Safety latch

A safety latch for securing doors, windows and the like includes a plunger slidably received within a housing and movable between extended and retracted positions. A first end of the plunger is freely available for engagement with a hole, recess, strikeplate, or the like externally of the housing, and a second end of the plunger within the housing includes a cam member. A retracting member is interconnected with the plunger through the use of an intermediate member located between and connected at its opposite ends to the plunger and the retracting member. Either a first end of the intermediate member or the retracting member includes a cam follower engageable with the cam member included on the plunger. When a force is applied to the retracting member to pull the plunger into the housing from the extended position toward the retracted position, the plunger is freely movable within the housing to the retracted position. However, when a force is applied in an attempt to push the plunger into the housing from the extended position toward the retracted position, the cam member acts against the cam follower to cause a locking member on the intermediate member to engage with an opening in the housing to prevent movement of the plunger to the retracted position.

FIELD OF THE INVENTION 
The invention pertains to latches for doors, windows, access panels, 
trunks, tail gates, handicap equipment, and the like. 
BACKGROUND OF THE INVENTION 
There are numerous devices that require latches to secure such things as 
doors, windows and access panels, one example being a shipping container. 
There are also numerous latches available for such applications. However, 
they are susceptible to becoming inadvertently or undesirably opened due 
to jarring impacts, vibrations, or forced entry. 
A latching mechanism developed in part to overcome the problem of forced 
entry is disclosed in U.S. Pat. No. 2,644,705. That latching mechanism 
includes a dead latching dog for preventing someone from prying open an 
inclined-face latch bolt used in conjunction with a dead latch in a door 
knob assembly. While this latching mechanism may provide some degree of 
security in the particular environment for which it was designed, it does 
not provide completely sufficient security, it is extremely complicated 
and costly, and it has little or no applicability to other situations. 
Other examples of latch and bolt mechanisms are disclosed in U.S. Pat. Nos. 
2,650,123; 1,516,628; 1,615,120; 1,910,102; and 2,499,107. These disclosed 
mechanisms likewise are unduly complicated, insufficiently secure and/or 
limited in their applicability. 
Thus, there remains a need for a secure safety latch of simplified and cost 
effective construction that has broad applicability. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a safety 
latch that preferably has broad applicability to a variety of devices. 
It is another object of the present invention to provide a safety latch 
that is secure but yet preferably has a relatively simple and 
cost-effective construction. 
To achieve these and other objects, and to overcome the shortcomings of 
existing latches discussed above, a preferred embodiment of the safety 
latch of the present invention includes a plunger movable between extended 
and retracted positions, a first end of the plunger being freely available 
for engagement; a cam member interconnected with the plunger; a cam 
follower engageable with the cam member; a locking member interconnected 
with the cam follower; and a retracting member interconnected with the 
plunger. The plunger is freely movable from the extended position to the 
retracted position when a force is applied to the retracting member to 
pull the plunger toward the retracted position. However, when a force is 
applied in an attempt to push the plunger from the extended position 
toward the retracted position, the locking member prevents movement of the 
plunger to the retracted position. 
In accordance with other aspects of the present invention, a second end of 
the plunger preferably includes the cam member and/or the cam member 
preferably acts against the cam follower to cause the locking member to 
prevent movement of the plunger to the retracted position when the force 
is applied in an attempt to push the plunger. The safety latch of the 
present invention also preferably includes a spring for biasing the 
plunger into the extended position, the retracting member acting against 
the biasing spring when a pulling force is applied to the retracting 
member. The cam member and cam follower may include inclined surfaces, a 
cylindrical-shaped member and inclined surface, a cylindrical-shaped pin 
and inclined slot, or other alternative structures. 
The locking member and cam follower may be positioned on an intermediate 
member located between the plunger and the retracting member. 
Alternatively, the locking member and the cam member may be positioned on 
the intermediate member, and the cam follower may be located on the 
retracting member. The plunger and the retracting member preferably are 
connected to opposite ends of the intermediate member, by means of a 
protruding coupler/receiving groove arrangement, a cylindrical 
pin/hole/inclined slot arrangement, or other alternative arrangements. The 
intermediate member may be substantially Z-shaped, substantially L-shaped, 
or otherwise. 
The retracting member may be equipped so that force may be applied to the 
retracting member to pull the plunger toward the retracted position by 
means of an in-line mechanism. Alternatively, force may be applied to the 
retracting member in other ways, such as by means of a rotational 
mechanism. 
The safety latch may also include a housing. In this case, the plunger is 
slidably received within a first opening in the housing so that a first 
end of the plunger is freely available for engagement externally of the 
housing. The retracting member preferably extends through a second opening 
in the housing. The plunger is freely movable within the housing to the 
retracted position when a force is applied to the retracting member to 
pull the plunger into the housing toward the retracted position, whereas 
when a force is applied in an attempt to push the plunger into the housing 
toward the retracted position, the locking member engages with the housing 
to prevent movement of the plunger to the retracted position. 
These and other objects, features and advantages of the present invention 
will be understood more clearly from the following detailed description 
and accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1A through 1C, a safety latch 10 according to a first 
embodiment of the present invention is shown. Safety latch 10 includes a 
plunger or bolt 11 that extends from a first opening 12 of a housing 13, 
opening 12 extending into and forming a hollow chamber through the 
housing. The plunger, housing and housing opening may be of various 
alternative shapes and sizes, but preferably constitute a 
cylindrical-shaped plunger extending through a square opening of a housing 
that has a square cross section. 
The plunger 11 is slidably movable within the housing between extended and 
retracted positions. A first end 11a of plunger 11 is freely available for 
engagement with a hole, recess, strikeplate, etc. on a device such as an 
access panel frame of a shipping container as illustrated in FIG. 6 and 
discussed more fully below. A second end 11b of plunger 11 includes a cam 
member 14, unitarily formed on the end of the plunger in this embodiment 
as an inclined surface in the shape of a cone. 
The safety latch of this embodiment also includes a retracting member 15 
interconnected with the plunger 11 by means of a substantially Z-shaped 
intermediate member 16, whose overall cross section preferably is shaped 
the same as but is slightly smaller than that of the opening 12 of the 
housing 13. Intermediate member 16 includes U-shaped protruding couplers 
17, 18 at its respective ends engaged with annular grooves 19, 20 
unitarily formed adjacent the inwardly confronting ends of plunger 11 and 
retracting member 15, respectively. Intermediate member 16 also includes 
an inclined surface 21 serving as a cam follower for engagement with cam 
member 14. Intermediate member 16 further includes a locking member 22 for 
engagement with an opening 23 in the side of the housing 13. 
Retracting member 15 extends through yet another opening 24 in the housing 
13 at the opposite end of the housing from opening 12. Retracting member 
15 and opening 24 may be of various alternative shapes, but preferably 
constitute a cylindrical-shaped retracting member extending through a 
circular hole 24. A coil spring 25 is situated between and acts against 
shoulders 26, 27 on the housing 13 and an abutting portion 28 unitarily 
formed on retracting member 15 to normally bias plunger 11 into a position 
in which it extends from housing 13. A ring 29 is provided through a hole 
30 in the externally protruding end 15a of retracting member 15. Ring 29 
provides a vehicle for applying a pulling force to the safety latch and 
also serves to prevent the safety latch components from falling out of the 
housing through opening 12. 
