Gas generator

Abstract

A gas generator (1) comprises a housing having a cylindrical part (10), a bolt (2), and a joining part (6). The bolt (2) has a rod-shaped part (3) and is joined to an outer circumferential surface (10a) of the cylindrical part (10). The joining part (6) is obtained by melting and then solidifying at least one of the outer circumferential surface (10a) and an axial end portion (4) of the rod-shaped part (3), and thus joins the cylindrical part (10) and the bolt (2). The rod-shaped part (3) includes a male screw portion (3a). The cylindrical part (10) has a plate thickness of less than 1.3 mm. The gas generator (1) satisfies L > (A × S1) / (t × S2 × G), where L is the perimeter of the outer edge of a boundary part between the joining part (6) and the outer circumferential surface (10a), A is the effective cross-sectional area of the male screw portion (3a), S1 is the bolt strength of the bolt (2), t is the plate thickness of the cylindrical part (10), S2 is the tensile strength of the cylindrical part (10), and G is the shear modulus of the cylindrical part (10).

Description

Gas generator

[0001] The present invention relates to a gas generator incorporated in an occupant protection device for protecting an occupant in the event of a vehicle collision, and more particularly to a gas generator incorporated in an airbag device mounted on an automobile or the like.

[0002] Airbag devices, which are passenger protection devices, have become widespread from the viewpoint of protecting passengers in automobiles, etc. Airbag devices are installed to protect passengers from impacts that occur during a vehicle collision, and the airbag instantly inflates and deploys during a vehicle collision, thereby acting as a cushion to support the passenger's body.

[0003] The gas generator is incorporated into this airbag device. When a vehicle crashes, the control unit energizes the igniter, which then ignites the igniter with the flame generated by the igniter, burning the gas generating agent and instantly generating a large amount of gas, which inflates and deploys the airbag.

[0004] There are gas generators with various configurations based on specifications such as the installation position relative to a vehicle, etc., and output, one of which is called a cylinder-type gas generator. The cylinder-type gas generator has an elongated cylindrical outer shape and is suitably incorporated into a side airbag device, a curtain airbag device, a knee airbag device, a seat cushion airbag device, etc.

[0005] Stud bolts for attachment to a retainer of an airbag device or the like are sometimes provided on the outer peripheral surface of the housing of a cylinder-shaped gas generator. Japanese Patent Laid-Open No. 2005-247289 (Patent Document 1) discloses a technique for attaching stud bolts by welding them to the outer peripheral surface of a flat-machined gas generator housing. Also, Japanese Patent Laid-Open No. 2005-313752 (Patent Document 2) discloses a technique for attaching a head of a headed bolt, which has a curved surface, by welding it to the curved outer peripheral surface of the gas generator.

[0006] JP 2005-247289 A JP 2005-313752 A

[0007] Here, in order to achieve safe operation of the gas generator, it is essential to prevent deformation, damage, etc. from occurring at the joint formed by welding the housing and the stud bolt even when some kind of unintended external force is applied to the gas generator, retainer, etc. This issue becomes particularly pronounced when the plate thickness of the housing is reduced to meet the recent need for lighter gas generators.

[0008] Therefore, the present invention has been made to solve the above-mentioned problems, and has an object to provide a gas generator that is lightweight and in which damage is less likely to occur at the joint between the housing and the bolt when some kind of external force is applied.

[0009] A gas generator according to the present invention ejects gas to the outside and includes a housing having a cylindrical portion, a bolt, and a joint. The bolt has a rod-shaped portion and is joined to the curved outer peripheral surface of the cylindrical portion. The joint joins the cylindrical portion and the bolt to each other by melting at least one of the outer peripheral surface of the cylindrical portion and an axial end of the rod-shaped portion facing the cylindrical portion and then solidifying. The rod-shaped portion includes a male thread portion formed by providing a spiral groove on the circumferential surface of the rod-shaped portion. The cylindrical portion has a plate thickness of less than 1.3 mm. The gas generator according to the present invention satisfies the following formula (1), where L is the circumferential length of the outer edge of a boundary between the joint and the outer peripheral surface of the cylindrical portion, A is the effective cross-sectional area of ​​the male thread portion, S1 is the bolt strength of the bolt, t is the plate thickness of the cylindrical portion, S2 is the tensile strength of the cylindrical portion, and G is the shear modulus of the cylindrical portion.

