FR2846040A1 - Controlling the nitrogen oxide storage catalyst of an engine comprises abandoning switchover from one lean burn regime to another in favor of early regeneration if a regeneration request is expected within a predetermined time - Google Patents

Abstract

Controlling the nitrogen oxide (NOx) storage catalyst (18) of an internal combustion engine (10) comprising an engine control unit (22) and a NOx sensor (20) downstream from the catalyst comprises switching the engine from one lean burn regime to another lean burn regime depending on the expected NOx storage capacity of the catalyst, the switchover being abandoned in favor of early regeneration if there is reason to expect a regeneration request within a predetermined time.

Description

The invention relates to a method for controlling

  an NOx accumulation catalyst of an internal combustion engine, comprising an NOx sensitive measuring device placed downstream of the NOx accumulation catalyst, as well as an engine control apparatus.

  It is known to purify the exhaust gas catalytically for the post-treatment of exhaust gases of internal combustion engines. For this purpose, the exhaust gases pass through at least one catalyst, which converts one or more harmful components of the exhaust gases into products which are harmless or less polluting to the environment. Different types of catalysts are known. Oxidation catalysts promote the oxidation of impregnated hydrocarbons (HC) and carbon monoxide (CO), while catalysts of

  reduction contribute to a reduction of the nitrogen oxides (NOx) contained in the exhaust gas. 3-way catalysts are also used in order to simultaneously catalyze the conversion of the three components (HC, CO, NOx) mentioned above.

  Accumulation catalysts are furthermore known, for example NOx accumulation catalysts. These are used for the purification of exhaust gases of internal combustion engines which, for the purpose of optimizing consumption, operate, at least temporarily, in a poor operating mode, namely with gases. With these marginal conditions, NOX nitrogen oxides can not be fully converted to environment-neutral nitrogen with conventional 3-way catalysts. As a remedy, the above-mentioned NOx accumulation catalysts are arranged in the exhaust gas channels of internal combustion engines which, in lean phases, store NOx as the nitrate. During storage of NOX in poor exhaust gas, increasing saturation of the NOx accumulation catalyst occurs, so that nitrogen oxides pass more and more. As soon as the cumulative mass of NOx or the concentration of NOx downstream of the accumulation catalyst, or the mass of NOx accumulated in the accumulation catalyst, exceeds

  threshold values that can be predetermined, a regeneration of NOx is triggered. For this purpose, the low engine speed (SCH mode regime or HMM poor homogeneous diet) is interrupted in favor of a homogeneous substoichiometric regime (HOMREG).

  Each switching of the regime, both between the two modes of lean diet (SCH or HMM) and between the lean diet and the homogeneous stoichiometric regime (HOMST) or the homogeneous substoichiometric regime (HOMREG), leads to a brief phase. over-consumption of fuel compared to the state set in the target operating regime, inter alia, because the air path reacts much more inert to changes in the set-point than the fuel and fuel paths. ignition can adapt quickly. Depending on the operating point, this transition phase lasts between 0.2 and 3 seconds. In the transition phase, each operating regime switching is also associated with some increase in gross emission (HC, CO, NOx). For the optimized adaptation to emissions of the vehicle, a fixed threshold value, which defines the NOx gross emissions that charge the NOx accumulation catalyst in a lean regime, is predetermined according to the state of the art for the low-end regime. . If this threshold value is exceeded, the

  HOMST is asked which, depending on the filling level of the NOx accumulation catalyst, is first preceded by a regeneration of NOx (HOMREG).

  According to the state of the art, this threshold value is a fixed value over the entire NOx accumulation phase. However, this method also has disadvantages, since the mass flow of NOx arriving, which can be accumulated with a predetermined effective accumulation rate of 99 A, for example, decreases with the accumulation of NOx. On the other hand, when the NOx accumulation catalyst is already partially charged, changes during the lean phase to another lean operating regime are not energy and / or emission rational if they are not can not be maintained thereafter for a sufficiently long time interval without regeneration of NOX. The aforementioned drawbacks lead to greater fuel consumption, and to a higher

  higher emission of harmful substances.

