Abstract:
A manifold arrangement for exhaust systems of internal combustion engines, especially multi-cylinder motorcycle engines, for installation between the exhaust gas outlet pipes from the or each cylinder and at least one muffler is configured such that the exhaust gas outlet pipes of the cylinders are combined stepwise, if applicable, so as to finally form one joint pipe where behind the joint pipe a branch is provided that divides the exhaust gas flow into at least two pipes which are separated from each other, are parallel in a flow-wise manner and together having a larger cross-sectional surface than the joint pipe and behind the pipes, parallel a joining element is provided again so as to form one single collector pipe. In order to achieve an increase in the efficiency over the full speed range, while eliminating adverse resonance phenomena and providing adequate sound damping, while at the same time having the smallest possible size, the arrangement is characterized in that the collector pipe has a free flow cross-section that matches at least the surface sum of the parallel pipes and that in the continuing collector pipe a component serving as a wave impedance is installed, which component allows the exhaust gas volume flow to pass unhindered while pressure waves are forced to perform a total reflection on the component, which total reflection is as complete as possible.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This application is a continuation of International Application PCT/AT00/00115, filed May 3, 2000. The present and foregoing application claim priority to Austrian Application Serial No. A789/99 filed May 3, 1999. All of the foregoing applications are incorporated herein by reference to the extent permitted by law.  
           [0002]    The invention relates to a manifold arrangement for exhaust systems of internal combustion engines, especially multi-cylinder motorcycle engines, for installation between the exhaust gas outlet pipes coming from the, or each, cylinder and at least one muffler, where the exhaust gas outlet pipes of the cylinders are combined stepwise, if applicable, so as to finally form one joint pipe where behind said joint pipe a branch is provided that divides the exhaust gas flow into at least two pipes which are separated from each other, are parallel in a flow-wise manner and together having a larger cross-sectional surface than the joint pipe, and behind said pipes a joining element is provided, so as to again form one single collector pipe where the collector pipe has a free flow cross-section that matches at least the surface sum of the parallel pipes and performs a wave impedance function in said collector pipe.  
           [0003]    It is generally known in the field of designing exhaust systems that the exhaust system is able to contribute to an increase in the efficiency of the engine for which primarily the length of the exhaust pipes connected to the engine is responsible. The energy source for such an increase in the engine&#39;s efficiency is the high residual pressure on the inside of the cylinder at the end of the operating cycle, which residual pressure discharges abruptly into the exhaust system when the outlet valve or valves open. Modern simulation and design models for exhaust systems favor the wave method for definition and calculation, according to which a large portion of the energy from the exhaust gas goes into a shock wave that propagates in the exhaust system and that is partially reflected on sharp increases or decreases in the cross-sectional surfaces as an overpressure or low pressure wave, depending on the direction of the change in size. Each cylinder induces oscillations that are maintained at least until the next outflow cycle of said same cylinder, where complex resonance patterns of residual oscillations can develop if multiple cylinders are provided, which are in resonance with the shock waves coming from the cylinders in the critical speed and frequency ranges and which in said resonance ranges will result in a decrease in the performance and an increase in the noise level.  
           [0004]    The known solutions do not achieve the objective because “tuning” the resonance frequency downward, for example, would require an unrealizable extension of the collector pipe, especially in the design of motorcycles.  
           [0005]    “Tuning” to a higher resonance frequency is not promising as the residual oscillation could finally be interpreted as harmonic waves of the ignition frequency of the individual cylinders. Acoustically damping the collector pipe will not change the resonance behavior and therefore achieves only a slight quantitative improvement. In contrast, it is highly efficient to install an expansion volume in the exhaust gas line into which the exhaust pipes that determine the increase in efficiency are leading if said volume is large enough. This is also faced by structural limitations, especially in motorcycles.  
