FR2849896A1 - Internal combustion engine exploiting process for use in automobile vehicle, involves exploiting engine based on values of function of preset division of local temperature, and determining conversion of polluting agent - Google Patents

Abstract

The process involves arranging a temperature model of a catalyst (6, 7) with a function of preset division of local temperature (T1(t), T2(t), T3(t)) in a volume of the catalyst. An internal combustion engine is exploited based on values of the function of preset division of the local temperature. Conversion of a polluting agent is determined to find an exhaust gas mass flow and/ or polluting agents composition. The conversion of the polluting agent is determined based on the function of predefined dynamic division of the local temperature. The function of division/repartition is determined by a calculation model that has multiple zones for a number of partial zones of the volume of the catalyst. An Independent claim is also included for an internal combustion engine exploiting device.

Description

The present invention relates to a method and a

  apparatus for operating an internal combustion engine, comprising an exhaust system with at least one catalyst mounted downstream of the internal combustion engine and with a motor control apparatus for influencing the operating parameters of the engine internal combustion.

  In motor vehicles equipped with modern combustion engines, which have lower fuel consumption in lean and stratified charge modes, further reprocessing of exhaust gases for the reduction of nitrous oxide emissions is necessary to meet the legal requirements for exhaust gas. To solve this problem, NOx accumulator catalysts are preferably used. Spark-ignition-type engines equipped with NOx accumulator catalysts in the present case impose particularly high demands on an engine control 20 to achieve optimum results with regard to exhaust gas emissions and fuel consumption. fuel consumption under the most possible operating conditions. Thus, an NOx storage catalyst with poor exhaust gas obtains sufficiently high nitrogen oxide conversion rates only in a relatively narrow temperature range. This is why the catalyst must be maintained in a wide operating range in this temperature range, in order to allow a lean regime improving the yield if possible without restrictions. If the exhaust gas temperatures increase, for example, with increasing vehicle speeds or higher loads of the internal combustion engine, the lean regime should be abandoned when the catalyst temperature exceeds the upper temperature limit. On the other hand, the lean diet must be allowed again as early as possible when the catalyst temperature falls back to the permissible temperature range.

  In lean conditions, significantly lower exhaust gas temperatures are established compared to a homogeneous internal combustion engine speed for X = 1, which can result particularly in the phases of the low load regime. that the catalyst temperature falls below the permissible temperature range, for which reason also the lean diet must be abandoned again. At the same time, low temperatures also result in poorer conversion of other pollutant components, particularly HC hydrocarbon compounds. A switching 15 for example in the stoichiometric regime results in the one hand that the temperatures of the exhaust gas increase and the space velocity of the catalysts decreases, resulting in a better conversion of pollutants, and secondly the consumption fuel increases. In order to find a favorable compromise between the variations of the polluting emissions and the consumption, it is necessary to carry out a precise coordination between the speed of the internal combustion engine and the catalysts which work in the range of temperatures known as Light25 Off ".

  In addition, the current NOx catalysts have significantly lower high temperature stability over the three-way catalysts. In addition to a protective design with regard to the temperatures of the exhaust gas installation, it is often necessary to have a strategy for the thermal protection of the components, in order not to exploit the catalyst system, even with very dynamic operating conditions, above the limit of thermal load capacity, which could lead to significant unacceptable aging.

  A precise knowledge of the catalyst temperature is therefore advantageous. For this purpose, US Pat. No. 5,747,049 A proposes a temperature model for a NOx storage catalyst, for which the temperature is determined on the inlet side and the outlet side of the accumulator catalyst, and the motor control is influenced accordingly. Similarly, EP Publication 1 067 279 A2 discloses a temperature model for monitoring and maintaining the operational availability of a NOx storage catalyst.

  DE 198 36 955 A1 discloses a temperature model for a NOx storage catalyst, with which the temperature is calculated separately for two partial ranges and the motor control is influenced accordingly. The NOx storage catalyst therefore comprises two partial catalysts. A poor diet is initiated only in cases where the two partial catalysts are within a permitted temperature range.

  However, effects that occur in the dynamic regime due to an inhomogeneous temperature distribution in the catalyst are difficult to record with known methods. With internal combustion engines that can operate in a lean regime, a wide margin of safety with respect to critical temperatures, for example a thermal desorption threshold, is therefore respected in order to avoid NOx breakpoints. Accordingly, the internal combustion engine must therefore operate for higher time fractions than necessary in a disadvantageous consumption regime.

