JP2001158315A - Airbag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce discomfort which an occupant may feel when an airbag is deployed in a nearby position, while assuring the impact absorption characteristic of the airbag. SOLUTION: A third ground fabric portion 23 smaller than first and second ground fabric portions 21 and 22 which constitute an outer shell is positioned between the first and second ground fabric portions 21 and 22. The third ground fabric portion 23 covers a gas inlet 28 formed in the first ground fabric portion 21 and is sewn to the first ground fabric portion 21 at four connections 33. Circular vent holes 31 are formed to overlap communicating portions 25 situated between the connections 33. When the occupant approaches the airbag too close to fully deploy a space surrounded by the first ground fabric portion 21 and the third ground fabric portion 23, gas is smoothly exhausted from the vent holes 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an airbag provided on a steering wheel of a vehicle, for example.

[0002]

2. Description of the Related Art Conventionally, for example, an airbag device for a driver's seat provided in a steering wheel of an automobile and inflating a bag-shaped airbag by inflow of gas to reduce the impact of a collision applied to an occupant has been used. ing. The airbag used in this airbag device is formed in a flat bag shape by sewing together the outer peripheries of two circular woven fabric base fabrics. Further, in this airbag, a gas introduction hole is formed in the base cloth on the vehicle body side, gas is introduced from the inflator through the gas introduction hole, and the periphery of the gas introduction hole is fixed to the steering wheel body, It is folded small and stored in the cover. When the inflator operates, the airbag breaks the cover body by the pressure of the gas injected from the inflator and swells toward the occupant, receives and restrains the occupant thrown forward, and reduces the impact. Further, the gas in which the airbag is deployed is discharged outside through a vent hole (exhaust port).

[0003] In addition, the airbag has a reduced protruding dimension,
For example, a configuration in which the base cloth on the occupant side and the base cloth on the vehicle body side are connected by a tether belt is known. However, since the tether belt is provided inside the airbag, there is a problem that operations such as sewing are complicated, a mounting structure is complicated, and it is difficult to reduce a manufacturing cost.

In this respect, for example, Japanese Patent Application Laid-Open No. Hei 7-232607
Is known. In this configuration, the outer peripheral edges of the occupant-side base cloth and the vehicle-body-side base cloth are joined together to form a bag-shaped airbag, and cover the gas introduction holes provided in the vehicle-body-side base cloth. It has an intermediate base fabric. The intermediate base cloth has an outer peripheral edge located on the inner peripheral side with respect to the outer peripheral part of the base cloth on the vehicle body side and is partially joined, and a central part is formed at a central part of the occupant side base cloth. When the airbag is actuated, the occupant-side base cloth is restricted from expanding toward the occupant.

[0005]

Furthermore, today, a driver who takes a normal riding posture has a sufficient shock absorbing force, and furthermore, the driver gets on the front side of the seat (handle side) extremely. Out of position (abbreviated as OOP), it has appropriate shock absorption,
It is required to suppress the unpleasant problem, which is the unpleasant sensation felt by the driver or the like when the airbag is deployed, and it is important to set the vent hole arrangement position.

In this respect, in the configuration described in Japanese Patent Application Laid-Open No. 7-232607, although there is a description that the exhaust hole is formed on the outer peripheral side of the opening into which the inflator is inserted, the operation during the close deployment is described. No mention was made of discomfort to the elderly.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an airbag having sufficient shock absorption characteristics and capable of suppressing the influence on an object to be protected.

[0008]

According to the first aspect of the present invention, there is provided an airbag having a first base cloth portion provided with a gas introduction portion, and an outer peripheral portion which is superimposed on a side of the first base cloth portion to be protected. A second base cloth portion connected to the first base cloth and forming an outer shell of the bag together with the first base cloth; and a second base cloth portion disposed to cover the protected object side of the gas introduction portion, A third base cloth section joined to the first base cloth section by a plurality of joint sections provided via a communication section communicating from the gas introduction section side to the outer peripheral side; and the gas introduction section and the communication section. A vent hole that is provided on the first base fabric portion and located on a straight line connecting the vent holes and that communicates with the first base fabric portion on the side opposite to the object to be protected.

