JP2009143460A - Curtain airbag device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a curtain airbag device capable of surely deploying a head part position cell between window glass and a head part of an occupant, regardless of the position of the head part of the occupant, and more quickly inflating and deploying the head part position cell. <P>SOLUTION: This curtain airbag device has a gas passage 4 provided in an upper part of a curtain airbag 2 to make gas for inflation and deployment generated in an inflator 3 flow in, a first cell 5 provided on a lower side of the gas passage 4 to be inflated and deployed to a lower side due to inflow of gas from the gas passage 4, and a second cell 6 which is adjacent to the first cell 5 and is inflated and deployed to the position H of the head part of the occupant along the window glass of a vehicle due to inflow of gas from the first cell 5 provided on the lower side of the gas passage 4. The device is provided with a main introduction passage 9 for connecting the first cell 5 and the second cell 6 in the horizontal direction, and a sub-introduction passage 10 inclined to an obliquely lower side from the gas passage 4 to connect the gas passage 4 and the second cell 6 on an upper side of the main introduction passage 9 and to make gas from the gas passage 4 flow in. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a curtain airbag device capable of controlling an inflating and deploying action.

As a curtain airbag device that covers a side window portion of a vehicle when an automobile collides, the one shown in Patent Document 1 is known. The curtain airbag shown in Patent Document 1 is provided with a gas passage through which an inflating and deploying gas ejected from an inflator flows from a gas introduction portion, and a gas passage is provided below the gas passage. A plurality of cells that are inflated and deployed from the bottom and inflated and deployed downward are provided adjacent to each other, and a communication passage that communicates each cell is provided below the curtain airbag. Each cell of Patent Document 1 has a gas intake port (inlet) of almost the same form with respect to the gas passage, and is formed in a form in which expansion and deployment gas can flow in from the adjacent cell by the lower communication passage. Yes. Accordingly, each cell expands downward from the cell closer to the gas introduction portion while being expanded at a time by the inflow of gas.
Japanese Patent Laying-Open No. 2005-96572 (FIG. 10)

  In the curtain airbag disclosed in Patent Document 1 that is deployed while being inflated in this manner, cells corresponding to the head position of the occupant (hereinafter referred to as “head position cell”) are also inflated at a stretch like other cells. While developing. Therefore, in the state where the head of the occupant is in contact with the window glass (head-on-glass state, hereinafter referred to as “HOG state”), the portion of the head position cell that is greatly expanded enters between the occupant head and the window glass. Therefore, there is a problem that the curtain airbag is deployed inside the vehicle at the head of the occupant and the occupant cannot be protected.

  The present invention was devised in view of the above conventional problems, and even if the occupant head is in the HOG state, the head position cell can be reliably deployed between the window glass and the occupant head. An object of the present invention is to provide a curtain airbag device capable of inflating and deploying the head position cell more quickly when the head of the passenger is not in the HOG state.

  A curtain airbag device according to the present invention is provided at an upper portion of a curtain airbag, and is provided with a gas passage through which an inflating and deploying gas generated by an inflator flows, and below the gas passage. A first cell that is inflated and expanded downward, and is provided below the gas passage adjacent to the first cell, and the gas is introduced from the first cell along the vehicle window glass. A curtain airbag device having a second cell that is inflated and deployed at a head position of the vehicle, wherein a main introduction path that connects the first cell and the second cell in a lateral direction; In order to inflate and deploy toward the window glass side of the head position, the gas passage and the second cell are inclined obliquely downward from the gas passage, and are connected above the main introduction passage. Sub-introduction path through which the gas flows Characterized in that is provided.

  It is preferable that the connecting portion of the sub-introduction passage with the gas passage and the connecting portion with the second cell are provided at a position where they do not overlap in the vertical direction.

  It is desirable that the minimum cross-sectional area of the sub-introduction path is set smaller than the minimum cross-sectional area of the main introduction path.

  In the curtain airbag device according to the present invention, even if the occupant head is in the HOG state, the head position cell can be reliably deployed between the window glass and the occupant head, When the occupant head is not in the HOG state, the head position cell can be inflated and deployed more quickly.

  Hereinafter, a preferred embodiment of a curtain airbag device according to the present invention will be described in detail with reference to the accompanying drawings. As shown in FIGS. 1 to 3, the curtain airbag device according to the present embodiment corresponds to the side window of a three-row seat vehicle (such as a wagon car) and is installed along the side roof inner panel of the vehicle. Is done. Hereinafter, in the present embodiment, “front” refers to the front of the vehicle, “rear” refers to the rear of the vehicle, “upper” refers to the vehicle ceiling, “lower” refers to the vehicle floor, and “lateral” Means the longitudinal direction of the vehicle. The outline outline of the curtain airbag 2 in the illustrated example is roughly formed in a laterally long rectangular shape corresponding to the vehicle, and has a height dimension that covers the window glass G from the ceiling side edge of the passenger compartment. A protrusion 2a for attachment to the vehicle is appropriately formed on the upper peripheral edge of the curtain airbag 2. The curtain airbag device 1 mainly includes a curtain airbag 2 formed in a bag shape, and an inflator 3 for introducing a gas for inflating and deploying (hereinafter referred to as “deployed gas”) into the curtain airbag 2 to deploy and inflate it. With.

  The curtain airbag 2 is formed into a sheet shape with a well-known material having soft flexibility so that the curtain airbag 2 can be wound and folded. The curtain airbag 2 is formed, for example, as a woven fabric or a knitted fabric. As will be described later, the curtain airbag 2 is formed with a sleeve-like gas passage 4 and cells 5 to 8 for protecting passengers. These gas passages 4 and the cells 5 to 8 and the like may be formed integrally with the curtain airbag 2 by weaving or knitting when the curtain airbag 2 is formed, or two base fabrics are stacked. You may make it form by joining these base fabrics suitably after match | combining.

  On the upper side of the curtain airbag 2, a sleeve-like gas passage 4 is formed along the lateral direction. The sleeve-like gas passage 4 into which an inflating and deploying gas (hereinafter simply referred to as “gas”) flows is formed. In the gas passage 4, a dividing portion 4 c is formed for attaching the inflator 3. The dividing portion 4c is provided at a position where the gas passage 4 is divided forward and backward. The dividing portion 4c in the present embodiment is provided corresponding to the position of the C pillar slightly behind the center of the gas passage 4. A gas guide 30 for introducing the gas from the inflator 3 into the gas passage 4 is disposed in the dividing portion 4c. The gas guide 30 is formed in a T shape by a main pipe connected to the inflator 3 and a pair of branch pipes inserted into the gas passage 4 from the dividing portion 4c. The gas guide 30 is attached to the curtain airbag 2 by fastening each branch pipe to the gas passage 4 with a ring-shaped bracket or the like. The gas passage 4 guides the inflowing gas laterally above the passenger head M. The cells 5 to 8 are provided below the gas passage 4.

  Each of the cells 5 to 8 of the curtain airbag 2 in the present embodiment includes a plurality of first cells 5, second cells 6 and independent cells 7 adjacent to the first cells 5, and connection cells 8. The first cell 5 is formed in the vertical direction below the gas passage 4. The first cell 5 is connected to the gas passage 4 through a connection port 5a, and is formed from immediately below the gas passage 4 to the vicinity of the lower peripheral edge of the curtain airbag 2. The first cell 5 is formed in front of or behind the passenger's head position H (hereinafter simply referred to as “head position H”). In the present embodiment, the “head position H” means an area in which the head M of the passenger fixed to the seat by the seat belt can move. In the curtain airbag 2 in the present embodiment, three first cells 5 are formed at intervals in the front portion, the central portion, and the rear portion, respectively. The first cell 5 is directly connected to the gas passage 4, and expands and develops downward with the gas flowing in from the gas passage 4. The first cell 5 can be easily expanded downward along the window glass G without being obstructed by the passenger head M. The first cell 5 may be in any form such as being inclined in the horizontal direction as long as it is in the vertical direction.

  A side portion of each first cell 5 is connected to a side portion of each adjacent second cell 6 by a main introduction path 9 described later. The first cell 5 expands downward along the window glass G of the vehicle by the gas from the gas passage 4 to protect the passenger and at the same time has a function as a chamber for introducing the gas into the second cell 6.

