Latch assembly

An adjustable over-center latching assembly (11) for securing aircraft panels (13A, 13B) is operated by a worm shaft (21) and segmental gear (25) in order to obtain the rotational directional change required to move a latching member (15) into and out of engagement with a keeper (17). A secondary locking feature is provided due to the irreversible nature of the gear and worm arrangement.

TECHNICAL FIELD 
This invention generally relates to a latch assembly and more particularly, 
to an adjustable, flush mounted, over center latch assembly having a 
secondary locking feature. 
BACKGROUND ART 
Aircraft are provided with a substantial number of outwardly exposed, flush 
mounted panels. Typically, these panels are removable or hinged to the 
surrounding surface of the aircraft to provide, for example, an opening 
for accessing the engine of the aircraft, particularly for maintenance 
thereon. Various types and designs of latch assemblies have been used to 
secure these flush mounted panels in place. 
One such latch assembly is the over center hook latch as shown, for 
example, in U.S. Pat. No. 2,712,955. In this particular latching assembly, 
the fulcrum axis of the latch handle is mounted to a bracket on the 
aircraft panel and the latch hook engages a keeper on the aircraft 
structure. The latch is designated as an over center latch because, in the 
closed position, the load on the latch handle creates a moment arm on the 
latch handle about the fulcrum axis in a direction which maintains the 
latch in its closed position. 
Known over center latch assemblies have primarily emp1oyed lever arms or 
cam action to provide the necessary pull-up force required to bring the 
complementary panel components together. While operationally quite 
efficient, these arrangements do possess certain definite disadvantages. 
Due to high operational friction, the pull-up capabilities of the latch 
assemblies of the type concerned here are poor, thus often requiring the 
exertion of an inordinate amount of force in order to operate the latch. 
Another disadvantage of the known latch assemblies, such as that disclosed 
by U.S. Pat. No. 4,053,177, is that the upper surface of the latch handle 
is mounted so as to be flush with the outer skin of the aircraft when the 
latch is in the closed position. While this configuration does mitigate 
air flow disturbances in the vicinity of the latch assembly, the resulting 
external surface roughness of this type of flush mounted latch assembly 
generates large surface area aerodynamic disturbances which increase drag 
as well as cause undesirable flow characteristics. 
Additionally, due to the high forces exerted on the suface of the aircraft, 
proper adjustment between the hook latch and corresponding keeper arm is 
critical and must be maintained. If the distance is too great, the latch 
either will not close or will create excessive compressional forces on the 
aircraft components resulting in possible damage to the components or 
latch. If the distance is too close, the hook will not engage the keeper 
with suitable tension to maintain the panel on the aircraft, thus 
resulting in a questionable locking condition. 
Because of the possible damage or even total loss of an aircraft should the 
latch fail. great care is exercised to make sure that the latch is secure 
and that any play or free movement between the hook latch and its keeper 
is eliminated. While latching assemblies are known having means for 
providing such adjustment when the latch is either engaged or disengaged, 
poor adjustment capabilities have resulted due to the limited amount of 
adjustable travel offered by the known adjustment arrangements. 
Also, the known latching assemblies are, typically, configured with 
numerous moving parts which not only diminish the reliability of operation 
of the latch, but also make the replacement of the component parts of the 
latch difficult, particularly while the latch assembly is installed in the 
panel. Furthermore, the the feature of a secondary locking capability 
incorporated into the normal operation of the latch to provide back-up 
locking is, heretofore, unknown. 
DISCLOSURE OF THE INVENTION 
It is, therefore, an object of the present invention to provide an over 
center latch assembly having a secondary locking feature incorporated into 
the normal operation of the latch. 
Another object is to provide a flush mounted latch assembly which is 
operated by a conventional drive tool adapted for insertion through a 
small opening in the panel, the remaining components of the latch assembly 
being concealed by the panel. 
A further object is to provide a flush mounted, over center latch assembly 
adapted for low friction operation while providing improved pull-up 
capabilities. 
Yet another object of the present invention is to provide a flush mounted, 
over center latch assembly which is economical and feasible to 
manufacture. 
The principal feature of the present invention is the provision of a 
totally new approach for providing pull-up capabilities in an over-center 
latch assembly, which function is now accomplished in the art by means of 
levers, cam action or the like. In accordance with the present invention, 
operation of the latch assembly is faciliated by a worm shaft and 
segmental gear wheel as a simple means to obtain the rotational 
directional change required to move the latch hook into and out of 
engagement with the keeper. 
A further important feature of the invention is the provision of a worm 
shaft and segmental gear wheel assembly as described which provides a 
secondary locking capability incorporated into the normal operation of the 
latch assembly. A major difficulty and consequent expense of present 
over-center latch assemblies has been the need to provide a separate 
secondary locking arrangement to assure against inadvertent separation of 
the latch assembly. Such arrangements must, necessarily, be situated 
within the latch assembly, thus complicating the overall mechanism. In 
accordance with the invention, the irreversible nature of the worm gearing 
arrangement provides the secondary locking feature. 
In addition to the highly desirable feature of secondary locking, the 
invention is further characterized by the ability to replace the component 
parts of the latch assembly while installed in the panel. 
In accordance with these and other objects, advantages and features of the 
present invention, there is provided an adjustable over-center, 
flush-mounted latch assembly for securing cowling panels comprising a 
manually operated shaft provided with a worm, the worm shaft being secured 
to one of the panels for rotational movement. A segmental gear, which 
meshes with and is operated by the worm, has a first shaft defining a 
first pivot axis about which the gear rotates. A latching member is 
pivotally connected to the segmental gear by a second shaft defining a 
second pivot axis about which the latching member pivots. The latching 
member is provided with engaging means, at its distal end, for engaging a 
keeper and at its proximal end with a shoulder. A lug is positioned on the 
face of the segmental gear for engaging the shoulder of the latching 
member when the gear is rotated to an open position. Biasing means for 
biasing the latch member towards a closed position is also included as 
well as adjusting means for adjusting the keeper relative to the latching 
member. In operation, the rotation of the worm shaft in a first direction 
causes the second shaft of the latching member to pass over dead center of 
the first shaft to thereby begin to release the load on the keeper. 
