This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-74536 filed on Mar. 22, 2007; the entire contents of which are incorporated herein by reference.
The invention relates to a muffle duct applicable for an intake system of, for example, an internal combustion, an air conditioner or an air compressor.
A general intake duct causes a noise when allowing air to be taken or be discharged therethrough.
A related intake duct includes a resonator for muffling the noise. The resonator is required to have 4 to 8 L (liter) for a low frequency and 0.2 to 0.5 L (liter) for a middle frequency (Refer to Patent Document 1).
Another intake duct includes a nonwoven fabric adhered to the internal. This nonwoven fabric produces an effect of preventing resonance of a noise in the duct (Refer to Patent Document 2).
Another intake duct includes a sound absorption material wound around the outer circumference (Refer to Patent Document 3).
Another intake duct includes an expansion chamber. This expansion chamber produces an effect of muffling a noise of a high frequency range (Refer to Patent Document 4).
Patent Document 1: Japanese Patent Application Laid-open No. Hei 6-159174
Patent Document 2: Japanese Patent Application Laid-open No. 2003-343373
Patent Document 3: Utility Model Application Laid-open No. Hei 5-38352
Patent Document 4: Japanese Patent Application Laid-open No. Hei 9-144986
Any of the intake ducts, however, produces the effect of muffling a noise of a predetermined frequency range. An intake duct has not been developed, producing the effect of muffling noises of all frequency ranges.
The invention is directed to a muffle duct to muffle noises of high, middle and high frequency ranges.
The first aspect of the invention provides the following muffle duct. The muffle duct includes a pipe incorporated in an intake system and having a first hole for a noise in the intake system to be released therethrough. The muffle duct includes a cover covering the pipe for attenuating the noise and having a second hole coinciding with the first hole circumferentially of the pipe.
The cover may include a guide for guiding a noise from the second hole.
The second hole may have a slit.
The first hole may have a slit.
Embodiments of the invention will be described below with reference to the accompanying drawings.
With reference to
With reference to
With reference to
With reference to
The inner pipe 11B has slits 11d arranged in two rows in the axial direction (Refer to
With reference to
The cylindrical outer pipe 13 is placed between the flanges 11b of the inner pipe 11, covering the sound absorption material 12. The outer pipe 13 has a slit 13a as a second hole extending in the axial direction (Refer to
With reference to
With reference to
Next, a method of operating the intake system 1 is described.
With reference to
Then, with reference to
The released intake noise is guided by the guide pipe 15a outward of the outer pipe 13 to strike against the second guide plate 15b. The first guide plate 15b bends the travel direction of the intake noise at a right angle relative to the guide pipe 15a. The second guide plate 15c bends the travel direction of the intake noise at a right angle relative to the first guide plate 15b. The intake noise strikes against the outer pipe 13 to travel along the third guide plate 15d to radiate outside.
When water tends to enter the muffle duct 5, the guide pipe 15a encloses the inlet of the slit 13a and the first to third guide plates 15b, 15c and 15d provide complication to the path of entering of the water, thus preventing water from entering.
According to the above muffle duct 5, it efficiently attenuates intake noises of low, middle and high frequency from 20 Hz to 2000 Hz.
The guide 15 provides complication to the path to the slit 13a of the outer pipe 13, thus preventing water from entering.
The slit 13a provides directionality to the direction of radiating the intake noise.
Next, with reference to
The graph illustrated in
The example shows a large attenuation of around 20 dB at the maximum for noises of substantially whole low and middle frequency ranges from 20 Hz to 1000 Hz, comparing to the comparative example 1.
The graph illustrated in
According to the above description, it is shown that the example attenuates intake noises of low and middle frequency ranges from 20 Hz to 2000 Hz. The example shows a preferable attenuation for intake noise of a high frequency range.
With reference to
The inner pipe 21 includes a pair of flanges 21b at both the ends in the axial direction.
The inner pipe 21 has a slit 21a extending between the flanges 21b in the axial direction (Refer to
The inner pipe 21 has circular holes 21d placed opposite to the slit 21a. The circular holes 21d are arranged in the axial direction.
With reference to
The outer pipe 23 covers the circumferential surface of the sound absorption material 22. The outer pipe 23 has relief holes 23a arrayed in the axial direction. These relief holes 23a are positioned on the straight line with the slit 21a of the inner pipe 21 and the elongated holes 22a of the sound absorption material 22. Therefore, the relief holes 23a coincide with the slit 21a and the elongated holes 22a, facing them 21a and 22a.
The above-described muffle duct 5A muffles intake noises of low, middle and high frequencies, as well as the first embodiment.
The slit 21a provides directionality to the direction of radiating the intake noise.
The elongated hole 22a of the sound absorption material 22 allows dust to pass from outside through the slit 21a to come out of the inner pipe 21, thus preventing the sound absorption material 22 from being clogged.
With reference to
Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.
The muffle ducts 5 and 5A according to the first and second embodiments may be applied to not only the intake system but also an exhaust system.
The muffle duct 5 and 5A may be applied to not only an internal combustion but, for example, an air conditioner or an air compressor of a device causing noise. According to the aspect of the invention, an noise in the intake system travels through the first hole of the pipe to enter the cover. The cover attenuates noises of middle and high frequencies. The cover radiates a noise of a low frequency range from the second hole. Thus, the noise in the intake system attenuates in the low, middle and high frequency ranges.
The guide renders the path to the second hole complicated, allowing entering of water to be difficult.
The first and second holes are formed in a slit, providing directionality to the direction of radiating the intake noise.
Number | Date | Country | Kind |
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2007-074536 | Mar 2007 | JP | national |