Patent Publication Number: US-2011047996-A1

Title: Exhaust gas treatment apparatus with improved pressure pulse damping

Description:
PRIOR ART 
     The invention is based on known methods and apparatuses for posttreatment of exhaust gases, in particular exhaust gases of internal combustion engines, for instance in the automotive field, in energy generation, or in similar fields in natural science and technology. From such fields, techniques are known in which various pollutant-reducing media, especially fluid media (such as liquids or gases) are metered, for instance injected into the exhaust gas. Various techniques and various types of pollutant-reducing media are employed. Examples of such pollutant-reducing media are urea-water solutions, which as a reducing agent reduce nitrogen oxides selectively. Such methods are often also called SCR methods (SCR: selective catalytic reduction). 
     Other methods are based on the injection of hydrocarbons, as pollutant-reducing media, into exhaust gases. Such methods, which are often also called HCI methods (HCI: hydrocarbon injection), can serve various purposes. For one, an injection of fuel, such as diesel fuel, as a reducing agent can be for instance serve to reduce nitrogen oxides. Other methods are based on a reaction of the injected fuel in an oxidation catalytic converter, which for instance leads to a brief temperature increase in the exhaust tract. This temperature increase can be employed for instance for regenerating an exhaust gas posttreatment apparatus, for instance for regenerating a diesel particle filter by burning off soot. 
     Without limiting the further possibilities for embodying the pollutant-reducing medium, reference will be made hereinafter essentially to HCI systems. However, it will be pointed out that other types of pollutant-reducing media, especially liquids, can also be employed. 
     Various apparatuses for introducing the pollutant-reducing medium into the exhaust gas are known from the prior art. For instance, German Patent Disclosure DE 10 2005 040 918 A1 describes a system in which fuel is diverted from a low-pressure part of a reservoir-type injection system and metered into the exhaust gas. The low-pressure part has a pressure maintenance valve, for maintaining a minimum pressure in the low-pressure part. 
     In the system shown in DE 10 2005 040 918 A1, the low-pressure reservoir, with its liquid volume, ensures a certain calming of pressure fluctuations. Nevertheless, pressure fluctuations in the low-pressure circuit of an injection system of that kind can only seldom be avoided. In other types of furnishing the pollutant-reducing medium as well, such pressure fluctuations occur. Pressure fluctuations can also, depending on the injection system, also be generated by the return from the injectors in the fuel injection system or as a result of pumping. 
     To avoid these problems of pressure fluctuations, German Patent Disclosure DE 10 2005 034 704 A1 discloses an apparatus and a method for regenerating particle filters. In the apparatus proposed there as well, a calming volume of fuel is employed in order to ensure a certain compensation for pressure fluctuations. It is also proposed that a pressure control valve, which opens and dissipates the pressure if the supplied fuel exceeds a certain value, be disposed in a branch line from the calming volume. 
     Despite these calming provisions known from the prior art, it has been demonstrated that under some circumstances, there can nevertheless be a potential for improvement. For instance, pressure peaks can still occur and influence the injection of the pollutant-reducing medium. Moreover, cavitation in the supply line of the pollutant-reducing medium, for instance in the low-pressure circuit, can also occur. Such pressure peaks and cavitation can even lead to damage of the components of the system, such as the HCI components, and the hydraulic behavior can be adversely affected. 
     DISCLOSURE OF THE INVENTION 
     An apparatus for metering at least one pollutant-reducing medium into an exhaust system is therefore proposed which at least largely avoids the above-described disadvantages of known apparatuses and systems and which ensures that the injection of the pollutant-reducing medium is made uniform. With regard to the embodiment of the pollutant-reducing medium, the above descriptions of known systems can for instance be referred to, especially HCI systems. Especially preferably, the apparatus can be used for regenerating a diesel particle filter, the apparatus being used such that diesel fuel is injected and catalytically combusted into an exhaust tract, for instance upstream of an oxidation catalytic converter. As a result, the temperature in the exhaust system is actively raised, until the burnoff temperature for the soot deposited in the diesel particle filter has been reached. 
     The proposed apparatus includes at least one injection valve, in particular a pressure-regulated injection valve, for injecting the pollutant-reducing medium into the exhaust system. This can for instance involve a pressure-regulated injection valve, for instance pressure-regulated injection valves, which is already being used on a mass production basis for injecting fuels into combustion chambers of internal combustion engines, and/or for modifying such valves. 
     The apparatus furthermore includes at least one supply line for supplying the pollutant-reducing medium to the injection valve. 
