Abstract:
An exhaust system, especially of a motor vehicle has at least one heating device positioned in an area in which condensate accumulates, which is arranged within the exhaust system and in which condensate can accumulate depending on operating states and/or environmental parameters. The formation of condensate accumulation is reduced or prevented by the heating device and a condensate accumulation already formed is removed. As a consequence of the corrosive property of the condensate, the service life of the exhaust system is increased by the removal of such condensate accumulations or by preventing such accumulations from forming. At the same time, the freedom of designing the exhaust system concerning the location and position of the individual components is increased.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2010 007 013.0 filed Feb. 5, 2010, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention pertains to an exhaust system, especially of a motor vehicle. 
       BACKGROUND OF THE INVENTION 
       [0003]    Combustion water, which may lead to problems on the components of the exhaust system, for example, during wintertime operation, is formed during the combustion of fuels. Depending on the composition of the fuel, a volume of combustion water may be released by the combustion, which is comparable to the volume of fuel consumed. This combustion water generated is usually blown off as vapor together with the hot exhaust gases via the exhaust system during the normal medium-load operation of the motor vehicle. However, the temperature may drop below the dew point and liquid combustion water may precipitate in the wintertime as well as during the transition times close to winter. Thus, the dew point of exhaust gases of an internal combustion engine in a motor vehicle may be between about 20° C. and 60° C. Condensate may thus accumulate at such temperatures in the exhaust system. This leads in practice to the possibility of the accumulation of condensate on all components in the exhaust system that are in contact with the exhaust gas and remain below such temperatures because of the environmental conditions of the exhaust system. Most components of current exhaust systems usually reach markedly higher temperatures after a short operating time and the condensate formed can thus be evaporated after a short time and carried by the exhaust gas flowing by. However, increased accumulation of condensate, which may form a condensate sump in the exhaust system, may develop at low outside temperatures especially during operation over short distances, because the difference between the vapor pressures of a hot section of the exhaust system and of a cold section of the exhaust system leads to a constant transport and precipitation of the combustion water and the water will therefore gather at the lowest points of the exhaust system and can form a condensate sump there. Critical in such a condensate sump is the possible increase in the concentration of acid-forming components of the exhaust gas or of other exhaust gas components, which leads to a permanent corrosion burden of precisely these sections of the exhaust system, in which such an accumulation of condensate or such a condensate sump can form. A great variety of measures are therefore currently taken to reduce such a recurring corrosion burden of the exhaust system. For example, the hot exhaust gas can be allowed to flow effectively by, for example, in the last exhaust muffler at the deepest point by placing the exhaust pipe in a low position. The gathering condensate can as a result be both entrained with the flow and heated and possibly evaporated hereby. 
         [0004]    However, if it is possible for design reasons to place the exhaust pipe in the last exhaust muffler in a lower position, one can attempt to draw off the condensate with suction tubes in the manner of a water jet pump and to remove it from the exhaust system. A choking may be additionally inserted for this at the inlet of the pipe in the main pipe in order to lower the pressure at high exhaust gas throughputs to such an extent and hence to generate such a great pressure difference between the condensate collection and the exhaust gas flowing in the exhaust pipe that the collected condensate is entrained by the flow. The drawback of this is that such measures usually only help at medium to high loads of the internal combustion engine. The accumulated condensate can be normally discharged with short accelerations, but the pressure differences developing in the process are usually insufficient for the comprehensive removal of the accumulated condensate during stop-and-go travel in city traffic or in local traffic. 
         [0005]    It may happen without such measures that, for example, the rear muffler may fill with condensate as a consequence of the usually oblique installed position in relation to the rear of the vehicle and to the relatively highly positioned end pipe at correspondingly low outside temperatures. This leads to noise burden as a consequence of sloshing and bubbling noises in this section of the exhaust system and may lead to clogging of the exhaust system in the worst case as a consequence of the freezing of an ice plug in case of return of condensate and permafrost or correspondingly low temperatures. 
         [0006]    The situation may be especially disadvantageous in case of newer components in the exhaust system, for example, in case of Helmholtz resonator chambers connected via pipes or in case of active volumes of active noise suppression means having loudspeakers. Exhaust gas does not obligatorily flow through such components and these are therefore heated by the exhaust gas more poorly and more slowly, but they are nevertheless exposed to the combustion water contained in the exhaust gas just as the areas of the exhaust system through which exhaust gas flows and may experience accumulation of condensate in corresponding operating states of the motor vehicle and low temperatures associated therewith. Attempts are therefore made to usually arrange such components of the exhaust system such that a gradient will always develop from the deepest point of such a component to the hot exhaust pipe, so that condensate formed can run off and it can be driven out of the exhaust system or these components as completely as possible. However, this may lead to unfavorable installation positions in the vehicle in respect to such components, but also in respect to components of the exhaust system that are connected thereto. Thus, the freedom of design of the exhaust system is limited because of the necessity to discharge accumulated condensate from the exhaust system. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention pertains to the object of proposing for an exhaust system with a heating means an improved or at least different embodiment, which is characterized especially by a weaker tendency towards the development of condensate accumulations and by a greater freedom in designing the exhaust system, which is associated therewith. 
