Abstract:
The invention suggests a procedure for the desulfurization of a storage catalyst, whereby the storage catalyst is run with a desulfurization temperature range that is required for the desulfurization, and whereby the storage catalyst is admitted with a regeneration gas with an air lambda of max. 1, as well as a device for the implementation of the procedure. During the desulfurization the storage catalyst is admitted in temporal shifts with a regeneration gas with an air lambda of max. even 1 during a desulfurization phase and a regeneration gas with an air lambda of higher than 1 during a desulfurization pause. Upstream before the storage catalyst an incoming lambda signal and downstream after the storage catalyst an outgoing lambda signal is acquired. By comparing the two signals that have been acquired during a desulfurization phase at least one favorable point of time for terminating the desulfurization process can be noticed. According to the invention it is possible to run a desulfurization of a storage catalyst with a least possible expenditure of energy and with a least possible thermal exposure with abating undesired side-products like hydrogen sulfide H2S.

Description:
TECHNICAL FIELD 
       [0001]    The invention is based on a procedure for the desulfurization of a storage catalyst and the device for the implementation of this procedure according to the category of independent claims. 
       BACKGROUND 
       [0002]    DE 197 39 848 A1 describes different operation procedures of a combustion engine, which has a NOx-storage catalyst arranged in its exhaust gas area. Due to the storage capacity of the NOx-storage catalyst a regeneration of the NOx-storage catalyst has to be provided now and then. The regeneration of the NOx-storage catalyst takes place due to the supply of hydrocarbon/carbon monoxide/hydrogen, which are provided interior powered. The provision of hydrocarbon/carbon monoxide is achieved by the rich operation of the combustion engine during the regeneration with an air level lambda smaller 1 or highest equal 1. 
         [0003]    Because of the sulfur content in fuel a sulfur contamination of the NOx-storage catalyst occurs, which lowers the storage capacity of NOx-compounds. 
         [0004]    DE 198 43 859 A1 describes a procedure for the desulfurization of NOx-storage catalyst. The sulfur contamination can be largely eliminated by impinging the NOx-storage catalyst at a high operating temperature of e.g. 600° C.-800° C. with hydrocarbon/carbon monoxide/hydrogen, which are provided for example interior power-operated by a rich operation of the combustion engine. 
         [0005]    DE 100 40 010 A1 describes a procedure for obtaining the end of the desulfurization from the progress of a lambda signal of a lambda sensor, which is arranged downstream after the NOx-storage catalyst. 
         [0006]    The required operating temperature of the storage catalyst for the implementation of the regeneration can be achieved by e.g. increasing the exhaust gas temperature or by e.g. directly heating the storage catalyst. The increasing of the exhaust gas temperature can be achieved for example by declining the effectiveness of the combustion engine. An advantageous possibility provides that combustive exhaust gas ingredients are brought in to the exhaust gas area of the combustion engine, which react exothermic on an available catalytic effective surface of the storage catalyst. 
         [0007]    The punctual detection of at least one advantageous point of time for the ending of the desulfurization process lowers the thermal exposure of the storage catalyst. The detection of an advantageous point of time for the ending of the desulfurization process furthermore reduces the demand for reagents and limits the environmental pollution. 
       SUMMARY 
       [0008]    According to the invention for the desulfurization of a storage catalyst, particularly a NOx-storage catalyst there is the advantage that the process of the desulfurization is not maintained needless long. Where necessary the end of the desulfurization process coincides with the complete regeneration from a sulfur contamination of the catalytic converter. The desulfurization process thereby requires the lowest amount of reagent, which can be attained for example from fuel. 
         [0009]    The storage catalyst is furthermore thermally encumbered as little as possible with a desulfurization temperature that is higher than the operating temperature. 
         [0010]    According to the invention furthermore the release of hydrogen sulfide is almost completely prevented. A lower encumbrance of the environment with undesired substances is moreover achieved. 
         [0011]    An essential advantage according to the invention is that the desulfurization of the storage catalyst can be monitored and influenced during the operation of the combustion engine by measurands instead of factors which are calculated by models. 
         [0012]    Advantageous improvements and configurations of the invented procedure arise from dependent claims. 
         [0013]    One configuration provides that at least one signal difference between the two measured signals is determined and that the most advantageous point of time for the ending of the desulfurization process is detected when the signal difference falls below a signal difference threshold. 
