CN116601380A - Method for operating an exhaust gas aftertreatment system - Google Patents

Abstract

The invention relates to a method for operating an exhaust gas aftertreatment device having a plurality of series-connected catalytic converters (3, 4), which comprise a first three-way catalytic converter (3) and a second three-way catalytic converter (4), to which exhaust gas from an internal combustion engine (1), in particular an otto engine, is supplied via an exhaust gas path (2). According to the invention, the oxygen filling level of the second three-way catalytic converter (4) is determined by means of a measuring device (8) and/or by simulation, wherein, when the oxygen filling level is determined, secondary air is introduced into the exhaust gas path (2) between the first and the second three-way catalytic converter (4) by means of a secondary air source (7), so that the oxygen filling level is increased.

Description

Method for operating an exhaust gas aftertreatment system

technical field

The invention relates to a method for operating an exhaust gas aftertreatment system for aftertreatment of exhaust gases of an internal combustion engine, in particular an Otto engine, which has the features of the preamble of claim 1 . Furthermore, the invention relates to an exhaust gas aftertreatment system which is suitable for carrying out the method according to the invention or which can be operated according to the method according to the invention.

Background technique

Exhaust gas aftertreatment of the exhaust gases of internal combustion engines in order to comply with the limit values for the emission of harmful substances required by law in most countries. Here, at least one catalytic converter, for example a three-way catalytic converter, is used. The pollutant emission components contained in the exhaust gas, more precisely CO, HC and NO _x , can be converted by means of a three-way catalytic converter (Three Way Catalyst, TWO).

In current and future Otto engines, two three-way catalytic converters connected in series are increasingly being used for exhaust gas aftertreatment. This is done in order to comply with the requirements for high conversion rates in terms of activation/heating and in the case of high exhaust gas volume flows. For regulating/monitoring the exhaust gas aftertreatment, lambda probes are usually arranged upstream and downstream of the first three-way catalytic converter. They should help to adjust the catalytic converter as optimally as possible. For this purpose, the exhaust gas intake quantity (λ) (air/fuel ratio) is adjusted by means of a sensor which achieves the best possible conversion of all exhaust gas species to be converted. Up to now, regulation/monitoring of the second three-way catalytic converter has generally not been provided. The reason is that, on the one hand, its proportion in the conversion of the emission components of harmful substances is small. On the other hand, possible damage processes first involve the first three-way catalytic converter and can therefore be detected by monitoring it.

The pollutant emissions as a whole are converted as best as possible only when both catalytic converters are optimally tuned. Precisely in the transient mode of operation, the risk of non-optimal alignment of the individual or both TWCs and breakthroughs in pollutant emissions is higher, so that increased emission requirements cannot always be met.

Contents of the invention

The object underlying the invention is therefore to detect such breakthroughs in pollutant emissions or unfavorable operating states of the second TWC at an early stage and prevent them by targeted countermeasures. In this case, these countermeasures should be executable independently of the current driving situation.

To solve this object, a method with the features of claim 1 and an exhaust gas aftertreatment system for an internal combustion engine with the features of claim 9 are proposed. Advantageous developments of the invention can be obtained from the corresponding subclaims.

A method is proposed for operating an exhaust gas aftertreatment system having a plurality of catalytic converters connected in series, the catalytic converters comprising a first three-way catalytic converter and a second three-way catalytic converter, an internal combustion engine, in particular an Austrian The exhaust gas of the Torque engine is supplied to the first three-way catalytic converter and the second three-way catalytic converter. In this case, the oxygen fill level is ascertained by means of a measuring device and/or simulated, wherein, when the oxygen fill level is determined, the secondary air is introduced between the first and the second three-way catalytic converter via the secondary air source. in the exhaust gas path between them, thereby increasing the oxygen filling level of the second catalytic converter.

The simulated determination of the oxygen filling level is based on a catalyst model which can sufficiently effectively describe the state of the catalyst. Model calculations are performed in existing and/or separate controllers and/or cloud-based. The input variables necessary for the model calculations come from the engine controller and/or a separate controller and/or the cloud and/or one or more measuring devices located before the first three-way catalytic converter and /or before the second three-way catalytic converter and/or after the second three-way catalytic converter.

