Fastening means for safety belts
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improved fastening means for safety belts for cars and the like which fastening means is designed especially for resisting the very high G-forces to which the system is subjected in connection with, e.g. a collision. Said safety belt system may, if desired, also be provided with a device reacting very rapidly to a collision and then causing rapid tightening of the safety belt. 
     2. Description of the Prior Art 
     Research of late years disclosed that it is of the utmost importance that a person remains sitting as immovably strapped up to the car seat as possible during a car crash if personal injuries are to be avoided in connection with such a crash. This scientifically supported fact is, inter alia, based on the recognition that only a person being completely strapped up to the car seat will be able to benefit fully from the so called deformation zone inherent in the car which is, in turn, crucial to the stopping distance of the car. As known, very high G-forces occur in a collision and the absolute magnitude of said forces will decrease with an increasing stopping distance. With a slack safety belt system, or if the safety belt is stretched the stopping distance will be reduced and the G-forces will, thus, increase. 
     From the above mentioned it should be obvious that one should aim at having a person/persons follow the deformation cycle of the car to a highest possible extent in a collision, and to achieve this the person/persons must be strapped up so as to become as immovable as possible during the entire collision cycle. 
     In order to achieve such a result there are, inter alia, developed pyrotechnic devices causing a tightening of the safety belt in the first phase of a collision. This technology involves G-sensitive members (sensors) to be provided and which are calibrated to react at a certain G-value in the front part of the car. When reacting, said sensors generate a signal that is, e.g. via a detonating fuse or electrically, transmitted to a pyrotechnic charge that is ignited and is connected with the shaft of the belt roll which is, in turn, immediately activated to tighten the safety belt. All this occurs during the initial phase of the collision and before any critical G-values are reached. In this manner the person/persons will be kept strapped up to the car seat and will, thus, be in the most advantageous position to face the crash. 
     As regards the stretchability of the safety belt system, this should, obviously, be as low as possible, ideally the safety belt system should be &#34;dead&#34;. When the pyrotechnic charge is ignited G-forces of 2000 to 3000 G will occur at the moment of ignition and these forces are very rapidly transmitted to the safety belt system and, thus, to the fastening means per se. This momentary tightening involving very high G-forces is, thus very critical to the fastening means since the mechanism of the fastening means will &#34;float&#34;. Tightening of the safety belt system mainly occurs in the longitudinal direction of the fastening means with a resulting downward pressure on all members of the fastening means. Conventional fastening means are not designed to resist the above mentioned conditions which, inter alia, imply that the fastening means is subjected to exceptionally high G-forces. Consequently, the fastening means will be rendered more or less inoperative, the mechanism, e.g. being unintentionally opened. 
     Another fact to be mentioned is that developent tends towards more light-weight cars. This will, inter alia result in said stopping or retardation distances becoming shorter than before. This will, in turn, cause greater stress, inter alia, on the fastening means during the catch up phase following after the rapid tightening phase. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a fastening means for a safety belt that is able to resist the very high G-forces, inter alia, occurring in the initial phases of a collision, when a preliminary tightening of the safety belt system takes place or/and with use of a safety belt system that is not stretchable to any degree worth mentioning, i.e. a safety belt system that is approximately &#34;dead&#34;. It will easily be understood that the achievement of said aim is quite critical, since the fastening means must be intact and functional in order to meet and resist the forces that follow and are transferred to the fastening means when the person in question is caught and held firmly by the safety belt system, said forces, in fact, accompanying the entire collision cycle. 
     The above mentioned object is achieved by a fastening means according to the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described in more detail with reference to the accompanying drawing showing one embodiment, and wherein: 
     FIG. 1 is an exploded perspective view showing the components of the fastening means of the invention 
     FIG. 2 is a vertical cross-sectional view of the fastening means in an open position; 
     FIG. 3 is a view similar to FIG. 2 showing the fastening means in a locked position; and 
     FIG. 4 is a view similar to FIG. 3 showing some of the force components occurring in a collision. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1 an expeller 1 is shown having an expeller cam 1a, expeller lugs 1b, and expeller legs 1c; a locking flap 2 with its supporting lug 2a, its hinge arms 2b, and rivet 2c; a blocking flap 3 with its legs 3a, bearing pin 3b, cross bar 3c, and lugs 3d for securing springs; locking/expeller springs 4; a case member 5 with its rear portion 5a, fixing hole 5b for mounting in a car, guide hole 5c, and recesses 5d for mounting a blocking flap, a recess 5e for receiving the supporting lug 2a of blocking flap 2, and a space 5f between the parallel plates; a push-button 6 having raising cams with a lateral plate 6a, and lug cams 6b; a locking tongue 7 with its tongue projection 7a; push-button springs 8; an interior frame 9 with uprights 9a provided with cams to hold a guide the blocking flap, and guide edges 9b for guiding locking tongue 7 to be inserted; and an outer casing 10. 
