Patent Publication Number: US-6698259-B2

Title: Dual action detent for tamper resistant lever lock mechanism

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to lever locks and more particularly, the present invention relates to detents for use with such mechanisms. 
     2. Description of the Prior Art 
     Lever locks have been used for some time in a wide variety of applications and situations to lock and secure doors, gates, safety deposit boxes, and the like. Lever locks typically comprise a sliding bolt mechanism. When the bolt is extended outwardly from the case in which it is housed, it typically engages into a hole or mortise in a doorjamb or other fixed member. The bolt is thrown from side to side by way of a portion of an inserted key. As the key turns, the bit end of the key usually contacts the bolt and causes it to slide from side to side as the key is turned. 
     The lever lock incorporates a plurality of swinging detainers, i.e., a plurality of plate-like levers which swing up and down, or side to side, typically under the force of a spring which biases the levers into a locking position. The key is specifically designed to move or raise these different levers to unique but varying positions or heights such that when the levers are in a particular combination or configuration of heights, a detent is able move due to an external force such as gravity or more typically by a spring force into a specific position. Once in that specific position the detent releases the bolt mechanism allowing it to freely slide into locking or unlocking engagement with the mortise. Typically levers include openings or recesses known as “gates” which are aligned so that a portion of the detent actually slides into the gates of the levers to free the movement of the bolt. The portion of the detent that slides into the gates is known as a fence. 
     Other lever locks do not use a detent, but instead have the fence connected to the bolt itself. Once the levers are properly aligned, the fence is free to move, thus allowing movement of the bolt. 
     Three common methods used to defeat lever locks include picking, impressioning and fence breaking. All these methods rely on the ability of the attacker to control the amount of pressure the fence exerts against the levers. The pressure is usually caused using a pick wherein pressure applied to the pick is transferred to pressure of the fence against the levers. As an example, the pressure may be exerted on the fence through the keyhole using a special pick tool that turns the cam, which in turn exerts pressure on the bolt which transfers pressure to the detent, and hence, the fence. 
     In picking, the pressure of the fence against the levers holds the levers in position while other levers are individually raised to their respective “unlocked” position, i.e., a position where all lever gates are properly aligned to allow the fence to move. In impressioning, a large pressure causes levers that are not at a gate to leave a mark on the key being cut. In fence breaking, a substantial pressure is exerted on the bolt, typically using a crowbar or similar tool, causing the fence to actually break thus allowing the lock to open. 
     Previously, locks have been constructed that were intended to be pick or tamper resistant. For example, locks have been designed to incorporate false gates, jagged-edged levers/fences, detector levers, a spring to compress the stack of levers, a tail on a monitor lever, among others in an attempt to make the above described tamper techniques more difficult. Yet in every design, the attacker still has control over the amount of pressure exerted by the fence against the levers. Hence, while the above methods of attack are made more difficult by these improvements, they are still possible. 
     For example, in one prior-art lock, a “detector lever” is used to resist tampering. In such a lock, the detector lever is designed to be “caught” by a spring if it is raised too high. This prevents any further tampering with the lock, as the lock will not open until the detector lever is “released.” Unfortunately however, this does not completely prevent picking of the lock by the usual method, instead it only interrupts the picking process when a lever is raised too high. 
     In another prior-art lock, the tail on a “monitor lever” is used to foil would-be attackers. In this case, the tail of the monitor lever covers a portion of the keyhole when the lever is raised which makes it difficult to insert the lock picking tools. The tail however, does not directly affect the lock picking process. Similarly, in yet other lock designs, such as locks that use false gates and jagged edges, the features make it difficult to keep the levers in alignment, but do not completely avert picking and do not affect impressioning or fence breaking. 
     It is with respect to these and other considerations that the present invention has been made. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a lever lock apparatus having a detent which removes or limits an attacker&#39;s ability to control the amount of force exerted by a fence against the levers. More specifically, when a force is applied to the bolt, the fence of the present invention is forced away from the levers. In essence, the present invention relates to a lever lock apparatus having a detent that performs differently when the lock is being tampered with than when the lock is operated using the correct key. This dual-acting detent swings toward the levers when using the correct key thus allowing the lock to open. However, when an attempt is made to defeat the lock, the detent swings away from the levers preventing the lock from opening and hindering the attempts to defeat the lock. 
     An aspect of the present invention relates to the directional forces applied to a detent causing both movement to open the lock and movement to prevent the lock from being attacked. 
