EP1255922A2 - Device and method for controlling operation of a multi-cylinder engine for motor vehicles having a multi-flow emission control system - Google Patents

Abstract

The invention relates to a method and a device for controlling operation of a multi-cylinder engine for motor vehicles having a multi-flow emission control system. According to the invention, the emission control system consists of at least two exhaust gas sections which are allocated to a number of cylinders (bench) and have at least one NO>x< storage catalyst respectively and a gas sensor. According to the inventive method and device, the operating modes of each bench are adjusted (co-ordinated control) in all exhaust gas sections according to a co-ordination mode and a catalyst state and/or an exhaust gas emission.

Description

 Device and method for controlling an operation of a

Multi-cylinder engine for motor vehicles with a multi-flow

emission control system

The invention relates to a device and a method for controlling an operation of a multi-cylinder engine for motor vehicles with a multi-flow exhaust gas cleaning system with the features mentioned in the preambles of the independent claims.

Multi-cylinder engines are often divided into sub-units, each of which groups a number of cylinders (bank). For example, a twelve-cylinder engine can be divided into three banks of four cylinders. Each bank is assigned a separate exhaust line, at least in certain areas, in which components of the exhaust gas cleaning system can be accommodated. Such components include, for example, particle filters and catalysts, which enable conversion of pollutants formed during a combustion process into less environmentally relevant products. Examples include oxidation catalysts for the oxidation of reducing agents, such as carbon monoxide CO and incompletely burned hydrocarbons HC, and reduction catalysts for reducing nitrogen oxides NO _x .

Furthermore, actuating means can be assigned to each bank, which allow the combustion process in the respective banks to be designed separately from one another. Such actuating means can comprise, for example, exhaust gas recirculation devices, injection systems or throttle valves arranged in separate intake pipes. Furthermore, it is known to implement a sensor system in the exhaust gas lines that makes it possible to detect the air conditions in the exhaust gas or also selected proportions of pollutants in the exhaust gas. Usually, the signals detected by the sensor system are read into a control device, which then specifies manipulated variables according to predefined models. In this way, for example, homogeneous or stratified lean operation, stoichiometric operation or rich operation of the multi-cylinder engine required at very high loads can be realized. If a NO _x storage catalytic converter is integrated in each of the exhaust gas stretches of the exhaust gas purification system, this requires special operating modes in order to prevent undesirably high pollutant emissions and permanent damage to the catalytic converter. In single-flow exhaust gas purification systems, numerous procedures for carrying out the operating modes of the NO _x storage catalytic converter are known. In lean operation, in particular in the consumption-optimized area for gasoline engines with lambda around 1.1, a raw NO _x emission from the engine is greatly increased, and at the same time the reducing agents CO and HC required for conversion are greatly reduced. To remedy this, the NO _x is therefore absorbed as nitrate in a lean atmosphere in a NOx storage component of the catalyst, until either an NOχ storage capacity is exhausted or a desorption temperature is exceeded. Before this point in time, therefore, if possible, NO _x regeneration must take place by changing to a stoichiometric or rich atmosphere. For this purpose, a procedure can be stored in a control unit with which a specification for the suitable actuating means takes place as a function of signals from a gas sensor detected downstream of the NO _χ storage catalytic converter. Other measures, for example desulfurization or heating of the catalyst to a minimum operating temperature, can also be carried out in the same manner. However, the solutions shown cannot simply be transferred to multi-flow exhaust gas purification systems of the type mentioned above, since catalytic converter states and operating parameters can differ significantly from one another in the respective exhaust gas lines.

The invention has for its object to provide a device and a method with which a coordinated control of the operating modes of each bank with regard to a low pollutant emission but also taking into account fuel consumption and operating parameters of the multi-cylinder engine is made possible.

According to the invention, this object is achieved by a device and a method for controlling an operation of a multi-cylinder engine for motor vehicles with a multi-flow exhaust gas cleaning system with the features mentioned in the independent claims. In the method according to the invention, the operating modes of each bank are set as a function of a coordination mode and a catalyst state and / or pollutant emission in all exhaust gas lines. The device according to the invention has means for carrying out the method steps, for example a control device, in which a procedure for coordinated control is stored in digitized form. The control unit can preferably be part of an engine control unit.

