Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to door lock mechanisms, and
particularly to a driver for connecting a doorknob or the
like to a bolt-retracting knob sleeve and adapted to shear
under conditions of excessive torque to prevent the
transmission to the lock mechanism of excessive torque
applied to the doorknob. As used berein, the term knob is
intended to include a lever handle.
Door locks are subject to attack by the exertion of
high torque on the doorknob sufficient to damage or override
the lock mechanism and thus to jeopardize the security of the
lock. Lever handle knobs are particularly Rusceptible to the
application of such excessive torque, since a strong person
may be able to manually twist the lever handle with
sufficient force to apply such high torque, and lever handles
are also liable to attack by the application of force with
the use of a tool applied to the projecting lever of the
handle. Nevertheless, lever handle knobs are desirable and
in some cases mandatory to facilitate operation of door locks
by handicapped or other persons who are not able to grip and
turn a round knob.
Door lock Dechani~ms may include a positive
^, driver of the type shown in U.S. Patent No.
4,394,821, to provide a positive drive between
the door knob and the knob sleeve.
Application of excessive torque to the lever handle of such a
mechanism can rotate the knob sleeve through the driver to
break or override the locking lug which normally limits lock
operation to use of a proper key, and thus open a locked
door.
Alternatively, door lock mechanisms may include a
torgue-releasable driver of the type shown in
U.S. Patent No. 4,655,059, and more
fully shown in our U.S. Patent No. 4,394,821.
The tor~ue-releasable driver is biased to its
engaged position to connect the doorknob to rotate the knob
; sleeve under normal operating torque, but releases under
excessive torque to permit the knob to rotate with respect to
the knob sleeve, and thus to prevent damage and improper
operation of the lock mechanism. Following such interruption
of the drive connection, the knob can be rotated to a
; position where normal drive connection is re-established, as
it more fully explained in U.S. Patent No.
4,655,059.
With a round knob there it a rela-tively wide margin
between the torque which can be applied manually to the knob
and the torque nece6~ary to damage the lock mechanism, and
torque-releasable drivers can effectively transmit manual
torque with little likelihood of release under normal
; operating conditions. With a lever handle, on the other
hand, there is a relatively narrow margin between the torque
which can be applied manually in ordinary u6e and the torque
that will damage the lock. Accordingly, it l desirable with
lever hand}es to control such ~ore-closely the torque at
which the handle will be released from its driving connection
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to the knob sleeve. The present invention provides such
close control, by utilizing a break-away driver which will
transmit a high torque for normal operation but will break
away under a predetermined higher torque below what is likely
to damage or override the lock mechanism. The invention
further provides simple means for retaining the driver in
place during assembly and which permits easy replacement of a
driver which has been broken by excess force.
In accordance with the invention, a lever handle or
other desired knob is rotatably mounted on a knob sleeve or
the like and is connected to transmit torque to the sleeve by
a driver mounted transversely in the knob sleeve and having a
drive lug extending into engagement with a recess, preferably
an axial groove, in the knob. The lug is made of a material
and in such shape that it will shear or break away under a
predetermined drive torque applied to the handle.
Preferably, the driver is in the form of a generally
rectangular body which fits slidably in a slot at one side of
the knob sleeve and the lug is a narrower projection on such
body which fits slidably through a narrower slot in the
opposite side of the sleeve. The lug thus extends through
the wall of the knob sleeve and across the shear plane
between the cylindrical surfaces of the knob sleeve and knob,
and into the recess or groove in the knob. Torque
transmitted from the knob to the sleeve exerts shear stress
at such plane, and the lug is made so as to break away at
such shear plane and release the drive connection between the
knob and sleeve.
The driver may have a central opening to provide
clearance for a throw member connecting a key-operated key
plug to the roll-back cam which it operates. The driver is
desirably trapped in the knob sleeve when a knob is in place
on such sleeve, but is also desirably held in place by other
means for purposes of manufacturing assembly and to prevent
inadvertent loss during field service.
In further accordance with the present invention,
the driver is held in place by a resilient member, preferably
a ball of rubber or other resilient material mounted in a
hole in the driver which lies across the inner surface of the
knob sleeve. The ball is larger than the thickness of the
driver so that it projects from one or both sides of the
driver into resilient engagement with the inner edge of the
slot of the sleeve in which the wide body of the driver is
mounted. The driver is desirably held against movement in
the direction of the lug by shoulders on the driver body
which engage the opposite wall of the knob sleeve.
