BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to initiators and more specifically to creating a robust interface between an initiator body and an initiator holder.
2. Description of Related Art
Initiators or “popcorn” squibs are well-known in the art. They are used in a variety of applications such as but not limited to deploying airbags or pretensioning of seat belts during rapid deceleration of an automobile. These known initiators are designed to conform to certain industry standards for size and shape. Unfortunately, these conventional designs fail to provide a sufficiently robust device that can withstand the rigors of rapid, hot gas expansion and high pressure.
For example, in microgas generators (MGGs) which use initiators, the conventional initiator retainer or holder 10, as seen in FIG. 1, has a circular hole 12 for receiving the header 20. The diameter of that circular hole 12 is typically about 6.6 mm. This unit is a holder or retainer, and it holds or retains the initiator in place. This may be done by a crimping process to apply compression on an O-ring to obtain a good seal. This retainer may be welded onto a housing, a large cup, molded into another device, or the like to position the initiator for use.
Now, the initiator has an explosive primary charge which may be used to initiate or ignite a secondary charge. The initiator may include a header 20 with a stainless steel body, a piece of glass, and two pins (it is called a glass to metal seal interface). A bridge wire is placed between the centerpin, that is insulated by glass, over to the body. This bridge wire creates an electrical connection between the two pins. When current is sent though the pin, the current heats the bridge wire and causes the initiator to ignite its charge. This explosion in an inflator makes an airbag begin to expand. This explosion in an MGG lights propellant that is housed in another can on top of the initiator and generates a pressure wave that will push a piston that may be used in situations such as (but not limited to) tightening a seat belt. In an airbag application, the initiator will ignite airbag propellant which generates gas and inflates an airbag.
As discussed above, the standard retainer or holder for use with the header has a circular hole as seen in FIG. 1. The diameter of that hole is to allow the initiator when it is being assembled to have some freedom to rotate around, allow for manufacturing tolerances. Because the diameter of the hole and the outer diameter of the initiator that fits in the cup are fairly close, the known device has a reduced capability to withstand the heat and backpressure of the charge igniting.
To determine the robustness of these initiators, there are certain safety and performances tests where there is a fairly high amount of pressure in the test chamber. The only thing that prevents the pressure from exiting through a “rearward” direction as indicated by arrow 30 in FIG. 2 is the interface between the holder and the initiator body. This backpressure from the detonation may sometimes cause either the retainer or the body of the initiator to fail, causing the initiator to fire out the rear of the device as indicated by arrow 30. Backpressure wants to push the initiator out and that backpressure is caused by hot gas (several hundred degrees Celsius) from the detonation of the charge. In some situations, this hot backpressure gas will cause the nylon body of the initiator to melt at around 500 degrees C. This backpressure gas is strong (several thousand PSI), and it is very hot. In a functional gas seal integrity test (FGSI), a small test chamber is filled with powder and an initiator is mounted in a holder in this chamber. Then, the powder is ignited and the pressure needs to exit the chamber somehow. The gas is hot enough to melt the plastic body of the initiator and the pressure will want to push the header out of the holder. Since the hole in the retainer is fairly large, what happens is the header with the body melted away will be shot out of the chamber via several thousand PSI of pressure.
This failure of the interface between the header and the retainer or holder is extremely undesirable due to the potentially lethal chain reaction that could result from high velocity ejection of the header from the holder.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide improved header and retainers to withstand the extreme pressures and heat associated with charge detonation.
Another object of the present invention is to provide improved design without significantly increasing manufacturing cost or difficulty.
Yet another object of the present invention is to design the holder to allow a user to visually observe the polarity of the electrode pins during assembly of the initiator into the holder.
A still further object of the present invention is to provide a holder and initiator that is correctly sized for use in MGGs and inflators.
At least some of these objects are achieved by some embodiments of the present invention.
In one aspect of the present invention, an initiator is provided for use with an initiator holder. The initiator comprises a can; at least two electrodes; an explosive charge positioned to be ignited when electrical charge is passed through said electrodes; and a body portion surrounding the electrodes. The body portion may have a first portion with a first cross-sectional area and a second portion having a second cross-sectional area, wherein the second cross-sectional area has a shape different from the first cross-sectional area and wherein the second cross-sectional area is less than 40% of the first cross-sectional area; wherein the second portion is shaped to extend outward from an opening in the holder when the body portion is seated in the holder.
