Locking mechanism for folding tool

[0001] This invention relates to hand tools such as knives and multi tools that incorporate folding implements, and more specifically to a blade or implement locking mechanism for use in such tools that facilitates secure locking of the implement in the open or extended position. The lock mechanism incorporates a safety mechanism.

[0002] Many types of hand tools such as knives and multi tools incorporate folding mechanisms that allow an implement to be moved between a folded position in which the implement is safely stowed in the tool handle, and an extended position in which the implement is ready for work. One typical example of such a folding tool is a knife having a folding blade. The knife handle typically has two opposed handle portions defining a blade-receiving groove. A blade pivots on a shaft attached to the handle such that in a folded position the blade is stowed with the cutting portion of the blade retained safely in the groove, and such that in an extended position the blade is extended away from the handle, ready for use.

[0003] To increase the safety of folding tools such as knives, many such tools incorporate locking mechanisms of one type or another. When the knife blade pivots into the open position, it's pivotal movement is stopped with a blocking mechanism such as a transverse blade stop pin housed in the handle. Many kinds of knives include a locking mechanism that prevents the blade from unintentionally pivoting back from the open into the closed position.

[0004] There are many types of locking mechanisms. One common type is a “liner lock.” This kind of mechanism relies upon a resilient lever formed as part of a handle liner. When the blade is pivoted to the open or extended position, the resilient lever engages a cooperatively formed shoulder on the blade and thereby locks the blade in the open position.

[0005] There are other types of blade locks in addition to the liner locking mechanisms just described but there is a need therefore for improved locking mechanisms for folding hand tools.

[0006] The present invention relates to a hand tool—typically embodied as a knife—that incorporates a lock mechanism for securely locking the implement such as a blade in the open position, and for releasing the lock to allow the implement to be folded back into the closed position. The locking mechanism incorporates a safety mechanism that prevents the blade engaging lock from becoming disengaged unintentionally.

[0017] A preferred embodiment of a hand tool 10 incorporating a locking mechanism and safety mechanism in accordance with the illustrated invention is shown in the figures. Although the invention is described with respect to its embodiment in a particular type of tool—a knife—it will be appreciated that references to this type of a knife, and indeed this particular type of hand tool, are for illustrative purposes to describe the invention. Those of ordinary skill in the art will appreciate that the invention claimed herein is not limited to knives, but instead extends to any hand tool having the features claimed herein.

[0018] With particular reference now to FIGS. 1 and 2, knife 10 includes a handle 12 with a blade 14 pivotally attached to one end of the handle at a blade pivot shaft 16. Handle 12 comprises three primary structural components, a first handle half or side wall 18, a second handle half or side wall 20, and a spacer 22 that is fixed therebetween when the knife is assembled (see, e.g., FIGS. 3, 8). Spacer 22 holds the handle halves 18 and 20 in a spaced apart orientation to define a blade-receiving groove or slot 24 between the halves. When the blade is in the closed position, the working portion 26 of blade 14 is safely stowed in slot 24. Blade 14 is pivotally movable about pivot shaft 16 between the fully closed position (FIG. 1) and the fully open position (FIG. 2).

[0019] With reference now to FIG. 8, additional structural parts of knife 10 will be identified beginning with blade 14, which includes a tang 28 having a bore 30 through which pivot shaft 16 extends. Specifically, pivot shaft 16 comprises a cylindrical bushing 32 that fits into bore 30 and has outer cylindrical portions 34 on both lateral sides that have stepped-down diameters relative to the central portion of bushing 32, and which are received into bores 37 formed in handles 18 and 20 in the assembled knife 10 (only one bore 37 is shown). Pivot shaft 16 includes a threaded screw 36 that extends through bushing 32 and engages a nut (not shown) to secure the blade to the handle 12. Blade 14 preferably includes a thumb lug 27 to assist with opening and closing the blade. The rearward end of tang 28 is formed into a flattened section 44, which as detailed below cooperates with a spring member to lock the blade in the open position.

[0020] The handle halves 18 and 20 are assembled with the blade 14 as just described. Spacer 22 is held in place with plural screws 38, which as shown best in FIG. 8, engage threaded openings 42 in spacer 22. It will be appreciated that the structural peculiarities such as number of screws 38 is not particularly important so long as the knife 10 is securely assembled. Some of the screws 38 may attach plates 40 to recesses 42 formed in the handle halves for added structural strength and/or aesthetics, and of course the screws 38 may thread completely through both handle halves and the spacer if desired. Screw 39 (FIGS. 3 through 7) acts as a blade stop pin, preventing rotation of the blade beyond the fully open position shown in FIG. 2.

[0021] The blade locking mechanism, identified generally with reference number 50, will now be described in detail. Handle half 20 is preferably made of a resilient material such as a variety metals and alloys. Handle half 20 comprises an integrally formed, bifurcated sheet comprising a base 52 having an elongate, L-shaped slot 54 extending from a relatively thinner wall section 56 in a forward direction and turning at a 90° angle and extending through the edge of the handle half at exit point 58. The elongate slot 54 defines a spring arm 60 having a free end 62 at the forward end of the spring arm, and an elongate fixed body portion 55 opposite of slot 54 from spring arm 60. The slot 54 further defines a base end 64 at a thinner wall section 56 near the rearward, terminal end of slot 54. A bore 65 may optionally be formed at the rearward, terminal end of slot 54 to provide more resiliency to the spring arm 60. The forward end of free end 62 of spring arm 60 is flattened to define a flattened face 66.

[0022] It will be appreciated that base end 64 extends integrally from base 52 in a one-piece construction. During fabrication of handle half 20, spring arm 60 is pre-stressed so that the spring arm is given an initial bias inwardly in the direction toward the blade-receiving slot 24—that is, generally into the plane of the paper in FIG. 1. The relatively thinner wall section 56 aids in facilitating the initial inward bias, but should be seen as optional. The inward bias is preferably sufficiently strong that the free end 62 of spring arm 60 will normally continue to be biased under spring pressure inwardly in the direction toward slot 24 until constrained against further movement by another structural component of the knife.

[0023] With reference to FIG. 1, blade 14 is in the closed position. In this position, the free end 62 of spring arm 60 is pressing inwardly against the blade and applying force thereto. The spring force applied against the blade in this manner helps retain the blade in the closed position.

[0024] The blade 14 is shown in the open position in FIG. 2. Here, blade 14 has rotated to the point where the flattened face 66 of free end 62 of spring arm 60 snaps behind the flattened portion 44 of tang 28 and blade stop pin 39 abuts an upper portion of tang 28. The spring force applied to spring arm 60 maintains the spring arm in this locking position, wherein the blade cannot be rotated from the open to the closed position because the free end 62 of the spring arm 60 is in an abutting relationship with the flattened portion 44 of tang 28. Preferably, the respective mating faces of flattened portion 44 and flattened face 66 of free end 62 may be cooperatively sloped in opposite directions relative to one another, in the manner of a conventional liner lock, to assist with the locking engagement between these two structures.

[0025] It will be appreciated that both handle halves may preferably be fabricated from the same type of material. Alternately, while handle half 20, which comprises locking mechanism 50, must be a resilient material, handle half 18 may be made of a different material if desired.

[0026] As noted above, the locking mechanism 50 of knife 10 includes a safety mechanism, which is identified generally with reference number 80. As detailed herein, safety mechanism 80 is operable to secure the locking mechanism 50 in the locked position of FIG. 2 to thereby prevent unintentional unlocking of blade 14 where it could inadvertently close, and also to prevent spring arm 60 from being forced so far in the unlocking direction when the blade is unlocked such that the spring arm could be damaged. Safety mechanism 80 further is operable to prevent spring arm 60 from moving in the direction transverse to the direction of the spring force, which further minimizes potential damage to the spring arm.

