Abstract:
A procedure to introduce a reagent substance into the exhaust duct of an internal combustion engine and a device to implement the procedure are proposed. At least one catalytic converter is disposed in the exhaust duct of the internal combustion engine. In front of the aforementioned catalytic converter(s), a reagent substance subjected to pressure is sprayed into the exhaust gas. The reagent substance pressure set point is established as a function of a parameter. The procedural approach allows for a targeted employment of the reagent substance and a high degree of utilization of the converter.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention concerns a procedure for the introduction of a reagent substance in an exhaust duct of an internal combustion engine and a device for implementation of the procedure according to the class of the independent claims.  
       BACKGROUND  
       [0002]     In the German patent DE 101 39 142 A1 an exhaust gas after treatment system of an internal combustion engine is described; whereby in order to decrease the NOx emissions, a SCR-catalytic converter (Selective-Catalytic-Reduction) is employed which reduces the nitrogen oxides NO and NO 2  with the reducing agent ammonia. The ammonia is obtained from a urea water solution in an hydrolysis catalytic converter located upstream from the SCR-catalytic converter. The hydrolysis catalytic converter converts the urea contained in the urea water solution to ammonia and carbon dioxide. To assure an exact metering, provision is made to ascertain the concentration of the urea water solution.  
         [0003]     The urea water solution is brought to a predetermined pressure using a pump. A metering valve fixes a predetermined rate of flow. Compressed air is mixed in with the reagent substance in a mixing chamber. The urea water solution is sprayed together with the added air into the exhaust gas in such a way, that a largely even, consistent flow into the SCR-catalytic converter is achieved. If need be flow elements like deflection plates are to be provided.  
         [0004]     From the patent EP 1 024 254 A2 an exhaust gas after treatment system of an internal combustion engine is made known, whereby a SCR-catalytic converter is employed to decrease the NO x  emissions. Provision is made for ammonia to be the reducing agent, that is obtained in the exhaust duct from a urea water solution. The amount of urea water solution, which is measured out, is determined based on an operating parameter of the internal combustion engine, for example, the amount of fuel injected and/or the number of revolutions per minute and at least one parameter of the exhaust, for example the exhaust temperature.  
         [0005]     In the German patent DE 100 65 105 A1 a procedure is specified that provides for the modeling of an exhaust temperature of an internal combustion engine. The exhaust temperature is calculated as a function of an air signal, that is supplied by an air sensor and as a function of the number of revolutions per minute.  
         [0006]     In the professional publication “Otto engine—Management/Bosch”, first edition, published by Vieweg, Braunschweig, 1998, pages 333-335. A torque structure for operating an internal combustion engine was made known.  
         [0007]     The task underlying the invention is to specify a procedure for the introduction of a reagent substance into an exhaust duct of an internal combustion engine and a device for implementation of the procedure, which allows for an exact as possible metering of a reagent substance and a high utilization of the catalytic converter.  
         [0008]     The task is respectively achieved by way of the characteristics specified in the independent claims.  
       SUMMARY  
       [0009]     Provision is made according to the invention, that the pressure of a reagent substance, which is introduced into the exhaust of an internal combustion engine upstream of at least one catalytic converter, is established as a function of a parameter to a predetermined reagent substance pressure set point.  
         [0010]     The procedural approach of the invention allows for the achievement of a good atomization and an even, continuous distribution of the reagent substance in the exhaust gas flow before at least one catalytic converter. The reagent substance strikes the entire surface area, which the catalytic converter has facing the direction of the flow of the exhaust gas. The reagent substance can, therefore, reach the entire available catalytic surface area within the catalytic converter. The procedural approach according to the invention allows, therefore, for the best possible utilization of the catalytic surface made available by the catalytic converter. By way of the efficient utilization of the catalytic converter, the desired cleaning of the exhaust is achieved with the least possible amount of reagent substance.  
         [0011]     Advantageous embodiments and further configurations of the procedural approach according to the invention result from dependent claims.  
