JPS6248047B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an introduction pipe for guiding sound emitted from a pulsation source or a sound source to a muffler, and particularly to an introduction pipe used in an automobile engine.

Conventionally, this type of introduction tube has been constructed from a single fixed tube, so resonance may occur depending on the conditions inside the introduction tube.To avoid this, a large and complicated silencer has been installed. I needed it. In particular, when used in automobile engines, the operating conditions change significantly, so even if it does not resonate at a certain rotation speed, it will resonate at a different rotation speed, so a new noise-reducing structure is added to muffle this noise. This complicates the structure of the silencer and makes the design of the silencer difficult.

Therefore, the present invention provides a chamber in the middle of the introduction pipe that forms a boundary structure whose communication or isolation with the introduction pipe is controlled by an electromagnetic movable valve, and controls the opening and closing of the movable valve as appropriate. It is an object of the present invention to provide an anti-resonance introduction tube which is constructed so that the resonance does not always occur, and which eliminates the above-mentioned drawbacks.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

As shown in FIG. 1, the introduction pipe 1 connects a pulsation source or sound source 2, such as an engine, and a muffler 3. A hole 1a is bored in the center of the introduction pipe 1, and the hole 1a communicates with a chamber 5 surrounded by sound absorbing material and sealed except for the entrance.

This chamber 5 forms a boundary structure, and the boundary structure here refers to a structure that forms an acoustic boundary. Also, forming an acoustic boundary is explained as follows. In other words, the complex ratio between the average sound pressure p and the volume velocity U on a plane perpendicular to the direction of sound propagation in the medium is called acoustic impedance Z, and Z〓=p〓/U〓 (“・” means It is expressed as a complex effective value including the angular frequency ω and the phase angle θ), but the sound pressure and volume velocity on the left and right sides of the vertical plane including the point A as shown in Fig. 6 are respectively expressed as p〓 ₁ , U〓 ₁ and p〓
₂ , U〓 ₂ , the respective impedances Z〓 ₁ = p〓 ₁ /U〓 ₁ , Z〓 ₂ = p〓 ₂ /U
〓 When Z _{1 ≠} Z ₂ , the vertical plane containing point A is said to be acoustically bounded.

The hole 1a can be opened and closed by a movable valve 6, and the movable valve 6 is opened against a spring 8 by the excitation of an electromagnetic coil 7, as shown in FIG. The electromagnetic coil 7 is energized or de-energized by a power source 12 by a switching operation of an arithmetic switch 11, which is an arithmetic device operated based on a frequency detector 10 detected by the engine rotational speed or the like.

By the way, since the introduction pipe 1 according to this embodiment has one end closed and the other end open, when the movable valve 6 is closed, the pipe system resonates at a frequency of f _c =(2n-1)c/4l. . Note that here n
is a natural number such as 1, 2, or 3, c is the speed of sound, and l is the length of the introduction pipe 1. This is illustrated by the broken line a in FIG. 3. That is, in this tube system, n
Frequencies c/4l, 3c/4l, 5c/4l, . . . calculated by the above formula when = 1, 2, 3, . . .
... (these are indicated by fa), so the relationship between the frequency and the amount of sound amplification is as shown by the dotted line a in Fig. 3. Furthermore, if the movable valve 2 is opened and the chamber 5 is made to communicate with the center of the introduction pipe 1 through the hole 1a, and a boundary structure is provided at the center of the introduction pipe 1, then if the effect of the boundary itself is ignored, As shown by b, the resonant frequency appears at a position out of phase with the resonant frequency fa indicated by the broken line a. In this case, the two insertion tubes are equivalent: the insertion tube with one end closed and the other end open (the left half of introduction tube 1), and the insertion tube with both ends open (the right half of introduction tube 1). .

For the part with one end closed, the length l of the original pipe is
Since it is equal to 1/2, the resonant frequencies calculated from the above equation are 2c/4l, 6c/4l, 10c/4l, . . . for n=1, 2, .

Also, the formula expressing the resonant frequency f _c in the case of a pipe with both ends open (L is the length of the pipe, n and c are the same as the previous formula) fc = nc/2L, where L = l/2, n = 1, 2 , . . . , the resonant frequencies at the portion where both ends are open are 4c/4l, 8c/4l, .

Therefore, the frequencies of both parts as a whole are 2c/4l, 4c
/4l, 6c/4l, 8c/4l, ...... (these are fb)
In the case of , resonance occurs, and the relationship between the frequency and the amount of sound amplification is as shown by the dashed-dotted line b in FIG.

