JP2005504224A - Method for protecting an exhaust gas purification system of an internal combustion engine prior to thermal overload - Google Patents

Abstract

The invention comprises a method for operating an internal combustion engine of a motor vehicle, in particular with an exhaust gas device comprising an exhaust gas purification system, wherein the engine lambda value is at least one of the exhaust gas devices. Depends on the temperature modeled or measured at at least one critical position of the exhaust gas device if the temperature detected at one position exceeds a preset first temperature value. Thus, it relates to such a method in which the exhaust gas temperature is reduced to a temperature-dependent engine lambda value in a state different from steady state operation. In the case of the present invention, the engine lambda value is determined for the steady operation only when the measured temperature exceeds the preset first temperature value for a preset time interval, due to a decrease in the exhaust gas temperature. The value is changed to a temperature dependent engine lambda value.

Description

【Technical field】
[0001]
The invention relates to a method for operating an internal combustion engine of an automobile, in particular, having an exhaust gas device with an exhaust gas purification system according to the superordinate concept of claim 1,
At that time, the engine lambda value is
When the temperature detected at at least one position of the exhaust gas device exceeds a preset first temperature value,
Depending on the temperature that has been modeled or measured at at least one critical location of the exhaust system, the exhaust gas temperature is reduced.
The engine lambda value is adjusted depending on the temperature in a state different from the steady operation.
[Background]
[0002]
For example, a catalytic device of an internal combustion engine in an automobile deteriorates under a load at a high temperature, in which case the light-off characteristic is reduced, ie the same conversion rate is initially a relatively high catalyst. The peak conversion, which is typically> 99% for HC, CO and NOx, is reduced in the three-way catalytic device, which is reached at the device temperature. This process increases excessively with increasing degradation rates.
[0003]
In the exhaust gas line of an internal combustion engine, extremely high exhaust gas temperatures and catalytic device temperatures of 1000 ° C. or more are generated, which in some cases allow the catalytic device to be allowed within a short working time. The exhaust gas emission limit value is no longer maintained. This is especially true in the case of an exhaust gas purification system having a catalyst device (pre-catalyst device or main catalyst device) close to at least one engine. This is because very little heat is released through the short non-adiabatic exhaust gas conduit.
[0004]
It is known to limit the exhaust gas temperature by engine operation below the stoichiometric air-fuel ratio, at least at about full engine load. The fuel introduced into the combustion chamber is not completely burned due to lack of oxygen. This causes the combustion chamber gas to reach a relatively low temperature at the same supplied energy. Additionally, the fuel vaporization enthalpy cools the combustion chamber gas. Furthermore, within this mode of operation, residual oxygen is reduced in the exhaust gas, so that a slight exotherm is formed in this or these catalytic devices.
[0005]
Usually, the maximum allowable exhaust gas catalytic device temperature is given in advance, and the engine lambda value depends on the difference of the detected exhaust gas catalytic device temperature from the maximum allowable exhaust gas catalytic device temperature. Adjusted. Similarly, additionally, monitoring one or multiple exhaust gas temperatures, or catalytic device temperatures, for differences from a preset maximum temperature at different locations of the exhaust gas purification system, and the engine It is known to adjust the lambda value depending on the critical position.
[0006]
It is a disadvantage that these measures are associated with an unfavorable increase in fuel consumption. Accordingly, efforts have been made to limit the excessive consumption of these structural member protection measures as much as possible. Therefore, for example, German Patent No. 196 09 923 (Patent Document 1) describes a phase-in introduction of overheat protection measures. First of all, firstly, a relatively weak effect (ausgepraegte) measure is taken and the result of this measure is examined for a temperature drop, in the event of an insufficient temperature drop, the second Relatively strong and effective measures are taken. The disadvantage of this method is that certain overloads of exhaust gas purification must be accepted in order to achieve a reduction in fuel consumption.
[Patent Document 1]
German Patent 196 09 923 [Disclosure of the Invention]
[Problems to be solved by the invention]
[0007]
Therefore, the problem underlying the present invention is that the method of the above-described manner reduces the excess consumption by adjusting the engine lambda value due to the exhaust gas temperature and the exhaust gas purification device temperature without overloading the exhaust gas purification. It is to improve for the purpose of being achieved.
