Rear seat airbag and rear seat airbag device

Abstract

To restrain an occupant on a rear seat of a vehicle stably when a collision with the vehicle occurs regardless of a physical frame of the occupant on the rear seat of the vehicle, a seat position of a front seat of the vehicle, or an angle of a backrest.SOLUTION: A rear seat airbag 10 expands and deploys in a vehicle inner direction from a door trim of a rear seat and includes: a first expansion air chamber 20 which expands and deploys to a space including an upper part of a knee part KN of an occupant CR on the rear seat; and a second expansion air chamber 30 which expands and deploys in a space between the first expansion air chamber 20 and the occupant CR on the rear seat.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a rear seat airbag and a rear seat airbag device. [Background technology]

[0002] In automobiles and other vehicles, a collision detection unit such as an acceleration sensor is provided at the front of the vehicle body to detect a collision from the front of the vehicle, and when this collision detection unit detects a collision from the front of the vehicle, an airbag device is activated to protect occupants in the vehicle cabin.

[0003] In addition, vehicles with front and rear seats are known to be equipped with front seat airbag devices that protect occupants seated in the front seats, such as the driver's seat and passenger seat, as well as rear seat airbag devices that protect occupants seated in the rear seats located behind the front seats.

[0004] One such rear seat airbag device disclosed is a rear seat airbag that inflates and deploys from the bottom of the front seat toward the rear side of the backrest of the front seat, and includes a front inflation section that inflates and deploys upward along the rear side of the backrest, a rear inflation section that inflates and deploys rearward from the tip of the front inflation section, and a restraint means that restrains the rear inflation section against the front inflation section so that the rear inflation section covers the upper thighs of the rear seat occupant (see, for example, Patent Document 1).

[0005] Airbag systems that deploy from the lap belts that make up the seatbelts are also being considered. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-96653 Summary of the Invention [Problem to be solved by the invention]

[0007] However, with a rear seat airbag that inflates and deploys from the bottom of the front seat of the vehicle onto the back side of the backrest of the front seat of the vehicle, as described in Patent Document 1, there is a risk that if the occupant in the rear seat of the vehicle is small, for example, a gap will form between the airbag and the vehicle occupant, and the airbag may not be able to properly restrain the small occupant.

[0008] Furthermore, rear seat airbags, such as those described in Patent Document 1, which inflate and deploy from the bottom of the front seat of the vehicle to the rear side of the backrest of the front seat, have a problem in that, due to their structure, the restraining force on rear seat occupants varies depending on the seat position and backrest angle of the front seat of the vehicle.

[0009] In addition, with regard to the airbag system that deploys from the lap belt, due to the characteristics of the seat belt, it is constantly in a frictional environment, and there is a possibility that the airbag may not deploy stably due to the influence of moisture, etc.

[0010] Therefore, the present invention has been made in consideration of the above-mentioned problems, and aims to provide a rear seat airbag and a rear seat airbag device that can stably restrain a rear seat occupant in the event of a vehicle collision, regardless of the physique of the rear seat occupant or the seat position or backrest angle of the front seat of the vehicle. [Means for solving the problem]

[0011] Mode 1: One or more embodiments of the present invention are a rear seat airbag that inflates and deploys from a rear seat door trim toward the inside of a vehicle, and includes a first inflation air chamber that inflates and deploys into a space including the upper knees of a rear seat occupant, and a second inflation air chamber that inflates and deploys into a space between the first inflation air chamber and the rear seat occupant, The first inflation air chamber and the second inflation air chamber have a deployed shape that is a triangular prism with a triangular cross section, an inflator is connected to the first inflation air chamber, the first inflation air chamber and the second inflation air chamber are connected at a joint at a lower portion, a first vent hole is provided at the joint, the first inflation air chamber is provided with a second vent hole for contraction, and the second vent hole opens as an exhaust port when pressure is applied from the occupant. A rear seat airbag featuring the following features. [Effects of the Invention]