         [0012]     An embodiment allows for the use of at least one operating parameter of the internal combustions engine as a characteristic parameter. An air signal, for example, is well suited to be an operating parameter. Additionally or alternatively a torque and/or a fuel signal can respectively be used in conjunction with the number of revolutions per minute. The one or more operating parameters are known to the control unit. Additional sensors will not be necessary.  
         [0013]     An embodiment allows for the use of one parameter of the exhaust as the characteristic parameter. The volume of exhaust gas flow, respectively the exhaust gas speed and/or the exhaust gas pressure and/or the exhaust gas temperature, is suitable as a parameter of the exhaust. At a known mass of exhaust gas flow, the knowledge of the exhaust gas temperature alone is, for example, sufficient. The one or more parameters of the exhaust gas can be ascertained from the known operating parameters of the internal combustion engine. Additional sensors are also not necessary in this case. If need be, provision can be made for and exhaust gas temperature sensor to record the exhaust gas temperature. The measured exhaust gas temperature can be used to authenticate the calculated exhaust gas temperature.  
         [0014]     An embodiment allows for the reagent substance temperature to be used as a parameter. The reagent substance temperature can, for example, be estimated on the basis of a temperature signal of an existing temperature sensor, which records the air temperature. Preferably a reagent substance temperature sensor is employed.  
         [0015]     Additional advantageous modifications and embodiments of the procedural approach according to the invention result from additional dependent claims and from the following description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]     The FIGURE shows an internal combustion engine, in whose environment a procedure according to the invention is operating. 
     
    
       [0017]     The FIGURE shows an internal combustion engine  10  in whose intake area and air sensor  11  and in whose exhaust duct  12  a spray device  13 , an exhaust gas temperature sensor  14  as well as a catalytic converter are disposed.  
       DESCRIPTION  
       [0018]     The control unit  20  receives at its disposal an air signal mL supplied by the air sensor  11 , a number of revolutions per minute N supplied by the internal combustion engine  10 , an exhaust gas temperature Tabglw measured by the exhaust gas temperature sensor  14 , a reagent substance pressure actual value pRealw supplied by a reagent substance pressure sensor  21 , a compressed air pressure actual value pDLlw supplied by a compressed air pressure sensor  22 , a reagent substance temperature TRea supplied by a reagent substance temperature sensor  23  as well as a torque set point mifa.  
         [0019]     The control unit  20  emits a fuel signal mK to the internal combustion engine  10 , a metering valve activation signal qRea to a metering valve  30 , a reagent substance pump activation signal  31  to a reagent substance pump  32  and a compressed air regulating valve activation signal  33  to a compressed air regulating valve  34 .  
         [0020]     The control unit  20  contains a first functional block  41  to ascertain the exhaust gas speed vabg, a second functional block  42  to ascertain the exhaust gas pressure pabg, a third functional block  43  to ascertain a calculated exhaust gas temperature TabgR and a fourth functional block  44  to ascertain a torque Md.  
         [0021]     The control unit  20  additionally contains a reagent substance pressure set point setting  50 , which emits a reagent substance pressure set point pReaSw to a reagent substance pump trigger (activation)  51 , which supplies the reagent substance pump activation signal  31 , and also contains a compressed air pressure set point setting  52 , which emits a compressed air set point pDLSW to a compressed air regulating valve trigger (activation)  53 , which supplies the compressed air regulating valve activation signal  33 .  
         [0022]     The reagent substance temperature sensor  23  records the temperature of a reagent substance stored in a reagent substance container  60 . The compressed air regulating valve  34  adjusts the compressed air set point pDLSw of a compressed air, which is available in a compressed air container  61 .  
         [0023]     The compressed air passes through a super critical choke  62  and a check valve  63  and moves thereafter into a mixer  64 , which mixes the compressed air with the reagent substance introduced by the metering valve  30 . The mixer  64  is connected to the spray device  13 .  