     In accordance with other preferred aspects, the present invention relates to lever-lock levers that have frictional components that are much greater than the friction of the fence against the lever end. In order to achieve higher frictional components, i.e., those components other than the fence/lever friction component, the plate faces are roughed or the spring constants can be adjusted to increase the lever frictional components. Additionally, the fence/lever frictional component may be lowered using polished surfaces, rounded edges, lubrication or a reduced spring-biasing force. In preferred embodiments, the amount of possible force exerted by the fence on the levers is insufficient for impressioning and fence breaking. 
     The invention may be embodied in a key actuated lever lock housed in a case adapted to be mounted in or on a door, gate or the like. Alternatively, the invention may be incorporated into a padlock. The lock includes a bolt housed in the case and adapted to be thrown between a locking position and an unlock position by a thrower mechanism. The bolt has a bolt head adapted for locking engagement in a mortise and a bolt tail plate extending from the bolt head. The tail plate has a bottom edge and defines a notch extending into the plate and opening into the bottom edge. The notch defines opposed talons integral with the tail plate. A recessed area is formed in the tail plate above the talons, and is bounded by internal edges including a recessed bottom edge. The plate further defines a pair of spaced notches opening into the recessed bottom edge that are separated by an upwardly projecting dovetail boss having downwardly and inwardly sloping side edges. An L-shaped detent is pivotally mounted on a detent pivot in the case and defines an arm having a cam rider formed thereon at the lower end thereof. A detent cam is rotatably mounted in the case. A spring biases the detent to hold the cam rider against the detent cam. The detent further defines an elongated laterally extending tail having an upper edge, with a trapezoidal stump integral with the laterally extending detent tail and extending laterally from the upper edge of the tail and defining opposed downwardly and outwardly sloping surfaces. 
     The stump is adapted to be selectively received in one of the spaced notches, with a sloping edge of the stump in interference engagement with a corresponding sloping edge of the boss. 
     A key actuated swinging tumbler thrower mechanism is provided for rotating the detent cam to release the detent for spring biased pivoting movement about the detent pivot to release the stump from engagement with the boss and for engaging the talons to throw the bolt when the proper key is used. When the proper key is not used, and a force is applied to the bolt in the unlock direction, the shape of the boss acts on the stump to exert a force on the detent tail urging the detent arm away from the cam and levers thereby thwarting efforts to unlock the lock without a key. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a lock embodying the present invention with a part of the lock case removed. 
     FIG. 2 is a perspective view similar to FIG. 1 with the levers or detainers removed for clarity of illustration. 
     FIG. 3 is a perspective view of the bolt of the lock shown in FIG.  1 . 
     FIGS. 4A,  4 B and  4 C are expanded, front elevation views of the tail portion of the bolt shown in FIG. 3, expanded to illustrate details of the tail portion and its relationship to the detent at distinct stages during an opening event using the appropriate key. 
     FIGS. 4D,  4 E and  4 F are expanded, front elevation views of the tail portion of the bolt shown in FIG. 3, expanded to illustrate details of the tail portion and its relationship to the detent at distinct stages during an attempted opening event using an inappropriate object, e.g., a pick or a blank key. 
     FIG. 5A is a perspective view of the detent of the lock shown in FIG.  1 . 
     FIG. 5B is a perspective view of an alternative embodiment of a detent for the lock shown in FIG.  1 . 
     FIGS. 6A,  6 B,  6 C and  6 D are front elevation views of the detent shown in FIG. 5A to illustrate details of the detent and its relationship to the cam shown in FIG. 1 at distinct stages during an opening event. 
     FIG. 7 depicts a bolt mechanism for an alternative embodiment of the present invention. 
     FIGS. 8A,  8 B and  8 C depict alternative embodiments of a detent that incorporates aspects of the present invention. 
     FIG. 9 is an expanded, front elevation view of an alternative embodiment of the tail portion of the bolt and cam mechanism shown in FIG.  2 . 
     FIGS. 10A and 10C depict a detent for an alternative embodiment of the present invention at distinct stages of operation. 
     FIGS. 10B and 10D depict force diagrams for the alternative embodiment shown in FIGS. 10A and 10C, respectively. 
     FIGS. 11A,  11 B and  11 C depict various uses of springs to increase the frictional components exerted on the levers of the lock shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     The present invention is embodied in a key actuated lock mechanism  10  housed in a case  12  having a face plate  14 , as shown in FIGS. 1 and 2. The case  12  is adapted to be inserted in an appropriately sized recess in one edge of a door panel (not shown) and secured therein by screws (not shown) extending through screw holes  16  in the case  12  into engagement with the edge of the door. Alternatively, the lock could be attached to the face of the inside of a door. 
