JPS6160254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sound reduction cover that reduces medium and high frequency noise emitted from an engine.

In diesel engines, there is a period of ignition delay because it takes time for the injected fuel to vaporize.
Especially during idling operation or low-speed, low-load operation, the ignition delay period is long, and the fuel accumulated by the time of ignition is burned all at once, increasing the rate of pressure rise in the cylinder, resulting in so-called diesel knock.
This increases the noise level of medium and high frequencies,
The problem is that it causes discomfort. The engine noise especially during idling is 1KHz~
The main noise is at a frequency of 3KHz, causing audible discomfort. Also, even during high-speed, high-load operation, medium- and high-frequency noise components caused by combustion pressure are the main components. For this reason, it is desired to reduce noise components in medium and high frequencies, and it is important to improve the timbre of the noise and eliminate auditory discomfort as well as to reduce the overall value.

Since a large amount of engine noise is emitted through various covers such as the oil pan and rocker cover, it is advantageous to provide sound insulating covers for the various covers such as the oil pan and rocker cover in order to reduce engine noise. For this reason, various sound insulation covers have been proposed to cover various engine covers. (Reference: Jitsukaiaki
(No. 55-163419) However, all conventional sound insulation covers are intended to have a simple sound insulation effect, and a resonance phenomenon occurs in the space between various types of covers and the sound insulation cover, causing the noise level of a specific frequency to increase. There is an increasing problem, and no solution to this problem has been found so far.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide a sound reduction cover that can absorb particularly unpleasant middle and high frequency noise components, improve the noise timbre, and reduce the overall value.

For this reason, the present invention focuses on areas with a high noise generation rate,
For example, a sound reduction cover with a large number of holes is provided on the outside or inside of various covers such as oil pans and rocker covers, and by selecting the dimensions of these holes, the resonance effect can be actively used and maintained. It is characterized by reducing noise components in the middle and high frequency ranges that cause timbre problems, and also providing an overall sound insulation effect.

That is, in the present invention, each hole of the sound reduction cover acts as a resonance tube, thereby obtaining a sound absorption effect in a narrow frequency range.
This sound absorption effect is used to reduce noise components in the desired frequency range and improve the tone.

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows oil pan 2 of diesel engine 1.
It shows a state in which a sound attenuation cover 3 according to a first embodiment of the present invention is attached to the outside. This sound reduction cover 3
has almost the same shape as the oil pan 2, but is formed deeper, and the mounting flange 3A on the periphery overlaps the mounting flange 2A of the oil pan 2 and is fixed together to the cylinder block 4 with bolts 5. ing. By fixing this bolt, the sound reduction cover 3
A space 6 is formed between the oil pan 2 and the oil pan 2, and the oil pan 2 is installed with sufficient vibration isolation. As shown in FIG. 1A, the sound attenuation cover 3 also includes a peripheral member 3' made of a steel plate having a flange 3A, and a vibration isolator made of a vibration absorbing material fixed to the peripheral member 3' by any means such as adhesive. It is made up of 3" members and suppresses vibration as much as possible. However, the whole can also be integrally formed from a steel plate or a vibration absorbing material.

As shown in FIG. 2, this sound reduction cover 3 has a large number of openings or holes 3B formed over almost the entire surface thereof. Furthermore, an operation port 3C is formed to operate a drain tank 7 (FIG. 1) provided in the oil pan 2, and a blind plug 8 (FIG. 1) is attached to the operation port 3C.

Here, the hole 3B, which is a feature of the present invention, will be explained with reference to FIG. , and the spatial volume of each hole 3B is assumed to be V. In such an arrangement, each hole 3B can be regarded as having a cavity 9 and a neck 10 as shown in FIG. 4A.
When the sound source is located further outward and the dimension of the cavity 9 is smaller than the wavelength, the air moves as one mass in the network 10, and mechanically the spring 11 has a mass 12 as shown in FIG. 4B. Consider a single resonant system in which the The resonance frequency o in this case is given by the following equation.

o=C/2π√...(1) C: Speed of sound G: S/le S: Cross-sectional area of the net le: Effective length of the net (=l+δ) δ: Tube end correction value V: Cavity volume ∴ o=C /2π〓S/leV=C/2π〓S/V(
l+δ) (2) This single resonator produces a sound absorption effect in an extremely narrow frequency range around its resonant frequency. Therefore, by selecting each dimension, it is possible to reduce any unpleasant noise in the middle or high frequency range, for example.

Furthermore, when there is a sound source inside the cavity 9, it can be regarded as a pipe with one end open and the other end closed, and the frequency in that case is given by the following equation.