         [0014]    One improvement of this configuration provides the determination of at least one signal difference variation of at least one ascertained signal difference between the measured signals in a foreseen desulfurization phase and at least one ascertained signal difference between the measured signals in the following desulfurization phases, and the most advantageous point of time for ending the desulfurization progress, when the signal difference variation falls below a signal difference variation threshold. 
         [0015]    The detection of at least the most advantageous point of time for ending the desulfurization process on the basis of a comparison of an incoming lambda signal upstream before the storage catalyst with an outgoing lambda signal downstream after the storage catalyst, is possible with technical signal by using simple methods. Preferably an average value of at least two instead of one signal differences of a further signal evaluation is underlying. The averaging lowers the influence of noise and/or of interfering signals on the detection of the regeneration end. 
         [0016]    A further configuration provides that at least one surface variation between the ascertained surface of a previous desulfurization phase and a subsequent desulfurization phase is detected between the two measured signals and that the most advantageous point of time for ending the desulfurization process is ascertained, when the surface variation falls below a surface variation threshold. 
         [0017]    The detection of at least one advantageous point of time for terminating the desulfurization process based on the evaluation of the surface that is between both measured signals, provides a high accuracy, since the surface detection corresponds with an averaging. Preferably the whole surface that appears during the desulfurization phase between both measured signals is detected and taken as a basis for the evaluation. Using this method the best signal-noise-rate can be achieved. 
         [0018]    One configuration provides a delay time during which the desulfurization process is continued after a lower threshold deviation. The initiation of the delay time ensures that the desulfurization process of the storage catalyst is as complete as possible. 
         [0019]    According to the invention for the desulfurization of a storage catalyst an especially customized controller for the implementation of the procedure is provided. 
         [0020]    The controller contains preferably at least one electric storage, which stores the steps of the procedure as a computer operation. 
         [0021]    The invention concerns furthermore a program that shows all steps of the procedure, when it runs in a controller. 
         [0022]    The invention furthermore concerns a program product with a program code, which is saved in a machine-readable media, for the implementation of the procedure, when the program is performed in a controller. 
         [0023]    Further advantageous improvements and configurations of the invented procedure arise from further dependent claims and the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    It shows: 
           [0025]      FIG. 1 : technical surrounding, which contains the invented procedure and 
           [0026]      FIGS. 2 and 3 : signal progresses depending on the time. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 1  shows a combustion engine  10 , which has an air detection  12  in its intake area  11  and a storage catalyst  14  in its exhaust gas area. Upstream before the storage catalyst  14  there is a first lambda sensor  15  and downstream after the storage catalyst  14  there is a second lambda sensor  16 . 
         [0028]    The air detection  12  provides an air signal ms_L for the controller  20 . The combustion engine  10  provides an engine speed n. The first lambda sensor  15  provides an incoming lambda signal lam_vK_mess and the second lambda sensor  16  an outgoing lambda signal lam_mK_mess. The controller  20  provides a fuel signal m_K for the fuel awarding  21 . 
         [0029]    The controller  20  contains a fuel signal determination  22 , which is supplied with an air signal ms_L, the engine speed n, a torque set point Md_Soll as well as a desulfurization signal Reg_Sig and also a fuel signal m_K. 
         [0030]    The desulfurization signal Reg_Sig provides a desulfurization-regulation  30  subject to a desulfurization-demand Reg. The desulfurization signal Reg_Sig is furthermore made available for a signal difference-storage  40 , for a signal difference-comparator  41 , for an integrator  50 , for a surface-storage  51  as well as for a surface-comparator  52 . 
         [0031]    The incoming lambda signal lam_vK_mess and the outgoing lambda signal lam_nK_mess are made available for the difference ascertainment  60 , which is provided for the signal difference-storage  40  and the integrator  50 . 
         [0032]    The signal difference-storage  40  provides a first signal difference d_n and a second signal difference d_n−1 for the signal difference comparator  41 . The signal difference comparator  41  is furthermore supplied with a signal difference threshold D_Lim as well as with a signal difference variation threshold DD_Lim. The signal difference storage  41  provides a first desulfurization procedure-termination signal E 1  for the desulfurization-regulation  30 . 