     The key actuated lock mechanism  10  is of the type commonly referred to as a lever tumbler or detainer lock mechanism and includes a sliding bolt  18 , having a bolt head  20  adapted to be extended into or drawn from a mortise in a doorjamb (not shown), and a plate-like bolt tail  22  integral with or secured to the bolt head  20  and extending into the case  12 . The bolt  18  is shown in FIG. 3 apart from the remaining components for clarity. 
     The bolt head  20  is thrown or drawn into a locking or unlocking position by a key-operated detent cam  24  which operatively engages the bolt tail  22 . For the purposes of operative engagement with the cam  24 , the bolt tail  22  defines an inverted V-shaped downwardly opening notch  26  (shown in FIG.  3 ), the sloping edges  28  and  30  of which form talons or shoulders engageable by the cam  24  to slide the bolt  18 , as discussed in more detail below. 
     The cam  24  is formed as part of a thrower plate  32  which has an axially extending support sleeve or stem  34  secured thereto and defining a key slot  36 . The case walls  14  define key holes (not shown) corresponding to the key slot  36  in the stem  34 . 
     For operatively engaging the bolt tail  22 , the cam plate  32  defines a radially projecting thrower  38 . As the cam plate  32  is rotated by a key inserted in the key slots, the thrower  38  enters the downwardly opening notch  26  on the tail plate  22  and engages a talon  28  or  30 , depending on the direction of rotation of the cam plate  32 . Further rotation of the key and cam plate  32  causes the thrower  38  to cammingly engage a talon  28  or  30  and force the bolt  18  to slide or shoot in the desired direction. This motion is discussed in more detail in conjunction with FIGS. 4A-4C below. 
     The operation of the cam  24  and the bolt  18  is lockingly controlled by a detent  40  in operative association with lever tumblers or detainers  42 . The lever tumblers or detainers  42  comprise a plurality of plate-like levers or detainers (hereinafter, “levers”) swingably mounted on a lever pivot pin  44  mounted in the case  12 . Each lever  42  is individually biased in a counter-clockwise direction by a leaf spring  46  acting between the lever  42  and a spring support  64  mounted on the detent  40 . In this manner, each lever  42  is independently movable or swingable in an arc about the axis of the lever pivot pin  44 . 
     Each lever  42  defines a detent receiving slot, notch or “gate”  50  on its forward edge. To align the various gates  50  into detent receiving position, i.e., to receive a fence portion  52  of the detent  40 , the levers  42  are pivoted by engagement with projecting teeth on the bit of a key (not shown) designed to open the lock  10 . When the gates  50  are in alignment, the fence  52  projecting laterally from a pivotally mounted detent  40  drops into the aligned gates  50  allowing the detent  40  to swing and release the bolt  18 . 
     In the embodiment shown in FIG. 1, the detent  40  is a generally L-shaped piece, and is pivoted at its apex  54  on a pivot pin  56  mounted in the case  12 . The detent  40  (also shown in FIGS. 5A and 5B) includes a depending arm  58  terminating at its lower end in a cam follower or rider  60  (FIG.  5 A). The fence  52  extends laterally therefrom between the pivot pin  56  and the cam rider  60 . In alternative embodiments discussed below in conjunction with FIGS. 7 and 8, the detent does not necessarily have to be L-shaped. 
     The detent  40  further defines an elongated, laterally or horizontally extending tail  62 . It is engaged by biasing springs  46  that contact a shelf-like protrusion  64  of the tail  62 . The detent  40  also has a laterally extending stump  66  adapted to extend into locking engagement with the bolt tail  22 . The springs  46  bias the detent  40  in a counter-clockwise direction (as shown) about pin  56  to urge the detent  40  into its unlocking position by biasing the arm  62  upward (as shown). Alternatively, a spring  68  (FIG. 5B) may also be used on its own or in combination with springs  46  to bias the detent  40  into its unlocking position. The detent  40  is held in a locking position by the engagement of the cam rider or follower  60  on its depending arm  58  with a cam surface or edge  70  of cam  24 . 
