Seat belt buckle pretensioner

Abstract: An automotive seat belt pretensioner assembly is provided which includes a housing assembly (12) for receiving a cable (18) that is driven by a piston (16) toward an open end (54) of an actuator housing (24) in response to the operation of a pyrotechnic gas generating device (20). A plastic end cap (26) is provided for covering the housing end (54). The cap (26) includes a frangible end wall (54) for permitting passage of an end (46) of the cable (18). The frangible end wall(54) includes a pattern of reduced wall thickness (56).

Description: The present invention relates generally to automotive occupant restraint systems, and more specifically to the construction of mechanisms for providing condition responsive pretensioning force to the buckle end of the automotive seat belt systems. It is well-known in the automotive industry to provide pretensioning devices for enhancing the efficacy of occupant restraint systems that employ seat belts. In one particular type of pretensioning device, a pyrotechnic gas generator is employed to drive the end of a cable supporting a seat belt buckle in response to a predetermined deceleration of the vehicle in which the buckle is installed. US-A-5 403 037 US-A-3 942 819 and US-A-4 917 210 are exemplary of such pretensioning devices. US-A-3 942 819 discloses the features of the preamble of claim 1. One important design constraint in providing such a pretensioner is to provide a housing for accommodating the travel of the mechanism that is displaced by the gases in the pyrotechnic device. This space for travel must be provided in the design of this automotive component with regard to the overall desire of designers and manufacturers of automobiles to minimise the weight and cost of the components used in the assembly of the vehicle. Since the movement that must be accommodated is not normal and repetitive movement in the use of occupant restraint systems, but rather is emergency condition responsive, it is particularly true that the weight and cost of the component incurred through the provision of such space be of particular importance. It has been found that the cost and weight of such a pretensioning device may be improved through the design of a housing that permits movement of a portion of the pretensioning structure including a structure attaching it to the seat belt system outside of the housing of the pretensioner itself. It is also a design constraint in such designs to economically and effectively seal the movable components of the pretensioner from the surrounding vehicle environment. According to the present invention, there is provided an automotive seat belt buckle pretensioner assembly comprising: an elongated actuator housing having a first end and a second free end and having a bore formed therethrough from said first end to said second end; a seat belt buckle; a cable having a first end fixedly secured to said buckle and a second end located in said elongated actuator housing; a piston member fixedly receiving said cable second end axially therethrough and being slidably received in said bore of said elongated actuator housing; a pyrotechnic gas generator operatively connected to said piston member to selectively drive said piston member toward said second end of said elongated actuator housing; and an end cap mounted on said actuator housing and substantially closing said actuator housing second end; characterised by: a base housing adapted to be secured to an automotive vehicle body and having a bore formed therethrough; said bore of said elongated actuator housing being in registration with said base housing bore; a swage collar fixedly secured proximate said cable second end to hold said piston member axially fast to said cable; and said end cap including a frangible end wall for permitting passage of said cable second end and said swage collar when said piston is driven toward said actuator housing second end. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-sectional view of the automotive seat belt buckle pretensioner assembly of the present invention illustrated in its operative position in which a seat belt buckle is pretensioned; Figure 2 is a view similar to Figure 1, shown in an intermediate operative position; Figure 3 is a view similar to Figure 2, illustrating the assembled inoperative position of the invention automotive seat belt buckle pretensioner assembly; Figure 4 is a side view of one embodiment of an end cap of the invention pretensioner assembly; Figure 5 is an end view of the cap of Figure 4; Figure 6 is a cross-sectional view of Figure 4; Figure 7 is an end view of an alternative embodiment of the cap of Figure 4; and Figure 8 is an end view of yet another alternative embodiment of the cap of Figure 4. Turning now to the drawings, and in particular to Figures 1-3 thereof, an automotive seat belt buckle pretensioner assembly is illustrated as comprising generally a housing assembly 12 that is adapted to be secured to internal surfaces of a passenger compartment of an automotive vehicle (not shown), a seat belt buckle 14, a piston 16, a cable 18 interconnecting the buckle 14 and the piston 16, and a pyrotechnic gas generating device 20. The housing assembly 12 is illustrated as comprising a base housing 22, an elongated actuator housing 24, and an end cap 26. The base housing 22 includes a mounting portion 28 illustrated as having a pair of apertures 30, 32 formed through it for receiving suitable fasteners for fixing the automotive seat belt buckle pretensioner assembly to a portion of the automotive vehicle. The base housing 22 further includes a manifold portion 34 for operatively mounting the pyrotechnic gas generating device 20 and the cable 18. To that end, the manifold portion 34 includes a stepped bore for receiving the automotive seat belt buckle pretensioner assembly and includes a through-bore 38 allowing passage of the cable 18. A recess 40 is formed extending inwardly from one end of the manifold portion 34 for receiving the actuator housing 24, and an annular gas communicating passage 42 is formed to communicate with the recess 40 and the inner end 37 of the stepped bore. The seat belt buckle 14 may be of any suitable design and is fixedly secured to one end 44 of the cable 18, which is preferably of known construction. The cable 18 passes through the bore 38 and terminates in its other end 46 having passed through a similar bore (not shown) in the piston 16. The piston 16 includes a swage collar portion 48, or similar device formed integral therewith or separately, for making the piston 16 axially fast on the cable 18 through mechanism deformation. The piston 16 may be chosen from many suitable designs, but necessarily defines an outer cylindrical surface as indicated at 50 for freely slidable engagement within actuator housing 24. The actuator housing 24 is preferably formed as an elongated tubular member that is fixedly secured within the recess 40 of the base housing 22 and having an internal through-bore 52 having an axis registering with the axis of the bore 38 in the base housing 22. The elongated housing 24 includes a free end 54 that is closed from the atmosphere by the end cap 26 in assembled and operative positions of the assembly as shown in Figures 2 and 3. The actuator housing 24 is preferably fabricated as a metallic component. End cap 26 is preferably formed as a cup-like plastic member. It is fixedly secured over the free end 54 of the actuator housing 24 and secured in axially fast relationship. This may be accomplished through shrink-fitting the end cap 26 over the actuator housing 24 or by securing the cap 26 to the housing 24 through suitable adhesive. Other fixing mechanisms are also suitable. The end cap 26 preferably includes a frangible end wall 54, as may best be seen Figures 4-8. The frangible end wall may be formed by defining a pattern of reduced wall thickness in the end wall, as indicated at 56. Figures 5-8 illustrate desired patterns for the area of reduced wall thickness 56. Figures 5 and 8 show the cross-patterns 60, 62 and Figure 7 shows an elongated slot 64. When installed in an automotive vehicle body, the seat belt buckle pretensioner assembly of the present invention assumes the position shown in Figure 3. When so assembled, the end cap 26 provides a barrier to contaminants entering within the bore 52 of the actuator housing 24, reducing the risk of interference with operation. As is well-known, modern automotive vehicles employing passive occupant restraint systems employ acceleration sensors transmitting electrical signals in response to the occurrence of deceleration events above a predetermined threshold. Such an electrical signal is selectively transmittable through an electrical conductor, such as indicated diagrammatically at 66, to the pyrotechnic gas generating device 20, the design of which is not itself important to an understanding of the present invention. It is well-known in the automotive occupant restraints art that such gas generators, upon receiving a proper signal through a conductor 66, may be operated to generate gas that in the pretensioner assembly of the present invention flow through passage 42 to displace the piston 16 rightwardly, as illustrated in Figures 1-3. Movement of the piston 16 draws the cable 18 through the bore 38 and urges the cable end 46 toward the free end 54 of the actuator assembly 24. This motion draws the buckle 14 downwardly, pretensioning any seat belt component to which it is connected in a known manner. The fully extended position shown in Figure 1 is reached when the cable end 46 pierces the frangible wall 54 of the end cap 26 with reduced thickness sections 56 that enhance the frangible nature of the end wall 54 and accordingly do not interfere with the pretensioning movement of the piston 16.

