Multiple chamber inflator

A multiple-chamber inflator (10) for a vehicle occupant protection system. The inflator (10) includes a housing (12) having a first end and a second end, and a divider disc (18) positioned in an interior of the housing (12) intermediate the housing ends to form a first (primary) propellant chamber (20) and a second (secondary) propellant chamber (22) within the interior of the housing (12). The divider (18) has a first surface (59) in communication with the first propellant chamber (20), a second surface (57) in communication with the second propellant chamber (22), and at least one aperture (60) extending between the first and second surfaces to provide fluid communication between the first propellant chamber (20) and the second propellant chamber (22). A pressure-resistant shim (62) fabricated from a low-melting point material is fixed on the divider first surface (59) over the at least one aperture (60) to block the aperture. The shim (62) is configured to melt upon exposure to a predetermined temperature generated by combustion of the propellant (48) in the first propellant chamber (20), thereby opening the at least one aperture (60). The shim (62) isolates the first chamber (20) from the second chamber (22). The shim (62) also facilitates an increase in pressure in the first chamber (20) during combustion of the first gas generating propellant (48), thereby increasing the efficiency of the combustion reaction in the first chamber (20).

BACKGROUND OF THE INVENTION

The present invention relates to gas generators used to inflate air bags in a vehicle occupant protection system and, more particularly, to an improved multiple-chamber gas generator containing an improved structure for isolating the propellant chambers of a multiple-chamber inflator so as to ensure proper deployment of the airbag.

Inflation systems for deploying an air bag in a motor vehicle generally employ a single gas generator in fluid communication with an uninflated air bag. A firing circuit typically triggers the gas generator when the sensed vehicle acceleration exceeds a predetermined threshold value, as through the use of an acceleration-responsive inertial switch. However, air bag inflation systems utilizing a single gas generator may be disadvantaged in that the onset pressurization/inflation rate is generally set to provide aggressive initial inflation in order to achieve a particular inflation time related to occupant position. An aggressive onset rate of pressurization may be problematic in situations where the occupant is out of position. Stated another way, rapid onset pressurization of the air bag may cause the air bag to impact against the occupant, thereby affecting the optimum kinematics of the occupant.

Consequently, multiple-chamber inflators have been developed which allow selective activation of either a single chamber or multiple chambers, depending on such factors as crash severity, occupant position sensing, and the weight and/or height of the occupant. Activation-of a single chamber provides softer deployment of the airbag, while simultaneous activation of multiple chambers provides the inflation force necessary to help prevent injury to heavier occupants of a vehicle. However, complete isolation of the propellant chambers of a multiple-chamber airbag inflator is critical to soft deployment of the airbag. It is also beneficial to facilitate an increase in pressure in an activated propellant chamber, because propellant residing in an enclosed chamber will bum more efficiently at higher chamber pressures.

SUMMARY OF THE INVENTION

The present invention relates to an improved structure for isolating the propellant chambers of a multiple-chamber inflator so as to insure proper airbag deployment, while enabling multiple chambers to be activated if so desired. A multiple-chamber inflator for a vehicle occupant protection system is provided. The inflator includes a housing having a first end, a second end, and a divider positioned in an interior of the housing intermediate the housing ends to form a primary propellant chamber and a secondary propellant chamber within the interior of the housing. The divider separates the primary and secondary chambers such that independent operation of each chamber may be assured. At least one aperture extends through the divider, enabling fluid communication between the primary and secondary chambers. A low-melting temperature, pressure-resistant shim is fixed to a surface of the divider over the aperture to block the aperture. The shim is configured to melt upon exposure to a predetermined temperature in the range of 175°–400° F. generated by combustion of a propellant in a propellant chamber in communication with the surface of the divider. The shim may be formed from a metal, an alloy, or a polymer. The shim isolates the primary chamber from the secondary chamber. The shim also facilitates an increase in pressure in the first chamber during combustion of the first gas generating propellant, thereby increasing the efficiency of the combustion reaction.

DETAILED DESCRIPTION

As stated above, the present invention includes a low-melting temperature shim positioned to cover an aperture in a divider which separates two propellant chambers in an inflator housing. U.S. Pat. No. 6,764,096 provides a detailed description of one example of an inflator in which the shim may be incorporated. The '096 patent issued on Jul. 20, 2004, and is incorporated herein by reference.

As seen inFIGS. 1 and 2, an inflator10, in accordance with one embodiment of the present invention, contains a housing12formed from a cap16welded or otherwise fixed to a base14to define opposite first and second ends of the housing. A divider disc18divides the housing12into a primary propellant chamber20and a secondary propellant chamber22in the interior of the housing. Chamber20is formed within base16and chamber22is formed within base14.

Base14, cap16, and divider disc18are formed from stamped steel, or by using other known and accepted methods and materials. Base14contains a first annulus24and a second annulus26. Divider disc18contains a third annulus28and a fourth annulus30, each in corresponding axial alignment with first annulus24and second annulus26, respectively.

As shown inFIGS. 1 and 2, a first igniter chamber32is formed when a first igniter tube34is inserted through and welded to the first and third annuli24and28, respectively, wherein tube34and annuli24and28are substantially equal in circumference. Similarly, a second igniter chamber36is formed when a second igniter tube38is inserted through and welded to the second and fourth annuli26and30, respectively, wherein tube38and annuli26and30are also substantially equal in circumference.

