US3863476A

US3863476A - Pick resistant lock

Info

Publication number: US3863476A
Authority: US
Inventors: George P Patriquin
Original assignee: HUDSON LOCK Inc
Current assignee: HUDSON LOCK Inc
Priority date: 1973-02-09
Filing date: 1973-02-09
Publication date: 1975-02-04
Anticipated expiration: 1992-02-04

Abstract

Disclosed is a cylinder lock with a plug rotatably mounted in a housing and including a keyway for receiving a key. A cam actuator operates a lock controlling cam and is rotatably mounted in the housing behind the plug and receives the end of the key as it passes through the plug. One or more restraining wafers interact with a proper key and releasably hold the cam actuator in a locked position with respect to the housing. Restraining wafers in the plug maintain it in a preselected position with respect to the cam actuator and the housing. A proper key is received by both the plug and cam actuator and releases both for rotational motion to unlock the device and supplies torque to both therefor. Attempting to pick the subject lock in the normal manner only releases the plug from the cam actuator and thus the lock remains locked. The spline arrangement is such that the cam actuator cannot be picked without first picking the plug, thus rendering the lock time consuming to pick even for one familiar with its construction. Auxiliary splines are provided and the wafers can define contoured edges for interacting with a plurality of splines simultaneously.

Description

United States Patent 1 1 Patriquin 1 Feb.4,1975

[ PICK RESISTANT LOCK [75] Inventor: George P. Patriquin, Gardner, Mass.

[73] Assignee: Hudson Lock, Inc., Hudson, Mass.

[22] Filed: Feb. 9, 1973 [21] Appl. No.: 330,971

[52] US. Cl. 70/419, 70/375 [51] Int. Cl E05b 63/00 [58] Field of Search 70/35 B, 364 R, 375, 377,

Primary ExaminerRobert L. Wolfe Attorney, Agent, or Firm-J0hn E. Toupal ABSTRACT Disclosed is a cylinder lock with a plug rotatably mounted in a housing and including a keyway for receiving a key. A cam actuator operates a lock controlling cam and is rotatably mounted in the housing behind the plug and receives the end of the key as it passes through the plug. One or more restraining wafers interact with a proper key and releasably hold the cam actuator in a locked position with respect to the housing. Restraining wafers in the plug maintain it in a preselected position with respect to the cam actuator and the housing. A proper key is received by both the plug and cam actuator and releases both for rotational motion to unlock the device and supplies torque to both therefor. Attempting to pick the subject lock in the normal manner only releases the plug from the cam actuator and thus the lock remains locked. The spline arrangement is such that the cam actuator cannot be picked without first picking the plug, thus rendering the lock time consuming to pick even for one familiar with its construction. Auxiliary splines are provided and the wafers can define contoured edges for interacting with a plurality of splines simultaneously.

17 Claims, 13 Drawing Figures VPATENTEDFEB 41975 3, 863 ,476

SHEET 2 OF 3 PICK RESISTANT LOCK BACKGROUND OF THE INVENTION most instances represent the major protective device 7 for the safety of persons and property against unauthorized interference. These locks generally are comprised of a housing and an inner cylinder plug. The inner cylinder plug has a plurality of openings along its surface which align with openings or a groove or spline in the housing. Spring loaded pins or wafers in the plug project into the spline when a key is not in use, preventing the plug from being rotated unless a proper key is inserted. When a proper key is used, the wafers rest at the shear line so that the plug can be revolved to lock and unlock the device.

In the past, when an unauthorized person desired to pick" such a lock, a torque was applied to the plug to force the wafers to the edge of the groove and the picking device was placed in the cylinder plug through the keyway to move the wafers to their proper alignment one at a time. As each wafer reached its shear position, the edge of the wafer would catch on the ledge of the spline and be held at shear. Consequently, the cylinder could be revolved.

Various modifications have been made in the manufacture of locks of this nature. Such modification include varying the type of wafers employed or disposing the wafers in a non-aligned manner. The cost of the locks was substantially increased, yet they could still be actuated to free the inner plug for rotation by manipulating wafers with apparatus other than the proper key.

