Abstract:
A master/valet lock and keyset provides a means of permitting limited one-time entry after locking a door to individuals possessing a valet key. In an embodiment, the mechanism relies on the use of a special master key to access a secondary lock cylinder, by means of which the full range of lock positions is allowed. Using the valet key, only the primary lock cylinder is accessed, restricting the range of positions to allow the user to unlock and relock the lock just once. This system may provide a means to allow occasional entry without granting unlimited access to the premises. For example, maintenance personnel could be given a valet key with which they could visit a home to perform repairs. The homeowner would be secure in the knowledge that the key could not be used to enter the home a second time.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is related to the field of lock mechanisms and, more particularly, to multiple-key lock mechanisms. 
     2. Description of the Related Art 
     There are many situations calling for limited access to a home or business, for example, by custodial or repair persons. In many such cases, one-time access may be all that is required. However, giving out a key in these situations grants unlimited entry and therefore compromises security. It would be desirable to have a means of locking a door that would allow one-time access to designated persons, and unlimited access to the owner. 
     Auto-makers have recognized the usefulness of this concept as applied to automobiles, and a number of currently-manufactured cars are equipped with master and valet keys, which differ in that the valet key provides limited access to the vehicle. For example, the glove compartment and trunk typically cannot be unlocked with the valet key. In some cases, the length of time the engine will operate when started with the valet key is also limited. However, such systems are not directly applicable to building access, where what must be restricted is not the number or type of doors that the valet key can unlock, but rather the number of times it can be used to open them. Furthermore, the access restriction systems used in automobiles are often electronic, and may become non-functional in the event of power loss. This is completely unacceptable in a building security system. 
     Key lock security systems exist based on master/service keys, which provide different levels of access. For example, a master key might allow a hotel manager to enter any of the rooms in a hotel, while the service key issued to a tenant permits entry only to the tenant&#39;s own room. U.S. Pat. No. 2,422,600 to Swanson, for instance, describes such a system. U.S. Pat. No. 4,631,941 to Sjunnesson (hereinafter, Sjunnesson) illustrates another variant of this idea. Sjunnesson describes a door lock that may be set in either a normal lock or a service lock position, depending on whether the occupant wishes to allow access by service personnel in his absence. The service key provided to janitorial staff in a hotel, for example, would work to unlock only those doors that had been left in the service lock position, thus restricting access. Neither of these simple master/service key arrangements, however, provides the advantage of limiting the service key to one-time access. 
     SUMMARY OF THE INVENTION 
     The problems outlined above are in large part solved by a master/valet keyset and lock as described herein. The mechanism comprises a lock that may be locked in either a master or a valet mode. Furthermore, the lock may be opened with either a master key or a valet key. These keys provide different levels of access. Using the master key, the lock can be locked and unlocked any number of times. Furthermore, when the lock has been locked in the master mode only the master key can be used to unlock it. When locked in the valet mode, the lock can be unlocked only once using the valet key. After it has been opened with the valet key and subsequently relocked, it can only be unlocked again by the master key. This system provides a means whereby the owner of the master key can permit one-time access to the building to an individual possessing a valet key, for example, a maintenance person. After the individual has entered the building using their valet key and relocked the door, only the master key will unlock the door again. Thus, if the valet key were to be lost or stolen it could not be improperly used to gain entry. 
     The master/valet keyset and lock may further comprise a turnstile system and a barrier pin. The turnstile system allows a valet key to turn in only one direction and the barrier pin prevents the valet key from rotating the lock from the valet locked position to the master locked position. Thus, a lock left in the valet lock position can be turned once to the unlocked position, and once more to the master locked position. At this point, the valet key is incapable of unlocking the door a second time; only the master key can restore the lock to the valet locked position. By this means, one-time access is provided to the holder of the valet key. 
     A method is also contemplated for locking a door in either a master mode or valet mode and for providing two types of keys, corresponding to these modes. The method further involves the use of a master key that can unlock the door and can lock it in either the master or the valet mode, and a valet key that can only lock the door in the master mode and can only unlock the door if it is locked in the valet mode. 