In another embodiment, the present invention comprises an initiator having a can; at least two electrodes; an explosive charge positioned in the can and configured to be ignited when electrical charge is passed through the electrodes; and a body portion surrounding the electrodes, wherein the body portion having a first portion with a first cross-sectional area and a second portion having a second cross-sectional area; a holder configured to engage at least a portion of the body portion, wherein the holder is capable of holding the body portion in a manner sufficient to withstand a backpressure of at least about 200 megapascals pushing the body portion against an inner surface of the holder.
A microgas generator may use an initiator and/or a holder as described herein.
In another embodiment, the present invention provides a method of manufacturing an initiator comprising: providing a can, at least two electrodes, and an explosive charge positioned in the can and configured to be ignited when electrical charge is passed through said electrodes; forming a body portion surrounding at least a portion of said electrodes, said body portion having a first portion with a first cross-sectional area and a second portion having a second cross-sectional area, said second cross-sectional area having a shape different from said first cross-sectional area and wherein said second cross-sectional area is less than 40% of said first cross-sectional area; wherein said second portion is shaped to extend outward from an opening in the holder when the body portion is seated in the holder.
A further understanding of the nature and advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of an initiator and holder known in the art.
FIG. 2 shows a perspective view of an initiator seated in a holder.
FIG. 3 shows a cross-section view of one embodiment of a header according to the present invention.
FIG. 4 shows a cross-section view of one embodiment of an initiator according to the present invention.
FIG. 5 shows a perspective view of an initiator according to the present invention.
FIG. 6 is a bottom-up view of the initiator of FIG. 5.
FIG. 7 is a cross-sectional view as indicated by lines 7-7 in FIG. 6.
FIG. 8 is a cross-sectional view of one embodiment of an initiator and a holder according to the present invention.
FIG. 9A is a bottom up view of the holder of FIG. 8.
FIG. 9B shows a perspective view a microgas generator.
FIG. 9C shows a close-up view of the holder of FIG. 8.
FIGS. 10A-10H are bottom up views of a various embodiments of the second portion of the initiator body.
FIGS. 11A-11D various views of a various embodiments of the first portion of the initiator body.
FIGS. 12A and 12B show the cross-sectional areas described in FIG. 7.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. It may be noted that, as used in the specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a material” may include mixtures of materials and the like. References cited herein are hereby incorporated by reference in their entirety, except to the extent that they conflict with teaching explicitly set forth in this specification.
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:
“Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, if a device optionally contains a feature for having a shorting bar, this means that the shorting bar feature may or may not be present, and, thus, the description includes structures wherein a device possesses the shorting bar feature and structures wherein the shorting bar feature is not present.
Referring now to FIG. 3, one embodiment of a header 100 according to the present invention will now be described. The header 100 may include a stainless steel body 102, at least one piece of glass 104, and two electrically conductive pins 106 and 108. These structures form a glass-to-metal field interface. A bridge wire 110 is placed between the centerpin 108, which is insulated by glass 104, over to the body 102. This bridge wire 110 creates an electrical connection between the two pins or electrodes 106 and 108. When current flows though the pins 106 and 108, the current flow heats the bridge wire 110 and causes the explosive charge 112 to ignite. Upon ignition, the explosive charge 112 will explode outward as indicated by arrows 114. The can 116 may include a scored portion 118 across a top surface of the can 116 to allow the metal can 116 to fail in a controlled manner. In one embodiment, the scores may be at equal angles to about half the depth of the material, to encourage even opening of the can top when the generator is used. Of course, other score depths and score patterns may be used with the present invention. It should also be understood of course, that other headers which use other designs and techniques to ignite the explosive charge, such as but not limited to semiconductor bridge initiators, may also adapted for use with the present invention as described herein. Suitable semiconductor bridge initiators are described in copending U.S. patent application Ser. No. 10/914,969 (Attorney Docket No. 37073-0009C1C1).
Referring now to FIG. 4, this embodiment of the initiator 125 may also include another can 120 and a body 130 to house and support the various elements described above for FIG. 3. The cans 116 an d120 may be made of a variety of material including but not limited to various metals and alloys such as low-corrosion metals and alloys, passivated stainless steel, for example of about 0.4 mm thickness, 304 Stainless Steel. The body 130 may be made of a variety of materials including but not limited to engineering grade reinforced thermoplastics: glass filled engineering polyesters such as polybutylene terephthalate, polybutylene naphthalate, and the like; high strength polyamides such as nylon 6,12, nylon 10,12, nylon 12,12, nylon 66, and the like; thermoplastic aromatic polyamides such as Amodel™ polyphthalamide (BP Chemicals); polyether-amides; polyimides such as Aurum™ (MTC America); polyether-imides; and the like; and polyether-ketones (PEK), polyether-ether-ketones (PEEK), polyether-ketone-ether-ketone-ketones (PEKEKK), and similar high temperature thermoplastic aromatic polyketone polymers, liquid crystal polymers (LCP), Vectra™ A515, and compatible mixtures of any two or more of the above. In the present embodiment, the body 130 may be overmolded or otherwise formed over the elements in FIG. 3 and over the can 120.
