JP2008297942A - Engine cover - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an engine cover exert attenuation action on engine noise over a wide frequency band. <P>SOLUTION: In an engine cover 30, a skin layer 16 is formed under an arrangement condition where a separation width of a separation space part with an engine 8 is set to get larger continuously or in stepwise from a first separation space part 18 formed on an anti-occupant room side of an engine 8 toward a second separation space part 12 direction formed in a space with a vertical wall part 14 extending toward a lower part on an occupant room side of the engine 8. A sound absorbing layer 20 is laid on an inner surface of a skin layer 16 to get thicker toward the occupant room C side from the anti-occupant room side corresponding to a separation width of each separation space part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an engine cover, and more particularly, to an engine cover that is mounted above an engine installed in an engine room at the front or rear of a vehicle.

  This type of engine cover has a skin layer that covers the upper part of the engine and a sound absorbing layer that is laid on the inner surface of the skin layer on the engine side, and is typically shaped to correspond to the engine. The noise generated from the engine of the vehicle is sound-insulated by the skin layer, and the noise is absorbed by the sound-absorbing layer (see FIG. 7).

And in this engine cover, the noise of a specific frequency may be attenuated by interference action. That is, engine noise (emission wave) of a specific frequency is reflected on the skin layer to generate a reflected wave whose phase is inverted by 180 °, and the reflected wave and the emitted wave interfere with each other so as to cancel each other. In the space between the engine and the skin layer, a standing wave (synthetic wave) with a reduced sound pressure (amplitude) is generated by the interference of the reflected wave and the emitted wave, and the sound absorption layer laid on the inner surface of the skin layer The sound is effectively absorbed by the layer (see FIG. 3). The noise attenuation action described above occurs when the separation width of the separation space formed between the engine and the skin layer coincides with 1/4 (or 3/4) of the wavelength λ of the specific noise. Therefore, the frequency of noise subjected to a damping action can be calculated by the following calculation formula (1). For example, if the separation width between the skin layer and the engine is 8 mm (= 1 / 4λ), noise having a frequency of 10.6 kHz can be attenuated by the following calculation formula (2).
(1) [Frequency f (Hz)] = [Sonic velocity c (about 340 m / sec)] / [Wavelength λ (m)]
(2) [Frequency f] = 340 / (0.008 × 4) = 10,600 (Hz)
As a technique related to sound attenuation, there is a technique described in Patent Document 1, for example.
JP 2004-44526 A

By the way, the engine noise is a mechanical noise of a valve system that is generated mainly around the cylinder head cover of the engine. This mechanical noise has a wide frequency band of 1 to 10 kHz.
However, the engine cover described above has a shape corresponding to the engine as described above. That is, referring to FIG. 7, the skin layer formed on the side opposite to the passenger compartment of the engine (the vehicle front side in the example of the figure), the separation width r1 of the separation space portion of the engine, and the skin layer facing the passenger compartment side The separation width r2 between the rear end and the engine is substantially the same size, and the thickness of the sound absorbing layer is also substantially constant. For this reason, the above-mentioned engine cover can attenuate noise of a specific frequency (for example, frequency 10.6 kHz), but cannot effectively attenuate noise over a wide range of frequencies.
The present invention has been devised in view of the above points, and a problem to be solved by the present invention is to exhibit a damping action against engine noise over a wide frequency band.

  As means for solving the above-mentioned problems, the engine cover of the first invention is characterized in that a skin layer for insulating noise generated from a vehicle engine is disposed at a position above the engine at a distance from the engine, and the engine of the skin layer is formed. The engine cover has a sound absorbing layer that fills the inner space on the side with the engine and absorbs engine noise, and the skin layer has a separation width of the space between the engine and the engine layer. From the first spaced-apart space portion formed on the side opposite to the passenger compartment toward the second spaced-apart space portion formed between the vertical wall portion extending downward on the passenger compartment side of the engine. The sound absorbing layer becomes thicker from the non-occupant compartment side toward the passenger compartment side corresponding to the separation width of each separation space portion. On the inner skin layer It has been set.