         [0033]    The integrator  50  provides a surface signal a_lam for the surface-storage  51 . The surface storage  51  provides a first surface a_n and a second surface a_n−1 for the surface-comparator  52 . The surface-comparator  52  is furthermore supplied with a surface-threshold A_Lim as well as with a surface variation threshold AA_Lim. The surface-comparator  52  provides a second desulfurization procedure-termination signal E 2  for the desulfurization-regulation  30 . 
         [0034]      FIG. 2  shows signal progresses subject to the time t. The incoming lambda signal lam_vK-mess and the outgoing lambda signal lam_nK_mess, lying in the range of 0.89-1.04, are shown in the upper sub frame of  FIG. 2 . A dimension for the sulfur concentration % S, which is within the range of 0-500 ppm, is shown in the lower sub frame of  FIG. 2 . 
         [0035]    Within the cycle duration ti_p a desulfurization phase ti_Reg and a desulfurization pause ti_Pause occur in a temporal alternation. The desulfurization phase ti_Reg and a desulfurization pause ti_Pause occur in a temporal alternation during the desulfurization, whereby  FIG. 2  shows a period of 0-150 seconds. The upper sub frame lists signal difference d_lam and a surface  70 , which occur in between the two measured signals lam_vK_mess, lam_nK_mess. 
         [0036]      FIG. 3  shows signal progressions depending on the t which correspond with the signal progressions shown in  FIG. 2 , whereby the period is I a range of 450-600 seconds. 
         [0037]    According to the invention it is proceeded as follows: 
         [0038]    The combustion engine  10  can at least be operated in a fuel saving operation mode (lean operation), which can result in increased NOx-emissions. To eliminate these NOx-emissions the storage catalyst  14  is provided, which has a particular storage capacity, that is depending amongst others on the temperature of the storage catalyst  14 . The storage catalyst  14  is charged cyclically and is exempted from the stored NOx within the framework of the regeneration. 
         [0039]    The fuel saving operating mode is determined amongst others by the fuel signal m_K, which determines the point of time of at least one fuel injection and the amount of fuel that has to be measured per cycle segment of the combustion engine  10 . The determination of a fuel injection moment is synonymous with the determination of the fuel injection to at least one of a fixed wave position of the combustion engine  10 . 
         [0040]    The fuel signal m_K is determined by the fuel signal determination  22  depending at least on the air signal ms_L, on the speed engine signal n and on the torque set point Md_Soll as well as on the desulfurization signal Reg_Sig. 
         [0041]    During the operation of the storage catalyst  14  a sulfur contamination occurs, which advances subject to the sulfur concentration in the fuel and lubricant of the combustion engine. The sulfur contamination lowers the NOx-storage capacity of the storage catalyst  14 . To regenerate the NOx-storage capacity a desulfurization of the storage catalyst  14  is proper from time to time. 
         [0042]    The requirement of a desulfurization can be recognized by the mentioned sate of art according to the patent application DE 100 40 010. A required desulfurization is signalized by a desulfurization demand Reg. 
         [0043]    The sulfur contained in the fuel can be specifically stored in a sulfur trap (not demonstrated), which is arranged in the exhaust gas area  13  of a combustion engine  10  upstream before the storage catalyst  14 . The desulfurization of the sulfur trap is analog to the desulfurization of the storage catalyst  14 . The sulfur trap is therefore equated with the storage catalyst  14  corresponding to the present patent application. 
         [0044]    The desulfurization of the storage catalyst  14  takes places with a reagent substance, which contains for example carbon monoxide/hydrocarbon/hydrogen. Preferably the reagent substance is produce interior powered, as long as the exhaust gas of the combustion engine  10  can provide the required reagent substance by a suitable control of the combustion engine  10 . In the displayed implementation model it is assumed that the combustion engine  10  can provide the reagent substance by a rich operation, during which an air lambda of at most even 1 occurs in the exhaust gas of the combustion engine  10 . Alternatively or additionally the reagent substance can be introduced directly into the exhaust gas area  13  downstream of the combustion engine  10 . 
         [0045]    The rich operation of the combustion engine  10 , during which a exhaust gas lambda of at most even 1 occurs, is achieved by a lambda regulator (not demonstrated), which is supplied with the actual value of the incoming lambda signal lam_vK_mess provided by the first lambda sensor  15 . The first lambda sensor  15  is a broadband lambda sensor, which can provided a dimension for the air lambda at a rich as well as at a lean exhaust gas lambda. 