Continued rotation of the worm shaft in the first direction relieves all 
of the latch load and causes the lug to engage the shoulder of the 
segmental gear thereby overcoming the bias of the biasing means and 
rotating the latch member out of engagement with the keeper.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIGS. 1-3 illustrate the latch assembly, generally indicated at 11, of the 
present invention in combination with an aircraft structure with which it 
is preferably used, however it is understood that the latch could also be 
used for other purposes. The aircraft structure, as illustrated, comprises 
a pair of panel members 13A, 13B which are, for example, secured by hinges 
to the frame of the aircraft. 
The latch assembly 11, which secures the panels 13A, 13B in the closed 
position, comprises a latching member or link 15 having a substantially 
L-shaped configuration as seen in FIGS. 2-3 and a keeper or hook 17. The 
latching member 15 is moved into and out of engagement with the keeper 17 
by means of a manually operated shaft 19 having a worm 21. The worm shaft 
19, which is secured to one of the hinged panels 13B, is rotatable in a 
first direction to move the latching member 15 to an open position and in 
a second direction to move member 15 to a closed position so as to engage 
the latching member 15 with the keeper 17. In order to operate the worm 
shaft 19, a socket 23 is adapted to accept a standard insertable wrench. 
Alternatively, the socket 23 takes the form of a nut which is rotatably 
driven by a standard socket and drive arrangement. 
A segmental gear 25 is operated by the worm 21. The gear 25 is provided 
with a first shaft 27 which defines a first pivot axis about which the 
gear 25 rotates. The latching member 15 is pivotally connected to the gear 
25 by a second shaft 29 which defines a second pivot axis about which the 
latching member 15 pivots. 
The latching member 15 is provided, at its distal end, with engaging means 
31 for engaging the keeper 17. A shoulder 33 is provided at the proximal 
end of the member 15 for engaging a lug or protrusion 35 formed on the 
face of the segmental gear 25. The lug 35 is positioned on the gear 25 so 
as to engage the shoulder 35 of the latching member 15 when the gear 25 is 
rotated to the open position. 
About first axis 27 is a biasing means 37 for biasing the latching member 
15 towards the closed position. In the embodiment illustrated, biasing 
means 37 takes the form of a torsion spring: however, any other suitable 
biasing means can be employed, such as a conventional wire spring. 
As illustrated, keeper 17 includes an integrally formed, threaded bolt 
shank 39. The keeper 17 is removably attached to the other of the panel 
members 13A by inserting the shank 39 through an aperture provided in 
panel portion 41 and tightening tension nut 43. 
In order to provide proper alignment of the keeper 17 with respect to the 
latching member 15, a key-way or slot 45, as is best shown in FIG. 4, 
cooperates with tooth 47 of locking tab 49. Proper positioning of the 
locking tab 49 is achieved by means of a recess 51 provided in panel 
portion 41. 
Adjustment of the keeper 17 relative to the latching member 15 is provided 
by adjusting means, generally indicated at 53. Movement of the keeper 17 
towards and away from the latching member 15 is facilitated by turning 
tension nut 43 until the proper tension is established and then tightening 
jam nut 55. 
Referring to FIGS. 2 and 3, the operation of the latch assembly 11 is quite 
straight forward. The only tool required is a standard wrench A, such as, 
for example, an allen wrench which is inserted into socket 23 to rotate 
shaft 19, an external hole 57 being provided in panel 13B to allow access 
of the tool A. Rotation of the worm 21 in, for example, the counter 
clockwise direction, drives the gear 25 in an opening direction causing 
second shaft 29 to pass over dead center of the first shaft 27 to being 
releasing the load on keeper 17. Continued rotation of the worm 21 
relieves all of the link load and causes lug 37, on the face of the gear 
25, to strike shouldder 33 on the proximal end of latching member 15. As 
lug 35 engages shoulder 33, the biasing of biasing means 37 is overcome 
and engaging means 31 is rotated out of link slot 59. This allows the pair 
of panel members 13A, 13B to be separated. 
After the panel members 13A, 13B are brought back together, rotation of the 
worm 21 in the opposite direction, for example, in the clockwise 
direction, allows biasing means 37 to drive the engaging means 31 of 
latching member 15 back into slot 59 of keeper 17. Continued rotation in 
this direction pulls the panels 13A, 13B, together until second shaft 29 
reaches dead center over the first shaft 27. Further operation moves 
second shaft 29 past dead center thus locking the latch assembly 11 in the 
closed position. Because latch assembly 11 is driven by a worm and gear 
arrangement, an irreversible condition is established thus providing a 
secondary lock. 
One particular feature and a significant advantage of the latch assembly 11 
is the ability to replace the component parts of the assembly 11, while 
installed in the panels 13A and 13B. By removing tension nut 43 from shank 
39, keeper 17 is removed from panel 13A in a simple operation. Snap ring 
61, as best seen in FIG. 4, is removed to replace worm shaft 19, while 
gear 25 is removed by tapping out first shaft 27. Similarly, second shaft 
29 is tapped out in order to remove latching member 15 from gear 25. 
While the present invention has been described with reference to a 
particular embodiment, it is understood that various changes in form and 
detail may be made therein without departing from the spirit and scope of 
the appended claims.