     In order to provide for operative engagement between the bolt tail plate  22  and the detent  40  either to lock the bolt  18  against being drawn or thrown or released, the tail plate  22  has an upper surface  72  (FIG. 3) and defines an inverted trapezoidal or dovetail shaped boss  74  projecting upwardly therefrom and defining on either side thereof two stump receiving pockets  76  and  78 . The pockets  76  and  78  are adapted to receive the detent stump  66  which, when positioned in a pocket  76  or  78 , engages the boss  74  and locks the bolt  18  against being thrown or drawn. By positioning the levers  42  to align the gates  50  therein to receive the detent fence  52 , thereby releasing the detent  40  and freeing the detent arms  58  and  62  to swing counter clockwise away from engagement of the stump  66  thereon with the boss  74 , the bolt  18  is released or freed to slide under the influence of the operative engagement between the thrower tab  38  and talons  28  or  30  as the key is turned. 
     The boss  74  is of an inverted trapezoidal configuration and defines opposed downwardly and inwardly sloping surfaces  80  and  82 . The stump  66  likewise is trapezoidal in configuration and defines downwardly and outwardly sloping surfaces  84  and  86 . Engagement of a sloping surface on the boss  74  and a juxtaposed sloping surface on the stump  66 , i.e., interfering engagement locks the detent  40  and further urges the detent arm  62  downwardly and thereby urges the cam rider  60  away from the cam surface  70  on the cam  24 , and urges the detent fence  52  away from, instead of toward, the end surfaces of the levers  42 . The slopes of the boss  74  and the stump  66  interferingly engage to form a dovetail contact. 
     Although shown and described as an inverted trapezoidal or dovetail shape, this shape and the respective angles are relative and thus alternative embodiments are possible. That is, an inward force applied to the bolt  18  causes a force to be transferred to the detent  40  at the point of contact. At this point of contact, the vector representing the force exerted by the bolt  18  on the detent  40  can be resolved into two orthogonal vectors: (a) a vector that is parallel with the vector of rotation for the detent, and (b) a vector that is perpendicular to the vector of rotation of the detent. Vector (b) has no effect on the rotation of the detent. Vector (a) determines the direction and magnitude of the rotational force applied to the detent. The lock is designed so that vector (a) contains a sufficient portion/fraction of the inward force and (a) is oriented so that the resulting force on the detent  40  will cause it to pivot in the counter clockwise direction, against the spring pressure of the spring(s)  46 , and away from contact with the levers  42 . Thus, the angle is with reference to a center line for the pivot of the detent. It is possible to design a lock that does not have this dove tail feature yet includes the features of the present invention, such as the detent shown in FIG. 10, as discussed below. 
     A properly formed key (not shown) having appropriate slots and projections on its bit, when inserted in the key hole of the lock and turned to engage the levers  42 , lifts each individual lever  42  to a certain position at which point the gate  50  in the forward edge of each lever  42  is aligned with other gates  50  to form a groove for receiving the detent fence  52 . At this point, the detent  40  is biased to force the fence  52  into the groove by the detent biasing springs  46  and/or spring  68  (FIG.  5 B). This movement of the detent releases the stump  66  from engagement with the bolt tail boss  74  and allows the thrower tab  38  to move the tail plate  22  to either throw or draw the bolt head  20  from the mortise. 
     Importantly however, before the fence is biased into the groove, another action must occur. As shown in FIGS. 4A-4C and FIGS. 6A-6D, the protrusion  74  must be moved a slight distance away from the stump  66 , simultaneous with the alignment of the gates  50 , to allow the biasing springs  46  to bias the fence  52  into the gates  50 . Otherwise the boss protrusion  74  prevents stump  66  from moving thus preventing the fence from entering the gates. 
     Although shown and described as having the protrusion  74  attached to a movable bolt object in FIGS. 1-4, the lock may be designed where the pivot for the levers  44  is attached to the tail of the bolt (not shown). In such a lock, the pivot for the detent  56  is also attached to the bolt and protrusion  74  would then be attached to the lock case. The levers and detent move back and forth with the bolt. In such a design, protrusion or boss  74  would remain fixed and stump  66 , pivotally attached to the bolt via  56  would then move. 
     In an embodiment of the invention, as shown in FIG. 4A, the sloped portion  28  comprises at least two distinct regions,  28   a  and  28   b.  Region  28   a  has an angle and positional relationship to both the thrower  38  and the protrusion  74  such that as the thrower  38  is in sliding contact with the region  28   a,  the protrusion  74  is held so the detent can rotate. Region  28   a  may be curved to have a circular radius to achieve this function. The region  28   b  is angled or otherwise shaped, and positioned, so that when thrower  38  is in sliding contact with region  28   b,  the bolt tail  22  is actually forced, or camed outward or to the left as shown in FIG.  4 B. Forcing the tail  22  in this direction forces the boss  74  away from the stump  66 , which in turn, provides the clearance needed for the stump  66  to eventually swing (move counter-clockwise as shown). Allowing the stump to swing in this manner is necessary for the bolt to be able to slide in the unlocked direction. 