[Means for Solving the Problems]
[0008]
This problem is solved according to the invention by a method of the above-mentioned type having the typical features in claim 1. Advantageous embodiments of the invention are given in the dependent claims.
【The invention's effect】
[0009]
For this purpose, according to the present invention, the engine lambda value is only for the reduction of the exhaust gas temperature when the detected temperature exceeds a preset first temperature value for a preset time interval. It is changed from a value for steady operation to a temperature dependent engine lambda value.
[0010]
This can be recognized as a short-term excess of the limit temperature for the exhaust gas purification system, which can be reconciled again in time by the subsequent cooling phase,
Therefore, there is no reduction in the numerical value of the engine lambda value in steady operation,
Thus, in the state of full operation (Gesamtbetrieb), the reduced fuel consumption has the advantage that it is given with a change in the engine lambda value by means of structural member protection measures that show a slightly more abrupt effect. Yes. Furthermore, the different importance of different temperature critical positions (Wichtung) is reached during the adjustment due to the protection of the structural member of the engine lambda value and, for example, a short load during the acceleration process and uphill A distinction is made between a relatively long-lasting load, for example during full throttle travel.
[0011]
In order to take into account the different thermodynamic conditions of temperature changes at different locations within the exhaust system, a preset time interval is selected differently for the different critical positions of this exhaust system. . For example, the closer the critical position of the exhaust gas device is to the engine block of the internal combustion engine, the longer this preset time interval is selected.
[0012]
Advantageously, the temperature is measured upstream or downstream of the at least one critical position and / or in the main catalyst device and / or in the pre-catalyst device.
[0013]
In order to prevent irreversible damage to the exhaust gas purification system, the detected temperature is greater than the preset first temperature value within a preset time interval. If a preset temperature value is exceeded, the engine lambda value is shifted from a value for steady operation to a temperature dependent engine lambda value before the preset time interval elapses.
[0014]
In order to take into account the different thermodynamic conditions of temperature changes at different locations in the exhaust gas device, the preset second temperature value is different due to the different critical positions of this exhaust gas device. Selected. For example, the closer the critical position of the exhaust gas device is to the engine block of the internal combustion engine, the higher the preset second temperature value is selected.
[0015]
Suitably, the engine lambda value is transferred directly or filtered from a steady state value to a temperature dependent engine lambda value.
[0016]
Further features, advantages and advantageous embodiments of the invention are given by the dependent claims and the following description of the invention based on the attached figures.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017]
According to the invention, the operating time of the temperature or exceeding a preset first temperature is used as a reference for adjusting the engine lambda value. Throughout the preset time interval, the temperature limit of the continuous load is exceeded without an initial setting of the temperature-dependent engine lambda value in a state that differs from steady operation by a given temperature difference. If the temperature overload persists for a relatively long time, the engine lambda value will depend on the temperature, either directly or filtered, to avoid or reduce the damage caused by the continuous thermal load. Transition to lambda value.
[0018]
Furthermore, the location of the occurrence of over temperature is taken into account in the detection of temperature dependent engine lambda values in the exhaust gas system. In the vicinity of the cylinder head, due to the slight thermal inertia of the exhaust gas system up to this working section (Laufstrexke), there exists a thermodynamic state that follows the load very quickly, and this thermodynamic The situation is clearly reduced further downstream and in particular behind one or more catalytic devices. Therefore, the heating process and the cooling process proceed more quickly before the front catalytic device near the engine than the large-volume main catalytic device disposed in the middle far from the engine. Thus, the temperature overload in the exhaust gas is allowed for a longer time interval upstream of the first catalytic device near the engine than the temperature overload at the critical exhaust gas device location that follows. Is done. Because of the relatively quick cooling, and therefore critical, at locations near the engine, during adverse load changes or speed changes, or when adjusting temperature-dependent engine lambda values This is because the removal of new situations can be taken into account.
[0019]
If the measured temperature has already exceeded a preset second temperature value that is higher than the preset first temperature value for this measurement position within the preset time interval, i.e. In other words, if the temperature difference between the measured temperature and the preset first temperature value is greater than the preset value, an engine lambda value that depends on the temperature is already given in advance. It is meaningful to adjust to eliminate irreversible catalytic device damage before the lapse of a given time interval.
[0020]
1 and 2 graphically illustrate dynamic structural member protection according to the present invention. In this case, the time is indicated on the horizontal axis 10, the exhaust gas temperature in front of the front catalyst device on the first vertical axis 12, and the engine lambda value on the second vertical axis 14. ing. The value 16 on this axis 14 corresponds to an engine lambda value of 1, the line 18 corresponds to a preset first temperature value (900 ° C. in this example), and the line 20 This corresponds to the set second temperature value (940 ° C. in this example). Graph 22 shows the temperature course of the exhaust gas over time without structural member protection treatment, and graph 24 shows the temperature course of the exhaust gas over time with the structural member protection treatment according to the known art, And graph 26 shows the temperature course of the exhaust gas over time with a structural member protection procedure according to the method according to the invention. Graph 28 shows the course of engine lambda value over time without structural member protection treatment, and graph 30 shows the course of engine lambda value over time with structural member protection treatment according to the known art, And graph 30 shows the course of the engine lambda value over time with the structural member protection procedure according to the method according to the invention. Reference numeral 34 indicates the first time point T0, reference numeral 36 indicates the second time point T1, reference numeral 38 indicates the third time point T2, and reference numeral 40 indicates the fourth time point T3. The reference numeral 42 indicates the fifth time point T4. In FIG. 2, reference numeral 44 indicates the sixth time point TKR. The time difference between the third time point 38 and the fourth time point 40 corresponds to a preset time interval 46.
[0021]
FIG. 1 graphically illustrates, for example, the load jump, ie partial load-full load, at time T0 34, when entering a relatively long strong gradient. The exhaust gas purification system includes, for example, a pre-catalyst device close to the engine and a main catalyst device disposed further downstream. In this case, in FIG. The time series of the axis 12) is specifically explained. This exhaust gas temperature rises rapidly as a result of the load jump at the time T0 34, after the time T0 34, and before the pre-catalyst device, and at a preset 900 ° C. A critical temperature limit time point T1 36 in the manner of one temperature value 18 is approached. In the prior art (graphs 24, 30), the engine lambda value (graph 30) is already adjusted from time T1 36 to a value <1 in order to ensure that exhaust gas temperatures> 900 ° C. are excluded (graph 30). Graph 24). According to the method according to the invention, first of all, within the time interval 46 between T2 38 and T3 40, a temperature difference limit value of 40 K (Kelvin) or a preset second temperature value of 940 ° C. It is checked whether the limit has been exceeded. In the embodiment according to FIG. 1, this is not the case, and thus, for example, by the gradual (or immediate) adjustment of the corresponding engine lambda value (graph 32) after the passage of the time interval 46 of 5 seconds. After the time point T340, the exhaust gas temperature (graph 26) is lowered below the continuous load limit value 18. Thus, the overconsumption resulting from this change in engine lambda value will begin for the first time at a later point in time. Overall, the exhaust gas temperature (graph 26) is located above the continuous load limit 18 during the time interval from T2 38 to T4 42.
[0022]
In a further embodiment according to FIG. 2, the temperature difference limit value (strict limit value), or a preset second temperature of 940 ° C., at the time TKR 44, is also within the time interval 46. The value 20 is exceeded and the engine lambda value (graph 32) is set to the value required to fall below the continuous load limit value 18 with a steep slope. Thus, the time interval from T2 38 to T4 42 results in being shorter than in the embodiment according to FIG.
[0023]
FIG. 3 specifically illustrates the significance of the different time intervals (preset time intervals) for allowing thermal overloads with respect to two different positions in the exhaust gas device, namely the measurement position. ing. The temperature is marked on the vertical axis 48 and the time is marked on the horizontal axis 40. Line 52 shows the maximum allowable temperature for the pre-catalyst device, and line 54 shows the maximum allowable temperature for the main catalyst device. Graph 56 shows the course of the exhaust gas temperature before the front catalyst device without the structural member protection treatment, and graph 60 shows the exhaust before the front catalyst device with the structural member protection treatment according to the present invention. The progress of gas temperature is shown. The graph 62 shows the progress of the exhaust gas temperature before the main front catalyst device without the structural member protection treatment, and the graph 64 shows the front of the main front catalyst device with the structural member protection treatment according to a known technique. The graph 66 shows the progress of the exhaust gas temperature before the main catalyst device having the structural member protection treatment according to the present invention.
[0024]
In front of the pre-catalyst (graph 60), based on the slight thermal inertia of the exhaust gas system, a change in the adjustment of the engine lambda value (graph 64) can cause a temperature drop very quickly. On the other hand, at the measuring position in the middle of the main catalyst unit, also in the immediate adjustment of the low engine lambda value due to temperature, only after the critical temperature limit value 54 has been exceeded, only a slow structural member Only the removal of temperature must be taken into account. Long time intervals here increase the risk of thermal overload.
[0025]
At the exhaust gas temperature in front of the pre-catalyst device (graph 60), due to the load jump, the continuous load limit value 52 is crossed at the time TA 68 and the structural member protection is started at the time TB 70. Is done. At time TC 72, this exhaust gas temperature is again below the continuous load limit value 52.
[0026]
At a temperature in the main catalyst device (graph 64), structural member protection is initiated at time TA ′ 74 by a similar load jump. This time interval from time TA ′ 74 to TB ′ 76 corresponds to the time interval from time TA 68 to TB 70. This temperature rises more slowly than the exhaust gas temperature in front of the front catalyst device due to the relatively high thermal inertia of the exhaust gas device connected in front. For this reason as well, cooling continues for a relatively long time, and generally the structural member critical time interval from this time TA ′ 74 to TC ′ 78 is from time TA 68 to TC 72. Longer than the time interval to reach. Especially for temperature-sensitive NOx storage catalytic devices, even if the temperature peak does not exceed the continuous load limit value 54 much stronger than the exhaust gas temperature (graph 60) before the previous catalytic device, the long working time Can be very severely damaged. In the case of the method according to the invention according to graph 66, the temperature peak and the duration of the over temperature (time interval from time TA ′ 74 to TC ″ 80) are basically less.
[Brief description of the drawings]
[0027]
FIG. 1 shows the engine lambda value for a first temperature course of the exhaust gas temperature before the pre-catalyst device and for a time with and without an engine lambda value treatment according to the method according to the invention. FIG.
FIG. 2 is a graph of engine lambda value against a second temperature course of the exhaust gas temperature before the pre-catalyst device and with and without engine lambda value treatment according to the method according to the invention; It is a typical figure.
FIG. 3 is a graphical diagram of the temperature course of the exhaust gas temperature with and without engine lambda value over time before the pre-catalyst and before the main catalyst. is there.

Claims (9)

A method for operating an internal combustion engine of a motor vehicle, in particular with an exhaust gas device comprising an exhaust gas purification system,
At that time, the engine lambda value is
When the temperature detected at at least one position of the exhaust gas device exceeds a preset first temperature value,
Depending on the temperature that is modeled or measured at at least one critical location of the exhaust gas device, the exhaust gas temperature is reduced.
In the above method in a manner that is adjusted to a temperature dependent engine lambda value in a state different from steady state operation,
The engine lambda value depends on the temperature from the value for steady operation only when the measured temperature exceeds the preset first temperature value for a preset time interval, in order to reduce the exhaust gas temperature. A method characterized by being changed to an engine lambda value. 2. The method according to claim 1, wherein the preset time intervals are selected differently for different critical positions of the exhaust gas device. 3. A method according to claim 1 or 2, characterized in that the closer the critical position of the exhaust gas device is to the engine block of the internal combustion engine, the longer the preset time interval is selected. . 4. The detected temperature is measured upstream or downstream of at least one critical position and / or in the main catalytic device. Method. 5. The detected temperature is measured upstream or downstream of at least one critical position and / or in a pre-catalyst device. Method. If the detected temperature exceeds a second preset temperature value that is greater than the first preset temperature value within a preset time interval, the engine lambda value is: 6. The method according to claim 1, wherein a transition from a value for steady operation to a temperature-dependent engine lambda value is made before the elapse of a preset time interval. Method. The method according to claim 6, wherein the preset second temperature value is selected differently for different critical positions of the exhaust gas device. 8. The preset second temperature value is selected to be higher as the critical position of the exhaust gas device is closer to the engine block of the internal combustion engine. The method described. 9. The engine lambda value is transferred directly or filtered from a steady-state value to a temperature dependent engine lambda value. The method described.