JP7381256B2 - grommet - Google Patents

Description

The present invention relates to a grommet that protects a wire harness passing through a panel.

Various vehicles such as automobiles, ships, and aircraft are divided into multiple spaces by panels made of steel, etc., and equipment placed in different spaces can be connected using wire harnesses that pass through holes formed in the panels. It is supposed to connect. When wiring a wire harness through a through hole in such a panel, a grommet is installed in the through hole to prevent damage to the wire harness due to contact with the panel, and to prevent noise, water, dust, etc. from coming from the through hole. It is designed to prevent intrusion. For example, in a vehicle such as a car, the passenger compartment and engine room are separated by a vehicle body panel such as a dash panel, and a wire harness may be inserted through the cylindrical part of a grommet attached to a through hole formed in the dash panel. Therefore, as a power supply source installed in the engine room, a battery is connected to various electrical devices placed in the passenger compartment to supply power (for example, Patent Document 1).

In addition to the main penetrating cylindrical part (penetrating pipe part) through which the wire harness is inserted, as described above, wire harnesses and piping are inserted separately into this grommet as necessary, such as when adding equipment to the passenger compartment. Some devices have an auxiliary cylindrical section (one-sided closed tube section) that increases expandability. Such an auxiliary tubular part is formed with one end closed, and when the auxiliary tubular part is not in use, it separates the inside and outside of the vehicle body panel to prevent sounds from outside the vehicle from entering the inside of the vehicle. At the same time, if necessary, such as when adding equipment, the closed end is cut and necessary wire harnesses and piping are inserted into the auxiliary tubular part.

Japanese Patent Application Publication No. 2016-159890

However, although a grommet with an auxiliary tubular part can improve its expandability, when the auxiliary tubular part is not used, it may be affected by the driving noise of the engine or motor, which is the power source, and the load during driving. Noise, etc. enters the inside of the auxiliary tubular part from the open end, and the sound generated by the resonance phenomenon in the auxiliary tubular part is transmitted to the passenger compartment, causing discomfort to passengers and impairing the quietness of the cabin. Become. Although such a resonance phenomenon can be prevented by attaching a silencer such as that disclosed in Patent Document 1 to the open end of the auxiliary cylindrical part, it is necessary to prepare and attach a silencer separately. This makes the work complicated, and there is also concern that the silencer may fall off due to vibrations while driving.

That is, an object of the present invention is to provide a grommet having a one-sided closed pipe portion that can suppress discomfort caused by resonance phenomena.

In order to overcome the above problems and achieve the intended purpose, the first means is to:
A grommet attached to a through hole formed in a panel,
A frustum-shaped frustum portion whose inner diameter gradually decreases;
a penetrating tube portion provided on the small diameter side of the frustum portion and open at both ends, through which the cord-like body can be inserted;
a panel engaging portion provided on the large diameter side of the frustum portion and engaged with an inner peripheral edge of the through hole;
a one-sided closed pipe part provided in the frustum part and having one end closed,
The gist is that the tube length from the closed part to the open end of the one-sided closed tube section is formed to a length such that the resonance frequency of the one-sided closed tube section is 2,000 Hz or less or 4,000 Hz or more.
In this way, by forming the single-side closed tube section so that the tube length from the closed section to the open end is 20 mm or less or 45 to 60 mm, the resonant frequency of the single side closed tube section can be set to 2,000 Hz or less or 4,000 Hz or less. 000Hz or higher. As a result, it is possible to make it difficult to hear the sound generated by the resonance phenomenon in the one-side closed pipe section, so that the discomfort caused to personnel can be reduced without using a separate component such as a muffler. Furthermore, since there is no need to use a muffler, it is possible to improve the work of attaching the grommet to the panel, and it is possible to reduce unnecessary materials generated when using the one-sided closed pipe section when adding equipment.

The second means is
The gist is that the one-side closed tube section is formed to be expandable and contractible, and the length of the tube in the shortened state is such that the resonance frequency of the one-side closed tube section is 2,000 Hz or less or 4,000 Hz or more. do.
In this way, since the one-side closed tube section is expandable and retractable, the sound generated by the resonance phenomenon can be made difficult to hear by shortening the one-side closed tube section when not in use, and the one-side closed tube section can be shortened when not in use. By putting the tube in an expanded state, it is possible to improve the retention of wire harnesses, piping, etc. that are inserted into the one-side closed tube section.

The third means is
The one-side closed tube section includes a base tube section that connects to the truncated cone section, a closed tube section whose protruding end side is closed by the closing section, and a connecting tube section that connects the base tube section and the closed tube section,
A first state in which the connecting pipe portion is located so as to be connected to the outside of the base pipe portion, and a second state in which the connecting pipe portion is located inside the base pipe portion so as to be reversed from the first state. The gist is that the tube length of the one-side closed tube portion can be expanded and contracted by deforming the tube to the state shown in FIG.
In this way, the length of the one-sided closed tube section can be easily changed by pushing the closed tube section into or out of the base tube section.

The fourth means is
The gist of the one-sided closed tube section is that the length of the tube can be expanded and contracted at both end sides of the closed end and the open end that are closed by the closed section.
In this way, by making the tube length expandable and retractable at both the closed end and the open end, it is possible to shorten the one side closed tube section when not in use, making it difficult to hear the sound generated by the resonance phenomenon. When in use, by putting the one-sided closed tube section in an expanded state, it is possible to improve the retention of wire harnesses, piping, etc. that are inserted through the one-sided closed tube section.

According to the present invention, it is possible to suppress discomfort due to a resonance phenomenon in the one-side closed tube portion when not in use.

1 is a schematic diagram of a vehicle equipped with a grommet according to the present invention. FIG. 2 is a schematic perspective view of a grommet according to a first embodiment. FIG. 2 is a longitudinal cross-sectional view of a grommet according to a first example. FIG. 2 is a graphical diagram showing an isocloud curve. FIG. 6 is an enlarged vertical cross-sectional view of the main part of the grommet according to the second embodiment, in which (a) shows a state in which the one-sided closed pipe section is in a reference state, and (b) shows a state in which the one-sided closed pipe section is shortened. Indicates the state of the state. FIG. 7 is an enlarged vertical cross-sectional view of the main part of the grommet according to the third embodiment, in which (a) shows a state in which the one-sided closed pipe section is in a reference state, and (b) shows both ends of the one-sided closed pipe section. Shows the shortened state.

Next, the grommet of the present invention will be described below with reference to the accompanying drawings. In this embodiment, a grommet that is attached to a through hole provided in a dash panel of a vehicle such as an automobile will be exemplified and explained.

(First example)
As shown in FIG. 1, this grommet 10 is connected to a wire harness WH that is wired through a through hole 50a provided in a dash panel 50 that separates the engine room ER provided in front of the vehicle interior HR of the automobile MT from the inside of the vehicle interior HR. It is made of an elastic body that can be elastically deformed, such as EPDM rubber. As shown in FIG. 2 or 3, this grommet 10 includes a frustum-shaped frustum portion 12 whose inner diameter gradually decreases, and a frustum portion 12 extending in the axial direction of the frustum portion 12 from the small-diameter end of the frustum portion 12. It is provided with a penetrating tube part 14 provided so as to protrude. This penetrating tube part 14 is formed in a cylindrical shape with an open protruding end and both ends that are open so as to be connected to the inside of the frustum part 12 at the proximal end side connected to the frustum part 12. The base portion 12 and the penetrating tube portion 14 form a funnel shape. Thereby, the wire harness WH passed through the inside of the frustum portion 12 from the engine room ER side can be inserted into the penetrating tube portion 14 and wired to the vehicle interior HR side.

In addition, this grommet 10 is provided with an annular large-diameter portion 16 that is formed in a larger diameter than the through hole 50a of the dash panel 50 at the end of the large-diameter side of the frustum portion 12. A groove-shaped panel engaging portion 18 that can be engaged with the inner circumferential edge of the through hole 50a of the dash panel 50 is provided between the large diameter side end portion of the dash panel 12 and the large diameter portion 16. Here, the outer peripheral edge of the large-diameter end of the frustum portion 12 is formed to have a larger diameter than the through-hole 50a of the dash panel 50, and the panel engaging portion 18 has a diameter that is approximately the same as that of the through-hole 50a. It is formed by the diameter. That is, when the small diameter side (penetrating tube part 14) of the frustum part 12 is inserted into the through hole 50a from one side of the dash panel 50 (for example, the engine room ER side), the frustum part 12 is elastically deformed. The grommet 10 is attached to the dash panel 50 by engaging the inner peripheral edge of the through hole 50a with the panel engaging portion 18. In this way, by inserting the wire harness WH through the grommet 10 attached to the through hole 50a of the dash panel 50, the wire harness WH is protected from the edge of the through hole 50a of the dash panel 50, and the wire harness WH is protected from the edge of the through hole 50a of the dash panel 50. This prevents water, dust, etc. from entering the vehicle interior through the

