Inflation Time Control For Safety Device

Abstract

Apparatus for transmitting an electrical current from a power supply to a gas source during a time interval which varies in direct proportion to the ambient temperature within the portion of a vehicle in which the apparatus is disposed. A portion of the gas is released from the gas source upon receipt of the electrical pulse. Another portion of the gas is released from the gas source independently of the pulse. The released gas passes into a bag, which inflates during a time interval independent of the ambient temperature, thereby serving to protect occupants or other mobile objects within the vehicle.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a safety device for passengers of motor vehicles, such as automobiles, and more particularly to apparatus for inflating a bag with gas upon collision of a vehicle equipped with the apparatus, wherein the inflation time is independent of the ambient temperature within the portion of the vehicle in which the apparatus is disposed.

2. Description of the Prior Art

The recent development of passive vehicle occupant restraint systems gives promise of significantly decreasing the number of fatalities and serious injuries resulting from motor vehicle accidents. Among the passive restraint systems suggested in the prior art, the inflatable bag restraint system is the most promising.

One of the problems encountered in adapting inflatable bag restraint systems for use in different seasons and geographical regions is the difficulty of controlling the time interval during which the bag is inflated. The inflation time interval commences at impact of a vehice, whereupon an electrical signal is transmitted from a power source to a gas source housed within the vehicle. Gas released from the gas source is directed into a bag or cushion which inflates during a preselected time interval to protect passengers or other mobile objects within the vehicle. Changing climatic conditions within the different environments to which the inflatable bag restraint system is ordinarily exposed can markedly alter the ambient temperature within the portion of the vehicle in which the gas source is located. When vehicular impact occurs at higher ambient temperatures, gas is released from the gas source at a higher pressure than if the impact occurs at lower ambient temperatures. The inflation time interval is inversely proportionate to the pressure of the released gas. Thus, upon impact of the vehicle at higher ambient temperatures, the bag inflates during a time interval considerably shorter than obtains if the impact occurs at lower ambient temperatures.

I have found that, particularly at lower impact velocities, a bag inflated at relatively high ambient temperatures moves in the direction of an occupant within the vehicle at excessively high speeds. An occupant moving forward at the time of impact can be pushed backward with considerable force by the rapidly inflating bag. Use of increased inflation time intervals provides protection against such rebound problems but reduces the protection afforded at lower ambient temperatures, wherein the bag is both filled and caused to move in the direction of the occupant at a much slower speed. Under the latter temperature conditions, and particularly at relatively higher impact velocities, gas released from the gas source upon impact of the vehicle may flow into the bag in insufficient volume and pressure to prevent an occupant moving forward at the time of impact from penetrating through the front of the bag and into contact with hard portions of the vehicle on the reverse side of the bag.

The protection afforded to an occupant disposed within a vehicle can be significantly increased if, upon impact of the vehicle at a given velocity, the bag inflates during a preselected time interval calculated as that best suited to protect the occupant. Such preselected inflation time interval cannot be consistently achieved if the inflation time interval at the given velocity tends to vary in proportion to the ambient temperature. An inflation assembly not equipped with means to compensate for changes in the ambient temperature can result in inflation time intervals somewhat faster or slower than those best suited to protect the occupant. In accordance with the invention, the bag inflates during a time interval which is independent of the ambient temperature, whereby upon impact of the vehicle at the given velocity the preselected inflation time interval can consistently be achieved.

SUMMARY OF THE INVENTION

Briefly stated, the invention provides an apparatus for transmitting an electrical current from a power source to a first portion of a gas source within a fixed first time interval, and to a second portion of the gas source within a second time interval which varies in direct proportion to the ambient temperature of the portion of the vehicle in which the apparatus is disposed, hereinafter referred to as the ambient temperature. An impact detecting means causes the current to pass from the power source to a first and second circuit means upon impact of the vehicle. Part of the current is transmitted through the first circuit means to the first portion of the gas source during the first time interval. Another part of the current is transmitted through the second circuit means to the second portion of the gas source during the second time interval. The first and second portions of the gas source each respectively comprise a pressurized gas, a gas generating material, or a hybrid combination of the same housed within a container. Means are provided for releasing the pressurized gas, gas developed by combustion of the gas generating material, or mixture thereof from the container upon receipt of the electrical current. Preferably, the first and second portions of the gas source are separated within a pressurized tank by a pressure sensitive barrier. Such barrier forms a wall common to a first and second container in which the first and second gas portions are respectively housed. The second time interval is caused to vary in direct proportion to the ambient temperature, by a control means, responsive to the ambient temperature. Gas released from combined portions of the gas source flows into an inflatable bag during a time interval which is then independent of the ambient temperature whereby upon impact of the vehicle, the bag can be consistently inflated during the said time interval.

