FR2848601A1 - METHOD AND DEVICE FOR MONITORING AND CONTROLLING A CATALYST OF A MOTOR VEHICLE - Google Patents

Abstract

In a method for monitoring and regulating a catalyst (2) of an internal combustion engine (15) of a motor vehicle, the sorption processes and the desorption processes of the different compounds of the gases exhaust in the catalyst (2) are calculated for the calculation of its state of accumulation by algorithms which are based on the principle of minimum production of entropy (PME), the calculation being carried out using a characteristic emission field predetermined internal combustion engine (15), and the thus calculated state of accumulation of the catalyst (2), relating to the different compounds of the exhaust gases, being used for optimizing or regulating the speed of the combustion engine internal (15) with regard to its consumption.

Description

The invention relates to a method and a device.

  intended for monitoring and regulating a catalyst of an internal combustion engine of a motor vehicle, as well as the use of determined state quantities 5 of the catalyst for monitoring and controlling the operation of the catalyst and engine, especially for operation that minimizes fuel and harmful substances.

  Numerous algorithms are implemented in the current control devices of internal combustion engines, which are used for regulating and monitoring the operation of the internal combustion engine, as well as of the catalyst placed downstream. In the case of modern internal combustion engines capable of operating in lean mode, the control apparatus as well as its memory contain in particular numerous characteristic curves and characteristic fields, with the aid of which various calculations of operating parameters, intended for the control of the engine and of the catalyst can be carried out by suitable algorithms as well as suitable measures, in order to obtain an operation of the internal combustion engine with as low fuel consumption as possible, and compatible with the environment.

  Thus, for the calculation of the state of a NOx accumulation catalyst of an internal combustion engine capable of operating in lean mode, therefore for example of the filling state, it is useful to know the regeneration interval, the activity of the catalyst, etc., and the distribution of the temperature along the axis of the catalyst.

  The temperature of the catalyst is for example currently determined by measuring the temperature of the exhaust gases both upstream and downstream of the catalyst. It can also be determined by measuring the temperature of the exhaust gases upstream of the catalyst, and by calculating a homogeneous temperature of the catalyst, mainly by an analysis of the heat transfer between the catalyst and the exhaust gases. .

  With the average temperature of the catalyst thus determined, it is however not possible to detect effects which may intervene in the dynamic operation due to an uneven distribution of the temperature in the catalyst. Thus, by a determined average temperature of the NOx accumulation catalyst close to the limit of thermal desorption of NOx, it is for example not possible to detect whether, in the event of very large actual temperature differences between the front zone and the rear zone of the catalyst, NOx from the front zone of the catalyst is already thermally desorbed, and if an NOx crossing takes place as a result. In order to exclude such effects, the calculated temperature threshold of the catalyst, to which it is switched to lambda operation = 1 in the case of internal combustion engines capable of operating in lean mode in order to avoid NOx crossings, has a large safety margin compared to the actual thermal desorption threshold.

  This results in an operating regime with more unfavorable consumption for longer time intervals than necessary. By means of a determination of the temperature development in the NOx accumulation catalyst, it is by analogy also possible to observe sufficient cooling below the thermal desorption threshold after operating at full load at very high temperatures of the catalyst, so that it can be switched to a time as soon as possible of operation with lambda = 1 on a lean speed.

  It is also possible to determine the distribution of the temperature inside a catalyst by an approximate calculation of the corresponding differential equation of the thermal conduction inside the catalyst. Such calculations, even approximate, however far exceed the capacity of the processor of an engine control unit, and are therefore not practicable. The object of the invention therefore consists in proposing a method, as well as a device, intended for monitoring a catalyst, in which the physical and chemical states of the catalyst in resolution in space and in time are calculated as efficiently as possible, and go into monitoring.

  This objective is achieved by a method intended for monitoring and regulating a catalyst of an internal combustion engine of a motor vehicle, in which the axial distribution of the temperature inside the catalyst is calculated by means fast algorithms using a plurality of support points, the fast algorithms being based on the principle of minimum production of entropy, and the method taking into account the heat transfer between the flow of exhaust gases and the wall of the catalyst, of the heating of the catalyst, as well as of the heat losses of the catalyst delivered to the environment, and the calculated axial distribution of the temperature being used for the regulation of the catalyst, process characterized in that the sorption processes and the desorption processes of the various compounds of the exhaust gases in the catalyst are calculated for the calculation of its state of accumulation. n, and this by algorithms which are based on the principle of minimum production of entropy, the calculation being carried out using a predetermined emission characteristic field 30 of the internal combustion engine, and the state of accumulation thus calculated of the catalyst, relating to the various compounds of the exhaust gases, being used for optimizing or regulating the speed of the internal combustion engine with regard to its consumption, and a device intended for carrying out the method comprising a control unit, data memory, calculation unit for calculating fast PME algorithms, and one or more detectors which transmit measured values to the calculation unit.

