JPS6019906A - Muffler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muffler in which noise levels at frequencies resulting from gas inertance and effective tailpipe gas inertance are canceled.

In motor vehicles, it is frequently necessary to position a muffler close to the rear end of the motor vehicle. Positioning behind the rear axle is often required. When this is done, low frequency noise is generated which the inventors have discovered as a resonance of the compliance of the muffler's high frequency resonator volume and effective gas inertance. Curl pipes are relatively short. This resonance (±characteristically at a low frequency, aggressive noise is usually -30 to 10
It is within the range of 0Hz.

To date, this problem has been widely recognized.

The only satisfactory solution is to increase the tail pipe inertance. The reference example is Australian patent application No. 48297/with Mr. Ishida as the patent applicant.
It can be seen in 79. In the specification accompanying the application, the tail pipe is considerably combed, and the muffler's 11
One side was extended outward from the head plate, with the bent portion extending toward the rear of the vehicle. This is probably extremely effective at suppressing unwanted noise, due to its physical structure. The cost was inevitably high. It is therefore an object of the present invention to provide a device in which effective sound cancellation at low frequencies can be achieved without the use of tail pipes.

In an embodiment of the invention. The muffler contains two Helmholtz resonators. The first Helmholtz resonator is a high frequency resonator whose resonant frequency is very close to the range of 1,000 Hz. However, this resonator necessarily exhibits the side effect of having a short tail pipe, resulting in a very low frequency resonance with a value of possibly 5 Q H 2, which in the present embodiment is undesirable. The noise is canceled by a second-order Helmholt resonator, which approximately corresponds to the resonant frequency caused by the conformance of the muffler volume in the high frequency chamber and the inertance of the gas in the short tail vibe.

The high frequency resonator in the present invention is approximately 1,000
If a secondary muffler system is introduced which significantly cancels frequencies within the resonant frequency range of Hz, but which corresponds substantially to the set low frequency resonance, a phenomenon unknown to date in the present invention. ．． The phenomenon of significant muffling occurring within this low frequency range has been disclosed. Furthermore, a muffler with a short tailpipe and containing only high frequency Helmholt resonators will naturally muffle the mid to high frequency range due to the inertance of the gas in the tailpipe, so it will be close to the low frequency resonance. The use of the adjusted secondary muffler system increases the effective silencing range and causes the silencing effect to occur over a very wide frequency range.

If the Helmholtz resonator volume of the low frequency side leg is set in gas flow communication with the muffler near the point where the pressure exhaust pipe enters, low frequency sounds will be generated even if the frequency is in the low range of 30 to 40 Hz. Attenuated. This is caused by the provision of side limb links extending substantially the entire length of the muffler, so that the diameter of the limb can be large enough to produce an acoustic effect.

As is known. The Helmholtz resonator on the lower frequency side limb has a resonant frequency determined by the following formula.

Here, rr - Resonance frequency D Diameter (or equivalent diameter) of the one-segment canal C One sound velocity ■ = Volume of the resonant chamber l ゛ Length of the one-segment canal From the above formula, the length of the one-segment canal should be as long as possible. It will be understood that the ward is different. Although the volume of the resonator does not necessarily need to be larger in terms of volume than the high-frequency partial limb resonator, this volume should also be as large as possible. However,
The long limb tube and resonator volume constitute a low frequency partial limb resonator that produces a highly effective acoustic impedance mismatch at low frequencies, thus producing the required low frequency silencing effect.

Embodiments of the invention will now be described in some detail and illustrated in the accompanying drawings.

In the first embodiment of FIGS. 1 and 2, the muffler 10
The muffler has a short tail pipe (not shown) arranged to be positioned near the rear of the vehicle and adjacent behind the rear axle housing.

The muffler 10 includes a main body 11 including an intermediate baffle plate 12. A main pipe 13 extends from the upstream end wall to the downstream end wall of the main body 11, and the main pipe has a branch pipe 14, which extends from its upstream end to the rear of the muffler. It extends into the low frequency resonator space 15 towards the end.

The main pipe 13 is provided with a plurality of holes 16, which open into an upstream space 17 in the muffler, and the upstream space serves as a high frequency resonator.
I! An insert 20 is provided, the limiting insert 20 including a plurality of holes 21 at its upstream end and having a wall that flares very gently in the downstream direction, the abutting wall defining the diffuser. is forming.

In use, the muffler is connected at its downstream end to the engine's exhaust pipe and to a short oar pipe at its downstream end. The high frequency resonator upstream space 17 is extremely effective in attenuating medium to high frequency noise levels. A resonator space, designated 22, is provided between the main tube 13 and the limiting insert 20, which resonator space is also effective for canceling very high frequency sounds.

However, the inventor of the present application has found that a resonance setting condition inevitably exists between the upstream space 17, which is a high frequency resonator, and the tail pipe, and that this resonance condition is at an extremely undesirable level. It has been discovered that the frequency is as low as 100Hz. The combination of the low frequency resonator space 15 and the branch pipe 14 is obtained from the upstream air IJ 117 and the effective tail gas inertance.
It is arranged to have a resonant frequency that is approximately the same as the resonant frequency that cancels the noise level from subsequent undesirable low frequency resonances. The restriction insert 20 forms part of the effective tail pipe and helps to maximize the inertance of the gas within the effective tail pipe. Since the restriction insert has a gently flared downstream portion, flow separation is avoided and high backpressures are not created by using this muffler.