Therefore, the frequency of the sound introduced into the pipe 1 is detected by a frequency detector 10 using means such as engine rotation speed measurement, and if the frequency is fa, the calculation switch 11 is closed and the electromagnetic coil is 7 is energized and the movable valve 6 is opened. As a result, the resonant state of the introduction tube 1 with respect to the frequency becomes the state shown by the dashed-dotted line b in FIG.
changes along.

When a sound with frequency fb is introduced, when it is detected by the frequency detector 10 and the movable valve 6 is closed, the resonance state of the introduction pipe 1 becomes the state shown by the broken line a, so the amount of amplification is as shown in Fig. 3. It begins to change along the bottom part e of the broken line a.

By opening and closing the movable valve 6 in accordance with the frequency of the sound introduced in this way, the introduction tube 1 can be prevented from resonating significantly, and the bottom portions d and e of each line a and b can be
It is possible to reduce the amount of amplification along the lines and allow the sound to pass through.

Next, as shown in Fig. 4, both ends are open, or there is a boundary 15 where both ends are open, and the position is l/3 from the rear end of the introducing tube 1' having a length l. An example in which a boundary structure is provided will be explained. In this case, when the movable valve 6 is closed, the resonance state of the introduction pipe 1' becomes the state indicated by the broken line a' in FIG. 5, and when the movable valve 6 is opened, the resonance state becomes the state indicated by the dashed-dotted line b'. Therefore, if the frequency of the sound is detected by the frequency detector 10 and the movable valve 6 is opened and closed, the broken line a' and
Along the bottom portions d' and e' of the dashed-dotted line b', the amount of amplification can be reduced to allow the sound to pass. However, in this example, since the hole 1a' is not in the center of the introduction pipe 1', the resonance positions of the 2/3l length front part and the 1/3l length rear part of the pipe 1' overlap. Since there are frequencies, there are high peak values of the amplification amount at positions 3c/2l, 3c/l, . . . of the dashed-dotted line b'. Since this position overlaps with the peak position of the broken line a', the amplification value cannot be made smaller than the peak value of the broken line a' even if the movable valve 6 is operated.
Therefore, in this case, consideration must be given to attenuating the sound of this frequency by other means. In this case as well, resonance at the frequency of 3c/2l can be prevented by providing the boundary structure of the hole 1a' at a position 1/6 from the rear end of the introduction tube 1'.

As explained above, the present invention provides a sealed chamber 5 in the middle of an introduction pipe whose communication and isolation with the introduction pipe is controlled by a movable valve 6, and utilizes the boundary structure formed by this chamber 5. Since the chamber 5 and the introduction pipe are communicated with each other or cut off so that the inside of the introduction pipe does not become in a resonance state, resonance amplification within the introduction pipe can be avoided, and the muffler 3 is designed to silence only the pulsation source or the sound source 2. All you have to do is take this into account, and the design of the muffler becomes very easy. Especially when used in automobile engines,
To always avoid resonance amplification despite a wide range of frequency changes, and to achieve further noise reduction effects with a simple and inexpensive muffler without the need for a large and complicated muffler as in the past. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an introduction tube according to the present invention;
Fig. 2 is a sectional view showing the movable valve, and Fig. 3 is a sectional view showing the movable valve.
FIG. 4 is a side sectional view of the introduction tube showing another embodiment, FIG. 5 is a frequency characteristic diagram thereof, and FIG. 6 is an explanatory diagram of acoustic boundaries. 1, 1': introduction pipe, 1a, 1a': hole, 2: pulsation source or sound source, 3: muffler, 5: chamber, 6: movable valve,
7: Electromagnetic coil, 8: Spring, 10: Frequency detector, 11: Arithmetic device, 12: Power supply, 15: Boundary.

Claims (1)

[Scope of Claims] 1. In an introduction pipe that guides sound emitted from a pulsation source or a sound source to a muffler, an introduction pipe is provided in the middle of the introduction pipe, which can be sealed and freely communicated with the inside of the introduction pipe via an electromagnetic movable valve 6. A frequency detector 10 is provided with a chamber 5 forming a boundary structure for the tube, and detects the frequency of the pulsation source or sound source, and this frequency detector 10 detects the arrival of a sound wave that brings the interior of the introduction tube 1 into a resonant state. An anti-resonance introduction pipe equipped with a calculation device that drives the movable valve 6 in a direction to prevent a resonance state based on the output of the anti-resonance introduction pipe. 2. The anti-resonance introduction tube according to claim 1, wherein the pulsation source or sound source is an automobile engine, and the frequency is detected based on the engine rotation speed.