More specifically, the impact detecting apparatus includes an electroconductive material connected to the power source. The current is caused to flow from the power source to the first and second circuit means when forces resulting from impact of the vehicle displace the electroconductive material against a preselected resisting force and into contact with an electroconductive member connected to the first and second circuit means. A control means is additionally provided which comprises an electroconductive component connected to the power source, a control element connected to the second circuit means, and means for varying the control element in direct proportion to the ambient temperature.

In one embodiment of the invention a resistance element is connected at one end to the second circuit means. An electroconductive component connected to the power source is maintained in continuous contact with the resistance element. The electroconductive component is displaced along the surface of the resistance element a variable distance from the end of the resistance element connected to the second circuit means. The distance varies in direct proportion to the ambient temperature. As the ambient temperature decreases, for example, the electroconductive component is displaced toward the end of the resistance element connected to the second circuit means. The electroconductive component contacts the resistance element at a shorter distance from the end of the resistance element connected to the second circuit means, and the current travels through a shorter portion of the resistance element. The electroconductive component is displaced by means which comprise at least two thermally conductive members, each respectively having a different thermal coefficient of expansion. Such members are joined together to form a composite member. One end of the composite member is fixed. The other end of the composite member is connected to the electroconductive component, thereby permitting the electroconductive component to be displaced over at least a portion of the deflection characteristic curve of of the composite member by a change in the ambient temperature. Such composite member may be in the form of a spiral having one end fixed and the other end connected to the electroconductive component. An increase or decrease in the ambient temperature causes the electroconductive component to be angularly displaced over a portion of the deflection characteristic curve of the composite member. In either case, the electroconductive component is displaced relative to the resistance element so that the current is caused to pass through a portion of the resistance element which varies in direct proportion to the ambient temperature. In another embodiment of the invention, the control means is comprised of a resistance element, such as a thermistor, having a temperature coefficient of resistance which varies in proportion to the ambient temperature.

Upon impact of the vehicle, the impact detector causes part of the current to flow from the power source through the first circuit means to the first portion of the gas source during the first fixed time interval. Another part of the current reaches the second portion of the gas source via the second circuit means during the second time interval. The electroconductive member of the control means cooperates with the resistance element to make the time interval during which the electrical current is transmitted from the power source through the second circuit means to the second portion of the gas source proportional to the temperature. The electrical current is transmitted from the power source through the first circuit means to the first portion of the gas source during a constant time interval which may equal but not exceed the time interval during which the electrical current is transmitted to the second portion of the gas source. Gas is released from the first portion of the gas source upon receipt of the electrical current from the first circuit means. Such release does not cause gas to be released from the second portion of the gas source; such gas is not released until receipt of the electrical current from the second circuit means. The released gas is preferably discharged from the gas source through a conduit and into a shock-absorbing bag or cushion. For example, as the ambient temperature increases, the electroconductive component is displaced along the surface of the resistance element in a direction away from the end of the resistance element which is connected to the second circuit means. Upon impact of the vehicle the current travels through a correspondingly larger portion of the resistance element. Alternatively, as the ambient temperature increases, the resistance of the thermistor correspondingly increases. In either case, the electrical current reaches the second portion of the gas source within a longer time interval. Thus, the time interval during which the electrical current is transmitted from the power source to the second portion of the gas source to effect the release of gas therefrom varies in direct proportion to the ambient temperature.

A unique means is thereby furnished for variably controlling the time during which an air bag or cushion is inflated. For substantially any impact velocity the bag can be consistently inflated during a preselected time interval despite changes in the ambient temperature. Since the noise associated with inflation of air cushions of the type described generally increases with decreased inflation time intervals, and since, in accordance with the invention, bags need not be inflated during a time interval shorter than the preselected time interval, it is also possible to reduce the sound resulting from inflation. Accordingly, the invention affords increased protection against sound and rebound problems and, in general, results in a safer disposition of the bag when the vehicle which carries it is involved in a collision.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and further advantages will become apparent when reference is made to the following detailed description of the preferred embodiment of the invention and the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of apparatus for transmitting an electrical current to a first portion of a gas source within a fixed time interval, and to a second portion of the gas source within a variable time interval.