     Similarly, the sloped edge  30  also comprises two portions so that the thrower  38  can effectively force the boss  74  away from the stump  66  when sliding along  30   b,  and hold the boss in an “away” position when sliding along  30   a.    
     To illustrate the sliding action, assume that the lock is in locked position with the key removed, and that there is an inward force, I, exerting on the bolt. The cam  24  and detent  40  are, at this point, arranged as in FIG.  6 A. The key is inserted and turned clockwise until the thrower  38  first contacts the tail  22  of the bolt  18  at the lower end of the linear portion,  28   b,  as shown in FIG.  4 A. Until this position is reached, the stump  66  of the detent  40  is in contact with the boss  74  on the bolt. Here, edge  84  of the stump  66  on the detent is in contact with edge  80  on boss  74 . This is illustrated in FIG. 4A by the location of stump  66  (shown in phantom). As the key turns further clockwise, the thrower  38  moves along the surface  28   b,  which forces/wedges the bolt outward (to the left relative to the stump  66 , as shown). Once the thrower  38  has reached the point of intersection of  28   a  and  28   b,  the bolt has moved to the left a sufficient distance, as shown in FIG. 4B such that stump  66  can now clear boss  74  when the detent rotates counter clockwise. FIG. 4C illustrates this clearance as the detent rotated under the spring bias caused by springs  46  (FIG.  1 ). 
     The cam  24  (FIG. 6A) has held the detent back until this point. That is, while the bolt  22  is being moved by thrower  38 , the cam rider portion  60  of detent  40  is in contact with cam surface  70  which keeps the detent  40  from pivoting, as shown in FIG.  6 A. Referring to FIG. 6B, as thrower  38  reaches the intersection of portion  28   b  and  28   a  of tail  22  (FIG.  4 ), then a further clockwise turning of the cam  24  causes the detent  40  to glide down surface  90  until the surface of rider  60  is in contact with surface  92  as shown in FIG.  6 C. That is, cam rider  60  has been in contact with the larger diameter portion  70  of the cam  24  until the cam  24  rotates a sufficient amount, causing the rider to then come in contact with the transition surface  90 . Until the rider  60  glides down surface  90 , the fence  52  is held away from the levers  42 , and the stump  66  of the detent  40  is held in its lower position, i.e., the position shown in FIG.  4 B. During this process, the key also aligns the levers  42  so that the gates  50  are aligned with the fence  52 . Indeed, if the key did not align the levers  42 , the fence  52  would not slide into the gates  50  and the rider  60  would not rotate to move into contact with portion  92 , as depicted in FIG.  6 C. 
     Assuming the key aligned the levers  42 , the key turns the cam  24  further clockwise and thrower  38  slides along surface  28   b  as shown in FIG. 4B while the detent moves from the position shown in FIG. 6B to the position shown in FIG.  6 C. Again, this movement is made possible because the levers  42  have been aligned and the fence  52  enters the gates  50 . Once the fence has moved into the gates, the relative positioning of the cam  24  and the detent  40  is as shown in FIG. 6C wherein the rider  60  follows along a smaller diameter surface  92 . Accordingly, the stump  66  has moved relative to the boss  74 , going from the position shown in FIG. 4B to the position shown in FIG.  4 C. 
     As the key turns further clockwise (as shown), thrower  38  enters notch  94  (depicted in FIGS. 4A-4C) and throws the bolt to the right as it proceeds in its clockwise direction of turning. The final operation of the key (detent being forced down by cam, levers are lowered, key is removed) is relatively symmetrical with the above description. In an alternate embodiment, the lock maybe secured in the open position using less secure technology, e.g., prior art methods of maintaining the lock open as opposed to the more secure dual detent technology of the present invention since the extra security of the dual detent is primarily needed when the lock is in the locked position. 
     In the case of attack, as depicted in FIGS. 4D,  4 E, and  4 F, the cam is turned clockwise using either a blank key in the case of impressioning or with the use of some type of pick. With the thrower  38  at the upper end of  28   a,  the detent  40  is allowed to rotate a small amount (as shown in FIG. 4E) until the fence  52  contacts the far-left edge of the levers  42  (not shown). In this case, the detent  40  moves only a very small amount in the counter clockwise direction. Thus, the stump  66  remains essentially in the down position as shown in FIG.  4 E. The force exerted by the fence  52  against the levers  42  is the spring force caused by springs  46  acting on the shelf-like protrusion  64  attached to the detent  40 . This force is not sufficient to allow impressioning. The design prevents additional forces to act on the fence, such that the degree of force remains defined by the springs  46 . This low force also makes it difficult to feel the gates  50  due to the significantly low friction caused by the fence  52  against the levers  42  in relation to the other frictional forces acting on the levers  42 . 
