Lock conversion mechanism

A safety device is disclosed for converting the inside cylinder of a double cylinder deadbolt assembly to one which captivates a key inserted into the assembly to permit it to rotate to operate the deadbolt. The device prevents removal of the inside key under normal circumstances. This is accomplished by a base member, which is attached to the face of the inside cylinder or cylinder lock assembly. The base member has a circular opening in it, defined by an inwardly-turned shoulder. A key-holding member is rotatably captured between the shoulder of the base member and the face of the cylinder lock assembly, when it is secured to the face of the lock assembly, to permit insertion and rotation of a key in the lock assembly. The key-holding member includes a device for securing the key against removal from it when the assembly is in place. No modification of the cylinder lock assembly is necessary.

BACKGROUND 
To significantly improve the security of homes and business against 
break-ins by unauthorized persons, double-cylinder lock deadbolts are 
widely used Insurance companies and police highly recommend the use of 
such locks as a deterrent to burglaries. The greatest security is obtained 
from double-cylinder locks, which are key operated from both the inside 
and outside of the door in which they are placed. When the bolt is engaged 
(that is, when the door is locked) and both keys are removed, a 
significant deterrent against break-ins is provided. 
When a key in the inner cylinder is used, however, a safety hazard is 
presented to the occupant of the dwelling if the bolt of the lock is 
engaged and the key is removed from the cylinder. In the event of a fire, 
or if for any other reason the occupants need to leave the room or 
building quickly, the time required in a panic situation to locate a key 
to release the lock, could result in a disaster. 
Consequently, in some areas laws have been enacted which prevent locksmiths 
from installing double-cylinder key operated deadbolts, because of this 
fire or panic danger. The inside of a deadbolt lock typically then is 
provided with a permanently affixed handle to permit its operation While 
the level of protection against unauthorized use of the door is reduced 
when a handle permanently affixed to the inner operation of the deadbolt 
is used, the safety problem is alleviated. 
Many dwellings, particularly homes, already exist, which have a key 
operated cylinder on the inside of a double-cylinder deadbolt. It is 
expensive to replace such a lock with a non-key operated lock, and many 
cases it is necessary to replace the entire locking mechanism if the key 
operated inner cylinder is no longer desired. 
Some efforts have been made to retain the inside key in a double-cylinder 
deadbolt lock, whenever the occupants of the dwelling are located inside 
the dwelling, to prevent it from being missing in the event of an 
emergency such as a fire when the persons inside the building desire to 
leave quickly. This has been accomplished by specially designed lock 
mechanisms, for example the lock mechanism shown in the Oliver U.S. Pat. 
No. 4,315,420. That lock mechanism is designed with a mechanical latch in 
it to engage with a notch on a specially designed inside key, to retain 
the inside key at all times in the lock unless removal of the key is 
desired. Such removal is effected by operation of a cam on the key plug on 
the outside locking cylinder. A problem with the lock mechanism of this 
patent, however, is that it is a specially designed lock mechanism. It is 
not a standard double-cylinder deadbolt lock. 
Another patent, which uses a non-standard lock mechanism to trap the key on 
the inside lock, is disclosed in the patent to Allemann U.S. Pat. No. 
4,109,496. This mechanism is designed so that whenever the deadbolt is 
extended to a locked position, the inside key cannot be removed from the 
lock. Consequently, the lock provides the desired safety features; but, 
again, a non-standard specially designed double-action lock must be used. 
Two older patents, to Helms U.S. Pat.No. 2,441,067 and Kindler U.S. Pat. 
No. 2,528,757, disclose a rotating arm for captivating old-fashioned keys 
in the keyhole of a deadbolt lock. This prevents removal of the key. The 
lever arm extends close to the shaft of the key in the device of Kindler, 
and blocks the operating end of the key from being withdrawn from the 
keyhole. This is possible with keys of this type, since they are not 
modern keys, and the operating part of the key is substantially wider than 
the shaft. Consequently, a simple swinging lever retains the key. 
The device of Helms is directed to the same type of key as used in the 
device of Kindler, but includes additional apparatus which is clamped to 
the shaft of the key to provide means for turning the key. These devices 
would not work with keys of the type currently used for deadbolt locks, 
since the keys currently used do not have an elongated shank on them, 
which is necessary for the devices of Kindler and Helms. 
It is desirable to provide a lock conversion mechanism to retain the key in 
the key operated cylinder of a deadbolt lock, which can be used on 
conventional deadbolt locks without modifying the lock in any way, and 
which is simple in structure, simple to use, and simple to install. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved lock conversion 
mechanism. 