The operation of the safety latch of the first embodiment is hereby 
described with reference to FIGS. 1A through 1C. FIG. 1A illustrates 
safety latch 10 when plunger 11 is in a completely or sufficiently 
extended position, i.e., a position into which plunger 11 is normally 
biased by spring 25 before any force is applied to retract the plunger, 
and a position of the plunger when it is properly engaged with any 
corresponding hole, recess, strikeplate, etc. In an extended position of 
the plunger, locking member 22 is offset toward the plunger side of 
opening 23 by at least a small amount as shown in FIG. 1A, or 
alternatively is situated over opening 23, and in either case is unengaged 
with opening 23. When a force is applied to the retracting member 15 as 
shown in FIG. 1B to pull the plunger from its extended position into the 
housing against the force of spring 25 toward a retracted position--i.e., 
a position in which the plunger is completely retracted into the housing 
or at least sufficiently retracted into the housing to disengage the 
plunger from any corresponding hole, recess, strikeplate, etc. with which 
it may otherwise be engaged when it is in its extended position--locking 
member 22 moves past and remains unengaged with opening 23 so that plunger 
11 is able to freely move within the housing to the retracted position. On 
the other hand, when a force is applied in an attempt to push plunger 11 
from its extended position into the housing toward a retracted position as 
shown in FIG. 1C, cam member 14 acts against the inclined surface of cam 
follower 21 positively causing locking member 22 to protrude into opening 
23 so that a portion 31 on intermediate member 16 engages with an edge 32 
on housing 13, thereby limiting movement of the plunger and preventing it 
from reaching the retracted position. In this way, it is possible to pull 
plunger 11 out of any hole, recess or strikeplate with which it is engaged 
so as to open any door, access panel, etc. with which the safety latch is 
utilized. On the other hand, disengagement of plunger 11 by means of a 
pushing force is precluded, whether that pushing force is the result of 
inadvertent jarring impacts, attempts at forced entry, or otherwise. 
A safety latch 110 according to a second embodiment of the present 
invention is depicted in FIGS. 2A through 2C. This embodiment is the same 
as or similar to the first embodiment in most respects, and it is 
therefore unnecessary to repeat the description of the components that are 
the same as or similar to those of the first embodiment. The second 
embodiment differs from the first embodiment in terms of the specific 
configurations and interconnections of the intermediate member and the 
confronting internal ends of the plunger and the retracting member. As 
shown in FIG. 2A, end 111b of plunger 111 is formed with a single inclined 
surface serving as cam member 114, rather than being cone-shaped as in the 
case of cam member 14 of the first embodiment. Intermediate member 116 
includes an inclined surface cam follower 121, and a locking member 122 
engageable with an opening 123 in the side of housing 113. Moreover, 
straight-edged protruding couplers 117 and 118 of intermediate member 116 
are received into shallow grooves or recesses 119 and 120 formed in 
plunger 111 and retracting member 115, respectively, in lieu of the 
U-shaped coupler/annular groove arrangement of the first embodiment. This 
arrangement of the second embodiment is particularly useful in the event 
that the confronting inner ends of the plunger and retracting member are 
square or rectangular in cross section instead of cylindrical-shaped as in 
the first embodiment. 
The operation of safety latch 110 of the second embodiment is similar to 
the operation of safety latch 10 of the first embodiment, and is hereby 
described with reference to FIGS. 2A through 2C. FIG. 2A illustrates 
safety latch 110 when plunger 111 is in an extended position and locking 
member 122 is situated over or offset to the plunger side of and is 
unengaged with opening 123. When a force is applied to retracting member 
115 as shown in FIG. 2B to pull plunger 111 from its extended position 
into housing 113 against the force of the spring 125 toward a retracted 
position, locking member 122 moves past and remains unengaged with housing 
opening 123 so that plunger 111 is able to freely move within the housing 
to the retracted position. On the other hand, when a force is applied in 
an attempt to push plunger 111 from its extended position into the housing 
toward a retracted position as shown in FIG. 2C, cam member 114 acts 
against the inclined surface of cam follower 121 positively causing 
locking member 122 to protrude into housing opening 123 so that portion 
131 on intermediate member 116 engages with an edge 132 on housing 113, 
thereby limiting movement of plunger 111 and preventing it from reaching 
the retracted position. 
