Abstract:
A silencer is disclosed with a bypass resonator ( 4; 9, 12 ) connected by at least one tubular connection ( 3   a   , 3   b   ; 7, 8; 13 ) to a sound-transmitting channel ( 1 ). The tubular connection ( 3   a   , 3   b ) can have various lengths (La, Lb), tubular connections ( 7, 8 ) of different thicknesses can be connected, or the volume (V 1 , V 2 , Vn) of the bypass resonator ( 13 ) can be variable.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a noise suppressor with a bypass resonator. 
     Connecting a bypass resonator to a noise suppressor in the air intake duct of an internal combustion engine is already disclosed in AT Patent 216,292. Such a bypass resonator leads to an improvement of the noise suppressor, especially near its natural resonance frequency, this frequency being determined by the dimensions and geometric configuration of the bypass resonator, also known as a Helmholtz resonator in shunt. To make it possible to adapt to different sound conditions, complex mechanical devices or a separate resonator for every sound condition are often necessary. 
     OBJECT OF THE INVENTION 
     It is the object of the invention to provide a noise suppressor of the kind referred to above such that the (noise) damping characteristics can be influenced in a simple manner. 
     SUMMARY OF THE INVENTION 
     The noise suppressor according to the invention is advantageously able, to achieve the stated object as described and claimed hereinafter. Because the tubular connections between the sound-carrying duct and the bypass resonator are exchangeable parts which extend with various respective lengths into the bypass resonator, different natural resonances of the system can be adjusted in a simple manner. 
     In a second advantageous working embodiment of the invention, at least two tubular connections each having a different diameter are present, which are respectively connected with the bypass resonator through an alternately closing and opening flap valves; in an additional position, both can also be open or both can be closed. This control flap is mechanically simple to make, and its switching operation—in the case of a rotating control flap, for example, which depending on its rotational position respectively closes one opening and opens the other—can be accomplished by an electric motor or also by a pressure chamber. 
     In a third working embodiment, the tubular connection is connected to a bypass resonator of a type whose volume which can be coupled to the tubular connection can be increased or decreased by means of a control flap. For example, the tubular connection can be coupled to the cylindrical outer surface of a hollow cylindrical bypass resonator, and the volume in the interior of the bypass resonator can be defined on one side by a stationary wall from the central axis to the outside wall and on the other side by movable wall which is continuously displaceable around the central axis or which can locked in various position settings. 
     Advantageously, the adjustment of the above-described pivotable flap or the wall can be effected by means of an electric motor or a pressure chamber. In the case of adjustment by means of the pressure chamber a push rod operated by the pressure chamber, which can be stopped in prescribed positions, can be provided. The latching of the push rod in the stops or switching positions can be achieved for example by a ball which catches under the pressure of a spring in recesses in the push rod. Without this push rod according to the embodiment, a pressure chamber operation, for example through a magnetic control valve, would catch only in the front and in the rear position when the vacuum is applied or is not applied. 
     In the case of a preferred application, the sound carrying duct is the intake duct for the intake air of an internal combustion engine and the noise emissions to be suppressed are generated by the air intake pulses of the individual cylinders. In the above-described embodiment with a pressure chamber and a push rod, one adjustment position for the adjustment of the resonator can be set in a state in which the intake duct vacuum is greatest in the low rotational speed range of the internal combustion engine and thus the vacuum box spring is compressed. A second adjustment position can be set in the case of weaker intake duct vacuum in the middle rotational speed range, and a third adjustment position can be set in the case of very weak intake duct vacuum in the higher rotational speed range and stronger spring force of the pressure chamber toward the push rod. 
     These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, whereby the individual features can be realized individually or jointly in the form of subcombinations in embodiments of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the noise suppressor of the invention with a bypass resonator will be further explained with reference to the figures of the drawing. 