[0016] According to one or more embodiments of the present invention, it is possible to stably restrain a rear seat occupant of a vehicle in the event of a vehicle collision, regardless of the physique of the rear seat occupant or the seat position or backrest angle of the front seat of the vehicle. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a top view showing a deployed state of a rear seat airbag according to an embodiment of the present invention; [Figure 2] 1 is a perspective view showing a configuration of a rear seat airbag according to an embodiment of the present invention; [Figure 3] 1 is a perspective view showing a deployed form of a rear seat airbag according to an embodiment of the present invention when inflated and deployed; [Figure 4] 2 is an electrical configuration diagram of the rear seat airbag device according to the embodiment of the present invention; FIG. [Figure 5] 4 is a diagram showing a processing flow of a vehicle control unit in a rear seat airbag device according to an embodiment of the present invention. FIG. [Figure 6] 3A to 3C are diagrams illustrating the transition of the deployment form of a rear seat airbag according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] <Embodiment> A rear seat airbag device 1 according to this embodiment will be described with reference to FIGS. 1 to 6. FIG. In Figures 1 to 3 and 6, the front side of the vehicle is indicated by arrow FR, the rear side of the vehicle is indicated by arrow BK, the upper side of the vehicle is indicated by arrow UP, the left side of the vehicle (one side in the vehicle width direction) when viewed from above the vehicle is indicated by arrow LH, and the right side of the vehicle (the other side in the vehicle width direction) is indicated by arrow RH. In the following description, when the terms up / down, front / rear, and left / right are used, they refer to the up / down direction of the vehicle, the front / rear direction of the vehicle, and the left / right direction of the vehicle, unless otherwise specified.

[0019] <Rear seat airbag device 1> As shown in FIG. 1, a rear seat airbag device 1 according to this embodiment is provided on a door trim on the side of a rear seat of a vehicle, and a rear seat airbag 10 is inflated and deployed from the door trim on the side of the rear seat of the vehicle toward the inside of the vehicle. The door trim is also provided with a weak portion that serves as an opening when the rear seat airbag 10 is inflated and deployed. In the present embodiment, a rear seat airbag device 1 for restraining an occupant seated in a seat on the left rear side of a vehicle will be described below as an example.

[0020] As shown in FIG. 2, the rear seat airbag 10 in the rear seat airbag device 1 according to this embodiment is configured to include a first inflation air chamber 20 and a second inflation air chamber 30.

[0021] The first inflation chamber 20 is an airbag that inflates and deploys into a space including above the knees KN of a rear seat occupant CR. As shown in FIG. 2, the expanded shape of the first inflation chamber 20 is a substantially triangular prism, and the first inflation chamber 20 functions as a reaction bag.

[0022] The second inflation air chamber 30 is an airbag that inflates and deploys in the space between the first inflation air chamber 20 and the rear seat occupant CR. As shown in FIG. 2, the second inflation chamber 30 has a deployed shape that is a triangular prism with a triangular cross section, and the second inflation chamber 30 functions as an occupant restraint bag.

[0023] As shown in FIG. 2, the first inflation chamber 20 and the second inflation chamber 30 are connected by a tether sewn into the connecting portion 11 at the bottom. More specifically, it is preferable that the joint 11 extends from near the abdomen of the rear seat occupant CR toward the backrest of the front seat when the first inflation air chamber 20 and the second inflation air chamber 30 are inflated and deployed. In addition, the connecting portion 11 is provided with first vent holes 13A, 13B, and 13C for discharging high-pressure gas supplied from an inflator (not shown) to the first inflation chamber 20 into the second inflation chamber 30. The diameter of the exhaust port of first vent holes 13A, 13B, 13C is determined by the volume of first inflation chamber 20 and second inflation chamber 30 and the amount of high-pressure gas supplied from the inflator. On the other hand, the upper portion 12 of the first inflation chamber 20 and the upper portion of the second inflation chamber 30 are not connected, and the upper portion 12 of the first inflation chamber 20 is provided with second vent holes 12A, 12B for deflation. The diameter of the exhaust port of the second vent holes 12A, 12B is determined by the volume of the first inflation chamber 20, the amount of pressure exerted by the occupant CR, and the desired deformation pattern of the first inflation chamber 20 over time.

[0024] In addition, when the first inflation air chamber 20 and the second inflation air chamber 30 are normally deployed, the exhaust ports of the second vent holes 12A, 12B are blocked by the second inflation air chamber 30, and as shown in Figure 3, when pressure is applied from the occupant CR and the internal pressure of the second inflation air chamber 30 increases, the exhaust port opens and some of the high-pressure gas in the first inflation air chamber 20 is discharged to the outside.

