1. Field of the Invention
The present invention relates to a seat belt buckle, and in particular, to an improved structure for a buckle incorporated in a seat belt which is provided on the seat of an automobile for protecting a passenger in the event of a collision.
2. Description of the Prior Art
Conventionally, a seat belt as illustrated in FIG. 6 is provided on the seat of an automobile for protecting a passenger in the event of an accident such as a collision.
The seat belt has a webbing 1 which is a restraining member on one side, and a flexible wire 3 which is a restraining member on the other side.
A tongue plate 2 engaged with the webbing 1 and a buckle 4 engaged with the flexible wire 3 are matingly engaged when the seat belt is used.
When an impact occurs, a passenger seated in a seat 5 is prevented from being catapulted in the forward direction by the linkage of the two restraining members 1, 3.
When alighting from the vehicle, the linkage of the buckle 4 and the tongue plate 2 is released by pressing a metal buckle button on the buckle 4. As a result, the restraining members 1, 3 do not obstruct the passenger when quitting the seat.
Simplification of the action of engaging and disengaging the buckle 4 and the tongue plate 2 is necessary to allow smooth entry to and quit from the automobile. Accordingly various types of buckles for seat belts are known conventionally, such as those disclosed in Japanese Laid-Open Utility Model Applications 61-134306 and No. 61-153511.
The structure of this type of conventionally known buckle 4 is illustrated in FIG. 7 to FIG. 9. Some parts of the buckle shown in FIG. 7 differ in shape slightly from parts of the buckle as shown in FIG. 8 and FIG. 9. However, these points of difference bear no relation whatsoever to the essential features of the present invention.
A buckle base 8 is fabricated by bending a metal plate with adequate rigidity, such as a steel plate or the like, into a U-shape in cross-section. The buckle base 8 is maintained inside a space enclosed by an upper cover 6 and a lower cover 7. The buckle base 8 has a flat base plate 9 maintained in a position immediately above the lower cover 7, and a pair of plates 10, 10 bent upright from the flat base plate 9. The upright plates 10, 10 are erected at right angles to the base plate 9 at the edges of the two side sections of the base plate 9. In addition, one end of the flexible wire 3 (see FIG. 6), which acts as a restraining member, is linked to one end of the buckle base 8.
A buckle latch piece 11 forms a latching and unlatching mechanism for engaging the buckle base 8 of the buckle 4 with the tongue plate 2. The buckle latch piece 11 has a depending hook leaf 12 on its front end (closer to the tip of the buckle 4, the left side in FIG. 7 to FIG. 9), a pair of projecting leaves 13, 13 on its rear end (on the right side in FIG. 7 to FIG. 9), and a pair of bent leaves 26, 26 on its lateral sides. The projecting leaves 13, 13 project from each of the two sides in a width direction laterally, and the pair of bent leaves 26, 26 project downward from the buckle latch piece 11, respectively.
The projecting leaves 13, 13 are inserted into a pair of first through-holes 14, 14 formed in the upright plates 10, 10, respectively, so that the buckle latch piece 11 is supported by and between the upright plates 10, 10 and freely pivoted or swung around its rear secion.
A lock plate 15 is provided on the latch piece 11 and has the role of maintaining the buckle latch piece 11 in the lock position (the position in which the hook leaf 12 is adjacent to the base plate 9 of the buckle base 8), until the passenger operates a buckle button 18 (later described). The two sides of the lock plate 15 are inserted into a pair of second through-holes 16, 16 formed in the upright plates 10, 10, respectively, in a manner which allows a certain amount of free vertical and lateral displacement of the lock plate 15. A lock plate spring 17, which is a compression spring, is provided between the rear edge of the lock plate 15 and the buckle latch piece 11. The lock plate spring 17 applies an elastic force against the lock plate 15 in the forward direction.
A push-out spring 21, which is a compression spring, is provided between a buckle slider 19 and an engaging section 20 formed on the base plate 9 of the buckle base 8. The push-out spring 21 applies an elastic force against the buckle slider 19, always in the forward direction.