The object of this invention, therefore, is to provide a cylinder lock which is extremely difficult, if not impossible to pick and is inexpensive to manufacture, yet is reliable in action and can easily be operated with a proper key.

SUMMARY OF THE INVENTION This invention is characterized by a lock with a housing that rotatably retains a cam actuator for operating a lock controlling cam. Also rotatably mounted in the housing is a plug. The cam actuator and the plug each define a keyway and the keyways are aligned when the two elements are in a preselected, locked position. Restraining wafers in the actuator project into a spline and respond to a proper key in the cam actuator keyway to releasably restrain the cam actuator in the preselected position. It should be appreciated that the key extending into the cam actuator also supplies torque for rotation. Similarly, plug restraining wafers project into a spline and interact with the proper key in the plug keyway and releasably restrain the plug in the preselected position. When it is attempted to pick the lock in the conventional manner, the torque wrench is applied to the plug and the wafers are picked one at a time. However, since torque is only applied to the plug and not to the cam actuator, only the plug is picked. When the plug is picked, rotation thereof misaligns the two keyways and creates an obstruction to any attempt to later pick the cam actuator. If the thief is familiar with the construction of the lock he will attempt to pick the cam actuator directly. However this is difficult inasmuch as his torque wrench must extend through the plug keyway and he must attempt to pick the wafers through a keyway holding that tool. Consequently, the subject lock is difficult to pick even to one familiar with its split plug construction.

Certain features of the invention further inhibit the attempt to pick the cam actuator initially. One direction of plug rotation from the preselected, locked position is referred to as the release direction. That is the direction that the cam actuator must be rotated in order to unlock the lock. A stop washer affixed to the cam actuator that abuts against a stop prevents rotation of the cam actuator in the direction opposite the release direction. Consequently, the cam actuator cannot be rotated in that opposite direction to establish a shelf for picking. Furthermore, the plug and the cam actuator comprise mating bosses at their intersection that prevent the cam actuator from being rotated in the release direction without corresponding rotation of the plug. The converse is not true. The plug can rotate 135 in the release direction before any motion is required of the cam actuator. When the plug and cam actuator are in the preselected position, the cam actuator wafers and the plug wafers project into a primary spline system. The primary splines are arranged so that when torque is applied to the cam actuator (and thus to the plug via the bosses) the plug wafers engage a plug restraining wall of the primary spline prior to the engagement of the cam actuator wafers with a cam actuator restraining wall. Consequently, an operator familiar with the split plug construction cannot pick the cam actuator initially because the necessary contact of the cam actuator wafers with the cam actuator restraining wall cannot be achieved until the plug has been picked. Thus it is seen that an attempt to pick the subject lock by one unfamiliar with its construction is a frustrating experience and an attempt to pick the lock by one familiar with the locks construction is at the very least an arduous time consuming task.

Another feature of the subject lock is the inclusion of auxiliary splines. For example, rotation of the plug following picking will cause the plug wafers to be trapped by an auxiliary spline. When an operator unfamiliar with the locks construction attempts to pick it, the plug will be picked without the cam actuator. Upon a 90 rotation, the plug wafers will be received by the auxiliary spline. Observing that the lock is not yet open, the operator will probably assume a 180 turn requirement. After rotating another 45, to a total of the bosses on the plug and cam actuator again come in contact and prevent further rotation until the cam actuator is picked. Clearly, picking the cam actuator is impossible at the point due to the misalignment of the keyway. Consequently, if the operator wishes to continue his picking efforts, he must return the plug to the preselected position and in an effort to do so must repick the plug out of the auxiliary spline. It is felt that the process of picking the subject lock is so time con suming that most thieves will not complete the job for fear of being caught.

Still another feature of the invention is the inclusion of wafers with contoured wafer edges defined by a plurality of fingers projecting therefrom. Several closely spaced fingers can interact with a. plurality of similarly closely spaced splines. Thus, little rotation is required before the wafers are retrapped in the splines following initial picking. A difficulty encountered with prior closely spaced splines was lack of strength in the divisions between the splines and lack of strength in the wafers due to their small size. The contoured wafer edge obviates this structural problem that led to violation of the lock by force inasmuch as each wafer interacts with several splines and effectively acts as several smaller wafers. Thus the large number of fingers provided by several wafers provides an adequate total strength and resistance to violation by force. An advantage of the plurality of splines is, of course, that trapping occurs with little rotation after picking. For example, it was pointed out above that the plug must be picked before the cam actuator can be picked. The splines can be spaced closely enough that following picking of the plug and rotation of the cam actuator the distance necessary to provide a shelf for picking the cam actuator wafers, the plug will be trapped by a set of auxiliary splines thus providing added frustration for the thief.