FIG. 2 is a schematic electrical diagram of the firing circuit of FIG. 1.

FIG. 3 is an isometric view of the impact detector of FIGS. 1 and 2, including an electrically conductive material and a conductive element.

FIG. 4 is a sectional front elevation of an electronic means for controlling the time during which the electrical current is transmitted from the power source to the gas source.

FIG. 5 is a sectional side elevation of an alternate means for controlling the time during which the electrical current is transmitted from the power source to the gas source.

FIG. 6 is a schematic electrical diagram of a transmission circuit employing the means of FIGS. 4 and 5.

FIG. 7 is a schematic electrical diagram of a transmission circuit employing another form of transmission control apparatus for use with the present invention.

FIG. 8 is a graph illustrating the pressure of gas within the gas source as a function of time after impact.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, there is illustrated in FIG. 1 a preferred form of electrical apparatus for transmitting an electric current to a first portion of a gas source within a first fixed time interval and to a second portion of the gas source within a second variable time interval. The apparatus, shown generally at 10, includes a power source 12, which may comprise a battery of the type conventionally used in a motor vehicle. An auxiliary power supply, such as a capacitor connected in parallel to the battery, may be used as the power source in the event that the battery is not supplying power to the system. Under normal operating conditions an electrical current 20 flows from the power source 12 through firing circuit 22 and back to the power source 12. When a vehicle in which apparatus 10 is disposed is involved in a collision, impact detector 24 directs current 20 by switch means, shown at 26 in FIG. 2, to a first portion 28 of a gas source, shown generally at 30. The current 20 also passes through transmission circuit 32 to a second portion 36 of gas source 30 during a time interval controlled by transmission control means 34. Thus, current 20 passes from power source 12 to the first and second portions 28 and 36 of the gas source 30 by a first and second circuit means, both of which may include the firing circuit 22 and the impact detector 24. The first circuit means connects the power source 12 to the first portion 28 of gas source 30. The second circuit means connects the power source 12 to the second portion 36 of gas source 30.

The first and second gas portions of which gas source 30 is comprised may each respectfully utilize a pressurized gas, gas generated by combustion of a gas generating material, or a hybrid combination of the same. In a preferred embodiment of the invention, the gas source comprises a hybrid combination of pressurized gas and a gas generating material, separately housed within a vessel having means for releasing the pressurized gas and gas developed by combustion of the gas generating material from the vessel upon receipt of the electrical current 20. Nitrogen, or other suitable gas which can be stored for prolonged periods without leaking from a gas containing vessel is generally used as the pressurized gas. Black powder nitro-cellulose, composite propellants, or other material which generates gas and heat upon combustion can be used as the gas generating material. The volume and pressure of the stored gas selected will depend upon the volume of the bag, the pressure to which it is filled and the volume of gas produced by the gas generating material in combination with its heat liberation. Preferably, the volume and pressure of the stored gas is at least about 25 percent of the volume and pressure of gas generated by combustion of the gas generating material.

In the embodiments shown in FIGS. 1, 2, 6 and 7, the first portion 28 of gas source 30 comprises a pressurized gas, and the second portion 36 comprises a gas generating material. A pressure sensitive barrier 42 separates the first portion 28 from the second portion 36 of gas source 30. Gas can be released from the first portion 28 by detonating an electroexplosive device comprised, for example, of a detonator, a pressure cartridge, or a shape charge 41, upon receipt of the electrical current 20. The shape charge is located adjacent to a plug 40, which is removabl mounted in and extends through a full thickness of the housing of gas source 30. The explosion of shape charge 41 dislodges plug 40 and creates a conduit in communication with the first portion 28 of gas source 30 and an inflatable bag 101. When the electrical current reaches the second portion 36 of the gas source 30, combustion of the gas generating material commences. The gas pressure within the second portion 36 increases to a preselected level, whereupon barrier 42 ruptures, and the gas sequentially flows through the first portion 28 and the conduit into bag 101. The construction and operation of the gas source 30, including the first portion 28, the second portion 36 and apparatus connected thereto for inflating an air cushion is described in the copending application of Robert L. Stephenson, Ser. No. 81,947, filed Oct. 9, 1970, which disclosure is specifically incorporated by reference.

