Self-locking nut having divided and undivided circumferential portions

A self-locking nut fitted into a fitting hole of a reflector with which an aiming screw engages for adjusting an inclination angle of a reflector of a vehicular lamp, the self-locking nut comprising: a nut leading portion having slits extending in radius direction; a flange arranged below said nut leading portion; a fitting portion formed below said flange, said fitting portion having slits extending in radius direction and a pair of legs for fitting into the fitting hole of the reflector, said pair of legs being elastically expandable and having a wedge shape; a shaft hole having an inner surface, said shaft hole passing through the nut leading portion, the flange and the fitting portion in vertical direction; and a threaded portion formed on the inner surface of said shaft hole engageable with the aiming screw, the threaded portion comprising: first grooves extending from said slit of said fitting portion; second grooves positioned perpendicular to said slit of said fitting portion; a divided circumferential portion divided in the circumferential direction by said first and second grooves; and an entire circumferential portion having a circular shape in section, said entire circumferential portion being positioned at said fitting portion, wherein a pitch diameter of said entire circumferential portion being slightly smaller than that of the aiming screw.

BACKGROUND OF THE INVENTION 
The present invention relates to an aiming device for adjusting an optical 
axis of a vehicle lamp. More particularly, the invention relates to a 
self-locking nut which engages with an aiming screw for tilting a 
reflector of the lamp. 
An aiming device for adjusting an optical axis, as shown in FIG. 2, is 
constituted such that a reflector 3, which is accommodated within a lamp 
chamber defined by a lamp body 1 and a front lens 2 attached to a front 
opening of the lamp body 1, is tiltable with respect to the lamp body 1. 
The aiming device is provided with a ball joint 4 serving as a fulcrum 
disposed on the reflector 3 for tiltably supporting the reflector 3 
together with a lamp bulb 10 on the lamp body. The ball joint 4 has a ball 
receptacle member 5 fitted in a bracket 3a provided on the reflector 3 and 
a ball bolt 6 extending from the lamp body 1. A vertical and horizontal 
aiming adjustment sections are arranged in the vertical and horizontal 
directions, respectively, with respect to the ball joint 4. 
As shown in FIG. 2, a vertical aiming adjustment section 7 includes, for 
instance, a self-locking nut 8 attached to a bracket 3b extending from a 
back side of the reflector 3, and confronting therewith an aiming screw 9 
rotatably supported on the lamp body 1. The aiming screw 9 engages with 
the self-locking nut 8. When the aiming screw 9 is operated to screw 
externally from the lamp body 1, the reflector 3, together with the 
self-locking nut 8 engaging with the aiming screw 9, is moved in the axial 
direction of the aiming screw 9. Therefore, the reflector 3 is tilted in 
the vertical direction around the ball joint 4 serving as the fulcrum, so 
that the optical axis of the lamp bulb 10 is vertically adjusted. 
There have been proposed the self-locking nuts thus constructed as shown in 
FIG. 6A and disclosed by, for instance, Unexamined Japanese Utility Model 
Application No. Hei. 6-64305 or as shown in FIG. 6B and disclosed by, for 
instance, Post-examined Japanese Utility Model Publication Hei. 6-45050, 
which can be used as self-locking nut 8 of FIG. 2. 
Both proposed self-locking nuts 101 and 201 shown in the FIGS. 6A and 6B, 
which replace self-locking nut 8 of FIG. 2, are formed of resin. The 
self-locking nut 101 is formed with a shaft hole 102 at the center 
thereof, into which the aiming screw is inserted. At an end portion, the 
self-locking nut 101 is formed with a fitting portions 103 having a pair 
of legs to be fitted with a fitting hole formed in the bracket of the 
reflector 3 in order to secure the nut to the bracket. The threaded 
portion 104 is provided on an inner surface of the shaft hole 102, and the 
aiming screw 9 engages with the threaded portion 104. 
In the nut 101 thus constructed, as the aiming screw is screwed to the 
fitting portion 103 after the aiming screw 9 is inserted into the threaded 
hole 104, a distance between the pair of legs of the fitting portion 103 
expands according thereto. Therefore, the fitting portion 103 is surely 
fitted with the fitting hole of the bracket 3b, so that there is no 
clearance between the nut 101 and the bracket 3b. 
The self-locking nut 201 is similar to the self-locking nut 101. That is, 
the self-locking nut 201 has a shaft hole 202 at the center thereof, into 
which the aiming screw is inserted. At an end portion, the self-locking 
nut 201 has a fitting portion 203 having a pair of legs to be fitted with 
a fitting hole formed on the bracket of the reflector 3 in order to secure 
the nut to the bracket 3b. The threaded portion 204 is provided on an 
inner surface of the shaft hole 202, and the aiming screw 9 engages with 
the threaded portion 204. 
In the nut 201 thus constructed, as the aiming screw 9 engages with the 
threaded hole 204 and the aiming screw is screwed into the fitting portion 
203, the distance between the pair of legs of the fitting portion 203 
expands. Therefore, the fitting portion 203 is surely fitted with the 
fitting hole of the bracket 3b, so that there is no clearance between the 
nut 201 and the bracket 3b. 
