Patent Application
20080314105
This invention relates to pin tumbler cylinder locks and to pin configurations.
Normal rotating cylinder, pin tumbler key lock assemblies consist of a cylinder received in a lock body bore having an entrance face substantially flush with the lock body face. The cylinder has a key slot milled into it from its outer face longitudinally of the cylinder. The slot may be provided with wards limiting the type key blade which may be received in the slot. The cylinder is rotatable in the lock body and is provided with a series of longitudinally spaced pinholes extending radially of the key slot and open to the slot and to the cylinder O.D. The pinholes line up with a similar series of spaced pinholes in the lock body above the cylinder. A shear line exists between the rotating cylinder and the lock body bore receiving the cylinder. In the normal locked position pins in each pinhole span the shear line preventing rotation of the cylinder in the lock body.
Each pinhole combination of cylinder pinhole and lock body pinhole receives at least a pair of pins, generally referred to as a lower pin and an upper pin. The pinholes in the lock body are closed at one end remote from the cylinder and a spring is entrapped between the upper pin received in that pinhole and the closed end or bottom of the pinhole. This spring then biases the upper pin into contact with the lower pin pushing both pins into the cylinder pinhole. The cylinder pinholes, where they intersect with the key slot have a larger diameter than the cross section of the key slot such that the lower pins cannot pass entirely into the key slot, thereby retaining the lower pin in the lock, however, positioned substantially within the cylinder. Upon insertion of the key into the key slot, the pin engaging edge of the key will push the lower pins against the upper pins moving the lower and upper pins against the spring pressure a distance determined by the bitting cut into the key edge. When a properly bitted key is fully inserted into the cylinder, usually determined by an abutment of a shoulder on the key head with an exterior face of the lock, the various bittings or cuts in the pin engaging edge of the key will be aligned with the lower pins in the respective pinholes, and the lower pins will be lifted a distance determined by the depth of cutting of the bitting on the key blade.
When a properly bitted key is received in its appropriate lock, the bitting will raise the lower pins so that the ends of each of the lower pins and the bottom end of the respective upper pin will lie along the shear line and the cylinder will be able to be rotated by rotating the key. The pins are of different lengths so that the bitting must move some pins a greater distance than other pins.
When an improperly bitted key is inserted into the lock, one or more of the pin sets will not be moved against the spring pressure to the proper distance and therefore either the upper pin or the lower pin will extend across the shear line preventing rotation of the cylinder.
Because standard pin tumbler locks employ a multiplicity of pinholes, normally five or more, the compressive force of the springs used to exert pressure against the pins is relatively low for two reasons. First, it is desired to keep the overall height of the lock within acceptable limits and therefore the space available above the upper pin for receipt of the spring is limited. Second, it is desired to allow easy insertion of the key into the lock. Thus, the force necessary to move the pins axially in the pinholes against the spring is relatively minor.
While such pin tumbler locks offer an acceptable degree of security in most instances, there are known methods of opening such locks without having a properly bitted key. Some methods, such as picking the lock, require considerable skill and training and are generally not a concern for most installations.
There exists, however, one known brute force method of opening a pin tumbler lock known as “key bumping.” While this technique, which will not be described here, has been known to professional locksmiths for a considerable period of time, that knowledge was generally not widespread. Recently, with the advent of the worldwide web, instructions on key bumping have become widely available to anybody. Since key bumping will work with many standard pin tumbler locks, and does not require proper bitting of the key, it would be an improvement in security of the locks to provide a key bumping resistant standard pin tumbler lock.
This invention overcomes disadvantages in prior art standard pin tumbler locks and provides a modification which is retrofittable into existing locks which reduces the ability to open the lock by key bumping techniques.
In the preferred embodiment an upper pin, which is headed in the manner of a nail, is provided. The pin consists of a cylindrical body portion of smaller diameter than the pinhole, the body portion having an axial length and having at one end thereof an enlarged diameter section or head, which is of relatively short axial length and which has an outer diameter of generally standard pin dimension for the pinhole. A coil spring is received around the cylindrical body portion and bottomed against the under surface of the head. The coil spring extends beyond the axial end of the body portion remote from the head in its free state. The headed pin and coil spring are received in the lock body pinhole, and the overall dimensioning is such that when the cylinder pinholes are aligned with the lock body pinholes, the head of the pin will extend beyond the shear line into the cylinder pinhole with the end of the coil spring opposite the head bottomed against or adjacent to the blind end of the lock body pinhole and with the coil spring being either in a slightly compressed or generally uncompressed condition. The spring, since it is received around the cylindrical body portion, can therefore be longer and stiffer than springs in other pinholes which bottom against the upper pins top.
