Pretensioner gas generator

Abstract

This pretensioner gas generator used for a seat belt comprises: a gas generating unit having a gas generating agent for generating a gas for drawing in a wire; and an ignition unit having an ignition agent for burning the gas generating agent, wherein the pretensioner gas generator has a maximum pressure of 40-60 MPa in a closed tank having a volume of 10 cc, and the time to reach half of the maximum pressure is 1.7 msec or less from the start of operation of the pretensioner gas generator.

Description

Pretensioner gas generator

[0001] The present disclosure relates to a gas generator for a pretensioner used in a seat belt.

[0002] Seatbelt devices, which are occupant protection devices, have been widely used to protect occupants of automobiles, etc. Seatbelt devices are installed to protect occupants from impacts that occur during vehicle collisions, and restrain the occupants in their seats by wrapping a belt around their bodies, thereby preventing the occupants from being thrown into or out of the vehicle during a vehicle collision.

[0003] Seatbelt devices equipped with so-called pretensioners incorporate a small gas generator known as a micro gas generator. A pretensioner is a device that instantly tightens a seatbelt to remove any slack caused by factors such as the thickness of clothing when a vehicle collision is detected. This function is achieved by tightly retracting one end of the seatbelt due to the gas pressure output from the gas generator.

[0004] The gas generator is equipped with a gas generating unit that generates a large amount of gas, and various compositions have been investigated for this gas generating agent. Smokeless powder, primarily composed of nitrocellulose, has been used as the gas generating agent.

[0005] However, while smokeless powder excels at generating large amounts of gas, it also has the problem of generating harmful substances such as carbon monoxide. In particular, the gas generator incorporated in a lap pretensioner holds a wire connected to one end of a seat belt in a manner that penetrates the pressure vessel inside the gas generator, creating gaps in the pressure vessel. Therefore, if smokeless powder is used in a gas generator incorporated in a pretensioner, there is a possibility that carbon monoxide will leak from the gaps in the pressure vessel when gas is generated.

[0006] Therefore, in recent years, attention has been focused on the use of non-nitrocellulose gas generants, which produce extremely low amounts of harmful substances such as carbon monoxide. For example, there is a gas generant containing guanidine nitrate as a fuel and a basic metal nitrate as an oxidizer (Patent Document 1), and a gas generant composition containing a guanidine compound and ammonium nitrate granules containing ammonium nitrate and a water-dispersible polymer (Patent Document 2).

[0007] JP 2022-59557 A JP 2016-216322 A

[0008] On the other hand, in tests where a gas generator using a non-nitrocellulose gas generant was incorporated into a pretensioner and activated, a malfunction in which the wire broke was confirmed in a delayed ignition mode, a test that assumes that the belt is locked and the wire cannot be retracted. This is because the heat generated by non-nitrocellulose gas generants is high, causing the wire to reach a higher temperature than smokeless powder.

[0009] Therefore, the present invention provides a gas generator that is incorporated into a pretensioner used in a seat belt and that suppresses breakage of a wire provided in the pretensioner.

[0010] The present invention provides the following gas generator for a pretensioner: (1) A gas generator for a pretensioner used in a seat belt, comprising: a gas generating unit provided with a gas generating agent that generates gas for retracting a wire; and an ignition unit provided with an ignition charge for burning the gas generating agent, wherein the maximum pressure of the pretensioner gas generator is 40 MPa or more and 60 MPa or less in a sealed tank having a volume of 10 cc, and the time required for the pressure to reach half of the maximum pressure is 1.7 msec or less, calculated from the start of operation of the pretensioner gas generator.

[0011] (2) A gas generator for a pretensioner used in a seat belt, comprising: a gas generating unit having a gas generating agent that generates gas for retracting a wire; and an ignition unit having an ignition charge for burning the gas generating agent, wherein the amount of heat generated by burning the ignition charge is 13% or more of the amount of heat generated by burning the gas generating agent.

[0012] (3) The gas generator for a pretensioner according to (1) or (2), wherein the gas generating agent includes a mixed explosive.

[0013] (4) The gas generator for a pretensioner according to (3), wherein the mixed explosive contains at least one compound selected from the group consisting of guanidine nitrate, nitroguanidine, and 5-aminotetrazole, at least one oxidizer selected from the group consisting of perchlorates and nitrates, and a binder.

