Method of recognizing deactivation of an exhaust gas catalytic converter

Abstract

A method of recognizing deactivation of an exhaust gas catalytic converter is disclosed. For this purpose, coverage of storage sites of the exhaust gas catalytic converter with rich gas components is modeled (60) and the deactivation is recognized from a proportion of the occupied storage sites in a total number of storage sites.

Claims

1. A method of controlling an internal combustion engine with an exhaust gas catalytic converter (20), the method comprising: modelling occupation of storage sites of the exhaust gas catalytic converter (20) with rich gas components; recognizing deactivation from a proportion of the occupied storage sites in a total number of storage sites when a gradient of the proportion of the occupied storage sites at least for a settable period of time exceeds a gradient threshold (42); and initiating reactivation by actuation of the internal combustion engine, wherein, by means of an input lambda probe upstream of the exhaust gas catalytic converter and an input emission model (50) of the exhaust gas catalytic converter (20), proportions by mass of oxygen, hydrogen, water and the rich gas components of the exhaust gas upstream of the exhaust gas catalytic converter are ascertained (50), wherein the proportions by mass are ascertained without the use of an output lambda probe downstream of the catalytic converter.

2. The method according to claim 1, wherein, for the reactivation, the internal combustion engine is actuated such that it produces a lean exhaust gas.

3. The method according to claim 1, wherein the reactivation is ended when the proportion of the occupied storage sites goes below a given threshold or the output lambda probe downstream of the exhaust gas catalytic converter (20) indicates a lean exhaust gas having a lambda value of more than 1.

4. The method according to claim 1, wherein the modeling (60) takes account of adsorption of gaseous rich gas components at the storage sites and oxidation of adsorbed rich gas components.

5. The method according to claim 1, wherein the modeling (60) takes account of occupation of the storage sites of the exhaust gas catalytic converter with oxygen.

6. The method according to claim 5, wherein the occupation of the storage sites of the exhaust gas catalytic converter with oxygen is ascertained by taking account of adsorption of gaseous oxygen at the storage sites, oxidation of gaseous rich gas components with adsorbed oxygen, oxidation of gaseous hydrogen with adsorbed oxygen, and breakdown of gaseous water and adsorption of the oxygen released.

7. The method according to claim 1, wherein the modeling (60) involves dividing the exhaust gas catalytic converter (20) into multiple zones (21, 22) in axial succession.

8. A non-transitory, computer-readable storage medium containing instructions which when executed on a computer cause the computer to recognize deactivation of an exhaust gas catalytic converter and to control an internal combustion engine by modelling occupation of storage sites of the exhaust gas catalytic converter (20) with rich gas components; recognizing deactivation from a proportion of the occupied storage sites in a total number of storage sites when a gradient of the proportion of the occupied storage sites at least for a settable period of time exceeds a gradient threshold (42); and initiating reactivation by actuation of the internal combustion engine, wherein, by means of an input lambda probe upstream of the exhaust gas catalytic converter and an input emission model (50) of the exhaust gas catalytic converter (20), proportions by mass of oxygen, hydrogen, water and the rich gas components of the exhaust gas upstream of the exhaust gas catalytic converter are ascertained (50), wherein the proportions by mass are ascertained without the use of an output lambda probe downstream of the catalytic converter.

9. An electronic control device (30) set up to recognize deactivation of an exhaust gas catalytic converter (20) and to control an internal combustion engine, the electronic control device comprising: an electronic processor configured to model occupation of storage sites of the exhaust gas catalytic converter (20) with rich gas components; recognize deactivation from a proportion of the occupied storage sites in a total number of storage sites when a gradient of the proportion of the occupied storage sites at least for a settable period of time exceeds a gradient threshold (42); and initiate reactivation by actuation of the internal combustion engine, wherein, by means of an input lambda probe upstream of the exhaust gas catalytic converter and an input emission model (50) of the exhaust gas catalytic converter (20), proportions by mass of oxygen, hydrogen, water and the rich gas components of the exhaust gas upstream of the exhaust gas catalytic converter are ascertained (50), wherein the proportions by mass are ascertained without the use of an output lambda probe downstream of the catalytic converter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) One working example of the invention is shown in the drawings and is elucidated in detail in the description that follows.

(2) FIG. 1 shows a schematic of an exhaust gas catalytic converter, the deactivation of which can be recognized by means of a working example of the method according to the invention.

(3) FIG. 2 shows a flow diagram of a working example of the method according to the invention.