Although the invention will be described hereinafter with reference to apparatus for releasing gas from a single gas source upon a single vehicular impact, it is intended that the invention can be used with apparatus for successively inflating a bag with gas from a plurality of gas sources when multiple impacts occur within a short period of time. In such apparatus, the electrical current can be transmitted from the power source through the first and second circuit means to a primary gas source upon a first impact of the vehicle, and to a secondary gas source upon a subsequent impact. A pressure sensitive control means electrically connected to the circuit means and responsive to the pressure of gas within the primary gas source electrically connects the primary gas source to the circuit means prior to an impact of the vehicle and electrically connects the secondary gas source to the circuit means after the impact. The bag is successively inflated and reinflated upon a first and second impact of the vehicle by gas sequentially released from the primary and secondary gas source upon receipt of the electrical current. Moreover, for one or more gas sources, the invention as described herein can additionally be used with apparatus in which the electrical current is transmitted from a power source through the first circuit means to the first portion of a gas source during a fixed time interval, and through the second circuit means to the second portion of the gas source during a variable time interval of at least the same duration as the fixed time interval; but wherein the variable time interval is inversely proportional to the impact velocity of the vehicle. The construction and operation of apparatus for successively inflating a bag with gas from a plurality of gas sources disposed in a vehicle subject to a plurality of impacts, and for inflating the bag during a a time interval which varies in inverse proportion to the impact velocity of the vehicle, is respectively disclosed in the copending applications of Donald G. Radke et al., Ser. No. 192,971 and Donald J. Lewis, Ser. No. 192,850 filed of even date with the present application, which disclosures are specifically incorporated by reference.

In FIG. 2 there is illustrated a schematic electrical diagram showing the firing circuit of FIG. 1. Upon application of voltage from battery 14, current 20 flows through line 16 and at least one diode 18 to capacitor 38. The resistance of resistor 40 is higher than the resistance of the uncharged capacitor 38. Accordingly, current 20 flows through and charges the capacitor 38. The capacitor is large, having a capacitance of from about 10,000 to about 20,000 microfarads, for example. In the preferred embodiment of the invention the capacitor 38 is charged to substantially the potential of the battery during a time period of from about 1-5 seconds after the ignition switch 15 is closed. When the capacitor 38 has been charged, the resistance value of resistor 40 is lower than the resistance of capacitor 38. Thus, the current passes through resistor 40 instead of capacitor 38 and returns to battery 14 through line 44. Diode 18 functions to prevent an external short circuit resulting from a collision, for example, from discharging capacitor 38 through line 16. The system is more reliable if redundant diodes are connected in parallel in one or more sets in place of the single diode 18. This redundant arrangement of the diodes insures proper operation of the system despite the failure of any one of the diodes. If any of the diodes becomes open circuited, its companion diode in the parallel set is operative to carry the current. If any of the diodes become short circuited, the other parallel pair provides the unidirectional current limiting capability. Resistor 40 may also be replaced by redundant resistors to provide increased reliability to the apparatus 10. In a preferred embodiment, the resistors 40 have a relatively low resistance, such as approximately 180 ohms each. Redundant resistors 40 are connected in parallel so that in the event one of the resistors becomes open, the path resistance will not be increased appreciably.

Normally, switch 26 is open and the current 20 is prevented from passing through line 46 and line 48 to the gas source 30. When a vehicle carrying apparatus 10 is involved in a collision, the impact detector 24 throws switch 26, which is connected to line 46 in the direction of the arrow and into contact with line 48. Lines 46 and 48 have a lower resistance than the resistor 40. Thus, the current 20 flows from the power source 12 through the firing circuit 22 and lines 46 and 48 to gas source 30. In the event that the battery 14 fails or is disconnected from the system by impact of the vehicle, the capacitor 40 discharges through lines 46 and 48. The capacitor 40 thus forms an auxiliary source for supplying electrical power to the first and second portions of gas source 30.

