Controlling gas flow in a hybrid inflator

Abstract: A hybrid inflator for an inflatable safety system is provided. The hybrid inflator is configured to provide for efficient mixing of hot combustion gases from combustion of the propellant and other combustible materials with the cooler pressurised medium in the stored gas housing. The mixing of the combustion gases and the pressurised medium provides an output gas having a substantially uniform composition and temperature. The mixing means (122) define an outlet path for said inflation gases from the inflator (54) and the propellant gas generator (66) to the outlet (78) to promote mixing of the inflation gases, said outlet path defining a first direction and a second direction which is different to said first direction in which inflation gases move.

Description: The present invention relates to an apparatus for controlling flow of inflation gases according to the precharacterising part of claim 1 and to a method for controlling gas flow in an inflation apparatus according to the precharacterising part of claim 6. The evolution of inflators for automotive inflatable safety systems has resulted in the development of pressurised gas-only inflators, propellant-only inflators, and hybrid inflators. There are of course many design considerations for each of the above-noted types of inflators. In all three systems, two primary design considerations are that the air/safety bag must be expanded a predetermined amount in a predetermined amount of time in order to be operationally effective. As such, substantial development efforts have been directed to how the flow path is established between the inflator and the air/safety bag and how the subsequent flow is provided to the air/safety bag such that the above-identified objectives can be met. In hybrid inflators, which utilise both a release of a stored, pressurised gas and an ignition of a heat-generating material, such as a propellant, the manner of establishing the flow path to the air/safety bag and the manner of igniting the propellant must both be addressed in a way which meets the above-noted objectives. WO-A-95/34448 discloses a hybrid inflator having a container for storing compressed gas and a pyrotechnic gas generator for adding heat and mass flow to the compressed gas during operation. Mixed inflation gases flow directly into a manifold which leads from the container to an air bag. US-A-5360232 discloses a hybrid inflator having a filter structure through which inflation gases flow. According to a first aspect of the present invention, there is provided apparatus for controlling flow of inflation gases, the apparatus comprising: an inflator housing for storing a gas under pressure; a propellant gas generator for generating propellant gas for heating said stored gas; an initiator for initiating the generation of propellant gas by the propellant gas generator; an after burner tube for receiving inflation gases and providing an exit for said inflation gases from the apparatus, said inflation gases including at least a propellant gas generated by the propellant gas generator and a gas initially stored under pressure by the inflator; and, outlet closure means for blocking passage of the inflation gases to the afterburner tube until after activation of the initiator; characterised by: a wall defining an outlet path for said inflation gases from the inflator and the propellant gas generator to the after burner tube to promote mixing of said inflation gases, the wall being located within the inflator housing and outwardly of the afterburner tube and extending at least partly along the length of the afterburner tube to define a space between the wall and the afterburner tube such that said inflation gases move in a first direction outwardly of the wall and towards the exit end of the afterburner tube and then in a second direction opposite the first direction and in the space between the wall and the afterburner tube. Particular embodiments of the invention as defined in claim 1 are the subject of the dependent claims 2 to 5. In a preferred embodiment, the present invention relates to a hybrid inflator for an inflatable safety system that provides a novel path for inflation gases to an air/safety bag. The hybrid inflator has an inflator housing which stores an appropriate pressurised medium (e.g. fluid and/or gas) and a gas generator which stores an appropriate gas/heat-generating material or propellant for augmenting the flow to the air/safety bag of the inflatable safety system. A closure disk (or outlet closure device) initially isolates the hybrid inflator from this air/safety bag. An activation (or initiator) assembly is provided which includes at least one combustible material which is ignited when activation of the system is desired/required. Combustion products resulting from the activation assembly come into direct contact with the propellant to ignite the same. These same combustion products from the activation assembly also propel a projectile through this particular closure disk to initiate the flow from the inflator to the air/safety bag via an outlet in the inflator housing. In the preferred embodiment, the hybrid inflator includes a mixing device operatively associated with the gas generator for mixing the combustion products from the combustible material in the activation assembly, the gas from combusting the propellant, and/or the pressurised medium (collectively referred to as the "inflation gases"). The device in this embodiment causes the inflation gases to move