The coordination mode preferably comprises an autonomous mode, a dominant mode, a weighted mode or an interactive mode, between which a change is made as a function of status and operating parameters of the motor vehicle and its aggregates during the operation of the multi-cylinder engine. The status and operating parameters can preferably include a driver's request, a load situation, a total NOx emission downstream of all exhaust gas lines, a raw NOχ emission of the multi-cylinder engine and the catalytic converter status, so that, for example, an operating situation-optimized choice of the coordination mode is made possible with a complex map.

It is further preferred to characterize the catalyst state in the form of a sulfur loading and / or a NO _x loading and / or a catalyst temperature. It is also conceivable to estimate the catalytic converter state by comparing a current NO _x storage capacity of the NO _x storage catalytic converter with a measured or modeled NO 2 storage capacity of a fresh NO _χ storage catalytic converter. The operating modes of the banks preferably include procedures for performing NOχ regeneration, desulfurization and catalyst heating. Overall, a large number of parameters are thus available for the control according to the invention, with which almost all measures necessary for optimal operation of the exhaust gas cleaning system can be taken.

In a preferred embodiment of the method, each bank is controlled in the autonomous mode only as a function of the catalytic converter state and / or the pollutant emission in the respectively assigned exhaust line. Under such a condition, the total emission of the multi-cylinder engine is particularly low, but in certain circumstances an increased fuel consumption has to be accepted.

In the dominant mode, the catalytic converter status and / or the pollutant emission is only recorded in one of the exhaust gas lines and used for the synchronous control of all banks. Such a method is particularly easy to implement and requires only a relatively small amount of storage space and computing capacity. Such a control is always appropriate if one of the banks temporarily or permanently has a major share in the total emissions of the multi-cylinder engine. In the weighted mode, the state of the catalyst and / or the pollutant emission in each exhaust line is recorded and multiplied by a weighting factor. The weighted quantities are then combined into an average, and all banks are controlled synchronously on the basis of the average. In the simplest case, the weighting factor can only take into account the number of cylinders per bank, so that, for example, in the case of a twelve-cylinder engine consisting of three banks of four cylinders, the weighting factor per bank is one third. However, the weighting factor is preferably determined as a function of the catalytic converter state, so that, for example, as irreversible damage to a NO _x storage catalytic converter progresses, the weighting factor becomes smaller, so that overall the pollutant emission from a bank can increase slightly, but an increase in fuel consumption as a result of unnecessarily frequent regeneration the NOχ storage catalysts of the other banks is avoided. It has also proven to be advantageous to determine the weighting factor separately for each procedure to be carried out.

In the interactive mode, the catalytic converter status and / or the pollutant emission in each exhaust line is recorded and used for the synchronous control of all banks. In a preferred embodiment of the mode, an initial impulse for NO für regeneration, desulfurization or catalyst heating is set if there is a need for these measures in one of the exhaust gas lines. An ending impulse for the NO _x regeneration, the desulfurization or the catalyst heating is present when the measure in each of the exhaust lines is finished. In this way it can be ensured, similarly as in the self-sufficient mode, that the measures are carried out completely for each of the catalysts. In contrast to the self-sufficient mode, such simultaneous implementation of the measures can be implemented much more easily and integrated into the existing engine control system and is therefore the preferred mode in the case of rapidly changing operating situations.

Further preferred embodiments of the invention result from the other features mentioned in the subclaims.

The invention is explained in more detail in an exemplary embodiment with reference to the accompanying drawings. Show it: Figure 1 is a schematic diagram for controlling an operation of a

Multi-cylinder engine after a self-sufficient and an interactive mode;

FIG. 2 shows a course of the air conditions in different exhaust gas lines of the multi-cylinder engine over time;

Figure 3 is a schematic diagram for controlling the operation of the

Multi-cylinder engine in a weighted mode;

FIG. 4 shows a course of pollutant emissions in the exhaust gas lines over time;

Figure 5 is a schematic diagram for controlling the operation of the

Multi-cylinder engine after a dominant mode and

Figure 6 is a flow chart for coordinated control.