[0027] With reference to FIGS. 1 and 2, safety mechanism 80 comprises a semi-circular cam wheel or disk 82 rotatably attached with a screw 84 to a cooperatively sized, semi-circular cavity 86 formed near free end 62 of spring arm 60. Screw 84 is threaded into a cooperatively threaded opening 85 in the spring arm 60. The cam wheel 82 is shown in isolation in FIG. 9. In FIG. 9 it may be seen that the cam wheel includes a flattened portion 90 that bisects part of the generally circular cam and which extends across the cam toward a tab 92 that is formed opposite the flattened portion 90. A ramped or sloping section 94 extends annularly from tab 92 around a peripheral section that preferably measures between about 90° to about 160° along the peripheral edge of the cam wheel. Ramped portion 94 is defined by the cam wheel being milled so that the ramped portion is relatively thinnest near tab 92, and the thickness of the ramped portion gradually increasing along the length of the ramped portion until the terminal end 96 of the ramped portion, where the thickness of the ramped portion is the same as the thickness of the cam wheel. The cam wheel 82 includes a knurled peripheral edge portion 98 between the terminal end 96 and the flattened portion 90. The knurled peripheral edge allows the cam to be conveniently gripped by the user during operation of the cam wheel.

[0028] Cam wheel 82 is rotatably attached to spring arm 60 with a screw 84 as indicated in FIGS. 1, 2 and 8 in a cavity 86 milled into the spring arm. The cavity 86 is generally cylindrical so that it accepts cam wheel 82 and allows the cam wheel to rotate in the cavity. The radius of cam wheel 82 measured from its center to knurled edge portion 98 is greater than the distance from opening 85 in spring arm 60 to the exposed edge 100 of the spring arm. As such, when the cam wheel is attached to the spring arm as shown in the drawings, the knurled portion is exposed so that a user may conveniently rotate the cam wheel with one finger, as best illustrated in FIGS. 1 and 2.

[0029] With specific reference to FIGS. 8 and 10, and as described below, a cooperatively formed notch or cavity 110 is milled or otherwise formed in fixed body portion 55 in a location so that portions of cam wheel 82 spans or extends across slot 54 and engage the cavity 110 as the cam wheel 82 as it is rotated. Cavity 110 is semi-circular in shape and is formed so that it has an annular ramped portion 112 that is cooperatively formed and oppositely sloped relative to ramped portion 94 of cam wheel 82.

[0030] When cam wheel 82 is assembled as shown in FIGS. 1 and 2 it may be rotated in the clockwise and counter clockwise directions between two ending positions. In the first position, shown in FIG. 1 where blade 14 is in the closed position, cam wheel 82 is rotated fully counter clockwise (from the perspective of the viewer in the drawing). In this position, flattened portion 90 of cam wheel 82 is parallel to and abuts flattened surface 102 of elongate body 55 in slot 54, thereby preventing further rotation of the cam wheel in the counterclockwise direction. This position of the cam wheel 82 is referred to as the open or unlocked position, and is also shown in FIGS. 4, 5 and 6, wherein it may be seen that tab 92 extends across slot 54 so that the tab extends at least partially into cavity 110.

[0031] Referring now to FIGS. 2 and 3, blade 14 is shown in the fully open position and locked in that position by the locking engagement described above between flattened face 66 of spring arm 60 and rearward flattened portion 44 of tang 28. Spring arm 60 may be safely locked in this locking position by rotation of cam wheel 82 fully in the clockwise direction in FIG. 2—this position of the cam wheel is referred to as the locked position. This same position is shown in FIG. 3, but because FIG. 3 shows the opposite side of knife 10 from the view of FIG. 2, the rotational direction of cam wheel 82, as shown by arrow A, is reversed and thus counter clockwise.

[0032] In this position, annular ramped portion 94 of cam wheel 82 engages the oppositely sloped ramped portion 112 of cavity 110. Accordingly, as cam wheel 82 is rotated toward the locked position, the ramped portion 94 on cam wheel 82 engages and abuts the ramped portion 112 of cavity 110. As the wheel is rotated, the abutting, oppositely sloped ramped portions 110 and 112 bear against and thus exert pressure against one another, with the result being that pressure is exerted by cam wheel 82 on elongate body portion 55. This inwardly directed pressure (i.e., toward the blade receiving groove 24) further drives and urges spring arm 60 toward the locked position, in addition to the normal spring force that drives the spring arm toward the locked position. The cam wheel 82 is retained in this position by virtue of the frictional contact between ramped portions 94 and 112. The blade is thus safely locked in the fully open position, and the spring arm 60 cannot be moved to the unlocking position because cam wheel 82 is engaging the elongate body portion 55.