     The protrusion  64  also acts as a spacer to stabilize the detent  40 . Protrusion  64  stabilizes detent  40  by slidably contacting the lock housing (not shown). Although the protrusion  64  may touch the housing, it may not touch the housing at all times, it merely keeps the detent substantially in place. Indeed, the protrusion performs both the function of interacting with a spring to bias the detent in a predetermined direction and the function of stabilizing the detent. Prior art locks use more than one device to perform these functions. 
     Also, in an embodiment of the invention, an additional spring  96 , shown in FIG. 2, causes friction between the levers by compressing the levers against the lock case to create friction between the levers and against the lock case. This friction masks the friction of the fence against the levers making the detection of the gates even more difficult. 
     As the thrower  38  reaches the upper portion of  28   a,  and is about to enter notch  94 , shown in FIG. 4E, the stump  66  is positioned in the relatively down position as shown in FIG.  4 E. Moreover, since the proper key is not being used and the gates are not aligned, the detent and cam are positioned relative to each other as shown in FIG.  6 D. In this position, rider  60  is not in contact with the cam  24  because the gates are not aligned such that the fence  52  contacts the levers  42  thus holding the detent down in locked position. 
     When picking, spring pressure does not produce enough friction between  52  and  42  to allow the levers to stay in position. Therefore, when picking, each lever must be held up independently. Also, friction between  42  and  52  is small versus the other frictions, such as from spring  96 , making it difficult to “feel” the gates. 
     If the cam  24  is turned further clockwise, then the thrower  38  will enter notch  94  and contact the right side of  94  as shown in FIG.  4 F. In prior art designs, clockwise turning pressure of the cam  24  at this point causes the thrower  38  to transfer this pressure to the fence against the levers  42 . In the present invention however, this clockwise turning pressure forces the bolt tail  22  toward the right (as shown in FIG. 4F) causing the face  80  of boss  74  to contact the face  84  on the stump  66  on the detent. Further pressure exerted by the would-be attacker on the bolt causes the detent to rotate clockwise about point  54  (FIG. 5A) causing the fence  52  to actually move away from contact with the levers to thereby prevent impressioning, picking or fence breaking. 
     Alternative attack methods may apply inward pressure on the bolt as per I (FIG.  4 A). In this position, the fence is away from the levers. Thus, the lock is secure with all the pressure taken up by the detent between the stump  66  and the pivot  54 . There is no pressure on the fence at this point. The downward portion of the L-shaped detent,  40 , merely “floats” within the lock case and does not take up any of the pressure applied to the bolt. Since the pressure of springs  46  is not sufficient to break the fence, and since continued pressure moves the fence away from the levers, this eliminates the possibility of fence breaking. 
     When someone endeavors to open the lock without using a key, the conventional procedure is to push the bolt head towards the unlocked position with sufficient force to hold the fence against the edge surfaces of the levers  42 . According to the present invention, the sloping surfaces on the boss  74  and stump  66  with respect to the center line cause pressure or force on the bolt towards the unlock position to preclude the detent fence  52  from riding against the levers  42 , thus preventing opening of the lock by feeling or sensing the position of the levers  42  and their respective gates  50 . 
     FIGS. 7 and 8 provide an alternative embodiment incorporating aspects of the present invention. FIG. 7 illustrates the tail portion  22  of the bolt having boss  74 . In this particular embodiment, boss  74  protrudes out from the tail portion  22  towards the detent, instead of upwards from the upper surface of the tail  22  as shown in FIG.  4 . Boss  74  (FIG. 7) is an inverted trapezoidal configuration and defines opposed downwardly and inwardly sloping surfaces  80  and  82 . 
     In an embodiment, boss  74  operates in combination with detent  41  shown in FIG.  8 A. In this case, detent  41  is not L-shaped as is detent  40  shown in FIGS. 5 and 6. Indeed, the detent  41  in FIG. 8A, has a single arm and moves in the opposite direction as compared to the detent  40 , shown and described above in conjunction with FIGS. 5 and 6. That is, the detent  41  moves clockwise (as shown) when the lock is opened by the correct key and it moves counter clockwise (as shown) when the lock is attacked. Spring  68  biases the detent into an unlocked position so that when the gate(s)  50  are aligned, fence  52  is moves downward (as shown) into the gates. Thrower  38  is in an alternate orientation with respect to the keyhole  36  in this particular embodiment to allow the levers to be properly raised or positioned prior to throwing the bolt to a new position. Additionally, since boss  74  protrudes from tail  22 , protrusion  66  need not extend into the bolt layer. Importantly, the detent  41  moves counter-clockwise and away from the levers  42  when an inward force is applied to the bolt (as shown). 