  DE 100 36 942 A1 discloses a function of distributing the temperature of a catalyst volume by means of a multi-zone calculation model. The catalyst is divided here into partial zones along the flow of the exhaust gas and a location-dependent temperature distribution in the catalyst is determined. A similar temperature model is known for example from DE 100 38 461 Ai.

  The object of the present invention is therefore the creation of a method which makes it possible to operate an internal combustion machine advantageously from the point of view of consumption and with a low emission of pollutants and a device for the application of the method.

  According to the invention, a catalyst temperature model is provided with a predefined dynamic distribution function of the local temperature in the catalyst volume and the internal combustion engine operates according to the values of this distribution function. In this way, an improved control of the local thermal load of the catalyst is allowed and the optimization of the consumption and emissions of the internal combustion engine is improved.

  According to a preferred embodiment of the invention, the distribution function is determined by means of a multi-zone calculation model for a plurality of partial areas of the catalyst volume. An operating state of the internal combustion engine, which results in an increase of the exhaust gas temperature, may be initiated when a number of predefined partial areas remain below a permitted temperature level and above a lower critical temperature. When the operating state of the internal combustion engine results in a reduction of the exhaust gas temperature, it can be activated when a predefined number of partial areas exceeds a permitted temperature level below a critical temperature. higher. Instead of a number of partial areas, a predefined sum of the volume of the partial areas can also be used as a criterion.

  In advantageous designs, a correction factor relating to the aging of a catalyst and / or a quantity of stored pollutants and / or a conversion to be discounted as a function of a local and current temperature can be taken into account. The advantage of the invention lies in the fact that operating parameters of the internal combustion engine 10 are optimized with regard to a conversion of the pollutants of the catalyst, a authorized mode of operation and thermal protection of the components. For example, it is possible for the internal combustion engine to be able to operate at a low speed already when only a portion of the catalyst is within the permitted temperature range. This means that a favorable low-consumption diet may already be activated at an early stage.

  It is also possible to finish earlier measurements for the heating of the catalyst, for example after a cold start or after a longer phase of slow idling or low load, or apply these measurements with a lower intensity, allowing save fuel and charge the catalyst less thermally.

  Measurements for the thermal protection of components against unacceptable high temperatures can be made dependent on the temperature distribution function in the catalyst volume. In the case where protection measures for the components have to be implemented, this allows a reduction of the safety supplements, with which it must be prevented from exceeding a higher critical temperature and thus, for example, enrichment of the mixture. late and / or weaker. Due to the improved operating mode of the internal combustion engine and the thus improved exhaust behavior, it is possible to reduce the noble metal content of a catalyst compared with known systems if the limit values of predefined programs.

  In the accompanying drawings: FIG. 1 shows an internal combustion engine with an associated exhaust system, FIG. 2 shows the curve as a function of time of an exhaust gas temperature, a distribution of the catalyst temperature. in different areas of a catalyst volume, as well as the associated speed of the vehicle.

  FIG. 1 shows an internal combustion engine 1, for example a positive-ignition engine capable of operating in a lean state or an internal combustion diesel engine with an exhaust system 2 and an engine control unit 3, preferably for the operation of a motor vehicle. The internal combustion engine 1 has a number of cylinders 4 (the corresponding components are identified only by a single reference), downstream of which is disposed an exhaust path of exhaust gas 5. In the installation of Exhaust 2 is arranged an exhaust gas purification device with an optional precatalyst 6 and a main catalyst 7 for the conversion of the harmful or undesirable components of the exhaust gases into other components. The precatalyst 6 is preferably designed as a three-way catalyst and the main catalyst 7 as a NOx storage catalyst. Downstream of the cylinders 4, optional exhaust gas sensors or NOx sensors are arranged in the exhaust paths 5 with which the NOx concentration of the exhaust gas guided through the exhaust system is respectively controlled. 2 of the internal combustion engine 1 can be measured. Before the precatalyst 6 is disposed another exhaust gas sensor 8 'optional. In an area of the exhaust system 2 between the precatalyst 6 and the main catalyst 7, upstream of the precatalyst 6 and downstream of the main catalyst 7, there is disposed another exhaust gas sensor 9. Another sensor 10 is disposed downstream of the main catalyst 7 in the exhaust system 2. It goes without saying that, with a structured exhaust gas cleaning device with several parts, sensors can be arranged upstream and downstream of the exhaust system 2. downstream of the respective parties.

