Abstract:
An exhaust system for internal combustion engines, in particular two-cycle internal combustion engines, includes a resonance-type exhaust part having at least one diffuser-cone unit formed with a diffuser, a countercone, and a connecting part with a preferably constant cross section extending between the diffuser outlet cross section and cone inlet cross section. In order to provide the resonance-type exhaust part as compact as possible by employing a simple production method, the connecting part is formed as a first deflection arc, preferably with an angle of deflection of about 180°±30°.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an exhaust system for internal combustion engines, in particular two-cycle internal combustion engines, with a resonance-type exhaust part which includes at least one diffuser-cone unit with a diffuser and a countercone, with a connecting part having a preferably constant cross section arranged between the diffuser outlet cross section and cone inlet cross section. 
     DESCRIPTION OF THE PRIOR ART 
     In an exhaust system of the kind mentioned above, an exhaust pipe with an initially constant progress of cross section is led away from the port via an outlet conduit. To produce a returning suction wave, a diffuser is connected thereto which opens into a countercone or baffle plate after a short transition element. A pressure wave running from the cylinder is produced in said constriction of cross section, which wave supplies the cylinder chamber with fresh air which reaches the exhaust system during the scavenging phase from the inlet slot through the cylinder chamber. 
     U.S. Pat. No. 4,424,882 A shows an arrangement for an exhaust system. This arrangement describes exhaust mufflers in which the exhaust gas from the engine flows into a large volume and from there further into a second chamber through at least two similarly long nozzles, such as diffuser-type tubes, situated adjacent to one another. Systems of this type aim at obliterating the gas-dynamic activity, as a result of which they cannot be used for reducing the scavenging losses and for the improvement of the torque characteristics. 
     AT 399 914 B describes an exhaust system for two-cycle internal combustion engines with a muffler pipe, with the initial region thereof being bordered by conical regions formed by diffusers, which regions are connected on the one hand via piping of different length with the initial region of the muffler pipe and open on the other hand into a common collecting vessel to which the tail pipe, comprising a catalyst and/or a muffler, is connected. This system ensures that a pressure wave coming from the cylinder is reflected twice as a suction wave and reaches the still open exhaust port in a time staggered manner as a result of the different run length. In this way the duration of action of the suction wave in comparison with other exhaust systems which utilize the exhaust reflection wave is extended with a single resonance chamber in order to convey back the fresh gases to the cylinder which have entered the exhaust towards the end of the scavenging phase. 
     Exhaust systems with resonator-type exhaust parts which are provided with at least one diffuser-cone unit require a relatively large amount of space due to the relatively high length of the diffuser and the conical part. 
     From DE 614 775 C a sound absorber is known with several chambers which are arranged behind one another in the direction of flow of the exhaust gases, with a deflection arc being provided after each chamber. Embodiments of exhaust systems with deflection arcs before each diffuser are shown in the already mentioned AT 399 914 B in order to arrange the diffusers mutually parallel on a common collecting vessel. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide a compact exhaust system with a resonator-type exhaust part which is easy to produce. 
     This is achieved in accordance with the invention in such a way that the connecting part is arranged as a first deflection arc, preferably with an angle of deflection of about 180° ± 30°. The resonator-type exhaust part can thus be provided with a very compact arrangement. A particularly compact solution is obtained when a second deflection art is provided in the initial zone of the diffuser whose angle of deflection is preferably 180°±30°. It is particularly advantageous if the center line of the second deflection arc is substantially arranged in a second plane which is disposed inclined to a first plane which is defined by the center line of the first deflection arc, with the second plane preferably being arranged approximately normal to the first plane. 
     It is preferably further provided that in the end zone of the countercone a third deflection arc is arranged whose angle of deflection is preferably 180° ± 30°. The third deflection arc can be arranged in a third plane which is inclined to the first plane, with the third plane preferably enclosing an angle of approx. 90° to the first plane and being arranged particularly preferably approximately parallel to the second plane. This leads to an arrangement in which the central line of the resonance-type exhaust part is connected in at least three planes and the exhaust gas flows through the resonance-type exhaust part in at least four passes, with the first and fourth pass being formed by the inlet part and the end part, the second pass comprising the diffuser and the third pass the countercone. The resonance-type exhaust part can thus be provided with a particularly compact design. 