in a first direction and then in a second direction opposite the first direction. The first and second directions are oriented relative to the longitudinal axis of the inflator housing. In one configuration, the mixing device includes an inner shroud that extends from a location adjacent to the gas generator along the longitudinal extent of the inflator housing. An outer shroud, that extends for a shorter length along the longitudinal extent of the inflator housing, can also be disposed radially outwardly from the inner shroud to facilitate mixing. The inner and outer shrouds collectively define an annular outlet. The mixing device can provide inflation gases exiting the outlet from the inflator housing that have a substantially uniform composition and temperature. As will be appreciated, the pressurised medium has a temperature that is substantially the same as the ambient temperature outside of the inflator housing before activation of the activation assembly. The combustion products from the activation assembly and the propellant gases from combusting the propellant (collectively referred to as "the combustion gases") have relatively high temperatures when generated. The mixing device causes efficient mixing of the hot combustion gases and the cooler pressurised medium and thereby causes heat to be transferred rapidly from the hot combustion gases to the pressurised medium. An important objective served by the mixing device is a sufficient or desired reduction associated with the temperature of resulting inflation gases that exit the inflator housing after activation of the inflator. In that regard, such mixing is expected to eliminate the possibility of erosion (and enlargement) of outlets located in the path of flow of the inflating gases and/or flaming of the inflation gases upon or after discharge from the outlet of the inflator housing. In the embodiment mentioned above, the projectile can provide a sealing function in addition to rupturing the first closure disk to initiate the flow to the air/safety bag. The projectile may be disposed within an end of the gas generator and at least partially aligned with the first closure disk. By selecting an appropriate configuration for the projectile and/or its interrelationship with the end of the gas generator through which it passes to rupture the first closure disk, the projectile can seal this end of the gas generator. This may be desirable to force the propellant gases and/or other combustion products from the activation assembly to flow from the gas generator and into the stored gas housing before exiting the inflator through the ruptured first closure disk. When a propellant is used which generates combustible propellant gases, this reduces the potential for these propellant gases combusting within the air/safety bag and promotes their more efficient combusting inside the inflator housing. A transfer tube can be disposed internally of and spaced from the gas generator housing. All of the propellant is disposed in this embodiment in the space between the gas generator housing and the transfer tube, and the transfer tube includes a plurality of ports. The output from the activation assembly is directed into the interior of the transfer tube and then out through its ports to ignite the propellant. This reduces the potential for the initiation of the activation assembly adversely impacting the structural integrity of the propellant. The transfer tube may also be used to direct the output from the activation assembly to the above-noted projectile to propel the same through the first closure disk. The hybrid inflator can have multiple chambers. For example, the inflator may include a first housing and a second housing assembly. The second housing assembly may be interconnected with the first housing and disposed interiorly thereof (e.g. concentrically disposed). The second housing assembly may include a first chamber in which an appropriate gas/heat-generating material or propellant is disposed. A second chamber may be defined by the space between the first housing and the second housing assembly and contain an appropriate pressurised medium in the static state or prior to activation of the inflator. The second chamber may be in constant fluid communication with the first chamber such that the first chamber also contains pressurised medium. The second housing assembly can further include a third chamber. A first closure disk may be associated with the third chamber and provides the initial isolation between the air/safety bag and the inflator. The third chamber may be fluidly interconnectable with the second chamber, but substantially isolated from the first chamber. As such, upon ignition of the propellant within the first chamber, propellant gases flow from the first chamber into the second chamber, and then into the third chamber. After the first closure disk is ruptured, the flow is established from the inflator to the air/safety bag. The second housing assembly can include a central housing having a sidewall and two open ends. The inflator activation assembly may be disposed within and close one of the open ends of the central housing and be appropriately secured thereto (e.g. via welding). A partition may be disposed within the interior of the central housing (e.g. via a press-fit) to define the first chamber of the second housing assembly together with the activation assembly. A diffuser assembly may be disposed within and close the other open end of the central housing and be appropriately secured thereto (e.g. via