         [0008]    The present invention is based on the general idea of equipping an exhaust system, especially of a motor vehicle, with a heating means and of positioning at least one heating device of the heating means in an area in which accumulation of condensate is possible, wherein the area in which the accumulation of condensate is possible is arranged within the exhaust system and wherein accumulation of condensate can develop in this area, in which the accumulation of condensate is possible, depending on operating states of the motor vehicle and/or environmental parameters of the exhaust system, wherein the heating device is positioned such that accumulated condensate can be heated and/or evaporated at least by such a heating device. By warming or heating such an area of the exhaust system, in which accumulation of condensate is possible, the vapor pressure ratio between the accumulated condensate and exhaust gas can be shifted in favor of the exhaust gas, so that, on the one hand, less combustion water will separate from the exhaust gas and, on the other hand, condensed water already separated can be returned into the exhaust gas by evaporation. Thus, the formation of condensate can be reduced or prevented and the effect of the condensate on the exhaust system, which is a damaging effect because of corrosion, can be reduced or eliminated by arranging one or more heating devices in the respective critical areas of the exhaust system. This advantageously leads to a prolongation of the service life of the entire exhaust system. 
         [0009]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    In the drawings: 
           [0011]      FIG. 1  is a schematic view of an exhaust system according to the invention; 
           [0012]      FIG. 2  is a schematic view of an alternate embodiment of the exhaust system according to the invention; 
           [0013]      FIG. 3  is a schematic view of an alternate embodiment of the exhaust system according to the invention; 
           [0014]      FIG. 4  is a schematic view of an alternate embodiment of the exhaust system according to the invention; 
           [0015]      FIG. 5  is a schematic view of an alternate embodiment of the exhaust system according to the invention; and 
           [0016]      FIG. 6  is a schematic view of an alternate embodiment of the exhaust system according to the invention; 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Referring to the drawings in particular,  FIG. 1  schematically shows a section of an exhaust system  8  of a motor vehicle. The exhaust system  8  is shown with a flow passage, through which exhaust gas flows as indicated by arrows  4 , having a wall with an exhaust system area  10  in which condensate accumulates and in which accumulation of condensate may take place depending on operating states and/or environmental parameters. The exhaust system  8  has a higher temperature area  12  which has a temperature higher than the temperature of the area  10  in which condensate accumulates to said area in which condensate accumulates. 
         [0018]    A heating means  20  for the exhaust system may have a plurality of heating devices  22 , which may be arranged in different positions at the exhaust system and which have different functionalities concerning the heating of the exhaust system. For example, a heating device  22  may thus be positioned in the area of a catalytic converter  6  arranged in the exhaust system, in which case such a heating device  22  is designed such that it can heat up the catalytic converter  6  to the operating temperature with respect to its catalytic effect. As was already described above, according to the invention a heating devices  22  is provided for avoiding, reducing or removing accumulated condensate. 
         [0019]    Such condensate accumulations may develop in cold areas of the exhaust system. For example, condensate accumulations, which can flow together along the oblique surfaces to the deepest point in the exhaust system, forming a condensate sump, may thus also develop on oblique surfaces. It is consequently advantageous to heat both the areas at which accumulations of condensate can develop and those that tend to form sumps. Consequently, the heating device  22  is to be advantageously provided at precisely these areas  10  of the exhaust system. These may comprise both areas of the flow path of the exhaust gas in the exhaust system  8  and secondary areas  16  of the exhaust system, through which no exhaust gas flow, for example, components of a Helmholtz resonator in an exhaust muffler means, as well as the spaces of an active exhaust muffler exposed to sonic waves by an active actuator. 
         [0020]    Such a heating device  22  for heating areas  10  in which condensate accumulates may be designed as a heat-conducting element, electrically heatable and/or Peltier element and/or have a memory element. Combinations of these embodiments are possible as well. 
         [0021]    As shown in  FIG. 2 , the heating device  22  may have a heating element  24  that is formed of a heat-conducting material, by means of which heat can be transmitted from a hot area  12  of the exhaust system to a cold area  10  of the exhaust system. The heating element  24  is connected for this purpose to the hot area  12  of the exhaust system and to the cold area  10  of the exhaust system. Thus, such a heat-conducting element  24  may be designed as a heat-conducting plate, a heat-conducting rod or the like. 