[0014] According to the present invention, a gas generator for a pretensioner can be provided that can suppress breakage of a wire provided in a pretensioner mechanism due to combustion of a gas generating agent.

[0015] Fig. 1 is a schematic cross-sectional view of a gas generator according to an embodiment. Fig. 2 is a diagram showing changes in pressure in a 3.5 cc non-sealed tank test. Fig. 3 is a diagram showing changes in pressure in a 10 cc sealed tank test.

[0016] The present invention relates to a gas generator for a pretensioner used in a seat belt. The gas generator for a pretensioner may be referred to simply as a gas generator hereinafter. When a vehicle body detects a collision or the like, the gas generator quickly retracts a wire to take up slack in the seat belt and restrain the occupant. An example of a pretensioner is a lap pretensioner with a wire passing through it.

[0017] [Gas Generator] The gas generator 1 in this embodiment includes an ignition unit 10 and a gas generating unit 20.

[0018] FIG. 1 is a schematic diagram of a gas generator according to this embodiment. When the gas generator 1 detects a vehicle collision, an ignition charge (not shown) contained in an ignition unit 10 first burns. The combustion of the ignition charge then burns a gas generating agent 21 contained in a gas generating unit 20. A large amount of gas is then generated and ejected into the operating space of the pretensioner. The operating space filled with gas moves in a direction that increases its volume, and simultaneously, the piston moves in the same direction as the operating space. The wire included in the pretensioner is attached to the piston, so the wire also moves with the movement of the piston, retracting the slack in the seat belt. Due to the structure of the pretensioner, the wire passes through the operating space.

[0019] The ignition unit 10 contains an ignition charge that ignites and burns to generate a flame when a vehicle collision is detected, and a resistor for igniting the ignition charge, and a pair of terminal pins 13 are connected to the ignition unit 10 to ignite the ignition charge, and the ignition unit 10 is covered by a cover 12. The ignition charge is generally also called a squib charge.

[0020] More specifically, the resistor is attached inside the ignition unit 10 so as to connect the tips of a pair of terminal pins 13, and an ignition charge is loaded so as to surround or be close to the resistor.

[0021] When a vehicle collision is detected, a predetermined amount of current flows through the resistor via the pair of terminal pins 13. The predetermined amount of current flowing through the resistor generates Joule heat in the resistor, causing the ignition charge to start burning. The high-temperature flame produced by the combustion ruptures the cover 12 containing the ignition charge, and transfers heat to the gas generating agent 21 loaded in the gas generating unit 20 located outside the cover 12. In this embodiment, the start of combustion of the ignition charge is defined as the start of operation of the gas generator 1.

[0022] The gas generating section 20 contains a gas generating agent 21 , and the entire gas generating section 20 is covered by a cup 30 .

[0023] The gas generating agent 21, receiving heat from the ignition charge, is ignited and burns, generating a large amount of gas in the gas generating unit 20. This combustion of the gas generating agent 21 causes the internal pressure of the gas generating unit to rise rapidly, which opens the bottom wall portion 31 of the cup 30 and allows the large amount of generated gas to be discharged to the outside of the gas generator 1.

[0024] The large amount of gas released from the gas generator 1 is then directed to the operating section of the pretensioner in which the gas generator 1 is incorporated, thereby driving the pretensioner and strongly pulling in one end of the seat belt attached to the seat belt device.

[0025] <First Aspect> In the gas generator of the first aspect, in a sealed tank having a volume of 10 cc (described below) (hereinafter referred to as a sealed tank test), the maximum pressure is 40 MPa or more and 60 MPa or less, and the time required to reach half of the maximum pressure (hereinafter also referred to as "time Ta") is 1.7 msec or less, calculated from the start of operation of the gas generator.

[0026] The inventors found that the pressure behavior in a sealed tank test is related to the susceptibility of wire breakage when a gas generator is incorporated into a pretensioner, and after further investigation, discovered that when the maximum pressure in a sealed tank test is 40 MPa or more and 60 MPa or less, wire breakage due to combustion of the gas generating agent can be suppressed by setting the time Ta, calculated from the time the gas generator is activated, to 1.7 msec or less. The time Ta is more preferably 1.5 msec or less, and even more preferably 1.0 msec or less. The pressure behavior in the sealed tank is correlated with the progress of combustion of the gas generating agent 21, and it is understood that rapid progress of combustion of the gas generating agent 21 can suppress wire breakage.

