Patent Publication Number: US-6908126-B2

Title: Enhanced security catch assembly for retaining a handle on a spindle

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to devices that attach a door handle to a spindle on a lock mechanism to prevent the handle from being removed. More specifically, this invention relates to catch assemblies that prevent the handle from being removed when the lock mechanism is in the locked state and allow the handle to be removed when the lock mechanism is in the unlocked state. 
   2. Description of Related Art 
   Door locks are typically provided with a catch assembly that prevents the outer handle from being removed from the outer spindle when the door is locked. A conventional catch assembly includes a spring loaded catch oriented perpendicular to the spindle on the lock. The catch can be pressed inward when the door is unlocked to allow the base of the handle to slide over the catch and on or off the spindle. A retaining opening, such as a hole or slot to match the catch, is formed in the base of the handle perpendicular to the spindle. As the handle slides into position on the spindle, the retaining opening reaches alignment with the catch, allowing the catch to spring outward and engage the handle. 
   The handle cannot be removed until the catch is again pressed to the inward position. The retaining opening extends through the handle base so that the catch can be disengaged. Provided that the door is unlocked, the catch can be pressed inward against its spring pressure by inserting a tool into the retaining opening from the outside to apply inward pressure against the end of the catch. 
   When the door is locked, however, a lock element moves underneath the bottom end of the catch to prevent the inward motion necessary to remove the handle. This prevents the catch from being disengaged from the retaining opening in the handle base and thereby prevents the handle from being removed while the door is locked. 
   Although this system is quite effective, and is very widely used in bored lock designs, it is susceptible to a determined brute-force attack. The security of the catch assembly depends upon the strength of the catch and the support of the underlying lock element to prevent the catch from being driven inward. There are specialized tools available to locksmiths that can apply extreme force to the catch through the retaining opening in the handle base. The force available is sufficient to axially collapse the catch and/or crush the underlying lock element that supports the catch against inward motion. The catch is thereby forced out of engagement with the handle base, allowing the handle to be removed even though the lock mechanism remains in the locked state. Removing the handle allows access to the lock mechanism, which may permit the locked door to be opened. 
   Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a catch assembly for retaining a handle on a spindle that provides increased resistance to brute-force attacks. 
   Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. 
   SUMMARY OF THE INVENTION 
   The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention, which is directed to a catch assembly for securing a handle to a spindle of a lock mechanism. The catch assembly engages a retaining opening in the handle and prevents the handle from being removed from the spindle except when a disengage opening in a moveable lock element is in a predetermined position relative to the catch assembly. Generally, the moveable lock element is in that position only when the lock mechanism is unlocked so that the handle cannot be removed when the lock mechanism is locked. 
   The catch assembly includes a base and a threaded retaining pin. The base has a threaded opening axially aligned with the retaining opening in the handle when the handle is mounted on the spindle. The retaining pin includes a head end adapted to receive a tool for rotating the retaining pin through the retaining opening, a bottom end opposite the head end, and a threaded body between the head end and the bottom end. 
   The diameter of the threaded body is greater than the diameter of the retaining opening through which the head end of the pin is accessed by the tool so that threaded body will not pass through the retaining opening and the pin cannot be removed through that opening. The threaded body engages the threaded opening in the base and the retaining pin moves axially between an outward position and an inward position as the tool rotates the pin. In the outward position the head end of the pin engages the handle to prevent removal of the handle. In the inward position the bottom end of the pin must extend into the disengage opening in the moveable lock element. 
   The retaining pin has sufficient length that the head end always engages the handle when the bottom end is not in the disengage opening. The bottom end cannot, enter the disengage opening of the moveable lock element unless the moveable lock element is in the predetermined position, which may correspond to the unlocked position for the lock mechanism, or which may be a special position reachable by rotating a key in the lock mechanism. 
   In the preferred embodiment of the invention, the head end of the retaining pin is a torque limiting head that limits the torque that can be applied to rotate the retaining pin. This prevents the pin from being forced out of the retaining opening by turning it in the threads of the base under a high torque. The torque may be limited by a special shape or construction for the head and/or it may be limited by the material properties of the head. 
   In another aspect of the invention, the head end of the retaining pin is softened. This causes the head end to mushroom out under impact or high axial forces into engagement with the retaining opening in the handle. This locks the handle onto the spindle. The softened head end may also be used to provide torque limiting alone or in combination with a special shape for the head of the pin. 
   The base of the catch assembly may be a separate element attached with a screw or other fastener, or it may be integrated into the spindle or another element of the lock mechanism. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. 
     The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
       FIG. 1  is a perspective, partially exploded, view of a handle, a spindle (comprising part of a lock mechanism) and a catch mechanism according to the present invention installed on the spindle. 
       FIG. 2  is another perspective view of the handle, spindle and catch mechanism of  FIG. 1  except that the items shown are more completely exploded to show component parts. 
       FIG. 3  is a top plan view of the catch assembly according to the present invention. 
