Seat belt tensioning device
RELATED APPLICATION 
     Reference is made to our related copending application Ser. No. 20,045 filed Mar. 13, 1979, and to our priority document, Japanese Application No. 612821/1978, the contents of both of which are incorporated hereinto by reference. 
     PREAMBLE 
     The present invention relates to a seat belt tensioning device for use in vehicles such as automobiles, more specifically to a seat belt tensioning device which prevents a passenger from a secondary impact by restraining the passenger by means of a tensioned seat belt at an urgent time such as upon a vehicle impact due to an accident or the like, and prevents the passenger from being injured due to the shock by absorbing kinetic energy of the passenger. 
     Tensioning devices are installed in seat belts which are stretched over the shoulder, the waist, etc. of a passenger or occupant with a little slack in the normal driving condition of a vehicle. 
     They prevent him from a secondary impact by tensioning the seat belts and holding him on his seat at an urgent time such as an impact of his vehicle. Since the body of the passenger is fixed to his vehicle firmly through the seat belts, his shock due to the impact can be decreased in some degree by making use of the ridedown effect due to the crush of his vehicle. However, when the shock is very large, he is injured by the tensioned seat belts, since all the large kinetic energy of the passenger which is generated due to the impact cannot be absorbed only by restraining him by seat belts. 
     Hence, it is desirable to provide seat belts which absorb the kinetic energy of the passenger generated due to the shock at a time of an impact, etc. Various seat belt tensioning devices which absorb the kinetic energy of the passenger as well as tension of the seat belts have been proposed. 
     One of such devices has a construction that a double cylinder consisting of an inner cylinder and outer cylinder which is engaged with the inner cylinder is provided and a seat belt is tensioned by a piston moving within the inner cylinder disposed within the outer cylinder. When the load applied to the seat belt reaches a predetermined value, the piston and the inner cylinder are locked by a return stop means and then the outer cylinder is plastically deformed by an engaging member formed in an outer periphery of the inner cylinder, relative to the outer cylinder, so that the inner cylinder moves relative to the outer cylinder to absorb the kinetic energy of the passenger. 
     Tensioning devices effecting a tensioning function and a kinetic energy-absorbing function have generally become too large since it has become difficult to install them in a limited space within a vehicle. Also, the mechanism of such a device has become complex. 
     In another conventional tensioning device steel balls are provided on an outer periphery of a piston so as to cut into the cylinder when the piston moves in one direction, pulled by the seat belt, to absorb the kinetic energy of the passenger while the cylinder is plastically deformed by the steel balls. 
     In this device, since the wall of the cylinder must be made thin, there is a problem in that the cylinder wall is easily broken during the deforming process theeof so as not to effect the energy-absorbing function with certainty. 
     Accordingly, an object of the present invention is to provide a seat belt tensioning device which restrains the passenger on his seat and absorbs his kinetic energy with certainty at an urgent time. 
     Another object of the present invention is to provide a small-sized seat belt tensioning device having a simple construction for use in automobiles. 
     Still another object of the present invention is to provide a seat belt safety tensioning device without danger of breaking a cylinder thereof. 
    
    
     Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings wherein: 
     FIGS. 1 to 3 are sectional views of the tensioning device of the first embodiment of the present invention; 
     FIG. 1 shows a condition of the device before operation; FIG. 2 shows a condition of the device when the tensioning of the seat belt is completed; 
     FIG. 3 shows a condition of the device when the operation of absorbing the kinetic energy of the passenger is performed; 
     FIGS. 4 to 6 are sectional views of the tensioning device of the second embodiment of the present invention; 
     FIG. 4 shows a condition of the device before operation; 
     FIG. 5 shows a condition of the device when the tensioning of the seat belt is completed; 
     FIG. 6 shows a condition of the device when the operation of absorbing the kinetic energy of the passenger is performed; 
     FIGS. 7 and 8 are sectional views of the tensioning device of the third embodiment of the present invention; 
     FIG. 7 shows a condition of the device before operation; and 
     FIG. 8 shows a condition of the device when the operation of absorbing the kinetic energy of the passenger is performed. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Reference is now made to the first embodiment illustrated in FIGS. 1-3. Within a bottomed cylinder 1 which is adapted to be fixed to a floor, roof, etc. in a desired space of a vehicle, a piston 2 is movably disposed for movement in only one direction (leftward in the drawings). Piston 2 is provided with a return stop means 3 in the outer periphery thereof. The return stop means 3 includes steel balls 31 which are supported and confined in a wedge-shape cavity defined by an inwardly inclined surface formed on the outer peripheral surface of the piston and the inner wall of the cylinder. 
