Dual control lock
United States Patent 1 l 3,875,773 Thimot Apr. 8, 1975 l DUAL CONTROL LOCK Primary Eraminer-Roy D. Frazier [75] lmemor&#39; Robert Thlmm&#39; Marlbom&#39; MASS Ass-man: Eraminer-Peter A. Aschenhrenner Assignfici Hudson Loc Inc&#34; Hudson. Muss. A/mrney. Agent. or FirmJ0hn E. Toupal 221 Filed: Sept. 5, 1973 2l Appl. No.: 394.498 1571 ABSTRACT Disclosed is a lock comprising a housing that defines 52] US CL 70/337, 70/364 R, 70/119 on its inner surface a primary spline and. generally [5]] Int C 05) 35712 parallel thereto. a secondary spline. A trapping spline 5 Field 339 340 is also defined on the inner surface. A plug. defining a keyway, is rotatably retained in the housing. A prii mary tumbler projects from the plug and interacts [56] References cued with the primary spline to selectively retain the lock in an unlocked position and interacts with the secondary UNITED STATES PATENTS spline to selectively retain the lock in a locked posil.l4l.4fi3 (I/i915 Hurd 70/337 [i0n Furthermore a trapping tumbler prgjects from 1.233.206 4/l9l7 Ru)&#39; 70/337 the plug and selectively retains the plug in the locked position by interacting with the trapping spline The $57.85, 5/1934 Ruhnerw trapping tumbler does not interact wlth the prlmary 2.358.164 90944 Hiinger.t..........4..t...... 1:... 70 342 Splme the secondary P Two keys are supplied 2102.075 10/1952 Gallagher et all 70/337 x one P i P&#39;Y the lz g I I I I FOREIGN PATENTS OR APPLICATIONS 0pm 9 mppmg l.95u.0ll 5/1971 Germany 70 337 10 Claims 6 Drawing Figul&#39;fis PAIENTEDAPR&#39; 81975 875,77 3  
 FIG!  
 DUAL CONTROL LOCK BACKGROUND OF THE INVENTION This invention relates to locks and, more particularly, to cylinder locks that are responsive to two keys wherein either key can be utilized to move the lock to a locked position but only one of the two keys will permit the lock to be moved to an unlocked position.  
  It is often desirable to leave a cabinet or other enclosure unlocked for the duration of a business day but to have it locked at the end of that time. Furthermore, it is often desired that the person performing the locking operation not have access to the cabinet once it is locked. Such devices as plunger locks or combination locks are often utilized to fulfill this requirement. However. when utilizing either of these devices it is possible to inadvertently lose the ability to lock the cabinet. For example, ifa plunger lock is utilized and the plunger is accidentally pushed with the aperture to the device to be locked in an unlatching position, the ability to later lock the cabinet will be lost.  
  Consequently, a lock responsive to two keys, wherein either key can perform the locking operation but only one key can perform the unlocking operation, was thought to be advantageous. When such a lock is used the possibility of accidentally losing the ability to lock is abviated when the designated employee is in possession of locking key. but does not insert it into the lock until it is time to perform the locking operation. After the locking operation is performed the cabinet can only be unlocked by a person in possession of the second type of key.  
  Locks that respond to two keys as described above are known. For example. see U.S. Pat. No. 2,667,785. A problem associated with locks such as that depicted in the referenced patent is high manufacturing cost. For example, note that in the device disclosed some of the tumbler wafers are provided with ramp shaped edges and some are not. Consequently, the number of parts in the lock is increased and thus cost is increased.  
  An object of this invention. therefore, is to provide a lock that is responsive to two different keys in the manner described above and can be manufactured at a cost lower than heretofore possible.  
 SUMMARY OF THE INVENTION This invention is characterized by a lock comprising a housing that defines on its inner surface a primary spline and. parallel thereto. a secondary spline. A trapping spline is also defined on the inner surface. In order to simplify fabrication, the trapping spline can be simply an extension of the secondary spline. Rotatably retained within the housing is a plug defining a keyway. Biased to project from the plug are one or more primary tumbler wafers that are received by the primary spline to retain the lock in an unlocked position and are received by the secondary spline to retain the lock in a locked position. Also spring biased to project from the plug are one or more trapping wafers that releasably hold the plug in the locked position when they are received by the trapping spline. At no time are the trapping wafers received by the first or second splines. The splines and the wafers are preferably of a rectangular shape to insure good interaction therebetween and to minimize the cost of fabrication.  
  A primary key operates only the primary tumbler wafers and an auxiliary key operates both the primary wafers and the trapping wafers. When the lock is in the unlocked position the trapping wafers are urged against the inner surface of the housing but do not restrain the plug from rotation. However, the primary wafers are then restrained by the primary spline. Insertion of ei ther key withdraws the primary wafer to shear and thus permits the plug to be moved to the locked position. In the locked position, the primary wafers are received by the secondary spline and the trapping wafers are received by the trapping spline. Thus. only the auxiliary key, which operates both sets of wafers, will function to move the plug from the locked position.  
  In a preferred embodiment described herein the primary wafers are disposed between the keyway opening and trapping wafers. Thus the primary key, which does not operate the trapping wafers, can simply be a shorter key, such as a cut off auxiliary key that does not extend sufficiently far into the plug to reach the trapping wafers. Consequently, the cost of supplying two different keys is kept to a minimum.  