Further, the frustum portion 12 of the grommet 10 is provided with a one-side closed tube 20 having one end closed so as to extend in the axial direction of the frustum portion 12 . This one-sided closed tube 20 extends in the axial direction of the frustum portion 12 so as to be connected to the outer surface side (smaller diameter side) of the frustum portion 12, and has a closed tube portion 24 whose protruding end side is closed by the closing portion 22. , an open tube part 26 extending in the axial direction of the frustum part 12 so as to be connected to the inner surface of the frustum part 12 and having both ends open. That is, the single-sided closed tube 20 is formed so that the closed tube section 24 and the open tube section 26 communicate with each other, and one end is closed by the closed section 22 to form a closed tube. Further, the closing tube section 24 is provided with a flange section 28 that projects outward in the radial direction in an annular shape at a projecting end of the closing tube section 24 and at a position spaced apart from the projecting end toward the proximal end. There is. The closing portion 22 of the closing tube portion 24 is provided so as to be located closer to the protruding end of the closing tube portion 24 than between the two flange portions 28, and one side is closed in the gap 28a between the two flange portions 28. By cutting the pipe 20, the closed portion 22 can be removed and the wire harness WH and other piping can be inserted into the single-sided closed pipe 20.

This one-side closed tube 20 is a closed tube whose one end is closed with a closed section 22, and a resonance phenomenon occurs when sound enters from the open end (the end of the open tube section 26). Here, the sounds that humans can hear (audible range) are generally in the frequency range of 20Hz to 20,000Hz, and the human hearing senses the perceived loudness depending on the frequency even if the physical sound pressure is the same ( It is known that the loudness) is different. Equal loudness curves representing the relationship between frequencies and sound pressures that humans perceive as equal sound loudness have been standardized in the international standard ISO 226:2003 (see FIG. 4). In other words, this equal loudness curve shows that human ears can easily hear sounds in the audible range, particularly in the frequency range of 2,000 Hz to 4,000 Hz. In other words, sounds with frequencies in the range of 2,000Hz to 4,000Hz are easily perceived by people, even if the sound pressure is small, and can impair quietness and cause discomfort to people. I understand.

Therefore, in the grommet 10 according to the present invention, the pipe length L of the one-sided closed pipe 20 (the length from the inner surface of the closed part 22 to the open end of the open pipe part 26) is determined by the resonance caused by the sound incident on the one-sided closed pipe 20. The frequency f (Hz) is set so that F<2,000Hz or F>4,000Hz. Here, the resonant frequency f (Hz) of a closed tube with one end closed is expressed by the formula (1): f= It can be determined by (2n-1)V/4L. Table 1 shows the relationship between the pipe length L and the resonant frequency in a standard environment (standard atmosphere (1 atm, 15°C), sound velocity V = 340 m/s) in which a vehicle in which the grommet 10 of the present invention is used is used. show.

That is, by forming the one-side closed pipe 20 of the grommet 10 so that the pipe length L is in the range of L≦20 mm, 45 mm≦L≦60 mm, the single-side closed pipe 20 is formed to have a length in the standard atmosphere when not in use. The resonance frequency of the single-sided closed tube 20 can be set to 2,000 Hz or less or 4,000 Hz or more. Specifically, in this embodiment, the pipe length L is 60 mm. Thereby, it is possible to make it difficult to hear the sound generated by the resonance phenomenon in the one-side closed pipe 20, and as a result, it is possible to suppress the discomfort given to the occupants, and it is possible to improve the quietness in the vehicle interior HR. That is, the discomfort caused to the occupant can be suppressed without attaching a separate component such as a muffler to the grommet 10. Furthermore, since there is no need to use a muffler, the grommet 10 can be easily attached to the panel, and unnecessary materials generated when using the one-side closed pipe 20, such as when adding equipment, can be reduced. Furthermore, since there is no need to attach a muffler to the one-sided closed pipe 20, problems such as the muffler falling off due to external factors such as vibrations during running do not occur, and good quietness can be maintained.

