Abstract:
A method is described for operating an internal combustion engine in motor vehicles, in which air is supplied to a combustion chamber via a throttle valve and an air supply channel, and in which exhaust gas is conducted through a particulate filter and is returned at least intermittently and at least partially through an exhaust gas recirculation valve into the air supply channel, and in which an oxygen proportion in the exhaust gas is detected using at least one lambda probe. In this context, in an overrun operation, the throttle valve is controlled to close and the exhaust gas recirculation valve is controlled to open, a variable characterizing the oxygen concentration in the exhaust gas is compared to a boundary value, and as a function of the result of the comparison, it is concluded that there is a leakage in the air supply channel.

Description:
RELATED APPLICATION INFORMATION 
       [0001]    The present application claims priority to and the benefit of German patent application no. 10 2009 001 626.0, which was filed in Germany on Mar. 18, 2009, and German patent application no. 10 2009 027 519.3, which was filed in Germany on Jul. 8, 2009, the disclosures of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method, as well as a computer program, an electrical storage medium and a control and/or a regulating device for a system for exhaust gas aftertreatment in motor vehicles. 
       BACKGROUND INFORMATION 
       [0003]    An internal combustion engine is understood to be known in the market, that is equipped with a particulate filter, and in which the soot burn-off is controlled or checked, in order to protect the particulate filter. Such a system, with the corresponding method, is discussed in DE 10 2007 010 189 A1, in order to regulate the temperature of the exhaust gas during a regeneration process of a particulate filter. 
         [0004]    In the regeneration operation of a particulate filter, a high oxygen supply in the overrun phase of the internal combustion engine would, for instance, lead to a locally reinforced soot burn-off. At lower engine speeds, the exhaust gas mass flow is too low for a sufficient heat dissipation, which may lead to thermally conditioned damage to the particulate filter. For this reason, by closing the throttle valve and opening the exhaust gas recirculation valve, exhaust gas may be pumped in circulating fashion, in order to make no, or little oxygen available to the particulate filter. In the case of a leakiness of the air system or its components, such as an untight throttle valve, this measure no longer acts within the desired scope, and the temperature stress of the particulate filter could become greater than desired. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an object of the exemplary embodiments and/or exemplary methods of the present invention to increase the service life of the exhaust gas system. 
         [0006]    This object may be attained by a method, as well as a computer program, an electrical storage medium and a control or/a regulating device for a system for exhaust gas aftertreatment in motor vehicles. Advantageous further developments are indicated in the dependent claims. Important features for the exemplary embodiments and/or exemplary methods of the present invention are also found in the following description and in the drawings, the features being able to be essential for the exemplary embodiments and/or exemplary methods of the present invention both alone and also in different combinations, without further explicit reference being made to it. 
         [0007]    The exemplary embodiments and/or exemplary methods of the present invention have the advantage that leakage in the air supply channel is able to be detected. Consequently, appropriate measures may be taken in order to prevent an undesirably high temperature in the Diesel particulate filter in the regeneration operation, which is of advantage to the service life of the Diesel particulate filter. It is understood, in this context, however, that leakage in the air supply channel may have quite different causes: a wall of the air supply channel may have a hole in it, for example, a connection may have become loose or there may be a leakage place in the region of the throttle valve (throttle valve does not quite close). The measure according to the exemplary embodiments and/or exemplary methods of the present invention may be implemented without additional built-in components, in this context, so that hardly any additional costs are created. 
         [0008]    Starting from a diagnosis of leakiness of the air supply channel, reactions are able to take place. For instance, the regeneration of the particulate filter may be limited, interrupted or broken off, or a late post-injection may be released into the oxidation catalyst of the exhaust gas aftertreatment system during an overrun phase of the internal combustion engine. 
         [0009]    The stress on a control unit is reduced if the comparison of a variable, characterizing the oxygen concentration in the exhaust gas, to the boundary value is only carried out if the current rotational speed of the internal combustion engine (engine speed) is below a boundary value. A leakage would be harmful only in this operating range. 
         [0010]    It is also favorable if the comparison of a variable, characterizing the oxygen concentration in the exhaust gas, to a boundary value is only carried out if no faults at the throttle valve and the exhaust gas recirculation valve have been diagnosed. In the case of such defects, a substitute reaction will usually already have been provided. 
         [0011]    The diagnosis of a leakiness in the air system is particularly certain if the comparison of a variable, characterizing the oxygen concentration in the exhaust gas, to a boundary value is only carried out if a rotational speed gradient of an engine speed lies below a boundary value for a certain minimum time period. Using this presupposition, operating conditions are excluded which could lead to fluctuations in the variable and could falsify the diagnosis of leakiness. In connection with a motor vehicle, this would include, for instance, shifting gears. 