In the first invention, the skin layer includes a vertical wall portion extending downward toward the passenger compartment side. Then, the “second space between the vertical wall portion formed on the passenger compartment side and the engine is larger than the separation width of the“ first separation space portion ”between the skin layer formed on the side opposite to the passenger compartment of the engine and the engine. The separation width of “the separation space portion” is set large. For this reason, when the first noise is set to be attenuated in the first separation space, the second noise having a longer wavelength than the first noise (in other words, the first noise is set in the second separation space). It is possible to attenuate the second noise having a frequency lower than that of the noise.
The skin layer has a separation width of the separation space portion between the engine and the engine, the second separation space formed on the passenger compartment side of the engine from the first separation space portion formed on the counter passenger compartment side of the engine. It is formed as an arrangement state that is set large continuously or stepwise toward the part. For this reason, it is possible to attenuate noise in a wide frequency band in the range of at least the first noise to the second noise in each of the separation spaces between the first separation space and the second separation space. is there.
The sound absorbing layer is laid on the inner surface of the skin layer so as to increase in thickness from the opposite passenger compartment side toward the passenger compartment side corresponding to the separation width of each separation space portion. The synthesized wave (standing wave) generated in each separated space between the two separated spaces can be effectively absorbed.

The engine cover of the second invention is the engine cover of the first invention, wherein the skin layer is made of natural fiber, and the vertical wall portion is a wall on the passenger compartment side that constitutes the engine room of the vehicle. It has a curved shape corresponding to the shape.
In the second invention, the vertical wall portion has a curved shape corresponding to the shape of the passenger compartment side wall body (for example, the dash panel) constituting the engine room, and therefore, between the dash panel and the vertical wall portion in the engine room. The flow of air passing through becomes smooth. For this reason, generation | occurrence | production of the wind noise in an engine room can be prevented or reduced. And a skin layer provided with the vertical wall part of such a shape can be easily manufactured, for example by pressing and molding a natural fiber mat with a pressure molding machine.

The engine cover of the third invention is the engine cover of the first invention or the second invention, wherein the sound absorbing layer is made of natural fiber and has a density stepwise or continuously from the engine toward the skin layer. Has been raised.
In the third invention, the density of the sound absorbing layer composed of natural fibers is increased stepwise or continuously from the engine toward the skin layer. For this reason, noises having different wavelengths (frequencies) are reflected stepwise from the engine in the thickness direction of the sound absorbing layer in the skin layer, and noises of a wider frequency range can be attenuated.

  According to the first invention, it is possible to provide an engine cover that exhibits a damping effect on noise in a wide frequency band. According to the second invention, it is possible to provide an engine cover that is more excellent in soundproofing effect. According to the third aspect of the present invention, it is possible to provide an engine cover that exhibits an attenuation action against noise in a wider frequency band.

Hereinafter, the best mode for carrying out the present invention will be described. In addition, the following description is description (when an engine is mounted in the vehicle front part) (example).
[Embodiment 1]
FIG. 1 is a longitudinal sectional view of an engine room.
The engine cover 30 according to the present embodiment is a sound absorbing member assembled to the engine 8 so as to cover the upper side of the engine 8 (horizontal type) disposed in the engine room 6. The engine room 6 is provided at the front of the vehicle, and includes a hood panel 4 disposed above the engine 8 and a dash panel 2 serving as a wall on the passenger compartment C side.
In the engine cover 30 of the present embodiment, the skin layer 16 for insulating the noise generated from the engine 8 is disposed at a position above the engine 8 at a distance from the engine 8. A sound absorbing layer 20 that fills a space portion away from the engine 8 and absorbs noise of the engine 8 is laid on the inner surface of the skin layer 16 on the engine side.

FIG. 2 is a vertical cross-sectional view of the engine cover, showing engine noise as indicated by a dotted line. FIG. 3 is an explanatory diagram for explaining that a synthetic wave is generated by interference between engine noise (emission wave) and its reflected wave.
The skin layer 16 of the present embodiment is separated from the engine 8 substantially continuously or stepwise from the vehicle front F side (anti-occupant compartment side) of the engine 8 to the passenger compartment C side as seen in the longitudinal section of FIG. It is spaced apart, and its middle part bulges slightly in a convex shape.
The skin layer 16 includes a vertical wall portion 14 extending in a bent shape toward the lower side of the passenger compartment C of the engine 8. The vertical length formed on the passenger compartment C side of the engine 8 is larger than the separation width R1 of the “first separation space 18” between the skin layer 16 formed on the vehicle front F side of the engine 8 and the engine 8. A separation width R2 of the “second separation space portion 12” between the wall portion 14 and the engine 8 is set large.