In FIG. 3 there is illustrated the impact detection means of FIGS. 1 and 2. Such means may comprise at least one roller 56 of metal such as stainless steel, gold plated copper, or other suitable conductive material. The roller 56 is electrically connected to the power source 12 and moveably mounted on a nonconductive support 53 made, for example of plastic, lexon, polycarbonate, glass or ceramics. A thin band of electrically conductive material 54, such as stainless steel, gold plated copper, or the like, wrapped around roller 56 and spot welded or otherwise secured to support 53 provides a resisting force against which the roller 56 acts. Conductive element 58, comprised of electroconductive material of the type used to make band 54 is fixedly mounted on support 53. If roller 56 is displaced along the surface 60 of support 53 in the direction of the arrow, band 54 is brought into contact with conductive element 58. When the vehicle is involved in an impact of the type intended to inflate bag 101, the roller 56 is displaced along the surface 60 of support 53 until band 54 contacts conductive element 58. The current 20 flows from the power source 12 or from the capacitor 40, as the case may be, through the firing circuit 22, line 46, switch 26 and line 48. Thereafter the current 20 flows through line 50 to the first portion 28 of gas source 30 during a constant time interval and through line 52 and transmission circuit 32 to the second portion 36 of gas source 30 during a time interval which varies in direct porportion to the ambient temperature, as will be described hereinafter in more detail.

In FIG. 4 there is shown a control means 34 for controlling the time during which the electrical current is transmitted from the power source to the second portion of the gas source. Such means may include at least two thermally responsive members 62 and 64 comprised, for example, of such metals as copper, tin, stainless steel, iron, nickel, brass, or other suitable conductive metal, each respectively having a different thermal coefficient of expansion. Such members are welded or otherwise adhered together to form a composite member, shown generally as 66. In the embodiment of the invention shown in FIG. 4, the composite member 66 forms a relatively straight bimetallic element. Invar (iron-nickel alloy) and brass are commonly paired to create such bimetallic elements, and these metals are suitable for use in the embodiment of FIG. 4. One end 68 of the composite member 66 is fixed, as by riveting 67, spot welding or otherwise firmly securing the end 68 to a stationary support 70. The other end 72 of composite member 66 is connected to a rigid arm 73 by spot welding, metallic fasteners 69 such as rivets, or the like. Arm 73 is connected by metallic fasteners 75, such as rivets or the like to an electroconductive component 74. Such electroconductive component 74 is electrically connected to the power source through lines 52 and 48. As the ambient temperature increases, end 72 of composite member 66 deflects throughout a portion of a deflection characteristic curve in direct proportion to the temperature increase. Resistance element 76, comprised of carbon film or other material that will provide a suitable value of resistivity, is fixedly mounted on a nonconductive support 78 for continuous contact with electroconductive component 74 during movement of the component 24 throughout a preselected portion of the deflection characteristic curve of composite member 66. A protective sheath or armor 77 surrounds the assembly. The resistance element 76 is electrically connected to the second portion 36 of the gas source 30. End 72 of composite member 66 is deflected in the direction of the arrow by an increase in the ambient temperature, thereby causing electroconductive component 74 to be displaced relative to the resistance element 76 so that upon impact of the vehicle the current 20 flows through a correspondingly larger portion of the resistance element 76. The current 20 thus passes through the resistance element 76 during a longer time interval. Accordingly, the time interval during which the electrical current 20 travels from the power source through the second circuit means to the second portion 36 of the gas source 30 increases.

It will be understood that current 20 from firing circuit 22 which is directed by impact detector 24 through lines 48 and 50 to the first portion 28 of the gas source 30 is not delayed in the above manner. Thus, at a higher ambient temperature gas is released from the first portion 28 before gas is released from the second portion 36, and the air cushion inflates during a longer time interval than would obtain if gas were to be simultaneously released from the first and second portions 28 and 36 of the gas source 30 at the higher ambient temperature. The same result can be achieved if the first and second portions 28 and 36 of gas source 30 each comprise pressurized gas within a gas containing vessel; or alternatively, gas generated within a vessel upon receipt of the electrical current 20. The time interval between release of gas from the first portion 28 and the second portion 36 of gas source 30 is, in effect, the time during which current 20 passes from firing circuit 22 through impact detector 24 and transmission circuit 32 to gas source 30. Control means 34 makes that time interval vary in direct proportion to the ambient temperature. As long as the gas source 30 comprises a first gas portion which can be released, as described, independently of a second gas portion 36, the air cushion can be consistently inflated during a preselected time interval, despite marked changes in the ambient temperature. In a preferred embodiment, such preselected inflation time interval can be consistently achieved even though the ambient temperature ranges from about 40.degree. to 185.degree. F.

