Method and apparatus for producing a homogeneous exhaust gas mixture in an exhaust system for an internal combustion engine having two banks of cylinders
The invention relates to a method for producing a homogeneous exhaust gas mixture in an exhaust system in accordance with the introductory part of claim 1 and to apparatus for the practice of the method. 
     To be able to conform to the emissions standards with regard to the composition of exhaust gases, it is necessary to regulate the composition of the fuel-air mixture such that, insofar as possible, a stoichiometric mixture will be present in all ranges of operation. This is attempted by so-called lambda control, in which the oxygen content in the exhaust is measured with a lambda probe. In internal combustion engines having two banks of cylinders, especially so-called V-engines, it is necessary for reasons of space, among other things, to provide two catalysts, each taking half of the total exhaust stream. To avoid the cost of two lambda probes and the corresponding controls, in a known exhaust system (MTZ 46 (1985) P. 305) a cross connection is provided between the exhaust pipes which runs each from one cylinder bank to a catalyst. The lambda probe is disposed in this cross connection. The cross connection is said to achieve a sufficient mixing of the exhaust streams from the two cylinder banks and to assure correct control by the lambda probe. It has been found in practice, however, that with a cross connection of this kind a homogeneous exhaust mixture cannot be produced, though it is essential for complete detoxification in the two catalysts. 
     It is the purpose of the invention to create a method which will assure that the exhaust fed to the two catalysts will have a largely identical composition, without the need for any measures which would undesirably increase the back pressure in the exhaust system. 
     This purpose is accomplished in accordance with the invention by the features specified in the specific part of claim 1. 
     In the proposal according to the invention, dividing the exhaust stream from each cylinder bank into two parts and bringing a portion of the one exhaust stream together with a portion of the other exhaust stream brings it about that exhaust streams of identical composition and also of identical volume are carried to the two catalysts. The lambda probe can then be disposed in one of the two pipes leading to the catalysts. 
     Apparatus for the practice of the method are described in the subordinate claims. 
    
    
     A number of embodiments of the invention are described below in conjunction with the drawings, wherein: 
     FIG. 1 is a diagrammatic representation of an exhaust system for a V-6 internal combustion engine in a first embodiment, 
     FIG. 2 is a diagrammatic representation of an exhaust system for a V-6 internal combustion engine in a second embodiment, 
     FIG. 3 is a section taken along line 3--3 in FIG. 2, 
     FIG. 4 is a section taken along line 4--4 in FIG. 2, 
     FIG. 5 is a diagrammatic cross section taken through an additional embodiment of a mixing chamber, 
     FIG. 6 is a section taken along line 6--6 in FIG. 5, 
     FIG. 7 is a section taken along line 7--7 in FIG. 5, 
     FIG. 8 is a section taken along line 8--8 in FIG. 5, 
     FIG. 9 is a diagrammatic cross section taken through a third embodiment of the mixing chamber, 
     FIG. 10 is a section taken along line 10--10 in FIG. 9, 
     FIG. 11 is a section taken along line 11--11 in FIG. 9, and 
     FIG. 12 is a section taken along line 12--12 in FIG. 9. 
    
    
     The internal combustion engine 1 represented diagrammatically in FIG. 1 has two cylinder banks 2 and 3 whose exhaust pipes 4, 5 and 6, and 7, 8 and 9, respectively, are combined in exhaust manifolds 10 and 11, respectively. Each manifold 10 and 11 is connected to a divergent wye coupling 12 and 13, respectively, from which two connecting pipes 14, 15, and 16, 17, respectively run. Connecting pipe 15 is connected to a convergent wye coupling 18 into which the branch pipe 17 runs. In the same manner the connecting pipe 16 is connected to a convergent wye coupling 19 into which the connecting pipe 14 runs. An exhaust pipe 20 runs from the convergent wye 15 [18] to a first reactor 21 and a second exhaust pipe 22 runs from the second convergent wye 19 to the second reactor 23. 
     The divergent wyes 12 and 13 divide the exhaust streams from the two cylinder banks 2 and 3 into substantially equal streams, and the convergent wyes 18 and 19 combine a portion of the exhaust from the one cylinder bank with a portion of the exhaust from the other cylinder bank, so that the composition as well as the volume of the exhaust gases flowing through exhaust pipes 20 and 22 are largely identical. It is thus possible by means of a single lambda probe 24 to detect the oxygen content in the exhaust gas and the composition of the fuel-air mixture fed to the cylinders can be regulated such that a mixture varying only slightly, by lambda=1 is always present, which is necessary for a maximum conversion rate for NO x  and HC in the catalysts 21 and 23. 