  In the engine cover 30 of the present embodiment, the separation width R1 of the first separation space 18 is set to match 1/4 (or 3/4) of the wavelength λ1 of the specific noise n1. Then, referring to FIG. 3, the noise n1 {the emission wave w1 shown by (I) in the figure] is reflected by the skin layer 16, and the reflected wave w2 whose phase is inverted by 180 ° {shown by (II) in the figure] } Occurs. Then, the reflected wave w2 and the emission wave w1 interfere with each other so as to cancel each other in the first separation space 18 to generate a synthesized wave w3 {denoted by (III) in the figure} having a reduced sound pressure (amplitude A). It becomes. For example, by setting the separation width R1 of the first separation space 18 to 8 mm (= 1/4 · λ1), 10.6 kHz noise (first noise n1) is calculated from the above-described calculation formula (2). It can be attenuated.

In the second separation space 12, the separation width R <b> 2 is wider than that of the first separation space 18 as described above. Therefore, when the first noise n1 is set to be attenuated in the first separation space 18, the second noise n2 having a wavelength longer than that of the first noise n1 (in other words, in the second separation space 12). Then, it is possible to attenuate the second noise n2) having a frequency lower than that of the first noise n1. For example, by setting the separation width R2 of the second separation space 12 to 85 mm (= 1/4 · λ2), 1.0 kHz noise (second noise n2) can be obtained from the following equation (3). It can be attenuated.
(3) [Frequency f] = 340 / (0.085 × 4) = 1,000 (Hz)

The skin layer 16 is formed on the passenger compartment C side of the engine 8 so that the separation width of the separation space portion between the engine 8 and the engine 8 is larger than the first separation space portion 18 formed on the vehicle front F side of the engine 8. It is formed as an arrangement state that is set continuously or stepwise in the direction of the second spaced space 12. Therefore, noise in a wide frequency band in the range of at least the first noise n1 to the second noise n2 in the separation space between the “first separation space 18” and the “second separation space 12”. Can be attenuated.
For example, as described above, the separation width R1 of the first separation space 18 is set to 8 mm so as to attenuate 10.6 kHz noise (first noise n1). Then, the separation width R2 of the second separation space 12 is set to 85 mm, and 1.0 kHz noise (second noise n2) is set to be attenuated. Then, in the engine cover 30 of the present embodiment, a frequency band of at least 1.0 kHz to 10.6 kHz is provided by each separation space between the “first separation space 18” and the “second separation space 12”. Noise (for example, mechanical noise) can be attenuated to generate a composite wave having a reduced amplitude A.

In the engine cover 30, the inner surface of the skin layer 16 is formed so that the sound absorbing layer 20 becomes thicker from the vehicle front F side (anti-occupant compartment side) toward the passenger compartment C side corresponding to the separation width of each separation space portion. Laid. For this reason, as described above, it is possible to effectively absorb the synthesized wave generated in each separation space between the “first separation space 18” and the “second separation space 12”.
That is, the synthesized wave generated in each of the separated spaces (for example, the synthesized wave w3 in the first separated space 18) is a node having the smallest amplitude A on the skin layer 16 side with reference to FIGS. The (sound source) side is the antinode with the maximum amplitude A. For this reason, the antinode of the synthetic wave is located in the vicinity of the engine 8 as a sound source. Therefore, in the present embodiment, the sound absorbing layer 20 is thickened (disposed in the vicinity of the engine 8) so as to correspond to the separation width of each separation space portion, so that the synthesized wave generated in each separation space portion is generated in the vicinity of the engine 8. It can absorb sound effectively.
Further, the engine cover 30 has a particularly large thickness of the sound absorbing layer 20 between the vertical wall portion 14 formed on the passenger compartment C side and the engine 8, and the thickness of the engine cover 30 other than the standing wave increases toward the passenger compartment C side. The noise absorption effect of the engine noise is increased and the transmitted noise is reduced. For this reason, according to the engine cover 30, noise (so-called in-vehicle sound) in the passenger compartment C is particularly reduced, so that quietness is further improved.

Next, each component of the engine cover 30 will be described.
[Skin layer]
The skin layer 16 only needs to have rigidity capable of reflecting the noise of the engine 8, and can be formed of a resin molded body such as metal or polyamide, or a laminate of natural fibers.
Here, natural fibers include animal fibers such as animal hair and silk, bast fibers such as kenaf, ramie, jute and flax, leaf vein fibers such as zaisal hemp, seed hair fibers such as cotton and kapok, Plant fibers obtained from fruit fibers such as palm, and mineral fibers such as asbestos. The skin layer 16 made of such a laminated body of natural fibers has an uneven surface as compared with the resin molded body, so that the softness is improved.