(Second example)
Next, a grommet according to a second embodiment will be explained. The basic configuration of the grommet according to the second embodiment is basically the same as the configuration of the grommet 10 according to the first embodiment described above, but differs in the configuration of the one-side closed pipe 20. Therefore, in the following description, configurations different from the grommet 10 according to the first embodiment will be explained, and common configurations will be given the same reference numerals and explanations will be omitted.

The one-sided closed pipe part 30 of the grommet 10 according to the second embodiment is a base pipe that extends in the axial direction of the frustum part 12 and is open at both ends so as to be connected to the outer surface side (small diameter side) of the frustum part 12. 32 , a closed pipe part 34 whose protruding end side is closed by the closed part 22 , and a connecting pipe part 36 that connects the base pipe part 32 and the closed pipe part 34 . The base tube section 32, the closed tube section 34, and the connecting tube section 36 are formed to form a series of cylinders that communicate with each other. That is, the connecting tube section 36 is provided to connect the open end (projecting end) of the base tube section 32 and the open end of the closed tube section 34. Note that the base tube section 32, the closed tube section 34, and the connecting tube section 36 are formed so that their axes coincide with each other. Further, on the inner surface side of the frustum portion 12, an open tube portion 26 whose both ends are open is provided, as in the first embodiment, and the open tube portion 26 communicates with the base tube portion 32. It is formed to form a closed tube with one end closed by a closing portion 22 .

Here, the connecting tube section 36 is formed so that its outer diameter is smaller than the inner diameter of the base tube section 32, and the closing tube section 34 is formed so that its outer diameter is smaller than the inner diameter of the connecting tube section 36. ing. That is, in the reference state (first state, see FIG. 5(a)) in which the connecting pipe part 36 is located so as to be connected on the outside of the base pipe part 32, the closed pipe part 34 is placed on its protruding end side (closed end side). By pushing the connecting tube portion 36 toward the proximal end side, the connecting tube portion 36 is reversed and located inside the base tube portion 32, and the closed tube portion 34 is located inside the reversed connecting tube portion 36 (the shortened state). 2 (see FIG. 5(b)), and in this second state, by pulling out the closed tube section 34 from its proximal end side toward the protruding end side (closed end side), the connecting tube The portion 36 can be deformed to a reference state in which the portion 36 is connected to the outside of the base tube portion 32. In this way, the one-side closed tube 20 of the grommet 10 according to the second embodiment is capable of expanding and contracting its tube length L. Further, the flange portion 28 provided on the protruding end side of the closing tube portion 34 is located outside the base tube portion 32 and the connecting tube portion 36 in the shortened state, and when the flange portion 28 is pinched, the closing tube portion 34 It is designed so that it can be easily pulled out.

The one-side closed pipe 20 of the grommet 10 according to the second embodiment is formed so that the pipe length L in the shortened state is in the range of L≦20 mm, 45 mm≦L≦60 mm, and specifically In the embodiment, the pipe length L in the shortened state is set to 50 mm. By setting the pipe length L of the single-sided closed tube 20 as described above, the resonance frequency of the single-sided closed tube 20 in standard atmosphere when the single-sided closed tube 20 is not in use can be set to 2,000 Hz or less or 4,000 Hz or more. I can do it. As a result, by shortening the single-sided closed pipe 20 when not in use, it is possible to make it difficult to hear the sound generated by the resonance phenomenon in the single-sided closed pipe 20, and as a result, the discomfort caused to the occupants is suppressed. At the same time, the quietness of the room can be improved, and other effects similar to those of the grommet 10 according to the first embodiment can be expected. When the wire harness WH, piping, etc. are inserted through the single-sided closed pipe 20 when equipment is added, etc., the single-sided closed pipe 20 is brought into the standard state (stretched state), thereby ensuring a sufficient length of the single-sided closed pipe 20. This makes it possible to improve the retention of the wire harness WH, piping, etc. that are inserted into the one-side closed pipe 20. Further, by pushing the occlusion tube section 34 into or out of the base tube section 32, the length of the one-sided occlusion tube 20 can be easily changed, and work efficiency can be improved.

(Third example)
Next, a grommet 10 according to a third embodiment will be explained. The basic configuration of the grommet 10 according to the third embodiment is basically the same as the configuration of the grommet according to the second embodiment described above, but differs in the configuration of the one-side closed tube. Therefore, in the following description, configurations different from the grommet 10 according to the second embodiment will be explained, and common configurations will be given the same reference numerals and explanations will be omitted.