     Piston 2 is prevented from moving rightwardly in the illustrated embodiment by abutment against the cylinder bottom portion 11. However, in another embodiment the piston could be normally disposed in a position slightly to the left of bottom portion 11 and return stop means 3, acting as a stopper, would prevent piston 2 from moving in the rightward direction in FIGS. 1-3 while allowing leftward movement. An O ring 21 is fitted with the inner wall of the cylinder and the outer periphery of piston 2 to effect a seal therebetween. 
     Piston 2 has an inner cavity 2 wherein a corrugated iron sheet 4 is accomodated as a deformable member. One end of the iron sheet 4 is fixed to a piston head 23. The other end of the iron sheet extends at least into a passage 10 which is narrower than cavity 22 and passes through an opening in the right end of piston 2 and penetrates the bottom portion 11 of cylinder 1 as hole 12 through which passes seat belt S which connects to deformable sheet 4 at least partially inside piston 2 in the illustration. 
     A powder chamber 5 is attached to the bottom portion 11 of the cylinder 1, and the powder chamber is communicated with the interior of the cylinder 1 through a cylinder chamber 13 which is provided in the bottom portion 11 of cylinder 1. The powder chamber 5 is charged with a propellant 51 which explodes when electric signals generated in an impact sensor (not shown) are transmitted through a lead wire 52. 
     In operation, when propellant 51 explodes due to the impact signals at an urgent time such as upon impact of the vehicle, plenty of gas is generated to raise the gas pressure within the cylinder chamber 13. Then the piston 2 is moved to the left of FIGS. 1-3 due to the high pressure gas. At this time, since iron sheet 4 has a deforming stress value larger than the operating force of piston 2, seat belt S is drawn within cylinder 1 together with the piston 2 to restrain the passenger on his seat. 
     When the passenger is completely restrained by a predetermined high tension force of the seat belt S when piston 2 moves to the left, if a further tension force larger than the operating force of the piston 2 is applied to the seat belt S, return stop means 3 comes into operation. That is, steel balls 31 cut into the inner wall of cylinder 1 and the piston is locked relative to the cylinder 1. As a result, the passenger is completely restrained. 
     Furthermore, if still more tension force exceeding the deforming stress value of the iron sheet 4 is applied to the seat belt S, the corrugated iron sheet 4 is stretched out or elongated as the seat belt S is drawn out and gradually extended to the right for a substantial but limited distance as shown in FIG. 3. 
     In this process, the kinetic energy of the passenger is absorbed. 
     In the first embodiment, seat belt S is directly connected to the iron sheet 4 as a deformable member. However, if seat belt S is made of such a material as to be easily damaged or broken by high pressure gas or heat, it may be connected to the iron sheet 4 indirectly through a rod as in one embodiment disclosed in our above-mentioned copending application. If a rod is used, the air tight condition between the hole 12 penetrating the bottom portion of the cylinder and the rod sliding through the hole 12, is preferably better maintained compared with that in the embodiment illustrated in FIGS. 1-3. 
     FIGS. 4 to 6 show a second embodiment wherein the same parts as those of the first embodiment are designated by the same reference numerals as those of the first embodiment, and the explanation of the portions common to those of the first embodiment is omitted. 
