seen in  FIGS. 1 and 5 ; however, as seen in  FIG. 3 , extending proximally from bolt head  16 T is bolt stem  28  with flange  27  intermediate the ends of this bolt stem. Coiled spring  26  encircles stem  28 , with a distal end  26 D of spring  26  bearing against frame  11 , and proximal end  26 P urging flange  27  and attached bolt stem  28  in the proximal or retracted position indicated by arrow  29 . The proximal end  28 P of stem  28  is coupled through the latch mechanism  10  to door lever spindle  29  and lever  24  as will be described below. 
         [0035]      FIG. 5  shows door  12  having pivoted to its fully closed position within door frame  20 , and with bolt  16  having moved axially and distally to its extended position where bolt head  16 T has extended through aperture  19  of strike plate  18  also seen in  FIG. 1 . 
         [0036]      FIG. 6  is a top plan view in section similar to  FIG. 3 , taken along line  6 - 6  in  FIG. 5 , but showing bolt  16  in its extended position as also shown in  FIG. 5 . Accordingly, bolt head  16 T has extended distally outward through cover plate  17  on the door edge  21 . In this extended position, seen in  FIG. 6 , bolt stern  28  has simultaneously moved in the distal direction and spring  26  has been compressed. Transition of the bolt from its retracted to its extended state will occur when the door has been pivoted to its closed state so that bolt  16  is well aligned with aperture  19  in the strike plate, as seen in  FIGS. 5 and 6 . 
         [0037]      FIG. 6  further illustrates bolt  16  having moved axially outward of door  12  and axially through aperture  19  of strike plate  18 . Inwardly of strike plate  18  in the bolt-extended direction is a bolt-receiving area or chamber  30  conforming generally in shape to the outward surface of bolt head  16 T. Further, inward of chamber  30  is magnet  40  which attracts bolt head  16 T to move axially outward of door  20  and axially inward through the strike plate  18  and into chamber  30 . When the door closes a magnetic force Fm (see arrow Fm) will pull bolt head  16 T axially outward against said spring force Fs (see arrow Fs) of spring  26  since the magnetic force Fm is greater than the spring force Fs. In one preferred embodiment the magnet is of neodynium ¾″ in diameter and ⅜″ long with Surface Field=4667 Gauss and bolt travel of about ⅝″ to ¾″. Magnetic attraction between the bolt head and the magnet in the strike can be enhanced by addition of a secondary magnet(s) secured in the bolt head similar to the above-mentioned magnet of Neodynium ¼″ diameter by ⅜″ long, Surface Field=6261 Gauss. 
         [0038]      FIG. 6A  is a rear elevation view and  FIG. 6B  is a side elevation view in section of a lock bolt  16 X with a pair of magnets  16 Y installed in the bolt head to enhance magnetic attraction of the bolt into the strike when the door is closed. These magnets may be secured in the bolt head, for example by fit or glue. 
         [0039]    The axial force Fm of magnet  40  can be varied (a) by axially positioning magnet  40  closer to the strike plate as seen in  FIG. 4A  or farther from the strike plate as seen in  FIG. 4B , or (b) by selecting a magnet having a greater or lesser magnetic force. An exemplary structure for axially moving magnet  40  is magnet holder  42  threadedly situated in threaded bore  44 . Moving magnet  40  distally away per  FIG. 4B  will reduce the effective magnetic force and thus reduce the speed and/or impact of bolt head  16 T into its extended position, and reduce the resultant noise when the doors closed. 
         [0040]      FIGS. 4D-4F  illustrate a preferred arrangement for adjustment of magnet  50  in the strike plate  18 . Magnet  50  can be moved in the direction of arrow M and locked in place by set screws  52 . Element  54  is a small projection or bumper or other friction element to slow down closing the door when it's edge approaches strike plate  18  in the door jam 
         [0041]    Sound damping can also be achieved by a cushion  46  seen in  FIG. 4C  in front of magnet  40  or some other restrictive element in the vicinity of bolt head  16 T, by a damper or shock absorber  48  seen in  FIG. 1  or  2 , may be applied to stem  16 S of bolt  16  or applied to a movable frame  16 F to which stem  16 S is coupled. In a preferred embodiment the damper restricts bolt movement to 69 in/sec, while bolt may travel three times that speed without a damper. 