[0025] The first inflation chamber 20 is provided with a connection portion 21 for connecting to an inflator (not shown). That is, when the inflator is activated, high-pressure gas from the inflator is supplied to the inside of the first inflation chamber 20, causing the first inflation chamber 20 to inflate and deploy. Along with this, a portion of the high-pressure gas supplied from the inflator is supplied to the second inflation chamber 30 via the first vent holes 13A, 13B, 13C, and the second inflation chamber 30 also inflates and deploys.

[0026] The inflator is housed in a case together with the rear seat airbag 10 and is arranged in the door trim on the side of the rear seat, and supplies high-pressure gas to the first inflation chamber 20. Specifically, the inflator is arranged to connect to a first inflation chamber 20 which is connected to a second inflation chamber 30 via first vent holes 13A, 13B, 13C.

[0027] <Electrical configuration of rear seat airbag device 1> The electrical configuration of the rear seat airbag device 1 according to this embodiment will be described with reference to FIG.

[0028] As shown in FIG. 4, the rear seat airbag device 1 includes a vehicle control unit 100, a vehicle front collision sensor 110, an occupant detection unit 120, and an inflator .

[0029] The vehicle control unit 100 is an electronic control unit (ECU) that includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., and performs various calculations for vehicle control. In this embodiment, the vehicle control unit 100 controls the operation of the inflator 130 based on the detection information from the occupant detection unit 120 and the sensing signal from the vehicle front collision sensor 110 described later when an occupant CR is seated in the rear seat.

[0030] When a collision occurs from the front of the vehicle, the vehicle front collision sensor 110 outputs a sensing signal to the vehicle control unit 100 indicating that a collision has been detected. A specific example of the vehicle front collision sensor 110 is an acceleration sensor that detects impacts and vibrations applied to the vehicle as acceleration. The acceleration sensor may be either a piezoresistance type that utilizes changes in the electrical resistance of a semiconductor, or a capacitance type that detects changes in the gap between the movable and fixed parts of the comb-shaped electrodes as capacitance. Furthermore, an acceleration sensor for detecting a collision and another acceleration sensor for detecting floor acceleration may be provided, and collision determination may be made based on acceleration values ​​from both acceleration sensors.

[0031] The occupant detection unit 120 detects the occupants CR seated in the seats on both sides of the rear seat. The occupant detection unit 120 may be a load sensor disposed inside the seat surface of each seat on either side of the rear seat, or may be a detection method that analyzes an image captured inside the vehicle cabin.

[0032] The inflator 130 is disposed in the door trim on the side of the rear seat, and is configured to include a folded rear seat airbag 10, an ignition device, an ignition agent, a gas generating agent, and a storage box for storing these. When the ignition device of the inflator 130 is activated by a control signal from the vehicle control unit 100, the ignition agent ignites, generating a large amount of gas, which inflates and deploys the second inflation chamber 30 through the first inflation chamber 20 and the first vent holes 13A, 13B, and 13C that constitute the rear seat airbag 10.

[0033] <Control of rear seat airbag device 1> 5, the vehicle control unit 100 determines whether or not an occupant CR has been detected in the rear seat (step S110). Specifically, the vehicle control unit 100 determines whether or not a signal indicating that an occupant CR has been detected in the rear seat has been received from the occupant detection unit 120.

[0034] Then, when the vehicle control unit 100 detects an occupant CR in the rear seat ("YES" in step S110), the process proceeds to step S120. On the other hand, if the vehicle control unit 100 does not detect an occupant CR in the rear seat ("NO" in step S110), the process returns to the original state and waits.

[0035] Next, the vehicle control unit 100 determines whether a collision has occurred in front of the vehicle (step S120). At this time, if the vehicle control unit 100 determines that no collision has occurred in front of the vehicle, that is, that no sensing signal has been received from the vehicle front collision sensor 110 ("NO" in step S120), the processing returns to step S110.

