JP7475932B2 - Automotive soundproof cover structure - Google Patents

Description

This disclosure relates to a soundproof cover structure for an automobile that is provided around a noise source such as an engine or transmission.

Around noise sources such as the engine and transmission, soundproof covers for automobiles are installed to absorb the noise generated by the noise sources.

Japanese Patent Application Laid-Open No. 9-302717 JP 2004-316368 A

Meanwhile, automobile soundproof covers are constructed by fixing sound-absorbing material to a cover body made of resin. Therefore, the sound-absorbing performance depends on the characteristics of the sound-absorbing material. Generally, sound-absorbing materials used to absorb noise in the high frequency band (roughly 1250 Hz and above) are inexpensive, but have poor sound-absorbing performance in the low frequency band (400 Hz to 1250 Hz: hereafter referred to as the low frequency band). For this reason, expensive sound-absorbing materials with high sound-absorbing performance in the low frequency band are used for trucks that generate noise in the low frequency band.

Patent documents 1 and 2 also describe a technique for enhancing the sound absorption effect in the low frequency range by providing a back air layer between the cover body and the sound absorbing material. With this technique, the sound absorption effect in the low frequency range is improved according to the thickness of the back air layer. However, the installation space for an automobile soundproof cover is limited. For this reason, there is a problem in that it is difficult to obtain a sufficient sound absorption effect in the low frequency range with inexpensive sound absorbing materials.

Therefore, this disclosure was devised in consideration of the above circumstances, and its purpose is to provide a soundproof cover structure for automobiles that can improve the sound absorption effect in the low frequency band.

According to one aspect of the present disclosure,
A cover body formed in a plate shape and disposed opposite the noise source;
A sound absorbing material provided on the noise source side of the cover body;
A back air space is formed between the cover body and the sound absorbing material,
The soundproof cover structure for an automobile is characterized in that a plate-shaped rib is provided on the cover body so as to extend toward the sound-absorbing material and to divide the back air space into a plurality of small chambers.

Preferably, the cover body that divides the small room is formed with an inclined surface to reflect noise from the noise source toward the rib.

Preferably, the thickness of the rib is set to be thinner than the thickness of the cover body.

Preferably, the cover body is made of a resin that contains fibers, and the ribs are made of a resin that does not contain fibers.

The ribs may also be provided on the cover body to form multiple types of small chambers with different volumes.

The cross-sectional shape of the chamber may be hexagonal, rectangular, triangular or circular.

The above aspect can improve the sound absorption effect in the low frequency range.

FIG. 2 is a rear cross-sectional view of an engine compartment according to an embodiment of the present disclosure. FIG. 1 is a perspective view of a soundproof cover for an automobile. 3 is a cross-sectional view taken along line AA in FIG. 2. 4 is a cross-sectional view taken along line BB in FIG. 3. 1 is a line graph showing the sound absorbing effect of an automobile soundproof cover.

Embodiments of the present disclosure will be described below with reference to the attached drawings. Note that the directions of front, rear, left, right, top and bottom in the embodiments described below refer to the respective directions of the vehicle. However, the directions in the present embodiments are used for convenience of explanation and represent the relative positional relationships between the components described below.

Figure 1 is a cross-sectional view of the engine room 2 of a truck 1 according to this embodiment, seen from the rear. Note that the engine room 2 may be something other than a truck 1. For example, the engine room 2 may be something other than a truck 1, such as a bus or other large vehicle.

As shown in FIG. 1, the engine 3, which is a noise source, is disposed between the left and right side members 4L and 4R. The engine room 2 is formed by surrounding the engine 3 from above, below, left and right with partitions 5a, 5b, 5c, 5d, 5e and 5f. Among the partitions 5a, 5b, 5c, 5d, 5e and 5f surrounding the engine 3, the upper partition 5c disposed vertically above the engine 3, the upper left partition 5a disposed between the left side member 4L and the upper partition 5c, and the upper right partition 5b disposed between the right side member 4R and the upper partition 5c are provided with the automotive soundproof cover structure according to this embodiment.

Figure 2 is a perspective view of the upper left bulkhead 5a as viewed diagonally from above, and Figure 3 is a cross-sectional view taken along line A-A in Figure 2. As shown in Figures 2 and 3, the automobile soundproof cover structure comprises a cover body 7 formed in a plate shape and arranged facing the engine 3, a sound-absorbing material 8 provided on the engine 3 side of the cover body 7, and a back air space 9 formed between the cover body 7 and the sound-absorbing material 8.

The cover body 7 is made of a resin containing glass fiber, i.e., glass fiber reinforced resin. This makes the cover body 7 lightweight and highly rigid, and makes it easy to reflect noise. Since the cover body 7 can be made highly rigid, it is possible to improve the handling properties when attaching the cover body 7 to the truck 1. The cover body 7 may also be made of fiber reinforced plastics (FRP) that contains other fibers such as carbon fiber.