The accompanying drawings illustrate the
invention and show embodiments exemplifying the best mode of
carrying out the invention as presently perceived. In the
drawings:
Fig. 1 is a horizontal axial section of a
cylindrical lock mechanism in accordance with the invention
and having a lever handle as its knob;
Fig. 2 is a transverse section on the line 2-2 of
Fig. 1;
Fig. 3 is a section taken on the line 3-3 of jig. 1
showing a break-away driver which is positively held against
retraction and includes a break-away drive lug, the driver
being removably secured in the knob sleeve by a resilient
ball;
Fig. 4 is an isometric view of the break-away
driver as shown in Figs. 1 and 3;
Fig. 5 is a sectional view similar to Fig. 3 but
showing a positive driver releasably held in the knob sleeve
by a resilient ball; and
Fig. 6 is a section taken on the line 6-6 of
Fig. 3 showing the resilient ball holding the driver in the
knob sleeve.
The lock mechanism shown in Figs. 1, 2, and 3
comprises a door handle 10 having an outer hand-hold
portion 11 which carries a handle lever 12 and has a neck
portion 14 by which it is mounted on a generally
cylindrical knob sleeve 16. The sleeve is mounted for
rotation in a hub 18 fixed to a chassis side plate 20 of a
cylindrical lock mechanism, as more fully shown in Patent
No. 3,955,387. The inner end of the knob sleeve 16 carries
a roll-back cam 19 (110 in such patent) adapted to engage
a retractor for retracting the bolt of the door. A trim
ring assembly 22 is threaded on the outside of the hub 18
and extends outward into overlapping relation with the
neck portion 14. A key-actuated roll-back cam sleeve 24
iB rotatable mounted within the knob sleeve 16 and
carries at its inner end a second roll-back cam 25
(114 in the patent). For convenience of illustration,
the roll-back cams 19, 25 are shown only in Fig. 2 and are
not shown in Fig. 1. Also, in this and other aspects, the
showing in Fig. 1 may be considered somewhat diagrammatic
in that certain parts are shown in a rotational orientation
different from what they may take in the actual lock
mechanism.
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For purposes of locking the knob sleeve 16 against
rotation and thus to limit lock actuation to that provided by
key actuation of the cam sleeve 24, a locking lug bushing 26
(122 in the patent) is slidably mounted within the roll-back
cam sleeve 24. This carries at its inner end a locking lug
28 which in its normal position extends radially from the
bushing 26 outward across the end face of the knob sleeve 16
and into a notch in the hub, as more fully shown in said
patent. The bushing 26 is adapted to be moved outward
against its biasing spring, as by a thumbpiece on the
associated inside knob, to carry the locking lug 2~ into a
notch 30 in the end of the knob sleeve 16 so as to lock such
knob sleeve 16 against rotation relative to the hub 18. When
the knob sleeve is thus locked against rotation, the lock
mechanism may be operated by a key-operated core 32 mounted
in the handle 10 as more fully explained below. The core 32
is connected by a throw member 34 to the key-actuated cam
sleeve 24.
As shown, the handle 10 comprises a hollow body 36
which at its inner end forms the neck 14 of the handle and
which has an outward-extending body shell portion 38,
conveniently of cylindrical shape and having at its outer end
a flat end face 40. The inner face of the body shell is
desirably cylindrical and defines a circular end opening.
The neck portion 14 of the hollow body 36 includes
a relatively thick cylindrical portion 42 in rotative bearing
engagement with the outer surface of the sleeve 16. Inward
beyond such thick portion 42, the neck has a thinner portion
44 which is telescopically received between the trim ring
; 30 assembly 22 and the outer end of the hub 18.
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For purposes of retaining the handle 10 on the
knob sleeve 16, the knob body 36 is formed with a
circumferentially continuous radial face 46 at the outer end
of the thick portion 42. Such face is engaged by a
projecting lug 47 on a retainer 48 mounted for radial
movement in cro6s slots in the knob sleeve 16, and biased to
engaged position by a biasing spring 50, as more fully shown
in U.S. Patent No; 4,394,821.
The outward cylindrical shell portion 38 of `the
handle body 36 is telescopically received within a
cylindrical Hell 66 which extends from the rear of such body
Hell 38 forward past the end face 40. At its forward end,
such outcr shell 66 it formed with an inward-extending flange
6B desirably having an inner cylindrical wrface aligned with
the inner cylindrical surface of the body shell 38. Such
flange 68 has an inward end face 70 in spaced relation to the
end face 40 of the body Hell 38, so as to define
therebetween a radially inward-opening circumferenti31
groove 72.
