Patent Application
20090151323
The present invention relates to a method for operating a motor vehicle exhaust-gas after-treatment system and also to an exhaust-gas after-treatment system with a connected internal combustion engine.
From U.S. Pat. No. 6,843,052, it is known that a rich-lean cycle can be used so that the oxygen accumulator of an exhaust-gas after-treatment component is used for the oxidation of HsS. The accumulator is filled during a lean phase and at least partially emptied during a rich phase. For regulating O2 content, a lambda probe placed downstream of the exhaust-gas after-treatment component is used. Here, if a substoichiometric air ratio is detected, a lean transition is triggered. For a hyperstoichiometric air ratio, a rich transition is triggered. In EP 0 893 154 B1, an oxygen accumulator connected downstream of an NOx-accumulating catalytic converter (NAC) is used for supplying oxygen for the H2S oxidation.
From DE 197 47 222 C1, an internal combustion engine system with NAC and secondary air injection with a method for desulfurization of the NAC is known. In this system, the desulfurization control system is regulated by the output signal of a lambda probe placed downstream.
From DE 198 27 195 A1, it is known that for a lean-rich transition, initially SO2 is produced for a short time and formation of H2S follows with a time delay. Therefore, H2S emission can be suppressed by an early rich-lean transition.
In DE 101 26 455 A1, a method for the desulfurization of an NAC is described that follows the regeneration of a particulate filter, whereby the heating to a desulfurization temperature is eliminated or shortened.
From DE 199 22 962 C2, it is known that the air ratio in the exhaust gas can be set by supplying secondary air during NAC desulfurization.
The regulation or control system concepts emerging from the above documents relate to a lambda probe signal downstream of an oxygen-storing component in the exhaust-gas train. Especially at high temperatures, the lambda probe here shows a value that is not equal to one only when an oxygen accumulator is completely filled (λ>1) or is completely empty (λ<1). Therefore, e.g., for desulfurization, rich breakthroughs with accompanying H2S emission can appear.
The task of the present invention is to create an improvement in the operating behavior of an exhaust-gas after-treatment system that takes into account, in particular, the actual conditions in an exhaust-gas after-treatment system and allows a rapid and also reliable reaction.
This task is achieved with a method with the features of claim 1 and also with an exhaust-gas after-treatment system with the features of Claim 19. Other advantageous configurations are specified in each subordinate claim.
According to the invention, a method for operating a motor-vehicle exhaust-gas after-treatment system is proposed in which oxygen is fed to and removed from an oxygen accumulator of an exhaust-gas after-treatment system, wherein at least one variable parameter influenced by the oxygen accumulator and its oxygen content is determined and is used for operation of the motor-vehicle exhaust-gas after-treatment system.
Advantageously, the oxygen quantity in the oxygen accumulator is determined and, according to one improvement, a rich-lean cycle is influenced as a function of the determined oxygen quantity. For example, an oxygen quantity in the oxygen accumulator can be included as a parameter for setting a rich-lean cycle. An example configuration provides that the oxygen quantity is used as a regulating or control parameter for a rich-lean cycle. Another example configuration provides that an oxygen quantity in the oxygen accumulator is regulated by means of at least one rich-lean cycle, advantageously by means of different rich-lean cycles. One possible realization has a motor control system that controls or regulates the rich-lean cycles, wherein the oxygen content in the oxygen accumulator is controlled or regulated. For this purpose, the motor control system can use, for example, a plurality of characteristic engine maps or an oxygen calculation that is performed continuously or discontinuously.
In particular, a fill level of the oxygen accumulator is taken into account. Thus, for control or regulation systems with respect to individual components or all of the components of the exhaust-gas after-treatment system, not only is a lambda probe signal taken into account, but the current state of the oxygen accumulator is detected and taken into account insofar as this is in the position, for example, to discharge oxygen for operation in a rich section of the rich-lean cycle or, conversely, to be able to store oxygen in a lean range of the rich-lean cycle.
In addition, an additional oxygen supply into the motor-vehicle exhaust-gas after-treatment system can be provided as a function of the determined oxygen quantity of the oxygen accumulator. Such an oxygen supply can be performed, for example, by means of an air supply, also like an oxygen supply into the exhaust-gas after-treatment system. There is also the possibility, for example, to change the air supply in the exhaust-gas after-treatment system additionally or also independently through corresponding valve overlap in a connected internal-combustion engine.
Preferably, the oxygen quantity is calculated by means of an oxygen balance across the oxygen accumulator. This can be realized, for example, by means of a first probe and a second probe. The first probe is preferably arranged in the flow direction before the oxygen accumulator, advantageously at least directly before the oxygen accumulator. The second probe is preferably arranged in the immediate vicinity downstream of the oxygen accumulator. In addition, there is the possibility that at least one of the two probes is arranged directly on an opening of the oxygen accumulator. There is also the possibility that at least one of the probes is arranged in the oxygen accumulator. For example, the entire accumulation behavior of the entire oxygen accumulator can be determined from the partial behavior of the oxygen accumulator.