     It is considered advantageous to have the capability to lock a door in a limited access mode, whereby authorized individuals are allowed one-time access. This capability might serve well, for example, when it was necessary to enter an office after hours once each week, say, to collect waste paper for recycling. The individual performing this service would be issued a valet key, and on the day the collection service was to be performed the office door would be locked in the valet mode. Using the valet key, the office could be entered just once and relocked after collecting the papers. The valet key would not allow entry at any other time. Thus, even if the key were lost or stolen, the security of the office would not be seriously compromised. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
     FIG. 1 a  is a cross sectional view of an embodiment of the master/valet lock, shown with the corresponding valet key inserted in the lock; 
     FIG. 1 b  is a view of the embodiment of FIG. 1 a , but with the corresponding master key inserted; 
     FIG. 1 c  is a cross section of the master/valet lock of FIGS. 1 a  and  1   b , shown with the valet key inserted in the lock and turned approximately 180°; 
     FIG. 1 d  is a view of the keyset and lock configured as in FIG. 1 c , but with the master key inserted; 
     FIG. 2 is a detailed view of the primary cylinder and turnstile of FIG. 1, illustrating an embodiment of a method by which the primary cylinder is permitted to rotate in only one direction; 
     FIG. 3 a  is an end view of the main barrel of the keyset and lock of FIG. 1 b  along cross section  1 — 1  of FIG. 1 b , illustrating the three positions (i.e., unlocked, valet locked and master locked) from which the key may be withdrawn from the lock; 
     FIG. 3 b  is an end view along cross section  2 — 2  of FIG. 1 b , showing the arm on the main barrel of the lock, together with the turnstile system and barrier pin, and with the orientation of the arm corresponding to the unlocked position of the lock and the direction of rotation permitted by the turnstile system indicated by the arrow; 
     FIG. 3 c  is the same view as that of FIG. 3 b , except that the arm is rotated into the master locked position; and 
     FIG. 3 d  is the same view as that of FIG. 3 c , except that the arm is rotated into the valet locked position. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1 a , a cross sectional view of one embodiment of a master/valet keyset and lock is shown. Other embodiments are possible and contemplated. The components of the lock are shown in FIG. 1 a  as they appear when a valet key  10  associated with the lock is inserted. A slot  12  in the primary lock cylinder  16  is dimensioned to receive the key. 
     Primary lock cylinder  16  is contained within the lock housing  14 . Holes  20 , typically cylindrical, in the lock housing contain lock tumblers  22 , behind which are springs  24 . Each of the tumblers  22  has a corresponding pin  26  within the lock cylinder  16 . When a key is inserted into the lock, the notches on the key push pins  26  upward against the opposing force of the tumbler springs and displace the tumblers into their respective holes. If the notches are of the correct depth neither the tumblers nor the pins protrude from their holes, allowing the lock cylinder to turn within the lock housing; otherwise, the lock cylinder is prevented from turning. Although not explicitly shown, it should be understood that the cylinder is coupled to the lock bolt and, by rotating, can deploy the bolt to lock the door. 
     A preferred embodiment contemplated herein also comprises a secondary lock cylinder  18 , with an associated tumbler  42 , spring  46  and pin  48 . In the embodiment of FIG. 1 a , valet key  10  does not have an appropriately dimensioned notch for pin  48 . Therefore, tumbler  42  protrudes into the hole in secondary cylinder  18 , preventing rotation of the secondary cylinder. Appended to primary cylinder  16  may be an arm  28  extending into a circular cavity  30  within the lock housing  14 . The cavity extends a full 360° within the lock housing to accommodate the arm as the primary cylinder rotates. In the embodiment of FIG. 1 however, primary cylinder  16  is constrained to rotate in one direction. One means of accomplishing this is through the use of turnstiles  32 , which interact with the arm on the primary cylinder. However, other mechanisms, such as a ratchet system, might also be used. When the cylinder is rotated in the preferred direction the turnstile revolves, allowing the arm to pass. When the cylinder is rotated in the opposite direction, however, the turnstile blocks the arm. This mechanism is discussed further with reference to FIG. 2 below. Furthermore, a barrier  34  moving within a slot  36  in lock housing  14  may be thrust into circular cavity  30  by the action of a spring  38 . This barrier blocks the arm  28 , preventing rotation of the primary cylinder beyond a certain point in either direction. 
     In the embodiment of FIG. 1, secondary lock cylinder  18  is equipped with a protrusion  40  which can push barrier  34  back into slot  36  against the action of spring  38 . For this to occur, secondary cylinder  18  must be rotated into the proper position. But, as previously noted, the valet key is not correctly notched to allow the secondary lock cylinder to rotate; therefore, the valet key cannot rotate primary lock cylinder  16  past the angle where arm  28  encounters barrier  34 . 
