Method for manufacturing grommet, and grommet
A method for manufacturing a grommet, which is fixed to a wire harness W inserted into an opening portion of a panel P and which is fitted and attached to the opening portion to thereby support the wire harness W on the panel P. The grommet includes peripheral walls that surrounds the wire harness W to form a sound shield space S around the wire harness W, and a soundproof wall that is formed in the sound shield space S so as to cross a longitudinal direction of the wire harness W. The soundproof wall is designed by use of an expression of TL=20 log(ρ×f)−42.5 where TL designates transmission loss of the soundproof wall, ρ designates surface density of the soundproof wall, and f designates a frequency.
1. A grommet which is fixed to a wire harness inserted into an opening portion of a panel and which is fitted and attached to the opening portion to thereby support the wire harness on the panel, the grommet including:
a fitting portion fitted into the opening portion of the panel;
a pair of peripheral walls that extend on axially opposite sides from the fitting portion and surround the wire harness to form a sound shield space around the wire harness;
a soundproof wall provided on an inner circumference of the fitting portion and formed in the sound shield space between the pair of peripheral walls so as to cross a longitudinal direction of the wire harness; and
a panel engagement portion that can be engaged with an inner circumferential edge of the opening portion of the panel; wherein:
the panel engagement portion includes a first side wall and a second side wall that are opposed to each other to form an engagement groove to which the panel can be fitted;
a first lip portion is formed in the first side wall so that the first lip portion can abut against a first surface of the panel to push the panel toward the second side wall;
a second lip portion is formed in the second side wall so that the second lip portion can abut against a second surface of the panel to push the panel toward the first side wall, the second surface being an opposite surface to the first surface, and
wherein a thickness of each of the soundproof walls and one or two of the soundproof walls are designed so that a sound pressure level transmitted by the panel can be suppressed by at least 3 dB in a frequency band not lower than 1,000 Hz and not higher than 4,000 Hz in comparison with that in a case where the soundproof walls are absent.
2. The grommet of claim 1 , wherein the soundproof wall is formed as an annular wall plate formed into a corrugated shape made of concentric circles.
3. A method for manufacturing a grommet, which is fixed to a wire harness inserted into an opening portion of a panel and which is fitted and attached to the opening portion to thereby support the wire harness on the panel, the grommet including:
a fitting portion fitted into the opening portion of the panel;
a pair of peripheral walls that extend on axially opposite sides from the fitting portion toward the wire harness and surround the wire harness to form a sound shield space therebetween and around the wire harness; and
a soundproof wall provided on an inner circumference of the fitting portion and formed in the sound shield space and between the pair of peripheral walls so as to cross a longitudinal direction of the wire harness; wherein:
the soundproof wall is designed by:
TL=20 log(ρ× f )−42.5
where TL designates transmission loss of the soundproof wall, p designates surface density of the soundproof wall, and f designates a frequency,
wherein a sound pressure level transmitted by the panel can be suppressed by at least 3 dB in a frequency band not lower than 1,000 Hz and not higher than 4,000 Hz in comparison with that in a case where the soundproof walls are absent.
4. The method for manufacturing a grommet according to claim 3 , wherein:
the soundproof wall is designed so that the transmission loss TL satisfies:
TL≥20
at least in a part of a frequency band not lower than 1,000 Hz and not higher than 4,000 Hz.
5. A method for manufacturing a grommet, which is fixed to a wire harness inserted into an opening portion of a panel and which is fitted and attached to the opening portion to thereby support the wire harness on the panel, the grommet including:
a fitting portion fitted into the opening portion of the panel;
a pair of peripheral walls that extend on axially opposite sides from the fitting portion toward the wire harness and surround the wire harness to form a sound shield space therebetween and around the wire harness; and
soundproof walls provided on an inner circumference of the fitting portion and formed in the sound shield space and between the pair of peripheral walls so as to cross a longitudinal direction of the wire harness; wherein:
thickness of each of the soundproof walls and one or two of the soundproof walls are designed so that a sound pressure level transmitted by the panel can be suppressed by at least 3 dB in a frequency band not lower than 1,000 Hz and not higher than 4,000 Hz in comparison with that in a case where the soundproof walls are absent.
6. A method for manufacturing a grommet according to claim 3 , the grommet further including:
a panel engagement portion that can be engaged with an inner circumferential edge of the opening portion of the panel; wherein:
the panel engagement portion includes a first side wall and a second side wall that are opposed to each other to form an engagement groove to which the panel can be fitted;
a first lip portion is formed in the first side wall so that the first lip portion can abut against a first surface of the panel to push the panel toward the second side wall; and
a second lip portion is formed in the second side wall so that the second lip portion can abut against a second surface of the panel to push the panel toward the first side wall, the second surface being an opposite surface to the first surface.
7. A method for manufacturing a grommet according to claim 5 , the grommet further including:
a panel engagement portion that can be engaged with an inner circumferential edge of the opening portion of the panel; wherein:
the panel engagement portion includes a first side wall and a second side wall that are opposed to each other to form an engagement groove to which the panel can be fitted;
a first lip portion is formed in the first side wall so that the first lip portion can abut against a first surface of the panel to push the panel toward the second side wall; and
a second lip portion is formed in the second side wall so that the second lip portion can abut against a second surface of the panel to push the panel toward the first side wall, the second surface being an opposite surface to the first surface.
8. The method for manufacturing a grommet of claim 3 , wherein the soundproof wall is formed as an annular wall plate formed into a corrugated shape made of concentric circles.
9. The method for manufacturing a grommet of claim 8 , wherein the corrugated shape includes a bellows-like shape.
10. The method for manufacturing a grommet of claim 5 , wherein the soundproof wall is formed as an annular wall plate formed into a corrugated shape made of concentric circles.
11. The method for manufacturing a grommet of claim 10 , wherein the corrugated shape includes a bellows-like shape.
12. The grommet of claim 2 , wherein the corrugated shape includes a bellows-like shape.