[0010] L>(A×S1) / (t×S2×G)...(1)

[0011] According to the present invention, it is possible to provide a gas generator that is lightweight and in which damage is unlikely to occur at the joint between the housing and the bolt when some external force is applied.

[0012] Fig. 4 is a schematic diagram of a cylinder-shaped gas generator according to an embodiment. Fig. 5 is a perspective view, a side view, and a bottom view of the bolt shown in Fig. 1 in a state before welding. Fig. 6 is a schematic view showing how the bolt shown in Fig. 2 is attached to a housing. Fig. 7 is a side view of the cylinder-shaped gas generator shown in Fig. 1. Fig. 8 is an enlarged cross-sectional view of a main part in the vicinity of the joint shown in Fig. 4. Fig. 9 is a graph showing measurement results of verification test 1. Fig. 10 is a graph showing measurement results of verification test 2.

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments shown below exemplify the case where the present invention is applied to a cylinder-type gas generator incorporated in a side airbag device. In the embodiments shown below, the same or common parts are designated by the same reference numerals in the drawings, and their description will not be repeated.

[0014] (Embodiment) Fig. 1 is a schematic diagram of a cylinder-shaped gas generator according to an embodiment. First, with reference to Fig. 1, the configuration of cylinder-shaped gas generator 1 according to the present embodiment will be described. Note that arrows DR1 and DR2 shown in Fig. 1 indicate the axial direction of housing body 10 and the axial direction of bolt 2 constituting cylinder-shaped gas generator 1, respectively (the same applies to Figs. 2 to 5 described later).

[0015] As shown in FIG. 1, cylinder-shaped gas generator 1 includes housing 90 having a long, generally cylindrical outer shape with one axial end and the other axial end closed, and two bolts 2 joined via joints 6 (see FIG. 5 , etc., described later) to curved outer peripheral surface 10 a of housing main body 10, which serves as the cylindrical portion constituting housing 90.

[0016] A retainer of an airbag device or the like is attached to the bolt 2. The bolt 2 is made of a material such as cold heading carbon steel (SWCH). The number of bolts 2 is not limited to two, and may be one, or three or more.

[0017] The housing 90 has a housing main body 10, a holder 20, and a closing member 30. The housing 90, which is composed of the housing main body 10 and other components, accommodates internal components such as an igniter 40, a partition member 50, a storage chamber defining member 60, a gas generating agent 70, and a filter 80. The housing 90 is also provided with a combustion chamber R1, in which the gas generating agent 70, among the above-mentioned internal components, is mainly disposed, and a filter chamber R2, in which the filter 80 is disposed.

[0018] The housing body 10 constitutes the peripheral wall of the housing 90. The housing body 10 is a long, substantially cylindrical member with openings formed at both ends in the axial direction (see arrow DR1). Materials used to constitute the housing body 10 include, for example, general structural carbon steel pipe (STK) and mechanical structural carbon steel pipe (STKM). The outer diameter of the housing body 10 is preferably, for example, 15 mm to 40 mm.

[0019] Furthermore, the plate thickness of housing body 10 is preferably less than 1.3 mm, for example, more preferably less than 1.1 mm, and even more preferably less than 0.9 mm, thereby enabling reduction in weight of cylinder-shaped gas generator 1. Furthermore, the plate thickness of housing body 10 is preferably greater than 0.5 mm, for example.

[0020] The holder 20 is fixed to the housing body 10 so as to close one end of the housing 90 in the axial direction. The closing member 30 is fixed to the housing body 10 so as to close the other end of the housing 90 in the axial direction of the housing body 10.

[0021] The igniter 40 is used to combust the gas generating agent 70, and is mounted to one end of the housing 90 by being supported by the holder 20. As a result, the igniter 40 is disposed so as to face the space inside the housing 90.

[0022] A partition member 50 serving as a partition is disposed at a predetermined position in the space inside the housing 90. This divides the space inside the housing 90 into a combustion chamber R1 and a filter chamber R2 in the axial direction of the housing body 10.

[0023] Within the space inside the housing 90, a storage chamber defining member 60 and a gas generating agent 70 are disposed in a space sandwiched between the holder 20 and the partition member 50 (i.e., a combustion chamber R1).

[0024] The storage chamber defining member 60 is a member that defines the gas generating agent storage chamber R1A that contains the gas generating agent 70. The storage chamber defining member 60 is made of a relatively fragile material so that it will burst or melt as the gas generating agent 70 burns.