FIGS. 3A through 3D depict a safety latch 210 according to a third 
embodiment of the present invention. Again, many of the components of the 
third embodiment are the same as or similar to those of the first and 
second embodiments, and it is therefore unnecessary to repeat a 
description of those like components here. The third embodiment differs 
from the first and second embodiments in terms of the specific 
configurations and interconnections of the intermediate member and the 
confronting internal ends of the plunger and the retracting member. In 
this embodiment, as shown in FIG. 3A, a substantially L-shaped 
intermediate member 216 is pivotally connected to retracting member 215 by 
means of a cylindrical pin 220 on the retracting member extending through 
a hole 218 in the intermediate member. Intermediate member 216 is 
slidingly connected to plunger 211 by means of a cylindrical pin 219 
unitarily formed on or otherwise fixedly provided on inner end 211b of the 
plunger 211 and extending through an inclined slot 217 on the intermediate 
member. Plunger 211 and retracting member 215 may be machined for 
positioning of intermediate member 216 centrally within housing 213 as 
shown in FIG. 3D, or they may be machined for positioning of intermediate 
member 216 adjacent one of the walls of housing 213. 
In this third embodiment, cylindrical pin 219 serves as the cam member on 
the inner end 211b of plunger 211, and inclined slot 217 serves as the 
corresponding cam follower on intermediate member 216. Intermediate member 
216 also includes a locking member 222 engageable with an opening 223 in 
the side of housing 213. 
The operation of this third safety latch embodiment is hereby described 
with reference to FIGS. 3A through 3C. FIG. 3A illustrates safety latch 
210 when plunger 211 is in an extended position and locking member 222 is 
situated over or offset to the plunger side of and is unengaged with 
opening 223. When a force is applied to retracting member 215 as shown in 
FIG. 3B to pull plunger 211 from its extended position into housing 213 
against the force of the spring 225 toward a retracted position, locking 
member 222 moves past and remains unengaged with housing opening 223 so 
that plunger 211 is able to freely move within the housing to the 
retracted position. On the other hand, when a force is applied in an 
attempt to push plunger 211 from its extended position into the housing 
toward a retracted position as shown in FIG. 3C, the cylindrical pin cam 
member 219 acts against inclined slot cam follower 217 positively causing 
locking member 222 to protrude into housing opening 223 so that portion 
231 on intermediate member 216 engages with an edge 232 on housing 213, 
thereby limiting movement of plunger 211 and preventing it from reaching 
the retracted position. 
A safety latch 310 according to a fourth embodiment of the present 
invention is described with reference to FIGS. 4A through 4D. Many of the 
components of this fourth embodiment are the same as or similar to 
components of the first, second and third embodiments, and it is therefore 
unnecessary to repeat a description of those like components here. The 
fourth embodiment differs from the first three embodiments in terms of the 
specific configurations and interconnections of the intermediate member, 
the plunger and the retracting member. More particularly, safety latch 310 
includes a substantially L-shaped intermediate member 316 that is 
pivotally connected to plunger 311 by means of a cylindrical pin 319 on 
the plunger inserted through a hole 317 on one end of the intermediate 
member. The other end of intermediate member 316 is slidably connected to 
retracting member 315 by means of a cylindrical pin 318 on the 
intermediate member extending through an inclined slot 320 on the 
retracting member. The intermediate member also includes a locking member 
322 that is engageable with an opening 323 in the side of the housing 313. 
Plunger 311 and retracting member 315 may be machined for central 
positioning of intermediate member 316 within housing 313 as shown in FIG. 
4D, or the plunger and retracting member may be machined for positioning 
of intermediate member 316 adjacent one of the walls of housing 313. In 
this fourth embodiment, since the intermediate member 316 is pivotally 
connected to plunger 311, it can be said that the inner end 311b of 
plunger 311 includes cylindrical pin cam member 318, although cam member 
318 is not unitarily formed on or otherwise fixedly provided on end 311b 
of plunger 311. Inclined slot 320 on retracting member 315 serves as the 
cam follower. 