     FIG. 2 shows the fastening means in an open position. Expeller 1 sliding in locking case member 5, in fact, in the space provided between the bottom and top members, respectively, of locking case member 5 is situated in its foremost position and locking/expeller springs 4 are slightly biased. Said springs 4 are at one end secured to expeller lugs 1b and at the other end secured to lugs 3d of blocking flap 3. By the aid of bearing pins 3b said blocking flap 3 is mounted in recesses 5d of locking case member 5. Supporting lug 2a of locking flap 2 rests on the rear portion of expeller 1, and locking flap 2 is, thus, in an open position. Blocking flap 3 has its legs 3a pushing against locking flap 2. The hinge arms 2b of locking flap 2 are guided around the rear portion 5a of locking case member 5. The locking flap will always be in contact with blocking flap 3 preventing rivet 2c of locking flap 2 from disengaging the guide hole 5c in locking case member 5. When the push-button is depressed, the raising cams of the push-button 6 with guide plate 6a will raise the locking flap 2 to a greatest possible degree. 
     When nose 7a of locking tongue 7 is pushed all the way into the fastening means expeller 1b will be pushed inwards into a rear position and locking/expeller springs 4 will have a maximum bias, as indicated in the dotted line 4a. In spite of the maximum bias of springs 4 the downward force on blocking flap 3 will not be unfavorably high due to the distance between the center line of force 4a and the bearing pins 3b of blocking flap 3. In other words, the moment arm is increasingly reduced the further rearward expeller lugs 1b are placed. 
     FIG. 3 shows the fastening means in a locked position. The spring 4 force is now higher and the locking force per se is high due to the fact that blocking flap 3 is lowered into a locking/blocking position and has, thus, an almost maximum moment arm against the spring force. The upper angular leg of blocking flap 3 having cross-bar 3c thereon is designed to be as light-weight as possible and the lower angular leg having lugs 3d thereon is made relatively heavy. 
     Locking flap 2 is, now, in a locking position and rivet 2c is in place extending through locking hole 5c in locking case member 5, and the nose portion 7a of locking tongue 7 is pushed against rivet 2c by expeller leg 1c. Normally, rivet 2c will not be in contact with locking case member 5, a fact that will ensure reduced friction in use. When loaded, however, rivet 2a will be in contact with the locking case member and this is due to the hinge arms 2b which will will yield. In this manner a pure shear force will affect rivet 2c resulting in a maximum utilization of the tensile strength of materials. 
     When said fastening means is opened, the upper cams 6b of push-button 6 will initially push cross bar 3c of blocking flap 3 down and pass over it. When said cross bar is pushed sufficiently far down the raising cams of push-button 6 with side plate 6a will raise locking flap 2. Due to the fact that blocking flap 3 will, now, swing out it is pushed up. When springs 4 are gradually biased the force will only increase marginally because the moment arm is reduced. When locking flap 2 is almost at its uppermost position expeller 1 will expel locking tongue 7 from the fastening means. Expeller cam 1a will lift supporting lug 2a of locking flap 2 and, thus, hold the locking flap in its upper position. 
     Similar to FIG. 3, FIG. 4 shows the fastening means in a locked position and illustrates the forces affecting the fastening means in cases of high G-loads. I shows a typical section of G-forces in connection with a preliminary tightening of a safety belt. The resultant force Ia is relatively typical. Blocking flap 3 will have its center of gravity beneath bearing pins 3b due to the light weight of the upper part of the blocking flap 3, which part includes the cross bar 3c. Thus the blocking flap is locked proportionally with the G-load. Push-button 6 will move downward when subjected to a G-load. Both push-button springs 8 and the contact with cross bar 3c of blocking flap 3 will hold back. The angle of the upper cams 6b of push-button 6 are adapted and balanced in relation to the weight of push-button 6 and, furthermore, the tension of push-button springs 8, and the weight of blocking flap 3, resulting in a static balance in cases of G-loads. The fastening means will, thus, not be opened even though there might be a very high G-load. 
     In FIG. 4 
     N=the opening moment of the push-button, and 
     G 1  and G 2  =the locking moment of the blocking flap along resultant of force Ia.