  In addition to the aforementioned sensors, there is provided downstream and upstream of the precatalyst 6 and upstream of the main catalyst 7 lambda probes 11 and 12, as well as temperature sensors 13, 13 'to determine the operating temperature of the devices. catalysts. It is also understood that, in addition or in addition, other temperature sensors may be provided for measuring the exhaust gas temperature or the operating temperature of the exhaust gas cleaning device or parts thereof. -this. In particular, it is possible to provide temperature sensors for detecting a temperature distribution in the volume of the main catalyst 7 and / or of the precatalyst 6. For the recirculation of the exhaust gas, the internal combustion engine 1 has an internal combustion system. exhaust gas recirculation 15 with a controllable valve.

  The engine control unit 3 records in known manner by means of other sensors, not shown, operating parameters of the internal combustion engine 30 1, such as, for example, the position of the throttle valve, the recirculation rate of the throttle exhaust, the ignition point, the injection timing of the pre-injections, the main injections and subsequent injections, the injection pressure, the position of the tumble valve, the inlet pressure, the phase actuator of the the camshaft, the speed, the position of the accelerator pedal, the load, the running speed and the like, and may possibly influence these parameters by means of actuators (not shown), a cable system 14 or the like being provided for communication between the motor control apparatus 3 and the sensors or actuators. The engine control apparatus 3 also includes a lambda sensor setting apparatus 3a for adjusting the oxygen concentration in the exhaust gas or the lambda value. The engine control apparatus 3 receives from the exhaust gas sensors signals with which the concentration of certain exhaust gas components, such as, for example, the NOx gross emission concentration of the internal combustion engine 1 and the NOx concentration upstream of catalyst units 6 and / or 7 can be calculated.

  The NOx accumulator catalyst 7 usually operates in an accumulation cycle, which comprises at least one usually fairly long absorption mode and a fairly short regeneration mode. The storage takes place here with a lambda value> 1, and the destocking at a later time with a lambda value <1 or = 1.

  Since NOx storage catalysts have much lower stability at high temperatures than three-way catalysts and high temperatures associated with high oxygen concentrations result in high acceleration of aging, temperature stress must be avoided. In the same way, efforts should be made to maintain the temperature of the catalyst within a permissible temperature range above a critical temperature below and below a temperature T 0. superior criticism, in order to allow sufficient conversion rates for nitrogen oxides.

  The invention is described below with reference to the main catalyst 7, in particular to a NOx storage catalyst. However, it can be advantageously applied also to other types of catalyst as well as to catalyst systems which comprise several catalysts.

  According to the invention there is provided a temperature model of the catalyst with a predefined thermal distribution function of the local temperature in the catalyst volume and the internal combustion engine operates according to the values of this distribution function. The temperature model is preferably implemented in the motor control apparatus 3.

  The invention is based on the following considerations. In actual rolling mode, the catalysts are rarely stressed for extended periods of time with a constant exhaust gas temperature. Very often, there are relatively large local temperature differences within the catalyst volume. In order to meet the multiple boundary conditions for operation of a NOx storage catalyst, it is advantageous to provide means for determining local temperature differences in the catalyst volume. These may be temperature sensors which record local temperature values within the catalyst volume and transmit them to the motor control unit 3 or preferably a calculation model which takes into account differences in temperature. local temperatures and variations in temperature time. In particular, a temperature distribution function in the catalyst volume is preferably determined in a main flow direction of the exhaust gas. The actual temperature variations are thus represented in a simple way.

  The catalyst 7 is preferably spatially divided into a plurality of partial sectors and the temperature of the individual partial sectors is determined. This results in a temperature distribution function for the plurality of partial areas. In this case, the subdivision can in principle be done in any way, a subdivision in the axial direction, particularly along the main flow of the exhaust gas through the catalyst 7, being appropriate.

  In the same way, one can also proceed to a radial subdivision. The exact number of partial areas will depend on the size of the catalyst and / or the nature of the flow approaching the front surface, in order to capture the irregularities and / or temperature gradients actually occurring or expected. A number of 3 to 5 partial sectors is preferred. It is possible to base for different operating regimes of the internal combustion engine 1 each time on a different number of partial zones of the catalyst 7.