By direct/indirect measurement or simulation of the oxygen filling level, it can be ascertained early whether an emission breakthrough is imminent because the oxygen filling level is too low. Accordingly, it is possible to increase the oxygen filling level in the second three-way catalytic converter early on by introducing the secondary air upstream of the second three-way catalytic converter. Since the secondary air is introduced downstream of the first three-way catalytic converter, the second three-way catalytic converter can be arranged lean-burning independently of the first three-way catalytic converter. Correspondingly, the first three-way catalytic converter can be operated in a range optimized for this, ie with a minimally oily mixture. Likewise, pollutant emissions can be reduced by introducing secondary air.

In a preferred embodiment of the invention, the oxygen filling level of the second three-way catalytic converter is ascertained from the measured values of the NO _x sensor and/or the lambda probe in the exhaust gas. The lambda probe is preferably designed as a jumping lambda probe with which the oxygen content in the exhaust gas is ascertained in a known manner. Accordingly, the _NOx sensor ascertains the _NOx content and also provides the oxygen content in the exhaust gas. These sensors or detectors are known and commercially available in various embodiments. Thus, such a measuring device can be realized in a simple manner. In a further preferred embodiment of the invention, the oxygen filling level in the second three-way catalytic converter is ascertained. Preferably, the oxygen filling level is measured directly in the second three-way catalytic converter. Alternatively or additionally, the oxygen filling level may be simulated. For the measurement, the measuring device is arranged in such a way that a measured value can be ascertained in the second three-way catalytic converter. This has the advantage that such a measuring device can indirectly ascertain the local oxygen filling level. As a result, it is possible to react more quickly to changes in the oxygen filling level, so that the amount of emitted harmful substances can be further reduced.

Alternatively, the oxygen fill level is ascertained downstream downstream of the second three-way catalytic converter. Due to the measurement after the three-way catalytic converter compared to the measurement inside the second three-way catalytic converter, _NOx , CO, THC, _NH3 after exhaust gas treatment in the second three-way catalytic converter are treated as the whole The end result of exhaust gas treatment. The release of hazardous substances into the surrounding environment is thereby measured. Correspondingly, corrective interventions can be made in good time by adjusting the fuel-air ratio or by secondary air feed-in and pollutant emissions can be reduced.

In an advantageous refinement, the secondary air to be introduced into the exhaust gas path is provided by means of a conveying device, for example a pump. Thus, a sufficient pressure differential can be created between the exhaust path and the secondary air to add secondary air to the exhaust path. In this case, the pump is preferably an already existing pump, for example an air pump from cold-start emission optimization, from an exhaust gas burner or for preheating an electrically heated catalytic converter. Therefore, no additional components are necessary, so that secondary air can be supplied to the exhaust gas path in a simple and economical manner.

In a further advantageous embodiment, the secondary air supply is carried out starting from a threshold value measured by the measuring device. In this case, the threshold value is designed such that the oxygen filling level is still sufficient to avoid a direct breakthrough of pollutants, so that the secondary air can be supplied to the second three-way catalytic converter before the breakthrough. Preferably, the threshold value corresponds to the threshold value of the jump detector and/or the signal threshold value of the _NOx sensor.

Preferably, the secondary air supply is terminated when the measuring device shows that the determined value is below a threshold value. In other words, only the same amount of air is supplied as has been consumed in the three-way catalytic converter. This reduces the energy consumption and noise generation for the secondary air supply to the necessary minimum.

According to one expedient embodiment, the secondary air supply is increased as the oxygen filling level decreases. Here, it is not necessary to wait below a certain threshold value. Here, secondary air is already supplied when the falling oxygen filling level is ascertained. Thus, the oxygen filling level can be kept constant, apart from adjusting for technical deviations. Accordingly, the reduced oxygen filling level is counteracted accordingly, so that a state in which noxious substances break through is not reached. A further reduction of the emitted pollutants can thereby be achieved, since an oxygen fill level optimized for oxidation of the pollutants is achieved to the greatest extent possible.

