Abstract: In a buckle for a seat belt, lower ends of side walls of an operational button is positioned at a level lower than lower ends of guide portions of a base, and an upper surface of a portion of a lower cover defining a tongue-insertion opening is positioned at a level higher than an upper surface of a bottom of the base. Therefore, when a tongue is engaged with the buckle, an engaging portion of the tongue touches at least one of the side walls of the operational button made of resin, and the portion of the lower cover made of resin. Thus, the tongue is prevented from touching the guide portions and the bottom of the base made of metal, thereby preventing a noise due to the metal-to-metal contact when the tongue 3 is inserted into the buckle and engaged with the buckle. Therefore, a jar on an occupant's nerve when wearing the seat belt can be avoided.

Abstract: A buckle is provided with a non-contact buckle switch improved in durability to be securely operated. The non-contact buckle switch is switched by detecting a movement of one of an ejector, latch member and lock member of the buckle. The buckle switch includes a magnet and a Hall element for generating an electromotive force by a magnetic field of the magnet. One of the magnet and the Hall element is attached to a fixed member, and the other of the magnet and the Hall element is attached to one of the ejector, latch member and lock member.

Abstract: In a latched state of a buckle in which a tongue is engaged, an inertia lever member of a movement preventing device enters into a path of a lock pin. When the buckle is pulled by a buckle pretensioner in this state, the inertia lever member moves in the longitudinal direction, and pressed portions of the inertia lever member are held by a holding portion, so that the inertia lever member does not pivot and the levers are thus held in the path of the lock pin. At the end of pretensioning, the buckle is stopped. Since the moment produced by the inertia force acting on the center of gravity of mass body of the movement preventing device is larger than the moment produced by the inertia force of an operational button, the inertia lever member does not pivot, so that the inertia lever member can be held in the path of the lock pin. In the buckle, the inertia release can be effectively prevented with a simple structure.

Abstract: A buckle is formed of a base, a latch member supported by side walls of the base so that the latch member can pivot between its non-engaged position and its engaged position, an operational member manipulated to cancel an engagement between the tongue and the latch member; and a lock member. The latch member is biased to the engaged position, and pivots to the engaged position when a tongue is inserted into a predetermined position to engage the tongue. The lock member holds the latch member to the engaged position when the tongue and the latch member are engaged, and is able to be moved by the operational member to a position capable of canceling the engagement between the tongue and the latch member. The lock member is arranged to move only in the longitudinal direction of the buckle. Thus, the movement of the lock member is simplified to improve controlling ability of the latch member.

Abstract: In a buckle of the present invention, inertia force F.sub.1 acts in a direction opposite to a direction toward a disengaging position of a main body 4d of a lock member when the buckle is pulled by a pretensioner. Clockwise torque T.sub.1 is developed on a lever 12b and counter-clockwise torque T.sub.2 is developed on a mass body 12c. Since the torque T.sub.2 of the mass body 12c is larger generally, the lever 12b and the mass body 12c rotate together in the counter-clockwise direction so that the lever is set in the restricting position. At the bottoming of the pulling action of the buckle, the inertia force F.sub.2 acts in a direction toward the disengaging position of the main body 4d. Therefore, the mass body 12c rotates in the clockwise direction and the lever 12b is held in the restricting position so that the movement of the lock member in the direction toward the disengaging position of the main body 4d is prevented.