  In the control apparatus of an engine 3, a multi-zone calculation model for the NOx storage catalyst 7 is preferably deposited, optionally also for the catalyst 6.

  FIG. 2 shows, for example, the correlation between an exhaust gas temperature AT (t) as a function of time t, a temperature curve in time Tl (t), T2 (t), T3 (t) in a catalyst volume with a plurality of partial zones TI, T2, T3 in the upper part and a specific velocity-time function vfzg (t) in the lower part. The catalyst 7 is decomposed here into three partial zones T1, T2, T3, as indicated in the upper part. The allowable temperature range for sensible catalyst operation is between a lower critical temperature Tu and a higher critical temperature To.

  A mass flow of exhaust gas approaches the front face of the catalyst 7, which is indicated in the upper part by an arrow. The main flow direction of the exhaust gas corresponds to the axial extension of the catalyst 7. A comparative calculation with a one-zone calculation model, on which the catalyst 7 is not subdivided into several partial zones, is drawn. in the upper image as a dashed line.

  Given the thermal inertia of the NOx accumulator catalyst 7, the temperature of the catalyst rapidly follows the temperature of the exhaust gas AT (t), for example after an acceleration phase. It appears that in the present case and at least in an axial direction, there are significant local and time differences in temperature between the different partial areas T 1, T 2, T 3.

  If an idling point of operation or a low load operating point is sought directly after a short acceleration phase, it appears that the catalyst is in places rapidly again below of the catalyst's critical upper temperature T.sub.7 With the only weak mass flows which follow then and which are also generally accompanied by low NOx mass fluxes, only low space velocities are also established. Thus it is already sufficient for sufficient NOx conversion that only part of the total volume of the catalyst 7 is at a correspondingly low and permissible temperature. In this case, it is acceptable to allow a fuel-efficient lean regime for the internal combustion engine 1 already at an early stage, although some of the catalyst 7 is still above the internal combustion engine 1. the higher critical temperature To.

  The lower part illustrates a characteristic driving situation. On the basis of a low vehicle speed vO at time t0 with low exhaust gas temperatures, an acceleration phase is passed which results in an increase in the exhaust gas temperature AT ( t). Then, the vehicle is moved only briefly with a higher speed vl until a deceleration phase starts just after the moment t2 and we continue just 5 before the moment t4 with a speed v2 plus weak and constant. During the deceleration phase, the exhaust gas temperature AT (t) decreases and reaches an approximately constant level during the consecutive path performed at the constant speed v2.

  For the described driving profile, the behavior of the temperatures can be compared as a result of a simple zone calculation model (dashed curve) and a preferred multi-zone calculation model (solid lines), here a three zone calculation model for the three partial zones. The one-zone calculation model is made because of the simplicity so that the maximum temperature of the catalyst 7 corresponds approximately to the maximum T2 temperature of the partial zone of the medium T2.

  The temperature, calculated with the simple one-zone calculation model, of the catalyst 7 exceeds between the times t2 and t5 the upper critical temperature To of the permitted temperature range. Thus, the lean diet would be blocked by the engine control apparatus 3 in this time interval. In the individual partial areas T1, T2, T3 of the three zone calculation model with the specific temperature curves T1 (t), T2 (t), T3 (t), however, the critical temperature higher than To is reached or exceeded with a delay. The actual temperature variations in the catalyst 7 are thus restored in a more precise manner. This has in the embodiment the consequence that, in all the partial areas T1, T2, T3, the upper temperature To is certainly exceeded temporarily, but never at the same time.

  Consequently, at least some of the partial regions T 1, T 2, T 3 of the catalyst 7 or the catalyst volume areas which are sufficiently suitable for the conversion of NOx in the lean state and therefore used in this way can be provided at any time. because their temperature is lower than the critical temperature greater than To within the permissible temperature range at the time the partial zone is solicited with exhaust gases, as shown in the overview: Time interval Zone Partial with temperature T <To tlt2 T2, T3 t2-t3 T3 t3-t4 Tl, T3 t4-t5 Tl t5-t6 Tl, T2 In the whole time interval between t1 and t7, it is therefore not necessary according to the invention to give up a poor diet advantageous from the point of view of consumption because of too high catalyst temperatures.