1 shows a schematic diagram of a multi-cylinder engine 10. The multi-cylinder engine 10 is divided into a total of three banks 1, 2, 3, each with four cylinders 50. An exhaust gas cleaning system 60 is arranged downstream of the multi-cylinder engine 10. Each of the banks 1, 2, 3 opens into an exhaust line 11, 12, 13 that is separate at least at the beginning. For cleaning an exhaust gas that arises during the combustion process of an air-fuel mixture in the banks 1, 2, 3, FIG The NOx storage catalytic converters 21, 22, 23 each integrate the exhaust gas lines 11, 12, 13. Of course, other components for purifying the exhaust gas, such as pre-catalysts and particle filters, can also be present in the exhaust lines 11, 12, 13, but have not been included here for reasons of clarity.

Likewise, for the sake of clarity, a representation of a sensor system assigned to the respective exhaust lines 11, 12, 13 has been dispensed with. The sensors include, for example, temperature sensors with which a catalyst temperature or an exhaust gas temperature can be detected. Furthermore, the sensor system can include gas sensors which make it possible to determine an air ratio downstream and upstream of the NO _x storage catalytic converters 21, 22, 23 or also a proportion of one Determine pollutant on the exhaust gas. The gas sensors are then designed, for example, as lambda sensors or NO _x sensors.

Furthermore, the individual banks 1, 2, 3 are assigned control units, which detect signals provided by the sensor system and, depending on these signals, output control variables for the actuating means assigned to the individual banks 1, 2, 3. The control units can be part of a control unit with which a coordinated control of the individual banks 1, 2, 3, which will be explained in more detail below, is carried out. The actuating means include, for example, separate injection systems, exhaust gas recirculation devices or throttle valves arranged in separate intake pipes. For the sake of clarity, the positioning means and the control device or the control units are not shown.

A catalytic converter state K of the NO _x storage catalytic converters 11, 12, 13 can be determined, for example, on the basis of its sulfur loading, NO _x loading,

Catalyst temperature or its irreversible degree of damage can be characterized. The necessary sensors and the corresponding methods for determining the catalytic converter state K are known and are therefore not to be explained in more detail here. The measures M _j are also known, which must be taken for optimal and permanent operation of the NO _x storage catalytic converters 21, 22, 23. In this way, procedures can be stored in the control unit which are used to carry out NO _x regeneration, desulfurization and catalyst heating. In the configuration of the control for multi-flow exhaust gas cleaning systems 60 according to the invention, these procedures are accompanied by a change in the operating modes of banks 1, 2, 3.

FIG. 1 and FIGS. 3 and 5 to be explained in more detail below also contain a time window in which it is shown which measures Mj are currently being taken in the individual banks 1, 2, 3. Triangles stand for an end of the catalyst heating, hexahedra for a start of NO _χ regeneration and diamonds for a start of desulfurization. Filled areas indicate when the measures Mj were actually taken, while unfilled characters indicate when the respective measure Mj was taken in completely self-sufficient banks 1, 2, 3. FIG. 6 shows a flowchart for a method for controlling the operation of the multi-cylinder engine 10, in which the operating modes of each bank 1, 2, 3 as a function of a coordination mode and the catalytic converter state K and / or a pollutant emission EM in all exhaust lines 11, 12, 13 can be carried out (coordinated control). First, status and operating parameters P of the motor vehicle and its aggregates are read into the control unit. The Zustandsund operating parameters P can be, for example, a driver's request FW, a load situation LS, a total NOx emissions GE downstream of all the exhaust pipes 11, 12, 13, a NO _x -Rohemission RE of the multi-cylinder engine 10 and the catalyst state K. The parameters P mentioned are recorded, for example, in a map which is used to determine the coordination mode.

Without going into more detail at this point, the coordination mode can be an autonomous mode A, a dominant mode D, a weighted mode G or an interactive mode I. Each of these modes determines how the recorded catalyst states or pollutant emissions are to be evaluated. For this purpose, a pulse that initiates or ends the measure Mj is determined. The introductory pulse can be determined in such a way that a characteristic value KW _{j D} is initially specified in accordance with the determined mode, which is compared with a threshold value SW j _D. If the characteristic value KWj b exceeds the threshold value SW, _D , the measure Mj is initiated. Measure Mj is terminated in an almost equivalent manner after a stop pulse has been issued. For this purpose, characteristic values KWj _e and threshold values SWj _e are compared with one another.