     FIG. 1 shows a first working embodiment with different insert parts as tubular connections between the sound carrying passage and the bypass resonator; 
     FIG. 2 shows a second working embodiment with two respective alternately opening and closing tubular connections between the sound carrying passage and the bypass resonator; 
     FIG. 3 shows a detail view in section I—I of FIG. 2 of a pivotable flap for closing and opening the respective tubular connection according to FIG. 2; 
     FIG. 4 shows a third working embodiment with an adjustable flap in the bypass resonator; 
     FIG. 5 shows a schematic view of a pressure chamber control of the bypass volume with a push rod, and 
     FIG. 6 shows a diagram of the course of the pressure of the pressure chamber and of the path of movement of the push rod according to FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the first embodiment according to FIG. 1 of the drawing an air intake duct  1  is shown as the sound carrying duct which serves to supply aspirated air to an internal combustion engine, not described in further detail here. On the intake duct  1  there is an opening  2  to which a tubular connection  3   a  to a housing volume V is coupled, which acts as a bypass resonator  4  for the sound vibrations of the pulsating intake air in the intake duct  1 . The tubular connection  3   a  here with the length La is exchangeable with another tubular connection  3   b  with the length Lb. 
     The sound damping characteristic of the arrangement illustrated in FIG. 1 is determined in particular by the volume V, by the lengths La and Lb of the tubular connection  3   a ,  3   b  and by the respective cross-sectional area A of the tubular connection  3   a ,  3   b . These three above-mentioned magnitudes determine the natural resonance frequency of the bypass resonator  4 . In the working embodiment according to FIG. 1, the length L (La, Lb) represents the variable parameter for adapting the value of the natural resonance frequency to the desired sound damping characteristics. 
     In the working embodiment according to FIG. 2, there are two openings  5  and  6  for two tubular connections  7  and  8  with the respective cross-sectional areas A 1  and A 2 . At the respective points of connection to the bypass resonator  9  with the volume V a pivotable flap  10  is mounted with which the openings  5  and  6  can be alternately closed and opened, or also both can be opened or closed. In FIG. 3 the pivotable flap  10  can be seen in a plan view. 
     By rotating about a pivot point  11  the vane of the rotary valve  10  can alternately close the openings  5  and  6  so that here the cross-sectional areas A 1  and A 2  represent the variable parameters for adjusting the natural resonance frequency. The rotation of the pivotable flap  10  can be realized, for example, by an electric motor or also by a pressure chamber. For this purpose the vacuum from the intake duct or from a vacuum reservoir can be used in combination with a magnetic control valve. 
     A third working embodiment according to FIG. 4 has a bypass resonator  12  which comprises a hollow cylinder with a variable volume V 1 , V 2  and Vn. The connection to the intake duct  1  here is formed by a tubular connector  13  having a constant cross-sectional area A and a constant length L. Here a wall  14  is fixedly mounted in the hollow cylinder on one side of the connection to the tubular connection  13 ; an adjustable wall  15  is mounted for rotation about a central axis  16 . 
     In a first position a volume V 1  can be achieved with the walls  14  and  15  according to FIG. 4, and in a second position, shown here in broken lines, a volume V 2  can be achieved. Additional volumes Vn can be created in any desired rotational position of the wall  15  by a catch mechanism or by continual adjustment of the wall  15 . As in the second working embodiment according to FIG. 2, the adjustment of the wall  15  can be accomplished by an electric motor or by a pressure chamber. 
     In FIG. 5 can be seen a pressure chamber  20  which can be used for controlling the pivotable flap  10  or the wall  15 . 
     With the pressure chamber spring, which is not visible here, in the interior of the pressure chamber  20  a push rod  21  is operated which can be stopped in the position settings P 1 , P 2  and P 3 , and which thereby achieves the aforedescribed adjustment possibilities by catching the pivotable flap  10  or wall  15 . The catching can be performed here with a stationary ball  22  which is urged into engagement in the position settings P 1 , P 2  or P 3  by a spring  23 . 
     In FIG. 6 there is shown a diagram which indicates on the one hand the descending pressure curve  24  in the vacuum chamber  20  and on the other hand the stepped progress  25  of the push rod  21  with the detents at the position settings P 1 , P 2  and P 3  in relation to the distance s and to the course of the pressure P u  P 1  here corresponds to the state in which the intake duct vacuum P u  in the low rotational speed range of the internal combustion engine is at its highest and the vacuum chamber spring is thereby compressed. P 2  corresponds to the second position setting at a weaker intake duct vacuum P u  in the middle rotational speed range, and P 3  to the third position setting at a very weak air intake duct vacuum P u  in the high rotational speed range and stronger spring force of the pressure chamber  20  in the direction of the push rod  21 .