       FIG. 4  is a cross-sectional view of the catch assembly of  FIG. 3  taken along the line  4 — 4  in FIG.  3 . The retaining pin is shown in the inward position, which allows the handle to be removed or installed. The relative locations of surfaces of the handle base, the retaining opening in the handle base, the movable lock element and the disengage opening in the lock element are all shown in phantom. The bottom end of the retaining pin is shown extending into the disengage opening. The disengage opening is shown in phantom in the position it reaches when the lock mechanism is unlocked. 
       FIG. 5  is another top plan view of the catch assembly, similar to  FIG. 3 , except that the retaining pin is shown turned 90 degrees from the orientation in FIG.  3 . The retaining pin is in the outward position, but this can be seen only in FIG.  6 . 
       FIG. 6  is a cross-sectional view of the catch assembly, similar to  FIG. 4 , taken along the line  6 — 6  in FIG.  5 . This view shows the retaining pin in the outward position with the head end of the retaining pin extending into a retaining opening in the handle, shown in phantom. The shape of the head end of the retaining pin can be seen which provides a torque limiting function. The lock mechanism has been locked in this view, which rotates the underlying lock element with the disengage opening. Accordingly, the disengage opening is not aligned with the retaining pin and cannot be seen in this view. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
   In describing the preferred embodiment of the present invention, reference will be made herein to  FIGS. 1-6  of the drawings in which like numerals refer to like features of the invention. 
     FIG. 1  shows a handle  10 , a spindle  12 , a rose  14 , a lock cylinder  16  and a key  18 . The specific spindle  12  that is illustrated is part of a unique high security lever handle lock mechanism of the type sold by Sargent Manufacturing Company under the trademark “11-Line,” which is the subject of U.S. patent application Ser. No. 09/772,268 filed Jan. 29, 2001. However, the spindle may be any generic lock mechanism of the type that attaches a handle to a spindle. 
   The term “spindle” as used herein is intended to include “rollups,” “sleeves,” and any other type of lock mechanism element to which a handle may be connected to operate the lock mechanism. 
   The catch assembly of the present invention includes a base  20  and a retaining pin  22 . The retaining pin  22  can move inward or outward along the line indicated by arrow  24 . When the retaining pin  22  is in the outward position, it engages a retaining opening  26  in the handle  10  (see  FIGS. 4 and 6 ) located approximately at the position indicated by reference No.  28  in FIG.  1 . 
   The engagement between the pin  22  and the retaining opening  26  prevents the handle  10  from being removed from the spindle  12 . In order to remove the handle  10  from the spindle  12  it is necessary to move the retaining pin  22  inward to disengage it from the retaining opening  26 . 
   Referring to  FIG. 2  it can be seen that the retaining pin  22  includes a head end  22   a , a threaded body  22   b  and a bottom end  22   c . The base  20  includes a threaded opening  30  that receives the retaining pin  22 . The retaining pin  22  can be moved between the inward position and the outward position by rotating the head end  22   a  with a tool that extends through the retaining opening in the handle  10 . 
   The base  20  also includes an attachment opening  32 . In the design illustrated, a screw  34  extends through opening  32  and attaches the base  20  to the spindle  12 . Alternatively, the base may be integrated into the spindle or some other element of the lock mechanism. 
   Although a specific design for a lock mechanism is shown in  FIGS. 1 and 2 , the invention may be used in any lock having a spindle and a removable handle. The operation of different lock mechanisms varies widely and need not be understood in detail to understand the operation of the catch assembly of the present invention and its interaction with different types of lock mechanisms. When key  18  is turned, it operates lock cylinder  16 , which rotates the key tail  36 . The key tail  36  rotates movable lock element  38 , which includes a disengage opening  40 . As lock element  38  turns, the disengage opening  40  is moved into and out of position beneath the retaining pin bottom end  22   c.    
   For this invention to be implemented into another type of lock mechanism in which a handle is removed from a spindle, it is simply required that a disengage opening in a lock element be moveable into and out of position below the retaining pin. Many lock mechanisms already have a lock element of this basic type that interacts with a conventional catch. 
   In order for the retaining pin  22  to move to the inward position, the disengage opening  40  must be located below the pin so that the bottom end  22   c  of the pin can enter the disengage opening  40 . This allows the head end  22   a  to move out of engagement with the retaining opening  26 , which frees the handle. 
     FIGS. 3 and 4  illustrate the catch assembly of the present invention with the retaining pin  22  in the inward position and show the lock mechanism unlocked.  FIGS. 5 and 6  illustrate the catch assembly with the retaining pin  22  in the outward position and the lock mechanism locked. As can be seen in  FIG. 4 , with the retaining pin  22  in the inward position, the head end  22   a  is disengaged from the retaining opening  26  in the handle  10 . This allows the handle  10  to slide off the spindle  12  in the direction indicated by arrow  42 . 
   As can also be seen in  FIG. 4 , in order for the retaining pin  22  to move to the inward position, the disengage opening  40  in the movable lock element  38  must be axially below the retaining pin  22 . This is the “predetermined position” for the movable lock element  38 . The lock element  38  is in the predetermined position when the lock mechanism is unlocked or when the key  18  is inserted and the lock cylinder  16  is rotated to a special position that does not correspond to the normal locked position. 