     To this extent, the system can largely correspond for instance to the systems described in DE 10 2005 040 918 A1 and/or DE 10 2005 034 704 A1. However, still other designs are also possible. In contrast to the systems known from the prior art, however, in the proposed system at least one pressure damper is received in the supply line, upstream of the injection valve. The term “pressure damper” is to be understood here to mean a device, which damps pressure peaks in the pollutant-reducing medium in the supply line by providing that the excess energy from these pressure peaks is dissipated to and at least partly absorbed by an element, acting as an energy absorber, that is different from the pollutant-reducing medium and that differs from conventional provisions on the inlet side, such as pressure control valves or simple throttle bores. This additional element that receives the excess energy can, as described below, for instance include a solid, porous, or elastic, or (although this is less preferable) a plastic element. Various possibilities are discussed below as examples. 
     By means of the at least one pressure damper provided according to the invention, the pressure is accordingly efficiently made uniform, and thus an improvement is brought about in the process of injecting the pollutant-reducing medium. Dissipating excess pressure through an additional pressure control valve can be dispensed with, which can bring about a cost saving as well as simplification. Such pressure control valves, however, can, as described below, be provided as additional safety provisions, or provisions for making the pressure uniform. It is also possible to dispense with a calming volume of the kind provided in DE 10 2005 034 704 A1 or also, in the form of the low-pressure reservoir, for instance in DE 10 2005 040 918 A1, or else such a calming volume may be provided as an additional damping measure. 
     It is especially preferred if the pressure damper has at least one porous element received in the supply line. The porous element can for instance include a highly porous material of open porosity, that is, a material in which the pores form continuously open pore ducts. In particular, a porous element of this kind can be integrated upstream of components of the apparatus that do not resist high pressure peaks. The pressure damper can for instance include a ceramic material, a metal material, a metal alloy, or a combination of that and/or other materials as the porous element. In particular, sintered metals, sintered metal alloys, or sintered ceramics can be used, optionally also in combination. 
     The pressure damper and/or the porous element may have various geometries. The porous element can for instance be solidified by compaction or molding and ensuing drying and sintering of ceramic slips and/or metal slurries. The damping properties can be adapted to the various most frequently occurring operating conditions, that is, for instance liquid properties, pressures, temperatures, and/or the like that frequently occur during operation. An adaptation to the component geometry, for instance to spatial installation conditions, can also be purposefully made. By means of a purposeful choice of porosity, pore size, or similar parameters of the porous element and/or of a rib thickness of the porous element and/or a length of the porous element or of the pressure damper, the lowering of the pressure level can be optimized in a purposeful way. 
     Alternatively or in addition to the porous element, the pressure damper can also include at least one hydraulic pressure damper. This hydraulic pressure damper should preferably be arranged in such a way that it includes at least one hydraulic volume of the pollutant-reducing medium. For instance, this hydraulic volume can be a closed-off hydraulic volume, which is received in a widened portion (for instance a pressure vessel). This pressure vessel can be in communication with the supply line via an inlet and an outlet, for instance, or integrated with the supply line. 
     The hydraulic pressure damper further includes at least one energy reservoir that is different from the hydraulic volume and is in operative communication with the hydraulic volume. While in the case of the use of the porous element, the porous element itself acts as an additional element absorbing the excess energy or excess pressure in the case of pressure peaks, in the case of the hydraulic pressure damper, the energy reservoir acts as an additional element for absorbing the excess energy contained in the pressure peaks and thus for making the pressure uniform. 
     The energy reservoir may for instance include a mechanical energy reservoir, such as an at least partly elastically deformable plastic or some other elastic element, for instance a spring element. Alternatively or in addition, the energy reservoir can also contain at least one compressible closed-off fluid volume, in particular a gas volume, in particular air. Still other kinds of energy reservoirs are conceivable. The energy reservoir may also be designed such that while it absorbs brief pressure peaks, nevertheless the excess energy of these pressure peaks is returned to the pollutant-reducing medium again once the pressure peak has faded. In this way, besides pressure peaks, pressure incursions, for instance, can also be reduced. The pressure damping properties can optionally be adapted using throttle elements (such as inflow throttles and outflow throttles) received in the supply line, with the pressure level prevailing at the time, and optionally with an overflow valve or a pressure control valve and/or an overpressure valve. 
     As discussed above, it is especially preferred if the supply line connects a low-pressure system of a fuel system, in particular a reservoir-type injection system (such as a diesel common rail system) with the injection valve. 
     Furthermore, upstream of the injection valve in the supply line, at least one metering unit can also be received, and the metering unit has at least one valve for controlling a procedure of injection of the pollutant-reducing medium. This metering unit can for instance be controlled by a separate controller and/or by a controller integrated with an engine control unit. 