DETAILED DESCRIPTION

(4) An internal combustion engine 10, in the form of a gasoline engine, is shown in FIG. 1. This emits an exhaust gas in its exhaust gas conduit 11. In the exhaust gas conduit 11 there is disposed an exhaust gas catalytic converter 20 in the form of a three-way catalytic converter. In one working example of the method according to the invention, this is divided into two zones 21, 22 that follow successively along the longitudinal axis of the exhaust gas catalytic converter 20 in the direction of the exhaust gas stream 23. An electronic control device 30 controls the internal combustion engine 10. It receives sensor signals of a first lambda probe 31 which is arranged upstream of the exhaust gas catalytic converter 20 in the exhaust gas conduit 11, and a second lambda probe 32 which is arranged downstream of the exhaust gas catalytic converter 20.

(5) After a start 40 of a working example of the method according to the invention, there is a test 41 as to whether a proportion of the storage sites of the exhaust gas catalytic converter 20 that is occupied by rich gas components exceeds a proportion threshold. This proportion threshold in the present working example is 20%. In addition, there is a test 42 as to whether a low-pass-filtered gradient of the proportion, at least for a settable period of time which, in the present working example, is two seconds, exceeds a gradient threshold which, in the present working example, is 2%/s. If the result of one of the two tests 41, 42 is that one of these conditions is satisfied, deactivation of the exhaust gas catalytic converter 20 is recognized 43 and a measure for reactivation thereof is initiated. For this purpose, the electronic control device 30 actuates the internal combustion engine 10 in such a way that it produces a lean exhaust gas. During this reactivation measure, two further tests 44, 45 run continuously. The third test 44 examines whether the occupation of the storage sites of the exhaust gas catalytic converter 20 with rich gas components has gone below a threshold which, in the present working example, is 5%. The fourth test 45 examines whether the second lambda probe 32 is indicating a lean exhaust gas having a lambda value of more than 1. If at least one of these two conditions is satisfied, the reactivation measure is ended 46, and the internal combustion engine 10 is actuated again according to its conventional operating strategy. Thereafter, the exhaust gas catalytic converter 20 is monitored again for deactivation by means of the first two tests 41, 42.

(6) In order to ascertain the occupation of storage sites of the exhaust gas catalytic converter 20 with rich gas components, an input emission model 50 of the exhaust gas catalytic converter 20 is first created. The signal from the first lambda probe 31, by means of characteristics, is used to ascertain the proportions by mass w.sub.O.sub.2 of oxygen, w.sub.H.sub.2 of hydrogen, w.sub.H.sub.2.sub.O of water, and the proportion by mass of the rich gas components. There follows a description of the modeling in simplified form solely with reference to the rich gas component carbon monoxide, and so only the proportion by mass w.sub.CO thereof from the input emission model is used. Using these proportions by mass, the occupation of the storage sites of the exhaust gas catalytic converter 20 with rich gas components is then modeled 60. This takes account of six chemical reactions. Gaseous oxygen O.sub.2 is adsorbed at unoccupied storage sites * according to formula 1:

(7) $\begin{array}{cc}{O}_2+2[*]\stackrel{r_{O_2}^{\mathrm{ads}}}{.fwdarw.}2\left[O\right]& \left(\mathrm{Formula}1\right)\end{array}$

(8) Adsorbed components are shown in square brackets in formula 1 and all subsequent formulae. The reaction rate r.sub.O.sub.2.sup.ads of the reaction according to formula 1 can be calculated according to formula 2:
r.sub.O.sub.2.sup.ads=k.sub.1.Math.w.sub.O.sub.2.Math.Θ.sub.[*].sup.2  (Formula 2)

(9) k.sub.1 here denotes the collision factor (rate constant) of the reaction. Just like all the collision factors mentioned in the formulae that follow, this can be represented by an Arrhenius approach. Θ.sub.[*] denotes the proportion of unoccupied storage sites. In all the formulae below, proportions of the storage sites are referred to as Θ.sub.x, where x may represent unoccupied storage sites ([*]); oxygen-occupied storage sites ([O]) or carbon monoxide-occupied storage sites ([CO]).