In the proposed self-locking nut 101, for instance, as shown in FIG. 6A, 
the shaft hole 102 into which the aiming screw is inserted has a circular 
shape in section having a constant diameter over substantially the entire 
length thereof in the axial direction. Accordingly, it would suffer from a 
problem in that a contact area between the aiming screw 9 and the threaded 
portion 104 formed on the inner surface of the shaft hole 102 becomes 
large, so that a frictional force between the aiming screw 9 and the 
threaded portion 104 is large. As a result, a large operative force is 
required to rotate the aiming screw 9, that is, the adjusting operation is 
difficult to perform. 
To the contrary, because the nut 201 as shown in FIG. 6B has a slit or 
groove 205 extending along the shaft hole 202, a total length in the 
circumferential direction of the inner surface of the hole 202 is 
relatively small. Therefore, an area of the threaded portion 204 is 
reduced, that is, a contact area between threaded portion 204 and the 
aiming screw 9 is decreased to the extent of the slit or groove 205. As a 
result, the frictional force is reduced, so that the operative force 
required can be relatively small. 
With the nut 201 of FIG. 6B, however, since the contact area of the 
threaded portion 204 contacting with the aiming screw 9 is reduced, an 
elastic force of the nut concentrates on such contact area. Accordingly, a 
contact pressure generated between the aiming screw 9 and the threaded 
portion 204 increases, so that the aiming screw 9 tends to dig into the 
threaded portion 204. Therefore, the pair of legs of the fitting portion 
203 do not sufficiently expand outwardly when the aiming screw 9 is 
screwed into the nut 204. As a result, an undesirable gap defined between 
the fitting hole of the bracket 3b and the fitting portion 203 still 
remains, and the nut 201 is not secured to the bracket 3b. This 
contributes to an error in accuracy of the aiming adjustment and 
deteriorate the required precision of the adjustment. 
SUMMARY OF THE INVENTION 
The present invention was made in view of the foregoing problems or 
difficulties accompanying the proposed self-locking nut. Therefore, an 
object of the present invention is to provide a self-locking nut in which 
an operative force for an aiming adjustment can be reduced while an 
undesirable gap defined between the self-locking nut and a part of a lamp 
body can be suppressed. 
To achieve the above-mentioned and other objects, there is provided a 
self-locking nut in which a threaded portion formed on an inner surface of 
a shaft hole which, according to the present invention, includes an entire 
circumferential portion having a circular shape in section and a divided 
circumferential portion divided in the circumferential direction by plural 
grooves. 
A contact area between the entire circumferential portion and a screw 
engaged therewith becomes relatively large, that is, a contact pressure 
generated at the contact area is reduced, so that a dig of the screw into 
the threaded portion is suppressed. Therefore, a pair of legs are allowed 
to sufficiently expand outward. On the other hand, a contact area between 
the divided circumferential portion and the screw becomes relatively 
small, that is, a frictional force between these members can be reduced, 
so that the operative force for driving the screw is reduced. As the areas 
of the entire and divided circumferential portions are appropriately 
arranged, the operative force of the screw can be reduced as well as the 
undesirable gap can be suppressed in fitting condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with referring to the 
accompanying drawings. 
FIG. 1 is an external perspective view showing a self-locking nut 11 
according to the present invention. In this embodiment, the nut 11 may be 
applied instead of the locking nut 8 of the aiming adjustment section 7 
provided with the reflector 3 of the lamp as shown, for example, in FIG. 
2. The nut 11 is fitted into a rectangular fitting hole 3c formed on a 
bracket 3b integrated with a back side of the reflector 3 and is secured 
to the bracket 3b, as shown in FIG. 1. 
FIGS. 3A to 3D respectively show a plan view, a front view, a cross 
sectional view of line I--I, and a cross sectional view of line II--II of 
the nut 11. The nut 11 is formed with a rectangular body 12 slightly 
elongated in a vertical direction and is made from resin, where the 
vertical direction is defined as a reference as indicated in FIG. 1, 
wherein the vertical direction is the direction of the axis of a shaft 
hole 13. The shaft hole 13 is formed at the center of the body 12 so as to 
pass through the body 12 in the vertical direction. An upper part of the 
nut 11 includes the body 12 which is formed with a flange portion 14 
having a square shape, and a nut leading portion 15 having a circular 
shape which is formed on an upper part of the flange portion 14. A middle 
portion is arranged right below the flange portion 14 such that a length 
in an axial direction of which is substantially the same as a thickness of 
the bracket 3b. A lower part lower than the middle portion has a fitting 
portion 17 comprising a pair of wedge shaped legs. 