   As can be seen in  FIG. 6 , which shows the lock element  38  in the locked position and the retaining pin  22  in the outward position, the head end  22   a  of the retaining pin  22  extends into the retaining opening  26 . This prevents the handle  10  from moving in the direction indicated by arrow  42 , which prevents it from being removed. As can be seen by comparing  FIGS. 4 and 6 , the retaining pin  22  is sufficiently long that the head end  22   a  of the retaining pin always engages the retaining opening  26  in the handle  10  when the bottom end  22   c  is not in the disengage opening  40 . Further, the bottom end  22   c  cannot enter the disengage opening  40  of the moveable lock element unless the door is unlocked, which puts the moveable lock element in the predetermined position and aligns the disengage opening  40  below the retaining pin  22 . 
   The catch assembly of the present invention provides four distinct features that operate to prevent the retaining pin  22  from being disengaged from the retaining opening  26  in the handle  10 . The first such feature resists a simple brute-force attack in which an axial force is directly applied to the head end  22   a  of the retaining pin. Such extreme forces can be generated by available locksmith tools that apply a leveraged crushing force or by impact through a hammer and punch. 
   The axial force is dissipated and transferred from the retaining pin to the base through the threaded engagement between them. It is substantially impossible to drive the threaded pin axially through the base without rotating it in the threads. The base is well supported by the spindle to resist such a brute force attack. No force is directly applied to the lock element  38  or the bottom end  22   c  of the pin. 
   In a prior art catch assembly the retaining pin slides within the base, and is not connected with threads. Thus, in such a prior art design, the applied forces must be directly resisted by the lock element  38  and by the resistance to axial compression of the bottom end  22   c  of the retaining pin. If either of these elements fail, the applied force will drive the retaining pin out of the retaining opening  26 , which allows the handle to be removed. By transferring the applied force to the base through the threaded engagement with the retaining pin and from there to the spindle  12 , the applied force is distributed evenly and security is improved. 
   A second preferred security feature of the invention is that the head end of the retaining pin  22  may be softened relative to the rest of the pin, which is preferably made of hardened steel. When a force is applied axially to the head end of the retaining pin  22 , such as by striking it with a hammer through a hardened steel punch, the softened steel head of the pin  22  is sufficiently ductile that it mushrooms outward into locking engagement with the handle  10  in the retaining opening  26 . This spreading action of the head end  22   a  securely attaches the retaining pin to the handle  10  and prevents the handle from being removed. 
   A third security feature of the invention is that the head end  22   a  of the retaining pin  22  is given a smaller diameter than the diameter of the body portion  22   b  with the threads. This prevents the retaining pin from being unscrewed out through the retaining opening  26  and removed. The body portion  22   b  is given a diameter sufficiently greater than the diameter of the retaining opening  26  that there is no tendency for the threads on the body portion  22   b  to begin to tap into the handle  10  in the retaining opening  26 . The threaded length of the pin is set based on the distances of the underlying lock element  38  and the overlying handle so that the pin is captured between the handle above and the lock element below and cannot be completely unthreaded in either direction with the handle installed. 
   As can be seen in  FIGS. 3-5 , the head end  22   a  includes a slot  44  that allows the retaining pin to be turned by inserting a small flat blade screwdriver through the retaining opening  26  into engagement with the slot  44 . When the screwdriver is rotated the pin  22  turns and moves between the inward position seen in FIG.  4  and the outward position seen in  FIG. 6. A  fourth security feature of the invention is the torque limiting head design that can be seen by examining the cross-sectional shape of the torque limiting head end  22   a  in FIG.  6 . 
   The retaining pin in  FIG. 6  is shown turned 90 degrees relative to the retaining pin in FIG.  4 . As can be seen in  FIG. 6 , the slot  44  is not flat at the bottom, but instead, is curved upwards at the outer edges near the circumference of the pin. The bottom has a radius of curvature that automatically limits the depth that a wide flat blade screwdriver can penetrate into the slot  44 . The wider the screwdriver, the shallower the entry into the slot. 
   The torque that can potentially be applied to a retaining pin increases as the width of the screwdriver increases and as the depth of the slot increases. With the special shape for the slot  44  shown in  FIG. 6 , the torque that can be applied to the retaining pin is limited to a value below the torque needed to force the pin out of opening  26  when opening  40  is not below the pin  22 . 
   The torque limiting function is also aided by the optional softening of the steel head, as described above, which allows the head to deform when excess torque is applied. By limiting the torque that can be applied, the retaining pin  22  cannot be forcibly turned and driven down into the lock element  38  out of engagement with the handle  10 . 
   The specific torque limiting design shown in  FIGS. 3-6  for the head end of the retaining pin is only one possible design from among many designs that can provide the desired torque limiting function. For example, the head end may include a plastic insert, or a small diameter hexagonal or other shape opening may be used to limit the torque that can be applied to the pin by a tool extending through the retaining opening  26 . 
   While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.