Yet other features of the invention provide obstructions in the keyway to render the lock difficult to pick even by one familiar with its construction. For example, the wafers in the cam actuator and those in the plug are diammetrically opposed, thereby creating a substantial blockage of the two keyways. In addition, a blocking spring loaded ball in the keyway is easily displaced by an inclined face on the proper key, but presents a real obstacle to a picking tool. In addition, wards are extremely effective as obstructions in the subject lock inasmuch as picking is not done in a conventional manner, but rather by the involved process of extending a torque wrench through the plug keyway to the cam actuator keyway and then attempting to pick the wafers in both the plug and the cam actuator. Furthermore, a formed opening of the cam actuator keyway makes the seating ofa torque wrench therein very difficult. Thus, the lock is rendered difficult to pick even if the potential thief is familiar with its construction.

DESCRIPTION OF THE DRAWINGS These and other features and objects of the present invention will become more apparent upon a perusal of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a sectional view of the subject lock;

FIG. 2 is a frontal view of the lock depicted in FIG. 1;

FIG. 3 is a rear view of the lock of FIGS. 1 and 2;

FIGS. 4a and 4b schematically depict picking action with a conventional lock torqued in the improper direction;

FIGS. 5a and 5b schematically depict picking action with a conventional lock torqued in the proper direction;

FIG. 6 is a frontal view of the cam actuator utilized in the lock shown in FIG. 1;

FIG. 7 is a top view of the cam actuator shown in FIG. 6;

FIG. 8 is a rear view of the cam actuator;

FIG. 9 is a sectional view of the housing of the lock shown in FIG. I taken on the line 9-9 to show the spline arrangement therein;

FIG. 10 is a sectional view similar to FIG. 9 but taken on the line 10-10; and

FIG. 11 shows a combination of auxiliary splines and a contoured wafer that can be utilized in the subject lock.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1, 2 and 3, there is shown a lock 21 including a cylindrical housing 22 with a threaded outer portion. Referring to FIG. 2 it is seen that the lock 21 looks like a conventional cylinder lock. Rotatably retained within the housing 22 are a cam actuator 23 and a plug 24. The cam actuator 23 operates a lock controlling cam 25 and is affixed to a stop washer 26 that interacts with a stop 27 in the housing 22 to control the rotation of the cam actuator 23. The cam 25 and the stop washer 26 are affixed by a screw 30. A plurality of plug tumbler wafers 28 and a plurality of diammetrically opposed cam actuator tumbler wafer 29 are projected into

primary splines

31 and 32 in the interior of the housing 22 by bias springs (not shown) and are part of a restraining apparatus and a plug restraining apparatus that releasably restrain the plug 24 and cam actuator 23 in a preselected position with respect to the housing 22. Also included in the plug restraining apparatus is a plug boss 33 and a cam actuator boss 34 that restrain the plug in a preselected position with respect to the cam actuator 23.

The plug 24 defines a plug keyway 35 and the cam actuator 23 defines another keyway therethrough. The two keyways are aligned when the cam actuator 23 and plug 24 are in the preselected locked positions. A plu rality of wards 36 around the plug keyway 35 help restrict the insertion of any apparatus therein with the exception of a proper key. The plug wafers 28 and the cam actuator wafers 29 are responsive to a key inserted in the keyways and retract to a shear position within the cam actuator 23 and the plug 24 in the conventional manner. It will be appreciated that torque for rotating the cam actuator 23 is supplied directly by the proper key as it extends into the cam actuator.

The plug 24 is retained within the housing 22 by a retaining slide 37 that rides in a groove 38 around the inside of the housing 22. The slide 37 is spring biased to remain in the groove 38. Removal of the plug 24 is achieved by pressing a pin through an opening 39 against the slide 37 and pressing the slide toward the plug 24 until it is released from the groove 38. Then the plug 24 can be removed from the front of the housing 22.