welding). The partition, due to its interface with the central housing and the lack of any ports in the partition, substantially limits any substantial fluid flow from the first chamber directly into the third chamber. Moreover, by press-fitting the partition into the central housing, this also allows the propellant to be loaded into the central housing after all welds, which are located near the propellant, have been made. According to a second aspect of the present invention, there is provided a method for controlling gas flow in an inflation apparatus which includes an inflator housing having stored therein a gas under pressure, a propellant gas generator for generating propellant gas for heating said stored gas, an afterburner tube for receiving inflation gases and providing an exit for said inflation gases from the apparatus, and a wall defining an outlet path for said inflation gases from the inflator and the propellant gas generator to the afterburner tube to promote mixing of said inflation gases, the wall being located within the inflator housing and outwardly of the afterburner tube and extending at least partly along the length of the afterburner tube to define a space between the wall and the afterburner tube, the method comprising the steps of: generating propellant gas by the propellant gas generator; mixing generated propellant gas with the stored gas to provide inflation gases; flowing said inflation gases in a first direction outwardly of the wall and towards the exit end of the afterburner tube and then in a second direction opposite the first direction and in the space between the wall and the afterburner tube. Particular embodiment, of the invention as defined in claim 6 are the subject of the dependent claims 7 to 11. The present invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of an automotive inflatable safety system; Fig. 2 is a cross-sectional view of an embodiment of a hybrid inflator; and, Fig. 3 is a cross-sectional view of another embodiment of a hybrid inflator. The present invention will be described with regard to the accompanying drawings which assist in illustrating various features of the invention. In this regard, the present invention generally relates to hybrid inflators for automotive inflatable safety systems. That is, the invention relates to an inflator which utilises both a stored, pressurised gas and a gas and/or heat-generating propellant. Various types of hybrid inflators are disclosed in US-A-5230531 and co-pending U.S. Patent Application Serial No. 08/680,273 filed July 11, 1996, entitled "Hybrid Inflator", which are both assigned to the assignee of this application. One embodiment of an automotive inflatable safety system is generally illustrated in Fig. 1. The primary components of the inflatable safety system 10 include a detector 14, an inflator 26, and an air/safety bag 18. When the detector 14 senses a condition requiring expansion of the air/safety bag 18 (e.g. a predetermined deceleration), a signal is sent to the inflator 26 to release gases or other suitable fluids from the inflator 26 to the air/safety bag 18 via the conduit 22. The inflator 50 illustrated in Fig. 2 is a hybrid inflator and may be used in the inflatable safety system 10 of Fig. 1 in place of the inflator 26. The hybrid inflator 50 includes a cylindrical inflator or stored gas housing 54 which contains an appropriate pressurised medium 58 (e.g. a pressurised fluid and including one or more liquids or one or more gases or both), a cylindrical gas generator 62 which contains an appropriate gas/heat-generating material or propellant 66 for augmenting the flow to the air/safety bag 18 (Fig. 1) (e.g. at least about 85% of the heat used to augment the inflation capabilities of the system results from combustion of the propellant 66), an activation assembly 70 for both releasing the pressurised medium 58 (by establishing a flow path between the inflator 50 and the air/safety bag 18 (Fig. 1)) and igniting the propellant 66, and a diffuser 74 for directing the flow from the inflator 50 to the air/safety bag 18 (Fig. 1). Preferably, the inflator 50 utilises the known compositions of gun type propellants and/or hybrid propellants, together with a multi-component pressurised medium (e.g. one component being oxygen and the other component being at least one inert fluid (e.g. gas/liquid)). As such, the inflator 50 further includes an afterburner tube 78 disposed "upstream" of the diffuser 74 to allow for sufficient combustion of the flow prior to exiting the inflator 50 through the diffuser 74. Portions of the inflator 50 define a pressure vessel in that these portions contain the pressurised medium 58 in the static state or prior to initiation of the activation assembly 70. Generally, the activation assembly 70 closes one end of the stored gas housing 54, including a first weld 82 which interconnects the stored gas housing 54 and an activation assembly housing 86 of the activation assembly 70 and which provides a seal. The opposite end of the stored gas housing 54 is closed by the afterburner tube 78 and the diffuser 74 which are secured to the stored gas housing 54 by welds 90 and 94, respectively. Pressurised medium 58 is introduced into the completely assembled inflator 50 through a fill port 98 on the wall of the stored gas housing 54. When the desired amount of pressurised medium 58 has been provided to the inflator 50, the fill port 98 is sealed by a plug 102 which is appropriately secured to the stored gas housing 54 (e.g. a steel ball disposed within