Abstract:
An apparatus for adjusting the position of a seat comprises a rack and a clock nut that grips the rack. The rack comprises a threaded rod, while the clock nut comprises a short cylindrical body that is drilled and threaded along its diameter with internal threads corresponding to the thread diameter and pitch of the rack. Circumferential reliefs are then formed in the threaded bore to enable the clock nut to be “clocked” from a position in which the threads of the clock nut engage the threads of the rack to a second position in which the threads of the clock nut disengage the threads of the rack. A pair of linkages are provided to rotate the clock nut between the engaged and disengaged positions and to transmit loads from the clock nut. Because the clock nut engages multiple teeth of the rack simultaneously, the seat track locking mechanism of the present invention is capable of extremely fine position adjustment without sacrificing ruggedness and because of the design of the linkages, the seat track locking mechanism locks bi-directionally and with little or no backlash.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The application claims priority of U.S. provisional application No. 60/908,133 filed Mar. 26, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to vehicle seat systems and, more particularly, to locking mechanisms for adjustable vehicle seats. 
     Many aircraft and other vehicle seating applications have a requirement that the seat be able to translate in one or more directions. Once translated, the seat must be securely locked in its new location and once locked, the seat must be able to withstand various use/abuse loads, in-flight gust loads, and crash loads. Conventional seat track locking mechanisms typically employ a track member that contains a plurality of slots or holes spaced along the length of the track. The other track member has a pin or shaft that is selectively engaged with one of the holes or slots to lock the track members together. When the pin is disengaged from the hole, the tracks can move relative to one another. Once the seat is in the desired position, the pin is re-engaged in a corresponding slot or hole. 
     A disadvantage of this type of locking assembly is that there are only a finite number of adjustment positions, since each slot or hole defines one seat position. In order for the locking mechanism to be sufficiently robust to meet the load requirements, the pins and holes of the locking mechanism must be made sufficiently robust (i.e., large) and therefore the pitch between available locked positions is relatively coarse. Additionally, with the conventional pin and hole locking mechanisms, sufficient clearance between the pin and hole must be allowed to facilitate easy engagement of the pin with the hole. This, however, can lead to undesirably noisy and uncomfortable backlash when the seat is in the locked position. 
     Another type of seat locking mechanism employs a unidirectional friction lock consisting of a rod and a collar that slides over the rod. The collar is biased along one edge by a spring that causes the collar to wedge against the rod. This type of mechanism enables infinite adjustment, but because the collar can only hold in a single direction, two complete mechanisms are required to lock the seat in position. Moreover, because this type of mechanism relies on friction to hold the seat in position, it will slip if a heavy load is applied. Accordingly, seats equipped with this type of mechanism must be moved to a special position and locked in place if heavy loads are anticipated, for example, during aircraft takeoff and landing. What is needed is a seat locking mechanism that is capable of holding in two directions with a single mechanism that is sufficiently robust to meet the foregoing load requirements yet is capable of fine adjustments with little or no backlash in the locked position. 