[0025] The gas generating agent 70 is an agent that generates gas by being ignited by thermal particles generated by activation of the igniter 40 and burning. A non-azide gas generating agent is preferably used as the gas generating agent 70, and the gas generating agent 70 is generally formed as a molded body containing a fuel, an oxidizer, and an additive.

[0026] A filter 80 is disposed in the space within the housing 90, which is sandwiched between the blocking member 30 and the partition member 50 (i.e., the filter chamber R2). The filter 80 functions as a cooling means that cools the gas by removing high-temperature heat contained in the gas generated by the combustion of the gas generating agent 70 when the gas passes through the filter 80, and also functions as a removal means that removes residue (slag) and the like contained in the gas.

[0027] A plurality of gas outlets 31 are provided in the housing body 10 in the portion that defines the filter chamber R2, along the circumferential and axial directions of the housing body 10. These gas outlets 31 are for directing the gas that has passed through the filter 80 to the outside of the housing 90.

[0028] Figures 2(A), 2(B), and 2(C) are respectively a perspective view, a side view, and a bottom view showing the state before welding of the bolt shown in Figure 1. Next, with reference to Figure 2, the configuration of bolt 2 in this embodiment in the state before welding will be described.

[0029] As shown in Figures 2(A), 2(B), and 2(C), before welding, the bolt 2 has a solid, approximately cylindrical rod portion 3 extending along its axial direction (see arrow DR2) and a flange portion 4 serving as an axial end portion provided at one end of the rod portion 3 in the axial direction of the bolt 2. When viewed along the axial direction of the bolt 2, the flange portion 4 has a track shape. Here, the track shape refers to a rounded rectangular shape whose outer edge is composed of two straight portions positioned parallel to each other and two curved portions positioned parallel to each other. Note that the shape of the flange portion 4 is not limited to a track shape and may be approximately circular, approximately elliptical, approximately rectangular, or the like.

[0030] The rod-shaped portion 3 includes a male thread portion 3a formed by providing a spiral groove 3a1 (see FIG. 5 described later) on its circumferential surface. The flange portion 4 has a facing surface 8. The facing surface 8 is a surface that faces the outer circumferential surface 10a of the housing body 10 when the bolt 2 is welded to the outer circumferential surface 10a.

[0031] FIG. 3 is a schematic diagram showing how the bolt shown in FIG. 2 is attached to the housing. FIG. 4 is a side view of the cylinder-shaped gas generator as viewed from the direction of arrow IV in FIG. 1. FIG. 5 is an enlarged cross-sectional view of a main portion near the joint shown in FIG. 4. FIG. 5(A) is an enlarged cross-sectional view of a main portion near the joint taken along line VA-VA shown in FIG. 4, and FIG. 5(B) is an enlarged cross-sectional view of a main portion near the joint taken along line VB-VB shown in FIG. 4. Next, with reference to FIGS. 3 to 5, a method of attaching bolt 2 to housing main body 10 in this embodiment and the configuration near joint 6 in cylinder-shaped gas generator 1 according to this embodiment will be described. Note that FIG. 3 illustrates housing main body 10 in cross section. For ease of understanding, FIG. 4 depicts joint 6 with a pattern.

[0032] When attaching the bolt 2 to the curved outer peripheral surface 10a of the housing main body 10, first, a voltage is applied to the bolt 2 and the housing main body 10, which are arranged facing each other at a distance, as shown in Fig. 3. Next, while maintaining the state in which the voltage is applied to the bolt 2 and the housing main body 10, the bolt 2 is moved in the direction of arrow AR1 in Fig. 3, whereby the flange portion 4 of the bolt 2 is pressed against the outer peripheral surface 10a of the housing main body 10.

[0033] At this time, discharge occurs between the flange portion 4 and the outer peripheral surface 10a, causing these portions to be locally heated. This heating causes a part of the flange portion 4 and a part of the outer peripheral surface 10a of the housing main body 10 to melt and dissolve. Hereinafter, the melted part of the flange portion 4 and the outer peripheral surface 10a of the housing main body 10 will be collectively referred to as the molten part.

[0034] As the bolt 2 is further pressed against the housing body 10, the molten portion is sandwiched between the unmelted portion of the flange portion 4 and the unmelted portion of the outer peripheral surface 10a of the housing body 10. As a result, the molten portion is stretched along the curved outer peripheral surface 10a of the housing body 10.