         [0024]     The procedure according to the invention works in the following manner:  
         [0025]     The catalytic converter  15 , which is disposed in the exhaust area of the internal combustion engine  10  is preferably a SCR-catalytic converter which reduced the nitrogen oxides NO and NO 2  contained in the exhaust gas to nitrogen. The SCR-catalytic converter  15  needs ammonia for the reduction reaction. The ammonia can be obtained from a urea water solution in an hydrolysis catalytic converter which is disposed upstream from the SCR catalytic converter and is not depicted. The solution is then introduced into the exhaust gas flow with a spray device  13 . The urea water solution is an example of a reagent substance.  
         [0026]     The reagent substance stored in the reagent tank  60  is brought to the reagent substance pressure set point pReaSw of, for example, 4 bar by a reagent substance pump  32  and subsequently fed to the metering valve  30 . The amount of reagent substance/unit of time is predetermined by the metering valve activation signal qRea. The control unit  20  can ascertain the metering valve activation signal qRea from a predetermined engine characteristic map, which is constructed from the number of revolutions per minute N and the fuel signal mK or which is constructed from the number of revolutions per minute and the torque Md. The metering valve activation signal qRea induces the metering valve  30 , for example, to provide clearance of a certain opening width for the reagent substance. In the mixer  64  the reagent substance is mixed with compressed air.  
         [0027]     The compressed air is limited to a pressure of, for example, 8 bar in the pressure regulating valve  34 . The pressure after the super critical choke  62  is to be fixed to a value, which is sufficient enough, that the check valve  63  in front of the mixer  64  is opened and the compressed air can penetrate into the mixer  64 . After passing through the super critical choke  62 , a pressure of, for example, 4.6 bar emerges. Taking into account the pressure drop at the check valve  63  of, for example, 0.6 bar, the compressed air pressure in the mixer  64  amounts to ultimately 4 bar.  
         [0028]     The torque Md is established as a function of torque set point mifa and as a function of known parameters of the internal combustion engine  10  according to the state of the art named at the beginning of the application.  
         [0029]     Provision is made according to the invention to preset the reagent substance pressure set point pReaSw and if need be the compressed air pressure set point pDLSw. The preset (predetermined) reagent substance pressure set point pReaSw and if necessary preset (predetermined) compressed air set point pDLSw are preferably assessed in such a manner, that after the spray device  13  a good atomization and an even, continuous distribution of the reagent substance are achieved over the cross section of the exhaust duct  12 . In so doing, the size of the reagent substance droplets play a role.  
         [0030]     This measure causes the catalytic surface area available to the SCR-catalytic converter  15  to be completely utilized. It is, therefore, to be assured, that after the entrance of the reagent substance into the SCR-catalytic converter, no possibility exists anymore for its further mixing with the exhaust gas or its distribution on the catalytic surface area. The procedural approach according to the invention allows furthermore for a decrease in the required amount of reduction substance by way of a conforming to the actual need in the SCR-catalytic converter.  
         [0031]     The pressure of the reagent substance stored in the reagent substance container  60  can by way of a respective fixing of the reagent substance pump activation signal  31  in the reagent substance pump trigger (activation)  51  be brought to a preset (predetermined) reagent substance set point pReaSw, which, for example can amount to 4 bar. In order to realize a regulation to the preset (predetermined) reagent substance pressure set point pReaSw, the reagent substance pressure actual value pRealw can be recorded by the reagent substance pressure sensor  21  and then provided to the reagent substance trigger (activation)  51  for the implementation of the regulation.  
         [0032]     If need be, the compressed air pressure of the compressed air built-up in the compressed air container  61  can additionally be fixed to a preset (predetermined) reagent substance pressure set point pReaSw before its introduction into the mixing chamber  64 . A compressed air regulating valve  34  is provided for the fixing of the compressed air pressure. This regulating valve is activated by the compressed air regulating valve activation signal  33  which is supplied by the compressed air pressure trigger (activation)  53 . In order to realize a regulation to the preset compressed air pressure set point pDLSw, the compressed air pressure actual value pDLlw can be recorded by the compressed air pressure sensor  22  and fed to the compressed air pressure trigger (activation)  53  to implement the regulation.  