  It is the same for the case of a cooling of the catalyst 7 when the internal combustion engine 1 operates for example for a prolonged period of idling or low load regime and that the catalyst 7 cools and descends according to a simple calculation model at a zone at a temperature below the lower critical temperature Tu. There again, local temperature differences appear which result in the inlet side and in the front zone of the catalyst 7, some partial zones being cooled already below the lower critical temperature Tu, whereas in the rear zone of the catalyst 7, there are still partial zones with sufficiently high temperatures in the allowed temperature range between Tu and To.

  Preferably, a lean regime of the internal combustion engine 1 is therefore allowed as a function of a certain number of partial zones T 1, T 2, T 3 when a sufficient number of partial regions T 1, T 2, T 3 having a temperature level that allows a conversion of NOx in a lean regime with a sufficient reduction of the polluting agents.

  An operating state of the internal combustion engine 1, which results in an increase in the temperature of the exhaust gas, can be initiated preferably as soon as a predefined number of partial areas T1, T2, T3 is below an allowed temperature level higher than a lower critical temperature Tu. An operating state of the internal combustion engine 1, which results in a reduction in the temperature of the exhaust gas, can then be adjusted preferably as soon as a predefined number of partial areas T1, T2, T3 exceeds a temperature level. The required number of partial zones Tl, T2, T3 may depend on the size of the catalyst 7, the temperature of the exhaust gas, the thermal conductivity and / or the thermal capacity. catalyst 7, the local temperature in the partial areas T1, T2, T3 of the catalyst 7 and parameters of this type.

  Authorization of the respective operating state can be made dependent also on a sum of the volumes of the partial areas T1, T2, T3 available with the desired temperature.

  On the basis of the calculated number or calculated total of the volumes of the partial zones T 1, T 2, T 3 available in a desired temperature range, a mass flow of NOx and / or a maximum permitted mass flow of exhaust gas is preferably defined. and it is decided by comparison with the respective value calculated in the motor control apparatus 3 for the current operating point if the lean regime can be allowed. As an alternative, depending on the temperature of the partial zones TI, T2, T3, it is also possible to obtain a low speed with other operating parameters of the motor, such as for example the ignition angle and / or the moment of ignition. injection or another type of lean diet, which has lower gross NOx emissions. On the other hand, a mass currently incorporated in the pollutant NOx accumulator catalyst, for example NOx, can also be taken into account and / or the authorized mass flow of NOx and / or the mass flow degass. escape can be corrected accordingly. In the same way, it is possible to take into account accordingly an aging of the catalyst 7 and / or other components 15 in the exhaust system 2 and / or masses of pollutants stored currently forming, for example appropriate characteristic values in the engine control apparatus 3 which determine the permissible values for the mass flow of NOx and / or the mass flow of exhaust gas with these characteristic values.

  It is also advantageous to evaluate the respective temperature of a partial zone T1, T2, T3 as a function of its influence on the conversion of pollutants which can thus be obtained and to form correction factors for authorized mass flow of NOx and / or the mass flow of exhaust gas. In this way, it can be taken into account that a quantity of pollutants that can be stored, in particular NOx, is not constant in the allowed temperature range between Tu and To, but generally has a maximum .

  In another advantageous application, the process according to the invention can be used to reduce the emission of pollutants after a cold start of the internal combustion engine 1 or possibly following an extended idling phase or low charge. Again, the invention is described below with the aid of the main catalyst 7; but it can be applied also to other catalysts or types of catalysts. During the operating phases mentioned, the temperature level of the catalyst is generally too low to provide sufficiently high conversion rates for subsequent operating phases, particularly with regard to HC emissions. If the internal combustion engine operates after a cold start, for example in an acceleration with relatively high powers, the higher HC mass flows inherent in these powers and also other mass flows of exhaust gases lead to breaks. as the heating of the catalyst 7 is delayed by its heat capacity and only a part of the pollutants can be converted. However, in order to reach as quickly as possible the so-called "Light-Off" of the main catalyst 7 and to avoid emission failure points, it would be possible to implement generally known heating measurements for the catalyst 7, e.g. ignition point retardation and the like. These heating measures, however, lead to an increase in fuel consumption. Alternatively, the catalyst 7 may however be heated also with external means.