Both the interactive mode I and the autonomous mode A for the measures Mj selected as an example can be seen from the time window in FIG. The self-sufficient mode A corresponds to the unfilled character or the dashed outline. Such a mode is always preferred when relatively constant operating conditions of the motor vehicle are present and the lowest possible emission of pollutants is desired. Since such a mode can only be coordinated with existing engine control systems for drive control with a considerable amount of computation, this mode is particularly advantageous when there are phases of constant load.

In interactive mode I, the catalytic converter state K and / or the pollutant emission EM in each exhaust line 11, 12, 13 is recorded and used for the synchronous control of all banks 1, 2, 3. For example, the catalyst heating is only ended, when a minimum operating temperature of the NO _x storage catalytic converters 21, 22, 23 is reached in all exhaust lines 11, 12, 13. All measures Mj are consequently initiated and ended simultaneously in all banks 1, 2, 3, so that it can be ensured that optimum conditions prevail for the operation of the exhaust gas cleaning system 60.

FIG. 2 shows a course of the air conditions in the individual exhaust lines 11, 12, 13 downstream of the catalysts 21, 22, 23 in the case of NOχ regeneration. There are lean conditions in all banks 1, 2, 3. At a time T- _{j there} is a need for regeneration for all three catalysts 21, 22, 23, and the composition of the exhaust gas is changed in accordance with a rich target specification. During the regeneration, the lambda value downstream of the catalysts 21, 22, 23 initially remains at a stoichiometric value. Banks 1 and 3 would already have a pulse ending the regeneration at times T2 and T3, namely after reaching a rich threshold value SWf, but instead of going straight back to normal operation, banks 1 and 3 remain in stoichiometric operation, even in Bank 2 the regeneration is completed at time T4.

FIG. 3 shows, inter alia, a time window of a weighted mode G. The characters in the lower three rows which have not been filled in again show the self-sufficient mode A for clarification, while the characters in the upper row which are filled in characterize the times at which the measure Mj in each of banks 1, 2, 3 is taken. In the weighted mode G, the catalytic converter state K and / or the pollutant emission in each exhaust line 11, 12, 13 is recorded and multiplied by a weighting factor F _w . The weighted quantities are then averaged (mean value MW), the mean value MW then being used for synchronous control of all banks 1, 2, 3. It then corresponds to the characteristic values KW _{j D} and KWj _e of FIG. 6.

In the simplest case, the weighting factor F _w can only take into account a ratio of the number of cylinders 50 in the individual banks 1, 2, 3 to one another, so that in this case it would be one third each. In addition, it is also conceivable that it is determined depending on the catalyst state K and, if appropriate, the procedure to be carried out in each case. In this way, the actual conditions can be taken into account particularly easily. For example, if the catalytic converter 21 of bank 1 is already severely limited in its storage capacity due to thermal damage, this would become too frequent Lead to regeneration and thus considerable additional fuel consumption. In such a case, the weighting factor F _w for bank 1 is expediently reduced, so that the influence of the remaining banks 2 and 3 is greater.

FIG. 4 shows the profiles of NO _x emissions in the exhaust gas lines 11, 12, 13 downstream of the catalysts 21, 22, 23 (curves 76, 78, 80) and an average profile according to the weighted mode G (curve 82) , In a self-sufficient system, NO _x regeneration measures would already be initiated at points T5 and T5 if a threshold value SWR N <D ^{for the} NOχ regeneration in the respective bank was exceeded. If the NO _x emissions are averaged as described, the regeneration is initiated from a time T7, even if NO _x storage capacity is still present in one of the banks.

FIG. 5 shows a time window for dominant mode D. In the dominant mode D, the catalytic converter state K and / or the pollutant emission EM is only detected in one of the exhaust gas lines 11, 12 or 13 and is used for synchronous control of all banks 1, 2, 3. In this case, Bank 1 has been given such a dominant position as an example. Such a measure can always be taken if, due to an operational situation or due to permanent structural changes, the pollutant emissions of Bank 1 far exceed those of the other banks.