[0027] <Second Aspect> In a gas generator of the second aspect, the amount of heat generated by burning the ignition charge in the ignition section 10 (hereinafter referred to as the heat generation amount of the ignition section) accounts for 13% or more of the amount of heat generated by burning the gas generating agent 21 in the gas generating section 20 (hereinafter referred to as the heat generation amount of the gas generating section). The heat generation amounts of the ignition charge and the gas generating agent can be found by multiplying the specific heats (J / g) at the respective component ratios by the masses (g) of each.

[0028] The inventors discovered that the susceptibility of the wire to break is affected by the heat generation amount of the ignition part of the gas generator and the total heat generation amount of the gas generation part. After further investigation, they discovered that the heat generation amount required for pretensioner operation can be reduced by making the heat generation amount of the ignition part 13% or more of the heat generation amount of the gas generation part, thereby preventing wire breakage. The heat generation amount of the ignition part is preferably 16% or more and 22% or less of the heat generation amount of the gas generation part. Furthermore, the total heat generation amount of the ignition part and the gas generation part is preferably 4000 J or more and 6000 J or less. By making the heat generation amount of the ignition part 16% or more of the heat generation amount of the gas generation part, the ignition part can efficiently promote combustion of the gas generation part, thereby reducing the amount of explosive required for normal operation of the pretensioner. This is believed to prevent wire breakage.

[0029] Here, the state in which the wire breaks refers to a state in which the wire is heated by the heat of the gas from the gas generator 1, and the tensile strength of the wire becomes less than the tension applied by the occupant.

[0030] <Ignition Charge> The ignition charge in this embodiment is characterized by containing at least one metal powder selected from the group consisting of zirconium powder, tungsten powder, molybdenum powder, aluminum powder, titanium powder, and magnesium powder, and a perchlorate.

[0031] The metal powder undergoes oxidation in part or all of its content during the ignition and combustion process, generating heat and generating metal thermal particles. From the viewpoint of ease of handling during production, zirconium powder, tungsten powder, or molybdenum powder is preferably used as the metal powder, and zirconium powder and tungsten powder are particularly preferred. The metal powder preferably has a spherical shape formed by a known method.

[0032] The ignition charge of this embodiment uses a perchlorate, which functions as an oxidizing agent and oxidizes the metal powder. Examples of the perchlorate include alkali metal perchlorates, alkaline earth metal perchlorates, and ammonium perchlorate. Alkali metal perchlorates are particularly preferred, and potassium perchlorate and sodium perchlorate are preferably used.

[0033] <Gas Generating Agent 21> As described above, what is called a mixed explosive is used as the gas generating agent 21. The mixed explosive refers to a compacted explosive of a non-azide-based composition that includes an organic nitrogen compound, an oxidizer, and a binder.

[0034] The organic nitrogen compound in the explosive mixture functions as a fuel component, and one or more types may be used. The organic nitrogen compound is not particularly limited, and organic nitrogen compounds typically used in gas generant compositions for gas generators for vehicle occupant safety devices can be suitably used. Preferred examples include guanidine or a derivative thereof, triazole or a derivative thereof, tetrazole or a derivative thereof, bitriazole or a derivative thereof, bitetrazole or a derivative thereof, azodicarbonamide or a derivative thereof, hydrazine or a derivative thereof, and hydrazide derivatives.

[0035] More specifically, preferred examples include 5-oxo-1,2,4-triazole, tetrazole, 5-aminotetrazole, aminotetrazole nitrate, nitroaminotetrazole, bitetrazole (5,5'-bi-1H-tetrazole), 5,5'-bi-1H-tetrazole diammonium salt, azobistetrazole, 5,5'-azobistetrazole diguanidium salt, guanidine, guanidine nitrate, nitroguanidine, cyanoguanidine, triaminoguanidine nitrate, aminoguanidine nitrate, biuret, azodicarbonamide, carbohydrazide, carbohydrazide nitrate complex, oxalic acid hydrazide, hydrazine nitrate complex, and ammine complex. Among these organic nitrogen compounds, tetrazole derivatives, bitetrazole derivatives, and guanidine derivatives are preferred because they are inexpensive, highly reactive, and relatively easy to handle. Guanidine nitrate, nitroguanidine, and 5-aminotetrazole are more preferred, and guanidine nitrate is even more preferred.