     An embodiment that is particularly easy to produce provides that the diffuser and preferably also the inlet part and/or the second deflection arc and/or at least partly the first deflection arc are formed by a diffuser insert which is preferably arranged as a deep-drawing part. The countercone, as preferably also the end piece and/or the third deflection arc and/or at least partly the first deflection arc, can be formed by a cone insert which is preferably arranged as a deep-drawing part. Diffuser insert and cone insert are joined with screws for example, with a separating plate being arranged between the diffuser insert and the cone insert. 
     In order to avoid burbling and turbulence in the zone of the strongly bent deflection arcs, it can further be provided that in the zone of the first, second and/or third deflection arcs baffle plates are arranged, with the baffle plates preferably being fastened to the separating plate. 
     In a further development of the invention it is also possible that the diffuser is arranged as a double diffuser, with a secondary diffuser, preferably with the same inlet/outlet cross-sectional ratio as the diffuser, being arranged within the diffuser, with the secondary diffuser preferably being fastened to the separating plate. 
     In a particularly preferred embodiment it is provided that the resonance-type exhaust part is provided with at least two diffuser-cone units which are switched in parallel in respect of flow and are preferably arranged symmetrically with respect to a central plane and branch off from a common inlet piece and open into a common end piece, with the branches and/or the opening being arranged in the zone of the central plane. In this manner two or more diffuser-cone units can be arranged in a common housing in a particularly compact manner. The diffusers and countercones can also be formed in this case by separate inserts which are arranged as deep-drawing parts for example, thus allowing a particularly simple and inexpensive production. 
     In order to improve the exhaust gas quality it can be further provided that the separating plate, the diffuser insert, the cone insert, the baffle plates and/or the secondary diffuser are catalytically coated. 
     It is naturally also possible that the resonance-type exhaust part consists of ceramic at least in sections. 
     The tail pipe is preferably disposed in the zone of the central plane and in a central section of the resonance-type exhaust part, so that a heat discharge occurs according to the principle of reverse flow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is now explained below in closer detail by reference to the enclosed drawings, wherein: 
     FIG. 1 shows an exploded view of the resonance-type exhaust part; 
     FIG. 2 shows a schematic view of the flow paths in the resonance-type exhaust part and 
     FIG. 3 shows a known resonance-type exhaust part. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 3 shows a known resonance-type exhaust part  50  which is provided with a diffuser-cone unit  51  formed of a diffuser  52 , connecting part  53  and countercone  54 . Reference numeral  55  indicates the inlet pipe and reference numeral  56  of the tail pipe of this known exhaust system with a stretched diffuser-cone unit  51 . The disadvantage is the relatively high amount of required space. 
     The resonance-type exhaust part  1  according to the present invention is shown in FIG.  1  and is provided with two diffuser-countercone units  2 ,  3 . Each diffuser-countercone unit  2 ,  3  includes a diffuser  4 ,  5  and a countercone  6 ,  7 . A connecting part in the form of a first deflection arc  8 ,  9  is provided between the diffuser outlet cross section  4   a,    5   a  and the cone inlet cross section  6   a,    7   a,  the connecting part having an angle of deflection of 180° ± 30°. 
     A second deflection arc  10 ,  11  is provided in the initial zone of each diffuser  4 ,  5 . A third deflection arc  12 ,  13  is further arranged in the end zone of the countercone  6 ,  7 . Second deflection arc  10 ,  11  and third deflection arc  12 ,  13  are each provided with an angle of deflection of 180° ± 30°. The angle of deflection is always defined by the change in direction of the central line  8   a,    9   a,    10   a,    11   a,    12   a,    13   a  between inlet and outlet into the deflection arcs  8 ,  9 ,  10 ,  11 ,  12 ,  13 . 
     The central lines of the first deflection arcs  8 ,  9  are designated with  8   a,    9   a,  the central lines of the second deflection arcs  10 ,  11  with  10   a,    11   a  and the central lines of the third deflection arcs with  12   a,    13   a.  The central lines  8   a,    9   a,    10   a,    11   a,    12   a  and  13   a  each form a first plane  8   b  or  9   b,  a second plane  10   b  or  11   b  and a third plane  12   b  or  13   b.  The second planes  10   b  and  11   b  and the third planes  12   b  and  13   b  are provided an arrangement which is inclined preferably by an angle of about 90° to the first plane  8   b.  The second planes  10   b  and  11   b  are arranged approximately parallel to the third plane  12   b,    13   b.  Accordingly, the resonance-type exhaust part  1  is provided with at least four passes which are indicated by the arrows  14 ,  15   a,    15   b,    16   a,    16   b  and  17  in FIG.  2 . The first pass of flow  14  is formed by a common end part  19 . As is shown in FIGS. 1 and 2, the resonance part  1  is provided with two diffuser-cone units  2 ,  3  which in respect of flow are switched in parallel and which are arranged symmetrically with respect to a central plane  20 . The diffuser-cone units  2  start out from the common inlet part  18  and open into the common end part  19 . The branch  21  of inlet part  18  and the opening  22  into the end part  19  are located in the zone of the central plane  20 . 