It is another object of this invention to provide an improved mechanism for 
captivating the key of a key operated cylinder of a deadbolt lock. 
It is an additional object of this invention to provide a key-holding 
member, which is secured to the face of a deadbolt lock cylinder. 
It is further object of this invention to provide an improved lock 
conversion mechanism for the inside cylinder of a deadbolt lock, which is 
secured to the lock cylinder without requiring modification of the 
cylinder, and which rotatably secures the key for operation of the 
deadbolt lock while preventing removal of the key from the mechanism. 
In accordance with a preferred embodiment of this invention, a mechanism 
for retaining the key in the key operated cylinder of a deadbolt lock is 
provided This is accomplished by means of a base member, which is secured 
to the face of the key operated cylinder lock assembly, typically by means 
of the screw or screws which hold the lock assembly together on the door 
with which it is used. The base member has a circular opening in it, 
defined by an inwardly turned shoulder, which is spaced from the face of 
the cylinder lock assembly when the base member is secured to the lock 
assembly. A key holding member then is rotatably captured between the 
shoulder of the base member and the face of the cylinder lock assembly to 
permit insertion and rotation of a key in the key operated cylinder. The 
key is secured in the key holding member to prevent its removal from the 
key holding member; so that it is retained in the key operated lock 
cylinder to which the lock conversion mechanism is attached.

DETAILED DESCRIPTION 
Reference now should be made to the drawings, in which the same reference 
numbers are used in the different figures to designate the same 
components. FIG. 1 is an illustration taken from the end of a door 10, 
showing the installation of a typical double-cylinder key operated 
deadbolt lock having a deadbolt 14 extending from a plate 11 mounted in 
the edge of the door. The lock has two operating cylinders 16 and 18 
located on the inside and the outside, respectively. A key 20 is inserted 
into either of the cylinders 16 or 18 to operate the bolt 14 from either 
side. This is a standard commonly used lock in widespread use today. 
The lock of FIG. 1 also is shown in FIG. 2, which, additionally, shows the 
use of an elongated bolt 24 extending through the face of the cylinder 16 
on the inside of the lock to secure the two portions of the 
double-cylinder locks 16 and 18 together with the locking mechanism for 
operating the bolt 14. The bolt 24 clamps the cylinders 16 and 18 to the 
opposite surfaces of the door 10 in a conventional manner, and is used to 
hold the lock mechanism in place on the door 10. The arrangement shown in 
FIG. 2, using a single bolt 24, is of a standard widely used lock. Many 
double-cylinder deadbolt locks, however, use two spaced-apart bolts, such 
as the bolts 24', shown in dotted lines in FIG. 2, to secure the lock 
together. It should be understood that the ensuing description directed to 
the specific lock cylinder 16 shown in FIG. 2 also can be applied to a 
lock cylinder which is secure with two or more bolts 24 of the type 
illustrated in FIG. 2. 
A preferred embodiment of the invention for converting the key operated 
inner cylinder 16 of the double-cylinder deadbolt lock to one which is 
similar to a standard lever-operated inner cylinder (in FIGS. 2, 3 and 4). 
This embodiment includes a base member having an outer ridge 30, and an 
inwardly turned flange 31, with a circular opening in its center. Inserted 
into the circular opening is a key holding member 25, with an outwardly 
turned flange 26 on it spaced downwardly from the face of the member 25. 
The details of the assembled device shown in FIG. 2 are readily apparent 
from the cross-sectional view of FIG. 3, and the exploded view of FIG. 4. 
The device is assembled, as illustrated in FIG. 4, where the base member 30 
has three (or more) legs or tabs 35, 37 and 40 extending from it. Each of 
the legs has a corresponding hole 36, 38 and 41, respectively, as shown 
most clearly in FIG. 4. The key holding member 25 is inserted into the 
circular opening in the center of the flange 31 of the device 30 to the 
position illustrated in FIGS. 2 and 3. It is especially apparent from FIG. 
3 that the flange 26 underlies the shoulder 31 to prevent withdrawal of 
the member 25 outwardly through the hole in the shoulder 31 of the base 
member 30. After the key holding member 25 is in place, the legs 35, 37 
and 40 are bent inwardly, as shown in FIGS. 2 and 3, to underlie the 
flange 26 on the device 25. 