  The second cell 6 is formed in the vertical direction immediately below the gas passage 4 and adjacent to the first cell 5. The second cell 6 is formed adjacent to the dividing portion 4 c side of the first cell 5. The second cell 6 in the present embodiment is a “head position cell” corresponding to the head position H. The curtain airbag 2 in the present embodiment is formed with three second cells 6 one by one corresponding to the occupant at the front, center, and rear portions. The second cell 6 has a one-to-one relationship with the first cell 5. However, a plurality of first cells 5 may be provided for one second cell 6. The second cells 6 in the front part and the center part of the curtain airbag 2 are formed on the rear side of the adjacent first cell 5, that is, on the dividing part 4c side, and the second cell 6 in the rear part is adjacent to the second cell 6. It is formed on the front side of one cell 5, that is, on the dividing portion 4c side. The second cell 6 has a function of protecting the occupant head M by expanding the gas from the first cell 5 toward the window glass G at the head position H. If the 2nd cell 6 can protect the passenger | crew head M, the shape will not be limited. The side surfaces of the second cell 6 and the first cell 5 adjacent to the second cell 6 are connected in the lateral direction by the main introduction path 9. The main introduction path 9 in the present embodiment is formed in a form in which an opening provided on the side surface of the first cell 5 is shared as an opening on the side surface portion of the second cell. The second cell 6 adjacent to each first cell 5 by the main introduction path 9 is formed as an integral cell. The main introduction path 9 has the function of causing the gas that has flowed into the first cell 5 to flow into the second cell 6, inflating and deploying the second cell 6 in the lateral direction, and positioning the head cell H toward the window glass G side. have.

  A sub-introduction path 10 is provided in the second cell 6. The sub introduction path 10 is provided above the main introduction path 9 and below the gas passage 4. The sub-introduction path 10 is provided so as to be inclined obliquely downward from the gas passage 4 to connect the gas passage 4 and the second cell 6. The sub-introduction channel 10 is formed in an elongated sleeve shape that is inclined forward and downward with respect to the flow direction of gas flowing into the gas passage 4 on the upper side of the second cell 6 to be connected (hereinafter referred to as “gas traveling direction”). The gas is introduced from the gas passage 4 and the sub-introduction path 10 is obliquely positioned at the head position H. In the curtain airbag 2 in the present embodiment, a total of three sub-introduction paths 10 are formed one above the second cells 6. The sub-introduction paths 10 at the front part and the center part of the curtain airbag 2 are formed so as to be inclined forward and downward, that is, downward in the gas traveling direction. On the other hand, the sub-introduction path 10 at the rear part of the curtain airbag 2 is formed to be inclined rearward and downward, that is, downward in the gas traveling direction. The sub-introduction path 10 is not limited in its overall shape as long as it has an inclined path having a length. That is, the sub-introduction path 10 may have a bent portion, and the cross-sectional shape thereof may change midway.

  The connection port 10a (hereinafter referred to as “upper connection port 10a”) and the connection port 10b (hereinafter referred to as “lower connection port 10b”) of the second cell 6 of the sub introduction path 10 in the present embodiment are connected to each other. It arrange | positions so that it may not overlap in an up-down direction (refer FIG. 3). In the present embodiment, “so as not to overlap in the vertical direction” means that the front end portion α of the upper connection port 10a is located behind the rear end portion β of the lower connection port 10b. Thereby, the subintroduction path 10 is formed in an elongated tube shape extending in an oblique direction. For this reason, the auxiliary introduction path 10 is likely to be blocked when the occupant head M is in the HOG state. By closing the sub-introduction path 10, the pressure in the sub-introduction path 10 rises when the gas flows in, and the force to separate the occupant head M from the window glass G is secured and the HOG state can be easily eliminated. Gas easily flows into the first cell 5 that has not risen, and the expansion and expansion of the first cell 5 is promoted. Further, when the HOG state is released or not in the HOG state, the gas flowing from the gas passage 4 into the sub introduction path 10 is introduced obliquely along the gas traveling direction, so that the resistance is reduced and the gas is sub introduced. It circulates through the path 10 reliably and smoothly.

