Lock structure for box

A lock structure for a box includes a first box member having a retaining projection, and a second box member having an elastic retaining arm. The retaining arm has at its distal end a retaining portion for engagement with the retaining projection. The first box member has an arm restraint rib which restricts a releasing movement of the retaining arm in a condition in which the retaining arm and the retaining projection are engaged with each other. When the arm restraint rib is pressed by the elastic retaining arm, the arm restraint rib is deformed by a pressing force of the elastic retaining arm. A retaining distance of the retaining projection relative to the retaining portion of the elastic retaining arm is larger than a gap between the elastic retaining arm and the arm restraint rib in the engaged condition.

BACKGROUND OF THE INVENTION

This invention relates to a lock structure for a box which is applied to a box such as an electric connection box mounted on a vehicle or an exterior box for receiving it.

As a box lock structure of this type, various structures have heretofore been proposed. A first related technique is shown inFIGS. 7 and 8.

InFIGS. 7 and 8, a retaining projection101is formed on an inner side surface of an upper cover100. An elastic retaining arm103is formed in an upstanding manner at a side wall of a lower cover102, and a distal end retaining portion103ais formed in a projecting manner at a distal end of this elastic retaining arm103.

In the above construction, when the upper cover100and the lower cover102are assembled together, the elastic retaining arm103is moved in a locking direction. With this movement, first, the distal end retaining portion103aof the elastic retaining arm103is brought into abutting engagement with the retaining projection101, and the elastic retaining arm103is elastically bent and deformed, so that the distal end retaining portion103apasses over the retaining projection101. When the distal end retaining portion103amoves to a position where it completely passes over the retaining projection101, the elastic retaining arm103is bent and restoringly deformed, so that the distal end retaining portion103ais retained by the retaining projection101. With the foregoing, a locked condition is established between the upper cover100and the lower cover102.

In the lock structure of this first related technique, when a high lock canceling force acts on the elastic retaining arm103in the locked position to elastically bend and deform the elastic retaining arm103, the lock is canceled. Therefore, the lock retaining force depends only on the elastic restoring force of the elastic retaining arm103.

Also, in order to form the first related technique into a structure in which the lock is made even a little harder to be canceled, a lock structure of a second related technique shown inFIGS. 9 to 11has been proposed.

As shown inFIGS. 9 to 11, in the lock structure of this second related technique, an arm restraint rib104is formed on an inner surface of an upper wall of an upper cover100. This arm restraint rib104is disposed at a rear side of an elastic retaining arm103which is to be retained by a retaining projection101. When a height of the retaining projection101is represented by d, and a gap between the arm restraint rib104and the elastic retaining arm103located in a locked position is represented by D, the position of the arm restraint rib104is set such that d<D is established. Therefore, in the process of movement of the elastic retaining arm103in a locking direction, a distal end retaining portion103aof the elastic retaining arm103can pass over the retaining projection101without interference by the arm restraint rib104as shown inFIG. 10.

In the lock structure of this second related technique, the elastic retaining arm103located in the locked position can not be shifted in a large amount in an elastically-bending direction as shown inFIG. 11, and therefore in this structure, the lock is harder to be canceled as compared with the first related technique. Further, the following publication exists as the prior art.

However, even in the lock structure of the second related technique, the lock retaining force basically depends only on the elastic restoring force of the elastic retaining arm103, and therefore this structure has not sufficiently met the requirement that the lock should be made hard to be canceled.

Here, if the position of the arm restraint rib104is set such that d>D is established, the lock retaining force can be enhanced, but in this structure, in the process of movement of the elastic retaining arm103in the locking direction, the distal end retaining portion103aof the elastic retaining arm103interferes with the arm restraint rib104, and can not pass over the retaining projection101.

SUMMARY OF THE INVENTION

Therefore, this invention has been made in order to overcome the above problems, and an object of the invention is to provide a lock structure for a box in which an elastic retaining arm can be moved in a locking direction, and besides is hard to be unlocked in a locked position.