(10) Gaseous carbon monoxide CO is oxidized with stored oxygen according to formula 3, where the reaction rate r.sub.CO thereof is a function of the collision factor k.sub.2 of the reaction from formula 4:

(11) $\begin{array}{cc}\mathrm{CO}+\left[O\right]\stackrel{r_{\mathrm{CO}}}{.fwdarw.}[*]+{\mathrm{CO}}_2& \left(\mathrm{Formula}3\right)\\ r_{\mathrm{CO}}=k_2.Math.w_{\mathrm{CO}}.Math.{\Theta }_{\left[O\right]}& \left(\mathrm{Formula}4\right)\end{array}$

(12) Gaseous hydrogen H.sub.2 is oxidized with stored oxygen according to formula 5, where the reaction rate r.sub.H.sub.2 of this reaction is found as a function of its collision factor k.sub.3 from formula 6:

(13) $\begin{array}{cc}{H}_2+\left[O\right]\stackrel{r_{H_2}}{.fwdarw.}[*]+H_{2}O& \left(\mathrm{Formula}5\right)\\ r_{H_2}=k_3.Math.w_{H_2}.Math.{\Theta }_{\left[O\right]}& \left(\mathrm{Formula}6\right)\end{array}$

(14) The breakdown of gaseous water and the adsorption of the oxygen released proceed according to formula 7, where the reaction rate r.sub.H.sub.2.sub.O.sup.ads of this reaction is found, taking account of its collision factor k.sub.4, from formula 8:

(15) $\begin{array}{cc}{H}_{2}O+[*]\stackrel{r_{H_{2}O}^{\mathrm{ads}}}{.fwdarw.}\left[O\right]+H_2& \left(\mathrm{Formula}7\right)\\ r_{H_{2}O}^{\mathrm{ads}}=k_4.Math.w_{H_{2}O}.Math.{\Theta }_{[*]}^2& \left(\mathrm{Formula}8\right)\end{array}$

(16) Gaseous carbon monoxide is adsorbed according to formula 9, where the reaction rate r.sub.CO.sup.ads of this reaction is found with the collision factor k.sub.5 from formula 10:

(17) $\begin{array}{cc}\mathrm{CO}+\eta [*]\stackrel{r_{\mathrm{CO}}^{\mathrm{ads}}}{.fwdarw.}\left[\mathrm{CO}\right]& \left(\mathrm{Formula}9\right)\\ r_{\mathrm{CO}}^{\mathrm{ads}}=k_5.Math.w_{\mathrm{CO}}.Math.{\Theta }_{[*]}& \left(\mathrm{Formula}10\right)\end{array}$

(18) Adsorbed carbon monoxide is oxidized with gaseous oxygen according to formula 11 with a reaction rate r.sub.CO.sup.oxi which can be calculated taking account of the collision factor k.sub.6:

(19) $\begin{array}{cc}\left[\mathrm{CO}\right]+\frac{1}{2}{O}_2\stackrel{r_{\mathrm{CO}}^{\mathrm{oxi}}}{.fwdarw.}{\mathrm{CO}}_2+\eta [*]& \left(\mathrm{Formula}11\right)\\ r_{\mathrm{CO}}^{\mathrm{oxi}}=k_6.Math.w_{O_2}.Math.{\Theta }_{\left[\mathrm{CO}\right]}& \left(\mathrm{Formula}12\right)\end{array}$

(20) Since carbon monoxide and other rich gas components can simultaneously occupy multiple storage sites, the number of occupied storage sites in the formulae 9 and 11 is denoted by η.

(21) The formulae 1 to 12 result in the two coupled differential equations according to the formulae 13 and 14:

(22) $\begin{array}{cc}\frac{\partial {\Theta }_{\left[O\right]}}{\partial t}=2.Math.r_{O_2}^{\mathrm{ads}}-r_{\mathrm{CO}}-r_{H_2}+r_{H_{2}O}^{\mathrm{ads}}& \left(\mathrm{Formula}13\right)\\ \frac{\partial {\Theta }_{\left[\mathrm{CO}\right]}}{\partial t}=\eta .Math.\left(r_{\mathrm{CO}}^{\mathrm{ads}}-r_{\mathrm{CO}}^{\mathrm{oxi}}\right)& \left(\mathrm{Formula}14\right)\end{array}$

(23) If the proportions by mass w.sub.x of the exhaust gas components from the input emission model 50 are known, these two differential equations can be solved in the model 60, and the relationship that the number of unoccupied storage sites corresponds to the number of available storage sites reduced by the number of storage sites occupied by oxygen and by carbon monoxide can be used to model the number of storage sites occupied by carbon monoxide as rich gas component. In the present working example, this is done in such a way that, in a first calculation step 61, the calculations for the first zone 21 are first conducted, then, in a second calculation step 62, the calculation for the second zone 22 is conducted, and then the results of the two calculation steps 61, 62 are combined 63, in order thus to obtain the overall proportion of the storage sites of the exhaust gas catalytic converter 20 occupied by rich gas components.

(24) The input emission model 50 is adapted to remedy uncertainties by further taking account of the sensor signal of the second lambda probe 32 in the input emission model 59. The model 60 of the occupation of the storage sites can also be adapted by taking account of the signal of the lambda probe 32 in the model 60.