Although mechanically appearing different, the second embodiment illustrated in FIGS. 3 and 4 functions in substantially the same manner as described above. The holes 16 passing through the main pipe 13 are therefore connected to the holes 24 of the second group of surrounding pipes 25 surrounding the main pipe 13 and the gas flow i! ! ! is in a lotus state. This allows the main pipe 13
-1: The stream side end 4i1 is 0; As in the above, it is in a state of resonance with the upstream space 17 which is a high frequency resonator. However, the envelope tube 25 opens into the low frequency resonator space 15,
The annular space between the main tube 13 and the surrounding tube 25 is associated with a circular space of Φ- with a cross-sectional area between, so that the diameter of the circular space can be considered as the same diameter of the annular space. As before, the limiting insert 20 has the effect of suppressing noise over a wide range of frequencies, and the resonator space 22 has the function of canceling high frequencies as in the first embodiment.

The invention can be better understood by considering the electrical analogs shown in FIGS. 5, 6, 7, 8 and 9.

In FIG. 5, a low frequency resonator space [5] which is a low frequency side partial limb resonator is shown as an inductance 30 connected in series with a capacitor 31. (Electrical inductance is similar to acoustic inertance, and electrical capacitance corresponds to acoustic inertance.) Similarly, the upstream space 17, which is the high frequency side limb resonator, is connected to the capacitor 33. It is shown as an inductance 32 in series with . The effective tail pipe (the portion extending from the hole 16 to the end of the tail pipe) is shown as an inductance 34, and the two-turn material relationship is shown as having an impedance Zr.

At the low frequencies of interest, the inductance 32 can be considered zero. At resonance of an effective tailgate with a high frequency limb volume, the impedance of the resonator upstream space 17 is essentially capacitive and is shown in FIG. The impedance at this resonant frequency is denoted as ("Z,), while the impedance of the tail vibration is the inductance.

(+Z). (The two impedances have equal amplitudes and opposite signs at the time of resonance.) As shown in FIG. 6, the impedance of the inductance 34, which is Z, is an imaginary number and is expressed by the following equation.

pwl Δ Here, p is the gas density.

W is the frequency (in radians per second) l is the length of the tail pipe A is the lateral side of the tail pipe [cross-sectional area j is the square root of -1. After that, on the tail pipe side where the low frequency side limb is attached:l! The impedance during vibration is -Z, -T-
It's Chiyu.

Since r Z is an imaginary number, Z is a real number, a negative number, and a large negative number,
It is an imaginary number of , and its value is extremely large when compared with Zl.

Therefore, the high frequency side limb of the tail pipe and the air passage section in the tail pipe and the high frequency resonator resonance appear as high impedance with respect to the low frequency side limb. Since the tail pipe resonance and the volume of the high frequency resonator also cause the low frequency side limb to resonate, (Low 2)
is O.

(Excluding low resistance). The low frequency limb thus avoids tail pipes with high impedance mismatch.

In a series of tests conducted, noise from a multi-cylinder engine was reduced by approximately 20 dB using a high-frequency resonance fence.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a muffler according to a first embodiment. FIG. 2 is a sectional view taken along line 2-2 in FIG. 1. FIG. 3 is a sectional view taken along line 3-3 in FIG. 4. FIG. 4 is a diagram similar to FIG. 1, illustrating a different method of achieving a long limb canal. FIG. 5 is a diagram showing an analog electric circuit. FIG. 6 shows the impedance of FIG. 5 at the resonance frequencies of the two problems. FIG. 7 shows a summary of the impedance shown in FIG. FIG. 8 is a diagram similar to FIG. 7. FIG. 9 is a diagram showing the results of FIG. 8 following the calculation process. In the figure, 10: muffler, 13: main pipe. 15: Low frequency resonator space, 17: Upper i% indicates between side bumps. Engraving of the drawings (no changes to the contents) #ηG4 3″′″ryg Fxs procedural amendment dated September 16, 1980 Kazuo Wakasugi, Commissioner of the Patent Office 1, Indication of the case, Patent Application No. 124890-1988 2, Name of the invention Muffler 3, relationship to the amended case Patent applicant address South Australia 944-956 South Road, Edwardstown, Australia Name Kenneth George Fogow Representative of Hills Industries Limited Nationality Australian 4, Agent Man

Claims (1)

[Claims] 1) A 2f14 Helmholt resonator, one of which has a relatively high resonant frequency and the other a relatively low resonant frequency, and a tail pipe that is in fluid communication with each resonator of πI; and a main exhaust pipe in fluid communication, the low resonant frequency approximately corresponding to the resonance of the high resonant frequency eL number resonator volume compliance combined with the effective tailpipe gas inertance. A muffler that is characterized by: 2) a muffler housing, the main exhaust pipe extending through the muffler housing, a device for fixing the main exhaust pipe to the housing, and a division for dividing the housing into the two Helmhole resonators; The wall includes a wall, each resonator is a side limb resonator, and the main exhaust pipe Ql at one upstream end of the muffler is penetrated, and the inside of the exhaust pipe is connected to the relatively high resonance frequency resonator and the gas area. At least one hole that communicates with the muffler extends almost to the downstream end of the muffler. The muffler according to claim 1), characterized in that the muffler comprises a branch pipe opening into the interior of the exhaust pipe. 3) The ↓λ muffler as set forth in claim 2), further characterized in that the branch pipe is formed into a dome on the wall of the exhaust pipe and passes through the dividing wall. 4) The exhaust pipe is further larger in diameter than the exhaust pipe defining a gas flow conduit that surrounds the exhaust pipe within the muffler over most of its length and opens at the rear end to the low frequency resonator. A pipe is inserted into the limb j, and the front end of the limb pipe and the nil end of the exhaust pipe have a hole passing through the wall near the front end of the muffler. , H2). 5) The muffler as described in each of the above items, further characterized in that the exhaust pipe includes a reli limiter inside the muffler. 6) Furthermore, said restriction body is defined by the wall of the exhaust pipe, and only part of its length forms the overall cross-sectional shape of the figure 8, and for the remainder of its length it has a circular shape. The muffler according to claim 5).