A lock structure for a box, comprising:

a first box member which has a retaining projection; and

a second box member which has an elastic retaining arm,

wherein the retaining arm has at its distal end a retaining portion for engagement with the retaining projection;

wherein the first box member has an arm restraint rib which restricts a releasing movement of the retaining arm in a condition in which the retaining arm and the retaining projection are engaged with each other;

wherein when the arm restraint rib is pressed by the elastic retaining arm, the arm restraint rib is deformed by a pressing force of the elastic retaining arm; and

wherein a retaining distance of the retaining projection relative to the retaining portion of the elastic retaining arm is larger than a gap between the elastic retaining arm and the arm restraint rib in the engaged condition.

Preferably, the retaining portion is formed on a first surface of the retaining arm. The arm restraint rib is disposed so as to be opposed to a second surface of the retaining arm which is opposite to the first surface.

Preferably, the arm restraint rib has a pair of arm restraint rib pieces. The pair of arm restraint rib pieces are formed so as to surround the second surface of the retaining arm. A gap between the pair of arm restraint rib pieces is disposed at a position corresponding to a central position of the second surface of the retaining arm.

In the present invention, the elastic retaining arm is moved in a locking direction, and when the distal end retaining portion of the elastic retaining arm is brought into abutting engagement with the retaining projection, the elastic retaining arm is elastically bent and deformed, and at this time the retaining portion interferes with the arm restraint rib. However, the arm restraint rib, while receiving the pressing force of the elastic retaining arm, is also elastically bent and deformed, and therefore the retaining portion can pass over the retaining projection. Then, when the retaining portion moves to a position where it completely passes over the retaining projection, the elastic retaining arm is bent and restoringly deformed, so that the distal end retaining portion of the elastic retaining arm is retained by the retaining projection (The engaged condition). When an external force in a lock canceling direction acts on the elastic retaining arm disposed in the locked position, so that the elastic retaining arm is slightly elastically bent and deformed, the elastic retaining arm interferes with the arm restraint rib. Therefore, unless an external force large enough to even elastically bend and deform the arm restraint rib acts, the lock will not be canceled. With the foregoing, the elastic lock arm can be moved in the locking direction, and besides is hard to be unlocked in the locked position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One embodiment of the present invention will hereafter be described with reference to the drawings.

FIGS. 1 to 6show the one embodiment in which a lock structure of the present invention is applied to an electric connection box, andFIG. 1is an exploded perspective view of an important portion of the electric connection box,FIG. 2is a cross-sectional view of the lock structure for the electric connection box before it is locked,FIG. 3Ais a perspective view of an arm restraint rib,FIG. 3Bis a perspective view of the arm restraint rib and an elastic retaining arm,FIG. 4is a cross-sectional view of the lock structure for the electric connection box in a lock-proceeding position,FIG. 5is a cross-sectional view of the lock structure for the electric connection box in a locked position, andFIG. 6is a plan view explanatory of the behavior of the arm restraint rib obtained when the elastic retaining arm in the locked position is elastically bent and deformed.

As shown inFIGS. 1 and 2, the electric connection box1which is a box includes a synthetic resin-made upper cover2(first box member), and a synthetic resin-made lower cover4(second box member)to be attached thereto. A retaining projection3is formed on an inner side surface of the upper cover2. The elastic retaining arm5is formed in an upstanding manner at a side wall of the lower cover4, and a distal end retaining portion5a is formed at a distal end of this elastic retaining arm5on a first surface5bthereof

Further, the arm restraint rib6is formed on an inner surface of an upper wall of the upper cover2. This arm restraint rib6is disposed so as to be opposed to a second surface5cof the retaining arm opposite the first surface5b. When a retaining distance (retaining length) of the retaining projection3relative to the distal end retaining portion5aof the elastic retaining arm5is represented byd, and a gap between the arm restraint rib and the elastic retaining arm5located in the locked position is represented by D as shown inFIG. 5, the position of the arm restraint rib is set such that the condition, d>D, is satisfied.

As shown inFIGS. 3A and 3B, the arm restraint rib6is divided in two by a gap at a central position of its frame-like shape surrounding the rear side of the elastic retaining arm5, and is formed by a pair of left and right arm restraint rib pieces6a,6aformed by this two-division arrangement. When the pair of arm restraint rib pieces6a,6aare pressed by elastic bending deformation of the elastic retaining arm5, these pieces are elastically bent and deformed by this pressing force. Therefore, a force of moving of the elastic retaining arm5in a locking direction can be adjusted by an elastic bending force of the elastic retaining arm5itself and an elastic bending force of the pair of arm restraint rib pieces6a,6a. Here, the elastic bending force of the pair of arm restraint rib pieces6a,6acan be adjusted by a width B of the gap, a plate thickness T, a length Z and a height H.