Once the base member 30 and the key holding member 25 are assembled 
together, they may be placed on the front face of the inner lock cylinder 
16. This is accomplished by removing the bolt 24 to the position shown in 
FIG. 2, and in FIG. 3. The bolt 24 is inserted through one end of an 
elongated slot 28 in the face of the key holding member 25. The slot 28 is 
sufficiently wide to permit the shank of the bolt 24 and the head of the 
screw to pass fully through it. The length of the slot 28 is chosen to 
overlie the bolt hole (or holes) in the face of the cylinder 16 when the 
member 25 is rotated to cause the slot 28 to assume a vertical orientation 
(not shown in FIGS. 2 and 3). The shank of the bolt 24 then is passed 
through a hole in one of the inwardly bent legs 35, 37 or 40, such as the 
hole 36 in the leg 35, and is aligned with the bolt opening in the lock 
cylinder 16, which is normally used to insert the bolt 24. The bolt 24 
then is tightened through the hole 36 in the leg 35 to the point where the 
head of the screw firmly pulls the leg 35 into tight engagement with the 
face of the inner cylinder 16 of the deadbolt lock to secure the assembly 
in place on the face of the lock. In this position, sufficient space is 
provided between the in-turned legs 35, 37 and 40 of the member 30 and the 
shoulder 31 to permit free rotational movement of the key holding member 
25 in the base member 30, which is held firmly against the face of the 
inner cylinder of the deadbolt lock by the bolt 24. 
The next step is to insert two key retaining plates 50 and 60 into the 
elongated slot 28 cut in the face of the key holding member 25. These two 
plates are loosely held in place by tilting them slightly to insert a pair 
of outwardly facing tabs 51 and 61 through a slot 28 into the position 
shown in FIGS. 2 and 3. The width of the slot 28 and the length of the 
tabs 51 and 61, which extend perpendicularly to the faces of the plates 50 
and 60, are selected to permit this ready insertion and removal of the two 
plates 50 and 60 from the slot 28. 
The slot 28 is selected to permit alignment of the center of the slot with 
the keyhole opening 21 in the face of the inner cylinder 16 of the 
deadbolt lock mechanism. Consequently, a key 20 may be inserted between 
the plates 50 and 60 to the position shown in dotted lines in FIG. 3. The 
hole 27 through the end of the key 20 is aligned with a pair of slots 53 
and 63 in the plates 50 and 60. A bolt 70 then is passed through the slots 
53 and 63 and through the hole 27 in the key 20, and is secured in place 
by means of a nut 71, as illustrated in FIG. 3. This is done after the key 
20 is inserted fully into the keyhole opening 21 in the lock. 
Consequently, the key, along with the plates 50 and 60 and key holding 
member 25, may be rotated in a normal manner to engage and disengage the 
bolt 14 of the lock. Accidental removal of the key 20 from the device, 
however, will not occur, since it is firmly held in place by means of the 
bolt 70 and the nut 71. Alternatively, if the permanent attachment of the 
key 20 to the key retaining member 25 is desired, it may be braised, 
soldered, or otherwise permanently secured between the plates 50 and 60; 
so that the key cannot be removed unless the entire mechanism is removed. 
It should be noted that the head of the bolt 24 is seated into a chamfered 
recess in the hole 36; so that it is clear of any interference, either 
with the shoulder 26 or any other part of the rest of the key retaining 
member 25 which is held in place by the base member 30. 
The plates 50 and 60 also may be made larger to completely cover the end of 
the key 20. The outer edges of these plates then may be provided with 
facing ribs to abut one another; so that no gap between the plates is 
present when they are drawn together by the bolt 70 to hold the key 20. 
Reference now should be made to FIGS. 5 through 8, which illustrate another 
embodiment of the invention. The embodiment shown in FIGS. 5 through 8 is 
similar to the embodiment shown in FIGS. 2, 3 and 4, with the exception 
that the functions of the key holding member 25 and the plates 50 and 60 
are combined together in a key holding member comprising a pair of plates 
100 and 120, thereby effectively eliminating the separate rotatable key 
holding member 25 of the embodiment of FIGS. 2, 3 and 4. In all other 
respects, the embodiment of FIGS. 5 through 8 operates in the same manner 
as the one shown and described above for FIGS. 2, 3 and 4. 
FIG. 5 illustrates a fully assembled perspective view of a lock conversion 
mechanism; and the structure of that mechanism is illustrated in detail in 
the exploded view of FIG. 8, and the vertical and horizontal 
cross-sectional views of FIGS. 6 and 7. The base member of the mechanism 
shown in FIGS. 5 through 8 includes an outer edge 30, and an inwardly 
turned flange 31 with a circular opening in its center. This is same as 
the base member used in the embodiments of FIGS. 2 through 4. In place of 
the three inwardly turned legs or tabs of the embodiment shown in FIG. 4, 
however, the base member of FIG. 6 has six inwardly turned tabs 90 
abutting one another to form a circular opening in the center. This 
opening obviously is smaller than the circular opening formed by the 
flange 31. Tapered holes 91 then are formed in each of the tabs 90 to 
accommodate the shank of a corresponding bolt 24A or 24B, as illustrated, 
to secure the base member to the face of the cylinder 16 in the same 
manner described above for the embodiment shown in FIG. 2. The manner in 
which this attachment is effected is indicated in FIGS. 6 and 8. 