The sound-absorbing material 8 is made of a sheet-like nonwoven fabric. The sound-absorbing material 8 made of nonwoven fabric is relatively inexpensive. The sound-absorbing material 8 is attached to the cover body 7 with clips 13. The sound-absorbing material 8 may also be made of a sheet-like glass wool. In this case, the cost of the sound-absorbing material 8 increases, but a higher sound-absorbing effect can be obtained in the low frequency range.

Incidentally, Patent Documents 1 and 2 describe a technique for providing a back air layer between the sound-absorbing material and the cover body. This technique can improve the sound-absorbing performance of the sound-absorbing material in the low-frequency range. However, the installation space for automobile soundproof covers is limited. For this reason, there is an issue that it is difficult to obtain a sufficient sound-absorbing effect in the low-frequency range emitted by the engine and transmission of a large vehicle with inexpensive sound-absorbing materials.

In this embodiment, therefore, plate-shaped ribs 10 are provided on the cover body 7 to divide the rear air space 9 into a number of small rooms. The ribs 10 are provided on the cover body 7, extending toward the sound-absorbing material 8.

As shown in Figures 3 and 4, the rib 10 includes an outer frame portion 10a that surrounds the outer periphery of the sound-absorbing material 8, and a partition portion 10b that is disposed in the area surrounded by the outer frame portion 10a. The extension length a of the outer frame portion 10a is set to be longer than the extension length b of the partition portion 10b. As a result, the tip of the partition portion 10b abuts against the back surface 8a of the sound-absorbing material 8, and the outer frame portion 10a extends toward the engine 3 side beyond the back surface 8a of the sound-absorbing material 8. The outer frame portion 10a is formed so as to surround the entire outer periphery of the sound-absorbing material 8, and abuts against the outer periphery of the sound-absorbing material 8. The partition portion 10b is formed in a honeycomb shape in cross section. In other words, the cross-sectional shape of each of the small rooms 11 partitioned by the partition portion 10b is hexagonal.

The cross-sectional shape of the small room 11 is not limited to a hexagon. The cross-sectional shape of the small room 11 may be a rectangle, a triangle, or a circle. By changing the cross-sectional shape of the small room 11, the sound absorption characteristics (sound absorption frequency) can be changed. The sound absorption characteristics can also be changed by changing the size of the small room 11 or the distance between the walls that divide the small room 11.

The outer frame 10a and the partitions 10b are set to a constant thickness t, and the cover body 7 is set to a constant thickness T. The thickness t of the outer frame 10a and the partitions 10b is set to be thinner than the thickness T of the cover body 7. For example, the thickness t of the outer frame 10a and the partitions 10b is set within a range of 0.5 mm or more and 0.8 mm or less (0.5 mm≦t≦0.8 mm). In addition, the outer frame 10a and the partitions 10b are made of a resin that does not contain glass fiber. This makes the outer frame 10a and the partitions 10b more likely to vibrate when exposed to noise, and more likely to absorb the sound energy of the noise.

The cover body 7 and the ribs 10 are press-molded together using a thermoplastic resin (glass mat reinforced thermoplastic) containing glass fiber. Glass fiber has the property of not permeating parts that do not have a certain thickness. Therefore, by adjusting the thickness t of the outer frame 10a and the partition 10b, it is possible to make the glass fiber permeate only the cover body 7 and not the outer frame 10a and the partition 10b. The outer frame 10a and the partition 10b may be formed separately from the cover body 7 in advance and attached to the cover body 7 with adhesive or the like.

The cover body 7 that defines the small chamber 11 is formed with an inclined surface 12 for reflecting noise from the noise source toward the rib 10. The inclined surface 12 is formed by recessing the cover body 7, which is spaced from the base end of the rib 10, on the opposite side to the engine 3. Specifically, the inclined surface 12 is formed three-dimensionally by recessing the cover body 7 into a cone shape or a V-shaped cross section so that it is most recessed at the center of the small chamber 11. This allows the rib 10 to receive greater sound energy. This allows the rib 10 to vibrate more strongly, and noise to be absorbed more efficiently.

Next, we will explain the operation of this embodiment.

As shown in Figure 3, the noise generated by the engine 3 is attenuated as it passes through the sound-absorbing material 8 due to viscous friction of the air and friction between the air and the sound-absorbing material 8. This causes the noise to be absorbed and reduced in size.

In addition, noise that hits the inclined surface 12 of the cover body 7 is reflected towards the rib 10. When the rib 10 receives the noise and reflects the noise, it bends and vibrates slightly due to the sound pressure. This further attenuates and reduces the noise reflected from the inclined surface 12. At this time, a back air layer 9 is formed between the sound-absorbing material 8 and the cover body 7. Therefore, low-frequency noise is also efficiently absorbed and reduced. Noise is also absorbed by friction between the rib 10, which vibrates in response to the noise, and the sound-absorbing material 8.