[0035] Thereafter, the molten portion solidifies, forming a joint 6 between the bolt 2 and the housing main body 10, as shown in Figures 4, 5(A), and 5(B). As a result, the bolt 2 is joined to the outer peripheral surface 10a of the housing main body 10 via the joint 6.

[0036] Here, cylinder-shaped gas generator 1 according to the present embodiment is configured to satisfy formula (1) described below in order to make joint portion 6 between housing body 10 and bolt 2 less susceptible to damage when some kind of external force is applied to gas generator 1, etc. This point will be described in detail below.

[0037] When assembling a cylinder-shaped gas generator to a retainer, etc., or when a vehicle equipped with the cylinder-shaped gas generator is involved in a collision, an unintended external force may be applied to the cylinder-shaped gas generator. If no measures are taken to prevent this, there is a concern that the external force will be applied to the joint between the bolt and the housing body, causing deformation or damage to the joint. If this deformation or damage occurs to the joint, there is a risk that the planned operation will not be achieved when the cylinder-shaped gas generator is activated, resulting in a malfunction.

[0038] Therefore, if bolt 2 can be caused to break before excessive external force is applied to joint 6, it will be possible to prevent damage or deformation from occurring in joint 6, in the unlikely event that such damage occurs. As a result, safe operation of cylinder-shaped gas generator 1 can be achieved.

[0039] There are three possible fracture modes of the joint 6: fracture in the tensile direction, fracture in the shear direction, and fracture in the torque direction. Of these, it is unrealistic for fracture in the torque direction to occur. Furthermore, tensile strength generally tends to be greater than shear strength. Therefore, if fracture in the tensile direction of the joint 6 is suppressed, fracture in the shear direction will also be suppressed accordingly. Therefore, in the cylinder-shaped gas generator 1, it is important to prevent fracture in the tensile direction of the joint 6.

[0040] In other words, in cylinder-shaped gas generator 1 , the weld strength at joint 6 is required to be greater than the tensile strength of bolt 2 .

[0041] Here, assuming that the effective cross-sectional area of ​​the male thread portion 3a is A, the bolt strength of the bolt 2 is S1, the circumferential length of the outer edge 6a (see FIGS. 4 and 5) of the boundary between the joint 6 and the outer peripheral surface 10a of the housing main body 10 is L, the plate thickness of the housing main body 10 is t, the tensile strength of the housing main body 10 is S2, and the shear coefficient of the housing main body 10 is G, the tensile strength T1 of the bolt 2 is expressed by the following formula (11), and the weld strength T2 at the joint 6 is expressed by the following formula (12). The validity of formulas (11) and (12) was confirmed by verification tests 1 and 2, which will be described later.

[0042] T1 = A × S1 (11) T2 = L × t × S2 × G (12) The effective cross-sectional area A of the male thread portion 3a is expressed by the following formula (13). ２ indicates the effective diameter of the male screw portion 3a, and d ３ indicates the root diameter of the male thread portion 3a. As shown in FIG. 5(A), ２ is the diameter of an imaginary cylinder such that, when the pitch of the male screw portion 3a is dimension P, the width of the spiral groove 3a1 and the width of the thread of the male screw portion 3a that is provided to form a pair with the spiral groove 3a1 are both P / 2. ３ is the diameter of an imaginary cylinder that contacts the bottom of the spiral groove 3a1.

[0043] A=(π / 4)×((d ２ +d ３ ) / 2) ２ ...(13) Cylinder-shaped gas generator 1 according to the present embodiment satisfies the following formula (1), which is obtained by establishing the inequality T2>T1 between tensile strength T1 of bolt 2 expressed by the above formula (11) and weld strength T2 at joint 6 expressed by the above formula (12) and rearranging this.

[0044] L > (A × S1) / (t × S2 × G) ... (1) That is, in the cylinder-shaped gas generator 1 according to this embodiment, the circumferential length L of the outer edge 6a of the boundary between the joint 6 and the outer peripheral surface 10a of the housing body 10 is configured so as to satisfy the above formula (1).

[0045] In this way, by configuring the circumferential length L to be sufficiently long so as to satisfy the above formula (1), when a tensile load is applied to the bolt 2 and the joint 6, the bolt 2 will break before an excessive external force is applied to the joint 6. Therefore, even if this happens, damage or deformation to the joint 6 can be prevented in advance.

[0046] Therefore, by making the cylinder-shaped gas generator 1 according to this embodiment, it is possible to make a gas generator that is lightweight and is less likely to suffer damage at the joint between the housing and the bolt when some external force is applied.

