When two resin molded parts are joined together, a lock mechanism is widely used in which a lock arm having flexibility is formed on one resin molded part and a lock projection is provided on the other resin molded part, the locking projection being adapted to be brought into engagement with an engagement projection on the lock arm by making use of the flexure of the lock arm.
FIG. 4 shows the configuration of a lock mechanism of a type described in Patent Literature 1, for example. FIG. 4(a) shows a pre-lock state, and (b) shows a post-lock state at (b). Reference numeral 120 denotes a lock arm provided on the one resin molded part, and an engagement projection 121 is provided at a distal end thereof. In addition, a lock projection 111 is provided at a lock portion 110 of the other resin molded part, the lock projection 111 being adapted to be brought into engagement with the engagement projection 121 of the lock arm 120.
In this lock mechanism, when the lock arm 120 moves upwards (in a direction indicated by an arrow J) relative to the lock portion 110 from the state shown in FIG. 4(a), the engagement projection 121 rides over the lock projection 111 by making use of the flexure of the lock arm 120. Then, as shown in FIG. 4(b), the engagement projection 121 and the lock projection are brought into engagement with each other in the position where the engagement projection 121 has ridden over the lock projection 111. Thus, the locked state is ensured.