The handle lever 12 is integral with the outer
Hell 66, and ùch shell 66 is fixed to the body 36 by a
pre~s-in pin 74, which it finished off flush with the surface
of the Hell 66, desirably located in the 6ame plane with the
handle lever 12.
An end face closure member 76 is rotatably mounted
in the end opening defined by the inner faces of the flange
68 and the body shell 38, and is rotatably locked in place by
a buried ring 80 which has a portion engaged in the groove
72. The face closure member 76 is formed with a figure-8
opening B2 for the reception of the key-operated core 32
containing a key plug coaxial with the handle body 36 and
knob sleeve 16 and connected to the throw member 34 so that
key operation of the key plug will rotate the throw member
34 to actuate the cam member 24 for retracting the latch bolt
of the lock mechanism.
Desirably, the face closure member 76 is formed
with a rearward-extending circular flange 84 which is
non-rotatably interlocked with the forward end of the knob
sleeve 16.
This rotative mounting of the face closure member
76 interacts with the break-away drive connection between the
handle and knob sleeve 16, in that it permits the handle to
rotate relative to the face closure member and hence relative
to the core 32 and knob sleeve 16 when excessive torque
breaks the break-away drive connection between the handle and
the knob sleeve.
In the embodiment of Figs. 1 and 3, a drive
connection between the handle 12 and the knob sleeve 16 is
formed by a break-away driver 52. The driver 52 has a
generally rectangular body portion 53 which is slidable
through and engaged in a relatively wide slot 54 at the
bottam of the knob sleeve 16. At its opposite end, the
driver 52 aarries a driving lug 56 which extends through an
opposite narrower slot 58 in the knob sleeve. The drive lug
56 includes a proximal portion integrally fixed to one end of
the body portion 53 and a distal portion which engages in an
axial groove 60 in the heavy wall 42 of the handle body 14 to
provide a drive connection between the handle and the knob
sleeve. The central body has side shoulders 55 adjacent the
lug 56 which engage against the inner face of the knob sleeve
16 at opposite sides of the slot 58, and has a central
opening 51 to clear the throw member 34.
To prevent excessive torque from being transmitted
between the lever handle 10 and the knob sleeve 16, the drive
lug 56 is weakened so as to break away or shear at the shear
plane between the handle portion 42 and the knob sleeve 16
when excessive torque is applied to the lever handle, and
then to allow that handle to rotate about the knob sleeve.
In the arrangement shown, the lug 56 is weakened by
forming it with an end recess 57 which leaves two upstanding
ears 59 at its sides which are designed to transmit full
normal operating torque but break away when a predetermined
torque is applied to the handle. To this end, the driver 52
is made of such material and the ears 59 have such a cross
section that under such predetermined high torque the lug 56
will break away in the shear plane between the handle body
portion 42 and the knob sleeve 16 and will thus prevent the
excess torgue from being transmitted to the lock mechanism.
The driver 52 extends diametrically across the knob
sleeve 16 from the lug 56 and has its opposite or butt end in
abutting relationship with the surrounding body portion 42 of
the knob so that it is trapped in place when the parts are in
assembled operating condition. For purposes of retaining the
driver 52 in place in the knob sleeve 16 when no handle body
36 is present, the driver 52 is formed with an opening 62
which intersects the inside surface of the knob sleeve 16,
and a rubber ball 64 or other elastic element is press-fitted
in such opening. The ball-receiving opening 62 is
essentially a round hole, but to avoid a thin section between
it and the butt end of the driver, the opening is extended
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through such butt end to leave a pair of opposed jaws 63.
The ball resiliently engages the side edges of the slot 54 in
the wall of the driver, as indicated in Fig. 6, so as to
retain the driver 52 in place. In the event the driver lug
56 is broken away, the driver 52 is readily removed and
replaced by first removing the knob to expose the broken
driver, then pressing such driver out of the knob sleeve, and
then inserting a new driver 52 and ball 62 through the
slot 54.
EXAMPLE
A torque-releasable driver in accordance with the
present invention was manufactured from powdered nickel steel
to produce a sintered low-density powdered metal part. A
material in compliance with the Metal Powder Industries
Federation (MPIF) specification FN-0208-R was used. An
alternative nickel steel material is MPIF-FN-0405-R.