and/or over the fill port 98 which may be press-fit and/or welded therein). The pressurised medium 58 is contained within multiple chambers within the inflator 50 during the static state, and these chambers are fluidly interconnected in a manner which defines the flow path for exiting the inflator 50 during operation. The gas generator 62 includes a gas generator housing 106 which is concentrically disposed within the stored gas housing 54 and which defines a first chamber 110. Propellant 66 is contained within this first chamber 110 in the gas generator housing 106. Fluidly interconnected with the first chamber 110 of the gas generator housing 106 is a second chamber 114 which contains pressurised medium 58 during the static state or prior to initiation of the activation assembly 70. The second chamber 114 is defined in part by the annular space between the stored gas housing 54 and the gas generator 62, and in part by the annular space between the stored gas housing 54 and the afterburner tube 78. The fluid interconnection between the first chamber 110 and the second chamber 114 is present at all times such that during the static state or prior to initiation of the activation assembly 70, the first chamber 110 within the gas generator housing 106 also contains pressurised medium 58. The gas generator housing 106 includes a first end 118 and a second end 122. The first end 118 of the gas generator housing 62 interfaces with and is closed by a portion of the activation assembly 70 which assists in the retention of pressurised medium 58 within the inflator 50 in the static state as will be discussed in more detail below. The second end 122 of the gas generator housing 106 has a slightly larger diameter than the first end 118 of the gas generator housing 106, is open, and is disposed radially outwardly from a portion of the afterburner tube 78. The space between the second end 22 of the gas generator housing 106 and the afterburner tube 78 may be considered as either a part of the second chamber 114 or as part of a flow path between the second chamber 114 and a third chamber 126 which is defined by an orifice sleeve 130. Fluid communication between the second chamber 114 and the third chamber 126 is provided by at least one and preferably a plurality of orifice sleeve ports 134 which are radially spaced on the orifice sleeve 130 and which are open at all times. The orifice sleeve 130 interconnects the afterburner tube 78 and the gas generator 62. One end of the orifice sleeve 130 is appropriately secured to a second end wall or partition or nozzle plate 138 of the gas generator 62 which provides for closure or near closure (there may be a slight gap in some embodiments) of one end of the first chamber 110 in the gas generator housing 106 (e.g. by a crimped interconnection). The opposite end of the orifice sleeve 130 is interconnected with an end of the afterburner tube 78 by a weld 142. In order to seal the third chamber 126 to retain the pressurised medium 58 within the first chamber 110, second chamber 114, and third chamber 126 during the static state or prior to initiation of the activation assembly 70, a second closure disk 146 is disposed between an end of the afterburner tube 78 and the orifice sleeve 130 and is retained in this position by the weld 142. The second closure disk 146 provides the main isolation between the inflator 50 and the air/safety bag 18 (Fig. 1) and may be characterised as the output disk. Note that the second closure disk 146 may be characterised as being disposed at an intermediate location within the inflator 50. In the illustrated embodiment, the second closure disk 146 is disposed at generally a mid portion of the stored gas housing 54 and is disposed interiorly thereof. Consider the distance between the two opposing ends of the stored gas housing 54 to be L 1 . In one embodiment the above-noted "intermediate" location of the second closure disk 146 may be characterised as being disposed at least about 40% of L 1 from both ends of the stored gas housing 54. The afterburner tube 78 communicates with the third chamber 126 after the second closure disk 146 is ruptured or opened in a manner discussed in more detail below. The afterburner tube 78 in turn communicates with the diffuser 74 which includes a plurality of diffuser ports 150 and a diffuser screen 154. Flow exiting the diffuser 74 is then directed to the air/safety bag 18 (Fig. 1). The afterburner tube 78 and the diffuser 74 are part of an outlet passage for the inflator 50. Note that the end of the afterburner tube 78 which interfaces with the diffuser 74 has a divergent end section 158 which has a diameter larger than the end of the afterburner tube 78 which interfaces with the second closure disk 146. This divergent end section 158 reduces the velocity of the flow exiting the inflator 50. As mentioned, the first chamber 110 is located within the gas generator 62, and more specifically is defined by a hollow transfer tube 162 which is concentrically disposed within the gas generator housing 62 and an annular retainer 166 which seats against the interior surface of the gas generator housing 106 and the exterior surface of the transfer tube 162. The propellant 66 is disposed radially outwardly of the transfer tube 162 (e.g. to reduce the potential for damaging the propellant 66 during ignition) and between the retainer 166 and the first end 118 of the gas generator housing 106 proximate the activation assembly 70. At least one and typically a plurality of gas generator outlet ports 170 