[0036] The content of the organic nitrogen compound used in the explosive mixture composition in this embodiment is preferably 30% by mass or more and 70% by mass or less, and more preferably 50% by mass or more and 70% by mass or less.

[0037] In this embodiment, guanidine nitrate used as the organic nitrogen compound in the composition of the mixed explosive contains oxygen in its molecule, and therefore has the advantages of being able to reduce the amount of oxidizer component blended, having good thermal stability, being low cost, and being expected to have a high gasification rate during combustion.

[0038] The guanidine nitrate is preferably in powder or granular form for ease of handling, and its 50% particle size is preferably 3 μm or more and 80 μm or less, and more preferably 5 μm or more and 50 μm or less. If the 50% particle size of guanidine nitrate is less than 3 μm, a large cost will be required for pulverization, while if it exceeds 80 μm, the strength of the mixed explosive compact will decrease. In the present invention, the 50% particle size means the 50% particle size based on the number of measured particles, and can be measured, for example, by laser diffraction / scattering method.

[0039] The content of guanidine nitrate in the composition of the mixed explosive is preferably 20% by mass or more and 60% by mass or less, and more preferably 40% by mass or more and 50% by mass or less. If the content (mixing ratio) of guanidine nitrate is less than 20% by mass, the number of moles of gas generated from the gas generant 21 decreases, and there is a tendency for excess oxygen to increase the generation of nitrogen oxides. On the other hand, if the content (mixing ratio) of guanidine nitrate is more than 60% by mass, there is a tendency for a shortage of oxidizer components to result in the generation of large amounts of harmful carbon monoxide.

[0040] The explosive mixture contains, as an oxidizer, at least one compound selected from the group consisting of perchlorates and nitrates. Specific examples of the perchlorates include sodium perchlorate, potassium perchlorate, and ammonium perchlorate. Among these, potassium perchlorate is particularly preferred because of its low burning rate and thermal stability.

[0041] The content of perchlorate in the explosive mixture varies depending on the type and amount of guanidine nitrate used and the binder and additives described below, but is usually preferably in the range of 25% by mass or more and 75% by mass or less relative to the explosive mixture, and more preferably in the range of 30% by mass or more and 50% by mass or less in order to reduce the concentrations of carbon monoxide and nitrogen oxides in the generated gas.

[0042] The perchlorate is preferably in powder or granular form for ease of handling, and its 50% particle size is preferably 1 μm or more and 80 μm or less, more preferably 1 μm or more and 50 μm or less. If the 50% particle size of the perchlorate is less than 1 μm, it may be difficult to uniformly mix it with the fuel components, and the grinding required for preparation will be very costly. On the other hand, if the 50% particle size of the perchlorate exceeds 80 μm, the strength of the mixed explosive compact will decrease.

[0043] Nitrate may be added as an oxidizer to the explosive mixture. Nitrates include alkali metal nitrates, alkaline earth metal nitrates, and ammonium nitrate, and can be produced using sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, etc. Furthermore, phase-stabilized ammonium nitrate containing potassium salt or copper salt may be used as the ammonium nitrate.

[0044] The explosive mixture contains a binder. The combustion characteristics of the explosive mixture are affected by the shape of the compact of the explosive mixture. The binder imparts moldability and shape retention to the explosive mixture so that it can exhibit desired combustion characteristics, and by maintaining the shape of the compact of the gas generating agent even in the harsh environment in which the gas generator is used, it functions to maintain combustion performance.

[0045] The binder for the explosive mixture can be used without any particular limitation as long as it does not significantly adversely affect the combustion behavior of the explosive mixture. For example, water-soluble organic binders such as celluloses such as hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate, nitrocellulose, and microcrystalline cellulose, polysaccharide derivatives such as guar gum and starch, and water-soluble synthetic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylamide are preferred. In addition, inorganic binders such as molybdenum disulfide, synthetic hydrotalcite, acid clay, talc, bentonite, diatomaceous earth, kaolin, silica, and alumina can also be used.