Surprisingly, it has been found that by providing such a headed upper pin and coil spring positioned around a reduced diameter portion and bottomed against the undersurface of the head, that the resultant pin tumbler cylinder lock will be highly resistant to key bumping since the bumping pressure exerted against the lower pin associated with the headed pin will be insufficient to cause the headed pin's head bottom to lift to the shear line. The pin of this invention can be retrofitted into existing locks or provided in new locks. More than one such pin may be used in a lock.
It is therefor an object of this invention to provide an improved pin tumbler lock employing a headed upper pin which is resistant to key bumping.
It is another and more specific object of this invention to provide a key bump resistant pin tumbler cylinder lock having a headed pin with a reduced diameter portion projecting from the pin head, the reduced diameter portion surrounded by a coil spring bottomed against an under surface of a pin head.
It is another and more specific object of this invention to provide an improved key bumping resistant pin tumbler cylinder lock retrofit comprising a headed pin having an enlarged head portion at one end of a cylindrical body portion, the head having an outer diameter approximately normal for pins received in upper pinholes in such locks, the cylindrical body portion having a smaller diameter than the pin head and projecting therefrom, a coil spring received around the cylindrical body portion and extending beyond an end of the cylindrical body portion remote from the head, the coil spring being bottomed against the undersurface of the head of the pin.
It is another of this invention to provide a unique pin and coil spring combination for use in pin tumbler cylinder locks having pinholes for receipt of pins, the unique pin having a head of relatively short axial distance and a diameter approximately normal for receipt in normal pinholes, a projecting cylindrical body portion extending from an under surface of the pin head, a coil spring received around the body portion and bottomed against an under surface of the pin head, the coil spring extending beyond an axial end of the body portion remote from the head, the coil spring having an outer diameter approximately the same as the diameter of an upper pin or spring which would be normal to the pinhole of the lock.
Other objects, features and advantages of this invention will be apparent to those of ordinary skill in the art from the following detailed description of a preferred embodiment.
A standard pin tumbler cylinder lock is shown in
While such pin cylinder locks are extremely common and provide adequate security in most instances, there is a known technique called key bumping which employs a key not having bittings cut to properly mate with the varying axial dimensions of the lower pins but which, in certain circumstances, can be used to open a standard pin cylinder lock. Key bumping causes the upper and lower pins to move into position with respect to the shear line such that by application of high torque to the key, the pins can be held in position to allow the lock to be opened.
This invention uses a headed pin and coil spring assembly 50 in at least one of the upper bores 30 to resist key bumping. The headed pin 51, best shown at
Because the spring can be longer than normal, since it extends all the way to the upper surface 54 of the head, and because it can be generally stiffer than standard pin springs, the resistance to movement of the pin assembly 50 is greater than normal pin assemblies. 5 Preferably the overall pin and spring assembly 50 will be such that in the uncompressed or slightly compressed condition of the spring the pin will project into the cylinder pinhole, in the absence of key, as will a length of the spring 60. In this manner, the spring itself acts as an anti-rotation element substantially the same as upper pins. The length of the reduced diameter section 52 is short enough to allow full travel of the pin 51 to the shear line point where the under surface 55 of the pin 51, lying in contact with and opposition to its associated lower pin will be positioned along the shear line as shown in
Surprisingly it has been determined that the use of a headed pin and spring combination such as shown in
It will be apparent to those of ordinary skill in the art that the particular dimensions both axially and radially of the spring, the reduced diameter section 52 and the head 53 as well as the axial length of the spring can be subject to modification to properly fit and work within a given lock. Other variations of this invention are also within the level of ordinary skill of persons within the art, and for example instead of a coil spring, and compressible elastomaric material spring can be used having a bore for receipt of the reduced diameter section 52.