         [0022]    It is equally conceivable to design the heating device as an electrically heatable heating device  26  such as a mat, wire or plate, and a design as a Peltier element is advantageous as well. Such an electrically heatable heating device  26  may be controlled by a heating device control  34 . In  FIG. 3 , the a Peltier element  28  is an electrically heatable heating device. In the case of using a Peltier element  28  as the electrically heatable heating device, such a heating device can be used not only to heat the area  10  of the exhaust system in which the Peltier element is arranged, but also to cool same. This is especially beneficial in the area of the active actuator of an active exhaust muffler means, because accumulation of condensate can be reduced and/or accumulated condensate can be removed by heating the actuator area by means of the Peltier element  28  and, on the other hand, precisely this actuator can be cooled in case of rising exhaust gas temperature during running operation in order to guarantee proper function. Furthermore, such a moveable heating device  32  may be provided having a memory element  30 , for example, a bimetal strip as shown in  FIG. 4 . The heating of the area  10  in which accumulation of condensate is possible is made possible at a correspondingly low temperature, whereas the mechanical thermal contact with the area  10  in which accumulation of condensate is possible is interrupted (as shown in dashed line) beginning from a predefined temperature because of the deformation of the memory element  30  such that heating of said area  10  will not take place any longer. 
         [0023]    Any desired meaningful combinations of these above-described embodiments are also conceivable. For example, it is thus possible to provide a heat-conducting element with a memory effect or, e.g., to design it as a bimetal, so that the contact between the hot area of the exhaust system and the cold area of the exhaust system is established at a low temperature. The heat-conducting element  32  provided with only one memory effect will be deformed beginning from a certain temperature, as a result of which the contact between the heat-conducting element and the cold or hot area of the exhaust system is interrupted. The heat conduction is thus very extensively interrupted and the further introduction of heat from the hot area of the exhaust system into the cold area of the exhaust system is suppressed. This combination of a memory element  30  is also analogously conceivable in an electrically heatable heating device  26  or the like. 
         [0024]    Such a heating device  22  may be arranged at the exhaust system  8  on the inside and/or on the outside and/or such that it passes through the walls of the exhaust system. For example, as shown in  FIG. 5 , it is thus possible to arrange precisely such a heat-conducting element  25  such that it passes through the wall of the exhaust system, so that one end of the heat-conducting element is swept by the hot exhaust gas and the introduction of heat from the exhaust gas into the heat-conducting element  25  is thus increased. The other end of the heat-conducting element may surround, on the outside in the cold area of the exhaust system, precisely this area, so that the heat-conducting area acting as a warm protective area reduces or prevents the accumulation of condensate as a consequence of the heating of this area based on this outside arrangement. Furthermore, the heating devices  22  may be arranged in a flow path of the exhaust system or even in secondary areas  16  as described above. Thus, any desired combination is possible concerning the arrangement and design of the heating device, as this appears from the above-described examples. 
         [0025]    Moreover, insulation  16 , which improves the heat output of the heating device based on the heat-insulating property, may be applied in the area of the heating device, especially if the heating device is arranged on the outside on the exhaust system. This is, of course, also definitely advantageous for an inside arrangement of the heating device. However, a splash guard  18  is also advantageous, especially for the outside arrangement of the heating device, so that corrosion, among other things, of the heating device due to especially salt-containing splash water can be reduced or prevented. 
         [0026]    Such a heating device  22 , especially an electrically heatable heating device  26 , can be controlled by the control  34 , especially the vehicle system control. Thus, the heating device  22  can be operated depending on the operating state of the motor vehicle and depending on environmental parameters. It is also advantageous to switch the heating device  22  preferably into the active state during short-term operation of the motor vehicle and/or during the initial operation of the motor vehicle and/or in stop-and-go operation in city traffic. In addition, activation of the heating device  22  is, of course, also possible beginning from a predetermined outside temperature in the area of the exhaust system. Furthermore, it is also possible to take into account other operating states and environmental parameters if condensate formation may preferably occur in connection with these operating states and environmental parameters. 
         [0027]    The formation of condensate accumulation is advantageously prevented by such a heating device already in advance, because if such an accumulation of condensate develops, mainly acid-forming components of the exhaust gas may dissolve in this accumulated condensate, and the composition of the condensate may change disadvantageously due to such dissolution of acid-forming components of the exhaust gas. If, for example, sulfur dioxide contained in the exhaust gases dissolves in the condensed water, sulfurous acid is formed by the reaction of sulfur dioxide with the condensed water, and this sulfurous acid has a considerably higher boiling point than pure condensed water, so that it may be considerably more difficult to remove an accumulated condensate than to prevent the formation of such an accumulation. Thus, it is definitely advantageous to prevent the formation of condensate accumulations already in advance. 
         [0028]    While specific embodiments of the invention have been described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.