           [0006]    An exhaust system is specified in U.S. Pat. No. 4,819,426 A where one single collector pipe is provided between the exhaust gas pipes coming from the engine and two branch lines leading to two mufflers. The problem of the resonance of residual oscillations in the exhaust system with the shock waves of the exhaust gas is not discussed in any way.  
           [0007]    The objective for the muffler in DE 37 12 495 A is limited to sound damping and no reference is found regarding special designs of the pipes that precede the muffler.  
           [0008]    EP 421 724 discloses an arrangement where the exhaust gas flow is divided into at least two pipes which are subsequently recombined. Said arrangement works by damping standing waves by means of interference based on the parallel pipes having varying lengths. It is mentioned several times that pressure reactions in the preceding sections of the exhaust gas line, such as a wave impedance, for example, should be prevented. It is also of considerable importance that the cross-sectional surface of the parallel pipes is at least equal or larger than the inlet cross-sectional surface and also at least equal or larger than the downstream sections.  
           [0009]    In the U.S. Pat. No. 4,206,177, according to which a catalytic converter is disposed in a muffler and which provides a wave reflection wall between an expansion section and a sound damping section, the objective is to dispose a catalytic converter in such a way that it causes the least possible reaction on the pressure reflections while being fully efficient.  
           [0010]    Therefore, this relates to damping mechanisms that are very different from those mentioned above. Furthermore, U.S. Pat. No. 4,206,177 relates to the design of the actual muffler at the very end of the exhaust gas line.  
           [0011]    Finally, a design as characterized above is specified in U.S. Pat. No. 4,953,352, but in this case, the full cross-sectional surface of the pipes is merely equal to that of the joint pipe.  
         SUMMARY OF THE INVENTION  
         [0012]    Therefore, the objective of the invention is a manifold arrangement as described above offering an increase in efficiency continuously over the full range of speed of a multi-cylinder engine while largely preventing adverse resonance phenomena while providing adequate sound damping, which can be achieved at the same time with the smallest possible size so as to especially allow it to be used in motorcycles or so as not to excessively reduce the available space for other components in automobiles.  
           [0013]    This is achieved in accordance with the invention in that the collector pipe has a free flow cross-section matching at least the surface sum of the parallel pipes and that a component serving as a wave impedance is installed in said continuing collector pipe, which component allows the exhaust gas volume flow to pass unhindered while pressure waves are forced to perform the most complete possible total reflection on said component. The division of the exhaust gas flow from the single joint pipe into at least two parallel pipes causes a pressure wave, which is undivided before the branch, to be divided into multiple waves whose total energy is equal to the original wave and which pass through the downstream parallel channels in the form of individualized and independent wave fronts. Because in accordance with the invention an increase in the surface in relation to the free flow cross-section of each separate individual parallel channel is given at the junction of the parallel pipes into the single joint continuing collector pipe the individualized wave fronts passing through the individual channels are forced to perform an effective partial wave reflection at the respective channel opening at the junction. The (low pressure) waves resulting from said reflection travel back in each of the individual parallel channels in the direction to the branch. Because the surface on the branch increases in relation to the free flow cross-section of each individual interconnected channel similar to the increase at the junction the proposed arrangement of the invention causes multiple reflections of the wave energy from one and the same pressure wave, thereby working off a large portion of the wave energy entering the proposed arrangement because the reflection is inevitably tied to energetic losses.  
           [0014]    The proposed inventive installation of a component into the collector pipe after the parallel pipes or channels are joined where, in contrast to the preceding surface increases, arriving pressure waves are forced to perform a total reflection instead of a partial reflection, causes the intensity of the decrease in the wave energy to double in the preceding parallel pipe sections, because the portion of the original pressure wave which has passed the branch, then the parallel pipes and their junction into the joining element so as to form the common collector pipe is also reflected on said wave impedance, thus adding a considerable further portion of the wave energy to the alternating reflection and the resulting decrease. Another advantage of the “wave impedance” component is that it dissolves the portion of the wave energy that escapes the total reflection and passes the component into a diffuse wave pattern, thereby preventing the development of undesired resonance oscillations in a muffler installed downstream. Also, the low pressure waves resulting from the alternating reflections in the proposed arrangement, which would travel in the direction to the muffler after the collector pipe, are reflected as similar low pressure waves in the direction to the engine whereby an additional portion of the original pressure wave energy is utilized for supporting the charge changing.  