[0033] Moreover, with cam wheel 82 in the locked position shown in FIG. 3, the outer peripheral annular edge of the cam wheel at ramped portion 94 lies in close tolerance proximity to the annular border of cavity 110. As a result, the free end 62 of spring arm 60 cannot move in the direction toward elongate body portion 55. Stated another way, slot 54 is wide enough that absent cam wheel 82, the free end 62 could be deflected slightly in the direction toward spacer 22. This movement can cause wear between the abutting surfaces at 66 and 44 when the blade is in the open position. Wear on these surfaces could loosen the locking relationship. However, because the outer periphery of the cam wheel is in close tolerance to the wall of cavity 110, movement of the spring arm in this direction is eliminated, thus eliminating wear on the surfaces at 66 and 44.

[0034] The procedure for unlocking the knife will now be described with reference to FIGS. 4 and 5. With blade 14 in the open position the blade locked by virtue of blade lock mechanism 50 (FIG. 2), and with safety mechanism 80 in the locked position, cam wheel 82 is rotated in the direction of arrow B in FIG. 4 (clockwise in FIG. 4, which correlates to counter clockwise in FIG. 1). The cam wheel is rotated until flattened section 90 abuts surface 102, thereby stopping rotation of the cam wheel. As noted above, in this position, tab 92 spans slot 54 and extends into cavity 110. However, as noted the cam wheel 82 is relatively thinnest at tab 92. This, combined with the fact that body 55 is relatively thinner at cavity 110 allows the free end 62 of spring arm 60 to move outwardly, out of the locking position a sufficient distance so that the blade may be disengaged from the lock-that is, the flattened face 66 of spring arm 60 may be disengaged from the flattened portion 44 of tang 28. Once the locking engagement between the blade tang and the spring arm is disengaged, blade 14 is free to be rotated toward the closed position, as shown in FIG. 5.

[0035] Because the tab 92 extends across the slot 54 and into the cavity 110, free end 62 of spring arm 60 is prevented from moving outwardly, i.e., away from blade 14, more than is necessary to allow the blade to be closed. Stated another way, with cam wheel 82 in the position shown in FIGS. 1, 4, 5 and 6, when the free end 62 of spring arm 60 is moved outwardly, away from blade 14, the tab 92 engages or contacts body 55 in cavity 110, limiting movement of the free end in the direction away from the blade, thereby preventing movement of the free end beyond the position where the tab contacts the wall of the cavity. There is a sufficient amount of movement of free end 62 to disengage the locking mechanism, but the amount of movement is limited, which prevents the spring arm from being “hyper extended” in the outward direction, against the spring force of the spring arm, which could damage the spring arm and render it inoperable for its locking functionality, or diminish the functionality of the locking mechanism.

[0036] It will be appreciated by those of ordinary skill in the art that various modifications may be made to the mechanisms described above without departing from the scope of the invention defined in the claims. For example, the safety mechanism 80 may be fabricated with a longitudinally slidable button attached to the spring arm and slidable in a direction generally transverse to the longitudinal axis of the handle toward and into cooperatively formed slot in the fixed body portion, the button and the fixed body portion preferably having cooperatively and oppositely sloped mating surfaces. Similarly, although the cam wheel 82 and the slidable button just described preferably include cooperatively sloped mating surfaces so that the spring arm is driven toward the locked position, an equivalent safety mechanism may be made without the sloping surfaces.

[0037] The length of the spring arm, and also the relative biasing strength of the spring arm, may be varied widely by varying the length of slot 54.

[0038] Furthermore, the tab 92 may be eliminated from cam wheel 82. Although removal of tab 92 will allow spring arm 60 to be moved outwardly and hyper extended as described above, the safety mechanism 80 remains functional to secure the locking mechanism 50 in the locked position. Finally, the safety mechanism defined by cam wheel 82 may be reversed from the position shown in the drawings.

[0039] While the present invention has been described in terms of a preferred embodiment, it will be appreciated by one of ordinary skill that the spirit and scope of the invention is not limited to those embodiments, but extend to the various modifications and equivalents as defined in the appended claims.