In addition, the skin layer 16 made of a laminate of bast fibers such as kenaf is excellent in appearance because it is superior in antifouling property and shape retention as compared with a polyamide resin molded product. For example, a fiber (kenaf fiber) obtained from kenaf has low chargeability as compared with a polyamide resin, and therefore, dust adhesion due to charging is small. Further, since the thermal expansion coefficient of kenaf fibers is low, the skin layer 16 made of the kenaf fiber laminate is less warped or deformed by the heat of the engine 8.
Kenaf fibers have a lower thermal conductivity than resins such as polyamide. Specifically, the thermal conductivity of polyamide (PA6) is 0.2 W / m · K, whereas the thermal conductivity of the fiber obtained from kenaf is 0.1 W / m · K. For this reason, the skin layer 16 made of a laminate of kenaf fibers can reduce the feeling of heat when the skin layer 16 is touched when the oil of the engine 8 is changed.

Here, the manufacturing method of the skin layer 16 made of a laminate of natural fibers will be described. First, a fiber mat in which natural fibers are laminated by a technique such as carding, fleece, air laying, and entangled by a needle punch method or a spunlace method. Form. This fiber mat is impregnated with a binder resin (for example, a thermosetting resin such as lignin or a thermoplastic resin). Then, the skin layer 16 can be manufactured by heating and pressurizing while bending or curving the rear end of the skin layer 16 downward (forming the vertical wall portion 14) in a pressure molding machine such as a hot press machine. it can. At this time, it is also possible to press the fiber mat with a cold press after melting the binder resin of the fiber mat with a heater in advance.
When the skin layer 16 is manufactured with resin, the vertical wall portion 14 and the other skin layer 16 portions are manufactured by injection molding, and then both are bonded to form the skin layer 16.

[Sound absorbing layer]
The sound absorbing layer 20 is a laminate formed by entanglement of chemical fibers and natural fibers such as foam (urethane foam) made of urethane resin, chip urethane obtained by crushing and compressing foam of urethane resin, and polyethylene terephthalate (PET). (Including felt). When the natural fiber laminate is used as the sound absorbing layer 20, the natural fiber laminate is preferably waterproofed so as not to be adversely affected by water vapor in the air in the engine room 6. For example, a natural fiber sound absorbing layer 20 having waterproofness equivalent to that of the chemical fiber sound absorbing layer 20 can be produced by performing a formalization treatment in which natural fibers are crosslinked with formaldehyde.
The engine cover 30 of the present embodiment can be manufactured by making the sound absorbing layer 20 into a desired shape corresponding to the skin layer 16 and then fixing the sound absorbing layer 20 to the skin layer 16 by adhesion or heat caulking.

  The engine cover 30 is preferably configured such that at least one of the skin layer 16 and the sound absorbing layer 20 is formed of a laminate of natural fibers. By constituting at least one of the skin layer 16 and the sound absorbing layer 20 with natural fibers, the engine cover 30 is more environmentally friendly than the conventional engine cover 30 made of metal or resin. That is, the skin layer 16 or the sound absorbing layer 20 made of a laminate of natural fibers is carbonized without being dissolved by the heat of the engine 8, so that no harmful gas is generated due to its thermal decomposition, and it is safer at the time of collision or at a high temperature. It is.

[Embodiment 2]
4A is a longitudinal sectional view of an engine cover according to the second embodiment in the engine room, and FIG. 4B is a longitudinal sectional view of a conventional engine cover in the engine room.
Since the basic configuration of the engine cover according to the second embodiment is substantially the same as that of the engine cover according to the first embodiment, the detailed description thereof will be omitted by attaching the corresponding reference numerals to the members corresponding to the first embodiment. .
In the engine cover 30a of the second embodiment, referring to FIG. 4A, the vertical wall portion 14 corresponds to the shape of the wall (dash panel 2) on the passenger compartment C side that forms the engine room 6 of the vehicle. It has a curved shape.

  By the way, it is known that an air flow having a wind speed of about 1/3 of the air flow flowing outside the vehicle is generally generated in the engine room 6 while the vehicle is running. For this reason, referring to FIG. 4 (B), the rear end of the engine cover 40 is separated with a substantially T-shaped longitudinal section (the rear end of the skin layer 46 is opposed to the vertical wall portion 44). In the state of projecting toward the passenger compartment C), air is swirled by the rear of the rear end of the projecting skin layer 46, and air vortex is generated, wind noise is generated, and the engine cover 40 is vibrated. There was something to do.