Preferably, a first probe for a continuous measurement of the oxygen content before the oxygen accumulator is used. Here, instead of the oxygen content, the air content before the oxygen accumulator can also be determined, and the oxygen content can be determined from this. The second probe preferably determines the oxygen content after the oxygen accumulator, at least at time intervals. It is preferred that a continuous measurement of the oxygen content or the air ratio is performed. For example, it is provided that, of the two probes, at least the probe in front in the flow direction is a broadband lambda probe. In contrast, the other of the two probes can be a transition probe. However, two broadband lambda probes can also be used. Advantageously, at least one of the probes is in a position to also record the temperature.
According to one improvement, the exhaust-gas after-treatment system is equipped with a separate control device. The control device stores, advantageously, not only a control or regulation system with respect to the oxygen accumulator. Advantageously, other components of the exhaust-gas after-treatment components are also included in the control device. In addition to the oxygen accumulator, this can be additional catalysts, particulate filters, injection devices in the exhaust-gas after-treatment system, for example, ammonia-containing means or the like. A configuration provides that such functionality is implemented in a motor control device. Another configuration provides that the control device is arranged separately from the motor control system.
According to one configuration, the method is used to achieve a targeted influence on the rich-lean cycle with the oxygen quantity stored in the oxygen accumulator. For example, it is possible through targeted filling and emptying of the oxygen accumulator to be able to change a quantity of heat released per unit of time. Thus there is the possibility to be able to influence, for example, the temperature of the oxygen accumulator or a component that has the oxygen accumulator.
For example, it is provided that regeneration of an exhaust-gas purification component of the motor vehicle has to be performed within a certain temperature range. This is the case, for example, for a regeneration of a diesel particulate filter, as well as for a desulfurization of a nitrogen oxide-accumulating catalytic converter. For example, in a particulate filter, if an internal combustion engine is operated in a lean mode, then soot collects. For burning off soot, advantageously a temperature greater than 500° C. is set. If, for example, an uncoated particulate filter is used, a temperature greater than 600° C. is used. For a catalytically- coated filter, for example, a temperature greater than 550° C. exhaust gas temperature is set on the particulate filter. According to one configuration, a rich-lean cycle is used for increasing temperature during regeneration. Here, an oxygen accumulator is at least partially filled and emptied cyclically. Reactions performed in this way in the oxygen accumulator generate heat that is used for increasing the temperature. The temperature increase can be performed, for example, before the actual regeneration, so that for triggering the actual regeneration, advantageously only little enthalpy must still be provided. For example, the oxygen quantity present in the oxygen accumulator can be used to generate, at least partially, a required temperature and/or temperature increase for regeneration. For this purpose, the oxygen accumulator stores oxygen accordingly in phases of an oxygen excess supply, wherein this oxygen can be output in phases of regeneration.
Such an operation of the oxygen accumulator in interaction with regeneration is supported, for example, in various ways by means of the motor control system and/or the separate control device. For example, the temperature increase can be achieved in such a way that an exhaust-gas temperature is detected at the internal combustion engine or else also for operation of a turbine at the outlet of the turbine. For example, in an internal combustion engine, this can be realized by a reduction of the air ratio, for example, by post injection, through a change of an injection angle and also through throttling of the air fed to the engine or a turbine. To allow an amplification of the temperature increase, fuel that has not combusted or that has combusted only incompletely can be fed to the oxygen accumulator. For example, for this purpose, a delayed post injection of fuel can be used in an expansion cycle of the internal combustion engine. Furthermore, there is the possibility to provide an injection of the fuel into a displacement cycle. In addition there is the possibility of direct fuel supply into the exhaust-gas flow, for example, by means of an additional injection. There is also the possibility of reforming fuel and supplying it as synthesis gas. For example, there is also the possibility that, in a motor vehicle that has a bivalent drive, for example, a liquid gas accumulator, a natural gas accumulator, or the like is used in addition, in order to allow a corresponding fluid inflow into the exhaust-gas after-treatment system.
The oxygen to be stored in the oxygen accumulator is fed, for example, from residual oxygen from the engine combustion. However, there is also the possibility of providing an external air supply into the exhaust gas. For this purpose, for example, a secondary air fan can be used. There is also the possibility of being able to use a charging device of an internal combustion engine for this purpose. In addition there is the possibility of using oxygen stored at other locations of the exhaust-gas after-treatment system for enriching the oxygen output from this system in the oxygen accumulator.