In FIG. 5 there is illustrated an alternate means for controlling the time during which the electrical current is transmitted from the power source to the second portion of the gas source. Such means may include a bimetallic element of the type described in connection with FIG. 4. The composite member 88 comprising the bimetallic element is in the form of a spiral. One end 80 of composite member 88 is fixed by rivet 81, othermetallic or nonmetallic fasteners or the like to a rigid member 83. Member 83 is secured by rivet 84 or other suitable fastening means to a stationary support 82. The other end 89 of the composite member 88 is connected to a link 86 which is connected to bar 90. The bar 90 pivotally connects link 86 with one end 92 of pen arm 94. The other end 96 of the pen arm 94 is spot welded, riveted or other wise firmly connected to electroconductive component 98. Such electroconductive component is electrically connected to the power source through lines 52 and 48. As the ambient temperature increases, end 89 of the composite member 88 is angularly deflected through a portion of a deflection characteristic curve in direct proportion to the temperature increase. Link 86, bar 90 and pen arm 94 cooperate to linearize displacement of the electroconductive component 98 resulting from ambient temperature changes. Resistance element 100, comprised of a deposited carbon film or other material that will provide a suitable value of resistivity is fixedly mounted on support 102 beneath electroconductive component 98. The resistance element 100 is electrically connected to the second portion 36 of the gas source 30. As end 89 of the composite member 88 is angularly deflected by an increase in the ambient temperature, the electroconductive component 98 is displaced along the resistance element 100 in the direction of the arrow. Upon impact of a vehicle in which apparatus 10 is disposed, the current 20 is caused to flow through a correspondingly larger portion of the resistance element 100 than would obtain if the impact occurred at a lower ambient temperature. Thus, at higher ambient temperatures, the current 20 passes through the resistance element during a longer time interval. The time interval during which current 20 travels from the power source 12 through the second circuit means to the second portion 36 of the gas source 30 increases, and the system compensates for the increased gas pressure resulting during inflation at higher ambient temperatures.

In FIG. 6 there is shown a schematic electrical diagram of the means of FIGS. 4 and 5. Current 20 from power source 12 and firing circuit 22 passes through switch 26, which is thrown by impact detector 24. Part of the current 20 travels through line 50 directly to the first portion 28 of gas source 30. Another part of the current travels through a portion of variable resistor 104, charging capacitor 106. When the peak point of unijunction transistor 108 is reached, the current 20 is emitted from the unijunction transistor 108 in the form of an electrical pulse. Such pulse passes through resistor 118 and produces a voltage at the gate of silicon controlled rectifier 110, which allows current 20 to flow through line 112 and silicon controlled rectifier 110 to bridgewire 114 within the second portion 36 of gas source 30.

The time interval during which current 20 is allowed to pass through the transmission circuit 32 to gas source 30 is directly proportional to the resistance value of the variable resistor 104. Since the value time interval is determined by the transmission control means 34, gas can be released from the gas source 30 at a preselected pressure which is independent of the ambient temperature.

In the schematic electrical diagram of FIG. 7, another form of transmission control apparatus is employed. As illustrated, current 20 from power source 12 travels through firing circuit 22 and switch 26 thrown by impact detector 24. Part of the current 20 passes through line 50 directly to the first portion 28 of gas source 30. As noted above, portion 28 may comprise either a pressurized gas or a gas generating material. Another part of the current 20 passes through a resistance element 116 having a temperature coefficient of resistance which varies in direct proportion to the ambient temperature. In a preferred embodiment such resistance element comprises a thermistor, which remains stable and is particularly suited to offset changes in the ambient temperature at relatively high impact velocities. When the peak point of unijunction transistor 108 is reached, current 20 is emitted from the unijunction transistor 108 in the form of an electrical pulse, which passes through resistor 118 and produces a voltage at the gate of silicon controlled rectifier 110. The system then functions in the same manner as the transmission circuit of FIG. 6 to inflate bag 101 during a preselected time interval which is independent of the ambient temperature.

Resistor 118 limits the current passing through the gate of the silicon controlled rectifier 110. Resistor 120 functions to bleed down capacitor 106 when power is not supplied to apparatus 10 by power source 12.