           [0015]    Multiple reflections of a pressure wave in the sequence as per the invention with cross-sectional changes and wave impedance causes a system immanent optimization of the sound damping in the exhaust system by means of efficiently working off the pressure wave energy already in the pipe sections that precede the actual muffler. Furthermore, it also causes an increase in the energy portion from the original pressure wave which is reflected as low pressure in the direction to the engine. Therefore, the arrangement proposed in the invention is able to compensate the loss of efficiency which is usually related to the installation of a muffler in the exhaust pipe of known exhaust system arrangements.  
           [0016]    In order to ensure an effective reflection of the pressure wave coming from a cylinder outlet of the engine in the exhaust gas line of the exhaust system and an initial significant decrease in the energy in the proposed arrangement, the total cross-sectional surface of the parallel pipes is at least 25% larger than the free flow cross-section of the joint pipe, preferably between 40% and 60% larger. This refers to the surface of the joint pipe that precedes the parallel pipes or channels at its junction with the branch. In order for the partial reflection of the pressure wave induced at the branch to the downstream parallel pipes to be optimally effective in supporting the charge changing of the engine it is advantageous to place the branch in the exhaust pipe at such a distance from the engine that a favorable wave travel time is ensured for the returning low pressure wave resulting from said reflection.  
           [0017]    The length of the parallel pipes between the branch and the joining element should advantageously be equal to at least twice the respective diameter of said pipes so as to ensure that separate and independent wave fronts are able to develop in the parallel channels and that the original wave is not merely briefly spread open. One advantage of the proposed arrangement is that the total length of the parallel pipe sections is irrelevant for the function as the travel times of the individual reflection waves within the arrangement are uncoupled from the ignition frequency of the engine because of the multiple wave reflections induced between the components of the invention. The result of this characteristic feature of the system, combined with the fact that the partial wave reflection taking place on the opening of the branch on the engine-side approximately halves the energy of the waves returning through the exhaust system, is that the downstream components of the exhaust system, where the muffler or mufflers are normally installed, are uncoupled from the wave reflections on the outlet pipes installed directly downstream of the engine causing the potential increase in efficiency of the exhaust system while at the same time suppressing adverse resonance phenomena.  
           [0018]    In order to securely ensure said uncoupling it is advantageous to configure the joint pipe as a joining element between the preceding outlet pipes and the arrangement of the invention having a pipe length that is at least equal to the diameter of said pipe.  
           [0019]    An arrangement where, according to another characteristic feature of the invention, the parallel pipes are configured as pipe sections running parallel having substantially parallel axes is structurally very simple and also highly effective for cooling.  
           [0020]    A division into multiple separate wave fronts, which travel at different velocities because of the statistical distribution of the energies, and thus optimally preventing harmful resonances in the exhaust system while intensifying the reduction of the wave energies is possible when more than two, preferably three parallel pipes are provided. Of course, the more pipes that are provided, the larger the required installation space, so that embodiments with a maximum of three pipes have found to be advantageous, especially for motorcycles.  
           [0021]    In a structurally especially simple embodiment the wave impedance is configured as a metal sheet provided with holes or slots.  
           [0022]    In accordance with an especially advantageous embodiment the wave impedance is configured as a perforated plate cylinder that is oriented substantially parallel to the axis whose side facing the parallel pipes is sealed, while the other side facing the components of the exhaust system installed downstream, especially the muffler, is open. With this design, because the perforated plate cylinder is easily bypassed, an adequately sized perforated plate surface and thus an adequately dimensioned wave impedance can be provided in the exhaust pipe with minor effort and a small structural volume.  