In order to fully appreciate the many features of the subject lock 21, a basic understanding of the process of picking a conventional lock is necessary. Consequently, a brief discussion of lock picking follows. Construction of a conventional lock can be adequately understood if the lock 21 depicted in FIG. 1 is modified so that the plug 24 and the cam actuator 23 are one piece and, thus, any movement thereof is directly reflected in the cam 25.

FIG. 4a shows the stop washer 26 and the stop lug 27 as seen from the rear of the lock 21 with all other parts removed. It should be noted that the stop washer 26 defines a square aperture that tits on a square cam actuating portion 41 (FIG. 1). Thus, the stop washer 26 will not slip with respect to the cam actuator 23. If the torque is applied to the plug 24 in the direction shown by the arrow T in FIG. 4a, the stop washer is forced against the stop 27 as shown.

As shown more clearly in the diagrammatic FIG. 4b the

splines

31 and 32 are longitudinal grooves on the inner surface of the housing 22. A bias spring 42, diagrammatically shown in FIG. 4b, biases the wafer 28 outwardly as shown. When torque in the direction T, as depicted in FIG. 4a, is applied, the wafer 28 is held in a central position in the spline 31. Therefore, no shelf can be established for picking and the lock cannot be picked in the direction T as shown in FIG. 4a.

Shown in FIG. 5a there is a stop washer 26 and stop lug 27 as they appear when torque is applied in the direction T. As shown in FIG. 5a, torque in the direction T separates the stop washer 26 and the stop 27. Consequently, as shown more clearly in FIG. 5b, the wafers 28 are pressed against the side wall of the spline 31. The wafers 28 are picked one at a time with a sharp instrument in the keyway, making use of the lateral play of the wafers, until they come to rest at shear with the edge thereof outside of the spline 31. As shown in FIG. 5b, the wafer 28 has been picked but the wafer 28a has not been picked. An experienced thief can quickly pick all the wafers in a conventional cam lock and then continued application of torque in the direction of T opens the lock.

Referring now to FIG. 6, 7 and 8 there is shown the cam actuator 23. As shown in FIG. 7, the wafers 29 are retained in slots 44 with channels 45 on the ends thereof for retaining the bias springs 42. The aforementioned cam actuator keyway is shown in phantom in FIG. 7 and is numbered 46. A broken-away portion near the boss 34 clearly shows the contoured end 47 of the keyway 46. The countoured end 47 is designed to make it more difficult to seat a torque wrench in the keyway 46. Also shown clearly in the broken-away portion is a blocking ball 48 held in the keyway 46 by a spring 49. It will be appreciated that the ball 48 rests in the keyway between the front of the lock and the wafers 29. Consequently, access to the wafers 29 is inhibited by the spring loaded ball 48 and thus picking the wafers 29 is more difficult. However, the ball 48 is easily displaced by a sloped surface on the proper key.

Referring now to FIGS. 9 and 10 there is shown the housing 22 sectioned at two different points. Raised inner portions of the housing 22 form annular retaining walls 51 that rotatably retain the cam actuator 23 and the plug 24 in the housing. Observing FIGS. 9 and 10 it is clear that the sectional view of the lock 21 shown in FIG. 1 passed through the

splines

31 and 32 and that is why there is a space shown between the cam actuator 23 and the plug 24 and the interior of the housing 22. The cam actuator 23 and the plug 24 are in contact with the wall portions 51 and the

primary splines

31 and 32 receive the

wafers

28 and 29. A plug retaining wall 52 is in the primary spline 31 and a cam retaining wall 53 is in the primary spline 32. The

splines

31 and 32 are slightly larger at the location of the section shown in FIG. 10 than they are at the section shown in FIG. 9. The

splines

31 and 32, as they appear in FIG. 9, are shown in FIG. 10 in phantom. Also shown in FIGS. 9 and 10 are

auxiliary splines

54 and 55.

