DE9207838U1 - silencer - Google Patents

Description

Description:

The invention relates to silencers, in particular for exhaust systems of internal combustion engines, according to the preamble of claim 1.

When reducing unwanted noise components, for example in the exhaust systems of combustion engines, three basic physical principles are applied: absorption with sound-damping materials, reflection from sudden wave resistance jumps in the pipes carrying the noise, and interference through the superposition of sound waves of the same frequency that are 180 degrees out of phase with the original sound.

A technically relatively simple implementation of the reflection principle is the Helmholtz resonator coupled to the exhaust gas pipe. The disadvantage here is that each Helmholtz resonator only has one resonance frequency. To dampen sound over a wider frequency range, either several resonators are required, which requires a considerable amount of space, or the resonance frequency of the He Imho 11z resonator must be changed using suitable adjusting devices. Proposals have already been made for this, for example in the form of making a boundary wall of the Helmholtz resonator movable and adjusting it using a computer-controlled stepper motor.

Another technically simple implementation of the reflection principle is the lambda quarter-L line in the form of a pipe section of defined length closed at the end, coupled laterally to the exhaust gas pipe.

The present invention is based on the object of specifying a sound damper of the type mentioned at the beginning, which makes it possible to dampen several frequencies with a defined frequency spacing using a Helmholtz resonator of constant volume and with simple mechanical measures.

This object is achieved by a generic silencer with the features according to the characterizing part of claim 1.

The simplest implementation of the silencer principle according to the invention is the two-necked Helmholtz resonator, supplemented by a flap or a valve that closes one of the two pipes leading to the resonator. If the flap is open, a high-frequency resonator is created. If the flap is closed, a low-frequency resonator and a quarter-wave line are created.

The main difference between the invention and earlier proposals is that the two coupling necks are coupled with a short connecting pipe section. This creates a phase coupling between the two with a preselectable phase shift. This makes it possible to select the second resonance frequency to be almost arbitrarily related to the first, so that, depending on the flap or valve position, the 3/4 lambda or the 5/A lambda resonance can be dampened, for example.

According to an advantageous development of the invention, the coupling necks can have different lengths and diameters. The pipe section between the coupling necks can be greatly reduced in diameter to improve the reflection properties. At higher speeds with a higher gas throughput, opening the flap or valve not only switches to the higher frequency but also the exhaust gas flow through the resonator volume

and thus the back pressure is reduced.

In the simplest case, a rotary valve is installed in the end of the lockable coupling pipe. Alternatively, a valve plate can be used, which is placed on the end of the coupling pipe.

The invention will be explained in more detail in the form of three simple embodiments using the drawing. Each shows schematically

Fig. 1 shows a first embodiment of a silencer with a two-necked Helmholtz resonator,

Fig. 2 a second embodiment of a silencer with a two-neck Helmholtz resonator and

Fig. 3 a third version of a Heimholtz resonator with a short, thin connecting tube, where the exhaust gas flow can be guided through the resonator volume.

Fig. 1 shows a pipeline 1, for example part of an exhaust system of combustion engines. A Helmholtz resonator 2 can also be seen, coupled via two tubular coupling necks 3, 4. One coupling neck 3 is shorter, the other coupling neck 4 is longer. Both coupling necks 3, 4 are spaced apart from one another and connected to one another by means of a connecting pipe section 5, so that there is a phase shift between the two with regard to the sound frequencies present in the pipeline 1. The longer coupling neck 4 can be closed with a rotary flap 5 at its end facing away from the pipeline 1.

Fig. 2 shows a further embodiment. Here, the exhaust pipe 1 is led through the Helmholtz resonator 2.

The longer coupling neck 4 can be closed with a valve 6 that can be placed on its end. Both coupling necks 3, 4 are folded to save space.

A prototype designed according to Fig. 2 had the following values:

Volume of the HeLmho 11z resonator: 8 L Length of the shorter head neck 3: 200 mm Length of the longer head neck 4: 400 mm Length of the connecting tube 5: 400 mm

The following three resonance frequencies resulted:

f1: 60Hz
f2: 100Hz

f3: 170Hz

Fig. 3 shows a third design. Here too, the exhaust pipe 1 is led through the Helmholtz resonator 2, but in the form of two separate pipe sections. The connecting pipe 5 connects the two exhaust pipe sections 1, so that exhaust gas flow is possible even when the valve plate 6 is in place. The diameter of the connecting pipe 5 is reduced compared to the diameter of the exhaust pipe sections 1 or the coupling necks 3, 4, so that an additional reflection effect is created, which enables a further reduction in the noise. The reduced cross section of the connecting pipe 5 does not cause interference. The valve plate 6 is closed when low resonance frequencies are required, which is the case at low speeds. At low speeds, however, the exhaust gas throughput is also low. At higher speeds, the valve plate 6 is opened to increase the resonance frequency of the He lmho 11z resonator 2, whereupon the exhaust gases can also find their way through the volume of the He lmho 11z resonator 2.

It is understood that by using additional closable connecting tubes, additional resonance frequencies can be generated, whereby the volume of the Helmholtz resonator remains constant.

Claims (8)

; Seita;6. Protection claims: 1. Silencer, in particular for exhaust systems of internal combustion engines, with a Helmholtz resonator (2) acoustically coupled to an exhaust gas-carrying pipe (1), characterized in that the Helmholtz resonator (2) has at least two tubular coupling necks (3, 4), that the two coupling necks (3, 4) are spaced apart from one another and connected to one another via a connecting pipe (5), and that at least one coupling neck (4) can be closed completely or partially. 2. Silencer according to claim 1, characterized in that the coupling necks (3, 4) are of different lengths. 3. Silencer according to claim 1 and 2, characterized in that the coupling necks (3, 4) have different diameters. 4. Silencer according to claim 1, 2 or 3, characterized in that at least the longer coupling neck (4) is closable. 5. Silencer according to one of claims 1 to 4, characterized in that the coupling neck (4) can be closed at the end facing away from the pipe (1). 6. Silencer according to one of claims 1 to 5, characterized in that a rotary flap (7) is installed in the end of the coupling neck (4). 7. Silencer according to one of claims 1 to 5, characterized in that a valve plate (6) can be placed on the end of the coupling neck (4). 8. Silencer according to one of claims 1 to 7, characterized characterized in that the connecting pipe (5) between the coupling necks (3, 4) has a diameter which is reduced compared to these.