           [0023]    In this case, the wave impedance can be increased with a given hole diameter provided that the holes or slots have a non-negligible longitudinal dimension or that they are axially extended by means of short pipe sections or protuberances in the metal sheet. This easily allows producing the desired wave impedance with easily achieved hole sizes.  
           [0024]    Advantageously the wave impedance can also be a catalytic converter body having honeycombed pits, for example, with which the required noise and exhaust gas emission limits can easily be met with a very small structural size while optimally and evenly increasing the output, even in motorcycles.  
           [0025]    In accordance with another advantageous embodiment the wave impedance is a porous metal or ceramic body, preferably made of sintered material. The wave impedance could also be an easily produced knit or woven device of metal filaments.  
           [0026]    When in any of the above embodiments the total cross-section of the through-openings in the wave impedance component is larger than the total cross-section of the parallel pipes the flow resistance is not or only slightly higher than that of the preceding exhaust system, thereby preventing an adverse effect on the performance of the engine. Advantageously, the total cross-section of the through-openings is between approx. 30% and 40% larger than the total cross-section of the pipes.  
           [0027]    In order to prevent that the pipe between the joining element and the wave impedance component acts as a volume resonator building up auto-oscillations that have an adverse effect on the preceding system the wave impedance is advantageously disposed directly behind the joining element with the distance to its end being max. about twice the local pipe diameter.  
           [0028]    In accordance with an advantageous embodiment for further increasing the efficiency of the arrangement of the invention, at least two branches and at least two joining elements can be provided parallel relative to each other where the pipes of each branch lead to different joining elements.  
           [0029]    In this case, it is advantageous to provide at least one connecting element between the parallel pipes before the or each branch. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    The following description is intended to explain the invention in more detail by means of the enclosed drawings of preferred exemplary embodiments of an exhaust system of the invention for motorcycles.  
         [0031]    [0031]FIG. 1 shows a first embodiment of the invention for four-cylinder engines.  
         [0032]    [0032]FIG. 2 illustrates another variant for four-cylinder engines.  
         [0033]    [0033]FIG. 3 and the profile A-A illustrate a special embodiment of the parallel pipes.  
         [0034]    [0034]FIG. 4 illustrates another embodiment of the exhaust system of the invention having two branches, two parallel pipe arrangements and two wave impedance components. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    In the arrangement of FIG. 1, the commonly configured primary outlet pipes  1  to  4  of the individual cylinders of a four-cylinder engine are combined in pairs, as is also known and common, into two secondary continuing exhaust gas pipes  5  and  6 . A similar arrangement is also standard for six-cylinder engines where groups of three primary outlet pipes are combined into one secondary continuing pipe. The secondary exhaust gas pipes  5 ,  6  can have a non-circular cross-section, if applicable, for example when they are structurally configured as two separated pipe halves as a result of dividing a single pipe. The secondary exhaust gas pipes  5 ,  6  associated with a group of primary outlet pipes are combined into a single collector pipe  7  in said known arrangement, which combines the exhaust gas flow of all cylinders and where devices such as mufflers or catalytic converters  14  are usually connected. The latter can also be combined in one single component. Similar arrangements are also common for eight- or twelve-cylinder engines where one series of cylinders is equipped with such an exhaust gas elbow. Combining the primary exhaust gas pipes that are installed directly downstream of the individual cylinders into a joint continuing exhaust gas pipe is also common in two- or three-cylinder engines with the difference that based on the lower number of cylinders the primary outlet pipes run directly into the single collector pipe  7  that leads to a muffler or catalytic converter  14 .  