[0046] From the viewpoint of maintaining the shape of the mixed explosive compacts, the binder content in the mixed explosive is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 8% by mass or less. If the binder content is less than 0.1% by mass, it may be difficult to maintain the shape of the mixed explosive compacts. If the binder content is more than 10% by mass, the number of carbon and hydrogen elements in the composition increases, which increases the concentration of carbon monoxide gas, a product of incomplete combustion of carbon elements, and may reduce the quality of the generated gas and inhibit combustion. Furthermore, it becomes necessary to increase the relative abundance of the oxidizer component, which reduces the relative abundance of the fuel component in the mixed explosive, which may make it difficult to put the gas generator into practical use.

[0047] In this embodiment, the explosive mixture may further contain additives that are normally used in gas generating agents, such as a slag forming material, a lubricant, and a combustion adjuster.

[0048] The slag-forming agent is an additive that makes it possible to easily filter the combustion residue generated after combustion of the gas generant composition, and is ignited to prevent the residue from being released outside the gas generator. Specific examples of the slag-forming agent include silicon nitride, silicon carbide, silicon dioxide, silicates, aluminum oxide, titanium oxide, acid clay, clay, and other natural minerals.

[0049] When a slag-forming agent is used in this embodiment, its content in the mixed explosive composition is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass. If the content of the slag-forming agent exceeds 10% by mass, combustibility is reduced and the number of moles of gas generated is also reduced, which may result in insufficient occupant protection performance.

[0050] Lubricants are added to improve the mixing and flowability of raw material components when preparing a mixed explosive. Specific examples of such lubricants include graphite, magnesium stearate, zinc stearate, calcium stearate, sodium stearate, boron nitride, highly dispersed silica (silicon dioxide), and talc. Among these, highly dispersed silica (silicon dioxide) is particularly useful because it has the function of suppressing adhesion and aggregation during raw material mixing, thereby uniformly dispersing and mixing the components, and maintaining the particle size characteristics and effects of each component.

[0051] When a lubricant is used in this embodiment, the content of the lubricant in the mixed explosive is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 0.1% by mass or more and 2% by mass or less. If the content of the lubricant exceeds 5% by mass, there is a risk of a decrease in combustibility, a decrease in the number of moles of generated gas, and an increase in the concentration of carbon monoxide in the generated gas.

[0052] Specific examples of combustion modifiers include metal oxides such as iron oxide, nickel oxide, copper oxide, zinc oxide, manganese oxide, chromium oxide, cobalt oxide, molybdenum oxide, vanadium oxide, and tungsten oxide; metal oxides such as copper hydroxide, cobalt hydroxide, zinc hydroxide, and aluminum hydroxide; and carbons such as activated carbon powder, graphite, and carbon black.

[0053] In this embodiment, various shapes are used for the compact of the explosive mixture, such as granular, pellet-like, cylindrical, etc., as well as disk-like, elliptical, and strand-like shapes. For cylindrical compacts, perforated compacts having through holes inside the compact (for example, single-hole cylindrical or multi-hole cylindrical shapes) are also used. These shapes are preferably selected appropriately depending on the specifications of the pretensioner into which the gas generator is incorporated. For example, it is preferable to select a shape that causes the gas generation rate to change over time when the explosive mixture is burned. In addition to the shape, the size of the compact is selected taking into consideration the linear burning velocity, pressure exponent, etc.

[0054] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Contents expressed as "%" and "parts" in the examples and comparative examples are % by mass and parts by mass unless otherwise specified.

[0055] [Example 1] The ignition charge was a mixture of zirconium powder, tungsten powder, and potassium perchlorate. The calorific value of this ignition charge was 4600 J / g, as measured by filling the measuring cylinder of a calorimeter (IKA C5000) with 1.5 MPa of argon gas and using heat generated by passing electricity through a nichrome wire as the ignition source. The gas generant used was a mixture of guanidine nitrate, potassium perchlorate, basic copper nitrate, and hydroxypropyl methylcellulose, molded using an extruder equipped with a die. The calorific value of this gas generant was 4900 J / g, as measured using the same method as for the ignition charge. 240 mg of the resulting ignition charge and 835 mg of the gas generant were loaded into a gas generator to form the gas generator of Example 1.

[0056] [Example 2 and Comparative Example 1] The same ignition charge as in Example 1, 180 mg, and gas generant 875 mg were loaded into a gas generator to form a gas generator of Example 2, and 120 mg of ignition charge and gas generant 970 mg were loaded into a gas generator to form a gas generator of Comparative Example 1.