 DESCRIPTION OF THE DRAWING 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. I is a sectional elevational view of the subject lock apparatus;  
  FIG. 2a is a sectional view taken along the line 22 in FIG. 1;  
  FIG. 2 is a sectional view of the housing alone taken along the line 22 in FIG. I;  
  FIG. 3 is a sectional view of the housing alone taken along the line 3-3 in FIG. 1;  
 FIG. 4 shows a primary key; and  
 FIG. 5 shows an auxiliary key.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 there is shown a lock apparatus 21 including a housing 22 with a flange 23 for mounting. A cylindrically shaped plug 24 is retained within the housing 22. A lug 25, projecting from the rear of the plug 24, is coupled to the device that the lock 21 is to control Projecting from the one side ofthe plug 24 are four primary tumbler wafers 26 and two trapping tumbler wafers 27. The plug 24 defines a keyway with a keyway opening 30 shown in a broken portion of FIG. 1.  
  Referring now to FIG. 20 there is shown a sectional view taken along the line 2-2 in FIG. 1 and showing one of the primary wafers 26 slidably retained in the plug 24 and biased to project therefrom by a small spring 28. As shown in FIG. 2a, the wafer 26 is received by a spline 29 and thus restrains rotational motion of the plug 24. Also visible in FIG. 2a is a secondary spline 31. An opening 32 within the wafer 26 permits a key to pass therethrough. It will be appreciated that all of the wafers 26 and 27 are similar.  
  Referring now to FIGS. 2 and 3 there are shown two sectional views of the housing 22 taken along, respectively, the lines 22 and 33 in FIG. I. In FIG. 2 the primary spline 29 and the secondary spline 31 are visible. However, in FIG. 3, only a trapping spline 33 is present. While the secondary spline 31 and the trapping spline 33 may in fact be one continuous elongated spline. that is not necessary. Observation of FIG. 1 will give a better understanding of the spline configuration. The primary spline 29 and the secondary apline 31 interact with the primary wafers 26. The trapping spline 33 interacts only with the trapping wafers 27.  
  Referring now to FIG. 4 there is shown a short primary key 34. Comparison of FIGS. 1 and 4 shows that the key 34 actuates only the primary wafers 26. Referring now to FIG. 5 there is shown a longer auxiliary key 35. Comparison of FIGS. 1 and 5 will show that the auxiliary key 35 actuates both the primary wafers 26 and the trapping wafers 27.  
  To understand the operation of the lock 21 assume that is is in the unlocked position as depicted in FIG. I. That is, the primary wafers 26 are received by the primary spline 29 and the trapping wafers 27 are urged against the smooth inner surface of the housing 22. Ohservation of FIG. 20 makes clear that the plug 24 cannot be moved while the wafers 26 are in the position depicted in FIG. 1. Insertion of either key 34 or 35 will withdraw the primary wafers 26 to the shear line. Consequently, the plug 24 can then be rotated 90 in a clockwise direction as viewed in FIG. 211. At that time, if the key is remove, the primary wafers 26 will project into the secondary spline 31 thus retaining the lock in a locked position. If the short key 34 was used, the trapping wafers 27 snap into the trapping spline 33 immedi ately upon becoming aligned therewith. If the long key 35 was used. the trapping wafers 27 enter the trapping spline 33 upon withdrawal of the key 35.  
  In order to move the lock 21 to the unlocked position. only the long key 35 will suffice. That is because the primary wafers 26 are interacting with the secondary spline 3i and the trapping wafers 29 are interacting with trapping spline 33. It is only the long key 35 that will withdraw both sets of wafers 26 and 27 to shearv Thus. it will be appreciated that while the short key 33 is sufficient to move the lock 21 from the unlocked position to the locked position, the converse is not true. Only the long key 35 will unlock the lock.  
  Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood. therefore, that the invention can be practiced otherwise than as specifically described.  
 What is claimed is:  
 l. A lock apparatus comprising:  
 housing means defining, on an inner surface thereof,  
 primary spline means and secondary spline means substantially parallel thereto and further defining trapping spline means;  
 Ill  
 plug means rotatably retained in said housing, said plug means defining a keyway therethrough;  
 a primary tumbler for releasably restraining said plug means in an unlocked position with said primary tumbler interacting with said primary spline means, and for releasably restraining said plug means in a locked position with said primary tumbler interacting with said secondary spline means and wherein said primary tumbler is releasable by a primary key to allow rotation of said plug from said unlocked to said locked position; and  
 a trapping tumbler non-responsive to the primary key and engageable with said trapping spline means to releasably trap said plug means in the locked position so as to prevent rotation thereof, both said primary tumbler and said trapping tumbler being releasable by an auxiliary key so as to permit rotation of said plug to said unlocked position, and wherein said trapping tumbler is disposed so as not to engage said primary spline means or said secondary spline means during plug rotation between said locked and unlocked positions.  
  2. A lock apparatus according to claim 1 wherein said secondary spline means and said trapping spline means comprise a single elongated spline.  
  3. A lock apparatus according to claim 1 comprising a plurality of primary tumblers.  
  4. A lock apparatus according to claim 1 wherein said tumblers are of a substantially rectangular cross section.  
  5. A lock apparatus according to claim I wherein said primary tumbler and said trapping tumbler comprise wafers.  
  6. A lock apparatus according to claim 1 wherein said primary tumbler and said trapping tumbler are of the same shape.  
  7. A lock apparatus according to claim 1 wherein said spline means are of a substantially rectangular cross section.  
  8. A lock apparatus according to claim I wherein the keyway defines a keyway opening and said trapping spline means is spaced farther from said opening than is said primary spline means.  
  9. A lock apparatus according to claim 8 comprising a primary key to which said primary tumbler is responsive and an auxiliary key to which said primary tumbler and said trapping tumbler are responsive.  
  10. A lock apparatus according to claim 9 wherein said auxiliary key is longer than said primary key.  
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