Pin Tumbler Lock With Pull-Resistant Key Plug

This invention relates to lock construction, especially to the construction of the key plug and its mounting in a pin tumbler lock mechanism to improve the resistance of the key plug to forced pulling of the plug out of the lock.

The invention is especially applicable and is disclosed as applied to a key-removable core of the type shown in U.S. Pat. Nos. 1,564,463 of Dec. 8, 1925 and 3,206,959 of Sept. 21, 1963. As there shown, the key-removable core comprises a body of figure-8 cross section having a lower lobe which is bored to receive a thin cylindrical sleeve having an upstanding boss that forms a core-retaining lug. A key plug is inserted from the front in the bore of the sleeve and is held axially therein by engagement of a flange on the key plug in a counterbore in the face plate of the core, and by a key stop plate fixed to the rear end of the plug by rivets integral with the key plug. Cores of this type have become a standard in the industry and are of advantage in that they can be readily removed from and replaced in a lock cylinder, padlock, doorknob, or other core receptacle by using a special control key to rotate the sleeve and retract the core-retaining lug. There are many thousands of such applications in existence in which key removal and replacement of such a standardized core is useful.

In recent years, pin tumbler locks have been subject to forced pulling attack by a procedure in which a hardened screw is threaded into the key slot of the key plug, and pulling force is applied either continuously or with an impact puller so as to pull the key plug out of the lock.

It is the general object of the present invention to increase the pull resistance of the key plug in a pin tumbler lock, and especially in a key-removable core of the type described, and to do so while maintaining the standard configuration and dimensions of the standard core so that the improved core will fit the same core receptacles as the prior standard core. The present invention not only accomplishes this purpose, but also improves the dimensional control and ease of manufacture and assembly of the core.

In accordance with the invention, the core body and sleeve are made substantially as before, but the core plug is formed with an integral heavy peripheral flange or head at its rear end, wide enough to engage both the sleeve and the lower lobe of the core body from the rear so as to strongly oppose forward pull on the plug. The plug is axially broached to form a key slot, and a key stop is formed by inserting a small disk segment in a cross slot ahead of the rear flange so that it is trapped in such slot by the surrounding sleeve. The forward end of the key plug is formed with a peripheral groove in which a C-shaped retaining ring is mounted. The ring overlaps the sleeve and core body at the front so as to hold the plug against rearward movement. The C-shaped ring defines a key-pass opening and is held with such opening in alignment with the key slot. A face plate is secured to the front of the body by a known blind riveting operation. The face plate has an internal counterbore which surrounds the retaining ring and traps it permanently in place.

In manufacture, the inner face of the rear flange and the retaining ring groove can both be made or finished in the same operation so that their spacing is held to exact dimensions, and the core body and sleeve can be accurately finished to a corresponding dimension so that an accurate interfitting relationship can be obtained between the parts; and it is not necessary to counterbore the face plate after its assembly to the core body as was done to obtain a suitable length dimension in prior standard cores. The body, sleeve, and plug can be preassembled for purposes of drilling the tumbler pin holes, and the parts then disassembled to clear out burrs and chips, whereas this could be done with prior standard cores because they required the key stop to be riveted to the key plug in place before the tumbler pin holes are drilled, in order to prevent misalignment of such holes resulting from the riveting operation. After the body and sleeve and plug have been thus prepared, they are finally assembled and the retaining ring applied. The face plate is then fixed to the body and permanently traps the ring in place.

With prior standard cores, production of a plated front requires plating after assembly of the key plug in the body because of the requirements mentioned above. In consequence, plating metal is deposited in clearance spaces, which causes binding and requires special lubricant. With the present invention, a plated front can be obtained by plating the parts separately and before assembly, which avoids such problems.

Whereas the plug in the prior standard core was subject to pulling failure and does not meet a proposed standard strength test, the plug and core construction of the present invention provides a plug having a pull resistance substantially exceeding the proposed standard.

The accompanying drawings illustrate the invention and show an embodiment of the best mode of carrying out the invention as presently perceived. In such drawings:

FIG. 1 is a perspective view of a key-removable core embodying the invention and which has an external appearance which is substantially the same as the prior standard core;

FIG. 2 is a sectional view of a known lock cylinder formed to receive a key-removable core of a standard configuration as shown in FIG. 1;

FIG. 3 is an axial sectional view of a core in accordance with the present invention;

FIG. 4 is a fragmental view illustrating the blind rivet fastening of the face plate;

FIG. 5 is a section on the line 5--5 of FIG. 3, with a portion of the key plug shown in end elevation; and

FIG. 6 is a section taken on the line 6--6 of FIG. 3.