     FIGS. 8B and 8C illustrate two additional detent embodiments  43  and  45  having similar characteristics of detent  41  shown in FIG.  8 A. Essentially, each is biased by spring  68  so that the detents  43  and  45  move downward when the gates are properly aligned. However, each detent  43  and  45  has a protrusion  66  with sloped sides  84  and  86  that contact boss  74  such that the detent moves away from the levers  42  when a force is applied to the bolt. Additionally, detent  45  moves linearly, as opposed to rotating about a pivot point. 
     FIG. 9 illustrates yet another embodiment of the present invention which may be used in higher security situations such as for safes, vaults, jails, safety deposit boxes, etc. The key does not turn a full 360° but only turns 180° from left to right. In this embodiment, the portion  28   b,  shown in FIG. 4A, is not required. Instead, the curved portion  28   a  is extended farther down so that the thrower  38  holds the bolt in the position indicated in FIG. 4B with the detent stump  66  being held away from the boss  74  on the bolt. In this embodiment, the bolt is not wedged/forced outward but is rather simply held in the position of FIG.  4 B. The thrower,  38 , moves along surface  28   a  and holds the bolt in this outward position while the levers are being aligned and while the detent pivots into the unlocked position. The thrower is then allowed to enter  94  and throw the bolt to the right (as shown). 
     FIGS. 10A,  10 B,  10 C and  10 D illustrate an alternative detent  100  and some of its functional details that might replace detent  40  for another embodiment of the present invention wherein the dovetail shape of the boss  74  and stump  66  are split to form  102 ,  104 ,  106  and  108 . In this embodiment, there is a protrusion  102  on the bolt  18 . Extension  104  interacts with stump  106  when the lock is locked (FIGS. 10C and 10D) while extension  108  interacts with protrusion  102  when the lock is unlocked (FIGS. 10A and 10B.) Thus, a dove tail/bevel is not necessary, but only how the relative forces interact in the design to produce the desired result. Importantly, the angles relative to the centerlines  101  and  103  of the arms  62  of detent  100  and  40  (FIG. 6A) have the same relationship. To obtain detent  100  shown in FIG. 10, surfaces  84  and  80  (FIGS. 3 and 5B) are conceptually rotated about the pivot  54  a few degrees counter clockwise while surfaces  82  and  86  in FIGS. 3 and 5B were rotated about the pivot  54  a few degrees clockwise. 
     FIG. 10C illustrates the relative positioning of  102 ,  104 ,  106  and  108  while the lock is in a locked position. As is shown in FIG. 10D, should a force F total  be applied to the bolt, object  104  would contact  106  such that the detent would actually pivot the fence  52  away from the levers (not shown) in the direction Of F rotate . In this case, the force on the bolt, F total , is resolved into two forces, F in  and F rotate . Force F rotate  causes the detent to rotate while F in  is exerted against pivot  56  preventing the locks from opening. FIG. 10A illustrates the relative positions when the lock is in the open position and correspondingly FIG. 10B illustrates the forces acting on the detent when the bolt is forced in the outward direction. Thus, detent  100  operates in a manner similar to detent  40  in FIG. 1, wherein only the relative positions of some of the parts have changed.  13  The approach to solving the problem of unauthorized opening of the lock provided by the present invention is quite different from the prior art. Here, a dual-action detent is used to take away the control an attacker of the lock has on the amount of pressure the fence exerts against the levers. This effectively hinders all the above methods of attack simultaneously. In the present invention, the force exerted by the fence against the levers is limited to the force exerted by a spring internal to the lock mechanism itself and, as such, is predetermined by the design engineers. This force is sufficient enough to allow the lock to open when the correct key is inserted. This is the primary action of the detent. However, when exerting an inward force (F total  shown in FIG. 10D) on the bolt in an attempt to defeat the lock, the detent is forced to rotate in the opposite direction (along F rotate  as shown in FIG.  10 D), i.e., the fence moves away from the levers. Therefore, this dual-action of the detent causes the fence to move away from the levers when an inward force is applied. Instead of the force on the bolt being directly transmitted to the levers via the fence, the force is taken up entirely by the detent. Thus, the only force exerted by the fence on the levers is due to the internal spring. 