=C/2lαn...(3) αn=n-1/2=1/2, 3/2, 5/2... In this case, when the frequency of the sound source matches one of the reference frequencies of this resonator, Radiation from the network 10 becomes maximum, intensifying the reference tone and its odd harmonics.

Therefore, considering this, the thickness of the sound reduction cover 3,
By selecting the dimensions of the holes 3B, their number, the dimensions of the space, etc., it is possible to reduce noise in any frequency range. Moreover, the noise level can be reduced due to the sound insulation effect of the sound reduction cover 3 itself.

That is, the interval space 6 formed by the sound reduction cover 3 and the hole 3B constitute a resonator with a sound source inside, and the resonance is enhanced because it has the effect of strengthening the reference tone determined by equation (3) and its odd harmonics. If the frequency is selected in a frequency range with a low noise level, it is possible to reduce the overall noise level despite the increase in volume due to this resonance.

FIG. 5 shows another embodiment, in which holes 3B' and 3B'' of different sizes are formed, and sound absorption in a wider frequency range is made possible by combining the sound absorption frequency ranges due to their respective effects. There is.

FIG. 6 shows still another embodiment in which metal steel 13 is provided along the inside of the sound attenuation cover 3 to reduce noise increase due to the resonance phenomenon caused by the hole 3B and the space 6.

Still another embodiment of the invention is shown in FIG. This embodiment is the sound reduction cover 3 in the embodiment described above.
A protective cover 21 is further provided on the outside of the sound absorbing member 20 having the hole 20A corresponding to the hole 20A, so that the above-described sound absorbing effect of the sound absorbing member 20 can be obtained even more advantageously. As described above, the sound absorbing member 20 and the protective cover 21 are preferably made of a vibration isolating material, each having an operation opening for the drain plug 7 and a blind stopper 8 attached thereto. In this case, protective cover 2
1, it is desirable to create a state in which the sound sources are on both sides of the sound absorbing member 20 without forming holes, and to absorb sound through the holes 20A. However, similar to the embodiment of FIG. 5, holes of different sizes can also be formed.

Although not described in the above explanation, it is desirable to form an opening 22 for cooling the oil pan 2, and from the viewpoint of cooling effect and sound insulation effect, this opening 22 should be formed only at positions corresponding to the front and rear of the engine. It is desirable to be prepared. A similar effect can also be obtained by placing a sound reduction cover inside the oil pan or inside the rocker cover.

As explained above, in the present invention, the hole formed in the sound reduction cover and the space formed along the sound reduction cover are used to actively utilize the resonance phenomenon and absorb sound. In addition to the sound absorption effect, the sound absorption effect is effective in reducing the noise level in the desired frequency range.
The timbre of the noise emitted by the entire engine can be improved, and a great effect can be obtained that eliminates discomfort.

[Brief explanation of the drawing]

FIG. 1 is a schematic partially cutaway side view showing an engine with a sound reduction cover installed according to an embodiment of the present invention. FIG. 1A is a partially enlarged view of the sound reduction cover shown in FIG. FIG. 2 is a plan view of the sound reduction cover shown in FIG. 1.
FIG. 3 and FIGS. 4A and 4B are explanatory diagrams showing the sound reduction principle of the sound reduction cover of the present invention. FIG. 5 is a plan view of a sound reduction cover according to another embodiment of the present invention. FIG. 6 is a plan view showing holes in a sound reduction cover according to still another embodiment. FIG. 7 is a schematic partially cutaway side view showing a sound reduction cover according to another embodiment of the present invention when it is attached to an engine. 1...diesel engine, 2...oil pan, 3
...Sound reduction cover, 3'...peripheral member, 3''...vibration isolating member,
3B, 3B', 3B''...opening or hole, 4...cylinder block, 5...bolt, 6...interval space, 7
...Drain pot, 8...Blind stopper, 9...Cavity part, 10...
net, 11... spring, 12... square, 13... wire mesh,
20... Sound absorbing member, 20A... Hole, 21... Protective cover, 22... Opening.

Claims (1)

[Scope of Claims] 1. A sound reduction cover having a number of holes installed outside or inside a part of an engine with a high noise generation rate with a space between the part and the space, the cover having a plurality of holes, the holes, the space, etc. An engine reduction method characterized in that a resonator is formed by selecting dimensions to cause engine sound to resonate, and this resonance phenomenon reduces noise components in a frequency range determined by each of the predetermined dimensions. sound cover. 2. A patent claim characterized in that a protective cover is further disposed with a space provided on the outside of the sound reduction cover, and a resonator is formed by the space formed on both sides of the sound reduction cover and the hole. A sound reduction cover for the engine described in item 1.