  The upper connection port 10a of this embodiment is arrange | positioned from the connection port 5a at the parting part 4c side. That is, the upper connection port 10a and the connection port 5a are formed in the gas passage 4 sequentially from the dividing portion 4c side in the gas traveling direction. Therefore, the sub introduction path 10 can start the inflow of gas before the first cell 5 and the second cell 6. On the other hand, the lower connection port 10 b of this embodiment is provided adjacent to the main introduction path 9 of the second cell 6. For this reason, the expansion and deployment of the second cell 6 by the gas from the sub introduction path 10 and the expansion and deployment of the second cell 6 by the gas from the main introduction path 9 can be performed in the same direction (lateral direction). Thereby, the 2nd cell 6 can be expanded and expanded from the 1st cell 5 side expand | deployed below along the window glass G, and it becomes easy to expand and expand the 2nd cell 6 to the window glass G side of the head position H.

  The minimum cross-sectional area of the sub introduction path 10 in the present embodiment is set smaller than the minimum cross-sectional area of the main introduction path 9. The minimum cross-sectional area of the sub-introduction passage 10 is set smaller than the cross-sectional area of the gas passage 4, and the minimum cross-sectional area of the main introduction passage 9 is set larger than the cross-sectional area of the gas passage 4. The minimum cross-sectional area of the main introduction path 9 is the minimum inner cross-sectional area of the portion into which the gas flows. For this reason, the amount of gas inflow from the auxiliary introduction path 10 to the second cell 6 is smaller than the amount of gas inflow from the main introduction path 9 to the second cell 6. Therefore, the second cell 6 performs preliminary expansion and expansion with the gas from the sub-introduction path 10 and performs main expansion and expansion with the gas from the main introduction path 9. Further, the flow velocity of the gas passing through the sub-introduction passage 10 becomes faster than the flow velocity of the gas passing through the main introduction passage 9, and accordingly, the pressure of the gas passing through the sub-introduction passage 10 is also increased accordingly.

  The connection cell 8 in this embodiment is a wide tube-like cell in which the gas passage 4 is extended. The connection cell 8 is directly connected to the gas passage 4 and extends downward from above, and is formed to extend laterally along the lower peripheral edge on the lower side of the curtain airbag 2. The extended end of the connected cell 8 is connected to the independent cell 7 and the second cell 6. The connected cell 8 has a function of protecting a passenger while securing a passage for supplying gas to the independent cell 7 and the second cell 6. In the curtain airbag 2 of the present embodiment, two connection cells 8 are formed. One connecting cell 8 is formed downward between the second cell 6 at the front portion and the second cell 6 at the central portion, and extends laterally along the lower peripheral portion of the curtain airbag 2. It is formed in an “inverted T shape”. The second cell 6 and the independent cell 7 at the front portion of the curtain airbag 2 are connected to the end portion of the “inverted T-shaped” connection cell 8 extending in the forward direction, and the end portion extending backward is The first cell 5 at the center of the curtain airbag 2 is connected. The other connecting cell 8 is formed to be inclined slightly rearward between the second cell 6 at the center of the curtain airbag 2 and the second cell 6 at the rear, and the lower peripheral portion of the curtain airbag 2. And is formed in an “inverted L shape” extending forward. The end portion extending forward of the “inverted L-shaped” connection cell 8 is connected to the second cell 6 at the center of the curtain airbag 2 and the independent cell 7 below it.

  The independent cell 7 is formed around the second cell 6. The independent cell 7 is a bag-like cell connected to the connected cell 8 and is not connected to cells other than the connected cell 8. The independent cell 7 has a function of inflating and expanding with the gas from the connection cell 8 to protect the occupant. The independent cell 7 expands and develops later than the other cells. Accordingly, the curtain airbag 2 can quickly inflate and deploy other cells that are more important for passenger protection.