The core 10 shown in FIGS. 1 and 3-6 is of figure-8 cross section and has a lower lobe 12 which contains the key plug 14 and a sleeve 42 that carries a core-retaining lug 16, and has an upper lobe 18 which contains the pin tumblers and their biasing springs. The core also has a face plate 20 with a solid upper lobe and with a circular lower lobe portion 21 which surrounds the front end of the key plug 14.

Such core is adapted to be mounted in a standard receptacle such as the cylinder shown in FIG. 2. This comprises a generally cylindrical body 22 having a core-receiving chamber 24 defined by two parallel overlapping axial bores 25 and 26 which leave between them at their sides inwardly projecting ribs 28. At their inner ends, such side ribs 28 are milled away so as to define rearwardly presented shoulders 30 at the two sides of the chamber. The core-retaining lug 16 of the core 10 is adapted to be projected behind such a shoulder 30 to retain the core in the chamber 24. The rear wall of the cylinder is formed with a shouldered opening in which a throw member 32 is rotatably mounted. The throw member 32 carries a pair of diametrically-spaced throw pins 34 which take into corresponding eccentric bores 36 in the rear of the key plug. (See FIG. 5.) The throw member and throw pin assembly is fixed to a cam 38 for transmitting key-plug rotation to a secondary lock mechanism, as is known in the art, and as shown in U.S. Pat. No. 1,564,463.

As shown in FIGS. 3, 5, and 6, the lower lobe 12 of the core body is formed with a cylindrical bore 40 in which the thin-walled sleeve 42 is mounted for limited rotation. The bore 40 is in open communication with a wide fantail slot 44 formed in the upper lobe 18. At the rear of the core body, the side wall of the slot 44 is milled away as shown in FIG. 5, to pass the retaining lug 16 which is formed integral with a boss 46 on the sleeve 42. The limited rotation of the sleeve moves the lug 16 between a projected, core-retaining position as shown and a retracted release position.

The key plug 14 is rotatably mounted within the sleeve 42. Pin tumbler bores 48 extend downward from the top of the upper lobe 18 through that lobe and through the boss 46 on the sleeve 42 and into the key plug 14, in the usual fashion. The interface between the key plug 14 and the boss 46 defines an operating shear line at which abutting faces of pin tumbler segments 50 in those bores can be brought into registry by use of a suitable operating key 52, to permit the key plug to be rotated for usual key operation of the lock. The interface between the upper lobe 18 and the boss 46 defines a control shear line at which pin tumbler faces can be brought into registry by the use of a special control key so as to permit the control key to rotate the sleeve 40 and its boss 46 and the retaining lug 16 from its projected position shown to a retracted release position for purposes of releasing the core for inserting and removing the core from a core chamber such as the core chamber 24 of the cylinder shown in FIG. 2.

In accordance with the present invention, the key plug 14 comprises a cylindrical body portion 54, desirably made from solid stock, which extends completely through the sleeve 42 and has a close working fit within that sleeve. The rear end of the plug carries an integral heavy peripheral flange 56 which forms a rear head on the key plug 14 and which overlaps the end of the sleeve 14 and at least a substantial portion of the rear end face of the core body formed by the two lobes 12 and 18. As shown in FIGS. 3 and 5, such flange 56 desirably extends outward substantially to the periphery of the lower lobe 12. The front face of the flange 56 lies in engaged relation with the rear face of the core body and sleeve over a substantial peripheral area thereof, so that it fixes the axial position of the plug in the core and opposes forward pull on the plug 14.

The plug 14 is formed with an axial broached key slot 58. For purposes of providing a key stop at the rear end of such key slot, a shallow transverse slot 60 is cut in the cylindrical body portion 54 of the key plug at or close to the front face of the flange 56. A small disk segment 62 is inserted in that slot and has an outer cylindrical edge which substantially conforms to the circular cross section of the key plug body 54. When the segment 62 is in place in the cross slot 60 and the key plug is inserted in its bore, such segment is trapped in place by the surrounding wall of the sleeve 42. It thus stands across the key slot 58 to form a key stop for engagement for a key stop shoulder 64 at the end of a key 52 as shown in FIG. 3.

The key plug 14 is retained and held against rearward movement by a C-shaped retaining ring 64 received in a circumferential groove 66 aligned with the front face of the core body 12, 18, as shown in FIG. 3. The space between the ends of the retaining ring 64 forms a key-pass opening and this is disposed so as to clear the key slot 58, and the retaining ring is held from rotation across such slot as by forming the groove 66 with a flat upper portion 68 and forming the ring 64 with a portion which fits against that flat 68.