     The two exhaust manifolds 10 and 11 as well as the connecting pipes 15 and 16 run substantially parallel to one another on either side of the internal combustion engine 1. When an internal combustion engine of this kind is installed with the exhaust system represented, in order to interfere as little as possible with the ground clearance of the crossing connecting pipes 14 and 17, since they must run underneath the transmission 25 indicated in broken lines, the crossover point of the two connecting pipes 14 and 17 is situated not in the center between the connecting  pipes 15 and 16, but is offset laterally. 
     In the embodiment in FIGS. 2 to 4, in which equal or similar parts are designated by the same reference number as in FIG. 1, but with a prime, the exhaust manifolds 10&#39; and 11&#39; lead into a chamber 30 from which the exhaust pipes 20&#39; and 22&#39; lead to the catalysts 21&#39; and 23&#39;. The chamber 30 has two entrances 32 and 33 which are separated from one another by a first wall 31, and to which the exhaust pipes 20&#39; and 21&#39; are connected. The walls 31 and 34 are perpendicular to one another as can be seen in FIGS. 3 and 4. Thus, a mixing of the two exhaust streams fed from the exhaust manifolds 10&#39; and 11&#39; takes place because, as in the first embodiment, half of each of the exhaust streams from the exhaust manifolds 10&#39; and 11&#39; flows into each exhaust pipe 20&#39; and 22&#39;, respectively. To represent this mixing, the exhaust gases from the manifold 10&#39; are indicated by circles and the exhaust gases from manifold 11&#39; are indicated by triangles. On account of the largely identical composition of the exhaust gases flowing through the exhaust pipes 20&#39; and 22&#39; the control of the fuel-air mixture can again be performed through a single lambda probe 24&#39;. 
     With the embodiment in FIGS. 5-8, a mixing effect similar to that of the embodiment in FIGS. 2-4 is achieved, but with a less complicated construction. In this embodiment the chamber 30a, to which the two exhaust manifolds 10a and 11a are connected on the one side, and the two exhaust pipes 20a and 22a are connected on the other, is divided by a separating wall 40 into two subchambers 41 and 42. The desired production of a homogeneous exhaust mixture in both exhaust pipes 20a and 22a is achieved by the fact that the one exhaust pipe 20a is in communication with the one subchamber 41 and the other exhaust pipe 22a is in communication only with the other subchamber 42, while the two exhaust manifolds 10a and 11a are in communication with both subchambers 41 and 42. The dividing of the exhaust streams from the exhaust manifolds 10a and 11a is achieved in the embodiment represented, by the fact that the dividing wall 40 is provided with tab-like prolongations 42 and 44 which reach into the mouths of the exhaust pipes 22a and 22a and are bent in opposite directions, so that the exhaust stream from the first subchamber 41 in FIG. 6 is deflected into the exhaust pipe 20a and the exhaust stream from the second subchamber 42 is deflected into the exhaust pipe 22a. The dividing wall 40 divides the mouth of each exhaust manifold 10a and 11a into an upper section 46 and a lower section 47, so that each exhaust manifold is in communication both with the first chamber 41 and with the second subchamber 42 (see FIG. 8). In the wall of the chamber 30a, a lambda probe 24a is provided in the plane of the dividing wall 40, and dividing wall 40 is provided with a cutout 45 in the area of the lambda probe 24a, so that the lambda probe 24a is reached by the exhaust gas in both chambers 41 and 42. Alternatively, the lambda probe 24a can also be disposed in one of the exhaust pipes 20a or 22a, as in the preceding examples. 
     The embodiment in FIGS. 9 to 12 differs from the one in FIGS. 5 to 8 basically only in that the two exhaust manifolds 10b and 11b are in communication each with only one subchamber 41 and 42, respectively, while the two exhaust pipes 20b and 22b issue from both subchambers 41 and 42. For this purpose the tabs 42 [43] and 44 of the dividing wall 40 are bent in opposite directions and extend into the mouths of the exhaust manifolds 10b and 11b, while the dividing wall 40 divides the mouths of the exhaust pipes 20a and 20b into two sections 48 and 49 of which one is in communication with subchamber 41 and the other with subchamber 42. In this manner the same mixing effect is achieved as in the embodiment in FIGS. 5 to 8, which is indicated by the arrows A and B of which arrows B represent the exhaust from the manifold 10a and 10b and arrows A the exhaust from the manifold 11a and 11b, respectively. The advantage of the embodiment in FIGS. 9 to 12 over those of FIGS. 5 to 8 lies in the fact that the pulsations of the two exhaust streams A and B affect one another to a lesser extent, so that the total exhaust back pressure is less.