  With regard to the method according to the invention 5 intended for monitoring and regulating a catalyst of an internal combustion engine of a motor vehicle, the axial distribution of the temperature inside the catalyst is calculated by means of fast algorithms using a plurality of support points, the fast algorithms being based on the principle of minimum production of entropy (PME). The process here takes into account the heat transfer between the flow of exhaust gases and the wall of the catalyst, the heating of the catalyst, as well as the heat losses of the catalyst delivered to the environment, and the calculated axial distribution of the temperature is used for regulating the catalyst.

  The principle of the minimum production of entropy, abbreviated PME, means that processes take place in such a way that their production of entropy P reaches a minimum with regard to so-called "free thermodynamic forces", while the process of "fixed thermodynamic forces" is maintained in progress. It is in this case determining that said free thermodynamic forces depend on process parameters a, so that the minimum formation according to the joint rule of differential calculus only has to be carried out according to these process parameters. Expressed in other words: P (a) = Minimum -> dP (a) / da = 0.

  The production of entropy is in this case the integral of the density of production of entropy P 'relative to the volume, which is in principle derived from the fundamental Gibbs theorem known in the field of thermodynamics of equilibrium and equations balance sheet. In practice, this means that the MSY is equivalent to the balance sheet equations usually used, but in many cases offers easier access to solutions, or is the only one to allow the determination of certain parameters for physical, numerical or other reasons. 5 economical. Other explanations relating to PME are given in B. Reiser "Real Processing RP I: The Principle of Minimal Entropy Production PME of Irreversible Thermodynamics and the Principle of Minimal Deformation PMD of Hydrodynamics, their Dependence and 10 Applications", Physica A, 227 / 3-4, June 1, 1996.

  PME algorithms preferably include the calculation of catalytic reactions inside the catalyst, the timing of the cut-off of heating measurements of the catalyst possibly being derived in particular from the calculated axial distribution of temperature. After the internal combustion engine has been switched off, the calculation of the axial temperature distribution can also be continued so that, when restarted, any residual heat from the catalyst can be taken into account.

  At one or more locations, the calculated axial distribution of the catalyst temperature can be compared with measured values, the difference being a criterion for the activity of the catalyst, so that an OBD function can be activated when a predetermined activity threshold is not reached.

  From a predetermined characteristic emission field and the axial temperature profile, it is in particular possible to calculate a time profile of activity of the catalyst as a function of its running time, using a modeling of irreversible accumulation process and / or oxidation process of different exhaust gas compounds in the catalyst, the modeling being based on the principle of minimum production of entropy (PME). The emission characteristic field preferably includes both transitions in the driving dynamics as well as the emissions during cold start. The catalyst limit can further be determined from the calculated time activity profile of the catalyst.

  In another embodiment of the method according to the invention, intended for monitoring and regulating a catalyst of an internal combustion engine of a motor vehicle, the sorption processes and the desorption processes of the various compounds exhaust gases in the catalyst are calculated for the calculation of its state of accumulation, and this by algorithms which are based on the principle of the minimum production of entropy (PME), the calculation being carried out using a predetermined emission characteristic field 15 of the internal combustion engine, and the thus calculated state of accumulation of the catalyst, relating to the various compounds of the exhaust gases, being used for optimizing or regulating the speed of the combustion engine internal with regard to its consumption.

  The exothermic reactions in the catalyst, due to the axial distribution of the temperature and / or the state of accumulation of the catalyst, can in particular be controlled. A device according to the invention, intended for implementing the method described above, comprises a control device, a data memory, a calculation unit for the calculation of fast PME algorithms and one or more detectors, the detectors transmitting measured values to the computing unit.

  The data memory notably includes engine time data, one or more engine characteristic fields, one or more emission characteristic fields, catalyst characteristic data and / or catalyst time data.