The one-side closed pipe 40 of the grommet 10 according to the third embodiment is configured such that the pipe length L can be changed at both the closed end side and the open end side closed by the closing part 22. Specifically, the one-sided closed pipe 40 of this grommet 10 has a base pipe part 32, a closed pipe part 34, and a connecting pipe part 36 (hereinafter referred to as In the third embodiment, a first connecting pipe section) is provided. In addition, in the following explanation, a reference state in which the first connecting pipe part 36 is located so as to be connected on the outside of the base pipe part 32 will be referred to as a first reference state, and a reference state in which the first connecting pipe part 36 is inverted and connected to the base pipe part 32 will be referred to as a first reference state. A shortened state in which the closed pipe part 34 is located inside the section 32 and inside the inverted first connecting pipe part 36 is referred to as a first shortened state.

Then, on the inner surface side of the frustum part 12, there is a first open pipe part 42 connected to the frustum part 12, and a first open pipe part 42 that is provided at the protruding end of the first open pipe part 42 in the axial direction of the frustum part 12. A second connecting pipe part 44 extending in the axial direction of the frustum part 12 is provided at the protruding end of the second connecting pipe part 44 and a second open pipe part 46 extending in the axial direction of the frustum part 12. ing. Each of the first open tube section 42, the second connecting tube section 44, and the second open tube section 46 has the same axis and is open at both ends to form a series of mutually communicating cylinders. At the same time, the first open tube section 42 is formed to communicate with the base tube section 32 to form a closed tube in which one end of the one-side closed tube 40 is closed by the closing section 22 .

Here, the second connecting pipe part 44 is formed so that its outer diameter is smaller than the inner diameter of the first open pipe part 42, and the second open pipe part 46 is formed so that its outer diameter is smaller than the inner diameter of the first open pipe part 42. The inner diameter of the connecting pipe portion 44 is smaller than that of the connecting pipe portion 44 . That is, in the second reference state (third state, see FIG. 6(a)) in which the second connecting pipe part 44 is located so as to be connected to the outside of the first open pipe part 42, the second open pipe part 44 is connected to the first open pipe part 42. By pushing the section 46 from its protruding end side (open end side) toward the proximal end side, the second connecting tube section 44 is inverted and located inside the first open tube section 42, and the inverted state is It can be transformed into a second shortened state (fourth state, see FIG. 6(b)) in which the second open pipe part 46 is located inside the second connecting pipe part 44, and in this second state, By pulling out the second open tube section 46 from its proximal end side toward the protruding end side, the second connecting tube section 44 is transformed into a second reference state where it is connected outside the first open tube section 42. I'm starting to get it. In this way, the one-side closed tube 40 of the grommet 10 according to the third embodiment is capable of expanding and contracting the tube length L at both ends (closed end and open end). Further, a flange portion 48 that protrudes radially outward in an annular shape is provided on the protruding end side of the second open tube portion 46, and this flange portion 48 is in the second shortened state when the first open tube portion 46 is in the first open state. It is located outside the tube section 42 and the second connecting tube section 44, and the second open tube section 46 can be easily pulled out by pinching the flange section 48.

The one-side closed tube 40 of the grommet 10 according to the third embodiment has a tube length L of L≦20 mm, 45 mm≦L≦60 mm, at least in either the first shortened state or the second shortened state. It is formed to have a range of length. Specifically, in this embodiment, the pipe length L in the first shortened state and the second shortened state is 50 mm. By setting the pipe length L of the single-sided closed pipe 40 as described above, the resonance frequency of the single-sided closed pipe 40 in standard atmosphere when the single-sided closed pipe 40 is not in use can be set to 2,000 Hz or less or 4,000 Hz or more. I can do it. As a result, by shortening the single-sided closed pipe 40 when not in use, it is possible to make it difficult to hear the sound generated by the resonance phenomenon in the single-sided closed pipe 40, and as a result, the discomfort caused to the occupants is suppressed. At the same time, the quietness of the room can be improved, and other effects similar to those of the grommet 10 according to the first embodiment can be expected. When the wire harness WH, piping, etc. is inserted through the single-sided closed pipe 40 when adding equipment, etc., the single-sided closed pipe 40 is placed in the first reference state and the second reference state (extended state), so that the single-sided closed pipe 40 is closed. A sufficient length of the tube 40 can be ensured, and the retention of the wire harness WH, piping, etc. inserted through the one-side closed tube 40 can be improved. Furthermore, the length of the single-sided closed tube 40 can be reduced by pushing or pulling out the closed tube section 34 into the base tube section 32 or the second open tube section 46 into the first open tube section 42. It can be easily changed and the workability can be improved.