Furthermore, an exhaust gas aftertreatment system for an internal combustion engine, in particular for an Otto engine, is proposed, which has a plurality of catalytic converters connected in series, the catalytic converters comprising a first three-way catalytic converter and a second three-way catalytic converter , the exhaust gas of the internal combustion engine may be supplied to the first three-way catalyst and the second three-way catalyst through the exhaust gas path. According to the invention, a mixing point is arranged downstream of the first three-way catalytic converter and upstream of the second three-way catalytic converter, via which mixing point the secondary air of the secondary air source can be supplied to the exhaust gas path, and in the second three-way catalytic converter A measuring device is arranged in the area of the through-catalyst, with which the oxygen filling level of the second three-way catalytic converter can be determined.

The proposed exhaust gas aftertreatment device is particularly suitable for carrying out the method according to the invention described above or can be operated according to this method. The oxygen filling level of the second three-way catalytic converter can thus be ascertained separately. Furthermore, a lean setting of the second three-way catalytic converter is achieved without affecting the operating mode of the first three-way catalytic converter.

According to a further expedient embodiment, the measuring device is designed as a lambda probe or NO _x sensor and is arranged downstream of or in the second three-way catalytic converter. A corresponding arrangement of the sensors has the advantages mentioned in the method for such a measuring position.

Description of drawings

Subsequently, a preferred embodiment of the invention is explained in more detail on the basis of the accompanying drawings. The plot shows:

1 shows a schematic representation of an internal combustion engine with an exhaust gas aftertreatment device according to the invention, and

FIG. 2 shows a flow chart for diagrammatically depicting the sequence of the method according to the invention.

Detailed ways

FIG. 1 shows an internal combustion engine 1 which is connected on the outlet side to an exhaust gas path 2 . Exhaust gas produced during the combustion process of the internal combustion engine 1 is conducted via the exhaust gas path 2 . In this case, the exhaust gas is subjected to exhaust gas aftertreatment. For this purpose, two three-way catalytic converters 3 , 4 connected in series are arranged in the exhaust gas path 2 .

In the exhaust gas path shown, a mixer 5 is arranged in the exhaust gas path 2 between the first three-way catalytic converter 3 and the second three-way catalytic converter 4 . The mixer 5 is additionally connected via a secondary air line 6 to a secondary air source 7 , for example a secondary air pump. Thus, secondary air can be supplied to the mixer 5 in addition to the exhaust air. The secondary air is mixed with the exhaust gas in the mixer 5 and passed to the second three-way catalytic converter 4 arranged downstream. Therefore, the second three-way catalytic converter 4 can be operated lean-burn. Such lean operation is especially necessary when the oxygen filling level of the second three-way catalytic converter 4 falls. In such a case, CO, HC, NH ₃ and H ₂ not converted by the first three-way catalyst 3 may also be converted by the second three-way catalyst 4 . Otherwise they may be discharged into the surrounding environment.

In order to avoid this, in the exemplary embodiment a measuring device 8 is arranged downstream of the second three-way catalytic converter 4 , with which the oxygen fill level can be measured indirectly. In this exemplary embodiment, the measuring device 8 is designed as a NO _x sensor, so that the lean gas components NO _x and O ₂ as well as the model-based NH ₃ can be ascertained. In this case, the oxygen filling level can be deduced from the output signal. The measured value M is transmitted to the controller 9 . Starting from a defined threshold value for the measured value M, a signal is output from the controller 9 to the secondary air source 7 , so that secondary air is supplied to the exhaust gas path 2 . Due to the second three-way catalytic converter 4 operating lean-burn, the oxygen filling level is again increased, thereby reducing CO, HC and NH ₃ emissions.

In the exhaust gas path 2 , a broadband lambda sensor 10 is additionally arranged upstream of the first three-way catalytic converter 3 , and a jumping lambda sensor 11 is arranged downstream of it. Likewise, these detectors 10 , 11 are connected to a controller 9 . The air-fuel mixture is measured by a broadband lambda probe 10 so that it can be set to a value of approximately lambda=1. The oxygen content downstream of the first three-way catalytic converter 3 is measured by means of a jump lambda probe 11 .