  The object of the invention therefore is to provide a method for the control of a NOx accumulation catalyst, with which a change during a lean regime phase to another poor operating regime (HMM - * SCH or SCH -> HMM) is only allowed if it can be maintained for a sufficiently long time interval without regeneration of NOX, so as not to cause disadvantages in terms of

  fuel and emissions of harmful substances.

  According to the method according to the invention, it is provided that an operating mode switching during a low speed phase on another poor operating regime (HMM - * SCH or SCH -> HMM) is made dependent on the expected NOx accumulation capacity of the NOx accumulation catalyst, an operating regime switching being to be suppressed

  for the benefit of premature NOx regeneration if there is reason to expect a demand for NOx regeneration in the "energy amortization time interval", or a time interval can be predetermined.

  According to a first variant of the process according to the invention, the following is provided: the mass of NOX accumulated in the NOx accumulation catalyst and / or the cumulative past mass of NOx and / or the concentration of NOx in downstream of the accumulation catalyst are determined in a first step. This can be done in the known manner, preferably by means of a NOx sensor

  disposed downstream of the accumulation catalyst.

  - It is then proceeded to a request for change of

operating regime.

  Following this request, the mass flow rate of NO upstream of the accumulation catalyst is first suitably determined in the target operating regime. This is usually done by models stored in a device

engine control.

  - Then, and after switching to the target operating regime, the remaining residual duration20 of the lean phase in the

  The target operation until initiation of NOx regeneration is calculated using the data determined in the first step, and a criterion for evaluating the catalyst accumulation efficiency of the catalyst. NOx accumulation.

  - The criterion for the evaluation of the accumulation efficiency may consist of a known NOx accumulation model. This contains at least one of the following input parameters: mass flow of NOx upstream of the accumulation catalyst NOX concentration upstream of the accumulation catalyst mass flow of the exhaust gas catalyst temperature - catalyst volume - geometric area - rate of conversion or accumulation depending on precious metals and the nature of accumulated NOx. Other parameters, not mentioned, may furthermore

to be entered in this model.

  The starting parameter of the NOx accumulation model is at least the effective accumulation rate based on the already accumulated NOx mass, and / or the catalyst temperature, and / or the mass flow rate of the exhaust gases and or the mass flow rate of NOx upstream of the accumulation catalyst.

  After determining the remaining time, a query is made as to whether the residual duration of the lean phase is below a threshold value that can be predetermined according to an operating point.

  If the residual duration of the low-power phase is less than the threshold value, the poor target operating mode is eliminated in favor of premature triggering of the regeneration of

  NOx, and the regeneration of NOx is required.

  If the residual duration of the low-power phase is greater than the threshold value, the

  Poor target operation is allowed.

  Alternatively, the method according to the invention can also be modified as follows:

  The first two steps of the aforementioned process variant remain unchanged.

  A direct interrogation is then made as to whether threshold values can be predetermined for the mass of accumulated NOx and / or for the cumulative mass of NOx and / or for the NOx concentration downstream of the catalyst.

accumulators are exceeded.

  - If the threshold values for triggering a regular regeneration are practically reached, at least 80%, optimally at least 90%, ideally at least 95%, which gives 5 threshold values for premature NOx regeneration, it is to be expected after switching to the target operating regime at consecutive NOx regeneration, so fast that switching is not rational for energy reasons. This is why premature regeneration of NOx is required when

  at least one of the threshold values is exceeded.

  - When all threshold values are not

  For premature NOx regeneration, the target operating regime is allowed.

  The advantage of this variant of the process is that the calculation cost is significantly reduced, since it is possible, in particular, to give up

to the expensive accumulation model.

  Another variant of the process according to the invention comprises the following steps: the first three steps of the process variant

  described in the first place remain unchanged.

  The mass flow rate of NOx determined during the third step upstream of the accumulation catalyst in the target operating regime is correlated

  with at least one coefficient, which is multiplied with predetermined threshold values for regular initiation of NOx regeneration. These values represent threshold values for premature NOx regeneration.