In this configuration, when the gas is introduced from the gas introduction section, the gas swells the third base cloth section toward the object to be protected, and also causes the first base cloth section and the third base cloth section to bulge. Between the base cloth. Further, the gas is supplied to the outer peripheral side of the airbag via the communication portion, and is filled between the first base fabric portion and the second base fabric portion. At this time, a large opening area of the communicating portion is ensured, and at the initial stage of deployment, the gas flow rate is large, and the amount of gas exhausted from the vent hole is small, so that the airbag is efficiently and sufficiently deployed.
Further, after the space between the first base cloth and the second base cloth is filled with the gas and developed, the gas is naturally exhausted from the vent hole, and the gas to be protected is received. Exhausted from vent hole to absorb impact. Further, when gas is introduced from the gas introduction section in a state where the object to be protected is very close to the airbag, the gas causes the third base cloth portion to bulge toward the object to be protected and the first base cloth to be expanded. The gas is filled between the cloth portion and the third base cloth portion, but in a state where the swelling is suppressed by the protected object, the gas quickly flows from the vent hole located on a straight line connecting the gas introduction portion and the communication portion. And the pressure on the object to be protected is appropriately alleviated.

According to a second aspect of the present invention, there is provided the airbag according to the first aspect, wherein the vent hole is disposed so as to at least partially overlap an outer edge of the third base cloth constituting the communicating portion. It is.

[0011] In this configuration, the gas is introduced from the gas introduction section in a state where the object to be protected is very close to the airbag, and the space between the first base cloth section and the third base cloth section is sufficiently provided. Even if it does not swell and the opening area of the communication part is not sufficiently ensured, gas is quickly exhausted from the vent hole with swelling suppressed by the protected object, and the pressure on the protected object is appropriately relaxed Is done.

According to a third aspect of the present invention, there is provided the airbag according to the first or second aspect, wherein the edge of the opening forming the gas introducing portion, the first base cloth and the second base cloth are provided. When the length from the opening to the outer peripheral joint is 1 on a line connecting the joined outer peripheral joint, the vent hole is at least 1/3 or more, 2 / At least a part of them is arranged so as to be overlapped at three or less positions.

[0013] With this configuration, both the sufficient deployment characteristics of the airbag and the relaxation of the pressure on the object to be protected when the object to be protected is extremely close to the airbag are compatible.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an airbag according to the present invention will be described below with reference to the drawings.

1 to 6, reference numeral 1 denotes an airbag. The airbag 1 constitutes an airbag device (not shown). The airbag device is a steering wheel body as a member to be mounted on a steering wheel of an automobile. And protects the occupant A, which is the protected object shown in FIGS. 5 and 6, from the impact of a collision. In addition,
The steering wheel body is usually mounted on an inclined steering shaft and used in an inclined state. Hereinafter, the protected object side to which the airbag device is attached is referred to as an occupant side, an upper side, or a front side. The side opposite to the protected object side, that is, the occupant side will be described as the vehicle body side, the lower side, the bottom side, or the back side.

The steering wheel body has an annular rim as a grip, also called a grip or a ring, a boss located inside the rim, and the rim and the boss are connected. For example, three or four spoke portions are provided, and a steering shaft (not shown) is fitted and fixed to the boss provided on the boss portion.

The airbag apparatus has a base plate constituting a support member, an airbag 1 attached to the base plate, and an inflator shown in FIGS.
12, a retainer, a cover body, and the like. The inflator 12 has a substantially cylindrical main body.
12a, and a flange 12
In addition, a plurality of gas injection ports 12c for injecting gas are radially arranged toward the outer peripheral side above the flange portion 12b. A bolt mounting hole communicating with the bolt mounting hole of the base plate is formed in the flange portion 12b.

The airbag 1 has a first base cloth portion which is a circular body and is a body-side base cloth located on the vehicle body side.
21 and a second base cloth portion which is an occupant side base cloth facing the occupant side
22 and a small circular third base cloth portion 23 disposed between the base cloth portions 21 and 22. The base cloth portions 21, 22, and 23 are made of, for example, nylon woven cloth.
It is also called a plate (lower plate portion, upper plate portion, middle plate portion) or panel (back panel, front panel, center panel), and the like. In the circular shape of the same size, the peripheral portion of the outer peripheral portion is integrally sewn along the outer peripheral joining portion 24 to be continuously connected, and the first base cloth portion 21 and the second base cloth portion 22
A flat bag-shaped outer shell is formed.