The essential steps of the method according to the invention for operating an exhaust-gas aftertreatment system are illustrated by way of example in FIG. 2 . In order to ascertain whether the second three-way catalytic converter 4 is sufficiently filled with oxygen or whether there is no breakthrough of pollutant emissions, in a first step A, with the aid of the _NOx arranged downstream of the second three-way catalytic converter The sensor 8 infers the oxygen filling level of the second three-way catalytic converter 4 . In a subsequent step B, it is checked whether the measured value M of the NOx sensor exceeds a threshold value S. From the measured value M, inferences can be drawn here about the oxygen filling level in the second three-way catalytic converter 4 . If the measured value M is below the determined threshold value S, then in step C no secondary air is supplied. Alternatively, after this step C, the method starts again with finding the oxygen filling level.

If in step B the measured value M is above the determined threshold value S, then in the following step D the secondary air source 7 is actuated in such a way that the quantity of secondary air corresponding to the measured value M is supplied to the three-way catalytic converter 3 , between 4 supply to the exhaust gas path 2. Immediately afterwards, return to the first step A.

Claims (9)

1. A method for operating an exhaust gas aftertreatment system with a plurality of catalytic converters (3, 4) connected in series, the method comprising a first three-way catalytic converter (3) and a second three-way catalytic converter (4), The exhaust gas of the internal combustion engine (1), in particular the Otto engine, is supplied to the first three-way catalytic converter and the second three-way catalytic converter via the exhaust gas path (2), It is characterized in that the oxygen filling level of the second three-way catalytic converter (4) is ascertained by means of a measuring device (8) and/or analogously, wherein at a certain oxygen filling level, the secondary air A source (7) introduces secondary air into the exhaust gas path (2) between the first three-way catalytic converter and the second three-way catalytic converter (4), thereby increasing the second catalytic Oxygen filling level of tank (4). 2. The method according to claim 1, characterized in that the oxygen filling level of the second three-way catalytic converter (4) is obtained according to the measured values of the _NOx sensor and/or lambda detector in the exhaust gas . 3. The method as claimed in claim 1 or 2, characterized in that the oxygen filling level downstream downstream of the second three-way catalytic converter (4) is ascertained. 4. The method as claimed in claim 1 or 2, characterized in that the oxygen filling level in the second three-way catalytic converter (4) is ascertained. 5. The method as claimed in any one of the preceding claims, characterized in that the secondary air to be introduced into the exhaust gas path (2) is provided by means of a conveying device, such as a pump. 6. The method according to any one of the preceding claims, characterized in that the secondary air supply is performed starting from a threshold value (S) measured by the measuring device (8). 7. A method according to any one of claims 1 to 5, wherein the secondary air supply is increased as the oxygen filling level decreases. 8. An exhaust gas aftertreatment device for an internal combustion engine (1), in particular an Otto engine, for carrying out the method according to any one of the preceding claims, said exhaust gas aftertreatment device having A plurality of catalytic converters (3, 4) connected in series, the plurality of catalytic converters connected in series include a first three-way catalytic converter (3) and a second three-way catalytic converter (4), through which the exhaust gas path (2) can supplying the exhaust gas of the internal combustion engine (1) to the first three-way catalytic converter and the second three-way catalytic converter, It is characterized in that a mixing part is arranged downstream of the first three-way catalytic converter (3) and upstream of the second three-way catalytic converter (4), through which the secondary air source (7) can be Secondary air is supplied to the exhaust gas path (2), and a measuring device (8) is arranged in the region of the second three-way catalytic converter (4), with which the second three-way Oxygen fill level of catalytic converter (4). 9. The exhaust gas aftertreatment device according to claim 8, characterized in that the measuring device (8) is configured as a lambda probe or a _NOx sensor and is arranged downstream of the second three-way catalytic converter (4) or in the second three-way catalytic converter.