Patent Publication Number: US-4545097-A

Title: Lock for a safety belt

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     The following application is related to the present application: application Ser. No. 231,012, filed by Franzwier on Feb. 3, 1981, entitled &#34;Lock for a Safety Belt&#34;. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a lock for a safety belt into which an insertion tab can be inserted and can be locked by a locking latch. The lock has a pushbutton which can be shifted parallel to the insertion path of the insertion tab against a spring force. Through the operation of the pushbutton, the locking latch can be moved against the force of a compression spring from a locking position into the opening position. 
     2. Description of the Prior Art 
     In known safety belt systems of the aobve-mentioned type, the locking latch is pressed into the locked position by a spring force if the pushbutton is not operated. If the pushbutton is pushed in, the first-mentioned spring force must be overcome for moving the locking latch along a shift path which is perpendicular to the shift path of the pushbutton, possibly in addition to the spring force which pushes the pushbutton into the unoperated position; this spring force increases with increasing pushbutton stroke, which makes the operation of the pushbutton more difficult. The two above-mentioned spring forces progressively increase with increasing pushbutton stroke. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a lock of the above-mentioned type in which the operation of the pushbutton is facilitated. 
     With the foregoing and other objects in view, there is provided in accordance with the invention a lock for a safety belt comprising a belt lock having a metallic support with two spaced plates defining an insertion path, an insertion tab attached to a belt end for insertion in the insertion path of the metallic support, a latching bolt movable transversely to the insertion path of the blocked position in which the bolt is interposed in the path of said tab and to the open position in which the bolt does not block passage of the tab in the insertion path, a pushbutton mounted on the metallic support movable parallel to the insertion path against the force of a spring to move the latching bolt from the blocked position to the open position against the force of a compression spring urging the latching bolt to closed position, said compression spring is a spring tab which is clamped on one side and arranged approximately parallel to the movable path of the pushbutton whereby movement of the pushbutton along its movable path causes an increase of distance between the clamping point of the spring and point at which said force of the compression spring is applied with consequent decrease in said force at said latter point. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a lock for a safety belt, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention, however, together with additional objects and advantages thereof will be best understood from the following description when read in connection with the accompanying drawings, in which: 
     FIG. 1 shows a cross-sectional view of the lock for a safety belt according to the invention, showing the relationship of insertion path, locking latch, movable pushbutton and spring tab, and 
     FIG. 2 shows an exploded view of the pushbutton, locking latch and spring tab according to FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the invention, a spring tab which is clamped on one side and is arranged substantially parallel to the shifting or moving path of the pushbutton is provided as the compression spring. The pressure of the spring tab decreases when the push button is shifted into the opening position, as the effective spring length, that is, distance, between the clamping point and the point of attack of the force becomes larger. 
     Thus, by the particular arrangement of the spring tab, when the pushbutton is pressed-in the direction of its opening position, the effective pressure force of the spring tab becomes accordingly less due to the increasingly longer lever arm between the clamping point and the point of attack of the force. In this manner the force required for pushing-in the pushbutton becomes relatively smalle due to this spring force. If this pushbutton is further under the action of one or several other springs, the spring force attacking, i.e. pressing, at the locking latch is not increasingly added to the additional spring forces during movement of the pushbutton, whereby overall the operation of the pushbutton is facilitated substantially. 