  - During a subsequent interrogation, it is checked whether at least one of the threshold values for a premature regeneration of NOX is exceeded. If this is the case, premature regeneration of NOx is required and the regime switching of

operation is deleted.

  - If all threshold values are not reached for premature NOX regeneration, the

target operation is allowed.

  The advantage of the third variant of the method over the second lies in the more precise adaptation of the suppression of the switching to the target operating regime, implying only a small over-torque.

as regards calculation.

  With the method according to the invention, it is advantageously obtained that regime mode switching from one lean operating mode to another is only allowed if it is indeed efficient from

  point of view of consumption and emissions.

  Other preferred arrangements of the invention result from the other features indicated in the

following the document.

  The invention is described below in greater detail by means of exemplary embodiments shown in the accompanying drawings, in which: FIG. 1 is a basic representation of an internal combustion engine with a purification plant a downstream exhaust gas in which an NOX accumulation catalyst is disposed; Figure 2 is a block diagram of the method according to the invention; Figure 3 is a block diagram of the method according to the invention of a second variant; and Figure 4 is a block diagram of the method according to the invention of a third variant. An exhaust gas installation 12 is arranged downstream of the internal combustion engine 10 shown in FIG. 1. The exhaust gas installation 12 comprises an exhaust gas channel 14 in which a pre-catalyst 16 , as well as a large volume NOx accumulation catalyst 18, are arranged near the engine. In addition to the pre-catalyst 16 and the NOX accumulation catalyst 18, the exhaust gas channel 14 usually comprises different gas and / or temperature sensors for the regulation of the combustion engine.

  internal 10, which are not represented here.

  Only one NOx sensor 20, which is arranged downstream of the NOx accumulation catalyst 18, and which delivers at least one signal relating to the NOx content in the exhaust gases, is represented by way of example at the

  FIG. 1. The signal is transmitted to a control apparatus 22 of the engine, in which the latter is used for controlling the operating speeds of the internal combustion engine 10. A control unit 24 is furthermore integrated into the engine. control apparatus 22 of the engine.

  By means of the control apparatus 22 of the motor and the control unit 24, at least one operating parameter of the internal combustion engine 10, in particular a

  air / fuel mixture to be fed (combustion lambda) 20 is influenced as a function of the signal of the NOX sensor 20.

  FIG. 2 represents a first variant of the method according to the invention for controlling a NOx accumulation catalyst 18. During a first step S100, the accumulated mass of NOx and / or the cumulative mass passed NOx and / or the NOx concentration downstream of the NOX accumulation catalyst 18 are first determined by the NOx sensor 20 downstream of the NOx accumulation catalyst 18. If a change of regime request of operation of the internal combustion engine 10 occurs during

  In the following step S102, the mass flow of NOx upstream of the NOx accumulation catalyst 18 in the target operating regime is first determined in step S104 using models stored in the apparatus. control 22 of the engine.

  Then, and after switching to the target operating regime, the expected residual duration of the lean phase in the target operating regime until the initiation of a NOx regeneration is calculated in step S106, at the using data determined during the first step S100, and a criterion for evaluating the accumulation efficiency of the NOX accumulation catalyst 18, the criterion for evaluating the effectiveness accumulator consisting of a NOx accumulation pattern 10 stored in step S108. In a next step S110, a query is made as to whether the determined residual duration of the lean phase is below a threshold value that can be predetermined as a function of an operating point. If the determined residual duration is less than this threshold value, the poor target operating regime is eliminated in a step S112 in favor of premature initiation of NOx regeneration. Instead, and insofar as the determined residual duration is greater than the threshold value, the operating mode switching is

  allowed during a step S114.