  The design of the heating measurement with respect to intensity and duration over time must be such that, in the subsequent driving regime, no unacceptably high level of emission failure is achieved. in order to comply with predefined limit values of polluting agents. In order to have a sufficiently high conversion efficiency, however, it is sufficient for many driving states that only part of the surface or volume of the catalyst 7 or catalysts 6, 7 in the exhaust system is sufficient for the invention. 2 has reached an appropriate temperature level, especially with a recent or relatively new catalyst. It is therefore sufficient in a preferred application of the invention to apply a heating measure for the catalyst 7 by means of the influence of the internal combustion engine 1 only until a desired degree of heating is achieved. achieved. Inconvenient disadvantages regarding fuel consumption can thus be avoided.

  Since in this case the catalyst 7 is heated from front to rear along an exhaust gas flow path and in general from the inside out, there is with increasing duration of a larger and larger surface with a temperature level sufficient for the conversion of pollutants. Thus, a larger number of the partial areas T 1, T 2, T 3 which have a sufficient power during the conversion of the polluting agents are available with increasing duration of the heating measurement. The heating measurement can therefore be completed prematurely, which saves fuel.

  In the same way, it is possible to switch after a lean phase temporarily to the so-called homogeneous regime with X = 1, in order to raise, by the resulting higher exhaust temperatures, a sufficient number of zones. partial T1, T2, T3 at a higher temperature.

  Preferably, the length and / or intensity of a heating means for the heating of the catalyst 7 is adjusted as a function of the temperatures T1 (t), T2 (t), T3 (t) of the different partial zones T1. , T2, T3 of the catalyst 7.

  In the simplest case, it is possible to form a sum of the volumes of the partial zones T1, T2, T3 which are above a predefined temperature. It may be for example a lower critical temperature Tu which represents the lower temperature limit for a sufficient conversion of pollutants, for example an HC conversion of the catalyst 7. On the other hand, the temperature level in the different partial zones T1, T2, T3 can be evaluated as a function of the influence on a conversion rate of a pollutant in the catalyst 7. From there, it is possible to form in the various partial zones T1, T2 , T3 an evaluation factor relating to the conversion efficiency that can be obtained, so that the decisive sum of the volumes of the partial areas T1, T2, T3 which must be available to complete the measurement of heating.

  In the same way, it is possible to select accordingly an appropriate operating mode of the internal combustion engine 1 to ensure a sufficient active surface area for the conversion of pollutants into the catalyst 7. In addition, it can be taken into account. the influence of aging by the characteristic values, formed in the motor control unit 3, of the aging of the catalyst 7 by determining a necessary number or volumes of the partial areas T1, T2, T3 with a sufficient temperature as a function of characteristic values.

  If the internal combustion engine 1 operates with a very high power, it often becomes necessary to limit the temperature of the exhaust gas by enriching the mixture to protect the catalyst 7 or the catalysts 6, 7 in the plant. exhaust 2 against thermal overload. Since this operation results in a substantial increase in both fuel consumption and pollutant emissions, this measure is limited by the invention to a minimum essential operating range of the internal combustion engine 1. Catalyst 7 can represent here also in the dynamic driving mode very different temperatures locally. It is therefore advantageous to design an enrichment of the mixture and to operate the internal combustion engine 1 so that the hottest point in the catalyst 7 has precisely a maximum permitted temperature, preferably a higher critical temperature To *. In this way, a compromise is reached between a limitation of the fuel consumption and a consequent limitation in the thermal plane of the aging of the catalyst 7.

  In contrast to a simple one-zone calculation model, which describes the catalyst temperature globally with a single value, a preferred multi-zone computation model provides better adaptation to the actual local and temporal distribution function. If the distribution is taken into account, the enrichment of the mixture can be started at a later time, since the uncertainties regarding the maximum local temperature are substantially lower. In particular, the exhaust gas temperature can be omitted as a determining indicator of the maximum permissible temperature and, in the event of this temperature being exceeded, the mixture can be enriched immediately in order to To prevent a thermal overload of the catalyst 7. Since the temperature of the exhaust gases increases much more rapidly than the temperature in the first partial zone of the catalyst T1, the enrichment of the mixture would be switched on as soon as the temperature of the gases of exhaust reached the critical temperature. If the function of the temperature distribution in the catalyst 7 is taken into account, it is recognized, however, whether the temperature of the most advanced partial zone T 1 at the inlet of the catalyst 7 is still lower at this time than the maximum permissible value and enrichment of the mixture for temperature limitation is not yet necessary.

  In stationary mode, for example with a maximum vehicle speed, the enrichment of the mixture is then comparable in both cases.