     FIG. 1 b  illustrates the situation when the associated master key  50  is inserted into the lock of FIG. 1 a . Note that, in contrast to valet key  10 , master key  50  is extended to include a notched section for the secondary cylinder  18 . The notch at the tip of the master key displaces pin  48 , shoving tumbler  42  up into its hole  44 , such that secondary cylinder  18  is free to rotate within the lock housing  14 . As the master key is turned, both primary cylinder  16  and secondary cylinder  18  rotate together, and protrusion  40  rotates in conjunction with arm  28 . Ann  28  is thus prevented from colliding with barrier  34  by the protrusion, which pushes the barrier back into slot  36  as the arm approaches it. FIG. 1 c  shows what happens in the embodiment of FIG. 1 when the valet key is used to attempt to rotate the primary lock cylinder  16  more than 180° within the lock housing  14 . As the primary cylinder turns, arm  28  is blocked by barrier  34 , which is thrust into circular cavity  30  by spring  38 . The valet key can only be rotated in the opposite direction to the point where the arm encounters turnstile  32 ; consequently, 360° rotation is impossible. This is in contrast to the situation of FIG. 1 d , where the master key  50  is used instead of the valet key. The notch at the tip of the master key displaces pin  48  in secondary cylinder  18  upward, preventing tumbler  42  from protruding from its hole  44  in the lock housing. This allows the secondary cylinder to rotate in conjunction with the primary cylinder. When the key is rotated 180°, protrusion  40  is positioned such that it is able to push back the barrier  34 . With the barrier thus disabled, arm  28  is free to continue to turn the remaining 180°, accomplishing a full 360° of rotation. 
     FIG. 2 illustrates how the direction of rotation of the lock is restricted in the embodiment of FIG.  1 . Primary lock cylinder  16  is shown, with attached arm  28  and keyslot  12 . In this view, the key would be inserted into the cylinder from the left. As the cylinder rotates in the direction indicated by the arrow, arm  28  encounters turnstile  32 , which is designed to rotate only in the direction denoted by the smaller arrow. If the cylinder turns in the direction shown, it meets with no resistance from the turnstile. If it turns in the opposite direction, however, arm  28  is blocked by one of the turnstile arms. It should be noted that this particular configuration is merely one possible method of constraining the rotation of the cylinder, and other means could be adopted to achieve a similar effect. 
     FIG. 3 a  shows an end view along cross section  1 — 1  of FIG. 1 b , displaying the lock housing  14  and primary cylinder  16 . This perspective is as seen from the inner surface of the door. Tumblers  22 , springs  24  and associated holes  20  are shown for three positions: unlocked, master locked and valet locked, and the lock is shown with master key  50  inserted in the unlocked position. Note that a key may be inserted or withdrawn from the lock only when it is in one of these three positions, which, for simplicity, are shown to be at 120° intervals. As discussed above, the notches on the key drive pins  26  upward to force the tumblers  22  into their respective holes  20 , allowing the primary cylinder to rotate. FIG. 3 b  shows an end view along cross section  2 — 2  of FIG. 1 b , displaying the secondary lock cylinder  18  and circular cavity  30 , along with arm  28  and barrier  34 . As before, the orientation of the components is for the unlocked position of the lock. Also shown are cross sections of three turnstiles  32 , one for each of the three lock positions. The direction of rotation permitted by the turnstiles is indicated by a curved arrow, and corresponds to someone outside the door turning the key counterclockwise in the lock. 
     FIG. 3 c  shows the components of FIG. 3 b  with the lock in the master locked position. To reach the position of FIG. 3 c , the secondary cylinder  18  has turned 120° and has passed the turnstile  32  at the upper right. Similarly, FIG. 3 d  shows the configuration of the lock components in the valet locked position. Note that in order to go from the master locked position to the valet locked position the arm  28  must pass by the barrier  34 . As discussed above, this is accomplished when protrusion  40  displaces barrier  34 , preventing it from interfering with the arm. This cannot happen when using the valet key, since the secondary cylinder  18  is not allowed to rotate in that case. 
     A typical sequence of events for operation of the lock begins with a master key-holder leaving the lock in the valet locked position. In this position the door is locked, but can be unlocked by a valet key. When the valet key is inserted, the mechanism described in the preceding paragraphs allows the lock cylinder to be rotated clockwise to the unlocked position. Upon leaving the premises, the valet key-holder may reinsert the valet key into the lock and turns it another 120° clockwise, placing it in the master locked position. Note that the valet key-holder cannot turn the key in the opposite direction to return to the unlocked position because of the turnstile system. Furthermore, the valet key cannot be turned an additional 120° clockwise to the valet locked position because of the barrier  34 . Thus, the valet key lock system limits the valet key-holder to one entry. The master key-holder however, can turn the key a full 360° from any position, allowing him to lock the door in the either the master or valet locked positions. 
     Although the present discussion refers to a key inserted from the outside surface of the door, the mechanism described herein could be also combined with a thumbturn (or key) operating from the inside surface of the door. The components of the master/valet locking mechanism are preferably made of metal; however, other suitable materials may also be used. Other modifications, such as different angular orientations for the three locking positions, a different direction of rotation of the lock cylinder, or variations in the design, number or location of the turnstiles are also anticipated, and should be considered within the scope of the present invention. 
     It will be appreciated by those skilled in the art having the benefit of this disclosure that this invention is believed to present a system and method for implementing a master/valet keyset and lock. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. It is intended that the following claims be interpreted to embrace all such modifications and changes and, accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.