         [0042]    To open a closed and latched door  FIG. 1  shows a lever  24  that can be pivoted to rotate spindle  29  and retract bolt  16 . Pivoting of lever  24  of a closed door will retract bolt  16  by manually overcoming the magnetic force Fm of magnet  40  situated inward of the strike plate. With the bolt  16  retracted and door  12  pivoted to an open position away from magnet  40 , spring  26  would reassert its role of maintaining bolt  16  in its retracted mode. 
         [0043]    In  FIG. 2  is schematically shown a cam finger  32  rotated by spindle  29 , coupled to lever  24  (not shown). Cam finger  32  engages link  34  which pivots about pivot axle  36  and has an arm portion  38  engaged to the proximal end  16 P of bolt  16 . To open a closed door, counterclockwise motion of spindle  29  drives link  34  in a counterclockwise motion which pulls bolt  16  into its retracted position which overcomes magnetic force Fm, and withdraws bolt  16  to be fully (proximally) outward of strike plate  18 , so that the door can be opened. After the door is opened and magnet  40  is no longer affecting bolt head  16 T, spring  26  can resume its primary role to maintain bolt  16  in its retracted position, regardless of whether lever  24  and link  34  are urging bolt  16  to its retracted position. Thus, when the door is open bolt  16  is normally retracted because of the spring force Fs. Bolt  16  will be extended only when the door is closed and the magnetic force Fm is applied, and finally will be pulled to its retracted position can be lengthened by an extension or other means not shown to compensate for a larger door Between the edge of the door and the door jam. 
         [0044]    Also seen in  FIG. 2  and three is coupling of the upper end  38  of link arm  34  to bolt stem  16 S. Numerous different couplings well known in the prior art may be selected for retracting a bolt by rotation of a lever. This retraction also moves flange  27  in the proximal direction of arrow A1 which allows spring  26  to again exert force urging bolt stem  16 S and bolt  16  to their retracted position. As noted above the magnetic force Fm is stronger than the spring force Fs, so that manual pivoting of lever  24  is required to overcome the magnet force. Thereafter, when the door is open and the lever is released, the spring force without opposition of a magnet force, will maintain the bolt in its retracted position, until such time as the door is closed again. 
         [0045]      FIGS. 7 and 8  further illustrate how the independent keylock cylinder and its cam  62  can bar opening of this door when it is closed and its bolt is extended into the strike plate of the door frame.  FIG. 7  shows that spindle  29  and its collar  31   6  and its camming finger  32  are positioned, if pivoted counterclockwise to bear against link  34  which would pivoted about pivot  36 , and in so pivoting pull and retract the bolt. Pivoting of link  34  is precluded by cam finger  62  of keylock cylinder not shown, to thus bar opening the door by pushing on the lever. 
         [0046]      FIG. 2  shows bolt head  16 T slidable in front housing sleeve  4 , and bolt stem  16 S is slidable in rear housing sleeve  5 . Link  34  is situated on the near side of rear housing sleeve  5  as viewed in  FIG. 2 , while blocking link  55  is situated on the far side of rear housing sleeve  5 , namely on the far or opposite side of housing  5 . Link  34  is coupled to the rear portion  16 P of the bolt stem by a transverse pin extending from said stem into slot  37  and link  34  seen in  FIG. 3 .  FIGS. 2 and 8  show more clearly that link  34  is in the foreground, while link  55  is behind or rearward of rear housing  5 . 