Chamber32contains a proximate end40and a distal end42. A first igniter44is inserted through the proximate end40and is thereby disposed within ignition chamber32. Igniter44is then crimped or otherwise secured to tube34. At least one gas exit aperture46extends through distal end42thereby facilitating fluid communication between chamber32and a primary gas generant48within the primary propellant chamber20.

Chamber36contains a proximate end50and a distal end52. A second igniter54is inserted through the proximate end50and is thereby disposed within chamber36. Igniter54is then crimped or otherwise secured to second tube38. At least one second gas exit aperture56extends through proximate end50thereby facilitating fluid communication between ignition chamber36and a secondary primary gas generant propellant58within secondary propellant chamber22.

An annular filter64is peripherally and radially spaced from an axis extending through chambers20and22. A second plurality of gas exit apertures66are circumferentially and homolaterally disposed within the housing12and about the primary propellant chamber20, thereby providing fluid communication between the chamber20and an airbag (not shown). In one embodiment, foil covers each aperture in the third plurality of apertures66, thereby sealing chamber20.

As shown inFIGS. 1 and 2, divider18is welded to tubes34and38and to cap16. Tubes34and38are also welded to cap16, thereby enhancing structural integrity of the inflator. As seen inFIG. 1, divider18also has a first surface59in communication with primary propellant chamber20and a second surface57in communication with secondary propellant chamber22.

A first initiator composition68is provided within the first ignition chamber32. A second initiator composition70is provided within the second chamber36. Second initiator composition70may have the same composition or a different composition from first initiator68.

In operation, a vehicle occupant protection system generates a signal indicating sudden deceleration or a crash event that is then sensed by igniter44thereby triggering ignition of the first initiator propellant68. Upon ignition of composition68, the heat, flame, and combustion gases produced flow into the primary gas generant chamber20thereby igniting primary gas generant48. The resultant gases then flow from chamber20through filter64and out apertures66into an airbag (not shown).

Secondary chamber22is selectively operated based on factors such as crash severity, occupant position sensing, and the weight and/or height of the occupant. Divider disc18contains at least one aperture60for transfer of secondary gas from chamber22into chamber20. In the embodiment shown inFIGS. 1–3, divider disc18includes a plurality of gas exit apertures60. A low-melting temperature, pressure-resistant shim62covers the plurality of apertures60on surface59of disc18, thereby isolating primary chamber20from chamber22and facilitating an increase in combustion pressure in primary chamber20when chamber20is activated. Shim62is configured to melt upon exposure to a predetermined temperature generated by combustion of propellant48in primary propellant chamber20, thereby opening plurality of apertures60.

Shim62is formed from a metal, metal alloy, polymer, or other substance that has a melting point in the range 175°–400° F. For example, shim62may be formed from a metal or metallic alloy containing a eutectic mixture of two or more elements selected from the group including tin, bismuth, lead, cadmium, indium, gold, silver, and copper. As shim62isolates primary chamber20from secondary chamber22, shim62enables chamber20to be singularly operated without simultaneous operation of chamber22in the event air bag activation is required for a lower weight vehicle occupant.

Alternatively, given a heavier vehicle occupant, chambers20and22may be selected to simultaneously operate based on seat weight sensor and/or occupant position sensing algorithms known in the art. During simultaneous operation of the chambers20and22, gas pressure produced from combustion of propellant58melts shim62and gas passes from chamber20through the aperture(s)60, enabling gases produced in both chambers20and22to co-mingle as they exit the gas exit apertures66.

The wire mesh filter64can be formed from multiple layers or wraps of metal screen, for example. Although not limited thereby, U.S. Pat. Nos. 6,032,979 and 5,727,813, herein incorporated by reference, illustrate typical metal filters.

The low-melting temperature, pressure-resistant shim described herein may be used in multiple-stage inflators that operate one or more chambers either simultaneously or in stepwise form. When the chambers containing the low melting point shims are activated, the remaining chambers are isolated and remain inactive by virtue of the shim. The shim melts as the combustion reaction propagates in the activated chamber thereby opening access to an adjoining chamber. Thus, the shim acts to suppress combustion of any inactive propellant beds in the adjoining chambers. Also, unlike conventional burst shims, the shim of the present invention is disabled in response to a predetermined temperature rather than by an increase in chamber pressure. Thus, the shim facilitates an increase in combustion pressure in the activated chamber, thereby increasing the efficiency of the combustion reaction in the activated chamber.

The above description illustrates the use of exemplary embodiments of the low-melting temperature, pressure-resistant shim in one particular multi-chamber inflator construction. However, use of the shim described herein is not limited to the particular inflator construction described above. Rather, the shim described herein may be used in any multi-chamber inflator incorporating propellant chambers separated by a perforated divider, where adjoining chambers are connected by a passage extending through the divider.

It will be understood that the foregoing description of an embodiment of the present invention is for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications commensurate with the abilities of one of ordinary skill in the art, none of which departs from the scope of the present invention as defined in the appended claims.