     SUMMARY OF THE INVENTION 
     The present invention solves the foregoing problem by providing an apparatus for adjusting the position of the seat that comprises a rack and a clock nut. According to one embodiment of the invention, the rack comprises a threaded rod having a standard Unified, American National or SI thread profile. The clock nut of the illustrative embodiment comprises a short cylindrical “hockey puck” shaped body that is drilled and tapped along a diameter of the cylinder with internal threads corresponding to the thread diameter and pitch of the rack. In the illustrative embodiment, a second hole is cut along the cylindrical axis of the puck that intersects the threaded bore leaving two discrete threaded bores near the perimeter of the puck. Circumferential reliefs are then cut in the threaded bore to enable the puck to be “clocked” from a position in which the threads of the clock nut engage the threads of the rack, to a second position in which the threads of the clock nut disengage from the threads of the rack. A pair of linkages are provided to rotate the clock nut between the engaged and disengaged positions and to transmit loads from the clock nut. The linkages are designed so that lateral loads from the clock nut are reacted bi-directionally and with little or no backlash. Because the clock nut engages multiple teeth of the rack simultaneously, the seat track locking mechanism of the present invention is capable of extremely fine position adjustment without sacrificing ruggedness and because of design of the linkage, the seat track locking mechanism does so bi-directionally and with little or no backlash. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which: 
         FIG. 1  is an exploded perspective view of a seat track locking mechanism incorporating features of the present invention; 
         FIG. 2  is a top perspective view of the seat track locking mechanism of  FIG. 1  as assembled; 
         FIG. 3  is a bottom perspective view of the seat track locking mechanism of  FIG. 2 ; 
         FIG. 4  is a top view of the seat track locking mechanism of  FIG. 1  with the cover plate removed showing the mechanism in the disengaged position; 
         FIG. 5  is the seat track locking mechanism of  FIG. 4  in the engaged position; and 
         FIG. 6  is a perspective view of a seat frame incorporating the seat track locking mechanism of  FIGS. 1-5 . 
     
    
    
     DETAILED DESCRIPTION 
     The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention. 
     With reference to  FIGS. 1-5 , seat track locking mechanism  10  comprises a rack  12 , which in the illustrative embodiment is mounted to the vehicle frame so that the longitudinal axis  14  of rack  12  is parallel to the direction of motion of the vehicle seat  16  along its track  18  ( FIG. 6 ). Rack  12  is formed with a series of external threads  20  formed, for example by machining on a geared lathe or by running rack  12  through a threading die, so that external threads  20  run substantially the entire length of rack  12 . In the illustrative embodiment threads  20  comprise 5/8-18 UNF class 2 threads. Rack  12  is further formed, e.g., by machining a pair of longitudinal grooves  22 , leaving rack  12  with a substantially “I”-shaped cross-section with a continuous web portion  24  and flanges  26  incorporating the external threads  20 . In addition to reducing the unnecessary weight of rack  12 , grooves  22  center rack  12  as it slides across the guide lands  52  located on lower cover plate  28  and upper cover plate  30 . 
     Seat track locking mechanism  10  further comprises a clock nut  32  which comprises a generally short cylindrical “hockey puck” shaped body which is formed, e.g., by machining to include a first bore  34  along a chord of the circular face  36  of clock nut  32 , preferably along the diameter of the circular face  36  of clock nut  32 . A second bore  38  is formed in clock nut  32 , e.g., by machining, to intersect first bore  34  thereby separating first bore  34  into a discrete first jaw portion  40  and second jaw portion  42 . First bore  34  is formed, e.g., by tapping, to have internal threads  44  and  46  that correspond to the diameter and pitch of external threads  20  of rack  12  (e.g., 5/8-18 UNF class 2). The internal threads  44  and  46  of first bore  34  may be formed either before or after second bore  38  is formed but in either event are formed in a continuous operation so that internal threads  44  and internal threads  46  have a continuous helical pitch and, therefore, a threaded rod inserted and threaded into internal thread  44  would continue to thread without binding through internal thread  46 . 
     A portion of each internal threads  44  and  46  are removed, e.g., by machining away, to form reliefs  48  and  50 , the function of which can be seen most clearly with reference to  FIGS. 4 and 5 . As can be seen from  FIG. 4 , first jaw portion  40  and second jaw portion  42  have internal threads  44  and  46  respectively that are the same diameter and pitch as the external threads  20  of rack  12  and therefore grip rack  12  as would a conventional nut. Reliefs  48  and  50 , however, enable clock nut  32  to be rotated (“clocked”) to a position where internal threads  44  and  46  are disengaged from external threads  12  and rack  12  is capable of simply sliding through clock nut  32  by passing through reliefs  48  and  50 . When clock nut  32  is clocked back into the position shown in  FIG. 5 , internal threads  44  and  46  of first jaw portions  40  and  42  engage external threads  20  of rack  12  as jaw members  40  and  42  engage the sides of rack  12 . 