As seen in the embodiment of FIG. 4, the body 130 may have a first portion 132 and a second portion 134. The first portion 132 is designed to remain inside the retainer or holder while the second portion 134 is designed to protrude outward from an opening in the holder. In the present embodiment, the second portion 134 also supports the pins 106 and 108 which also extend out ward from the opening, allowing for electrical connection to a current source. The second portion 134 may be designed to provide protection to the pins and allow them to be properly positioned through the hole in the retainer. In some embodiments, the second portion 134 or lower part of the body may be shaped to engage a clip or other interface from the wiring harness of the automobile, carrying trigger wires from the sensor circuit. Additionally, as seen in the cross-section of FIG. 4, the center pin 108 may include a bend 109 so that the pin 108 outside the second portion 134 is symmetrical about the centerline 136.
FIG. 5 shows a perspective view of one embodiment of initiator 125 according to the present invention. The body 130 is shaped to surround the side portions of at least two of the electrodes or pins 106 and 108. As seen in FIG. 5, the portion 132 may include a conical or beveled portion with a surface at a 45 degree angle. Of course, the surface of the cone may also be designed to be at angles other than 45 degrees. The second portion 134 is designed to surround the side walls of the pins 106 an 108 to provide electrical insulation and physical protection.
Referring now to FIG. 6, a bottom up view of the initiator 125 will now be described. As seen, the second portion 134 has a race track configuration. The embodiment may optionally include a cutout area 140. This cutout 140 allows the user to orient the pins 106 and 108 for the proper polarity during assembly with the holder. The X associated with the cutout 140 will be visible to the user through the opening.
As seen in FIG. 6, the cone shape of the first portion 132 has a widest diameter indicated by reference number 150 and the smallest diameter indicated by reference number 152 on the surface 154. In the present embodiment, the dimensions for the largest diameter and smallest diameter are 11.10 and 6.45 respectively. It should be understood that a range of sizes may be suitable for the present invention such as 12.0 and 7.00. The first portion 132 with the cone shape has a circular cross-section. As seen for this embodiment, the second portion 134 has a different cross-sectional shape (i.e. race track) than the cross-sectional shape of the first portion 132 (i.e. circular). The area of surface 154 is 90 sq. mm, and the area of surface 134 is 9.34 sq. mm.
FIG. 7 shows another cross-sectional view of the body 130 (as indicated by lines 7-7 in FIG. 6). The surface 154 is designed to rest against an inner surface 202 of the retainer 200 as more clearly seen in FIG. 8. The surface 154 may be viewed as a backpressure resistance surface as it will press against the surface 202 of the retainer 200 of an initiator holder to prevent ejection of the initiator due to backpressure. In the present embodiment, the greater the area for surface 154, the greater its resistance to backpressure. Of course, the holder or retainer 200 would also be designed to have a surface 202 of sufficient size to support the surface 154. The greater the area of overlap between surface 154 and the inner surface 202 of the retainer, the greater the resistance to backpressure during detonation. In the present embodiment, the surface 154 is perpendicular to the longitudinal axis of the electrodes.
Referring now to FIG. 8, it should be understood that the size and shape of the second portion can be selected to increase the robustness of the initiator header. FIG. 8 shows one embodiment where the cross-sectional area of second portion 134 is minimized (as indicated by arrows 210) so that there is greater overlap between surface 154 and surface 202. From a pressure point of view, the standard holder will withstand up to 100-150 megapascals of force. The present embodiment of an improved holder shown in FIG. 8 can withstand up to about 250 megapascal, which is beyond the amount of pressure that a typical air bag inflator can produce. The bottom interface is designed to withstand higher pressures while having a 1.33 mm height. This reduced cross-sectional shape and reduced hole size in the retainer 200 address the high MGG and inflator backpressure issue. It should be understood that this holder or retainer 200 may be individually formed and then attached or welded to a housing. In some embodiments the holder or retainer 200 may be integrally formed with the housing.
FIG. 9A shows a bottom up view of the embodiment of the retainer 200 shown in FIG. 8. As seen, the retainer 200 has a race-track shaped opening 230 shaped to receive the second portion 134. The opening 230 is minimized in size so that there is more overlap between the retainer and the surface 154. In some embodiments, the retainer 200 may be part of a microgas generator.