     The metering unit can for instance include a shutoff valve, which as a whole turns the injection operation on or off. Alternatively or in addition, the metering unit can include a metering valve which is operated for instance in clocked fashion and subjects the injection valve to pressure in clocked fashion, so that the injection procedure takes place in clocked fashion as well. 
     Moreover, the metering unit can include one or more pressure measuring devices. For instance, one pressure measuring device can be provided for determining a metering quantity, for instance between a shutoff valve and a metering valve. Alternatively or in addition, one pressure measuring device can be provided between the metering valve and the injection valve, for instance in the form of a pressure sensor for detecting leaks. If at least one such pressure measuring device is provided, then the pressure damper can in particular be disposed upstream of this at least one pressure measuring device, for instance upstream of a pressure measuring device for a metering quantity. In particular, the pressure damper can be integrated entirely or in part in the metering unit, or it may also be provided entirely or in part upstream of the metering unit. 
     As described above, in addition to the pressure damper, further devices can optionally be provided for making the pressure in the apparatus uniform. In particular, at least one overpressure valve may for instance be provided, which is received in a branch line branching off from the supply line upstream of the pressure damper. Alternatively or in addition, a damping supply of the pollutant-reducing medium can also be received upstream of the pressure damper in the supply line, for instance in a widened part of the supply line and/or in a vessel communicating with the supply line, such as a pressure vessel. To this extent, the apparatus can for instance be supplemented with the additional provisions described in DE 10 2005 034 704 A1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are shown in the drawings and described in further detail in the ensuing description. 
       Shown are: 
         FIG. 1 , a schematic structure of an internal combustion engine having exhaust gas posttreatment; 
         FIG. 2 , a schematic detailed view of the exhaust gas posttreatment of  FIG. 1 ; 
         FIG. 3 , a first exemplary embodiment of a pressure damper with a porous element; and 
         FIG. 4 , a second exemplary embodiment of a pressure damper with an energy reservoir. 
     
    
    
     In  FIG. 1 , highly schematically, an internal combustion engine  110  is shown. The internal combustion engine includes a combustion motor  112 , with an air intake tract  114  and an exhaust tract  116 . The combustion motor  112  is designed for instance as a turbo diesel motor and includes a turbocharger  118  coupled with the intake tract  114  and the exhaust tract  116 . Also provided in the intake tract  114  are a charge air cooler  120  and a throttle valve  122 . The internal combustion engine  110  further has an exhaust gas recirculation  124 , which branches off from the exhaust tract  116  between the combustion motor  112  and the turbocharger  118  and discharges into the intake tract  114  before the throttle valve  122  and the combustion motor  112 . Valves  126  and further coolers  120  can be provided in the exhaust gas recirculation  124 . 
     In this exemplary embodiment, an oxidation catalytic converter  128 , symbolically represented in  FIG. 1  by “DOC”, is disposed downstream of the turbocharger  118  in the exhaust tract  116 . Downstream of this oxidation catalytic converter  128  is in turn a particle filter  130 , for instance a diesel particle filter, which is symbolically indicated in  FIG. 1  by “DPF”. 
     An injection valve  132  is provided between the turbocharger  118  and the oxidation catalytic converter  128 . By means of this injection valve, which is subjected to pollutant-reducing medium, such as diesel fuel, via a supply line  134 , pollutant-reducing medium  136 , which in the HCI process is for instance diesel fuel, is injected into the exhaust tract  116 . The diesel fuel is catalytically combusted by the oxidation catalytic converter  128 , as a result of which the temperature in the exhaust tract  116  is actively raised until the burnoff temperature for the soot deposited in the diesel particle filter  130  is reached. In this way, regeneration of the diesel particle filter  130  can be accomplished. 
     A metering unit  138  is also disposed in the supply line  134 . This metering unit  138 , like the supply line  134  and the injection valve  132 , is a component of an apparatus  140  for metering the pollutant-reducing medium  136 . This apparatus  140  is shown schematically in further detail in  FIG. 2  and will be described in further detail below. 
     Furthermore, in the exemplary embodiment shown in  FIG. 1 , the apparatus  140  optionally includes a controller  142 , which can for instance be integrated entirely or in part with an engine controller (or engine control module, ECM) of the internal combustion engine  110 . As shown in  FIG. 1 , this controller  142  can for instance be subjected to various sensor signals, such as pressure and/or temperature signals, from measurements of various points in the exhaust tract  116 . Signals from various pressure sensors  146 ,  148  integrated with the metering unit  138  can also be sent to the controller  142 . The controller  142  generates a first control signal  150  for a shutoff valve  152  (symbolically represented in  FIG. 1  by “SV”). The controller  142  also generates a second control signal  154  for triggering a metering valve  156  (symbolically represented by “DV” in  FIGS. 1 and 2 ), downstream of the shutoff valve  152  in the supply line  134 , in the metering unit  138 . The control signal  154  is also shown schematically in  FIG. 1 , on the left. 
