[0001] The present invention relates to a thumb turn latch designed to be turned by the
thumb and finger through an angle of 90 degrees for releasably holding the flap of
a bag-like article in a closing position.
[0002] A typical example of thumb turn latch of the type described is disclosed in Italian
Utility Model Registration No. 201901. The disclosed latch includes a latch body having
a grip head and a cylindrical stem extending centrally from a lower surface of the
grip head. The grip head has a locking ridge disposed on and extending diametrically
across the lower surface. The cylindrical shank terminates in an enlarged foot having
an upwardly tapering cam surface. The latch body is rotatably mounted on a retainer
attached to the body of a bag-like article. The retainer includes a split sleeve rotatably
receiving therein the shank of the latch body, and a crisscross groove formed in an
upper surface of the retainer for receiving the locking ridge of the latch body to
lock the latch body selectively in a locking and a releasing position which are angularly
spaced by 90 degrees. When the latch body is held in the locking position or the releasing
position in which the locking ridge is received in the crisscross groove, the lower
end of the split sleeve is held in abutment with the upwardly tapering cam surface
of the shank of the latch body. In this instance, due to the camming action of the
upwardly tapering cam surface, the latch body is urged downwardly toward the retainer.
When the grip head is turned to move the latch body from the locking position to the
releasing position and vice versa, the locking ridge is released from the crisscross
groove and slides up onto the upper surface of the retainer, causing the latch body
to be moved upwardly. With this upward movement of the latch body, the upwardly tapering
cam surface of the enlarged foot is forced into the split sleeve of the retainer,
whereupon the split sleeve, which is composed of two opposing resilient thin walls,
is spreaded by the cam surface. This forcible deformation of the two opposing walls
of the split sleeve continues until the locking ridge is received again in the crisscross
groove to lock the latch body in the releasing position.
[0003] The known thumb turn latch of the foregoing construction is however disadvantageous
in that the split sleeve of the retainer is likely to be damaged or broken due to
fatigue caused by repeated bending of the two opposing resilient thin walls of the
split sleeve during use of the bag-like article.
[0004] With the foregoing drawbacks of the prior art device in view, the present invention
seeks to provide a thumb turn latch which is durable in construction and has a long
service life.
[0005] According to the present invention, there is provided a thumb turn latch comprising
a latch body and a retainer movably holding thereon the latch body. The latch body
has a grip head and a split shank extending perpendicularly from a lower surface of
the grip head and terminating in an enlarged foot. The grip head has on the lower
surface at least one locking ridge extending radially relative to a central axis of
the split shank. The retainer includes a bearing portion slidably receiving therein
the split shank of the shank body. The bearing portion has a stepped hole including
a small-diameter portion extending downwardly from an upper surface of the bearing
portion, and a large-diameter portion contiguous to the small-diameter portion and
receiving therein the enlarged foot of the split shank. The large-diameter portion
has an upwardly tapering cam surface disposed adjacent to the small-diameter portion
and engageable with the enlarged foot to urge the latch body downwardly toward the
retainer. The bearing portion further has in its upper surface a crisscross guide
groove extending radially outwardly from the stepped hole for receiving therein the
locking ridge to lock the latch body in position against rotation relative to the
retainer.
[0006] Many other advantages and features of the present invention will become manifest
to those versed in the art upon making reference to the detailed description and the
accompanying sheets of drawings in which a preferred structural embodiment incorporating
the principles of the present invention is shown by way of example.
Figure 1 is a schematic perspective view of a briefcase incorporating a thumb latch
according to the present invention;
Figure 2 is a view similar to Figure 1, showing the briefcase as it is closed by the
thumb turn latch;
Figure 3 is an enlarged front elevational view of a latch body of the thumb turn latch;
Figure 4 is a side view of Figure 3;
Figure 5 is a bottom view of Figure 3;
Figure 6 is an enlarged plan view of a retainer of the thumb turn latch;
Figure 7 is a cross-sectional view taken along line VII - VII of Figure 6; and
Figures 8 and 9 are enlarged cross-sectional views illustrative of the operation of
the thumb turn latch.
[0007] Figures 1 and 2 show a briefcase 1 having a closure composed of a pair of laterally
spaced thumb turn latches 10, 10 embodying the present invention.