Claims: An automotive seat belt buckle pretensioner assembly comprising: an elongated actuator housing (24) having a first end and a second free end and having a bore (52) formed therethrough from said first end to said second end; a seat belt buckle (14); a cable (18) having a first end (44) fixedly secured to said buckle (14) and a second end (46) located in said elongated actuator housing (24); a piston member (16) fixedly receiving said cable second end (46) axially therethrough and being slidably received in said bore (52) of said elongated actuator housing (24); a pyrotechnic gas generator (20) operatively connected to said piston member (16) to selectively drive said piston member (16) toward said second end of said elongated actuator housing (24); and an end cap (26) mounted on said actuator housing (24) and substantially closing said actuator housing second end; characterised by: a base housing (22) adapted to be secured to an automotive vehicle body and having a bore formed therethrough; said bore (52) of said elongated actuator housing (24) being in registration with said base housing bore; a swage collar (48) fixedly secured proximate said cable second end (46) to hold said piston member (16) axially fast to said cable (18); and said end cap (26) including a frangible end wall for permitting passage of said cable second end (46) and said swage collar (48) when said piston (16) is driven toward said actuator housing second end. An automotive seat belt buckle pretensioner assembly as claimed in claim 1, wherein said end cap (26) comprises a cup-shaped cap receiving said actuator housing (24) second end and fixedly secured to said actuator housing. An automotive seat belt buckle pretensioner assembly as claimed in either claim 1 or claim 2, wherein said end cap (26) is substantially imperforate. An automotive seat belt buckle pretensioner assembly as claimed in any one of the preceding claims, wherein said end cap (26) is formed of plastic. An automotive seat belt buckle pretensioner assembly as claimed in any one of The preceding claims, wherein said frangible end wall (54) of said end cap (26) comprises a pattern of reduced wall thickness (56). An automotive seat belt buckle pretensioner assembly as claimed in claim 5, wherein said pattern comprises a diametrically extending blind slot (64). An automotive seat belt buckle pretensioner assembly as claimed in claim 5, wherein said pattern comprises two mutually perpendicular blind slots (62).

Inventors: ANDRUS MICHAEL J, KMIEC TIMOTHY M, SHELTON WILLIAM C, ANDRUS, MICHAEL J., KMIEC, TIMOTHY M., SHELTON, WILLIAM C.
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S. A., FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1996
Main classification: B60R22
IPC codes: B60R22