On the other hand, in the engine cover 30 a of the present embodiment, the vertical wall portion 14 is curvedly extended from the skin layer 16 and has a curved shape corresponding to the shape of the dash panel 2 constituting the engine room 6. For this reason, in the engine room 6, the flow of the air which passes between the dash panel 2 and the vertical wall part 14 becomes smooth, and generation | occurrence | production of a wind noise can be prevented or reduced. Further, vibration of the engine cover 30a caused by air vortices can be reduced. And since the air flow in the engine room 6 becomes smooth, the cooling performance of the engine 8 and the exhaust manifold installed in the engine room 6 is also improved.
And the skin layer 16 provided with the vertical wall part 14 of such a shape can be easily manufactured by pressure-molding with a pressure-molding machine, for example using a natural fiber mat as a base material.

[Embodiment 3]
FIG. 5 is a longitudinal sectional view of the engine cover of the third embodiment.
Since the basic configuration of the engine cover according to the third embodiment is substantially the same as that of the engine cover according to the first or second embodiment, detailed description thereof will be omitted by assigning corresponding reference numerals to members corresponding to the first or second embodiment. I decided to.
In the engine cover 30b of the third embodiment, the sound absorbing layer 20 is made of natural fibers, and the density is increased stepwise or continuously from the engine 8 toward the skin layer 16. Features.
For this reason, in the engine cover 30b of the present embodiment, noises having different wavelengths (frequencies) are reflected stepwise from the engine 8 in the thickness direction of the sound absorbing layer 20 in the skin layer 16, thereby attenuating noise having a wider frequency range. Can be made.

An example of manufacturing the sound absorbing layer 20 as described above will be described. First, natural fibers (φ100 to 200 μm) having a large fiber bundle diameter, such as kenaf, jute, and sisal, are laminated. A thin natural fiber (φ20 to 40 μm) such as ramie, cotton, or rayon is laminated thereon and entangled by a technique such as a needle punch. As a result, the lower part of the sound absorbing layer 20 arranged on the engine 8 side is in a low-density state in which the natural fibers having a large fiber bundle diameter are slightly entangled with each other so that there are many voids between the fibers. On the other hand, the upper part of the sound absorbing layer 20 disposed on the skin layer 16 side is entangled in a dense state with natural fibers having a small fiber bundle diameter, and thus has a high density state with few gaps between the fibers.
At this time, the density of the sound absorbing layer 20 is continuously increased from the lower part to the upper part by gradually increasing the content ratio of the natural fibers having a large fiber bundle diameter to the natural fibers having a small fiber bundle diameter. You can also make it bigger. Moreover, the density of the sound absorbing layer 20 can be increased stepwise from the lower part to the upper part by combining the nonwoven fabrics made of natural fibers having different fiber bundle diameters in multiple layers.

[Example]
Next, the engine cover of the present embodiment will be specifically described with reference to the drawings.
[Engine Cover of Example 1]
FIG. 6 is a manufacturing process diagram of the engine cover of the embodiment. This example corresponds to the engine cover 30 of the first embodiment described above.
[Skin layer]
Using a technique such as a card, kenaf fibers were laminated so as to have a basis weight of 100 to 200 g / m ² (140 g / m ² in this example), and then entangled with a needle punch to obtain a fiber mat 19. Then, lignin 50 (liquid) was spray applied to the fiber mat 19. At this time, the lignin 50 was adhered to the fiber mat 19 so that the fiber mat: lignin = 6: 4 in the weight ratio after drying. Then, after passing through the dryer 72 (set at 120 ° C. to 130 ° C.) and sufficiently dried, the fiber mat 19 was cut into a predetermined size with a cutter 74. The fiber mat 19 was set between the molds 76 and 78 of the hot press machine 80. And the press surface temperature of the shaping | molding dies 76 and 78 was 150 degreeC-about 200 degreeC which the lignin 50 hardens | cures, and it pressurized for 3 minutes with the pressure of 20-50 kgf / cm < ² >. In this way, a skin layer 16 (density: 1.36 kg / m ² ) having a thickness of 1.4 to 2.1 mm (2.1 mm in this example) was formed (see FIG. 2). Then, the surface of the skin layer 16 after molding was painted and waterproofed to improve the design.