  Next, the operation of the curtain airbag device 1 according to the present embodiment will be described. First, in the case where the occupant head M is not in the HOG state, a basic inflating and deploying operation of the curtain airbag device 1 will be described. When the inflator 3 is activated, gas flows into the gas passage 4 of the curtain airbag 2 through the gas guide 30. Gas flows from the gas passage 4 into the sub introduction path 10, the first cell 5, and the connection cell 8. As each first cell 5 and each connected cell 8 is inflated and deployed, the curtain airbag 2 is deployed from above to below. During this expansion and expansion, the upper connection port 10a of the sub-introduction channel 10 is formed before the connection port 5a of the first cell 5 in the gas traveling direction. Gas flows in before the expansion and deployment. Due to the gas from the sub-introduction path 10, the second cell 6 starts to expand and deploy. Following the inflow of gas from the sub-introduction path 10, the first cell 5 starts to expand and expand, and the gas also flows from the main introduction path 9 into the second cell 6. Since the minimum cross-sectional area of the sub-introduction path 10 is smaller than the minimum cross-sectional area of the main introduction path 9, the gas from the sub-introduction path 10 performs the initial expansion and expansion of the second cell. The main gas expands and expands the second cell 6. Expansion and deployment of the second cell 6 is performed in the lateral direction from the first cell side. The connecting cell 8 is inflated and deployed in parallel with the expansion and deployment of the sub-introduction channel 10, the first cell 5, the main introduction channel 9 and the second cell 6, and then the independent cell 7 is inflated and deployed to curtain air bag. 2 expansion and deployment is completed.

  In the inflating and expanding operation, since the auxiliary introduction path 10 is formed in an elongated tube shape, there is little possibility of coming into contact with the occupant head M, and it is reliably between the occupant head M and the window glass G, that is, the head. Gas can be circulated to the window glass G side at the position H. Further, since the gas flows into the sub-introduction passage 10 prior to the first cell 5, the expansion and deployment of the second cell 6 is performed on the window glass G side at the head position H when the expansion of the first cell 5 is small. It is possible to start, and the development direction of the second cell can be guided in the direction along the window glass G in advance of the first cell 5. Therefore, it becomes possible for the second cell 6 to reliably start expansion and deployment toward the window glass G side of the head position H. Furthermore, since the gas is introduced into the second cell 6 through the two paths of the main introduction path 9 and the sub introduction path 10, the second cell 6 can be expanded and deployed more quickly.

  Next, a case where the sub-introduction path 10 is blocked due to the occupant head M being in the HOG state will be described. FIG. 4 shows an inflated and deployed state of the first cell 5, the second cell 6, the auxiliary introduction path 10, etc. in the front part of the curtain airbag 2 in a state where the auxiliary introduction path 10 is closed by the occupant head M. In FIG. 4, the arrows indicate the gas inflow direction. The gas flows into the gas passage 4 by the operation of the inflator 3, and the gas flows from the gas passage 4 into the auxiliary introduction passage 10, the first cell 5, and the connection cell 8 (FIG. 4A). Even if the sub-introduction path 10 is closed by the occupant head M, the sub-introduction path 10 is an elongated tube and is formed in an oblique direction, so that the contact point between the window glass G and the occupant head M is not reached. Gas can flow in (FIG. 4B). That is, the middle part (closed part) of the sub-introduction path 10 can be inflated and deployed and positioned on the window glass G side of the head position H. Since the sub-introduction channel 10 is formed obliquely in the gas traveling direction and gas easily flows in, the gas pressure is increased in a state where the intermediate portion is closed. For this reason, the pressure rise due to the inflow of gas from the gas passage 4 to the sub-introduction passage 10 causes the gap between the window glass G and the occupant head M to be spread like a wedge, and the occupant head M is inserted into the window glass. It is possible to float from G. As a result, the blockage of the sub-introduction path 10 is released, the gas flows to the window glass G side at the head position H, and the expansion and deployment of the second cell 6 can be guided to the window glass G side at the head position H. . At the same time, gas from the gas passage 4 via the first cell 5 and the main introduction path 9 flows into the second cell 6, and the second cell 6 expands and expands from the main introduction path 9 side (FIG. 4C). In the second cell 6, gas flows in from both the main introduction path 9 and the sub introduction path 10, and the expansion and expansion are completed quickly (FIG. 4D).

  A curtain airbag device 1 according to the present embodiment is provided at an upper portion of a curtain airbag 2 and is provided below a gas passage 4 into which an inflating and deploying gas generated by an inflator 3 flows and a gas passage 4. A first cell 5 that flows in and expands downward when gas is introduced from the passage 4, and is provided below the gas passage 4 adjacent to the first cell 5, and gas is introduced from the first cell 5 and window glass of the vehicle. A second cell 6 that inflates and expands to the head position H along G, and a main introduction path 9 that connects the first cell 5 and the second cell 6 in the lateral direction; In order to inflate and deploy toward the window glass G side at the position H, the gas passage 4 and the second cell 6 are inclined obliquely downward from the gas passage 4 so as to be connected to the upper side of the main introduction passage 9. Since the sub-introduction passage 10 into which the vehicle flows is provided, the occupant head M is in the HOG state. Even the second cell 6 to reliably can be inflated and deployed on a window glass G side of the head position H. Moreover, gas can be made to flow into the second cell 6 by two systems of the main introduction path 9 and the sub introduction path 10, and rapid expansion and expansion of the second cell 6 is ensured.