     In  FIG. 2 , highly schematically, the apparatus  140  for metering the pollutant-reducing medium  136  is shown in a modification according to the invention. It can be seen, first, that the supply line  134  connects the injection valve  132 , symbolically represented by “IV”, with a low-pressure part  158  of a fuel system (symbolically represented in  FIG. 2  by “LPC”). For possible details of this optional communication with the low-pressure part  158 , DE 10 2005 040 918 A1 can for instance be consulted. The fuel, as the pollutant-reducing medium  132  flows via the supply line  134 , via an optional throttle element  160 , to the metering unit  138 , which is symbolically represented in  FIG. 2  by “MU”. In addition, analogously to the embodiment in DE 10 2005 034 704 A1, for instance, it is optionally possible for a pressure damper volume, not shown in  FIG. 2 , to be disposed for instance between the throttle element  160  and the metering unit  138 . 
     Inside the metering unit  138 , the shutoff  152 , at regeneration intervals, initially interrupts the inflow of pollutant-reducing medium  136 . Optionally, an overpressure valve  162  can be received in the branch line  164 , similarly to the embodiment in DE 10 2005 034 704 A1, for example, which valve connects the supply line  134  with the tank  166 . In this way, a pressure level can be reduced, and pressure fluctuations can also be compensated for to a limited extent. 
     In the metering unit  138 , downstream of the shutoff valve  152 , is the first pressure sensor  146 , whose signal can be used for instance for calculating the clocking of the metering valve  156  and thus for increasing the metering quantity precision. This metering quantity is then made available via the metering valve  156  and delivered to the injection valve  132 . A second pressure sensor  148 , as a pressure measuring device, for instance for detecting leaks, can optionally be disposed between the injection valve  132  and the metering valve  156 . 
     The injection valve  132  may for instance be a structurally adapted fuel injection valve, which opens at a defined supply pressure and injects pollutant-reducing medium  136  into the exhaust tract. A structurally adapted “K-Jetronic” valve can for instance be used for this. 
     The apparatus  140  shown in  FIG. 2  is modified according to the invention by providing at least one pressure damper  168  upstream of the injection valve  132 . For example, a pressure damper  168  of this kind can be disposed at one of the places marked A, B, or C in  FIG. 2 , or at some or all of these places. Alternatively or in addition, such pressure dampers  168  can be fundamentally disposed at other points in the supply line  138  as well. 
     Exemplary embodiments of pressure dampers  168  according to the invention that can be provided for instance in an apparatus  140  as in  FIG. 2  are shown in  FIGS. 3 and 4 . 
       FIG. 3  shows an exemplary embodiment of a pressure damper  168  which functions passively and includes at least one porous element  170  of open porosity. This porous element  170 , which for instance, as shown above, can include a ceramic, a metal, a metal alloy, or a combination of these or other materials, is received for instance in a pressure housing  172 . This pressure housing  172  is incorporated into the supply line  134  via an inlet  174  and an outlet  176 . 
     The porous element  170  may for instance have nonlinear properties with regard to the permeability for the pollutant-reducing medium  136 , so that there is a disproportionate ratio exists for example between the pressure difference at the inlet  174  and outlet  176  and the delivered quantity of pollutant-reducing medium  136 . This means that pressure peaks can be intercepted especially effectively by the pressure damper  168 . The excess energy contained in the pressure can be absorbed by the porous element  170 , for instance. 
     In  FIG. 4 , a second possible exemplary embodiment of a pressure damper  168  is shown. In this case, the pressure damper again includes a pressure housing  172 , with an inlet  174  and an outlet  176 , by way of which inlet and outlet the pressure damper  168  is incorporated into the supply line  134 . In the interior of the pressure housing  172 , a hydraulic volume  178  of the pollutant-reducing medium  136  is received, which is operatively connected via a ram  180  to a spring element  182 , shown in simplified form, as an energy reservoir  184 . Instead of the spring element  182 , other types of energy reservoirs may for instance be used, as discussed above. A spring chamber  186 , in which the spring element  182  is received, can for instance be pressure-relieved via a bore, not shown in  FIG. 4 . All in all, the hydraulic pressure damper  168  shown in  FIG. 4  represents one example of a piston spring reservoir. Still other types of energy reservoirs may be employed, however.