         [0046]    After the occurrence of the desulfurization demand Reg the desulfurization regulation  30  provides the desulfurization signal Reg_Sig, which causes the fuel signal ascertainment  22  to change the fuel signal m_K accordingly, in order to allow the desulfurization of the storage catalyst  14 . In a first not displayed step the operating temperature of the storage catalyst  14  is increased from the nominal operating temperature to a required desulfurization operating temperature, which is within the range of e.g. 600° C.-800° C. When the storage catalyst  14  reaches the desulfurization operating temperature, the storage catalyst  14  is impinged in a temporal variation with a regeneration gas and an oxygen containing gas, which can—as already mentioned—be provided interior powered. In the displayed implementation model it is assumed that the temporal variations between the desulfurization phase ti_Reg and the desulfurization pause ti_Pause occur during the desulfurization, which generally can last for a couple of minutes, with a cycle duration ti_P, which is for example 10 seconds. The desulfurization phase ti_Reg can last for example for 5 seconds and the desulfurization pause ti_Pause for 5 seconds as well. The indicated times can vary during the desulfurization. 
         [0047]    The guideline for the desulfurization phase ti_Reg and the desulfurization pause ti_Pause during the desulfurization prevents the development of hydrogen sulfide H2S. During the desulfurization pauses ti_Pause the storage catalyst  14  is impinge with oxygen containing exhaust gas in order to fill up the oxygen storage of the storage catalyst. The exhaust gas lambda is determined to be for example 1.1-1.4 during the desulfurization pauses ti_Pause. The exhaust gas lambda upstream before the storage catalyst  14  is at about 0.94 during the desulfurization phases ti_Reg. 
         [0048]    Downstream after the storage catalyst  14  a second lambda sensor  16 , which is a broadband lambda sensor as well, detects the outgoing lambda signal lam_nK_mess, this progress being each shown in the upper sub frame of  FIGS. 2 and 3 . 
         [0049]    It has been determined experimentally that a favorable point of time for terminating the desulfurization process of the storage catalyst  14  can be determined with only one comparison of both signals lam_vK_mess, lam_nK mess by a proper lambda sensor  15 ,  16 , which provides at least one dimension for each of the actually occurring exhaust gas lambdas. Proper lambda sensors are broadband lambda sensors, which are described for example in the specialist book “Ottomotor-Management/Bosch”, published by Vieweg, 1. edition, 1998, page 22-23. 
         [0050]    As long as the oxygen storage of the storage catalyst  14  is at least partly deactivated during the desulfurization process, the desulfurization process can be terminated according to the invention, since a further performance of the regeneration would not result in a further desulfurization. 
         [0051]    According to a first implementation model at least one difference between both signals lam_vK-mess, lam_nK_mess during the desulfurization phase ti_Reg acquired by the difference determination  60  and provided as a signal difference d_lam to the signal difference storage  40 . As a matter of principle the comparison of one signal difference d_lam with the signal difference threshold D_Lim is sufficient. In this case the first signal difference d_n equals the second signal difference d_lam. But preferably more signal differences d_lam are averaged before a comparison with the signal difference threshold lam_vK_mess, in order to minimize the influence on the result of interfering impulses on the one hand, and signal fluctuations of the signals lam_vK_mess, lam_nK_mess on the other hand. 
         [0052]    The at least one signal difference d_lam is acquired by the scanning level of the two signals lam_vK_mess, lam_nK_mess, whereas the scanning cycle duration is significantly shorter than the cycle duration ti_P. A special advantage is to acquire the signal difference d_lam at the end of the desulfurization phase ti_Reg since both signals lam_vK_mess, lam_nK_mess, especially the outgoing lambda signal lam_nK_mess, demonstrate stabilized levels at this point of time. 
         [0053]    According to the self-improvement it is intended that signal differences d_lam are acquired in different desulfurization phases ti_Reg and evaluated with regard to a variation. The at least one signal difference d_lam, that has been acquired in different desulfurization phases ti_Reg, is deposed in the signal difference storage  40 , which provides the first and second signal difference d_n, d_n−1 simultaneously, whereby the first signal difference d_n has been acquired in a different desulfurization phase ti_Reg than the second signal difference d_n−1. Preferably an averaging of signal differences d_lam is intended before the comparison as well, which were acquired during one desulfurization phase ti_Reg. The signal difference comparator  41  provides a difference between the first and second signal difference d_n, d_n−1, the acquired difference, which corresponds with a variation of differences, with a signal difference variation threshold DD_Lim. 