are disposed on the gas generator housing 106 to fluidly interconnect the stored gas housing 54 and the gas generator housing 106 at all times and particularly the first chamber 110 of the gas generator housing 106 where the propellant 66 is located. These outlet ports 170 are positioned on the gas generator housing 106 between the retainer 166 and the first end 118 of the gas generator housing 106. Most inflation gases resulting from combustion of the propellant 66 and any from the activation assembly 70 flow out of the gas generator housing 106 through the gas generator outlet ports 170 to augment the flow to the air/safety bag 18 (Fig. 1), although some moves past the nozzle plate 138 to mix with the gas in the diffuser 74. In order to reduce the potential for the combusting propellant adversely impacting the performance of the inflator 50, a screen 174 may be disposed in the interior of the gas generator housing 106 over at least the gas generator outlet ports 170. The propellant 66 is ignited within the gas generator housing 106 by the activation assembly 70 which includes the activation assembly housing 86. The activation assembly housing 86 is attached to the stored gas housing 106 at the first weld 82 and also to the first end 118 of the gas generator housing 106 at a second weld 178 to achieve a preferably hermetic seal since the both the stored gas housing 54 and the gas generator housing 106 contain pressurised medium 58 in the static state or prior to initiation of the activation assembly 70. The activation assembly housing 70 retains an appropriate initiator 182 (e.g. an electrically activatable squib or other suitable pyrotechnic device) which provides combustion products to cause the ignition of the propellant 66. In order to isolate the initiator 182 from the pressurised medium 58 within the inflator 50 and further to provide a seal for the inflator 50, a first closure disk 186 is disposed between the gas generator 62 and the initiator 182. In the illustrated embodiment, this is effected by disposing the first closure disk 186 between a first end wall 190 of the gas generator 62 (which first end wall 190 is crimped onto one end of the transfer tube 162) and an end of the activation assembly housing 86, the first end wall 190 and the end of the activation assembly housing 86 being secured to each other by a third weld 194. The cylindrical transfer tube or housing 162 is concentrically disposed within and relative to the gas generator housing 106, and is aligned with the initiator 182 to receive a "flow" of combustion by-products or inflation gases which are generated by initiation of the activation assembly 70. As mentioned, the propellant 66 is disposed in the first chamber 110 in the gas generator housing 106, or radially outwardly from the transfer tube 162. As such, the transfer tube 162 reduces the potential for the initiation of the activation assembly 70 adversely impacting the propellant 66, principally by reducing the potential for having the pressure wave or pulse, produced from activation of the initiator 182, cracking the grains of the propellant 66 which would change the burn characteristics of the propellant 66. In order to communicate combustion products from the activation assembly 70 to the propellant 66 to ignite the same by direct contact therewith, at least one and preferably a plurality of transfer tube ports 198 are provided on the wall of the transfer tube 162. These transfer tube ports 198 may be radially disposed about the transfer tube 162 and longitudinally spaced along the length of the transfer tube 162. The activation assembly 70 further includes an appropriate ignition/booster material 200 to augment the capabilities of the activation assembly 70 (e.g. an RDX/aluminium booster material having a composition of about 89 wt% RDX, 11 wt% aluminum powder, possibly with about 0.5 wt% to about 5.0 wt% hydroxypropyl-cellulose added replacing from about 0.5 wt% to about 5.0 wt% of the RDX and aluminum proportionally). The ignition/booster material 200 may be positioned between the initiator 182 and the propellant 66 in alignment with the discharge or output from the initiator 182. Activation of the initiator 182 ignites its combustible material, which in turn ignites the ignition/booster material 200. Combustion products from the initiator 182 and/or the ignition booster material 200 then ignite the propellant 66 by passing through the transfer tube 162 and its transfer tube ports 198 to directly contact the propellant 66 and ignite the same. Since the ignition/booster material 200 is in powder form, it is contained within a thin-walled cup 204. This cup 204 is disposed on one end of the transfer tube 162 on the inside thereof and may be for example a press-fit therein. The transfer tube 162 conveys combustion products for ignition of the propellant 66. Initiation of the activation assembly 70 not only ignites the propellant 66, but it also establishes a flow path between the inflator 50 and the air/safety bag 18 (Fig. 1) by causing rupture of the second closure disk 146 which is the main isolation between the inflator 50 and the air/safety bag 18. In this regard, the activation assembly 70 further includes a projectile/valve 208. This projectile/valve 208 is partially disposed within the end of the transfer tube 162 opposite the ignition/booster material 200, is aligned with both the initiator 182 and the ignition/booster material 200, is initially retained in a fixed position by a shear ring 212, extends through the second end wall 138 of