         [0012]    One meaningful design occurs when the comparison of a variable, characterizing the oxygen concentration in the exhaust gas, to a boundary value is only carried out if there exists an overrun operation of the internal combustion engine for a certain minimum time period. With that, sufficient stable conditions set in for the variables used for the diagnosis of leakiness. 
         [0013]    In addition, it is proposed that, under certain conditions in an overrun operation, fuel be injected for holding down the lambda value, and the fact that there is a leakage in the air supply channel should only be concluded if the certain conditions are present, and that, in spite of the fuel injection, the lambda value reaches and/or exceeds a boundary value, or if these certain conditions are not present. With that, the detection of leakage in the air supply channel compared to the possible holding down of the lambda value is assigned a lower priority, so that the measures, provided under the certain circumstances, may first of all be carried out. This is based on the following consideration: 
         [0014]    In order to prevent damage in a Diesel particulate filter in the overrun operation, based on too high an oxygen concentration in the exhaust gas, it may be provided that a small post-injection be performed in order to keep the lambda value low. The time of such a post-injection may occur in such a way that the post-injected fuel quantity is combusted. This reduces the oxygen in the exhaust gas. Such a post-injection is, however, carried out only if particularly certain conditions are present in the overrun operation. This includes, for instance, that the lambda value before the Diesel particulate filter is above a certain boundary value, and also perhaps that this has been true for a certain minimum time. Now, according to the exemplary embodiments and/or exemplary methods of the present invention, it is proposed that one should only conclude that there is a leakage in the air supply channel if (a) the lambda value is higher than desired in spite of fuel injection, or (b) if the certain conditions, under which the fuel injection for holding down the lambda value is taking place at all, are just not present, this function is also not activated. However, if this function of the injection of fuel for the purpose of holding down the lambda value is active, that is, if the certain conditions are satisfied, this injection has priority, and leakage in the air supply channel is only regarded as a given for the abovementioned case (a). 
         [0015]    This ensures that measures for the protection of the Diesel particulate filter have precedence, and that, by such measures, the detection of leakage in the air supply channel is not disturbed. 
         [0016]    After it has been concluded that there is a leakage (above a minimum value), it is advantageous if the carrying out of a regeneration operation is blocked. Otherwise, as a result of a greater leakage, in spite of closing the throttle valve and opening the exhaust gas recirculation valve at low mass flows, the oxygen supply in the particulate filter could become too high and could lead to damage. 
         [0017]    One useful embodiment of the method provides that, when has been concluded that there is leakage, an entry is made in a fault memory, and this may be done after the expiration of a defect detection time. Results are thereby able to be stored durably in a control and/or regulating device of the motor vehicle, and are also ready for a later diagnosis. Such a fault memory is executed as an EEPROM, for example. 
         [0018]    An exemplary embodiment of the present invention is explained below, with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows a schematic representation of an internal combustion engine in a motor vehicle. 
           [0020]      FIG. 2  shows a flow chart of a method for operating the internal combustion engine of  FIG. 1 . 
           [0021]      FIG. 3  shows three diagrams for a lambda probe signal, a temperature curve in a particulate filter and an air mass signal. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows a schematic representation of an internal combustion engine  10  in the form of a Diesel engine having a cylinder block  12 , a fuel metering system  11 , an air supply channel  20 , in which an air supply flow  21  is guided, and an exhaust gas channel  30  in which an exhaust gas flow  32  of internal combustion engine  10  is guided. In air supply channel  20  there is a throttle valve  24 . An exhaust gas recirculation  25  connects air supply channel  20 , at least intermittently, to exhaust gas channel  30  via an exhaust gas recirculation valve  26 . After cylinder block  12 , in the flow direction of exhaust gas flow  32 , as components of an exhaust gas aftertreatment system  40  that is associated with internal combustion engine  10 , the following are shown: a first lambda probe  43 , a fuel supply  45  (optional), an oxidation catalytic converter  41  in the form of a Diesel oxidation catalytic converter, a second lambda probe  44  and a Diesel particulate filter  42 . The exhaust gas system of a Diesel engine could also be equipped with only one lambda probe, which would be fully sufficient for the function described. This one lambda probe might then be situated either at position  43  or  44 . A control and/or regulating device  100  is also shown schematically, which is used to control various processes of internal combustion engine  10  and system  40  for the exhaust gas aftertreatment, and in which are also located means for the diagnosis of leakage of an air system formed among other things by air supply channel  20  and throttle valve  24 , which we shall discuss below. 