  The detectors can be located in the catalyst or downstream of the catalyst in the direction of flow.

  When only one detector is used, it is placed in the catalyst and measures the temperature of the catalyst. The detector - or detectors - placed downstream of the catalyst can be a temperature detector, 5 and / or a 02 detector and / or an HC detector and / or a NOx detector.

  A preferred embodiment of the invention is explained below with the aid of a figure, which is a schematic representation of a device according to the invention, intended for monitoring and regulating a catalyst. an internal combustion engine.

  The figure shows a device 1 for monitoring and regulating a catalyst 2. The device in this case comprises a control device 15 3, a data memory 4 and a device 5 for the calculation of PME algorithms. The control device 3 communicates with the data memory 4 via a bidirectional link 6, as well as with the calculation device 5 via another bidirectional link 7. The calculation device communicates on its side with the data memory 4, also via a bidirectional link 8. The data memory 4 contains in particular time data 9 of the engine, a characteristic field 10 of the engine, a characteristic field d emissions 11, characteristic data 12 of the catalyst and time data 13 of the catalyst. EGR (exhaust gas recirculation) data 14, engine data 15 and KSM (cold start device 30) data 16 are transmitted to the control unit 3 as input data. Data from the catalyst of a temperature detector 17 placed in the catalyst 2 and of detectors 18 arranged downstream of the catalyst 2, for example of a temperature detector 35 and / or of an O 2 detector and / or of a HC detector and / or a NOx detector are further transmitted to the calculation unit 5. The control unit 3 and / or the calculation unit 5 further transmits data by means of an OBD display 19.

  PME algorithms are based on thermodynamic principles using the principle of minimum production of entropy, abbreviated PME. The possibility of applying this PME principle to technical systems leads to a non-homogeneous system of equations, the resolution of which is carried out with current processors at a speed such that these can already be used for online calculations and for hardwarein-the-loop applications. This results in multiple possibilities of application for OED functions (on-board diagnostics), regulation strategies, as well as for continuous monitoring of technical components which are subjected to an aging process as a function of known influence quantities. , including engine parameters. This method makes it possible to advantageously use values from the literature, and missing coefficients 20 can be transformed so that they become accessible to a measurement technique.

  A concrete application case for PME algorithms is an integral description of a catalyst at each operating point, which takes account of its running capacity.

  The local temperatures in the catalyst are calculated here taking into account the thermodynamic processes taking place in the catalyst.

  For the axial temperature distribution, account is also taken of the heat transfer between the flow of exhaust gases and the wall of the catalyst, as well as the heating of the catalyst and the heat losses delivered to the environment. The starting behavior of catalysts, at least of new catalysts, can therefore be determined with precision.

  All the measurements of heating the catalyst, both direct (for example catalyst E) and indirect (for example with secondary air), are necessarily included in the calculation. The measures for heating the catalyst can therefore be cut off at the appropriate time.

  After the engine has been switched off, the cooling of the catalytic converter continues to be calculated, so that any possible residual heat can be taken into account when restarting.

  The memorization of different exhaust gas compounds is carried out by chemisorption of the atoms dispersed in the washcoat. If this incrustation is irreversible under the conditions prevailing in the exhaust gases of an engine, an enrichment of this compound occurs in the washcoat, which is generally described as poisoning. If the chemisorption can be reversed again at a certain engine operating point, the catalyst can be regenerated.

  As soon as such chemical processes are known, these can be described with the PME method, the existing system of equations having only to be supplemented by other equations.

  With appropriate control strategies, it is therefore possible to control the oxidation-reduction and oxidation processes in the catalyst so that the engine can run on a minimum of fuel during an entire cycle. the accumulation and regeneration phase.

  For a precise regulation strategy, it is not sufficient to take into account only a single compound of the exhaust gases. Knowledge of the state of accumulation of different exhaust gas compounds implies a corresponding emission characteristic field which takes into account not only dynamic transitions, but also emissions during a cold start.

  This characteristic field is stored in the data memory of the engine control unit.

  Known mechanisms, which describe the decline in catalyst activity, are thermal sintering and irreversible oxidation processes, or irreversible accumulation processes of different exhaust gas compounds in the catalyst. These and other mechanisms can be formulated with the PME method.