Referring to FIGS. 8a, 8b, and 8c, the gas pressure in the first portion of gas source 30 is shown as a function of time after impact. The impact occurs at time T.sub.o. In each of FIGS. 8a, 8b and 8c an equal volume of pressurized gas 122 and an equal mass of gas generating material is stored within the gas source 30. Plug 40 is removed by means described above and an outlet is thereby created in the first portion 28 of gas source 30 at time T.sub.o. The pressurized gas 122 starts to flow from the first portion 28 of gas source 30 through the outlet and into the inflatable bag 101. A second gas 124, generated by combustion of the gas generating material, enters the first portion 28 of gas source 30 at times T.sub.1, T.sub.2 and T.sub.3.

The pressure of gas 122 stored within the first portion 28 of gas source 30 is increased by contact with generated gas 124, which is generally at a higher temperature and pressure than the stored gas 122. Such contact occurs when the pressure of gas within the second portion 36 of gas source 30 reaches a preselected pressure. The pressure sensitive barrier 42 is removed to create an inlet to the first portion 28 of gas source 30. Gas 124, generated by combustion of the gas generating material, passes through the inlet and mixes with a portion of the pressurized gas 122 within the first portion 28 of gas source 30. In FIG. 8c the pressure in the first portion 28 is reduced initially as the pressurized gas 122 passes through the outlet of gas source 30. Upon contact with the generated gas at time T.sub.1, the pressure of the stored gas increases. The ambient temperature is higher in FIG. 8b than in FIG. 8c. Thus, at time T.sub.o gas 122 is released at a higher pressure, and the gas pressure within portion 28 is initially decreased at a faster rate. Upon contact with the generated gas 124 at time T.sub.2, the volume of the gas 122 of FIG. 8b is lower than the volume of the pressurized gas 122 of FIG. 8c at time T.sub.1, and the pressure of the stored gas 122 is increased to a lesser extent by contact with the generated gas 124. The ambient temperature is highest and the volume of pressurized gas 122 is smallest when the generated gas 124 enters the first portion 28 at time T.sub.3. Accordingly, the pressure of gas 122 is increased by the least amount upon contact with the generated gas 124.

The air cushion will inflate during a preselected time interval which is independent of ambient temperature changes so long as the sequential release of gas from the gas source 30 is correlated to the ambient temperature as hereinbefore described. When the ambient temperature decreases, the pressure of gas 122 within gas source 30 is proportionately decreased. The transmission control means 34 provides for transmission of the current 20 through transmission circuit 32 within a shorter time interval. Generated gas 124 contacts and heats a proportionately larger volume of the pressurized gas 122 within portion 28 of gas source 30, and bag 101 is inflated during the preselected time interval. When the ambient temperature and the pressure of gas 122 within gas source 30 increase, the transmission control means 34 provides for transmission of the current 20 through transmission circuit 32 within a longer time interval. Generated gas 124 contacts and heats a proportionately smaller volume of the pressurized gas 122 within portion 28 of gas source 30, and bag 101 is inflated during the preselected time interval. Passengers or other mobile objects stationed relatively near portions of a vehicle from which the air cushion inflates will be pushed backward with less force as the air cushion is filled, than if the inflation time interval were to increase in proportion to an increase in the ambient temperature.

The preselected time interval at which the bag 101 can be inflated by apparatus 10 will depend on many factors, including the volume and construction of the air cushion, and the weight of an occupant or mobile object. Such factors can be controlled by auxiliary means known to those skilled in the art. For substantially any ambient temperature, sound, rebound and other problems resulting from inflation of air cushions during a time interval somewhat shorter or longer than the preselected time interval calculated to best protect the occupant can be eliminated.

The apparatus disclosed is relatively simple in construction, and is easily fabricated and installed. No difficulty is encountered with respect to the ability of the apparatus to consistently compensate for ambient temperature changes in the above described manner. When employed to inflate bag 101 during a preselected time interval within environment in which the ambient temperature ranges from -40.degree.. to 185.degree. F., for example, the apparatus accurately compensates for the ambient temperature of the environment and causes the bag 101 to be consistently inflated during the preselected time interval.

Having thus described my invention in rather full detail, it will be understood that these details need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention as defined by the subjoined claims.

Claims

I claim:

1. Apparatus for transmitting an electrical current to a gas source disposed in a portion of a motor vehicle subject to impact, within a time interval which varies in direct proportion to the ambient temperature within said portion of the vehicle, comprising:

a. a power source for supplying the electrical current;

b. first circuit means for transmitting the current from the power source to a first portion of the gas source during a first fixed time interval;

c. second circuit means for transmitting the current from the power source to a second portion of the gas source during a second variable time interval;

d. impact detecting means for causing the current to pass through said first and second circuit means upon impact of the vehicle; and

e. control means connected to the second circuit means and responsive to the ambient temperature, for varying the second time interval in direct proportion to the ambient temperature.