         [0033]     At least one operating parameter of the internal combustion engine  10  is suitable as a parameter to establish the reagent substance set point pDLSw and if need be to establish the compressed air pressure set point pDLSw. The air signal mL can already alone be used in this regard. Furthermore, the torque Md as well as the fuel signal mK are both suitable when used respectively in combination with the number of revolutions per minute N. Especially suitable are the last named combinations of at least two operating parameters mL, mK.  
         [0034]     In an engine characteristic map, which is not depicted, a one- or multidimensional connection is produced between the individual operating parameters N, mL, Md, mK and the set point(s) which is (are) to be preset, namely the reagent substance pressure set point pReaSw and if need be the compressed air pressure set point pDLSw.  
         [0035]     The operating parameters N, mL, Md, rnK, which have been named, have an influence on the parameters of the exhaust gas. Parameters of the exhaust gas are exhaust gas speed vabg, respectively the exhaust gas volume flow, the exhaust gas pressure pabg and, for example, the exhaust gas temperature TabgR, Tabglw. The parameters vabg, pabg, TabgR of the exhaust gas can be ascertained in the functional blocks  41 ,  42 ,  43 , which are inscribed inside of the control unit  20 , from known operating parameters N, mL, Md, mK.  
         [0036]     The exhaust gas speed vabg can already be ascertained from the air signal mL in the first functional block  41 . If need be, the fuel signal mK can be taken with it into consideration.  
         [0037]     Using a known geometry of the exhaust gas system and a known flow resistance of the catalytic converter  15 , the exhaust gas pressure pabg can be ascertained from the exhaust gas speed vabg in the second functional block  42 . The exhaust gas speed vabg and/or the exhaust gas backpressure pabg are preferably ascertained on the basis of a two dimensional engine characteristic map, which is constructed from the number of revolutions per minute N and from the fuel signal mK or from the number of revolutions per minute N and from the air signal mL.  
         [0038]     In case provision is made for a turbocharger, the charging-air pressure and/or charging temperature can be taken into consideration.  
         [0039]     The exhaust gas temperature TabgR, which is ascertained in the third functional block  43 , has, furthermore, an influence on the atomization of the reagent substance. The exhaust temperature TabgR might particularly have an influence on the size of the droplets of the reagent substance. The ascertainment can, for example, be carried out according to the German patent DE 100 65 125 A1 named at the beginning of the application, according to which the exhaust gas temperature TabgR is modeled from the number of revolutions per minute N and the air signal mL.  
         [0040]     The parameters of the exhaust, which have been described up till now, are ascertained in the functional blocks  41 ,  42 ,  43  from the operating parameters N, mL, Md, mK of the internal combustion engine  10 . The parameters of the exhaust can be alternatively or additionally measured with sensors. The exhaust gas temperature sensor  14  can be employed to measure the exhaust gas temperature, which passes on the exhaust gas temperature actual value Tabglw to the control unit  20 . Furthermore, the exhaust gas pressure could be measured with an exhaust gas pressure sensor, which is not depicted.  
         [0041]     In establishing the reagent substance set point pReaSw and if need be the establishing of the compressed air pressure set point pDLSw, the reagent substance temperature TRea, which the reagent temperature sensor  23  records, can be taken into consideration. The temperature sensor can be disposed in the reagent substance tank  60 .  
         [0042]     The reagent substance temperature TRea corresponds generally to the ambient air temperature, which can be measured by a temperature sensor, which is not depicted. In this case, the additional reagent substance temperature sensor  23  can be omitted.  
         [0043]     It is assumed in the depicted example of embodiment, that the reagent substance is mixed with compressed air in the mixer  64  before being introduced into the exhaust duct  12 . The procedural approach according to the invention can, of course, also be employed in systems without the support of compressed air. In systems of this kind, the metering valve  30  can be mounted directly at the exhaust duct  12 , so that the metering valve  30  will be identical to the spray device  13 .