     Seat track locking mechanism  10  further comprises the necessary linkage for clocking or rotating the clock nut from the disengaged to the engaged position and for locking it in the engaged position against unintentional release. Clocking linkage  56  comprises a first toggle linkage  58  that is loaded in compression when moving clock nut  32  into the closed position and a second toggle linkage  60  that is loaded in tension when moving clock nut  32  into the closed position. First toggle linkage  58  comprises a compression link  62  and a toggle input link  64 . Toggle input link  64  is pinned at the central pivot point  66  by pin  68  which passes through lower cover plate  28 , upper cover plate  30 , and input lever  70 . Pin  68  is retained to input lever  70  with cotter pin  72  and spacer washers  74  as required. The output end  76  of input lever  70  is pinned to the end  78  of toggle input link  64  and crossover link  80  by means of pin  82  which is retained by means of cotter pin  84 , spacer  86  and washer  88  as required. 
     Compression link  62  is pivotably connected to clock nut  32  at pivot  90  and is pivotably connected to toggle input link  64  at pivot  92 . As first toggle linkage  58  moves clock nut  32  from the disengaged position as shown in  FIG. 4  to the engaged position as shown in  FIG. 5 , first toggle linkage  58  moves from a substantially over-center position to a very slightly (approximately 5°) over-center position on the opposite side with toggle input link  64  coming to rest against limit stop  94 . Once in this position, any force on clock nut  32  attempting to move clock nut  32  from the engaged to the disengaged position merely presses toggle input link  64  against limit stop  94  and does not break the linkage open. 
     Second toggle linkage  60  comprises a tension link  96  and slave links  98   a  and  98   b . Tension link  96  is pivotably attached to clock nut  32  at pivot  100  and is pivotably attached to slave links  98   a  and  98   b  and to crossover link  80  at pivot  102 . Slave links  98   a  and  98   b  are pivotably attached to lower cover plate  28  and upper cover plate  30  at pivot  104 . As second toggle linkage  60  moves clock nut  32  from the disengaged position as shown in  FIG. 4  to the engaged position as shown in  FIG. 5 , second toggle linkage  60  moves from a substantially before bottom-dead-center position as shown in  FIG. 4  to a slightly (approximately 5°) after bottom-dead-center position with slave links  98   a  and  98   b  and/or tension link  96  operatively resting against limit stop  106 . With second toggle linkage  60  in this position, any force attempting to move clock nut  32  from the engaged position into the disengaged position places tension link  96  in tension and merely causes slave links  98   a  and  98   b  and/or tension link  96  to press against limit stop  106  but does not cause second toggle linkage to rotate past bottom-dead-center and therefore clock nut  32  is held firm. As can be seen from  FIGS. 4 and 5 , as clock nut  32  is rotated by first and second linkages  58  and  60 , clock nut  32  is constrained to move in a circular path by means of guides  108  and  110  secured between lower cover plate  28  and upper cover plate  30 . 
     To allow for minute adjustments, e.g., for controlling backlash, tension member  96  is adjustable in length. This is accomplished by passing tension member  96  through a pillow block  116  that forms the connection between tension member  96  on the one hand and slave links  98   a  and  98   b  and crossover link  80  on the other hand. The tip  118  of tension link  96  is threaded to accept a nut  120  that prevents tension link  96  from withdrawing out of pillow block  116  when placed under tension. An anti-rattle spring  122  holds nut  120  firmly against pillow block  116 . 