Operation of the lock 21 begins when the proper key is inserted in the

keyways

35 and 46 to withdraw the

wafers

28 and 29 from the

splines

31 and 32 to the shear line. The cam actuator 23 and the plug 24 are then restrained only by the action of the stop washer 26 and the stop 27. The proper key extends into the cam actuator 23 and thus turning the key applies proper turning torque to both the cam actuator 23 and plug 24. Any degree of rotation up to 180 can be required to open the lock 21 as is desired by the user. Consequently, from the viewpoint of the user, operation of the lock 21 with the proper key is precisely the same as operation of conventional cylinder locks.

Efforts to pick the lock 21 should be described with reference to two possibilities. The first possibility is that the potential thief is not familiar with the construction of the lock 21 and the second posibility, of course, is that the potential thief is familiar with the split plug construction.

If the potential thief is not familiar with the construction of the lock 21 he will apply his torque wrench to the keyway 35 in the plug 24. Upon attempting to rotate the plug 24 clockwise (as viewed in FIG. 2) he will discover that a shelf cannot be established and thus the

wafers

28 and 29 cannot be hung. This is because the action of the

bosses

33 and 34 on. each other, coupled with the action of the stop washer 26 on the stop 27, holds the

wafers

28 and 29 centrally in the

splines

31 and 32 as shown in FIG. 4b. Consequently, he will attempt to torque the plug counterclockwise. Inasmuch as the

primary splines

31 and 32 are narrower in the vicinity of the plug wafers 28 than they are in the vicinity of cam actuator wafers 29, the plug wafers first engage the plug retaining wall 52. The thief will then proceed to pick the plug. When the plug 24 is picked the

bosses

33 and 34 separate and the plug freely rotates counterclockwise. It must be emphasized however, that the cam actuator 23 has not been picked and thus the cam 25 remains in a locked position. Upon rotation of the plug 90 counterclockwise the plug wafers 28 fall into the auxiliary spline 54. The thief may then assume a I" turn requirement and try to repick the plug 24 to continue rotation. However this is impossible inasmuch as the

bosses

33 and 34 come together after l35 of rotation of the plug. Consequently, the thief cannot further pick the plug 24 in a counterclockwise direction. It is believed that at this point most thieves unfamiliar with the locks construction would cease further efforts inasmuch as a substantial amount of time has been expended and the plug 24 is now locked in the auxiliary spline 52 and must be repicked to be moved.

Now assume a thief is familiar with the split plug construction. He will realize that picking the plug 24 alone does nogood. He knows that the cam actuator 23 must be picked. Consequently, he will extend a torque wrench through the plug keyway 35 and try to seat it in the opening 47 of the keyway 46. However he will find this a difficult thing to do because the opening 47 of the keyway is contoured. Nevertheless, assuming he is successful in seating his torque wrench in the opening 47, he will next try to torque the cam actuator 22 in a counterclockwise direction to force the cam actuator wafers 29 to engage the cam actuator restraining wall 53. However, this cannot be done because the

bosses

33 and 34 rotate the plug 24 with the cam actuator 23 and, due to the smaller size of the spline 31 near the wafers 28 as compared to the size of the spline 32 near the wafers 29, the wafers 28 engage the plug restraining wall 52 first. Therefore, in order to establish a shelf for the cam actuator wafers 29 he must pick the plug wafers 28 first. After he picks the plug 23, he rotates it slightly to firmly seat the plug wafers 28 on the wall 51. This action, however, misaligns the

keyways

35 and 46 with the plug 24 acting as an obstruction apparatus thus rendering it very difficult to pick the cam actuator wafers 29. In addition to misalignment problems, it should be recalled that the two keyways still contain the torque wrench extending to the cam actuator 23. Also, the thief must forcibly displace the spring loaded ball 48 in order to gain access to the cam actuator wafers 29. Furthermore, the

wafers

28 and 29 are diammetrically opposed about the

keyways

35 and 46 and thus only central portions of the keyways are available for the picking tool. Also, the wards 36 make manipulation of the pick difficult. Consequently, even for a thief familiar with the construction of the lock 21, the act of picking the lock is a frustrating, time consuming experience and it is believed that the time involved is greater than a potential thief will be willing to spend for fear of being discovered in the act of picking the lock.