A gas inlet 28, which is an inflator opening serving as a gas inlet, is formed in the center of the first base cloth portion 21 located on the lower side. At the same time, a bolt mounting hole 29 which is a bag fixing hole is formed around the gas inlet 28, and an annular mounting portion 30 including the bolt mounting hole 29 and surrounding the gas inlet 28 is formed. Have been.

Further, a vent hole 31 as an exhaust portion is formed in a circular shape at one or a plurality of predetermined positions in the first base cloth portion 21.

The third base fabric portion 23 can be called an intermediate base fabric, and is a circle having a smaller diameter than the first and second base fabric portions 21 and 22, for example, the first and second base fabric portions. Base fabric parts 21 and 22
And is concentric with the first and second base cloth portions 21 and 22 so as to cover the gas inlet 28 and the peripheral portion of the gas inlet 28. Are located.

The third base cloth portion 23 is placed on the first base cloth portion 21 in a plurality of places near the outer edge 32 of the third base cloth portion 23 in this embodiment. In the embodiment, the first base cloth portion 21 is intermittently joined to the first base cloth portion 21 at four places by sewing or the like. In the present embodiment, as shown in FIG. 4, each joining portion 33 has an arc-shaped arc-shaped portion 33a along the outer edge portion 32, and an edge extending from both ends of the arc-shaped portion 33a toward the outer periphery. The portions 33b are formed by sewing, and are arranged at substantially equal intervals in a so-called radial manner so as to surround the gas inlet 28.

Therefore, a portion between the first base cloth portion 21 and the third base cloth portion 23, which is an unsewn portion of the portion between the joint portions 33, is connected to the gas introduction port 28 through the gas inlet 28, respectively. A communication section 35 through which the introduced gas can pass is provided.

The third base cloth portion of these communication portions 35
Each vent hole 31 is provided in advance at a position overlapping the outer edge 32 of the 23.

Further, near the center of the third base cloth portion 23, for example, a connecting portion 37 which is an annular stitching portion is provided.
And stitched together.

The manufacturing process of the airbag 1 is as follows.
First, the third base cloth portion 23 is aligned and placed on the first base cloth portion 21 in which the predetermined gas inlet 28 and vent hole 31 are formed in advance, and the third base cloth portion 23 is joined and joined by the joining portion 33. I do.
Next, the first base cloth part 21 to which the third base cloth part 23 is sewn
Of the second base cloth portion 22 on the side opposite to the third base cloth portion 23.
And the outer peripheral portions are sewn together at the outer peripheral joint portion 24. Then, the second base cloth part 22 and the third base cloth part 23 are pulled out and turned over via the gas inlet 28 of the first base cloth part 21 or one of the vent holes 31. Further, the second base fabric portion 22 and the third base fabric portion 23 are sewn together at the connecting portion 37 to form the airbag 1.

When assembling the airbag apparatus, an annular retainer is inserted inside the airbag 1 and mounting bolts protruding from the retainer are inserted into the bolt mounting holes 29 of the airbag 1 and the base plate. Then, the airbag 1 is folded into a predetermined shape such as a petal shape, and fitted with a cover from above. Further, an inflator mounting hole of the base plate and a gas inlet of the airbag 1 are provided.
The upper portion of the inflator 12 is inserted into the airbag 1 from below through the connector 28, and the mounting bolt of the retainer is inserted into the bolt mounting hole of the flange portion 12b, and tightened with a nut from below. In this state, the airbag 1 and the base plate are fastened together between the retainer and the inflator 12, and the airbag device 2 is assembled. And
In this airbag device, a mounting piece provided on a base plate is fixed to a core metal of a boss portion of a steering wheel body using bolts or the like, and is mounted on a steering wheel.

When a collision impact is applied to an automobile equipped with the airbag device, the control unit (not shown) activates the inflator 12 and gas is rapidly injected into the airbag 1 from the gas injection port 12c of the inflator 12. It is injected. Then, the airbag 1 breaks the cover body into a door shape along the tear line to form a projecting port, swells through the projecting port, and swells in a predetermined shape in front of the occupant A,
The occupant A thrown forward is received and restrained, and the impact applied to the occupant A is reduced.