A combustible gas component can be converted in the exhaust-gas after-treatment system through sufficient oxygen made available, for example, by means of oxygen fed exclusively from the oxygen accumulator or additionally from the oxygen accumulator, in particular, as a supplement from the oxygen accumulator. For the operation of the motor vehicle exhaust-gas after-treatment system, it is geared in a targeted way to the use of the present oxygen accumulator in a controlled way. For example, there is the possibility of performing a temperature control or regulation of the particulate filter, in particular, when the particulate filter itself has the ability to act as an oxygen accumulator.
According to another configuration, the determined oxygen quantity of the oxygen accumulator is included as a parameter in a desulfurization process of an oxide accumulator advantageously for influencing a rich-lean cycle. The oxide accumulator can be, for example, a nitrogen oxide-accumulating catalytic converter and/or a sulfur oxide accumulator. In desulfurization, an oxygen supply from the oxygen accumulator is used to oxidize, for example, H2S created during substoichiometric operation into SO2. By determining the current oxygen content in the oxygen accumulator, it is advantageously implemented in the corresponding operating strategy that complete emptying of the oxygen accumulator is avoided especially during rich operation. Thus, a risk of H2S output is prevented. In particular, if it is provided as an operating strategy that the oxygen accumulator may never be completely emptied, then instead of a lambda probe after the oxygen accumulator, in particular, a transition probe can also be provided.
Advantageously, not just a determination of a beginning of a desulfurization process and/or a regeneration process can be determined by means of the considered oxygen quantity. There is also the possibility that the determined oxygen quantity is incorporated as a parameter for determining a time period of the desulfurization and/or the regeneration.
Advantageously, not just a determination of a beginning of a desulfurization process and/or a regeneration process can be determined by means of the considered oxygen quantity. There is also the possibility that the determined oxygen quantity is incorporated as a parameter for determining a time period of the desulfurization and/or regeneration. [sic; repeated paragraph (except for one “the”)]
The oxygen quantity required for the method in the oxygen accumulator is determined, according to one configuration, through integration of the oxygen mass flow exchanged with the accumulator. The oxygen mass flow is here calculated with reference to a difference in the probes, in particular, the lambda probes, and also the exhaust-gas mass flow. For this purpose, the following formula is used:
{dot over (m)}02={dot over (m)}A·L·(λbeforeCat−λafterCat)
m02=∫ {dot over (m)}02dt where
m02—stored oxygen mass
m02—exchanged oxygen mass flow
m02—exhaust-gas mass flow
L—stoichiometric factor
λ—air ratio
The result of such a calculation or another may be incorrect, for example, due to inaccurate lambda signals or an inaccurate exhaust-gas mass flow, so that the calculated oxygen content does not correspond to the actual oxygen content. Also, through integration, an error can continue to grow over time. It is then possible that undesired rich or lean breakthroughs are realized. If such a breakthrough should occur, with reference to this breakthrough the actual state of the accumulator can be identified and the calculation can be reset to a certain value. In addition, a targeted breakthrough situation can be created, in order to also achieve a calibration of the measurement. There is also the possibility for initiating a calibration from the operating behavior of the oxygen accumulator. For example, a maximum storage state can also be tested through corresponding air or oxygen supply and advantageously a calibration for the storage capacity and the storage state of the oxygen accumulator can be determined.
One improvement provides that, in the scope of a control or regulation system, the oxygen accumulator, advantageously also its oxygen storage capacity and, in particular, the current, determined stored oxygen quantity are used to set at least one threshold value. When this threshold is exceeded, a cycle change is triggered between lean and rich operation. The threshold value can be fixed. However, there is also the possibility that the threshold value can be adapted, for example, due to aging of the oxygen accumulator. For example, for a calibration of the oxygen storage capacity or the calculation of the oxygen storage capacity, the threshold value can be increased or decreased. For example, the threshold value is stored in the control device of the exhaust-gas after-treatment system. However, it can also be provided, for example, in the motor control system. Preferably it is provided that a lower and an upper threshold are set with respect to the oxygen quantity and a cycle change between lean and rich operation is triggered when the threshold is exceeded. A trigger time point for the cycle change can here be provided when the threshold is reached but also only after the threshold is exceeded. Preferably, a hysteresis response can be triggered for a cycle change. This means that after a threshold is reached, the oxygen accumulator either continues to store oxygen in a slowed manner before discharging the oxygen or, in the inverse case, a discharge of the oxygen is performed in a slowed manner before oxygen is stored again in the oxygen accumulator. Advantageously it is provided that the threshold with respect to the oxygen quantity in the oxygen accumulator can be exceeded once the threshold is reached and then after the cycle change has been completed and the operating behavior with respect to the oxygen discharge or absorption of the oxygen accumulator has been reversed.