Referring to FIG. 11 there is shown another sectional view of a lock including a housing 61 and

primary splines

62 and 63 with

auxiliary splines

64, 65, 66 and 67. Diagrammatically shown in the housing 61 there is a wafer 68 with a contoured edge that defines a plurality of

fingers

69, 70 and 7l. It will be appreciated that such a spline and wafer configuration can be utilized in the disclosed lock 21. For example, the configuration shown in FIG. 11 can be utilized with the plug 24. Then, when a thief familiar with the lock construction picks the plug 24 he will rotate it slightly to assure that the wafers 68 do not slip off the shelf. However, with the configuration shown in FIG. 11, even a slight rotation causes the

fingers

69, 70 and 71 to fall into the

splines

62 and 64. Consequently, incorporation of the wafer and spline configuration shown in FIG. 11 renders the picking of the subject lock 21 even more frustrating and time consuming.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, the wafers in the locking apparatus could be replaced with pins and the plug and cam actuator could have wafers on each side of the keyways. It is to be understood, therefore, that the invention can be practiced otherwise than as specifically described.

What is claimed is:

l. A lock comprising:

a housing comprising annular retaining means that defines spline means;

cam actuator means rotatably mounted in said annular retaining means and for operating a locking cam, said cam actuator means defining a keyway for receiving a key; tumbler restraining means received by said spline means and responsive to a proper key in said keyway for releasably restraining said cam actuator in a preselected position with respect to said housing;

a plug rotatably mounted in said annular retaining means and defining a plug keyway for receiving a key, said keyway and said plug keyway being aligned such that access to said keyway by a key is through said plug keyway when said cam actuator means and said plug are in their preselected positions;

stop means coupled to said cam actuator means for preventing rotation of said cam actuator means in a direction opposite a release direction when said cam actuator means is in said preselected position; and

plug restraining means comprising plug tumbler means received by said spline means and responsive to the proper key when placed in said plug key way for releasably restraining said plug in a preselected position with respect to said cam actuator means, said plug restraining means further comprising means for preventing rotation of said cam actuator means in the release direction from the preselected position without corresponding rotation of said plug in the release direction, and wherein said spline means comprises a cam actuator restraining wall spaced a given distance from said tumbler means and disposed so as to be engaged thereby when said cam actuator means is rotating in the release direction, and a plug restraining wall spaced less than said given distance from said plug tumbler means so as to be engaged thereby prior to engagement between said tumbler means and said cam actuator restraining wall during rotation of said cam actuator means in the release direction.

2. A lock comprising:

a housing comprising annular retaining means that defines spline means;

a plug rotatably mounted in said annular retaining means and defining a plug keyway for receiving a key, said keyway and said plug keyway being aligned such that access to said keyway by a key is through said plug keyway when said cam actuator means and said plug are in their preselected positions; and

plug tumbler restraining means received by said spline means and responsive to the proper key when placed in said plug keyway for releasably restraining said plug in a preselected position with respect to said cam actuator means, said tumbler means and said plug tumbler means being received by said spline means in diametrically opposed positions about said keyway and said plug keyway.

3. A lock according to claim 2 wherein said annular retaining means comprises auxiliary spline means for receiving said plug tumbler means when said plug is rotated from the preselected position in a direction opposite the release direction.

4. A lock according to claim 2 wherein said plug comprises obstruction means for inhibiting access to said keyway when said plug is displaced from its preselected position and said cam actuator means is in its preselected position.

5. A lock according to claim 2 wherein said plug keyway is partially bounded by wards for inhibiting lock picking motions therein.

6. A lock according to claim 2 comprising blocking means for restricting access to said keyway.

7. A look according to claim 2 comprising stop means coupled to said cam actuator means for preventing rotation of said cam actuator means in a direction opposite a release direction when said cam actuator means is in said preselected position.

8. A lock according to claim 7 wherein said plug restraining means further comprises means for preventing rotation of said cam actuator means in the release direction from the preselected position without corresponding rotation of said plug in the release direction.

9. A lock according to claim 8 wherein said spline means comprises primary spline means into which said tumbler means and said plug tumbler means project when said cam actuator and said plug are in their preselected position and wherein said primary spline means comprises a cam actuator restraining wall for engaging said tumbler means when said cam actuator means is rotating in the release direction, and wherein said primary spline means further comprises a plug restraining wall for engaging said plug tumbler means prior to engagement between said tumbler means and said cam actuator restraining wall during rotation of said cam actuator means in the release direction.