         [0023]    Exhaust gas recirculation valve  26  is used to mix a part of the exhaust gas flow  32 , in the part throttle range of internal combustion engine  10 , with the aspirated fresh air flow  21 , in a controlled manner. This lowers the combustion temperature of internal combustion engine  10 , and reduces the formation of nitrogen oxides (NO x ). Undesired compounds contained in the exhaust gas are reduced or removed, using catalytic processes, in oxidation catalytic converter  41 . For example, carbon monoxide (CO) and uncombusted hydrocarbons react with nitrogen oxides (NO x ) and oxygen (O 2 ) to form carbon dioxide (CO 2 ) and nitrogen (N 2 ). In Diesel engines, particulate filter  42  is used for reducing the particles present in the exhaust gas, in order to satisfy legal conditions. 
         [0024]    The particles filtered out of the exhaust gas in particulate filter  42  collect in particulate filter  42  over time. In order to prevent particulate filter  42  from becoming clogged or the exhaust gas counterpressure from reaching an inadmissibly high value, particulate filter  42  is regenerated from time to time. In order to do this, the collected soot particles are combusted in an exothermic reaction. This is brought on, for example, by a brief increase in the exhaust gas temperature. In this context, care should be taken that the temperature of particulate filter  42  does not exceed a critical value, since otherwise its structure could become damaged. A higher temperature of particulate filter  42  or an increased exothermic reaction occurs, for instance, when there is an increase in the oxygen proportion contained in the exhaust gas. In the overrun operation at low mass flows, throttle valve  24  is closed and exhaust gas recirculation valve  26  is opened, in order to stop the oxygen supply in particulate filter  42 . An undesired increase in the oxygen proportion then comes about, for example, as a result of a leakage in the air system, by which fresh air is aspirated even when throttle valve  24  is closed. The method described below is used to diagnose such a leakage. In certain cases there is the possibility that the diagnosis will also detect leakiness within the scope of exhaust gas recirculation  25 , of exhaust gas recirculation valve  26  or of exhaust gas channel  30 . 
         [0025]      FIG. 2  shows a flow chart of a method, for instance, for processing by a computer program stored on control and regulating device  100  for diagnosing a leakiness in the air system of internal combustion engine  10  described in  FIG. 1 . A start block  102  is shown first and a block  104  for querying whether a regeneration operation is currently in progress. In block  106  a query is made as to whether a fault (for instance mechanical jamming or an electrical short circuit) of throttle valve  24  has been detected. Other diagnostic methods are used for this, on which we shall not go into further detail at this point. 
         [0026]    In block  108  it is queried whether a fault in the exhaust gas recirculation valve  26  for exhaust gas recirculation  25  has been detected. This, too, is ascertained using a separate diagnostic method, which will not be explained in detail here. A block  110  is used to query whether exhaust gas recirculation valve  26  is in an open state for exhaust gas recirculation  25 . In  112  it is queried whether a control command of control and/or regulating device  100  for closing throttle valve  24  is present, and in  114  it is queried whether internal combustion engine  10  has been in overrun operation at least since a specified time interval. 
         [0027]    In block  116  it is checked whether the current speed of internal combustion engine  10  is below a specified threshold value, while it is possible, in an exemplary embodiment that is not shown, that an engine speed is involved that is averaged over a specified time interval. Furthermore, a block  118  is used to query whether a change in a rotational speed (rotational speed gradient) of internal combustion engine  10  since a specified time interval is below a specified threshold. The last two tests ensure that the internal combustion engine is in an at least approximately stationary operating state (no gear change) at a relatively low engine speed. 
         [0028]    Now, in block  120  the actual diagnosis of the tightness of the air system takes place. There the query is whether the measured value given by lambda probes  43 ,  44  has been above a specified threshold since a specified minimum time interval. In a monitoring  126 , it is checked whether a countermeasure for an injection of fuel in the overrun operation of the internal combustion engine is active in a process that is taking place outside of  FIG. 2 , and is not explained in greater detail here. However, provided this countermeasure is indeed active, but shorter than a specified time span T 1  (defect detection time), an output signal via monitoring  126  is set to “FALSE”. In all other cases, monitoring  126  accepts output signal “TRUE”, and thus releases block  130 . Blocks  104  to  120  and  126  pass their logical information to a block  130 , where they are linked to a logical AND. If block  130  supplies the value “TRUE”, which is the case if all tests in  104  to  120  and  126  simultaneously supply the value TRUE, then, after a filtering in a block  131 , in a block  122  an alarm is triggered on the dashboard of the motor vehicle that incorporates internal combustion engine  10  (both not shown). This indicates a faulty function to the driver at once. In addition, in a block  124  specific reactions are triggered, for instance a regeneration operation is blocked. Moreover, in a block  134  an entry may be made in a fault memory. After blocks  122 ,  124  and  134  the method ends in block  132 . The method may also be carried out repeatedly, so that one may detect changes in operating behavior at once. Block  131  permits filtering and/or delaying, as required, the output signal of AND operation  130 . 