Next, with reference to FIGS. 5 and 6, the operation when the airbag 1 inflates will be described in detail.

First, when the occupant A as a driver is in a normal sitting posture when the airbag 1 is deployed, a predetermined distance is secured between the occupant A and the airbag device. In this case, as shown in FIG. 5A, first, the gas supplied from the inflator 12 is supplied to the third base cloth portion 23.
Bulges to the occupant A side, and the first chamber 41, which is a space formed by the third base cloth part 23 and the first base cloth part 21, is filled with gas. In this state, the third base cloth 23 and the first base cloth 21
Is sufficiently secured, and a large cross-sectional area of each communication portion 35, which is a portion where the third base fabric portion 23 and the first base fabric portion 21 are not joined, is secured.

Next, as shown in FIG.
The second chamber 42, which is a space formed by the first to third base cloth portions 21, 22, and 23, passes through these widely opened communication portions 35.
To fill the second chamber 42. In addition, gas is supplied to the first chamber 41
When flowing into the second chamber 42, the flow rate of the gas passing through each communication part 35 is extremely high, so that the amount of gas exhausted from the vent hole 31 disposed so as to overlap with these communication parts 35 to the outside is It is slight.

Further, after the second chamber 42 is filled with gas, that is, after the airbag 1 is deployed, as shown in FIGS. 5 (c) and 1, the gas further injected from the inflator 12 is communicated. Vent hole 31 provided over part 35
When the occupant A is received by the airbag 1, the vent holes 31 are used to absorb the impact.
It is exhausted from. Further, even when the occupant A is not received, the gas is naturally exhausted from the vent hole 31.

On the other hand, when the airbag 1 is deployed, the occupant A, who is the driver, is in a sitting position extremely positioned in front of the seat (steering wheel side).
If a predetermined distance is not secured between the occupant A and the airbag device, first, as shown in FIG. Although swelling toward the occupant A, the swelling of the third base cloth portion 23 is regulated by the occupant A. At this time, the third base cloth portion
When the first chamber 41 between the first base cloth portion 23 and the first base cloth portion 21 is developed in the same manner as the normal riding posture as shown in FIG. 5, the gas pressure in the first chamber 41 increases, and the occupant A The airbag 1 is further inflated to the side, and as a result, the occupant A becomes uncomfortable. In this regard, in the configuration of the present embodiment, during close deployment, as shown in FIG. 6B, the deployment of the airbag 1 to the occupant A side is restricted by the occupant A, and the first chamber 41 is narrowed. The cross-sectional area of the communication portion 35 is not sufficiently secured. For this reason, the amount of gas exhausted from the vent hole 31 disposed over the communication part 35 is larger than the amount of gas flowing from the first chamber 41 to the second chamber 42 via the communication part 35, and the first chamber
The gas pressure in 41 does not rise more than necessary, and as shown in FIG. 6C, the expansion of the first chamber 41 and the second chamber 42 is suppressed, and the occupant A feels discomfort due to the expansion of the airbag 1. Is suppressed.

As described above, according to the vehicle airbag 1 and the airbag apparatus of the present embodiment, the passenger A can be protected by securing the shock absorbing force for the passenger A in the normal riding posture. Further, even when the occupant A is in a sitting position extremely positioned in front of the seat (the steering wheel side), the shock can be absorbed and the occupant A can be protected, and the gas is smoothly exhausted from the vent hole 31. Discomfort due to deployment of the airbag 1 for the occupant A can be suppressed.

The deployment behavior of the airbag 1 differs depending on the capacity of the inflator 12, the size of the airbag, the riding posture of the occupant A, and the like. On the other hand, vent hole 31
Is provided near the gas inlet 28 in the first chamber 41 or the like,
Although it is easy to reduce the discomfort to the occupant A during the close deployment, the gas exhausted from the vent hole 31 in the initial stage of deployment of the airbag 1 increases, and the inflator is adjusted to adjust the deployment characteristics of the airbag 1. Needs to be increased,
This causes an increase in the size of the airbag device and an increase in manufacturing cost. On the other hand, if the vent hole 31 is provided in the second chamber 42 or the like largely separated from the gas inlet 28 and the communication portion 35, it becomes difficult to reduce the discomfort to the occupant A during the close deployment. Furthermore, even in a normal riding posture, in the deployment behavior of the folded airbag 1, a part of the vent hole 31 is closed, and it becomes difficult to exhaust gas, and the internal pressure of the airbag 1 may increase. There is.