         [0036]    In the arrangement of the invention as per FIG. 1, a branch  8  is installed behind the collector or joint pipe  7  which divides the exhaust gas flow into at least two downstream parallel pipe sections  9  and  10 . Said pipe sections  9 ,  10  are subsequently recombined by means of the joining element  11  into a single collector pipe  12  in which a wave impedance  13  is installed.  
         [0037]    In accordance with the invention, the device  14 , for example the muffler or catalytic converter, is connected to said collector pipe  12  containing the wave impedance  13 . As shown by the profile A-A in FIG. 1, the wave impedance  13  is advantageously disposed concentrically in the collector pipe  12 .  
         [0038]    The special effectiveness of the proposed arrangement is based on the following physical reasons: the nature of the propagation of a shock wave induced by opening an engine outlet, and the fundamental difference between partial and total reflection of said waves. The shock waves induced in the rhythm of the operating cycle of a piston-type engine propagate at the local speed of sound in the exhaust gas as a transmission medium on the inside of the exhaust pipe in the direction of the exhaust opening. Said waves are individualized events strictly correlating with opening an engine outlet. Their nature corresponds to that of a shock wave caused by an explosion or a sonic boom as they too are the result of an abrupt introduction of pressure energy into the transmission medium spreading there as a singular pulse with one single prominent amplitude.  
         [0039]    Being a singular pulse said shock waves should not erroneously be mistaken for standing waves that develop on the inside of an exhaust system, because the singular wave fronts of shock waves can pass through each other without changing their pulse, similar to two different waves on the surface of a lake, while two different standing waves on the inside of the exhaust pipes overlay each other based on the resonance or interference mode, depending on the phase difference. Such standing waves on the inside of the exhaust gas system are induced by said shock waves, but they differ from said shock waves similar to the cause differing from its effect.  
         [0040]    EP 0 421 724 A1 specifies a pipe arrangement for attenuating standing waves by means of interference. In order to effectively attenuate said waves whose basic frequency naturally corresponds to the ignition frequency of the engine, therefore lying between 100 and 400 Hz, pipe lengths are required that considerably exceed the available space, especially in a motorcycle.  
         [0041]    Adding to the problem is that a considerable difference in length is required between the parallel pipes so as to generate a phase difference that is adequate for an interference with the standing waves. In contrast, the difference in length of the parallel pipes  9  and  10  of the proposed arrangement is completely irrelevant for its function, which is also documented by a respective series of tests carried out on the test stand.  
         [0042]    In accordance with the invention, the arrangement with the branch  8  that divides the exhaust gas flow from the collector pipe  7  into two parallel continuing pipes  9  and  10  which are subsequently rejoined by means of a joining element  11  serves as a means for producing increased surfaces within the free flow cross-section in the exhaust gas pipe of the exhaust system. It is known that on such surface jumps as those on the branch  8  and the joining element  11 , a partial reflection of the shock wave takes place based on which its pulse is divided into two waves, one of which maintains the original propagation direction toward the end of the exhaust while the second wave is reflected in the opposite direction.  
         [0043]    The following dimensioning rules define the lower limit of the geometric proportions in an exhaust system of the invention which are relevant for the efficiency of the partial wave reflection. The minimum length of the parallel pipes  9  and  10 , which should preferably be equal to at least twice the respective diameter of said pipes, ensures that a shock wave pulse, which is undivided before the branch  8 , is divided into two pulses whose total energy ideally, i.e., not taking into account unavoidable wall losses, is equal to that of the original pulse. At the joining element  11  each of the partial waves propagating in the pipes  9  and  10  in the direction to the end of the exhaust is partially reflected on the increased surface represented by the free flow cross-section of said component relative to the individual surface of the pipes  9  and  10 . The partial character of said reflection causes one part of the pulse energy of each partial wave to be reflected again as partial shock waves opposite to the original direction of the exhaust gas flow back to the branch  8  through the respective pipes, while the other part of the pulse energy propagates as partial shock waves in the original propagation direction.  