  In case of cooling, it is possible to proceed in a similar manner when for example the internal combustion engine 1 5 operates first with a high speed and very high loads and then goes on to an operation with lower speeds or loads weaker or even in the meantime to a mode of power failure. There, the catalyst 7 cools under the effect of the freshly arrived exhaust gas.

  Since the catalyst 7 then cools in the flow direction of the exhaust gases from front to rear, a thermal protection of the components is ideally maintained until the temperature the rearmost zone T3 at the outlet of the catalyst 7 has dropped below a maximum permitted temperature. It is preferably another higher critical temperature To **, which must not coincide with the first higher critical temperature To *. As a result, the entire catalyst 7 can be protected against thermal overload. Taking into account, according to the invention, the function of distribution of the temperature in the catalyst 7, it is prevented that a protective measure of the components is completed too early, since the maximum temperatures which appear locally and / or at times in the catalyst are not neglected.

  In a preferred application of the invention, the switching on or off and / or the intensity of a mixing enrichment according to the function of distribution of the temperature in the catalyst 7 is thus chosen, taking into account in particular the temperature T1 (1), T2 (t), T3 (t) of the hottest partial zone T1, T2, T3. This may also lead to a delayed supply of feed shutoff to avoid a strong oxygen supply to the catalyst 7 in the case of unacceptably high catalyst temperatures. Since the moment of authorization of the thrust supply cutoff depends on the catalyst temperature distribution function, it is advisable to give an authorization only in the case where the rearmost part T3 is Catalyst 7 is also sufficiently cooled. Overall, this allows switching on and off according to the needs of the thermal protection measures of the components.

  With the aid of the process according to the invention, the catalyst 7, or a catalyst system contained in the exhaust system 2, operates in an optimized manner by the operation of the internal combustion engine. Catalyst 7 is used more efficiently. In this way, it is possible to lower the noble metal content of the catalyst 7 or possibly other catalysts.

  Vehicles with internal combustion engine 1 20 capable of operating at a low engine speed, meeting the requirements of the new European NEFZ driving cycle and achieving HC <0.07 g / km and NOx <0.05 g / km with catalysts not thermally damaged with a stored sulfur mass of less than 0.2 g / l of catalyst volume and a lean-time fraction under control with no lump-off phase with a lambda value> 1 At least 250 seconds, in particular at least 350 seconds, an HC emission of less than 0.07 g / km and a NOx emission of less than 0.05 g / km, are nowadays commonly equipped with catalysts that have noble metal contents greater than 100 g / ft3. If catalyst systems which have at least one NOx storage catalyst and optionally upstream three-way catalyst as precatalyst and which operate with the process according to the invention are used, the noble metal content may be down to 100 g / ft 3, preferably up to 80 g / ft 3, preferably up to 60 g / ft 3. Even after experimental oven aging of the NOx storage catalyst, which has a noble metal content correspondingly reduced, at 850 C for 4 hours and the possible precatalyst at 1100 C for 4 hours in an atmosphere having 2% of At 02 and 10% H 2 O, an HC emission of 0.1 g / km and an NOx emission of 0.08 g / km was not exceeded in a subsequent NEFZ test.

Claims (23)