[0036] On the other hand, if the vehicle control unit 100 determines that a collision has occurred in front of the vehicle ("YES" in step S120), more specifically, when the vehicle control unit 100 receives a sensing signal from the vehicle front collision sensor 110 indicating that a collision has occurred in front of the vehicle, the vehicle control unit 100 activates the inflator 130 and executes control to inflate and deploy the first inflation chamber 20 and the second inflation chamber 30 (step S130).

[0037] Next, the vehicle control unit 100 determines whether or not the time period during which the gas is supplied by the inflator 130 has elapsed a predetermined time period (step S140). If the vehicle control unit 100 determines that the time period during which gas is supplied by the inflator 130 has not elapsed beyond the predetermined time period ("NO" in step S140), the process returns to the original state and the vehicle control unit 100 waits. Here, the predetermined time is, for example, the time required to supply sufficient gas to inflate and deploy the first inflation chamber 20 and the second inflation chamber 30.

[0038] On the other hand, if the vehicle control unit 100 determines that the time that the inflator 130 has supplied gas has elapsed a predetermined time ("YES" in step S140), the vehicle control unit 100 controls the inflator 130 to stop the supply of gas by the inflator 130 (step S150) and terminates the processing.

[0039] Here, the deployment forms of the first inflation chamber 20 and the second inflation chamber 30 will be explained in chronological order using FIG.

[0040] As shown in Figure 6(A), when a collision occurs in front of the vehicle and the inflator 130 is activated by an activation signal from the vehicle control unit 100, high-pressure gas from the inflator 130 flows into the first inflation chamber 20, and the first inflation chamber 20 inflates and deploys so as to slide into a space including the upper part of the knees KN of the rear seat occupant CR.

[0041] At this time, some of the high-pressure gas that has flowed into the first inflation chamber 20 flows into the second inflation chamber 30 through the first vent holes 13A, 13B, and 13C, and the second inflation chamber 30 also begins to expand and develop.As shown in Figure 6(B), after a predetermined time has passed, the expansion and development of the first inflation chamber 20 and the second inflation chamber 30 is completed, and a reaction force is generated in the first inflation chamber 20.

[0042] Next, when the vehicle collides head-on, the upper body of the rear seat occupant CR falls toward the front of the vehicle, and the chin of the occupant CR comes into contact with the nearest second inflation chamber 30, applying pressure to the second inflation chamber 30 and causing it to deform. This increases the internal pressure of the second inflation chamber 30, and as a result, as shown in Figure 3, the exhaust ports of the second vent holes 12A and 12B of the first inflation chamber 20, which were buried between the second inflation chamber 30, open, discharging high-pressure gas to the outside. Then, as shown in Figures 6(C) and (D), as the upper body of the occupant CR leans forward and high-pressure gas is released from the first inflation chamber 20 near the knees KN, the first inflation chamber 20 and the second inflation chamber 30 are twisted between the door and the occupant CR and begin to lean forward.

[0043] Then, as shown in Figure 6(E), when all of the high-pressure gas in the first inflation chamber 20 is discharged, the occupant CR begins to lean forward, and the second inflation chamber 30 moves toward the front of the vehicle, acting to relieve pressure on the occupant CR's chest, abdomen, etc.

[0044] <Actions and Effects> As explained above, the rear seat airbag 10 of the rear seat airbag device 1 according to this embodiment is a rear seat airbag 10 that inflates and deploys from the rear seat door trim toward the inside of the vehicle, and is configured to include a first inflation air chamber 20 that inflates and deploys in a space including the upper part of the knees KN of the rear seat occupant CR, and a second inflation air chamber 30 that inflates and deploys in a space between the first inflation air chamber 20 and the rear seat occupant CR. That is, the first inflation chamber 20 functions as a reaction bag because it inflates and deploys into the space including the area above the knees KN of the rear seat occupant CR. Also, the second inflation chamber 30 functions as an occupant restraint bag because it inflates and deploys into the space between the first inflation chamber 20 and the rear seat occupant CR. Therefore, the rear seat airbag 10 of the rear seat airbag device 1 has both the function of a reaction force bag and the function of an occupant restraint bag, and can stably restrain the rear seat occupant CR in the event of a vehicle collision, regardless of the physique of the rear seat occupant CR. Furthermore, the rear seat airbag 10 of the rear seat airbag device 1 is inflated and deployed from the rear seat door trim toward the inside of the vehicle, so that the rear seat occupant CR can be stably restrained in the event of a vehicle collision, regardless of the seat position or backrest angle of the front seat.