         [0044]    The defined minimal surface of the pipes  9  and  10  ensures an adequately sized surface on the branch  8  where another and partial reflection is caused of the (partial) waves returning through said pipes. This second partial reflection within the arrangement again generates two pairs of shock waves propagating in different directions, one pair in the direction to the engine and the other pair being the products of the second reflection having the orientation of the original pulse.  
         [0045]    The partial wave reflection of one and the same shock wave on the joining element  11  and the branch  8  ties up a large proportion, ideally half, of the pulse energy of the original shock wave within the arrangement in that it is forced to perform alternating multiple reflections between the ends of the pipes  9  and  10 . The Carnot pulse loss inevitably taking place in each of said parallel wave reflections causes the pulse energy to convert into heat and thus working off the original shock wave.  
         [0046]    An arrangement of parallel pipes having a length as described in EP 0 421 724 A1, for example, would not be feasible for the exhaust system of a motorcycle and in addition, by itself it causes only a marginal reduction of the sound pressure and even changes the efficiency of the engine for the worse compared to a conventional, i.e., non-branched exhaust gas system, as was determined by tests. This phenomenon is explained in that such parallel pipes represent a highly oscillating system which is an advantageous characteristic for exhaust gas systems operating on the principle of producing wave interference, but which is disastrous for the intended application of the invention. Because the overall exhaust system is naturally very short, especially in a motorcycle, the distance between the primary exhaust pipes connected directly to the cylinder outlets and the pipes of said arrangement is also short. Because the oscillation within said arrangement is induced at the engine, i.e., the ignition frequency, it is possible to overlay said oscillations with the preceding primary elbows. This interferes with the recovery of the pulse energy of the shock wave at the opening of the primary elbows by means of wave reflection, whose pulse energy is utilized for advantageously supporting the charge changing in the engine.  
         [0047]    Instead the energy of the shock wave induced by opening a cylinder outlet in a primary elbow is assimilated in the overlaying in that they intensify residual standing waves. It is known that the installation of a “wave impedance” in the exhaust gas system, such as described in U.S. Pat. No. 4,206,177 A, at best has a negligible effect on the sound emission and, based on experience, it will not alter the resonance behavior of an exhaust system. In motorcycle engines, which usually have a considerable valve overlap, the installation of a catalytic converter body in the joint pipe between the exhaust elbow and the muffler will frequently result in discrete efficiency losses in certain speed ranges. The reason for this is that on the front side of a catalytic converter, which usually consists of honeycombed cells, the shock waves coming from the engine experience a total reflection and return to the cylinder as an overpressure pulse where they interfere with the charge changing.  
         [0048]    The proposed inventive structural combination of the characteristic features of dividing and subsequently recombining the exhaust gas flows using a downstream wave impedance, but placing it before the actual muffler, not only prevents any negative effect on the engine&#39;s efficiency because of adverse overlaying oscillations and returning (overpressure) shock waves, it also provides an internal sound damping of around 3 db(A) within the presented arrangement, thus halving the sound pressure even before the actual muffler. The proposed installation of a medium directly after the parallel pipes are joined whose passageways allow the exhaust gas volume flow to pass unhindered, but which are so small that they force arriving shock waves to perform a total reflection, such as a finely perforated metal sheet or a catalytic converter body, compared to the arrangement of EP 0 421 724 A1, causes an exponential multiplication of the pulse energy quantity which is tied up in alternating partial reflections between the ends of the parallel pipes  9  and  10  in the arrangement.  