the gas generator housing 106 beyond the end of the transfer tube 162, is axially aligned with the second closure disk 146, and is spaced from the second closure disk 146. Generally, the combustion products from the activation assembly 70 (the initiator 182 and/or the ignition/booster material 200) are partially directed down through the transfer tube 162 and exert a force on the projectile/valve 208 to "break" the shear ring 212 and propel the projectile/valve 208 through the second closure disk 146. This allows pressurised medium 58, propellant/inflation gases, and other combustion products to flow from the second chamber 114, into the third chamber 126 through the orifice sleeve ports 134, into the afterburner tube 78 through the ruptured second disk 146, and into the diffuser 74 to exit the inflator 50 for direction to the air/safety bag 18 (Fig. 1). The projectile/valve 208 of the activation assembly 70 provides a sealing function in addition to initiating the flow from the inflator 50 in the described manner. Specifically, the projectile/valve 208 forces most of the propellant/inflation gases and other combustion products from the activation assembly 70 within the first chamber 110 to flow out of the gas generator 62 through the gas generator outlet ports 170 and into the second chamber 114, although some moves past the nozzle plate 138 to mix with gas in the diffuser 74. This is provided by the configuration of the projectile/valve 208 and/or the manner in which the projectile/valve 208 interfaces with the gas generator 62. The projectile/valve 208 includes a first conically-shaped head 216 which projects towards the initiator 182 and which has a maximum diameter that is substantially equal but slightly less than the inner diameter of the transfer tube 162 such that the projectile/valve 208 may slide relative thereto. The projectile/valve 208 further includes a second conically shaped head 222 which projects toward the second closure disk 146 and which has a maximum diameter which is less than the maximum diameter of the first head 216. Interconnecting the first head 216 and the second head 222 is a body 226 which includes a first body section 230 and a second body section 234. The first body section 230 slidably interfaces with the second end wall 138 of the gas generator 62, while the second body section 234 extends from the first body section 230 beyond the second end wall 138 for interconnection with the second head 222. The second body section 234 has a smaller diameter than the first body section 230. The projectile/valve 208 is retained in a fixed position in the static state or prior to activation of the activation assembly 70 by the shear ring 212. The annular shear ring 212 is seated within a groove formed on the first body section 230. The shear ring 212 is further retained between the second end wall 138 of the gas generator 62 and the end of the transfer tube 162. Once the activation assembly 70 is activated, the resulting ignition combustion products from the initiator 182 and the ignition/booster material 200 exert a force on the projectile/valve 208 which is sufficient to shear off the shear ring 212 to allow the projectile/valve 208 to be propelled through the second closure disk 146. The projectile/valve 208 is moved solely by these ignition combustion products, and not from combustion of the propellant 66. The projectile/valve 208 continues to be axially advanced by the combustion products from the activation assembly 70 until the first head 216 abuts the second end wall 138 of the gas generator. Since the diameter of the first head 216 exceeds the diameter of the hole or aperture in the second end wall 138 through which the projectile/valve 208 passes, the first head 216 seals the first chamber 110 such that substantial portions of the inflation gases flow out of the gas generator 62 via the gas generator outlet ports 170 and into the second chamber 114 and then exit the inflator 50 in the above-described manner. The pressure within the first chamber 110 due to the combustion of the propellant 66 maintains the projectile/valve 208 in this type of sealing engagement. Another embodiment of a hybrid inflator which may be used in the inflatable safety system 10 of Fig. 1 is illustrated in Fig. 3. The hybrid inflator 300 differs from the hybrid inflator 50 of Fig. 2 in that the hybrid inflator 300 is configured to provide efficient mixing of hot combustion gases from the combustion of the igniter/booster material 200 and the propellant 66 with the cooler pressurised medium 58. The mixing can cause an inflating gas having a relatively homogeneous composition and temperature to be output from the diffuser 146 into the air/safety bag 18. With respect to inflator temperature after activation thereof, it is desired that the temperature of inflation gases used to inflate the air/safety bag be sufficiently controlled or reduced to avoid potential erosion of certain metal parts including gas passageways within the inflator housing. A reduction in temperature is appropriate when a relatively high output is sought from the activated inflator. A relatively high output can be defined in the context of a representative hybrid inflator being tested using a 60-litre tank. When such a hybrid inflator is activated using such a tank, a relatively high output in the tank constitutes a pressure greater than about 500 KPa being developed in the tank when the hybrid inflator is activated. When such a relatively high output occurs, the temperature adjacent the outlet of the