     Picking is made difficult by this dual-action detent because the force exerted by the spring is not sufficient to hold the levers up. The feel of the gates is also easier to mask because the pressure the fence exerts against the levers is fixed at the factory. Adding a spring to compress the stack of levers is very effective here. It can be used to increase the friction between the levers to such a level that it completely masks the pressure exerted by the fence against the levers. 
     In an embodiment, frictional masking means are added to the lock that result in other frictional components that are greater than the friction of fence against lever end, which significantly impacts the ability to pick the lock. These frictional masking means thus perform at least one of the following two functions: 1) increase or create other lever frictional components apart from fence-lever friction or 2) decrease fence-lever friction. To increase the lever frictions, the faces of the levers  42  can be made rougher to increase the friction between the levers (not shown). The rougher faces of the levers still slide relatively smoothly when operated with the appropriate key, yet the face is slightly roughed to increase the frictional component and hamper the picking of the lock. 
     Alternatively, the frictional masking means may relate to one or more of springs  110 ,  114  and  118  as in FIGS. 11A,  11 B and  11 C respectively may be added to increase the frictional forces on the levers  42 . In FIG. 11A, spring  110  creates friction on the lever at point  112 . In FIG. 11B, the end of spring  114  creates more of a grinding type friction. In FIG. 11C, the edge of the lever  122  is rough or jagged such that spring  118  a makes a stronger grinding or clicking at  120 . In FIGS. 11A,  11 B and  11 C, one spring can be used for all levers, or one spring can be used for each individual lever. The use of springs  110 ,  114  and  118  effectively masks/disguises the feel of the gates. Yet other frictional masking means that increase lever frictional components, independent of the fence-lever frictional components, may also be added. 
     Other frictional masking means may relate to decreasing fence-lever friction. To decrease the fence-lever friction, the movement of the fence (at the point of contact with the levers) is made perpendicular to the movement of the levers, which pivot around the pivot point  44 . This helps minimize the frictional force. Next, the edge of the levers and the fence (the parts that are in contact) are made smooth to eliminate any “bumps”, etc. that would cause friction. This edge can also be lubricated to further reduce friction. In an embodiment, metal having impregnated oil that keeps a constant lubrication is used to reduce the friction. 
     Also, since it is not possible to make all the levers have exactly the same diameter it may be possible that there will be a “ledge” at the gates and false gates. To eliminate this problem, the levers are rounded, beveled or otherwise shaped slightly near the gates and false gates to ensure that there is a smooth transition as the fence goes past the gate or false gate. 
     In previous designs, it was always possible to increase the pressure the fence exerts against the levers to overcome any other friction imposed on the levers and thus detect the gates. In the present invention, the friction of the fence against the levers is determined by the spring bias. Thus, while a would-be attacker of prior-art lever locks could always increase this friction by simply increasing the force the fence exerts on the levers, this is not possible in the present invention. 
     By increasing the magnitude of the other frictional components that act on the levers as compared to the magnitude of the friction of the fence against the levers, the present invention prevents the attacker from feeling the gates. For example, assuming that an attacker can feel the gates if the friction of the fence against the levers is 10% or greater when compared to all other frictions on the lever. For current designs, all the would-be attacker needs to do is increase the pressure he exerts on the fence against the levers until a 10% or greater friction is obtained. However, in an embodiment of the invention, the relative friction factors can be adjusted until a maximum force of less than the 10% is reached. 
     Additionally, impressioning is essentially impossible because the friction of the fence against the levers due to the force exerted by the spring is very small and can be minimized by the design of the lock. The force of the fence against the levers can be made perpendicular to the movement of the levers themselves, thus limiting the force to frictional effects only. Any marks left on the key due to a lever not being at a gate are indistinguishable from the marks left by the levers themselves due to the force of the lever spring and the friction between the levers. Fence breaking is impossible because the fence can easily be made strong enough to withstand the pressure exerted by the spring on the detent. Many of the above mentioned ideas for hindering attack could also be incorporated with this design. False gates, tail of monitor lever, detector lever, etc. can all be added to this design to increase the difficulty of attack. 
     While certain illustrative embodiments of the present invention have been shown in the drawings and described above in considerable detail, it should be understood that there is no intention to limit the invention to the specific forms disclosed. For example, the invention may be used in both new locks and be implemented as a modification to existing locks. Therefore, the intention is to cover all modifications, alternative constructions, equivalents and uses falling within the spirit and scope of the invention as expressed in the appended claims.