     Within this scope of the present invention the possibility exists of clamping the spring tab in a stationary manner at the support of the belt lock, preferably at the height of the end of the pushbutton on the pressure side, where the pushbutton can be moved relative to this spring tab, slowly increasing its spring length, or, in accordance with the subsequently described embodiment example, the spring tab can be fastened directly to the pushbutton according to an advantageous embodiment in which the spring tab is fastened at the front end, as seen in the shifting direction of the pushbutton and pushes the locking latch which can be shifted perpendicularly to the shifting path, against a lifting surface of the pushbutton which is inclined relative to the shifting path. Further advantageous embodiments of the invention are seen from the embodiment example which is shown in the drawing and will be described in the following: 
     In the view according to FIG. 1, a belt lock is generally designated by numeral 1 and an insertion tab with 2. The belt lock consists substantially of a metallic support 3/4 with two plates 3 and 4 which define the insertion path 5 for the insertion tab 2. The belt lock 1 can be fastened, for instance, by means of a cable, to the bottom of the motor vehicle. Shown as a detail in FIG. 2, is a pushbutton 6, a locking latch 7, as well as of a fork-like spring tab 8. The pushbutton 6 has guide slots 9 arranged on both sides, by which it is guided in corresponding guide edges of the upper plate 3 of the support 3/4, parallel to the insertion direction (arrow FIG. 1). At cantilevered pins 10 of the pushbutton 6, compression springs not shown, are held which are braced against an abutment, likewise not shown, of the support 3/4. The pushbutton 6 can be moved against the spring force in the direction of the arrow by pushing by hand on a handle 11. 
     The pushbutton 6 further has, offset on both sides relative to the center of the insertion path, two inclined track-like lifting surfaces 12. A projection-like detent element 13 is centered at the height of the ends of the lifting surfaces 12. A mounting 14 is disposed at the rear end of pushbutton 6. A spring tab 8 having two spring tines 16 is supported in an opening 15. The common fastening end of a bent-off extension 17 of the spring tab 8 extends around the mounting 14, while a spring lug 18 is clamped in the opening 15. The spring tab 8 which in FIGS. 1 and 2 is pretensioned upward, is braced against the detent element 13 and pushes the locking latch 7 with its two inclined sliding surfaces 19 onto the lifting surfaces 12 of the pushbutton 6. The locking latch 7 is C-shaped in design in the embodiment example, its free legs having latch extensions 20 which are provided with bevels 21. 
     FIG. 1 shows the locking or latching position of the lock, in which the locking latch 7 is pushed by the spring tab 8 into the uppermost lifting position of the lifting surfaces 12 and in which the locking latch is detented with the lower edge 22 of the middle or non-free leg behind the detent element 13. In this position, the latch extensions 20 of the locking latch 7 are at the height of the insertion path 5 as well as in a locking opening 23 of the insertion tab 2, the latching edge 24 of which is braced against the vertical part of the latch extensions 20. To open the lock, the pushbutton 6 is shifted in the direction of the arrow against the force of a spring, whereby the locking latch 7 and the detent extension 13 become disengaged and whereby the locking latch 7 is shifted along the lifting surfaces 12 against the force of the spring tab 8 downward into the opening position, the locking latch 7 being guided in guide openings in the plates 3, 4. In a certain shift position, the locking edge 24 comes into an engagement with the inclines 21, whereby a force component directed in the opening position acts on the locking latch 7 and pushes the latter into the opening position, in which the locking latch is detented again with its upper edge 25 behind the detent element 13 of the pushbutton 6 which has returned into the rest position, and is locked. Additionally, the locking latch 7 can be held in the opening position by a resilient ejector, not shown, which is guided in the insertion path 5, and blocks the shifting path of the latch extensions 20 as the insertion tab 2 is withdrawn. During the shifting motion of the locking latch 7, the latter is continuously pushed by the spring tab 8 against the lifting surfaces 12, and in the course of the shifting of the push button, the effective spring travel of the spring tab 8 becomes larger and the pressure force to be supplied at the pushbutton 6 becomes therefore smaller. In FIG. 1, the lowest position of the spring tab 8, i.e. after the pushbutton 6 is pushed-in completely, is indicated dash-dotted. 
     If the insertion tab 2 is inserted into the insertion path 5, the front edge 26 of the insertion tab 2 comes into contact with a stop 27 of the pushbutton 6, extending into the insertion path 5, and shifts the latter so far that the detent connection between the detent element 13 and the locking latch 7 is released, whereby the locking latch 7 drops back abruptly and with an audible click into the locking position under the force of the spring tab 8.