As a result of various studies on the deployment behavior of the airbag 1 and the positional relationship between the airbag 1 and the occupant, the first
First, the position of the vent hole 31 provided in the base cloth portion 21 is supplied from the inflator 12 by being present in a radial range which is a straight line connecting the gas introduction port 28 and the communication portion 35. By providing the gas on the main flow path, desired behavior of the airbag 1 can be obtained.

Further, preferably, in a state where the airbag 1 is spread on a plane, the airbag 1 is located at a position where the outer edge portion 32 of the third base cloth portion 23 is in contact with the communicating portion which is not joined to the first base cloth portion 21. By providing the airbag 1, desired behavior of the airbag 1 is obtained.

Further, preferably, as shown in FIG.
A line segment L from the edge of the circular hole of the gas inlet 28 to the outer peripheral joint 24 where the first base cloth 21 and the second base cloth 22 which are the outer peripheral edges of the airbag 1 are joined. when the length L ₁ and 1, the vent hole 31 is on the line segment L, the gas inlet 28
It is more preferable that at least a part of the circular hole be overlapped at a position of not less than 1/3 and not more than 2/3 from the edge of the circular hole.
The desired behavior of the airbag 1 can be obtained by arranging the vent hole 31 so that the center of the circular hole constituting the vent hole 31 is located at a position of 3 or more and 2/3 or less.

In the present embodiment, the third base cloth 23
Thus, the gas is guided to the outer peripheral side of the airbag 1 and the outer peripheral side of the airbag 1 is deployed, so that the deployment characteristics of the airbag can be easily improved.

Further, in the present embodiment, the second base cloth portion
Since the vicinity of the center between the second base cloth part 22 and the third base cloth part 23 is connected by the connecting part 37, the protrusion dimension of the second base cloth part 22 located on the occupant side can be easily and reliably regulated.

Further, in the present embodiment, each of the base cloth portions 21,
Since the shapes of 22 and 23 are simple and easy to manufacture, manufacturing costs can be reduced.

As described above, the size, shape, number, etc. of the vent holes are set according to the characteristics such as the size of the airbag and the capacity of the inflator.
As shown in FIG. 7, the vent holes 31 are respectively connected to the respective communication portions.
In 35, a total of four locations can be provided.

In addition to the opening of the vent hole,
The base fabric portion may be formed by partially increasing the air permeability.

Further, the third base cloth may be polygonal, such as elliptical, hexagonal or octagonal, in addition to circular. Further, the first to third base cloth portions may be formed integrally as appropriate, or may be formed by joining or overlapping a plurality of base cloths. Further, a reinforcing cloth, a flameproof cloth, or the like may be provided between the second base cloth section and the third base cloth section, as long as the vent hole is not closed. Also,
In the above-described embodiment, the first and second base fabrics are joined to form a bag, and then the bag is turned back so that the ears are located inside the bag. With an exposed shape,
Alternatively, it is also possible to fold and sew only the ear part.

Further, the connecting portion for connecting the third base fabric portion to the second base fabric portion is not limited to an annular shape, and may have another shape or may be omitted.

Further, the central portion of the third base cloth portion 23 and the like are
The protrusion of the third base cloth portion 23 is restricted by being connected to a connection support portion which is provided by extending to a member fixedly provided on the vehicle body side, such as the base plate, the inflator 12 or the retainer. Can also.

The airbag device is used not only for a driver attached to the steering wheel body, but also for a passenger in a passenger seat provided on an instrument panel, for protecting a side portion provided on a side portion of a seat, or for a rear portion of a seat. The present invention can be applied to an airbag of an airbag device for a rear seat provided in a vehicle, and can be widely applied to an airbag of an airbag device that absorbs an impact of a protected object.