[0008] The thumb turn latches 10 are mounted on a body 2 of the briefcase 1 and releasably
engageable with a pair of eyelets 4, 4, respectively, attached to a flap 3 of the
briefcase 1 to close the briefcase 1. Each of the thumb turn latches 10 includes a
latch body 11 rotatably mounted on a retainer 12 secured to the body 2 and adapted
to be turned by the thumb and finger to move between a releasing position shown in
Figure 1 in which the latch body 11 is freely receivable in the corresponding eyelet
4, and a locking position shown in Figure 2 in which the latch body 11 is held in
locking engagement with the eyelet 4. The locking and releasing positions are angularly
spaced apart by an angle of 90 degrees.
[0009] The thumb turn latch body 11 is molded of synthetic resin and includes, as shown
in Figures 3 - 5, a grip head 13 adapted to be gripped by user's fingers for turning
the latch body 11, and a split cylindrical shank 14 disposed centrally on and extending
perpendicularly from a lower surface 13a of the grip head 13.
[0010] The grip head 13 has on its lower surface 13a four locking ridges 15 angularly equidistant
from one another and extending radially inwardly from the outer peripheral edge of
the grip head 13 toward the central axis of the split cylindrical shank 14. The locking
ridges 15 have rounded upper edges for camming action described later. The number
of the locking ridges 15 is not limited to four as in the illustrated embodiment but
only one locking ridge may be employed. The split cylindrical shank 14 terminates
in an enlarged foot 16 of an interrupted circular shape. The enlarged foot 16 has
a sharp outer edge 17 at an upper side thereof. The split cylindrical shank 14 has
two longitudinal slits 18 extending perpendicular to one another in crisscross fashion
to divide the shank 14 into four identical segments. With the slits 18 thus provided,
the split shank 14 is resiliently contractible radially inwardly.
[0011] The retainer 12 is molded of synthetic resin and includes, as shown in Figures 6
and 7, a flat base 20 and a bearing portion 21 disposed centrally on and projecting
perpendicularly from an upper surface of the base 20 for movably receiving therein
the shank 14 of the latch body 11.
[0012] The retainer 12, as shown in Figure 8, is attached to a fabric C of the briefcase
body 2 (Figure 1) with the fabric C is sandwiched by and between the base 20 and a
back plate 30. The back plate 30 and the base 20 are joined together by a pair of
rivets 31 extending respectively through a pair of countersunk holes 20a, 20a in the
base 20 and also through a pair of holes (not designated) in the back plate 30.
[0013] The bearing portion 21 of the retainer 12 has a stepped axial through-hole composed
of an upper small-diameter portion 22 and a lower large-diameter portion 23 separated
by a flat shoulder 25. The large-diameter portion 23 has an upwardly tapering cam
surface 24 disposed adjacent to the small-diameter portion 22 and blending into the
flat shoulder 25. The cam surface 24 has a height or length substantially equal to
or slightly larger than the height of the locking ridges 15. The bearing portion 21
has on its upper end surface 21a (Figure 7) a crisscross guide groove 26 extending
radially outwardly from the stepped hole for receiving the locking ridges 15, respectively,
of the latch body 11. The crisscross guide groove 26 has a shape complementary in
contour with the shape of the locking ridge 15. The retainer 12 further has an annular
groove 27 disposed concentrically outwardly of the stepped through-hole. This groove
27 is povided for purposes of reducing the weight of the retainer 12 and saving the
material used.
[0014] The latch body 11 and the retainer 12 are assembled together by forcibly inserting
the split shank 14 into the stepped through-hole in the bearing portion 21 from the
small-diameter portion 22 thereof until the enlarged foot 16 on the shank 14 is snapped
with the large-diameter portion 23 of the stepped through-hole, as shown in Figure
8. In this assembled condition, the upwardly tapering cam surface 24 acts on the upper
edge 17 (Figure 3) of the enlarged foot 16 to urge the shank 14 and hence the latch
body 11 downwardly, thereby moving the lower surface 31a (Figure 3) of the grip head
13 toward the upper end surface 21a (Figure 7) of the bearing portion 21. In this
instance, if the locking ridges 15 on the grip head 13 are disposed in registry with
the guide grooves 26 in the bearing portion 21, the locking ridges 15 will fit into
the guide groove 26 by the interaction between the cam surface 25 and the resilient
split shank 14, thereby lock the latch body 11 in position against rotation relative
to the retainer 12. In this locked position, the lower surface 13a of the grip head
13 is held in abutment with the upper end surface 21a of the bearing portion 21.