The retaining ring 64 is trapped in place and concealed by the face plate 20. This has a peripheral portion 21 which surrounds the front end of the key plug 14, and such portion is counterbored from the rear to provide a rabbet groove 70 which fits over the peripheral edge of the retaining ring 64 with sufficiently close clearance to prevent escape of that ring from the key plug groove 66.

The face plate must of course be applied after the retaining ring 64 has been mounted on the key plug 14, and is desirably mounted by a blind annular rivet as shown in FIG. 4. The upper lobe of the face plate 20 is formed in its rear face with a circular cavity 74, and the upper lobe 18 of the core body is formed with an annular rib 76 of tapered cross section and having a cylindrical outer face. The cylindrical wall of the cavity 74 in the face plate 20 is deformed inward by a staking operation which forms a groove 78 in the rear face of the face plate 20, circumferentially about the cavity 74. The face plate 20 is then forced against the circular rib 76 so as to flatten that rib and deform it outward into the undercut periphery of the cavity 74. This securely fixes the face plate 20 onto the core body and holds the lower lobe of such face plate in position surrounding the retaining ring 64, as shown in FIG. 3. This permanently traps the retaining ring 64 in place so as to hold the key plug 14 in the assembly.

The construction described substantially simplifies the manufacture and the accuracy and convenience of assembly of a lock core in comparison with that of the prior standard core. In such prior standard core, the key plug had a shoulder at the front which seated in a counterbore in the face plate of the core, and the plug was held in place by a stop plate riveted to the rear face of the plug. In order to obtain satisfactory accuracy and avoid misalignment of the parts, especially of the pin tumbler bores, it was considered necessary to counterbore the face plate after its assembly with the core body, so as to obtain an accurate dimension from the bottom of the front counterbore to the back face of the assembly, and to make that dimension fit the corresponding dimension of the key plug between its front flange and rear face. The counterboring operation requires precise control if it is to produce the necessary dimensional accuracy, because of build-up of tolerances. It was also considered necessary to install the sleeve and key plug in this assembly and rivet the rear plug-retaining key stop against the rear face of the key plug before drilling the pin segment bores, since riveting after such drilling was found to create misalignment of the pin segment bores. In the present construction, the front face of the rear flange 56 can be formed concurrently with and by the same tool set-up as the groove 66 for the plug-retaining ring 64 so that a precise and uniform length dimension between those elements can be obtained early. Further, these parts are so arranged that they match the length of the core body 12, 18 and the corresponding length of the sleeve 42, and those lengths can also be controlled with high accuracy, so that a close match can be obtained between the length dimensions of the core body and the plug. It is no longer necessary to counterbore the face plate 20 to an accurate dimension after assembly, since the rear counterbore which forms the rabbet groove 70 need only have sufficiently close clearance to prevent escape of the retaining ring 64 from the groove 66 at the front of the plug 14. Further, because of these factors, it is readily possible to assemble the core body and the sleeve and the key plug 14 in a preliminary and temporary assembly, to then drill the pin tumbler bores 48 in all three parts while so assembled, then to disassemble the parts and clear them of burrs and chips, before final assembly of the parts with the retaining ring 64 and the face plate 20.

Accordingly, manufacture and assembly of the core in accordance with the present invention is relatively simple and easy. The several parts can be manufactured to final dimensions independently and with sufficient accuracy to permit subsequent random assembly. The core body 12, 18 may be temporarily assembled with a sleeve 42 and key plug 16, and the parts held in assembled position in a jig while the pin tumbler bores 48 are drilled in the three parts. The parts may then be disassembled and cleared of burrs and chips, and then reassembled together with a key stop segment 62 and a retaining ring 64. A face plate 20 is then mounted against the front of the assembly so as to enclose and trap the retaining ring 64 in place and fix the face plate 20 on the body by the blind rivet shown in FIGS. 3 and 4.

Further, when the core is to have a plated surface, there are further advantages relative to the prior standard core. In that prior standard core it was considered necessary to assemble the core body, face plate, sleeve, plug, and riveted rear key stop before plating, and then to plate that assembly. In the plating operation, plating metal inevitably entered the interfaces between the parts at which relative motion was to occur, and this produced variations in tolerances and caused the parts to bind and required special lubricants. In contrast, with the present construction it is feasible to plate the parts, or their desired surfaces, separately and before assembly, and subsequently to assemble the core with such pre-plated components. This avoids the problems which arose by reason of plating after assembly.