[0045] Furthermore, the first inflation air chamber 20 and the second inflation air chamber 30 of the rear seat airbag device 1 according to this embodiment have a substantially triangular prism shape when deployed. In other words, the cross section of the first inflation air chamber 20 and the second inflation air chamber 30 when viewed from the front-rear direction of the vehicle is substantially triangular. Therefore, by deploying the approximate plane including one side of the approximately triangle of the first inflation air chamber 20 approximately parallel to the space including the upper part of the knees KN of the rear seat occupant CR, the first inflation air chamber 20 can generate a stable reaction force against the occupant CR. In addition, by inflating and deploying the second inflation air chamber 30 so that an approximate plane including an edge that intersects with one edge of the first inflation air chamber 20 that is approximately parallel to the space including the upper part of the knees KN of the rear seat occupant CR faces the approximate plane of the second inflation air chamber 30, the reaction force generated by the first inflation air chamber 20 can be stably applied to the second inflation air chamber 30. Furthermore, by inflating and deploying the second inflation air chamber 30 so that an approximate plane including an edge of the first inflation air chamber 20 that is approximately parallel to the space including the upper part of the knees KN of the rear seat occupant CR faces the approximate plane of the second inflation air chamber 30, the upper body of the occupant CR is restrained by the convex second inflation air chamber 30, and therefore, by deforming the deployment form of the second inflation air chamber 30 so that the convex shape bends inward toward the center, the upper body of the occupant CR can be restrained while appropriately reducing the impact on the upper body of the occupant CR. Furthermore, by maintaining an approximately plane including one side of the approximately triangle of the first inflation air chamber 20 that is deployed approximately parallel to the space including the upper part of the knees KN of the rear seat occupant CR, and deforming the deployed form so that the first inflation air chamber 20 deflates, the upper body of the occupant CR can be restrained while further reducing the impact on the upper body of the occupant CR.

[0046] In addition, an inflator 130 is connected to the first inflation air chamber 20 of the rear seat airbag device 1 of this embodiment, and the first inflation air chamber 20 and the second inflation air chamber 30 are connected at a lower connecting portion 11, and the connecting portion 11 is provided with first vent holes 13A, 13B, and 13C. In other words, when the inflator 130 is activated, the generated high-pressure gas is supplied to the first inflation chamber 20, and a portion of the supplied high-pressure gas flows into the second inflation chamber 30 through the first vent holes 13A, 13B, and 13C. Therefore, the first inflation air chamber 20 is fully inflated and deployed upward at a position away from the occupant CR, and then the second inflation air chamber 30 is fully inflated and deployed, obtaining a reaction force from the first inflation air chamber 20. That is, when a collision occurs in front of the vehicle, the first inflation air chamber 20 first inflates and deploys to generate a stable reaction force, and before the rear seat occupant CR receives the impact of the collision in front of the vehicle and falls toward the front of the vehicle, the second inflation air chamber 30 inflates and deploys. Therefore, after the first inflation air chamber 20 generates a stable reaction force, the second inflation air chamber 30 inflates and deploys to restrain the rear seat occupant CR who falls toward the front of the vehicle due to the impact of a collision in front of the vehicle, so that in the event of a vehicle collision, the rear seat occupant CR can be stably restrained without applying more force than necessary to the upper body of the rear seat occupant CR.

[0047] Further, the first inflation chamber 20 of the rear seat airbag device 1 according to this embodiment is provided with second vent holes 12A and 12B for deflation. Therefore, when the upper body of the rear seat occupant CR falls toward the front of the vehicle due to the impact of a collision at the front of the vehicle and external pressure is applied to the inflated first and second inflation air chambers 20 and 30, the internal pressure of the inflated first and second inflation air chambers 20 and 30 increases, and high-pressure gas is discharged to the outside from the exhaust ports of the second vent holes 12A and 12B of the first inflation air chamber 20, causing the first inflation air chamber 20 to deform in its deployed form and deflate, thereby reducing the impact on the upper body of the occupant CR and restraining the upper body of the occupant CR.