     A piston 20 is provided with a return stop means 3 and is disposed within cylinder 1 so as to move in only one direction (to the left in FIGS. 4 to 6). Tightly inserted in a conical cavity 24 of the piston is a conical end portion 412 of a cylindrical body of iron 41, the other end of which is formed to a flange shaped stopper 411. A rod 42 which is formed integrally with the conical end portion 412 is tightly inserted in the narrow passage 10 of the piston 20 and on through hole 12 in cylinder bottom 11 to the exterior. The outer end of rod 42 is connected with the seat belt S by a joint 43. The piston operating means of the second embodiment may be similar to that of the first embodiment. 
     In the second embodiment, piston 20 is moved to the left by gas pressure due to an explosion of the propellant at an urgent time such as upon an impact of the vehicle. When the tension force of the seat belt reaches a predetermined value, the piston 20 is locked to the cylinder 1 by the return stop means 3. Then, when the tension force applied to the seat belt exceeds the deforming stress value of the iron cylindrical body 41, the conical end portion 412 is squeezed by the piston, and the iron cylindrical body 41 is drawn out or extended to the right a substantial but limited distance as shown in FIG. 6. 
     Thus, the kinetic energy due to the impact of the passenger against the seat belt is absorbed in this stage. 
     FIGS. 7 and 8 show the third embodiment of the present invention. 
     Provided within the piston 200 is an inner cavity 201 having a columnar shape the axis of which is perpendicular to the longitudinal axis of piston 200 and cylinder 1. Rotably accommodated inside cavity 201 is a columnar reel 43 having a diameter larger than the radius of cavity 201. One end of iron sheet 42 is fixed to and wound about the columnar reel 43 and then the iron sheet is curved along a corner portion 202 defined by the inner wall of the piston for forming the cavity 201 and narrow passage 10 in piston 200 in which it is connected to the seat belt S. 
     In the third embodiment, when a tension force not less than the bending stress value of the iron sheet 42 is applied to the seat belt S, after piston 200 is forcibly moved to the left in FIG. 8 and the tensioning operation of the passenger is completed, reel 43 unwinds due to the pull on iron sheet 42 which continuously bends around corner portion 202 and is drawn out of piston 200 and extended a substantial but limited distance as shown in FIG. 8. The piston is prevented by rightward movement by return stop means 3 as before. As a result, the kinetic energy of the passenger can be absorbed. 
     Various modifications can be made. For example, an iron wire can be used in place of the iron sheet 42. Furthermore, in the above embodiments of the present invention, propellant is used for operating the piston. Instead, other means of pouring high pressure stored gas into the cylinder at an urgent time, or of making use of a spring, etc. can be used to operate the piston. 
     Also, by changing the material, shape, etc. of the deformable member, the tensioning load on the passenger and the kinetic energy absorbing characteristic of the seat belt can be freely selected. Likewise, as the means for preventing the return movement of the piston, other conventional suitable means can be used instead of or in addition to the means of cutting steel balls into the cylinder. 
     As described above, the present invention relates to a seat belt tensioning device comprising a piston slidably disposed in a cylinder in only one direction, an operating means for sliding the piston at an urgent time and a deformable member equipped in the piston which is plastically deformed and thereby moved or elongated in the opposite direction by a predetermined tension force. 
     The tensioning device of the present invention is of small size, has a simple construction and operates with certainty to prevent the passenger from a secondary impact by restraining him by a predetermined tension force at an urgent time and to decrease his injury as far as possible by absorbing the kinetic energy of him due to the impact. Since the energy-absorbing means of the present invention does not deform the cylinder plastically, there is no danger of breaking the cylinder thereby. 
     As is apparent from the above, the tensioning device of the present invention can be applied to a seat belt for use in a vehicle, etc. with an excellent practical effect. 
     Having now fully described several embodiments of the invention, it will be apparent to one of ordinary skill in the art that may additional changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein including the following claims.