     As noted above, any force attempting to rotate clock nut  32  from the engaged position to the disengaged position merely causes first toggle linkage  58  and second toggle linkage  60  to press against their respective limit stops thereby preventing clock nut  32  from rotating. The lateral loads on clock nut  32  are also reacted through first toggle linkage  58  and second toggle linkage  60 , but in a unique and innovative way. With reference in particular to  FIG. 5 , a load tending to move cover plate  28  and the balance of seat track locking mechanism  10  along rack  12  to the right of  FIG. 5  will cause clock nut  32 , which is engaged with rack  12  to place tension link  96  in tension. Because toggle linkage  60  is already in a slightly beyond bottom-dead-center position with slave links  98   a  and  98   b  and/or tension link  96  pressing against limit stop  106  (through pillow block  116 ), the lateral load placing tension link  96  in tension merely causes slave links  98   a  and  98   b  and/or tension link  96  to press against limit stop  106  but does not cause second toggle linkage to rotate and therefore clock nut  32  is held firm against the lateral load. Simultaneously, because tension link  96  is offset from the points of contact between jaws  40  and  42 , and rack  12 , the torque couple caused by the lateral load acting on tension link  96 , causes jaws  40  and  42  to rotate more firmly into engagement with rack  12 . As can be determined from the foregoing, the action of tension link  96  is effectively load-responsive, since the greater the lateral load, the more firmly clock nut  32  grips rack  12 . 
     To ensure that the lateral load is reacted entirely by tension link  96 , clearance  67  between the pin and hole forming first pivot  90  (and/or clearance between the pin and hole forming second pivot  92 ) prevents a lateral load in this first direction from reacting against first toggle linkage  58 . Absent this clearance, that portion of the load reacted against compression link  62  would tend to reduce the torque couple that causes clock nut  32  to grip rack  12  and therefore would diminish the load-responsive action of tension link  96 . By ensuring that all of the lateral load in this first direction is reacted by tension link  96  the load-responsive action of tension link  96  is maintained. 
     A load in the opposite direction, i.e. tending to move cover plate  28  and the balance of seat track locking mechanism  10  along rack  12  to the left of  FIG. 5  will cause clock nut  32 , which is engaged with rack  12  to place compression link  62  in compression. Because toggle linkage  58  is already in a slightly over-center position with toggle input link  64  against limit stop  94 , the lateral load placing compression link  62  in compression merely presses toggle input link  64  against limit stop  94  and does not break the linkage open. Therefore, clock nut  32  is held firm against the lateral load. Simultaneously, because compression link  62  is offset from the points of contact between jaws  40  and  42 , and rack  12 , the torque couple caused by the lateral load acting on compression link  62 , causes jaws  40  and  42  to rotate more firmly into engagement with rack  12 . Thus, in this second direction, the action of compression link  62  is effectively load-responsive, since the greater the lateral load, the more firmly clock nut  32  grips rack  12 . 
     At the same time, because tension link  96  is capable of sliding through pillow block  116 , a lateral load in this second direction does not place tension link  96  in compression. Absent this sliding connection, that portion of the load reacted against tension link  96  would tend to reduce the torque couple that causes clock nut  32  to grip rack  12  and therefore would diminish the load-responsive action of compression link  62 . By ensuring that virtually all of the lateral load in this second direction is reacted by compression link  62 , (the force of anti-rattle spring  122  is at least an order of magnitude less than the tensile strength of compression link  62 ), the load-responsive action of tension link  96  is maintained. 
     Manual operation of seat track locking mechanism  10  is accomplished by means of an actuator rod (not shown) which is attached to the actuator hole  112  formed in input lever  70 . A resilient member such as compression spring  114  urges clock nut  32  into the engaged position and locks first and second toggle linkages  58  and  60  by urging crossover link  80  in the appropriate direction. 
     Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. For example, although in the illustrative embodiment the rack is secured to the vehicle and the clock nut is attached to the seat in certain circumstances, for example, if the clock nut is solenoid-actuated, it may be preferable to mount the clock nut mechanism to the vehicle and mount the rack to the vehicle seat. Additionally other threads including Square, Acme, Whitworth, BSF, buttress and even gear or other teeth profiles (helical or non-helical) may be incorporated, all without departing from the scope of the present invention. Accordingly, it is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.