  A second variant of the method according to the invention is illustrated by the block diagram of FIG. 3. The first two steps S200, S202 correspond to the steps S100, S102 according to FIG. 2. The NOX data are determined correspondingly to FIG. during step S200. In the next step S202, a change in the operating speed of the internal combustion engine 10 is again requested. An inquiry is then made during a step S204 as to whether predetermined threshold values for premature regeneration of NOx are exceeded with respect to accumulated NOx mass and / or past cumulative NOx mass and / or NOx concentration downstream of the accumulation catalyst 18. If at least one

  threshold values are exceeded, a premature regeneration of NOX is requested during a step S206.

  Otherwise, the target operating regime is allowed in step S208, if none of the threshold values is reached. With regard to the third variant of the method according to FIG. 4, the first three steps S100, S102, S104 of the method according to FIG. 2 are repeated. Thus, NOx data is again determined initially in step S300. If, during a subsequent step S302, a request is made for a change in the operating speed of the internal combustion engine 10, the mass flow of NOx upstream of the NOx accumulation catalyst 18 in the target operating regime is determined in step S304. The determined mass flow rate of NOx is then correlated during a step S306 with at least one coefficient, which is multiplied by the threshold values for the regular initiation of the NOx regeneration, which are predetermined during the step S308. The results of the multiplication, namely the threshold values for a premature regeneration of NOx, then constitute the input criterion for a step S310. In step S310, it is questioned whether the threshold values for the premature regeneration of NOx are exceeded. If one

  at least threshold values are exceeded, premature regeneration of NOX is requested during a step S312. Otherwise, the target operating regime is allowed in step S314, if none of the threshold values are reached.

  Although the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be readily understood by those skilled in the art that changes in form and detail can be made.

  without departing from the spirit or scope of the invention.

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LIST OF DIGITAL REFERENCES

12 5 14

16 18 20 22 10 24

  Internal combustion engine Exhaust gas system Exhaust gas channel Pre-catalyst NOx accumulation catalyst NOx sensor Motor control unit Control unit so00 S102 S104 S106 S108 silo 20 S112 S114 S200 S202

S204 S206 30

  S208 Determination of NOX data Request for a change of operating mode Determination of the NOx mass flow rate Determination of the residual duration of the lean phase Storage of the NOx accumulation model Query Request for a NOx regeneration without switching of NOx operating regime Authorization of operating mode switching Determination of NOx data Request for a change of operating mode Query Request for NOx regeneration without operating mode switching Authorization of operating mode switching

S300 35 S302

  Determination of NOx data Request for a change in the operating speed of S304 Determination of NOX mass flow rate S306 Determination of threshold values for premature NOX regeneration S308 Prescription of threshold values for regular S310 NOX regeneration Inquiry S312 Request NOx regeneration without operating mode switching S314 Authorization of operating regime switching

Claims (13)