[0048] Further, the second vent holes 12A, 12B of the rear seat airbag device 1 according to this embodiment open as exhaust ports when pressure is applied from the occupant CR. In other words, the exhaust ports of the second vent holes 12A, 12B are closed until pressure is applied from the occupant CR, and when pressure is applied from the occupant CR, the internal pressure of the first inflation chamber 20 increases, causing the exhaust ports to open. Therefore, the first inflation chamber 20 maintains the generated reaction force until pressure is applied from the occupant CR, and when pressure is applied from the occupant CR, the reaction force is gradually released, thereby making it possible to restrain the upper body of the occupant CR while reducing the impact on the upper body of the occupant CR.

[0049] In addition, when the vehicle control unit 100 of the rear seat airbag device 1 of this embodiment receives a signal from the occupant detection unit 120 indicating that an occupant CR has been detected in the rear seat and determines that a collision has occurred in front of the vehicle, it activates the inflator 130 and executes control to inflate and deploy the first inflation chamber 20 and the second inflation chamber 30. That is, in general, the frequency of the occupant CR sitting in the rear seat of the vehicle is lower than the frequency of the occupant CR sitting in the passenger seat of the vehicle. Therefore, only when a signal is received from the occupant detection unit 120 indicating that an occupant CR has been detected in the rear seat and when it is determined that a collision has occurred in front of the vehicle, can the inflator 130 be activated and control be executed to inflate and deploy the first inflation chamber 20 and the second inflation chamber 30.

[0050] <Variation 1> In this embodiment, the rear seat airbag 10 has been described as being composed of a first inflation chamber 20 and a second inflation chamber 30, but it is also possible to provide multiple second inflation chambers 30, such as an inflation chamber that supports the head of the occupant CR and an inflation chamber that supports the chest of the occupant CR. With this configuration, each expansion chamber restrains the vehicle in a manner that corresponds to the behavior of each main part, thereby safely protecting rear seat passengers.

[0051] The rear seat airbag device 1 of the present invention can be realized by recording the processing of the vehicle control unit 100 on a recording medium that can be read by a computer system, and having the vehicle control unit 100 read and execute the program recorded on this recording medium. The computer system here includes hardware such as an OS and peripheral devices.

[0052] Furthermore, if a WWW (World Wide Web) system is used, the "computer system" also includes the homepage provision environment (or display environment). The above program may be transmitted from a computer system that stores the program in a storage device or the like to another computer system via a transmission medium or by transmission waves in the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) like the Internet or a communication line (communication line) like a telephone line.

[0053] The program may also be a program for implementing some of the above-mentioned functions, or may be a so-called differential file (differential program) that can implement the above-mentioned functions in combination with a program already stored in the computer system.

[0054] The above describes an embodiment of the present invention in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0055] 1; Rear seat airbag device 10. Rear seat airbags 11;Joint part 12;Top 12A: Second vent hole 12B: Second vent hole 13A: First vent hole 13B: First vent hole 13C: First vent hole 20: First expansion chamber 21;Connection part 30: Second expansion chamber 100: Vehicle control unit 110; Vehicle front collision sensor 120: Occupant detection unit 130; Inflator

Claims

[Claim 1] A rear seat airbag that inflates and deploys from the rear seat door trim toward the inside of the vehicle, a first inflation chamber that is inflated and deployed into a space including an upper portion of the knees of the rear seat occupant; a second inflation chamber that is inflated and deployed into a space between the first inflation chamber and the rear seat occupant; Including, A rear seat airbag that inflates and deploys from the rear seat door trim toward the inside of the vehicle, a first inflation chamber that is inflated and deployed into a space including an upper portion of the knees of the rear seat occupant; a second inflation chamber that is inflated and deployed into a space between the first inflation chamber and the rear seat occupant; Including, The first inflation air chamber and the second inflation air chamber each have a triangular prism shape in expanded form, an inflator is connected to the first inflation chamber, the first inflation chamber and the second inflation chamber are connected at a lower joint, and a first vent hole is provided at the joint; The first inflation chamber is provided with a second vent hole for deflation, The second vent hole is configured to open as an exhaust port when pressure is applied from the occupant.

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