Land vehicles: bodies and tops – Bodies – Structural detail
Reexamination Certificate
2002-07-29
2004-09-21
Dayoan, D. Glenn (Department: 3612)
Land vehicles: bodies and tops
Bodies
Structural detail
C296S001030, C296S193070
Reexamination Certificate
active
06793276
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the structure of an automobile body floor panel and an automobile with this body floor panel, and in particular relates to a body floor panel that excites vibration in a specific mode with a low acoustic radiation efficiency with respect to the input of vibrations in a predetermined frequency band that results in road noise.
Road noise, that is, the noise within an automobile interior that is caused by tire cavity resonance and suspension vibration or the like while the automobile is in motion, is a problem. In general, road noise due to tire cavity resonance peaks in a specific frequency band from 200 to 300 Hz, and road noise due to suspension vibration peaks near 160 Hz. Accordingly, a variety of anti-vibration and anti-noise measures have conventionally been employed at various parts of the automobile body, with particular focus on the floor panel, which is one of the sources of road noise.
For example, numerous beads are formed on the floor panel or the thickness of the panel is increased to raise its surface rigidity and thereby shift its natural frequency to a high frequency band that is higher than 300 Hz. This means that the floor panel is made to not vibrate near 160 Hz, due to suspension vibration, or at the frequency band of tire cavity resonance, and thus road noise is reduced. With these approaches, however, high frequency vibrations subsequently become a problem that requires measures such as attaching sound absorbing material to the floor panel in order to absorb the high frequency noise.
However, the use of large amounts of sound absorbing material increases material costs and makes the automobile body heavier.
In response to these problems, we noticed that sound radiated from a vibrating panel changes significantly depending on the vibration mode, and thus we propose that the floor panel shape and the boundary conditions, for example, are established such that, in specific frequency bands where road noise is a concern, a vibration mode with a low acoustic radiation efficiency is excited. This proposal is described in JP-H09-202269A.
More specifically, the number of antinodes of the stationary waves excited lengthwise and widthwise in a substantially square panel are given as n and m, respectively, and when the vibration mode is n×m=even number, then sounds radiated from opposite phase, adjacent sections in the panel cancel each other out and are reduced. As shown in
FIG. 5B
, the acoustic radiation efficiency is lowest particularly when the vibration mode is the 2×2 mode.
Accordingly, in the reduced radiation sound structure of the body panel disclosed in the above application, a substantially square region (vibration mode adjustment region) is set at both the left and right sides of the floor tunnel of the body floor panel, and the distribution of surface rigidity in the panel is adjusted so that the vibration mode of the regions is the 2×2 mode. Consequently, even if vibrations of a specific frequency band caused by tire cavity resonance or suspension vibration, for example, are input and resonate the floor panel, road noise resulting from this is sufficiently suppressed and the degree of silence inside the automobile can be increased.
However, as mentioned previously, the frequency bands that result in road noise are very nearly fixed, and establishing a region in which 2×2 mode vibration is excited with respect to vibrations input in these frequency bands requires that a flat surface with a wide area is secured in the floor panel.
In general, however, a floor tunnel portion extending in the length direction of the body is formed in the body floor panel. Moreover, side frames, side sills, and reinforcing members such as cross members are joined to the body floor panel. These not only ensure automobile body rigidity and increase steering stability but are also critical from the standpoint of increasing the automobile's ability to protect passengers during impact. Consequently, it is not possible to make large changes to their dimensions, shape, and layout. Therefore, adopting the above floor panel structure for exciting 2×2 mode vibration for the body of the automobile is difficult to achieve because it is difficult in practice to secure a wide flat surface.
SUMMARY OF THE INVENTION
The present invention has been arrived at in light of these issues, and it is an object thereof to utilize the layout of the floor tunnel portion and side frames, for example, in the floor panel of an automobile and simultaneously set vibration mode adjusted areas within the floor panel to both ensure body rigidity and safety and reduce road noise by adjusting the vibration mode.
To achieve the above objects, in the present invention, an area of a floor panel partitioned by the floor tunnel portion and the various reinforcing members, and which is oblong in the length direction of the automobile body, is made so that a 2×1 mode vibration resulting in two antinodes in the length direction of the automobile and one antinode in the width direction of the automobile is generated, and is adjusted so that the natural frequency of the 2×1 mode is effective in reducing road noise due to tire resonance.
That is, the present invention is for an automobile floor structure in which the automobile floor is partitioned into a plurality of areas by a floor tunnel portion extending in the lengthwise direction of the automobile along the central portion in the automobile width, left and right side sills extending in the lengthwise direction of the automobile body along both side portions of the automobile width, side frames extending in the lengthwise direction of the automobile body between the floor tunnel portion and the left and right side sills, and cross members extending in the automobile width direction,
wherein the floor panel of at least one area of the plurality of areas is bound at its perimeter by the one of the side frames, two cross members and the floor tunnel portion or one of the side sills, and has a floor panel structure in which the vibration mode is adjusted so that a 2×1 mode vibration resulting in two antinodes in the lengthwise direction of the automobile body and one antinode in the automobile width direction is generated and the natural frequency of the 2×1 mode is 240 to 260 Hz.
According to the invention, vibration of a 2×1 mode occurs in the vibration mode adjusted floor panel when vibrations of between 240 and 260 Hz are input to the floor panel from the outside. This means that in the floor panel, two sections that are adjacent in the length direction of the automobile vibrate with opposite phase but with the same amplitude, so that there is a considerable drop in the acoustic radiation efficiency and thus road noise between 240 and 260 Hz can be significantly reduced.
The perimeter of the vibration mode adjusted floor panel is bound by the floor tunnel portion and strengthening members (area partitioning members) such as the side frames, and thus it easily forms independent vibration systems and is beneficial in exciting the intended 2×1 vibration mode.
The vibration mode adjusted floor panel is also effectively reinforced by the floor tunnel portion extending in the lengthwise direction of the automobile, the side frames, the side sills, and the cross members that intersect with these and extend in the width direction of the automobile. Thus, the automobile body rigidity and its ability to protect passengers can be adequately ensured.
This means that with the present invention, a floor panel structure is formed that utilizes the automobile body reinforcement structure for increasing the automobile's body rigidity and ability to protect passengers and that employs areas that are partitioned by these reinforcing members (strength members) to generate a 2×1 mode vibration and thereby significantly reduce road noise at 240 to 260 Hz due to tire cavity resonance.
The vibration mode adjusted floor panel can be adjusted
Fujii Yoshio
Ikeda Toshiharu
Kamura Takanobu
Naganuma Tsutomu
Nanba Shoji
Dayoan D. Glenn
Gutman H.
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
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