The buckle button 18 moves freely in the longitudinal or front-rear direction between the lower surface of the upper cover 6 and the upper edges of the upright plates 10, 10 of the buckle base 8. A button spring 24, which is a tension spring, is provided between an engaging section 22 at the rear end of the buckle button 18 and an engaging section 23 at the front of the buckle latch piece 11. The button spring 24 contributes an elastic force to the buckle button 18 in the forward direction, and an elastic force to the buckle latch piece 11 to rotate the buckle latch piece 11 in the clockwise direction of FIG. 9.
When the buckle 4 and the tongue plate 2 are to be connected, the passenger presses a tip section 2a of the tongue plate 2 into a slot-shaped aperture 25 (FIG. 9) between the lower edge of the buckle button 18 and the upper surface of the base plate 9 of the buckle base 8. The passenger then presses the buckle slider 19 against the elastic force of the push out spring 21 to the rear (to the right in FIG. 7 to FIG. 9).
As the buckle slider 19 moves toward the rear, a rear surface 19a of the buckle slider 19 presses a pair of bent leaves 26, 26, to the rear. This causes the buckle latch piece 11 to pivot in the counterclockwise direction in FIG. 9, around its rear section (the section where the first through-holes 14, 14 are engaged with the projecting leaves 13, 13) opposed to the elastic force of the button spring 24. As a result, the hook leaf 12 formed at the front end of the buckle latch piece 11 enters an opening 28 formed in the tip section 2a of the tongue plate 2. The tongue plate 2 and the buckle 4 are thus connected with each other and cannot be separated while in this state.
A notched groove 27 formed in the center of the lock plate 15 is engaged with a jaw section of the engaging section 23. This causes the lock plate 15 to combine with the buckle latch piece 11 to freely slide in the direction of their surfaces only. Therefore, as the buckle latch piece 11 pivots or swings, the lock plate 15 pivots or swings in the same direction as the buckle latch piece 11 (counterclockwise in FIG. 9). As a result, the lock plate 15 is pressed by the elastic force of the lock plate spring 17 into a pair of narrow sections 16a, 16a formed in the front side of the second through-holes 16, 16. The lock plate 15 is stable when pressed into the narrow sections 16a, 16a. The lock plate 15 then prevents the upward movement of the front end of the buckle latch piece 11. As a result, the engagement of the hook leaf 12 of the buckle latch piece 11 with the opening 28 in the tongue plate 2 cannot be inadvertently released.
To release the engagement of the buckle 4 with the tongue plate 2, the passenger presses the buckle button 18 into the upper cover 6 against the elastic force of the button spring 24. The passenger then pushes the lock plate 15 to the rear from a rear surface 18a (FIG. 9) of the side wall section formed in the buckle button 18.
As a result, both sides of the end section of the lock plate 15 are disengaged from the narrow sections 16a, 16a of the second through-holes 16, 16 and moved to a pair of wide sections 16b, 16b which are continuation of the narrow sections 16a, 16a on the rear side thereof. This makes it possible to move the lock plate 15 upward, so that the buckle latch piece 11 freely pivoted or swung in the clockwise direction in FIG. 9 around the axis where the projecting leaves 13, 13 are engaged with the first through holes 14, 14. The buckle latch piece 11 is then pivoted or swung in the clockwise direction in FIG. 9 by the elastic force of the button spring 24. This results in the hook leaf 12 formed on the front end of the buckle latch piece 11 being extracted from the opening 28 of the tongue plate 2. The tongue plate 2 and the buckle 4 then become freely separable in this state.
In this conventional seat belt buckle, the buckle button 18 for disengaging the tongue plate 2 and the buckle 4 is mounted to the buckle base 8 such that it is freely displaced to some extent with respect to the buckle base 8. Because of this, a slight gap exists between the buckle base 8 and the buckle button 18, which results in a tendency for play to occur between the buckle base 8 and the buckle button 18 from the movement and vibration of the vehicle. A discordant noise is produced from play in the buckle button 18, which causes some discomfort to the passenger.
The play between the buckle button 18 and the buckle base 8 could be eliminated in spite of the existence of the slight gap mentioned above by providing a button spring 24 with strong elastic force which puts tension on the buckle button 18. However, considerable force must be required against the button spring 24 to release the buckle 4 and the tongue plate 2, which is not desirable. This is a drawback when there is a strong elastic force in the button spring 24.