FIG. 9B shows a perspective view of one embodiment of a microgas generator with the retainer 200. As seen, the second portion 134 will be received in the opening 230. As more clearly indicated in FIG. 9C, the cutout 140 can be seen through the opening 230 to indicate the appropriate orientation of the initiator.
Referring now to FIGS. 10A-10H, it should be understood that the second portion 134 may be designed to have a variety of shapes and still conform to the spirit of the present invention. FIGS. 10A-10H are bottom up views of only the second portions 134. FIG. 10A shows a second portion 134 having a rectangular cross-sectional shape. FIG. 10B shows a substantially rectangular shape that is square on one end and rounded on the other. FIG. 10C shows that the pins 106 and 108 may be protected by separate formations, one having a square shape and the other a circular shape. FIG. 10D-10E shows various combinations of square, triangular, and circular cross-sectional shapes. It should understood that these shapes may be combined in any manner including all round, all square, any other combination, or with shapes where one is larger is area than the other. FIG. 10F shows a single circular device with a pin 250 in the middle and a conductive outer portion 252 that may function as a second pin. FIG. 10G shows a dumbbell shaped cross-section and FIG. 10H shows a three-legged shape. Of course, the holders or retainers would have openings shaped to receive these cross-sectional shapes.
Referring now to FIGS. 11A-11D, it should be understood that the first portion 132 may be designed to have a variety of shapes and still conform to the spirit of the present invention. FIG. 11A shows an embodiment from the side where the portion 132 appears square. FIG. 11B shows an embodiment where a larger area of portion 132 is tapered. FIG. 11C shows a top down view where the portion 132 has a square shape. FIG. 11D shows a top down view where the device has a polygonal shape. It should be understood that the device have a portion 132 that may be triangular, rectangular, square, circular, polygonal, any single or multiple combination of these shapes, whether view from top down or from the side. In some embodiments, these portions 132 are designed to minimize the opening for portion 134 and maximize the area of overlap with the inner surface of the holder or retainer 200.
FIGS. 12A and 12B more clearly illustrate the cross-sectional areas discussed with regards to FIGS. 6 and 7. The cross-sectional area in FIG. 12A corresponds to the cross-section of the second portion 134. The cross-sectional area in FIG. 12B corresponds to the cross-section of the first portion 132 at the interface with portion 134. As seen, the cross-sectional area in FIG. 12B is significantly larger than the cross-sectional area of the area show in FIG. 12A. In one embodiment, the cross-sectional area in FIG. 12A is less than 40% of the cross-sectional area of FIG. 12B. In another embodiment, the cross-sectional area in FIG. 12A is less than 30% of the cross-sectional area of FIG. 12B.
In another view, the exposed surface area of backpressure resistance surface 154 (FIG. 6) is greater than the cross-sectional area of FIG. 12A, which is the cross-section of portion 134. In one embodiment, the exposed area 154 is at least 10% greater than the cross-sectional area of FIG. 12A. In another embodiment, the exposed area 154 is at least 20% greater than the cross-sectional area of FIG. 12A. In another embodiment, the exposed area 154 is at least 50% greater than the cross-sectional area of FIG. 12A. In another embodiment, the exposed area 154 is at least 100% greater than the cross-sectional area of FIG. 12A. The shape of the cross-section of the area of FIG. 12A is also shaped to prevent rotation about the longitudinal axis of the initiator. Some embodiments may have the shape of the section 134 “keyed” with a notch or protrusion to prevent misorientation. Some embodiments will have the opening 230 shaped to match the cross-sectional shape of the portion 134.
While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention. For example, with any of the above embodiments, notches or cutouts may be incorporated onto the body or other initiator portions to indicate correct orientation or other indicator. The device may also include protrusions to “key” into notches on the holder, or vice versa. These elements may be found on the body portions or other housing on the initiator or holder. For any of the embodiments above, the device may include a shorting bar connecting the electrodes to prevent accidental detonation. Suitable materials for use in the present invention and shorting bar designs may be found in copending U.S. patent application Ser. No. 10/953,468 (Attorney Docket No. 37073-0010C1). Various embodiments of an improved initiator and holder can withstand up to about 160, 170, 180, 190, 200, 210, 220, 230, 240, and/or 250 megapascal of force resulting from detonation of explosive charge.
The publications discussed or cited herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed. All publications mentioned herein are incorporated herein by reference to disclose and describe the structures and/or methods in connection with which the publications are cited.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either both of those included limits are also included in the invention.
Expected variations or differences in the results are contemplated in accordance with the objects and practices of the present invention. It is intended, therefore, that the invention be defined by the cope of the claims which follow and that such claims be interpreted as broadly as is reasonable.
Patent Application
20060137559