[0047] Furthermore, in cylinder-shaped gas generator 1 according to this embodiment, the orientation of bolt 2 is adjusted so that the longitudinal direction of flange portion 4 coincides with the axial direction of housing body 10 when bolt 2 is joined to outer peripheral surface 10a of housing body 10.

[0048] More specifically, as shown in Figure 4, when viewed along the axial direction of the rod-shaped portion 3, the bolt 2 is joined to the outer peripheral surface 10a of the housing body 10 so that the outer dimensions of the flange portion 4 in a direction parallel to the axial direction of the housing body 10 (see arrow DR1) are larger than the outer dimensions of the flange portion 4 in a direction perpendicular to the axial direction.

[0049] With this configuration, even if the flange portion 4 is made flat without any special shape, it is possible to ensure a long circumferential length L while reducing the gap between the outer peripheral surface 10a of the housing body 10 and the flange portion 4. Therefore, with this configuration, it is possible to prevent damage or deformation of the joint portion 6.

[0050] (Verification Test 1) In Verification Test 1, the validity of Equation (11) was confirmed by comparing the actual measured values ​​of the tensile strength of the bolt samples prepared for Verification Test 1 with the theoretical value calculated by Equation (11) representing the tensile strength T1 of the bolt described above.

[0051] In this verification test, 10 pieces of each of Sample 1, which is a bolt with a bolt strength of 667 MPa, and Sample 2, which is a bolt with a bolt strength of 776.25 MPa, were prepared. The material of Sample 1 and Sample 2 was cold heading carbon steel (SWCH18A), and the effective cross-sectional area of ​​Sample 1 and Sample 2 was both 20.1 cm ２ is.

[0052] To conduct the verification, first, each sample was attached to a housing body. The attachment method was the same as that described in the above embodiment. The material of the housing body used here was carbon steel pipe for machine structures (STKM13C).

[0053] Next, a tensile test was carried out on the sample and the housing body joined together via the joint, and the tensile strength of the sample was measured when the sample broke.

[0054] Figure 6 is a graph showing the measurement results of Verification Test 1. The horizontal axis represents bolt strength (MPa), and the vertical axis represents bolt tensile strength T1 (kN). In Figure 6, the theoretical value calculated by equation (11) is shown by a dashed line. The standard deviation of the measured values ​​of ten samples 1 was 0.049 kN, and the standard deviation of the measured values ​​of ten samples 2 was 0.154 kN.

[0055] The graph of this verification test shown in Figure 6 confirms that the difference between the theoretical and measured values ​​is considerably small. From the above, it has been confirmed that Equation (11), which expresses the tensile strength T1 of a bolt, is a valid equation.

[0056] (Verification Test 2) In Verification Test 2, the validity of Equation (12) was confirmed by comparing the actual measured value of the weld strength at the joint for attaching the bolt to the housing body with the theoretical value calculated by Equation (12) representing the weld strength T2 at the above-mentioned joint.

[0057] In this verification test, in order to fracture the joint in the tensile direction, bolts with a high enough strength to prevent fracture of the bolt before the joint were prepared and attached to the housing body. The material of the housing body used here is carbon steel pipe for mechanical structures (STKM13C), and the plate thickness of the housing body is 1.0 mm.

[0058] Next, the circumference of the joint (more specifically, the circumference of the outer edge of the boundary between the joint and the outer peripheral surface of the housing body) was measured. Next, a tensile test was conducted on the bolt and the housing body joined together via the joint, and the weld strength of the joint when fracture occurred was measured. This verification test was conducted a total of three times, changing the circumference of the joint.

[0059] 7 is a graph showing the measurement results of Verification Test 2. The horizontal axis represents the perimeter (mm) of the joint, and the vertical axis represents the weld strength T2 (kN) of the joint.

[0060] From the graph of this verification test shown in Figure 7, it was confirmed that the difference between the theoretical value and the measured value was considerably small. From the above, it was confirmed that Equation (12) expressing the weld strength T2 at the joint is valid.

[0061] (Additional Note) The characteristic configurations of the gas generators disclosed in the above-described embodiments can be summarized as follows.