Claims

1. A method for controlling an operation of a multi-cylinder engine for motor vehicles with a multi-flow exhaust gas purification system, which consists of at least two exhaust gas lines assigned to a number of cylinders (bank), each with at least one NO _x storage catalytic converter and a gas sensor, and in which the operating modes of each bank depending on a coordination mode and a catalytic converter state and / or pollutant emissions in all exhaust lines (coordinated control). 2. The method according to claim 1, characterized in that the coordination mode comprises a self-sufficient mode (A), a dominant mode (D), a weighted mode (G) or an interactive mode (I), between which depending on the state and Operating parameters (P) of the motor vehicle and its units is changed during the operation of the multi-cylinder engine (10). 3. The method according to claim 2, characterized in that the state and operating parameters (P) a driver request (FW), a load situation (LS), a total NOχ emission (GE) downstream of all exhaust lines (11, 12, 13), one NOχ raw emission (RE) of the multi-cylinder engine (10) and the catalytic converter state (K) include. 4. The method according to any one of the preceding claims, characterized in that the operating modes of the banks (1, 2, 3) include procedures for performing a NO _x regeneration, desulfurization and a catalyst heater. 5. The method according to any one of the preceding claims, characterized in that for the characterization of the catalyst state (K) a sulfur loading and / or a NO _x loading and / or a catalyst temperature and / or an irreversible degree of damage and / or a current NO _x storage capacity of the NO _x storage catalytic converter (11, 12, 13) compared to a measured or modeled NO _x storage capacity of a fresh NO _x storage catalytic converter. 6. The method according to any one of claims 1 to 5, characterized in that in the self-sufficient mode (A) each bank (1, 2, 3) only in dependence on the catalyst state (K) and / or the pollutant emission (EM) in each assigned exhaust line (11, 12, 13) is controlled. 7. The method according to any one of claims 1 to 5, characterized in that in the dominant mode (D) the catalyst state (K) and / or the pollutant emission (EM) only in one of the exhaust lines (11, 12, 13) and synchronized Control of all banks (1, 2, 3) is used. 8. The method according to any one of claims 1 to 5, characterized in that in the weighted mode (G) the catalyst state (K) and / or the pollutant emission (EM) in each exhaust line downstream of the at least one NO _x storage catalyst (11, 12, 13) recorded, multiplied by a weighting factor (F _w ), the weighted values are averaged (mean value MW) and then the mean value (MW) is used for the synchronous control of all banks (1, 2, 3). 9. The method according to claim 8, characterized in that the weighting factor (F _w ) is determined as a function of the catalyst state (K). 10. The method according to any one of claims 8 or 9, characterized in that the weighting factor (F _w ) is determined separately for each procedure to be carried out. 11. The method according to any one of claims 1 to 5, characterized in that in the interactive mode (I) the catalyst state (K) and / or the pollutant emission (EM) in each exhaust line (11, 12, 13) detected and for the synchronous control of all Banks (1, 2, 3) is used. 12. The method according to claim 11, characterized in that in the interactive mode (I) - An initial impulse for NO _x regeneration, desulfurization or catalyst heating is present if there is a need for these measures in one of the exhaust lines (11, 12, 13) and - An ending impulse for NOχ regeneration, desulfurization or catalyst heating is present when the measure in each of the exhaust lines (11, 12, 13) has ended. 13. The method according to any one of the preceding claims, characterized in that a NO _x sensor is used as the gas sensor, which detects a NO _x emission downstream of the NO _x storage catalytic converter. 14.Device for controlling an operation of a multi-cylinder engine for motor vehicles with a multi-flow exhaust gas purification system, which consists of at least two exhaust gas lines assigned to a number of cylinders (bank), each with at least one NO _x storage catalytic converter and a gas sensor, and in which means are available, with which the operating modes of each bank can be set as a function of a coordination mode as well as a catalyst state and / or a pollutant emission in all exhaust lines (coordinated control). 15. The apparatus according to claim 14, characterized in that these means comprise a control device in which a procedure for coordinated control is stored in digitized form. 16. The apparatus according to claim 15, characterized in that the control unit is part of an engine control unit. 17. The device according to one of claims 14 to 16, characterized in that the gas sensor is a NO _x sensor and / or a lambda sensor.