  With knowledge of the characteristic emission field, the axial temperature profile and the undesirable processes described above taking place in the catalyst, it is possible to calculate an activity profile decreasing over time (aging of the catalyst on the walking time). With this continuously updated activity profile, it is possible to determine the limit of the catalyst. This is the time when the OBD function becomes active.

  The start-up behavior changes as long as the limit of the catalyst is not reached. In this case, the catalyst heating measures must therefore remain in operation longer.

  Analogous to the sorption and desorption processes, this PME method also makes it possible to calculate the catalytic reactions, these calculations being necessary for establishing a temperature profile. After the initiation of the reaction in the catalyst, and in addition to the waste heat from the exhaust gases, the latter is also heated by exothermic reactions.

  Other processes taking place in the catalyst can only be calculated beforehand with a precise knowledge of the axial temperature profile.

  The calculation of a temperature profile also includes its cooling, as well as the catalytic reactions and subsequent reactions when idling, and during engine downtime (hybrid concepts, power supply cut-out, short cuts engine, for example at traffic lights).

  HC peaks, which can lead to thermal destruction, may temporarily appear in engine speed 5. If there is a characteristic emission field, the catalyst can be protected against overheating by an appropriate control strategy.

  Precisely in the case of hybrid concepts, knowledge of the activity profile and the temperature profile in the catalyst is necessary so that the engine can operate with optimized emissions.

  The use of PME algorithms leads to knowledge of the physical and chemical state of a catalyst at all times. This knowledge makes it possible to perform the following functions: - all types of catalyst heating measurements can be stopped at the appropriate time, which saves fuel.

  - Given the control of the exothermic reactions in the catalyst, the latter can be largely protected from thermal deterioration.

  This leads to a higher running capacity of the catalyst. - In the case of an accumulation catalyst, the cycle of the accumulation charge can be optimized. This leads to fuel economy.

  - The catalyst limit is detected on the basis of the calculated activity profile.

  - All types of detectors can be used as assistance. New type detectors can be considered at any time.

  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 modifications in form and in detail can be made without departing from the spirit or the field of the invention.

LIST OF NUMERICAL REFERENCES

  1 Monitoring device 2 Catalyst 3 Control unit 4 Data memory Calculation unit 6 Bidirectional link 7 Bidirectional link 10 8 Bidirectional link 9 Engine time data Engine characteristic field il Emission characteristic field 12 Catalyst time data 15 13 Catalyst time data 14 (EGR) Exhaust gas recirculation Engine 16 (KSM) Cold start device 17 Temperature sensor 20 18 Sensor 19 (OBD) On-board diagnostic

Claims (7)

  1. Method for monitoring and regulating a catalyst (2) of an internal combustion engine (15) of a motor vehicle, characterized in that the sorption processes and the desorption processes of the different compounds of the exhaust gases in the catalyst (2) are calculated for the calculation of its state of accumulation by algorithms which are based on the principle of minimum production of entropy (PME), the calculation being carried out using a predetermined emission characteristic field of the internal combustion engine (15), and the thus calculated state of accumulation of the catalyst (2), relating to the various compounds of the exhaust gases, being used for the optimization or the regulation of the speed of the internal combustion engine (15) with regard to its consumption.   2. Method according to claim 1, characterized in that the exothermic reactions taking place in the catalyst (2), due to the state of accumulation of the catalyst (2), are controlled.   3. Device for implementing the method according to any one of the preceding claims, characterized in that it comprises a control device (3), a data memory (4), a calculation unit (5 ) for the calculation of PME fast algorithms and one or more detectors (17, 18) which transmit measured values to the calculation unit (5).   4. Device according to claim 3, characterized in that the data memory (4) comprises time data (9) of the engine, characteristic fields (10) of the engine, characteristic emission fields (11), characteristic data (12) of the catalyst (2) and / or time data (13) of the catalyst.   5. Device according to claim 3 or 4, characterized in that the detector (s) (17, 18) is (are) located (s) in the catalyst (2) or downstream of the catalyst (2) in the direction of the 'flow.   6. Device according to claim 5, characterized in that, in the case of a single detector (17), it is arranged in the catalyst (2) and measures its temperature.   7. Device according to claim 5, characterized in that the detector (s) (18) 10 disposed (s) downstream of the catalyst (2) is (are) a temperature detector, and / or a 02 detector and / or a HC detector and / or a NOx detector.