     In the embodiment as shown in FIG. 1, the two diffusers  4 ,  5 , the inlet part  18  as well as the two deflection arcs  10 ,  11  are formed by a diffuser insert  23  arranged as a deep-drawing part. The countercones  6 ,  7  and the end part  19  are formed by a cone insert  24  arranged as a deep-drawing part. The flange facings  23   a  and  24   a  of the diffuser insert  23  and the cone insert  24  face one another and are mutually detachably connected, with a separating plate  25  being arranged between the diffuser insert  23  and the cone insert  24 . The second and third planes  10   b,    11   b,    12   b,    13   b  are arranged approximately parallel to the flange facings  23   a  and  24   a.  The first planes  8   b  and  9   b  are arranged approximately parallel to the central plane  20  and normal to the flange facings  23   a,    24   a.  The separating plate  25  partly separates the interior chambers of the diffusers  4 ,  5  and the countercones  6 , 7  from one another and thus creates meander-like flow paths. All parts of the resonance part  1  are housed in one housing which consists of the input-side housing part  26  and the output-side housing part  27 . 
     Exhaust gases coming from engine flow through the inlet opening  28  in the input-side housing part  26  and through the inlet line  29 . The inlet line  29  is connected to the connection piece  30  of the diffuser insert  23 , thus allowing the exhaust gases to travel further through the inlet part  18 , the second deflection arcs  10 ,  11  and into the diffusers  4 ,  5 . From there the exhaust gases flow through the first deflection arcs  8 ,  9  which are formed on the one part by the diffuser insert  23  and on the other part by the cone insert  24 , with respective pass-through windows  31 ,  32  are passed through the separating plate  25 . The exhaust gases further reach the countercones  6 ,  7  via the first deflection arcs  8 ,  9  and further to the third deflection arcs  12 ,  13  and to the opening  22  into the end piece  19 . The exhaust gases now leave the outlet cross section  19   a  of the end part  19  and, by flowing around the diffuser-cone units  2 ,  3  parallel to the central plane  20 , reach the outlet opening  33  of the output-side housing part  27  where they leave the resonance-type exhaust part  1  into the exhaust line not illustrated in further detail. 
     Flow baffle plates  34  can optionally be inserted in the zone of the deflection arcs  8 ,  9 ,  10 ,  11 ,  12 ,  13  in order to favorably influence the flow. The baffle plates  34  can be fastened to the separating plate  25 , as is indicated by the broken lines in FIG. 1 for the deflection arcs  12 ,  13  for example. In order to achieve a favorable heat transmission, diffuser insert  23 , cone insert  24  and the separating plate  25  are preferably made of thin-walled sheet metal. 
     It is further possible to arrange the diffusers  4 ,  5  as double diffusers, with a secondary diffuser  4 ′ which has the same cross-sectional ratio between inlet and outlet and is made of sheet metal being each inserted between the diffusers  4 ,  5 . 
     It is also possible to provide parts of the resonance-type exhaust part  1  such as the diffuser insert  23 , cone insert  24  or the separating plate  25  with a catalytic coating. In addition or as an alternative, a metal carrier catalyst can be welded into the sheet metal parts or a ceramic catalyst can be inserted between the sheet metal parts. Obviously, individual parts of the resonance-type exhaust system can be made of ceramics. 
     In order to improve the exhaust gas quality it is possible to supply blower cooling air also in the zone of the end part  19  or in the zone of the output-side housing  27 . 
     It is further possible, for the purpose of further sound reduction in the zone of the output-side housing part  27 , to provide a reflection plate  35 , as is indicated in FIG. 1 with the broken line. The exhaust gas flows in this case through the apertures  36  of the reflection plate  35  into a reflection chamber  37  and leaves the housing part  27  through the output opening  33   a.  The output opening  33  is omitted in this embodiment.