  Here, the molds 76 and 78 of the above-described hot press machine have shapes that allow the fiber mat 19 to be molded into a desired shape, which will be described later. That is, with reference to FIG. 2, the vertical wall portion 14 is formed to be bent and formed at the rear end portion of the skin layer 16 when finished. As described above, the separation width of the separation space portion between the skin layer 16 and the engine 8 is larger than the second separation space portion 12 (separation) than the first separation space portion 18 (the separation width R1 is set to 8 mm). The width R2 is set to 30 mm) and the molding is performed in an arrangement state in which the width R2 increases continuously or stepwise.

[Sound absorbing layer]
After laminating PET fibers having a fiber length of 100 to 500 mm extruded in a solvent, they are entangled by a needle punch and thickened from the front F side to the passenger compartment C side corresponding to the shape of the skin layer 16 described above. However, what was molded into a predetermined shape, density and hardness was used as the sound absorbing layer 20 (see FIG. 2).

  The sound absorbing layer 20 was bonded to the inner surface of the skin layer 16 by adhesion or heat caulking to obtain the engine cover 30 of Example 1.

Then, the engine cover 30 of Example 1 was attached to the engine 8 by providing sealing materials (made of urethane resin) (not shown) at the four corners so that no gap was generated.
By the way, in the engine cover 30 attached to the engine, referring to FIG. 2, in the first separation space 18 (separation width R1 = 8 mm), a 10.6-kHz noise (first The noise n1) is attenuated, and the 2.8 kHz noise (second noise n2) is attenuated by the following calculation formula (4) in the second separation space 12 (separation width R2 = 30 mm). For this reason, the engine cover 30 is provided with engine noise in a frequency band of at least 2.8 kHz to 10.6 kHz by the separate space portions between the “first separate space portion 18” and the “second separate space portion 12”. (For example, mechanical noise) was assumed to be attenuated.
(4) [Frequency f] = 340 / (0.030 × 4) = 2,800 (Hz)

[Engine Cover of Comparative Example 1]
FIG. 7 is a longitudinal sectional view of an engine cover (conventional engine cover) of a comparative example.
As the engine cover 40 of Comparative Example 1, a skin layer 46 (made of PA6-MD40) having a thickness of 2.4 mm, on which the sound absorbing layer 47 made of urethane foam is laid, is used.
In the engine cover 40 of the comparative example, the separation width r1 of the first separation space 48 on the vehicle front F side is set to 8 mm, and the separation width r2 of the second separation space 42 on the passenger compartment C side is set to 8 mm. Set. The thickness of the sound absorbing layer 47 laid on the inner surface of the skin layer 46 was set to about 8 mm.

[Volume absorption test]
FIG. 8 is a diagram illustrating a method for performing a sound absorption volume measurement test.
In the sound absorption volume measurement test, a direct 4-gasoline engine 8 was used, and a micro horn 82 was disposed 0.2 m above the engine 8 (H). Then, after the engine cover 30 of the first embodiment is mounted on the engine 8, the engine 8 is accelerated and decelerated at 1,200 to 6,000 rpm in the 2nd range, and the noise of the engine 8 generated at that time is reduced to the microphone 82 above the engine 8. Measured with. This measurement result was analyzed by a computer (not shown), and a 1/3 OCT analysis value was calculated.
Further, after the engine cover 40 of Comparative Example 1 was attached to the engine 8, the noise of the engine 8 was measured under the same conditions as in Example 1 described above, and a 1/3 OCT analysis value was calculated.
Then, with the engine 8 in an exposed state, the noise of the engine 8 was measured under the same conditions as in Example 1 described above, and this 1/3 OCT analysis value was used as a control (reference) of the sound absorption volume described later.

[Test results]
FIG. 9 is a diagram showing the results of the sound absorption volume measurement test. The vertical axis of the graph shown in the figure represents the sound absorption volume (dB), and the horizontal axis of the graph represents the center frequency in 1/3 OCT analysis. Here, the sound absorption volume indicates the sound absorption volume (dB) calculated by subtracting the noise value when each engine cover is used from the noise value of the control described above.
From FIG. 9, it was found that the total sum of the sound absorption volume of the engine cover 30 of Example 1 was reliably increased in the frequency band of 1 to 5 kHz as compared with the engine cover 40 of Comparative Example 1. This result supports the above-described assumption that the engine cover 30 of the first embodiment absorbs the noise of the engine 8 in the frequency band of 2.8 kHz to 10.6 kHz.
Moreover, the engine cover 30 of Example 1 showed a sound absorption effect comparable to the engine cover 40 of Comparative Example 1 in a frequency band of 250 Hz to 500 Hz (so-called “boom sound”).
The engine cover 30 of Example 1 was about 70 g lighter than the engine cover 40 of Comparative Example 1.