A slit 18 extending in a radial direction runs from the nut leading portion 
15 to an upper surface of the flange portion 14. A tapered slit 23 formed 
under the flange portion 14 defines the pair of legs 16 at the fitting 
portion 17. When the fitting portion 17 is inserted into the fitting hole 
13c, the fitting portion 17 is elastically deformed such that the legs 16 
come close to each other in order for its external size to be smaller, and 
then the fitting portion 17 is passed through the fitting hole 3c. After 
that, the fitting portion 17 releases from the elastic deformation, and 
steps at a boundary between the middle portion and wedge portions is 
locked at an inner edge of the fitting hole 3c. Accordingly, the nut 11 
maintains in locking state with respect to the fitting hole 3c. 
As shown in FIG. 4, the nut leading portion 15 provided at the upper part 
of the flange portion 14 is in the form of a conical surface along a 
peripheral edge of the shaft hole 13 so that the conical surface correctly 
guides a tip of the aiming screw 9, as shown in FIG. 2, into the shaft 
hole 13. At two circumferential positions extending from the slit 18 and 
two circumferential positions perpendicular to the slit 18, U-grooves 
extend in the axial direction from the nut leading portion 15 to a middle 
of the fitting portion 17. Accordingly, because of the U-grooves 19, the 
inner surface of the shaft hole 13 remains only between these U-grooves 
19. 
On the contrary, the U-grooves 19 do not run under the middle of the 
fitting portion 17, and the inner surface of the shaft hole 13 still 
remains over the entire circumference. A screw thread is formed at the 
inner surface thus remaining, for serving as the threaded portion 20. In 
other words, the threaded portion 20 is formed thereon with a divided 
circumferential portion 21 divided by the U-grooves in the circumferential 
direction and an undivided circumferential portion 22 having threads along 
the entire circumference of each leg 16 of the fitting portion 17. A pitch 
diameter of the entire circumferential portion 22 is slightly smaller than 
that of the aiming screw 9. 
In this embodiment, while the fitting portion 17 of the nut 11 is fitted in 
the fitting hole 3c of the bracket 3b, the tip of the aiming screw 9 is 
guided into the shaft hole 13 in use of the nut leading portion 15 and 
engaged with the threaded portion 20. In this condition, since the aiming 
screw 9 is inserted into the shaft hole 13 and engaged with the threaded 
portion 20, the legs 16 are expanded outwardly to the extent of the 
difference between the pitch diameters at the entire circumferential 
portion 22. Therefore, an outer surface of the legs 16 is secured to the 
inner edge of the fitting hole 3c, so that the undesirable gap is 
suppressed. 
In this embodiment, the entire circumference of inner surface of the shaft 
hole 13 remains at the entire circumferential portion 22. The contact 
pressure generated between the aiming screw 9 and the threaded portion 22 
is distributed to the entire circumference, so that the contact pressure 
generated therebetween is reduced. Therefore, a dig of the aiming screw 9 
into the entire circumferential portion 22 of the shaft hole 13 can be 
suppressed. The problem that the legs of the nut are urged inwardly 
because the digging action is prevented. Especially, since the entire 
circumferential portion 22 is positioned at a substantially middle 
position of the fitting portion 17 with respect to the vertical direction, 
digging is suppressed and the problem of inwardly urging the leg 16 is 
effectively avoided. 
In addition, because the divided portion 21 is formed by the U-grooves 19 
on the inner surface of the shaft hole 13 of the nut 11, the contact area 
generated between the aiming screw 9 and the threaded portion 20 can be 
reduced to the extent of the area of the U-grooves 19 cut the 
circumference. Therefore, the frictional force produced between the aiming 
screw 9 and the threaded portion 20 can be reduced, and the relatively 
small operative force is sufficient to operate the aiming screw. 
In this embodiment, the entire circumference of the inner surface of the 
shaft hole 13 remains at the entire circumferential portion 22. In order 
to prevent the aiming screw from digging into the self-locking nut, it is 
sufficient that the contact area between the threaded hole and the aiming 
screw becomes relatively large. Accordingly, a small part of the 
circumference is removed, instead of remaining the entire circumference. 
As the axial length of the entire circumferential portion 22 is suitably 
changed, the contact pressure generated between the threaded hole 204 and 
the aiming screw 9 may be set at a desired value. 
As described above, the present invention provides a self-locking nut in 
which a threaded portion formed on an inner surface of a shaft hole 
includes an entire circumferential portion having a circular shape in 
section and a divided circumferential portion divided in the 
circumferential direction by plural grooves. A contact area between the 
entire circumferential portion and a screw engaged therewith becomes 
relatively large, that is, a contact pressure at the contact area is 
reduced, so that digging of the screw into the threaded portion can be 
suppressed. Therefore, a pair of legs can sufficiently expand outward. 
On the other hand, a contact area between the divided circumferential 
portion and the screw becomes relatively small, that is, a frictional 
force between them is reduced, so that the operative force of driving the 
screw is reduced. As the areas of the entire and divided circumferential 
portions are appropriately arranged, the operative force of the screw can 
be reduced as well as the undesirable gap can be suppressed in fitting 
condition. 
It should be understood that the form of the invention herein shown and 
described is to be taken as a preferred example of the invention and that 
various changes in the shape, size and arrangement of parts may be 
resorted to without departing from the spirit of the invention or the 
scope of the subjoined claims.