[0057] [Non-sealed Tank Test 1] Gas generator 1 was placed in the center of a tank with a volume of 3.5 cc and an opening with a diameter of 1.5 mm, and an ignition charge was burned. The relationship between the change in pressure inside the tank due to the gas emitted by gas generator 1 and the elapsed time was measured. This simulated a situation in which a lap pretensioner cannot be sealed due to its structure, in which the wire penetrates the pressure vessel, and it has been found that there is a strong correlation with the retraction performance of the pretensioner.

[0058] 2 shows the change in pressure in the 3.5 cc non-sealed tank test for Examples 1 and 2 and Comparative Example 1. The maximum pressure in the non-sealed tank test was 65 MPa for all of Examples 1 and 2 and Comparative Example 1. In other words, these gas generators are expected to exhibit equivalent retraction performance when installed in a lap pretensioner.

[0059] [Sealed Tank Test 1] Gas generator 1 was placed in the center of a sealed tank with a capacity of 10 cc, and an ignition charge was burned. The time when the ignition charge started to burn, i.e., the time when gas generator 1 started to operate, was set as 0 msec, and the relationship between the change in pressure inside the sealed tank due to the gas emitted by gas generator 1 and the elapsed time was measured.

[0060] 3 shows the change in pressure in a 10 cc sealed tank test for Examples 1 and 2 and Comparative Example 1. For Examples 1 and 2 and Comparative Example 1, the maximum pressures were 44 MPa, 45 MPa, and 50 MPa, respectively, and the times Ta from the start of operation of the gas generator until the pressure reached half of the maximum pressure were 1.0 msec, 1.5 msec, and 1.9 msec, respectively.

[0061]

[0062] Table 1 shows the calorific values ​​of the ignition charge and the gas generant, their total values, and the ratio of the calorific value of the gas generant to the total calorific value for Examples 1 and 2 and Comparative Example 1. It can be seen that the ratio of the calorific value of the gas generant to the total calorific value was 10.4% for Comparative Example 1, whereas Example 1 had a calorific value of 21.6% and Example 2 had a calorific value of 16.2%, resulting in a reduced total calorific value.

[0063] The results of Non-Sealed Tank Test 1 showed that Examples 1 and 2 and Comparative Example 1 all exhibited equivalent retraction performance when installed in a lap pretensioner, while the calculated values ​​shown in Table 1 showed that Examples 1 and 2 generated less heat than Comparative Example 1, demonstrating a high effect of suppressing wire breakage. Furthermore, the results of Sealed Tank Test 1 confirmed the differences in characteristics in the sealed tank test between Examples 1 and 2 and Comparative Example 1.

[0064] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include all documents within the scope of the claims that have the same meaning as the claims and are within the scope of the claims.

[0065] 1 Gas generator, 10 Ignition part, 12 Cover, 13 Terminal pin, 20 Gas generating part, 21 Gas generating agent, 30 Cup, 31 Bottom wall part.

Claims

1. A gas generator for a pretensioner used in a seat belt, comprising: a gas generating unit equipped with a gas generating agent that generates gas for retracting a wire; and an ignition unit equipped with an ignition charge for burning the gas generating agent, wherein the maximum pressure of the pretensioner gas generator is between 40 MPa and 60 MPa in a sealed tank having a volume of 10 cc, and the time required to reach half of the maximum pressure is 1.7 msec or less, calculated from the start of operation of the pretensioner gas generator.

2. A gas generator for a seat belt pretensioner, comprising: a gas generating unit equipped with a gas generating agent that generates gas for retracting the wire; and an ignition unit equipped with an ignition charge for burning the gas generating agent, wherein the amount of heat generated by burning the ignition charge is 13% or more of the amount of heat generated by burning the gas generating agent.

3. A gas generator for a pretensioner according to claim 1 or 2, wherein the gas generating agent includes a mixed explosive.

4. The gas generator for a pretensioner according to claim 3, wherein the mixed explosive contains at least one compound selected from the group consisting of guanidine nitrate, nitroguanidine, and 5-aminotetrazole, at least one oxidizer selected from the group consisting of perchlorates and nitrates, and a binder.

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