The noise then passes from the cover body 7 side of the sound-absorbing material 8 to the engine 3 side, where it is further attenuated.

Figure 5 is a line graph showing the sound absorption effect of the automobile soundproof cover structure. In the figure, the thick solid line represents the sound absorption coefficient of the automobile soundproof cover structure of this embodiment (where the cross-sectional shape of the small chamber 11 is hexagonal), the thick dashed line represents the sound absorption coefficient when the cross-sectional shape of the small chamber 11 is made rectangular, and the thin dashed line represents the sound absorption coefficient of the conventional structure (without the small chamber 11).

As shown in FIG. 5, it was confirmed that the sound absorption coefficient (thick solid line) in the low frequency band of 400 Hz to 1250 Hz of the automotive soundproof cover structure according to this embodiment is improved over the sound absorption coefficient (thin dashed line) of the conventional structure.

It was also confirmed that even when the cross-sectional shape of the small room 11 is made rectangular, the sound absorption coefficient in the low frequency band (thick dashed line) is improved compared to the sound absorption coefficient of the conventional structure (thin dashed line). It was also confirmed that when the cross-sectional shape of the small room 11 is rectangular, the sound absorption characteristics change so that the sound absorption coefficient is higher around 400 Hz, 800 Hz, and 1250 Hz than when the cross-sectional shape is hexagonal, and the sound absorption coefficient is lower around 500 Hz and 1000 Hz.

In this way, the cover body 7 has ribs 10 that divide the rear air space 9 into multiple small rooms 11, improving the sound absorption effect in the low frequency range. Furthermore, even if an inexpensive sound absorbing material with poor sound absorption performance in the low frequency range is used, low frequency noise can be effectively absorbed, reducing costs.

In addition, because the automobile soundproof cover structure is provided with ribs 10, the rigidity of the cover body 7 can be improved, and sound insulation performance can be improved. Furthermore, the thickness T of the cover body 7 can be reduced, resulting in weight reduction and reduced material costs.

In addition, the sound absorption characteristics can be adjusted by changing the cross-sectional shape and size of the small room 11, making it easy to tune according to the noise characteristics.

Although the embodiments of the present disclosure have been described in detail above, other embodiments of the present disclosure are also possible, such as the following:

(1) In the above embodiment, the ribs 10 are provided on the cover body 7 so as to form multiple small chambers 11 of the same shape and volume, but this is not limited to the above. The ribs 10 may be provided on the cover body 7 so as to form multiple types of small chambers 11 with different shapes and volumes. This allows the sound absorption characteristics to be changed. And by adjusting the sound absorption characteristics to match the characteristics of the noise, the noise can be absorbed efficiently.

(2) Although the case where the rib 10 is set to a constant thickness t has been described, this is not limited to the case. The thickness t of the rib 10 may be partially different. This allows the sound absorption characteristics to be changed.

(3) Although the extension length a of the outer frame portion 10a is set to a constant value and the extension length b of the partition portion 10b is also set to a constant value, this is not limited to the above. The sound absorption characteristics can be changed by partially changing the extension length a of the outer frame portion 10a or the extension length b of the partition portion 10b.

(4) The inclined surface 12 is formed three-dimensionally by recessing the cover body 7 into a cone shape so that it is most recessed at the center of the small room 11, but is not limited to this. For example, the inclined surface 12 may be formed three-dimensionally by raising the cover body 7 into a cone shape so that it is most raised toward the engine 3 at the center of the small room 11 (not shown). The inclined surface 12 may also be formed by undulating in one direction (not shown).

3. Engine (noise source)
7 Cover body 8 Sound absorbing material 9 Back air space 10 Rib 11 Small room 12 Sloping surface

Claims (5)

A cover body formed in a plate shape and disposed opposite the noise source;
A sound absorbing material provided on the noise source side of the cover body;
A back air space is formed between the cover body and the sound absorbing material,
The cover body is provided with a plate-like rib extending toward the sound-absorbing material and dividing the rear air space into a plurality of small chambers.
The cover body is provided with an inclined surface for each of the small chambers to reflect noise from the noise source toward the rib,
The inclined surface is
The cover body is recessed in a V-shaped cross section on the opposite side to the noise source so that the recess is greatest at the center of the small room.
A soundproof cover structure for an automobile. The automobile soundproof cover structure according to claim 1 , wherein the thickness of the rib is set to be thinner than the thickness of the cover body. The cover body is made of a resin containing fibers,
The automobile soundproof cover structure according to claim 1 or 2, wherein the rib is made of a resin that does not contain fibers. The vehicle soundproof cover structure according to claim 1 , wherein the ribs are provided on the cover body so as to form a plurality of types of small chambers with different volumes. The automobile soundproof cover structure according to any one of claims 1 to 4, wherein the cross-sectional shape of the small chamber is a hexagon, a rectangle, a triangle or a circle.

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