  A method for controlling an NOX accumulation catalyst (18) of an internal combustion engine (10), comprising an NOx-sensitive measuring device (20) located downstream of the accumulation catalyst NOX (18), as well as an engine control unit (22), characterized in that, during a lean phase, the operating speed of the internal combustion engine (10) is switched at another speed. of lean operation is rendered dependent on the expected NOx accumulation capacity of the NOX accumulation catalyst (18), an operating regime switching being to be suppressed in favor of premature NOx regeneration if applicable to expect a demand for NOx regeneration within a predetermined time interval. 2. Method according to claim 1, characterized in that - the mass of NOx accumulated in the NOx accumulation catalyst (18) and / or the cumulative mass of NOx and / or the NOx concentration downstream of the catalyst of NOx (18) are initially determined, - then a request is made to change the operating speed of the internal combustion engine (10), - following this request, the mass flow of NOX upstream of the combustion engine The accumulation (18) is first determined in the target operating regime, after switching to the target operating regime, the expected residual duration of the lean phase in the target operating regime until a regeneration of NOx is calculated using the accumulated NOX mass in the NOx accumulation catalyst (18) and / or the cumulative mass of NOx and / or the NOX concentration downstream of the accumulation catalyst NO x (18) determined initially, and a criterion for evaluating the accumulation efficiency of the NOx accumulation catalyst (18), and - after the determination of the residual duration, a interrogation takes place to determine whether the residual duration of the lean phase is below a threshold value that can be predetermined according to an operating point, - if the residual duration of the lean phase is below the threshold value, the poor target operating regime is suppressed in favor of premature initiation of NOx regeneration, and the regeneration of NOx is required, or - if the residual duration of the lean regime phase   is greater than the threshold value, the poor target operating regime is allowed.   3. Method according to claim 2, characterized in that the criterion for the evaluation of the accumulation efficiency consists of a model of NO accumulation, the starting parameter of which is at least 25%. effective accumulation based on already accumulated NOx mass, and / or catalyst temperature, and / or exhaust mass flow rate and / or NOx mass flow rate upstream of the accumulation catalyst (18) . 4. Method according to claim 2 or 3, characterized in that the criterion for the evaluation of the accumulation efficiency consists of a NOx accumulation model containing at least one of the input parameters following: mass flow of NOX upstream of the accumulation catalyst; - NOx concentration upstream of the accumulation catalyst; mass flow rate of the exhaust gas - temperature of the catalyst; - volume of the catalyst; - geometric area - conversion or accumulation rate depending on the   precious metals and the nature of accumulated NOx.   5. Process according to claim 1, characterized in that - the mass of NOx accumulated in the NOx accumulation catalyst (18) and / or the cumulative mass of NOx and / or the NOx concentration downstream of the catalyst (18) are initially determined, - a change in the operating speed of the internal combustion engine (10) is then made, - threshold values for premature regeneration of NOx are at least part of them, which may, after switching to the target operating mode, give rise to a regeneration of NOx after a period of time which can be predetermined, so that switching is not possible. not rational for energy reasons, - premature regeneration of NOx is required when at least one threshold value is exceeded, or - when all threshold values are not   For premature NOx regeneration, the target operating regime is allowed.   6. Method according to claim 5, characterized in   that the threshold values for premature NOx regeneration substantially correspond to predetermined threshold values for regular NOX regeneration.   7. Method according to claim 5, characterized in that the threshold values for a premature regeneration of NOx correspond at least to 80 t to predetermined threshold values for regular NOx regeneration. 8. Process according to claim 5, characterized in   the threshold values for premature NOx regeneration correspond at least to 90% to predetermined threshold values for regular NOx regeneration.   9. Process according to claim 5, characterized in   the threshold values for premature NOx regeneration correspond at least to 95% to predetermined threshold values for regular NOx regeneration.   10. Process according to claim 1, characterized in that - the mass of NO, accumulated in the NO accumulation catalyst, (18) and / or the cumulative past mass of NOx and / or the NOx concentration downstream of the accumulation catalyst (18) are determined in a first step, then a request is made for a change of operating regime, - following this request, the mass flow of NOX upstream of the accumulation catalyst (18) is first determined in the target operating regime, - the mass flow of NOx upstream of the accumulation catalyst (18) determined in the target operating mode is correlated with at least one factor, which is multiplied by values of predetermined threshold for the regular initiation of the NOx regeneration, which gives threshold values for premature regeneration of NOx, their at least partial overshoot being able to give rise, after the switching to the firing regime; target operation, at a regeneration of NO, after a period of time that can be predetermined, so that switching is not rational for energy reasons, - a premature regeneration of NOx is required when at minus a threshold value is exceeded, or - when all threshold values are not reached for premature NOx regeneration, the   target operating regime is allowed.   11. Process according to any one of   Claims 2 to 10, characterized in that the mass of NOX accumulated in the NO accumulation catalyst, (18) and / or the cumulative mass of NOx and / or the concentration of NOx downstream of the accumulation catalyst 15 (18) are determined by means of the measuring device   NOx sensitive downstream of the catalyst NOx accumulation (18).   12. Process according to claim 11, characterized   in that the NOx sensitive measuring device is a NOx sensor (20).   13. Process according to any one of   Claims 2 to 4, 10 to 12, characterized in that, in the target operating mode, the mass flow rate of NO upstream of the accumulation catalyst (18) is determined by a model stored in the control apparatus (22) engine.