hybrid inflator is greater than 1000°C (such as at least about 1100°C). Consequently, in conjunction with a hybrid inflator that produces the relatively high output and such an associated temperature, it is desirable to reduce the temperature of inflation gases at the exit of the inflator housing. The desired mixing for temperature reduction is achieved using an inner shroud 304 that (a) is disposed radially outward from the afterburner tube 78, radially inward of the exterior walls of the gas generator housing 316 (also referred to as the outer shroud), and symmetrically relative to the longitudinal axis 308 of the stored gas housing 54 and (b) preferably extends from a point adjacent to the gas generator 302 to a point beyond the second closure disk 146. An annular space 312, which is a part of the second chamber 114, is defined by the concentric afterburner tube 78 and inner shroud 304 through which the inflating gases must pass to exit the stored gas housing through the afterburner tube 78. The length L 2 of the inner shroud 304 is preferably in the range from about 0.25 to about 0.75 of the length L 1 of the stored gas housing 54. An additional flow path 318 from the first chamber 110 into the second chamber 114 for the combustion gases generated by the propellant 66 and the ignition booster material 200 is provided to complement the flow path from the first chamber 110 into the second chamber 114 defined by the gas generator outlet ports 170. The flow path 318 is defined by a first gap between the annular retainer 320 and the interior walls of the gas generator housing 316, a second gap between the open end 320 of the gas generator housing 316 and the second end wall 138, and the annular outlet 322 defined by the second end 122 of the gas generator housing 316 and the second end wall 138. The second end 122 of the gas generator housing 316 terminates before the second closure disk 146. The operation of the hybrid inflator 300 is similar to that of the hybrid inflator 50 of Fig. 2. The detector 14 (Fig. 1) transmits a signal to the activation assembly 70 and the initiator 182 ignites the ignition/booster material 200. High temperature combustion products from the igniter/booster material 200 ignite the propellant 66 which generates a high temperature and high pressure gas. The high temperature and high pressure combustion gas due to the ignition combustion products from the igniter/booster material force the projectile/valve 208 towards the diffuser end of the stored gas housing 54, thereby rupturing the second closure disk 146 and sealing the first chamber 110 from the third chamber 126. An "O" ring 330 prevents backflow of the combustion gases around the edges of the activation assembly 70 and consequent escape of the gases from the stored gas housing 54. A first portion of the high temperature combustion gas is forced outward into the second chamber 114 through the gas generator outlet ports 170 while a second smaller portion is forced outward into the second chamber 114 along the additional flow path 318. The first portion of the combustion gas experiences a drop in flow velocity as it enters the second chamber 114 while the second portion experiences an increase in flow velocity along the flow path 316. As a result, turbulence in the combustion gases and the pressurised medium is induced near the second end 122 of the gas generator 302 where the lower velocity first portion combines with the higher velocity second portion. Some mixing of the combustion gases and the pressurised medium will occur in response to the turbulent flow conditions. The partially mixed pressurised medium and combustion gases (collectively referred to as "inflation gases") move in a first direction 324 towards the diffuser end of the stored gas housing 54 and then in an opposing second direction 326 towards the activation assembly end of the stored gas housing 54. The first and second directions are substantially parallel to the longitudinal axis 308 of the stored gas housing 54. The restricted flow area of the annular outlet 312 (i.e. the decrease in area of flow upon entry into the annular outlet 312) causes an increase in flow velocity of the combustion gases and the pressurised medium leading to further mixing. Compared to the hybrid inflator 50 of Fig. 1, the flow path of the gases through the first chamber 110 is much longer in the hybrid inflator 300 as a result of the inner shroud 304. The change in flow direction and the longer flow path coupled with the changing flow directions can substantially prevent the occurrence of a flame after the inflation gases exit the diffuser 146. The now fully mixed, substantially homogeneous (in composition and temperature) pressurised medium and combustion gases, or inflation gas, flows in a third direction 328 after passing through the orifice sleeve ports 134 into the third chamber 126, and through the afterburner tube 78. The third direction 328 is opposite to the second direction 326 but the same as the first direction 324. The inflation gas then passes through the diffuser 146 and into the air/safety bag 18 (Fig. 1). The inflation gas has a substantially lower temperature than the combustion gases. This can prevent a change in size (i.e. enlargement) of the orifice sleeve ports 134 due to passage of relatively hot inflation gas into the afterburner tube 78. The foregoing description of the invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and the skill or knowledge of the relevant art, are possible within the scope of the appended claims.