Next, an operation for assembling the electric connection box1will be described.

In the condition ofFIG. 2, when the upper cover2and the lower cover4are assembled together, the elastic retaining arm5is moved in the locking direction. In this moving process, first, when the distal end retaining portion5aof the elastic retaining arm5is brought into abutting engagement with the retaining projection3, the elastic retaining arm5is elastically bent and deformed, and the rear surface of the distal end retaining portion5aof the elastically-bent and displaced elastic retaining arm5interferes with the pair of arm restraint rib pieces6a,6a. As a result, the pair of arm restraint rib pieces6a,6a, while receiving a pressing force of the distal end retaining portion5a, are also elastically bent and deformed in a direction of an arrow ofFIG. 4as shown inFIG. 4, so that the distal end retaining portion5acan pass over the retaining projection3. When the distal end retaining portion5aof the elastic retaining arm5is moved to a position where this distal end retaining portion5acompletely passes over the retaining projection3, the elastic retaining arm5is bent and restoringly deformed as shown inFIG. 5, so that the distal end retaining portion5ais retained by the retaining projection3. With the foregoing, the locked condition is established between the upper cover2and the lower cover4.

In the locked condition, when an external force in a lock canceling direction acts on the elastic retaining arm5, the elastic retaining arm5tends to be elastically bent and deformed. When the elastic retaining arm5is elastically bent and displaced by a small distance in a direction of an arrow ofFIG. 6, the rear surface of the elastic retaining arm5is brought into abutting engagement with the pair of arm restraint rib pieces6a,6a. As a result, the pair of arm restraint rib pieces6a,6aare also elastically bent and deformed in directions of arrows ofFIG. 6, and elastic restoring forces of the pair of arm restraint rib pieces6a,6aact on the elastic retaining arm5. As a result, the elastic bending deformation of the elastic retaining arm5is suppressed. Namely, unless an external force large enough to even elastically bend and deform the pair of arm restraint rib pieces6a,6ain a large amount acts, the lock will not be canceled. With the foregoing, the elastic lock arm5can be moved in the locking direction, and besides is hard to be unlocked in the locked position.

In this embodiment, the arm restraint rib6is divided in two by the gap at the central position of its frame-like shape surrounding the rear side of the elastic retaining arm5, and is formed by the pair of left and right arm restraint rib pieces6a,6aformed by this two-division arrangement. However, the arm restraint rib is not limited to such a structure, and may be of any structure in so far as it, when pressed by the elastic retaining arm5, can be elastically bent and deformed by this pressing force.

In the above embodiment, the arm restraint rib6is disposed at the rear side of the elastic retaining arm5which is to be retained by the retaining projection3, and it is defined that when the retaining distance of the retaining projection3relative to the distal end retaining portion5aof the elastic retaining arm5is represented byd, and the gap between the arm restraint rib and the elastic retaining arm5located in the locked position is represented by D, the position of the arm restraint rib is set such that the condition, d>D, is satisfied. However, it may also be considered that when the thickness of the distal end retaining portion5ain the elastically-shifting direction is represented bye, and the gap between the arm restraint rib6and the retaining projection3is represented by E, the position of the arm restraint rib is set such that the condition, e>E, is satisfied.

Incidentally, in the above embodiment, although the retaining projection3is formed at the upper cover2, while the elastic retaining arm5is formed at the lower cover4, the elastic retaining arm5may, of course, be formed at the upper cover2, while the retaining projection3may be formed at the lower cover4. Furthermore, although the box is shown as the electric connection box1, it may be an exterior box for covering the electric connection box1from the outer side thereof or a box other than it.

Although the present invention has been described in detail with reference to the specific embodiment, it will be manifest to those skilled in the art that various changes and modifications can be added without departing from the spirits and scope of the invention and the intended scope.

The present invention is based on a Japanese Patent Application (Patent Application No. 2005-363189) filed on Dec. 16, 2005, and its contents are incorporated herein as a reference.