         [0049]    The introduction of such a medium directly after the parallel pipes are joined causes a total reflection of all occurring shock waves, including the partial waves resulting from the shock wave which is undivided before the arrangement in the collector pipe  7 , i.e., the split waves as well as their numerous deriving multiple (partially) reflected following waves and which based on the partial character of the wave reflection at the ends of the pipes  9  and  10  maintain the propagation direction of the original wave. Said exponential multiplication of the partial waves deriving from the original shock wave, which, based on the total reflection on the wave impedance  13 , are forced to perform alternating partial wave reflections in the preceding pipe arrangement causes a respective multiplication of the Carnot pulse losses and thus an exponentially increasing conversion of wave energy into heat in the process of partial reflections. This not only explains the efficient reduction of the sound pressure of the proposed arrangement, it also realizes another advantage of our invention: the intensification of the Carnot pulse losses causes the exhaust gas to heat up internally independently directly before a catalytic converter, but not, as is common in the known catalytic converter arrangements, at the back-up point on its front surface. With this method, the catalytic converter body, even when it is placed comparatively far from the engine, quickly reaches the operating temperature after cold starting the engine, but without overheating at full load operation.  
         [0050]    The exponential multiplication of each individual shock wave generated by opening a cylinder outlet into multiple sub-waves that takes place in the proposed arrangement also effectively prevents any oscillation interference with the preceding primary elbows of the exhaust system on whose opening, as is known in the art, the shock waves generated at the ignition frequency of the engine experience an advantageous (partial) wave reflection optimizing the efficiency of the engine. The reason for this is not only the above mentioned decrease in the pulse energy of the shock waves, which also reduces the activation of any residual standing waves, the reason is basically that the exponential splitting and dividing the original wave into multiple sub-waves is accompanied by a similar multiplication of the natural frequency of standing waves that are activated by said sub-waves.  
         [0051]    This method ensures that the basic frequency of the oscillations from said arrangement is considerably above the ignition frequency of the engine to which the exhaust system is connected, thereby preventing undesired interference and resonances. FIG. 2 shows an arrangement of the invention where two exhaust mufflers  14  and  14 ′ are coupled to the joint pipe  7  at the branch  8  in that the branch  8  divides the exhaust gas flow into two pairs of parallel pipe sections  9  and  10  and  9 ′ and  10 ′ each having devices the  11  to  13  and  11 ′ to  13 ′ installed downstream.  
         [0052]    A structural alternative to two separate parallel pipes in the arrangement of the invention is illustrated in FIG. 3 and the profile A-A. In this case, instead of guiding the exhaust gas parallel in the pipe sections  9 ,  10 , it is guided through only one pipe whose cross-sectional surface advantageously is equal to that of the collector pipe  12  and whose continuation it represents. Said pipe is divided into two channels by means of a divider sheet  15  through which the exhaust gas has to flow. The wave impedance  13  is placed at the end of said channels, preferably as described above, truly axial in the collector pipe  12  where the muffler or catalytic converter  14  is connected, again in the conventional manner.  
         [0053]    In an arrangement as that shown in FIG. 3, the function of the branch  8  that divides the exhaust gas coming from the joint pipe  7  into the channels defined by the divider sheet  15  is preferably performed by a conical expansion member that widens the cross-section of the joint pipe  7  to the cross-section of the collector pipe  12 .  
         [0054]    [0054]FIG. 4 shows an especially favorable embodiment of an arrangement of the invention where the two secondary exhaust pipes  5  and  6  that jointly transport the exhaust gas from a cylinder or a group of cylinders of an engine and between which a connection  15  may be provided are associated with a wave impedance  13  or  13 ′ with a downstream muffler  14  and  14 ′.  
         [0055]    After the branch  8  or  8 ′ continuing pipes  9  and  10  or  9 ′ and  10 ′ are installed such that the exhaust gas flow from the pipes  5  and  6  is divided into both wave impedances  13  and  13 ′ and mufflers  14  and  14 ′. The additional division of the exhaust gas causes another increase in the efficiency of the proposed arrangement in working off the pressure wave energy because the wave portions from the pipes  9  and  10  or  9 ′ and  10 ′, which are subsequently totally reflected on the wave impedance  13  or  13 ′, are thus forced to perform wave reflections both in the branch  8  and in the branch  8 ′.  
         [0056]    As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.