The operation of the fourth safety latch embodiment is described with 
reference to FIGS. 4A through 4C. FIG. 4A illustrates safety latch 310 
when plunger 311 is in an extended position and locking member 322 is 
situated over or offset to the plunger side of and is unengaged with 
opening 323. When a force is applied to retracting member 315 as shown in 
FIG. 4B to pull plunger 311 from its extended position into housing 313 
against the force of the spring 325 toward a retracted position, locking 
member 322 moves past and remains unengaged with housing opening 323 so 
that plunger 311 is able to freely move within the housing to the 
retracted position. However, when a force is applied in an attempt to push 
plunger 311 from its extended position into the housing toward a retracted 
position as shown in FIG. 4C, cylindrical pin cam member 318 acts against 
inclined slot cam follower 320 positively causing locking member 322 to 
protrude into housing opening 323 so that portion 331 on intermediate 
member 316 engages with an edge 332 on housing 313, thereby limiting 
movement of plunger 311 and preventing it from reaching the retracted 
position. 
Each of the four safety latch embodiments described above has been depicted 
with an in-line mechanism for applying a force to the retracting member to 
pull the plunger toward a retracted position, namely a ring (e.g., ring 
29) in conjunction with a protruding end of the retracting member (e.g., 
retracting member end 15a). As alternatively depicted in FIGS. 5A and 5B, 
a rotational mechanism 401 may instead be utilized for this purpose with 
any of the four safety latch embodiments. By way of example, a knurled 
knob 402 connected by a shaft 403 to a rotatable lever 404 may be used to 
impart translational force to retracting member 415. In this case, 
retracting member 415 includes an annular abutment element 415a that is 
engageable by a flange or flanges 404a on the lever 404. When knob 402 is 
rotated in either direction, a translational force is applied to the 
retracting member to pull the plunger (e.g., plunger 11) toward a 
retracted position. This rotational mechanism, as well as any of the 
described in-line mechanisms, may also be equipped with a conventional 
key-actuated or other locking mechanism to preclude unauthorized operation 
of the safety latch. 
One possible application of any of the safety latches of the present 
invention is illustrated in FIG. 6. As shown by way of example, two safety 
latches 10 of the present invention--or any of the alternatively described 
and illustrated safety latches 110, 210, 310--are mounted on a hinged 
access panel 502 of a shipping container 501. The plungers 11 of the 
safety latches are engageable with recesses 503 in the access panel frame 
of the shipping container to secure the access panel. Through the use of 
the safety latches, the access panel can be easily opened by 
simultaneously pulling on rings 29 of safety latches 10 directly or by 
means of a connecting cable 504. At the same time, the safety latches 10 
prevent inadvertent opening of the access panel by jarring impacts of the 
shipping container or otherwise. Moreover, the safety latches cannot be 
pried open by unauthorized persons attempting to forcibly enter the 
shipping container. Of course, authorized entry can be provided for by 
devising a special tool for engaging rings 29 or cable 504 through a hole 
in the top of the shipping container, by provision of key-actuated 
rotational mechanisms described above and accessible from outside the 
shipping container, or in other ways that will be appreciated by those 
skilled in the art reading this description. 
While the present invention has been described in conjunction with specific 
embodiments, it is evident that many alternatives, modifications and 
variations will be apparent to those skilled in the art. For example, 
although the components of the various safety latch embodiments are 
illustrated with certain relative shapes and dimensions, a variety of 
shapes and dimensions are possible as will be readily apparent from the 
foregoing description. By way of further example, although in the various 
preferred embodiments illustrated and described the cam member acts 
against the cam follower to positively cause the locking member to engage 
with the housing so as to prevent the plunger from being pushed to the 
retracted position, it is also possible--although not as preferable--to 
arrange the cam member and cam follower such that a pulling force applied 
to the plunger causes the cam member and cam follower to disengage from 
the housing a locking member that is normally biased or otherwise held in 
engagement with the housing when the plunger is in an extended position. 
Accordingly, the preferred embodiments of the invention set forth above 
are intended to be illustrative, not limiting, and various changes may be 
made without departing from the spirit and scope of the invention as 
defined in the following claims.