JPH0481512A - Exhaust flexible tube - Google Patents

Abstract

PURPOSE:To reduce exhaust resistance and eliminate increasing of a weight and rising of a cost by setting that the height of projection and a plate thickness of bellows used for a flexible tube inserted in the way of an exhaust tube, have a specified relation. CONSTITUTION:A bellows 1 is inserted in an exhaust flexible tube. The height of the projection of the bellows 1 is set at (h)mm, and the plate thickness of the bellows 1 is set at (t)mm. When the exhaust flexible tube is designed, most effective combination of the height (h) of the projection and the plate thickness (t), in response to different noise, is h=(6t + 6.3)+ or -0.5. Since an inner blade is not provided in the exhaust flexible tube, it is possible to reduce exhaust resistance, while obtaining most effective noise reduction effect without causing any increase of a weight and rising of a cost.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a flexible tube inserted into the middle of an exhaust tube of a vehicle or the like equipped with an internal combustion engine.

(Prior Art) FIG. 7 shows an example of a conventional exhaust flexible tube. In the figure, 1 is a bellows, and 2 is an inner blade, which is a cylindrical mesh body inserted to cover the inner surface of the bellows 1 in order to reduce abnormal noise generated when the bellows part is excited by the exhaust flow. , 3 is an outer blade placed over the outer periphery of the bellows 1.

(Problem to be Solved by the Invention) However, as described above, when the inner blade 2 is inserted inside the bellows l, since the inner blade 2 has a net shape, the resistance to the exhaust flow increases, and the weight of the exhaust pipe system increases. There was a problem in that the manufacturing cost also increased as the number increased.

(Means for Solving the Problems) In order to solve the above-mentioned problems, in the present invention, in the bellows part used for the flexible tube inserted in the middle of the exhaust tube, the height of the peak of the bellows is hmm, When the plate thickness is tmm, h −
The exhaust flexible tube is configured as (6t+6.3)±0.5.

(Function) The resonant frequency of the bellows changes depending on the height of the bellows' ridges and the thickness of the plate, but the height of the ridges cannot be too high or too low. There is a peak height that maximizes the frequency.

There is also a certain relationship between the height of the peak that maximizes the resonance frequency and the thickness of the plate.

That is, when the height of the bellows peak is hInII+ and the plate thickness is t and m, there is a relationship shown by h = 6t + 6.3.

Also, the sound level that can be reduced by the pitch and shape of the bellows peaks is said to be approximately 5 cfB, but if this is converted into frequency, it becomes 700) + 2, and if the height of the bellows peaks is approximately 0.5 mm. becomes.

Therefore, the range of h=(6t+6.3)±0.5 is the combination of the height of the hemlock and the plate thickness that has the most effective sound deadening effect in a flexible tube without an inner blade.

As mentioned above, according to the present invention, since no inner blade is provided in the exhaust flexible tube, exhaust resistance can be reduced accordingly, and the most effective method can be achieved without causing an increase in weight or cost. It is possible to obtain a sound deadening effect.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

In Fig. 1, 1 is the bellows inserted into the exhaust flexible tube, h is the height of the bellows (unit: mm), p is the pitch, and t is the plate thickness of the bellows (unit: -). .

The generation of abnormal noise within the bellows is due to resonance within the bellows, and the relationship between the resonance frequency and the level of the abnormal noise is as shown in Figure 2. As the resonance frequency becomes larger than this, the abnormal noise is generated. It can be seen that the level is reduced.

The following three methods can be considered as methods for increasing the resonant frequency.

(1) Increase the plate thickness t of the alloy 1.

As shown in Fig. 3, this method is effective because increasing the plate thickness t increases the resonant frequency, but on the other hand, increasing the plate thickness increases the weight of the exhaust pipe system and There is a drawback that manufacturing costs also increase.

(2) Reduce the pinch p of the bellows 1.

This method has little effect as shown in FIG.

(3) Select the height h of the peak of the bellows 1.

This method is as shown in FIG. 5, and the resonant frequency of the bellows reaches its maximum value at point A. That is, the height of the mountain in this case is the optimum value, and the effect of selecting the height h of this mountain is large.

Therefore, the most effective method is method (3).

Further, FIG. 6 shows the relationship between the optimum peak height h and the plate thickness t, which can be expressed by the following equation.

h= 6t +6.3...■By the way, the second
As shown in the figure, the level of abnormal noise that can be reduced by the pitch of the bellows, the shape of the ridges, etc. is said to be approximately 5 dB, but when converted to frequency, it is 700 Hz, which is based on the axial resonance mode in Figure 5. The height of the mountain is approximately 0.5 mm.

Therefore, from the formula (■) above, h = (6t +6.3) ±0.5...■The above formula allows for a margin that can be reduced by measures other than the height h of the bellows peak and the plate thickness t. This is the area that includes. Therefore, (2) is the combination of peak height h and plate thickness t that is most effective against abnormal noise in the exhaust flexible tube design.

Points B and 0 in FIG. 6 indicate the specifications of other companies' exhaust flexible tubes, and both are outside the scope of the present invention.

(Effects of the Invention) As mentioned above, the resonant frequency of the bellows changes depending on the height of the bellows' peaks and the plate thickness, but the height of the peaks cannot be too high or too low; In the middle there is a peak height that maximizes the resonant frequency (
(See point A in Figure 5).

There is also a certain relationship between the height of the peak that maximizes the resonance frequency and the thickness of the plate.

In other words, the height of the bellows peak is hmm, and the plate thickness is t.
When mm, there is a relationship expressed by the equation h = 6t + 6.3.

Also, the sound level that can be reduced by the pitch and shape of the bellows peaks is said to be about 5 dB, but if you convert this into a frequency, it becomes 700t (z), and if you measure the height of the bellows peaks, it is about 0.5 dB. Becomes anus.

Therefore, in a flexible tube without an inner blade, the range h=(6t+6.3)±0.5 is the combination of the height of the bellows and the plate thickness that has the most effective silencing effect.

As mentioned above, according to the present invention, since no inner blade is provided in the exhaust flexible tube, exhaust resistance can be reduced accordingly, and the most effective method can be achieved without causing an increase in weight or cost. This provides an excellent sound silencing effect.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional view of the bellows according to the present invention, Figure 2 is a diagram of the relationship between the resonance frequency and abnormal noise level, Figure 3 is a diagram of the relationship between the plate thickness of the bellows and the resonance frequency, and Figure 4 is a diagram of the relationship between the bellows plate thickness and the resonance frequency. Fig. 5 is a relational diagram between the pitch of the bellows and the resonant frequency, Fig. 6 is a characteristic diagram showing the range of the present invention according to the plate thickness of the bellows and the height of the crests. FIG. 7 is a longitudinal sectional view showing an example of a conventional bellows. ■...Bellows 2...Inner blade 3...Outer blade h...Mountain height t...
Plate thickness p...Pitch Figure 1 Figure 3 Figure 2 vlI Figure 4 ε0 Tsuchi p (mm) Wood ash f@t=0.3x2 Mountain 0 Height Cmm) Figure 6 Sales ftt (mm)

Claims (1)

[Claims] 1. In the bellows part used for the flexible tube inserted in the middle of the exhaust tube, when the height of the bellows peak is hmm and the plate thickness is tmm, h = (6t + 6.3) ± 0.5 Exhaust flexible tube characterized by: