DE102014004714A1 - Method for operating a drive device and corresponding drive device - Google Patents

Abstract

The invention relates to a method for operating a drive device, which has at least one catalyst with an oxygen storage for purifying exhaust gas, wherein upstream of the catalyst, a Vorkatalysatormolmasse a first material and a Vorkatalysatorsauerstoffmolmasse of oxygen are determined. It is provided that for calculating a Nachkatalysatorlambdawerts a Nachkatalysatorsauerstoffmolmasse is determined by a first reaction equation, the reaction of the oxygen with the first material is taken into account, and that in determining the Nachkatalysatorsauerstoffmolmasse additionally a second reaction equation, the reaction of the first substance with in oxygen stored in the oxygen storage, and a third reaction equation, which describes the entry of oxygen from the exhaust gas into the oxygen storage, are taken into account, wherein a reaction rate of the second reaction equation and a reaction rate of the third reaction equation enters a level of the oxygen storage. The invention further relates to a drive device.

Description

The invention relates to a method for operating a drive device, which has at least one catalyst with an oxygen storage for purifying exhaust gas, wherein upstream of the catalyst, a Vorkatalysatormolmasse a first material and a Vorkatalysatorsauerstoffmolmasse of oxygen are determined. The invention further relates to a drive device.

The method is used to operate the drive device, which is for example part of a motor vehicle or serves to drive the motor vehicle. The drive device has an exhaust-generating device, such as an internal combustion engine, a fuel cell or the like. For purifying the exhaust gas, the catalyst is provided, which has the oxygen storage and is designed in this respect as a storage catalytic converter. The oxygen storage is, for example, as a separate element. Alternatively or additionally, it may also be provided by a catalytically active element of the catalyst.

To operate the drive device, it is advantageous if the lambda value of the exhaust gas is known. Thus, it may be provided, for example, upstream of the catalyst by means of a first lambda probe a first lambda value and downstream of the catalyst by means of a second lambda probe to determine a second lambda value and on this basis the composition of a fuel-air mixture, which is converted or burned in the drive device is set to. Alternatively, it is also possible to measure the first lambda value by means of the first lambda probe and to determine the second lambda value with the aid of a model. However, this is often inaccurate, so that adjusting the composition of the fuel-air mixture is limited possible.

From the prior art, for example, the publication US 5,214,915 which describes a method for simulating the dynamics of an exhaust gas catalytic converter.

It is an object of the invention to provide a method for operating a drive device, which has advantages over the prior art, in particular a more accurate modeling of a Nachkatalysatorlambdawerts, for example, according to the second lambda value described above, allows.

This is achieved according to the invention by a method having the features of claim 1. It is provided that for calculating a Nachkatalysatorlambdawerts a Nachkatalysatorsauerstoffmolmasse is determined by a first reaction equation, the reaction of the oxygen with the first material is taken into account, and that in determining the Nachkatalysatorsauerstoffmolmasse additionally a second reaction equation, the reaction of the first substance with in The oxygen stored in the oxygen storage describes, and a third reaction equation, which describes the entry of oxygen from the exhaust gas into the oxygen storage are taken into account, wherein a reaction rate of the second reaction equation and a reaction rate of the third reaction equation enters a level of the oxygen storage. In principle, therefore, the goal is to determine the post-catalyst lambda value. For this purpose, the pre-catalyst molar mass of the first material and a pre-catalyst oxygen molar mass of oxygen are first determined upstream of the catalyst. For example, a lambda probe, in particular the first lambda probe, is used for this purpose.

Starting from the pre-catalyst molar mass and the pre-catalyst oxygen molar mass, the behavior of the catalyst together with its oxygen storage is modeled. For this purpose, initially three reaction equations are used which at least approximately describe a part of the reactions taking place in the catalyst. Each reaction equation is assigned a specific reaction rate, which in turn is determined from specific variables. Using the reaction equations and the respective reaction rate, the postcatalyst oxygen molar mass, that is to say the molar mass of oxygen which is present downstream of the catalyst, is determined based on the precatalyst mass of the first material and the precatalyst oxygen molar mass. Using this Nachkatalysatorsauerstoffmolmasse can be determined in a simple manner, the Nachkatalysatorlambda value, in particular because the amount of fuel used to operate the drive means per unit time is known.

The post-catalyst lambda value can therefore be determined, for example, according to Brettschneider, for example by means of the relationship

The square brackets represent the concentration in% by volume of the corresponding species, H _{CV represents} the molar ratio of hydrogen to carbon in the fuel used, O _{CV represents} the molar ratio of oxygen to carbon in the fuel. The value C ₁ is fuel-specific. The species additionally used in addition to the (molecular) oxygen in the relationship and / or its molecular weight and consequently the concentration can be determined in any desired manner, preferably by means of one or more reaction equations which are used simultaneously with the reaction equations for the oxygen.

The first reaction equation now directly takes into account the reaction of the oxygen with the first substance. In principle, any substance present in the exhaust gas which reacts with the oxygen can be used as the first substance. For example, hydrogen, in particular molecular hydrogen, is used as the first substance. However, the reaction equations explained in the context of this description are transferable to any other exhaust gas species, provided that the reaction rates and the reaction ratios are adjusted accordingly.

However, the first reaction equation completely disregards the oxygen storage and only describes the immediate reaction of the first substance with the oxygen, which is already present in the exhaust gas, that is already upstream of the catalyst. In order to improve the accuracy of the determined Nachkatalysatorsauerstoffmolmasse, therefore, additionally apply the second reaction equation and the third reaction equation application. The second reaction equation is directed to the fact that the first substance as it flows through the catalyst reacts not only with the oxygen present in the exhaust gas but additionally with the oxygen stored in the oxygen reservoir. Finally, the third reaction equation takes account of the fact that the oxygen present upstream of the catalyst can be introduced into the oxygen reservoir at its throughflows of the catalyst.

Both the second reaction equation and the third reaction equation are so far directed to the oxygen storage. Accordingly, it is necessary that at least the level of the oxygen storage enters into the corresponding reaction rates. The reaction rates of the second reaction equation and the third reaction equation thus exist as a function of the fill level.

beträgt. Der Ausdruck M steht dabei für den ersten Stoff, also die zu oxidierende Spezies. Entsprechend wird deutlich, dass dieser im Rahmen der ersten Reaktionsgleichung molekular, also in der Form M₂, vorliegt.A further embodiment of the invention provides that as the first reaction equation M ₂ + ½O ₂ → M ₂ O is used, wherein a reaction rate of the first reaction equation

is. The term M stands for the first substance, ie the species to be oxidized. Accordingly, it becomes clear that this is molecular, ie in the form of M ₂ , in the context of the first reaction equation.

In the equation for the reaction rate, y stands for the partial pressure or the molar mass of the respective substance, k for the reaction rate present under standard ambient conditions, in particular at a temperature of 300 ° C. for the respective reaction equation, E for the activation energy of the respective reaction equation, R for the universal gas constant, which has, for example, the value R = 8.314 Joule / (K / mol), and T is the absolute temperature of the exhaust gas in the unit Kelvin.

For example, the absolute temperature is determined approximately for the catalyst by taking the temperature immediately upstream of the catalyst, the temperature immediately downstream of the catalyst, or an average of these two temperatures. Overall, it is clear that the reaction rate for the first reaction equation in addition to the molecular weights depends essentially on the temperature of the exhaust gas. Other parameters are not considered.

beträgt. Dem Subskript „sp” ist zu entnehmen, dass die jeweilige Komponente dem Sauerstoffspeicher zugeordnet ist. Der Ausdruck „O_2,sp” deutet also auf molekularen Sauerstoff hin, der in dem Sauerstoffspeicher vorliegt.A further embodiment of the invention provides that as a second reaction equation M ₂ + ½O _{2, sp} → M ₂ O is used, the reaction rate for the second reaction equation

is. The subscript "sp" indicates that the respective component is assigned to the oxygen storage. The term "O _{2, sp} " thus indicates molecular oxygen present in the oxygen reservoir.

The equation of the reaction rate for the second reaction equation, in addition to the variables already described above, in particular the storage capacity of the catalyst, which is referred to as OSC ("Oxygen Storage Capacity"). In addition, the relative level of ROL ("Relative Oxygen Load") of the oxygen storage is taken into account.

The variable k _{ROL, x} describes the influence of the availability of the oxygen stored in the oxygen storage on the reaction, because it can not be arbitrarily quickly added to the oxygen storage or discharged from this. The subscript "x" stands for the species that is mainly considered in the reaction equation, for example "H ₂ ". The size k _{ROL, x} is determined experimentally, for example, so that the actual conditions in the catalyst are described as precisely as possible. Based on this size so can be done a calibration of the reaction rates. It can be seen that, in addition to the temperature, the reaction rate for the second reaction equation additionally takes into account the storage capacity and the level of the oxygen storage.

beträgt. Auch hier finden also neben der Temperatur die Speicherkapazität sowie der Füllstand des Sauerstoffspeichers Anwendung. Bereits die zusätzliche Verwendung der zweiten Reaktionsgleichung und der dritten Reaktionsgleichung verbessert die Ergebnisse für die Nachkatalysatorsauerstoffmolmasse qualitativ deutlich.A preferred embodiment of the invention provides that as a third reaction equation O ₂ → O _{2, sp} is used, the reaction rate for the third reaction equation

is. Again, in addition to the temperature, the storage capacity and the level of the oxygen storage are used. Even the additional use of the second reaction equation and the third reaction equation improves the results for the Nachkatalysatorsauermolmolmasse qualitatively clear.

In a further embodiment of the invention it is provided that in addition a fourth reaction equation is taken into account, which describes the influence of the stored oxygen on a reaction of water contained in the exhaust gas with a second substance, wherein in a reaction rate of the fourth reaction equation enters the level of the oxygen storage , For the application of the fourth reaction equation, it is therefore necessary to determine a Vorkatalysatormolmasse for the water, thus a Vorkatalysatorwassermolmasse and a Vorkatalysatormolmasse the second material. The second substance is for example carbon monoxide. In that regard, the fourth reaction equation describes a water gas shift reaction, which basically with the reaction equation CO + H ₂ O → CO ₂ + H ₂ can be described. In addition, this water gas shift reaction should now be supplemented by taking into account the oxygen stored in the oxygen storage.

beträgt. Mit der genannten Reaktionsgleichung kann der üblicherweise erhebliche Anteil von Wasser in dem Abgas besser berücksichtigt werden. Es wird deutlich, dass die Reaktionsgeschwindigkeit für die vierte Reaktionsgleichung ebenfalls wie die vorstehenden neben der Temperatur auf der Speicherkapazität und der Beladung des Sauerstoffspeichers beruht.A further embodiment of the invention provides that as the fourth reaction equation H ₂ O → H ₂ + O _{2, sp} is used, the reaction rate for the fourth reaction equation

is. With the above reaction equation, the usually significant proportion of water in the exhaust gas can be better taken into account. It is clear that the reaction rate for the fourth reaction equation is also based on the storage capacity and oxygen reservoir loading, as well as the above.

A preferred embodiment of the invention provides that in addition a fifth reaction equation is taken into account, which describes the discharge of stored oxygen into the exhaust gas, wherein the level of the oxygen storage enters into a reaction rate of the fifth reaction equation. The fifth reaction equation is directed to the fact that the oxygen reservoir is all the more prone to the release of oxygen into the exhaust gas the fuller it is, without necessarily having to react with another element.

beträgt. Auf die Bedeutung der fünften Reaktionsgleichung und der entsprechenden Reaktionsgeschwindigkeit wurde bereits vorstehend eingegangen. Auch die hier beschriebene Reaktionsgeschwindigkeit ist neben der Temperatur von der Speicherkapazität und dem Füllstand unmittelbar abhängig.In a further embodiment of the invention, it is provided that as the fifth reaction equation O _{2, sp} → O ₂ is used, the reaction rate for the fifth reaction equation

is. The importance of the fifth reaction equation and the corresponding reaction rate has already been discussed above. The reaction rate described here is directly dependent on the temperature of the storage capacity and the level.

Finally, it can be provided that the fill level is determined by integrating by means of at least one reaction equation, the at least one reaction equation being selected from the second reaction equation, the third reaction equation, the fourth reaction equation and the fifth reaction equation. In carrying out the method, it is of course necessary to recognize the level of the oxygen storage as accurately as possible. By contrast, the storage capacity usually remains essentially constant, although of course a model or measured values can also be used for these.

The level is determined in a particularly simple manner from the at least one reaction equation and its reaction rate, this being done by integrating from the beginning of the process, starting from a starting value. Preferably, at least one reaction equation is used which takes into account the oxygen stored in the oxygen reservoir, for example the second reaction equation, the third reaction equation, the fourth reaction equation or the fifth reaction equation. More preferably, several of these reaction equations, in particular all of these reaction equations, are used to determine the fill level with the highest possible accuracy.

The invention further relates to a drive device, in particular for carrying out the method described above, wherein the drive device for cleaning exhaust gas at least one Catalyst having an oxygen storage, wherein it is provided upstream of the catalyst to determine a Vorkatalysatormolmasse a first material and a Vorkatalysatorsauerstoffmolmasse of oxygen. It is provided that the drive device is designed to determine a Nachkatalysatorlambdawerts Nachkatalysatorsauerstoffmolmasse in which by a first reaction equation, the reaction of oxygen with the first material is taken into account, and that in determining the Nachkatalysatorsauerstoffmolmasse additionally a second reaction equation, the describes a reaction of the first substance with oxygen stored in the oxygen storage, and a third reaction equation, which describes the entry of oxygen from the exhaust gas into the oxygen storage are taken into account, wherein in a reaction rate of the second reaction equation and a reaction rate of the third reaction equation, a level of Oxygen storage enters.

On the advantages of such a drive device or such a method has already been discussed. Both the drive device and the method can be developed according to the above statements, so that reference is made to this extent.

The invention will be explained in more detail with reference to the embodiments illustrated in the drawings, without any limitation of the invention. Showing:

1 Charts in which a pre-catalyst lambda value, a determined and an actual post-catalyst lambda value, a pre-catalyst molar mass of a first material, a precatalyst oxygen molar mass, a post-catalyst molar mass of the first material and a post-catalyst molar mass and an oxygen storage level of a catalyst are plotted over time, taking into account only a first reaction equation becomes,

2 a diagram in which reaction rates of a second and a third reaction equation are shown,

3 Diagrams, which values are analogous to the 1 additionally taking into account the second reaction equation and the third reaction equation,

4 a diagram in which reaction rates for the second, the third and a fourth reaction equation are shown,

5 Diagrams showing values analogous to 1 additionally taking into account a fourth reaction equation,

6 a diagram in which reaction rates for the second reaction equation, the third reaction equation, the fourth reaction equation and a fifth reaction equation over the level of the oxygen storage are shown, and

7 Diagrams, which values are analogous to the 1 show, in addition, the fifth reaction equation is taken into account.

The 1 shows several diagrams in which a course 1 a pre-catalyst lambda value and a history 2 describe a post-catalyst lambda value over time t. A second diagram shows gradients 3 . 4 . 5 and 6 over time t. The history 3 describes a precatalyst oxygen molecular weight, the course 4 a Vorkatalysatormolmasse a first substance, the course 5 a Nachkatalysatorsauerstoffmolmasse and the course 6 a Nachkatalysatormolmasse the first substance. Finally, the third diagram shows a course 7 , which represents a level of oxygen storage of a catalyst over time t. The history 2 is determined using the first reaction equation described above and the corresponding reaction rate.

The 2 shows a diagram in which a course 8th a reaction rate of a second reaction equation as a function of the level of the oxygen storage shows. The history 9 on the other hand, describes the reaction rate of a fourth reaction equation, also on the level.

The 3 shows diagrams analogous to the 1 However, the values shown here were determined on the basis of the first reaction equation, the second reaction equation and the third reaction equation, in each case with the corresponding reaction rates. The additional course 2 ' reflects the actual post-catalyst lambda value. It turns out that the modeled Aftercatalyst lambda value, which depends on the course 2 is already clearly closer to the actual course 2 than this is within the framework of 1 the case was.

The diagram of 4 shows next to the progressions 8th and 9 as they already are from the 2 are known, a course 10 , This describes the reaction rate of a fourth reaction equation over the level of the oxygen storage. The fourth reaction equation essentially represents a water gas shift equation.

The in the 5 diagrams shown correspond to those of 1 and 3 however, the values shown therein are based on the reaction equations 1 to 4 were determined. It shows a further improvement of the results in comparison with those in the 3 shown.

The 6 finally shows a diagram which again the gradients 8th . 9 and 10 shows. In addition, there is a history 11 reproduced, which represents the reaction rate of a fifth reaction equation. The fifth reaction equation describes the transition of oxygen from the oxygen storage into the exhaust gas.

The results with consideration of the reaction equations 1 to 5 are in the diagrams of the 7 played. It turns out that the course 2 with the course 2 ' matches. This means that taking into account the reaction equations 1 to 5 in the modeling of the Nachkatalysatorsauerstoffmolmasse and thus the calculation of the Nachkatalysatorlambda value results are achieved, which reflect the theoretical results with good accuracy.

LIST OF REFERENCE NUMBERS

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QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5214915 [0004]

Claims (10)

A method of operating a propulsion device having at least one catalyst with oxygen storage for purifying exhaust gas, wherein a precursor molecular mass of a first material and a precatalyst oxygen molecular weight of oxygen are determined upstream of the catalyst, characterized in that an aftercatalyst oxygen molecular weight is determined by calculating a post-catalyst lambda value by by means of a first reaction equation, the reaction of the oxygen with the first substance is taken into account, and in determining the postcatalyst oxygen molecular weight, additionally a second reaction equation which describes a reaction of the first substance with oxygen stored in the oxygen reservoir, and a third reaction equation which describes the entry of Oxygen from the exhaust gas into the oxygen storage describes to be considered, wherein in a reaction rate of the second reaction equation and a Reaktionsge Speed of the third reaction equation enters a level of oxygen storage. A method according to claim 1, characterized in that as the first reaction equation M ₂ + ½O ₂ → M ₂ O is used, wherein a reaction rate of the first reaction equation

is. Method according to one of the preceding claims, characterized in that as a second reaction equation M ₂ + ½O _{2, sp} → M ₂ O is used, the reaction rate for the second reaction equation

is. Method according to one of the preceding claims, characterized in that as a third reaction equation O ₂ → O _{2, sp} is used, the reaction rate for the third reaction equation

is. Method according to one of the preceding claims, characterized in that in addition a fourth reaction equation is taken into account, which describes the influence of the stored oxygen on a reaction of water contained in the exhaust gas with a second substance, wherein in a reaction rate of the fourth reaction equation, the level of the oxygen storage received. Method according to one of the preceding claims, characterized in that as a fourth reaction equation H ₂ O → H ₂ + O _{2, sp} is used, the reaction rate for the fourth reaction equation

is. Method according to one of the preceding claims, characterized in that in addition a fifth reaction equation is taken into account, which describes the discharge of stored oxygen into the exhaust gas, which enters into a reaction rate of the fifth reaction equation, the level of the oxygen storage. Method according to one of the preceding claims, characterized in that as the fifth reaction equation O _{2, sp} → O ₂ is used, the reaction rate for the fifth reaction equation

is. Method according to one of the preceding claims, characterized in that the level is determined by integrating by means of at least one reaction equation, wherein the at least one reaction equation from the second reaction equation, the third reaction equation, the fourth reaction equation and the fifth reaction equation is selected. Drive device, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device for purifying exhaust gas having at least one catalyst with an oxygen storage, wherein it is provided upstream of the catalyst to determine a Vorkatalysatormolmasse a first material and a Vorkatalysatorsauerstoffmolmasse of oxygen characterized in that the drive means is adapted to determine a Nachkatalysatorlambdawerts a Nachkatalysatorsauerstoffmolmasse by a first reaction equation, the reaction of the oxygen with the first material is taken into account, and that in determining the Nachkatalysatorsauerstoffmolmasse additionally a second reaction equation, the reaction of the first substance with oxygen stored in the oxygen storage, and a third reaction equation describing the entry of oxygen from the A Be considered in the oxygen storage, are considered, wherein in a reaction rate of the second reaction equation and a reaction rate of the third reaction equation enters a level of oxygen storage.

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