[0062] [Supplementary Note 1] A gas generator that ejects gas to the outside, comprising: a housing having a cylindrical portion; a bolt having a rod-shaped portion joined to a curved outer peripheral surface of the cylindrical portion; and a joint portion that joins the cylindrical portion and the bolt to each other by melting and then solidifying at least one of the outer peripheral surface of the cylindrical portion and an axial end portion of the rod-shaped portion on the cylindrical portion side, wherein the rod-shaped portion includes a male thread portion that is formed by providing a spiral groove on the circumferential surface of the rod-shaped portion, and the cylindrical portion has a plate thickness of less than 1.3 mm, and wherein the gas generator satisfies the following formula (1) when a circumferential length of an outer edge of a boundary portion between the joint portion and the outer peripheral surface of the cylindrical portion is L, an effective cross-sectional area of ​​the male thread portion is A, a bolt strength of the bolt is S1, a tensile strength of the cylindrical portion is S2, the plate thickness of the cylindrical portion is t, and a shear modulus of the cylindrical portion is G:

[0063] L>(A×S1) / (t×S2×G) (1) [Supplementary Note 2] The gas generator according to Supplementary Note 1, wherein, when viewed along the axial direction of the rod-shaped portion, an outer dimension of the axial end portion in a direction parallel to the axial direction of the cylindrical portion is larger than an outer dimension of the axial end portion in a direction perpendicular to the axial direction of the cylindrical portion.

[0064] [Supplementary Note 3] The gas generator according to Supplementary Note 2, wherein the axial end portion is configured by a flange portion.

[0065] [Supplementary Note 4] The gas generator according to Supplementary Note 3, wherein the flange portion has a track shape when viewed along the axial direction of the rod-shaped portion.

[0066] [Supplementary Note 5] The gas generator according to any one of Supplementary Notes 1 to 4, wherein the plate thickness of the cylindrical portion is less than 1.1 mm.

[0067] (Other Embodiments, etc.) The shape, configuration, size, number, material, etc. of each part shown in the above-described embodiment of the present invention can be changed in various ways without departing from the spirit of the present invention.

[0068] Furthermore, the characteristic configurations shown in the above-described embodiments of the present invention can naturally be combined with each other within the scope of the present invention.

[0069] As such, the above-described embodiments disclosed herein are illustrative in all respects and are not restrictive. The technical scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims.

[0070] REFERENCE SIGNS LIST 1 Cylinder-type gas generator, 2 Bolt, 3 Rod-shaped portion, 3a Male thread portion, 3a1 Spiral groove, 4 Flange portion, 6 Joint portion, 6a Outer edge, 8 Opposing surface, 10 Housing body, 10a Outer peripheral surface, 20 Holder, 30 Closing member, 31 Gas outlet, 40 Igniter, 50 Partition member, 60 Storage chamber defining member, 70 Gas generating agent, 80 Filter, 90 Housing, R1 Combustion chamber, R1A Gas generating agent storage chamber, R2 Filter chamber.

Claims

1. A gas generator which ejects gas to the outside, comprising: a housing having a cylindrical portion; a bolt having a rod-shaped portion and joined to a curved outer circumferential surface of the cylindrical portion; and a joint portion which joins the cylindrical portion and the bolt to each other by melting and then solidifying at least one of the outer circumferential surface of the cylindrical portion and the axial end portion of the rod-shaped portion on the cylindrical portion side, the rod-shaped portion includes a male thread portion formed by providing a spiral groove on the circumferential surface of the rod-shaped portion, the cylindrical portion has a plate thickness of less than 1.3 mm, and satisfies the following formula (1) when the perimeter of the outer edge of the boundary portion between the joint portion and the outer circumferential surface of the cylindrical portion is L, the effective cross-sectional area of ​​the male thread portion is A, the bolt strength of the bolt is S1, the tensile strength of the cylindrical portion is S2, the plate thickness of the cylindrical portion is t, and the shear coefficient of the cylindrical portion is G. L>(A×S1) / (t×S2×G)...(1) 2. A gas generator as described in claim 1, wherein, when viewed along the axial direction of the rod-shaped portion, the outer dimension of the axial end portion in a direction parallel to the axial direction of the cylindrical portion is larger than the outer dimension of the axial end portion in a direction perpendicular to the axial direction of the cylindrical portion.

3. A gas generator according to claim 2, wherein said axial end portion is constituted by a flange portion.

4. The gas generator according to claim 3, wherein said flange portion has a track shape when viewed along said axial direction of said rod-shaped portion.

5. A gas generator as set forth in claim 1, wherein the wall thickness of the cylindrical portion is less than 1.1 mm.

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