In place of the three parts 25, 50 and 60 described previously, the device 
shown in FIGS. 5 through 8 includes two key retaining plates 100 and 120, 
having outwardly turned semicircular legs or tabs 101 and 121, 
respectively, on them. As is readily apparent from an examination of FIGS. 
5, 6 and 8, the plates 100 and 120 each have shoulders (103 and 104 for 
plate 100; and 123 and 124 for the plate 120) which overlie the outer 
surface of the flange 31 on the base member. The width of the semicircular 
tabs 101 and 121, at the point where these two tabs are attached, 
respectively, to the plates 100 and 120 is less than the diameter of the 
circular opening formed by the shoulder 31 in the base member. This 
permits the tabs 101 and 121 to be inserted beneath the shoulder 31, with 
the plates 100 and 120. The plates then are moved apart, respectively, to 
place the tabs 101 and 121 beneath the shoulder 31 in the space between 
the shoulder 31 and the surface of the legs 90. 
After the tabs 101 and 121 are inserted into place into the positions shown 
in FIGS. 5, 6 and 7, the key 20 is inserted between the plates 100 and 
120, as shown most clearly in FIGS. 6 and 7. It is to be noted that the 
plates 100 and 120 have recesses 106 and 126, respectively, formed in them 
to provide a space for the head of the key 20 while the outer edges of the 
plates 100 and 120 abut one another to form a closed, attractive 
appearance to the overall structure, as seen most clearly in FIG. 5. When 
the key 20 is in place and is fully inserted into the opening 21 of the 
lock, a bolt 70 is passed through slots 108 and 128 in the plates 100 and 
120, respectively, and through the hole in the key. The bolt 70 then is 
secured tightly in place by means of the nut 71 (FIGS. 7 and 8) to secure 
the entire assembly together. 
The key may be rotated by rotating the composite structure formed by the 
key 20 and the plates 100 and 120 to lock and unlock the door. The tabs 
l01 and 120, however, prevent withdrawal of the key from the inner 
cylinder of the deadbolt lock, producing the same effect as is 
accomplished by the embodiment described previously in conjunction with 
FIGS. 2, 3 and 4. 
FIGS. 9 and 10 are top and bottom views, respectively, of a variation of 
the device shown in FIG. 8. Instead of having six adjacent inwardly bent 
legs 90 to form the surface of the base member for attachment to the face 
of the lock cylinder 16, a single piece solid-formed ring 80 is used. 
Tapered holes 81 then are formed, as illustrated, to accommodate the bolts 
24A and 24B (or a single bolt, or more than two bolts, as required) to 
secure the base member to the face of the lock cylinder 16. The operation 
of the device is the same as the one described above in conjunction with 
FIG. 8. 
FIG. 11 is yet another variation of the attaching portion of the base 
member, which is similar to the one shown in FIGS. 9 and 10, which has a 
flange 80A, in which two opposing arcuate slots 83 and 85 are used in 
place of individually drilled holes 81 of the type shown in FIGS. 9 and 
10. The slots 83 and 85 have tapered edges to act as a countersink for the 
heads of the bolts 24A and 24B; but the operation of the device is the 
same as described above in conjunction with all of the other embodiments. 
Although the structure of the base member 30, which is illustrated, is 
simple to manufacture and install, the manner of capturing the key holding 
member 25 in the base member 30 may be effected by other structures or 
manufacturing techniques, if desired. For example, a rolled edge or 
shoulder may be formed on the opposite edge of the flange 30 from the 
shoulder 31 to captivate the flange 26 of the member 25 (or the tabs 101 
and 121) in place after it has been inserted to the position shown in 
FIGS. 2 and 3. It is necessary, however, that whatever structure for the 
base member 30 is chosen, a provision needs to be made to permit it to be 
secured to the face of the inner cylinder 16 of the lock. The bolt 24 is a 
convenient and readily available technique for securing the base member 30 
to the face of the lock. The base member 30, however, also could be 
permanently attached to the face of the lock by means of brazing, welding 
or suitable adhesives, if so desired. Various changes and modifications 
will occur to those skilled in the art without departing from the true 
scope of the invention, which is defined in the appended claims. 
The above description of the preferred embodiment is to be considered 
illustrative of the invention, and not as limiting.