Claims: Apparatus (50) for controlling flow of inflation gases, the apparatus comprising: an inflator housing (54) for storing a gas under pressure; a propellant gas generator (66) for generating propellant gas for heating said stored gas; an initiator (70) for initiating the generation of propellant gas by the propellant gas generator (66); an afterburner tube (78) for receiving inflation gases and providing an exit for said inflation gases from the apparatus (50), said inflation gases including at least a propellant gas generated by the propellant gas generator (66) and a gas initially stored under pressure by the inflator (54); and, outlet closure means (146) for blocking passage of the inflation gases to the afterburner tube (78) until after activation of the initiator (70); characterised by : a wall (106,122,304) defining an outlet path for said inflation gases from the inflator (54) and the propellant gas generator (66) to the afterburner tube (78) to promote mixing of said inflation gases, the wall (106,122,304) being located within the inflator housing (54) and outwardly of the afterburner tube (78) and extending at least partly along the length of the afterburner tube (78) to define a space between the wall (106,122,304) and the afterburner tube (78) such that said inflation gases move in a first direction outwardly of the wall (106,122,304) and towards the exit end of the afterburner tube (78) and then in a second direction opposite the first direction and in the space between the wall (106,122,304) and the afterburner tube (78). Apparatus according to claim 1, wherein said wall is provided by an inner shroud (304) that extends from adjacent to said propellant gas generator (66). Apparatus according to claim 2, wherein the inner shroud (304) has a length such that the inner shroud (304) extends beyond the outlet closure means (146). Apparatus according to any of claims 1 to 3, wherein the wall (106,122,304) has a length which is in the range 0.25 to 0.75 of the length of the inflator housing (54). Apparatus according to any of claims 1 to 4, wherein the propellant gas generator (302) has an annular outlet (322) arranged such that at least some of said propellant gas flows through the annular outlet (322) into a space between the wall (304) and the inflator housing (54). A method for controlling gas flow in an inflation apparatus (50) which includes an inflator housing (54) having stored therein a gas under pressure, a propellant gas generator (66) for generating propellant gas for heating said stored gas, an afterburner tube (78) for receiving inflation gases and providing an exit for said inflation gases from the apparatus (50), and a wall (106,122,304) defining an outlet path for said inflation gases from the inflator (54) and the propellant gas generator (66) to the afterburner tube (78) to promote mixing of said inflation gases, the wall (106,122,304) being located within the inflator housing (54) and outwardly of the afterburner tube (78) and extending at least partly along the length of the afterburner tube (78) to define a space between the wall (106,122,304) and the afterburner tube (78), the method comprising the steps of: generating propellant gas by the propellant gas generator (66) ; mixing generated propellant gas with the stored gas to provide inflation gases; flowing said inflation gases in a first direction outwardly of the wall (106,122,304) and towards the exit end of the afterburner tube (78) and then in a second direction opposite the first direction and in the space between the wall (106,122,304) and the afterburner tube (78). A method according to claim 6, comprising the step of rupturing an outlet closure disk (146) to allow inflation gases to pass to the exit. A method according to claim 6 or claim 7, wherein said wall is provided by an inner shroud (304) that extends from adjacent to said propellant gas generator (66). A method according to claim 8, wherein the inner shroud (304) has a length such that the inner shroud (304) extends beyond the outlet closure means (146). A method according to any of claims 6 to 9, wherein the wall (106,122,304) has a length which is in the range 0.25 to 0.75 of the length of the inflator housing (54). A method according to any of claims 6 to 10, wherein the propellant gas generator (302) has an annular outlet (322) arranged such that at least some of said propellant gas flows through the annular outlet (322) into a space between the wall (304) and the inflator housing (54).

Inventors: RENZ ROBERT N, RENZ, ROBERT N.
Applicants: AUTOLIV ASP INC, AUTOLIV ASP, INC.
Application year: 1998
Main classification: F42B3
IPC codes: B60R21