In addition, the pipe length can be changed at both the closed end side and the open end side of the single-sided closed pipe 40, and the shortened state (first shortened state or second shortened state) can be changed by operating one end side. When the resonant frequency of the one-sided closed tube 40 is set to 2,000 Hz or less or 4,000 Hz or more by doing so, both ends are operated to shorten the tube (first shortened state and second shortened state). The workability of installing the grommet 10 can be further improved compared to the case where the grommet 10 is installed. In addition, in the configuration in which both ends of the single-sided closed tube 40 are operated to shorten the state (first shortened state and second shortened state), the single-sided closed tube 40 can be made more compact when not in use, and one side closed tube 40 can be made more compact when not in use. The obstruction tube 40 can be prevented from interfering with other structural members.

(Example of change)
The present invention is not limited to the configuration of the embodiment described above, and may be modified as follows, for example.
(1) Although a configuration in which the grommet is provided with one one-side closed tube is illustrated, the present invention is not limited to this, and a plurality of one-sided closed tubes may be provided. Further, the plurality of one-sided closed pipe parts included in the grommet do not need to have the same configuration, and may be different, such as the one-sided closed pipe part 20 according to the first embodiment and the one-sided closed pipe part 30 according to the second embodiment. A one-sided closed tube portion may be provided.
(2) The structure for making the length of the single-sided closed tube expandable and retractable is not limited to the configurations shown in the second and third embodiments, and the single-sided closed tube may be formed into a bellows shape. , various conventionally known configurations for varying the length of the tubular body can be employed.
(3) In the second embodiment, the length of the single-sided closed tube 30 is configured to be expandable and retractable at the closed end, and in the third example, the length of the single-sided closed tube 40 is configured to be expanded and contracted at both the closed end and the open end. However, the tube length may be configured to be expandable and retractable only at the open end of the one-sided closed tube.

DESCRIPTION OF SYMBOLS 10 grommet, 12 frustum part, 14 penetrating pipe part, 18 panel engaging part 20,30,40 one side closed pipe part, 22 closed part, 32 base pipe part, 34 closed pipe part,
36 Connecting pipe section

Claims (2)

A grommet attached to a through hole formed in a panel,
A frustum-shaped frustum portion whose inner diameter gradually decreases;
a penetrating tube portion provided on the small diameter side of the frustum portion and open at both ends, through which the cord-like body can be inserted;
a panel engaging portion provided on the large diameter side of the frustum portion and engaged with an inner peripheral edge of the through hole;
a one-sided closed pipe part provided in the frustum part and having one end closed,
The one-sided closed tube section includes a base tube section connected to the frustum section, a closed tube section whose protruding end side is closed by the closing section, and a connecting tube section that connects the base tube section and the closed tube section,
A first state in which the connecting pipe portion is located so as to be connected to the outside of the base pipe portion, and a second state in which the connecting pipe portion is located inside the base pipe portion so as to be reversed from the first state. By deforming into the state of
A grommet characterized in that the tube length from the closed portion to the open end in the shortened state is set to such a length that the resonant frequency of the one-sided closed tube portion is 2,000 Hz or less or 4,000 Hz or more. A grommet attached to a through hole formed in a panel,
A frustum-shaped frustum portion whose inner diameter gradually decreases;
a penetrating tube portion provided on the small diameter side of the frustum portion and open at both ends, through which the cord-like body can be inserted;
a panel engaging portion provided on the large diameter side of the frustum portion and engaged with an inner peripheral edge of the through hole;
a one-sided closed pipe part provided in the frustum part and having one end closed,
The one-side closed pipe section is formed so that the pipe length can be expanded and contracted at both ends of the closed end and the open end that are closed by the closed part, and the pipe length from the closed end to the open end in the shortened state is adjusted to the one-side closed pipe section. A grommet characterized by being formed to a length such that the resonant frequency of the pipe portion is 2,000 Hz or less or 4,000 Hz or more.

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