[0015] When the grip head 13 is turned in any direction to move the latch body 11 from the
locked position of Figure 1, the locking ridges 15 on the grip head 13 are released
from the corresponding guide grooves 26 and slide onto the upper end surface 21a (Figure
7) of the bearing portion 21, thereby moving the latch body 11 upwardly away from
the retainer 12. With this upward movement of the latch body 11, the enlarged foot
16 of the shank 14 is forced to slide upwardly along the upwardly tapering cam surface
24 in the large-diameter portion 23 of the stepped through-hole. During that time,
the enlarged foot 16 of the split shank 14 resiliently contracts radially inwardly.
The upward movement of the latch body 11 is limited when the upper sharp outer edge
17 (Figure 1) of the enlarged foot 16 engages the flat shoulder 25 (Figure 7) of the
stepped through-hole in the retainer 12.
[0016] As described above, the latch body 11 of the thumb turn latch 10 has a split shank
14 snap-fitted in a stepped through-hole in the retainer 12, and the retainer 12 has
an upwardly tapering cam surface 24 formed on the stepped through-hole adjacent to
a flat shoulder 25 thereof. The cam surface 24 acts on an enlarged foot 16 on the
split shank 14 when the latch body 11 is moved upwardly away from the retainer 11
as the grip head 13 is turned to move the latch body 11 between a locking position
and a releasing position. This combination of the radially contractible shank 14 and
the cam surface 24 enables it to use a thick and hence durable bearing portion, such
as the bearing portion 21 of the illustrated retainer 12. The thumb turn latch 10
having such durable retainer 12 has a long service life.
1. A thumb turn latch (10) comprising: a latch body (11) having a grip head (13) and
a split shank (14) extending perpendicularly from a lower surface (13a) of said grip
head (13) and terminating in an enlarged foot (16), said grip head (13) having on
said lower surface (13a) at least one locking ridge (15) extending radially relative
to a central axis of said split shank (14); and a retainer (12) movably holding thereon
said latch body (11) and including a bearing portion (21) slidably receiving therein
said split shank (14) of said shank body (11), said bearing portion (21) having a
stepped hole (22, 23) including a small-diameter portion (22) extending downwardly
from an upper surface (21a) of said bearing portion (21) and a large-diameter portion
(23) contiguous to said small-diameter portion (22) and receiving therein said enlarged
foot (16) of said split shank (14), said large-diameter portion (23) having an upwardly
tapering cam surface (24) disposed adjacent to said small-diameter portion (22) and
engageable with said enlarged foot (16) to urge said latch body (11) downwardly toward
said retainer (12), said bearing portion (21) further having in said upper surface
(21a) a crisscross guide groove (26) extending radially outwardly from said stepped
hole (22, 23) for receiving therein said locking ridge (15) to lock said latch body
(11) in position against rotation relative to said retainer (12).
2. A thumb turn latch (10) according to claim 1, the number of said locking ridge
(15) being four, said four locking ridges (15) being angularly equidistant from one
another.
3. A thumb turn latch (10) according to claim 1 or 2, said split shank (14) having
two longitudinal slots (18) extending perpendicular to one another.
4. A thumb turn latch (10) according to one of the preceding claims, said enlarged
foot (16) on said split shank (14) having an upper sharp outer edge (17), said stepped
hole (22, 23) including a flat shoulder (25) separating said small-diameter portion
(22) and said large-diameter portion (23) and lockingly engageable with said outer
edge (17) of said enlarged foot (17).
5. A thumb turn latch (10) according to one of the preceding claims, said cam surface
(24) having a height slightly larger than the height of said locking ridge (15).
6. A thumb turn latch (10) according to one of the preceding claims, said locking
ridge (15) having a rounded upper edge, said criss-cross guide groove (26) having
a shape complementary in contour with the shape of said locking ridge (15).
7. A thumb turn latch (10) according to one of the preceding claims, said latch body
(11) and said retainer (12) being molded of synthetic resin.