         [0054]    As long as the signal difference comparator  41  either detects a threshold lower deviation of the signal difference threshold D_Lim and/or of the signal difference variation threshold DD_Lim, the signal difference comparator  41  provides the first desulfurization process termination signal E 1 , which is induced the desulfurization regulation  30  to take the desulfurization signal Reg_Sig back in order to terminate the desulfurization process of the storage catalyst  14  this way. 
         [0055]    The first desulfurization process termination signal E 1  is preferably effective after a specified time delay. 
         [0056]    According to a very advantageous configuration, which can be intended alternatively or additionally for the first configuration, the comparison of both signals lam_vK_mess, lam_nK_mess is based on an evaluation of the surface  70  that is stretched between the two signals lam_vK_mess, lam_nK_mess. 
         [0057]    According to a simple configuration it can be intended that at least one part of the surface  70  is determined during a desulfurization phase ti_Reg between the two signals lam_vK_mess, lam_nK_mess. But preferably the whole surface  70  a desulfurization phase ti_Reg between the two signals lam_vK_mess, lam_nK_mess is used as a basis for the evaluation during. 
         [0058]    For this purpose the difference-determination  60  is for example added to the integrator  50  in form of individual scanning levels of the provided signal differences d_lam. During a part or the entire desulfurization phase ti_Reg the integrator undertakes an integration of the signal differences d_lam, which corresponds to a surface determination. The resulting surface signal a_lam is supplied to the surface signal storage  51 . 
         [0059]    According to a simple configuration it is intended that the surface signal a_lam is directly compared to the surface threshold A_Lim in the surface comparator  52 . According to another configuration it is intended that a possibly occurring variation of surfaces  70  is evaluated between the desulfurization phases ti_Reg. Therefore the surface storage  51  stores at least two acquired surface signals a_lam, that have been obtained in at least two different desulfurization phases ti_Reg, for example two directly sequenced desulfurization phases ti_Reg. These surface signals a_lam are supplied as surface signal a_n, a_n−1 to the surface comparator  52 , which determines the difference between the first and the second surface signal a_n, a_n−1 and which compares the corresponding difference of a variation of the surface to the surface variation threshold AA_Lim. 
         [0060]    As long as the surface comparator  52  detects a lower deviation of the surface threshold A_Lim and/or of the surface variation threshold AA_Lim, the surface comparator  52  provides the second desulfurization process termination signal E 2 , which induces the desulfurization regulation  30  to take the desulfurization signal Reg_Sig back in order to terminate the desulfurization process of the storage catalyst  14 . 
         [0061]    Preferably the second desulfurization process termination signal E 2  becomes effective after a specified time delay. 
         [0062]    In the lower sub frame of  FIG. 2  there is a dimension for the sulfide concentration % S in ppm listed, which can be determined downstream after the storage catalyst  14  during the desulfurization. The peak values of the dimension of the sulfide concentration % S occurs each time-delayed in relation to the beginning of the desulfurization phases ti_Reg. After an initial increase of the peak value of the dimension of the sulfide concentration S % up to the 50 th  second for example, there is a continuing decrease, until after a few minutes a dimension for the sulfide concentration % S is reached, which does not have to be fallen below for a successful desulfurization. 
         [0063]    In  FIG. 3  a situation is shown, which might occur for example between the 450 th -600 th  second. In the upper sub frame of  FIG. 3  is can be noticed that both signals lam_vK_mess, lam_nK_mess almost concur. An expansion of the desulfurization process until this time range would therefore—if at all—only cause a marginal improvement of the desulfurization result. In the displayed implementation model the perfect point of time would be therefore between the 150 th -450 th  second, e.g. at 300 seconds. The perfect point of time to detect the favorable point of time for the termination of the desulfurization process, at which the first and second desulfurization process termination signals E 1 , E 2  occur, can be acquired by a suitable determination of the at least one threshold D_Lim, DD_Lim, A_Lim, AA_Lim. Expediently it is proceeded experimentally.