The engine covers 30, 30a, 30b according to the above-described embodiments are not limited to the above-described embodiments, and may take other various embodiments.
That is, in the first embodiment, the example in which the vertical wall portion 14 extends in a bent shape at the rear end portion of the skin layer 16 has been described. Unlike this, the vertical wall portion 14 of the first embodiment is projected so as to form a substantially T-shape as viewed in the vertical cross section with reference to FIG. 7 as long as the second spaced-apart space portion can be formed. It is good also as a structure extended. Such a skin layer 16 can be manufactured by separately forming a bowl-shaped skin layer and a plate-like vertical wall portion, and bonding or bonding the vertical wall portion to the rear end of the skin layer.

  In Example 1, an asphalt layer having a thickness of 1.5 mm may be provided on the inner surface of the skin layer 16. In this way, the surface density of the skin layer 16 increases, so that the noise of the engine 8 can be more reliably insulated and reflected.

  In the first and third embodiments, the example in which the engine is mounted on the front portion of the vehicle has been described. Unlike this, the engine cover of Embodiment 1 or 3 can also be attached to an engine mounted on the rear portion of the vehicle. In this case, the vehicle rear side is the anti-occupant compartment side.

It is a longitudinal cross-sectional view of an engine room. It is the longitudinal cross-sectional view of an engine cover, and is the figure which showed the noise of the engine with the arrow dotted line. It is explanatory drawing explaining that engine noise (emission wave) and the reflected wave interfere with it, and a synthetic wave arises, (I) is a waveform of an emission wave, (II) is a waveform of a reflected wave , (III) is the waveform of the synthesized wave. (A) is a longitudinal cross-sectional view of the engine cover of Embodiment 2 in an engine room, (B) is a longitudinal cross-sectional view of the conventional engine cover in an engine room. It is a longitudinal cross-sectional view of the engine cover of Embodiment 3. It is a manufacturing-process figure of the engine cover of an Example. It is a longitudinal cross-sectional view of the engine cover (conventional engine cover) of a comparative example. It is a figure which shows the implementation method of a sound absorption volume measurement test. It is a figure which shows the result of a sound absorption volume measurement test.

Explanation of symbols

2 Dash Panel 4 Hood Panel 6 Engine Room 8 Engine 12 First Separation Space 14 Vertical Wall 16 Skin Layer 18 Second Separation Space 19 Fiber Mat 20 Sound Absorption Layer 30 Engine Cover of Embodiment 1 (Example 1) 30a Engine cover 30b of Embodiment 2 Engine cover 40 of Embodiment 3 Engine cover 50 of Comparative Example 1 Lignin 72 Dryer 74 Cutter 76, 78 Mold 80 Hot press machine 82 Microphone

Claims (3)

A skin layer for insulating noise generated from the engine of the vehicle is disposed at a position above the engine at a distance from the engine, and an inner space on the engine side of the skin layer is filled with a space between the engine and the engine. An engine cover provided with a sound absorbing layer for absorbing the noise of
In the skin layer, a separation width of a separation space portion between the engine and the engine extends from a first separation space portion formed on a side opposite to the passenger compartment of the engine toward a lower portion on the passenger compartment side of the engine. It is formed as an arrangement state that is set large continuously or stepwise toward the second separated space portion formed between the vertical wall portion to be installed,
The sound absorbing layer is laid on the inner surface of the skin layer so as to increase in thickness from the counter occupant chamber side toward the occupant chamber side corresponding to the separation width of each of the separation space portions. Engine cover. The engine cover according to claim 1,
The skin layer is composed of natural fibers,
The engine cover according to claim 1, wherein the vertical wall portion has a curved shape corresponding to a shape of a wall on the passenger compartment side that forms an engine room of the vehicle. The engine cover according to claim 1 or 2,
The engine cover according to claim 1, wherein the sound absorbing layer is made of natural fibers and has a density that is increased stepwise or continuously from the engine toward the skin layer.

Images