10. A look according to claim 1 wherein said annular retaining means comprises auxiliary spline means for receiving said plug tumbler means when said plug is rotated from the preselected position in a direction opposite the release direction.

11. A lock according to claim 10 wherein said tumbler means and said plug tumbler means are received by said spline means in diametrically opposed positions 10 about said keyway and said plug keyway.

12. A lock according to claim 11] wherein said plug tumbler means comprises plug wafers and said tumbler means comprises wafers.

13. A lock according to claim 12 wherein the outer edges of said wafers and said plug wafers comprise contoured wafer edges with a plurality of fingers thereon.

14. A lock according to claim 1 comprising blocking means for restricting access to said keyway.

15. A lock according to claim 14 wherein said blocking means comprises a spring loaded ball in said keyway.

16. A lock according to claim 1 wherein said plug keyway is partially bounded by wards for inhibiting lock picking motions therein.

17. A lock according to claim 1 wherein said plug comprises obstruction means for inhibiting access to said keyway when said plug is displaced from its preselected position and said cam actuator means is in its preselected position.

Claims

1. A lock comprising: a housing comprising annular retaining means that defines spline means; cam actuator means rotatably mounted in said annular retaining means and for operating a locking cam, said cam actuator means defining a keyway for receiving a key; tumbler restraining means received by said spline means and responsive to a proper key in said keyway for releasably restraining said cam actuator in a preselected position with respect to said housing; a plug rotatably mounted in said annular retaining means and defining a plug keyway for receiving a key, said keyway and said plug keyway being aligned such that access to said keyway by a key is through said plug keyway when said cam actuator means and said plug are in their preselected positions; stop means coupled to said cam actuator means for preventing rotation of said cam actuator means in a direction opposite a release direction when said cam actuator means is in said preselected position; and plug restraining means comprising plug tumbler means received by said spline means and responsive to the proper key when placed in said plug keyway for releasably restraining said plug in a preselected position with respect to said cam actuator means, said plug restraining means further comprising means for preventing rotation of said cam actuator means in the release direction from the preselected position without corresponding rotation of said plug in the release direction, and wherein said spline means comprises a cam actuator restraining wall spaced a given distance from said tumbler means and disposed so as to be engaged thereby when said cam actuator means is rotating in the release direction, and a plug restraining wall spaced less than said given distance from said plug tumbler means so as to be engaged thereby prior to engagement between said tumbler means and said cam actuator restraining wall during rotation of said cam actuator means in the release direction.

2. A lock comprising: a housing comprising annular retaining means that defines spline means; cam actuator means rotatably mounted in said annular retaining means and for operating a locking cam, said cam actuator means defining a keyway for receiving a key; tumbler restraining means received by said spline means and responsive to a proper key in said keyway for releasably restraining said cam actuator in a preselected position with respect to said housing; a plug rotatably mounted in said annular retaining means and defining a plug keyway for receiving a key, said keyway and said plug keyway being aligned such that access to said keyway by a key is through said plug keyway when said cam actuator means and said plug are in their preselected positions; and plug tumbler restraining means received by said spline means and responsive to the proper key when placed in said plug keyway for releasably restraining said plug in a preselected position with respect to said cam actuator means, said tumbler means and said plug tumbler means being received by said spline means in diametrically opposed positions about said keyway and said plug keyway.

7. A lock according to claim 2 comprising stop means coupled to said cam actuator means for preventing rotation of said cam actuator means in a direction opposite a release direction when said cam actuator means is in said preselected position.

10. A lock according to claim 1 wherein said annular retaining means comprises auxiliary spline means for receiving said plug tumbler means when said plug is rotated from the preselected position in a direction opposite the release direction.

11. A lock according to claim 10 wherein said tumbler means and said plug tumbler means are received by said spline means in diametrically opposed positions about said keyway and said plug keyway.

12. A lock according to claim 11 wherein said plug tumbler means comprises plug wafers and said tumbler means comprises wafers.