2. Apparatus as recited in claim 1 wherein the control means comprises a resistance element connected to the second circuit means, and means for varying the resistance of the resistance element in direct proportion to the ambient temperature.

3. Apparatus as recited in claim 2 wherein the resistance element is connected at one end to the second circuit means and the resistance of the resistance element is varied by means which comprise an electroconductive component connected to the power source, the electroconductive component being in continuous contact with the resistance element, and means for displacing the electroconductive component along the surface of the resistance element a variable distance from the end of the resistance element connected to the second circuit means, the distance varying in direct proportion to the ambient temperature.

4. Apparatus as recited in claim 3 wherein the electroconductive component is displaced by means which comprise at least two thermally conductive members each having a different thermal coefficient of expansion, said thermally conductive members joined together to form a composite member, one end of the composite member being fixed and the other end of the composite member being connected to the electroconductive component, whereby the electroconductive component is deflected over at least a portion of the deflection characteristic curve of the composite member in proportion to an increase in the ambient temperature.

5. Apparatus as recited in claim 4 wherein the composite member is in the form of a spiral.

6. Apparatus as recited in claim 2 wherein the control means comprises a resistance element connected to the second circuit means and having a positive temperature coefficient of resistance which varies in direct proportion to the ambient temperature.

7. Apparatus as recited in claim 6 wherein the resistance element is a thermistor.

8. Apparatus as recited in claim 3 which has associated therewith an auxiliary power supply connected between said power source and each of said first and second circuit means.

9. Apparatus as recited in claim 8 wherein the first and second circuit means include a firing circuit connected to the power source and to the impact detecting means, said firing circuit comprising means for transmitting the electrical current from the power source or from the auxiliary power supply to the impact detecting means upon impact of the vehicle.

10. Apparatus as recited in claim 9 wherein the power source comprises the battery of the motor vehicle.

11. Apparatus as recited in claim 10 wherein the first and second circuit means having such a configuration that either the power source or the auxiliary power supply is capable of discharging through the firing circuit upon impact of the vehicle.

12. Apparatus as recited in claim 10 wherein the auxiliary power supply comprises a capacitor, and the firing circuit includes the capacitor connected in parallel with the battery, and a diode connected between the battery and the capacitor and in series with the battery and the impact detecting means.

13. Apparatus as recited in claim 12 wherein the diode comprises redundant diodes connected in parallel.

14. Apparatus as recited in claim 3 wherein the first portion of the gas source comprises an enclosed gas containing means filled with a pressurized gas and provided with an inlet and outlet means; and the second portion of the gas source comprises a gas generating material within an enclosed gas generating means, disposed adjacent to the gas containing means and separated therefrom by a pressure sensitive barrier.

15. Apparatus as recited in claim 3 wherein the gas source comprises a hollow housing, a plug removably mounted within the housing, said plug extending through a full thickness of the housing and into contact with a pressurized gas within the housing, an explosive charge located adjacent to the plug, and a resistance material structurally connected to the explosive charge and electrically connected to the first circuit means, for exploding the charge when the current flows through the resistance material, whereby the plug is removed from the housing.

16. Apparatus as recited in claim 15 wherein an outlet is provided in the housing by removal of the plug, said outlet being in communication with the pressurized gas and with an inflatable bag, whereby gas flows from within the housing through the outlet and into the inflatable bag.

17. Apparatus as recited in claim 15 wherein the first portion of the gas source includes a pressurized gas within the housing, and the second portion of the gas source includes a gas generating material disposed within the housing adjacent to the pressurized gas and separated therefrom by a pressure sensitive barrier.

18. Apparatus as recited in claim 3 wherein the second circuit means includes a transmission circuit, connected to the impact detecting means, said transmission circuit comprising a variable resistor in series with means for transmitting an electrical pulse to the second portion of the gas source.

19. Apparatus as recited in claim 18 wherein the electrical pulse is transmitted by means which include a unijunction transistor and a rectifier in series with the variable resistor and a second resistor with the second portion of the gas source, and a capacitor connected in parallel with the power source.