FN-0208-R is characterized by a dry-density range
of 6.4 to 7.2 g/cc. FN-0208-R is obtainable from GKN POWDER
MET, INC., with offices in Worcester, Massachusetts. The GKN
number for FN-0208-R is SN-208. FN-0405-R is available from
the same source as SN-405.
Manufactured drivers of different densities were
tested to determine the actual break points of the upstanding
ears. It was found that for a driver 52 as shown, a density
within the range 6.4 _ 0.2 g/cc would shear in response to an
applied torque of 300 + 25 - 50 inch-pounds, and it was
determined that this would meet the requirements of the
present invention. A consistant density could be held in the
manufacture of the lug 56, and particularly in the
manufacture of the two ears 59 to assure that the
torque-releasable driver would shear under the desired torque
with the lever handle here shown and the locking lug 28 of a
standard construction. The break-away torque of
64 + 0.2 g/cc was determined to be desirable and effective,
both to give reliable operation and to protect the lock
mechanism from excessive torque.
An alternative driver of similar shape was
manufactured using 0.120 inch half-hard cold-rolled steel
material. This also gives effective results.
The use of a resilient ball 64 in an opening 62 for
releasably retaining a driver or the like in a knob sleeve or
other tubular member i6 useful and advantageous in other
applications beside that shown in Figs. 1, 3, and 6. One
such other application is shown in Fig. 5. Here, a positive
driver 152 is mounted in a tubular knob sleeve 116 in a
manner analogous to that in Figs. 1 and 3, and has drive lugs
156 and 157 at opposite ends, engaged in grooves 154 at
diametrically opposite points in the neck 142 of a knob, so
as to give a positive drive connection between the knob and
knob sleeve. The knob may be of any desired configuration,
including a lever handle knob as here shown or a knob of a
conventional round or other shape. The positive driver is
trapped in the knob sleeve when the parts are assembled, but
needs to be held in the knob sleeve when the knob neck 142 is
absent, as for purposes of assembly and to prevent its loss
during field service. To this end, the driver 152 is formed
with a round hole 162 which intersects the inner surface of
the knob sleeve 116, and a resilient ball 164 is pressed into
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~4~980
such hole. When the driver, with the ball in place, i6
inserted through its mounting slots in the knob sleeve, the
ball is carried to the position shown, where it resiliently
engages the transverse inner edges of the adjacent mounting
610t to releasably hold the driver in place. The resilient
ball serves the same purpose as the metal spring 62 shown in
Fig. 2 of U.S. Patent No. 4, 6S5, 059, but is less
expensive and less complex.
Asgembly of the embodiment of Figs. 1-4 may be as
follows: A driver 52 with a ball 64 in place in its opening
62 is inserted through the wide slot 54 in the knob sleeve
16, to carry its drive lug 56 through the narrower slot 58
and bring the shoulders 55 against the inside surface of the
knob sleeve, as shown in Fig. 3. This carries the ball 64
partway through the wide slot 54 to the position shown in
Fig. 6, where the ball engages the transverse inside edges of
that slot and holds the driver in place. A knob assembly 10
is then slid axially over the knob sleeve in an orientation
i which permits the drive lug 56 to enter the groove 60. As
the knob moves toward its final position, it engages the cam
surface of the knob retainer lug 47 80 as to retract the
retainer untll the knob face 46 passes the retainer. The
retainer then move to its retaining position as shown in
Fig. 1.
In operation, the break-away driver 52 gives a
po~ltlve connection to tansmit torgue from the lever handle
10 to the knob sleeve 16 to rotate the sleeve to retract the
latch bolt of the lock, under all normal conditions of
operation. When the knob sleeve is locked against rotation
by the lug 28, such lug will hold the knob sleeve and knob
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against rotation under torque which would normally be applied
to the lever handle 10. In the event an attempt is made to
force the lock by applying high torque to the handle, the
break-away lug of the driver will shear under a torque less
than what would damage or override the locking lug 28. This
will release the drive connection from the lever handle 10 to
the knob sleeve 16 and the handle will become inoperative to
operate the lock. The key-operating mechanism will remain
intact so that the lock will be operable by a proper key.
The broken driver 52 can be readily replaced. The core 32 is
first removed by use of a special key, and this permits
insertion of a tool to retract the knob retainer 48. The
handle 10 is then removed to expose the broken driver. Such
driver is driven out of the knob sleeve and replaced with an
intact driver, and the handle is then reinstalled on the knob
sleeve.
Although the invention has been described in detail
with reference to certain preferred embodiments and specific
examples, variations and modifications exist within the scope
and spirit of the invention as defined in the following
claims.
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