         [0029]    Monitoring  126  takes into account that, when certain conditions apply, a possible countermeasure may be activated which, outside of the method described, injects a certain quantity of fuel into the internal combustion engine, for holding down the lambda value and for protecting particulate filter  42 . In this case, at least one defect detection time T 1  is awaited to see whether the countermeasure demonstrates sufficient action, as a result of which one or more of the output signals of blocks  104  to  120  could assume a state of “FALSE” again. Thereupon AND operation  130  would also change from a “TRUE” state back to a “FALSE” state that is defined as fault-free. In this way, monitoring  126  prevents overly hasty reactions in blocks  122 ,  124  and  134 . In an in-common application of said countermeasure, using the method shown in  FIG. 2 , it is advisable to limit the fuel injection, brought about by the countermeasure, in such a way that no noticeable torque is generated. 
         [0030]    The main item shown in the partial procedure shown in  FIG. 2  is queries  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118 ,  120  and  126  of various operating values and parameters of the internal combustion engine shown in  FIG. 1 , as well as their logical linkage in block  130 , implemented presently as a Boolean AND operation. This linkage may either be performed in parallel by a digital logic circuit or, alternatively, by sequential processing in a computer programs. If all the input variables become valid, the output variable of the AND operation will also be valid, and thus leakiness of the air system is detected. It is clear that the logical linkages described, dependent on implementation, may also be described or produced using different logical states, for instance, using De Morgan&#39;s test. The logical linkages may also be structured differently. For instance, the filtering implemented in block  131  may also take place individually for each branch of blocks  104  to  120  and  126  before AND operation  130 , or the functioning of monitoring  126  may be implemented after AND operation  130 . 
         [0031]    In one embodiment, not shown, of the flow chart described in  FIG. 2 , the functioning of monitoring  126  is restricted to a temporary blocking of the fault memory in block  134 . In this context, the function of blocks  122  and/or  124  may be kept up independently of monitoring  126 . 
         [0032]      FIG. 3  shows various diagrams for explaining the physical connections of the abovementioned method: 
         [0033]    Diagram (a) shows the curve over time of a signal of lambda probe  44 , by which the oxygen concentration KO 2  contained in the exhaust gas is expressed, for four degrees of leakage, in air supply channel  20 . The corresponding curves are marked  52  (no leakage) to  58  (considerable leakage). It may be seen that, at a time t 1 , throttle valve  24  receives a control signal by which it is to be controlled to take up the completely closed position. If there is any leakage (curve  52 ) the lambda probe signal is comparatively low. If there is even only slight leakage (curve  54 ), a clearly increased lambda probe signal comes about. 
         [0034]    Diagram (b) shows the corresponding curve over time of temperature T 42  in Diesel particulate filter  42  for the four degrees of leakage, mentioned above, in air supply channel  20  as of time t 1 . The corresponding curves are characterized by  62  (no leakage) to  68  (considerable leakage). It will be seen that the temperature in the operating case shown (low engine speed, exhaust gas recirculation valve  26  open, exothermic regeneration reaction) at no leakage present (curve  62 ) is comparatively low, whereas it is increased even at low leakage (curve  64 ). 
         [0035]    Diagram (c) shows the curve over time of signals of an HFM sensor, that is not shown in  FIG. 1 , but that is situated in air supply channel  20 , again, corresponding to the four grades of leakage specified above. It will be seen that curve  72  (no leakage) and curve  74  (slight leakage) are almost coincident. 
         [0036]    It will be seen in  FIG. 3  that leakiness of an air system cannot be detected with sufficient accuracy by the evaluation of the signal of an HFM sensor (diagram (c)) in a control and regulating device  100 . Although curves  72  and  74  in diagram (c) lie close together, the reactions in particulate filter  42  (curves  62  and  64 ) are very different. Immediately after activating throttle valve  24  into the closed position, an inadmissible leakiness is able to be detected via lambda probe signal  52 ,  54 ,  56 ,  58 . It will be seen in  FIG. 3  ( a ) how lambda probe signals  54 ,  56 ,  58  differ from lambda probe signal  52 , which sets in in response to a closed throttle valve  24 . From this one may also derive the threshold values and time constants, by which this distinguishing is to be carried out.