In addition, it can be provided that an internal combustion engine is operated in a rich-lean cycle, wherein a temperature of the oxygen accumulator is determined and an operating parameter influencing the stored oxygen quantity is changed as a function of the determined temperature. In particular, there is also the possibility that temperature control of the exhaust-gas after-treatment component having the oxygen accumulator changes an oxygen quantity discharged per unit time from the oxygen accumulator for adjusting the temperature of the exhaust-gas after-treatment component. In the case of temperature regulation through the use of the oxygen accumulator, for example, a PI regulator can be used.
In addition, as well as also separately, an operation of the motor-vehicle exhaust-gas after-treatment system can be provided in which a rich-lean cycle is performed at least partially during desulfurization of an oxide, in particular, a nitrogen oxide-accumulating catalytic converter, and an air ratio is stored after the oxide, in particular, the nitrogen oxide-accumulating catalytic converter, wherein the oxygen quantity is determined and used to prevent substoichiometry and/or hyperstoichiometry of the air ratio after the oxide, in particular, the nitrogen oxide-accumulating catalytic converter. Here, reference is made, in particular, to one or more thresholds that can be set with respect to the storage quantity of oxygen in the oxygen accumulator. For example, there is the possibility that not just one threshold value, but several threshold values are provided. Here there is the possibility to be able to operate the oxygen accumulator with different temperatures or oxygen discharge or oxygen absorption.
The operation of the oxygen accumulator is integrated into the exhaust-gas after-treatment concept of the motor vehicle. Therefore, the oxygen accumulator can be arranged as an individual component in the exhaust-gas after-treatment system. It is preferred, however, that the oxygen accumulator is a part of a component of the exhaust-gas after-treatment system. This can be a catalytic converter, a particulate filter, or some other element in the exhaust-gas after-treatment system.
According to another concept of the invention, an exhaust-gas after-treatment system with a connected internal combustion engine is proposed, wherein the internal combustion engine has a motor control system and the exhaust-gas after-treatment system has at least one regulated catalytic converter and an oxygen accumulator, wherein a first probe is arranged before the oxygen accumulator and a second probe is arranged after the oxygen accumulator, wherein the first probe detects a first parameter characterizing an oxygen content, a signal transmission of the parameter recorded by the first and second probes to an evaluation unit is provided, and the evaluation unit is coupled with a motor control system with a regulation or control unit that takes into account a rich-lean cycle based on the determined parameter.
By means of such an exhaust-gas after-treatment system with connected internal combustion engine, the method described above is preferably performed for operating a motor-vehicle exhaust-gas after-treatment system.
One improvement provides that the second probe is a temperature probe whose parameter is included in a control or regulation system of a lambda value of the motor control system. Advantageously, a rich-lean cycle is included as a desired value in a lambda regulation of the internal combustion engine.
Another configuration of the exhaust-gas after-treatment system provides that the first and the second probes each determine a first parameter characterizing an oxygen content, and a signal transmission of the first parameter from the first and the second probes to an evaluation unit is provided; the evaluation unit determines, from the first parameters, a second parameter characterizing an oxygen content of the oxygen accumulator, and the motor control system is coupled with a device for setting an air ratio in the exhaust-gas after-treatment system, wherein an adaptation of the air ratio as a function of the second parameter is provided by means of the device.
One improvement of the exhaust-gas after-treatment system provides that the oxygen accumulator has a first part and a second part that are arranged in at least two different exhaust-gas after-treatment components. For example, the oxygen accumulator can be formed from an NOx catalytic converter and also from a particulate filter. These can also be provided separate from each other. In addition, there is the possibility that a three-way catalytic converter also includes an oxygen accumulator or a part of this oxygen accumulator. It is preferred when a measurement probe is provided for determining a temperature of the oxygen accumulator. This permits a direct coupling of the measured temperature for a calculation of the oxygen content of the oxygen accumulator. For example, this determined temperature value can be used for testing the oxygen content set, for example, by means of the oxygen balance. Alternatively or additionally, the determination of the temperature of the oxygen accumulator also allows one or more of the thresholds named above to change to influence the rich-lean cycle according to the temperature-dependent oxygen storage capacity.
Other advantageous configurations and improvements are specified in the following drawings. The resulting features, however, are not limited to the individual configurations. Instead, to form improvements, individual features can be combined with those of other configurations of the drawings and also with features of the above description. Shown are:
In a schematic view,
As an alternative to the schematic temperature regulation from
In an example schematic view,
In a schematic diagram,
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 025 050.8 | May 2006 | DE | national |
This application is the U.S. national phase of international patent application PCT/EP2007/004676 filed May 25, 2007, which claims priority to German patent application DE 10 2006 025 050.8 filed May 27, 2006.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/004676 | 5/25/2008 | WO | 00 | 11/26/2008 |