  In addition, since the connecting part of the sub-introduction path 10 to the gas passage 4 and the connecting part to the second cell 6 are provided at positions where they do not overlap with each other in the vertical direction, gas travels reliably in the sub-introduction path 10. It can be formed toward the front lower side with respect to the direction, and the gas can surely and promptly flow into the sub-introduction channel 10. Thereby, the space between the window glass G and the occupant head M can be surely expanded and the second cell 6 can be expanded and deployed in the direction of the window glass G at the head position H. Further, since the sub introduction path 10 is formed obliquely, the sub introduction path 10 is longer than simply formed in the vertical direction, and the time until the gas flows into the second cell 6 from the sub introduction path 10 is delayed. In the meantime, the first cell 5 is inflated and deployed downward along the window glass G, and the second cell 6 is inflated and deployed in the lateral direction mainly by the gas from the main introduction path 9. It becomes easy to inflate and deploy to the window glass G side of the head position H.

  Since the minimum cross-sectional area of the sub-introduction channel 10 is set smaller than the minimum cross-sectional area of the main introduction channel 9, the gas pressure is increased and the sub-introduction is reliably performed between the window glass G in the HOG state and the passenger head M. Road 10 can enter. The expansion and deployment of the second cell 6 is performed in the lateral direction mainly by the gas from the main introduction path 9. As a result, the function of smoothly inflating and deploying the second cell 6 to the window glass G side of the occupant's head position H can be secured, and the second cell 6 can be inflated and deployed more reliably to the window glass G side of the head position H. It can be made.

  The curtain airbag device described above is a preferred example of the present invention, and other embodiments can be implemented or performed by various methods. In particular, the present invention is not limited to the detailed shape, size, configuration, and the like of the components shown in the accompanying drawings unless otherwise stated in the present specification. In addition, expressions and terms used in the present specification are for the purpose of explanation, and are not limited thereto unless otherwise specified.

1 is a side view showing a preferred embodiment of a curtain airbag device according to the present invention. It is the (a) side view and (b) front view for demonstrating the relationship between the 2nd cell and passenger | crew head of the front part of the curtain airbag shown in FIG. FIG. 2 is an enlarged side view of a sub introduction path portion at a front portion of the curtain airbag shown in FIG. 1. It is a figure explaining the expansion | deployment deployment condition in the curtain airbag apparatus shown in FIG. 1 when a passenger | crew's head is in a HOG state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Curtain airbag apparatus 2 Curtain airbag 3 Inflator 4 Gas passage 5 1st cell 6 2nd cell 9 Main introduction path 10 Sub introduction path H Position of occupant's head G Vehicle window glass

Claims (3)

A gas passage provided at an upper portion of the curtain airbag and into which a gas for inflation and deployment generated by an inflator flows, and a gas passage provided below the gas passage and inflated and deployed downward when the gas is introduced from the gas passage. A first cell and a second cell adjacent to the first cell and below the gas passage; the gas flows from the first cell and expands and deploys along a vehicle window glass to a passenger's head position; A curtain airbag device having a cell,
A main introduction path for connecting the first cell and the second cell in the lateral direction;
In order to inflate and deploy the second cell toward the window glass side of the head position of the occupant, the gas passage and the second cell are inclined upwardly from the gas passage so that the gas passage and the second cell are located above the main introduction passage. A curtain airbag device, characterized in that a curtain air bag device is provided which is connected to a sub-introduction passage through which the gas from the gas passage flows.   2. The curtain airbag device according to claim 1, wherein a connecting portion of the sub-introduction passage with the gas passage and a connecting portion with the second cell are provided at a position where they do not overlap in the vertical direction. .   The curtain airbag device according to claim 1 or 2, wherein a minimum cross-sectional area of the sub-introduction path is set smaller than a minimum cross-sectional area of the main introduction path.

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