[0048]

According to the airbag of the first aspect, when the gas is introduced from the gas introduction portion, the gas causes the third base cloth portion to bulge toward the object to be protected, Is filled between the base cloth part and the third base cloth part, and gas is supplied to the outer peripheral side of the airbag through the communication part, and the first base cloth part and the second base cloth part are filled. At this time, the opening area of the communication part is secured large, and the flow rate of gas is large at the initial stage of deployment, the amount of gas exhausted from the vent hole is small, and the airbag is efficiently filled. Can be fully deployed. Further, after the space between the first base cloth and the second base cloth is filled with the gas and developed, the gas is naturally exhausted from the vent hole, and the gas to be protected is received. Exhausted from the vent hole can absorb the impact. Also, when a gas is introduced from the gas introduction part in a state where the object to be protected is extremely close to the airbag,
The third base cloth is swelled toward the protected object and filled between the first base cloth and the third base cloth, but in a state where the swelling is suppressed by the protected object, Gas is quickly exhausted from a vent hole located on a straight line connecting the gas introduction section and the communication section, and the pressure on the object to be protected can be easily and appropriately alleviated.

According to the airbag of the second aspect, in addition to the effect of the first aspect, the vent hole is arranged so as to at least partially overlap the outer edge of the third base cloth constituting the communicating portion. Therefore, the gas is introduced from the gas introduction section in a state where the object to be protected is extremely close to the airbag, and the space between the first base cloth section and the third base cloth section does not swell sufficiently. Even when the opening area is not sufficiently ensured, the gas is quickly exhausted from the vent hole in a state where the swelling is suppressed by the protected object, and the pressure on the protected object can be easily and appropriately alleviated.

According to the airbag of the third aspect, in addition to the effect of the first or second aspect, in addition to the edge of the opening constituting the gas introduction portion, the first base cloth and the second base cloth. When the length from the opening to the outer peripheral joint is 1 on a line connecting the outer peripheral joint and the outer joint, the vent hole is one-third or more and two-thirds from the opening on the line. By arranging at least a part of the airbag in the following position, sufficient deployment characteristics of the airbag and relaxation of pressure on the object to be protected when the object to be protected is extremely close to the airbag are compatible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a deployment operation showing an embodiment of an airbag of the present invention.

FIG. 2 is a perspective view of the airbag in a disassembled state.

FIG. 3 is a cross-sectional view showing a state where the airbag is expanded on a plane.

FIG. 4 is a plan view showing a state in which the airbag is deployed on a plane and a second base fabric portion is omitted.

FIG. 5 is an explanatory diagram of a deployment operation of the airbag during normal riding.

FIG. 6 is an explanatory diagram of a deployment operation of the airbag in a proximity deployment state in which an object to be protected is in proximity.

FIG. 7 is a plan view showing another embodiment of the airbag of the present invention in a state where it is developed on a plane and a second base fabric portion is omitted.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Airbag 21 1st base fabric part 22 2nd base fabric part 23 3rd base fabric part 24 Peripheral joint part 28 Gas inlet 31 as a gas introduction part 31 Vent hole 32 Outer edge part 33 Joint part 35 Communication part A Passenger L line segment as protected object

Claims (3)

[Claims] A first base cloth portion provided with a gas introducing portion; and a first base cloth portion which is superimposed on an object to be protected side of the first base cloth portion and has an outer peripheral portion connected to the first base cloth. A second base fabric portion that forms an outer shell of the bag together with the first base fabric, and a communication portion that is disposed to cover the protected object side of the gas introduction portion and communicates from the gas introduction portion side to the outer peripheral side. A third joint joined to the first base cloth by a plurality of joints provided via
And a vent provided on the first base cloth portion and located on a straight line connecting the gas introduction portion and the communication portion, and communicating with a counter-protected object side of the first base cloth portion. An airbag comprising a hole. 2. The vent hole according to claim 3, wherein the third hole comprises a communication portion.
The airbag according to claim 1, wherein at least a part of the airbag is disposed so as to overlap with an outer edge portion of the base cloth portion. 3. The line from the opening to the outer periphery on a line connecting the edge of the opening constituting the gas introduction part and the outer peripheral joint part joining the first base cloth part and the second base cloth part. When the length dimension to the joint is 1, the vent hole is at least partially overlapped with the opening at a position of not less than 1/3 and not more than 2/3 on the line segment. The airbag according to claim 1 or 2, wherein the airbag is provided.