  A method for operating an internal combustion engine, which has an exhaust system (2) with at least one catalyst (6, 7) mounted downstream of the internal combustion engine (1), characterized in that a catalyst temperature model with predefined dynamic distribution function of a local temperature (TI (t), T2 (t), T3 (t)) is provided in the catalyst volume and the internal combustion engine (1) 10 operates according to the values of this distribution function (T1 (t), T2 (t), T3 (t)).   2. Method according to claim 1, characterized in that, according to the temperature model, the catalyst (6, 7) and / or the volume of catalyst is divided into a number of predefined partial zones to which the local temperatures (Tl (t), T2 (t), T3 (t)) are assigned.   3. Method according to claim 1 or 2, characterized in that the internal combustion engine (1) operates according to a thermal conductivity and / or a heat capacity in the catalyst volume.   4. Method according to any one of claims 1 to 3, characterized in that an authorized mass flow of exhaust gas and / or a pollutant component with which the catalyst (6, 7) is determined. is powered.   5. Method according to claim 4, characterized in that a mass of a pollutant stored in at least one catalyst (6, 7) is taken into account to determine the authorized mass flow of exhaust gas and / or a component of pollutants.   6. Method according to claim 4 or 5, characterized in that a probable conversion of a polluting agent is determined according to the distribution function (T1 (t), T2 (t), T3 (t)) for the determining the mass flow of exhaust gas and / or a component of pollutants.   Method according to at least one of Claims 4 to 6, characterized in that the permissible mass flow of exhaust gas and / or a pollutant component is determined as a function of the state of aging of the catalyst (6, 7).   Process according to at least one of the claims   characterized in that - the distribution function (T1 (t), T2 (t), T3 (t)) is determined for a plurality of partial areas (T1, T2, T3) of the catalyst volume; - A regime of the internal combustion engine (1), which causes an increase in the temperature of the exhaust gas, is implemented as soon as a predefined number of partial areas (T1, T2, T3) remains below a permitted temperature level, higher than a lower critical temperature (To) or - a speed of the internal combustion engine (1), which causes a reduction in the temperature of the exhaust gas, is implemented as soon as a predefined number of partial areas (T1, T2, T3) exceeds a permitted temperature level, lower than a higher critical temperature (To).   9. The method according to at least one of the preceding claims, characterized in that the distribution function (T1 (t), T2 (t), T3 (t)) is determined by means of a calculation model.   10. Method according to at least one of the preceding claims, characterized in that the distribution function (T1 (t), T2 (t), T3 (t)) is determined by means of temperature sensors.   Method according to at least one of the preceding claims, characterized in that the distribution function (T1 (t), T2 (t), T3 (t)) is determined at least along a direction of main flow of the exhaust gas into the catalyst volume.   Method according to at least one of the preceding claims, characterized in that the distribution function (T1 (t), T2 (t), T3 (t)) is determined perpendicularly to a main flow direction of the exhaust gases. exhaust in the catalyst volume.   13. Method according to at least one of the preceding claims, characterized in that a space velocity in the catalyst volume is taken into account.   Process according to at least one of the preceding claims, characterized in that a lean engine internal combustion engine (1) is permitted when the temperature of a predefined part of the catalyst volume is within a range of between the lower critical temperature and the higher critical temperature (Tu, To).   Method according to at least one of the preceding claims, characterized in that the internal combustion engine (1) is operable in a lean regime and a low speed is required with reduced NOx emissions reduced by the internal combustion engine ( 1) in cases where, for a certain number of partial zones T1, T2, T3 or a predefined part of the catalyst volume, there is an excess of the critical temperature greater than T0 or an underflow of the lower critical temperature. You.   Method according to at least one of the preceding claims, characterized in that a heating measurement for the heating of the catalyst (6, 7) is stopped as soon as a predefined part of the catalyst volume is reached. above a lower critical temperature (Tu).   17. Method according to at least one of the preceding claims, characterized in that, when a higher critical temperature (To *) is exceeded by a predefined number of partial zones, in particular already with a partial zone, an enrichment of the mixture is switched on and maintained until the fall of the temperature below a higher critical temperature (To **) in a predefined number of partial zones (T1, T2, T3), in particular in each zone partial individual.   18. Device for operating an internal combustion engine, which has an exhaust system (2) with at least one catalyst (6, 7) mounted downstream of the internal combustion engine (1) and with an apparatus engine control unit (3) for influencing the operating parameters of the internal combustion engine, characterized in that the engine control apparatus (3) has means (3a) for implementing a control model. catalyst temperature with a predefined dynamic distribution function of the local temperature in the catalyst volume (Tl) and for the operation of the internal combustion engine according to the values of this distribution function (T1 (t), T2 ( t), T3 (t)).   19. Device according to claim 18, characterized in that means are provided for determining a state of aging of the catalyst (6, 7) and / or a quantity of pollutants stored in an exhaust system (2) and or a conversion efficiency of a catalyst (6, 7).   20. Device according to claim 18 or 19, characterized in that the distribution function (T1 (t), T2 (t), T3 (t)) is determined by means of temperature sensors.   21. Device according to at least one of claims 18 to 20, characterized in that means are provided for determining a calculation model for the distribution function (T1 (t), T2 (t), T3 (t). ) of the catalyst (6, 7).   22. Apparatus according to at least one of claims 18 to 20, characterized in that at least one main catalyst (7) and at least one pre-catalyst (6) mounted upstream of the main catalyst are provided in the plant. exhaust (2).   23. Device according to claim 22, characterized in that the at least one main catalyst (7) is a NOx storage catalyst and the at least one pre-catalyst (6) mounted upstream is a three-way catalyst.