         [0047]    As will be further explained below, door lever  24  can be pivoted to cause bolt  16  to retract from strike  18  so that the door can be opened. Keylock cylinder with its cam finger  62  can be rotated to lock mode to temporarily bar door lever  24  from being able to open the door. These two functions are achieved through two different links coupled to the door lever as follows.  FIG. 2  shows link  34  connected between spindle  29  (coupled to door lever  24  not shown) and stem  16 S of bolt  16  as seen in  FIG. 2 . In  FIG. 2  link  34  appears in the foreground adjacent one side of housing  11 , of the latch assembly and coupled to the proximal end  16 P of the bolt stem  16 S via a pin  37 P extending transversely from stem  16 S into a slot  37  at the top end of link  34  ( FIG. 3 ). Also seen in  FIGS. 2 ,  6  and  8  in the background or far side of housing  11  is link  55  having its upper portion  55 U coupled to keylock cylinder and its cam finger  62  and having its lower portion  55 L coupled to spindle  29  with its collar  31  and cam finger  56 . These links are also shown in the  FIG. 6  plan view where cam finger  32  pivoted by collar  31  engages link  34 , both in the foreground or near side of housing  11 , while cam finger  62  engages link  55  in the rear or far side of housing  11 . Further details of the foreground link  34  and background link  55  are explained as follows. 
         [0048]      FIG. 2  shows link  34  coupled to the bolts rear stem rear stem  16 P with bolt  16  in its retracted position and spring  26  in its expanded mode pushing and maintaining bolt  16  to remain in its retracted state until the door is closed and bolt  16  moves distally through strike  18  as seen in  FIG. 6 . This bolt can be retracted by rotating spindle  29 , its collar  30  and its cam finger  32  counterclockwise as seen in  FIG. 2  which would bear against link  34  and pull bolt stem  28  toward the left into its retracted state as seen in  FIG. 2 . Thus, the keylock cylinder in lock mode can block lever; however, if the keylock cylinder's cam finger  62  is pushing upper arm  55 U of link  55  in a counterclockwise direction, this pushes lower arm  55 L of link  55  into position adjacent cam finger  32  and blocks this finger and spindle  29  from turning to retract the bolt and opened the door. 
         [0049]    Further as regards the damping feature applied to bolt  16  to reduce or eliminate the sound associated with the magnet pulling the bolt into the strike plate, an alternative damping element is a hydraulic piston and cylinder  48  as seen in  FIG. 2  coupled through a linkage to bolt  16 . This slows and controls the movement of the bolt when it is under the influence of the magnetic pull. This hydraulic cylinder can be adjusted to affect the speed and/or force of movement of the bolt. An alternative adjustment of the damping effect can be achieved, as described above and as shown in  FIG. 6 , by adjusting the position of magnet  40  to alter the magnetic force affecting the bolt head, and a still further alternative damping element would be positioning a cushion proximally of the surface of the magnet to blunt or soften the impact and resulting sound. 
         [0050]    Returning now to  FIG. 6 , chamber  30  into which the bolt head  16 T will be inserted is tapered to reduce the possibility of patient suicide as follows. If such patient were to position a segment of a cord, twisted sheet or other ligature into this chamber  30  recess, intending to have the ligament captured therein when the door is closed with the opposite end used as a noose, such ligament would tend to fall out or at least not be captured due to the tapered walls. Accordingly, with the spring element in the latching mechanism maintaining the bolt in a retracted state, a ligature inserted in said chamber would simply fall out when any tension were applied thereto since there was nothing on which the ligature could hook onto. 
         [0051]    Although the best mode for carrying out the present invention has been described in the foregoing detailed description and illustrated in the accompanying drawings, it will be understood that the invention is not limited to the embodiments enclosed, but is capable of numerous rearrangements, modifications and substitutions of steps and elements without departing from the spirit of the invention. Accordingly, the present invention is intended to encompass such rearrangements, modifications and substitutions of steps and elements as falls within the scope of the claims.